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Metal-organic frameworks have developed into a formidable heterogeneous catalysis platform in recent years. It is well established that thermolysis of coordinated solvents from MOF nodes can render highly reactive, coordinatively unsaturated metal complexes which are stabilized via site isolation and serve as active sites in catalysis. Such approaches are limited to frameworks featuring solvated transition-metal complexes and must be stable toward the formation of "permanent" open metal sites. Herein, we exploit the hemilability of metal-carboxylate bonds to generate transient open metal sites in an In(III) MOF, pertinent to In-centered catalysis. The transient open metal sites catalyze the Strecker reaction over multiple cycles without loss of activity or crystallinity. We employ computational and spectroscopic methods to confirm the formation of open metal sites via transient dissociation of In(III)-carboxylate bonds. Furthermore, the amount of transient open metal sites within the material and thus the catalytic performance can be temperature-modulated.

Solvents with weak coordination bonding (e.g., TCM and DCM) confined in the nanopores of a metal–organic framework undergo dynamic coordination exchange with stronger Lewis-basic solvents (e.g., H2O), and they lead to enhanced catalytic efficiency.

Uncommon reversible guest-induced metal-hemilabile linker bond dynamics in MOF MFM-300(Sc) was unraveled to switch on/switch off catalytic open metal sites. The catalytic activity of this MOF with non-permanent open metal sites was demonstrated using a model Strecker hydrocyanation reaction as a proof-of-concept. Conclusively, the catalytic activity was evidenced to be fully reversible, preserving the conversion performance and structure integrity of MFM-300(Sc) over multiple cycles. These experimental findings were corroborated by quantum-calculations that revealed a reaction mechanism driven by the Sc-open metal sites. This discovery paves the way towards the design of new effective and easily regenerable heterogeneous MOF catalysts integrating switchable metal sites.

Nonradiative relaxation, a ubiquitous phenomenon in natural and artificial molecules and materials, has been extensively studied in contemporary chemistry. In this report, we show the nonradiative ...

Hydrogen bond (H-bond) of water molecules confined in nanopores is of particular interest because it is expected to exhibit chemical features different from bulk water molecules due to its interaction with the wall lining the pores. Herein, we show a crystalline behavior of hydrogen-bonded water molecules residing in the nanocages of a paddlewheel metal-organic framework, providing in situ and ex situ synchrotron single-crystal X-ray diffraction and Raman spectroscopy studies. The crystalline H-bond is demonstrated by proving the vibrational chain connectivity arising between hydrogen bonding and paddlewheel Cu−Cu bonding in sequentially connected Cu–Cu⋅⋅⋅⋅⋅coordinating H2O⋅⋅⋅⋅⋅H-bonded H2O and proving the spatial ordering of H-bonded water molecules at room temperature, where they are anticipated to be disordered with a high degree of freedom in their molecular motions. Additionally, we show a substantial distortion of the paddlewheel Cu2+ centers that arises simultaneously with water coordination. Also, we suggest the dynamic coordination bond character of the H-bond of the confined water molecules, by which an H-bond transitions to a coordination bond at the Cu2+ center instantaneously after dissociating a previously coordinated water molecule.

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.

Active, stable electrocatalysts based on non-precious metals for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are critical for the development of cost-effective, efficient renewable energy technologies. Here, Fe/Fe3C-embedded nitrogen-doped carbon was fabricated via pyrolysis of iron-porphyrin-encapsulated mesoporous metal–organic frameworks [PCN-333 (Fe), where “PCN” stands for “porous coordination network”] at 700 °C. The various characterization techniques confirmed that Fe- and Fe3C-containing Fe–N–C material (FeP-P333-700) was successfully prepared by pyrolysis of porphyrin-encapsulated PCN-333 (Fe). FeP-P333-700 exhibited superior electrocatalytic performance for the ORR and HER owing to the synergistic effect of Fe/Fe3C and Fe–N–C active sites.

Microwave is thought of as a useful electromagnetic radiation tool because it is often used in real life as well as in a variety of chemical processes. Meanwhile, activation of metal-organic frameworks (MOFs), which must be essentially done to remove coordinating and pore-filling solvents before the use of MOFs for various applications, has been performed commonly with the methods of heat supply or solvent exchange. Here, we show a new methodological microwave activation (MA), realizing it with various MOFs such as HKUST-1, UiO-66, and MOF-74s. For instance, microwave irradiation to the MOF samples for 4-35 min leads to the complete activation of the MOFs without structural damage. As described below, we further demonstrate that the solvent-assisted MA, which is the MA process performed after the solvent exchange, can substantially reduce the time for the activation by 4 min.

