Adsorption of Pb2+ and Cd2+ on the l‐cysteine‐functionalized graphene oxide/chitosan/polyvinyl alcohol hydrogel: Kinetic, isotherm, and thermodynamic study

Abstract In this study, polyvinyl alcohol‐chitosan‐cysteine‐functionalized graphene oxide (PCCFG) hydrogel was synthesized from l ‐cysteine‐functionalized graphene oxide (CFG), chitosan (CS), and polyvinyl alcohol (PVA). The hydrogel was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy and employed for removing lead ion (Pb 2+ ) and cadmium ion (Cd 2+ ) from aqueous solution. The effects of initial metal ion concentration, hydrogel dose, pH, time, and temperature were studied. The experimental data were well described by a pseudo‐second‐order kinetic model and Langmuir isotherm with maximum adsorption capacities of 250 and 192 mg g −1 at 25°C for Pb 2+ and Cd 2+ , respectively. The adsorption capacity of the PCCFG hydrogel increased with an increase in temperature. The value of ∆ G ° was negative, which shows the spontaneity of the reaction (electron exchange or ion exchange) between the metal ion and electron‐rich atoms (–N, –S, –O). The positive ∆ H ° shows that the adsorption reaction consumes energy and the positive ∆ S ° shows the strong affinity of PCCFG toward the Pb 2+ and Cd 2+ ions. Pb 2+ had better affinity and less spontaneity than Cd 2+ . The results show that the coexistence of Pb 2+ , Cd 2+ , and Cu 2+ in the solution inhibits the adsorption capacity of PCCFG.