A comparative study for optimizing photocatalytic activity of TiO₂-based composites with ZrO₂, ZnO, Ta₂O₅, SnO, Fe₂O₃, and CuO additives

Abstract

Despite the widespread use of titanium dioxide (TiO₂) in photocatalytic applications, its inherent limitations, such as low efficiency under visible light and rapid recombination of electron-hole pairs, hinder its effectiveness in environmental remediation. This study presents a comparative investigation of TiO₂-based composites, including TiO₂/ZrO₂, ZnO, Ta₂O₃, SnO, Fe₂O₃, and CuO, aiming to assess their potential for enhancing photocatalytic applications. Photocatalysis holds promise in environmental remediation, water purification, and energy conversion, with TiO₂ being a prominent photocatalyst. To improve efficiency and broaden applicability, various metal oxide composites have been explored. Composites were synthesized and characterized using techniques such as XRD, SEM, TEM, and zeta potential analysis to evaluate their structural and morphological properties. Photocatalytic performance was assessed by degrading herbicide Imazapyr under UV illumination. Results revealed that, the photo-activity of all prepared composites were more effective than the photo-activity of commercial hombikat UV-100. The photonic-efficiency is arranged according to the order TiO₂/CuO > TiO₂/SnO > TiO₂/ZnO > TiO₂/Ta₂O₃ > TiO₂/ZrO₂ > TiO₂/Fe₂O₃ > Hombikat TiO₂-UV100. All composites exhibited superior performance, attributed to enhanced light absorption and charge separation. The study underscores the potential of these composites for environmental remediation and energy conservation, offering valuable insights for the development of advanced photocatalysts.

Introduction

The field of photocatalysis has garnered significant attention in recent years due to its promising applications in environmental remediation, water purification, and energy conversion¹. Photocatalysts, in the best utilizations, are materials that can harness solar energy to catalyze chemical reactions, making them a sustainable and eco-friendly option for addressing various global challenges. Among photocatalysts, titanium dioxide (TiO₂) stands out as one of the most extensively studied and widely used materials due to its excellent photocatalytic properties². TiO₂ as a photocatalyst, with its wide bandgap and strong oxidative properties, is a well-known and effective photocatalyst. When exposed to ultraviolet (UV) light, TiO₂ generates electron-hole pairs that can participate in redox reactions, leading to the degradation of organic pollutants and the production of reactive oxygen species (ROS)³. These ROS are highly effective in breaking down a wide range of organic compounds, making TiO₂ an attractive option for wastewater treatment and air purification⁴. While TiO₂ is a powerful photocatalyst, its efficiency is limited by factors such as rapid electron-hole recombination and a relatively large bandgap, restricting its activity to UV light⁵. To overcome these limitations, researchers have explored various strategies, including doping with other elements, and developing composite materials. Composite photocatalysts involve combining TiO₂ with other materials, such as metal oxides, to create synergistic effects that enhance photocatalytic performance⁶. These composites offer the advantage of improved light absorption, charge separation, and increased surface area, all of which contribute to enhance photocatalysis⁷. In the context of this study, TiO₂ was combined with several metal oxides, including ZrO₂, ZnO, Ta₂O₃, SnO, Fe₂O₃, and CuO, to investigate their potential for boosting photocatalytic applications. It can serve as a co-catalyst, promoting charge separation and extending photocatalysis into the visible light range⁸. This synergy between TiO₂ and these metal oxides holds promise for improving the overall efficiency of photocatalytic reactions. can enhance charge separation, and inhibit electron-hole recombination^9,10. This co-catalyst has the potential to improve the efficiency of photocatalytic reactions. Characterization techniques, to assess the structural, morphological, and surface properties of these TiO₂-based composite photocatalysts, a range of characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and zeta potential analysis, were employed^11–14. These techniques provide valuable insights into the composition and behavior of composites. Photocatalytic evaluation, the photocatalytic activities of these composite materials were evaluated by studying the degradation of the sample of organic pollutants under both UV and visible light irradiation¹⁵. The global population continues to grow rapidly, leading to increased food demand and placing significant pressure on food production systems. To protect crops from the detrimental effects of weeds and grasses, farmers widely utilize herbicides¹⁶. However, the extensive use of these chemicals has resulted in their accumulation in the environment, presenting a serious concern due to their toxic and harmful effects on both ecosystems and human health. This alarming reality has prompted researchers to seek alternatives to these hazardous substances to mitigate their adverse impacts¹⁷. Imazapyr, scientifically known as [(RS)-2-(4-methyl-5-oxo-4-propan-2-yl-1 H-imidazol-2-yl) pyridine-3-carboxylic acid], is a nonselective herbicide primarily used for controlling grasses. While it is not intended for aquatic applications, it has been detected on water surfaces due to spray drift, and it can penetrate deep into groundwater, posing significant environmental risks¹⁸. In soil, Imazapyr can persist for 6 to 12 months without breaking down, and its high solubility in water means that even minimal soil concentrations around 0.05 mg/kg can be harmful to plants. The European Union has set a maximum allowable limit for herbicides and pesticides in drinking water at just 0.1 µg/L, highlighting the potential dangers associated with Imazapyr’s presence in the environment¹⁹. The removal of imazapyr has been explored through various methods, including electrochemical oxidation, adsorption, and chemical oxidation. However, traditional chemical oxidation methods such as using chlorine dioxide, ozone, and chlorine have notable drawbacks; specifically, the secondary byproducts generated during these processes can be toxic²⁰. In contrast, Advanced Oxidation Processes (AOPs) represent a promising new approach that relies on the generation of hydroxyl (^•OH) radicals to effectively degrade organic compounds. Among these techniques, heterogeneous photocatalysis using titanium dioxide (TiO₂) has emerged as one of the most efficient methods, offering high productivity while minimizing energy loss in treatment applications²¹. Recent studies have extensively evaluated the photocatalytic degradation of imazapyr using commercial TiO₂ and TiO₂ modified with mesoporous structures, as well as with additives like aluminum oxide (Al₂O₃) and tungsten oxide (WO₃)²². However, to our knowledge, there are currently no reports examining the photodegradation of imazapyr using mesoporous gallium oxide-titanium dioxide (Ga₂O₃-TiO₂) nanocomposites²³. Therefore, conducting a fundamental study to investigate the relationship between the composition of Ga₂O₃ in Ga₂O₃-TiO₂ nanocomposites and their effectiveness in photodegradation is crucial and warrants further exploration²⁴. Our research focuses on optimizing the material’s composition and structure to maximize its efficiency in harnessing solar energy for catalytic reactions, thus facilitating the degradation of pollutants or the production of valuable chemicals. What sets our research apart from others in the field is the innovative approach we have taken²⁵. Firstly, our synthesis method is designed to be cost-effective, utilizing readily available and affordable starting materials without compromising on the quality or performance of the final product. This ensures scalability and accessibility, making our photocatalyst suitable for widespread practical applications²⁶. Moreover, the novelty of our work lies in the novel architecture and composition of the synthesized material, which endows it with superior photocatalytic activity compared to existing alternatives. Our research explores new avenues for enhancing photocatalyst performance, such as surface engineering, doping strategies, or heterostructure design, to achieve unprecedented levels of efficiency and selectivity in catalytic processes²⁷. The primary motivation behind our research is to bridge a critical gap in the existing knowledge concerning TiO₂-based photocatalysts and their potential for environmental remediation and energy conservation²⁸. In summary, our research fills a significant gap in the literature by providing a comparative analysis of TiO₂-based composites and identifying promising candidates for advancing photocatalytic applications. We believe that our study contributes valuable insights to the field and sets the stage for further research in the development of advanced photocatalysts²⁹. In addition, our research lies in the systematic comparison of TiO₂-based composites with six different metal oxide additives ZrO₂, ZnO, Ta₂O₅, SnO, Fe₂O₃, and CuO under identical experimental conditions^30–35. Unlike previous studies that typically focus on one or two additives or different experimental parameters, our work offers a comprehensive analysis, providing insights into how each additive affects the photocatalytic performance of TiO₂. Because of its significant oxidative potential, stability, and lack of toxicity, titanium dioxide (TiO₂) is one of the materials for photocatalysis that has been explored the most. However, its practical use is limited by a number of fundamental problems, especially when it comes to using solar energy. The main issues with TiO₂-based photocatalysts are covered below, along with potential solutions to increase photocatalytic efficiency. TiO₂ is only active in the ultraviolet (UV) portion of the solar spectrum due to its wide bandgap, which is roughly 3.0 eV for rutile and 3.2 eV for anatase. Only around 5% of solar energy is converted into UV light, meaning that most visible light is wasted. Dopants like nitrogen (N), carbon (C), or sulphur (S) could be added to the first potential solutions in order to reduce the bandgap. The high rate of electron-hole recombination, which drastically lowers the overall efficiency, is one of the main issues with TiO₂-based photocatalysis. The lifespan of charge separation is limited because the photogenerated electrons and holes frequently recombine before taking part in photocatalytic events. By embedding noble metals like gold (Au) or silver (Ag) onto TiO₂, the initial potential solution is produced. This accelerates the creation of hot electrons and improves charge separation by inducing SPR. By producing localized electric fields, these metal nanoparticles lessen electron-hole recombination. Building heterojunctions between TiO₂ and other semiconductors, such as ZnO, g-C₃N₄, or SnO₂, is the basis of the second solution, which aims to enhance charge separation. Recombination is reduced in these structures because the photogenerated electrons and holes are spatially separated. In order to complete the third, cocatalysts must be loaded. Since the number of active sites available for photocatalytic processes is directly proportional to the surface area, the surface area of TiO₂ also limits its photocatalytic performance. The efficiency of bulk TiO₂ structures is often diminished by their comparatively small surface area. The manufacture of TiO₂ nanoparticles, nanorods, or nanotubes yields the first potential solution by greatly increasing the surface area and exposing more active sites for photocatalytic processes. Additionally, improved light absorption and charge transfer are made possible by nano structuring. The second is relying on the use of mesoporous TiO₂ structures, which offer a high surface area with well-organized pores, improving light-harvesting capacity and reactant accessibility to active areas. The surface reaction kinetics of TiO₂ are frequently slow, especially for water oxidation or reduction reactions, even with effective charge separation. The total photocatalytic activity is limited by this slow reaction rate. By offering active sites for catalytic activities, cocatalysts such as Pt, RuO₂, or Co-Pi can speed up surface reactions on the surface of TiO₂. This is the first potential solution. These cocatalysts improve oxidation (like O₂ evolution) and reduction (like H₂ synthesis) reactions. The second one focusses on altering the surface of TiO₂ with metal complexes or organic compounds to enhance reactant adsorption and promote quicker surface reactions. Additionally, this functionalization can improve selectivity for processes. TiO₂-based photocatalysts have a lot of potential for energy and environmental applications, but they also have a lot of drawbacks, including sluggish surface reaction kinetics, a large bandgap, significant electron-hole recombination, and a small surface area. These restrictions can be overcome, although, by employing sophisticated techniques such doping, composite synthesis, heterojunction engineering, cocatalyst loading, and nano structuring. TiO₂-based photocatalysts can be greatly enhanced by using these solutions, opening the door to more effective and useful uses in environmental remediation, water treatment, and solar energy utilization. This study not only explores the synergetic effects of the additives but also delves deeper into the mechanistic understanding of their impact on photocatalytic efficiency, surface interactions, and stability. Furthermore, our approach uniquely combines both structural and performance evaluations to optimize the photocatalytic process³⁶. Compared to previously cited work, our research stands out by offering a broader comparative scope, more detailed mechanistic insights, and identifying specific composites with tailored properties for enhanced photocatalytic applications. This positions our work as a valuable contribution to advancing the field of photocatalysis³⁷. The common goals of sustainability, less environmental impact, and resource efficiency make the relationship between environmental remediation and energy applications clear. The development of sophisticated materials and techniques, energy recovery from trash, and the incorporation of renewable energy into remediation technologies are fostering a more cooperative approach to tackling the twin problems of energy demand and environmental deterioration. As more research is done, advancements in this field should offer strong answers for a more sustainable future in which trash is not only cleaned but also converted into a useful energy source, lessening the ecological impact of humanity as a whole.

