Seawater lithium mining by zeolitic imidazolate framework encapsulated manganese oxide ion sieve nanomaterial

Lithium (Li) is an increasingly valuable commodity due to its utilization in energy storage devices for electric vehicles. Seawater mining of Li is a sustainable alternative to conventional land mining. Hydrogen manganese oxide (HMO) ion sieve exhibits promising Li selectivity in seawater; however, HMO requires highly alkaline conditions (pH 11–12) to perform, and Mg2+ in seawater severely impedes its performance. In this study, we developed a hybrid nanomaterial, HMO@ZIF, where zeolitic imidazolate frameworks (ZIF) passivated on HMO particles as a high Li-selective material. Molar ratios of the organic precursor to the zinc salt were varied, and it was found that HMO@ZIF(a) (1.6:48:8.4, HMO: 2-methylimidazole (HMIM): Zn) demonstrates the highest Li uptake capacity at seawater pH (8.0 ± 0.5). The Li uptake capacity of HMO@ZIF(a) (Langmuir Qmax 45.51 mg/g) was 2.5 times higher than neat HMO (Langmuir Qmax 18.16 mg/g). Further analysis indicates that the governing mechanism for high Li selectivity is due to the exclusive ion exchange between the proton and Li cation, both in hybrid and neat HMO particles. ZIF encapsulation onto HMO led to a higher surface area, additional functional groups for surface deprotonation, and Zn ion intercalation into the HMO lattice, resulting in enhanced Li uptake with improved kinetics. HMO@ZIF(a) maintained more than 92 % reuse capacity after five regeneration cycles.