Open coordination sites (OCSs) in metal–organic frameworks (MOFs) often function as key factors in the potential applications of MOFs, such as gas separation, gas sorption, and catalysis. For these ...applications, the activation process to remove the solvent molecules coordinated at the OCSs is an essential step that must be performed prior to use of the MOFs. To date, the thermal method performed by applying heat and vacuum has been the only method for such activation. In this report, we demonstrate that methylene chloride (MC) itself can perform the activation role: this process can serve as an alternative “chemical route” for the activation that does not require applying heat. To the best of our knowledge, no previous study has demonstrated this function of MC, although MC has been popularly used in the pretreatment step prior to the thermal activation process. On the basis of a Raman study, we propose a plausible mechanism for the chemical activation, in which the function of MC is possibly due to its coordination with the Cu2+ center and subsequent spontaneous decoordination. Using HKUST-1 film, we further demonstrate that this chemical activation route is highly suitable for activating large-area MOF films.
Do‐it‐yourself: Monolayers of molecules and nanoparticles should be prepared on substrates only by self‐assembly, but monolayers of microparticles can be produced by both self‐assembly and direct ...manual attachment as if they are tiles (see picture). The quality of the monolayers is better when they are assembled by hand than by self‐assembly.
Enhancement of hydrolytic stability of metal–organic frameworks (MOFs) is a challenging issue in MOF chemistry because most MOFs have shown limitations in their applications under a humid ...environment. Meanwhile, inner sphere electron transfer has constituted one of the most intensively studied subjects in contemporary chemistry. In this report, we show, for the first time, a new conceptual coordinative reduction of Cu2+ ion, which is realized in a paddlewheel MOF, HKUST-1, with a postsynthetic manner via inner sphere “single” electron transfer from hydroquinone (H2Q) to Cu2+ through its coordination bond. H2Q treatment of HKUST-1 under anhydrous conditions leads to the single charge (1+) reduction of approximately 30% of Cu2+ ions. Thus, this coordinative reduction is an excellent reduction process to be self-controlled in both oxidation state and quantity. As described below, once Cu2+ ions are reduced to Cu+, the reduction reaction does not proceed further, in terms of their oxidation state as well as their amount. Also, we demonstrate that a half of the Cu+ ions (about 15%) remains in paddlewheel framework with pseudo square planar geometry and the other half of the Cu+ ions (about 15%) forms Cu(MeCN)4+ complex in a small cage in the fashion of a ship-in-a-bottle after dissociation from the framework. Furthermore, we show that the coordinative reduction results in substantial enhancement of the hydrolytic stability of HKUST-1 to the extent that its structure remains intact even after exposure to humid air for two years.
The free primary hydroxyl groups in the metal–organic framework of CDMOF-2, an extended cubic structure containing units of six γ-cyclodextrin tori linked together in cube-like fashion by rubidium ...ions, has been shown to react with gaseous CO2 to form alkyl carbonate functions. The dynamic covalent carbon–oxygen bond, associated with this chemisorption process, releases CO2 at low activation energies. As a result of this dynamic covalent chemistry going on inside a metal–organic framework, CO2 can be detected selectively in the atmosphere by electrochemical impedance spectroscopy. The “as-synthesized” CDMOF-2 which exhibits high proton conductivity in pore-filling methanolic media, displays a ∼550-fold decrease in its ionic conductivity on binding CO2. This fundamental property has been exploited to create a sensor capable of measuring CO2 concentrations quantitatively even in the presence of ambient oxygen.
Threaded fasteners are widely used in mechanical structures primarily owing to their easy disassembly for maintenance and low cost. However, the loosening mechanism of threaded fasteners due to ...dynamic loading has remained unclear for the past six decades. Current researches on complex structures comprising three or more components are insufficient. The two most common failure modes of threaded fasteners subjected to dynamic loading are fatigue and vibration-induced loosening. This study focuses on the failure of threaded fasteners by vibration-induced loosening due to dynamic shear loads. This study comprises experimental analysis and numerical analysis. The loosening mechanism of threaded fasteners for complex structures is analytically and experimentally identified. This work provides the equations and assessment method for the loosening, and the criteria of primary and secondary loosening are established. To verify the proposed loosening mechanism, tightening and loosening experiments are conducted for three types of bolted joints. The primary and secondary loosening forces of each bolt are thus obtained, and the proposed loosening mechanism can be verified for complex structures. In numerical analysis, a three-dimensional finite element (FE) model for tightening and loosening analysis is proposed. A FE model is used to study the loosening process which is characterized by a decline of the preload and moving distance for predicting loosening states. The model seems to be well agreement in comparison with theoretical and experimental results. As a result, the assessment method shows good performance in predicting loosening state. It is expected to verify the safety of bolted structures at the design stage. The FE model is expected to be used for the effective and safe design for joint components in various industrial fields such as wheel assemblies and other mechanical components under dynamic vibration.
