Reduced graphene oxide-decorated CdS/ZnO nanocomposites for photoreduction of hexavalent chromium and photodegradation of methylene blue

CdS/ZnO/rGO, ZnO/CdS, and ZnO/rGO hetero-nanocomposites were successfully prepared by the facile one-pot solvothermal method. CdI2(benztsczH)(2) (where benztsczH = benzaldehyde thiosemicarbazone) for CdS and zinc acetate dihydrate for ZnO synthesis were used as single-source precursors (SSP) in the presence of two-dimensional graphene oxide. The obtained nanocomposites were well characterized using spectroscopic techniques. An ultrafast catalytic activity is observed for the photoreduction of toxic hexavalent to non-toxic trivalent chromium using ternary tandem CdS/ZnO/rGO in comparison with binary ZnO/CdS and ZnO/rGO. The reduced graphene oxide-decorated CdS/ZnO nanocomposites show complete photoreduction of Cr(vi) to Cr(iii) in 2 minutes. It is the shortest time frame for the reduction of toxic chromium without the use of noble metals like Pt, Pd, and Au. The complete photodegradation of MB was also achieved by the ternary nanocomposite in 50 minutes. The plausible mechanisms for harvesting sunlight by the binary and ternary nanocomposites are suggested by the valence and conduction band potential values and Mulliken electronegativity of individual cations. Experiments were also carried out using scavengers to strongly support the mechanism by showing the responsible reactive species involved in the MB dye photodegradation.

Automated summary

CdS/ZnO/rGO, ZnO/CdS, and ZnO/rGO hetero-nanocomposites were successfully prepared using a facile one-pot solvothermal method. The ternary tandem CdS/ZnO/rGO showed ultrafast catalytic activity in the photoreduction of toxic hexavalent chromium to non-toxic trivalent chromium, completing the reaction in just 2 minutes without the use of noble metals. Additionally, the ternary nanocomposite achieved complete photodegradation of methyl blue in 50 minutes. Mechanisms for sunlight harvesting and reactive species involved in dye photodegradation were suggested based on valence and conduction band potentials and Mulliken electronegativity values.