Oxidation of Sulfamethoxazole by Rice Husk Biochar-Activated Persulfate

Abstract

In the present study, biochars from rice husk were synthesized via pyrolysis at 400, 550, 700 and 850 °C for 1 h under a limited O2 atmosphere, characterized with a various techniques of and used as catalysts to activate persulfate and to degrade sulfamethoxazole (SMX). After physicochemical characterization of biochars. SMX degradation tests were performed using different water matrices, persulfate biochar and SMX concentrations and different initial pH solutions. Also, spiked solutions with bicarbonate, chloride, calcium nitrate, humic acid or alcohols were tested. It was found that catalytic reactivity rises with the pyrolysis temperature. Biochar is crucial for the oxidation of SMX and it can be described with a pseudo first–order kinetic model. Real matrices hinder the oxidation process, in waste water the SMX removal is 41% in 90 min, comparable with the inhibition obtained with spiked with bicarbonates solution (52% removal within 90 min) while complete removal can be achieved in ultrapure water matrices. The presence of alcohol slightly inhibits degradation contrary to the addition of sodium azide which causes significant inhibition, this is an evidence that degradation either under electron transfer/singlet oxygen control or dominated by surface-bound radicals.