Toward Base Heterogenization: A Zirconium Metal–Organic Framework/Dendrimer or Polymer Mixture for Rapid Hydrolysis of a Nerve-Agent Simulant

The base heterogenization is crucial for the practical applications of metal–organic frameworks (MOFs) as catalytic filters, such as masks or protective suits, for the deconstruction of chemical warfare agents (CWAs). Here, we performed the hydrolysis of a phosphate-based nerve agent simulant in the presence of different amine-based bases (i.e., a small organic molecule, dendrimers, and linear and branched polymers) using a Zr-MOF, NU-901, with 4,8-connected scu topology. Remarkably, the catalytic performances of NU-901 using the less-volatile branched polymers and dendrimers are comparable to the volatile N-ethylmorpholine solution

Outer-Sphere Redox Couples as Shuttles in Dye-Sensitized Solar Cells. Performance Enhancement Based on Photoelectrode Modification via Atomic Layer Deposition

Atomic layer deposition (ALD) has been used to create conformal TiO2 blocking layers on fluorine-doped tin-oxide substrates in dye-sensitized solar cells (DSSCs), effectively eliminating shunting. ALD has also been used to deposit, in controlled fashion, ultrathin coatings of alumina on nanoparticle-based TiO2 DSSC photoanodes. These modified electrodes enable ferrocenium/ferrocene, an outer-sphere redox couple, to be used as a shuttle. The photovoltaic performance and interfacial charge-transfer dynamics were investigated in DSSCs employing this shuttle. It was found that a single ALD cycle is able to passivate surface states, resulting in a dramatic improvement in photovoltaic performance. Subsequent alumina deposition resulted in exponentially increasing electron lifetimes as a function of alumina layer thickness, indicating that the layers behave as barriers to electron tunneling. The characterization of DSSC photovoltaic performance and interfacial charge-transfer dynamics was extended to cells employing derivatives of ferrocenium and ferrocene featuring more positive redox potentials; these cells yielded larger open-circuit photovoltages

An Example of Node-Based Postassembly Elaboration of a Hydrogen-Sorbing, Metal−Organic Framework Material

A robust, noncatenated, and permanently microporous metal−organic framework (MOF) material has been synthesized by combining a new nonplanar ligand, 4,4′,4′′,4′′′-benzene-1,2,4,5-tetrayltetrabenzoic acid, with a zinc(II) source under solvothermal conditions. The new material features cavities that are readily modified via activation and functionalization of framework nodes (as opposed to struts). A preliminary investigation of the “empty cavity” version of the material and six cavity-modified versions reveals that modification can substantially modulate the MOF’s internal surface area, pore volume, and ability to sorb molecular hydrogen

A Convenient Route to High Area, Nanoparticulate TiO₂ Photoelectrodes Suitable for High-Efficiency Energy Conversion in Dye-Sensitized Solar Cells

Ethanol-soluble amphiphilic TiO2 nanoparticles (NPs) of average diameter ∼9 nm were synthesized, and an α-terpineol-based TiO2 paste was readily prepared from them in comparatively few steps. When used for fabrication of photoelectrodes for dye-sensitized solar cells (DSSCs), the paste yielded highly transparent films and possessing greater-than-typical, thickness-normalized surface areas. These film properties enabled the corresponding DSSCs to produce high photocurrent densities (17.7 mA cm−2) and a comparatively high overall light-to-electrical energy conversion efficiency (9.6%) when deployed with the well-known ruthenium-based molecular dye, N719. These efficiencies are about ∼1.4 times greater than those obtained from DSSCs containing photoelectrodes derived from a standard commercial source of TiO2 paste

Postassembly Transformation of a Catalytically Active Composite Material, Pt@ZIF-8, via Solvent-Assisted Linker Exchange