Large single crystals of a novel lithium cobalt coordination compound, LiCo(NC5H3(CO2)2)2(H2O)2.125 [LiCo(PDC)2] were grown via a hydrothermal reaction in high yield. The electrochemical impedance spectroscopy (EIS) data measured on a large single crystal of LiCo(PDC)2 revealed very interesting anisotropic Li+ ion conductivity. The redox potential for Co3+/Co4+ observed at ca. 200 mV in the cyclic voltammogram was consistent with the electric potential where the ionic conductivity occurred. Detailed structural analysis on a series of stoichiometrically equivalent cobalt coordination compounds, ACo(PDC)2 (A = Na+, K+, and H3O+), indicated that the presence of ion channels as well as a suitable cation size is critical for the anisotropic ionic conductivity.

The 52nd President of the Korean Chemical Society (2020–2021).

Shape control of metal–organic materials on the meso- and macroscale has been an important theme due to emerging properties., Shape control of metal–organic materials on the meso- and macroscale has been an important theme due to emerging properties. Particularly, chemical etching has been useful to create various forms such as core–shells and hollow crystals in metal–organic frameworks. Here we present a unique chemical etching strategy to create trigonal patterned surfaces in metal–organic frameworks. The mechanism suggests that metal–organic polyhedron subunits serve as meta-atoms, playing a crucial role in the formation of trigons on the surface. Such a patterned surface in porous solids can be utilized in meta-surface applications in the foreseeable future.

Isolated one-dimensional (1-D) proton channels in a metal–organic framework, MOF-74, have been reasonably expected to show highly directional proton conductivity, although no evidence has been provided. As a result of dimensional anisotropy of the channels evenly aligned in the c-axis of MOF-74 single crystal, highly directional proton conductivity is demonstrated by using electrochemical impedance spectroscopy. In particular, single crystals treated with sulfuric acid or ammonium hydroxide displays a maximum ∼1200-fold-enhanced c-axis proton conductivity compared to its a-axis conductivity, demonstrating highly directional proton migration through the channels. Very low activation energies (e.g., 0.12 eV) for the c-axis conductivity of MOF-74 also suggest a high proton mobility that arises via Grotthuss proton transfer parallel to the channels.

Over the last two decades, metal–organic frameworks (MOFs) have received particular attention because of their attractive properties such as permanent nanoporosity and the extraordinary functionality of open coordination sites (OCSs) at metal nodes. In particular, MOFs with open-state OCSs have shown potential in applications such as chemical separation, molecular sorption, catalysis, ionic conduction, and sensing. Thus, the activation of OCSs, i.e., the removal of coordinated solvent to produce open-state OCSs, has been viewed as an essential step that must be performed prior to the use of the MOFs in the aforementioned applications. This Feature Article focuses on the chemical functions of the commonly unreactive chloromethanes, i.e., dichloromethane (DCM) and trichloromethane (TCM), including their coordination to OCSs and activation of OCSs. Treatment with a chloromethane is a chemical route to activate OCSs that does not require an additional supply of external thermal energy. Importantly, a plausible mechanism for the chemical process, in which DCM and TCM weakly coordinate to the OCSs and then spontaneously dissociate in an intermediate step, which is proposed based on the results obtained from Raman studies will be discussed. Possible applications of chloromethane treatment to activate large-area MOF films and MOF–polymer mixed matrices, which can be propagated in molecular capture, will also be described.

Open coordination sites (OCSs) in metal-organic frameworks (MOFs) have shown potential in applications such as molecular separation, sorption, catalysis, and sensing. Thus, the removal of coordinated solvent has been viewed as an essential step that needs to be performed prior to the use of the MOFs in the above applications. To date, a thermal method that is normally performed by applying heat and vacuum has been the most commonly employed activation method despite its negative influence on the structural integrity of the MOFs. In this report, we demonstrate that commonly inert trichloromethane (TCM) can activate OCSs; the TCM treatment process serves as an alternative chemical route to activation that does not require the external thermal energy. On the basis of the Raman study, we suggest a possible mechanism for the chemical activation process where TCM may weakly coordinate to the OCSs and then spontaneously dissociate. In addition, we prove that the chemical activation behavior is substantially boosted when a small amount of external heat energy (55 °C, 2.6 meV) is supplied during the TCM treatment. Using an HKUST-1-polyvinylidene fluoride (PVDF) mixed matrix (MM), we also demonstrate that this chemical activation strategy is a safe way to activate thermally deformable MOF-polymer mixed matrices.

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 Cu(2+) 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.

Ionic polymers that possess ion-exchangeable sites have been shown to be a greatly useful platform to fabricate mixed matrices (MMs) where metal–organic frameworks (MOFs) can be in situ synthesized, although the in situ synthesis of MOF has been rarely studied. In this study, alginate (ALG), an anionic green polymer that possesses metal-ion-exchangeable sites, is employed as a platform of MMs for the in situ synthesis of iconic MOFs, HKUST-1, and MOF-74(Zn). We demonstrate for the first time that the sequential order of supplying MOF ingredients (metal ion and deprotonated ligand) into the alginate matrix leads to substantially different results because of a difference in the diffusion of the MOF components. For the examples examined, whereas the infusion of BTC3– ligand into Cu2+-exchanged ALG engendered the eggshell-shaped HKUST-1 layers on the surface of MM spheres, the infusion of Cu2+ ions into BTC3–-included alginate engendered the high dispersivity and junction contact of HKUST-1 crystals in the al...

