Coupling modulation of crystalline-amorphous hetero-phase and oxygen vacancies for boosted lithium-ion adsorption performance

A crystal-amorphous strategy yields MDUC-2 with rich oxygen vacancies. • MDUC-2 adsorbent can achieve fast adsorption equilibrium within 30 min. • After five adsorption-desorption cycles, the adsorption capacity remains above 90%. Traditional metal-organic framework (MOF) adsorbents are plagued by critical bottlenecks, including structural collapse, active site leaching, and inadequate cycling stability, during lithium extraction from salt lake brines. To address these challenges, a crystalline–amorphous heterointerface coupling strategy was adopted, whereby amorphous UiO-66-(COOH) 2 was grafted onto crystalline manganese dioxide to afford a composite adsorbent. This material achieved a maximum adsorption capacity of 33.26 mg/g in solutions, and retained over 90% of its initial adsorption capability after five consecutive adsorption-desorption cycles. The improved performance was primarily attributed to the stable inorganic scaffold constructed by crystalline manganese dioxide, which was utilized as a high-strength structural support, whereby volume expansion and structural collapse of the MOF component in high-salinity aqueous media were effectively mitigated. Furthermore, the adsorption capacity toward lithium ions was synergistically enhanced by surface manganese hydroxyl groups, free and coordinated carboxyl groups within the MOF framework, and the amorphous architecture. Concurrently, abundant oxygen vacancies were generated at the crystalline–amorphous heterointerface. These vacancies functioned as supplementary Li + adsorption sites, further optimizing the lithium extraction performance of the composite. A novel avenue for the rational design and fabrication of high-performance MOF-based adsorbents was thereby opened, enabling efficient lithium recovery from salt lake brines. Download: Download high-res image (148KB) Download: Download full-size image