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 mgCytoC gadsorbent,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.

Agar/graphene oxide hydrogels as nano-bioadsorbents: a comparative analysis for dye removal.

Nano-biocomposite hydrogel samples were produced using graphene oxide (GO) and agar and applied as adsorbents of organic components in water. The hydrogels were prepared by varying the wt% of Agar and GO. The samples were characterized, and batch adsorption experiments evaluated the effect of initial pH, equilibrium isotherms, and kinetics for the adsorption of the anionic dye Acid Orange 7 (AO) and the cationic dyes Nile Blue A (NB) and methylene blue (MB) in an aqueous medium. Overall, both hydrogel samples exhibited satisfactory results for removing NB and MB; however, there was no effective removal for the anionic dye AO. Adsorption equilibrium isotherms were obtained, and Freundlich, Langmuir, and Sips models were fitted to the experimental equilibrium data; moreover, kinetic data were adjusted to driving force models and particle mass balance. The maximum experimental adsorption capacities, 141.48 mg·g-1 (MB) and 284.69 mg·g-1 (NB), were obtained, on a dry basis, for the sample produced with 70 wt% of agar and 30 wt% of GO. Both hydrogels exhibited remarkable regenerative potential for NB and MB, with the adsorption capacity remaining constant, even after five adsorption/desorption cycles.