Papers by Keyword: Silica Coating

Abstract: Ni and Ni-containing nanoparticles exhibit promising magnetic properties. In a preliminary experiment, these nanoparticles aggregated after synthesis. Because nanoparticle aggregation may degrade their unique properties, a method to prevent their aggregation is required. In this study, Ni-Pt nanoparticles were synthesized and coated with silica to suppress aggregation. A colloidal solution of Ni-Pt nanoparticles was synthesized in water exposed to air using nickel(II) acetate tetrahydrate (Ni source), hexachloroplatinate(IV) hexahydrate (Pt source), sodium borohydride (reducing agent), and citric acid (stabilizer). Silica-coated Ni-Pt nanoparticles (Ni-Pt/SiO₂) were synthesized by adding a tetraethylorthosilicate (TEOS)/ethanol solution to the colloidal Ni-Pt nanoparticle solution. The morphology of the Ni-Pt nanoparticles varied with reaction time. The Ni-Pt/SiO₂ nanoparticles consisted of Ni-Pt cores and SiO₂ shells, with their morphology dependent on the TEOS concentration. Furthermore, the Ni-Pt/SiO₂ nanoparticles were more dispersed than the uncoated Ni-Pt nanoparticles, suggesting that the silica coating suppressed aggregation.

Abstract: High nickel content in nickel manganese cobalt (NMC811, LiNi_0.8Mn_0.1Co_0.1O₂) resulted in high capacity but low structural stability. Surface modification of NMC811 via silica (SiO₂) coating is known to counter this problem, leading to better electrochemical performance. In this work, silica was synthesized from rice husk through sol-gel method with alkaline extraction followed by acidification process. The resulting silica was coated onto commercially available NMC811 to modify its surface via solid-state reaction method. The characterization results showed that the silica coated NMC811 demonstrated a higher conductivity and lithium diffusion coefficient of 2.85 x 10^-5 S/cm and 2.52 x 10^-14 cm²/s, respectively, compared to that of bare NMC811 (8.17 x 10^-6 S/cm and 1.75 x 10^-15 cm²/s, respectively). This result confirms that the silica derived from rice husk can be used as a potential low-cost material to modify the surface and thus to increase the electrochemical performance of commercial NMC811.

Abstract: Polyethylene glycol (PEG) coatings are developed for magnetite nanoparticles (NPs). The magnetic properties of superparamagnetic type, magnetite Fe₃O₄ nanoparticles are suitable for biosensing applications. Magnetic NPs were prepared by Co-precipitation method and oven dried. Using a Transmission Electron Microscope (TEM) and X-Ray Diffractometer (XRD), nanoparticles size and composition were found, including the presence of Fe₃O₄ peak. The magnetic properties are influenced by electron environments of the Fe³⁺ ions within the iron oxide structure. The magnetic properties were measured by Vibrating Sample Magnetometer (VSM), thus, the results of Fe₃O₄ NPs exhibited a high magnetic saturation (Ms) of 61.31 emu/g. In the case of PEG coated MNPs, confirmed by Fourier Transform Infrared Spectroscopy (FT-IR), a reduced Ms of 40.00 emu/g, which decreased further following surface modification with 3-aminopropyl triethoxysilane (NH₂) to 36.77 emu/g. The resulting size range of NPs of pure Fe₃O₄ NPs was 5-50 nm. In comparison, the PEG coated NPs were larger, 10-100 nm. In the part of protein binding and separation from solutions of bovine serum albumin (BSA) where investigated. This process will be beneficial to developing low cost sensors for biomolecules and biotechnologies in the future.

Abstract: Coating of magnetic nanoparticles (MNPs) is usually a requirement prior to their utilization in biomedical applications. However, coating can influence the magneto-structural properties of MNPs thereby imparting their applications. The present work highlights the combustion synthesis of Na-doped lanthanum manganites (LNMO) and the influence of silica coatings on the magneto-structural properties, colloidal stability and antimicrobial properties of LNMO MNPs with their biomedical applications in mind. The crystalline perovskite structure was the same both for the bare and silica coated LNMO samples while there was a slight increase in crystallite size after coating. The FTIR spectral analysis, reduction in agglomeration of the particles and the elemental composition of the coated nanoparticles confirmed the presence of silica. The magnetization values of 34 emu/g and 29 emu/g recorded for bare and coated LNMO samples, respectively show that LNMO MNPs retained its ferromagnetic behaviour after silica coating. The pH dependent zeta potentials of the coated sample is-22.20 mV at pH 7.4 (physiological pH) and-18 mV at pH 5.0 (cell endosomal pH). Generally, silica coating reduced the antibacterial activity of the sample except for Bacillus spp where the antibacterial activity was the same with the bare sample. These results showed that while silica coating had marginal effect on the crystalline structure, size and magnetization of LNMO MNPs, it reduced the antibacterial activity of LNMO MNPs and enhanced greatly the colloidal stability of LNMO nanoparticles. Keywords: Na-doped lanthanum manganites, Silica coating, magnetic nanoparticles, biomedical applications, antimicrobial properties, colloidal stability

Abstract: This work demonstrated the improvement of belite cement compressive strength by incorporating nanosilica coated single-walled carbon nanotubes (SWNTs@SiO₂) into the cement paste. The structure and chemical compositions of SWNTs@SiO₂ materials were characterized by transmission electron microscopy and energy dispersive X-ray spectroscopy techniques, respectively. Belite cement composites were prepared by mixing belite cement paste with different loadings of SWNTs@SiO₂ ranging from 0.02 – 0.1 wt%. In order to measure the early strength of cement composites, the samples were aged for 7 days, and then subjected to compression tests. Effects of uncoated SWNTs and silica coated SWNTs loadings on the compressive strength of belite cement composites were studied. Without pre-coating SWNTs with nanosilica, the SWNTs additives led to large decrease in compressive strength of belite cement composite. Improvements in compressive strength of belite cement are shown in samples that incorporated SWNTs@SiO₂ loadings. The coating layer helps enhance bonding strength between reinforced SWNTs and the matrix, as well as promote hydration reactions in the cement paste. The highest increase in the compressive strength of 18.8 % is found in the sample with the minimal SWNTs@SiO₂ loading of 0.02%.

