(135d) Graphene Oxide Nanocomposite Hydrogels Capable of Wastewater Dye Sequestration

Organic dyes are widely used in many chemical industries and, unfortunately, they are often discharged with wastewater without adequate treatment, becoming one of the main causes of harmful water pollution. Methylene blue (MB) is a cationic dye, and like many other cationic dyes, it is made from known carcinogenic aromatic compounds that can cause severe environmental problems and health risks. Various processes have been developed to purify water, such as membrane filtration, ion exchange, chemical oxidation, etc. However, they have many restrictions such as lack of practicality, formation of toxic by-products, production of high amounts of residues, or incapability of regeneration. Among these methods, adsorption has been preferred and widely used lately because of its comparable low cost, simplicity of operation, low generation of residues and recycling capabilities of the adsorbent. In recent years, graphene oxide (GO) has attracted attention as a potential dye adsorbent because of its unique two-dimensional (2D) structure with oxygen functional groups, a large surface area, strong π-π interactions and highly negatively-charged surface, allowing a superior adsorption of aromatic cationic dyes. Hydrogels are networks of crosslinked hydrophilic polymer and can potentially serve as three-dimensional templates to immobilize and present GO in the aqueous environments demanded by wastewater treatment applications. Thus, GO-laden hydrogels have the potential to efficiently sequester cationic dyes from wastewater and retain them for transport and disposal.

In this study, GO was integrated into hydrogels by entrapping GO in networks of polymerized acrylamide (AAm) crosslinked with polyethylene glycol dimethacrylate (PEGDMA). Both nanoporous gel structures with and without GO were investigated as candidate wastewater treatment materials. The porosity and swelling ratio of the gels were determined, and morphological characterizations of gels were carried out using scanning electron microscopy (SEM). MB and eosin Y (EY) were chosen as model adsorbates to evaluate and compare the adsorption capabilities of GO gels for cationic and anionic dyes, respectively. Samples from GO gel adsorption kinetic studies were analyzed via UV-vis spectrometry in order to assess dye sequestration capabilities. The isotherms at different dye concentrations, kinetic studies and regeneration of the gels are currently ongoing. So far, GO-laden and GO-free hydrogels showed similar inabilities to sequester anionic EY removal, as expected. However, GO-laden hydrogels exhibited the ability to efficiently remove cationic MB. Finally, dye-adsorbed GO hydrogels can easily be removed from the aqueous environment, suggesting a potential alternative for organic cationic dye removal in wastewater treatment.