Silica Nanowires Research Articles

Morphology and composition of silica nanowires synthesized on indium and tin catalysts

Silicon nanowires were synthesized by electron beam plasmaenhanced chemical vapor deposition. The synthesis was carried out using indium and tin catalyst with an average particle size of 100 and 660 nm, respectively, in the temperature range 100-270 °C for indium and 200-335 °C for tin. The minimum (optimum) temperature was found at which an oriented array of microropes was formed. This temperature was 200 °C for indium and 335 °C for tin. In addition, it was found that the formation of individual microropes on the tin catalyst occurred at a temperature lower than the eutectic temperature (232 °C). For indium, this effect was not observed. The silica nanowires synthesized on both catalysts consist of SiOx with x ranging from 1.9 to 2 for all temperatures.

Ternary Ag nanoparticles/natural-magnetic SiO2-nanowires/reduced graphene oxide nanocomposites with highly visible photocatalytic activity for 4-nitrophenol reduction

Agglomerate and reuse limit the promising application of silver nanoparticles (AgNPs) as catalyst. To eliminate those disadvantages, herein, Fe-containing silica nanowires (SiO2NWs) and reduced graphene oxide (RGO) are used as suitable substrates to prepare AgNPs/SiO2NWs/RGO nanocomposite via self-assembly approach. The nanocomposite mostly assembled with each other via intermolecular hydrogen bond and electrostatic adsorption to form a three-dimensional network structure. The AgNPs/SiO2NWs/RGO nanocomposite exhibit excellent photocatalytic activity for 4-nitrophenol reduction by NaBH4, originating from that the nearly mono-dispersed AgNPs are adhered on the surface of the SiO2NWs and RGO, allowing the effective contact of reactants with catalyst and facilitating the electron transfer between them in the reaction. The obtained nanocomposites exhibit the superior stability and can be easily recovered with their fully catalytic activities due to the hydrophobic and magnetic properties of the nanocomposites. It shows the great prospect for the 4-NP reduction in practice and is promising for wide applications in visible light catalytic reaction.

Highly Stable Luminous “Snakes” from CsPbX3 Perovskite Nanocrystals Anchored on Amine-Coated Silica Nanowires

CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) are known for their exceptional optoelectronic properties, yet the material’s instability toward polar solvents, heat, or UV irradiation gre...

Formation of Silica Nanowires by Using Silicon Oxide Films: Oxygen Effect

Formation of Silica Nanowires by Using Silicon Oxide Films: Oxygen Effect

Formation of silicon nanocrystal chains induced via Rayleigh instability in ultrathin Si/SiO2 core/shell nanowires synthesized by an inductively coupled plasma torch process

A new class of silicon (Si) nanohybrids is formed exploiting the Rayleigh instability experienced by Si nanowires (SiNWs) synthesized via inductively coupled plasma. These nanohybrids consist of three main categories of Si nanostructures: (i) core/shell silicon/silicon oxide nanowires (where the inner Si cores have diameters as small as 2–3 nm), (ii) sequences of almond-shaped silicon nanocrystals (SiNCs), having diameters in the range of 4–5 nm, connected by an ultrathin silicon nanowire (diameter of 1–2 nm) and embedded in a silica nanowire, and (iii) sequences of isolated spherical SiNCs (having diameters in the range of 4–7 nm) embedded in an otherwise continuous silica nanowire. The predominance of one morphology over the others can be tuned via post-synthesis thermal treatments, with a clear predominance of the spherical SiNC chain configuration after high-temperature annealing (1200 °C). It is demonstrated that the Rayleigh model describes very well the morphological transformations undergone by the Si core of the nanostructures when subject to the capillarity-related instability induced by the thermal annealing. More interestingly, we have been able, for the first time to our knowledge, to follow in situ the occurrence of Rayleigh instability in SiNWs leading to the breakage of their inner core and formation of smaller SiNCs. Finally, the optoelectronic properties of the Si nanohybrids, studied via photoluminescence measurements, have confirmed the occurrence of quantum confinement effects in the ultra-small SiNCs present in these new nanohybrids.

