Selective Enrichment vs Dynamic Recovery of Ga(III) Using Functionalized Hydrogels: A Comparative Study of Polypropylene Hydroxamic Acid and Polyacrylic Acid Hydrogels

Two amorphous hydrogels with polypropylene backbones were synthesized via free radical polymerization at room temperature, exhibiting high adsorption efficiency for Ga(III) at pH 3. The hydrogels achieved maximum adsorption capacities of 156.13 and 220.36 mg/g, with adsorption rates exceeding 95% at an initial Ga(III) concentration of 100 mg/L. Both poly(acrylic acid) (PAA) and polypropylene hydroxamic acid (PPHA) hydrogels demonstrated strong selectivity for Ga(III) in the presence of competing ions (Zn(II), Cu(II), Al(III), and In(III)). The adsorption kinetics followed a pseudo-second-order model, and the isotherms were well-described by the Langmuir model. PAA excelled in dynamic recovery, maintaining an efficiency of more than 97% after five adsorption–desorption cycles, highlighting its outstanding reusability. Meanwhile, PPHA exhibited superior selectivity for Ga(III), making it particularly effective for selective enrichment even in complex systems. Continuous dynamic column adsorption experiments confirmed PAA as an ideal material for Ga(III) recovery, while PPHA's high selectivity makes it superior for selective enrichment. Comprehensive characterization and DFT calculations further elucidate the adsorption mechanisms of Ga(III) on PAA and PPHA. With their simple preparation, cost-effectiveness, environmental friendliness, and high adsorption capacity, both hydrogels offer promising potential for recovering Ga(III) from Ga(III)-containing solutions.