Young-Uk Kwon

Electrochemical Synthesis of CdSe Quantum-Dot Arrays on a Graphene Basal Plane Using Mesoporous Silica Thin-Film Templates

A mesoporous silica film acts as a template and a potential equalizer between the edge/defect sites and the basal plane of a graphene sheet. Using an electrochemical deposition method of CdSe on these graphene sheets covered with a silica film results in CdSe quantum dots that are evenly distributed in regular hexagonal arrays (see figure).

Triply interpenetrating coordination polymers based on paddle-wheel type secondary-building units of M2(CO2R)4: [Ni3(2,6-NDC)3(bipy)1.5], [Co3(2,6-NDC)3(bipy)1.5], and [Co(1,3-BDC)(bipyen)] (2,6-NDC = 2,6-naphthalenedicarboxylate; 1,3-BDC = 1,3-benzenedicarboxylate; bipy = 4,4'-bipyridine; bipyen = trans-1,2-bis(4-pyridyl)ethylene)

Abstract Triply interpenetrating 3-dimensional nickel and cobalt coordination polymers, [M3(2,6-NDC)3(bipy)1.5], were prepared from metal nitrate {M(NO3)2·6H2O}, 2,6-naphthalenedicarboxylic acid (2,6-NDCH2), and 4,4′-bipyridine (bipy) under hydrothermal (M=Ni) or water–benzene hydro(solvo)thermal (M=Co) conditions. Both polymers have the same secondary building units (SBUs) of paddle-wheels of the type [M2(CO2R)4], which are composed of two metals and four di(monodentate) bridging carboxylates. On the other hand, the hydrothermal reaction of Co(NO3)2·6H2O with 1,3-benzenedicarboxylic acid (1,3-BDCH2) and trans-1,2-bis(4-pyridyl)ethylene (bipyen) gave a 2-dimensional polymer [Co(1,3-BDC)(bipyen)]. The structures of all products were determined by X-ray diffraction.

Direct preparation of 1-PSA modified graphene nanosheets by supercritical fluidic exfoliation and its electrochemical properties

In this paper, we report on 1-pyrene sulfonic acid sodium salt (1-PSA) modified graphene nanosheets (imGNS) prepared by a novel one-pot in situ supercritical fluid exfoliation and modification reaction. The 1-PSA molecules on the surface of the graphene layers acted as electron withdrawing groups resulting in an electron transfer from the GNS surface to the 1-PSA molecules. This was confirmed by a red shift of 1572∼1576 cm−1, in the graphitic ‘G’ band of the Raman spectra. This novel approach led to an increase in the yield of mono to double layer graphene sheets (about 60%). The charge–discharge measurement shows improved Li-ion charge–discharge properties of the imGNS with an increase in the concentration of 1-PSA molecules in comparison with starting graphite materials. This report provides a new direction for graphene exfoliation and surface modification for technological applications.

Combination effects of cation and anion of ionic liquids on the cadmium metal-organic frameworks in ionothermal systems.

The effects of cation and/or anion of two groups of ionic liquids ([EMI]X and [PMI]X, where EMI = 1-ethyl-3-methylimidazolium; PMI = 1-propyl-3-methylimidazolium; X = Cl, Br, and I) on the ionothermal reactions between Cd(NO 3) 2.4H 2O and 1,3,5-benzenetricarboxylic acid (H 3BTC) were studied. Three different Cd-BTC metal-organic frameworks, [EMI][Cd2(BTC)Cl2](1), [EMI][Cd(BTC)](2), and [PMI][Cd(BTC)](3), were formed into crystalline phases. 1 was obtained from reactions in [EMI]Cl, while the same reactions with Cl replaced by Br or I produced a known compound 2. The replacement of EMI(+) by PMI(+) produced 3, irrespective of the nature of X.

