Research Repository :: Browsing by Author "Kim, Hee Taik"

Browsing by Author "Kim, Hee Taik"

Now showing 1 - 13 of 13

BET Study of Silver-Doped Silica Based on an Inexpensive Method
(Materials Letters, 2012-04-28) Hilonga, Askwar; Kim, Jong-gil; Sarawade, Pradip B.; Quang,Dang Viet; Shao, Godlisten N.; Elineema, Gideon; Kim, Hee Taik
The aimof this study is to identify an acid precursor that ismost desirable for the synthesis of sodiumsilicate-based silver-doped silica for large-scale industrial production. The final products were developed based on the presence of silver (silver-doped silica) or the absence of silver (pure silica). The properties of the obtained final products were examined using the BET method. This method involves characterization based on N2 physisorption studies to determine the surface area, pore diameter, and pore volume. Various graphs were plotted using the obtained data to describe the pore size distribution, isotherms, and the properties of hysteresis loops. Silver-doped silica with a BET surface area of up to 357 m2/g and a pore size of 5.4 nm was obtained using the most desirable precursors—sodium silicate and sulfuric acid. This is an unprecedented step toward synthesis of silver-doped silica fromdesirable precursors. This approach to the synthesis of silica with desirable propertieswithout involving sacrificial templates (surfactants) will be convenient for many applications and suitable for large-scale economic industrial production.
Characterization of Calcium-Doped Silica Gel Prepared in an Aqueous Solution
(Resources Processing, 2012-02-20) Quang, Dang Viet; Park, Jin Koo; Kim, Jong-gil; Elineema, Gideon; Shao, Godlisten N.; Lee, Jae Eun; Kim, Hee Taik
In this study, calcium-doped silica was prepared by modifying sodium silicate-based silica gel in an aqueous solution of Ca(OH)2. Silica gels with less than 1 mm in size with different pH values were treated in Ca(OH)2 solution at concentrations ranging from 2 to 20 g/L and aged at 25, 60, and 90°C for 40 min. The BET surface area of the silica gel decreased while its pore size increased considerably after modification in Ca(OH)2 solution. The pH of 5% calcium-doped silica in water ranged from about 8.5 to 10, depending on the pH of silica gel, the aging temperature, and the concentration of the Ca(OH)2. When the concentration of the Ca(OH)2 solution was 20%, needle-like crystals of calcium silicate hydrate formed over the surface of silica gel.
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.
Facile, Single-pot preparation of nanoporous SiO2 particles (carrier) with AgNPs at core and crust for controlled disinfectant release
(Journal of Saudi Chemical Society, Elsevier B.V., 2019-03-11) Haider, M. Salman; Shao, Godlisten N.; Ahmad, Ahmad; Imran, S. Muhammad; Abbas, Nadir; Abbas, Ghulam; Hussein, Manwar; Kim, Hee Taik
This study demonstrates a novel, facile and one-pot approach to synthesize silica nanoparticles with silver at core and crust (SiNP-AgCC). A modified Stöber method was used to make SiNP-AgCC. A significant reduction in the size of SiO2 nanoparticles was seen, with 2–5 nm AgNPs being uniformly distributed on the surface and 10–20 nm AgNPs in the center. A typical mesoporous SiO2 particle (SiNP) produced using the Stöber method was transformed to nanoporous SiO2 by this modified Stöber method. Nanoporous SiO2 particles with silver in the center are advantageous for slow and consistent Ag+ release, which was confirmed by Ag+ ion release test. Antibacterial activities of the samples were tested to evaluate the disinfection performance of the samples on gram-negative bacteria (Escherichia coli) using disk diffusion and the LB-agar method. SiNP-AgCC showed prolonged silver release for more than 20 days and improved antibacterial properties even after five days of incubation.
A Gentle Method to Graft Thiol-Functional Groups onto Silica Gel for Adsorption of Silver Ions and Immobilization of Silver Nanoparticles
(2012-10-22) Quang, Dang Viet; Lee, Jae Eun; Kim, Jong-gil; Kim, You Na; Shao, Godlisten N.; Kim, Hee Taik
