Unraveling the synergistic mechanism of urea and sodium carbonate during biochar modification and peroxymonosulfate activation for wastewater decontamination

Abstract Biochar co-modified with urea and an alkaline substance exhibited superior performance in peroxymonosulfate (PMS) activation for wastewater decontamination. However, the mechanism underlying the synergistic relationship between urea and alkaline substance to functional groups and electronic structure of biochar during modification, and its impact on PMS activation pathway remains understudied. In this research, a modified biochar (NABC) was successfully synthesized via the one-pot pyrolysis of a mixture of urea, Na 2 CO 3 , and corncob. The synergistic effect of urea and Na 2 CO 3 during pyrolysis was elucidated using various characterizations. Urea provided N sources and small aromatic rings, while Na 2 CO 3 promoted the conversion of pyridinic N to graphitic N and signified the degree of graphitization; it also facilitated the retention of -COOH. Thus, NABC was porous and contained rich graphitic N and -COOH, along with high graphitization degree, endowing it with 5.2 times higher first-order kinetics than that of pristine biochar. Moreover, NABC shifted the PMS activation mechanism by inhibiting the formation of •OH and promoting generation of 1 O 2 and O 2 •– to degrade aniline. DFT calculations further confirmed that graphitic N and -COOH functioned as critical active sites, synergistically activating PMS. This research provides a theoretical foundation for optimizing the co-modification of biochar for more efficient wastewater purification. Graphical Abstract