Single solvent synthesis of lithium-selective hydrogen manganese oxide (HMO)-based mixed matrix membranes

The rising lithium-ion battery market drives lithium demand and requires efficient and selective lithium recovery methods from aqueous sources. Membrane technologies can address environmental and inherent efficiency issues in conventional lithium extraction methods. This study presents the synthesis of novel lithium-selective mixed matrix membranes (MMMs) by integrating 0–30 wt% of a lithium selective filler named hydrogen manganese oxide (HMO) into a sulfonated polyethersulfone (SPES)-Nafion polymer matrix. The membranes were produced by casting and thoroughly examined to assess their chemical, physical, morphological, thermal, and mechanical characteristics. The transport of lithium across membranes was evaluated in diffusion and electro-diffusion studies. The membrane containing 20 wt% of HMO exhibited the highest ideal selectivity values, which were 1.05 for Li⁺/K⁺, 1.20 for Li⁺/Na⁺, and 13.36 for Li⁺/Mg²⁺; and more than 97% increase in lithium-ion conductivity when compared with the control membrane without HMO. In diffusion experiments, the binary separation factors for Li⁺/K⁺, Li⁺/Na⁺, and Li⁺/Mg²⁺ were 0.71, 1.52, and 11.83, respectively, while under electro-diffusion conditions, the corresponding values were 0.82, 1.55, and 9.88. Above 20 wt% of HMO, membranes lose their separation capacity as HMO aggregates inside the membrane structure. The higher selectivity of membranes towards Li⁺ in the presence of Mg²⁺ is due to magnesium's larger hydrated radius and higher hydration energy compared to lithium. Overall, the prepared membranes demonstrated a promising potential for green lithium recovery. This study facilitates the advancement of sustainable lithium-selective MMM synthesis.