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. 2025 Dec 21;11(1):1293–1304. doi: 10.1021/acsomega.5c08742

Study on the UV Protection and Photocatalytic Activity of Cu2+ and Fe3+ Doped TiO2 Nanoparticles

Chih-Ling Shen †, Chao-Chin Su †, Yen-Ling Tsai ‡,*
PMCID: PMC12809333  PMID: 41552601

Abstract

Titanium dioxide (TiO2) is a safe inorganic sunscreen that provides broad-spectrum ultraviolet (UV) protection. It is usually mixed with organic materials or directly applied to the protected area. However, the photocatalytic activity of TiO2 can decompose organic substances upon UV light exposure, causing negative effects. To further extend the UV protection wavelength range of TiO2 and reduce its photocatalytic activity, copper/iron sulfate was added to titanium tetraisopropoxide (as TiO2 precursor) in isopropanol in the presence of hydrochloric acid (as catalyst), yielding Cu2+/Fe3+-doped TiO2 nanoparticles. X-ray diffraction analysis revealed the anatase crystal phase in doped TiO2 nanoparticles annealed at 100 and 400 °C, whereas annealing at 700 °C resulted in rutile phase formation. Doped TiO2 nanoparticles annealed at 100 °C exhibited an average particle size of approximately 10 nm, and the particle size distribution remained below 100 nm even when annealed at 700 °C, suggesting that Cu2+/Fe3+ inhibited the condensation and crystallization of TiO2. UV–Visible spectrophotometry analysis confirmed that Cu2+/Fe3+ doping effectively reduced UV light transmittance and enhanced visible light blocking, achieving broad-spectrum light protection. Moreover, by adjusting the weight percentage of Cu2+ or Fe3+, doped TiO2 nanoparticles annealed at 100 °C, 400 °C, or 700 °C demonstrated reduced photocatalytic activity, offering a considerable advantage for sunscreen applications containing organic materials.

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1. Introduction

Antiultraviolet (UV) agents, whether organic or inorganic, can be blended into polymers to impart UV resistance. Typically, incorporating organic and inorganic UV agents into a material provides protection against UVB rays, which are a primary cause of skin cancer, and UVA rays, which contribute to premature skin aging. Recent studies have demonstrated that various nanomaterials can effectively provide broad-spectrum UV protection, shielding against UVB and UVA rays. Notable examples include lignin colloidal spheres, plate-like titanate/calcia-doped ceria nanoparticles, and melanin-coated TiO2 nanoparticles prepared via freeze-drying. With improved understanding of the skin and the absorption spectra of endogenous and exogenous skin chromophores, studies have shown that visible light radiation, a key part of the electromagnetic spectrum, can induce erythema, pigmentation, thermal damage, and generate free radicals. , Inorganic sunscreens offer broader wavelength protection against UV radiation and generally cause less skin irritation and sensitization than their organic counterparts, making them promising candidates for effective sun protection. Titanium dioxide (TiO2) demonstrates good physicochemical properties, nontoxicity, long-term stability, and can effectively reflect UV light, supporting its wide use as a UV protection material. , TiO2 particles can be synthesized using various methods, including vapor deposition, liquid-heat method, microemulsion, , precipitation and sol–gel technique, , Among these, the sol–gel technique offers advantages such as ease of operation, low-temperature synthesis, and low operational cost, while also enabling the production of uniformly sized particles. − TiO2 particles have a white appearance, and nanonization can not only enhance their UV protection efficiency, but also improve their transparency and sensory feel.

TiO2 exists in three polymorphic forms: brookite, anatase, and rutile. Among them, the brookite form can be synthesized under low-temperature conditions using the sol–gel technique. Altering the precursor, employing an acid catalyst during synthesis, or annealing at different temperatures can yield anatase and rutile crystal forms. − Different annealing temperatures yield TiO2 particles in different crystal forms. For example, TiO2 particles can convert from the anatase to rutile structure with increased annealing temperature, , resulting in changes in particle size and optical properties. Given that pure brookite-phase TiO2 is difficult to synthesize, this form has been the subject of limited research. The arrangement of TiO2 structural units leads to differential crystal forms, each with distinct theoretical density, optical properties, and band gap. For example, the refractive indices of anatase and rutile are 2.49 and 2.61, respectively.

Multifunctional composite materials are prone to aging and potential functional failure due to UV radiation when exposed to environmental conditions. UV radiation creates microdefects in the structure of organic coatings that may serve as pathways for the penetration of corrosive agents, posing potential risks to the underlying substrate or skin-contact layers. , Moreover, the photocatalytic activity of TiO2 can promote the pyrolysis of adjacent organic molecules, necessitating careful evaluation of the use of TiO2 particles in outdoor UV-resistant materials or daily sunscreen products. The photocatalytic mechanism of TiO2 is mainly attributed to UV light irradiation, whereby excited electrons in atoms absorb energy and transition from the valence band to the conduction band, forming photoinduced conduction band electrons (e–). e– reacts with O2 to generate a superoxide radical (O2 •–), leaving behind a positively charged hole (h+). h+ reacts with water to form a hydroxyl radical (•OH). The reactive species O2 •–, •OH, and H2O2 possess strong oxidative abilities and can attack organic molecules, leading to their degradation. − The recombination time of e–/h+ pairs substantially affect the photocatalytic activity of TiO2, with prolonged e–/h+ recombination time enhancing photocatalytic efficiency. −

The size, crystal form, and distribution of TiO2 particles substantially impact their photocatalytic activity. , Li et al. synthesized TiO2 particles using the liquid-heat method, reporting that the photocatalytic activity of TiO2 particles exhibiting mixed anatase and rutile phases was significantly higher than that of TiO2 particles exhibiting a pure anatase or rutile crystal form. Metal ion doping has been employed to modify the crystal form and morphology of TiO2 particles, thereby altering their photocatalytic activity. For example, Cu2+-doped TiO2 particles with a predominant anatase phase were synthesized using the Pechini method, and those with an anatase structure were prepared via coprecipitation to reduce the band gap. Cu2+ doping reportedly enhanced the photocatalytic performance of TiO2. In addition, a previous study prepared TiO2 aerogels doped with Cu2+ or Fe3+, reporting that those calcined at 500 °C with anatase and brookite phases exhibited 10 times higher photocatalytic activity than those calcined at 900 °C with a rutile phase. Further, Zulkifli et al. synthesized anatase-phase TiO2 tridoped with Al, Fe, and Cu using an in situ hydrothermal method, reporting that its photocatalytic activity was significantly higher than that of pure TiO2.

While most research has focused on enhancing the photocatalytic activity of TiO2, only a few studies have investigated its UV-blocking capabilities and weakening its photocatalytic properties. Bansal et al. weakened the photocatalytic activity of doped TiO2 by varying the Cu concentration, Kadem et al. reported that doping TiO2 particles with Al under optimal preparation conditions can significantly reduce the photocatalytic activity of TiO2. To date, few studies have focused on decreasing the photocatalytic activity of TiO2 and enhancing its UV resistance through metal ion doping. This study aims to evaluate the UV-blocking performance of Cu2+/Fe3+-doped TiO2 nanoparticles and the associated suppression of photocatalytic activity by annealing at different temperatures to obtain various crystal phases. Cu and Fe were chosen for their relatively low cost and minimal toxicity compared to other metals.