A primitive version of a ruthenium complex [Ru(bpy)3(2+)] was employed for the first time as a new conceptual "single-component redox shuttle" for dye-sensitized solar cells. This single shuttle led to a large enhancement of the open-circuit photovoltage (VOC) to ∼940 mV relative to that of conventional iodine-based shuttle and greatly increased the efficiency of the solar-to-electric energy conversion at lower illumination levels by a factor of ca. 5.6.

The activation of open coordination sites (OCSs) in metal-organic frameworks (MOFs), i.e., the removal of solvent molecules coordinated at the OCSs, is an essential step that is required prior to the use of MOFs in potential applications such as gas chemisorption, separation, and catalysis because OCSs often serve as key sites in these applications. Recently, we developed a "chemical activation" method involving dichloromethane (DCM) treatment at room temperature, which is considered to be a promising alternative to conventional thermal activation (TA), because it does not require the application of external thermal energy, thereby preserving the structural integrity of the MOFs. However, strongly coordinating solvents such as N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), and dimethyl sulfoxide (DMSO) are difficult to remove solely with the DCM treatment. In this report, we demonstrate a multiple coordination exchange (CE) process executed initially with acetonitrile (MeCN), methanol (MeOH), or ethanol (EtOH) and subsequently with DCM to achieve the complete activation of OCSs that possess strong extracoordination. Thus, this process can serve as an effective "chemical route" to activation at room temperature that does not require applying heat. To the best of our knowledge, no previous study has demonstrated the activation of OCSs using this multiple CE process, although MeOH and/or DCM has been popularly used in pretreatment steps prior to the TA process. Using MOF-74(Ni), we demonstrate that this multiple CE process can safely activate a thermally unstable MOF without inflicting structural damage. Furthermore, on the basis of in situ

The fabrication of metal–organic framework (MOF) films on conducting substrates has demonstrated great potential in applications such as electronic conduction and sensing. For these applications, direct contact of the film to the conducting substrate without a self-assembled monolayer (SAM) is a desired step that must be achieved prior to the use of MOF films. In this report, we propose an in situ strategy for the rapid one-step conversion of Cu metal into HKUST-1 films on conducting Cu substrates. The Cu substrate acts both as a conducting substrate and a source of Cu2+ ions during the synthesis of HKUST-1. This synthesis is possible because of the simultaneous reaction of an oxidizing agent and a deprotonating agent, in which the former agent dissolves the metal substrate to form Cu2+ ions while the latter agent deprotonates the ligand. Using this strategy, the HKUST-1 film could not only be rapidly synthesized within 5 min but also be directly attached to the Cu substrate. Based on microscopic studies,...

Dye-sensitized solar cells, especially those comprising molecular chromophores and inorganic titania, have shown promise as an alternative to silicon for photovoltaic light-to-electrical energy conversion. Co-sensitization (the use of two or more chromophores having complementary absorption spectra) has attracted attention as a method for harvesting photons over a broad spectral range. If implemented successfully, then cosensitization can substantially enhance photocurrent densities and light-to-electrical energy conversion efficiencies. In only a few cases, however, have significant overall improvements been obtained. In most other cases, inefficiencies arise due to unconstructive energy or charge transfer between chromophores or, as we show here, because of modulation of charge-recombination behavior. Spatial isolation of differing chromophores offers a solution. We report a new and versatile method for fabricating two-color photoanodes featuring spatially isolated chromophore types that are selectively positioned in desired zones. Exploiting this methodology, we find that photocurrent densities depend on both the relative and absolute positions of chromophores and on "local" effective electron collection lengths. One version of the two-color photoanode, based on an organic push-pull dye together with a porphyrin dye, yielded high photocurrent densities (J(SC) = 14.6 mA cm(-2)) and double the efficiency of randomly mixed dyes, once the dyes were optimally positioned with respect to each other. We believe that the organizational rules and fabrication strategy will prove transferrable, thereby advancing understanding of panchromatic sensitization as well as yielding higher efficiency devices.

Iron(III)oxide in the form of hematite is, in many respects, an attractive material for the photocatalytic production of molecular oxygen from water. Especially over the past six years, several developments have advanced the performance of water oxidation cells based on this material. Nevertheless, the best versions of these photoelectrodes produce only about a fifth of the maximum photocurrent (and dioxygen) theoretically obtainable, while operating at photovoltages also well short of the theoretical maximum. Here we describe the factors limiting the performance of hematite as a photo-catalyst and outline approaches that have been, or might be, tried to overcome them. These factors include low hole mobility, bulk charge recombination, surface charge recombination, slow water oxidation kinetics, and poor light absorption. Whether hematite will soon become a practical photo-catalyst for water oxidation is uncertain. But, the schemes developed and the lessons learned will likely prove transferrable to other candidate photocatalyst materials.

