Browsing by Author "Kim, Heetaik"

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    Esterification of oleic acid by Heteropolyacid/ TiO2-SiO2 catalysts synthesized from less expensive precursors
    (Wiley, 2015-03-11) Sheik, R.; Shao, Godlisten N.; Kim, Heetaik
    A series of 12-tungstophosphoric acid [HPW, H3PW12O40 (HPW)] catalysts supported on mesoporous titania– silica composite (TSC) were prepared by impregnation method. Primarily, TSC with mesostructure was successfully prepared by a modified sol–gel process using a less expensive silica precursor (sodium silicate) and titanium oxychloride as a titania source. In order to develop catalysts with various properties, the HPW loading over mesoporous TSC was controlled between 5 and 50wt%. The surface morphology and structural properties of the prepared catalysts were characterized using N2 gas physisorption analysis, Fourier transform infrared spectroscopy, X-ray diffraction, ultraviolet spectroscopy, transmission electron microscopy, and scanning electron microscopy analysis. The X-ray diffraction and ultraviolet spectroscopy results were useful in determining the HPW dispersion on the support material. The catalytic activities of the samples were tested in liquid phase esterification of oleic acid with methanol. The results suggested that HPW dispersion on the support material was essential for the stability and performance of the catalysts during the esterification reaction. Even though the activity of the synthesized catalysts increased with increasing HPW loading, the homogeneity decreased in the samples with higher HPW content (30–50wt%). The 20%HPW/TSC sample was found to be an active and catalytically stable catalyst, which was successfully regenerated and recycled for three consecutive runs.
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    https://www.sciencedirect.com/science/article/abs/pii/S092633731500346X
    (Wiley, 2016) Imran, S.M; Shao, Godlisten N.; Kim, Heetaik
    We have synthesized unique flexible pressure-sensitivenanocomposites by means of a solution mixing method,by adding multiwalled carbon nanotubes (MWCNTs) into athermoplastic urethane (TPU) matrix along with poly(methyl methacrylate) (PMMA) microbeads of varioussizes. The influence of the various PMMA bead sizes onthe pressure sensing properties of the nanocompositeswas studied over a range of pressures. The PMMAmicrobeads were used to achieve an early percolationthreshold at low loadings of MWCNTs. We used scanningelectron microscopy to study the nanocomposites’ mor-phology, and conducted differential scanning calorimetryanalyses to investigate their thermal properties. The nano-composites’ electrical and thermal conductivities werealso measured under various applied pressures. Thenanocomposites displayed repeatable electricalresponses under various applied pressures, demonstrat-ing their suitability for use as pressure sensing materials.The proposed material is an ideal candidate for use in thepreparation of pressure-sensitive devices
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    Inexpensive sol-gel synthesis of multiwalled carbon nanotube-TiO2 hybrids for high performance antibacterial materials
    (Materials Science and Engineering: C, Elsevier, 2016-11-01) Abbas, Nadir; Shao, Godlisten N.; Kim, Heetaik
    This study reports an inexpensive sol-gel method to synthesize TiO2-CNT hybrid materials. Synthesized TiO2-CNT materials show strong antibacterial activity in the absence of light. Cheap TiO2 source TiOCl2 is used during synthesis in the absence of high temperatures, high pressures and organic solvents. TiO2-CNT materials with 0, 2, 5, 10, 15 and 20 wt% of CNT were synthesized and compared for antibacterial activity, surface area, porosity, crystalline structure, chemical state, and HaCaT cell proliferation. The antibacterial strength of hybrid materials increased significantly with the increase in CNT loading amount, and the TiO2-CNT samples with a CNT loading of 10 wt% or more nearly removed all of the E.coli bacteria. HaCaT cell proliferation studies of synthesized hybrid materials illustrated that prepared TiO2-CNT systems exhibit minimum cytotoxicity. The characteristics of prepared materials were analyzed by means of XRD, FTIR, Raman spectroscopy, XPS, TEM, and nitrogen gas physisorption studies, compared and discussed
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    Inexpensive synthesis of a high-performance Fe3O4-SiO2-TiO2 photocatalyst: Magnetic recovery and reuse
    (Springer, 2016) Abbas, Nadir; Shao, Godlisten N.; Kim, Heetaik
    A sol-gel technique has been developed for the synthesis of a magnetite-silica-titania (Fe3O4-SiO2-TiO2) tertiary nanocomposite with improved photocatalytic properties based on the use of inexpensive titania and silica precursors. The exceptional photocatalytic activity of the resulting materials was demonstrated by using them to photocatalyze the degradation of methylene blue solution. The best formulation achieved 98% methylene blue degradation. An interesting feature of the present work was the ability to magnetically separate and reuse the catalyst. The efficiency of the catalyst remained high during two reuses. The synthesized nanomaterials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, ultra-violet-visible spectroscopy, diffuse reflectance spectroscopy, and thermogravimetric analysis. XRD analysis revealed the formation of multicrystalline systems of cubic magnetite and anatase titania crystals. SEM and TEM characterization revealed well-developed and homo-geneously dispersed particles of size less than 15 nm. FTIR spectra confirmed the chemical interaction of titania and silica. It was further noticed that the optical properties of the prepared materials were dependent on the relative contents of their constituent metal oxides.
