Hexagon flower-shaped architectures constructed of Fe-composited lanthanum hydroxide nanosheets for superior phosphate removal: Synthesis and mechanism study

Abstract

In response to phosphorus pollution, developing functional materials for phosphate adsorption is an ideal method to reach an ultralow phosphate concentration in effluent. Herein, a hexagon flower-shaped architecture constructed of Fe-composited lanthanum (La)-based hydroxide nanosheets was fabricated from LaFe cyano-bridged metal frameworks (CMs) via a self-templating strategy using NH3‧H2O as the conversion reagent. The ion exchange process using weak alkaline reagent enables the formation of secondary nanosheets on the architecture, thus leading to a high surface area and a large number of mesopores that provide abundant active sites and mass transfer channels for phosphate adsorption. A superior adsorption capacity of 127.5 mg P/g can be obtained on the La/Fe-based architecture, which also shows satisfactory applicability over a wide pH range. A ligand exchange between -OH and phosphate ions is verified as the main adsorption mechanism, which properly accounts for its excellent selectivity for phosphate adsorption when coexisting with other anions/cations and natural organic matters. Overall, the present study provides a new method for constructing porous La-based hydroxide materials for phosphorus control in water.