Impact of precursor pretreatment on solid-state synthesized protonated lithium titanates and their subsequent lithium adsorption performance

The protonated product of lithium titanate (H 2 TiO 3 , HTO) is a promising adsorbent for lithium recovery from alkaline aqueous streams due to its high selectivity and cycling stability. This study investigates how precursor pretreatment influences the solid-state synthesis of its parent phase, monoclinic Li 2 TiO 3 (LTO), and the resulting lithium adsorption performance of HTO. Multiple commercial TiO 2 sources and pre-synthesis methodologies, including grinding, ball-milling, and ultrasonication in water, isopropanol, or ethanol, were evaluated for their impact on phase formation and textural properties. X-ray diffraction analysis revealed that high-energy ball-milling results in α-LTO after calcination, a phase that fails to produce effective Li-adsorbing HTO. In contrast, ultrasonication and conventional mixing preserve the desired monoclinic β-LTO structure. HTO derived from monoclinic LTOs exhibited superior performance, with adsorption capacities up to 25.84 mg g −1 and kinetic constants more than twice as high compared to untreated controls. All monoclinic HTOs followed pseudo-second-order kinetics and fit the Langmuir isotherm model, confirming monolayer adsorption. High lithium selectivity was maintained, as demonstrated by selectivity factors such as α C a L i = 660, and α N a L i = 2927 for HTOs obtained via ultrasonication in water. In contrast, materials derived from cubic LTO showed negligible lithium selectivity. Notably, HTO prepared via ultrasonication in water matched or exceeded solvent-based methods in performance, offering a more sustainable and scalable processing route. Repeated adsorption-desorption cycles using synthetic brines demonstrated consistent lithium recovery of approximately 30 % per cycle, and minimal titanium leaching. These findings underscore the critical role of precursor pre-treatment in tailoring the properties of lithium sorbents via solid-state synthesis, and identify ultrasonication in water as a scalable, eco-friendly approach to produce high-performance HTO. • Precursor pretreatment determines LTO phase formation and HTO adsorption performance. • Monoclinic β-LTO enables high-capacity, selective lithium sorption; cubic α-LTO does not. • Ultrasonication enhances adsorption kinetics and capacity, especially in water-based processing. • Water-based ultrasonication offers a scalable, sustainable route for producing high-performance HTO.