3D-Printed SiO₂–BaTiO₃/SrTiO₃‑Polymeric Composites for Enhanced Photocatalytic and Piezocatalytic Mitigation of Methylene Blue and Tetracycline Pollutants

Abstract

Effluents from textile, leather, paper, food, and cosmetic industries are recognized as major sources of dye pollution, while antibiotic contamination primarily originates from pharmaceutical, medical, and aquaculture activities. Both forms of pollution pose significant environmental and public health risks, necessitating the development of advanced multifunctional materials for wastewater remediation. In this study, a novel 3D-printed SiO₂–BaTiO₃/SrTiO₃-polymeric composite scaffold was developed, integrating a triple synergistic mechanism comprising adsorption, photocatalysis, and piezocatalysis for the efficient mitigation of methylene blue (MB) dye and tetracycline (TC) pollutants. The BaTiO₃ and SrTiO₃ nanoparticles were synthesized via a solution combustion method, while SiO₂ was sustainably obtained from bagasse ash, exhibiting surface areas of 11.88, 4.77, and 74.16 m²/g, respectively. The 3D-printed porous architectures, precisely designed using computer-aided modeling, enhanced active surface accessibility and facilitated mass transfer, thereby improving overall catalytic efficiency. The SiO₂–BaTiO₃-polymer and SiO₂–SrTiO₃-polymer composites achieved over 60% MB removal by adsorption, 18% by photocatalytic degradation under UV illumination, and over 20% by piezocatalytic degradation under ultrasonic vibration, resulting in total degradation efficiencies exceeding 88% for MB and 85% for TC. The integration of waste-derived SiO₂, functional titanate ceramics, and additive manufacturing underscores the novelty of this work, providing a sustainable and scalable pathway for next-generation wastewater treatment systems in alignment with the United Nations Sustainable Development Goals (SDGs).

Introduction

Dye mitigation is crucial in wastewater management because of the significant environmental and health impacts of untreated dye effluents. Dyes, commonly used in industries such as textiles, paper, plastics, and cosmetics, can cause severe environmental pollution when they are discharged into water bodies. They are often highly visible and can color large volumes of water, even at low concentrations, affecting the aesthetic quality and transparency of water bodies. This discoloration inhibits sunlight penetration, disrupting photosynthetic activity in aquatic plants and ecosystems. Additionally, many dyes are toxic to aquatic life, harming fish, invertebrates, and microorganisms. By implementation of effective dye mitigation, these negative impacts can be prevented, preserving aquatic ecosystems and maintaining biodiversity. Moreover, dye mitigation is essential for safeguarding human health, ensuring regulatory compliance, and enabling water and resource recovery. Some dyes contain hazardous substances, including heavy metals and aromatic compounds, posing serious health risks to humans through contaminated drinking water. Mitigating dyes in wastewater reduces human exposure to these harmful chemicals, ensuring safer water for communities. Many countries have stringent regulations on dye discharge, and compliance with these regulations is critical to avoiding legal repercussions and demonstrating environmental responsibility. Additionally, advanced dye mitigation technologies enable the recovery and reuse of water and valuable materials from wastewater, conserving resources and reducing operational costs. These efforts support sustainable industrial practices, promote environmental health, and contribute to a circular economy. The mitigation of antibiotics in water resources is crucial due to the significant environmental and public health impacts associated with the presence of antibiotics in aquatic systems. Antibiotics, commonly used in human medicine, veterinary practices, and agriculture, can enter water bodies through various pathways, including agricultural runoff, wastewater discharge, and improper disposal. These contaminants can disrupt natural microbial communities essential for nutrient cycling and other ecological processes, leading to the loss of biodiversity and the alteration of ecosystem functions. Additionally, antibiotics can be toxic to aquatic organisms, affecting their growth, reproduction, and survival. Effective mitigation of antibiotics in water resources helps to protect the integrity of aquatic ecosystems, ensuring ecosystem stability. One of the most significant concerns associated with antibiotics in water resources is the promotion of antibiotic resistance. When environmental bacteria are exposed to antibiotics, they can develop resistance mechanisms, leading to the emergence and spread of antibiotic-resistant bacteria. These ARBs can potentially infect humans, making infections harder to treat and increasing the risk of severe health outcomes. Removing antibiotics from water resources is essential to limit the spread of antibiotic resistance, protecting public health and ensuring the efficacy of antibiotics for medical use. Additionally, compliance with regulatory standards and the implementation of sustainable water management practices, including advanced treatment technologies for antibiotic removal, are critical for maintaining clean and safe water resources, supporting the circular economy and promoting long-term environmental and public health.

For these reasons, it is exceptionally important to remove organic pollutants from the treated wastewater. To mitigate the adverse effects of waterborne pollutants on both humans and ecosystems, numerous researchers have concentrated on eliminating organic and inorganic contaminants from wastewater using various methods such as adsorption and photocatalysis. The synergistic effect of combining both methods demonstrates their great potential for the removal of dyes from wastewater. This hybrid approach leverages the strengths of each technique, resulting in an enhanced efficiency in removing pollutants. It achieves this by utilizing complementary mechanisms: adsorption relies on physical or chemical interactions between the adsorbent and dye molecules, while photocatalysis involves generating reactive species that oxidize and degrade pollutants. By integration of these techniques, pollutants can be adsorbed onto the surface of the adsorbent and degraded by the reactive species produced during photocatalysis. Furthermore, adsorption allows for regeneration and reuse of the adsorbent material. When the adsorbent becomes saturated with pollutants, it can be easily regenerated by desorbing or removing the pollutants. Following this regeneration step, the desorbed pollutants can be further degraded by using photocatalysis. Hence, the synergy between adsorption and photocatalysis offers several advantages, including cost effectiveness, simplicity, and robustness.

Piezocatalysis is an emerging technology that leverages piezoelectric materials to treat wastewater by combining the principles of piezoelectricity and catalysis. Piezoelectricity is the ability of certain materials, such as lead zirconate titanate (PZT), barium titanate (BaTiO₃), strontium titanate (SrTiO₃), and zinc oxide (ZnO), to generate an electric charge in response to applied mechanical stress. Catalysis involves accelerating a chemical reaction using a substance that is not consumed in the reaction, with photocatalysis being a related concept where light energy activates the catalyst to degrade pollutants. Piezocatalysis uniquely uses mechanical energy instead of light to activate catalytic sites for contaminant degradation. The mechanism of piezocatalysis in wastewater treatment begins with the application of mechanical stress to the piezoelectric material through means such as vibration, ultrasound, or fluid flow, which can be generated naturally or artificially. This mechanical stress induces an electric charge on the surface of the piezoelectric material, creating an electric field or direct electric charges. These charges interact with water molecules, producing reactive oxygen species (ROS) like hydroxyl radicals (^•OH) and superoxide radicals (O₂ ^•–). , These ROS are highly reactive and can oxidize and break down a variety of organic pollutants, dyes, pharmaceuticals, and other contaminants, converting them into less harmful substances like carbon dioxide and water. Piezocatalysis offers several advantages for wastewater treatment. It utilizes mechanical energy, which is more efficient and sustainable compared to methods that require continuous electrical input. Unlike photocatalysis, piezocatalysis does not depend on light, making it suitable for treating wastewater in dark or turbid conditions. This method can also be integrated with existing water treatment systems and scaled up for large-scale applications. Moreover, it is versatile and effective against a wide range of contaminants, including organic compounds, heavy metals, and pathogens, making it a comprehensive solution for various wastewater treatment needs.

