Boron adsorption and isotopic separation from water by isostructural metal-organic frameworks MIL-100(M)

Adsorption has been expected to be promising for boron-containing water treatment , boron resources recovery and boron isotopic separation. Although metal-organic frameworks have been demonstrated to be potential adsorbent candidates, in-depth investigation of the structure-performance relationship remains insufficient. Herein, the performance and mechanism of boron adsorption and isotopic separation were systematically investigated with isostructural MOFs. Six isomorphic MIL-100(M) materials with metal species from the third main group (Al, Ga and In) and the fourth period (Sc, Cr and Fe) were solvothermally synthesized as boron adsorbents. Superior boron isotopic separation factors ( S ) with 10 B preference and comparable boron adsorption capacity ( Q ) were observed through batch boron adsorption experiments, where MIL-100(Al) exhibited the highest S of 1.618 and MIL-100(Sc) achieved the largest Q of 8.74 g-B/mol-MOF. A high correlation between metal atomic radius and performance was revealed and a plausible mechanism was proposed for boron adsorption and isotopic separation involving the important role of the metal center through post-adsorption characterization. This study will pave the way for designing boron adsorbents with improved properties and promote the efficient utilization of boron resources in water.