Constructing porous hydrophilic HMO/CTA@PDA composite hydrogel for super-high and ultrafast extraction of lithium ions

Abstract

Adsorption is recognized as an effective and eco-friendly strategy for extracting lithium from salt-lake brine. However, the lithium-ion sieves typically used are in powder form, which poses challenges such as poor fluidity, low permeability, and reduced recovery rates, thereby limiting their industrial utility. This work introduces the development of manganese lithium-ion sieves composite hydrogels (HMO/CTA@PDA), that which demonstrate rapid adsorption rates and enhanced cyclic stability. The HMO/CTA@PDA is synthesized via the nonsolvent-induced phase separation (NIPS) method, utilizing cellulose triacetate (CTA) as the matrix, H_1.6Mn_1.6O₄ (HMO) as the active material, and polydopamine (PDA) as the modification agent. The integration of PDA, rich in polar functional groups, notably improves the interfacial contact within an aqueous medium. This modification reduces the number of water molecules at the HMO/CTA@PDA interface through rapid dehydration, effectively lowering the energy barrier for Li⁺ migration. Additionally, the three-dimensional porous network of HMO/CTA@PDA facilitates enhanced diffusion channels for Li⁺, enabling more efficient ion transport. Comparative analyses indicate that HMO/CTA@PDA hydrogels possess significantly higher adsorption rates for Li⁺, achieving an adsorption capacity of 29.18 mg/g within 4 h, compared to 28.28 mg/g within 36 h for the unmodified HMO/CTA. At the same time HMO/CTA@PDA also exhibits high selectivity (superior K_d value for Li⁺ compared to other ions in sulfate-rich brines), and outstanding recyclability (stable adsorption capacity of ∼29.58 mg/g over 15 cycles with minimal Mn loss). The HMO/CTA@PDA offers a promising strategy for sustainable Li⁺ recovery from salt-lake brines.