Despite its promise, piezocatalysis faces challenges that need to be addressed for broader implementation. Ensuring the long-term stability and durability of the piezoelectric materials is crucial. Reducing the production and deployment costs of piezoelectric materials is also important for economic feasibility. Additionally, the overall environmental impact of piezocatalysis, including collection of the material after use, must be thoroughly assessed. With continued research and development, piezocatalysis could become a vital component in sustainable water management strategies, providing an innovative approach to wastewater treatment.

Barium titanate (BaTiO₃) and strontium titanate (SrTiO₃) can function as both a photocatalyst and a piezocatalyst due to their unique structural and electronic properties. As a photocatalyst, BaTiO₃ and SrTiO₃ can absorb light and use energy to drive chemical reactions. When exposed to light, typically in the ultraviolet (UV) range due to its wide bandgap of around 3.2 eV, BaTiO₃ absorbs UV photons. The energy from these absorbed photons excites electrons from the valence band to the conduction band, creating electron–hole pairs. These excited electrons and holes then migrate to the surface of the BaTiO₃ particles, where they participate in redox reactions with the adsorbed species. The resulting radicals and reactive species can degrade pollutants, perform water-splitting, or drive other photocatalytic reactions.

In its role as a piezocatalyst, BaTiO₃ utilizes mechanical energy to drive chemical reactions and exploits its piezoelectric properties. When BaTiO₃ is subjected to mechanical stress, such as vibration, compression, or ultrasonic waves, it generates an electric field because of the piezoelectric effect. This mechanical stress induces polarization within the crystal structure, leading to the separation of positive and negative charges, which then accumulate on the surface of the BaTiO₃ particles, creating a localized electric field. Similar to photocatalysis, these surface charges can participate in redox reactions, breaking down pollutants or facilitating other chemical transformations.

The synergistic effects of combining both photocatalytic and piezocatalytic properties can enhance the overall catalytic performance of BaTiO₃. For instance, applying both UV light and mechanical stress can simultaneously generate more electron–hole pairs through light absorption and induce additional charge separation via the piezoelectric effect. This dual activation can increase the efficiency of catalytic reactions. The ability of barium titanate to function as both a photocatalyst and a piezocatalyst rooted in its electronic structure and piezoelectric properties makes it a valuable material for various applications, from environmental remediation to energy conversion. Some functional materials have demonstrated promising dual capabilities in environmental remediation. For example, metal–organic frameworks (MOFs) constructed from azolium and bipyridine ligands exhibit multifunctionality, with Pd-functionalized Ni-MOFs showing high performance and reusability in C–C coupling reactions. This highlights the potential of MOFs for integrated dye removal and catalytic degradation.

Beyond synthetic systems, biobased adsorbents are gaining attention due to their sustainability, low cost, and environmental compatibility. Silica (SiO₂) derived from agricultural waste such as bagasse ash, rice husk, and wheat straw offers high surface area, porosity, and reactive silanol (Si–OH) groups, making it effective for removing heavy metals and dyes. Functionalization with biopolymers can further enhance performance. For instance, chitosan-modified, magnetized biochar from Citrus limetta peels achieved a high Cr­(VI) removal capacity (152.44 mg/g) and retained over 70% efficiency after five reuse cycles. Aligned with these developments, green-synthesized magnetite/carbon dots nanocomposites (GS-Fe₃O₄/Cdots) were fabricated using Moringa oleifera leaf extract and watermelon peel waste. Structural and magnetic analyses confirmed uniform nanoscale features and successful synthesis. These nanocomposites achieved 98% methylene blue degradation under UV light within 30 min and remained effective over three reuse cycles. Together, these examples highlight the growing potential of both functionalized and waste-derived materials as low-cost, eco-friendly solutions for wastewater treatment.

This study presents the development of a 3D-printed SiO₂–BaTiO₃-polymeric composite scaffold for the effective degradation of organic dyes and tetracycline. A comprehensive suite of analytical techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), elemental mapping, and Brunauer–Emmett–Teller (BET) analysis was employed to assess the structural and photophysical properties of the materials. Particular emphasis was placed on evaluating the adsorption capacity and photocatalytic performance of the scaffolds. Importantly, the study is framed within the context of the United Nations Sustainable Development Goals (SDGs), highlighting its relevance to global environmental challenges. While significant research has been conducted on individual approaches such as photocatalysis, adsorption, and piezocatalysis, few studies have successfully integrated these mechanisms into a single, structurally versatile, and reusable platform. The originality of this work lies in the innovative use of a 3D-printed composite that unites photocatalytic and adsorptive functionalities with the piezoelectric properties of BaTiO₃ to enhance the degradation of both dyes and antibiotics. Fabricated using environmentally responsible methods and materials, the composite exhibits excellent reusability and low environmental impact. The combination of sustainable design, multifunctionality, and rigorous material characterization establishes this work as a valuable contribution to the advancement of integrated, cost-effective solutions for wastewater treatment.

Results and Discussion

Phase Identification of the Synthesized Powder

The X-ray diffraction (XRD) patterns of the synthesized materials confirm the formation of single-phase BaTiO₃ and SrTiO₃, as shown in Figure . The observed diffraction peaks align well with the reference JCPDS standards (BaTiO₃: 01-075-0212 and SrTiO₃: 01-080-1935), indicating a high phase purity. Notably, the diffraction peaks of SrTiO₃ exhibit a slight shift toward higher 2θ values compared to BaTiO₃, suggesting a reduction in lattice parameters in SrTiO₃. This shift occurs due to the smaller ionic radius of Sr²⁺ (1.18 Å) compared with Ba²⁺ (1.35 Å) when occupying the A-site in the perovskite structure. The smaller Sr²⁺ ions lead to a decrease in interplanar spacing, which results in the observed peak shift according to Bragg’s Law.

1.

XRD patterns of BaTiO₃ and SrTiO₃ powders synthesized by solution combustion, along with SiO₂ synthesized from bagasse ash.

The XRD results also reveal that BaTiO₃ exhibits a tetragonal crystal structure, as made evident by the splitting of the (002) and (200) peaks in the BaTiO₃ phase. Deconvolution of the (002) and (200) XRD peaks (Figure ) shows significant peak splitting in BaTiO₃, while SrTiO₃ exhibits minimal splitting, confirming its predominantly cubic structure.

2.

Deconvolution of the (002) and (200) XRD peak splitting of BaTiO₃ and SrTiO₃.

In general, BaTiO₃ remains in the tetragonal phase at room temperature, with lattice parameters a ≈ 3.992 Å and c ≈ 4.036 Å, while SrTiO₃ exhibits a cubic structure at room temperature with a ≈ 3.905 Å. The larger splitting observed in BaTiO₃ further supports its higher degree of tetragonality, whereas the minimal peak splitting in SrTiO₃ confirms its predominant cubic nature.

