High and Tunable Proton Conduction in Six 3D-Substituted Imidazole Dicarboxylate-Based Lanthanide-Organic Frameworks.

Six isostructural three-dimensional (3D) Ln(III)-organic frameworks, {[Ln2(HMIDC)2(µ4-C2O4)(H2O)3]·4H2O}n [LnIII = GdIII (1), EuIII (2), SmIII (3), NdIII (4), PrIII (5), and CeIII (6)], have been fabricated by using a multifunctional ligand of 2-methyl-1H-imidazole-4,5-dicarboxylic acid (H3MIDC). Ln-metal-organic frameworks (MOFs) 1-6 present 3D structures and possess abundant H-bonded networks between imidazole-N atoms and coordinated and free water molecules. All the six Ln-MOFs demonstrate humidity- and temperature-dependent proton conductivity (σ) having the optimal values of 2.01 × 10-3, 1.40 × 10-3, 0.93 × 10-3, 2.25 × 10-4, 1.11 × 10-4, and 0.96 × 10-4 S·cm-1 for 1-6, respectively, at 100 °C/98% relative humidity, in the order of CeIII (6) < PrIII (5) < NdIII (4) < SmIII (3) < EuIII (2) < GdIII (1). In particular, the σ for 1 is 1 order of magnitude higher than that for 6, and it enhances systematically according to the decreasing order of the ionic radius, indicating that the lanthanide-contraction tactics can effectively regulate the proton conductivity while retaining the proton conduction routes. This will offer valuable guidance for the acquisition of new proton-conducting materials. In addition, the outstanding water stability and electrochemical stability of such Ln-MOFs will afford a solid material basis for future applications.

Proton-Conductive 3D LnIII Metal-Organic Frameworks for Formic Acid Impedance Sensing.

Metal-organic frameworks (MOFs) as new classes of proton-conducting materials have been highlighted in recent years. Nevertheless, the exploration of proton-conducting MOFs as formic acid sensors is extremely lacking. Herein, we prepared two highly stable 3D isostructural lanthanide(III) MOFs, {(M(µ3 -HPhIDC)(µ2 -C2 O4 )0.5 (H2 O))⋅2 H2 O}n (M=Tb (ZZU-1); Eu (ZZU-2)) (H3 PhIDC=2-phenyl-1H-imidazole-4,5-dicarboxylic acid), in which the coordinated and uncoordinated water molecules and uncoordinated imidazole N atoms play decisive roles for the high-performance proton conduction and recognition ability for formic acid. Both ZZU-1 and ZZU-2 show temperature- and humidity-dependent proton-conducting characteristics with high conductivities of 8.95×10-4 and 4.63×10-4  S cm-1 at 98 % RH and 100 °C, respectively. Importantly, the impedance values of the two MOF-based sensors decrease upon exposure to formic acid vapor generated from formic aqueous solutions at 25 °C with good reproducibility. By comparing the changes of impedance values, we can indirectly determine the concentration of HCOOH in aqueous solution. The results showed that the lowest detectable concentrations of formic acid aqueous solutions are 1.2×10-2  mol L-1 by ZZU-1 and 2.0×10-2  mol L-1 by ZZU-2. Furthermore, the two sensors can distinguish formic acid vapor from interfering vapors including MeOH, N-hexane, benzene, toluene, EtOH, acetone, acetic acid and butane. Our research provides a new platform of proton-conductive MOFs-based sensors for detecting formic acid.

Two Highly Stable Proton Conductive Cobalt(II)-Organic Frameworks as Impedance Sensors for Formic Acid.

Metal-organic frameworks (MOFs) have been extensively explored as advanced chemical sensors in recent years. However, there are few studies on MOFs as acidic gas sensors, especially proton conductive MOFs. In this work, two new proton-conducting 3D MOFs, {[Co3 (p-CPhHIDC)2 (4,4'-bipy)(H2 O)]⋅2 H2 O}n (1) (p-CPhH4 IDC=2-(4-carboxylphenyl)-1 H-imidazole-4,5-dicarboxylic acid; 4,4'-bipy=4,4'-bipyridine) and {[Co3 (p-CPhHIDC)2 (bpe)(H2 O)]⋅3 H2 O}n (2) (bpe=trans-1,2-bis(4-pyridyl)ethylene) have been solvothermally prepared and investigated their formic acid sensing properties. Both MOFs 1 and 2 show temperature- and humidity-dependent proton conductive properties and exhibit optimized proton conductivities of 1.04×10-3 and 7.02×10-4  S cm at 98 % relative humidity (RH) and 100 °C, respectively. The large number of uncoordinated carboxylic acid sites, free and coordination water molecules, and hydrogen-bonding networks inside the frameworks are favorable to the proton transfer. By measuring the impedance values after exposure to formic acid vapor at 98 % or 68 % RH and 25 °C, both MOFs indicate reproducibly high sensitivity to the analyte. The detection limit of formic acid vapor is as low as 35 ppm for 1 and 70 ppm for 2. Meanwhile, both MOFs also show commendable selectivity towards formic acid among interfering solutions. The proton conducting and formic acid sensing mechanisms have been suggested according to the structural analysis, Ea calculations, N2 and water vapor absorptions, PXRD and SEM measurements. This work will open a new avenue for proton-conductive MOF-based impedance sensors and promote the potential application of these MOFs for indirectly monitoring the concentrations of formic acid vapors.

