Two
unique polyoxometalate (POM)-encapsulated tubular materials
with the formula K(H2O)6[M6(btp)6(H2O)22](P2W18O62)3(Hbtp)5(btp)3·52H2O [M = Mn (1) and Co (2); btp =
2,6-bis(1,2,4-triazol-1-yl)pyridine] were designed and synthesized
based on the Dawson POM and V-type btp ligand, as confirmed by IR,
X-ray diffraction (XRD), and element analysis. Single-crystal XRD
analyses of compound 1 show that two kinds of remarkable
metal–organic supramolecular nanotubes, including trigonal
and hexagonal nanotubes, are constructed along the c-axis direction via π···π-packing interactions
between {Mn3(btp)3} rings and the btp ligands,
of which [α-P2W18O62]6– anions are confined in channels, making the entire structure extraordinarily
stable. Meanwhile, the coordinated [α-P2W18O62]6– anion within the hexagonal channel
makes the channel highly hydrophilic and attracts a number of guest
water molecules to fill in the free space, conducive to proton transport.
Therefore, the single-crystal sample of 1 exhibits a
high proton conductivity of 6.39 × 10–3 S cm–1 along one-dimensional channels, 30 times higher than
that of a pellet sample at 358 K and 98% relative humidity.
Hydrogen-bonded organic frameworks (HOFs) with inherent welldefined hydrogen-bond networks are promising proton conduction materials. Herein, four three-dimensional HOFs were controllably assembled from 1,2,4,5-benzenetetracarboxylic acid and guanidinium of different chain lengths with certain ratios, in which GC-1 has undergone a water-induced single-crystal-to-single-crystal (SCSC) transformation to a more stable GC-2 with successive π−π stacking interactions. Notably, the ideal single-crystal sample of GC-2 exhibits an ultrahigh proton conductivity of 1.78 × 10 −2 S cm −1 along the [100] direction at ambient temperature and 98% RH. This sample is highly anisotropic with 3−5 orders of magnitude higher than those along the [010] and [001] directions, which is closely related to favorable proton-transfer paths of 1D highly hydrophilic channels formed by the consecutive hydrogen-bonded network between protonated guanidinium cations and carboxylic acid anions along the a-axis direction. Compared with the pelletized samples of GC-2, GC-3, and GC-4, their composite membranes with Nafion show significant enhancement of proton conduction with remarkable
Shrinkage-reducing polycarboxylate superplasticizer (SRPC) has a good effect on reducing shrinkage of cement-based materials because of its low surface tension. However, the effect of SRPC on the properties of cement-based materials needs to be further explored. A comparative study of SRPC and polycarboxylate superplasticizer (PCE) was carried out with the aim of correlating the adsorption in fresh cement pastes with their dispersing capability and the impacts on cement hydration. The results indicate that the adsorption amounts of SRPC are less than PCE. Both of them exhibit a multilayer adsorption; the fluidity of cement pastes with SRPC and PCE are related to the first adsorbed layer, and the secondary adsorbed layer does not contribute to the enhancement of fluidity. The retarding cement hydration of SRPC is weaker than PCE because of weak adsorption capacity of SRPC.
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