2. Experimental Section

2.1. Preparation of TiO2 Nanoparticles

Briefly, 3 g of titanium tetraisopropoxide (TTIP, thermo scientific chemials, Massachusetts, USA) was added to 46 g of isopropanol (IPA, ECHO chemical, Taiwan) solution and stirred at room temperature for 30 min. The TTIP/IPA mixture was adjusted to pH 3 by dropwise addition of hydrochloric acid (HCl, NIHON SHIYAKU, Japan). After reacting for 12 h at room temperature, the mixture was centrifuged at 6000 rpm for 30 min. Subsequently, the supernatant was removed and the precipitate was dried in an oven at 60 °C for 24 h. The samples were annealed in a high-temperature furnace for 24 h, and the dried samples were ground with a mortar to obtain nondoped TiO2 nanoparticles.

2.2. Metal Ion Doping

First, 3 g of TTIP was added to 46 g of IPA solution and stirred at room temperature for 30 min. Next, equimolar copper sulfate (CuSO4, SHOWA, Japan) or ferric sulfate (Fe2(SO4)3, SHOWA, Japan) was added to the TTIP/IPA mixture, which was agitated for 30 min to achieve dissolution. HCl was gradually added to adjust the mixture to pH 3. After reacting at room temperature for 12 h, the mixture was centrifuged at 6000 rpm. The precipitate was dried in an oven at 60 °C for 24 h and then annealed at different temperatures (100, 400, and 700 °C) for 24 h. Subsequently, the sample was ground with a mortar to obtain Cu2+/Fe3+-doped TiO2 nanoparticles.

2.3. X-ray Diffraction Spectroscopy

The crystalline structure of TiO2 nanoparticles was characterized via X-ray diffraction spectrometry (XRD; Empyrean X-ray diffractometer, Malvern Panalytical) equipped with nickel-filtered Cu Kα radiation (λ = 1.5406 Å) operating at 40 kV, 30 mA, and 0.1°/s scan rate. XRD patterns were recorded in the 2θ range of 10°–80°.

2.4. Transmission Electron Microscopy

Briefly, 0.1 g of TiO2 nanoparticles was added to 50 mL of ethanol (ECHO chemical, Taiwan) and stirred to achieve uniform dispersal. One drop of the suspension was placed on a carbon-coated copper grid. After blotting the liquid with filter paper, the sample was air-dried at room temperature. The morphology and particle size of the TiO2 sample were analyzed via transmission electron microscopy (TEM; JEM-2100F microscope, JEOL Ltd.) at an acceleration voltage of 200 kV and various magnifications.

2.5. Electric Conductivity

Briefly, 0.1 g of TiO2 nanoparticles was added to 50 mL of deionized water and mixed well to form a suspension. The electrical conductivity of the sample was measured using a Laboratory Conductivity Meter (Mettler Toledo, conductivity range: 0.1–199.9 mS/cm, accuracy: ±0.5%, temperature range: 0.0 °C–100.0 °C, resolution: 0.1).

2.6. UV–Visible Spectrophotometry

Light absorption or transmittance of the samples was measured at various wavelengths using a single-beam UV/vis spectrophotometer (Model CT-2200, spectral bandwidth: 5 nm, wavelength range: 200–1000 nm).

2.7. Inductively Coupled Plasma–Optimal Emission Spectroscopy

Briefly, 0.1000 g of sample was diluted 1000 times (w/v) with 5% nitric acid. The solution was filtered through a 0.45 μm filter to remove particulate impurities. Next, 10 mL of the filtered solution was diluted 10,000 fold (w/v). The emission spectral intensity of the samples was measured via inductively coupled plasma–optimal emission spectroscopy (ICP-OES; iCAP-7600 analyzer, Thermo Fisher Scientific). The Cu2+ and Fe3+ concentrations in the original samples were calculated via interpolation from the standard calibration curve and multiplication by a total dilution factor of 10,000.

2.8. Energy-Dispersive X-ray Spectroscopy

Energy-dispersive X-ray spectroscopy (EDS) analysis was performed using an EMAX Evolution X-Max system with an accelerating voltage of 15 kV. The instrument identified the elements present in the sample and determined their weight percentages based on the characteristic X-ray peaks of each element.

2.9. Band Gap Energy Measurement

The absorbance data of TiO2 nanoparticles were obtained via UV–Vis spectrophotometry. The band gap was determined using the Tauc plot method, in which energy (hν) is plotted on the X-axis and (αhν) is plotted on the Y-axis, where α refers to the absorption coefficient, h denotes Planck’s constant, and ν represents the frequency of light. The linear portion of the plotted curve was extrapolated to intersect the X-axis, with the intersection point representing the band gap of the sample.

2.10. Photocatalytic Activity

First, 0.015 g of methylene blue was dissolved in sufficient deionized water to prepare 1 L of methylene blue solution. Next, 0.05 g of TiO2 nanoparticles was added to 100 mL of methylene blue solution and continuously stirred with a magnetic stirrer under 350–400 nm UV light for 3 h. Samples were collected every 30 min, and the absorbance at 664 nm was measured using the UV/vis spectrometer.

3. Results and Discussion

3.1. X-ray Diffraction Analysis

The XRD patterns of TiO2 nanoparticles annealed at different temperatures are presented Figure . The XRD patterns of TiO2 nanoparticles annealed at 100 and 400 °C exhibited diffraction peaks at 2θ values of 25.25° (101), 37.74° (200), 48.04° (200), 54.3° (022), and 62.7° (250), with the broad humped peak characteristic of the anatase phase indicating short-range ordering within the finite-size crystal phase. Most studies previously reported that the anatase structure was obtained at an annealing temperature of 400 °C, in contrast to the current findings that the anatase crystal structure was obtained upon annealing at 100 °C.

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X-ray diffraction patterns of the resultant TiO2 particles obtained by using the sol–gel method under (a) annealed at 100 °C, (b) annealed at 400 °C, and (c) annealed at 700 °C.

As previously mentioned, different precursors, acid catalysts, and annealing temperatures can affect crystallization during the sol–gel reaction. In addition, Yalcin pointed out that changing the pH will vary the band gap, which will affect the degree of conversion to the anatase or rutile structure. Their study also reported that employing 1.5 < pH < 7 has a better conversion effect during TiO2 crystallization. Herein, pH 3 was adopted during TiO2 synthesis, which fell within this suitable pH range. The XRD pattern of TiO2 nanoparticles annealed at 700 °C exhibited sharp peaks at 27.39° (110), 36.08° (111), 41.20° (220), 44.0° (210), 56.58° (231), 64.05° (330), and 68.9° (301), reflecting a rutile crystal of larger size. , The characteristic peaks of tetragonal crystal symmetry, indicating the presence of anatase and rutile phases, complied with JCPDS card nos. 00–049–1433 and 00–053–0619. The XRD peaks became higher and the full width at half-maximum became narrower with increased annealing temperature, which was attributed to increased crystal size. ,

The XRD patterns of TiO2 nanoparticles prepared with CuSO4 and annealed at different temperatures are presented in Figure . The XRD patterns revealed no peaks other than the characteristic peaks of the anatase (Figure a,b) and rutile (Figure c) phases, indicating that the Cu2+ dopant and TiO2 nanoparticles were well dispersed. The crystallinity of Cu2+-doped TiO2 nanoparticles was reduced compared to that of nondoped TiO2 nanoparticles, which was attributed to Cu2+ inhibiting the condensation and crystallization of TiO2. Figure presents the XRD patterns of TiO2 nanoparticles prepared with Fe2(SO4)3 and annealed at different temperatures. The XRD patterns revealed no peaks other than the characteristic peaks of the anatase phase ( Figure a,b). These results suggested that the Fe3+ content of Fe3+-doped TiO2 nanoparticles may have been lower than the detectable limit. Additionally, the similar ionic radii of Fe3+ and Ti4+ may have enabled Fe3+ to replace Ti4+ within the TiO2 lattice, implying that Fe3+ was uniformly integrated into the TiO2 matrix. The XRD pattern of Fe3+-doped TiO2 nanoparticles annealed at 700 °C exhibited a peak at 2θ = 33.3°, which is the main characteristic peak of Fe2O3. The results suggested that the Fe-containing components on the surface of the sample were oxidized and then converted to Fe2O3 under high temperature processing.

