Photocatalytic and biocidal activities of ZnTiO2 oxynitride heterojunction with MOF-5 and g-C3N4: A case study for textile wastewater treatment under direct sunlight.

The work aimed to synthesize three heterojunction photocatalysts (Eg = 2.65-2.78 eV) via in-situ encapsulation of 5% zinc doped titanium oxynitride (Zn0.05TiOxNy) catalyst into MOF-5 and bulk (BCN)/sulfur-doped (SCN) g-C3N4 supports using a microwave method. The prepared photocatalysts were characterized and utilized to purify textile industrial wastewater from the organic dye (e.g., methylene blue, MB) and microbial (e.g., E. coli, S. aureus, and C. albicans) contaminants under dark, visible, and solar lights. The output data confirmed the higher activity of Zn0.05TiOxNy@SCN and Zn0.05TiOxNy@MOF-5 for photo-induced microbial growth inactivation (> 90%) under visible light, with photo-biocidal efficiency of 0.91-1.69 mCFU/Einstein. Such a phenomenon is ascribed to the synergism between the high antimicrobial capacity of supports and photoactivity of Zn0.05TiOxNy. Also, Zn0.05TiOxNy@SCN exhibited far superiority to mineralize MB dye (Kphoto of 2.73 × 10-2 min-1) under direct sunlight due to its high photonic (ζ% of 4.4-8.3%)/quantum (QE of 0.56-0.54%) efficiencies for the generation of hydroxyl and superoxide (-•O2/•OH) oxidative species. As a practical case study, all heterojunction photocatalysts also demonstrated high-performance stability (5 cycles) for real textile wastewater treatment under sunlight (efficiency = 76.1-84.6%).