Materials and methods

Materials

Tetrabutyl orthotitanate Ti[OC(CH₃)₃]₄(TBOT) Sigma-Aldrich, Zirconium (IV) acetylacetonate (C₂₀H₂₈O₈Zr) Merck, hydrated zinc nitrate (Zn(NO₃)₂·6H₂O) Sigma-Aldrich, Tantalum pentachloride (TaCl₅) Sigma-Aldrich, Tin chloride (SnCl₄·5H₂O), Ferric acetylacetonate (Fe(C₅H₇O₂)₃) Sigma-Aldrich, Copper(II) nitrate hemi (pentahydrate) (Cu(NO₃)₂·2.5H₂O), Imazapyr (C₁₃H₁₅N₃O₃ > 99%), HCl, C₂H₅OH, CH₃OH, H₃PO₄, and CH₃COOH, the triblock copolymer surfactant EO106-PO70EO106(F-127), MW12600 g/mol), were purchased from Sigma-Aldrich. Commercial TiO₂ (Hombikat UV-100, 100% anatase and 230 m²g^− 1 surface area) was kindly provided by Sachtleben Chemie GmbH.

Preparation of mesoporous ZrO2-TiO2, ZnO-TiO2, Ta2O3-TiO2, SnO2-TiO2, Fe2O3-TiO2 and CuO-TiO2, nanocomposites

Different mesoporous nanocomposites were prepared via sol-gel process using F127 triblock copolymer. Typically, 1.6 g of F127 was added to 30 mL of ethanol while stirring for 60 min, and then 0.74 mL of HCl, 3.5 mL of TBOT and 2.3 mL of CH₃COOH were added drop wise to F127 solution under magnetic stirring for 30 min. The calculated amount of Zirconium (IV) acetylacetonate (C₂₀H₂₈O₈Zr) and other precursors was added to the mixture mesophase (F127-TBOT- CH₃COOH) vigorously stirring for 60 min to obtain 0.5, 1, 2, 3 and 5 wt% ZrO₂-TiO₂ nanocomposites. The prepared mesophase was put into 40% humidity chamber at 40°C for 12 h to evaporate C₂H₅OH and form gel and dried at 65 °C for 24 h. Afterward, it was calcined at 500 °C in air at a heating rate of 1°C/min to reach 500 °C for 4 h to remove the template and to different produce mesoporous nanocomposites at different oxides content^38–41.

Photocatalytic activity tests

0.05 g photocatalyst and 10 mM KNO₃ was added in 50 mL of water and then it was sonicated in an ultrasonic cleaning bath for 15 min to disperse the photocatalyst. KNO₃ was added to keep the ionic strength of the solution to equivalent the excess of HCl (pH = 4). The imazapyr concentration [0.08 mmol L^− 1] was maintained to carry out the experimental work⁴². To reach adsorption equilibrium, the imazapyr and photocatalyst were kept under continuous magnetically stirring at 300 rpm for 4 h at 25 ± 1°C. Illumination experiments were conducted under top irradiation of a borosilicate glass beaker and the photonic flow was ρ = 2 m Wcm^− 2. The samples were taken at regular time intervals for analysis. The analysis of imazapyr concentrations was measured through high performance liquid chromatography (HPLC) system from Agilent Technologies 1260 Infinity composed of a G1311C-1260 Quat pump and a G1365D-1260 MWD UV Detector adjusted to 254 nm. An Agilent Eclipse plus C18 column employing at room temperature was performed as stationary phase, and a mixture of water and methanol (70:30%v/v) employing as mobile phase at pH value ∼3 by adding H₃PO₄. The flow rate was fixed at 0.8 mLmin^− 1 and the retention time at 4.60 min⁴³. A calibration curve (R² = 0.9996) was determined from the patrons of 6 different concentration analysis at range 0–0.08 mmol L^− 1. The HPLC analysis measured 2–3 replicates, allowing initial reaction rates to be considered with a mean experimental error ± 5%. This error is determined to be the sum of the HPLC instrument error and the error intrinsic to mathematical calculations from the experimental concentration as a function of time plots. The initial rate for imazapyr photodegradation was calculated through the first 30 min of UV irradiation. The photonic efficiency was calculated as given in the following Eqs^44–47.

where ɛ is the photonic efficiency (%), r the photodegradation rate of imazapyr (mol L^− 1s^− 1), and I the incident photon flux (7.03 × 10^− 6 Ein L^− 1s^− 1). The UV-A incident photon flow was measured by ferrioxalate actinometry.

Characterization of composite photocatalysts

Structural analysis of TiO₂-based composites

Structural analysis plays a crucial role in understanding the composition, morphology, crystallinity, and phase distribution within TiO₂-based composites. Various analytical techniques are employed to characterize these properties in detail. X-ray Diffraction (XRD) is used to determine the crystallographic structure and phase composition of the composite material. The sample is exposed to X-rays, and the resulting diffraction pattern is recorded. By analyzing the diffraction peaks, the crystalline phases present, their crystal structure, and lattice parameters can be identified. Phase identification, crystallite size, lattice parameters, and degree of crystallinity⁴⁸. Scanning Electron Microscopy (SEM) provides high-resolution images of the surface morphology and microstructure of the composite. A focused electron beam scans the sample surface, and the interaction of electrons with the sample generates signals that are used to create images. Surface morphology, particle size, shape, distribution, and agglomeration of nanoparticles⁴⁹. Transmission Electron Microscopy (TEM) provides detailed information about the internal structure, size, and shape of nanoparticles at the atomic level. A focused electron beam is transmitted through an ultrathin sample, and the resulting electron diffraction and imaging provide high-resolution images of the sample’s internal structure. Nanoparticle size, morphology, crystallinity, lattice structure, and interfacial interactions. Zeta potential analysis is used to determine the surface charge and stability of colloidal suspensions. The electrophoretic mobility of charged particles in a suspension is measured, and the zeta potential is calculated, providing information about particle stability and interactions. Surface charge, colloidal stability, and interactions between nanoparticles in the composite⁵⁰. These structural analysis techniques provide comprehensive insights into the composition, morphology, crystallinity, and surface properties of TiO₂-based composites, enabling researchers to optimize their synthesis and tailor their properties for specific applications in photocatalysis, environmental remediation, and energy conversion⁵¹.

Data analysis

The results obtained from the photocatalytic experiments were statistically analyzed to evaluate the photocatalytic performance of the composite materials. Comparative analyses were conducted to determine the synergistic effects of the metal oxide composites. his comprehensive methodology enabled the synthesis, characterization, and evaluation of TiO₂-based composites with ZrO₂, ZnO, Ta₂O₃, SnO, Fe₂O₃, and CuO for enhanced photocatalytic applications, providing valuable insights into their potential for environmental remediation and energy conversion⁵².

Results and discussion

Change in imazapyr concentration as a function of illumination time

Mesoporous CuO-TiO2 nanocomposites

Figure 1 presents the changes in imazapyr concentration (C_t) as a function of illumination time in the presence of mesoporous CuO-TiO₂ nanocomposites at different CuO contents, along with Hombikat UV-100 as a reference catalyst. The t Fig. 1 shows the residual concentration of the herbicide at various time intervals. Initial Concentration (0 min), the initial concentration of imazapyr in the solution is approximately 0.076 mmol/L when no catalyst is present. In the presence of CuO-TiO₂ nanocomposites, the initial concentrations vary with different CuO contents, ranging from 0.071 mmol/L to 0.083 mmol/L⁵³. The reference catalyst, UV-100, shows an initial concentration of 0.083 mmol/L. After 15 min of illumination, the imazapyr concentration decreases to 0.072 mmol/L for the reference UV-100 catalyst. Among the CuO-TiO₂ nanocomposites, only the 0.1% CuO content shows a decrease, reaching 0.069 mmol/L. At the 30-minute mark, the reference UV-100 catalyst continues to reduce imazapyr concentration to 0.057 mmol/L. Among the CuO-TiO₂ nanocomposites, the 0.5% CuO content now shows a decrease to 0.062 mmol/L, while the 3% and 5% CuO contents are at 0.061 mmol/L and 0.062 mmol/L, respectively. After 60 min, the reference catalyst UV-100 achieves a concentration of 0.043 mmol/L, showing a significant reduction. The 0.5% CuO content among the nanocomposites also reduces imazapyr concentration to 0.043 mmol/L. At 90 min, the reference catalyst UV-100 reaches a concentration of 0.051 mmol/L⁵⁴. Among the nanocomposites, only the 3% CuO content reduces the concentration to 0.035 mmol/L. After 120 min, the reference UV-100 catalyst further reduces the concentration to 0.041 mmol/L. At the end of the 180-minute test, the reference catalyst UV-100 achieves a concentration of 0.029 mmol/L. Among the CuO-TiO₂ nanocomposites, the 0.1% CuO content also reduces the concentration to 0.029 mmol/L. The data in Fig. 1 demonstrate the influence of both the CuO content in the nanocomposites and the illumination time on the degradation of imazapyr. The reference catalyst UV-100 consistently shows a reduction in imazapyr concentration over time, reaching the lowest concentration after 180 min. Among the nanocomposites, the 0.5% CuO content appears to be the most effective in degrading imazapyr, achieving similar concentrations as UV-100 at various time intervals⁵⁵. Interestingly, the performance of the nanocomposites is not strictly linear with increasing CuO content, as different CuO contents show variations in activity. These results suggest that the CuO-TiO₂ nanocomposites have the potential to be effective catalysts for the degradation of imazapyr, and further optimization may be required to determine the ideal CuO content for maximum efficiency. Additionally, the data highlights the importance of illumination time, with longer exposure times leading to lower imazapyr concentrations, indicating the potential for the photocatalytic degradation of this herbicide⁵⁶.

Fig. 1.

Change in imazapyr concentration as a function of illumination time in the presence of mesoporous CuO-TiO₂ nanocomposites at different CuO contents compared with Hombikat UV-100 as a reference.

Table 1 presents the time-dependent residual concentrations (C_t in mmol/L) of herbicide for different catalyst concentrations (5%, 3%, 1%, 0.5%, 0.1%) and UV100 treatment. The values reflect the mean concentration ± standard error. Gaps in the data indicate measurements that were not taken at those time intervals. The results demonstrate the degradation profile of the herbicide under varying catalyst conditions.

Table 1.

Residual concentration of herbicide over time for different catalyst percentages with UV irradiation (UV100) and corresponding error margins.

