Functionalization of Metal–Organic Framework Nanochannels for Water Transport and Purification

Abstract

Artificial water nanochannels (AWCs) have drawn great attention due to their potential use in water purification. Herein, we propose an AWC design, which is based on coordinatively functionalizing unsaturated metal sites found in metal−organic frameworks (MOFs) with one-dimensional nanochannels. As a computational demonstration, we consider two MOFs, namely, Ni-CPO-27 and Ni-CPO-54, and graft proline, imidazolecarboxylic acid, imidazolecarboxaldehyde, pyrazolecarboxylic acid, and pyrazole carbaldehyde molecules into the MOF nanochannels. To assess the strength of the molecule-metal binding, binding energies were calculated using density functional theory. The results indicate that the MOFs containing either proline or 2-imidazolecarboxylic acid form waterstable AWCs with binding energies twice that of the binding energy of water. To shed light on the water diffusion mechanism in the proline-Ni-CPO-27/54 and 2-imidazolecarboxylic-Ni-CPO-27/54 AWCs, molecular dynamics simulations were performed to calculate the mean-squared displacement of water molecules and nonbonded interaction energies between select pairs of atoms in water and coordinated molecules were analyzed. It was found that the fastest water diffusion occurs in proline-Ni-CPO-54 with a self-diffusion coefficient of 7.2 ± 0.5 × 10 −8 cm 2 /s. In comparison, the fastest water self-diffusion coefficient reported in a carbon nanotube-based AWC is 9 × 10 −6 cm 2 /s. Nonbonded interactions between specific atom pairs regulate water diffusion in the functionalized MOF nanochannels. In particular, the change in water mean-squared displacement with changing water loading correlates well with the nonbonded energies between the partially positively charged hydrogen atoms in water and the partially negatively charged oxygen and nitrogen atoms in the proline and 2imidazolecarboxylic acid molecules. The results presented herein indicate that water-stable MOFs could perform well as AWCs, thereby lending support to the further design and synthesis of MOF-based AWCs for water purification.

Transdermal hydrogen sulfide delivery enabled by open metal site metal-organic frameworks

“…Having established that Mg2(dobdc) strongly and reversibly adsorbs H2S and is nontoxic to human cells at therapeutic concentrations, we explored whether alternative stimuli to vacuum could trigger H2S desorption from Mg2(dobdc) under more biologically relevant conditions. Given the strong binding of water in open metal site MOFs, 91 it is likely that water is capable of facilitating H2S release from the framework. To test this hypothesis, a known amount of H2S-dosed Mg2(dobdc) was suspended in a stirring solution of HEPES buffer (pH 7.4) (SI section 6).…”

Selective Water Transport in an Alanine-Functionalized Metal–Organic Framework: A Computational Study

“…Since the Ni atom contains unpaired electrons, all calculations were spin-polarized . As we demonstrated in our previous work, the ground state of Ni-CPO-27 was achieved when the initial spin state of the Ni atom was set to 2 …”

“…Using molecular simulations, we recently studied water diffusion in Ni-CPO-27 and Ni-CPO-54 MOFs, whose onedimensional pores were functionalized by grafting imidazolecarboxaldehyde/pyrazolecarboxaldehydes, zwitterionic imidazolecarboxylic acids, pyrazolecarboxylic acids, and proline on to the coordinatively unsaturated open metal sites. 27 This type of coordination bond found in the proposed AWCs (i.e., coordination of −COO− on to an open metal site) was experimentally demonstrated in Zn-CPO-27 with zwitterionic proline. 28 We found that the proline-grafted Ni-CPO-54 (proline-Ni-CPO-54) had the largest self-diffusion coefficient among the structures that were investigated.…”

“…35 As we demonstrated in our previous work, the ground state of Ni-CPO-27 was achieved when the initial spin state of the Ni atom was set to 2. 27 The binding energies of a single zwitterionic alanine and a single water molecule in Ni-CPO-27 were calculated according to…”

Nanoarchitectonics Design Strategy of Metal–Organic Framework and Bio-Metal–Organic Framework Composites for Advanced Wastewater Treatment through Adsorption

“…Metal–organic framework (MOF) is an extraordinary class of materials that potentially revolutionizes water purification technology. − MOFs are known for their unique structure and exceptional adsorption capabilities, which emerged as a beacon in the need for clean and accessible water for drinking and domestic applications. Additionally, MOF possesses exceptional reusability features by desorbing the adsorbed pollutant using simple solvent washing, demonstrating their superior advantage in reducing water purification costs and associated waste generation in comparison with many conventional adsorbents .…”