Synthesis of TiO₂-SiO₂ composite photocatalyst for efficient dye decolorization using a custom-built photocatalytic reactor

Zinc oxide is one of the most common photocatalysts utilized for the photocatalytic degradation of synthetic dyes aside from titanium dioxide. However, the application of ZnO in the treatment of wastewater containing synthetic dyes is limited due to the high energy band gap which allows ZnO to be efficient upon irradiation with ultraviolet radiation only. This study aims to evaluate the photocatalytic degradation efficiency of the zinc oxide photocatalyst and its derivatives, specifically 0.25, 0.5, 2.5 and 5 mol% Fe(II)-doped ZnO, 0.25, 0.5, 2.5 and 5 mol% Fe(III)-doped ZnO and 2.5 mol% Fe(II)-Fe(III)-doped ZnO. The performance of the photocatalysts was evaluated based on the effect of solution pH, effect of photocatalyst loading and nature of dye. The synthesis of photocatalysts were done using sol-gel synthesis method, and photodegradation tests were carried out under visible light exposure for 60 minutes. The photocatalysts were characterized with SEM, FTIR, and UV-Vis spectroscopy. The optical characterization results show that 2.5 mol% Fe(II)-Fe(III)-doped ZnO has the lowest band gap energy of 3.401 eV which was estimated using Tauc’s plot. This further validated the degradation performance of the 2.5 mol% Fe(II)-Fe(III)-doped ZnO photocatalyst where it displayed the highest photocatalytic degradation efficiencies at all pH and photocatalyst loading. The highest degradation achieved using methylene blue was 94.21% and 32.97% using congo red as model solute at optimum pH and 300 mg/L photocatalyst loading. In overall, the present study has proven that Fe-doped photocatalysts have the potential for the degradation of various synthetic dyes upon irradiation with visible light.

The objective of this research was to develop a photocatalytic reactor that will reduce the total organic carbon (TOC) concentration of a gray water influent. The system used a reactor packed with titanium dioxide ( TiO2 ) supported by silica gel ( SiO2 ) and was optimized with respect to several system parameters. The SiO2 – TiO2 composites (STCs) were capable of reducing the TOC concentration from 3,000 ppb to below the targeted concentration of 500 ppb in a recirculating system. An optimum empty bed contact time of 7 min was found based on the fastest destruction rate to reach below 500 ppb of TOC. Also based on destruction rate, a STC having a TiO2 loading of 12 g/100 mL of SiO2 precursor and approximately 120-A pore size was shown to have the best performance among several composites of different TiO2 loadings and pore sizes. The addition of activated carbon to the STC was found to improve the overall performance of the system by increasing the composite’s adsorption capabilities.

Synthesis of the photocatalysts with near-infrared light response usually involves upconversion materials or plasmon-assisted noble metals. Herein, NiTiO3/TiO2 was synthesized by using waste tobacco stem-silks as biotemplates and tetra-tert-butyl orthotitanate and nickel nitrate as precursors in a one-pot procedure. NiTiO3(1.0)/TiO2(TSS) with a mass percent of Ni 1.0% exhibited very high visible-light photocatalytic efficiency in photodegradation of tetracycline hydrochloride (TC), which is 8.0 and 2.3 times higher than TiO2 prepared without templates and TiO2(TSS) prepared without Ni, respectively. Interestingly, NiTiO3(1.5)/TiO2(TSS) even exhibited good activity under NIR light (λ = 840~850 nm) without upconversion materials or plasmon-assisted noble metals, which is 2.8 and 2.2 times than TiO2 prepared without templates and TiO2(TSS), respectively. The boosting photocatalytic activity has been shown to be attributed to efficient charge separation and transfer across a direct Z-scheme heterojunction between NiTiO3 and TiO2 and enhanced light-harvesting ability of special flaky structure reduplicated from tobacco stem-silks. This reported strategy provides a new idea for the multifunctional utilization of waste tobacco stem-silks and the synthesis of novel photocatalysts for the potential application in wastewater treatment.