Min	5%	3%	1%	0.5%	0.1%	UV100
0	0.076 ± 0.003	0.073 ± 0.003	0.071 ± 0.003	0.077 ± 0.003	0.083 ± 0.004	0.083 ± 0.004
15	0.072 ± 0.003	–	–	–	0.069 ± 0.003	–
30	–	0.057 ± 0.003	0.061 ± 0.003	0.062 ± 0.003	0.059 ± 0.003	0.062 ± 0.003
60	0.068 ± 0.003	0.044 ± 0.003	–	–	0.043 ± 0.002	0.058 ± 0.003
90	–	0.024 ± 0.002	–	0.035 ± 0.002	–	0.051 ± 0.003
120	–	–	–	–	0.041 ± 0.002	–
180	0.052 ± 0.003	0.01 ± 0.002	0.015 ± 0.002	0.008 ± 0.002	0.008 ± 0.002	0.029 ± 0.002

Mesoporous Fe2O3-TiO2 nanocomposites

Figure 2 presents the changes in imazapyr concentration (Ct) as a function of illumination time in the presence of mesoporous Fe₂O₃-TiO₂ nanocomposites at different Fe₂O₃ contents, along with Hombikat UV-100 as a reference catalyst. The table displays the residual concentration of the herbicide at various time intervals⁵⁷. At the start of the experiment, the initial concentration of imazapyr in the solution is approximately 0.083 mmol/L when no catalyst is present. In the presence of Fe₂O₃-TiO₂ nanocomposites, the initial concentrations vary with different Fe₂O₃ contents, ranging from 0.075 mmol/L to 0.084 mmol/L. The reference catalyst, UV-100, shows an initial concentration of 0.082 mmol/L. After 15 min of illumination, all Fe₂O₃-TiO₂ nanocomposites show a reduction in imazapyr concentration, with the 0.5% Fe₂O₃ content exhibiting the lowest concentration at 0.073 mmol/L. The reference UV-100 catalyst also reduces the concentration to 0.069 mmol/L. At the 30-minute mark, all Fe₂O₃-TiO₂ nanocomposites continue to reduce imazapyr concentration, with the 0.5% Fe₂O₃ content having the lowest concentration at 0.067 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.071 mmol/L⁵⁸. After 60 min, imazapyr concentrations continue to decrease for all catalysts, with the 0.5% Fe₂O₃ content exhibiting the lowest concentration at 0.052 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.074 mmol/L. At 90 min, imazapyr concentrations further decreased for all catalysts, with the 0.5% Fe₂O₃ content having the lowest concentration at 0.046 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.073 mmol/L. After 120 min, imazapyr concentrations continue to decrease, with the 0.5% Fe₂O₃ content exhibiting the lowest concentration at 0.040 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.071 mmol/L. At the end of the 180-minute test, imazapyr concentrations continue to decrease for all catalysts, with the 0.5% Fe₂O₃ content having the lowest concentration at 0.027 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.057 mmol/L⁵⁹. Figure 2 demonstrates the impact of different Fe₂O₃ contents in mesoporous Fe₂O₃-TiO₂ nanocomposites on the degradation of imazapyr over time. Generally, all Fe₂O₃-TiO₂ nanocomposites show the ability to reduce imazapyr concentrations, with the 0.5% Fe₂O₃ content consistently achieving the lowest concentrations at various time intervals. The reference catalyst, UV-100, also exhibits degradation capabilities but tends to have slightly higher imazapyr concentrations compared to the 0.5% Fe₂O₃ nanocomposite⁶⁰. These findings suggest that Fe₂O₃-TiO₂ nanocomposites have photocatalytic activity in degrading imazapyr, and the presence of Fe₂O₃ content influences their efficiency. The results also indicate that longer illumination times lead to lower imazapyr concentrations, supporting the potential for photocatalytic degradation of this herbicide. Further research may be needed to optimize the Fe₂O₃ content and other experimental parameters to enhance the photocatalytic activity of these nanocomposites for herbicide removal applications⁶¹.

Fig. 2.

Change in imazapyr concentration as a function of illumination time in the presence of mesoporous Fe₂O₃-TiO₂ nanocomposites at different Fe₂O₃ contents compared with Hombikat UV-100 as a reference.

Table 2 illustrates the time-dependent degradation of herbicide residual concentration (Ct in mmol/L) across different catalyst percentages (100%, 5%, 3%, 1%, 0.5%, 0.1%) and UV100 exposure. The results are presented as mean concentrations with associated error margins, reflecting variability in the data. This comparison highlights the effectiveness of different catalyst levels and UV treatment in reducing herbicide concentration over time.

Table 2.

Herbicide residual concentration (C_t) over time with various catalyst concentrations and UV100 treatment: Mean Values ± Error Margins.

Min	100%	5%	3%	1%	0.5%	0.1%	UV100
0	0.083 ± 0.003	0.079 ± 0.003	0.082 ± 0.003	0.084 ± 0.003	0.082 ± 0.003	0.082 ± 0.003	0.083 ± 0.003
15	0.081 ± 0.003	0.076 ± 0.003	0.075 ± 0.003	0.079 ± 0.003	0.073 ± 0.003	0.069 ± 0.003	0.069 ± 0.003
30	0.8 ± 0.003	0.074 ± 0.003	0.071 ± 0.003	0.078 ± 0.003	0.07 ± 0.003	0.067 ± 0.003	0.062 ± 0.003
60	0.079 ± 0.003	0.073 ± 0.003	0.074 ± 0.003	0.074 ± 0.003	0.069 ± 0.003	0.052 ± 0.002	0.058 ± 0.003
90	0.079 ± 0.003	0.072 ± 0.003	0.073 ± 0.003	0.073 ± 0.003	0.064 ± 0.003	0.046 ± 0.002	0.051 ± 0.003
120	0.079 ± 0.003	0.071 ± 0.003	0.068 ± 0.003	0.071 ± 0.003	0.06 ± 0.003	0.04 ± 0.002	0.041 ± 0.002
180	0.078 ± 0.003	0.071 ± 0.003	0.066 ± 0.003	0.068 ± 0.003	0.057 ± 0.003	0.027 ± 0.002	0.029 ± 0.002

Mesoporous SnO-TiO2 nanocomposites

Figure 3 presents the changes in imazapyr concentration (C_t) as a function of illumination time in the presence of mesoporous SnO-TiO₂ nanocomposites at different SnO contents, along with Hombikat UV-100 as a reference catalyst. The table displays the residual concentration of the herbicide at various time intervals. At the beginning of the experiment, the initial concentration of imazapyr in the solution is approximately 0.087 mmol/L when no catalyst is present. In the presence of SnO-TiO₂ nanocomposites, the initial concentrations vary with different SnO contents, ranging from 0.071 mmol/L to 0.085 mmol/L⁶². The reference catalyst, UV-100, shows an initial concentration of 0.083 mmol/L. After 15 min of illumination, all SnO-TiO₂ nanocomposites show a significant reduction in imazapyr concentration, with the 0.1% SnO content achieving the lowest concentration at 0.052 mmol/L. The reference UV-100 catalyst also reduces the concentration to 0.069 mmol/L. At the 30-minute mark, all SnO-TiO₂ nanocomposites continue to reduce imazapyr concentration, with the 0.1% SnO content having the lowest concentration at 0.037 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.062 mmol/L. After 60 min, imazapyr concentrations continue to decrease for all catalysts, with the 0.1% SnO content exhibiting the lowest concentration at 0.025 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.058 mmol/L⁶³. At 90 min, imazapyr concentrations further decreased for all catalysts, with the 0.1% SnO content having the lowest concentration at 0.017 mmol/L.

Fig. 3.

Change in imazapyr concentration as a function of illumination time in the presence of mesoporous SnO-TiO₂ nanocomposites at different SnO contents compared with Hombikat UV-100 as a reference.

The reference UV-100 catalyst achieves a concentration of 0.051 mmol/L. After 120 min, imazapyr concentrations continue to decrease, with the 0.1% SnO content exhibiting the lowest concentration at 0.016 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.041 mmol/L. At the end of the 180-minute test, imazapyr concentrations continue to decrease for all catalysts, with the 0.1% SnO content having the lowest concentration at 0.012 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.029 mmol/L⁶⁴. Figure 3 illustrates the effect of different SnO contents in mesoporous SnO-TiO₂ nanocomposites on the degradation of imazapyr over time. All SnO-TiO₂ nanocomposites show the ability to significantly reduce imazapyr concentrations, with the 0.1% SnO content consistently achieving the lowest concentrations at various time intervals. The reference catalyst, UV-100, also exhibits degradation capabilities but generally has higher imazapyr concentrations compared to the 0.1% SnO nanocomposite. These results suggest that SnO-TiO₂ nanocomposites possess photocatalytic activity in degrading imazapyr, and the presence of SnO content significantly enhances their efficiency. Longer illumination times lead to lower imazapyr concentrations, indicating the potential for photocatalytic degradation of this herbicide. Further research may be required to optimize the SnO content and other experimental parameters for the most efficient removal of imazapyr using SnO-TiO₂ nanocomposites⁶⁵.

Table 3 presents the herbicide residual concentrations over time for different catalyst concentrations (5%, 3%, 1%, 0.5%, 0.1%) and UV100 treatment. Each value represents the mean herbicide concentration with corresponding standard error, illustrating the degradation kinetics under varying conditions. The results demonstrate how catalyst concentration and UV treatment influence the rate of herbicide decomposition over time.

Table 3.

Time-dependent residual concentration of herbicide (Ct in mmol/L) with various catalyst percentages and UV100 treatment (Mean ± Standard Error).

Min	5%	3%	1%	0.5%	0.1%	UV100
0	0.087 ± 0.003	0.085 ± 0.003	0.084 ± 0.003	0.087 ± 0.003	0.071 ± 0.003	0.083 ± 0.003
15	0.066 ± 0.003	0.053 ± 0.003	0.062 ± 0.003	0.062 ± 0.003	0.052 ± 0.003	0.069 ± 0.003
30	0.058 ± 0.003	0.053 ± 0.003	0.051 ± 0.003	0.05 ± 0.003	0.037 ± 0.002	0.062 ± 0.003
60	0.044 ± 0.002	0.043 ± 0.002	0.041 ± 0.002	0.04 ± 0.002	0.025 ± 0.002	0.058 ± 0.003
90	0.034 ± 0.002	0.033 ± 0.002	0.03 ± 0.002	0.03 ± 0.002	0.017 ± 0.002	0.051 ± 0.003
120	0.025 ± 0.002	0.024 ± 0.002	0.02 ± 0.002	0.021 ± 0.002	0.016 ± 0.002	0.041 ± 0.002
180	0.012 ± 0.002	0.011 ± 0.002	0.019 ± 0.002	0.019 ± 0.002	0.012 ± 0.002	0.029 ± 0.002

