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°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 Kapp 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• and SO4•– contributed insignificantly while most of the degradation was attributed to superoxide radical (O2•–), singlet oxygen (1O2), 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 1O2 generation. Non-radical pathway proved dominant in the carbon/PDS catalytic process. Excellent reusability and stability for ACO was observed in repeated use experiments.