Preferable phosphate removal by nano-La(III) hydroxides modified mesoporous rice husk biochars: Role of the host pore structure and point of zero charge

Immobilizing La(OH)3 nanoparticles (NPs) to porous hosts has been widely applied to inhibiting their inherent aggregation as well as the subsequent low utilization efficiency of La. In this study, a series of rice husk biochars (RHBCs) with high mesoporous rates were prepared and the effects of host pore structure and point of zero charge (pHpzc) on phosphate adsorption by La-modified RHBCs was particularly focused. Characterization results confirmed that La(OH)3 NPs were both confined in the pore channel and external surface of RHBCs. Adsorption kinetics and isotherms showed that La-modified RHBCs with higher mesoporous rates of the host showed a faster adsorption rate and La-modified RHBCs exhibited superior La utilization efficiency than many reported La-incorporated adsorbents. Phosphate could be effectively captured over a wide pH of 3–10 due to the high pHpzc of La-modified RHBCs. Moreover, the La-modified RHBCs showed satisfactory affinity towards phosphate in the presence of coexisting anions and the phosphate adsorption by La-RHBC9 was enhanced in the presence of Ca2+, while it was inhibited in the presence of Mg2+. The mesoporous structure of RHBCs strengthened the stability of La-modified RHBCs and weakened the inhibition of coexisting humic substances on phosphate adsorption through the “shielding effect”.