Anchoring phosphorus on in-situ nitrogen-doped biochar by mechanical milling for promoted electron transfer from diclofenac sodium to peroxymonosulfate

Abstract

It is critical to design and synthesize superior metal-free PMS catalysts, particularly to optimize the interaction between non-metallic heteroatoms and biochar, facilitating electron conduction and the generation of reactive oxygen species. Hence, this work presented a feasible synthetic strategy for anchoring phosphorus on in-situ nitrogen-doped biochar via ball milling at room temperature. Mechanical forces triggered the dehydration reaction between phosphoric acid and C-OH bonds, forming COP bonds. In particular, the obtained N and P co-doped biochar (NPB) showed excellent catalytic activity. The reaction and removal rate of diclofenac sodium (DS) in the NPB/PMS system were 0.3974 min−1 and 90.08 % (only 10 min), respectively, significantly higher than those in the in-situ nitrogen-doped biochar/PMS system. The impressive catalytic efficiency was attributed to the coupling effect of high-efficiency adsorption and exceptional electron transfer capabilities. Anchoring P into the carbon structure effectively expedited the electron transfer from adsorbed DS molecules to metastable PMS complexes via the carbon-bridge effect, ultimately leading to DS degradation. The CO groups, pyridinic N, graphitic N, and defect sites were possible active sites for PMS activation. GC/MS identified the potential degradation paths of DS, but the toxicity of DS and its intermediates was noteworthy. Furthermore, the DS degradation efficiency of the NPB/PMS system was little hampered by pH (2.95–9.07), anions, humic acid, and actual water, suggesting its application potential in real-world wastewater. Overall, this study paves a new way for constructing effective N and P co-doped non-metallic PMS catalysts, which may be expanded to other carbon materials to fulfil the unique demands of various applications.