Papers by Keyword: Silica

Abstract: The technical issue of direct ethanol fuel cells is slow kinetics of ethanol electrooxidation by using noble metals such as Pt. We propose silica-embedded carbon nanofiber (SECNF) as a catalyst support for the electrooxidation of ethanol to improve catalytic activity of Pt. SECNF was prepared by electrospinning, then Pt nanoparticles were deposited on SECNF. Catalyst characterizations were performed by SEM, EDX, and XRD. Cyclic voltammetry was performed to analyze catalytic activity of Pt/SECNF. The mass activity of Pt/SECNF was 2.9 times higher than a commercially available Pt/carbon catalyst (Pt/C_com). Electrochemically active surface area of Pt/SECNF was lower than Pt/C_com. Hence, the activity enhancement is attributed to the improvement of specific activity for Pt/SECNF. This enhancement is attributed to the interaction between Pt and SiO₂ like hydrogen spillover. Pt/SECNF is a promising catalyst for direct ethanol fuel cells which can reduce Pt loading.

Abstract: The cellulose-silica composite aerogels (CAs) were fabricated through a permeation sol-gel process in the regenerated cellulose hydrogels followed by freeze drying. The precursor Na₂SiO₃ instead of traditional organic precursor was diffused in the cellulose matrix followed by permeating the catalyst into the cellulose nanofibers network gradually to promote the in situ condensation of Na₂SiO₃ to form a SiO₂ gel skeleton from outside to inside. The obtained CAs displayed the interpenetrating network (IPN) structure of the regenerated cellulose nanofibers network and the SiO₂ gel skeleton in nanoscale. In the IPN structure, the flexible cellulose nanofibers network was supported by the hard inorganic network effectively to sustain the compression and the silica gel skeleton protect the cellulose nanofibers to avoid the remodeling of their shape in the process of solvent replacement before freeze drying. Due to the synergic effects of the different network, the IPN structure endows the CAs with high compression modulus (as high as 15.48 MPa), high specific surface area (as high as 621 m² g^-1) and low density (less than 0.182 g cm^-3).

Abstract: Highly porous silica ceramics were prepared by in-situ gelation of an aqueous suspension with well dispersed silica particles and N’N-dimethylacrylamide (DMAA) monomer, followed by lyophilization and pressureless sintering. The gelcasting process was imparted by polymerization of DMAA. The silica raw materials used in this experiment are the dusts collected from the exhaust fumes of silicon industry. The as-obtained porous silica ceramics had three-dimensional and hierarchical pore structure and the porosity ranged from 75 to 88 % as the sintering temperature varied from 850 to 1050 °C. In addition, the porous silica ceramics appeared to have strong mechanical strength. Compressive strength of the porous silica ceramics was as high as 3.2 MPa even when the porosity was nearly 80%. The gelcasting-lyophilization method was proved to be a novel and promising route for the preparation of highly porous and mechanically strong materials.

Abstract: Silica extracted from rice husk was used as a support to synthesize the monometallic Ag, Co and bimetallic Ag-Co nanoparticles. The nanoparticles were prepared via a sol-gel method by adding glucose as the reducing agent. The prepared nanoparticles were designated as Ag-NP, Co-NP and AgCo-NP. The successful incorporation of Ag/Co onto the silica surface were evidenced by TEM, FT-IR and DR/UV-Vis analysis. The TEM analysis showed the presence of small spherical shape nanoparticles with an average mean size of 3.18-3.57 nm. Through DR/UV-Vis analysis, the presence of Ag⁺ and cobalt in the oxidation state of +2 and +3 were confirmed, while FT-IR verified the presence of M-O and Si-O-M⁺ bond.

Abstract: Nanostructure ZnO and Ag/ZnO were successfully synthesized from rice husk via an eco-friendly sol-gel method. Structural investigations by FT-IR and DR/UV-Vis analyses confirmed the successful inclusion of metal species into the silica framework. XRD and TEM studies evidenced the well-dispersion of silver and zinc onto the silica support. Modification of ZnO with Ag resulted in the maximum photocatalytic activity (90.5 %) of methylene blue, (40 mgL^-1) under compact fluorescent lamp irradiation. Minimal agglomeration, high dispersion and narrow band gap energy of Ag/ZnO was suggested to contribute to its excellent photocatalytic activity in comparison to ZnO.

Abstract: Colloidal particles based on iron oxides and silica were obtained by sol-gel method. Hysteresis curves at various temperatures were built by MPMS SQUID VSM. Theoretically calculated values of samples remanent magnetization were compared to experimental data. Despite of the average particles size about 10 nm sample has remanent magnetic moment. The phenomena may be explained on the basis of magnetostatic interaction between particles. The magnetic state of analyzed samples can be conditional on the presence of several phases with very different magnetic properties or the size effect.

