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Article

Photocatalytic Degradation of VOCs Using Ga2O3-Coated Mesh for Practical Applications

1
Department of Materials Science and Engineering, Korea Aerospace University, Goyang 10540, Republic of Korea
2
Department of Smart Air Mobility, Korea Aerospace University, Goyang 10540, Republic of Korea
3
K1Solution, Inc., Gwangmyeong 14322, Republic of Korea
4
Korea Institute of Ceramic Engineering and Technology, Jinju 52851, Republic of Korea
*
Authors to whom correspondence should be addressed.
These authors contributed equally to this work.
Catalysts 2025, 15(10), 972; https://doi.org/10.3390/catal15100972 (registering DOI)
Submission received: 29 August 2025 / Revised: 1 October 2025 / Accepted: 3 October 2025 / Published: 11 October 2025

Abstract

Volatile organic compounds (VOCs) are major contributors to air pollution, posing significant environmental and health risks. Here we report gallium oxide (Ga2O3)-coated mesh as a practical immobilized photocatalyst for VOC degradation under UVC irradiation. A 3 wt.% Ga2O3 suspension was spray-coated onto the stainless-steel mesh, yielding a uniform coating with strong adhesion properties, as confirmed by cross-sectional analysis. Under identical conditions to a Ga2O3 powder, the Ga2O3-coated mesh delivered comparable VOC degradation rates and first-order kinetics while offering superior mechanical stability and ease of handling. Over five consecutive cycles, 93–95% of the VOC degradation efficiency was retained with negligible loss of activity, confirming excellent reusability. Fourier Transform Infrared Spectroscopy (FTIR) spectra of the Ga2O3-coated mesh after degradation reaction revealed significantly reduced VOC peaks, such as C=O and C-O absorption peaks, whereas spectra for the uncoated mesh changed only slightly. These results indicate that VOC degradation originates from the coated photocatalyst. Overall, these findings demonstrate that Ga2O3-coated mesh is a highly efficient, stable, and reusable platform for VOC removal, suggesting its potential for practical applications in air purification and environmental remediation.

1. Introduction

Volatile organic compounds (VOCs) are significant air pollutants that pose substantial risks to human health and the environment. These compounds are commonly emitted from industrial processes, transportation, and household products. Due to their toxicity, VOCs can adversely affect human health, and they also contribute to the formation of secondary pollutants such as ozone and fine particulate matter [1,2,3,4]. The efficient removal of VOCs is therefore essential for sustainable air purification and environmental remediation.
Among the various methods developed for VOC removal, photocatalytic degradation has received significant attention as a promising strategy. Unlike conventional methods such as thermal incineration or adsorption, this approach utilizes photocatalysts to convert VOCs into carbon dioxide (CO2), water (H2O), and other relatively less harmful compounds under ambient conditions [5,6,7]. In this process, photogenerated electron–hole pairs promote redox reactions that oxidize VOCs on the photocatalyst surface, without producing secondary pollutants [8,9,10,11,12]. This significant advantage has spurred extensive efforts to develop photocatalysts with high degradation efficiency and long-term stability for practical applications.
Various materials have been explored as photocatalysts for VOC degradation, with titanium dioxide (TiO2) being the most widely studied. While TiO2 is effective under ultraviolet (UV) irradiation, it suffers from limitations such as poor charge separation or susceptibility to photocorrosion over prolonged reaction. Therefore, recent studies have focused on alternative materials, with gallium oxide (Ga2O3) emerging as a promising candidate. Ga2O3 possesses a wide bandgap (~4.8 eV), which enhances its redox capabilities and enables efficient charge separation compared with TiO2 and other conventional photocatalysts [13,14,15,16]. Moreover, Ga2O3 is known for its excellent chemical stability and resistance to photocorrosion, making it attractive for practical VOC degradation. Various forms of Ga2O3, such as nanofibers and thin films produced by various synthetic routes, have been reported and their use in the photocatalytic degradation of pollutants including VOCs, NOx, and CO has been demonstrated [17,18,19,20].
However, despite these advantages, the practical implementation of photocatalysts requires careful consideration of catalyst configuration [21]. Powder-type photocatalysts offer a large surface area and promising catalytic activity, but they often encounter difficulties in handling and reusability in practical continuous-flow systems, which limit their scalability for industrial applications [22,23,24]. To address these challenges, researchers have focused on immobilizing photocatalysts onto solid substrates, which not only improves their handling and stability but also facilitates their integration into continuous-flow systems [25,26,27]. In particular, metal mesh substrates offer several advantages, including mechanical stability, a large surface area for catalyst deposition, and excellent gas permeability, which enhances the contact between VOCs and active sites on the photocatalyst surface.
Herein, in this study, we systematically investigate Ga2O3-coated mesh substrates as immobilized photocatalysts for VOC degradation. By comparing the photocatalytic performance of Ga2O3 powders and Ga2O3-coated meshes under UVC irradiation, we elucidate the effect of catalyst configuration on VOC degradation efficiency. Ga2O3-coated meshes demonstrated VOC degradation efficiencies comparable to those of powder-type photocatalysts, while providing additional advantages such as enhanced mechanical stability, ease of handling, and reusability. This comparative study provides fundamental insights into the structure–performance relationships of Ga2O3 and offers the design principles for the development of practical, immobilized photocatalysts for industrial and environmental applications.