A Highly Proton-Conductive 3D Ionic Cadmium-Organic Framework for Ammonia and Amines Impedance Sensing.

Lately, the progressive study of metal-organic frameworks (MOFs) for the detection of ammonia and amines has made infusive achievements. Nevertheless, the investigation of proton-conductive MOFs used to detect the low concentrations of ammonia and amine gases at different relative humidities (RHs) at room temperature is relatively restricted. Herein, by solvothermal reaction of Cd(NO3)2 with 2-methyl-1 H-imidazole-4,5-dicarboxylic acid (H3MIDC), a three-dimensional ionic MOF {Na[Cd(MIDC)]} n (1) bearing ordered one-dimensional channels was successfully synthesized. Our research indicates that the uncoordination carboxylate sites are beneficial to proton transfer and the recognition of ammonia and amine compounds. The optimized proton conductivity of 1 reaches a high value of 1.04 × 10-3 S·cm-1 (100 °C, 98% RH). The room temperature sensing properties of ammonia and amine gases were explored under 68, 85, and 98% RHs, respectively. Satisfactorily, the detection limits of MOF 1 toward ammonia, methylamine, dimethylamine, trimethylamine, and ethylamine are 0.05, 0.1, 0.5, 1, and 4 ppm, respectively, which is one of the best room-temperature sensors for ammonia among previous sensors based on proton-conductive MOFs. The proton conducting and sensing mechanisms were highlighted as well.

Enhancing Proton Conductivity of a 3D Metal-Organic Framework by Attaching Guest NH3 Molecules.

By reaction of a newly designed organic ligand, [3-(naphthalene-1-carbonyl)-thioureido] acetic acid (C10H7C(O)NHC(S)NHCH2COOH; H3L), with Cu(OAc)2, a metal-organic framework [(CuI4CuII4L4)·3H2O] n (1) containing unique mixed-valence [CuI4Cu4IIL4] subunits has been successfully synthesized and structurally characterized. MOF 1 displays a three-dimensional open framework bearing one-dimensional channels. Consequently, a new derivative MOF [CuI4CuII4L4] n-NH3 (2) is procured upon exposure of 1 to NH3 vapors from 28 wt % aqueous NH3 solution, which bears 2 NH3 and 4 H2O molecules in accordance with the elemental and thermal analyses. Both 1 and 2 exhibit relatively high water stability, whose proton conduction properties under water vapor have been researched. Notably, 2 shows an ultrahigh proton conductivity of 1.13 × 10-2 S cm-1, which is 2 orders of magnitude larger than that of MOF 1 (4.90 × 10-4 S cm-1) under 100 °C and 98% RH. On the basis of the structural data, Ea values, H2O and ammonia vapor absorptions, and PXRD measurements, the proton transfer mechanisms were suggested. This is an efficient and convenient way to obtain suitable and highly proton-conducting materials by attaching NH3 molecules.

A Comparative Investigation of Proton Conductivities for Two Metal-Organic Frameworks under Water and Aqua-Ammonia Vapors.

Our investigation on the proton conductivities of two water-stable isostructural 3D Co(II) MOFs, {[Co3(DMPhIDC)2(H2O)6]·2H2O}n (1) [DMPhH3IDC = 2-(3,4-dimethylphenyl)-imidazole-4,5-dicarboxylic acid] and {[Co3(m-BrPhIDC)2(H2O)6]·2H2O} (2) [m-BrPhH3IDC = 2-(m-bromophenyl)-imidazole-4,5-dicarboxylic acid], under water or aqua-ammonia vapor shows that the optimized proton conductivities of both 1 and 2 under aqua-ammonia vapor are 4.41 × 10-3 S·cm-1 and 5.07 × 10-4 S·cm-1 (at aqua-ammonia vapor from 1.5 M NH3·H2O solution and 100 °C), respectively, which are approximately 1 order of magnitude greater than those maximum values (8.91 × 10-4 S·cm-1 and 7.64 × 10-5 S·cm-1) under water vapor (at 98% RH and 100 °C). The plausible proton pathways and mechanisms of the MOFs have been proposed in terms of the structural analyses, activation energy calculations, water and NH3 vapor absorptions, and PXRD determinations.

