Nak Cheon Jeong

Daegu Gyeongbuk Institute of Science and Technology | DGIST · Department of Emerging Materials Science

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 approac...

Hydrogen bonding (H-bonding) 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 their interaction with the wall lining the pores. Herein, we show a crystalline behavior of H-bonded water molecules residing in the nanocages of a paddlewheel...

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. , H 2 O), and they lead to enhanced catalytic efficiency.

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...

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 relaxation of Cu(II)-based paddlewheel metal-organic frameworks (MOFs), HKUST-1 and Cu-MOF-2 with Raman measurement. Irradiation of the Cu-based MOF crys...

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 proceeded to remove coordinating and pore-filling solvents before the use of MOFs for various applications, has be...

Shape control of metal-organic materials in meso- and macroscale has been an important theme due to emerging properties. Especially, chemical etching has been useful to create various forms such as core-shell and hollow crystals in metal-organic frameworks. Here we present a unique chemical etching strategy to create trigonal patterned surfaces in...

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...

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 c-axis of MOF-74 single crystal, highly directional proton conductivity is...

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 separ...

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 met...

Ionic polymers that possess ion-exchangeable sites have been shown to be a greatly useful platform to fabricate mixed matrices (MMs) where metal-organic framework (MOFs) can be in situ synthesized, although the in situ synthesis of MOF has been rarely studied. In this study, alginate, an anionic green polymer that possesses metal ion-exchangeable s...

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 me...

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...

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 o...

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...

Open coordination sites (OCSs) in metal-organic frameworks (MOFs) often function as key factors in the potential applica-tions 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 o...

A primitive version of ruthenium complex [Ru(bpy)32+] 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 and greatly increased the efficiency of solar-to-electric energy conversion at low...

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...

The present invention relates to a method for preparing composites of substrate-molecular sieve, in particular, to a method for preparing a composite of substrate-molecular sieve, which comprises applying a physical pressure to molecular sieve crystals against a substrate to form a chemical bond between the molecular sieve crystal and the substrate...

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 carboxylated functions. The dynamic covalent carbon-oxygen bond, associated with this chemisorptio...

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 o...

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...

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 harvestin...

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...

We have synthesized, characterized, and computationally simulated/validated the behavior of two new metal-organic framework (MOF) materials displaying the highest experimental Brunauer-Emmett-Teller (BET) surface areas of any porous materials reported to date (∼7000 m(2)/g). Key to evacuating the initially solvent-filled materials without pore coll...

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...

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 organ...

HKUST-1, a metal-organic framework (MOF) material containing Cu(II)-paddlewheel-type nodes and 1,3,5-benzenetricarboxylate struts, features accessible Cu(II) sites to which solvent or other desired molecules can be intentionally coordinated. As part of a broader investigation of ionic conductivity in MOFs, we unexpectedly observed substantial proto...

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 s...

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...

Innere Werte: Das Titanosilicat-Molekularsieb ETS-10 enthält TiO32−-Quantendrähte (QWs) unterschiedlicher Länge und lokaler Dichte entlang der [110]- und [10]-Richtung (siehe Bild). Eine Analyse eines Kristalls durch Laser-unterstütztes Raman-mikrospektroskopisches Abrastern zeigt, dass die QWs darin nicht gleichmäßig verteilt sind, sondern ein sym...

We studied temperature dependent internal deformation field distributions in zeolite microcrystals using coherent x-ray diffraction. We measured the coherent x-ray diffraction patterns around (200) and (020) Bragg peaks of the crystals. The three-dimensional real space images were obtained by phasing and inverting the oversampled diffraction patter...

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-tha...

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-pla...

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 neutra...

A pi-extended porphyrin possessing two anchoring groups has been synthesized and successfully applied to dye-sensitized solar cells with a power conversion efficiency of 5.5%, rendering it comparable to the performance of N719-sensitized solar cells under the conditions employed here.

We measured coherent x-ray diffraction (CXD) on zeolite microcrystals in order to gain information on internal density distribution and to learn more about the strain developed during the synthesis and attachment process on the substrate. From the distortion and asymmetry of the diffraction pattern on the (020) Bragg peak, the strain field distribu...

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 hydr...

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 t...

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 Lab...

We measured coherent X-ray diffraction (CXD) on zeolite microcrystals in order to get information on internal density distribution and to map deformation field of stress or strain during the fabrication process. The experiments were performed at the beamline 34-ID-C in Advanced Photon Source and employed monochromatic radiation with x-ray energy of...

Heating a gel consisting of briefly hydrolyzed tetraethyl orthosilicate (TEOS), 2–5-nm sized anatase, H2SO4, NaOH, KF, and H2O in the mole ratio of 5.5:1:2.2:8.4:1.43:350 at 200°C for 7h 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 struc...

We prepared CdS quantum dots (QDs) within zeolite Y by exposing rigorously dried Cd2+-exchangedzeolite 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...

(Figure Presented) Mind the gap! The titanosilicate zeolite ETS-10 contains TiO32- molecular wires (see picture). A reliable method has been developed to synthesize high-quality ETS-10 crystals of various sizes. Measurements on the crystals allow the dependence of the band-gap energy on the length of the TiO32- wires to be elucidated.

When dry Cd 2+ -exchanged zeolites Y are exposed to dry H 2 S 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 (λ max) e 290 nm are as...

When dry Cd2+-exchanged zeolites Y are exposed to dry H 2S 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 (λmax) ≤ 290 nm are assign...

(Figure Presented) 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 s...

Zeolite-intercalated semiconductor quantum dots (QDs) have long been proposed to give very high third-order nonlinear optical (3NLO) responses. However, measurements of their 3NLO responses have not been possible due to the lack of methods to prepare optically transparent QD-incorporating zeolite films supported on optically transparent substrates...

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...