Bio-functionalizing of α-MnO2 nanorods with natural L-amino acids: A favorable adsorbent for the removal of Cd(II) ions

alpha-MnO2 nanorods were prepared by hydrothermal method and then the surface of these nanorods were covalently biofunctionalized with natural L-amino acids (alanine, phenylalanine, leucine, isoleucine, methionine, and valine). The modified alpha-MnO2 nanorods were analyzed by Fourier transform infrared spectroscopy and X-ray diffraction. Morphological studies were carried out by field emission scanning electron microscopy and transmission electron microscopy. The morphology of nanorods was improved after biofunctionalization and aggregation was reduced. In addition, the thermal gravimetric analysis was used for demonstrating a successful grafting of amino acids to the surface of alpha-MnO2 nanorods and determine the degree of functionalization. The amount of amino acids grafted onto alpha-MnO2 surface was estimated to be 5-32 wt%. Finally, the alpha-MnO2 and alpha-MnO2-L-valine were investigated as adsorbents for the removal of cadmium ions from aqueous solution. The results showed that they have a potential to be used as effective adsorbents for cadmium ions removal from the aqueous solution. The equilibrium adsorption data showed the best fit for the pseudo-second-order and the Freundlich models. (C) 2017 Elsevier B.V. All rights reserved.