Modulation of Hydrophilic/Hydrophobic Character of Porous Environments in Metal–Organic Frameworks via Direct Polymer Capping Probed by NMR Diffusion Measurements

Abstract

The ability to create extended porous networks, such as those composed of metal–organic frameworks (MOFs), with tailored hydrophilic/hydrophobic character is crucial for adapting such widely used supports to different applications. To achieve this goal, direct polymer inclusion has proven to be a suitable strategy, and functional composite materials with multiple additional properties have been obtained in such a way. We have explored, by means of nuclear magnetic resonance diffusion experiments, the effect of polymer capping using a conducting polymer (polyaminobencylaminePABA), which results in the positioning of −NH2 moieties on the otherwise eminently hydrophobic surface of Zn-based ZIF-8 MOF nanocrystals. Our results demonstrate that increasingly higher amounts of PABA can confer, aside from conductivity, an increased hydrophilic character to the porous network, while also allowing for the identification of different environments available for water molecule diffusion.

Water Dynamics in NH2-MIL-125: Insights from a Combined 1H NMR Relaxometry and Computational Investigation

“…The self-diffusivity value of ∼10 −10 m 2 /s is close to that experimentally measured for water in fully loaded MIL-100(Al), 6 Al-fumarate, 5 and MIL-96(Al). 7 Only in the case of MIL-100(Al), self-diffusivity was measured at different loadings and found to decrease by ∼30 times at a filling factor of 0.2 compared to the value determined at full loading, which contrasts our MD data. The discrepancy may be due to the differences in nature of the inorganic and organic building blocks, pore size, pore window size, and porous topology of MIL-100(Al) and NH 2 -MIL-125.…”

“…To the best of our knowledge, this is the first time FFC NMR has been applied to a MOF with the aim of studying the dynamics of a guest molecule, although some of us have applied this technique to explore the dynamics of the amino group of the matrix and its electronic environment . On the other hand, PFG NMR has been employed to study the diffusivity of water or other small molecules in a few MOFs − and several investigations using molecular modeling have been reported regarding water in MOFs. − …”

Nanoarchitectonics of metal organic frameworks and PEDOT layer-by-layer electrodes for boosting oxygen reduction reaction

“…66,72 ZIF-8 films have been characterized as a 3-D arrange of crystallites exhibiting both hydrophobic intragrain microporosity and intergrain mesoporosity. 80 The ionic charge transport through ZIF-8 coatings in aqueous environments is purely dominated by solvent-filled intergrain mesoporosity. As proved by cyclic voltammetry experiments, redox probes are able to diffuse through the solvent-filled pores on the timescale of the electrochemical experiments.…”

“…81 Thus, instead of completely blocking the surface, the MOF coating provides an efficient pathway for molecular oxygen diffusion in the hydrophobic intragrain microporosity as well as it allows for the transport of electrolyte ions and solvent within the intergrain mesoporosity. 80,81 In this regard, the loss of ORR current when increasing the thickness of the MOF coating can be explained by either a loss in O 2 transport efficiency from bulk solution towards the electroactive material through the MOF microporosity, and/or slower transport of ions and solvent in the MOF mesoporosity as the film becomes thicker. Similar results were obtained for increasing potential sweep rates.…”

Zinc-Based Metal-Organic Frameworks in Drug Delivery, Cell Imaging, and Sensing

“…Magnetic resonance imaging (MRI) is widely acknowledged as one of the most prospective imaging methods that do not require ionizing radiation or a radioactive nucleus. Magnetic nanoparticles, on the other hand, can change the MRI signal by speeding up the relaxation phase of protons in nearby H 2 O molecules under an outside magnetic field [ 114 ]. Research studies on the fabrication of MOFs as MRI contrast agents have been ongoing since the mid 2000s [ 115 ].…”