The tetragonal phase is advantageous for piezoelectric and photocatalytic applications because of intrinsic lattice distortions. These distortions induce spontaneous polarization, enhancing the charge separation and photocatalytic efficiency. In piezocatalysis, the noncentrosymmetric structure generates localized electric fields under mechanical stress, promoting charge carrier migration and enhancing catalytic activity.

The presence of tetragonal BaTiO₃ also enables the coupling of piezoelectric and photocatalytic effects. Mechanical stimuli can induce internal electric fields via the piezoelectric effect, further improving the charge separation and overall catalytic performance. This synergy is vital for applications such as environmental remediation and energy conversion where efficient and stable charge transfer is essential.

In conclusion, XRD analysis confirms the formation of tetragonal BaTiO₃ and cubic SrTiO₃, highlighting the structural advantages of tetragonal BTO for both photocatalytic and piezocatalytic applications. The intrinsic lattice distortions in the tetragonal phase play a significant role in enhancing charge-carrier dynamics, making these materials promising candidates for advanced catalytic applications.

The XRD analysis also indicated that the diffraction peaks observed in SiO₂ synthesized from bagasse ash correspond to SiO₂ (JCPDS 01-075-8320). Additionally, SiO₂ exhibited sharp peaks, indicating an ordered structure. Crystalline SiO₂ may not be an ideal adsorbent for wastewater treatment, primarily due to its lower surface area. Amorphous forms of SiO₂ generally exhibit higher surface areas, which is crucial for effective adsorption because they provide more active sites for the adsorption of dye molecules.

Morphological and Surface Characteristics of the Synthesized Powders

As illustrated in Figure , the scanning electron microscopy (SEM) analysis of BaTiO₃ and SrTiO₃ synthesized through combustion and calcined at 900 °C for 2 h reveals that the particles predominantly exhibit spherical shapes, with average sizes of approximately 89.87 ± 19.48 nm and 107.53 ± 21.57 nm, respectively. The particle size distribution for BaTiO₃ and SrTiO₃ was assessed using histograms constructed from measurements of 500 particles. As shown in Figure , these histograms indicate that most particles fall within the 70 to 100 nm range, clustering near the mean size. This visual representation confirmed a relatively high uniformity in the synthesized powder. Despite this, a greater degree of particle agglomeration was observed in SrTiO₃, potentially resulting in a lower specific surface area for SrTiO₃.

3.

SEM images of (a) BaTiO₃ and (b) SrTiO₃ powders.

4.

Histogram showing the particle sizes of (a) BaTiO₃ and (b) SrTiO₃ particles, based on the measurements of 500 particles.

The specific surface area of the synthesized powders was measured using Brunauer–Emmett–Teller (BET) analysis. As shown in Figure and Table , the specific surface areas (SSA) for BaTiO₃ and SrTiO₃ were found to be 11.88 and 4.77 m²/g, respectively. The relatively low SSA of SrTiO₃ could be due to the particle agglomeration. In contrast, SiO₂ exhibited a significantly higher specific surface area of 74.16 m²/g, which is advantageous for adsorption. The adsorption isotherm of SiO₂ exhibited a Type IV isotherm, which is typical of mesoporous materials, with an average pore size of 5.96 nm. Despite differences in their isotherm shapes, BaTiO₃ and SrTiO₃ also showed mesoporous characteristics, with pore sizes of 7.65 and 6.05 nm, respectively. This indicates the presence of mesopores, defined by pore sizes between 2 and 50 nm, which are commonly used in adsorption and catalytic applications.

5.

BET adsorption-desorption isotherm of (a) SiO₂ prepared from bagasse ash and (b) BaTiO₃ and SrTiO₃ synthesized from the solution combustion technique.

1. Particle Size, Specific Surface Areas, and Pore Size of BaTiO₃, SrTiO₃, and SiO₂ from Bagasse Ash.

powders	particle size	SSA (m2/g)	pore size (nm)
BaTiO3	89.87 ± 19.48	11.88	7.65
SrTiO3	107.53 ± 21.57	4.77	6.05
SiO2	80.90 ± 12.62	74.16	5.96

Electronic Properties of BaTiO₃ and SrTiO₃ Powders

Bandgap energy serves as a fundamental parameter that governs the efficacy of organic pollutant mitigation through photocatalysis and other semiconductor-based degradation processes. This energy difference between the valence and the conduction bands of a semiconductor material determines the range of light wavelengths that can activate the catalyst. When photons of sufficient energy strike the semiconductor surface, electrons are excited from the valence band to the conduction band, generating electron–hole pairs. These energetic charge carriers play a pivotal role in initiating redox reactions with adsorbed organic pollutants, leading to their degradation. Notably, a narrower bandgap enables the utilization of a broader spectrum of light, including ultraviolet and visible radiation, potentially enhancing the catalyst’s efficiency in pollutant removal.

However, charge-carrier recombination poses a significant challenge to the effectiveness of photocatalytic processes. Recombination occurs when excited electrons in the conduction band recombine with valence-band holes, diminishing the number of available charge carriers for pollutant degradation. To mitigate this issue, various strategies are employed, such as using semiconductor materials with optimized band structures, introducing surface modifications to create charge-carrier trapping sites, engineering heterojunctions, or incorporating cocatalysts to facilitate efficient charge separation. By addressing recombination and optimizing bandgap energy, researchers aim to design semiconductor-based materials and processes that maximize the utilization of light energy and charge carriers for effective organic pollutant mitigation.

The bandgap energies of BaTiO₃ (BTO) and SrTiO₃ (STO), determined using Tauc plots, were found to be 3.07 and 3.21 eV, respectively (Figure ), which are in good agreement with previously reported values. While STO’s slightly wider bandgap may limit its ability to absorb visible light and may reduce its photocatalytic activity, photoluminescence (PL) spectra (Figure ) revealed a significantly lower emission intensity for STO. This suggests reduced radiative recombination of photogenerated electron–hole pairs, indicating more efficient charge separation. Although STO exhibits a slightly wider bandgap (3.21 eV) compared to BTO (3.07 eV), the photocatalytic degradation efficiencies remain comparable, which can be attributed to differences in charge-carrier dynamics rather than bandgap energy alone. Photoluminescence analysis suggests lower recombination rates of photogenerated electron–hole pairs in STO, which enhances charge carrier lifetime and increases the generation of ROS responsible for pollutant degradation. Therefore, improved charge separation efficiency can compensate for the wider bandgap of STO, resulting in comparable photocatalytic performance.

6.

Tauc plot of BaTiO₃ and SrTiO₃ showing optical bandgap determination.

7.

PL spectra at an emission wavelength of 411 nm for BaTiO₃ (BTO) and SrTiO₃ (STO).

