SiO2 Beads Research Articles

Determination of liquid viscosity based on dual-frequency-band particle tracking

Abstract An optical-tweezers-based dual-frequency-band particle tracking system was designed and fabricated for liquid viscosity detection. On the basis of the liquid viscosity dependent model of the particle’s restricted Brownian motion with the Faxén correction taken into account, the liquid viscosity and optical trap stiffness were determined by fitting the theoretical prediction with the measured power spectral densities of the particle’s displacement and velocity that were derived from the dual-frequency-band particle tracking data. When the SiO2 beads were employed as probe particles in the measurements of different kinds of liquids, the measurement results exhibited a good agreement with the reported results, as well as a detection uncertainty better than 4.6%. This kind of noninvasive economical technique can be applied in diverse environments for both in situ and ex situ viscosity detection of liquids.

Simple preparation of SiC@SiO2 nanofiber with bead-like structure by microwave sintering

SiC@SiO2 nanofiber material holds great potential for a wide range of applications in microelectronic devices and electromagnetic wave absorption. However, its development has been hindered by high energy consumption (＞1500 °C) and complex fabrication methods. This work introduces a sample approach to produce the SiC@SiO2 nanofiber at temperature of ∼1000 °C by using microwave heating. The SiC@SiO2 nanofiber possess a unique bead-like structure, which are composed of single-crystalline SiC nanowires and amorphous SiO2 beads. The growth mechanism under the action of microwave was explained. Moreover, the SiC@SiO2 nanofiber exhibits an Excellent electromagnetic wave absorption performance with a minimum refection loss (RLmin) value of −36.54 dB. The successful preparation of SiC@SiO2 nanofiber provides a new idea for preparing ceramic materials with low cost and high efficiency in the future.

One-step synthesis of single-crystal Si3N4 nanowires-amorphous SiO2 beads nanochains by chemical vapor deposition

One-dimensional (1D) nanochain heterojunctions have attracted wide attention due to their unique optical and electrical properties, while efficient and controllable synthesis of nanochains is still difficult. Herein, Si3N4/SiO2 nanochain heterojunctions (Si3N4 single-crystal nanowires and amorphous SiO2 beads) were successfully synthesized by a one-step chemical vapor deposition (CVD) process without using any templates and catalysts. A two-stage growth mode was proposed to explain the formation mechanism of the special nanochain. We found that carbon vapor induced the formation of Si3N4 nanowires and suppressed the formation of Si2N2O. The Si3N4/SiO2 nanochains can only be synthesized within a suitable concentration range of carbon vapor. The as-synthesized fascinating nanochain exhibits an extra strong emission at about 3.02 eV, showing great promise for optoelectronic nanodevices.

A strategy to enhance SERS detection sensitivity through the use of SiO2 beads in a 1536-well plate.

The development of rapid and accurate assays is crucial to prevent the rapid spread of highly contagious respiratory infections such as coronavirus (COVID-19). Here, we developed a surface-enhanced Raman scattering (SERS)-enzyme-linked immunosorbent assay (ELISA) method that allows for the screening of multiple patient samples with high sensitivity on a 1536-well plate. As the well number on the ELISA well plate increases from 96 to 1536, the throughput of the assay increases but the sensitivity decreases due to the low number of biomarkers and the increase in non-specific binding species. To address this problem, silica (SiO2) beads were used to increase the surface-to-volume ratio and the loading density of biomarkers, thereby enhancing sensitivity. Using a three-dimensional gold nanoparticle (AuNP)@SiO2 SERS assay platform on a 1536-well plate, an immunoassay for the nucleocapsid protein biomarker of SARS-CoV-2 was performed and the limit of detection (LoD) decreased from 273 to 7.83 PFU/mL compared to using a two-dimensional assay platform with AuNPs. The proposed AuNPs@SiO2 SERS immunoassay (SERS-IA) platform is expected to dramatically decrease the false-negative diagnostic rate of the currently used lateral flow assay (LFA) or ELISA by enabling the positive diagnosis of patients with low virus concentrations.

