A Programmable Bifunctional MOF Sponge for Ultrafast Continuous-Flow Oxoanion Scavenging and Reversible H2S...

Selective scavenging of hazardous oxoanions and toxic gas sequestration rank among the most demanding sustainable environmental remediation, wherein astutely functionalized metal-organic framework (MOF)-based reconfigurable composites can lead to practical waste management. Herein, we developed a robust noninterpenetrated MOF, CSMCRI-24 (CSMCRI = Central Salt & Marine Chemicals Research Institute) containing cationic [Ni2(μ2-OH)(CO2)2]+ secondary building units, nitrogen-rich channels, and flanked -NO2 group-decked pores. Building on its wide range of pH stability, high porosity, and the presence of exchangeable counter anions, the activated framework (24a) acts as a dual-functional platform for selective and reversible uptake of three oxoanions (CrO42-, MnO4-, and ReO4-) followed by their bi-phasic visible colorimetric transitions. Importantly, the maximum adsorption capacities of these oxoanions surpass that of contemporary materials, and the MOF demonstrates ultrafast adsorption kinetics with above 95% removal efficiencies even in the co-existence of 50-fold excess of competing anions. Potential applicability of this charged MOF is highlighted from its unaltered oxoanion scavenging performance for different water matrices as well as steady removal efficiency during continuous-flow fixed-bed column experiments under practical operating conditions. The framework further enables reversible H2S sequestration with concurrent naked-eye colorimetric detection, highlighting the versatility of task-specific pore functionality. Aiming at practical deployment, an in situ-engineered MOF-based ionic sponge is fabricated, which provides a robust and regenerable platform for visible and reversible scavenging of toxic oxoanions and H2S. Complementing a battery of experimental pieces of evidence, in-depth density functional theory calculations elucidate the molecular-level interactions of oxoanions and H2S with the pore-aligned MOF functionality, providing mechanistic insights into the adsorption and sequestration of these hazardous analytes. Collectively, the present work demonstrates a viable pathway for translating task-specific, site-integrated cationic MOFs into programmable ionic sponges, providing a multifunctional platform for sustainable water purification, toxic gas remediation, and nuclear waste management.