A doubly coaxial photoanode architecture based on templated SiO(2) aerogels was fabricated on transparent conducting oxides for use in dye-sensitized solar cells (DSSCs). These templates were coated with ZnO via atomic layer deposition (ALD) to yield an electronically interconnected, low-density, high-surface-area, semiconductor framework. Addition of a thin conformal layer of a second metal oxide (alumina, zirconia, or titania) via ALD was found to suppress the dissolution of ZnO that otherwise occurs when it is soaked in alcohol solutions containing acidic dyes used for sensitization or in acetonitrile solutions containing a pyridine derivative and the iodide/tri-iodide (I(-)/I(-)(3)) redox shuttle. Electron transport in SiO(2)-ZnO-TiO(2) photoelectrodes was found to be nearly 2 orders of magnitude faster than in SiO(2)-TiO(2) structures, implying that the interior ZnO sheath serves as the primary electron conduit. In contrast, rates of electron interception by the oxidized form of the redox shuttle were observed to decrease when a TiO(2) shell was added to SiO(2)-ZnO, with the decreases becoming more significant as the thickness of the titania shell increases. These effects lead to improvements in efficiency for DSSCs that utilize I(-)/I(-)(3), but much larger improvements for DSSCs utilizing ferrocene/ferrocenium, a notoriously fast redox shuttle. For the former, overall energy conversion efficiencies maximize at 4.0%. From a variety of experiments, the primary factor limiting aerogel-based DSSC performance is light loss due to scattering. Nevertheless, variants of the doubly coaxial structure may prove useful in devising DSSCs that can achieve excellent energy conversion efficiencies even with fast redox shuttles.

Localized surface plasmon resonance (LSPR) by silver nanoparticles that are photochemically incorporated into an electrode-supported TiO(2) nanoparticulate framework enhances the extinction of a subsequently adsorbed dye (the ruthenium-containing molecule, N719). The enhancement arises from both an increase in the dye's effective absorption cross section and a modest increase in the framework surface area. Deployment of the silver-modified assembly as a photoanode in dye-sensitized solar cells leads to light-to-electrical energy conversion with an overall efficiency of 8.9%. This represents a 25% improvement over the performance of otherwise identical solar cells lacking corrosion-protected silver nanoparticles. As one would expect based on increased dye loading and electromagnetic field enhanced (LSPR-enhanced) absorption, the improvement is manifested chiefly as an increase in photocurrent density ascribable to improved light harvesting.

Ethanol-soluble amphiphilic TiO(2) nanoparticles (NPs) of average diameter ∼9 nm were synthesized, and an α-terpineol-based TiO(2) 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 TiO(2) paste.

A series of hydrocarbon (HC)-coated cubic zeolite microcrystals (1.7 microm) was prepared. The HCs were n-octyl, n-dodecyl, methyl n-undecanoate, n-octadecyl, and n-heptadecafluorodecyl. The measured water contact angles (theta) of the corresponding HC-coated glass plates were 64, 77, 82, 102, and 105 degrees, respectively, indicating that the hydrophobicity of the surface-tethered hydrophobic chain (HC) increased in the above order. The HC-coated zeolite microcrystals readily formed closely packed monolayers at the air-water interface through interdigitation of surface-tethered HCs, and on glass plates after transferring onto glass plates by dip coating. Interestingly, while the mode of networking was face-to-face (FTF) contacting with n-octyl or n-dodecyl (thetaor =77 degrees) as HC, it changed to edge-to-edge (ETE) contacting mode with n-octadecyl or n-heptadecafluorodecyl (thetaor = 102 degrees) as HC. With methyl n-undecanoate (theta = 82 degrees) as HC, both modes appeared in the monolayers, with about equal populations. The resulting monolayers of cubic zeolite microcrystals with their three-fold axes oriented perpendicular to substrates would be useful for application of the zeolite monolayers for advanced materials.

Heating a gel consisting of briefly hydrolyzed tetraethyl orthosilicate (TEOS), 2–5-nm sized anatase, H2SO4, NaOH, KF, and H2 Oi n the mole ratio of 5.5:1:2.2:8.4:1.43:350 at 200 C for 7 h leads to production of ETS-10 crystals in fairly uniform size (� 500 nm) and shape having well-developed smooth facets in the truncated tetragonal bipyramidal structure. Characterization of the crystals revealed that the titanate ðTiO 2� 3 Þ quantum wires are well-preserved within the produced crystals. The required reaction period under our reaction condition (7 h) is much shorter than under the previously reported conditions which use Degussa P25 (a mixture of � 25 nm sized anatase and rutile) as the Ti source (>42 h at 200 C). The marked increase in crystallization rate and uniformity of size and shape is attributed to the use of very small anatase nanoparticles and briefly hydrolyzed tetraethyl orthosilicate (TEOS) as the Ti and Si sources, respectively. This report also demonstrates for the first time that TEOS can be used as the Si source. 2008 Elsevier Inc. All rights reserved.

