Effect of the structure of calix[4]arene-para-sulfonic acid on its transport properties

Abstract

The effect of a change in the ambient temperature and humidity on the behavior of calix(4)arene para sulfonic acid was studied. For the calixarene under study, at least two stable hydrates were observed: tetra and octahydrate. The number of water molecules in the crystalline hydrate of the acid was confirmed by simultaneous thermal analysis data and the shape of the IR spectra and diffraction patterns. The change in the composition of the hydrate from n = 4 to n = 20 affected the conductivity but slightly; in the region of phase transitions between the hydrates, the activation energy of conductivity changed abruptly.

Supramolecular Calix[n]arenes-Intercalated Graphene Oxide Membranes for Efficient Proton Conduction

“…The enhancement of proton conductivity under low RH was attributed to the reasons below: (i) the high density of sulfonic acid groups of SC­[ n ]­A (5.37 mmol g –1 ) favored the construction of well-connected channels for proton transfer even under low humidity; and (ii) the phenolic hydroxyl groups along the lower edge were able to form intramolecular hydrogen bonds. When a proton left, the oxygen anion could be stable due to the special structure of the SC­[ n ]­A and the generation of intramolecular H-bonding conjugate effect, and then other protons nearby would hop to this site easily, which was different from small molecules, promoting the proton hopping between SC­[ n ]­A, according to the Grotthuss mechanism …”

“…When a proton left, the oxygen anion could be stable due to the special structure of the SC[n]A and the generation of intramolecular H-bonding conjugate effect, and then other protons nearby would hop to this site easily, which was different from small molecules, 60 promoting the proton hopping between SC[n]A, according to the Grotthuss mechanism. 61 3.6. Single Fuel Cell Performance.…”

“…32 p-Sulfonato calix[n]arenes (p-SC[n]A, n = 4−8), an emerging family of hydrophilic supramolecular substances, have been extensively explored in molecular or ionic recognition and sensing, enzyme assays, and biological/medical chemistry et al 33−36 From the standpoint of proton conductivity, SC[n]A should be a preferred choice owing to its unique properties: a rigid fragment of an organic core, layers comprised of proton donors (−SO 3 H) that was surrounded by a large amount of bound water molecules, 37,38 an ultrahigh theoretical ion exchange capacity (IEC w ) of 5.37 mmol g −1 and easy modifiability. Previous investigations have found that SC[n]A exhibited high proton conductivity up to 10 −1 S cm −1 at room temperature, 80%−85% RH, 39,40 close to or even higher than that of heteropolyacids H 3 PW 12 O 40 •xH 2 O or Nafion, 41,42 and increased in the order of SC [4]A < SC [6]A < SC [8]A. 37,43 Thus, SC[n]As hold great promise in incorporating sufficient proton donors within GO nanosheets, while firmly supporting adjacent GO nanosheets with less space occupancy.…”