Efficient Uranium Uptake by the Eco-Designed Cocamidopropyl Betaine-Decorated Na-P1 Organozeolite - Elucidation Through Batch, Laboratory, and Synchrotron Spectroscopies

In this study, we report the optimized and fully controlled coal-fly-ash based Na-P1 (GIS) zeolite modification by employing biodegradable biosurfactant molecule - cocamidopropyl betaine (CAPB) aimed at effective aqueous U removal. The zeolite’s surface decoration renders three composites with varying amounts of CAPB molecules, named Na-P1@CAPB, with 0.44, 0.88, and 1.54 ECEC coverage. Batch U adsorption isotherms experiments revealed extremely high U adsorption capacity (qmax = 137.37 mg U/g) following the partitioning mechanism, thus preferential hydrophobic interactions between CAPB molecules and uranyl ions present in the solution, as well as ion-exchange with Na+ present in the GIS zeolite framework. Comprehensive spectroscopic studies after U adsorption, including FT-IR, XPS, and XAFS techniques, revealed a hexavalent oxidation state of U as well as no secondary release of the CAPB molecule to the solution, confirming excellent stability of the composite during the adsorption process. The FT of the EXAFS signals for zeolite compared to the reference U salt, show the changes in the interatomic distances of the engineered materials after U removal, implying a significant impact of the O and N, heteroatoms along with hydrocarbon tail chain present in the CAPB molecule on U binding mechanism. The presented research outcomes showcase the easy, scalable, chemically optimized, and environmentally friendly synthesis of advanced U scavenger, which is probably the most effective zeolitic material worldwide regarding U extraction performance. Moreover, the real-life U-bearing wastewaters from the vicinity of the Pribram deposit (Czech Republic) have been effectively purified by applying NaP1@CAPB composite, satisfying WHO guidelines.