Papers by Keyword: Silica Gel

Abstract: 3D printing of ceramics grabbed its attention recently because of its ease of shaping. The extrusion-based 3D printing technique is widely used for ceramics as it involves paste formulation. However, the slurry is often formulated and mixed initially by hand kneading and later by a high-speed mixer. This phenomenon leads to the evaporation of water quickly while combining or out of its insufficient time allowed for extrudable slurry or paste formulation. The slurry's printable time is also reduced due to this phenomenon. This study prepares a hybrid ceramic mixture comprising silica gel, and printable time is calculated. Triaxial porcelain is used as a model ceramic.

Abstract: Utilization of rice husk ash (RHA) as a pozzolanic material is a viable solution for reducing air pollution that is caused by open incineration of rice husk. Treatment of the rice husk with high-concentration acid and subsequently subjecting the treated rice husk to controlled incineration at high temperature can produce RHA that contains silica of a high purity, which can contribute to a high pozzolanic reactivity of concrete. However, the dependence of high-concentration acid and high incineration temperature will have an adverse effect on the environment. Therefore, in the present study, effect of treatment and incineration temperature on extraction of silica from RHA was investigated by conducting analytical and compressive strength tests on concrete samples. Raw and treated rice husks were incinerated for an hour at 400, 500 and 600°C to produce untreated and treated RHA, respectively. Hydrothermal synthesis was performed to execute gelation of silica from the RHA. The silica gel was converted into powder and then incorporated into concrete mixes for preparation of samples. The samples comprise the control sample, which does not contain any of the silica extracted from the RHA, and those that contain 5% silica from the untreated and treated RHA. Findings indicate that the treatment was necessary to produce concrete with adequate compressive strength relative to that of conventional concrete. Incorporation of 5% silica from treated RHA at the incineration temperature of 600°C resulted in the highest compressive strength of 6.44 MPa, which is an increase of 8.5% from that of the conventional concrete.

Abstract: Increasing amounts of agricultural and industrial wastes have prompted researchers to re‑use the wastes as prospective cement replacement materials. Sugarcane bagasse is an agricultural waste that is widely available as a by-product of sugar and ethanol industries. As sugarcane bagasse possesses a high pozzolanic reactivity owing to its high silica content, the potential of extracting silica from sugarcane bagasse ash (SCBA) for cement replacement has to be explored. In the present study, analytical and compressive strength tests were performed on concrete samples to determine the effect of replacing cement with silica extracted from SCBA. Influences of treatment and burning temperature for conversion of sugarcane bagasse to SCBA on the analytical and compressive strength test results were also investigated. Raw and treated bagasse were burned in a muffle furnace for one hour at 600, 700 and 800°C to produce untreated and treated SCBA, respectively. Hydrothermal synthesis was performed on the SCBA for extraction of silica gel. Three types of concrete samples were prepared, which are the control sample that does not contain any cement replacement material and samples that contain 5% silica from untreated and treated SCBA. Compressive strength tests were performed on the samples after seven days of curing. Findings indicate that treatment of the bagasse was essential to produce SCBA of adequate silica content that can improve the compressive strength of the concrete. The increase in compressive strength is at its highest at the burning temperature of 700°C, where a change of +8.05% was achieved.

Abstract: Encapsulation is one of the immobilization methods to increase the stability of the enzyme or other biomolecules by binding or trapping the molecules in a certain matrix. Silica gel was mostly chosen as a matrix to encapsulate the enzyme due to its high thermal stability. In this research, silica gel was used to encapsulate of lipase enzyme. Silica gel was synthesized from sodium silicate by the sol-gel technique. Silica from rice husk ash was extracted using 2 M NaOH to produce a sodium silicate solution. The silica gel was synthesized using the acidification of sodium silicate solution. The various mass and volume ratios of the enzyme and sodium silicate solution were 1:1; 1:2, and 2:1 (w/v). The amount of encapsulated enzyme was analyzed with UV-Vis spectrophotometry at a wavelength of 540 nm after complexing with biuret. The encapsulated enzyme activity test was carried out for the transesterification reaction of palm oil under various conditions. Fatty Acid Methyl Esther (FAME) analysis and surface analysis of the encapsulated enzyme was performed using GC-MS and SEM-EDX, respectively. The results showed that the lipase enzyme could be well encapsulated in silica gel after aging for eight days, at a lipase and sodium silicate ratio of 1:2 (w/v) with a percentage of 93.72%, and there were still 85.76% encapsulated lipase even after being washed seven times. The transesterification reaction resulted in the highest conversion of oil to FAME (33.87%) at a mole ratio of 1:3 oil: methanol and a lipase mass of 0.5 g.

Abstract: The conversion of silica gels into sulfated silicas (SO₄/SiO₂) have been carried out. The sulfation process of the catalysts was carried out by impregnation of sulfuric acids at concentrations of 1; 2; and 3 M and calcination temperatures of 500, 600, and 700 °C. Sulfation with 2 M H₂SO₄ and calcination temperature of 600 °C (SS2-600) produced a catalyst with the highest acidity value (5.13 mmol NH₃ g^-1). XRD analysis showed the formation of amorphous SiO₂ phase, whereas SSA analysis showed that the SS2-600 catalyst had a mesoporous structure with a surface area of 147.728 m²/g, a total pore volume of 0.25 mL/g and a pore diameter of 6.439 nm. Characterization results show that sulfated silica gels have potency as solid acid catalysts.