Thiol-functionalized silica that has been used to remove heavymetal from an aqueous solution and supportmetallic nanoparticles is usually synthesized by reflux in an organic solvent containing 3-mercaptopropyltrimethoxysilane (MPTMS). In this paper, we report a gentle method for grafting thiol-functional groups onto silica gel by an aging process that does not require mixing and refluxing in an organic solvent. Silica gel was synthesized by a sol–gel method from H2SO4 (40%) and sodium silicate, which was crushed into beads with sizes ranging from 180 to 450 μm. Silica beads (50 g) were mixed with 75 mL of a functionalization solution consisting of MPTMS, H2O, and C2H5OH and aged at 50 °C for 36 h in a box dryer. The success of the functionalization process was confirmed by FT-IR, BET, SEM and elemental analyses. The functionalization solution was percolated into pores and thiolfunctional groups were grafted onto the surface and pore walls of the silica beads. The ability of these functionalized silica beads to adsorb silver ionswas determined by the Langmuir isotherm equationwith amaximumadsorption of 75.8 mg/g. Silver nanoparticles with sizes ranging from 2 to 6 nmformed by chemical reductionwere located inside the pores and on the surfaces.
Influence of titania content on the mesostructure of titania–silica composites and their photocatalytic activity
(Powder Technology, 2012-08-28) Shao, Godlisten N.; Hilonga, Askwar; Jeon, Sun Jeong; Lee, Jae Eun; Elineema, Gideon; Quang, Dang Viet; Kim, Jong-Kil; Kim, Hee Taik
Titania–silica composites (TSC) with various Ti/Si ratios were synthesized via sol–gel process using less expensive precursors; sodium silicate solution as a silica source and titanium oxychloride as a titania source. The influence of varying Ti content in the composites was examined by FTIR, SEM, TEM, DTA/TGA, N2 physisorption studies, XRF and XRD. The BET surface area of the raw materials increased with increasing Ti/Si ratio up to 2.9 (461 m2/g) but further increase of Ti content beyond that ratio yielded compositeswith decreased surface area. The effect of aging evaluated in the samplewith Ti/Si=2.9 revealed that aging the composite for 2 h yields titania–silica powderwith the highest surface area (461 m2/g). The FTIR analysis displayed the presence of a vibration band at 945 cm−1, assignable to hetero linkage of the Si–O–Ti depicting the incorporation of TiO2 into SiO2 to form a composite.Moreover, photodegradation of methyl orange (MO) by the samples calcined at 800 °C showed that the TSC-5-800 (Ti/Si=5.6) exhibited the highest maximum photocatalytic activity of all the composites.
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.
Quantitative Recovery of High Purity Nanoporous Silica from Wste Products of the Phosphate Fertilizer Industry
(2012-06-12) Elineema, Gideon; Kim, Jong-gil; Hilonga, Askwar; Shao, Godlisten N.; Kim, You Na; Quang, Dang Viet; Sarawade, PB; Kim, Hee Taik
This study reports on the quantitative recovery of high purity nanoporous silica from wastes material (H2SiF6) of the phosphate fertilizer industry and Na2O SiO2. The silica recovered from the wastes was compared with silica from the reaction of H2SO4 and Na2O SiO2 because H2SO4 is commonly used. The product recovered from the wastes material and H2SO4 were 99.3% and 99.1% pure, respectively. The quantity recovered were 22.30 g and 20.11 g, respectively. The product had superior properties suitable for applications such as chromatography, reinforcing material for rubber and plastics. The process may significantly reduce the release of SiF4 gas into the environment.
Silver-Doped Silica Powder with Antibacterial Properties
(Powder Technology, 2011-10-08) Hilonga, Askwar; Kim, Jong-gil; Sarawade, Pradip B.; Quang, Dang Viet; Shao, Godlisten N.; Elineema, Gideon; Kim, Hee Taik
In this study a simple and reproduciblemethodwas used to develop silver-doped silica powder with antibacterial properties. Silicamatriceswere synthesized via a sol–gel route which allows one to easily tailor textural and chemical properties. A wide range of silica-materials/products was obtained via the present route. These are: pure silver nanoparticles (Ag0), silver in ionic state (Ag+), AgCl nanoparticles, and the mixture of Ag0 and AgCl. The efficacy of these products were tested against Escherichia coli and the results demonstrate thatmaterials that are suitable for antibacterial applications were obtained by this newly developed technique while utilizing sodium silicate, which is relatively inexpensive, as a silica precursor. This may significantly boost the industrial production of the inexpensive silver-doped silica products for various applications. A project on other innovative industrial applications of our products is in progress.
Specific capacitance–pore texture relationship of biogas slurry mesoporous carbon/MnO2 composite electrodes for supercapacitors
(Elsevier, 2019-02) Kibona, Talam Enock; Shao, Godlisten N.; Kim, Hee Taik; King’ondu, Cecil K.