Effect of indium catalyst particle size on the morphology of silicon oxide nanowires

Silicon oxide (SiOx, × ≤2) nanowires were synthesized on indium (In) catalyst particles by gas-jet electron beam plasma-enhanced chemical vapor deposition through the vapor-liquid-solid (VLS) mechanism. The synthesis was carried out on substrates of different average particle sizes in the range from 42 to 710 nm. Arrays of oriented microropes of nanowires were grown on catalysts with a particle size of 42 and 79 nm. On 170 nm catalyst particles, cocoon-like structures from nanowires were formed, and on 710 nm particles, the synthesis proceeded in the same way as on an indium tin oxide (ITO) film. The chemical composition of the synthesized nanostructures was studied by Fourier transform infrared spectroscopy. Under the assumption of a uniform distribution of silicon and oxygen atoms, the nanowires were found to consist of SiOx with x = 1.9. Energy dispersive spectroscopy showed that the catalyst particles consisted of non-stoichiometric indium oxide, rather than of pure indium. Therefore, during the synthesis of silicon oxide nanowires on an indium catalyst, hydrogen should be used.

Extraction of Cr (VI) by pickering emulsion liquid membrane using amphiphilic silica nanowires (ASNWs) as a surfactant

Pickering emulsion is the replacement of surfactants with solid, often nano-sized particles. The particle-stabilized emulsions have good thermodynamic and kinetic stability. Pickering emulsion liquid membrane (PELM) was prepared using mahua oil as a diluent, aliquat 336 (Trioctyl methylammonium chloride) as a carrier and amphiphilic silica nanowires (ASNWs) (10–40 ml ethanol addition) as a surfactant. Sodium hydroxide (NaOH) was used as stripping phase in the concentration range from 0.1 to 0.5 M for the extraction of hexavalent chromium [Cr (VI)] from aqueous solution. The variety of edible and non-edible oils was investigated for the stability of water in oil emulsion. Factors that influence silica-stabilized Pickering emulsions are pH, agitation speed, stripping phase concentration, the volume ratio of membrane to stripping phase (M/S), initial feed concentration, treat ratio(feed to emulsion volume ratio) and surfactant concentration for better PELM stability. And also, the extraction efficiency of Cr (VI) was investigated using aliquat as a carrier. The physicochemical properties of ASNWs were studied using Scanning Electron Microscopy (SEM), Fourier Transforms Infrared Spectroscopy (FTIR) and Dynamic Light Scattering (DLS) techniques. At an optimum condition, 99.69% of Cr (VI) removal from aqueous solution was obtained.

Silica Nanowire Growth on Coscinodiscus Species Diatom Frustules via Vapor-Liquid-Solid Process.

Diatom frustules are a type of porous silicon dioxide microparticle that has long been used in applications ranging from biomedical sensors to dye-sensitized solar cells. The favorable material properties, enormous surface area, and enhanced light scattering capacity support the promise of diatom frustules as candidates for next generation biomedical devices and energy applications. In this study, the vapor-liquid-solid (VLS) method is employed to incorporate silica nanowires on the surface of diatom frustules. Compared to the original frustule structures, the frustule-nanowire composite material's surface area increases over 3-fold, and the light scattering ability increases by 10%. By varying the gold catalyst thickness during the VLS process, tuning of the resultant nanowire length/density is achieved. Through material characterization, it is determined that both float growth and root growth processes jointly result in the growth of the silica nanowires. From a thermodynamics point of view, the preferential growth of the silica nanowires on frustules is found to have resulted from the enormous partial surface area of gold nanoparticles on the diatom frustules. The frustule-nanowire composite materials have potential applications in the development of novel biomedical sensing devices and may greatly enhance next generation solar cell performance.

