Synthesis of chitosan graft poly (acrylic acid-co-2-acrylamide-2-methylpropanesulfonic acid)/graphite oxide composite hydrogel and the study of its adsorption

Chitosan graft poly (acrylic acid-co-2-acrylamide-2-methylpropanesulfonic acid)/graphite oxide (CTS-g-P(AA-co-AMPS)/GO) composite hydrogel is synthesized and used to remove rhodamine 6G (R6G) and methyl violet (MV) from aqueous solutions by adsorption. The composite is characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The effect of the adsorption conditions, including the amount of graphite oxide (GO), the initial concentration of dye solutions, the adsorption time, ionic strength, and the mass of the composite, on the adsorption capacities has been studied in detail. It can be seen that small amount of GO can improve the adsorption capacities of both dyes. It is found that the adsorption capacities of R6G and MV can be increased by 57.26% and 26.39%, respectively, compared with CTS-g-P(AA-co-AMPS graft copolymer. The maximal adsorption capacity of R6G and MV is 625.3 and 326.4 mg/g, respectively. The interaction between GO and dye molecules are speculated. GO acts as crosslinking points and combine with the CTS-g-P(AA-co-AMPS) graft copolymer through hydrogen bonds and electrostatic actions. The adsorption isotherms and thermodynamics are discussed. The Gibbs free energy of R6G and MV is that Delta G(R6G)(theta) = -2.478 KJ/mol and Delta G(MV)(theta) = -2.577 KJ/mol and it indicates that the adsorption of R6G and MV on CTS-g-P(AA-co-AMPS)/GO is spontaneous and satisfied the Redlich-Peterson equation. Kinetic studies show that the adsorption is in accordance with the Lagergren pseudo first-order kinetic model.