This improved carrier separation in STO may be attributed to its cubic crystal structure, which provides a more uniform and isotropic lattice compared with the tetragonal phase of BTO. The high symmetry of the cubic structure suppresses spontaneous polarization and internal lattice strain, reducing the formation of defect states that typically act as recombination centers. As a result, STO exhibits longer charge-carrier lifetimes, as evidenced by its reduced PL intensity. In contrast, the tetragonal distortion in BTO, while beneficial for polarization-induced charge separation, can also introduce lattice strain and anisotropic charge transport, potentially increasing the recombination rates.

In summary, the cubic symmetry of STO offers a structurally and electronically favorable environment for reducing charge carrier recombination, effectively offsetting its slightly wider bandgap. As a result, STO demonstrates a photocatalytic performance comparable to that of BTO. These findings underscore the importance of considering structural and defect-related factors in addition to bandgap engineering when designing and optimizing photocatalytic materials.

Catalytic Properties of BaTiO₃ and SrTiO₃ Powders

To evaluate the catalytic degradation efficiency of the synthesized BTO and STO powders, this study investigated the adsorption, photocatalytic, piezocatalytic, and combined photocatalytic-piezocatalytic degradation of methylene blue (MB) dye and tetracycline (TC). The adsorption process was first examined over 12 h, followed by degradation experiments performed under photocatalytic, piezocatalytic, and combined conditions for 4 h.

As depicted in Figures and , the adsorption process alone did not result in significant removal of MB and tetracycline. This is expected for powder-based catalysts, where relatively low surface area limits passive uptake of dye molecules. In contrast, porous materials like activated carbon rely on adsorption as the primary removal mechanism, while perovskite-based catalysts such as BTO and STO depend on photocatalytic and piezocatalytic processes. These mechanisms involve the generation of charge carriers and surface activation driven by external stimuli such as light irradiation or mechanical energy. The catalytic performance was therefore evaluated under three conditions: (i) UV light exposure (λ = 365 nm) for photocatalysis, (ii) 40 kHz ultrasonic treatment for piezocatalysis, and (iii) simultaneous UV light and ultrasonic treatment for the combined effect.

8.

Normalized concentration (C/C ₀) of MB degradation with kinetic curves of BaTiO₃ and SrTiO₃ powders in MB.

9.

Normalized concentration (C/C ₀) of TC degradation with kinetic curves of BaTiO₃ and SrTiO₃ powders in TC.

To analyze degradation kinetics, ln­(C/C ₀) was plotted versus time (t), where C ₀ represents the initial absorbance of the dye solution and C denotes the absorbance at a given time. A linear relationship was observed, confirming that the degradation followed a first-order reaction model:

$$\ln \left(\frac{C}{C_0}\right)=-kt$$

where k is the rate constant (min^–1). The first-order behavior suggests that the reaction rate depends primarily on the concentration of the dye rather than interactions between multiple reactant species, which would be characteristic of a second-order reaction. This is typical for photocatalytic and piezocatalytic degradation, where active sites and reactive species such as hydroxyl radicals (^•OH) and superoxide radicals (O₂ ^–•) play a dominant role in breaking down the organic pollutants.

The calculated k values, which quantify the degradation efficiency of MB, are summarized in Table . For SrTiO₃, the obtained rate constants were 0.005 min^–1 for photocatalysis, 0.008 min^–1 for piezocatalysis, and 0.010 min^–1 for the combined photocatalytic-piezocatalytic process. In comparison, BaTiO₃ exhibited higher rate constants, with values of 0.007 min^–1 for photocatalysis, 0.009 min^–1 for piezocatalysis, and 0.012 min^–1 for the combined process. A similar trend was observed in tetracycline (TC) removal. For SrTiO₃, the obtained rate constants were 0.007 min^–1 for photocatalysis, 0.008 min^–1 for piezocatalysis, and 0.009 min^–1 for the combined photocatalytic-piezocatalytic process. BaTiO₃ exhibited higher rate constants, with values of 0.007 min^–1 for photocatalysis, 0.008 min^–1 for piezocatalysis, and 0.011 min^–1 for the combined process.

2. Rate Constant (k) for the Degradation of Methylene Blue Dye and Tetracycline.

sample		method	rate constant (k) value (min–1)	ref
TiO2	MB	photocatalysis	0.0041
Cu doped SrTiO3	MB	photocatalysis	0.0016
SrTiO3 nanofilm	MB	photocatalysis	0.0042
BaTiO3	MB	photocatalysis	0.0062
BaTiO3	MB	piezocatalysis	0.0064
SrTiO3	MB	photocatalysis	0.005	this work
		piezocatalysis	0.008
		photocatalysis +	0.010
		piezocatalysis
BaTiO3	MB	photocatalysis	0.007	this work
		piezocatalysis	0.009
		photocatalysis +	0.012
		piezocatalysis
SrTiO3	tetracycline	photocatalysis	0.007	this work
		piezocatalysis	0.008
		photocatalysis+	0.009
		piezocatalysis
BaTiO3	tetracycline	photocatalysis	0.007	this work
		piezocatalysis	0.008
		photocatalysis +	0.011
		piezocatalysis

These results indicate that BTO exhibited superior catalytic performance compared with STO. The higher rate constants observed for BTO are likely due to its greater specific surface area and tetragonality, which enhance spontaneous polarization and improve charge carrier separation, reducing electron–hole recombination. This structural advantage facilitates more efficient generation of ROS, leading to an enhanced pollutant degradation efficiency.

The obtained rate constants suggest a moderate degradation efficiency. While these values are consistent with previous studies of perovskite-based catalysts, further optimization may enhance performance. Strategies such as surface modification, defect engineering, or compositional tuning may help improve the charge carrier dynamics and increase active site availability. Overall, the results demonstrate the potential of perovskite-based photocatalysts and piezocatalysts for effective environmental remediation.

Characteristics of the 3D-Printed Composite

Previously, the characteristics of BaTiO₃ (BTO) and SrTiO₃ (STO) powders were examined, revealing their potential for photocatalytic and piezocatalytic degradations. However, the powders exhibited a limited adsorption capacity and were difficult to recover from aqueous media, posing a risk of secondary water contamination. To address these issues, 3D-printed SiO₂–BaTiO₃ and SrTiO₃-polymeric scaffolds were fabricated to improve catalyst recovery and floatability. The scaffolds were then evaluated for their photocatalytic and piezocatalytic performance in the degradation of MB and TC.

The scaffolds were designed as a gyroid spherical structure by using SolidWorks computer-aided design (CAD) software. The gyroid architecture was selected because of its triply periodic minimal surface structure, which provides a continuous and interconnected porous network that enhances mass transfer and increases the available surface area for catalytic reactions. The use of a floating scaffold offers a novel solution by anchoring the catalytic particles within the structure. This architecture not only prevents secondary nanoparticle pollution but also optimizes the light-harvesting efficiency of the embedded catalysts. The designed scaffold had a diameter of 3.0 cm, corresponding to a total volume of approximately 4.29 mL. The average mass of the printed scaffolds was 4.72 g. According to the CAD model, the total surface area of the gyroid scaffold was calculated to be 151.93 cm², which is significantly higher than the surface area of a solid sphere with the same diameter (28.27 cm²). This increase in surface area is beneficial for improving the contact between the catalyst surface and pollutants during adsorption, photocatalysis, and piezocatalysis processes. A schematic representation of the gyroid scaffold geometry obtained from the CAD model is presented in Figure a,b to illustrate the architecture and porous structure of the printed sample.

