Thermoresponsive Amphoteric Metal–Organic Frameworks for Efficient and Reversible Adsorption of Multiple Salts from Water

Abstract

Regenerable, high-efficiency salt sorption materials are highly desirable for water treatment. Here, a thermoresponsive, amphoteric metal-organic framework (MOF) material is reported that can adsorb multiple salts from saline water at room temperature and effectively release the adsorbed salts into water at elevated temperature (e.g., 80 °C). The amphoteric MOF, integrated with both cation-binding carboxylic groups and anion-binding tertiary amine groups, is synthesized by introducing a polymer with tertiary amine groups into the cavities of a water-stable MOF such as MIL-121 with carboxylic groups inside its frameworks. The amphoterized MIL-121 exhibits excellent salt adsorption properties, showing stable adsorption-desorption cycling performances and high LiCl, NaCl, MgCl , and CaCl adsorption capacities of 0.56, 0.92, 0.25, and 0.39 mmol g , respectively. This work provides a novel, effective strategy for synthesizing new-generation, environmental-friendly, and responsive salt adsorption materials for efficient water desalination and purification.

Versatile Amorphous Structures of Phosphonate Metal−Organic Framework/Alginate Composite for Tunable Sieving of Ions

“…It is noteworthy that amorphous structures of pMOF@Alg(Al) easily enable to induce dehydration of metal ions, which is rarely observed when ions are passing through sub‐nanometer pores with highly ordered structural arrangement . In addition, the adsorption capabilities for alkaline and alkaline earth metal ions are comparable to those of amphoteric MOFs that are capable of effective adsorption of multiple salts from water . Therefore, this strategy for manufacturing amorphous MOF via a facile method will give a great potential for the development of amorphous MOF nanomaterial accompanying with unique properties.…”

“…Amorphous metal–organic framework (MOF) is recently of great interest in innovative material science despite the absence of selective porosity, which is a crucial characteristics of crystalline MOF . Although highly ordered crystalline MOFs have exhibited high performance in the separation of gases and polymers and desalination, the argument that prevalent association between performance and ordered structural arrangement is flawed arises as a limitation for further development of the field of coordination polymer and MOF . Recently, mixed‐matrix membrane combined with in situ amorphized zeolitic imidazolate framework (ZIF)‐8 is proposed to have highest CO 2 /CH 4 selectivity compared to crystalline MOF‐loaded mixed‐matrix membranes .…”

Interaction of synthetic and lignin-based sulfonated polymers with hydrophilic, hydrophobic, and charged self-assembled monolayers

“…This reduction in the adsorption for both L-S and PVA-S polymers could be due to the weakening of electrostatic interaction between negatively charged polymers and the positively charged surface at higher temperatures. 78 Overall, comparing the adsorption of L-S on the NH 2 ( Fig. 3d) and CH 3 (Fig.…”

“…At room temperature, the carboxylate group exists in its deprotonated (-COO À ) form. By increasing the temperature, the carboxylate group becomes protonated (-COOH), 78 resulting in a decrease in the negative charge density of the surface. This phenomenon paves the way for hydrophilic interactions of L-S with the surface to become more dominant than electrostatic attraction.…”

Research on the effects of hydrothermal synthesis conditions on the crystal habit of MIL-121

“…[ 27 ] using the hydrothermal method at 210°C. It has been applied to metal salt adsorption [ 28 ], Ln 3+ -doped fluorescence MOF preparation [ 29 ], Ag + selective detection [ 30 ], separation of hydrogen [ 31 ] and other fields. However, there were no reports on the morphology and size control of MIL-121.…”