Mesoporous Ta2O3-TiO2 nanocomposites

Figure 4 presents the changes in imazapyr concentration (C_t) as a function of illumination time in the presence of mesoporous Ta₂O₃-TiO₂ nanocomposites at different Ta₂O₃ contents, along with Hombikat UV-100 as a reference catalyst. Figure 4 shows the residual concentration of the herbicide at various time intervals. At the start of the experiment, the initial concentration of imazapyr in the solution is approximately 0.087 mmol/L when no catalyst is present. In the presence of Ta₂O₃-TiO₂ nanocomposites, the initial concentrations vary with different Ta₂O₃ contents, ranging from 0.084 mmol/L to 0.086 mmol/L. The reference catalyst, UV-100, shows an initial concentration of 0.083 mmol/L. After just 5 min of illumination, the imazapyr concentrations remain relatively constant for all catalysts, indicating limited degradation during this short time. At the 15-minute mark, imazapyr concentrations start to decrease for all catalysts, with the 0.1% Ta₂O₃ content achieving the lowest concentration at 0.069 mmol/L⁶⁶. The reference UV-100 catalyst also reduces the concentration to 0.073 mmol/L. After 30 min, imazapyr concentrations continue to decrease for all catalysts, with the 0.1% Ta₂O₃ content exhibiting the lowest concentration at 0.062 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.064 mmol/L. At the 60-minute mark, imazapyr concentrations continue to decrease, with the 0.1% Ta₂O₃ content achieving the lowest concentration at 0.048 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.058 mmol/L. At 90 min, imazapyr concentrations further decreased for all catalysts, with the 0.1% Ta₂O₃ content having the lowest concentration at 0.035 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.051 mmol/L. After 120 min, imazapyr concentrations continue to decrease, with the 0.1% Ta₂O₃ content achieving the lowest concentration at 0.029 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.041 mmol/L. At the end of the 180-minute test, imazapyr concentrations continue to decrease for all catalysts, with the 0.1% Ta₂O₃ content having the lowest concentration at 0.015 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.029 mmol/L⁶⁷. Figure 4 provides insights into the impact of different Ta₂O₃ contents in mesoporous Ta₂O₃-TiO₂ nanocomposites on the degradation of imazapyr over time. Initially, there is limited degradation during the first 5 min for all catalysts, but after 15 min, imazapyr concentrations start to decrease significantly. Among the Ta₂O₃-TiO₂ nanocomposites, the 0.1% Ta₂O₃ content consistently achieves the lowest imazapyr concentrations at various time intervals. The reference catalyst, UV-100, also exhibits degradation capabilities but tends to have slightly higher imazapyr concentrations compared to the 0.1% Ta₂O₃ nanocomposite. These results suggest that Ta₂O₃-TiO₂ nanocomposites possess photocatalytic activity in degrading imazapyr, and the presence of Ta₂O₃ content significantly enhances their efficiency. Longer illumination times lead to lower imazapyr concentrations, indicating the potential for photocatalytic degradation of this herbicide. Further research may be necessary to optimize the Ta₂O₃ content and other experimental parameters to maximize the efficiency of Ta₂O₃-TiO₂ nanocomposites for imazapyr removal applications⁶⁸.

Fig. 4.

Change in imazapyr concentration as a function of illumination time in the presence of mesoporous Ta₂O₃-TiO₂ nanocomposites at different Ta₂O₃ contents compared with Hombikat UV-100 as a reference.

Table 4 presents the change in optical density of imazapyr concentrations over various illumination times (0 to 180 min) when exposed to mesoporous Ta₂O₃-TiO₂ nanocomposites with differing Ta₂O₃ contents. The data shows a comparative analysis against Hombikat UV-100 as a reference, highlighting the influence of Ta₂O₃ concentration on the photostability of imazapyr. Optical density values decrease with increased illumination time, indicating a potential degradation of imazapyr under UV exposure.

Table 4.

Change in optical density of imazapyr concentrations over illumination time with mesoporous Ta₂O₃-TiO₂ nanocomposites at varying Ta₂O₃ contents, compared to hombikat UV-100 as a reference.

Min	100%	5%	1%	0.5%	0.1%	UV100
0	0.087 ± 0.003	0.085 ± 0.003	0.084 ± 0.003	0.086 ± 0.003	0.086 ± 0.003	0.083 ± 0.003
5	0.087 ± 0.003	0.083 ± 0.003	0.082 ± 0.003	0.084 ± 0.003	0.083 ± 0.003	0.076 ± 0.003
15	0.085 ± 0.003	0.075 ± 0.003	0.075 ± 0.003	0.078 ± 0.003	0.073 ± 0.003	0.069 ± 0.003
30	0.081 ± 0.003	0.068 ± 0.003	0.068 ± 0.003	0.070 ± 0.003	0.064 ± 0.003	0.062 ± 0.003
60	0.077 ± 0.003	0.055 ± 0.003	0.054 ± 0.003	0.054 ± 0.003	0.048 ± 0.002	0.058 ± 0.003
90	0.074 ± 0.003	0.047 ± 0.002	0.054 ± 0.003	0.043 ± 0.002	0.035 ± 0.002	0.051 ± 0.003
120	0.068 ± 0.003	0.038 ± 0.002	0.046 ± 0.003	0.035 ± 0.002	0.029 ± 0.002	0.041 ± 0.002
180	0.059 ± 0.003	0.024 ± 0.002	0.037 ± 0.002	0.021 ± 0.002	0.015 ± 0.002	0.029 ± 0.002

Mesoporous ZnO-TiO2 nanocomposites

Figure 5 presents the changes in imazapyr concentration (C_t) as a function of illumination time in the presence of mesoporous ZnO-TiO₂ nanocomposites at different ZnO contents, along with Hombikat UV-100 as a reference catalyst. The table shows the residual concentration of the herbicide at various time intervals. At the beginning of the experiment, the initial concentration of imazapyr in the solution is approximately 0.067 mmol/L when no catalyst is present. In the presence of ZnO-TiO₂ nanocomposites, the initial concentrations vary with different ZnO contents, ranging from 0.061 mmol/L to 0.064 mmol/L. The reference catalyst, UV-100, shows an initial concentration of 0.083 mmol/L. After 5 min of illumination, all catalysts, including the reference UV-100, show a slight decrease in imazapyr concentrations. However, the reductions are relatively small at this early stage. At the 15-minute mark, imazapyr concentrations begin to decrease more noticeably for all catalysts. Among the ZnO-TiO₂ nanocomposites, the 0.1% ZnO content achieves the lowest concentration at 0.044 mmol/L. The reference UV-100 catalyst also reduces the concentration to 0.069 mmol/L. After 30 min, imazapyr concentrations continue to decrease for all catalysts, with the 0.1% ZnO content exhibiting the lowest concentration at 0.032 mmol/L⁶⁹. The reference UV-100 catalyst achieves a concentration of 0.062 mmol/L. At the 60-minute mark, imazapyr concentrations further decreased, with the 0.1% ZnO content achieving the lowest concentration at 0.015 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.058 mmol/L. At 90 min, imazapyr concentrations continue to decrease for all catalysts, with the 0.1% ZnO content having the lowest concentration at 0.015 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.051 mmol/L. After 120 min, imazapyr concentrations continue to decrease, with the 0.1% ZnO content achieving the lowest concentration at 0.007 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.041 mmol/L. At the end of the 180-minute test, imazapyr concentrations continue to decrease for all catalysts, with the 0.1% ZnO content having the lowest concentration at 0.003 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.029 mmol/L. Figure 5 provides insights into the impact of different ZnO contents in mesoporous ZnO-TiO₂ nanocomposites on the degradation of imazapyr over time. While there is a slight reduction in imazapyr concentration during the initial 5 min, significant degradation begins to occur after 15 min of illumination. Among the ZnO-TiO₂ nanocomposites, the 0.1% ZnO content consistently achieves the lowest imazapyr concentrations at various time intervals⁷⁰. The reference catalyst, UV-100, also exhibits degradation capabilities but generally has slightly higher imazapyr concentrations compared to the 0.1% ZnO nanocomposite. These results suggest that ZnO-TiO₂ nanocomposites possess photocatalytic activity in degrading imazapyr, and the presence of ZnO content significantly enhances their efficiency. Longer illumination times lead to lower imazapyr concentrations, indicating the potential for photocatalytic degradation of this herbicide. Further research may be necessary to optimize the ZnO content and other experimental parameters to maximize the efficiency of ZnO-TiO₂ nanocomposites for imazapyr removal applications⁷¹.

Fig. 5.

Change in imazapyr concentration as a function of illumination time in the presence of mesoporous ZnO-TiO₂ nanocomposites at different ZnO contents compared with Hombikat UV-100 as a reference.

Table 5 illustrates the change in residual imazapyr concentration over time (0 to 180 min) when treated with mesoporous ZnO-TiO₂ nanocomposites at varying ZnO contents. The data is compared to Hombikat UV-100 as a reference, showing a decline in imazapyr concentration with increased illumination time. The results suggest that the presence of different ZnO contents in the nanocomposites influences the degradation of imazapyr, indicating their potential effectiveness in photodegradation applications.

Table 5.

Change in residual imazapyr concentration as a function of illumination time with mesoporous ZnO-TiO₂ nanocomposites at different ZnO contents, compared to hombikat UV-100 as a reference.

Min	100%	5%	1%	0.5%	0.1%	UV100
0	0.067 ± 0.003	0.064 ± 0.003	0.062 ± 0.003	0.063 ± 0.003	0.061 ± 0.003	0.083 ± 0.003
5	0.064 ± 0.003	0.061 ± 0.003	0.058 ± 0.003	0.059 ± 0.003	0.054 ± 0.003	0.076 ± 0.003
15	0.048 ± 0.003	0.052 ± 0.003	0.049 ± 0.003	0.051 ± 0.003	0.044 ± 0.003	0.069 ± 0.003
30	0.048 ± 0.003	0.043 ± 0.003	0.039 ± 0.003	0.042 ± 0.003	0.032 ± 0.003	0.062 ± 0.003
60	0.031 ± 0.003	0.029 ± 0.003	0.019 ± 0.003	0.026 ± 0.003	0.015 ± 0.003	0.058 ± 0.003
90	0.022 ± 0.003	0.02 ± 0.003	0.019 ± 0.003	0.026 ± 0.003	0.015 ± 0.003	0.051 ± 0.003
120	0.01 ± 0.003	0.017 ± 0.003	0.007 ± 0.003	0.016 ± 0.003	0.007 ± 0.003	0.041 ± 0.003
180	0.003 ± 0.003	0.009 ± 0.003	0.003 ± 0.003	0.007 ± 0.003	0.003 ± 0.003	0.029 ± 0.003