2. Results and Discussion

To investigate the photocatalytic performance of immobilized Ga2O3, type 304 stainless-steel mesh (SUS304; thickness 0.10 mm) were used as a substrate. SUS304 was selected as it exhibits excellent corrosion and oxidation resistance with high mechanical strength and stability, ensuring reliable operation during reaction. In addition, the mesh architecture provides high gas permeability and a large geometric surface area, promoting efficient gas–solid contact within the reactor. A 3 wt.% Ga2O3 suspension was spray-coated onto the mesh substrates and dried at 60 °C for 15 h to ensure solvent removal and film stabilization. Optical microscopy (OM) images of the fabricated Ga2O3-coated mesh samples are shown in Figure 1a,b. The Ga2O3-coated mesh exhibited a continuous and homogeneous surface without visible defects. In addition, a reduction in surface gloss and the noticeable color change compared to the uncoated mesh indicated a uniform coating across the mesh surface.
The cross-sectional microstructure of the coated mesh was examined using field-emission scanning electron microscopy (SEM), as shown in Figure 1c. From the image, the Ga2O3 layer was continuous along the mesh surface, with a thickness of approximately 1.1–1.3 μm. Process optimization revealed that coatings thicker than 1.5 μm frequently exhibited poor adhesion and partial delamination. Therefore, maintaining the coating thickness below 1.5 μm is critical for achieving superior mechanical interlocking and minimizing residual stress at the interface between Ga2O3 coating layer and mesh substrate [28]. These factors collectively ensure strong adhesion, confirming the robustness of the spray-coating process.
Adhesion was further evaluated quantitatively using the ASTM D3359 cross-cut test. The coating achieved an adhesion classification of 4B or higher, indicating that less than 5% of the coating area was removed after the tape pull-off test. This result demonstrates that the Ga2O3 coating was well-formed and stably adhered without delamination, suggesting that it can function effectively as a photocatalyst with stable performance even during long-term operation.
To evaluate the photocatalytic performance for VOC degradation, an experimental setup was designed and utilized as shown in Figure 2a,b. In this setup, the positions of the reactor, photocatalyst, and VOC source were carefully optimized to promote effective VOC degradation. The VOC source was placed beneath the reactor to allow steady diffusion into the reactor, ensuring effective interaction with the Ga2O3-coated mesh placed inside. A UVC lamp positioned directly above the Ga2O3-coated mesh provides uniform irradiation of the photocatalyst surface, activating the photocatalyst and facilitating the generation of electron-hole pairs. The mesh architecture afforded a high geometric surface area, which enhanced surface reaction rates and facilitated VOC degradation [29,30,31,32]. Additionally, the real-time monitoring of VOC concentrations at the outlet was recorded using a sensor, providing reliable data on reaction kinetics. The overall reactor design ensured continuous activation of the photocatalyst, promoting the efficient degradation of VOCs throughout the experiment.
The reaction mechanism of the Ga2O3 photocatalyst is depicted in Figure 2c. Under 254 nm irradiation, Ga2O3 generates electron–hole pairs in the conduction and valence bands [12,13,33,34,35]. The band-edge positions of Ga2O3 relative to the O2/O2 and OH/•OH redox couples are shown based on previous reports [16,36,37]. The photogenerated electrons migrate to the surface, which reduces adsorbed oxygen to superoxide radicals (O2), while the photogenerated holes oxidize surface hydroxide or water to hydroxyl radicals (•OH). These reactive species are strong oxidants that initiate VOC oxidation and convert intermediates to CO2 and H2O [23].
The photocatalytic performance was then compared for Ga2O3-coated mesh and Ga2O3 powder under identical experimental conditions. As shown in Figure 3a, both catalysts exhibit a significant decrease in VOC concentration over reaction time, confirming their photocatalytic activity. Each catalyst was tested in five independent reactions, and each cycle showed similar reaction activity, as presented in the inset of Figure 3a. In addition, the VOC degradation rates of each catalyst were similar, indicating that the immobilized Ga2O3-coated mesh form exhibits a photocatalytic performance comparable to that of the Ga2O3 powder form.
