A novel multifunctional Ag and Sr2+ co-doped TiO2@rGO ternary nanocomposite with enhanced p-nitrophenol degradation, and bactericidal and hydrogen evolution activity

In the present study, a novel multifunctional Sr2+/Ag-TiO2@rGO ternary hybrid photocatalyst was prepared via facile sol-gel and hydrothermal methods. The prepared catalyst was well characterized by UV-vis, XRD, Raman, HRTEM and XPS. The synthesized composite was utilised for p-NP degradation, E. coli disinfection and H-2 generation under visible light. The Sr2+/Ag-TiO2@rGO catalyst showed enhanced photocatalytic H-2 evolution rate (64.3 mol h(-1)) compared with Ag-TiO2@rGO (30.1 mol h(-1)) and TiO2 (no activity). Nearly complete degradation of 15 mg l(-1)p-NP was achieved over Sr2+/Ag-TiO2@rGO after 3 h, while only 66% and 5% was achieved by Ag-TiO2@rGO and TiO2 respectively. Furthermore, TEM analysis was carried out on Escherichia coli (E. coli) before and after visible light irradiation to understand the inactivation mechanism and DNA analysis indicated no fragmentation during inactivation. Radical quantification experiments and ESR analysis suggested that OH and O-2(-) were the main ROS in the degradation and disinfection processes. The superior photocatalytic H-2 evolution rate of Sr2+/Ag-TiO2@rGO was attributed to the synergetic effect between the Ag, Sr2+ and TiO2 components on the rGO surface. The localized SPR effect of Ag induced visible light generated charge carriers into the conduction band of the TiO2 and Sr2+ which further transfer to the rGO for the reduction of H+ ions into H-2. The results suggest that Sr2+/Ag-TiO2@rGO structures could not only induce separation and migration efficiency of charge carries, but also improve charge collection efficiency for enhanced catalytic activity. Thus, we believe that this work could provide new insights into multifunctional nanomaterials for applications in solar photocatalytic degradation of harmful organics and pathogenic bacteria with clean energy generation during wastewater treatment.