Visible Light Photocatalytic Degradation of Methylene Blue Dye and Pharmaceutical Wastes over Ternary NiO/Ag/TiO₂ Heterojunction

Abstract

Ternary NiO/Ag/TiO 2 heterojunction photocatalyst was prepared by deposition coprecipitation for visible light photocatalytic applications. Physicochemical properties of the synthesized NiO/Ag/TiO 2 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 2 composite and compared to bare TiO 2 under visible light irradiation. The results indicate that NiO/Ag/TiO 2 has superior MB photodegradation efficiency with a high reaction rate constant and low degradation time (93.15% within 60 min) compared to Ag/TiO 2 , NiO/TiO 2 , and bare TiO 2 . NiO/Ag/TiO 2 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 2 and Ag−NiO interface, and the p−n heterojunction between NiO and TiO 2 . 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 2 , suppress the electron−hole recombination, and enhance the photocatalytic activity and stability as a result.

Fabrication of samarium doped MOF-808 as an efficient photocatalyst for the removal of the drug cefaclor from water

“…Whereas as UV light has less wavelength and high energy so the probability of reaction between drug and oxidizing species is increased that promotes the production of hydroxyl radicals on catalyst surface which leads to improvement of photocatalysis in ultraviolet light. 56 …”

Origin of the Improved Photoelectrochemical and Photocatalytic Activity in a ZnO-TiO2 Nanohybrid Revealed by Experimental and Density Functional Theory Studies

“…Thus, the formation of an optimal heterojunction is very important and depends mainly on the relative band edge position of the semiconductors and uniform interaction across the interface . The combination of zinc oxide (ZnO) and titanium dioxide (TiO 2 ) is suitable for the formation of a type II heterojunction through surface-to-surface contacts between the semiconductors. , Moreover, both semiconductors have shown great promise as photocatalysts and photoelectrodes due to their wide bandgap (∼3.2 eV) and high activity. − In addition, the high exciton binding energy of ZnO (60 meV) makes it an ideal counterpart for TiO 2 , which facilitates exciton dissociation . The type II heterojunction between ZnO and TiO 2 hinders quick recombination of photogenerated charge carriers in photocatalytic and photoelectrochemical applications. , …”

“… 25 , 26 Moreover, both semiconductors have shown great promise as photocatalysts and photoelectrodes due to their wide bandgap (∼3.2 eV) and high activity. 27 − 30 In addition, the high exciton binding energy of ZnO (60 meV) makes it an ideal counterpart for TiO 2 , which facilitates exciton dissociation. 31 The type II heterojunction between ZnO and TiO 2 hinders quick recombination of photogenerated charge carriers in photocatalytic and photoelectrochemical applications.…”