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X-ray patterns of the TiO2 particles obtained by using copper sulfate doping under (a) annealed at 100 °C, (b) annealed at 400 °C, and (c) annealed at 700 °C.

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X-ray patterns of the TiO2 particles obtained by using ferric sulfate doping under (a) annealed at 100 °C, (b) annealed at 400 °C, and (c) annealed at 700 °C.

3.2. TEM Analysis

The TEM images revealed that TiO2 nanoparticles annealed at 100 °C were well dispersed, with dimensions of <10 nm (Figure a). The particle size increased upon annealing at higher temperatures, and TiO2 nanoparticles tended to eventually aggregate, as shown in Figure b,c. TiO2 nanoparticle aggregation became more evident with increased annealing temperature. An increase in the annealing temperature decreased the band gap of TiO2 nanoparticles, weakening repulsion among nanoparticles, which led to nanoparticle aggregation and a larger crystal.

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TEM images of the TiO2 particles obtained by using the sol–gel method under (a) annealed at 100 °C, (b) annealed at 400 °C, and (c) annealed at 700 °C.

Figures and present the TEM images of TiO2 nanoparticles doped with Cu2+ and Fe3+, respectively. As shown in Figures a and a, the particle size of Cu2+/Fe3+-doped TiO2 nanoparticles annealed at 100 °C was similar to that of their nondoped counterparts (Figure a). TiO2 nanoparticles dispersed in water exhibit a negative charge. When Cu2+ and Fe3+ were doped into TiO2 nanoparticles, their positive charges neutralized the lone electron pairs of oxygen atoms in TiO2, reducing the charge of TiO2 nanoparticles. Consequently, the repulsive force decreased between nanoparticles, causing aggregation. The TEM images of Cu2+/Fe3+-doped TiO2 nanoparticles annealed at 700 °C are presented in Figures b and b. Although their particle size was larger than that of TiO2 nanoparticles annealed at 100 °C, it was smaller than that of their nondoped counterparts. This phenomenon was ascribed to the presence of metal ions destroying the TiO2 crystal phase, thereby decreasing the particle size and crystal form. ,

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TEM images of the TiO2 particles obtained by using the copper sulfate doping under (a) annealed at 100 °C, and (b) annealed at 700 °C.

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TEM images of the TiO2 particles obtained by using the ferric sulfate doping under (a) annealed at 100 °C, and (b) annealed at 700 °C.

3.3. Electric Conductivity

The electrical conductivity results of TiO2 nanoparticles annealed at 100 °C are presented in Figure . Nondoped TiO2 nanoparticles exhibited an electrical conductivity of 292 μm/cm. Electrical conductivity decreased with increasing metal ion concentration, with Cu2+-doped TiO2 nanoparticles exhibiting higher electrical conductivity than their Fe3+-doped counterparts. This finding was attributed to the stronger electropositivity of Fe3+ compared to Cu2+, resulting in a substantial reduction of electronegative effect on TiO2 particles. Therefore, repulsion among doped TiO2 nanoparticles was weaker than that between nondoped TiO2 nanoparticles, leading to their aggregation.

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Electric conductivity of pure TiO2 particles and TiO2 particles with copper and ferric ions, respectively.

3.4. UV–Visible Spectrophotometry

The light transmittance of nondoped TiO2 nanoparticles annealed at different temperatures was measured at 200–800 nm. As shown in Figure , nondoped TiO2 nanoparticles annealed at 100 °C almost completely blocked UVC rays (200–290 nm) but transmitted approximately 20% of UVB rays (290–320 nm), UVA rays (320–400 nm), and visible light (400–700 nm). The degree of UV and visible light blocking was substantially improved with increased annealing temperature. In particular, the transmittance of UVB rays, UVA rays, and visible light through TiO2 nanoparticles annealed at 700 °C was reduced to nearly 3%. The decrease in UV light transmittance was attributed to high-temperature annealing increasing the crystal size of TiO2, thereby changing its reflectance of light. These results were consistent with the XRD analysis results.

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UV and visible light transmittance of TiO2 particles without metal ions were annealed at different temperatures.

To investigate the anti-UV effect induced by introducing Cu2+ and Fe3+ into TiO2 nanoparticles, the light transmittance of Cu2+/Fe3+-doped TiO2 nanoparticles annealed at different temperatures was measured. As shown in Figure , UV light transmittance was greatly reduced regardless of annealing temperature or type of metal ion, and UVC, UVB, and UVA rays were completely blocked. Doped TiO2 nanoparticles annealed at 100 and 400 °C transmitted only approximately 1% and 0.5% of visible light (400–800 nm), respectively. Doped TiO2 nanoparticles annealed at 700 °C completely shielded UVC, UVB, and UVA rays and visible light. This finding was attributed metal ion doping altering TiO2 crystallization, resulting in different optical properties that affected the anti-UV effect.

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UV and visible light transmittance of TiO2 particles with metal ions were annealed at different temperatures (1.96 wt % of Cu2+/Fe3+).

3.5. ICP and EDS Measurements

ICP-OES and EDS analyses were performed to accurate determine the doping concentrations of Cu2+ and Fe3+ in the synthesized TiO2 nanoparticles. ICP-OES analysis revealed that the Cu2+ contents were 0.23, 0.67, 1.16, 1.51, and 1.96 wt %, while the Fe3+ contents were 1.93, 3.34, 3.71, 5.07, and 5.84 wt %, as shown in Figures and , respectively. The ICP-OES–derived Cu2+ and Fe3+ concentrations were mostly consistent with the elemental ratios of Cu/Ti/O and Fe/Ti/O determined via EDS. However, the Cu contents measured via EDS (2.3 and 3.9 wt %) at higher Cu2+ doping levels were higher than those obtained via ICP-OES (1.51 and 1.96 wt %). This discrepancy arose because ICP-OES measures the total composition after dissolving the sample, whereas EDS measures atoms on the material surface. These results indicated that Cu2+ tended to be more distributed toward the TiO2 particle surface with increasing Cu2+ concentration. By contrast, the Fe contents measured via EDS (0.3, 1.5, and 2.5 wt %) at lower Fe3+ doping levels were lower than those obtained via ICP-OES (1.93, 3.34, and 3.71 wt %), which suggested that Fe3+ was more likely to be embedded within the inner regions of TiO2 nanoparticles at lower Fe3+ concentrations.

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EDS of TiO2 nanoparticles doped with different copper contents (a) 0.23, (b) 0.67, (c) 1.16, (d) 1.51, and (e) 1.96 wt %.