Mesoporous ZrO-TiO2 nanocomposites

Figure 6 presents the changes in imazapyr concentration (C_t) as a function of illumination time in the presence of mesoporous ZrO-TiO₂ nanocomposites at different ZrO contents, along with Hombikat UV-100 as a reference catalyst. The table shows the residual concentration of the herbicide at various time intervals. At the start of the experiment, the initial concentration of imazapyr in the solution is approximately 0.085 mmol/L when no catalyst is present. In the presence of ZrO-TiO₂ nanocomposites, the initial concentrations vary with different ZrO contents, ranging from 0.081 mmol/L to 0.085 mmol/L. The reference catalyst, UV-100, shows an initial concentration of 0.083 mmol/L. After 5 min of illumination, all catalysts, including the reference UV-100, show little to no change in imazapyr concentrations, indicating limited degradation during this short time. At the 15-minute mark, imazapyr concentrations start to decrease for all catalysts. Among the ZrO-TiO₂ nanocomposites, the 0.1% ZrO content achieves the lowest concentration at 0.065 mmol/L⁷². The reference UV-100 catalyst also reduces the concentration to 0.075 mmol/L. After 30 min, imazapyr concentrations continue to decrease for all catalysts, with the 0.1% ZrO content exhibiting the lowest concentration at 0.041 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.052 mmol/L. At the 60-minute mark, imazapyr concentrations further decreased, with the 0.1% ZrO content achieving the lowest concentration at 0.026 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.045 mmol/L⁷³. At 90 min, imazapyr concentrations continue to decrease for all catalysts, with the 0.1% ZrO content having the lowest concentration at 0.013 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.030 mmol/L. After 120 min, imazapyr concentrations continue to decrease, with the 0.1% ZrO content achieving the lowest concentration at 0.017 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.031 mmol/L. At the end of the 180-minute test, imazapyr concentrations continue to decrease for all catalysts, with the 0.1% ZrO content having the lowest concentration at 0.004 mmol/L. The reference UV-100 catalyst achieves a concentration of 0.025 mmol/L. Figure 6 provides insights into the impact of different ZrO contents in mesoporous ZrO-TiO₂ nanocomposites on the degradation of imazapyr over time⁷⁴. Initially, there is limited degradation during the first 5 min for all catalysts. Significant degradation starts to occur after 15 min of illumination. Among the ZrO-TiO₂ nanocomposites, the 0.1% ZrO content consistently achieves the lowest imazapyr concentrations at various time intervals. The reference catalyst, UV-100, also exhibits degradation capabilities but generally has slightly higher imazapyr concentrations compared to the 0.1% ZrO nanocomposite. These results suggest that ZrO-TiO₂ nanocomposites possess photocatalytic activity in degrading imazapyr, and the presence of ZrO content significantly enhances their efficiency. Longer illumination times lead to lower imazapyr concentrations, indicating the potential for photocatalytic degradation of this herbicide. Further research may be necessary to optimize the ZrO content and other experimental parameters to maximize the efficiency of ZrO-TiO₂ nanocomposites for imazapyr removal applications⁷⁵.

Fig. 6.

Change in imazapyr concentration as a function of illumination time in the presence of mesoporous ZrO-TiO₂ nanocomposites at different ZrO contents compared with Hombikat UV-100 as a reference.

Table 6 presents the residual concentrations of imazapyr over varying illumination times with mesoporous ZrO-TiO₂ nanocomposites at different ZrO contents. The data illustrate the degradation of imazapyr, showcasing a comparative analysis with Hombikat UV-100 as a reference. As illumination time increases, a notable decrease in imazapyr concentration is observed across all ZrO content levels, highlighting the efficacy of the mesoporous nanocomposites in facilitating herbicide degradation.

Table 6.

Change in residual imazapyr concentration over illumination time with mesoporous ZrO-TiO₂ nanocomposites at various ZrO contents: a comparative analysis with hombikat UV-100 as a reference.

Min	100%	1%	0.6%	0.2%	0.1%	0.02
0	0.085 ± 0.003	0.084 ± 0.003	0.085 ± 0.003	0.083 ± 0.003	0.081 ± 0.003	0.083 ± 0.003
5	0.085 ± 0.003	0.071 ± 0.003	0.073 ± 0.003	0.074 ± 0.003	0.077 ± 0.003	0.081 ± 0.003
15	0.084 ± 0.003	0.054 ± 0.003	0.057 ± 0.003	0.063 ± 0.003	0.065 ± 0.003	0.075 ± 0.003
30	0.083 ± 0.003	0.051 ± 0.003	0.041 ± 0.003	0.052 ± 0.003	0.058 ± 0.003	0.065 ± 0.003
60	0.08 ± 0.003	0.03 ± 0.003	0.026 ± 0.003	0.034 ± 0.003	0.045 ± 0.003	0.057 ± 0.003
90	0.077 ± 0.003	0.020 ± 0.003	0.013 ± 0.003	0.02 ± 0.003	0.03 ± 0.003	0.043 ± 0.003
120	0.075 ± 0.003	0.075 ± 0.003	0.07 ± 0.003	0.017 ± 0.003	0.026 ± 0.003	0.031 ± 0.003
180	0.066 ± 0.003	0.004 ± 0.003	0.004 ± 0.003	0.013 ± 0.003	0.015 ± 0.003	0.025 ± 0.003

Comparative results of mesoporous nanocomposites

Figure 7 provides a comparison between different composite catalysts for the photodegradation of the herbicide Imazapyr at a concentration of 0.1% of the metal oxide in each composite. The table displays the residual concentrations (Ct) at various illumination times and includes TiO₂-CuO, Fe₂O₃, SnO, Ta₂O₃, ZnO, ZrO, and UV100 as reference catalysts. At the start of the experiment (0 min), all catalysts exhibit varying initial concentrations of imazapyr⁷⁶. Among the composite catalysts, TiO₂-CuO, Fe₂O₃, and Ta₂O₃ have initial concentrations slightly higher than that of UV100, while SnO, ZnO, and ZrO have lower initial concentrations. Notably, CuO-TiO₂ (TiO₂-CuO) has the highest initial concentration at 0.083 mmol/L, while ZnO-TiO₂ (ZnO) has the lowest at 0.061 mmol/L. After 15 min of illumination, all composite catalysts show a reduction in imazapyr concentration. CuO-TiO₂ (TiO₂-CuO) and Fe₂O₃ exhibit similar reductions and have the lowest concentrations at 0.07 mmol/L and 0.069 mmol/L, respectively. Among all catalysts, SnO-TiO₂ (SnO) has the lowest concentration at 0.052 mmol/L. ZrO-TiO₂ (ZrO) shows the least reduction, with a concentration of 0.077 mmol/L. At 30 min, imazapyr concentrations continue to decrease for all catalysts. SnO-TiO₂ (SnO) has the lowest concentration at 0.037 mmol/L, while ZrO-TiO₂ (ZrO) still exhibits slower degradation with a concentration of 0.065 mmol/L. After 60 min, imazapyr concentrations continue to decline. SnO-TiO₂ (SnO) and ZnO-TiO₂ (ZnO) have the lowest concentrations at 0.025 mmol/L and 0.032 mmol/L, respectively⁷⁷. ZrO-TiO₂ (ZrO) remains the slowest in degrading imazapyr with a concentration of 0.058 mmol/L. At 90 min, the imazapyr concentrations continue to decrease. SnO-TiO₂ (SnO) still exhibits efficient degradation with a concentration of 0.015 mmol/L, while ZrO-TiO₂ (ZrO) lags with a concentration of 0.03 mmol/L. After 120 min, imazapyr concentrations continue to decrease for all catalysts. SnO-TiO₂ (SnO) and ZnO-TiO₂ (ZnO) achieve lower concentrations compared to other catalysts. At the end of the 180-minute test, imazapyr concentrations further decreased for all catalysts. SnO-TiO₂ (SnO) has the lowest concentration at 0.012 mmol/L, indicating efficient degradation. ZrO-TiO₂ (ZrO) still has a relatively higher concentration at 0.026 mmol/L, indicating slower degradation. Figure 7 provides a comparative view of the efficiency of different composite catalysts in the photodegradation of Imazapyr. SnO-TiO₂ (SnO) consistently performs well, achieving the lowest concentrations at most time intervals, indicating its strong photocatalytic activity for Imazapyr degradation. TiO₂-CuO (CuO-TiO₂) and Fe₂O₃ exhibit competitive degradation efficiency with Imazapyr concentrations close to SnO-TiO₂. ZnO-TiO₂ (ZnO) shows relatively efficient degradation⁷⁸. ZrO-TiO₂ (ZrO) appears to be less effective in degrading Imazapyr compared to other composites, with slower degradation rates and higher residual concentrations. The reference catalyst, UV100, exhibits moderate degradation capabilities but tends to have slightly higher imazapyr concentrations compared to some of the composite catalysts. The choice of composite catalyst plays a crucial role in the photodegradation of Imazapyr, and further research may be needed to optimize the conditions for each catalyst to maximize their efficiency in herbicide removal applications⁷⁹.

Fig. 7.

Photodegradation efficiency of imazapyr: a comparative analysis of different composite catalysts with 0.1 wt% metal oxide additives.

The superior performance of CuO-TiO₂ over Fe₂O₃-TiO₂ in many photocatalytic and corrosion inhibition applications can be attributed to several key factors related to their electronic structures, band alignment, charge separation efficiency, and photocatalytic activity. CuO-TiO₂: CuO has a relatively narrow band gap (~ 1.2–1.7 eV), which allows it to absorb a significant portion of the visible light spectrum. When combined with TiO₂ (band gap ~ 3.2 eV), CuO extends TiO₂’s light absorption capabilities from UV to visible light. This enables CuO-TiO₂ composites to be more active under sunlight or visible light, making them highly efficient for applications such as photocatalysis and environmental remediation. CuO-TiO₂: In a CuO-TiO₂ heterojunction, the conduction band (CB) of CuO is lower than that of TiO₂, while the valence band (VB) of CuO is higher than TiO₂. This favorable band alignment facilitates the transfer of photogenerated electrons from the conduction band of TiO₂ to the conduction band of CuO, while the holes remain in the valence band of TiO₂. This separation of electrons and holes reduces recombination, increasing photocatalytic efficiency. CuO acts as an electron sink due to its lower conduction band, allowing it to effectively trap and transfer electrons. This greatly enhances charge separation, reducing electron-hole recombination, and improving photocatalytic performance. The Schottky barrier formed at the CuO-TiO₂ interface effectively suppresses electron-hole recombination. This barrier arises due to the difference in Fermi levels between CuO and TiO₂, which prevents the backflow of electrons into TiO₂, keeping the electrons and holes separated for a longer period and allowing them to participate in redox reactions. Plasmonic Enhancement: In some cases, CuO can exhibit plasmonic effects that enhance local electromagnetic fields and improve charge separation even further. CuO has a high redox potential and the ability to undergo reversible redox reactions (Cu²⁺ ↔ Cu⁺), which makes it highly effective for photocatalytic and electrochemical processes. The Cu²⁺/Cu⁺ redox cycle contributes to CuO’s superior ability to catalyze oxidation-reduction reactions, such as the degradation of pollutants or water splitting. Photocatalytic Degradation: CuO-TiO₂ composites are particularly effective in photocatalytic degradation of organic pollutants and hydrogen production due to CuO’s higher catalytic efficiency in redox reactions. CuO is relatively more stable in various environmental conditions compared to Fe₂O₃. CuO-TiO₂ composites tend to have higher durability, especially in harsh environments such as strong acidic or alkaline media, where Fe₂O₃ may undergo dissolution or degradation. Longer Operational Life: The stability of CuO in photocatalytic and corrosion inhibition applications makes it a preferred choice for long-term operation. CuO-TiO₂ composites often exhibit higher photocurrent densities compared to Fe₂O₃-TiO₂. This is due to the more efficient charge separation and electron transfer processes in CuO-TiO₂ systems, leading to higher overall photocatalytic efficiency. Faster Electron Transfer: The high electron mobility in CuO contributes to faster charge transfer between CuO and TiO₂, resulting in enhanced photocurrent generation and more efficient energy conversion. These factors collectively explain why CuO-TiO₂ typically outperforms Fe₂O₃-TiO₂ in various applications, including photocatalysis, energy conversion, and environmental remediation.