To quantify the reaction kinetics, the degradation data were fitted to a first-order reaction model, as shown in Figure 3b. The linear relationship for both Ga2O3-coated mesh and Ga2O3 powder confirmed that the degradation followed first-order kinetics. The rate constants derived from the slope of the linear fits were similar for both configurations, suggesting comparable degradation rates. In addition to these comparable performances, the Ga2O3-coated mesh offers superior mechanical stability and ease of handling compared to the powder form. Moreover, the mesh structure does not hinder light penetration or reduce the available active surface area, making it a more practical and effective photocatalytic platform for VOC removal.
To evaluate the recyclability and stability of the photocatalysts, five consecutive photocatalytic VOC degradation cycles were performed, as shown in Figure 3c. The VOC degradation rate remained nearly constant for both catalysts, maintaining a high degradation efficiency of 93–95%. These results demonstrate the excellent stability and reusability of the Ga2O3-coated mesh even after repeated use, highlighting its potential for practical and continuous VOCs abatement applications.
Furthermore, the structural and chemical stability of the Ga2O3-coated mesh was analyzed using XRD analysis and SEM image with EDS elemental mapping data. The XRD pattern of the cycled Ga2O3-coated mesh matches well with the previously reported pattern, along with the peaks of the stainless-steel substrate, as shown in Figure 3d. The peak pattern without the emergence of new phases confirmed the crystalline stability of the coating layer. The SEM image with the corresponding EDS mapping of Ga and O elements reveals an intact coating with a homogeneous elemental distribution after cycling (Figure 3e). These results indicate that the Ga2O3 coating was successfully deposited on the mesh, exhibiting strong adhesion to the substrate and remaining stable even under repeated reactions.
These findings demonstrate that immobilizing Ga2O3 onto a mesh substrate enhances the stability and handling of the photocatalyst while maintaining similar photocatalytic degradation efficiency.
To further investigate the photocatalytic activity, Fourier transform infrared spectroscopy (FTIR) was employed to monitor changes in the functional groups of VOCs on the surface of both Ga2O3-coated mesh and uncoated mesh samples after the degradation reactions. As shown in Figure 4a, the uncoated mesh sample exhibited absorption peaks at C=O (1711–1686 cm−1) and C–O (1593–1561 cm−1), which correspond to the characteristic functional groups of residual intermediates on the mesh surface [13]. However, the FTIR spectra of the Ga2O3-coated mesh exhibited significant reductions in the C=O and C–O absorption peaks after the VOCs photodegradation reaction [13,16,38]. The reduced peak intensity further indicates that no aliphatic intermediates containing these functional groups remained on the Ga2O3-coated mesh surface after the degradation process. These results suggest that the redox reactions promoted by the Ga2O3 photocatalyst successfully degraded the molecular structure of toluene at the surface [39,40]. These findings are consistent with the observed VOC degradation rates from the VOC concentration measurements, confirming the photocatalytic activity of Ga2O3-coated mesh in VOC removal.
Moreover, VOC degradation experiments were conducted using formaldehyde, as shown in Figure 4b. Similar to the results for toluene, the FTIR spectra of formaldehyde on the uncoated mesh exhibited prominent C=O (1711–1686 cm−1) and C–O (1593–1561 cm−1) absorption peaks, corresponding to the unreacted formaldehyde adsorbed on the mesh surface. However, the Ga2O3-coated mesh showed significant reductions in these peaks, indicating that formaldehyde was effectively degraded by the photocatalyst. The similar trends observed in the degradation of both toluene and formaldehyde suggest that the Ga2O3-coated mesh photocatalyst is highly effective in degrading a wide range of VOCs via photocatalytic redox reactions, further supporting its potential for practical applications.
Overall, this study demonstrates the potential of Ga2O3-coated mesh as a highly efficient and stable photocatalyst for VOC degradation, offering superior mechanical stability, ease of handling, and comparable performance to Ga2O3 powder. The findings highlight the effectiveness of immobilizing Ga2O3 on mesh substrates, making it a promising solution for practical applications in air purification and environmental applications.