Abstract: This paper demonstrates a technique to synthesize silica-coated single-walled carbon nanotubes (SWNTs@SiO₂) based on sodium dodecyl sulfate (SDS), 3-aminopropyltriethoxysilane (APTES), ammonium hydroxide (NH₄OH) and tetraethyl orthosilicate (TEOS). The coating of silica is done to promote bond strength between SWNTs@SiO₂ and other materials. The anionic surfactant used in the coating process helps create linkages between the silica coupling agent and the SWNTs’ walls without compromising the excellent properties of SWNTs. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX) were employed to characterize the sizes of SiO₂ particles, the structure of SWNTs@SiO₂, and the elements existed in the materials. The size of SiO₂ particles has shown to be dependent on the amount of TEOS concentration and reaction time. Higher TEOS concentration and longer reaction time led to larger SiO₂ particles. Successful coatings of SiO₂ on SWNTs have been demonstrated. Silica appeared to be uniformly coated on the SWNTs surfaces. The thickness of the coating layer was found to be approximately 3-7 nm.

Abstract: Silica coated alumina abrasives, used for abrading the surface of Yttria stabilized tetragonal zirconia polycrystal ceramics, were produced in order to achieve successful bonding with resin luting cement. The source of the silica coating was from Silicon Nanoparticles (SiNPs) that were produced from spark erosion in high pressure flushing of deionized water. SEM images verified average size distribution of the SiNPs to be between 30-50nm. In contrast to the tribochemical methods that are used widely to produce such abrasives, a completely novel dry physical process was opted for this experiment. By optimization of the conditions, 2g of purified SiNPs was mixed with 20g of alumina μ-particles (approximated diameter of 100μm), in presence of 25ml ethanol, mixed thoroughly to form slurry. Heated up to 120°C for 20 minutes to evaporate the ethanol, the resultant powder mix was compacted and uploaded in furnace at temperature of 1100°C for 2hrs. This formed an oxide layer on the SiNPs which consequently formed bonding with the alumina particles. SEM/EDS results validate substantial amount of coating of silica on alumina. The paper hereby demonstrates a novel method of producing silica coated alumina abrasives, which is a dry and cleaner substitution method compared to tribochemical approach.

Abstract: In this paper, Mn²⁺ doped ZnS (ZnS:Mn) nanoparticles were prepared by co-precipitation method. And then different thickness of TiO₂ and SiO₂ inorganic shell were coated on prepared ZnS:Mn through the hydrolysis reaction of tetrabutyl titanate (TBOT) and tetraethyl orthosilicate (TEOS). ZnS:Mn crystal and core/shell structure were described by X-ray diffraction (XRD) and scanning electron microscope (SEM). Optical property of all ZnS:Mn/XO₂ (X=Ti, Si) nanoparticles were investigated by photoluminescence (PL) spectrometer. The effect of Mn²⁺ concentration and XO₂ (X=Ti, Si) shell thickness on luminescence intensity of ZnS:Mn/XO₂ was studied. The results showed that with TiO₂ and SiO₂ shell thickening, Mn²⁺ emission of ZnS:Mn/XO₂ samples increased first and then decreased. When the thickness of inorganic shell (molar ratio of shell and core amount) reached to 0.5 (TiO₂) and 1.0 (SiO₂), the optimal luminescence intensity was obtained. The emission of ZnS:Mn/TiO₂ and ZnS:Mn/SiO₂ was 2.0 and 1.5 times more in intensity than that of uncoated ZnS: Mn, respectively.

Abstract: The acid resistance of ultramarine blue was greatly enhanced by silica coatings. Sodium metasilicate nonahydrate was used as silica precursor and ammonium chloride was used to react with it. Fourier transform infrared (FT-IR) spectroscopy was used to characterize surface structure on the coating layer. The effects of coating conditions on acid resistances of the coated ultramarine blue were investigated. The acid resistance was evaluated by immersing the pigment in 10 wt% hydrochloric acid. The results showed the optimal mass ratio of silicate to ultramarine was 3.75 and the proper solid content was 60 g/L. Under above conditions, the silica coated ultramarine blue exhibited an acid resistance of 8, while the uncoated ultramarine blue only showed an acid resistance of 1.

Abstract: Acid-resistant ultramarine blue pigment with a silica shell was prepared by dense silica coating process. From X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) analysis, it was confirmed that silica in the coating is attached on the ultramarine particles surface by characterizing the composition of elements and the microstructure on the surface of the silica coated particles. Orthogonal experimental design was applied to optimize the operating conditions of the coating process. The best acid resistance for the coated ultramarine blue reached the ninth grade under the following conditions: silica adding rate of 5 g/h, solid content of 6 g/l in the slurry and coating time of 2.5 h.