Effectiveness of reactive oxygen species generated from rGO/CdS QD heterostructure for photodegradation and disinfection of pollutants in waste water.

The present study investigates the role of reactive oxygen species (ROS) generated on surface of nanophotocatalyst in wastewater treatment discharged from exponentially growing industries. A facile synthetic route is presented to produce reduced graphene oxide/CdS quantum dot (rGO/CdS QD) heterostructure by monowave-assisted solvothermal method where room temperature ionic liquid 1-ethyl-3-methylimidazolium thiocyanate serves as a "green" precursor. The prepared photocatalyst was tested for: (1) photodegradation performance against various cationic dyes, anionic dyes, and antibiotics as model organic water pollutants; and (2) disinfection performance against gram-positive S. aureus and gram-negative E. coli bacterial strains as pathogenic water pollutants. The negative surface charge of rGO/CdS QD precisely attracted the cationic dye molecules to its surface and degraded the dyes at a higher rate. Moreover, excellent antibacterial activity of rGO/CdS QD were observed against S. aureus and E. coli with a minimum inhibitory concentration of 16 μg ml-1 and 32 μg ml-1, respectively. A plausible mechanism of the photocatalytic activity suggested that ROS with strong oxidizing ability reacts with the organic pollutants to mineralize them into CO2, H2O or some other small molecules, and reacts with pathogens to damage the macromolecules like proteins, lipids, DNA, etc in the bacterial cells. Among all the surface generated ROS, hydroxyl radicals was found to be the main contributor in the photodegradation and disinfection mechanism.