Single-step synthesis of nitrogen and phosphorus co-doped biochar and its application in dye removal: synergistic effects of adsorption and peroxymonosulfate activation

Abstract

In the field of advanced oxidation processes (AOPs), the development of catalysts with environmental friendliness and economic benefits faces multiple difficulties, mainly reflected in the catalytic efficiency, selection specificity, and complexity of the synthesis process. This study, we reported a nitrogen and phosphorus co-doped carbon catalyst (CANP800-1) synthesized by a one-step pyrolysis method. The co-doped catalyst was able to achieve 100 % removal of Acid Orange 7 (AO7) in about 30 min and had a high apparent rate constant (k_obs = 0.125 min⁻¹), which is better than unmodified carbon and other single-doped comparative materials. Structural analyses pinpointed that N, P co-doped enhanced specific surface area (1179 m²/g), introduced abundant mesopores, and created a wealth of active sites (such as graphitic nitrogen, C-P bonds) synergistically promoting adsorption and peroxymonosulfate (PMS) activation. The CANP800-1/PMS system had significant adaptability to various water matrices, including pH, coexisting ions, natural organic matter, and real water conditions. A mechanistic investigation confirmed that singlet oxygen (¹O₂) was essential to the reaction process, while electrochemical studies and DFT simulations validated that N/P-induced enhancement of electron transfer and PMS adsorption took place. This study established an innovative metal-free catalytic system that exhibited remarkable effectiveness in sustainable water treatment, providing distinctive solutions and a theoretical basis for ongoing technical difficulties in industrial wastewater treatment.