Enhanced photocatalytic inactivation of bacteria and degradation of pharmaceutical pollutant by rGO/N-TiO2 nanocomposites: a study of active radicals

A simple one-pot sol–gel process was used to synthesize the rGO/N-TiO2 nanocomposites with varying rGO concentrations. In this synthesis, ammonia played a dual role as a precipitating agent as well as a source of nitrogen for doping. Synthesized nanomaterials are characterized using various techniques. The UV–vis diffuse reflectance (UV-DRS) study shows the optical properties of N-TiO2 improve with increasing rGO concentration in nanocomposites up to an optimum ratio. After that, it decreases due to rGO covering the active sites on the N-TiO2 surface. X-ray diffraction (XRD) analysis confirms the presence of an anatase phase with a crystallite size in the range of 9–11 nm. Field emission scanning and transmission electron microscopic (FE-SEM and TEM) images confirmed the well-distribution of N-TiO2 NPs (with an average particle size ranging from 21 to 23 nm) on the rGO surface. Under visible light irradiation, electron paramagnetic resonance (EPR) analysis confirms the NO2−paramagnetic center with two new N-based paramagnetic centers. The photocatalytic application was studied with the inactivation of E. coli and the degradation of diclofenac sodium salt. Both studies revealed that the rGO/N-TiO2 nanocomposites show higher photocatalytic activity than N-TiO2 alone. The optimized rGO concentration (0.7 rGO/N-TiO2) shows an almost fourfold improvement in the photodegradation rate of diclofenac as compared to N-TiO2, with excellent stability. The scavenger experiment showed that holes (h+) and superoxide (O2•−) are the most important active radicals generated by rGO/N-TiO2 in the photodegradation of diclofenac. Graphical abstract