Critical impact of pyrolysis temperatures on biochars for peroxymonosulfate activation: Structural characteristics, degradation performance and mechanism

[Display omitted] •Pine needle biochars were prepared at different temperatures for PMS activation.•With temperature increasing, the degradation rates increase then slightly decrease.•BC-300 has more oxygenic groups/PFRs, BC-700 has higher porosity/graphitization.•1O2 plays important role in both BC/PMS systems.•Electron transfer is the key factor of the superior degradation rate of BC-700. In order to gain insights into the critical impact of pyrolysis temperatures, a series of pine needle biochars were prepared by one-step pyrolysis method at different temperatures, and were applied for peroxymonosulfate activation to degrade enrofloxacin. Interestingly, with the increase of temperature, the degradation efficiencies increase first, then slightly decrease. BC-700 (biochar synthesized at 700 °C) exhibited best performance, and the degradation rate could reach 97.7 % within 180 min under the optimized conditions. Characterization results demonstrated biochar synthesized at relatively low temperature exhibited more oxygen-containing functional groups and persistent free radicals, while biochar synthesized at high temperature contained more pore structure and higher graphitization degree. Mechanism studies demonstrated that biochar synthesized at relatively low temperature tend to generate transient radicals, while biochar synthesized at high temperature exhibited better electron transfer capability, which might be the key factor of the superior degradation rate of BC-700. In addition, singlet oxygen played an important role in both systems.