A comparative study of lysozyme adsorption with graphene, graphene oxide, and single-walled carbon nanotubes: Potential environmental applications

• Protein adsorption capacity of G, GO and SWNT was investigated.
• GO possess high capacity (∼500 mg/g) for lysozyme adsorption.
• Significant effect of ionic strength on lysozyme adsorption by GO and SWNT.
• G, GO and SWNT can remove proteins present in wastewater.

Wastewater contains numerous classes of organic molecules, primarily different types of soluble microbial products (SMPs) such as polysaccharides, nucleic acids, and proteins. The presence of these compounds in effluents increases the risk of toxic by-product formation during the chlorination process. In recent years, several studies have demonstrated the power of carbon-based nanomaterials to remove many chemical compounds and pollutants from aqueous solutions. In this study, we investigated the protein absorption capacity and the mechanisms of adsorption of three carbon-based nanomaterials: graphene (G), graphene oxide (GO) and single-walled carbon nanotubes (SWNT) in various water chemistries, using lysozyme as a model protein. The results showed that GO exhibited the highest adsorption capacity for lysozyme (∼500 mg protein/g nanomaterial) in the adsorption isotherm assays. The adsorption data were fitted to Langmuir, Freundlich, and Temkin models and the relevant parameters were determined. Lysozyme adsorption to GO and SWNT was found to be strongly influenced by the presence of monovalent and divalent salts. However, no significant pH dependency was observed for protein adsorption to any of the nanomaterials tested. Results also showed that the adsorption mechanism for GO was mainly electrostatic, while for G and SWNT was attributed to be van der Waals forces and some electrostatic interactions. Adsorption experiments of proteins present in wastewater were performed to test the efficacy of G, GO and SWNT as adsorbents for complex environmental samples. All three nanomaterials were found to remove more protein from wastewater than conventional adsorbent reported in the literature.

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