Silica nanowires with tunable hydrophobicity for lipase immobilization and biocatalytic membrane assembly

Silica nanowires (NWs) with tailored hydrophobicity are synthesized by capping different length of alkyl groups on surface via a one-pot anisotropic sol-gel growth approach. Lipase from Burkholderia Cepacia (BCL) is successfully immobilized onto the silica NWs via hydrophobic interaction. The specific activity of the immobilized BCL increases with the increasing length of the capping alkyl groups and surface hydrophobicity of the NWs. BCL immobilized onto the octadecyl groups-capped silica NWs displays the highest specific catalytic activity, which is also notably higher than that of BCL immobilized on octadecyl groups-modified mesoporous silicate. The superior performance can be ascribed to the combination of the interfacial activation of lipases induced by capped-octadecyl groups on the NWs and the improved mass transfer efficiency of reactants around the one-dimensional silica NWs. The BCL-loaded NWs are further used as “building blocks” to assemble filter paper-like biocatalytic membrane via vacuum-assisted filtration method. The free-standing biocatalytic membrane can be operated in a continuous mode to avoid the separation of catalyst from reaction products. This work provides new opportunity in enzyme immobilization and biocatalytic membrane preparation through using discrete silica NWs as supports and building blocks.

Frosted Slides Decorated with Silica Nanowires for Detecting Circulating Tumor Cells from Prostate Cancer Patients.

Developing low-cost and highly efficient nanobiochips are important for liquid biopsies, real-time monitoring, and precision medicine. By in situ growth of silica nanowires on a commercial frosted slide, we develop a biochip for effective circulating tumor cells (CTCs) detection after modifying epithelial cell adhesion molecule antibody (anti-EpCAM). The biochip shows the specificity and high capture efficiency of 85.4 ± 8.3% for prostate cancer cell line (PC-3). The microsized frosted slides and silica nanowires allow enhanced efficiency in capture EpCAM positive cells by synergistic topographic interactions. And the capture efficiency of biochip increased with the increase of silica nanowires length on frosted slide. The biochip shows that micro/nanocomposite structures improve the capture efficiency of PC-3 more than 70% toward plain slide. Furthermore, the nanobiochip has been successfully applied to identify CTCs from whole blood specimens of prostate cancer patients. Thus, this frosted slide-based biochip may provide a cheap and effective way of clinical monitoring of CTCs.

Deposition time dependence of the morphology and properties of tin-catalyzed silicon oxide nanowires synthesized by the gas-jet electron beam plasma chemical vapor deposition method

SiOx nanowires (SiOxNWs, x ≤ 2) were grown by gas-jet electron beam plasma chemical vapor deposition method according to the vapor-liquid-solid mechanism at different synthesis times (tdep = 0.5–5 min) using tin particles as a catalyst. Microropes of SiOxNWs were obtained at tdep of more than 1 min. The average growth rate of nanowires was about 19 nm/s. Fourier transform infrared (FTIR) spectroscopy shows that SiOxNWs synthesized at different tdep are very similar in chemical composition (x ≈ 2) and in the bonding network of SiOx. FTIR spectroscopy data on the chemical composition of nanowires are in good agreement with the results of X-ray energy dispersive spectroscopy (EDS) analysis. EDS mapping of silicon and oxygen indicates that the atoms are uniformly distributed in the nanowires. Also, FTIR measurements showed that a significant number of water-adsorbing silanol groups formed on the surface of the nanowires. Photoluminescence spectra of nanowires obtained at different tdep are typical of SiO2 and exhibit a broad band in the region 400–600 nm centered at ~475 nm. The contact angle for SiOxNWs is <21° and decreases to 4.4° with increasing tdep, indicating a superhydrophilic coating.

