Removal of Methylene Blue from Wastewater Using a Ternary Composite Hydrogel System: Pullulan Polysaccharides Grafted with Polyacrylamide and Decorated with Graphene Oxide

In this study, composite hydrogels were prepared by a simple synthetic technique to adsorb methylene blue from water. The hydrogel was composed of polyacrylamide (PAM) as the carrier, grafted with pullulan polysaccharide, and modified with graphene oxide. The morphology and properties of PUL/PAM/GO composites were characterized by Thermogravimetric Analysis (TGA), Fourier Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscopy (SEM). Then, the adsorption performance of PUL/PAM/GO hydrogel for MB was researched, including the dose, temperature, contact time, pH, adsorption isotherm, adsorption kinetics, and adsorption thermodynamics and swelling properties. The effects of various salts in real wastewater on adsorption were simulated. The removal rate of MB by PUL/PAM/GO was high-speed, and the sample can remove 83.2% of the dye in 140 min. The adsorption kinetics was more consistent with pseudo-second-order reaction, and the Langmuir model was suitable for describing the adsorption process. The maximum adsorption capacity was 438.7 mg g−1. Thermodynamic parameters covered the enthalpy changes (ΔH0), free energy (ΔG0), and entropy (ΔS0), which stated that adsorption by the PUL/PAM/GO hydrogels was exothermic and spontaneous.Graphical Abstract