Self-Assembled Sponge-like Chitosan/Reduced Graphene Oxide/Montmorillonite Composite Hydrogels without Cross-Linking of Chitosan for Effective Cr(VI) Sorption

Sponge-like chitosan (CS)/reduced graphene oxide (rGO)/montmorillonite (MT) porous composite hydrogels were synthesized with a facile strategy of in situ reduction of graphene oxide (GO) without cross-linking of CS. Integral pore structure can be formed in the hydrogels when proper amount of MT was introduced. The composite hydrogel can restore to the original shape and dimension after compressive deformation like a sponge and show good stability in acid condition. Batch equilibrium measurements on the composite porous hydrogel were carried out to optimize the parameters for the removal of hexavalent chromium ions (Cr­(VI)). The results reveal that the Cr­(VI) ion sorption of the composite hydrogels is highly pH dependent and is the most effective at pH = 2. The sorption capacity increases with increasing temperature and the maximum Cr­(VI) uptake of the composite hydrogel is 87.03 mg/g at 288 K. The sorption follows pseudo-second-order kinetic model and Langmuir isotherm. The composite porous hydrogels can be repeatedly used as adsorbent and a high sorption capacity after repeated usage can be maintained. Such an in situ GO reduction strategy can also be used to fabricate a variety of porous 3D polymer/rGO-based nanocomposites for biomaterials, energy storage materials, and adsorbent materials.