A comprehensive review on tailoring factors of porous bismuth oxyhalide photocatalysts for wastewater treatment application

Problem statement: Since bacteria mainly causes damage on fresh vegetables and fruits during transportation to market, anti-bacterial TiO2 photocatalyst was applied for their packaging films. However, it has been known that pure TiO2 exhibits low photocatalytic property due to rapid recombination of photo-activated electrons and holes. Doping with metal or metal oxide shows the improvement of photocatalytic activity and disinfection effect. Approach: Fe3+ was considered to dope into TiO2/3SnO2 photocatalyst in order to enhance the photocatalytic property and bacterial inactivation efficiency. The Fe3+ doped TiO2/3SnO2 nanoparticles were prepared by sol-gel method and calcined at 400 °C for 2 h. The synthesized powders were characterized by XRD, BET and SEM. Photocatalytic activity and bacteria killing effect were determined by means of degradation of methylene blue solution and inactivation of E. coli bacteria, respectively. These tests were performed under UV and visible light irradiations. Results: Fe3+ doping into TiO2/3SnO2 has an effect on inhibition of anatase crystal growth, led to the enlargement of the composite specific surface area. Therefore, the photocatalytic activity of Fe3+ doped TiO2/3SnO2 composite in proper concentration was greater than those of pure TiO2 and TiO2/3SnO2 and 0.5 mol% Fe3+ doping exhibited the highest photocatalytic activity and E.coli inactivation efficiency. The E. coli was completely killed within 90 min under UV irradiation or 99.7% inactivated under visible light exposure. Conclusion: Fe3+ doped TiO2/3SnO2 nanoparticles were successfully synthesized and identified as 100% anatase phase. The 0.5mol% Fe3+-doped TiO2/3SnO2 which has particle size of 12.89 μm and specific surface area of 117.61 m2 g-1, exhibited the highest activity and disinfection efficiency. An attractive feature of Fe3+ doped TiO2/3SnO2 photocatalytic disinfection is its potential to be activated by visible light. Therefore, these composite TiO2 nanoparticles can be utilized for fresh food packaging films.

Highly photocatalytic activity of pH-controlled ZnO nanoflakes

Cr(III)-doped, TiO2-coated active carbon (Cr–TiO2/AC) were prepared by a sol–gel method. The effect of supports, including TiO2 and active carbon (AC), on the molecular structure and photocatalytic activity of chromium oxide for complete decomposition of EDTA has been examined with respect to the content of Cr on the catalyst surface. The photocatalytic activity of the Cr–TiO2/AC composites was evaluated in the decomposition of EDTA solution under UV irradiation. The results indicate that Cr–TiO2/AC has a higher efficiency in decomposition of EDTA than TiO2, TiO2/AC or active carbon. This was attributed to the different functions of active carbon and chromate species. (1) Nanosize TiO2 particles on composites were not reunited, possible because active carbon retards transformation of anatase into rutile and decreases the crystallite size. (2) Production of high concentrations of organic compound near Cr–TiO2. (3) Carbon in active carbon causes some of the TiO2 to reduce to Ti3+ ions, which prevents electron–hole pair recombination. (4) Formation of polychromate species, with a stronger redox capability, on the surface of TiO2/AC. It was found that the addition of Cr to TiO2 sol could suppress the grain growth of TiO2 crystals and increase the hydroxyl content on the surface of TiO2/AC. The photocatalytic efficiency and activity of the composites remained good, even after three cycles.

Photodegradation and permeability of conventional photocatalytic reactor and two different submerged membrane photocatalytic reactors for the removal of humic acid in water

Background: Photocatalytic water splitting has emerged as a promising pathway for sustainable hydrogen production, addressing global energy demands and environmental concerns. By harnessing solar energy to split water into hydrogen and oxygen, photocatalytic technologies offer a carbon-neutral alternative to fossil fuels. Recent advances in material science have led to the development of high-efficiency photocatalysts capable of improving solar-to-hydrogen conversion rates. This study provides an in-depth analysis of the latest trends in photocatalyst design, fabrication, and application, with a focus on real-world scalability. Objective: To evaluate and synthesize recent developments in photocatalytic materials and their practical applications in water splitting for renewable hydrogen production. Methods: This technical review compiles and analyzes peer-reviewed research from the past five years on the synthesis and modification of photocatalysts including semiconductor-based, heterostructured, and plasmonic materials. Characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis spectroscopy were critically examined. Key strategies including surface modification, cocatalyst integration, and bandgap engineering were reviewed for their impact on photocatalytic efficiency. The operational performance of photoelectrochemical cells and photocatalytic reactors was also analyzed. Results: Recent studies demonstrated enhanced hydrogen evolution rates up to 61.5 mmol h⁻¹ g⁻¹ using dual cocatalyst systems on TiO₂. Apparent quantum yields have reached 42.5% under visible light, while solar-to-hydrogen (STH) efficiencies of up to 1.1% have been recorded using Al-doped SrTiO₃ with Rh/Cr₂O₃. Long-term durability studies showed 80% activity retention over 1300 hours. Modified BiVO₄ and GaN:ZnO photocatalysts demonstrated efficient charge separation and visible light absorption. Conclusion: Advances in photocatalyst materials and system integration are steadily improving the feasibility of photocatalytic water splitting for green hydrogen production. Future research should focus on cost-effective scaling and integration with renewable energy sources.

