Self-assembled biogenic melanin modulated surface chemistry of biopolymers-colloidal silica composite porous matrix for the recovery of uranium

A new composite porous matrix surface modulated by self-assembled melanin was developed and investigated for its affinity to bind uranium from an aqueous medium. The composite matrix was synthesized using biopolymers (i.e., agarose and alginate) and inorganic colloidal silica nanoparticles (AACS) by the process of cryotropic-gelation at subzero-temperature. Post-synthesis surface modification of AACS matrix with melanin (MAACS) was performed by green chemistry. The in situ sequestrial conversion of l-Dopa by the biocatalytic activity of tyrosinase enzyme allows the formation of melanin on the surface of AACS matrix. The functional moieties on the matrix display fast kinetics and high binding capacity with respect to uranium. MAACS matrix showed high porosity (similar to 90%) with interconnected pores, high swelling kinetics and permeability. Other physicochemical properties of the matrix, such as thermal stability, storage modulus, and surface charge potential were found to be increased, while percent degradation decreased, which demonstrate improved properties of the matrix after impregnation of silica nanoparticles and surface functionalization with melanin. Thermodynamic parameters suggest that the binding of uranyl ions is passive and spontaneous. The concentrated recovery of uranium was achieved with reusability potential of adsorbent. These results suggest an environment friendly and safer method for the recovery of uranium. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46937.