Efficient degradation of carbamazepine in a neutral sonochemical FeS/persulfate system based on the enhanced heterogeneous-homogeneous sulfur-iron cycle

In this study, a novel ultrasound enhanced FeS/persulfate Fenton-like system (US/FeS/PDS) was developed for the synergistic degradation of a typical drug carbamazepine (CBZ) under neutral circumstances. Factors such as FeS dosage, PDS dosage, initial pH and temperature, as well as coexisting anions were investigated. High dosages of FeS and PDS, elevated temperature and acidic circumstances were favorable for the oxidation of CBZ. Presence of HCO3− strongly inhibited the CBZ degradation in the US/FeS/PDS system, while slight suppression was observed with either NO3− or Cl−. Seven intermediates were identified as the products from the decomposition of CBZ by hydroxyl radicals (OH·) and sulfate radicals (SO4−·). Time-dependent radical examination indicated that homogeneous OH· and SO4−· would contribute to the CBZ removal from 22.6 to 34.7% and 12.9 to 50.5%, respectively, while the contribution of solid-liquid interfacial radicals decreased from 64.5 to 20.2%. Meanwhile, the oxidation of S2− occurred concurrently with reduction of Fe(III) to Fe(II). The reaction mechanism in the US/FeS/PDS system was proposed based on the sonochemical heterogeneous-homogeneous sulfur-iron cycle in the US/FeS/PDS system. US would firstly enhance the interfacial sulfur-iron electron transfer and the disintegration of the passivation layer, and then lead to the overall improvement in both interfacial and bulk sulfur-iron cycle, as well as the degradation of CBZ.