Synergetic effective lithium-ion adsorption and complexation by molecularly engineered Schiff base functionalized bio-composite: From molecular design to life cycle assessment

The functionalized bio-composite material, which is well-known for its stability, sustainability, and effective adsorption performance, was used to address the critical issue of energy shortages related to lithium resources. In this work, we synthesized a novel bio-composite material (CPPC) using carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and citric acid as a cross-linker. A Schiff base compound, (E)-2-((2-bromo-6-hydroxybenzylidene)amino)acetic acid (LG), was synthesized and then immobilized with the CPPC bio-composite to fabricate CPPC-LG. The CPPC-LG was characterized using SEM, EDS, XRD, FTIR, TGA, and BET analysis, which proved that the ligand is successfully immobilized on CPPC. The binding affinity of the CPPC-LG composite towards Li(I) was high, and adsorption capacity reached 199.7 mg/g at pH -6, 328 K, and an initial 300 mg/L concentration. CPPC-LG showed significant Li(I) selectivity, with distribution coefficients of 2369.1 mL/g in a simulated real Salt Lake brine. The kinetics followed pseudo-second-order kinetic models, which suggest a chemisorption process. Results fit Langmuir isotherms, which clearly indicates that adsorption occurs in a single layer on the surface (monolayer adsorption). Thermodynamic analysis proved that the reaction is spontaneous and endothermic. DFT analysis was performed for deeper understanding of the adsorption mechanism. The composites show excellent adsorption capacity and high recyclability, with 121.9 mg/g adsorption capacity after 6 cycles. An LCA assessment was performed to investigate the environmental impact for the production of CPPC-LG (1Kg), whereas a cost analysis was studied and proved an overall low reusability cost, which indicates their effectiveness in energy saving and lithium recovery.