Jeong Kuk Shon

Systematic phase control of periodic mesoporous organosilicas using Gemini surfactants

Highly ordered periodic mesoporous organosilica (PMO) materials with various mesostructures, including lamellar, bicontinuous cubic Ia3d, 2D hexagonal (P6mm), 3D hexagonal (P63/mmc) and cubic Pm3n, have been synthesized using Gemini surfactants with general formulas of [CnH2n+1N(CH3)2(CH2)sN (CH3)2CnH2n+1]Br2 (n = 6–18 and s = 3–12, Cn-s-n). The nature of the Gemini surfactant such as alkyl chain length (n) and spacer length (s), and the synthetic conditions such as reaction temperatures and molar compositions are controlling parameters for desired mesostructures. The PMO materials, synthesized at room temperature from Cn-6-n, exhibit phase transition from lamellar to bicontinuous cubic Ia3d, 2D hexagonal, 3D hexagonal and cubic Pm3n as the chain length decreases, whereas only the lamellar and 2D hexagonal PMO materials with different lattice parameters depending on the chain length are obtained at high reaction temperature (373 K). The Cn-8-n and Cn-10-n surfactants also yield 2D hexagonal PMO material in a very wide range of synthetic condition at 373 K. The PMO materials with various mesostructures thus obtained exhibit high BET surface areas in the range of 900–1500 m2 g−1 and total pore volumes of about 0.5–1.4 cm3 g−1.

Nano-propping effect of residual silicas on reversible lithium storage over highly ordered mesoporous SnO2 materials

Highly ordered mesoporous SnO2 materials with residual silica species were successfully synthesized from a mesoporous silica template (SBA-15) via nano-replication and simple etching processes. A tin precursor, SnCl2·2H2O, was infiltrated spontaneously within the mesopores of the silica templates by melting the precursor at 353 K without using a solvent. After the heat-treatment of composite materials at 973 K under static air conditions, the controlled removal of silica templates using NaOH or HF solutions with different concentrations results in the successful preparation of mesoporous SnO2 materials, where the amounts of residual silica species are in the range 0.9–17.4 wt%. The residual silica species induce a nano-propping effect enabling the mesoporous SnO2 material (containing 6.0 wt% of silica species) to remain stable up to 973 K without any significant structural collapse. More importantly, the optimum amount of residual silica species (3.9–6.0 wt%) results in a dramatic reduction in capacity fading after prolonged charging–discharging cycles in Li-ion battery. The mesoporous SnO2 material with 3.9 wt% of silica species still exhibits a large capacity (about 600 mAh g−1) after the 30th cycle, which is probably because the residual silica species act as a physical barrier to suppress the aggregation of Sn clusters formed in the mesoporous SnO2 materials during the reversible lithium storage.

Discovery of abnormal lithium-storage sites in molybdenum dioxide electrodes

Developing electrode materials with high-energy densities is important for the development of lithium-ion batteries. Here, we demonstrate a mesoporous molybdenum dioxide material with abnormal lithium-storage sites, which exhibits a discharge capacity of 1,814 mAh g−1 for the first cycle, more than twice its theoretical value, and maintains its initial capacity after 50 cycles. Contrary to previous reports, we find that a mechanism for the high and reversible lithium-storage capacity of the mesoporous molybdenum dioxide electrode is not based on a conversion reaction. Insight into the electrochemical results, obtained by in situ X-ray absorption, scanning transmission electron microscopy analysis combined with electron energy loss spectroscopy and computational modelling indicates that the nanoscale pore engineering of this transition metal oxide enables an unexpected electrochemical mass storage reaction mechanism, and may provide a strategy for the design of cation storage materials for battery systems.