Time-dependent optical response of three-dimensional Au nanoparticle arrays formed on silica nanowires

We present stationary and transient absorption measurements on 3D Au nanoparticle (NP)-decorated $\mathrm{Si}{\mathrm{O}}_{2}$ nanowire arrays. The 3D NP array has been produced by the dewetting of a thin Au film deposited on silica nanowires produced by oxidation of silicon nanowires. The experimental behaviors of the spectral and temporal dynamics observed in the experiment are accurately described by a two-step, three-temperature model. Using an arbitrary set of Au NPs with different aspect ratios, we demonstrate that the width of the experimental spectra, the energy shift of their position with time, and the asymmetry between the two positive wings in the dynamical variation of absorption can all be attributed to the nonuniform shape distribution of the Au NPs in the sample.

Indium‐Assisted Plasma‐Enhanced Low‐Temperature Growth of Silicon Oxide Nanowires

The nanowires of the silicon oxide SiOx (x ≤ 2) are synthesized on an indium catalyst by the gas‐jet electron beam plasma chemical vapor deposition (GJ EBP CVD) method using a monosilane‐argon‐hydrogen mixture with the simultaneous supply of the oxygen into the vacuum chamber. The arrays of the aligned microropes (bundles) of nanowires are formed at the substrate temperatures of 200–335 °С. At the temperature of 160 °С the cocoon‐like structures of SiOx nanowires are synthesized. The obtained results are explained within the synthesis model suggested previously. The Fourier transform infrared (FTIR) transmittance spectra are recorded to study the chemical composition of the nanowires. It is shown that the nanowires synthesized at temperatures of 200–335 °С consist of SiOx with x = 1.93 ± 0.04. The arrays of the oriented microropes of the SiOx nanowires exhibit the intense photoluminescence at a room temperature with a maximum in a range of the energies from 2 to 3 eV. The photoluminescence spectra of the oriented microropes synthesized on silicon substrates with the indium catalyst are shifted toward lower energies from 2.7–2.8 to 2.4–2.5 eV at the changing growth temperatures from 200 to 335 °C.

Hydrothermal synthesis and characterization of silica nanowires using rice husk ash: an agricultural waste

One-dimensional structures are the smallest dimension structures that represent a unique system for analyzing phenomena at the Nanoscale. Nanowires, which can be used for space confined transport phenomena and enhanced optical properties, are believed to play significant role in the function and integration of Nano electronics and Nano optoelectronics devices. Nanowires with well controlled morphology and extremely high aspect ratio can be obtained by various complex techniques but the demand of upcoming future technology is to synthesize large scale 1D nanostructures with simple and efficient cost effective methods. With this view, in the present study, large scale amorphous silica nanowires (SiO2 NWs) were synthesized from rice husk ash using Fe2O3 assisted hydrothermal method and characterizations of these nanowires along with rice husk ash (RHA) containing porous silica, were done using various techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis spectroscopy and photoluminescence (PL). The structural study of silica nanowires were studied using XRD, indicating the amorphous phases of silica in both RHA as well as nanowires. The chemical composition along with symmetric or anti-symmetric starching bonds of amorphous SiO2 NWs and RHA was confirmed using FTIR. The morphological study was done using SEM and TEM. The SiO2 NWs so obtained have diameter in the range from 15 to 35 nm and length about 0.5 µm. In optical study, the enhanced band gap of amorphous SiO2 NWs as compared to RHA was observed using UV–Vis spectroscopy. PL spectroscopy shows strong blue light emission by silica nanowires as compare to RHA. This study opens up new areas for research to modulate optoelectronic properties of SiO2 nanowires for the novel device application.

Fabrication of amorphous silica nanowires via oxygen plasma treatment of polymers on silicon

We demonstrate a facile non-catalytic method of fabricating silica nanowires at room temperature. Different polymers including photoresists, parylene C and polystyrene are patterned into pedestals on the silicon substrates. The silica nanowires are obtained via the oxygen plasma treatment on those pedestals. Compared to traditional strategies of silica nanowire fabrication, this method is much simpler and low-cost. Through designing the proper initial patterns and plasma process parameters, the method can be used to fabricate various regiment nano-scale silica structure arrays in any laboratory with a regular oxygen-plasma-based cleaner or reactive-ion-etching equipment.

