A Rational Approach for Controlled Adsorption of Metal Ions on Bovine Serum Albumin-Malachite Bionanocomposite

In this article, we demonstrate the preparation of a new bionanocomposite by surface modification of malachite [Cu-2(OH)(2)CO3] nanoparticles with bovine serum albumin (BSA). The conformation of protein in BSA-malachite nanocomposite has been analyzed by employing fluorescence and Fourier transform infrared (FT-IR) spectroscopic methods. The BSA molecule loses its tertiary and secondary conformation partially in BSA-malachite nanocomposite. For the first time, bare malachite nanoparticles and BSA-malachite nanocomposite have been used for the adsorption of a series of toxic and precious metal ions from single- and multicomponent aqueous solution. We report a reversal in adsorption behavior of selected metal ions upon surface modification of malachite nanoparticle with BSA. Among different metal ions studied here, the harder ions (according to HSAB principle), likely, Cu2+, Ni2+, Cr3+, and Zn2+, were preferably adsorbed on bare malachite surface but show less adsorption on BSA-malachite nanocomposite. After surface modification with BSA. this situation reversed, where the soft metal ions Hg2+, Ag+, Au3+, and Pd2+ were highly adsorbed on BSA-malachite nanocomposite compared to the harder metal ions. However, Pb2+ was found to adsorb on both surfaces equally. The adsorption of metal ions has been investigated quantitatively with the help of adsorption kinetics, isotherm, and selectivity coefficient (k) analysis. The binding affinity of metal ions reduces Cr3+ > Pb2+ > Ni2+ > Zn2+, Cu2+ on malachite nanoparticles, while on BSA-malachite nanocomposite, binding affinity is found in the order Au3+ > Pd2+ > Hg2+ > Pb2+ > Ag+. We have also put our effort into studying the adsorption behavior of these metal ions from a synthetic wastewater solution containing a variable amount of metal ions. The results with synthetic wastewater solution also reflect the reversal adsorption phenomena of harder and soft metal ions on these two alternative surfaces, similar to the equimolar competitive study.