Here, we report synthesis of biogas slurry mesoporous carbon/MnO2 composites by simple co-precipitation route followed by thermal treatment at 250 °C for 6 h. The texture, morphology, crystal structure, and microstructure of the composites are investigated by nitrogen sorption studies, FESEM, HRTEM, X-ray diffraction, and Raman spectroscopy. All samples exhibit type IV isotherms. The BET surface area decreased from 514 to 110 m2 g−1 while total pore volume decreased from 0.52 to 0.17 cm3 g−1 for samples loaded with 2×10−5 and 2×10−3 moles of Mn. The electrodes fabricated exhibit high specific capacitance of 709 F g−1 at scan rate of 5 mV s−1. The specific capacitance at scan rate of 5 mV s−1 increases with increasing MnO2 content. However, at 50 mV s−1, specific capacitance decreases with increasing MnO2 content. Varying the MnO2 content and hence the textural parameters, strongly influences the specific capacitances of the composite electrodes.
Synthesis of Mesoporous Silica with Superior Properties Suitable for Green Tire
(2012-04-26) Hilonga, Askwar; Kim, Jong-gil; Sarawade, Pradip B.; Quang, Dang Viet; Shao, Godlisten N.; Elineema, Gideon; Kim, Hee Taik
In this article we report synthesis of mesoporous silica with superior properties for application in green tire (environmentally friendly tire) as filler. The synthesis was done using a newly innovated apparatus which produce mesoporous silica with superior properties. The desired superior properties are big pore size, optimum BET, large pore volume, uniform properties, and improved performance in real application as tire filler. Mesoporous silica was characterized by BET method and final product with a pore diameter of up to 37 nm was obtained without using surfactants. This is unprecedented step toward synthesis of silica that is suitable for tire industry.
Synthesis of Silver Nanoparticles within the Pores of Functionalized-Free Silica Beads: The Effect of Pore Size and Porous Structure
(Materials Letters, 2011-10-29) Quang, Dang Viet; Sarawade, Pradip B.; Hilonga, Askwar; Kim, Jong-gil; Shim, YoungHo; Shao, Godlisten N.; Kim, Hee Taik
Here, we report on the synthesis of silver nanoparticles (Ag-NPs) manipulating the pores of silica beads (SBs) with sizes ranging from 0.5 to 1 mm. Silver ions were occluded inside the pores of SBs and in situ reduced to Ag-NPs using Sodium borohydride (NaBH4). SBs with different average pore diameters from 3.8 to 20 nm were used to assess the effect of their pore sizes and porous structures on the formation of Ag-NPs. Obtained results revealed that the silver amount occluded inside pores increases along with the increase of total pore volume. The particle sizes of the synthesized Ag-NPs mainly distribute from 8 to 15 nm and vary with the pore sizes and porous structure.
Two step synthesis of a mesoporous titania–silica composite from titanium oxychloride and sodium silicate
(Powder Technology, 2011-11-15) Shao, Godlisten N.; Elineema, Gideon; Quang, Dang Viet; Kim, You Na; Shim, YoungHo; Hilonga, Askwar; Kim, Jong-gil; Kim, Hee Taik
Mesoporous titania–silica composite (MTSC) with a large surface area (387 m2/g) and large pore volume was synthesized by a two step condensation sol–gel method. Transparent TiO2 sol was formed at room temperature through condensation and peptization of titanium oxychloride solution using ammonium hydroxide and aqueous nitric acid respectively. Sodium silicate was used as a silica source to form a composite with the preformed TiO2 sol. The physical properties of the composite were examined by Fourier Transform infrared (FTIR), BET surface area, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The nitrogen physisorption behavior of the synthesized composite was compared to that obtained from grafting and one-pot co-condensation methods using the same precursors in the presence of cetyltrimethylammonium bromide (CTAB). It was found that MTSC synthesized under this method possessed large pore sizes and pore volume but its thermal stability was comparatively low. FTIR spectra showed the formation of a Ti\O\Si bond at 940 cm−1 suggesting that titania was incorporated in silica to form a composite. The XRD patterns showed that the major phase of the titania had an anatase phase up to 900 °C but it transforms into rutile when calcined at 1000 °C. Furthermore the EDS studies of the as-synthesized and calcined samples substantiated the formation of titania–silica composites.

Browsing by Author "Kim, Hee Taik"

Results Per Page

Sort Options