Adsorption Properties of Arc Produced Multi Walled Carbon Nanotubes for Bovine Serum Albumin

Abstract

Abstract In this study, adsorption properties of arc produced Multi Walled Carbon Nanotubes (MWNT) were investigated for Bovine Serum Albumin (BSA) in aqueous phase. Solution pH, adsorbent amount and temperature effects were examined on protein adsorption. The results show that, the temperature and the adsorbent amount both increase the BSA adsorption, whereas the solution pH has a decreasing effect. The equilibrium behavior of protein adsorption was examined by Langmuir and Freundlich isotherms. The monolayer adsorption capacities at 40 °C for solution pH 4 and 5 were determined as 139.5 and 127.2 mg g−1, respectively, which were much higher than the BSA adsorption capacities of various metal oxides investigated in our previous studies. The adsorption rate data were compared by the pseudo-first and the second-order kinetics equations. Evaluation of the experimental kinetics data have shown that the adsorption of BSA by MWNT followed the pseudo-first-order kinetics. The pseudo-first order adsorption rate constants at pH 4 and 5 decreased with an increase in temperature which results in a decrease in diffusion rate of BSA molecules across the external boundary layer, and favors the sorption process. The adsorption behavior of protein by carbon nanotubes was explained also using the zeta potential measurements. The adsorption capacity decreased with increasing pH due to the electrostatic repulsions. The thermodynamic parameters evaluated to predict the nature of adsorption confirmed the non-spontaneous and endothermic behaviour of the BSA/MWNT adsorption process. Adsorption standard enthalpy values were found as ∆H0 =59.5 kJ mol−1 and ∆H0 =14.3 kJ mol−1 for pH 4 and 5, respectively indicating that the protein molecules are adsorbed electrostatically on the carbon nanotubes.