Abstract: Magnetic nanocomposite material composed of silica coated MgFe₂O₄ for potential biomedical applications were synthesized by a two-step chemical method including solution combustion synthesis, followed by silica coatings of the ferrite nanoparticles. The effects of silica coatings on the structural, morphological and magnetic properties were comprehensively investigated using powder X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), energy dispersive absorption x-ray (EDAX), Fourier Transform Infrared spectroscopy (FTIR), thermogravimetric analysis and differential thermal analysis (TG–DTA) and vibrating sample magnetometer (VSM). The colloidal behaviour of coated MNPs in physiological saline medium like water or phosphate buffer saline (PBS) was also studied by zeta potential measurements. The XRD patterns indicate that the crystalline structure is single cubic spinel phase and the spinel structure is retained after silica coating. Also, after silica coating, the crystallite size (from Scherrer formula) decreases from 53 to 47 nm. The magnetic results show that MgFe₂O₄ MNPs (bare and silica coated) is ferrimagnetic at room temperature. Zeta potential studies revealed that there is enhanced colloidal stability of MgFe₂O₄ MNPs after silica coating in aqueous media which is an applicable potential in biomedical applications.

Abstract: SrAl₂O₄:Eu²⁺,Dy³⁺ phosphors were synthesized under different temperature by high temperature solid phase method. Encapsulation modification of SrAl₂O₄:Eu²⁺,Dy³⁺ by using SiO₂ glycol were made over chemically unstable against water. Photoluminescence measurement result shows that when the sintering temperature is 1300 °C, the initial afterglow brightness of SrAl₂O₄:Eu²⁺,Dy³⁺ is up to the highest, 12101 mcd/m². FTIR results showed that new IR peaks at 1085 cm⁻¹ due to the vibration of Si-O-Si and at 931cm⁻¹ due to the vibration of Si-O-Al appeared after silica encapsulation. This verified that the silica encapsulation is not only a physical absorption process but also involving chemical bonding process. Both phosphors before and after encapsulation have same emission peak at 510 nm. A dense layer of silica formed on phosphor surface has the highest water-resistance after being encapsulated for 2h under the condition of pH 4 and encapsulation amount 10:1. The pH value of aqueous solution contained phosphor was steadily 8, and the initial afterglow brightness decreased only by 9%, that is, from 12101 to 11011 mcd/m².

Abstract: Rice husk is an agricultural residue from a rice-mill known as a rich source of silica. In this study, the rice husk was extracted for the contained silica by pretreatment with hydrochloric and calcination at 700 °C, and the white rice husk ash (WRA) mainly consisting of the silica was finally obtained. WRA was then investigated for its composition and structure with X-ray fluorescence (XRF) and X-ray diffractometer (XRD). The results showed that WRA contained a large amount of silica (90%) with amorphous structure. After that, WRA was used as filler for the preparation of natural rubber products. Two kinds of the natural rubber products were prepared here: 1) the pure natural rubber (PNR) product and 2) the deproteinized natural rubber (DNR) product. DNR was a protein removal natural rubber which is suitable for use as a dental material with the low allergenic properties caused from the proteins. Additionally, DNR used in this study could be provided by removing proteins from the natural rubber latex with 0.1 % urea in the presence of surfactant at room temperature. It was found that the nitrogen content (main element of proteins) of DNR was lower than PNR under the test condition. For the preparation of natural rubber products, WRA was mixed into the PNR and DNR latexes comparing with the commercial silica (Hisil-233). All finished latexes were compounded to obtain the natural rubber products. The viscoelastic properties and the cure characteristics of the entire products were investigated. It can be observed that WRA can be comparable with the commercial silica for use as filler for the natural rubber products. This is an attractive option to produce dental materials from the agricultural residues, which will reduce the cost of the production and also add value to the agricultural residues.

Abstract: Unsaturated polyester resins (UPRs) are most commonly used coating materials on steel among thermosetting polymers because of their low cost, easy application and good performance properties. However, UPRs show insufficient fire-resistance in respect of relatively high flammability accompanied by smoke production upon burning due to aromatic groups in the structure. Consequently, improving the fire retardancy of UPRs for extending their application becomes pivotal. Fire retardants (FRs) are widely used in polymers because they prolong the time to ignition, slow down the rate of flame spread, and generate less heat and smoke or toxic fume compared with the unmodified polymers. It has been a challenge to develop a cost effective, environmentally friendly fire retardant system which minimizes the negative effect on performance properties of the polymers [1 - 4].