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EDS of TiO2 nanoparticles doped with different iron contents (a) 1.93, (b) 3.34, (c) 3.71, (d) 5.07, and (e) 5.84 wt %.

3.6. Photocatalytic Activity

Regarding the study of the photocatalytic mechanism, some research has explored the underlying mechanism of photocatalytic activity and proposed several enhancing factors, including the formation of O2 •–, •OH, − , and abundance of H2O2, , improving the separation efficiency of e–/h+ pairs to reduce the probability of their recombination, − ,,, increasing electron transfer, ,, achieving an appropriate electron trap depth, , introducing suitable phase defects, and maintaining an optimal band gap. ,, Many studies have employed metal doping to enhance the photocatalytic activity of TiO2. For instance, Cu doping reportedly promotes electron transfer due to the excellent electrical conductivity of Cu, thereby reducing the e–/h+ recombination. Moreover, some studies have reported that the anatase phase exhibits higher photocatalytic activity than the rutile phase, ,, while other studies have suggested the reverse phenomenon. , Studies have also proposed that TiO2 with mixed anatase and rutile phases possesses enhanced photocatalytic activity owing to increased charge transfer across the mixed-phase interface, which reduces the e – /h+ recombination. − Given that the objective of the present study was to synthesize TiO2 nanoparticles with relatively lower photocatalytic activity, anatase and rutile single-phase TiO2 nanoparticles were prepared by controlling the annealing temperature, and the doping concentrations of Cu2+ and Fe3+ were varied to investigate their effects on photocatalytic activity.

Tables and list the degradation levels of methylene blue achieved using TiO2 nanoparticles under UV irradiation at 300 nm. Among nondoped TiO2 nanoparticles, those annealed at 400 °C (anatase crystal phase) exhibited higher photocatalytic activity, followed by those annealed at 700 °C (rutile crystal phase), which was consistent with the results of previous studies. , The lowest photocatalytic activity was observed for TiO2 nanoparticles annealed at 100 °C, which was attributed to only partial conversion to the anatase phase. As shown in Table , among Cu2+-doped TiO2 nanoparticles annealed at 100 °C, those with 1.51 wt % Cu2+ exhibited the weakest photocatalytic activity. Among Cu2+-doped TiO2 nanoparticles annealed at 400 °C, those with 0.23–1.51 wt % Cu2+ displayed reduced photocatalytic activity, while among those annealed at 700 °C, Cu2+-doped TiO2 nanoparticles with 0.23 wt % Cu2+ exhibited the greatest suppression of photocatalytic activity. As shown in Table , among Fe3+-doped TiO2 nanoparticles annealed at 100 °C, those with 1.93–3.71 wt % Fe3+ exhibited lower photocatalytic activity. Among Fe3+-doped TiO2 nanoparticles annealed at 400 and 700 °C, those with 1.93–5.07 wt % Fe3+ demonstrated weaker photocatalytic activity.

1. Degradation of Methylene Blue by Cu2+-Doped TiO2 Particles under 300 nm UV Irradiation .

    Cu2+ (wt %)
annealing temp. (°C) exposure time (min) 0 0.23 0.67 1.16 1.51 1.96
100 30 1.1390 1.2339 1.2395 1.2511 1.2874 1.0688
60 1.1053 1.1997 1.2287 1.2490 1.2773 1.0567
90 1.1002 1.1282 1.1238 1.1869 1.2630 1.0484
120 1.0658 1.1220 1.1193 1.1732 1.2740 1.0456
150 1.0398 1.1166 1.1016 1.1055 1.2714 1.0402
180 1.0254 0.9838 1.0670 1.0538 1.2657 1.0379
400 30 1.0842 1.2482 1.2536 1.2544 1.2673 1.0751
60 1.0782 1.2479 1.2539 1.2504 1.2601 1.0636
90 1.0349 1.2477 1.2530 1.2461 1.2582 1.0629
120 1.0325 1.2479 1.2527 1.2386 1.2498 1.0578
150 0.9854 1.2309 1.2502 1.2309 1.2473 1.0516
180 0.9532 1.2099 1.2439 1.2311 1.2400 1.0430
700 30 1.0735 1.2653 1.2042 1.1841 1.1623 1.0569
60 1.0680 1.2644 1.2001 1.1646 1.1590 1.0543
90 1.0670 1.2605 1.1948 1.1433 1.1465 1.0443
120 1.0576 1.2597 1.1980 1.1212 1.1336 1.0410
150 1.0304 1.2440 1.1941 1.1132 1.1320 1.0392
180 1.0089 1.2201 1.1940 1.0725 1.1005 1.0372
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a

Absorbance of 0.015g/L methylene blue solution: 1.3318.

2. Degradation of Methylene Blue by Fe3+-Doped TiO2 Particles under 300 nm UV Irradiation .

    Fe3+ (wt %)
annealing temp. (°C) exposure time (min) 0 1.93 3.34 3.71 5.07 5.84
100 30 1.1390 1.3202 1.2789 1.2899 1.2008 1.0742
60 1.1053 1.3185 1.2545 1.2823 1.1996 1.0534
90 1.1002 1.3110 1.2526 1.2803 1.1893 1.0405
120 1.0658 1.3111 1.2357 1.2776 1.1885 1.0271
150 1.0398 1.3042 1.2232 1.2674 1.1882 1.0234
180 1.0254 1.3020 1.2210 1.2526 1.1879 1.0057
400 30 1.0842 1.2504 1.2526 1.2715 1.2638 1.0872
60 1.0782 1.2499 1.2371 1.2627 1.2593 1.0626
90 1.0349 1.2490 1.2292 1.2573 1.2450 1.0348
120 1.0325 1.2412 1.2283 1.2540 1.2349 1.0285
150 0.9854 1.2401 1.2275 1.2478 1.2218 1.0199
180 0.9532 1.2383 1.1996 1.2326 1.1796 1.0127
700 30 1.0735 1.2567 1.2624 1.2717 1.2193 1.1127
60 1.0680 1.2562 1.2537 1.2688 1.2176 1.1117
90 1.0670 1.2551 1.2511 1.2675 1.2148 1.1060
120 1.0576 1.2504 1.2497 1.2651 1.2146 1.1018
150 1.0304 1.2392 1.2395 1.2609 1.2143 1.1006
180 1.0089 1.2384 1.2304 1.2605 1.2135 1.0997
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a

Absorbance of 0.015g/L methylene blue solution: 1.3318.

Table presents the band gaps of TiO2 nanoparticles annealed at different temperatures. The band gaps of nondoped TiO2 nanoparticles annealed at 100 °C, 400 °C, and 700 °C were 3.02, 2.80, and 2.72 eV, respectively. Other than Cu2+/Fe3+-doped TiO2 nanoparticles annealed at 700 °C, which exhibited an increased band gap when the Cu2+ content was >0.67 wt %, the band gap generally decreased with increasing metal ion content. The band gaps of Cu2+/Fe3+-doped TiO2 nanoparticles did not exhibit consistent correlations with the photocatalytic degradation behavior of methylene blue presented in Tables and , indicating that the magnitude of the band gap of TiO2 nanoparticles was not directly related to their photocatalytic activity. According to the literature, the factors affecting photocatalytic activity are complex. Although a narrower band gap facilitates electron excitation from the valence band to the conduction band, it also increases the likelihood of rapid e–/h+ recombination. Conversely, a wider band gap makes electron excitation more difficult but extends the lifetime of charge carriers.