When dry Cd 2+ -exchanged zeolites Y are exposed to dry H2S under a rigorously anhydrous condition, CdS quantum dots (QDs) are formed in the supercages of zeolite-Y regardless of the loading levels of CdS from 0.01% to 32% and regardless of the Si/Al ratio of zeolite-Y between 1.8 and 2.5. The absorptions with the maximums (Imax) e 290 nm are assigned as those arising from isolated CdS QDs with the sizes smaller than or equal to the size of a supercage (1.3 nm); the absorptions with Imax between 290 and 380 nm are assigned as those arising from interconnected CdS QDs that were formed by the interconnection of isolated CdS QDs through the supercage windows; and the absorptions with Imax > 400 nm are assigned as those arising from mesosized (3-10 nm) CdS QDs residing in or on the surfaces of amorphous aluminosilicate. The H + ions alone, which are generated during the formation of CdS, do not destruct the zeolite-Y framework causing the formation of amorphous aluminosilicate. Instead, the water-induced agglomeration of isolated and interconnected CdS QDs to mesosized CdS QDs in the presence of H + ions leads to the destruction of the zeolite-Y framework. The size of the interconnected CdS QD which is formed by moisture adsorption increases as the loaded amount of CdS increases for a given zeolite and as the size of the zeolite host increases. The presence of a tetraethylammonium ion in each supercage not only gives rise to the formation of very small QDs within zeolites Y but also prevents the zeolite framework from destruction.

Atoms, molecules, enzymes, proteins, DNAs, RNAs, nanoparticles, microparticles, tiles, and bricks are some of the most commonly encountered building blocks in chemistry and architecture. These building blocks can be grouped into subnanometer (atoms), nanometer (molecules, enzymes, proteins, DNAs, RNAs, and nanoparticles), micrometer (microparticles), and millimeter-to-centimeter (tiles and bricks) building blocks based on their sizes. One of the important applications of building blocks is to organize them as monolayers on various substrates. Selfassembly has been the method of choice for the monolayer assembly of nanometer and micrometer building blocks on substrates, whereas direct attachment of building blocks with the hands (referred to as “direct attachment” hereafter) on adhesive-coated substrates is the method for the monolayer assembly of millimeter-to-centimeter building blocks on substrates (floors and walls). Thus, the method for monolayer attachment of building blocks on substrates has to switch from self-assembly to direct attachment at some stage as the size of the building block increases. But what is the upper size limit for self-assembly?What is the lower size limit for direct attachment? At what size regime do both selfassembly and direct attachment work simultaneously for monolayer assembly? In the overlapping region, which method is better in terms of quality of the monolayer? Herein, we report that the upper size limit for selfassembly is 3 mm, the lower size limit for direct attachment is 0.5 mm, and direct attachment is superior to self-assembly in the overlapping region ( 0.5–3 mm) with respect to rate, degree of close packing, uniform orientation of the assembled microcrystals, substrate area, and ecological considerations. We used zeolite microcrystals as model system because they can be produced in fairly uniform sizes and shapes, and their monolayers can be applied as precursors for molecular sieve membranes, low-dielectric materials, supramolecular energy-transfer systems, nonlinear optical films, anisotropic photoluminescent films, and other advanced materials. Silicalite-1 and ETS-10 (see the Supporting Information) crystals were used in this study. In the case of silicalite-1, crystals with four different sizes were employed. The average sizes and volumes [a:b: c (volume)] were: 0.3 : 0.1 : 0.6 (0.02), 1.3 : 0.5 : 1.7 (1.11), 2.5 : 1.2 : 4.1 (12.3), and 4.6 : 1.5 : 11 mm (75.9 mm). In the case of ETS-10, only crystals with an average size of 12 : 12: 7 mm (1008 mm) were used. The volume ratio for these crystals was 1:56:615:3795:50400. Glass plates with two different sizes, 18 : 18 and 150: 150 mm, were used as the substrates. Among various tested types of bonding between microcrystals and substrates, we found that ionic bonding and hydrogen bonding (Figure 1) were most effective for the monolayer assembly of microcrystals by direct attachment. The ionic bonding was induced between trimethylpropylam

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.

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.

