Green Synthesis of ZnO and Black TiO₂ Materials and Their Application in Photodegradation of Organic Pollutants

ZnO and black TiO₂ have been selected as the most efficient materials for organic pollution abatement due to their increased efficiency when compared to other materials. However, the concept of green chemistry makes it desirable to design green synthesis approaches for their production. In this study, black TiO₂ was synthesized using an environmentally safe synthetic technique with glycerol as a reductant. ZnO was prepared by using ionic-liquid-based microwave-assisted extracts of Polygonum minus. To investigate the materials′ potential to photodegrade organic pollutants, methylene blue (MB) and phenol were chosen as model organic pollutants. Both materials were found to exhibit spherical morphologies and a mesoporous structure and were efficient absorbers of visible light. ZnO exhibited electron-hole pair recombination lower than that of black TiO₂. Black TiO₂ was discovered to be an anatase phase, whereas ZnO was found to have a hexagonal wurtzite structure. In contrast to black TiO₂, which had a surface area of 239.99 m²/g and a particle size of 28 nm, ZnO had a surface area of 353.11 m²/g and a particle size of 32 nm. With a degradation time of 60 min, ZnO was able to eliminate 97.50% of the 40 mg/L MB. Black TiO₂, on the other hand, could reduce 90.0% of the same amount of MB in 60 min. When tested for phenol degradation, ZnO and black TiO₂ activities were reduced by nearly 15 and 25%, respectively. A detailed examination of both ZnO and black TiO₂ materials revealed that ZnO has more potential and versatility for the degradation of organic pollutants under visible light irradiation.