Facile synthesis of sludge-derived MnOx-N-biochar as an efficient catalyst for peroxymonosulfate activation

Sewage sludge (SS), the inevitable byproduct of wastewater treatment plants, is facing numerous challenges of environmentally safe and cost-effective disposal. Thus, exploration of efficient SS valorization technique is highly desired. In this study, a sludge derived carbon-supported MnOx as a catalyst (ASMn-Nb) was synthesized through NH4OH activation and pyrolysis (800 degrees C) to enhance peroxymonosulfate (PMS) decomposition and subsequent degradation of acid orange 7 and rhodamine B. The sample characterization indicated that MnCl2 conditioning produces mixed valent Mn oxides on ASMn-Nb, while NH4OH activation significantly enhances N-heteroatoms, surface area, and microporosity. The as-synthesized hybrid catalyst exhibited excellent PMS decomposition ability in a wide range of pH, which enhances AO7 removal efficiency 16%-100% in 40 min compared with that treated with raw sludge biochar. Moreover, the catalyst is recyclable, chemically stable, and produce negligible metal leaching during catalysis. Further investigation of catalytic mechanisms revealed that both radicle and non-radicle processes governing PMS decomposition, whereas mediated electron transfer as the primary and O-1(2), SO4 center dot-, and (OH)-O-center dot radicals induced catalysis as the secondary mechanisms of PMS activation and subsequent AO7 degradation. Finally, a probable mechanism of PMS decomposition over ASMn-Nb and AO7 degradation path is proposed. This study concurrently provides a facile route of improving the catalytic performance of sludge derived-biochar and a probable SS valorization technique.