High-Performance Photocatalytic Degradation of Tetracycline and Ciprofloxacin by Ag-ZnO-Decorated Graphene Oxide Sponge
Shirley P. Onkani, Paul N. Diagboya, Samson O. Akpotu, Fanyana M. Mtunzi
Abstract
High Resolution Image Download MS PowerPoint Slide Nanophotocatalysts are preferred for aqueous organic contaminants degradation but suffer two major practical application drawbacks: high electron–hole recombination rates leading to low degradation efficiencies and cumbersome separation from water postdegradation, which results in reusability difficulty. Hence, the efficacy and reusability of Ag-doped ZnO (Ag-ZnO) photocatalyst supported on graphene oxide sponge (GOS) for aqueous antibiotics (tetracycline–TC and ciprofloxacin–CPF) photodegradation were investigated. The composite exhibited significantly improved properties, including enhanced specific surface area, decreased Ag-ZnO agglomeration, better photon absorption, and lowered band gap energy. The experimental antibiotics degradation data revealed that these properties positively impacted the degradation process by the Ag-ZnO-GOS composite, resulting in maximal degradation efficiencies of 89 and 100% for CPF and TC, compared to ≈50 and 43%, respectively, for the pristine Ag-ZnO. These high efficiencies of the Ag-ZnO-GOS composite were maintained even after reusing the composite for 4 cycles of antibiotic degradation, thus demonstrating excellent reusability. The optimum use parameters for the Ag-ZnO-GOS composite are ≈35 mg Ag-ZnO-GOS mass, 350 mL contaminant solution at pH ≈ 7, and a concentration of ≈7 mg/L, at an average irradiation time of 180 min. The Ag-ZnO-GOS composite is an effective photocatalyst for the degradation of low concentrations of TC and CPF, which are prevalent in most waters, and has potential practical application in water treatment plants.