Cobalt ferrite nanoparticles with controlled composition-peroxymonosulfate mediated degradation of 2-phenylbenzimidazole-5-sulfonic acid

Abstract

Magnetic spinel cobalt ferrite nanoparticles with variable composition (CoxFe3-xO4; x=0.1, 0.5, 0.7 and 1.0) were synthesized. The nanoparticles were characterized by various surface techniques. Average sizes and surface areas of ferrites were determined in the ranges of 11–34nm and 18.5–49.1m2/g, respectively. Surface analysis of the nanoparticles confirmed the spinel type structures in which Co(II) incorporated into the crystal lattice. The synthesized catalysts were used to dissociate peroxomonosulphate (PMS) into reactive sulfate radicals (SO4•−) and further into hydroxyl radicals (HO•) to degrade a target pollutant, 2-phenylbenzimidazole-5-sulfonic acid (PBSA) in absence of heat and light. As the molar ratio of cobalt (i.e., x) in the ferrite catalyst increased from 0.1 to 1.0, PBSA degradation enhanced from 24 to 75% in 240min. The removal of PBSA increased significantly with the increase in PMS concentration up to 0.1mM, followed by a decrease at PMS levels of >0.1mM. Nitrogen content in PBSA was mineralized by the cobalt ferrite-PMS system mostly into NO3− and NH4+ ions with minor formation of NO2−. Only 32% TOC removal was observed over a 240min reaction time, indicating carbon content in PBSA was not completely mineralized. A chemical probe method, based on free radical scavenging, revealed the contribution of both SO4•− and HO• species in PBSA degradation. Fifteen reaction intermediates were identified using LC/Q-TOF-ESI–MS analysis. Hydroxylation, elimination of sulfonate moiety, and ring cleavage processes were involved in the major degradation pathways. Catalyst reuse experiments demonstrated PBSA degradation efficiency either retained or increased with each subsequent reuse. The magnetic spinel Co-ferrite nanoparticles can be applied effectively to activate PMS without energy aiding for degrading harmful emerging organic contaminants in water.