Regulating Ga(III) Capture and Selectivity by O–Donor Coordination Environments in Functionalized Conjugated Microporous Polymers

Abstract

Selective enrichment of Ga(III) from acidic zinc hydrometallurgical solutions remains challenging because of the low Ga(III) concentration and the coexistence of competing metal ions. Herein, an ester-containing conjugated microporous polymer, CMP-mCOOCH3, was used as a precursor to construct hydroxamic acid-functionalized CMP-mCONHOH and carboxyl-functionalized CMP-mCOOH through postsynthetic modification. This design enables a direct comparison of how different O-donor coordination environments regulate Ga(III) adsorption within a similar porous framework. Both materials showed efficient Ga(III) uptake at pH 3 and 298 K, with adsorption capacities of 174.75 mg g–1 for CMP-mCONHOH and 249.47 mg g–1 for CMP-mCOOH. The adsorption processes followed pseudo-second-order kinetics and Langmuir isotherm behavior, indicating coordination-driven monolayer adsorption. In competitive systems, both adsorbents maintained good Ga(III) uptake in the presence of Al(III), Zn(II), and Cu(II), whereas In(III) showed stronger competition. CMP-mCOOH exhibited a higher adsorption capacity, while CMP-mCONHOH showed stronger chelation-driven recognition, especially for Ga/In separation. After five adsorption–desorption cycles, CMP-mCONHOH and CMP-mCOOH retained 90.4% and 92.2% of their adsorption efficiencies, respectively. Spectroscopic analyses and theoretical calculations revealed that Ga(III) binding mainly occurred through oxygen-donor coordination. These results provide guidance for designing regenerable porous polymer adsorbents for gallium recovery from acidic metallurgical systems.