Oxidative transformation of carbamazepine by manganese oxides

Abstract

This study presents oxidative transformation of carbamazepine by synthetic manganese oxide (δ-MnO(2)) as well as impact of variables including initial MnO(2) loading, pH, coexisting metal ions, and humic acid (HA) on transformation. Manganese oxide (δ-MnO(2)) was synthesized and stored in the form of suspension. The oxidative reactions were conducted in 50mL polyethylene (PE) centrifuge tubes with constant pH maintained by buffers. The kinetic experiment was carried out in the solution of pH 2.72 containing 5.0mg/L of carbamazepine and 130.5mg/L of MnO(2). Effects of initial MnO(2) loading (0-130.5mg/L), pH (2.72-8.58) and 0.01M of coexisting solutes (metal ions and HA) on carbamazepine oxidation were also determined. Reaction kinetics indicated that carbamazepine was rapidly degraded in the first 5min, and approximately 95% of carbamazepine was eliminated within 60min. The reaction exhibited pronounced pH dependence and increased with decreasing pH values. The transformation of carbamazepine was also accelerated with increasing MnO(2) loadings. Coexisting metal ions competed with carbamazepine for reactive sites leading to reduced carbamazepine removal, and the inhibitive capacity followed the order of Mn(2+) > Fe(3+) > Ca(2+) ≈ Mg(2+). Presence of HA in aqueous solution caused a significant reduction on the magnitude of carbamazepine transformation. This study indicated that carbamazepine can be effectively degraded by δ-MnO(2), and transformation efficiency was strongly dependent on reaction conditions. It suggests that amendment of soil with MnO(2) be a potential alternative to solve carbamazepine pollution.