Synthesis and Adsorption Behavior of Chitosan Graft Poly(acrylic acid)/Graphite Oxide/Attapulgite Composite Hydrogel

Chitosan graft poly(acrylic acid)/graphite oxide/attapulgite (CTS-g-PAA/GO/APT) composite hydrogel has been synthesized and used to remove rhodamine B (RB) and methyl orange (MO) from aqueous solutions through adsorption. The composite is characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The influence of adsorption conditions, i.e., the content of graphite oxide (GO) and attapulgite (ATP), the initial concentration of dye solutions, the adsorption time, ionic strength, pH values and dosage of the composite, on the adsorption capacities has been studied in detail. It is found that small amount of GO and ATP can improve the adsorption capacities of dyes significantly. Adsorption capacities of RB and MO onto CTS-g-PAA graft copolymer are 36.7 and 56.4 mg/g, respectively, while those onto CTS-g-PAA/GO/APT (GO 0.02 g, APT 0.05 g) composite hydrogel are 92.6 and 186.5 mg/g, respectively. Adsorption isotherms and thermodynamics are discussed. It indicates that the adsorption of RB is in accordance with both the Langmuir and R-P isotherm equations. However, that of MO meets the R-P equation. The adsorption of RB is spontaneous, while that of MO is not. Kinetic studies show that the adsorption of both RB and MO is in accordance with the Lagergren pseudo first-order kinetic model.