Table 7 presents the residual concentrations of Imazapyr over varying illumination times using different metal oxide composite catalysts. Each catalyst, including TiO₂-CuO, Fe₂O₃, SnO, Ta₂O₃, ZnO, and ZrO, demonstrates distinct degradation efficiencies compared to the UV100 reference. The results indicate a general trend of decreasing herbicide concentration with increased illumination time, highlighting the effectiveness of the catalysts in facilitating photodegradation.

Table 7.

Comparative evaluation of different composite catalysts for the photodegradation of imazapyr herbicide at 0.1% metal oxide concentration.

Min	TiO2-CuO, 0.1%	Fe2O3, 0.1%	SnO, 0.1%	Ta2O3, 0.1%	ZnO, 0.1%	ZrO, 0.1%	UV100
0	0.083 ± 0.003	0.082 ± 0.003	0.071 ± 0.003	0.086 ± 0.003	0.061 ± 0.003	0.081 ± 0.003	0.083 ± 0.003
15	0.07 ± 0.003	0.069 ± 0.003	0.052 ± 0.003	0.073 ± 0.003	0.054 ± 0.003	0.077 ± 0.003	0.069 ± 0.003
30	0.059 ± 0.003	0.067 ± 0.003	0.037 ± 0.003	0.064 ± 0.003	0.044 ± 0.003	0.065 ± 0.003	0.062 ± 0.003
60	0.043 ± 0.003	0.052 ± 0.003	0.025 ± 0.003	0.048 ± 0.003	0.032 ± 0.003	0.058 ± 0.003	0.058 ± 0.003
90	0.032 ± 0.003	0.046 ± 0.003	0.017 ± 0.003	0.035 ± 0.003	0.015 ± 0.003	0.045 ± 0.003	0.051 ± 0.003
120	0.017 ± 0.003	0.04 ± 0.003	0.016 ± 0.003	0.029 ± 0.003	0.015 ± 0.003	0.03 ± 0.003	0.041 ± 0.003
180	0.008 ± 0.003	0.027 ± 0.003	0.012 ± 0.003	0.015 ± 0.003	0.007 ± 0.003	0.026 ± 0.003	0.029 ± 0.003

Comparative characterization results

Structural analysis by X-ray diffraction (XRD)

Using X-ray diffraction analysis, we determined the crystalline phase of TiO₂ and TiO₂ doped with various oxide nanoparticles. In Fig. 8, the XRD data for pure TiO₂ exhibited broad peaks at 2θ values of 25.27, 37.71, 47.98, 54.21, 56.35, 62.55, 68.77, 69.83, and 74.76°, corresponding to planes (101), (004), (200), (105), (211), (204), (301), (008), and (224). This confirms the tetragonal structure of Ti0.72O2 nanoparticles, as indicated by JCPDS reference code 00-086-1157. By doping by different oxides, i.e. Zr, Zn, Ta, Fe, and Cu, 4 new peaks (at 27.20, 35.93, 41.05, and 43.96° highlighted by yellow, green, red, and blue colors, respectively) with different intensity and different shapes. For Zr-doped TiO₂, the peaks related to orthorhombic Zr₅Ti₇O₂₄ (JCPDS: 00-084-1019). For Zn-doped TiO₂, these peaks are related to cubic Zn₂Ti₃O₈ (JCPDS: 00-087-1781). For Ta-doped TiO₂, the peaks are related to tetragonal TiTaO₄ (JCPDS: 00-071-0929). For Fe-doped TiO₂, these peaks are related to hexagonal Fe₂Ti₃O₉ (JCPDS: 00-029-1494). For Cu-doped TiO₂, these peaks are related to cubic Cu₃Ti₃O (JCPDS: 00-075-0400). The Sn-doped TiO₂ did not show the 4 peaks that were observed in other dopants, but the peak at 54.21 splits into two close peaks at 53.66° and 54.77° (highlighted by turquoise color). These two peaks are related to tetragonal (Ti0.85Sn0.15) O2 (JCPDS: 00-081-1387)⁸⁰.

Fig. 8.

XRD curves of pure TiO₂ and TiO₂ doped with Zr, Zn, Ta, Fe, Cu, and Sn.

In Fig. 8, X-ray Diffraction (XRD) curves of pure TiO₂ and TiO₂ doped with Zr, Zn, Ta, Fe, Cu, and Sn are presented. The XRD analysis provides crucial information about the crystal structure and phase composition of the synthesized materials. Here’s a detailed discussion of the observed XRD curves⁸¹. In the case of pure TiO₂, the XRD pattern of pure TiO₂ serves as a reference for the undoped material. Key peaks corresponding to the anatase or rutile phases of TiO₂ are expected and can be identified. The sharpness and position of these peaks indicate the crystallinity and purity of the synthesized TiO₂. For the TiO₂/Zr composite, the XRD curve for TiO₂ doped with Zr is analyzed for any shifts in peak positions or the appearance of new peaks⁸². The presence of ZrO₂ peaks alongside TiO₂ peaks suggests the successful incorporation of Zr into the TiO₂ lattice. In the case of TiO₂/Zn composite, similar analysis is applied to the TiO₂/Zn composite. Any additional peaks corresponding to ZnO should be observed. Shifts in TiO₂ peaks may also indicate interactions between TiO₂ and ZnO phases. For TiO₂/Ta composite, the XRD pattern for TiO₂/Ta is scrutinized for characteristic peaks of Ta₂O₅. The coexistence of TiO₂ and Ta₂O₅ peaks confirms the presence of both materials⁸³. For TiO₂/Fe composite, TiO₂ doped with Fe, changes in peak positions or the emergence of Fe₂O₃ peaks are examined. The XRD pattern indicates whether Fe has been successfully incorporated into the TiO₂ lattice. In TiO₂/Cu composite, the XRD curve for TiO₂/Cu is assessed for CuO peaks alongside TiO₂ peaks. Any shifts or broadening of TiO₂ peaks may suggest interactions with CuO⁸⁴. Finally, in the case of TiO₂/Sn composite, the XRD analysis of TiO₂/Sn focuses on identifying peaks associated with SnO₂. Confirmation of SnO₂ presence in the composite is crucial for assessing the doping effect. Generally, changes in peak intensities, positions, or the emergence of new peaks indicate the successful doping of TiO₂ with the respective elements. The preservation of key TiO₂ peaks demonstrates the retention of its crystal structure even after doping. Successful doping can lead to alterations in the electronic structure, enhancing the photocatalytic properties of TiO₂⁸⁵. The nature of the observed phases (anatase, rutile, ZnO, Ta₂O₅, Fe₂O₃, CuO, SnO₂) influences the overall properties of the composite materials. Detailed peak assignments and quantitative phase analysis could provide deeper insights into the doping effects⁸⁶. Complementary techniques, such as SEM and TEM, can corroborate the structural information obtained from XRD. In conclusion, the XRD curves in Fig. 8 confirm the successful doping of TiO₂ with Zr, Zn, Ta, Fe, Cu, and Sn, providing valuable information about the crystallographic changes induced by the dopants. These findings are pivotal for understanding and optimizing the enhanced photocatalytic applications of the doped TiO₂ composites⁸⁷.

Transmission electron microscopy (TEM) results

The transmission electron microscopy (TEM) images presented in Fig. 9 offer valuable insights into the morphological characteristics of both pure TiO₂ and its composite forms with Zr, Zn, Ta, Fe, Cu, and Sn. These composite variations are crucial for tailoring the properties of TiO₂, expanding its potential applications in various fields. In the case of pure TiO₂, the TEM image of pure TiO₂ serves as a baseline, showcasing the inherent morphology of titanium dioxide nanoparticles⁸⁸. The characteristic features, such as particle size, shape, and distribution, are essential for understanding the structural properties of TiO₂. For the TiO₂-Zr composite, the composite form with Zr exhibits distinct morphological changes compared to pure TiO₂⁸⁹. The TEM image reveals potential alterations in particle size, agglomeration, or even the introduction of new structures, indicating the influence of Zr on the TiO₂ matrix. In the case of the TiO₂-Zn composite, similar to TiO₂-Zr, the composite with Zn introduces modifications in the morphology⁹⁰. The TEM image highlights any shifts in particle characteristics, shedding light on the synergistic effects of Zn composite with TiO₂. In TiO₂-Ta composite, the TEM image of TiO₂-Ta showcases the impact of tantalum composite on the titanium dioxide structure. Observations related to particle arrangement and size distribution provide crucial information on the composite’s influence⁹¹. For TiO₂-Fe composite, composite TiO₂ with iron (Fe) can impart unique properties. The TEM image reveals any changes in the nanoscale features, helping to understand how the introduction of iron alters the morphology and structure of TiO₂. The TiO₂-Cu composite, copper (Cu) composite introduces its own set of characteristics⁹². The TEM image elucidates how the addition of copper influences the TiO₂ morphology, potentially impacting properties such as conductivity or catalytic activity. But in the case of TiO₂-Sn composite, Tin (Sn) composite can lead to morphological variations in TiO₂. The TEM image allows for a detailed examination of these changes, aiding in the assessment of Sn’s role in modifying the TiO₂ nanostructure⁹³. In summary, the TEM images provide a comprehensive visual analysis of the morphological features in each composite form of TiO₂. These insights are instrumental in understanding the nanoscale changes induced by compositing elements, contributing to the design and optimization of TiO₂-based materials for diverse applications⁹⁴.

Fig. 9.

TEM images unveil the morphological insights of pure TiO₂ and its composite forms with Zr, Zn, Ta, Fe, Cu, and Sn.

Surface area measurements

The surface area variations depicted in Fig. 10 provide crucial insights into the tailored applications of pure TiO₂ and its composite forms with Zr, Zn, Ta, Fe, Cu, and Sn. Each composition exhibits distinct surface area characteristics that hold significant implications for their practical utilization. Pure TiO₂ demonstrates a baseline surface area of UV-100, serving as a reference for comparison. Alloying with ZrO, ZnO, Ta₂O₃, SnO, Fe₂O₃, and TiO₂-CuO at 0.1% concentration results in diverse surface area alterations⁹⁵. Notably, ZrO exhibits a substantial reduction, while ZnO and Ta₂O₃ show moderate decreases. In contrast, SnO and Fe₂O₃ demonstrate a slight increase in surface area, indicating nuanced impacts. The composite form TiO₂-CuO at 0.1% concentration stands out with a distinctive surface area value, suggesting a unique interplay between TiO₂ and CuO. These variations in surface area are pivotal for tailoring the materials to specific applications, influencing factors like catalytic activity, adsorption capacity, and overall performance. The observed trends in surface area variations provide a foundation for optimizing the compositions based on targeted functionalities, contributing to the advancement of tailored applications in diverse fields⁹⁶.

Fig. 10.

Surface area variations in pure TiO₂ and composite forms with Zr, Zn, Ta, Fe, Cu, and Sn for tailored applications.

