Nano-magnetite catalyzed heterogeneous Fenton-like degradation of emerging contaminants carbamazepine and ibuprofen in aqueous suspensions and montmorillonite clay slurries at neutral pH

Abstract

The widespread occurrence of pharmaceutically active compounds (PhACs) in the environment has prompted great concern due to their potential impacts on wildlife and humans. The degradation of two of the most commonly detected PhACs, carbamazepine (CBZ) and ibuprofen (IBP), was investigated by a nano-magnetite (Fe3O4) heterogeneous Fenton-like reaction in aqueous suspensions of nano-Fe3O4 in the absence and presence of montmorillonite clay. Experimental design and response surface methodology (RSM) were applied to evaluate the effects of important factors. The results showed that hydroxyl radical (OH) formation by the heterogeneous decomposition of H2O2 on the Fe3O4 nanoparticle surface (OHss) plays the dominant role in CBZ and IBP degradation at neutral pH. The degradation of CBZ and IBP followed pseudo-first-order kinetics, and the degradation rate constants (k) in aqueous suspensions were 0.182 and 0.121h−1, respectively. In addition, significant adsorption of CBZ to the montmorillonite clay occurs at neutral pH, while IBP is not adsorbed, due to electrostatic repulsion. As a result, an inhibition effect of adsorption on the degradation of CBZ (kCBZ=0.127h−1) in clay slurry was observed, but not for IBP degradation (kIBP=0.202h−1). The major intermediates, identified by solid phase extraction (SPE) followed LC–MS analysis, included hydroxy-CBZs, dihydroxy-CBZs, CBZ-10,11-diol, and hydroxy-CBZ-10,11-diols in CBZ degradation; and hydroxy-IBPs, dihydroxy-IBPs, trihydroxy-IBPs, tetrahydroxy-IBPs, 4-isobutylacetophenone and 1-(4-isobutylphenyl)ethanol in IBP degradation. The possible pathways of CBZ and IBP degradation were proposed based on the identified intermediates.