Integration of Graphene Oxide into Hydrophilic Polymeric Networks for Waste Water Treatment Applications

Since the dawn of the industrial revolution indiscriminate dumping of  wastewater from textile mills, metallurgical factories, and other manufacturing facilities have contaminated our water ways with toxic dyes and heavy metal ions. The removal of contaminants from wastewater has been successfully achieved using carbon-based materials such as C₁₈ silica and activated carbon but these materials often suffer from low adsorption capacities and lack of reusability. Graphene oxide (GO)  has recently been investigated as a solution to these problems. GO is a single atom thick nanomaterial with functionalized oxygen groups on its basal plane. Since GO is a flat sheet, there is tremendous surface area for interaction with other substances. The issue with GO is that it tends to aggregate, however, incorporating GO into a hydrogel matrix can overcome this limitation. In this study, the effectiveness of GO-loaded poly(ethylene glycol) (PEG) hydrogels were tested for their ability to adsorb different model wastewater contaminants. The effect of polymerization temperature was tested in these studies to compare the effect between the resulting hydrogels and cryogenic hydrogels (cryogels) on the system properties. The difference in polymerization temperatures caused a variation in pore size where cryogels formed a macroporous structure due to the freezing of water molecules during polymerization. GO was added to the hydrogels and cryogels at 0.75 weight% and swelling and adsorption tests were conducted. For adsorption experiments, three model contaminates were tested; methylene blue (MB), eosin Y (EY), and 4-nitrophenol (4NP). The compounds were chosen to represent cationic, anionic, and organic molecules respectively, and thus cover a large range of typical contaminants. Adsorption experiments were conducted where gel samples with an average mass of 0.1421 g were placed into 100 mL of a 0.01 mg/mL solution of each contaminant in an agitated beaker. The greatest adsorption potential of 1121 mg MB/g GO was seen by the PEG cryogel loaded with GO and little adsorption for 4NP was seen across all of the gels. For eosin Y, the greatest adsorption of 761 mg EY/g GO was seen by the PEG cryogel loaded with GO. Overall, the integration of GO into polymeric networks has shown great adsorption potential for model wastewater contaminates.