Selective Adsorption and Efficient Removal of Phosphate from Aqueous Medium with Graphene–Lanthanum Composite

Abstract

A three-dimensional adsorbent, i.e., lanthanum oxide decorated graphene composite (3D graphene–La2O3 composite), is prepared. The composite exhibits favorable adsorption performance to phosphate, providing a sorption capacity of 82.6 mg g–1 at pH 6.2. The adsorption behavior for phosphate fits the Langmuir model, and the adsorption kinetics fit a pseudo-second-order model, with rate constants of 0.1847 and 0.007 969 g mg–1 min–1 at phosphate concentrations of 35 and 142 mg L–1, respectively. For the removal of 25 mg L–1 phosphate in 1.0 mL aqueous medium, the commonly encountered anionic species in waters, e.g., Cl–, SO42–, and NO3–, pose no interfering effect at 8000 mg L–1, providing a favorable removal efficiency of 100% by 2.0 mg of composite. When 142 mg L–1 phosphate solution is treated, 100% and >80% adsorption efficiencies are achieved respectively in the presence of 1000 and 8000 mg L–1 of Cl–, SO42–, and NO3–. The high tolerance capacity against coexisting anionic species by the graphene–La2O3 composite makes it suitable for water cleanup by selective and fast adsorption/removal of phosphate.