Cr and N co-doped biochar driving controllable peroxydisulfate activation pathways to degrade tetracycline: Pyrrolic N inducing singlet oxygen generation

Efficiently inducing nonradical pathway in peroxydisulfate (PDS) activation is promising in environmental decontamination due to the oxidation selectivity and anti-interference ability, but still remains challenges, e.g., low efficiency and high cost. In this study, a series of Cr and N co-doped biochar (Cr-N/BC) was synthesized via pyrolysis by using melamine-retanned chrome shaving (MCS) as precursors, to activate PDS toward the tetracycline (TC) degradation. The introduction of pyrrolic N on Cr-N/BC not only boosted the catalyst reactivity, but also altered the complexation state of PDS, thus triggering a shift in oxidative modes from the radical pathway into a singlet oxygen (1O2) dominated nonradical pathway, in which, the relative contribution of the nonradical oxidation to the TC degradation increased from 0 to 98%. Structure-activity relationship determination unveiled that pyrrolic N on Cr-N/BC surface greatly changed the charge distribution and chemical property of biochar, thereby facilitating the decomposition of PDS and generation of 1O2. In addition, ecotoxicological safety of the intermediates of TC in the 1O2-dominated pathway was evaluated to validate the superiority of the nonradical process. This study advances our understanding of designing reaction-oriented nonradical carbon-catalysis for selective decontamination.