Effective Approach to Promoting the Proton Conductivity of Metal-Organic Frameworks by Exposure to Aqua-Ammonia Vapor.

We explored the proton conductivities of two 3D CoII metal-organic frameworks (MOFs), {[Co3(m-ClPhIDC)2(H2O)6]·2H2O}n [1; m-ClPhH3IDC = 2-(m-chlorophenyl)imidazole-4,5-dicarboxylic acid] and {[Co3(p-ClPhHIDC)3(H2O)3]·6H2O}n (2; p-ClPhH3IDC = 2-(p-chlorophenyl)imidazole-4,5-dicarboxylic acid), under water and aqua-ammonia vapors, respectively. The experimental results revealed that the proton conductivities of 1 and 2 at aqua-ammonia vapor were 2.89 × 10-2 and 4.25 × 10-2 S/cm, respectively, and approximately 2 orders of magnitude greater than those at water vapor. On the basis of the activation energy, water and ammonia vapor absorption, and powder X-ray diffraction patterns, their proton-conduction mechanisms have been discussed. We believe that this is a novel approach to drastically improving the proton conductivity of MOFs.

A simple compact UHV and high magnetic field compatible inertial nanopositioner.

We present a novel simple piezoelectric nanopositioner which just has one piezoelectric scanner tube (PST) and one driving signal, using two short quartz rods and one BeCu spring which form a triangle to press the central shaft and can promise the nanopositioner's rigidity. Applying two pulse inverted voltage signals on the PST's outer and inner electrodes, respectively, according to the principle of piezoelectricity, the PST will elongate or contract suddenly while the central shaft will keep stationary for its inertance, so the central shaft will be sliding a distance relative to quartz rods and spring, and then withdraw the pulse voltages slowly, the central shaft will move upward or downward one step. The heavier of the central shaft, the better moving stability, so the nanopositioner has high output force. Due to its compactness and mechanical stability, it can be easily implanted into some extreme conditions, such as ultrahigh vacuum, ultralow temperature, and high magnetic field.

Immobilization of horseradish peroxidase by electrospun fibrous membranes for adsorption and degradation of pentachlorophenol in water.

Horseradish peroxidase (HRP) is successfully in situ encapsulated into the poly(D,L-lactide-co-glycolide) (PLGA)/PEO-PPO-PEO (F108) electrospun fibrous membranes (EFMs) by emulsion electrospinning. The adsorption and degradation of pentachlorophenol (PCP) by HRP-EFMs are investigated. The experimental results show that the sorption kinetic of PCP on EFMs follows the pseudo-second-order model, and the sorption capacity is as high as 44.69 mg g(-1). The sorption mechanisms of EFMs for PCP can be explained by hydrogen bonding interactions, hydrophobic interactions and π-π bonding interactions. Profiting from the strong adsorption, the removal of PCP can be dramatically enhanced by the interaction of adsorbed PCP and HRP on the surface of EFMs. For PCP degradation, the optimal pH values for free HRP and immobilized HRP are 4 and 2-4, respectively. As pH>4.7, no adsorption and degradation are observed due to the deprotonation of PCP. The removal percentages reach 83% and 47% for immobilized HRP and free HRP, respectively, at 25 ± 1°C. The presence of humic acid can inhibit the activity of HRP and decreases the adsorption capacity of PCP because of competitive adsorption. The operational and storage stability of immobilized HRP are highly improved through emulsion electrospinning.

A simple method for the preparation of monodisperse protein-loaded microspheres with high encapsulation efficiencies.

A simple method for the preparation of monodisperse protein-loaded polymer microspheres is presented in this paper. The method is based on the co-extrusion of an internal phase of an aqueous protein solution and an external phase of an organic polymer solution through a 200-micron-sized hole. Controlled in the correct flow region, this process produces a core-shell-structured laminar liquid jet, which breaks to form monodisperse compound liquid droplets. Stabilized in a dilute aqueous polyvinyl alcohol (PVA) solution, the droplets are converted into solid protein-loaded polymer microspheres through evaporation of the organic solvent. Results show that preparation parameters such as polymer concentration, total flow rate, flow rate ratio of the aqueous to organic phase have significant effects on the mean particle size, particle morphology and protein encapsulation efficiency (EE). The results of biodegradation and the protein release characteristics of the polymer microspheres are also presented.