A rigid carboxylate ligand with a nitro functional group was selected to coordinate with Tb(III) cation, and Tb-MOF ({[Tb 4 (L) 4 (OH) 4 (H 2 O) 3 ]•8H 2 O} n , H 2 L = 2-nitroterephthalic acid) with large porous and excellent hydrophilicity was obtained successfully. The obtained Tb-MOF was filled into the Nafion matrix to improve its proton conduction performance. The Tb-MOF/ Nafion composite membrane was characterized by PXRD, IR, and thermogravimetry (TG) and for water uptake, area swelling, and proton conductivity. The activity energy, E a , value of the composite membrane, which is a very important factor affecting the proton conduction performance of the membrane, was fitted and calculated. It was revealed that Tb-MOF can improve the proton conductivities of composite membranes, and the improvement degree and E a value were both affected by Tb-MOF content. When Tb-MOF content was 5%, the proton conductivity of the composite membrane was 1.53 × 10 −2 S•cm −1 at 100% RH and 80 °C, which is 1.81 times that of the pure Nafion membrane. A MOF containing a nitro functional group was first doped into Nafion in this study and exhibited excellent performance for improving composite membrane proton conductivity. This study will provide a valuable reference for designing different functionalized MOFs to promote the proton conductivities of proton exchange membranes.
Two supramolecular Co-MOF isomers,
namely, {[Co(L)0.5(m-bimb)]·3H2O}
n
(LCU-115) and
{[Co(L)0.5(p-bimb)]·3H2O}
n
(LCU-116), were synthesized
from an amide-containing
carboxylic acid N,N″-(3,5-dicarboxylphenyl)benzene-1,4-dicarboxamide
(H4L) and two flexible positional isostructural N-containing
ligands m-bimb and p-bimb (m-bimb = 1,3-bis((1H-imidazol-1-yl)methyl)benzene; p-bimb = 1,4-bis((1H-imidazol-1-yl)methyl)benzene). The
carboxylate ligands connect Co(II) centers to form 2D metal-carboxylate
sheets, which are extended further by m-bimb and p-bimb to form a 2D bilayer with parallel stacking (LCU-115) and a 3D framework (LCU-116), respectively.
Luminescence measurements indicated that these two complexes exhibited
interesting multiresponsive sensing activities toward pH, biomarker
N-acetylneuraminic acid, and trivalent cations Ga3+/In3+. They show highly sensitive turn-on fluorescence responses
in the acidic range and can also be regarded as on–off–on
vapoluminescent sensors to typical acidic and basic gases HCl and
Et3N. It is worth noting that these complexes have excellent
turn-on ratiometric fluorescence sensing ability for N-acetylneuraminic
acid (NANA) with detection limits as low as 7.39 and 8.06 μM, respectively. Furthermore, they were successfully
applied for the detection of NANA in simulated urine and serum samples
with satisfactory results. For ion detection, LCU-116 could detect both Ga3+ and In3+, while LCU-115 could distinguish Ga3+ from In3+ with the latter showing luminescence quenching. The sensing mechanism
was investigated in detail by XRD, UV–vis, EDS, XPS, SEM, and
TEM. The results of interday and intraday precision studies gave low
RSD values in the range of 1.19–3.53%, ascertaining the reproducibility
of these sensors. The recoveries for the sensing analytes in simulated
urine/serum or real water are satisfactory from 96.7 to 103.3% (toward
NANA) and 96.6 to 115.0% (toward Ga3+ and In3+), indicating that these two complexes also possess acceptable reliability
for monitoring in real samples. The results indicated that the supramolecular
isomers LCU-115 and LCU-116 are promising
material candidates for application in biological and environmental
monitoring.
Three isostructural metal organic frameworks constructed by different metal cation {[M(L)1/2(H2O)2]•H2O}n (M = Co (1), Mn (2), Zn (3), H4L = 5,5’-(butane-1,4-diylbis(oxy)) diisophthalic acid) were obtained and characterized. According to...
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