Gun Dae Lee

Synthesis and properties of semifluorinated block copolymers containing poly(ethylene oxide) and poly(fluorooctyl methacrylates) via atom transfer radical polymerisation

Abstract Amphiphilic block copolymers of poly(ethylene oxide) (PEO) and poly(fluorooctyl methacrylates) were synthesised by atom transfer radical polymerisation of semifluorinated methacrylates such as 1H,1H-perfluorooctyl methacrylate, and 1H,1H,2H,2H-perfluorooctyl methacrylate using PEO macroinitiators. The use of mono- and difunctional initiator led to AB and ABA block copolymers with controlled molecular weights. The linear time dependence of ln([M]0/[M]) is consistent with a controlled polymerisation i.e. first-order in monomer concentration. Various block copolymers could be prepared by varying the ratio of monomer to macro-initiator. The copolymers self-assembled in chloroform to form micelles, which was evidenced by dynamic light scattering and transmission electron microscopy. Different morphologies of spheres and rods were observed by changing the copolymer composition. In addition, these surfactants lower the interfacial tension between water and supercritical carbon dioxide to stabilise water-in-carbon dioxide emulsions.

Microwave-accelerated energy-efficient esterification of free fatty acid with a heterogeneous catalyst.

This paper shows energy-efficiency of microwave-accelerated esterification of free fatty acid with a heterogeneous catalyst by net microwave power measurement. In the reaction condition of 5 wt% sulfated zirconia and 1:20 M ratio of oil to methanol at 60°C and atmospheric pressure, more than 90% conversion of the esterification was achieved in 20 min by microwave heating, while it took about 130 min by conventional heating. Electric energy consumption for the microwave heating in this accelerated esterification was only 67% of estimated minimum heat energy demand because of significantly reduced reaction time.

Photocatalytic decomposition of 4-nitrophenol over titanium silicalite (TS-1) catalysts

Abstract Titanium silicalite zeolites (TS-1) having Si/Ti ratios of 3.3, 13.7, and 26.3 were synthesized and used as photocatalysts for decomposition of 4-nitrophenol (4-NP) in aqueous solution. In the dark, the adsorption of 4-NP on TS-1 changed greatly depending on the Si/Ti ratio in TS-1 and the pH of the solution. The amount of 4-NP adsorbed on TS-1 increased with increasing Si/Ti ratio and decreasing pH of solution. The photocatalytic activities of TS-1 zeolites for the decomposition of 4-NP were found to be greatly affected by H 2 O 2 . In the absence of H 2 O 2 , the TS-1 having lower Si/Ti ratio, and consequently containing a larger amount of extra framework titanium, exhibited higher photocatalytic activity. In contrast, in the presence of H 2 O 2 , the TS-1 with higher Si/Ti ratio, in which the titanium content is lower while the fraction of framework titanium is higher, showed a higher increase in photocatalytic activity. Especially in acid conditions, the addition of H 2 O 2 to the reaction solution results in a remarkable enhancement of the photocatalytic activity of TS-1; the apparent rate constant increased with increasing Si/Ti ratio. Such results suggest that, upon UV illumination, OH radicals can be formed easily from the titanium-hydroperoxide species that are formed by the interaction of framework titanium in TS-1 with H 2 O 2 . The enhancement of photocatalytic activity of TS-1 for the decomposition of 4-NP by the addition of H 2 O 2 can be attributed to both the efficient formation of OH radicals and the close proximity of OH radicals to the reactant molecules.

Raney Ni catalysts derived from different alloy precursors Part II. CO and CO2 methanation activity

Catalytic activity, in conjunction with reaction mechanism, was studied in the methanation of CO and CO2 on three Raney Ni catalysts derived from different Ni-Al alloys using different leaching conditions. Main products were CH4 and CO2 in CO methanation, and CH4 and CO in CO2 methanation. Any other hydrocarbon products were not observed. Over all catalysts, CO methanation showed lower selectivity to methane and higher activation energy than CO2 methanation. The catalyst derived from alloy having higher Ni content using more severe leaching conditions, namely higher reaction temperature and longer extraction time, showed higher specific activity and higher selectivity to methane both in CO and CO2 methanation. In CO and CO2 methanation on Raney Ni catalyst, catalytic activity was seen to have close relation with the activity to dissociate CO

Formation of TiO2 nanoparticles in water-in-CO2 microemulsions

Titanium dioxide nanoparticles can be produced by the controlled hydrolysis of titanium tetraisopropoxide in water-in-CO2 (w/c) microemulsions stabilized with the surfactants ammonium carboxylate perfluoropolyether (PFPE-NH4) and poly(dimethyl amino ethyl methacrylate-block-1H,1H,2H,2H-perfluorooctyl methacrylate) (PDMAEMA-b-PFOMA); the greater control of hydrolysis and particle growth with PDMAEMA-b-PFOMA is consistent with the differences in the stabilities and interactions for these two microemulsions.