One-pot synthesis of core–shell-like Pt3Co nanoparticle electrocatalyst with Pt-enriched surface for oxygen reduction reaction in fuel cells

2–3 nm sized Pt3Co nanoparticles (NPs) with Pt-enriched shells on a carbon support were prepared by a one-step ultrasound polyol process on Pt(acac)2 (acac = acetylacetonate) and Co(acac)2. The ultrasound facilitates the conversion of Co(acac)2 and retards the conversion of Pt(acac)2 into NPs, which can be explained with the different vapour pressures of the metal precursors. The Pt-enriched shell structure of the NPs by this method, as opposed to the alloy-like elemental distribution of the NPs synthesized in similar conditions but without ultrasound, was evidenced by transmission electron microscopy, magnetism data, extended X-ray absorption fine structure analyses, and chemical replacement tests of Co with Ru3+. Electrochemical oxygen reduction reaction data of these NPs showed improved performance from the commercial Pt/C with the NPs with Pt-enriched shells showing the highest activity.

The use of phosphine chalcogenides in the preparation of cobalt chalcogenides

Abstract Dicobalt octacarbonyl reacts with TeP n Bu 3 , SeP n Bu 3 or SP n Bu 3 to give solid state cobalt telluride, cobalt selenide and cobalt sulfide, respectively. In each case a cluster compound of the form Co 6 E 8 (P n Bu 3 ) 6 can be isolated from the reaction of the phosphine chalcogenide with cobalt carbonyl, and subsequently carried on to the solid state product. In this sense the Co 6 E 8 clusters are intermediates in the molecules-to-solids processes. In the case of Se, another Co/Se cluster can be isolated: Co 4 Se 2 (CO) 6 (P n Bu 3 ) 4 . This complex also fits into the molecules-to-solids pathway inasmuch as it arises from Co 2 (CO) 8 and SeP n Bu 3 , and it is converted to the Co 6 Se 8 cluster when treated with phosphine selenide. These results show that molecules-to-solids pathways originally uncovered in studying reactions of TePEt 3 can be extended to other trialkylphosphines and other chalcogens.

Characteristics of Pt thin films on the conducting ceramics TiO and Ebonex (Ti4O7) as electrode materials

Abstract Electrochemical properties and morphologies of platinum thin films on the conductive ceramics TiO and Ebonex (Ti4O7) have been examined. While Ebonex is known to be good material for an electrode substrate, the electrodeposition of Pt at the Ebonex surfaces requires high overpotentials, which results in the growth of Pt grains with large holes probably caused by H2 evolution at the electrode surfaces from the electrolyte solution. After scanning a few decades of potential cycles between far positive and negative ranges continuously, the platinum films become more densely packed and spread evenly. TiO shows better characteristics as a substrate for electodeposition of platinum. The electrochemical properties of the Pt-deposited TiO is the same as those of the Pt electrode.

Thylakoids entrapped within porous silica gel: towards living matter able to convert energy

Thylakoids, photosynthetic sub-cellular plant structures, have been entrapped within silica network using the sol-gel process. The photocatalytic splitting of H2O into O2 by these structures has been studied using a Clark cell reactor. The influence of the silica precursor concentration on the chemical, morphological and diffusion properties of the matrix have been investigated and correlated with the enzymatic activity of entrapped thylakoids. Compared to the free thylakoid suspension, the bioactivity of entrapped thylakoids can be extended during several weeks. The addition of stabilizing agents (i.e.glycerol and bovine serum albumin) does not essentially improve the oxygen production. This work clearly demonstrates that through the immobilization of photosynthetic membranes, photocatalytic reactors capable of biomimicking photosynthetic processes, such as harvesting solar energy and splitting water molecules, can easily be targeted.

Mesoporous Titania Thin Film with Highly Ordered and Fully Accessible Vertical Pores and Crystalline Walls

We report the preparation of mesoporous titania thin films with the R

Systematic phase control of periodic mesoporous organosilicas using Gemini surfactants

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