Self-Assembled Graphene Hydrogel Composites for Selective Dye Removal

Graphene-based hydrogels are known as promising amphiphilic agents for water uptake and selective organic contaminant removal. However, it is a challenge to prevent graphene sheet restacking during the gelation as this factor significantly influences the adsorption behavior of organic contaminant. A porous reduced graphene oxide-starch hydrogel (rGOSH) with enhanced pore size is produced by a simple one-step method through starch-directed self-assembly of graphene sheets. This hydrogel demonstrated to be a promising candidate for the selective removal of organic dye molecules, where positive and neutral dyes are adsorbed, and the negative one is repelled. In particular, the hydrogel prepared with incorporation of starch between the graphene sheets, adsorbs positively charged dye ≈75% more than reduced graphene oxide hydrogel, due to better diffusion into larger pore size and strong electrostatic interaction with negatively charged oxygen groups. Furthermore, the Langmuir isotherm model and kinetic studies for dyes adsorption onto rGOSH reveal that the adsorption mechanisms are dominantly chemisorption within the porous hydrogel structure since the experimental data can be well fitted to the pseudo-second-order dynamic equation with the highest adsorption capacity (1106.950 µg g⁻¹) and kinetic (1.957E-05 g µg⁻¹ min^−0.5) toward the positively charged dye.