Adsorption and Advanced Oxidation of Diverse Pharmaceuticals and Personal Care Products (PPCPs) from Water Using Highly Efficient rGO-nZVI Nanohybrids
Engineered nanomaterials, like graphene with tunable adsorption sites and nanoscale zero-valent iron (nZVI) with unique redox chemistry, offer great prospect for removing pharmaceutical and personal care products (PPCPs) through adsorption and catalytic advanced oxidation process (AOP) in comparison to bulk materials. Although PPCPs are found to be as a complex mixture in wastewater and in the environment, most studies regarding nano-enabled PPCP removal reported results with only one PPCP at a time and typically at high initial concentrations. In this study, we utilized reduced graphene oxide (rGO) to support nZVI to synthesize rGO-nZVI nanohybrid (NH) and used rGO-nZVI NH for the removal of a complex mixture of 12 diverse PPCPs that includes antibiotic, anti-inflammatory, anti-seizure, and antidepressant pharmaceuticals, and are recalcitrant in the environment. We also tested the removal of PPCPs at their individual environmentally relevant concentrations at ppb level. The rGO-nZVI NH synergistically performed as both an adsorbent and a heterogeneous Fenton catalyst (for AOP) in the presence of H2O2, to remove ~95-99% of environmentally relevant concentrations (200 ppb) of the PPCPs within 10 minutes. Even in the absence of H2O2, the hybridization resulted in better adsorptive property (14-72% more removal) in the rGO-nZVI NH compared to the parent nanomaterials (rGO or nZVI) for various PPCPs in the mixture, removing ~82-99% of the PPCPs, at the end of 30 minutes, with comparatively slower kinetics (~3-5.5 times) than in presence of H2O2. Hydrophobic PPCPs were removed faster and more with both the adsorption and AOP. The potential of utilizing rGO-nZVI NH in drinking/wastewater treatment system, or even in point-of-use system where necessary, was substantiated by the enhanced and fast PPCP removal capacity of the nanohybrid.