Browsing by Author "Jeon, Sunjeong"

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    Enhancement of porosity of sodium silicate and titanium oxychloride based TiO2–SiO2 systems synthesized by sol–gel process and their photocatalytic activity
    (Microporous and Mesoporous Materials, 2012-11-09) Shao, Godlisten N.; Kim, You Na; Imran, S.M; Jeon, Sunjeong; Sarawade, Pradip B.; Hilonga, Askwar; Kim, Jong-gil; Kim, Hee Taik
    The textural properties of TiO2–SiO2 composites (TSCs) were successively enhanced using three approaches; (1) washing the hydrogels with different solvents, (2) using surfactant and (3) forming the TiO2 sol in ethanol medium. The sol–gel process was exquisitely used to form the composites using cost effective precursors. Initially, the precipitated hydrogels were washed with water or alcohol to evaluate the influence of washing on the dried hydrogels. Consequently, two composites were formed differently in the presence of stearic acid (SA) as a surfactant and the other by forming TiO2 sol in ethanol medium prior to reaction with silica source. The TSC powders were examined by XRD, N2 physisorption studies, FTIR, TGA, SEM, XRF and HRTEM. The BET surface area of the sample obtained after washing the hydrogels with ethanol (TSCE) was the largest (594 m2/g) while porosities of the composites obtained using stearic acid as a surfactant (TSCSA, 0.96 cm3/g) and ethanol as a medium to form the TiO2 sol (TSCES, 1.85 cm3/g) were relatively superior to those obtained under influence of changing washing solvent. Photocatalytic decolorization of methylene blue by the composites calcined at 800 C revealed that the TSCES-800 possessed the highest activity of all the composites due to its superior properties.
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    Peptization technique in the synthesis of titania–silica composites and their photocatalytic properties
    (Chemical Engineering Journal, 2012-05-18) Shao, Godlisten N.; Hilonga, Askwar; Kim, You Na; Kim, Jong-gil; Elineema, Gideon; Quang, Dang Viet; Jeon, Sunjeong; Kim, Hee Taik
    A comparative study of titania–silica composite (TSC) synthesized via peptization sol–gel method was conducted. Typically, titanium hydroxide gel (Ti(OH)4) was formed by condensation of titanium oxychloride solution using adequate amount of ammonium hydroxide solution. The preformed gel was peptized either in silicic acid (SA) or nitric acid (NA) to form a sol. The composite was characterized by XRD, FTIR, SEM, TEM, TGA, and N2 physisorption studies. The XRD patterns and the TEM micrographs confirmed that thermal-derived samples of the composite, formed using silicic acid as a silica source and peptizing agent (TSC–SA), yielded TiO2ASiO2 composite with a single-phase (anatase phase); while a mixture of both anatase and rutile phases were observed in the composite (TSC–NA), where nitric acid was used as a peptizing agent. FTIR analysis showed the vibration band assignable to the TiAOASi bond at 945 cm 1, suggesting that titania was incorporated into silica to form a composite. Furthermore, a simple experiment of photodegradation of methyl orange in the presence of sunlight was performed to demonstrate the practical efficacy of the composites synthesized via this method. The results indicated that the calcined samples of TSC–NA-800 had the highest activity due to its superior properties.
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    Sol–gel synthesis of photoactive zirconia–titania from metal salts and investigation of their photocatalytic properties in the photodegradation of methylene blue
    (Powder Technology, 2014-03-11) Shao, Godlisten N.; Imran, S.M; Jeon, Sunjeong; Engole, Marion; Abbas, Nadir; Haider, M. Salman; Kang, Shin Jae; Kim, HT
    Photoactivemetal oxide systems capable of reducing non-biodegradable pollutants are highly needed heterogeneous catalysts for environmental purification. Most of the currently available heterogeneous catalysts are obtained from complicated synthetic routes using expensive and perhaps hazardous precursors. The present study reports a novel sol–gelmethod to synthesize pure TiO2 and ZrO2–TiO2 samples using titanium oxychloride as TiO2 precursor and zirconyl nitrate hydrate as a ZrO2 source in the presence of the surfactant. The ratio of Zr-to- Ti was controlled between 0.75 and 3.2 to evaluate the effect of the amount of ZrO2 in the composites. Consequently, the precipitates were calcined at different temperatures to investigate the effect of removing the template at different sintering temperatures. The physico-chemical properties of the samples were examined by SEM, HRTEM, DT-TGA, XRD, FTIR, XRF, EDX, nitrogen gas physisorption and UV–visible diffusive reflectance spectrometry analyses. These analyses revealed that the crystallization, dispersion, particle size and shape of the samples are critically dependent upon the calcination temperatures and Zr-to-Ti ratios. Abnormal grain growth (AGG) was unexpectedly observed in the samples calcined at higher temperatures (≤800 °C). Comparisons of the activities of the samples toward decolorization of methylene blue indicated that the photocatalytic efficiencies of the composites with Zr/Ti ≤ 2.2 were superior to that of pure TiO2.
