RGO supported ZnO/SnO₂ Z-scheme heterojunctions with enriched ROS production towards enhanced photocatalytic...

In the present study, the excellent photocatalytic activity of n-ZnO/n-SnO₂ heterojunction integrated with reduced graphene oxide nanosheets was explored towards the elimination of different organic pollutants viz. p-bromophenol, bisphenol A, and ofloxacin from water. n-ZnO/n-SnO₂ heterojunction was decorated with a different weight percentage of reduced graphene oxide via a facile refluxing method. The structural, morphological and optical properties of the as-prepared n-ZnO/n-SnO₂ heterojunction-reduced graphene oxide nanocomposites were investigated systematically. XRD, Raman and FT-IR confirmed the hexagonal wurtzite and tetragonal rutile structures of ZnO and SnO₂ crystals in different nanocomposites. Cube and spherical-shaped surface structures were demonstrated by TEM and FE-SEM analysis for ZnO and SnO₂, respectively. The maximum photocatalytic productivity of nanocomposite with 5 wt% reduced graphene oxide was observed at about 98.64 % and 98.50 % towards the elimination of p-bromophenol and bisphenol A, respectively after 180 min exposure of UV light. Similarly, this productivity was also observed at about 99.13 % towards the elimination of ofloxacin after 120 min irradiation of UV light. The outstanding photocatalytic activity of nanocomposite with 5 wt% reduced graphene oxide has been proven by the presence of homotypic n-ZnO/n-SnO₂ and reduced graphene oxide nanosheets owing to the synergistic effect amongst them resulting in remarkable separation of charge carriers, which is responsible for the larger rate of reactive oxygen species generation and enhanced photodegradation of p-bromophenol, bisphenol A and ofloxacin. In this study, the results illustrated that the photocatalytic degradation of p-bromophenol, bisphenol A and ofloxacin using n-ZnO/n-SnO₂ heterojunction-reduced graphene oxide nanocomposites is predominantly based on the hydroxyl radicals and superoxide radical anion as main reactive oxygen species as compared to ¹O₂. A reasonable photodegradation mechanism using prepared nanocomposites under investigation has also been proposed.