Raney Ni catalysts derived from different alloy precursors (I) morphology and characterization

Ni-Al alloys containing 41.3, 49.2 and 59.9 wt% Ni were leached by reaction with 20 wt% aqueous NaOH solution under different temperature and time. The reactivities of alloys and morphologies of resultant catalysts were investigated. A large difference in reactivities of alloys toward alkali solution was revealed according to the composition of the alloy. As Al content in precursor alloy increased, the reactivity of alloy toward alkali solution increased. It was shown that, during leaching, reaction in Ni 41.3 wt% alloy is restricted to reaction interface, whereas that in Ni 49.9 wt% alloy occurs throughout the product layer. Surface area and pore size distribution were seen to be strongly dependent upon leaching conditions and relatively independent of the composition of precursor alloy.

A Study for Microwave Enhanced Synthesis of NIR Absorbing Materials

Symmetrically and unsymmerically substituted bis-dithiobenzil nickel complexes containing four substituted and unsubstituted methoxy groups were synthesized from a benzoin compound using phosphorous pentasulfide under the conventional thermal and microwave processing. The efficiency of microwave synthesis over the conventional thermal synthesis was illustrated by the yield of bisdithiobenzil nickel complex dyes. The samples were characterized by the means of elemental analyzer, 1HNMR, IR spectroscopy, Uv-vis spectroscopy and DSC.

Comparative study of photo- and thermal catalytic hydroxylation of phenol with H2O2OVER TS-1

The hydroxylation of phenol into catechol (CAT) and hydroquinone (HQ) with hydrogen peroxide and TS-1 catalyst was carried out via both photo- and dark (thermal) reactions. The conversion of phenol and the product ratio of CAT/HQ in the photocatalytic reaction were higher than those in dark (thermal) reaction.

Photocatalytic Hydroxylation of Phenol over Ti-Containing Zeolites (TS-1, Ti-MCM-41)

The photo-catalytic hydroxylation of phenol with hydrogen peroxide was carried out over TS-1 and Ti-MCM-41 catalysts. For comparison, the dark (thermal)-catalytic hydroxylation of phenol was also performed. The difference in catalytic behaviors of TS-1 and Ti-MCM-41 and product distribution in both the reactions were investigated. The TS-1 and Ti-MCM-41 catalysts having the Si/Ti ratio of 50 were prepared by in-situ crystallization and characterized using XRD, UV-DRS. In the all reactions, the main products were catechol (CAT), hydroquinone (HQ) and benzoquinone (BQ). In dark (thermal)-reaction, TS-1 showed a higher catalytic activity than Ti- MCM-41. In photo-reaction, however, the activity of Ti-MCM-41 was comparable to that of TS-1. The conversion of phenol and the selectivity to CAT in the photo-catalytic reaction were higher than those in dark (thermal)-reaction. In the all reactions, the selectivity to CAT increased remarkably when the selectivities to HQ and BQ decreased with reaction time.

The Preparation of Fibrous MCM-41 Using Microwave Heating

Mesoporous MCM-41 materials were prepared using the conventional thermal and microwave heating method. Both in conventional thermal and microwave heating synthesis of MCM-41, tetraethyl orthosilicate (TEOS) and cetyltrimethyl ammonium bromide (CTAB) were used as Si source and template, respectively. Microwave heating was carried out in a modified 400 W, 2.45 GHz microwave oven. In both methods, the crystallization temperatures was 70 °C and crystallization time was 3~12 h. The prepared MCM-41 samples were characterized by XRD, TEM and SEM. The XRD patterns of MCM-41 samples prepared from both the methods were typical of a relatively well ordered material. TEM results also revealed that the MCM-41 samples prepared from both the methods possess the regular hexagonal array of mesoporous channels. On the contrary, SEM has shown the difference in morphologies of the MCM-41 samples prepared from both the methods. The samples prepared by conventional thermal heating method mainly consist of irregular and small particles, whereas the samples prepared by microwave heating method have elongated rope-like structure and their length extends longer than 10 μm.