Weaving Gallium-Sulfide Clusters with Antimony Bridges into an Open-Framework for Ni²⁺ Adsorption

The efficient removal of Ni²⁺ from radioactive wastewater is crucial for environmental protection and nuclear safety, yet current ion exchangers often exhibit limited stability and selectivity. Herein, we report an open-framework gallium-antimony sulfide, K_3.6[NH₄]_0.1[CH₃NH₃]_0.3Ga₄SbS₉SH·0.9H₂O (GaSbS-2K), constructed from supertetrahedral T2-{Ga₄S₉SH} clusters and asymmetric Sb bridges. Its three-dimensional framework features intersecting chiral channels and tetrahedral voids that facilitate ion diffusion and exchange. GaSbS-2K exhibits rapid Ni²⁺ adsorption, achieving 67.66% uptake within 2 min and 97.54% removal at equilibrium, with a pseudo-second-order rate constant of 0.318 g mg^-1 min^-1. The material shows a maximum adsorption capacity of 90.78 ± 2.74 mg g^-1 under neutral conditions and remains stable across a wide pH range (3-12). It retains strong selectivity for Ni²⁺ in the presence of competing ions, maintaining >72% removal even in seawater. The rapid adsorption kinetics enable continuous-flow applications in both fixed-bed columns and composite membranes, achieving >99% removal of Ni²⁺. Notably, the GaSbS-2K/PTFE membrane with an 80 μm active layer completely removes Ni²⁺ from 1000 mL of solution at a flux of 1.91 mL min^-1 cm^-2 with only 0.25 s of contact time. Combined with its facile synthesis, radiation stability, and regenerability, GaSbS-2K represents a promising adsorbent for radionuclide-contaminated wastewater treatment.