Structure control and growth mechanism of beaded SiC nanowires with microwave absorption properties

Large-scale SiC nanowires (SiCnws) were successfully synthesized on graphite substrates by a catalyst-free carbon thermal reduction process using low-cost silicone oil, silica powder, and activated carbon. The control of different nanowire structures was achieved by parameter regulation. An in-depth discussion of their growth mechanisms is provided. Beaded SiCnws consisting of amorphous SiO2 beads and SiC strings were synthesized at 1400 °C. The formation of beads is mainly due to the supersaturation of SiO vapor, which leads to the reaction of excess SiO to form SiO2 at the defects of the SiCnws. The dielectric parameters of beaded SiCnws were analyzed, and it was found that the beaded SiCnws have a maximum effective absorption width of 1.84 GHz and a maximum reflection loss of −16.03 dB. The exploration of the growth mechanism of beaded SiCnws in this study provides a useful reference for the preparation of one-dimensional nanomaterials.

Effect of Porous Catalyst Support on Plasma-Assisted Catalysis for Ammonia Synthesis.

We report on the effect of catalyst support particle porosity on the conversion of NH3 synthesis from N2 and H2 in a coaxial dielectric barrier discharge (DBD) plasma reactor. The discharge was created using an AC applied voltage with the reactor at room temperature and near atmospheric pressure (550 Torr). Two different particles of almost equal diameter (∼1.5 mm)─porous silica (SiO2) ceramic beads (average pore size: 8 nm) and smooth, nonporous soda lime glass beads─were compared in the DBD reactor. As the pore size in the SiO2 particles was smaller than the Debye length, penetration of the plasma into the pores of the particles was unlikely; however, reactive species generated in the plasma outside the particles could diffuse into the pores. The N2 conversion and energy yield of NH3 increased with applied voltage for both particle types, and these values were consistently higher when using the SiO2 beads. Discharge and plasma properties were estimated from Lissajous plots and using calculations with the BOLSIG+ software. The effect of these two different catalyst supports on the physical properties of the discharge was negligible. High resolution optical emission spectra revealed that the concentrations of N2+, atomic N, and atomic H (Hα, Hβ) in the plasma discharge were lower with the porous SiO2 beads than with the glass beads at every applied voltage tested. This indicates that these active species participate in heterogeneous reactions at support particle surfaces and that the larger surface area presented by the porous particles led to higher rates of depletion of these intermediates and a higher rate of ammonia synthesis.

Methane decomposition by plasma-packed bed non-thermal plasma reactor

A dielectric barrier discharge reactor (DBD) was employed as a non-thermal plasma (NTP) source for non-oxidative conversion of methane at ambient condition. The reactor was later operated as packed-bed DBD and also served with catalyst coupling. In the bed, dielectric materials (glass beads, BaTiO3) as well as some catalytic support materials (TiO2, SiO2 and γ-Al2O3 beads) were introduced in order to find out the non-catalytic reaction mechanism. Typical results indicated that the non-catalytic mode could favorably activate the strong C-H bond to produce H2 and light hydrocarbons without applying any oxidant or thermal energy. Apart from the materials property (shape, size, surface area, dielectric constant) different plasma parameters has a strong influence on the reaction performance. The existence of highest methane conversion and products yield was experimentally observed form the catalyst coupled plasma mode which could be reasonably described by their dominant catalytic surface properties. Moreover, the present reactor model found to be able enough in limiting the solid coke formation on catalyst surface.