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    Investigation of the influence of vanadium, iron and nickel dopants on the morphology, and crystal structure and photocatalytic properties of titanium dioxide based nanopowders
    (Elsevier, 2016) Shao, Godlisten N.; Haider, M.S; Kim, Heetaik
    Photoactive V, Fe and Ni doped TiO2 (M-TiO2) nanopowders were synthesized by a modified two-step sol-gel process in the absence of additives. Titanium oxychloride, which is a rarely-used TiO2 precursor was used to yield M-TiO2 photocatalysts with preferential photochemical performance in the presence of natural solar irradiation. The obtained samples were calcined at different calcination temperatures ranging from 450 to 800 °C to evaluate the influence of the sintering on the physicochemical properties. The properties of the obtained samples were examined by XRF, XRD, Raman spectroscopy, UV–visible DRS, XPS, nitrogen gas physisorption studies, SEM-EDAX and HRTEM analyses. Structural characterization of the samples revealed the incorporation of these transition metal element into TiO2. It was also depicted that the morphology, crystal structure, optical and photochemical properties of the obtained samples were largely dependent on the calcination temperature and the type of dopant used during the preparation process. The photochemical performance of the samples was investigated in the photodegradation of methylene blue in the presence of natural sunlight. The experimental results indicated that the VT600 sample possessed the highest activity due to its superior properties. This study provides a systematic preparation and selection of the precursor, dopant and calcination temperature that are suitable for the formation of TiO2-based heterogeneous photocatalysts with appealing morphology, crystal structure, optical and photochemical properties for myriad of applications.
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    Sequential repetitive chemical reduction technique to study size property relationships of graphene attached Ag nanoparticle
    (Solid State Sciences, 2015) Haider, M.S; Shao, Godlisten N.; Kim, Heetaik
    The present study demonstrates a novel, systematic and application route synthesis approach to develop size-property relationship and control the growth of silver nanoparticles (AgNPs) embedded on reduced graphene oxide (rGO). A sequential repetitive chemical reduction technique to observe the growth of silver nanoparticles (AgNPs) attached to rGO, was performed on a single solution of graphene oxide (GO) and silver nitrate solution (7 runs, R1–R7) in order to manipulate the growth and size of the AgNPs. The physical–chemical properties of the samples were examined by RAMAN, XPS, XRD, SEM-EDAX, and HRTEM analyses. It was confirmed that AgNPs with diameter varying from 4 nm in first run (R1) to 50 nm in seventh run (R7) can be obtained using this technique. A major correlation between particle size and activities was also observed. Antibacterial activities of the samples were carried out to investigate the disinfection performance of the samples on the Gram negative bacteria (Escherichia coli). It was suggested that the sample obtained in the third run (R3) exhibited the highest antibacterial activity as compared to other samples, toward disinfection of bacteria due to its superior properties. This study provides a unique and novel application route to synthesize and control size of AgNPs embedded on graphene for various applications.
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    Sol-gel synthesis of less expensive mesoporous titania-tin dioxide systems: Investigation of the influence of tin dioxide on the phase structure, morphology and optical properties
    (Elsevier, 2017) Shao, Godlisten N.; Imran, S.M; Abbas, Nadir; Kim, Heetaik
    Herein the influence of SnO2 on the optical, morphology and phase structure of mesoporous TiO2-SnO2 composites was examined. Composites with Sn/Ti ratio ranging from 0.1 to 5 were synthesized using less expensive sources in the absence of additives. The obtained samples were examined by XRD, HRTEM, SEM-EDAX, XPS, UV–vis DRS, XRF, TGA and nitrogen gas physisorption studies analyses. The physicochemical properties of the TiO2-SnO2 systems depended mainly on the Sn-to-Ti ratio, calcination temperature and the interaction between Sn4+and Ti4+. XRD results depicted that samples with Sn/Ti = 0.1 calcined at ≤600 °C exhibited pure anatase TiO2 crystals and the tendency of increasing Sn4+ content facilitated a phase transformation to attain rutile structure. Optical analyses of the samples showed that the absorption of the samples can be extended into the visible region. This study provides a systematic and economical method for large-scale production of TiO2 based composites with desirable properties for various applications.
