The adsorption of phosphate by graphene from aqueous solution

Abstract

Graphene was prepared by a facile liquid phase exfoliation and characterized by Raman spectroscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy and zeta potential measurements. A systematic study of the adsorption process was performed by varying pH, ionic strength and temperature. The experimental results showed that graphene is an excellent phosphate adsorbent with an adsorption capacity of up to 89.37 mg g⁻¹ at an initial phosphate concentration of 100 mg L⁻¹ and temperature of 303 K. The adsorption kinetics was modeled by first and second order rate, Elovich and Weber and Morris intraparticle diffusion models. The rate constants for all of these kinetic models were calculated and the results indicate that the second order kinetics model was well-suited to model the kinetic adsorption of phosphate. The Langmuir, Freundlich and D–R isotherm models were applied to describe the equilibrium isotherms and the isotherm constants were determined. Equilibrium data were well-described by the typical Langmuir adsorption isotherm. Thermodynamic studies revealed that the adsorption reaction was a spontaneous and endothermic process.