Mesoporous transition metal dichalcogenide ME2 (M = Mo, W; E = S, Se) with 2-D layered crystallinity as anode materials for lithium ion batteries

Mesoporous transition metal dichalcogenides (TMDCs), composed of group VI metals (Mo and W) and chalcogens (S and Se), with 2-D layered crystalline frameworks and 3-D pore structures were successfully prepared via a melting-infiltration assisted nano-replication method using a mesoporous template KIT-6 with cubic Ia3d symmetry. Combined analysis using X-ray diffraction, N2 adsorption–desorption and electron microscopy indicated that the mesoporous TMDCs, thus obtained, exhibited high surface areas (87–105 m2 g−1), large pore volumes (0.21–0.25 cm3 g−1) and well-defined mesopores about 20 nm in diameters. The mesoporous TMDCs showed outstanding rate capabilities up to 2C as well as high reversible lithium storage capacities (MoS2 710 mA h g−1; MoSe2 744 mA h g−1; WS2 501 mA h g−1; WSe2 427 mA h g−1) without a remarkable fading of capacity.

SYNTHESIS OF MESOPOROUS IRON OXIDE NANOPARTICLES FROM MESOPOROUS SILICA TEMPLATE VIA NANO-REPLICATION

Highly ordered mesoporous iron oxide (α-Fe2O3) material has been successfully obtained from mesoporous silica template, KIT-6 (3-D Cubic Ia3d symmetry), through nano-replication method. The mesoporous α-Fe2O3 material thus obtained exhibits well-defined mesopores (2.7 nm in diameter), high surface area (148 m2/g), high pore volume (0.47 cm3/g) and crystalline frameworks. The morphology of the mesoporous α-Fe2O3 material is very uniform in spherical shape of which the average particle size is about 100 nm in diameter.

Effect of acid catalysts on carbonization temperatures for ordered mesoporous carbon materials

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Highly Ordered Mesoporous Antimony-Doped SnO2 Materials for Lithium-ion Battery

Highly ordered mesoporous antimony-doped tin oxide (ATO) materials, containing different amount of antimony in the range of 0–50mol%, are prepared via a nanoreplication method using a mesoporous silica template. The mesoporous ATO materials thus obtained exhibit high electrical conductivity, high reversible capacity, superior cycle stability and good rate capability as anode materials for lithium-ion batteries, compared to those of pure mesoporous tin oxide. Amongst the ATO materials in this work, the mesoporous ATO material with 10mol% of antimony has highest discharge capacity of 1940mAhg-1 (charge capacity of 1049) at the 1st cycle, best cycle performance (716mAhg-1 at 100th cycle) and excellent rate capability, which are probably due to the enhanced electrical conductivity as well as reduced crystalline size.

Nano-replication to mesoporous metal oxides using mesoporous silica as template

Mesoporous materials constructed with different framework compositions such as iron oxides and manganese oxides, etc. have been successfully obtained by the impregnation with desired metal precursors into the bicontinuous cubic Ia3d mesoporous silica, crystallization to metal oxides at desired temperature and subsequent silica removal using NaOH aqueous solution.

Preparation and Stabilization of Chitosan-Lipase Composite within Mesoporous Silica Material

To improve lipase activity and make the particulate carrier for practical application, lipase was conjugated to chitosan(Mwavg=80,000) by immine reaction. The lipase activity of conjugate was 93% of its initial activity at room temperature for 7 months, whereas the intact lipase activity decreased to 40%. And then, lipase-chitosan conjugate was intercalated within porous silica. The composite was characterized by X-ray diffraction, scanning electron microscopy, thermo gravimetric analysis. The Pore size was regulated in the range of 5~15nm. The maximum enzyme activity of lipase-chitosan conjugate needs the structure with 15nm pore of mesoporous silica. The resultant composite was found to have the free flowing property and keep up inner lipase activity.

Fixation of Carbon Nanotube Within Mesoporous Titania Particles

Carbon nanotube (CNT) and mesoporous TiO2 composite (CNT/meso-TiO2) was synthesized by a nanocasting method using CNT-implanted mesoporous silica material as the template. The CNT was successfully incorporated within a mesoporous TiO2 particle, and the CNT/meso-TiO2 composite obtained exhibits a high surface area and well-established mesoporosity. Moreover, the composite material exhibits much lower electric resistance than those of mesoporous TiO2 only and physical mixture of CNT and mesoporous TiO2, which probably due to the large interface area and strong junction between the implanted CNT and TiO2 framework in the composite.