SnO₂@ZnS photocatalyst with enhanced photocatalytic activity for the degradation of selected pharmaceuticals and personal care products in model wastewater

Pharmaceuticals and personal care products (PPCPs) are a new class of water contaminants that need to be effectively removed. In this work, SnO₂ is involved in enhancing the photocatalytic activity of ZnS-bearing waste for the photodegradation of selected PPCPs. The SnO₂@ZnS photocatalysts with various SnO₂:ZnS ratios were synthesized by a one-step hydrothermal route. The results of physicochemical characterization reveal the successful formation of SnO₂@ZnS photocatalyst. The photocatalytic activities of SnO₂@ZnS photocatalysts are evaluated for the degradation of selected PPCPs: metoprolol (beta-blocker), carbamazepine (antiepileptic), acetaminophen (nonsteroidal anti-inflammatory drug), and triclosan (antimicrobial). As a result, 70% of acetaminophen, 40% of carbamazepine, 67% of metoprolol, and 40% of triclosan are degraded by SnO₂@ZnS photocatalysts. Such discrepancy in the photocatalytic degradation of PPCPs is stemmed from different physicochemical properties of the photocatalysts, chemical structures of PPCPs, and interactions between the PPCP molecules and the photocatalyst surface. To gain more insights into the different photocatalytic removal efficiencies of PPCPs, the adsorption affinities of PPCPs and water molecules to the predominant crystal planes of SnO₂ (011) and ZnS (111) are computationally estimated. It is found that hydrated PPCPs are preferably adsorbed on the surface of SnO₂ rather than on the surface of ZnS, and the SnO₂@ZnS photocatalysts show a better adsorption affinity to PPCPs than individual SnO₂ or ZnS. This study demonstrates a simple route to develop low-cost photocatalysts for the efficient removal of PPCPs by utilizing zinc sulfide-bearing industrial waste.