Waste polypropylene filter induced synthesis of pure phase Fe3O4 and ZVI incorporated carbon composite for non-radical peroxymonosulfate activation dominated sulfamethoxazole degradation: Singlet oxygen versus electron transfer process

Abstract

In this study, waste polyethylene (PP) obtained from obsoleting water purifier filter was mixed with ferric chloride hexahydrate (FeCl3·6H2O) to prepare a series of single crystal phased iron compound incorporated carbon composites (Fe/PP-C). The prepared Fe/PP-Cx catalysts were then utilized to degrade sulfamethoxazole (SMX) in water by activating peroxymonosulfate (PMS). The results showed that with the assistance of pyrolysis temperature regulation, waste PP filter could control the crystalline phase of the iron compound in the prepared Fe/PP-Cx through releasing distinct gaseous atmospheres at respective pyrolysis temperature. When the pyrolysis temperature was set at 600 °C and 900 °C, pure phase ferric oxide (Fe3O4) and zero-valent iron (ZVI) incorporated carbon catalysts were obtained, respectively. 0.2 g/L of Fe/PP-Cx could completely degrade 0.02 mM of SMX within 20 min, in which the toxicity of the reaction solution was also effectively reduced. In both Fe/PP-Cx/PMS systems, non-radical mechanisms dominated the SMX degradation, in which singlet oxygen played the dominant role in the Fe/PP-C600/PMS system, whereas electron transfer process was primarily responsible for SMX degradation in the Fe/PP-C900/PMS system. High-valent iron-oxo species was also involved in SMX degradation in the Fe/PP-C900/PMS system. Since Fe/PP-C600 and Fe/PP-C900 respectively activated PMS via heterogeneous and homogeneous routes, Fe/PP-C600 maintained higher longtime use stability. This study aims to present a simple approach to manipulate the nonradical organic pollutant degradation mechanisms in PMS activated system, which also provides a new strategy of utilizing waste polymer.