3. Materials and Methods

β-phase Ga2O3 powder (99.9999%) was purchased from K1 Solution (Gwangmyeong, Republic of Korea). Type 304 stainless-steel mesh substrates (SUS304, 3 × 3 cm2, thickness 0.10 mm) were used as substrates, as they exhibit excellent corrosion and oxidation resistance with high mechanical strength and stability. The SUS304 substrate was coated with Ga2O3 powder using the spray coating method. The coating solution was prepared by mixing tetraethylsilicate (TEOS, 95%, Junsei Chemical Co. Ltd., Tokyo, Japan), 3-glycidoxypropyltrimethoxysilane (GPTMS, 98%, DAEJUNG, gwangyeoksi, Republic of Korea), anhydrous ethanol (99.9%), nitric acid (HNO3, 68.0–70.0%, Samchun Pure Chemical Co., Seoul, Republic of Korea), and distilled water to form an organic/inorganic hybrid binder solution. Subsequently, 3 wt.% Ga2O3 was added to the solution and mixed thoroughly until a homogeneous suspension was obtained. The suspension was applied to the mesh substrates using a spray airbrush at a pressure of 0.1 MPa. The coating process was repeated three times to ensure uniform coverage of the mesh surface. After coating, the samples were dried at 60 °C for 15 h to remove the residual solvent and solidify the binder matrix.
The microstructure of the Ga2O3 powder was analyzed using optical microscopy (OM, BX51, Olympus, Tokyo, Japan). The thickness and uniformity of the Ga2O3 coating on the mesh were observed by field-emission scanning electron microscopy (FE-SEM, JSM-7610F, JEOL, Tokyo, Japan). Fourier transform infrared spectroscopy (FTIR, Invenio, Bruker, Karlsruhe, Germany) was applied to identify the presence of any residual intermediates on the photocatalyst surface. The analysis focused on the wavenumber range of 4000–600 cm−1, corresponding to the characteristic absorption peaks of toluene. A control experiment was conducted in the absence of the photocatalyst to evaluate the spectral changes during VOC degradation, confirming that the observed VOC degradation originated from the photocatalytic effect.
The photocatalytic measurements were performed in a custom-designed setup, which included a UVC lamp as the light source, target VOCs, a VOC concentration detector, and photocatalysts such as Ga2O3 powder and Ga2O3-coated mesh. The Ga2O3 powder was uniformly distributed on a porous filter to ensure uniform exposure to the 4-W UVC lamp (UVG-11, Analytik Jena, Jena, Germany), which emits at a central wavelength of 254 nm with an intensity of 312 μW/cm2. The Ga2O3-coated mesh sample was positioned at the exact location for direct comparison. The initial concentration of toluene was adjusted to 9.80–9.60 mg/m3. The VOC degradation experiment was conducted under static conditions, and the VOCs flow rate was maintained at a constant level using a fixed fan speed. The photocatalytic degradation efficiency of each VOC was evaluated at room temperature using a commercial VOC concentration detector (KHALDER: KD-001). All measurements were conducted after the system achieved a steady state condition.

