Peroxymonosulfate activation by microplastics coagulated sludge-derived iron-carbon composite for effective degradation of tetracycline hydrochloride: Performance and mechanism

A simple one-step pyrolysis method was adopted to prepare microplastics (MPs) coagulated sludge into an iron-carbon composite (Fe-PSMPC), which was used to activate peroxymonosulfate (PMS) for the degradation of tetracycline hydrochloride (TC). The iron species in coagulated sludge were thermally reduced by carbon at 800 °C to produce abundant Fe0, which was successfully loaded on the surface of carbon derived from MPs. Then, the effects such as Fe-PSMPC dosage, PMS dosage, initial pH, and pollutant concentration on TC degradation were further investigated. The results showed that the Fe-PSMPC/PMS system was able to degrade TC effectively over a wide pH range. Under the optimal process conditions, the removal rate of TC could reach 87.5 % within 16 min. In addition, quenching experiments, electron paramagnetic resonance, electrochemical measurements, and X-ray photoelectron spectroscopy analyses indicated that the non-free radical (1O2 and electron transfer) pathway was dominant in the TC degradation system, and the free radical (•OH and SO4• −) pathway also showed significant contribution. Fe0 on Fe-PSMPC was the main active site, and the keto group (C = O) also acted as an active site to facilitate the generation of 1O2. Furthermore, three possible degradation pathways of TC were elaborated based on the 17 intermediates detected by liquid chromatography-mass spectrometry. This work provides an economical and convenient recycling strategy for the MPs coagulated sludge, which can be converted into an effective catalyst to activate PMS for the degradation of organic pollutants, thus realizing “treating waste with waste”.