Given that energy (exciton) migration in natural photosynthesis primarily occurs in highly ordered porphyrin-like pigments (chlorophylls), equally highly ordered porphyrin-based metal-organic frameworks (MOFs) might be expected to exhibit similar behavior, thereby facilitating antenna-like light-harvesting and positioning such materials for use in solar energy conversion schemes. Herein, we report the first example of directional, long-distance energy migration within a MOF. Two MOFs, namely F-MOF and DA-MOF that are composed of two Zn(II) porphyrin struts [5,15-dipyridyl-10,20-bis(pentafluorophenyl)porphinato]zinc(II) and [5,15-bis[4-(pyridyl)ethynyl]-10,20-diphenylporphinato]zinc(II), respectively, were investigated. From fluorescence quenching experiments and theoretical calculations, we find that the photogenerated exciton migrates over a net distance of up to ~45 porphyrin struts within its lifetime in DA-MOF (but only ~3 in F-MOF), with a high anisotropy along a specific direction. The remarkably efficient exciton migration in DA-MOF is attributed to enhanced π-conjugation through the addition of two acetylene moieties in the porphyrin molecule, which leads to greater Q-band absorption intensity and much faster exciton-hopping (energy transfer between adjacent porphyrin struts). The long distance and directional energy migration in DA-MOF suggests promising applications of this compound or related compounds in solar energy conversion schemes as an efficient light-harvesting and energy-transport component.

A major loss mechanism in dye-sensitized solar cells (DSCs) is recombination at the TiO(2)/electrolyte interface. Here we report a method to reduce greatly this loss mechanism. We deposit insulating and transparent silica (SiO(2)) onto the open areas of a nanoparticulate TiO(2) surface while avoiding any deposition of SiO(2) over or under the organic dye molecules. The SiO(2) coating covers the highly convoluted surface of the TiO(2) conformally and with a uniform thickness throughout the thousands of layers of nanoparticles. DSCs incorporating these selective and self-aligned SiO(2) layers achieved a 36% increase in relative efficiency versus control uncoated cells.

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.

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 Na(2)S (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 S(2-) 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.

ETS-10 is a highly intriguing microporous titanosilicate that has shown an excellent propensity for the selective removal of harmful heavy-metal ions, the potential to work as an effective catalyst for various reactions, and that can be used as a material for solar cells. Such important features arise from the TiO3 2 quantum wires with the diameter (d) of approximately 0.67 nm running along the [110] and [110] directions in the crystal (Figure 1). The TiO3 2 quantum wire is a one-dimensional (1D) extreme of three-dimensional (3D) bulk titanates, which are widely used in industry as, for example, capacitors. It also exhibits an interesting 1D quantum confinement effect. The TiO3 2 quantum wires are not expected to be connected all the way from one face to the opposite face of a crystal owing to the large number of randomly distributed defects. Now the questions are what is the average length of the wires, to what degree do the lengths vary (how does the length homogeneity vary), how does the local density of the quantum wire vary from one region to another within a crystal, do they vary randomly or in accordance with a certain pattern? Answers to the above questions will be highly useful for understanding the mechanism of ETS-10 formation and growth, the refinement of its structure, improvements of its catalytic activities, and its future applications. However, there have been no methods to gain such information. The TiO3 2 quantum wire in ETS-10 gives a strong Raman shift band between 724 and 840 cm , arising from a longitudinal vibrational mode of the -Ti-O-Ti-Ochain. Its frequency at the band maximum (nmax), its bandwidth (full width at half maximum, fwhm), and intensity (I) reflect the relative average length, length homogeneity, and density of the quantum wire, respectively. The Raman band frequency decreases as the length increases, owing to the increase in the reduced mass of the quantum wire. The smallest frequency ever observed is 724 cm . Bandwidths between 23 and 120 cm 1 have been observed, and the bandwidth decreases as the length uniformity increases. The intensity increases as the number of the TiO3 2 quantum wire increases. Accordingly, the frequency, bandwidth, and intensity have served as the three important criteria for comparison of the relative average lengths, relative average length uniformities, and relative average densities of the TiO3 2 quantum wires in the ETS-10 crystals. This information indicates that we can also apply the same principle to obtain their distribution pattern within an ETS-10 crystal if we can obtain a matrix of Raman spectra measured from a large number of artificially divided very small sections of a crystal. Furthermore, the obtained data would be more informative if we can obtain a map of these three data sets for the TiO3 2 quantum wires running along the [110] and [110] directions, respectively. We now report that laser scanning confocal polarized micro-Raman (LSC-PMR) spectroscopy is a highly useful tool for the above purpose and the novel fact that the TiO3 2 quantum wires are not evenly distributed within ETS-10 crystals but distributed in a symmetrical manner according to an interesting pattern. Figure 1. a) Illustrations of a typical morphology (truncated bipyramid) of an ETS-10 crystal and three-dimensional networks of SiO2 channels (cyan) and TiO3 2 quantum wires (red) in the case of polymorph B and b) a single TiO3 2 quantum wire.

A series of isostructural, noncatenated, zinc-pillared-paddlewheel metal−organic framework materials has been synthesized from 1,2,4,5-tetrakis(carboxyphenyl)benzene and trans-1,2-dipyridylethene struts. Substantial kinetic selectivity in the adsorption of propene over propane can be observed, depending on the pore apertures and the rectangular-plate morphology of the crystals.

