Browsing by Author "Kim, HT"

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    Aminated polyethersulfone-silver nanoparticles (AgNPs-APES) compositemembranes with controlled silver ion release for antibacterial and water treatment applications
    (Materials Science and Engineering C, 2016-02-10) Haider, M. Salman; Shao, Godlisten N.; Imran, S.M; Park, Seongsoo; Abbas, Nadir; Tahir, M.S; Hussain, Manwar; Bae, Wookeun; Kim, HT
    The present study reports the antibacterial disinfection properties of a series of silver nanoparticle (AgNP) immobilized membranes. Initially, polyethersulfone (PES) was functionalized through the introduction of amino groups to form aminated polyethersulfone (NH2-PES, APES). AgNPs were then coordinately immobilized on the surface of the APES composite membrane to formAgNPs-APES. The properties of the obtainedmembrane were examined by FT-IR, XPS, XRD, TGA, ICP-OES and SEM-EDAX analyses. These structural characterizations revealed that AgNPs ranging from 5 to 40 nm were immobilized on the surface of the polymer membrane. Antibacterial tests of the samples showed that the AgNPs-APES exhibited higher activity than the AgNPs-PES un-functionalized membrane. Generally, the AgNPs-APES 1 cm × 3 cm strip revealed a four times longer life than the un-functionalized AgNPs polymer membranes. The evaluation of the Ag+ leaching properties of the obtained samples indicated that approximately 30% of the AgNPs could be retained, even after 12 days of operation. Further analysis indicated that silver ion release can be sustained for approximately 25 days. The present study provides a systematic and novel approach to synthesize water treatment membranes with controlled and improved silver (Ag+) release to enhance the lifetime of the membranes.
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    Biodiesel production by sulfated mesoporous titania–silica catalysts synthesized by the sol–gel process from less expensive precursors
    (Chemical Engineering Journal, 2012-11-21) Shao, Godlisten N.; Sheikh, Rizwan; Hilonga, Askwar; Lee, Jae Eun; Park, Yeung-Ho; Kim, HT
    A sulfated titania–silica composite (S-TSC) was obtained through surface modification of mesoporous titania–silica composite synthesized using less expensive precursors; titanium oxychloride and sodium silicate as titania and silica sources respectively. A pre-formed titania sol facilitated the synthesis of a mesoporous composite with a high BET surface area (520 m2/g), suitable for surface modification using sulfuric acid to improve its catalytic performance. The materials synthesized via this process were examined by XRD, XRF, FTIR, SEM, TEM, TGA, and N2 physisorption studies. FTIR analysis showed the vibration band of the TiAOASi bond at 943 cm 1, suggesting the incorporation of titania into silica to form a composite. This vibration band was substantially shifted to 952 cm 1 after the attachment of the sulfate group. The catalytic activity of a series of as-prepared TSC, S-TSC calcined samples and pure H2SO4 were evaluated for esterification of oleic acid and transesterification of waste oil with methanol to yield methyl esters. It was observed that at these reaction conditions, S-TSC-450 and S-TSC-550 possessed high catalytic activity comparable to that of pure H2SO4 implying that surface modification of the titania–silica composite improves its acidic properties.
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    Electroconductive performance of polypyrrole/graphene nanocomposites synthesized through in situ emulsion polymerization
    (JOURNAL OF APPLIED POLYMER SCIENCE, 2014-11-22) Imran, S.M; Shao, Godlisten N.; Haider, M. Salman; Abbas, Nadir; Hussain, Manwar; Kim, HT
    The present study demonstrates a modified in situ emulsion polymerization (EP) approach convenient for the formation of polypyrrole/graphene (PPy/GN) nanocomposites with harnessed conductivities. A series of PPy/GN nanocomposites were prepared by loading different weight percent (wt %) of GN during in situ EP of pyrrole monomer. The polymerization was carried out in the presence of dodecyl benzene sulfonic acid, which acts as an emulsifier and protonating agent. The microstructures of the nanocomposites were studied by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy, UV–vis spectroscopy, Raman spectroscopy, photoluminescence spectroscopy and thermogravimetric analyses. The electrical conductivities of the nanocomposite pellets pressed at different applied pressures were determined using four probe analyzer. The electrical conductivities of the nanocomposites were considerably enhanced as compared to those of the individual PPy samples pressed at the same pressures. An enhanced conductivity of 717.06 S m21 was observed in the sample with 5 wt % GN loading and applied pressure of 8 tons. The results of the present study signify that the addition of GN in the PPy polymer harnesses both electrical and thermal properties of the polymer. Thus, PPy/GN nanocomposites with superior properties for various semiconductor applications can be obtained through direct loading of GN during the polymerization process.
