Facile preparation of metal-organic framework beads for effective capture of indium ion

Abstract

The adsorption and recovery of indium (In) ions from water is necessary while still faces challenges. Current adsorbents for this valuable metal commonly show powder states, which easily results in mass loss and goes against their convenient recovery. In this work, the nanoscale metal-organic framework UiO-66-(COOH)2 particles were successfully embedded in sodium alginate (SA)-calcium structure, to fabricate UiO-66-(COOH)2/SA composite beads. The beads show a homogenous size of ∼3 mm, cellular-like interior structure, and high MOF loading amount (70.4 wt%). Besides, their high water stability and anti-pressure property were proved. UiO-66-(COOH)2/SA beads exhibit a large adsorption amount for In3+ ions (81.2 mg g−1) and rapid adsorption equilibrium time (∼5 min) at low concentrations. Importantly, it is found that In3+ ions can diffuse into the interior frameworks of the beads via the transparent transmission channels. The optimal pH for adsorption locates at 4.0 and temperature may have only a slight effect. Furthermore, the beads can be regenerated based on a simple solvent elution method. The mechanism analysis confirms that the C–O–C and C–OH (or –COOH) groups from both SA and MOF contents contribute to the adsorption. So, our work provides an effective bead-state adsorbent for In3+ ions.