Treatment of dry M(2+)-exchanged zeolite Y (M(2+) = Cd(2+), Mn(2+), and Zn(2+)) with dry H(2)S leads to the formation of isolated, ligand-free, subnanometer MS quantum dots (QDs) in zeolite Y with no framework destruction and with H(+) as the countercation. Treatment of the dry H(+)/CdS QD-incorporating zeolites Y with dry NH(3) leads to the neutralization of H(+) to NH(4)(+). During this process, the framework structure remains intact. However, small amounts of interconnected CdS QDs were formed within the zeolite Y by coalition of isolated CdS QDs at the windows. With H(+) as the countercation, isolated CdS QDs rapidly aggregate into interconnected and mesosized QDs with accompanying destruction of ∼50% of sodalite cages leading to the framework rupture. With NH(4)(+) as the countercation, however, the isolated QDs and zeolite framework remain intact even after exposure to the moist air for 4 weeks. Interestingly, the interconnected QDs that were formed during neutralization of H(+) with NH(3) disintegrate into isolated QDs in the air. Similar results were obtained from ZnS and MnS QDs generated in zeolite Y. Thus, ligand-free, naked, subnanometer QDs can now be safely preserved within zeolite pores under the ambient conditions for long periods of time. This finding will expedite the generation and dispersion of various QDs in zeolite pores, their physicochemical studies, and applications.

The titanate quantum wires in ETS-10 crystals remain intact during ion exchange of the pristine cations (Na(+)(0.47) + K(+)(0.53)) with M(n+) ions (M(n+) = Na(+), K(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Pb(2+), Cd(2+), Zn(2+)) and during reverse exchange of the newly exchanged cations with Na(+). The binding energies of O(1s) and Ti(2p) decrease as the electronegativity of the cation decreases, and they are inversely proportional to the negative partial charge of the framework oxygen [-delta(O(f))]. At least five different oxygen species were identified, and their binding energies (526.1-531.9 eV) indicate that the titanate-forming oxides are much more basic than those of aluminosilicate zeolites (530.2-533.3 eV), which explains the vulnerability of the quantum wire to acids and oxidants. The chemical shifts of the five NMR-spectroscopically nonequivalent Si sites, delta(I(A)), delta(I(B)), delta(II(A)), delta(II(B)), and delta(III), shift downfield as -delta(O(f)) increases, with slopes of 2.5, 18.6, 133.5, 216.3, and 93.8 ppm/[-delta(O(f))], respectively. The nonuniform responses of the chemical shifts to -delta(O(f)) arise from the phenomenon that the cations in the 12-membered-ring channels shift to the interiors of the cages surrounded by four seven-membered-ring windows. On the basis of the above, we assign delta(I(A)), delta(I(B)), delta(II(A)), and delta(II(B)) to the chemical shifts arising from Si(12,12), Si(12,7), Si(7,12), and Si(7,7) atoms, respectively. The frequency of the longitudinal stretching vibration of the titanate quantum wire increases linearly and the bandwidth decreases nonlinearly with increasing -delta(O(f)), indicating that the titanate quantum wire resembles a metallic carbon nanotube. As the degree of hydration increases, the vibrational frequency shifts linearly to higher frequencies while the bandwidth decreases. We identified another normal mode of vibration of the quantum wire, which vibrates in the region of 274-280 cm(-1). In the dehydrated state, the band-gap energy and the first absorption maximum shift to lower energies as -delta(O(f)) increases, indicating the oxide-to-titanium(IV) charge-transfer nature of the transitions.

We measured coherent x‐ray diffraction (CXD), an emerging technique to obtain three‐dimensional internal and external images of crystals, on ZSM‐5 zeolite microcrystals to get internal density distribution and to map deformation field of strain. The experiments were performed at the beamline 34‐ID‐C in Advanced Photon Source at Argonne National Laboratory in the US. The CXD patterns of ZSM‐5 zeolite microcrystals with sizes of 2 μm by monochromatic coherent x‐rays with energy of 9 keV were obtained under continuously surrounding and Bragg conditions as a function of temperature. The oversampled diffraction patterns are inverted to obtain three‐dimensional images of the shapes and internal strain fields of zeolite microcrystals using phase retrieval algorithms of error reduction and a hybrid input‐output method. The internal density and strain distribution as a function of temperature are discussed.