3. Band Gap of Various TiO2 Nanoparticles.

  Cu2+ doping concentration (wt %)
 Fe3+ doping concentration (wt %)
annealing temp. (°C) 0 0.23 0.67 1.16 1.51 1.96 1.93 3.34 3.71 5.07 5.84
100 3.02 2.93 3.01 2.87 2.89 2.91 2.65 2.24 1.98 2.02 1.92
400 2.80 1.90 1.89 1.83 2.01 1.82 2.03 2.40 1.84 1.98 2.02
700 2.72 1.91 3.40 3.60 3.52 3.59 2.15 2.17 1.99 1.88 1.87
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TiO2 nanoparticles annealed at different temperatures exhibited distinct crystalline phases, and doping with different Cu2+ and Fe3+ concentrations further altered the TiO2 structure, potentially leading to variations in electron trap depths and affecting electron transfer pathways. In addition, the adsorption of water molecules plays a crucial role in photocatalytic reactions. Water molecules adsorbed on the photocatalyst surface can react with h+ in the valence band to produce O2, which then combines with electrons to form O2 •–, as well as •OH radicals. The relative numbers of O2 •– and •OH species significantly influence the degree of photocatalytic activity. Given that Cu2+ and Fe3+ possess strong positive charge characteristics, they can easily adsorb water molecules, facilitating the generation of O2 •– and •OH radicals. However, excessive water molecule adsorption may create barriers to electron transfer or prolong the e–/h+ recombination time. Therefore, achieving an appropriate band gap, suitable electron trap depth, and optimal water molecule adsorption can lead to a desirable reduction in photocatalytic activity.

4. Conclusions

TiO2 nanoparticles prepared using a simple sol–gel technique were doped with Cu2+ or Fe3+ and annealed at various temperatures. XRD analysis revealed that TiO2 nanoparticles annealed at 100 or 400 °C exhibited the anatase crystal phase, while those annealed at 700 °C exhibited the rutile phase. TiO2 crystallinity increased with increasing annealing temperature, with the characteristic peaks becoming more prominent at higher annealing temperatures. Cu2+/Fe3+-doped TiO2 nanoparticles annealed at 100 °C demonstrated 99% protection from 200–800 nm light, which reached 99.5% and 100% when annealed at 400 and 700 °C, respectively. Results indicated that Cu2+/Fe3+-doped TiO2 nanoparticles achieved strong, broad-spectrum light protection. Moreover, TiO2 nanoparticles annealed at 100 °C, 400 °C, and 700 °C exhibited weakened photocatalytic activity when doped with appropriate amounts of Cu2+ or Fe3+. The results of the study suggest that Cu2+/Fe3+ doping can provide substantial benefits in sunscreen formulations that incorporate TiO2 nanoparticles into organic materials.

Acknowledgments

We would like to express our gratitude to department of cosmetic science of Vanung University for providing experimental sites and materials. In addition, we acknowledge National Taipei University of Technology and Chang Gung University for providing related instruments.

This study was conceptualized by Y.-L.T. and C.-C.S.; C.-L.S. designed and established the research methodology, organized the experimental data, and verified the reproducibility of the experimental results; Y.-L.T. drafted the manuscript and supervised the work; C.-C.S. was responsible for review and editing of the manuscript.

The article processing charge (APC) for this study was supported by the Vanung University Industry–Academia collaboration project; Grant Number: 114-IRP-LC-CM-10-B-01.

The authors declare no competing financial interest.

