Boosting molecular oxygen activation through synergistic interaction of boron-doped biochar and ascorbic acid: Key role of BC2O and BC3

Ambiguous interpretations regarding the underlying mechanism of molecular oxygen (O 2 ) activation by the carbonaceous material/reductant system, especially in terms of the catalytic active site, have impeded the optimization and broader application of the system in environmental remediation. Here, we thoroughly investigated the role of boron-doped biochar (BBC) active sites in O 2 activation and optimized the ascorbic acid (AA) dosing strategy to improve the hydroxyl radical (•OH) production rate and pollutant removal. The introduction of boron facilitated O 2 activation through the successive one-electron transfer to generate •OH that predominantly occurred and accumulated on BBC surface, where •OH yield was nearly 5-fold and 9-fold higher than that in N-doped biochar/AA and zero-valence iron (ZVI) system, respectively. This results in better degradation performance of BBC/AA system for organic pollutants absorbed on the BBC surface and robust resistance to commonly occurring water anions and negatively charged organic matter. Moreover, the stepwise addition of low-concentration AA (0.5 mM) promoted the BPA removal (over 90 %) by maximizing the effective availability of AA and •OH. Characterization, galvanic oxidation process, and theory calculation results revealed that BC 2 O acted as the primary electron-accepting group to receive the electrons from AA, while BC 3 acted as both an electron-donating group and an O 2 adsorption site on BBC, which together facilitated O 2 activation and •OH production on the BBC surface. These findings provide a comprehensive understanding of O 2 activation within the BBC/AA system, highlighting its potential as a sustainable and effective approach for advanced environmental remediation applications.