Separation of the heme protein cytochrome C using a 3D structured graphene oxide bionanocomposite as an adsorbent

Proteins are of great importance for medicine and the pharmaceutical and food industries. However, proteins need to be purified prior to their application. This work investigated the application of a hydrogel bionanocomposite based on agar and graphene oxide (GO) for capturing cytochrome C (Cyto C) heme protein by adsorption from aqueous solutions with other proteins. Although applications of GO-based materials in adsorption are widely studied, the focus on semi-continuous processes remains limited. Adsorption experiments were carried out in batch and fixed bed columns. The effect of pH and ionic strength on adsorption was investigated, and there is evidence that electrostatic interactions between Cyto C and the nanocomposite were favoured at pH = 7; the adsorption capacity decreased as NaCl and KCl concentrations increased, ascribed to the weak electrostatic interaction between the protein and GO active sites in the bionanocomposite. All adsorption isotherm models (Langmuir, Freundlich, Sips) used gave suitable adjustments to the equilibrium experimental data and the kinetic models applied. The maximum adsorption capacity predicted by the Langmuir isotherm was ∼400 mg_CytoC g_{adsorbent,dry}^-1, and the adsorption thermodynamics indicated a physisorption process. Tests were performed to evaluate the co-adsorption in batch, and the composite was effective in adsorbing Cyto C in solution with bovine serum albumin (BSA) and L-phenylalanine. Fixed bed tests were performed, and although protein adsorption onto nanoparticles can be challenging, the Cyto C adsorbed could be successfully recovered after desorption. Overall, the GO-based hydrogel was an effective method for cytochrome C adsorption, exhibiting a notorious potential for applications in protein separation processes.