Seong-Soo Hong

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.

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

Catalytic combustion of benzene over supported metal oxides catalysts

Catalytic combustion of benzene over supported metal oxides has been investigated. The catalysts have been prepared by incipient wetness method and characterized by XRD, FT-Raman, ESR and TPR. Among supported metal oxides, CuOx, supported on TiO2 is found to have the highest activity for benzene oxidation. In addition, among the catalysts of copper oxide supported on TiO2, A12O3 and SiO2, titania-supported catalyst (CuOx/TiO2) gives the highest catalytic activity. CuOx/TiO2 (Cu loading 5.5 wt%) shows the total oxidation of benzene at about 250 °C. From the ESR and FT-Raman results, the CuO dispersed on the TiO2 surface acts as an active site of CuOx/TiO2 catalysts on the oxidative decomposition of benzene. The catalytic activity gradually increases with an increase of Cu loading on TiO2. When Cu loading reaches 5.5 wt%, the total conversion temperature is lowered to 300 °C. However, the catalytic activity considerably decreases at 7 wt% Cu loading. The catalytic activity increased with an increase of oxygen concentration but the concentration of benzene showed no difference in the benzene conversion. This result suggests that the rate determining step is the adsorption of oxygen.

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.

Synthesis of TiO2/SiO2 nanoparticles in a water-in-carbon-dioxide microemulsion and their photocatalytic activity

TiO2 and TiO2/SiO2 nanoparticles were prepared by controlled hydrolysis of titanium tetraisopropoxide and tetraethylorhtosilicate in water-in-carbon-dioxide microemulsion using ammonium carboxylate perfluoro-polyether (PFPE-NH4) as a surfactant. These particles were characterized by HRTEM, XRD, FT-IR, TGA and DTA. The particles calcined at 500°C were identified as a nanocrystalline anatase phase, regardless of the titanium tetraisopropoxide/teraethylorthosilicate (TTIP/TEOS) molar ratio. The crystallite size decreased with an increase of the silica content. From FT-IR analysis, the band for Ti-O-Si vibration was observed and the band intensity for Si-O-Si vibration increased with an increase of the silica content. The micrographs of HRTEM showed that the TiO2/SiO2 nanoparticles had a spherical morphology with a narrow size distribution and the lattice fringe was 0.35 nm, which corresponds to the lattice spacing of (101) plane in the anatase phase. In addition, TiO2/SiO2 particles showed higher photocatalytic activity than pure TiO2 and the TiO2/SiO2 (80:20) particles showed the highest activity on the photocatalytic decomposition of p-nitrophenol.

Synthesis of titanium dioxides in water-in-carbon dioxide microemulsion and their photocatalytic activity

Abstract Titania nanoparticles were prepared by controlled hydrolysis of titanium tetraisopropoxide (TTIP) in water-in-carbon dioxide microemulsion using ammonium carboxylate perfluoropolyether (PFPE-NH4) as a surfactant. The physical properties were examined by thermogravimetric-differential thermal analysis (TGA-DTA), X-ray diffraction (XRD) and transmission electron microscope (TEM). In addition, the photocatalytic decomposition of p-nitrophenol was also investigated using batch reactor in the presence of UV light. It is shown that the residual hydroxyl group and the organic compounds were completely removed in the calcining temperature from 250 to 450 °C and the amorphous phase transformed to anatase structure above 450 °C. The crystallinity and crystallite size of nanoparticles produced in water-in-carbon dioxide increased with an increase of W0 ratio. In the photocatalytic decomposition of p-nitrophenol, the photocatalytic activity was mainly determined by the crystallite size of titania and the reaction rate increased with a decrease of crystallite size.

Hydrothermal synthesis of titanium dioxide using acidic peptizing agents and their photocatalytic activity

We have prepared TiO2 nanoparticles by the hydrolysis of titanium tetraisopropoxide (TTIP) using HNO3 as a peptizing agent in the hydrothermal method. The physical properties of nanosized TiO2 have been investigated by TEM, XRD and FT-IR. The photocatalytic degradation of orange II has been studied by using a batch reactor in the presence of UV light. When the molar ratio of HNO3/TTIP was 1.0, the rutile phase appeared on the titania and the photocatalytic activity decreased with an increase of HNO3 concentration. The crystallite size of the anatase phase increased from 6.6 to 24.2 nm as the calcination temperature increased from 300 °C to 600 °C. The highest activity on the photocatalytic decomposition of orange II was obtained with titania particles dried at 105 °C without a calcination and the photocatalytic activity decreased with increasing the calcination temperature. In addition, the titania particles prepared at 180 °C showed the highest activity on the photocatalytic decomposition of orange II.

Catalytic combustion of chlorobenzene over V2O5/TiO2 catalysts prepared by the precipitation-deposition method

Catalytic combustion of chlorobenzene over supported vanadium oxides has been investigated. TiO2 was prepared by the sol-gel method from titanium isopropoxide. The supported vanadium oxide catalysts have been prepared by precipitation-deposition and impregnation method and characterized by XRD, FT-Raman and TPR. In the VOx/TiO2catalysts prepared using the impregnation method, when vanadium loading reaches 3 wt.%, the activity shows a maximum. However, in the VOx/TiO2catalysts prepared by precipitation-deposition, when vanadium loading reaches 7 wt.%, the activity shows a maximum. This result suggests that the precipitation-deposition can yield a higher metal loading on the support and a high dispersion compared to the impregnation method.

Photocatalytic decomposition of p-nitrophenol over titanium dioxide prepared by reverse microemulsion method using nonionic surfactants with different hydrophilic groups

TiO2 nanoparticles were prepared using the hydrolysis of titanium tetraisopropoxide (TTIP) in W/O microemulsions consisting of water, nonionic surfactant and cyclohexane. The photocatalytic degradation of p-nitrophenol has been studied by using a batch reactor in the presence of UV light. The crystallite size and crystallinity increase with a decrease of hydrophilic group chain length and an increase of calcinations temperature. In addition, the photocatalytic activity increases with an increase of hydrophilic group length.