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    Sol–gel synthesis of sodium silicate and titanium oxychloride based TiO2–SiO2 aerogels and their photocatalytic property under UV irradiation
    (Chemical Engineering Journal, 2013-07-26) Kim, You Na; Shao, Godlisten N.; Jeon, Sunjeong; Imran, S.M; Sarawade, PB; Kim, HT
    Binary titania–silica metal oxides (TiO2–SiO2) have preferentially been used as photocatalysts for the degradation of organic contaminants under UV irradiation. Herein we synthesized TiO2–SiO2 aerogel powders with different Si-to-Ti ratios suitable for decolorization of organic pollutants using less expensive silica source (sodium silicate) and titanium oxychloride as a titania precursor. Consequently, the surfaces of the alcogels were hydrophobized using trimethylchlorosilane (TMCS) as a silylating agent to yield hydrophobic aerogel powders at ambient pressure drying. The as-prepared samples were calcined at different temperatures ranging from 200 to 1000 C to evaluate the effect of the heat treatment in the microstructure of the aerogels. The physico-chemical properties of the aerogels were examined by XRD, FTIR, XRF, TEM, SEM, N2 gas physisorption studies, TGA/DTA and diffusive reflectance spectrometry analyses. It was found that calcination temperature is an important factor in improving the porosity and crystallinity of the aerogels however; it has a detrimental effect on the hydrophobicity and photochemical performance of the aerogels. The as-synthesized aerogels were hydrophobic and exhibited the highest activity toward decolorization of methylene blue. The hydrophilic aerogels were obtained after calcination at temperature P500 C however; the formed samples possessed lower activities. Hydroxyl radicals ( OH) detection experiment performed in the presence of the photocatalysts indicated that the generation of radicals during irradiation increases with increasing illumination time.
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    Sol–gel synthesis of sodium silicate and titanium oxychloride based TiO2–SiO2 aerogels and their photocatalytic property under UV irradiation
    (Elsevier, 2013-07-26) Kim, You Na; Shao, Godlisten N.; Jeon, Sunjeong; Imran, S.M; Sarawade, PB; Kim, HT
    Binary titania–silica metal oxides (TiO2–SiO2) have preferentially been used as photocatalysts for the degradation of organic contaminants under UV irradiation. Herein we synthesized TiO2–SiO2 aerogel powders with different Si-to-Ti ratios suitable for decolorization of organic pollutants using less expensive silica source (sodium silicate) and titanium oxychloride as a titania precursor. Consequently, the surfaces of the alcogels were hydrophobized using trimethylchlorosilane (TMCS) as a silylating agent to yield hydrophobic aerogel powders at ambient pressure drying. The as-prepared samples were calcined at different temperatures ranging from 200 to 1000 C to evaluate the effect of the heat treatment in the microstructure of the aerogels. The physico-chemical properties of the aerogels were examined by XRD, FTIR, XRF, TEM, SEM, N2 gas physisorption studies, TGA/DTA and diffusive reflectance spectrometry analyses. It was found that calcination temperature is an important factor in improving the porosity and crystallinity of the aerogels however; it has a detrimental effect on the hydrophobicity and photochemical performance of the aerogels. The as-synthesized aerogels were hydrophobic and exhibited the highest activity toward decolorization of methylene blue. The hydrophilic aerogels were obtained after calcination at temperature P500 C however; the formed samples possessed lower activities. Hydroxyl radicals ( OH) detection experiment performed in the presence of the photocatalysts indicated that the generation of radicals during irradiation increases with increasing illumination time