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

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 g(-1) mint 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.