This study investigated the epidemiology (prevalence, risk factors, and impact on quality of life) of knee pain and its severity in elderly Koreans. The subjects (n=3,054) were participants aged ≥50 ...yr from the fifth Korea National Health and Nutrition Examination Survey, conducted in 2010. Knee pain was defined as pain in the knee lasting ≥30 days during the most recent 3 months; severity was categorized as mild, moderate, or severe. EQ-5D was used to measure quality of life. The prevalence of knee pain was 23.1% (11.7% in men, 31.9% in women). The prevalences of mild, moderate, and severe knee pain were 4.3%, 9.1%, and 9.7%, respectively (2.8%, 5.4%, and 3.5% in men and 5.4%, 12.0%, and 14.4% in women). Old age, female gender, a low level of education, a manual occupation, obesity, and radiographic osteoarthritis were risk factors for knee pain, and were associated with increased severity of knee pain. Excluding men with mild knee pain, people with knee pain had significantly lower quality of life than those without knee pain. Early interventional approaches are needed to reduce the medical, social, and economic burden of knee pain in elderly Koreans.
Zeolites are crystalline aluminosilicate minerals featuring a network of 0.3-1.5-nm-wide pores, used in industry as catalysts for hydrocarbon interconversion, ion exchangers, molecular sieves and ...adsorbents. For improved applications, it is highly useful to study the distribution of internal local strains because they sensitively affect the rates of adsorption and diffusion of guest molecules within zeolites. Here, we report the observation of an unusual triangular deformation field distribution in ZSM-5 zeolites by coherent X-ray diffraction imaging, showing the presence of a strain within the crystal arising from the heterogeneous core-shell structure, which is supported by finite element model calculation and confirmed by fluorescence measurement. The shell is composed of H-ZSM-5 with intrinsic negative thermal expansion whereas the core exhibits a different thermal expansion behaviour due to the presence of organic template residues, which usually remain when the starting materials are insufficiently calcined. Engineering such strain effects could have a major impact on the design of future catalysts.
Recently, vehicle driving devices to support infotainment services are being designed for driver’s convenience. Especially, the automobile industry is developing vehicles that use a joy stick instead ...of a steering wheel from the concept car. The greatest strength of using a joy stick is that the driver feels less workload and fatigue than when using a steering wheel. However, this field still needs more research and experiments for more accurate results. Therefore, this study evaluated the workload when driving with different devices through a subjective questionnaire and measurement of physiological signals. The reason for using not only a survey but also physiological signals is to support the results of the subjective questionnaire, which are not enough to yield accurate results. There are two different kinds of methods to carry out this research: SWAT (subjective workload assessment technique) for the survey and Biopac equipment for the measurement of physiological signals. A thermal infrared camera is used for capturing the driver workload by measuring the facial skin temperature. Furthermore, a previously established driving simulator, GPS (global positioning system), and the virtual Kyeong-Bu highway are used for the experiment. As a result of the experiment with 13 subjects following both methods (the surveys and the measurement of physiological data), it is confirmed that using a drive stick device causes less workload and fatigue to the drivers than using a steering wheel. In addition, the statistical significance of the results is verified through the SPSS (statistical package for the social sciences) statistical analysis program.
Dye aggregation and concomitant reduction of dye excited-state lifetimes and electron-injection yields constitute a significant mechanism for diminution of light-to-electrical energy conversion ...efficiencies in many dye-sensitized solar cells (DSCs). For TiO2-based DSCs prepared with an archetypal donor–acceptor organic dye, (E)-2-cyano-3-(5′-(5′′-(p-(diphenylamino)phenyl)-thiophen-2′′-yl)thiophen-2′-yl)acrylic acid (OrgD), we find, in part via ultrafast spectroscopy measurements, that postdye-adsorption atomic layer deposition (ALD) of ultrathin layers of either TiO2 or Al2O3 effectively reverses residual aggregation. Notably, the ALD treatment is significantly more effective than the widely used aggregation-inhibiting coadsorbent, chenodeoxycholic acid. Primarily because of reversal of OrgD aggregation, and resulting improved injection yields, ALD post-treatment engenders a 30+% increase in overall energy conversion efficiency. A secondary contributor to increased currents and efficiencies is an ALD-induced attenuation of the rate of interception of injected electrons, resulting in slightly more efficient charge collection.
Zeolite Y films (0.35–2.5 μm), into which CdS and PbS quantum dots (QDs) were loaded, were grown on ITO glass. The CdS QD-loaded zeolite Y films showed a photovoltaic effect in the electrolyte ...solution consisting of Na2S (1 M) and NaOH (0.1 M) with Pt-coated F-doped tin oxide glass as the counter electrode. In contrast, the PbS QD-loaded zeolite Y films exhibited a negligible PV effect. This contrasting behavior was proposed to arise from the large difference in driving force for the electron transfer from S2– in the solution to the hole in the valence band of QDs, with the former being much larger (∼2 eV) than the latter (∼1 eV). In the case of CdS QD-loaded zeolite Y with a loaded amount of CdS of 6.3 per unit cell, the short circuit current, open circuit voltage, fill factor, and efficiency were 0.3 mA cm–2, 423 V, 28, and 0.1%, respectively, under the AM 1.5, 100 mW cm–2 condition. This cell was stable for more than 18 days of continuous measurements. A large (3-fold) increase in overall efficiency was observed when PbS QD-loaded zeolite Y on ITO glass was used as the counter electrode. This phenomenon suggests that the uphill electron transfer from ITO glass to S in the solution is facilitated by the photoassisted pumping of the potential energy of the electron in ITO glass to the level that is higher than the reduction potential of S by PbS QDs. Under this condition, the incident-photon-to-current conversion efficiency (IPCE) value at 398 nm was 42% and the absorbed-photon-to-current conversion efficiency (APCE) value at 405 nm was 82%. The electrolyte-mediated interdot charge transport within zeolite films is concluded to be responsible for the overall current flow.
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