Graphene-loaded agarose hydrogel for removal and release of organic compounds in oil and water

This thesis firstly presents a brief introduction to and a literature review of the dispersion of carbon-based nanomaterials in the aqueous phase and their applications. Details of experimental synthesis and characterization techniques are provided. The main focus is on the transfer of graphene oxide (GO)/ reducing graphene oxide (rGO) into its poor solventwith the help of agarose hydrogel.<br><br> Secondly, the transfer of GO-loaded agarose hydrogel (AgarBs) into oils such as hexadecane is reported via stepwise solvent exchange with no chemical modification of the GO hydrophilic surface and the agarose network. After transfer, the GO loaded in the agarose network effectively and efficiently adsorbs lipophilic dyes in oil via hydrogen bonding between the polar groups of the GO and the dyes. For instance, the maximum adsorption capacity was 355.9 mg·g-1 for Nile red, which is substantially greater than that of pristine agarose hydrogel and hydrophilic GO powder. The dye concentration for effective adsorption can be as low as 0.5 ppm.<br><br> Thirdly, GO-loaded AgarBs are used for lipophilic drug delivery. GO-loaded AgarBs can adsorb lipophilic organic compounds from their good organic solvent and swell in Phosphate Buffer solution (PBS) after dried in air. This is thanks to the GO in the agarose hydrogel network, which can adsorb organic compounds in its good solvent and enhance the swelling properties of composite hydrogel in water. The concentration of released organic compounds in the PBS solution is related with loaded capacity for organic compounds and the GO concentration in the composite hydrogel beads. In addition, the concentration of released organic compounds is suppressed under saturation concentration, which avoids secondary aggregation after the release of the dye. The lipophilic organic dye can also penetrate through pigskin by this method. These results prove the potential of composite hydrogel to be a new carrier for lipophilic drug delivery.<br><br> The loading of hydrophobic rGO into agarose hydrogel beads by the NaBH4 reduction of GO initially loaded in the AgarBs is then described. The resulting rGO-loaded AgarBs effectively adsorb organic compounds in water because of the attractive hydrophobic force between the rGOs loaded in the AgarBs and the organic compounds dissolved in the aqueous media. The adsorption capacity of the rGO-AgarBs is fairly high, even for reasonably watersoluble organic compounds such as rhodamine B (321.7 mg.g-1) and aspirin (196.4 mg.g-1).Moreover, the rGO-AgarBs exhibit salinity-enhanced adsorption capacity and preferential adsorption of organic compounds with lower solubility in water. This unusual adsorptionbehavior highlights the exciting possibility of the adoption of an adsorption strategy, driven by hydrophobic forces, in practical wastewater treatment processes.<br>