Activating peroxymonosulfate by high nitrogen-doped biochar from lotus pollen for efficient degradation of organic pollutants from water: Performance, kinetics and mechanism investigation

Nitrogen-doped biochars are promising metal-free catalysts for peroxymonosulafe (PMS) activation due to their low-cost, high chemical stability and metal-free leaching. However, the nitrogen content in the biochar is usually low with unsatisfactory performance, and the in-depth analysis on the kinetic of pollutant degradation is still insufficient. Herein, high nitrogen doped biochars were prepared by one-step pyrolysis of lotus pollen (LP) and melamine, which were used to trigger PMS for degrading organic pollutants in water. The optimized nitrogen-doped LP biochar (N-LPC-5) possessed ultrahigh nitrogen content (up to 15.75 at%) and abundant oxygen-containing functional groups, which exhibited the optimal performance in activating PMS to degrade reactive black 5, atrazine, ketoprofen and p-nitrophenol. The removal efficiency for all the organic pollutants in the N-LPC-5/PMS system can reach above 90 % in 20 min, and the degradation performance was outstanding in a wide pH range from 2.0 to 10.5. The pollutant degradation followed a two-stage process including a fast stage of initial oxidation and a slow stage. An appropriate mathematic kinetic model was proposed to describe the two-stage reaction. Fitting the experimental data with the proposed kinetic model, the initial removal rate and the maximal oxidation capacity can be obtained accordingly, and the correlation coefficients were very close to 1.0, indicative of the excellent fitness of the proposed model. In addition, the catalytic mechanisms such as the reactive oxygen species, electron-transfer pathway and active sites were also investigated by various techniques. The present study highlights the tremendous potential of N-biochar for wastewater remediation, and helps to understand the dynamic kinetics and catalytic mechanism of metal-free carbon activating PMS.