Polydopamine Enhanced Interactions of Graphene Nanosheets to Fabricate Graphene/Polydopamine Aerogels with Effectively Clear Organic Pollutants

Graphene/polydopamine aerogels (GPD(X)AG, where X represents the weight ratio of DA<middle dot>HCl to GO) were prepared by the chemical reduction of graphene oxide (GO) using dopamine (DA) and l-ascorbic acid as reducing agents. During the gelation process, DA was polymerized to form polydopamine (PDA). The introduction of PDA in the gelation of aerogels led to a deeper reduction of GO and stronger interactions between graphene nanosheets forced by covalent cross-linking and noncovalent bonding including pi-pi stacking and hydrogen bonding. The weight ratio of DA<middle dot>HCl to GO influencing the formation and morphology of GPD(X)AG was explored. With the increasing content of DA in gelation, the reduction of GO and the cross-linking degree of graphene nanosheets were enhanced, and the resulting GPD(X)AG had a more regular pore distribution. Additionally, introducing PDA into GPD(X)AG improved its hydrophobicity because of the adhesion of PDA to a network of aerogels. GPD(X)AG exhibited a higher removal efficiency for organic pollutants than the controlled graphene aerogels (GAG). Specifically, the adsorption capacity of GPD(X)AG for organic solvents was superior to that of GAG, and organic solvent was completely separated from the oil/water mixture by GPD(X)AG. The equilibrium adsorption capacity of GPD(X)AG for malachite green (MG) was measured to be 768.50 mg/g, which was higher than that for methyl orange (MO). In MG/MO mixed solutions, aerogels had obvious adsorption selectivity for the cationic dye. The adsorption mechanism of aerogels for MG was also discussed by simulating adsorption kinetic models and adsorption isothermal models.