10.

Design and preprocessing of the 3D-printed catalytic structure: (a) SolidWorks CAD model used for generating the gyroid spherical geometry and calculating the theoretical surface area and (b) chitubox software interface for print preparation, showing the estimated resin volume and printing parameters.

For consistent catalytic efficiency, a uniform dispersion of SiO₂, BaTiO₃, and SrTiO₃ within the polymeric matrix is essential. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to examine the distribution and morphology of the embedded particles. The results confirmed that the particles were uniformly distributed and well-embedded, ensuring good interfacial bonding between the ceramic and polymer components. EDS mapping further verified the presence and uniform distribution of Si, Ba, Ti, Sr, and O with no significant phase separation.

As shown in Figure , EDS mapping also detected carbon, which likely originated from the photopolymer matrix. In the BaTiO₃–SiO₂ composite, Ba, Ti, and Si were uniformly distributed, whereas in the SrTiO₃–SiO₂ composite, Sr, Ti, and Si were also uniformly dispersed. However, Sr and Ti appeared to form larger agglomerates compared to the more uniformly distributed Ba and Ti in the BaTiO₃–SiO₂ composite, which may reduce catalytic performance due to decreased active surface area and nonuniform charge distribution.

11.

SEM images of 3D-printed composites: SiO₂–BaTiO₃-polymer composite (left) and SiO₂–SrTiO₃-polymer composite (right). EDS mapping of carbon, silicon, barium, and titanium in the SiO₂–BaTiO₃-polymer composite and carbon, silicon, strontium and titanium in the SiO₂–SrTiO₃-polymer composite.

Degradation of Organic Contaminants

The previous section examined the photocatalytic and piezocatalytic properties of BaTiO₃ and SrTiO₃ powders, confirming their effectiveness in the degradation of organic contaminants. Additionally, the morphology of the 3D-printed composite incorporating SiO₂, BaTiO₃, and SrTiO₃ showed well-embedded particles. Building on these findings, this section evaluates the degradation of organic contaminants using 3D-printed SiO₂–BaTiO₃-polymer and 3D-printed SiO₂–SrTiO₃-polymer composites. These composites incorporate the unique properties of SiO₂, BaTiO₃, and SrTiO₃, which have previously shown strong performance in both photocatalytic and piezocatalytic applications. The 3D printing process allows for precise control over the structure and distribution of these materials, enabling the creation of composites with enhanced properties for organic contaminant degradation. By leveraging these advanced composites, the efficiency of degrading organic pollutants under both photocatalytic and piezocatalytic conditions can be significantly improved, offering a promising solution for water purification.

A major challenge in using these composites for organic contaminant degradation, similar to perovskite-based dye degradation, is the difficulty in recovering the material from the treated water. When BaTiO₃ and SrTiO₃ powders are dispersed in water, it becomes challenging to separate them after they have degraded the contaminants, leading to catalyst loss and potential environmental issues. To address this limitation, the use of a floating scaffold offers a novel solution. The scaffold acts as a structural framework that anchors the composite particles in place, preventing them from dispersing in the water. This ensures that the photocatalytic and piezocatalytic materials remain stable and can be easily recovered, allowing for reuse of the composites over multiple degradation cycles.

In addition to preventing dispersion, the floating scaffold improved the overall efficiency of the degradation process. By stabilizing the composite materials, the scaffold ensures a consistent interaction between the contaminants and the catalyst, which enhances degradation rates. The buoyant nature of the scaffold allows it to float on the surface of the treated water, making it easy to lift and recover once the reaction was complete. This not only improves the reusability of the material but also reduces the waste and increases the sustainability of the process. As a result, the use of 3D-printed SiO₂–BaTiO₃-polymer and 3D-printed SiO₂–SrTiO₃-polymer composites, combined with a floating scaffold, presents an effective and environmentally friendly solution for the degradation of organic contaminants in water.

The removal of MB dye and TC using 3D-printed SiO₂–BaTiO₃-polymer and 3D-printed SiO₂–SrTiO₃-polymer composites was evaluated by examining the UV–vis absorption of a water solution containing 5 ppm of MB and tetracycline during the immersion of the structures. The normalized absorbance (C/C ₀) for each dye was calculated and monitored over time. The effects of adsorption, photocatalysis, and piezoelectric degradation on dye removal efficiencies became evident after UV irradiation.

To rigorously distinguish between adsorption, photolysis, sonolysis, and true catalytic contributions, additional control experiments were conducted using contaminant-containing solutions without any scaffold or catalyst (true blank systems). These experiments followed the same protocol as the catalytic tests, including a 12 h dark stage followed by UV irradiation, ultrasonic treatment, and combined UV–ultrasonic conditions. Time-resolved kinetic profiles (C/C ₀ vs time) for both MB and TC are presented in Figure .

12.

Time-resolved kinetic profiles (C/C ₀ vs time) for the degradation of MB and TC in the absence of any scaffold or catalyst under (i) UV irradiation (photolysis), (ii) ultrasonic treatment (sonolysis), and (iii) combined UV–ultrasonic conditions (sonophotolysis). The initial 12 h dark stage shows no measurable change in concentration, confirming the absence of adsorption. Only a minor decrease in C/C ₀ is observed upon activation, indicating that photolysis and sonolysis contribute minimally to pollutant degradation under these conditions.

The results show that no measurable change in C/C ₀ occurred during the dark stage, confirming the absence of adsorption or spontaneous degradation in blank systems. Upon activation, only a minor decrease in concentration was observed under UV, ultrasound, and combined conditions, indicating that photolysis, sonolysis, and sonophotolysis contribute only marginally to pollutant degradation in the absence of any scaffold or catalyst.

In addition, temperature monitoring (temperature vs time) was performed under all operating conditions, including photocatalysis (UV only), piezocatalysis (ultrasound only), and combined photocatalysis–piezocatalysis (UV + ultrasound), to evaluate potential thermal contributions, shown in Figure . The results show that the initial temperature of the reaction solution was approximately 31–32 °C and increased only slightly to a maximum of ∼32–34 °C over the 4 h reaction period. The overall temperature variation was therefore limited to approximately 1–2 °C, with minor fluctuations (±1 °C) observed under pulsed ultrasonic conditions due to periodic energy input and heat dissipation. Under UV irradiation alone, the temperature remained nearly constant, fluctuating within ±1 °C. These findings confirm that thermal effects are minimal and well-controlled under all experimental conditions.

13.

Temperature profiles (temperature vs time) under (a) photocatalysis (UV only), (b) piezocatalysis (ultrasound only), and (c) combined photocatalysis–piezocatalysis (UV + ultrasound).