Incorporation of TiO2 into cementitious materials is an important technology in the field of photocatalytic pollution mitigation; however, the photocatalytic activity of TiO2 is limited by specific surface area, poor gas diffusion and light transmission performance of cementitious materials. In this study, a novel photocatalytic lightweight aggregate—photocatalytic ceramsite sand (PCS) was synthesized by loading TiO2 on activated porous ceramsite sand (CS) with negative pressure method to solve problems in application of photocatalysts in cementitious materials. Photocatalytic cement material (PCM) was prepared by loading PCS on the surface of cementitious materials, which improved the photocatalytic activity and efficiency of TiO2 in cementitious materials. It was found that the pore structure (pore volume, size distribution and interconnectivity) of ceramsite sand (CS) varies with particle size. The photocatalytic removal rate of benzene on PCS increased significantly through adjusting ceramsite sands in appropriate pore structure and TiO2 at best coating ratio. The photocatalytic activity of PCS slightly decreased but still remained active after incorporated into concrete. 2 μL benzene was degraded completely in 200 min by 5 g 4PCS-1.25~2.35 and 300 min by PCM-5, and was still degraded over 80% in 400 min by PCM-5 after exposure to natural environment for 6 months. The results suggested that the photocatalytic activity of TiO2 in cementitious materials was enhanced by the preparation of PCS and PCM, which could provide more gas diffusion, higher specific surface area, more TiO2 active sites, and prevent TiO2 particles from being influenced by the envelope of cement hydration products and the carbonation of cement.

The role of WO3 in enhancing the photocatalytic activity of TiO2 deposits has been investigated through the oxidation of salicylic acid using UV and vis-light irradiation. Different procedures of semiconductor loading and deposition were undertaken: firstly, TiO2-Degussa P25 was impregnated with tungstic acid solution and spread on the glass substrate. Secondly, precursor of WO3 was ammonium paratungstate, mixed with a monomer and spincoated on the glass. Finally, a gel of WO3–TiO2 was synthesized by sol–gel method and spincoated on the glass, TiCl4 was used as the titanium dioxide precursor and ammonium paratungstate was introduced in the sol before precipitation of TiO2.The films obtained were characterized by UV–vis spectrophotometry, X-ray powder diffraction and scanning electron microscopy in order to better understanding the behavior and the effective role of WO3.A red-shift in the absorption edge wavelength was observed for coupled catalysts prepared by the first procedure, the bang gap energy decreased to respectively 2.7 and 2.6 eV for 0.5% and 2.5 wt.% of WO3. A tendency to agglomeration and a higher percentage of rutile in the catalysts were observed after WO3 loading. The photocatalytic activity under visible light increased consequently for catalysts with 2.5 wt.% of WO3 and variable inhibition was observed for lower loadings, but only a positive effect of WO3 was observed under UV light. The inhibition of photocatalysis was also observed under visible light for some WO3 loadings for coupled catalysts prepared by the procedure 2 and a great enhancement was observed at the 0.5 wt % of WO3 under UV light.Concerning the catalysts prepared by the sol–gel method, a positive effect of the WO3 introduction was noted: the coverage on the glass was improved, the band gap energy decreased to 2.3 eV with 4 wt.% of WO3 and the corresponding photocatalytic activity was remarkably enhanced under visible light. A higher photocatalytic activity and a better response to WO3 introduction was also observed under UV irradiation. The introduction of tungsten precursor before the crystallization of TiO2 seems to be an appropriate method to ensure good contact and better charge transfer between the two semiconductors. As expected, the photocatalytic performances were generally higher under UV light than under visible light for all the catalysts and 0.5 wt.% WO3–TiO2 was the common optimal loading for the 3 procedures exhibiting the best activity under UV light.

Photocatalytic behavior of WO 3-loaded TiO 2 systems in the oxidation of salicylic acid

Hydrogen production from photocatalytic water splitting over mesoporous-assembled SrTiO 3 nanocrystal-based photocatalysts

Enhanced photocatalytic activity against crystal violet dye of Co and In doped ZnO thin films grown on PEI flexible substrate under UV and sunlight irradiations

Acridinium dyes have been broadly used as photocatalysts, but it remains synthetically challenging to fine-tune their catalytic performance by functionalization of their structural cores. Acridiniu...