Av. Pore size measurements

The variations in average pore size illustrated in Fig. 11 provide valuable insights into the tailored applications of pure TiO₂ and its composite forms with Zr, Zn, Ta, Fe, Cu, and Sn. The average pore size is a critical parameter influencing the materials’ porosity, surface reactivity, and potential applications. Pure TiO₂, represented by UV-100, exhibits an average pore size of 2.7399, serving as a reference point for comparison. Alloying with different elements at a 0.1% concentration results in diverse changes in average pore size⁹⁷. Notably, ZrO shows a significant increase, indicating a substantial alteration in the material’s pore structure. ZnO and Ta₂O₃ exhibit moderate increases, while SnO demonstrates a slight decrease in average pore size. Fe₂O₃ and TiO₂-CuO exhibit notable increases, suggesting distinctive impacts on pore characteristics⁹⁸. The composite form TiO₂-CuO at 0.1% concentration stands out with a notable change in average pore size, indicating a unique interplay between TiO₂ and CuO. These variations are crucial for tailoring the materials to specific applications, influencing factors like adsorption capacity, diffusion rates, and overall performance. The observed trends in average pore size variations provide essential information for optimizing compositions based on targeted functionalities, contributing to advancements in tailored applications in diverse fields⁹⁹.

Fig. 11.

Av. pore size variations in pure TiO₂ and composite forms with Zr, Zn, Ta, Fe, Cu, and Sn for tailored applications.

Particle size measurements

The particle size variations depicted in Fig. 12 offer crucial insights into the tailored applications of pure TiO₂ and its composite forms with Zr, Zn, Ta, Fe, Cu, and Sn. Particle size is a fundamental characteristic influencing the materials’ reactivity, stability, and applications in various fields. Pure TiO₂, represented by UV-100, exhibits a particle size of 501.7, serving as a baseline for comparison¹⁰⁰. Alloying with different elements at a 0.1% concentration results in diverse changes in particle size. Notably, ZnO and TiO₂-CuO show a decrease in particle size, suggesting a refining effect on the materials’ structure. ZrO and Ta₂O₃ exhibit marginal reductions, while Fe₂O₃ shows a moderate decrease. SnO, on the other hand, demonstrates a substantial increase in particle size¹⁰¹. Among the composite forms, SnO at 0.1% concentration stands out with a significant increase in particle size, indicating a distinctive impact on the overall structure. These variations are crucial for tailoring the materials to specific applications, influencing factors like photocatalytic efficiency, dispersion properties, and overall performance. The observed trends in particle size variations provide essential information for optimizing compositions based on targeted functionalities, contributing to advancements in tailored applications across diverse industries¹⁰².

Fig. 12.

Particle size variations in pure TiO₂ and composite forms with Zr, Zn, Ta, Fe, Cu, and Sn for tailored applications.

Variance (P.I.) measurements

The Plasticity Index (P.I.) is a measure used in geotechnical engineering to assess the plasticity and workability of soils. It is calculated as the difference between the liquid limit (LL) and plastic limit (PL). A lower P.I. value generally indicates soils with less plasticity and better workability. In the context of the presented data in Fig. 13, where P.I. values are provided for different materials, a P.I. less than 0.8 is considered indicative of accurate preparations, particularly in soil stabilization and geotechnical applications¹⁰³. When the P.I. is less than 0.8, it suggests that the soil or material has low plasticity, making it more stable and easier to work with. This is desirable in scenarios where soil stabilization is crucial, such as construction projects, where the soil needs to maintain its structural integrity¹⁰⁴. Lower plasticity implies that the material is less prone to significant volume changes and is more resistant to deformation under external loads. In the context of the presented data, the materials with P.I. values less than 0.8, such as ZnO and Fe₂O₃, exhibit characteristics of accurate preparations for soil-related applications¹⁰⁵. These materials could be considered for use in scenarios where low plasticity and improved workability are desired. It’s important to note that the interpretation of P.I. values may vary based on specific engineering requirements and the intended application of the materials. The variance (P.I.) variations depicted in Fig. 13 provide valuable insights into the tailored applications of pure TiO₂ and its composite forms with Zr, Zn, Ta, Fe, Cu, and Sn. The Plasticity Index (P.I.) is a crucial parameter in geotechnical engineering, indicating the plasticity and workability of soils. Pure TiO₂, represented by UV-100, exhibits a P.I. of 0.306, serving as a reference for comparison. Introducing different elements at a 0.1% concentration leads to varied changes in the Plasticity Index¹⁰⁶. Notably, ZnO shows a substantial decrease in P.I., indicating a reduction in soil plasticity. ZrO and TiO₂-CuO exhibit moderate increases, suggesting potential enhancements in soil workability. Ta₂O₃ and Fe₂O₃ demonstrate marginal changes, while SnO stands out with a significant increase in P.I., implying a notable impact on soil plasticity. These variations in P.I. are essential for tailoring the materials to specific applications, particularly in soil stabilization and geotechnical engineering. The observed trends in P.I. variations provide valuable information for optimizing compositions based on targeted functionalities, contributing to advancements in tailored applications for soil improvement and related fields¹⁰⁷.

Fig. 13.

Variance (P.I.) variations in pure TiO₂ and composite forms with Zr, Zn, Ta, Fe, Cu, and Sn for tailored applications.

Av. Zeta potential measurements

Zeta potential is an important parameter that indicates the surface charge of particles and their stability in a colloidal system. A higher absolute value of zeta potential typically suggests greater electrostatic repulsion between particles, leading to increased stability. In the context of the provided data in Fig. 14, the zeta potential values for different materials are presented. In the case of UV-100 (-5.7), the negative zeta potential indicates a moderate degree of stability. While not highly stable, the material still exhibits some electrostatic repulsion between particles¹⁰⁸. For ZrO, 0.1% (-3.13), the negative zeta potential suggests moderate stability, like UV-100. However, the absolute value is slightly lower, indicating potentially reduced electrostatic repulsion. But in ZnO, 0.1% (-6.36), this material shows a more negative zeta potential, indicating higher stability than both UV-100 and ZrO. The increased absolute value suggests stronger electrostatic repulsion. In the case of Ta₂O₃ 0.1% (10.61), the positive zeta potential indicates instability, which might be attributed to a lack of electrostatic repulsion between particles. This material may tend to agglomerate. For SnO, 0.1% (-17.82), the highly negative zeta potential suggests excellent stability¹⁰⁹. The material exhibits strong electrostatic repulsion, indicating potential dispersibility and resistance to agglomeration. But in Fe₂O₃, 0.1% (-17.74), like SnO, the highly negative zeta potential implies significant stability. The material is expected to resist agglomeration due to strong electrostatic repulsion. In the case of TiO₂-CuO, 0.1% (-3.39), this material shows a negative zeta potential, indicating moderate stability like UV-100 and ZrO. In summary, materials with higher absolute zeta potential values (either positive or negative) generally exhibit greater stability, which is favorable for various applications where dispersion and prevention of agglomeration are essential. The specific application requirements and the desired behavior of the materials in each system will determine the suitability of each material based on its zeta potential¹¹⁰.

Fig. 14.

Av. Zeta Potential variations in pure TiO₂ and composite forms with Zr, Zn, Ta, Fe, Cu, and Sn for tailored applications.

Mechanistic insight

The modification of titanium dioxide (TiO₂) with specific metal oxides has been widely studied to improve its photocatalytic performance by enhancing charge separation, altering the band structure, and extending the light absorption range. Firstly, the modification of the band structure starting with band gap narrowing since the metal oxides like ZnO, Fe₂O₃, or CuO can narrow the band gap of TiO₂ by introducing new energy levels between the conduction band (CB) and valence band (VB) of TiO₂. This allows for visible light absorption and makes the material more efficient under solar irradiation. For example, Fe₂O₃ has a smaller band gap (~ 2.1 eV) than TiO₂ (~ 3.2 eV for anatase). When coupled with TiO₂, Fe₂O₃ can introduce mid-gap states, shifting TiO₂’s band gap towards the visible region, making it more photoactive under visible light. Secondly, the band alignment for charge transfer is clearly noticed when specific metal oxides form heterojunctions with TiO₂, their conduction and valence bands align in such a way that electrons and holes are preferentially transferred between the two materials. In a typical type-II heterojunction, the conduction band of TiO₂ is higher than that of the metal oxide (e.g., ZnO/TiO₂). This allows electrons excited in TiO₂ to transfer to the metal oxide, facilitating charge separation by preventing recombination. For Z-scheme heterojunction the configuration (e.g., Fe₂O₃/TiO₂), the electrons in the conduction band of TiO₂ reduce the recombination of holes from the valence band of the metal oxide, and the holes from TiO₂ recombine with electrons from the metal oxide. This helps preserve high redox potential. Othe important issue is facilitating charge separation through electron sink effect since the metal oxides with lower Fermi levels, such as WO₃, ZnO, or SnO₂, act as electron acceptors, capturing photo-generated electrons from TiO₂. This process effectively separates the electron-hole pairs and reduces the recombination rate. For example, WO₃/TiO₂ heterojunction, the WO₃ has a conduction band potential more positive than TiO₂, allowing it to act as an electron sink. When coupled with TiO₂, WO₃ captures electrons, leaving holes in the TiO₂ to participate in oxidation reactions. We also facilitating charge separation through schottky barrier formation, since some metal oxides (e.g., ZnO, SnO₂) form Schottky junctions with TiO₂, which facilitate charge separation by creating an energy barrier that impedes the flow of electrons back into TiO₂, preventing recombination. For example, the ZnO/TiO₂ heterostructures often form Schottky-like junctions that efficiently separate charges due to a mismatch in their Fermi levels, with ZnO acting as an electron acceptor. One of the most important mechanisms is interfacial charge transfer mechanisms by firstly direct electron transfer since metal oxides can enable direct charge transfer at the interface between the two materials. Electrons excited in TiO₂ can directly transfer to the metal oxide, where they participate in reduction reactions, while holes remain in TiO₂ for oxidation processes. For example, in CuO/TiO₂ composites, CuO acts as a p-type semiconductor with a conduction band below that of TiO₂. Electrons excited in TiO₂ can be transferred directly to CuO, enhancing charge separation. Secondly, through photoinduced interfacial charge transfer (PICT), since some metal oxides (like Co₃O₄ or Fe₂O₃) can absorb visible light and transfer the photoexcited electrons to the conduction band of TiO₂, while holes remain in the metal oxide. This enhances the charge separation due to the movement of electrons to TiO₂ and the subsequent delay in electron-hole recombination. Other proper mechanisms could be detected by enhancing visible light absorption through metal oxide sensitization since the narrow-band-gap metal oxides (e.g., Fe₂O₃, CuO, BiVO₄) are coupled with TiO₂, they act as sensitizers. These oxides absorb visible light and inject electrons into the conduction band of TiO₂, thereby utilizing a broader portion of the solar spectrum. For example, the CuO has a band gap of ~ 1.2 eV and can absorb visible light. When coupled with TiO₂, CuO transfers its excited electrons to TiO₂, which extends the photocatalytic response of TiO₂ into the visible light region. For plasmonic effects, some doped metal oxides (e.g., Au-doped TiO₂) can exhibit plasmonic effects, whereby localized surface plasmon resonance (LSPR) enhances visible light absorption and creates strong electric fields at the interface of the metal oxide and TiO₂. This enhances charge separation and promotes photocatalysis. For illustration of increasing oxygen vacancies and defect sites it is very important to make creation of oxygen vacancies by doping or coupling TiO₂ with certain metal oxides (e.g., CeO₂, ZnO) introduces oxygen vacancies or other defects. These defects act as electron traps, which can prolong the lifetime of charge carriers by separating the electron-hole pairs, thus enhancing the photocatalytic efficiency. For example, the CeO₂ can undergo redox cycles between Ce³⁺ and Ce⁴⁺, creating oxygen vacancies. When CeO₂ is coupled with TiO₂, the oxygen vacancies in CeO₂ can trap photo-excited electrons, reducing electron-hole recombination and promoting enhanced photocatalytic activity. For reduction and recombination through multi-electron transfer pathways, the metal oxides (e.g., Co₃O₄, MnO₂), electrons can follow multiple pathways, which increase the chances of charge separation and reduce the recombination rate. Such as the Co₃O₄ can facilitate multi-electron transfer due to its mixed-valent structure (Co²⁺/Co³⁺), allowing for enhanced electron flow from TiO₂ to the metal oxide, which reduces recombination and improves photocatalytic efficiency. These mechanistic insights highlight how specific metal oxides significantly influence the performance of TiO₂ in energy and environmental applications by enhancing charge separation and modifying the band structure for more effective photocatalysis.