Metal oxides are widely used in industry and academia. As their electron-acceptor or acidic strengths play vital roles in their applications, there needs to be a general scale that can quantitatively compare their relative acidic strengths. Conventionally, calorimetric heat measurements during adsorption of probe molecules, infrared spectroscopic analyses of adsorbed bases or acids, application of indicator dyes, and temperature-programmed desorption of the pre-adsorbed bases are standard methods for the analyses of their acidic strengths. However, these methods are not suitable for a quantitative comparison. Thus, unlike metal ions in solution, no such scales have been available for metal oxides. One of the important types of interaction between adsorbates and metal oxides is the formation of coordinate covalent bonding between adsorbates and the surface metal ions. For instance, in the case of TiO2, those compounds that have enediol, carboxylate, and nitrile groups have been shown to form coordinate covalent bonding with the surface Ti ions. In this type of interaction, the adsorbateto-metal charge-transfer interaction is often the lowestenergy electronic transition. However, in the case of alizarin (Figure 1a, inset) on TiO2, a theoretical study has suggested that the intramolecular charge-transfer (IMCT) band from the catechol moiety to the entire ring system is the lowestenergy transition. Electronegativity (EN) is one of the most important fundamental properties of an atom, which represents “the power of an atom in a compound to attract electrons to itself”. Among various EN scales that have been developed, Sanderson s scale and the associated EN equalization principle are successful in calculating the bond energies of various compounds , elucidating the acidic and basic properties of zeolites, and establishing the relationship between the reactivity and the composition of the zeolite that served as the guideline for the preparation of optimum zeolite catalysts. These methods have also been used for various other purposes. However, owing to a lack of experimental data, Sanderson s EN scale has not been extended to lanthanides (Ln) during the last five decades, despite the fact that lanthanide-containing compounds are widely used. Herein, we report that the IMCT transition of alizarin is still the lowest-energy transition when it is adsorbed on various metal oxides and sulfides, regardless of the nature of the metal ion. The charge-transfer transition serves as a highly sensitive and accurate probe for the quantitative comparison of the acidic strengths of the metal oxides and sulfides. We also report the factors that govern the surface acidity, which allows us to assign for the first time the important Sanderson s EN values of Ln ions (SLn3+) and Ce . To experimentally verify the IMCT nature of the lowestenergy electronic transition from the catechol moiety to the entire ring, we also synthesized 4-methoxyalizarin (Figure 1a, inset; Supporting Information, SI-1). The UV/Vis spectra of the two compounds (Figure 1a) show that the lowest-energy transition (2.856 eV) shifts to the lower energy region (2.617 eV) upon introducing a methoxy group at the 4 position; that is, upon increasing the donor strength of the catechol moiety, which verifies the IMCT nature of the transition. The IMCT bands of alizarin and 4-methoxyalizarin adsorbed on various metal oxides and sulfides are shown in Figure 1b, with the order of energy increasing from bottom to top. The IMCT bands appear at 2.322–2.713 eV for alizarin and 2.288–2.536 eV for 4-methoxyalizarin (Supporting Information, Table SI-2). The red-shift from alizarin to 4-methoxyalizarin also suggests that the lowest-energy transition of the adsorbed alizarin is IMCT. Furthermore, the IMCT bands of alizarin and 4-methoxyalizarin are red-shifted when they are adsorbed onto oxides and sulfides. Such coordination-induced redshifts were also observed in solution. The IMCT band of alizarin (2.398 eV) red-shifts upon coordinating to Mg in ethanol relative to its uncoordinated state (2.856 eV; Supporting Information, Figure SI-3). We attribute the red shift to a decrease in the degree of electron withdrawal of the two phenoxide groups as a result of the replacement of the two strongly electron-withdrawing protons by a less strongly electron-withdrawing metal cation (Figure 1d, inset). In this context, the gradual blue shift of the IMCT band of the adsorbed alizarin and 4-methoxyalizarin on going from MgO to Ta2O5 is attributed to the increase in the degree of electron withdrawal from the two phenoxide ligands to a surface metal ion in the following order: MgO

We prepared CdS quantum dots (QDs) within zeolite Y by exposing rigorously dried Cd2+-exchanged zeolite Y to H2S under the dry condition. Contrary to the previous reports [ [1] , [2] ], our results unambiguously showed that the generated CdS QDs exist within the supercages of zeolite Y regardless of the loaded amount. We also found that while the moisture adsorption into the dry CdS-QD-incorporating zeolite Y leads to the formation of large pseudo spherical QDs with the diameter of 3-7 nm within the host by breaking the framework, coating of the surface of the dry CdS-QD-incorporating zeolite Y with octadecyltrimethoxysilane (ODM) leads to direct interconnection of the initially formed intrasupercage QDs into ‘interconnected QDs’ without breaking the framework. Interestingly, the degree of CdS QD interconnection increases with increasing the size of the zeolite for a given loaded amount of CdS.

Various MX (M = Cd, Zn, and Mn, X = S and Se) semiconductor quantum dots (QDs) were prepared in zeolite Y. While the QDs are readily expelled from zeolite interior upon exposure of the MX QD-incorporating zeolite Y ([MX]-Y) to the ambient atmosphere due to moisture adsorption, they remain tightly confined within zeolites even after exposure to the moist atmosphere for several weeks when the surfaces were silylated with various silylating agents. This methodology will facilitate the characterization of the zeolite-encapsulated QDs and the application of QD-incorporating zeolites.