References

  1. Qian Y., Zhong X. L. Y., Li Y., Qiu X.. Fabrication of uniform lignin colloidal spheres for developing natural broad-spectrum sunscreens with high sun protection factor. Crops Prod. 2017;101:54–60. doi: 10.1016/j.indcrop.2017.03.001. [DOI] [Google Scholar]
  2. Liu X., Yin S., Sato T.. Synthesis of broad-spectrum UV-shielding plate-like titanate/calciadoped ceria composite in different pH solution. Mater. Chem. Phys. 2009;116:421–425. doi: 10.1016/j.matchemphys.2009.04.016. [DOI] [Google Scholar]
  3. Li S., Wang Y., Li T., Ma P., Zhang X., Xia B., Chen M., Du M., Dong W.. Skin bioinspired anti-ultraviolet melanin/TiO2 nanoparticles without penetration for efficient broad-spectrum sunscreen. Colloid Polym. Sci. 2021;299:1797–1805. doi: 10.1007/s00396-021-04905-7. [DOI] [Google Scholar]
  4. Liebel F., Kaur S., Ruvolo E., Kollias N., Southall M. D.. Irradiation of skin with visible light induces reactive oxygen species and matrix-degrading enzymes. J. Invest. Dermatol. 2012;132:1901–1907. doi: 10.1038/jid.2011.476. [DOI] [PubMed] [Google Scholar]
  5. Mahmoud B. H., Hexsel C. L., Hamzavi I. H., Lim H. W.. Effects of visible light on the skin. Photochem. Photobiol. 2008;84:450–462. doi: 10.1111/j.1751-1097.2007.00286.X. [DOI] [PubMed] [Google Scholar]
  6. Shi L., Shan J., Ju Y., Aikens P., Prudhomme R. K.. Nanoparticles as delivery vehicles for sunscreen agents. Colloids Surf., A. 2012;396:122–129. doi: 10.1016/j.colsurfa.2011.12.053. [DOI] [Google Scholar]
  7. Lu P. J., Huang S. C., Chen Y. P., Chiueh L. C., Shih D. Y. C.. Analysis of titanium dioxide and zinc oxide nanoparticles in cosmetics. J. Food Drug Anal. 2015;23:587–594. doi: 10.1016/j.jfda.2015.02.009. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Manaia E. B., Kaminski R. C. K., Correa M. C., Chiavacci L. A.. Inorganic UV filters. Braz. J. Pharm. Sci. 2013;49:201–209. doi: 10.1590/S1984-82502013000200002. [DOI] [Google Scholar]
  9. Byun D., Jin Y., Kim B., Lee J. K., Park D.. Photocatalytic TiO2 deposition by chemical vapor deposition. J. Hazard. Mater. 2000;73:199–206. doi: 10.1016/s0304-3894(99)00179-X. [DOI] [PubMed] [Google Scholar]
  10. Zhang J., Xiao X., Nan J.. Hydrothermo-hydrolysis synthesis and photocatalytic properties of nano-TiO2 with an adjustable crystalline structure. J. Hazard. Mater. 2010;176:617–622. doi: 10.1016/j.jhazmat.2009.11.074. [DOI] [PubMed] [Google Scholar]
  11. Su H., Peng C., Wu J.. Effects of composition on the phase transformation behavior of anatase TiO2 in photocatalytic ceramics. Mater. Res. Bull. 2013;48:4963–4966. doi: 10.1016/j.materresbull.2013.07.033. [DOI] [Google Scholar]
  12. Bessekhouad Y., Robert D., Weber J. V.. Synthesis of photocatalytic TiO2 nanoparticles: Optimization of the preparation conditions. J. Photochem. Photobiol., A. 2003;157:47–53. doi: 10.1016/S1010-6030(03)00077-7. [DOI] [Google Scholar]
  13. Mashreghi A., Davoudi F.. Effect of TiO2 nanoparticle content in sol-gel derived TiO2 paste on the photovoltaic properties of TiO2 photoanode of dye-sensitized solar cells. Mater. Sci. Semicond. Process. 2014;26:669–676. doi: 10.1016/j.mssp.2014.06.012. [DOI] [Google Scholar]
  14. Yalcin M.. The effect of pH on the physical and structural properties of TiO2 nanoparticles. J. Cryst. Growth. 2022;585:126603. doi: 10.1016/j.jcrysgro.2022.126603. 2022.126603. [DOI] [Google Scholar]
  15. Machida M., Norimoto K., Watanabe T.. et al. The effect of SiO2 addition in super-hydrophilic property of TiO2 photocatalyst. J. Mater. Sci. 1999;34:2569–2574. doi: 10.1023/A:1004644514653. [DOI] [Google Scholar]
  16. Kontos A. I., Kontos A. G., Tsoukleris D. S., Vlachos G. D., Falaras P.. Superhydrophilicity and photocatalytic property of nanocrystalline titania sol-gel films. Thin Solid Films. 2007;515:7370–7375. doi: 10.1016/j.tsf.2007.02.082. [DOI] [Google Scholar]
  17. Ibrahim S. A., Sreekantan S.. Effect of pH on TiO2 nanoparticles via sol-gel method. Adv. Mater. Res. 2010;173:184–189. doi: 10.4028/www.scientific.net/AMR.173.184. [DOI] [Google Scholar]
  18. Chen H. S., Kumar R. V.. Sol-gel TiO2 in self-organization process: growth, ripening and sintering. RSC Adv. 2012;2:2294–2301. doi: 10.1039/c2ra00782g. [DOI] [Google Scholar]
  19. Silva, L. A. ; Araujo, R. E. D. In Evaluating the Influence of Titanium Dioxide Nanoparticle Size on Sunscreen UV Filters, SBFoton International Optics and Photonics Conference (SBFoton IOPC); IEEE Xplore, 2024; pp 1–3. [Google Scholar]
  20. Fytianos G., Rahdar A., Kyzas G. Z.. Nanomaterials in cosmetics: recent updates. Nanomaterials. 2020;10:979. doi: 10.3390/nano10050979. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Mutuma B. K., Shao G. N., Kima W. D., Kim H. T.. Sol-gel synthesis of mesoporous anatase-brookite-rutile TiO2 nanoparticles and their photocatalytic properties. J. Colloid Interface Sci. 2015;442:1–7. doi: 10.1016/j.jcis.2014.11.060. [DOI] [PubMed] [Google Scholar]
  22. Johari N. D., Rosli Z. M., Juoi J. M., Moriga T.. Heat treatment temperature influence on the structural and optical properties of brookite TiO2 thin film synthesized using green sol-gel route. J. Adv. Manuf. Technol. 2021;15:29–40. [Google Scholar]
  23. Saalinraj S., Ajithprasad K. C.. Effect of calcination temperature on non-linear absorption coefficient of nano-sized titanium dioxide (TiO2) synthesized by sol-gel method. Mater. Today Proc. 2017;4:4372–4379. doi: 10.1016/j.matpr.2017.04.008. [DOI] [Google Scholar]
  24. Jule L. T., Ramaswamy K., Bekele B., Saka A., Nagaprasad N.. Experimental investigation on the impacts of annealing temperatures on titanium dioxide nanoparticles structure, size and optical properties synthesized through sol-gel methods. Mater. Today Proc. 2021;45:5752–5758. doi: 10.1016/j.matpr.2021.02.586. [DOI] [Google Scholar]
  25. Rathore N., Kulshreshtha A., Shukla R. K., Sharma D.. Study on morphological, structural and dielectric properties of sol-gel derived TiO2 nanocrystals annealed at different temperatures. Phys. B. 2020;582:411969. doi: 10.1016/j.physb.2019.411969. [DOI] [Google Scholar]
  26. Muthee D. K., Dejene B. F.. Effect of annealing temperature on structural, optical, and photocatalytic properties of titanium dioxide nanoparticles. Heliyon. 2021;7:e07269. doi: 10.1016/j.heliyon.2021.e07269. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Johari N. D., Rosli Z., Juoi J. M., Yazid S. A.. Comparison on the TiO2 crystalline phases deposited via dip and spin coating using green sol–gel route. J. Mater. Res. Technol. 2019;8:2350–2358. doi: 10.1016/j.jmrt.2019.04.018. [DOI] [Google Scholar]
  28. Zeribi F., Attaf A., Derbali A., Saidi H., Benmebrouk L., Aida M. S., Dahnoun M., Nouadji R., Ezzaouia H.. Dependence of the physical properties of titanium dioxide (TiO2) thin films grown by sol-gel (spin-coating) process on thickness. ECS J. Solid State Sci. Technol. 2022;11:023003–023010. doi: 10.1149/2162-8777/ac5168. [DOI] [Google Scholar]