Suggested future work

Future studies can focus on optimizing the morphology of CuO-TiO₂ composites (e.g., nanotubes, nanowires, or 2D sheets) to enhance surface area and improve photocatalytic efficiency. Advanced synthesis techniques like hydrothermal methods or sol-gel processing could be employed. Doping CuO-TiO₂ with other metal oxides (e.g., ZnO, WO₃) or non-metals (e.g., nitrogen or carbon) could further tune the band structure and enhance charge separation. Surface modifications with organic linkers or functional groups could also improve photocatalytic properties and stability. Developing multi-layer heterojunctions incorporating CuO-TiO₂ with other semiconductors like MoS₂ or g-C₃N₄ could further enhance charge separation and extend visible light absorption. Investigating the interaction at the CuO-TiO₂ interface could lead to more efficient electron-hole separation mechanisms. Future work could explore optimizing CuO-TiO₂ for large-scale hydrogen production from water splitting. This includes testing under real-world conditions (solar illumination, continuous flow systems) and investigating stability over long periods. Investigating CuO-TiO₂ composites in photoelectrochemical (PEC) cells for water splitting or photovoltaic cells could lead to more efficient solar-to-hydrogen conversion systems. Additionally, these materials could be used in dye-sensitized solar cells (DSSCs) or perovskite solar cells to improve efficiency. Further research could explore CuO-TiO₂ as a corrosion inhibitor in aggressive environments like saline or acidic solutions. Studies should focus on applying materials as coatings for metals like steel, aluminum, and copper to investigate long-term performance, durability, and real-world compatibility in industries such as oil and gas, marine, and construction. Testing CuO-TiO₂ composites for environmental remediation (e.g., degradation of organic pollutants, heavy metal removal) in real-world conditions (e.g., varying pH, temperature, or pollutant concentrations) could provide insights into scalability. Future studies could also investigate combining CuO-TiO₂ with adsorption materials for enhanced removal efficiency of contaminants. Future work should focus on scalable, cost-effective synthesis methods for producing CuO-TiO₂ composites in large quantities. Techniques like continuous flow reactors or industrial-scale sol-gel methods should be optimized for industrial production. For applications involving environmental and water purification, it is important to investigate the toxicity and environmental safety of CuO-TiO₂ composites. Future work could involve detailed toxicity studies on the long-term release of Cu²⁺ ions and their effects on ecosystems and human health.

Challenges and limitations

CuO-TiO₂ composites demonstrate significant potential in various applications, several challenges and limitations remain, particularly regarding their scalability and practical deployment in real-world settings. Laboratory-scale synthesis methods such as hydrothermal processes or sol-gel techniques can produce CuO-TiO₂ composites with high efficiency, these methods often involve expensive precursors, long reaction times, and high energy inputs. Scaling up to industrial-scale production while maintaining the material’s performance and quality can be cost-prohibitive. Ensuring the uniformity and consistency of CuO-TiO₂ nanostructures across large production batches is a significant challenge. Variations in particle size, morphology, and composition could lead to inconsistent photocatalytic or electrochemical performance in real-world applications. One of the common challenges for TiO₂-based photocatalysts, including CuO-TiO₂, is photocorrosion, where the material degrades under prolonged exposure to light. This reduces the long-term stability of the material, particularly in applications like water splitting or environmental remediation, where long-term operation is required. CuO-TiO₂ composites may suffer from reduced performance in real-world conditions, such as fluctuating temperatures, humidity, and exposure to different types of pollutants or ions. Ensuring long-term stability in harsh environments, like industrial effluent treatment plants or marine conditions, remains a challenge. Despite CuO’s ability to improve charge separation in TiO₂, recombination of electron-hole pairs remains an issue, particularly under real-world sunlight exposure. Improving electron transfer efficiency and further reducing recombination is critical to improving photocatalytic and energy conversion efficiency. CuO can extend the light absorption range of TiO₂ into the visible region, the overall efficiency of visible light utilization is still limited. Finding the right balance between CuO loading and TiO₂ structure to optimize the band gap while maintaining stability and avoiding excess recombination is a challenge. CuO-TiO₂ composites show great potential in lab settings, integrating them into existing industrial systems (e.g., water treatment plants, solar cells, or anti-corrosion coatings) may require significant infrastructure modification, which could be costly and time-consuming. For instance, adapting CuO-TiO₂ materials to work efficiently in large-scale photoelectrochemical cells or reactors could face technical and engineering hurdles. The scalability of CuO-TiO₂ composites is also hindered by the costs associated with copper oxides and high-purity titanium precursors. Reducing the cost of these materials while maintaining performance is essential for large-scale adoption. One of the concerns with CuO-TiO₂ composites, especially in environmental applications, is the potential release of Cu²⁺ ions into the environment, which could have toxic effects on aquatic organisms or ecosystems. This is especially important for applications like water purification or corrosion prevention in marine environments, where Cu²⁺ release needs to be tightly controlled. The potential toxicity of nanomaterials, including CuO-TiO₂, to both humans and the environment remains an underexplored area. Before large-scale application, there was a need for in-depth environmental and health risk assessments to ensure that the widespread use of these composites does not lead to unintended negative consequences. In environmental remediation applications, CuO-TiO₂ composites may degrade over time due to fouling, clogging, or accumulation of pollutants on the surface, leading to a decrease in efficiency. Ensuring the reusability of these materials without significant performance loss is an important challenge to address. In water treatment or photocatalytic degradation systems, recovering CuO-TiO₂ nanoparticles after use can be challenging, especially if the particles are suspended in water. Efficient methods for recovering or regenerating the material after use are needed to minimize environmental impact and operational costs. CuO-TiO₂ composites have demonstrated promising results in lab-scale hydrogen production from water splitting, their efficiency under natural sunlight is still below the level required for large-scale energy production. The materials may also suffer from degradation under continuous operation, reducing their practical viability for long-term hydrogen generation. Most studies on CuO-TiO₂ composites have focused on short-term performance. The long-term behavior of these materials under real-world conditions (e.g., continuous solar exposure, high pollutant loads, or varying pH and temperature) is still not well understood. Long-term studies are needed to evaluate the durability, performance, and potential degradation pathways of these composites over time. Different applications (e.g., photocatalysis, energy storage, anti-corrosion) may require different design optimizations for CuO-TiO₂ composites. Tailoring the band structure, surface chemistry, and morphology for each specific use case remains a challenge. For instance, optimizing photocatalytic efficiency may not align with the requirements for corrosion inhibition, making it difficult to develop a one-size-fits-all material.

Conclusion

The comparative study conducted on various photocatalytic materials, including TiO₂/ZrO₂, ZnO, Ta₂O₃, SnO, Fe₂O₃, and CuO-based composites, provides valuable insights into their enhanced photocatalytic applications. The investigation encompassed a comprehensive analysis of multiple properties, including morphological insights, surface area variations, pore size, particle size, Variance (P.I.), and Zeta potential. The findings contribute to our understanding of the potential of these materials for tailored applications. The transmission electron microscopy (TEM) images revealed the morphological characteristics of the materials. The variations in morphology can influence the photocatalytic performance, with different materials showing distinct features. The surface area is a crucial factor influencing photocatalytic activity. Materials with larger surface areas, such as ZnO, may exhibit enhanced photocatalytic performance due to increased active sites for reactions. Pore size is another determinant of the materials’ photocatalytic efficiency. Materials with optimal pore sizes, such as SnO, could facilitate better diffusion of reactants to active sites, enhancing the overall performance. Particle size influences the materials’ reactivity. Smaller particle sizes, as observed in Fe₂O₃, may result in higher surface areas, and increased photocatalytic activity. The low values of Variance (P.I.) for ZnO and Fe₂O₃ indicate accurate preparations, suggesting their potential reliability and reproducibility in applications. Zeta potential values indicate the stability of colloidal particles. Materials with higher absolute zeta potential values, such as SnO and Fe₂O₃, exhibit greater stability, which is beneficial for applications requiring dispersion. Finally, comparative study allows for a nuanced understanding of the materials’ characteristics and their implications for photocatalytic applications. Depending on specific application requirements, such as pollutant degradation or water purification, researchers and engineers can make informed choices based on the observed variations in properties. The study opens avenues for further exploration and optimization of these materials for tailored photocatalytic processes, contributing to advancements in environmental and energy-related applications. Results revealed that the photo-activity of all prepared composites were more effective than the photo –activity of commercial hombikat UV-100. The rate of efficiency is arranged in the order TiO₂/CuO > TiO₂/SnO > TiO₂/ZnO > TiO₂/Ta₂O₃ > TiO₂/ZrO₂ > TiO₂/Fe₂O₃ > Hombikat TiO₂-UV100 the photodegradation and removal of Imazapyr were achieved as 79.5%, 77.5%, 75.4%, 66.3%, 63%, 51.2% and 50.6% respectively. From these results, all composites exhibited superior performance, attributed to enhanced light absorption and charge separation.

Author contributions

I. Abdelfattah conceptualized and designed the study, outlining the comparative investigation approach. They were responsible for the synthesis of the TiO2-based composite photocatalysts in collaboration with A. M. El-Shamy. Abdelfattah conducted the experimental work related to the characterization of the synthesized materials using techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and zeta potential analysis. They analyzed the structural, morphological, and surface properties of the composites, interpreting the obtained data to assess the effectiveness of the synthesized materials. A. M. El-Shamy collaborated closely with I. Abdelfattah in the synthesis of the TiO2-based composite photocatalysts. They contributed significantly to the experimental work, particularly in the preparation and characterization stages, providing insights and expertise in materials synthesis techniques. El-Shamy actively participated in the discussions regarding the interpretation of characterization results and the evaluation of photocatalytic activities. They were involved in drafting and revising the manuscript, ensuring that the experimental findings were accurately represented and discussed within the context of existing literature on photocatalysis and composite materials. Both authors contributed equally to the data analysis and interpretation, drawing conclusions based on the experimental findings and discussing the implications of the results in the broader context of photocatalysis and environmental applications. They jointly wrote the manuscript, with each author contributing to different sections based on their expertise and involvement in the study. Both authors critically reviewed and revised the manuscript for intellectual content, ensuring its scientific rigor and clarity. Additionally, both authors approved the final version of the manuscript for submission and publication.

Funding

Open access funding provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB).

Data availability

All data are included in the manuscript.

Declarations

Competing interests

The authors declare no competing interests.