Eun-Bum Cho

SAXS and NMR analysis for the cast solvent effect on sPEEK membrane properties.

The cast solvent effect on the structure and properties of sulfonated poly(ether ether ketone) (sPEEK) was studied. PEEK was sulfonated to have different sulfonation degrees of 65, 70, and 75%, and its membrane was prepared using the two types of solvents, N,N-dimethylacetamide (DMA) and 1-methyl-2-pyrrolidinone (NMP). Ionic cluster size was analyzed using small-angle X-ray scattering (SAXS), and it was correlated with a few essential membrane properties such as water uptake, methanol permeability, proton conductivity, and cell performance in direct methanol fuel cells (DMFCs). Synchrotron SAXS and solid state NMR data revealed the structural difference between the sPEEK membranes prepared using NMP and DMA, regarding the cluster dimensions of 3.22 and 2.70 nm, respectively. Although the water uptake, methanol permeability, and proton conductivity of the membranes prepared with NMP were higher than those with DMA, the overall cell performance was vice versa. The dimensional instability associated with high water swelling as well as high methanol permeability were the main causes for this inferior cell efficiency of NMP cast membranes. This report demonstrates the importance of selection of cast solvent in preparation of SPEEK electrolyte membranes for DMFC application.

Ultrabright fluorescent mesoporous silica nanoparticles.

The first successful approach to synthesizing ultrabright fluorescent mesoporous silica nanoparticles is reported. Fluorescent dye is physically entrapped inside nanochannels of a silica matrix created during templated sol-gel self-assembly. The problem of dye leakage from open channels is solved by incorporation of hydrophobic groups in the silica matrix. This makes the approach compatible with virtually any dye that can withstand the synthesis. The method is demonstrated using the dye Rhodamine 6G. The obtained 40-nm silica particles are about 30 times brighter than 30-nm coated water-soluble quantum dots. The particles are substantially more photostable than the encapsulated organic dye itself.

CO2 Adsorption on Amine-Functionalized Periodic Mesoporous Benzenesilicas

CO2 adsorption was investigated on amine-functionalized mesoporous silica (SBA-15) and periodic mesoporous organosilica (PMO) samples. Hexagonally (p6mm) ordered mesoporous SBA-15 and benzene-PMO (BPMO) samples were prepared in the presence of Pluronic P123 block copolymer template under acidic conditions. Three kinds of amine-containing organosilanes and polyethylenimine were used to functionalize SBA-15 and BPMO. Small-angle X-ray scattering and nitrogen adsorption isotherms showed that these samples featured ordered mesostructure, high surface area, and narrow pore size distributions. Solid-state (13)C- and (29)Si cross-polarization magic-angle spinning NMR spectra showed chemical linkage between amine-containing modifiers and the surface of mesoporous materials. The chemically linked amine-containing modifiers were found to be on both the inner and outer surfaces. N-[3-(trimethoxysilyl)propyl]ethylenediamine-modified BPMO (A2-BPMO) sample exhibited the highest CO2 uptake (i.e., ∼3.03 mmol/g measured on a volumetric adsorption analyzer) and the fastest adsorption rate (i.e., ∼13 min to attain 90% of the maximum amount) among all the samples studied. Selectivity and reproducibility measurements for the A2-BPMO sample showed quite good performance in flowing N2 gas at 40 mL/min and CO2 gas of 60 mL/min at 25 °C.