Abstract: Porous surface of silica gel (SG) have been modified with alkyl fatty amine compounds (octadecylamine, ODA) via wet impregnation process. The ODA-based adsorbents were physically characterized by XRD. The presence of crystalline peaks on ODA/SG diffractograms were ascertained the well-dispersion of ODA on the SG surface. XRD analysis displayed the increasing intensity of crystalline ODA with higher percent amine loaded and shifting of the several crystalline peaks of ODA verified the interaction of SG600-ODA. Capacity of CO₂ capture by prepared solid adsorbents were evaluated using CO₂ adsorption-desorption isotherms. This study shows that increasing percentage of ODA were improved the amount of CO₂ uptake by following this trend: 35ODA/SG > 25ODA/SG > 15ODA/SG > SG > 5ODA/SG. However, promotion of 5 wt.% ODA unabled to enhance the capacity of CO₂ captured due to pore blockage and reduction in SG pore surface, thus hindered the physisorption between CO₂ and SG.

Abstract: Nyamplung (Calophyllum inophyllum), widely spreads in Indonesia archipelago, is known to have many advantages. It has various benefits that can be utilized from its root, stem, leaf, and seed. C inophyllum’s seed contains bioactive compounds called calophyllolide. However, the utilization of C. inphyllum’s seed is limited because it contains harmful toxins. Therefore, C. inophyllum’s seed is generally used and investigated as a raw material of biodiesel. This research aimed to find the best condition to isolate calophyllolide, to know the yield of isolated calophyllolide and to know its purity percentage from crude C. inophyllum oil. Current research on calophyllolide is to extract the substance from C. inophyllum’s shell nut without further treatment on it. In this work, calophyllolide was separated from crude C. inophyllum oil by silica gel adsorption. Each fraction obtained was tested qualitatively using Thin Layer Chromatography (TLC) and quantitatively using Gas Chromatography (GC) to analyze calophyllolide mixture. In this study, the best separation method (12.92% purity, 8.03% yield, and 95.02% recovery of calophyllolide) was obtained by using crude C. inophyllum to silica gel mass ratio of 1:2 (g/g).

Abstract: Mathematical modelling of batch adsorption of Oryzanol separation from Rice Bran Oil (RBO) has been set-up and tested by generated experimental data. The proposed model takes into account mass transfer and equilibrium phenomena. The effects of intra-particle gradient were considered, so the adsorption rate is controlled by the rate of solute mass transfer from the bulk liquid to the surface of particles and the intra-particle diffusion. In this model, the rate of Oryzanol mass transfer from the bulk liquid to the surface of the particle is described by film theory, while the intra-particle diffusion is assumed to be through the liquid inside the pore. Furthermore the Oryzanol in the liquid in the pore was assumed to be in equilibrium with the Oryzanol on the adjacent pore surface, in which equilibrium model applied was coefficient distribution approach. The values of the parameters involved in the models were obtained by curve fitting to the experimental data. It turned out that model proposed can quantitatively describe the batch adsorption of Oryzanol adsorption from rice bran oil with silica gel.

Abstract: In order to control humidity in air conditioning system, various desiccants are used to dehumidify air in air conditioners. One of simple methods, which can be used to coat desiccant materials on surface of heat exchanger in air conditioners, is dip coating. Typical, desiccants used in dehumidifying system is silica gel in a form of solid-state powder. This powder has low adhesion with the heat exchanger surface. To improve adhesion of the silica gel powder, some glue is generally applied on the surface of heat exchanger. The dehumidification properties of silica gel, however, will be remarkably reduced because of less surface area of silica gel powder. Instead of silica powder, this work aims to synthesize silica gel using sol-gel method, which the sol-state material can be suitably used in dip coating. In experimental study, silica gel was synthesized by sol-gel method of precursors with 1 M sulfuric acid (H₂SO₄). The pH was adjusted using sodium silicate solution (Na₂O(SiO₂)_x.xH₂O) and rinsing with DI water. Surface area, pore volume and size, phase composition, morphology, and percentage of moisture adsorption of the synthesized silica gel were characterized. Silica gel fabricated with pH 5 showed the highest percentage of moisture adsorption compared with other samples. In addition to the highest percentage, silica gel with pH 5 could adsorb water up to 28 times of its own weight. X-ray diffraction (XRD) results showed that Na₂SO₄ impurity were successfully eliminated after rinsing with DI water more than 4 times. Finally, adhesive property of silica gel on aluminium-fin samples was tested with scalloped tape-test method. It was observed that, to improve the adhesion property of silica gel on the aluminium fins, prior to dipping of silica gel, the fins should be etched with sulfuric acid. The acid can adjust the surface of fines to be much rougher.

Abstract: Silica gels containing incorporated heteropolyacids (HPAs) were synthesized in acidic media by co-condensation of tetraethoxysilane (TEOS) with phosphotungstic or phosphomolybdic acids using the sol-gel technique. The effect of the synthesis conditions on their structure and morphology was studied. Yields of modified materials were somewhat lower compared to non-modified silica gels. All materials were mesoporous but contained micropores in their structures. Presence of bands of Keggin’s structures in FT-IR spectra along with absence of XRD patterns of crystalline HPAs confirmed their fine incorporation into silica network. Particle sizes of modified materials were 500-1100 nm except for the W-containing sample obtained with trimethylstearylammonium chloride, which was significantly lower. This unusual effect was attributed to stabilization of primary silica nanoparticles by interactions between the surfactant and HPA. High ratio HPA/TEOS resulted in partial loss of porosity. Obtained results might be used for optimization of synthesis of effective catalysts and adsorbents containing HPAs in mesoporous structure.