To better understand the role of the catalytic particles, control experiments were conducted using a 3D-printed polymer scaffold without inorganic fillers. These experiments were used to evaluate the effects of photolysis, piezocatalysis, and combined processes. For methylene blue (MB) degradation, the pure polymer scaffold exhibited removal efficiencies of 72.53% under UV irradiation, 70.77% under ultrasonic treatment, and 74.07% under combined UV–ultrasonic conditions. These values are close to those obtained under dark conditions, indicating that MB removal in the absence of catalytic particles mainly occurs through adsorption onto the polymer scaffold, rather than photocatalytic or piezocatalytic reactions. A similar trend was observed for TC degradation. The pure polymer scaffold showed removal efficiencies of 38.97% under UV irradiation, 40.37% under ultrasonic treatment, and 39.67% under combined conditions, again suggesting that the removal mechanism is largely dominated by adsorption.

In contrast, the SiO₂–BaTiO₃-polymer and SiO₂–SrTiO₃-polymer composites exhibited significantly higher degradation efficiencies, confirming that the improved performance originates from the photocatalytic and piezocatalytic activities of the titanate-based catalysts. For MB removal, as shown in Figure , an average efficiency of approximately 86.34% was achieved. The adsorption study demonstrated significant efficacy, with an overall removal efficiency surpassing 65%, while photocatalysis provided additional removal beyond adsorption of 18.55% and 15.51% in the 3D-printed SiO₂–BaTiO₃-polymer and 3D-printed SiO₂–SrTiO₃-polymer composites, respectively. The efficiency of MB removal by piezocatalysis showed average removals of 21.65% and 16.95% in the 3D-printed SiO₂–BaTiO₃-polymer and 3D-printed SiO₂–SrTiO₃-polymer composites, respectively. Simultaneous photocatalysis and piezocatalysis resulted in improved dye removal efficiency, with photopiezocatalysis achieving approximately 5% higher removal efficiency compared to either photocatalysis or piezocatalysis alone, on average.

14.

(a) Normalized concentration (C/C ₀) of MB degradation and (b) percentage degradation of MB for the 3D-printed SiO₂–BaTiO₃-polymer and SiO₂–SrTiO₃-polymer composites.

Similarly, the removal efficiency for TC, as depicted in Figure , was around 78.30%. Contributions from photocatalysis, piezocatalysis, and combined photopiezocatalysis processes ranged from 63.09% to 68.86%, 80.41% to 81.89%, and 85.89% to 89.71%, respectively.

15.

(a) Normalized concentration (C/C ₀) of TC degradation and (b) percentage degradation of TC for the 3D-printed SiO₂–BaTiO₃-polymer and SiO₂–SrTiO₃-polymer composites.

When comparing the removal of MB and TC, it was clear that adsorption played a smaller role in the TC removal. This difference is attributed to the surface charges of the adsorbent (SiO₂) and adsorbates (MB and TC). At pH 7, SiO₂ surfaces are generally negatively charged due to the deprotonation of silanol (Si–OH) groups, resulting in negatively charged silicate (SiO^–) groups.

MB, a cationic dye, retains a positive charge across a wide range of pH levels, including pH 7, due to the presence of iminium groups in its molecular structure. The positive charge of MB and the negative charge of SiO₂ facilitate adsorption of the dye. In contrast, TC at pH 7 tends to carry a net negative charge because of multiple ionizable groups that deprotonate at this pH, leading to a negative overall charge. The negative charges of both SiO₂ and TC result in the poor adsorption of tetracycline.

Reusability and Stability of the 3D-Printed Composite Catalysts

The reusability and operational stability of the fabricated scaffolds were evaluated through four consecutive degradation cycles using methylene blue (MB) and tetracycline (TC) as model contaminants. Three different samples were investigated: (i) a pure 3D-printed polymer scaffold (without catalyst), (ii) a 3D-printed SiO₂–BaTiO₃-polymer composite scaffold, and (iii) a 3D-printed SiO₂–SrTiO₃-polymer composite scaffold. As shown in Figure , all samples were tested under combined adsorption, photocatalysis, and piezocatalysis conditions. After each cycle, the scaffolds were recovered from the solution, thoroughly washed with deionized water, dried, and reused in the subsequent experiment.

16.

Reusability and operational stability of the 3D-printed scaffolds over four consecutive cycles for the degradation of (a) MB and (b) TC pollutants under combined adsorption, photocatalysis, and piezocatalysis conditions.

For MB degradation, the pure polymer scaffold exhibited an initial removal efficiency of 74.07%, which gradually decreased to 63.83% after the fourth cycle. In contrast, the SiO₂–BaTiO₃-polymer composite showed a significantly higher degradation efficiency of 96.36% in the first cycle, which decreased to 75.83% after four cycles. Similarly, the SiO₂–SrTiO₃-polymer composite demonstrated a degradation efficiency of 89.47% in the first cycle and retained 75.60% after the fourth cycle.

A comparable trend was observed for TC degradation. The pure polymer scaffold showed relatively low removal efficiency, decreasing from 38.97% in the first cycle to 33.17% after four cycles. In comparison, the SiO₂–BaTiO₃-polymer composite achieved 86.70% degradation efficiency in the first cycle and maintained 65.14% after the fourth cycle. The SiO₂–SrTiO₃-polymer composite exhibited an initial degradation efficiency of 84.71%, which decreased to 55.96% after four cycles.

On the basis of these results, a gradual decline in degradation efficiency was observed with repeated use. Nevertheless, both BaTiO₃- and SrTiO₃-based composite scaffolds retained relatively high catalytic activity after four cycles, indicating good structural stability and reusability. The slight decrease in performance may be attributed to partial surface fouling by intermediate degradation products, saturation of adsorption sites, or minor catalyst loss during washing and handling. In this study, regeneration between cycles was performed by using a simple washing step with deionized water to remove loosely adsorbed species. While this mild treatment demonstrates the practical reusability of the materials, it may not completely eliminate strongly adsorbed intermediates from the catalyst’s surface. More effective regeneration methods, such as washing with suitable organic solvents or mild chemical treatments, may further restore active sites and improve the catalytic efficiency in subsequent cycles.

Beyond catalytic performance, the structural configuration of the catalyst also provides important practical advantages for wastewater treatment applications. The 3D-printed scaffold configuration allows the catalyst to be easily recovered from the reaction medium. Unlike conventional powder catalysts, which typically require additional separation processes such as filtration or centrifugation, the 3D-printed polymeric scaffold can be directly removed from treated water. This characteristic reduces the risk of catalyst particle dispersion and minimizes the potential for secondary contamination caused by catalyst residues or nanoparticle release into aquatic environments. As a result, the scaffold-based configuration improves the practicality and environmental safety of the catalytic system for water remediation.

In addition to catalyst recoverability, the demonstrated reusability further contributes to the sustainability of the developed system. Reusability experiments conducted over four cycles showed that the composite catalysts maintain relatively high degradation efficiencies, indicating good structural stability and durability during repeated catalytic operations. The ability to reuse the catalysts over multiple cycles extends their operational lifetimes and reduces the need for frequent catalyst replacement. Consequently, this helps to minimize material consumption and reduces the generation of solid waste associated with catalyst disposal during practical wastewater treatment processes.

