Efficient degradation of phenol in water by ball-milling modulated nitrogen-doped structured biochar

Abstract

Presently, most kinds of biochar rely on the addition of transition metals to improve their electron transport capacity, thereby boosting the activation of oxidants. However, challenges such as the precipitation of transition metals and the chemical inertness of biochar are commonly encountered. Biochar with nitrogen-containing functional groups has emerged as a promising solution as oxidant activators. The nitrogen doping of biochar through ball milling is a straightforward, cost-effective, and efficient preparation method. To optimize the activation properties, a multi-step process involving roasting, ball milling, and tempering was employed to produce biochar. Sesame dregs was chosen as the precursor for this biochar. By optimizing the roasting temperature to 900 °C and using urea as the nitrogen source, biochar derived from sesame residue was successfully prepared. This biochar featured pyridine nitrogen as the primary functional group, exhibiting improved crystallinity and aromaticity. The activation of sodium persulfate (3.0 mM) with biochar eliminated phenol from wastewater with an initial concentration of 50 mg/L in just 15 minutes, achieving a remarkable mineralization rate of 96.77%. Even after undergoing six cycles of repeated use, the system consistently removed 97.73% of phenol within the same timeframe, maintaining a high mineralization rate of 86.77%. Notably, it was found that N-CN, N-6, and N-q were instrumental in stimulating reactive oxygen species (ROS), while ·OH, SO4·-, and 1O2 served as the primary ROS responsible for degrading phenol. The research also revealed a linear relationship between active oxygen sites and oxidized substances, offering insights into the mechanism of phenol degradation.