2-Methylimidazolate linkers of Pt@ZIF-8 are exchanged with imidazolate using solvent-assisted linker exchange (SALE) to expand the apertures of the parent material and create Pt@SALEM-2. Characterization of the material before and after SALE was performed. Both materials are active as catalysts for the hydrogenation of 1-octene, whereas the hydrogenation of <i>cis</i>-cyclohexene occurred only with Pt@SALEM-2, consistent with larger apertures for the daughter material. The largest substrate, β-pinene, proved to be unreactive with H₂ when either material was employed as a candidate catalyst, supporting the contention that substrate molecules, for both composites, must traverse the metal–organic framework component in order to reach the catalytic nanoparticles

An Example of Node-Based Postassembly Elaboration of a Hydrogen-Sorbing, Metal−Organic Framework Material

A robust, noncatenated, and permanently microporous metal−organic framework (MOF) material has been synthesized by combining a new nonplanar ligand, 4,4′,4′′,4′′′-benzene-1,2,4,5-tetrayltetrabenzoic acid, with a zinc(II) source under solvothermal conditions. The new material features cavities that are readily modified via activation and functionalization of framework nodes (as opposed to struts). A preliminary investigation of the “empty cavity” version of the material and six cavity-modified versions reveals that modification can substantially modulate the MOF’s internal surface area, pore volume, and ability to sorb molecular hydrogen

H₅PV₂Mo₁₀O₄₀ Polyoxometalate Encapsulated in NU-1000 Metal–Organic Framework for Aerobic Oxidation of a Mustard Gas Simulant

The immobilization of H5PV2Mo10O40 polyoxometalates (POMs) in the in the mesoporous channel-type metal–organic framework (MOF), NU-1000, via simple impregnation method is reported here. Characterization of the composite PV2Mo10@NU-1000 activated by supercritical CO2 revealed that the POMs occupy the mesopore. Upon heating as low as 40 °C in the absence of bulk solvent, the POMs migrate to the micropore. However, the presence of solvent, such as cyclohexane, impedes this transformation. The material was active for the aerobic oxidation of the mustard gas simulant, 2-chloroethyl ethyl sulfide (CEES), in cyclohexane using isobutyraldehyde a sacrificial reductant and O2 as the oxidant. The activity of the POM allowed for efficient oxidation of CEES in the dark and in air. Immobilization of the POM in the MOF was found to improve the initial turnover frequency compared to the POM itself. Further, the POM catalyst was found to be unstable under the chosen reaction conditions and no activity was found upon washing and reusing the POM. As a composite PV2Mo10@NU-1000, the POMs retained their catalytic activity and allowed for recycling of the catalytic material

High Propane and Isobutane Adsorption Cooling Capacities in Zirconium-Based Metal–Organic Frameworks Predicted by Molecular Simulations

Adsorption cooling systems are emerging alternatives to traditional compression-based cooling systems due to their reduced electricity costs. Metal–organic frameworks (MOFs) have the potential to be ideal adsorbent materials for this application, as they can be tuned to have desired adsorption behavior for different refrigerants. In this work, we studied the adsorption behaviors of propane and isobutane, which are environmentally friendly refrigerants that have been recommended as substitutes for (hydro)­chlorofluorocarbons, in two mesoporous Zr-based MOFs, namely, NU-1000 and NU-1003, which have the same topology but different pore sizes. Both MOFs showed high cooling capacities with the refrigerants, and for isobutane, the cooling capacities were 2 to 4 times higher than MIL-101, which is the only MOF with a previously reported isobutane adsorption cooling capacity

Linker Competition within a Metal–Organic Framework for Topological Insights

Efforts toward predictive topology within the design and synthesis of metal–organic frameworks (MOFs) have been extensively studied. Herein, we report an investigation of a linker competition for the nucleation of a Zr6-based mixed linker MOF. By varying the relative additions of two linkers and introducing prior seeding to the system, we discern that the scu topology is the kinetic product of the two competing linkers. Elemental mapping analysis indicates that the competing linkers are uniformly distributed throughout the MOF. The final ratios of the linkers in the dissolved MOFs align well with the initial synthetic ratio. Through the introduction of a prior nucleation phase to seed the system, the thermodynamic csq product is more readily achieved. The results reported will enhance the understanding of MOF growth process