Degradation of nonylphenol ethoxylate 10 in biochar-CoFe2O4/peroxymonosulfate system: Transformation products identification, catalysis mechanism and influencing factors

Abstract

Nonylphenol ethoxylate 10 (NPEO10) is an endocrine disrupting chemical, which can interfere with human endocrine secretion and is carcinogenic and teratogenic to humans. In this study, a peanut shell-based biochar-CoFe2O4 (Bio-CoFe2O4) catalyst with thin layer of fine CoFe2O4 nanoparticles on biochar surface was synthesized using a facile hydrothermal method. For the first time, the degradation of NPEO10 in Bio-CoFe2O4/peroxymonosulfate (PMS) system was studied. Bio-CoFe2O4 composite showed much higher removal efficiency (90.6%) and larger reaction rate constant (k = 0.059 min−1) than that of biochar or CoFe2O4 in presence of PMS (catalyst dosage, 1.5 g/L, PMS dosage, 1.5 mM, NPEO10 concentration, 20 mg/L, and initial pH, 7.0). The significantly enhanced catalytic performance was mainly ascribed to the more exposed reaction active sites induced by its well-dispersed CoFe2O4 with smaller grain size. The quenching experiments and EPR analysis revealed that radical (including SO4•- and •OH and O2•- radicals) and non-radical (i.e. 1O2) pathways worked together for the NPEO10 degradation, and the •OH was the major contributor. Besides, the stable redox cycle of Co(III)/Co(II) and Fe(III)/Fe(II), the graphitized structure and CO in Bio-CoFe2O4 composite were closely related with the activation of PMS to continuously generate these reactive species, thereby efficiently removing NPEO10. Furthermore, the possible transformation products, degradation pathways and catalytic mechanisms of NPEO10 were identified and proposed in detail. Overall, our study provides a potential way to activate PMS for the effective removal of complex organic pollutants from wastewater.