Macroporous flexible polyvinyl alcohol lithium adsorbent foam composite prepared via surfactant blending and cryo-desiccation

Abstract

Macroporous polyvinyl alcohol (PVA) foam composites with high loading of uniformly distributed lithium ion sieves (LIS) were successfully fabricated and evaluated for Li+ recovery. Surfactant blending combined with cryo-desiccation effectively produced LIS/PVA foams with hierarchical porosity composed of macro- and mesopores. Glutaraldehyde cross-linking rendered the LIS/PVA foams insoluble in water but exhibited high water absorbency and flexibility. Relative to the LIS powder, the foams exhibited minimal reductions in adsorption capacity (qe) and kinetic properties due to: (1) high total porosity and surface area, (2) hydrophilicity of PVA matrix, and (3) high LIS loading, which promoted particle exposure on the foam surface. These features facilitated easy convective flow of water through the matrix and allowed intimate contact between the Li+ feed source and the LIS surface. Thus, LIS/PVA foams with high loadings (200–300wt%) exhibited meager reductions in qe (7–13%) and kinetic properties compared to the LIS powder. With LIS loading increase, Li+ selectivity of LIS/PVA foams against other cations (i.e. Na+, K+, Mg2+, Ca2+) likewise approached that of the LIS powder. While 300wt% LIS/PVA had low mechanical property, lower LIS loadings of 200- and 250wt% were highly durable and exhibited no deterioration in adsorption performance and reusability. Among the prepared LIS/PVA, 250wt% demonstrated the highest adsorption performance and can be repeatedly used for long-term application. The developed LIS/PVA foams are promising Li+ adsorbents for secondary Li+ sources; application of these foams via a simple “absorb and squeeze” mechanism could be more practical than the energy-intensive processes like packed bed and membrane systems.