Chemically-Crosslinked Xylan/Graphene Oxide Composite Hydrogel for Copper Ions Removal

The chemically-crosslinked composite hydrogel based on acylated xylan and silanized graphene oxide was prepared via free radical polymerization as a novel adsorbent for the removal of Cu2+ ions from aqueous solution. The chemical structures and morphologies of the silanized graphene oxide and acylated xylan as well as the prepared hydrogels were characterized by FT-IR, XPS, SEM and TEM. The swelling ratios of the prepared hydrogels were determined, and the results showed that the chemically-crosslinked hydrogel was pH-sensitive, and the swelling kinetics of the hydrogels followed Schott second-order kinetic. The optimum pH for the adsorption of Cu2+ ions onto the chemically-crosslinked composite hydrogel was found at the value of 5 and the maximum adsorption amount of Cu2+ ions was evaluated to be 228 mg/g. The adsorption isotherm accorded with the Freundlich model, and the pseudo-second order kinetic model was suitable to describe the adsorption process. The study of adsorption thermodynamics indicated that the adsorption of Cu2+ ions onto the chemically-crosslinked composite hydrogel was endothermal and spontaneous, and the adsorption amount rose with an increase in temperature. In addition, higher desorption percentages of Cu2+ ions from the used hydrogel were also achieved (77.3% after recycling for 6 times). All obtained results indicated that the prepared chemically-crosslinked hydrogel is promising for water treatment and collection of metal ions.