Enrichment of persulfate activation sites on coffee waste grounds-derived carbonaceous materials via coal fly ash incorporation for efficient degradation of diclofenac: Reaction mechanisms and toxicity assessments

Abstract

The feasibility of coal fly ash (CFA) as a modification agent to reinforce peroxydisulfate (PDS) activation sites of coffee waste grounds-derived carbonaceous materials (CWCM) for the effective degradation of diclofenac (DCF) was comprehensively investigated. The degradation of DCF by PDS activation using CFA-incorporated CWCM (CFA@CWCM) was more effectively achieved than CWCM because of higher oxygen vacancy (OV) and iron (II) contents on CFA@CWCM surfaces. Heterogeneous catalytic activation of PDS on multiple active sites (i.e., OV, iron (II), aromatic rings, and ketones) of CFA@CWCM was primarily responsible for generating singlet oxygen and superoxide, which played the main roles in the degradation of DCF, with minor production of hydroxyl and sulfate radicals. The degradation pathways of DCF by the CFA@CWCM/PDS system were potentially hydroxylation, oxidation, dehydrogenation, and Csingle bondN cleavage. Additionally, the potential risks of DCF and its degradation intermediates were moderately reduced using the CFA@CWCM/PDS system. The CFA@CWCM/PDS system demonstrated effective DCF degradation in both lake water and secondary effluent. In particular, the CFA@CWCM/PDS system maintained reuse efficiencies of up to 76.2 % for four cycles of the catalytic degradation of DCF. Therefore, CFA is a potential alternative to pure chemicals for enriching the PDS activation sites of CWCM to purify DCF-containing water.