Enhancing adsorption performance and selectivity for uranium by constructing biaxial adsorption sites on eco-friendly bamboo strips

Abstract

Amidoxime-based materials are currently the most promising adsorbents for sustainable extraction uranium from seawater. However, in practical applications, the strong affinity of amidoxime-based materials for vanadium seriously interferes with the extraction uranium from seawater. Herein, a novel environmentally friendly and degradable adsorbent is firstly designed through grafting animal protein on natural bamboo strips (BS). In detail, the casein hydrolysates (sodium caseinate, acid hydrolyzed casein and casein phosphopeptide) are grafted with amidoximated bamboo strips (SCAOBS, AHCAOBS and CPPAOBS) by chemical cross-linking and amide reactions to construct biaxial adsorption sites, including amidoxime and amino acid branched chains. The optimal adsorption pH of SCAOBS, AHCAOBS and CPPAOBS were 5, 7 and 7, the adsorption capacities were 186.3, 204.0 and 68.6 mg g−1, and the attenuation was 23.1%, 17.7% and 20.2% after 5 cycles, respectively. Utilizing the weavability of BS, SCAOBS, AHCAOBS and CPPAOBS adsorbents are woven and floated in the Yellow Sea Basin, exhibiting that the adsorption capacity of uranium is 0.84, 1.21 and 0.81 mg g−1, respectively, much higher than that of vanadium. Evenly, the adsorption capacity of AHCAOBS for uranium is about 15.3 times that of vanadium (0.077 mg g−1). Through DFT spatial structure optimization, there are indeed biaxial dual adsorption sites (–COOH from amino acid and C = N-OH from amidoxime groups) between amino acids and amidoxime branched chains, and even the spatial structure of biaxial triple adsorption sites (–COOH from amino acid, O = C-N from amide bond and C = N-OH from amidoxime groups) is more stable, thereby breaking this bottleneck from the vanadium interference for the amidoxime-based adsorption materials.