Visible Light Photocatalytic Degradation of Methylene Blue Dye and Pharmaceutical Wastes over Ternary NiO/Ag/TiO Heterojunction.

Ternary NiO/Ag/TiO heterojunction photocatalyst was prepared by deposition coprecipitation for visible light photocatalytic applications. Physicochemical properties of the synthesized NiO/Ag/TiO composite were characterized by X-ray diffraction, Brunauer-Emmett-Teller surface area measurement method, transmission electron microscopy, energy-dispersive X-ray spectroscopy techniques, X-ray photoelectron spectroscopy technique, and ultraviolet-visible absorption spectroscopy. The results suggest that the well-dispersed small metallic silver nanoparticles (<3 nm) facilitate electron transfer and bridge nickel oxide and titanium oxide. The photocatalytic degradation and the methylene blue (MB) dye kinetics were carried out on a ternary NiO/Ag/TiO composite and compared to bare TiO under visible light irradiation. The results indicate that NiO/Ag/TiO has superior MB photodegradation efficiency with a high reaction rate constant and low degradation time (93.15% within 60 min) compared to Ag/TiO, NiO/TiO, and bare TiO. NiO/Ag/TiO nanocomposite was also investigated for the most common pharmaceutical waste degradation and exhibited excellent degradation efficiency. The enhancement of the composite's performance could be attributed to the surface plasmonic resonance of the Ag nanoparticles, the formation of Schottky junctions at the Ag-TiO and Ag-NiO interface, and the p-n heterojunction between NiO and TiO. Ag NPs act as a photosynthesizer and a photocatalyst, facilitate electron transfer, shift the absorption to the visible light region, reduce the band gap of TiO, suppress the electron-hole recombination, and enhance the photocatalytic activity and stability as a result.