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    Encapsulated Urea-Kaolinite Nanocomposite for Controlled Release Fertilizer Formulations
    (Hindawi Publishing Corporation,, 2015-05-20) Sempeho, SI; Kim, HT; Mubofu, Egid; Pogrebnoi, Alexander; Shao, Godlisten N.; Hilonga, Askwar
    Urea controlled release fertilizer (CRF) was prepared via kaolinite intercalation followed by gum arabic encapsulation in an attempt to reduce its severe losses associated with dissolution, hydrolysis, and diffusion. Following the beneficiation, the nonkaolinite fraction decreased from 39.58% to 0.36% whereas the kaolinite fraction increased from 60.42% to 99.64%. The X-ray diffractions showed that kaolinite was a major phase with FCC Bravais crystal lattice with particle sizes ranging between 14.6nm and 92.5 nm. Theparticle size varied with intercalation ratioswithmethanol intercalated kaolinite >DMSO-kaolinite > urea-kaolinite (KPDMU). Following intercalation, SEM analysis revealed a change of order from thick compact overlapping euhedral pseudohexagonal platelets to irregular booklets which later transformed to vermiform morphology and dispersed euhedral pseudohexagonal platelets. Besides, dispersed euhedral pseudohexagonal platelets were seen to coexist with blocky-vermicular booklets. In addition, a unique brain-form agglomeration which transformed into roundish particles mart was observed after encapsulation. The nanocomposites decomposed between 48 and 600∘C. Release profiles showed that 100% of urea was released in 97 hours from KPDMU while 87% was released in 150 hours from the encapsulated nanocomposite.The findings established that it is possible to use Pugu kaolinite and gum arabic biopolymer to prepare urea CRF formulations.
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    Enhancement of electroconductivity of polyaniline/graphene oxide nanocomposites through in situ emulsion polymerization
    (Journal of Material Science, 2013-10-23) Imran, S.M; Shao, Godlisten N.; Kim, You Na; Hussain, Manwar; Choa, Yong-Ho; Kim, HT
    The present study introduces a systematic approach to disperse graphene oxide (GO) during emulsion polymerization (EP) of Polyaniline (PANI) to form nanocomposites with improved electrical conductivities. PANI/ GO samples were fabricated by loading different weight percents (wt%) of GO through modified in situ EP of the aniline monomer. The polymerization process was carried out in the presence of a functionalized protonic acid such as dodecyl benzene sulfonic acid, which acts both as an emulsifier and protonating agent. The microstructure of the PANI/GO nanocomposites was studied by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV–Vis spectrometry, Fourier transform infrared, differential thermal, and thermogravimetric analyses. The formed nanocomposites exhibited superior morphology and thermal stability. Meanwhile, the electrical conductivities of the nanocomposite pellets pressed at different applied pressures were determined using the fourprobe analyzer. It was observed that the addition of GO was an essential component to improving the thermal stability and electrical conductivities of the PANI/GO nanocomposites. The electrical conductivities of the nanocomposites were considerably enhanced as compared to those of the individual PANI samples pressed at the same pressures. An enhanced conductivity of 474 S/m was observed at 5 wt% GO loading and an applied pressure of 6 t. Therefore, PANI/GO composites with desirable properties for various semiconductor applications can be obtained by in situ addition of GO during the polymerization process.
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    Sol–gel synthesis of mesoporous anatase–brookite and anatase– brookite–rutile TiO2 nanoparticles and their photocatalytic properties
    (Journal of Colloid and Interface Science, 2014-12-03) Mutuma, BK; Shao, Godlisten N.; Kim, Wonduck; Kim, HT
    TiO2 photocatalysts with a mixture of different TiO2 crystal polymorphs have customarily been synthesized hydrothermally at high temperatures using complicated and expensive equipment. In this study TiO2 nanoparticles with a mixture of TiO2 crystals were synthesized using a modified sol–gel method at low temperature. In order to form nanoparticles with different polymorphs a series of samples were obtained at pH 2, 4, 7 and 9. Raw samples were calcined at different temperatures ranging from 200 to 800 C to evaluate the effect of the calcination temperature on the physico-chemical properties of the samples. XRD results revealed that a mixture of anatase and brookite can be obtained in the as-synthesized samples and in those calcined up to 800 C depending on the pH used to obtain the final product. Indeed, a mixture of anatase brookite and rutile; or a sample with only rutile phase can be yielded through further calcination of the as-prepared samples at temperatures P600 C due to phase transformation. The photocatalytic performance of the samples with a mixture of anatase–brookite; anatase– brookite–rutile; and anatase–rutile (Degussa P25 TiO2) was exquisitely investigated in the degradation of methylene blue solutions. The samples obtained at pH 2 and calcined at 200 C possessed the highest activity of all due to its superior properties. This study elucidates a facile method suitable for the synthesis of TiO2 with different mixtures of TiO2 polymorphs with desirable properties for various applications.
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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
    (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
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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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    Two-step rapid synthesis of mesoporous silica for green tire
    (KOREAN JOURNAL OF CHEMICAL ENGINGERING, 2012-04-17) Hilonga, Askwar; Kim, Jong-gil; Sarawade, PB; Quang, DV; Shao, Godlisten N.; Elineema, Gideon; Kim, HT
    We report a two-step rapid route of synthesizing inexpensive mesoporous silica using the waste material (hexafluorosilicic acid, H2SiF6) of phosphate fertilizer industry and sodium silicate (Na2O·SiO2). The reaction was performed in a newly innovated manufacturing apparatus. This apparatus produces mesoporous silica with uniform properties through controlled mixing of source materials at predetermined equivalent ratio. The precursors are rapidly mixed within the nozzles to enable uniform control of physical properties of the final product. The obtained mesoporous silica was characterized using N2 physisorption studies, scanning electron microscope (SEM), and EDS. The final product was found to have superior properties that are suitable for green tire (environmentally friendly tire) as inorganic filler. The process reported in this study may significantly reduce the release of hazardous materials into the environment and it might confer economic benefits to the responsible industries. A project on innovative industrial application of our products for the tire industry is in progress.