Dithiourea-bridged cross-linked COF-COF for efficient and selective gallium recovery

Gallium is a strategic metal extensively applied in semiconductors, optoelectronics, and LED manufacturing. However, extracting Ga(III) from aqueous solutions remains challenging due to its typically low concentrations and interference from coexisting metal ions. In this study, a novel cross-linked COF-COF material (DPDA), enriched with nitrogen- and oxygen-containing functional groups, was synthesized and systematically evaluated for its ability to selectively adsorb Ga(III) from complex aqueous systems. DPDA exhibited outstanding adsorption performance under alkaline conditions and showed significantly enhanced Ga(III) uptake compared with its precursor. Kinetic analysis revealed that the adsorption process followed a pseudo-second-order model, indicating chemisorption played a predominant role. Langmuir isotherm fitting further demonstrated a monolayer adsorption pattern, yielding a maximum capacity of 112.4 mg·g −1 at 318 K. DPDA exhibited strong affinity for Ga(III) even in the presence of competing metal ions. In terms of reusability, DPDA maintained more than 67 % of its removal efficiency after 16 successive adsorption-desorption cycles, highlighting its structural robustness and practical applicability. Mechanistic analysis indicated that Ga(III) uptake by DPDA proceeds through a combination of coordination chemisorption, ion-exchange processes, and electrostatic interactions. DFT calculations identified stable adsorption configurations and quantified adsorption energies, confirming the synergistic contribution of -OH and -NH groups to Ga(III) binding. This work provides deeper insight into Ga(III) adsorption mechanisms and proposes a practical approach for its selective recovery from complex aqueous environments.