Promotion of Low-Humidity Proton Conduction by Controlling Hydrophilicity in Layered Metal–Organic Frameworks

Abstract

We controlled the hydrophilicity of metal-organic frameworks (MOFs) to achieve high proton conductivity and high adsorption of water under low humidity conditions, by employing novel class of MOFs, {NR(3)(CH(2)COOH)}[MCr(ox)(3)]·nH(2)O (abbreviated as R-MCr, where R = Me (methyl), Et (ethyl), or Bu (n-butyl), and M = Mn or Fe): Me-FeCr, Et-MnCr, Bu-MnCr, and Bu-FeCr. The cationic components have a carboxyl group that functions as the proton carrier. The hydrophilicity of the cationic ions was tuned by the NR(3) residue to decrease with increasing bulkiness of the residue: {NMe(3)(CH(2)COOH)}(+) > {NEt(3)(CH(2)COOH)}(+) > {NBu(3)(CH(2)COOH)}(+). The proton conduction of the MOFs increased with increasing hydrophilicity of the cationic ions. The most hydrophilic sample, Me-FeCr, adsorbed a large number of water molecules and showed a high proton conductivity of ~10(-4) S cm(-1), even at a low humidity of 65% relative humidity (RH), at ambient temperature. Notably, this is the highest conductivity among the previously reported proton-conducting MOFs that operate under low RH conditions.

Recent Advances on Anilato-Based Molecular Materials with Magnetic and/or Conducting Properties

“…In the last 20 years many efforts have been addressed to add in these materials a further physical property by playing with the functionality of the A + cations located between the bimetallic layers. This strategy produced a large series of multifunctional molecular materials where the magnetic ordering of the bimetallic layers coexists or even interacts with other properties arising from the cationic layers, such as paramagnetism [2,[76][77][78][79][80], non-linear optical properties [2,81,82], metal-like conductivity [83,84], photochromism [2,81,85,86], photoisomerism [87], spin crossover [88][89][90][91][92][93], chirality [94][95][96][97], or proton conductivity [2,98,99]. Moreover, it is well-established that the ordering temperatures of these layered magnets are not sensitive to the separation determined by the cations incorporated between the layers, which slightly affects the magnetic properties of the resulting hybrid material, by emphasizing its 2D magnetic character [2,[75][76][77][78][79][80]95,100,101].…”

A Family of Layered Chiral Porous Magnets Exhibiting Tunable Ordering Temperatures

“…Elem anal. Calcd for C 34 (7). An aqueous solution (5 mL) of CrCl 3 ·6H 2 O (320 mg, 1.2 mmol) was added dropwise to a hot aqueous solution (50 mL) of H 2 dhbq (500 mg, 3.6 mmol), NaOH (290 mg, 7.2 mmol), and NBu 4 Br (1160 mg, 3.6 mmol).…”

Removal of methylene blue from aqueous solutions by an adsorbent based on metal-organic framework and polyoxometalate

“…Recently, metal-organic frameworks (MOFs) have attracted more and more researchers' interests due to their ultrahigh porosity, big pore volume, rich topological structure and incredibly high surface areas. Exploring their various applications in different fields like storage and separation [26], pollutant removal [27], sensing [28], proton conduction [29] and drug delivery [30] is especially focused on.…”