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    Sol–gel synthesis of photoactive kaolinite-titania: Effect of the preparation method and their photocatalytic properties
    (Elsevier, 2015) Shao, Godlisten N.; Imran, S.M; Kim, Heetaik
    Supporting TiO2 on different materials is a potential strategy to improve the photochemical properties of the resulting composites. Kaolinite (K) was used as a support to synthesize a series of kaolinite-titania (K-TiO2) photocatalysts with desirable properties for decolorization of organic contaminants. Initially, TiO2 sol was formed through gelation of titanium oxychloride using ammonium hydroxide solution and subsequent peptization of the preformed gel in a low concentration of nitric acid. The sol was reacted with different concentrations of kaolinite at different pH conditions to yield K-TiO2 composites with different TiO2 compositions. The physicochemical properties of the photocatalysts were examined by XRD, FTIR, TGA, SEM-EDAX, XRF, UV–visible DRS, TEM and nitrogen gas physisorption studies analyses. XRD results revealed that through varying pH of the reaction a mixture of TiO2 crystals can be attained in the sintered samples. A simple photocatalytic experiment of the calcined photocatalysts was carried out to evaluate the decolorization of methylene blue in the presence of an artificial UV source. The obtained results were exquisitely compared to those of the ZrO2-TiO2 based composites obtained in our previous study. It was revealed that the amount of TiO2 in the composites and the calcination temperature had a profound effect on the microstructure and photocatalytic performance of the samples. Thus, the KT34- 600 sample exhibited the highest activity of all due to its superior properties. This study provides a criterion for selection of precursors, synthetic routes and support suitable for the formation of metal oxides composites with desirable properties for heterogeneous catalysis.
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    Sol–gel synthesis of TiO2-Fe2O3 systems: Effects of Fe2O3 content and their photocatalytic properties
    (Elsevier, 2016) Abbas, Nadir; Shao, Godlisten N.; Kim, Heetaik
    An inexpensive sol–gel technique to synthesize TiO2-Fe2O3 nanocomposites with improved structural and photochemical properties is introduced. A series of TiO2-Fe2O3 nanocomposites with different Fe2O3 contents were prepared through cheap TiO2 precursor titanium oxychloride (TiOCl2). The physicochemical properties of the samples were examined by XRD, XRF, SEM, EDX, HRTEM, UV–vis DRS, FTIR, TGA and nitrogen gas physisorption studies. The effects of calcination temperatures and Fe2O3 content on the mesostructure and photocatalytic strength of the prepared TiO2-Fe2O3 composites were investigated. Results showed that composites with distinct structural, optical and photochemical properties can be formed by varying Fe2O3 content.
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    Sol–gel synthesis of vanadium doped titania: Effect of the synthetic routes and investigation of their photocatalytic properties in the presence of natural sunlight
    (Elsevier, 2015) Shao, Godlisten N.; Imran, S.M; Kim, Heetaik
    The development of visible-light effective TiO2 allows low cost degradation of toxic non-biodegradable organic pollutants. In the present study a series of vanadium doped titania (V-TiO2) photocatalysts with V-to-Ti of 0.03, 0.06 and 0.1 were synthesized by either one-step or two-step modified sol-gel approaches. Titanium oxychloride solution was used as a titania source while vanadium pentaoxide was used as a vanadia source to form V-TiO2 in the absence of surfactants. One-step process was performed through the reaction of the TiO2 source with vanadium source. In two-step route the Ti(OH)4 gel was preformed through gelation of the TiO2 source using aqueous ammonium and then peptized in the acidic vanadium solution. The physicochemical properties of the samples were examined by XRF, XRD, UV-visible DRS, SEM-EDAX, TEM, DTA-TGA, XPS and nitrogen gas physisorption studies analyses. It was observed that the morphology, crystal structure and photochemical properties of the obtained samples were largely dependent on the calcination temperature, synthetic approach and V-to-Ti ratios. Calcination of the samples yielded large ultrafine and perhaps monodispersed particles with different sizes depending on the synthetic technique. The photocatalytic performance of the samples was tested in the photodegradation of methylene blue in the presence of natural sunlight. The photocatalytic activities of the samples synthesized by two-step route were higher than that of the samples yielded through one-step approach. Thus, the present report suggest systematic, convenient and cost-effective sol-gel techniques to yield V-TiO2 photocatalysts with harnessed photocatalytic performance for decolorization of toxic organic pollutants in the presence of natural solar irradiation.
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    Study of the Electroconductive Properties of Conductive Polymers-Graphene/Graphene Oxide Nanocomposites Synthesized via in Situ Emulsion Polymerization
    (Wiley, 2018) Imran, S.M; Shao, Godlisten N.; Kim, Heetaik
    The present study introduces a modified approach to synthesize polyaniline (PANI) and polypyrrole (PPy) doped with graphene oxide (GO) or graphene (GN) through an in situ emulsion polymerization (EP) technique. Dodecyl benzene sulfonic acid (DBSA) was used as a surfactant and doping agent as well during the polymerization reaction. The morphology and microstructure of the synthesized polymers and their nanocomposites were studied by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. All of these characterization techniques confirmed the superior morphology and thermal properties of the nanocomposites. The electroconductive properties of the synthesized polymers and their nanocomposite pellets containing 5 wt% of either GN or GO pressed at pressures of 2, 4, and 6 tons were investigated with a fourprobe analyzer. Nanocomposites showed very high electrical conductivity compared to individual PANI and PPy samples pressed at the same pressures. The addition of GO and GN not only improved the thermal stability but also significantly enhanced the electrical conductivity of the nanocomposites. Thus, the present work signifies the importance of the direct loading of GO and GN into conductive polymers during the EP process using DBSA as a surfactant to achieve nanocomposites with promising properties for various semiconductive applications.