Cold sintering yields first layered double hydroxides (LDH) monolithic materials

Layered double hydroxides (LDHs) are key inorganic compounds relevant to a wealth of applicative purposes, by exploiting their layered structure allowing for ion/molecular sequestration or release. However, a technological barrier exists in the fabrication of cohesive LDH monoliths in link with their metastability. In this work, a series of cohesive monoliths of different LDH ionic compositions and structures (namely hydrotalcite, pyroaurite and hydrocalumite) were successfully obtained for the first time, using cold sintering via spark plasma sintering (SPS) at 130 °C. Thanks to the low temperature involved in this non-conventional consolidation approach, the structure and chemical stability of the LDHs are preserved and allow preparing densified LDH scaffolds with internal cohesion, as evidenced by densification rates often above 80 %, SEM microstructural observations and mechanical testing assessments, mainly due to a better alignment of adjacent layered particles. By way of water vapor sorption measurements, we demonstrate that the interfacial/interlayer spaces of the LDH structure remain accessible after cold sintering. Also, the porous network of the monoliths and related access to interfacial surface are shown to be tunable by adding a leachable pore-forming agent such as SiO2 beads. Possible sintering mechanisms are discussed by complementary experiments-simulations coupling, unveiling the role of LDH composition as in the case of Cl-bearing LDH. By overcoming the challenge of monolith fabrication out of LDH compounds, applications are expected to benefit from these findings, as in electronics, energy storage, catalysis, biomaterials and depollution.

Variable Fitness Response of Two Rotifer Species Exposed to Microplastics Particles: The Role of Food Quantity and Quality.

Plastic pollution is an increasing environmental problem, but a comprehensive understanding of its effect in the environment is still missing. The wide variety of size, shape, and polymer composition of plastics impedes an adequate risk assessment. We investigated the effect of differently sized polystyrene beads (1-, 3-, 6-µm; PS) and polyamide fragments (5–25 µm, PA) and non-plastics items such as silica beads (3-µm, SiO2) on the population growth, reproduction (egg ratio), and survival of two common aquatic micro invertebrates: the rotifer species Brachionus calyciflorus and Brachionus fernandoi. The MPs were combined with food quantity, limiting and saturating food concentration, and with food of different quality. We found variable fitness responses with a significant effect of 3-µm PS on the population growth rate in both rotifer species with respect to food quantity. An interaction between the food quality and the MPs treatments was found in the reproduction of B. calyciflorus. PA and SiO2 beads had no effect on fitness response. This study provides further evidence of the indirect effect of MPs in planktonic rotifers and the importance of testing different environmental conditions that could influence the effect of MPs.

Synthesis and growth mechanism of SiC/SiO2 nanochains by catalyst-free thermal evaporation method in Ar/CO atmosphere

SiC/SiO2 nanochains were synthesized on a carbon fiber substrate by a catalyst-free thermal evaporation method in the Ar/CO atmosphere. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the as-synthesized SiC/SiO2 nanochains are composed of single-crystalline SiC nanowires and amorphous SiO2 beads. The introduction of CO can promote the formation of SiO2, so that the SiC/SiO2 nanochains are subsequently formed during cooling. In addition, the photoluminescence spectrum of SiC/SiO2 nanochains showed a broad emission peak at around 350 nm, which is ascribed to the oxygen discrepancy in the SiO2 beads as well as the SiC/SiO2 interfacial effect. These findings can provide guidance for further study of the vapor growth of 1D SiC-based materials.

Surface-Related Toxicity of Polystyrene Beads to Nematodes and the Role of Food Availability.

Microplastics released into freshwaters from anthropogenic sources settle in the sediments, where they may pose an environmental threat to benthic organisms. However, few studies have considered the ecotoxicological hazard of microplastic particles for nematodes, one of the most abundant taxa of the benthic meiofauna. This study investigated the toxic effects of polystyrene (PS) beads (0.1-10.0 μm) and the underlying mechanisms thereof on the reproduction of the nematode Caenorhabditis elegans. The observed effect of the PS beads on the nematodes correlated well with the total surface area of the beads per volume, with a 50% inhibition of reproduction at 55.4 ± 12.9 cm2/mL, independent of the bead size. The adverse effects were not explained by styrene monomers leaching from the beads because chemical activities of styrene in PS suspensions were well below the toxic levels. However, the observed effects could be related to the bead material because the same-sized silica (SiO2) beads had considerably less impact, probably due to their higher specific density. PS and SiO2 beads affected the food availability of C. elegans, with greater effects by the PS beads. Our results demonstrate the importance of including indirect food web effects in studies of the ecological risks posed by microplastics.