Reaction intermediate-induced vapor–liquid–solid growth of silicon oxide nanowires

Jellyfish-like SiOx nanowires were formed in a reaction intermediate-induced vapor–liquid–solid process, which provides a new method for nanowire growth.

Textural properties determined CO2 capture of tetraethylenepentamine loaded SiO2 nanowires from α-sepiolite

To understand the effect of porous parameters and chemical components on CO2 capturing performance of solid state amine absorbents and their kinetic parameters, a clay mineral-based CO2 absorbent was prepared by impregnating five different liquid amines onto SiO2 nanowire clusters from fibrous sepiolite (Sep). Characterization was conducted by XRD, SEM, FTIR, and N2 adsorption–desorption isotherm, CO2 adsorption performances were measured by TGA. After acid treatment, the raw Sep mineral changed into amorphous silica nanowires, and the largest SBET of the obtained SiO2 nanowires reached 320 m2/g, which was 8 times larger than the pristine mineral. Amongst the adapted amines, tetraethylenepentamine (TEPA) showed superiority in the CO2 adsorption capacity. The optimized adsorption capacity reached 3.7 mmol/g at 75 °C from a CO2 + N2 mixture on a ∼50 wt% TEPA loaded SiO2 sample, and the capacity remained 3.6 mmol/g after ten circles of adsorption/desorption tests. The pore size and pore structure of the matrix, rather than the surface area, will obviously affect the adsorption ability of the product. Kinetic parameters for the CO2 adsorption process fitted well with a fractional-order model, confirming that the CO2 adsorption process by the solid absorbent should be a combination of both physical and chemical reactions. Results in this article provide detailed parameters for preparing and understanding these clay mineral based solid state CO2 absorbents.

Self-assembly of silica nanowires in a microemulsion system and their adsorption capacity

The assembly process of nanostructures plays a crucial role in controlling the morphology of nanomaterial in a microemulsion system. However, controlling the assembly process of nanostructures becomes complex and difficult, due to the multiple factors of microemulsion system. Herein, we report a facile synthesis of amorphous caddice-like silica NWs by a self-assembly process in an oil-in-water (O/W) microemulsion system. In our method, the mass ratio of tetraethoxysilane (TEOS) to dimethylbenzene (DMB) would directly control the morphologies of silica nanostructures. Interestingly, the proper low-concentration TEOS in oil phase favors the formation of silica NWs due to the self-assembly of nanosized oil droplets with silica porous shell, driving by the surface tension of oil droplets. The mean diameters of NWs could be slightly adjusted from 67nm to 82nm by prolonging reaction time. The as-obtained silica NWs exhibited an excellent adsorption capacity and rapid adsorption rate for methylene blue dye due to the negatively charged hydroxyl groups and high specific surface areas.

Synthesis of silicon oxide microropes on the copper substrate with SiO2 interlayer

Nanostructuring of the surface is a promising technology for the processes of boiling. In this paper, we synthesized array of “microropes” from silicon oxide nanowires on the copper substrate with a silicon oxide intermediate layer by gas-jet electron beam plasma CVD method. The morphology for the synthesis time of 2 minutes 30 seconds and 5 minutes was obtained. The water droplet on the silicon oxide nanowires shows the measured contact angles 14° and 10° for deposition times of 5 min and 2 min 30 sec, respectively.

Enhancement of heat transfer at pool boiling on surfaces with silicon oxide nanowires

The boiling heat transfer on the local heaters with microstructured and nanomodified surfaces was studied. As nanomodified surfaces we used copper ones where the microropes of silicon oxide nanowires were grown. The aging of the nanomodified surface was observed after first series of experiments. It was shown that both finning and nanostructuring of the surface result in increase of heat transfer. The heat flux density of 1400 W/cm2 was reached.