Effect of Morphology and Pore Size of Sulfonated Mesoporous Benzene-silicas in the Preparation of Poly(vinyl alcohol)-Based Hybrid Nanocomposite Membranes for Direct Methanol Fuel Cell Application

Sulfonated mesoporous benzene-silicas were introduced into a poly(vinyl alcohol) (PVA) polymer matrix to act as a barrier for methanol crossover, to prepare composite electrolyte membranes for direct methanol fuel cell applications. Highly ordered 2D hexagonal mesoporous benzene-silicas were prepared using 1,4-bis(triethoxysilyl)benzene (BTEB) organosilica precursor and two kinds of organic templates, such as an octadecyltrimethylammonium bromide (ODTMA) and a Pluronic P123 poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer, to investigate the effect of the morphology and the pore size on the methanol permeability and the proton conductivity of the membranes. The sulfonated mesoporous benzene-silica and PVA were mixed with a sulfosuccinic acid (SSA) cross-linker to improve the membrane stability from mechanical and conductive viewpoints. The physical and chemical characterization of the hybrid electrolyte membranes was performed by varying the contents of sulfonated mesoporous benzene-silicas and SSA. All the hybrid membranes studied showed good performance in lowering the methanol crossover (i.e., approximately 68% reduction in comparison with the Nafion117 membrane), and mesoporous benzene-silica with smaller particle morphology and pores (2-3 nm) was observed to be a more effective additive.

Three-dimensional cubic (Im3m) periodic mesoporous organosilicas with benzene- and thiophene-bridging groups

Three-dimensional cubic (Im3m) periodic mesoporous organosilicas with aromatic benzene- and thiophene-bridging groups were synthesized using 1,4-bis(triethoxysilyl)benzene and 2,5-bis(triethoxysilyl)thiophene as organosilica precursors in the presence of a F127 PEO–PPO–PEO triblock copolymer under acidic conditions. Highly ordered 3D cubic (Im3m) mesostructure was confirmed by synchrotron small angle X-ray scattering and transmission electron microscopy. Nitrogen adsorption analysis of the aforementioned samples (extracted and additionally calcined in nitrogen at 375–400 °C) revealed their high surface area (460–630 m2 g−1) and accessible ordered large pores (in the range of 6–9 nm). High thermal stability of these benzene- and thiophene-PMO samples (up to 500 and 400 °C, respectively) was confirmed by thermogravimetric analysis, while their framework chemistry was studied by solid-state 13C and 29Si MAS NMR.

Synthesis of ordered mesoporous silica/ceria-silica composites and their high catalytic performance for solvent-free oxidation of benzyl alcohol at room temperature†

Highly ordered mesoporous Ce-incorporated MCM-41 and MCM-48 silica materials with Ce/Si ratio = 0.1–0.3 have been prepared in a surfactant-assisted hydrothermal method using hexadecyltrimethylammonium bromide (CTAB) as a structure-directing agent (SDA), cerium nitrate hexahydrate and tetraethyl orthosilicate (TEOS) as inorganic co-precursors under basic conditions. Thermal treatment at 823 K has allowed the removal of the organic template, resulting in the formation of long-range ordered 2D hexagonal (p6mm) MCM-41 and cubic (Ia3d) MCM-48, respectively, with ceria-rich particles. Highly ordered mesostructures for Ce-MCM-41 and Ce-MCM-48 materials were characterized with small angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (XRD), nitrogen adsorption–desorption isotherms, UV-visible diffuse reflectance spectroscopy (UV-DRS), transmission electron microscopy (TEM). The elemental compositions were analyzed using elemental mapping from EDS, inductively coupled plasma atomic emission spectra (ICP-AES), X-ray photoelectron spectroscopy (XPS), and solid-state magic angle spinning (MAS) NMR. These high cerium containing mesoporous ceria–silica materials of ∼30 wt% showed an impressive performance in solvent-free highly selective liquid phase oxidation of benzyl alcohol to benzaldehyde at room temperature. This controlled oxidation of primary alcohol to aldehyde over highly stable, completely heterogeneous, non-air sensitive, and reusable Ce-incorporated silica composite can be an excellent gateway for industrial fine chemical synthesis.

Bifunctional periodic mesoporous organosilicas with thiophene and isocyanurate bridging groups.