4. Conclusions

In this study, the photocatalytic properties and practical applicability of Ga2O3-coated mesh substrates were systematically investigated. The Ga2O3-coated mesh samples exhibited uniform coatings with strong adhesion, as confirmed by cross-cut adhesion tests and cross-sectional analysis. The coating thickness was maintained below 1.5 μm, which was critical for achieving both mechanical integrity and reliable adhesion performance. The photocatalytic activity of the Ga2O3-coated mesh was evaluated using a custom-built reactor system under UVC irradiation. 93–95% of the VOC degradation efficiency was retained over five consecutive cycles, with negligible activity loss and a nearly constant reaction rate constant (k), confirming both high activity and excellent reusability. The coated mesh demonstrated significant VOC decomposition efficiency, comparable to that of dispersed Ga2O3 powder, while offering advantages such as mechanical robustness and ease of handling. FTIR analysis further confirmed the photocatalytic performance and stability of the Ga2O3-coated mesh. After VOC degradation, the characteristic absorption peaks associated with C=O and C–O bonds decreased significantly by using Ga2O3-coated mesh, while minimal changes were observed for the uncoated mesh. This indicates that the Ga2O3 coating effectively decomposed VOC molecules without leaving substantial residual intermediates, demonstrating both catalytic activity and photostability. These results suggest that Ga2O3-coated mesh can serve as a practical, reusable, and efficient photocatalytic platform for VOC removal. The combination of high photocatalytic efficiency, strong mechanical adhesion, and stable performance highlights their potential for application in air purification and environmental remediation technologies.

Author Contributions

Investigation and Formal analysis, H.C. and S.K.; Resources, J.J.; Data curation, J.-H.P.; Project administration and Writing—review & editing, W.S.H., D.-W.J. and H.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry Education (No. RS-2022-NR070875), and Korea Aerospace University grant funded by the Department of Materials Science and Engineering.

Data Availability Statement

The datasets generated or analysed during this study are included in this published article.

