Comparative study of tetracycline degradation efficiency using peroxydisulfate activated with sludge biochar and activated coke: the role of surface defects

Both sludge biochar (BC) and activated coke (ACO) are hierarchical while their surface properties have a large disparity. We show that sludge biochar pyrolyzed at 600 degrees C (BC600) outperforms biochar produced at other temperatures for a range of biomass feedstock. BC600 displays lower carbon content, lower surface area, and importantly more abundant surface oxygen-containing functional groups when compared with ACO. BC600 and ACO were used to activate peroxydisulfate (PDS) for tetracycline oxidation while the degradation mechanisms were comprehensively discussed. Interestingly, ACO demonstrated a particularly higher performance where activating PDS compared with BC600. The K-app value for the synergetically combined ACO-PDS process was 2.15 times that of the sum of adsorption and PDS oxidation processes alone, while it was 1.72 times for the BC600-PDS process. Solution pH had a more dramatic influence on BC600 than on ACO. Quenching experiments proved that both OH center dot and SO4 center dot- contributed insignificantly while most of the degradation was attributed to superoxide radical (O-2(center dot-)), singlet oxygen (O-1(2)), and active holes (h(+)). After reducing carbonyl groups on both carbons by KBH4 in absolute alcohol, quenching experiments did not indicate the key role of carbonyl groups for O-1(2) generation. Non-radical pathway proved dominant in the carbon/PDS catalytic process. Excellent reusability and stability for ACO was observed in repeated use experiments.