Expanded Graphite Modified by CTAB-KBr/H3PO4 for Highly Efficient Adsorption of Dyes

Abstract

Expanded graphite (EG) modified by CTAB-KBr/H3PO4 was synthesized via composite intercalation agent of CTAB-KBr and natural flake graphite, followed by the activation of phosphoric acid under low temperature. The resultant modified expanded graphite (M-EG) architectures showed an interconnected and continuous open microstructure, in which the number, size and volume of the pores were larger than the EG before modification. Due to their unique structural characteristics, the resulting M-EG exhibited a wide applicability and superior adsorption capacity toward dyes. The saturated adsorption capacities of M-EG were as large as 159.71 mg/g for acid brilliant blue, 48.06 mg/g for methylene blue, 56.73 mg/g for disperse yellow and 81.73 mg/g for acid red with the time of 40, 60, 50 and 50 min respectively, exceeding largely the corresponding pristine EG. Furthermore, it is surprising that the M-EG under different adsorption conditions of temperature, initial pH and metal ions still maintain good removal efficiency and more importantly, the M-EG can be easily separated and do not generate secondary contaminants. Adsorption dynamics indicated pseudo second-order model was more suitable for the investigated adsorption process, which is controlled by chemical adsorption involving uptake of acid brilliant blue onto M-EG through functional groups, but not the only factor. Adsorption isotherm indicated the adsorption process from Langmuir model to Temkin model. According to Dubinin–Radushkevich model, the calculated mean free energy implied chemisorption between M-EG and acid brilliant blue. High removal capability, fast adsorption efficiency, excellent stability and broad applicability make M-EG ideal candidates for dyes removal in practical application.