Conflicts of Interest

Author Jinhan Jung was employed by the company K1 Solution. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. (a) Image of the Ga2O3 spray-coated mesh (b) OM of the Ga2O3-coated mesh highlighting the uniform coating on the mesh wires (c) SEM image of cross-section along A–A′ with scale bar of 5 μm.
Figure 1. (a) Image of the Ga2O3 spray-coated mesh (b) OM of the Ga2O3-coated mesh highlighting the uniform coating on the mesh wires (c) SEM image of cross-section along A–A′ with scale bar of 5 μm.
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Figure 2. (a) Schematic diagram of the UVC-driven photocatalytic reactor setup and reaction mechanism. The VOC source is positioned directly beneath the Ga2O3-coated mesh inside the reactor, allowing continuous diffusion of VOCs into the reactor. (b) Detailed view of the reactor, showing the Ga2O3−coated mesh, UVC lamp, VOC source, and the VOC detector used for real-time concentration monitoring. (c) Schematic illustration of the band structure of Ga2O3 and the proposed VOC degradation pathway.
Figure 2. (a) Schematic diagram of the UVC-driven photocatalytic reactor setup and reaction mechanism. The VOC source is positioned directly beneath the Ga2O3-coated mesh inside the reactor, allowing continuous diffusion of VOCs into the reactor. (b) Detailed view of the reactor, showing the Ga2O3−coated mesh, UVC lamp, VOC source, and the VOC detector used for real-time concentration monitoring. (c) Schematic illustration of the band structure of Ga2O3 and the proposed VOC degradation pathway.
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Figure 3. (a) Comparison of the photocatalytic VOC degradation using Ga2O3-coated mesh (red) and Ga2O3 powder (blue). Error bars indicate that each experiment was performed five times. The inset shows the first-order rate constant k of the Ga2O3-coated mesh for each cycle at 90 min. (b) Photocatalytic reaction kinetic data using first-order kinetics with linear fits for both catalysts. (c) VOC degradation rates obtained from each cycle during the five consecutive cycles. (d) XRD pattern of the Ga2O3-coated mesh after five consecutive cycles. (e) Cross-sectional SEM image and the corresponding EDS elemental mapping of Ga2O3-coated mesh after five consecutive cycles of reaction, with scale bar of 250 μm.
Figure 3. (a) Comparison of the photocatalytic VOC degradation using Ga2O3-coated mesh (red) and Ga2O3 powder (blue). Error bars indicate that each experiment was performed five times. The inset shows the first-order rate constant k of the Ga2O3-coated mesh for each cycle at 90 min. (b) Photocatalytic reaction kinetic data using first-order kinetics with linear fits for both catalysts. (c) VOC degradation rates obtained from each cycle during the five consecutive cycles. (d) XRD pattern of the Ga2O3-coated mesh after five consecutive cycles. (e) Cross-sectional SEM image and the corresponding EDS elemental mapping of Ga2O3-coated mesh after five consecutive cycles of reaction, with scale bar of 250 μm.
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Figure 4. (a) FTIR spectra of uncoated mesh and Ga2O3-coated mesh after toluene degradation reaction, depicted in dotted and red lines, respectively. (b) FTIR spectra after formaldehyde degradation reaction using uncoated and Ga2O3-coated mesh, shown in dotted and purple lines, respectively. Both samples were exposed to UVC irradiation for 1 h under each VOC.
Figure 4. (a) FTIR spectra of uncoated mesh and Ga2O3-coated mesh after toluene degradation reaction, depicted in dotted and red lines, respectively. (b) FTIR spectra after formaldehyde degradation reaction using uncoated and Ga2O3-coated mesh, shown in dotted and purple lines, respectively. Both samples were exposed to UVC irradiation for 1 h under each VOC.
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MDPI and ACS Style

Cha, H.; Kim, S.; Jung, J.; Park, J.-H.; Hwang, W.S.; Jeon, D.-W.; Kim, H. Photocatalytic Degradation of VOCs Using Ga2O3-Coated Mesh for Practical Applications. Catalysts 2025, 15, 972. https://doi.org/10.3390/catal15100972

AMA Style

Cha H, Kim S, Jung J, Park J-H, Hwang WS, Jeon D-W, Kim H. Photocatalytic Degradation of VOCs Using Ga2O3-Coated Mesh for Practical Applications. Catalysts. 2025; 15(10):972. https://doi.org/10.3390/catal15100972

Chicago/Turabian Style

Cha, Hyeongju, Sunjae Kim, Jinhan Jung, Ji-Hyeon Park, Wan Sik Hwang, Dae-Woo Jeon, and Hyunah Kim. 2025. "Photocatalytic Degradation of VOCs Using Ga2O3-Coated Mesh for Practical Applications" Catalysts 15, no. 10: 972. https://doi.org/10.3390/catal15100972

APA Style

Cha, H., Kim, S., Jung, J., Park, J.-H., Hwang, W. S., Jeon, D.-W., & Kim, H. (2025). Photocatalytic Degradation of VOCs Using Ga2O3-Coated Mesh for Practical Applications. Catalysts, 15(10), 972. https://doi.org/10.3390/catal15100972

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