Bifunctional periodic mesoporous organosilicas (BPMOs) with thiophene- and isocyanurate-bridging groups were prepared by one-pot co-condensation of 2,5-bis(triethoxysilyl)thiophene and tris[3-(trimethoxysilyl)propyl]isocyanurate precursors in the presence of a poly(ethylene oxide)-poly(DL-lactic acid-co-glycolic acid)-poly(ethylene oxide) (PEO-PLGA-PEO) triblock copolymer under acidic conditions. The resulting BPMOs exhibited 2D hexagonal ordering (p6mm), large mesopores of approximately 7.7 nm, and high BET surface area (approximately 600-700 m(2)/g). (13)C CP-MAS and (29)Si MAS NMR studies confirmed the presence of thiophene and isocyanurate bridging groups inside the framework of pore walls with the relative content reflecting the synthesis gel composition. Additional quantitative estimation was provided by N and S elemental analysis. Thermogravimetric analysis showed the thiophene-isocyanurate BPMOs are stable up to 250 degrees C in flowing air and up to 400 degrees C in flowing nitrogen.

Surfactant-assisted synthesis of mesoporous silica/ceria–silica composites with high cerium content under basic conditions

Ordered mesoporous silica/ceria–silica composites were synthesized using cerium(IV) hydroxide and tetraethyl orthosilicate (TEOS) as co-precursors in the presence of hexadecyltrimethylammonium bromide (CTAB) under basic conditions. These composites consisted of Ce-doped mesoporous silica particles (about 500 nm) with highly ordered 2D hexagonal (p6mm) and 3D bicontinuous cubic (Ia3d) structures and irregular ceria-rich silica–ceria particles. Wide angle XRD, diffuse reflectance UV-vis, and XPS analyses showed that 10–24% of cerium was at the Ce3+ oxidation level and the remaining predominant fraction of Ce was at the Ce4+ oxidation level. The cerium loading was varied in these composite materials up to 43 wt% (∼3.1 mmol g−1). The specific surface areas of the mesoporous silica/ceria–silica composite samples obtained on the basis of nitrogen adsorption isotherms were higher than 350 m2 g−1 and their pore widths were between 3.3 and 3.5 nm. The mesoporous silica/ceria–silica samples were reduced at 850 °C under flowing H2 in a N2 environment. The crystal structure of the reduced samples changed to a hexagonally structured phase with the oxidation state of Ce3+, while the ordered mesostructure of silica was preserved.

Ceria‐Containing Ordered Mesoporous Silica: Synthesis, Properties, and Applications

Structural architecture and unique physical, chemical, thermal, and mechanical properties of ordered mesoporous silica materials can be tuned. High flexibility of silica materials can provide good support for different metal nanoparticles, metal oxides, and organic functional groups. The properties of silica materials can vary to a great extent by introducing the optimum amount of metal species co‐doped, dispersed or composites with the silica mesostructure. The present study investigates the deposition of CeIII/IV/CeO2 on the silica surface by using different wet chemical engineering methods, illustrates the syntheses of those ceria–silica or metal doped ceria–silica nanomaterials and offers clear picture of the influence that incorporated ceria concentration has on the properties of the support material. Ceria–silica based ordered mesoporous materials can have numerous applications is also discussed in this article, emphasizing its use as a heterogeneous catalyst in particular.

Synthesis of acryl phosphate antistatic agent and its effect on the antistatic, thermal and mechanical properties of PMMA

A simple and economic antistatic agent, (2-methacryloyloxyethyl)acid phosphate (acryl phosphate), was synthesized via the reaction of 2-hydroxyethyl methacrylate with phosphorus pentoxide. The acryl phosphate antistatic agent, synthesized in this study, was introduced into poly(methyl methacrylate) (PMMA) resin via copolymerization with MMA. This antistatic agent provides the PMMA matrix with excellent antistatic properties, including surface resistance and electric charge. A comparison of the present antistatic agent with other commercial agents demonstrated the excellence of not only its electrical, but also its thermal and mechanical properties.