The influence of B heteroatom concentrations on the physiochemical properties of N, B-co-doped biochar for peroxymonosulfate activation in ciprofloxacin removal

N, B-co-doped biochars with varying boric acid (BA):urea mass ratio were prepared by two-step calcination of sawdust (NB-BC-x, where x = 1, 2, and 3 corresponds to the BA:urea mass ratio of 0.025:1, 0.05:1, and 0.1:1, respectively) and characterized. Generally, B doping prior to N doping can improve N doping because the presence of oxidized B during N doping can interact with NH3, facilitating N doping. The performance of NB-BCs in PMS activation for ciprofloxacin (CIP) removal was evaluated and it was found that the kapp increased in the order of: N-BC (0.010 min-1) < B-BC (0.016 min-1) < NB-BC-2 (0.031 min-1) < NB-BC-3 (0.039 min-1) < NB-BC-1 (0.053 min-1). Due to its large specific surface area and synergistic interaction between N and B moieties, NB-BC-1 presented the best PMS activator, achieving CIP removal of-45 and-80 % by adsorption and degradation in 60 min, respectively. Further performance study using NB-BC-1 revealed that the kapp increased with increasing catalyst loading and PMS dosage. Meanwhile, higher pH can reduce the CIP removal efficiency due to the electrostatic repulsion between NB-BC-1 and PMS. It was also demonstrated that NB-BC-1 can be reused and regenerated after deactivation using thermal treatment at 500 degrees C. From the chemical scavengers and electrochemical studies, it can be deduced that NB-BC-1 activates PMS through both radical and nonradical pathways. Lastly, the degradation pathway of CIP was also proposed by identifying the degradation in-termediates and their toxicity were accessed. Overall, this study showed that NB-BC-1 can potentially be used as a PMS activator for wastewater treatment.