Enhanced Phosphate Adsorption by Mg-Stirred Leaf Biochar in a Complex Water Matrix via Active MgO Facet Exposure

In phosphate adsorption, the interaction between MgO and the carbon network in Mg-biochar is an overlooked factor that contributes to active MgO facet generation for enhancing phosphate adsorption. However, the complex water matrix adsorption mechanism underlying the adaptability of MgO-biochar and enhanced phosphate adsorption are not fully studied. Herein, Mg-stirred leaf biochar (Mg-SLBC) was prepared by the Mg-stirring modification method. Mg-SLBC possessed the highest adsorption capacity (79.28 mg g–1) to phosphate among the adsorbents. In addition, Mg-SLBC had a good performance for phosphate adsorption in a complex water matrix. Phosphate adsorption by Mg-SLBC was not affected by Cl–, NO3–, SO42–, humic acid, metal ions, and Ca2+ but was inhibited by Mg2+ and HCO3–. For long-term adsorption, Mg-SLBC could constantly adsorb phosphate to avoid phosphate accumulation (<2 mg L–1). Meanwhile, phosphate adsorption by Mg-SLBC was a spontaneous process (ΔG, −6.884 kJ mol–1), which was dominated by inner-sphere complexation. Owing to high combination between MgO and the carbon network, there were more active MgO facets (e.g., (1 1 0) and (2 0 0)) to induce stronger unbalanced electron distribution in Mg-SLBC. Thereby, Mg-SLBC, with high adsorption capacity and adaptability, could effectively adsorb phosphate in a complex water matrix.