Role of schwertmannite or jarosite in photocatalytic degradation of sulfamethoxazole in ultraviolet/peroxydisulfate system

Abstract

• Photocatalytic activities of Sch and Jar were evaluated in UV/PDS system. • Synergetic effect in Sch/UV/PDS system accelerated the degradation of SMX and TOC. • UV irradiation accelerated ≡Fe 3+ /≡Fe 2+ redox cycle on Sch surface. • Production of OH and SO 4 •- was enhanced in Sch/UV/PDS system. • Sch exhibited wide pH adaptability and good recyclability. Ultraviolet (UV)/peroxydisulfate (PDS) system has been employed for degrading organic pollutants in water, but the insufficient production of reactive species in the system limits the mineralization of organic pollutants. This study evaluated for the first time the effectiveness of integrating iron hydroxysulfates, including schwertmannite (Sch) and jarosite (Jar), with UV/PDS system for sulfamethoxazole (SMX) degradation in water. The optimal conditions identified for 40 μM SMX degradation were PDS 2 mM, photocatalysts 1 g L -1 and pH 3 in both of Sch/UV/PDS and Jar/UV/PDS systems. A synergetic effect between UV/PDS and Sch/UV processes was found in Sch/UV/PDS system with synergistic factor of 1.15, which drastically enhanced the production of reactive species ( OH and SO 4 •- ) and consequently improved SMX degradation and TOC mineralization. Additionally, schwertmannite exhibited higher photocatalytic activity than jarosite in UV/PDS system for both SMX degradation and TOC mineralization. In Sch/UV/PDS system, ≡Fe(OH) 2+ on schwertmannite can be efficiently photolyzed to ≡Fe 2+ and OH under UV irradiation with O 2 – generation, in which the produced reactive species contributed to a relatively small fraction of SMX degradation. More importantly, the regeneration of ≡Fe 2+ accelerated PDS activation to SO 4 •- / OH, which was responsible for the degradation of most SMX. However, the photoreduction of ≡Fe 3+ to ≡Fe 2+ on jarosite by UV irradiation was insignificant, thus leading to the poor PDS activation to SO 4 •- / OH and a lower SMX degradation rate. The degradation pathways of SMX in Sch/UV/PDS system were further proposed based on the identified degradation intermediates of SMX. Besides, schwertmannite exhibited a good adaptability in wide pH (2–9) range, good stability, and recyclability for catalyzing SMX degradation in UV/PDS system. Therefore, integrating schwertmannite with UV/PDS system is an attractive method for efficiently removing organic pollutants in water.