This study investigates the role of hydrogen bonding in Hydrogen-Bonded Complex Extractants (HBCEs) for uranium extraction from wastewater. Through integrated experimental and theoretical approaches including electrostatic potential (ESP) analysis, molecular binding energy calculations, Atoms in Molecules (AIM) theory, and spectroscopic characterization, we reveal how structural variations (carbon chain length, unsaturation degree, spatial configuration, and functional groups) modulate hydrogen bond characteristics. Results show that extending carbon chains enhances hydrogen bond strength (TBPO-18: -24.28 kcal/mol binding energy), while increasing unsaturation initially weakens then strengthens interactions. Linear structures exhibit superior hydrogen bonding versus cyclic configurations (TBPO-OH vs TBPO-HOH: 18.60 vs 14.47 kcal/mol). Extraction performance correlates with hydrogen bond stability, where TBPO-12 achieves maximum capacity (40.55 mg/L) due to optimal acid resistance. Mechanistic studies via 31 P NMR titration confirm a two-step process: initial \({\text{UO}}_{2}^{2 + }\) complexation with TBPO’s P = O group, followed by hydrogen bond formation with HBDs. This work provides fundamental insights for rational design of high-efficiency HBCEs, highlighting hydrogen bond engineering as a key strategy for nuclear wastewater treatment.
First HDBM-TBPO synergistic system for Li + extraction from high Na/Li brine. • Under optimal conditions, Li + extraction reached 99.8% and β Li / Na =250. • The loaded organic phase stripped with 0.2 mol/L HCl and regenerated with 0.05 mol/L Na 2 CO 3 . As a core material of lithium-ion batteries, lithium is difficult to recover from salt lake brines because of complex procedures and excessive energy consumption. Herein, a variety of β-diketone extractants were screened by hydrophobicity (π) and Hammett substituent constant (σ) based on their electronic effects and Li + chelating strength. Subsequently, various neutral organophosphorus synergists were evaluated based on the steric hindrance around the P O group, as lower steric hindrance facilitates axial coordination with the Li-chelate complex. Dibenzoylmethane (HDBM) and tributylphosphine oxide (TBPO) were identified as the optimal extractant and synergist, respectively. Under the optimized conditions, the Li + extraction efficiency exceeded 99%, with a Li/Na separation factor of 250. The loaded organic phase was effectively stripped by 0.2 mol/L HCl and regenerated by 0.02 mol/L Na 2 CO 3 . The system retained 99% extraction efficiency after 11 cycles without emulsification, showing excellent reusability. Mechanistic investigations demonstrated that the extracted complex was Li•2HDBM•0.2TBPO, and the extraction was an enthalpy-driven process via chelation and coordination interactions. This synergistic system presents a promising and sustainable approach for lithium recovery from brines and aqueous resources.
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