Efficient activation of peroxymonosulfate by N-doped waste herb senna obtusifolia biochar for degrading NPX: Synergistic effect of carbonyl and nitrogen sites

In this work, waste herb senna obtusifolia was utilized as the biochar precursor, and a N-doped biochar (NSOBC6) was prepared to activate peroxymonosulfate (PMS) for degrading Naproxen (NPX). NSOBC-6 exhibited superior catalytic performance in activating PMS, which could degrade NPX completely within 60 min. The NSOBC-6/PMS system also had good reusability and effectiveness under a wide range of pH values and high salinity conditions. The significant contribution of singlet oxygen (O-1(2)) and superoxide radicals (O-2(center dot-)) in NPX degradation was revealed. The results of XPS and DFT calculations indicated C=O, pyridinic-N and graphitic-N participated as catalytic sites in the degradation of NPX. The differences in electron density and the ELUMO-EHOMO (Delta ELUMO-HOMO) gap were induced by N doping, enhancing the PMS activation capacity of NSOBC-6. This work presented a strategy to convert waste herbal into functional biochar materials, which was of great significance for the development of green and efficient catalysts.