Gamma radiation synthesized POSS crown ether polymers for efficient and selective lithium recovery from seawater

Abstract

The rapid increase in worldwide demand for lithium ions (Li⁺) is driven by progress in renewable energy storage systems and nuclear technology. The development of efficient recovery techniques has been required. Adsorption-based methods provided operational simplicity and environmental sustainability. However, it is limited by poor selectivity, low adsorption capacities, and complex synthesis processes. In this study, a novel and efficient strategy was developed to fabricate crown ether–functionalized polyhedral oligomeric silsesquioxane (POSS)-based polymers via gamma radiation-induced grafting followed by post-functionalization with 2-hydroxymethyl-12-crown-4 (2H12C4). The synthesized materials, P-POSS_MethylD<inf>4</inf>_2H12C4 and P-POSS_VinylD<inf>4</inf>_2H12C4, were thoroughly characterized using FT-IR spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and solid-state ¹³C NMR spectroscopy, confirming successful synthesis and robust structural formation. Both materials demonstrated notable Li⁺ adsorption capacities of 2.95 and 3.05 mg/g within 5 h and exhibited high selectivity toward Li⁺ in the presence of competing cations (Na⁺, K⁺, Mg²⁺, Ca²⁺), with selective separation factors exceeding 4.07. They also showed excellent regeneration performance, retaining their adsorption capacity over five consecutive adsorption–desorption cycles. Moreover, the materials showed successful Li⁺ extraction from actual seawater, highlighting their applicability in aqueous environments. This work presents a scalable, catalyst-free, and environmentally friendly platform for advanced Li⁺ extraction materials.