TiO2−x/Ag/rGO composites as effective photocatalysts for the degradation of organic pollutants

Abstract

We designed and fabricated a photocatalyst made of reduced titanium dioxide nanorods (TiO_2−x NRs) that incorporates silver nanoparticles (Ag NPs) and reduced graphene oxide (rGO) sheets, to narrow the band gap and improve the photoinduced degradation of methylene blue (MB). The morphological characterization showed that Ag NPs and rGO sheets were well-deposited on both the top surface and the outer walls of vertically oriented 1D TiO_2−x NRs. Energy dispersive spectroscopy and specific surface area analyses confirmed the presence of both Ag NPs and rGO sheets and the as-obtained TiO_2−x/Ag/rGO sample exhibited a large specific surface area (153.7 m² g⁻¹). Moreover, X-ray diffraction patterns contained peaks characteristic of tetragonal rutile TiO₂ and confirmed that there is no phase change after reduction treatment. The optical investigation revealed that the formation of Ti³⁺ ions, surface defects and oxygen vacancies were considered as major reasons for the red shift of the absorption edge towards the visible region (546 nm) compared with pristine TiO₂ NRs. The incorporation of Ag NPs and rGO with TiO_2−x NRs improved the light absorbance and the narrowing of the TiO_2−x bandgap energy (from 2.95 to 1.97 eV) as a result of the SPR effect of Ag NPs and the reduced light reflection in the presence of rGO. Therefore, among the various as-prepared photocatalysts, the TiO_2−x/Ag/rGO (2% wt) photocatalyst showed the best performance, degrading almost 100% of MB under 120 min visible light irradiation. Kinetic studies confirmed that degradation reactions over all photocatalysts followed first order kinetics. The photodegradation rate toward MB over TiO_2−x/Ag/rGO (2% wt) is 6.45, 1.85, and 1.6 times higher compared to that of pristine TiO₂ NRs, TiO_2−x and TiO_2−x/Ag, respectively. The TiO_2−x/Ag/rGO composite proves to be an exceptionally efficient photocatalyst for water treatment.