Immobilization of highly active titanium dioxide and zinc oxide hollow spheres on ceramic paper and their applicability for photocatalytic water treatment

A Review of Synthesis Methods, Modifications, and Mechanisms of ZnO/TiO2-Based Photocatalysts for Photodegradation of Contaminants

The environment being surrounded by accumulated durable waste organic compounds has become a critical crisis for human societies. Generally, organic effluents of industrial plants released into the water source and air are removed by some physical and chemical processes. Utilizing photocatalysts as cost-effective, accessible, thermally/mechanically stable, nontoxic, reusable, and powerful UV-absorber compounds creates a new gateway toward the removal of dissolved, suspended, and gaseous pollutants even in trace amounts. TiO2 and ZnO are two prevalent photocatalysts in the field of removing contaminants from wastewater and air. Structural modification of the photocatalysts with metals, nonmetals, metal ions, and other semiconductors reduces the band gap energy and agglomeration and increases the affinity toward organic compounds in the composite structures to expand their usability on an industrial scale. This increases the extent of light absorbance and improves the photocatalytic efficiency. Selecting a suitable synthesis method is necessary to prepare a target photocatalyst with distinct properties such as high specific surface area, numerous surface functional groups, and an appropriate crystalline phase. In this Review, significant parameters for the synthesis and modification of TiO2- and ZnO-based photocatalysts are discussed in detail. Several proposed mechanistic routes according to photocatalytic composite structures are provided. Some electrochemical analyses using charge carrier trapping agents and delayed recombination help to plot mechanistic routes according to the direction of photoexcited species (electron-hole pairs) and design more effective photocatalytic processes in terms of cost-effective photocatalysts, saving time and increasing productivity.

Creating anti-viral high-touch surfaces using photocatalytic transparent films

Antimicrobial and self-cleaning surface coatings are promising tools to combat the growing global threat of infectious diseases and related healthcare-associated infections (HAIs). Although many engineered TiO₂-based coating technologies are reporting antibacterial performance, the antiviral performance of these coatings has not been explored. Furthermore, previous studies have underscored the importance of the "transparency" of the coating for surfaces such as the touch screens of medical devices. Hence, in this study, we fabricated a variety of nanoscale TiO₂-based transparent thin films (anatase TiO₂, anatase/rutile mixed phase TiO₂, silver-anatase TiO₂ composite, and carbon nanotube-anatase TiO₂ composite) via dipping and airbrush spray coating technologies and evaluated their antiviral performance (Bacteriophage MS2 as the model) under dark and illuminated conditions. The thin films showed high surface coverage (ranging from 40 to 85%), low surface roughness (maximum average roughness 70 nm), super-hydrophilicity (water contact angle 6-38.4°), and high transparency (70-80% transmittance under visible light). Antiviral performance of the coatings revealed that silver-anatase TiO₂ composite (nAg/nTiO₂) coated samples achieved the highest antiviral efficacy (5-6 log reduction) while the other TiO₂ coated samples showed fair antiviral results (1.5-3.5 log reduction) after 90 min LED irradiation at 365 nm. Those findings indicate that TiO₂-based composite coatings are effective in creating antiviral high-touch surfaces with the potential to control infectious diseases and HAIs.