  29. Fukumura T., Toyosaki H., Yamada Y.. Magnetic oxide semiconductors. Semicond. Sci. Technol. 2005;20:S103–S139. doi: 10.1088/0268-1242/20/4/012. [DOI] [Google Scholar]
  30. Singh B., Sharma N.. Mechanistic implications of plastic degradation. Polym. Degrad. Stab. 2008;93:561–584. doi: 10.1016/j.polymdegradstab.2007.11.008. [DOI] [Google Scholar]
  31. Delor-Jestin F., Drouin D., Cheval P. Y., Lacoste J.. Thermal and photochemical ageing of epoxy resin – influence of curing agents. Polym. Degrad. Stab. 2006;91:1247–1255. doi: 10.1016/j.polymdegradstab.2005.09.009. [DOI] [Google Scholar]
  32. Zha Q., Yao Y., Yin Z., Deng Y., Li Z., Xie Y., Chen Y., Yang C., Luo Y., Xue M.. Facile construction of multi-functional 3D smart MOF-based polyurethane sponges with photocatalytic ability for efficient separation of oil-in-water emulsions and co-existing organic pollutant. Chem. Eng. J. 2024;490:151747. doi: 10.1016/j.cej.2024.151747. [DOI] [Google Scholar]
  33. Hoffmann M. R., Martin S. T., Choi W., Bahnemann D. W.. Environmental applications of semiconductor photocatalysis. Chem. Rev. 1995;95:69–96. doi: 10.1021/cr00033a004. [DOI] [Google Scholar]
  34. Hirakawa T., Nosaka Y.. Properties of O2•– and OḢ formed in TiO2 aqueous suspensions by photocatalytic reaction and the influence of H2O2 and some ions. Langmuir. 2002;18:3247–3254. doi: 10.1021/la015685a. [DOI] [Google Scholar]
  35. Zhang X., Sun D. D., Li G., Wang Y.. Investigation of the roles of active oxygen species in photodegradation of azo dye AO7 in TiO2 photocatalysis Illuminated by microwave electrodeless lamp. J. Photochem. Photobiol., A. 2008;199:311–315. doi: 10.1016/j.jphotochem.2008.06.009. [DOI] [Google Scholar]
  36. Hippargi G., Mangrulkar P., Chilkalwar A., Labhsetwar N., Rayalu S.. Chloride ion: A promising hole scavenger for photocatalytic hydrogen generation. Int. J. Hydrogen Energy. 2018;43:6815–6823. doi: 10.1016/j.ijhydene.2017.12.179. [DOI] [Google Scholar]
  37. Oviedo A. M., Thi H. T., Van Q. C., Nguyen H. H.. Physicochemical properties of Fe-doped TiO2 and the application in dye-sensitized solar cells. Opt. Mater. 2023;137:113587. doi: 10.1016/j.optmat.2023.113587. [DOI] [Google Scholar]
  38. Kumar R., Raheem A., Dutta S.. Enhanced photocatalytic seawater splitting using Cu-doped TiO2 nanoparticles anchored on Nb2O5 . Energy Fuels. 2025;39:11424–11436. doi: 10.1021/acs.energyfuels.5c01727. [DOI] [Google Scholar]
  39. Liang Z., Shen R., Ng Y. H., Zhang P., Xiang Q., Li X.. A review on 2D MoS2 cocatalysts in photocatalytic H2 production. J. Mater. Sci. Technol. 2020;56:89–121. doi: 10.1016/j.jmst.2020.04.032. [DOI] [Google Scholar]
  40. Luttrell T., Halpegamage S., Tao J., Kramer A., Sutter E., Batzill M.. Why is anatase a better photocatalyst than rutile? – Model studies on epitaxial TiO2 films. Sci. Rep. 2014;4:4043. doi: 10.1038/srep04043. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. Li H., Shen X., Liu Y., Wang L., Lei J., Zhang J.. Facile phase control for hydrothermal synthesis of anatase-rutile TiO2 with enhanced photocatalytic activity. J. Alloys Compd. 2015;646:380–386. doi: 10.1016/j.jallcom.2015.05.145. [DOI] [Google Scholar]
  42. Teodoro V., Longo E., Zaghete M. A., Perazolli L. A.. Influence of Cu-doped TiO2 on its structural and photocatalytic properties. Ecletica Quim. J. 2022;47:130–140. doi: 10.26850/1678-4618eqj.v47.1SI.2022.p130-140. [DOI] [Google Scholar]
  43. Prajapat K., Mahajan U., Dhonde M., Sahu K., Shirage P. M.. Synthesis and characterization of TiO2 nanoparticles: Unraveling the influence of copper doping on structural, surface morphology, and optical properties. Chem. Phys. Impact. 2024;8:100607. doi: 10.1016/j.chphi.2024.100607. [DOI] [Google Scholar]
  44. Mingmongkol Y., Trinh D. T. T., Phuinthiang P., Channei D., Ratananikom K., Nakaruk A., Khanitchaidecha W.. Enhanced photocatalytic and photokilling activities of Cu-doped TiO2 nanoparticles. Nanomaterials. 2022;12:1198. doi: 10.3390/nano12071198. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Katherine T. N. L., Vendula B., Jaroslav K., Jaroslav C.. Structure and photocatalytic properties of Ni-, Co-, Cu-, and Fe-doped TiO2 aerogels. Gels. 2023;9:357. doi: 10.3390/gels9050357. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Zulkifli R. C., Razali M. H., Azaman F., Ali A., Nor M. A. A. M.. Synthesis and characterization of Al-Fe-Cu tri-doped TiO2 by in-situ hydrothermal for degradation of methylene blue dyes. Mater. Sci. Eng. 2018;440:012019. doi: 10.1088/1757-899X/440/1/012019. [DOI] [Google Scholar]
  47. Ngoc T. A. N., Ly T. Q. T., Vo V. Q. G., Nguyen N. B., Nguyen Q. T., Doan H., Le T. K.. Sol–gel synthesis of Al-doped TiO2 nanoparticles as UV filters with diminished photocatalytic activity for the application in sunscreen products. J. Sol-Gel Sci. Technol. 2023;108:900–911. doi: 10.1007/s10971-023-06191-x. [DOI] [Google Scholar]
  48. Bansal J., Swami S. K., Tabassum R., Sharma S. N., Hafiz A. K.. Encapsulation of Cu-doped TiO2 nanocomposites with the understanding of weak photocatalytic properties for sunscreen applications. J. Dispersion Sci. Technol. 2022;43:364–374. doi: 10.1080/01932691.2020.1841653. [DOI] [Google Scholar]
  49. Kadem A. J., Carnie M., Dunlop T., Al-Shatty W., Sreekantan S., Ramakrishnan S.. Optimization and suppression of photocatalysis in Al-doped TiO2 particles using fractional factorial design to enhance optical performance in light-emitting diodes encapsulation. Opt. Mater. 2026;169:117550. doi: 10.1016/j.optmat.2025.117550. [DOI] [Google Scholar]
  50. Guo B., Liu P., Cui X., Song Y.. Colossal permittivity and dielectric relaxations in Tl+Nb co-doped TiO2 ceramics. Ceram. Int. 2018;44:12137–12143. doi: 10.1016/j.ceramint.2018.03.255. [DOI] [Google Scholar]
  51. Sharma A., Karn R. K., Pandiyan S. K.. Synthesis of TiO2 nanoparticles by sol-gel method and their characterization. J. Basic Appl. Eng. Res. 2014;1:1–5. [Google Scholar]
  52. Khomane R. B.. Microemulsion-mediated sol–gel synthesis of mesoporous rutile TiO2 nanoneedles and its performance as anode material for Li-ion batteries. J. Colloid Interface Sci. 2011;356:369–372. doi: 10.1016/j.jcis.2010.12.048. [DOI] [PubMed] [Google Scholar]
  53. Moongraksathum B., Shang J. Y., Chen Y. W.. Photocatalytic antibacterial effectiveness of Cu-doped TiO2 thin film prepared via the peroxo sol-gel method. Catalysts. 2018;8:352. doi: 10.3390/catal8090352. [DOI] [Google Scholar]
  54. Rtimi S., Pulgarin C., Kiwi J.. Recent developments in accelerated antibacterial inactivation on 2D Cu-titania surfaces under indoor visible light. Coatings. 2017;7:20. doi: 10.3390/coatings7020020. [DOI] [Google Scholar]
  55. Umar A., Harraz F. A., Ibrahim A. A., Almas T., Kumar R.. et al. Iron-doped titanium dioxide nanoparticles as potential scaffold for hydrazine chemical sensor applications. Coatings. 2020;10:182. doi: 10.3390/coatings10020182. [DOI] [Google Scholar]