From a broader environmental perspective, the eventual disposal of the composite materials should also be considered as part of the environmental assessment. Since the scaffolds consist of a polymer matrix embedded with BaTiO₃ or SrTiO₃ particles, improper disposal after the end of their service life could contribute to solid-waste accumulation. Therefore, appropriate end-of-life management strategies should be considered to mitigate the potential environmental impacts associated with the disposal of these composite materials.

To address this issue, environmentally responsible strategies such as recycling or upcycling may be implemented after the catalytic lifetime of the materials has been reached. For example, the spent scaffolds could be mechanically ground and reused as functional fillers in polymer composites or incorporated into construction materials, thereby extending their material lifecycle and reducing waste generation. Such approaches help to maintain the value of the materials even after their catalytic activity declines.

Furthermore, the incorporation of SiO₂ derived from agricultural waste (bagasse ash) into the catalyst formulation contributes to resource valorization and supports the circular economy principles. The use of waste-derived silica not only reduces reliance on conventional raw materials but also promotes the utilization of agricultural byproducts, thereby further improving the environmental sustainability of the developed catalyst system.

Overall, the combination of recoverable scaffold design, demonstrated catalyst reusability, and potential recycling or upcycling pathways provides a more environmentally responsible approach to catalyst design for wastewater treatment applications. Although appropriate end-of-life management must still be considered, these features collectively help to reduce the environmental footprint of the developed materials while enhancing their practicality for real-world implementation.

Conclusion

This research presents a novel approach by integrating advanced materials and innovative manufacturing techniques to tackle the environmental and health impacts of untreated dye and antibiotic effluents. By using 3D-printed SiO₂–BaTiO₃-polymer and SiO₂–SrTiO₃-polymer composites, the study leverages the synergistic effects of adsorption, photocatalysis, and piezocatalysis to effectively remove model dyes and antibiotic contaminants from wastewater. The unique combination of these methods, enhanced by precise CAD design and the utilization of sustainable materials, demonstrates significant advancements in dye and antibiotic mitigation.

By integrating efficient adsorbents, specifically SiO₂ derived from bagasse ash, and advanced ceramics (BaTiO₃ or SrTiO₃) into 3D-printed polymeric scaffolds, a significant improvement in the removal of organic pollutants was achieved. Specifically, the study revealed that the SiO₂–BaTiO₃-polymer and SiO₂–SrTiO₃-polymer composites exhibit excellent dye degradation efficiencies, with over 60% attributed to adsorption, 18% to photocatalytic degradation via UV light exposure, and more than 15% to piezocatalytic degradation through ultrasonic treatment. The combined effects of adsorption, photocatalysis, and piezocatalysis resulted in an overall dye degradation efficiency of exceeding 90%.

Additionally, these scaffolds demonstrated over 80% efficiency in the removal of tetracycline, which underscores their potential in mitigating antibiotic pollution. The utilization of sustainable materials like agricultural waste for SiO₂ derivation, coupled with advanced manufacturing techniques, not only provides an effective solution for reducing the environmental impact but also aligns with SDGs.

Experimental Procedure

Synthesis of BaTiO₃, SrTiO₃, and SiO₂

BaTiO₃ and SrTiO₃, employed as photocatalyst and piezocatalyst materials, are synthesized through a solution combustion process. As shown schematically in Figure , this process utilizes titanium isopropoxide (C₁₂H₂₈O₄Ti, TTIP, 95%, Alfa Aesar) and barium nitrate (Ba­(NO₃)₂, <99%, Himedia) or strontium nitrate (Sr­(NO₃)₂, <98%, Daejung Co. Ltd.) as the primary reagents, and glycine (C₂H₅NO₂, <99%, Daejung Co. Ltd.) serves as the combustion fuel. The initial reagents and fuel were combined with deionized water to form an aqueous solution with a total metal ion concentration of approximately 1 M. This solution was subsequently heated to approximately 300–400 °C until spontaneous combustion occurred. After combustion, the resulting powder was ground and calcined at 900 °C for 2 h.

17.

Schematic illustrating the synthesis process for BaTiO₃/SrTiO₃ and silica derived from bagasse ash. This figure was created by the authors using Inkscape and graphic-design software tools.

SiO₂ was prepared by treating bagasse ash with acid. The bagasse ash was leached in 0.1 M H₂SO₄ (95%, Fisher Scientific Korea Ltd.) at 95 °C for 90 min, using a mass ratio of 10 g of bagasse ash to 500 mL of acid solution. After leaching, the acid-leached bagasse ash was rinsed with deionized water for over 10 cycles until the rinsewater reached a pH of 7. The rinsed ash was then dried again at 80 °C for 24 h. Finally, the leached bagasse ash was calcined at 600 °C for 3 h.

Preparation of Composite Resin

The composite resin was prepared by dispersing SiO₂ together with BaTiO₃ or SrTiO₃ powders into a photocurable HD resin. The mixture was mechanically stirred for 30 min at room temperature (∼25 °C) to promote homogeneous distribution of the inorganic particles within the resin matrix. No dispersing agents or rheological additives were used in order to avoid interference with the photocuring process and catalytic activity.

Degassing was not performed prior to the printing. This approach was intentionally adopted to avoid premature curing and changes in resin viscosity that could affect the stereolithography (SLA) printing process. In addition, the presence of small air bubbles in the resin may contribute to the formation of additional microvoids within the printed scaffold, which can increase the effective surface area and improve the accessibility of active catalytic sites during pollutant degradation.

Because of the relatively high density of titanate powders, gradual sedimentation may occur during the SLA printing process. To maintain dispersion homogeneity, the printing process was periodically paused approximately every 10 min, and the resin was manually stirred for ∼10 min before continuing the printing procedure. This process was repeated until the printing was completed. The resulting printed scaffolds were subsequently cured and used for further characterization and catalytic experiments.

3D Printing Procedure

The composite scaffolds were designed by using SolidWorks CAD software. The designed structure consisted of a gyroid spherical scaffold with a diameter of 3.0 cm. This architecture was selected to provide a high surface area and a continuously interconnected porous network, which can enhance the interaction between the catalyst surface and the target contaminants.

The structures were fabricated by using a liquid crystal display (LCD)-based stereolithography (SLA) 3D printer (Phrozen Saturn 2). A high-definition (HD) photopolymer resin (Sync Innovation Co.) was used as the printing material. The printing process was carried out with a layer thickness of 0.05 mm, while the platform lifting and retraction speed was set to 65 mm min^–1.

After printing, the scaffolds were washed with ethanol to remove residual uncured resin from the surface. The printed structures were then postcured for 30 min to ensure complete polymerization and structural stabilization. The resulting printed scaffolds served as the polymeric matrix for incorporating SiO₂ together with BaTiO₃ or SrTiO₃ catalytic particles, which were subsequently used in adsorption–photocatalysis–piezocatalysis experiments.

Preparation of the 3D-Printed SiO₂–BaTiO/SrTiO₃-Polymeric Composite

As schematically shown in Figure , a 3D-printed SiO₂–BaTiO₃/SrTiO₃-polymeric composite, containing BaTiO₃ or SrTiO₃ and SiO₂, was fabricated using a liquid crystal display-based stereolithographic (SLA) technique. In this method, ultraviolet (UV) irradiation was used to selectively cure the liquid photopolymer resin layer by layer, thereby forming a solid three-dimensional structure.

