Polymer nano-rings with uranium specific clefts for selective recovery of uranium from acidic effluents via reductive adsorption

Abstract

Nanostructured polymeric materials, functionalized with appropriate receptor have opened up newer possibilities for designing a reagent that shows analyte-specific recognition and efficient scavenging of an analyte that has either detrimental influence for human physiology and environment or for its recovery for further value addition. Higher active surface area, morphological diversity, synthetic tuneability for desired surface functionalization, and the ease of regeneration of nanostructured material for further use have provided such material with a distinct edge over conventional reagents. Use of biodegradable polymeric backbone has an added significance owing to the recent concern over the impact of polymer on the environment. Functionalization of biodegradable sodium alginate with AENA (6.85 % grafting) as the receptor functionality led to a unique open framework nanoring (NNRG) morphology with a favourable spatial orientation for specific recognition and efficient binding to uranyl ions (U) in an aqueous medium over a varied pH range. Nanoring morphology was confirmed by TEM and AFM images. The nano-scale design maximizes the surface area for the molecular scavenger. A combination of all these features along with the reversible bindingphenomenon has made NNRG as a superior reagent for specific, efficient uptake of UO2 2+ species from an acidic (pH 3-4) solution and compares better than all existing UO22+-scavengers reported till date. This could be utilized for recovery of uranyl species from a synthetic acidic effluent of the nuclear power. Results of the U uptake experiments reveal a maximum adsorption capacity of 268 mg of U per g of NNRG in synthetic nuclear effluent. XPS studies revealed a reductive complexation process and stabilization of U(IV)-species in adsorbed uranium species (U@NNRG).