Characterization and application of expanded graphite modified with phosphoric acid and glucose for the removal of Ni(II) from aqueous solution

Three kinds of modified expanded graphite (EG), impregnated with phosphoric acid (H3PO4) (P-EG), impregnated with glucose (G-EG), and impregnated with H3PO4 and glucose (G-P-EG), were prepared under a low temperature (150 degrees C). The adsorption capacity of G-P-EG (Q(m) = 7.016 mg/g) is much higher than original expanded graphite (EG Q(m) = 0.423 mg/g) and other two kinds of modified expanded graphite (P-EG Q(m) = 0.770 mg/g; G-EG Q(m) = 0.507 mg/g). The physicochemical properties of EG and G-P-EG were characterized by N-2 adsorption/desorption, Boehm's titration and X-ray photoelectron spectroscopy (XPS). EG exhibited higher values of BET surface area (11.357 m(2)/g) and total pore volume (0.0303 cm(3)/g) than that of G-P-EG (4.808 m(3)/g and 0.0109 cm(3)/g). However, the results of Bohm's titration and XPS showed that G-P-EG contained more surface oxygen-containing functional groups. The Ni(II) adsorption equilibrium data agreed well with the Langmuir model. And the experimental data of EG and G-P-EG fitted better by pseudo-second order model. Based on the results of batch adsorption experiments and XPS analysis, there were several possible mechanisms for Ni(II) adsorption on the G-P-EG, including chemical adsorption, cation exchange, electrostatic attraction and surface complication. (C) 2015 Elsevier B.V. All rights reserved.