18.

Schematic of the fabrication process for 3D-printed SiO₂–BaTiO₃-Polymer and SiO₂–SrTiO₃-Polymer composite structures. This figure was created by the authors using Inkscape and graphic-design software tools.

The photocurable resin used for the stereolithography process consisted primarily of acrylic oligomers, diacrylate monomers, and a photoinitiator (HD Resin, Sync Innovation). BaTiO₃ or SrTiO₃ powders synthesized via a solution combustion method, together with SiO₂ derived from bagasse ash, were incorporated into the photocurable resin.

The composite resin was prepared using a weight ratio of 85:7.5:7.5 (photocurable resin/SiO₂/BaTiO₃/SrTiO₃). This composition enabled the formation of a printable composite while maintaining a sufficient loading of catalytic particles for adsorption, photocatalysis, and piezocatalysis applications.

Characterization of SiO₂, BaTiO₃, and SrTiO₃ and 3D-Printed Composite

The synthesized SiO₂, BaTiO₃, and SrTiO₃ powders were examined for their compositional, structural, and physical characteristics. Phase identification was performed using an X-ray diffractometer (Malvern Panalytical, Empyrean) with a scan rate of 3°/min and a step size of 0.02°. The powders’ morphology and specific surface area were assessed using a scanning electron microscope (Hitachi, SU3500) and a surface area analyzer (Micromeritics, 3Flex), respectively. Additionally, the morphology and composition of the 3D-printed SiO₂–BaTiO₃/SrTiO₃-polymeric composites were evaluated.

To determine the bandgap energy of BaTiO₃ and SrTiO₃, optical absorbance spectra were recorded using UV–vis spectroscopy (Agilent Technologies, Cary 5000 UV–vis-NIR). The powders were uniformly ground with a mortar and pestle, and diffuse reflectance measurements were conducted using a UV–vis spectrophotometer (200–800 nm). The instrument was calibrated, and the baseline was measured with a reference standard. The diffuse reflectance spectra were recorded and converted to the Kubelka–Munk function. Tauc plots were constructed to calculate the bandgap energy by extrapolating the linear portion to the x-axis. Photoluminescence (PL) spectroscopy (Horiba Scientific, Duetta) with an excitation wavelength of 411 nm was used to examine the charge-carrier recombination of the BaTiO₃ and SrTiO₃ samples.

Elemental mapping was performed to examine the distribution of SiO₂, BaTiO₃, and SrTiO₃ on the 3D-printed SiO₂–BaTiO₃/SrTiO₃-polymeric composites. This was achieved using a scanning electron microscope (Hitachi, SU3500) equipped with an energy-dispersive spectrometer (EDS) (Philips, XL30 and EDAX).

Assessment of Organic Contaminant Removal

The removal of organic contaminants was evaluated using methylene blue (MB) and tetracycline (TC) as model pollutants. The individual contributions of adsorption, photocatalytic degradation, and piezocatalytic degradation by the 3D-printed scaffolds were systematically investigated. As schematically illustrated in Figure , adsorption experiments were conducted by immersing the 3D-printed scaffold in 50 mL of an aqueous MB solution (5 ppm) or 50 mL of a TC solution (25 ppm). The suspensions were maintained in the dark for 12 h to establish adsorption–desorption equilibrium between the catalyst surface and the pollutant molecules.

19.

Schematic of organic dye and tetracycline removal process. This figure was created by the authors using Inkscape and graphic-design software tools.

Photocatalytic experiments were subsequently performed to evaluate the degradation performance of the fabricated catalysts toward the MB and TC. The catalytic experiments were conducted by using 0.05 g of BaTiO₃ (BTO) or SrTiO₃ (STO) as the active catalytic component in each system. For the scaffold-based catalysts, the printed structure had a diameter of 3 cm, corresponding to an approximate volume of 4.29 mL, an average mass of 4.72 g, and a calculated surface area of 151.93 cm² based on the CAD model. After the initial 12 h dark adsorption step, photocatalytic degradation was carried out under UV irradiation at 365 nm by using a UV lamp (UVP UVGL-58) with a power rating of 6 W (115 V, 60 Hz, 0.12 A). The distance between the UV lamp and the sample solution was maintained at 7 cm to ensure consistent irradiation conditions. The photocatalytic reaction was conducted for 4 h, and aliquots were collected at 1 h intervals for the composite scaffold samples and at 0.5 h intervals for the powder samples to monitor the degradation process.

Piezocatalytic degradation experiments were performed using an ultrasonic cleaner (GT Sonic-D3) operating at a frequency of 40 kHz with a nominal ultrasonic power of approximately 120 W. The ultrasonic bath had dimensions of 240 mm × 140 mm. The reaction solution (50 mL) was placed in a 1 L beaker with a diameter of 55 mm and positioned at the center of the ultrasonic bath to ensure uniform exposure to ultrasonic vibrations. Based on the nominal ultrasonic power and the reaction volume, the acoustic energy density in the reaction medium was estimated to be approximately 2.4 × 10⁶ W m^–3 (≈2400 W L^–1). It should be noted that in ultrasonic bath systems, this value represents an approximate estimate because the effective acoustic power delivered to the reaction medium depends on cavitation intensity, acoustic attenuation in the liquid, vessel geometry, and the position of the reaction vessel within the bath. Ultrasonic treatment was applied in a pulsed (intermittent) mode, consisting of repeated 10 min sonication intervals, while sampling was performed at longer intervals (30 min or 1 h, depending on the experiment). This distinction ensures consistency between the applied ultrasonic conditions and the reported kinetic sampling points.

For combined photocatalysis–piezocatalysis experiments, the reaction solution was simultaneously exposed to UV irradiation and ultrasonication for 4 h. Aliquots were collected at regular intervals to monitor pollutant degradation. The concentrations of MB and TC were determined using UV–visible spectroscopy (Hitachi UV-2900/2910), and the normalized concentration ratio (C/C ₀) was calculated to evaluate removal efficiency throughout the adsorption and irradiation periods.

Manasbodin Asava-arunotai: Methodology, investigation, data curation, and visualization. Thura Lin Htet: Methodology, formal analysis, and visualization. Kulanit Lanamkham: Methodology and investigation. Sira Sripirommit: Methodology and investigation. Angsuthorn Ngamprasit: Methodology and investigation. Tanyakorn Muangnapoh: Methodology, resources, and validation. Krissada Surawathanawises: Validation.

Funding acquisition, Resources and validation. Watcharapong Wararam: Methodology, funding acquisition, validation, and formal analysis. Kulpavee Jitapunkul: Funding acquisition and validation. Anusorn Seubsai: Funding acquisition, validation, and project coordination. Oratai Jongprateep: Conceptualization, supervision, formal analysis, project administration, funding acquisition, and writingreview and editing.

Declaration of generative AI and AI-assisted technologies in the writing process: During the preparation of this work, the authors used ChatGPT to improve language readability. After using this tool, the authors reviewed and edited the content as needed and take full responsibility for the content of the publication.

The authors declare no competing financial interest.