  56. Tang J. J., Chen Y. Q., Li S. F., Xie W. P.. Degradation of terbuthylazine by Fe/TiO2 with visible-light-driven photo-Fenton catalytic activity. J. Indian Chem. Soc. 2022;99:100583. doi: 10.1016/j.jics.2022.100583. [DOI] [Google Scholar]
  57. Teixeira M. C., Piccirillo C., Tobaldi D. M., Pullar R. C., Labrincha J. A., Ferreira M. O., Castro P. M. L., Pintado M. M. E.. Effect of preparation and processing conditions on UV absorbing properties of hydroxyapatite-Fe2O3 sunscreen. Mater. Sci. Eng.: C. 2017;71:141–149. doi: 10.1016/j.msec.2016.09.065. [DOI] [PubMed] [Google Scholar]
  58. Lal M., Sharma P., Ram C.. Calcination temperature effect on titanium oxide (TiO2) nanoparticles synthesis. Optik. 2021;241:166934. doi: 10.1016/j.ijleo.2021.166934. [DOI] [Google Scholar]
  59. Chen C., Marcus I. M., Waller T., Walker S. L.. Comparison of filtration mechanisms of food and industrial grade TiO2 nanoparticles. Anal. Bioanal. Chem. 2018;410:6133–6140. doi: 10.1007/s00216-018-1132-5. [DOI] [PubMed] [Google Scholar]
  60. Liu B., Bie C., Zhang Y., Wang L., Li Y., Yu J.. Hierarchically porous ZnO/g-C3N4S-scheme heterojunction photocatalyst for efficient H2O2 production. Langmuir. 2021;37:14114–14124. doi: 10.1021/acs.langmuir.1c02360. [DOI] [PubMed] [Google Scholar]
  61. Meng K., Zhang J., Cheng B., Ren X., Xia Z., Xu F., Zhang L., Yu J.. Plasmonic near-infrared-response s-scheme ZnO/CuInS2 Photocatalyst for H2O2 production coupled with glycerin oxidation. Adv. Mater. 2024;36:2406460. doi: 10.1002/adma.202406460. [DOI] [PubMed] [Google Scholar]
  62. Kim W., Tachikawa T., Kim H., Lakshminarasimhan N., Murugan P., Park H., Majima T., Choi W.. Visible light photocatalytic activities of nitrogen and platinum-dopedTiO2: Synergistic effects of co-dopants. Appl. Catal., B. 2014;147:642–650. doi: 10.1016/j.apcatb.2013.09.034. [DOI] [Google Scholar]
  63. Xu L., Wen L., Zhao X., Li N., Liu B.. Commonly existing hole-capturer organics adsorption-Induced recombination over metal/semiconductor perimeters: a possible important factor affecting photocatalytic efficiencies. Langmuir. 2024;40:11974–11987. doi: 10.1021/acs.langmuir.4c00462. [DOI] [PubMed] [Google Scholar]
  64. Shu S., Wang H., Guo X., Wang Y., Zeng X.. Efficient photocatalytic degradation of sulfamethazine by Cu-CuxO/TiO2 composites: Performance, photocatalytic mechanism and degradation pathways. Sep. Purif. Technol. 2023;323:124458. doi: 10.1016/j.seppur.2023.124458. [DOI] [Google Scholar]
  65. Liu X., Xu C., Wang X.. Incorporation of hydroquinone in the synthesis of Bi2Ti2O7–TiO2 contributes to higher efficiency of hydroquinone degradation: preparation, characterization, and photocatalytic mechanism. Langmuir. 2024;40:19260–19269. doi: 10.1021/acs.langmuir.4c02463. [DOI] [PubMed] [Google Scholar]
  66. Vequizo J. J. M., Matsunaga H., Ishiku T., Kamimura S., Ohno T., Yamakata K.. Trapping-induced enhancement of photocatalytic activity on brookite TiO2 powders: comparison with anatase and rutile TiO2 powders. ACS Catal. 2017;7:2644–2651. doi: 10.1021/acscatal.7b00131. [DOI] [Google Scholar]
  67. Žerjav G., Žižek K., Zavǎsnik J., Pintar A.. Brookite vs. rutile vs. anatase: What′s behind their various photocatalytic activities? J. Environ. Chem. Eng. 2022;10:107722. doi: 10.1016/j.jece.2022.107722. [DOI] [Google Scholar]
  68. Behjatmanesh-Ardakani R.. Theoretical insights into band gap tuning through Cu doping and Ga vacancy in GaSe monolayer: a first-principles perspective. J. Electron. Mater. 2024;53:2398–2409. doi: 10.1007/s11664-024-10977-2. [DOI] [Google Scholar]
  69. Sclafani A., Herrmann J. M.. Comparison of the photoelectronic and photocatalytic activities of various anatase and rutile forms of titania in pure liquid organic phases and in aqueous solutions. J. Phys. Chem. A. 1996;100:13655–13661. doi: 10.1021/jp9533584. [DOI] [Google Scholar]
  70. Li J., Xu X., Liu X., Qin W., Wang M., Pan L.. Metal-organic frameworks derived cake-like anatase/rutile mixed phase TiO2 for highly efficient photocatalysis. J. Alloys Compd. 2017;690:640–646. doi: 10.1016/j.jallcom.2016.08.176. [DOI] [Google Scholar]
  71. Sun J., Gao L., Zhang Q.. Synthesizing and comparing the photocatalytic properties of high surface area rutile and anatase titania nanoparticles. J. Am. Ceram. Soc. 2003;86:1677–1682. doi: 10.1111/j.1151-2916.2003.tb03539.x. [DOI] [Google Scholar]
  72. Shah A., Ali Z., Ali R.. et al. Defining limits of Sn doping in TiO2 microspheres and its role in phase transformation resulting in enhanced photocatalytic activity. J. Mater. Sci: Mater. Electron. 2022;33:13913–13925. doi: 10.1007/s10854-022-08322-6. [DOI] [Google Scholar]
  73. Linsebigler A. L., Lu G., Yates J. T.. Photocatalysis on TiO2 surfaces: principles, mechanisms, and selected results. Chem. Rev. 1995;95:735–758. doi: 10.1021/cr00035a013. [DOI] [Google Scholar]
  74. Cao J., Liu Q. Y., Han D. L., Yang S., Yang J. H., Wang T. T., Niu H. F.. One-step hydrothermal synthesis of shape-controlled ZnS-graphene oxide nanocomposites. J. Mater. Sci.: Mater. Electron. 2015;26:646–650. doi: 10.1007/s10854-014-2444-7. [DOI] [Google Scholar]
  75. Xia H. Y., He G. Q., Min Y. L., Liu T.. Role of the crystallite phase of TiO2 in graphene/TiO2 photocatalysis. J. Mater. Sci.: Mater. Electron. 2015;26:3357–3363. doi: 10.1007/s10854-015-2840-7. [DOI] [Google Scholar]
  76. Ibrahim A., Mekprasart W., Pecharapa W.. Anatase/Rutile TiO2 composite prepared via sonochemical process and their photocatalytic activity. Mater. Today: Proc. 2017;4:6159–6165. doi: 10.1016/j.matpr.2017.06.110. [DOI] [Google Scholar]
  77. Elsellami L., Dappozze F., Fessi N., Houas A., Guillard C.. Highly photocatalytic activity of nanocrystalline Ti02 (anatase, rutile) powders prepared from TiCl4 by sol-gel method in aqueous solutions. Process Saf. Environ. Prot. 2018;113:109–121. doi: 10.1016/j.psep.2017.09.006. [DOI] [Google Scholar]
  78. Ilkhechi N. N., Kaleji B. K.. High temperature stability and photocatalytic activity of nanocrystalline anatase powders with Zr and Si co-dopants. J. Sol-Gel Sci. Technol. 2014;69:351–356. doi: 10.1007/s10971-013-3224-1. [DOI] [Google Scholar]
  79. Murashkina A. A., Murzin P. D., Rudakova A. V., Ryabchuk V. K., Emeline A. V., Bahnemann D. W.. Influence of the dopant concentration on the photocatalytic activity: Al-doped TiO. J. Phys. Chem. C. 2015;119:24695–24703. doi: 10.1021/acs.jpcc.5b06252. [DOI] [Google Scholar]
  80. Thaines E. H. N. S., Oliveira A. C., Pocrifka L. A., Duarte H. A., Freitas R. G.. Influence of Fe-doping on the structural and electronic properties of the TiO2 anatase: rutile. J. Phys. Chem. C. 2023;127:22518–22529. doi: 10.1021/acs.jpcc.3c01780. [DOI] [Google Scholar]

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