FeNi-layered double hydroxide (LDH)@biochar composite for , activation of peroxymonosulfate (PMS) towards enhanced degradation of doxycycline (DOX): Characterizations of the catalysts, catalytic performances,degradation pathways and mechanisms

Abstract

In this study, FeNi-layered double hydroxides (LDH)@biochar composite material was prepared by hydrothermal method and used for peroxymonosulfate (PMS) activation towards the efficient degradation of doxycycline (DOX). The as-prepared materials were thoroughly characterized by SEM, BET, XRD, XPS and FTIR. The DOX removal in different systems (LDH@biochar + PMS, LDH + PMS and biochar + PMS) were compared accordingly. And the results demonstrated that the FeNi-LDH@biochar displayed a much higher DOX removal efficiency (88.1%) than FeNi-LDH (77.1%) and biochar alone (75.4%). In addition, the effects of catalyst dosage, PMS concentration, initial pH value on the DOX removal were evaluated. 88.1% of parent contaminant could be decomposed in the presences of 0.50 g/L catalyst, 0.75 g/L PMS at initial pH 4.5 (without pH adjustment), with TOC removal efficiency of 62.9%. The introduction of biochar to LDH catalyst could lead to the involvement of non-radical-based oxidation in DOX degradation. The DOX removal is less affected by the co-existing ions and organics of the actual aquatic environment. Three possible DOX decomposition pathways were inferred according to the identification of transformation intermediates by HPLC-MS. The ECOSAR analysis indicated that the toxic abatement was demonstrated for most of the transformation products during DOX degradation. In the reusability assay, the DOX removal efficiency dropped from 88.1% to 77.2% after five cycles, and recovered to 86.6% via regeneration. The results of both quenching experiment and EPR analysis showed that the SO4•-, •OH, •O2− and 1O2 all did contribute to the DOX decontamination. DFT calculation results showed that LDH@biochar composite exhibited stronger adsorption capacity for PMS and the thermodynamic feasibility of reaction was further demonstrated by the energy barrier of reaction pathways.