Graphene oxide-coated Ag-TiO2 hybrid nanocomposites for superior photocatalytic activity

Abstract

Graphene oxide (GO) has now emerged as one of the most promising materials in different areas such as photocatalysis, adsorption, and energy storage due to its high surface area, unique layered structure, etc. Among various types of precursors, anthracite coal has attracted a lot of attention nowadays as it affords GO a high concentration of sp² carbons resulting in high conductivity and superior absorbance in the visible region. In this report, we have prepared GO-TiO₂ nanocomposites as it is supposed to possess high photocatalytic activity owing to facile electron transmission from the conduction band of TiO₂ to the GO surface resulting in a much lower degree of electron-hole pair recombination. To boost the photocatalytic activity further, TiO₂ was coated with Ag nanoparticles as well. These hybrid structures were characterized by different analytical techniques, for example, XRD, HR-TEM, SEM, and Raman spectroscopy. The XRD pattern of these composites consists of characteristic peaks corresponding to GO, TiO₂, and Ag. The HR-TEM studies confirm the presence of GO layers, cube-shaped TiO₂, and spherical Ag nanoparticles. Phenol and 4-nitrophenol have been used as model pollutants to evaluate the photooxidation efficiencies under both UV and visible light irradiation. Under UV irradiation, the GO/Ag-TiO₂ ternary nanocomposite shows better photooxidation efficiency (62%) compared to Ag-TiO₂ (38%), GO-TiO₂ (9%), GO (17%), and TiO₂ (8%) toward phenol degradation. The GO/Ag-TiO₂ is also having the highest photocatalytic activity toward the removal of phenol under visible light irradiation (34%). The ternary heterostructure (85%) also possesses superior photooxidation activity compared to Ag-TiO₂ (44%) and GO-TiO₂ (71%) toward the degradation of p-nitrophenol under UV light radiation for 60 min. The above observation reveals that the cooperative effect of Ag, TiO₂, and GO is playing a crucial role to result in the high photooxidation activity of the GO/Ag-TiO₂ hetero-nanocomposites.

Keywords: Ag-TiO2; Coal-derived graphene oxide; Degradation of phenolic compounds; Hybrid composites; Photocatalysis.