Conductive Nanosized Magnéli-Phase Ti4O7 with a Core@Shell Structure.

Magnéli-phase Ti4O7, known for its high electrical conductivity and corrosion resistance, is typically prepared by hydrogen reduction at high temperatures (∼1000 °C), leading to large particles. Nanosized Ti4O7 have been explored for application toward high specific surface area electrode materials and electrocatalyst supports; nonetheless, the particle size of Ti4O7 is still insufficient for utilization as a support. In this study, we have pursued a novel synthetic approach for nanosized Ti4O7 platelets with a length of 10-80 nm and thickness of 3-10 nm even under high-temperature conditions. We herein describe the use of SiO2 beads as a core to obtain a SiO2 core coated with multilayers of TiO2 nanosheets exfoliated from layered H2Ti4O7 which is subsequently subjected to high-temperature reduction to prepare a SiO2-core@Ti4O7-shell structure. The pair distribution function technique has proven that the shell is transformed to single-phase Ti4O7. The electrical double layer capacitance of SiO2-core@Ti4O7-shell was much larger than that of conventionally synthesized Ti4O7 particles with a micrometer size. The results show the beneficial effects of the SiO2-core@Ti4O7-shell structure, and it is the first example of the synthesis for conductive Ti4O7 with a high specific surface area even under conditions of high-temperature synthesis.

Erratum: Preparation of Poly(pentafluorophenyl acrylate) Functionalized SiO2 Beads for Protein Purification.

Erratum: Preparation of Poly(pentafluorophenyl acrylate) Functionalized SiO2 Beads for Protein Purification.

Higher Speed of Yeast Adherence in Comparison with Speed of Bacteria Adherence to Silica Microparticles

Abstract The current study explored the possibility to attach bacteria and yeasts to micro-silica particles. The aim of the study was to determine possible differences in the speed of rates of turbidity (or speed of adherence) between suspensions of bacteria and yeasts with and without silica micro-particles. Some important findings were demonstrated, which might be promising for developing of a new diagnostic approach to distinguish bacteria from yeasts. Addition of SiO2 beads to bacterial suspensions resulted in a significantly faster decrease of turbidity rates in comparison with corresponding suspensions without SiO2 beads. However, yeasts adhered to silica micro particles quicker in comparison with the speed of adherence of bacteria to silica.

High-Temperature Plateau–Rayleigh Growth of Beaded SiC/SiO2 Nanochain Heterostructures

The Plateau–Rayleigh (P-R) crystal growth was recently proposed and dramatically extended the one-dimensional nanomaterials synthesis due to its tunable morphological features. Previously reported P-R growth is mainly focused on the relative low-temperature reactions (<1273 K, which is less than the melting point of reaction products or intermediate products), while high-temperature P-R growth with a molten state is rarely studied. To extend P-R growth to high temperature and reveal the underlying mechanism, herein we take the synthesis of SiC/SiO2 heterostructures as the prototype. With optimized growth temperature, we reported a novel high-temperature P-R growth of the beaded SiC/SiO2 nanochain heterostructures through a vapor-phase synthesis. The as-obtained SiC/SiO2 nanochain heterostructures involved the single-crystalline 3C-SiC core with diameters of ∼20 nm, the amorphous SiO2 shell with thicknesses of 200–300 nm, and many uniform periodic amorphous SiO2 beads with diameters of 800–1000 nm. Further...

Nitrogen-doped bi-modal porous carbon nanostructure derived from glycine for supercapacitors

We prepared a nitrogen-doped bi-modal porous carbon nanostructure (G-500/20) using a template method with 500 and 20nm SiO2 beads and glycine. The G500/20 has a surface area of 403m2g−1 with meso/macroporous structure and N-doping content of 5.9at%. In the supercapacitor performance, G-500/20 exhibits superior specific capacitances of 19.5 and 5.3Fg−1 at 200mVs−1 and 20Ag−1 in 6M NaOH, compared to a commercial activated carbon. In particular, the superior capacitances of G500/20 at high scan rates and current densities were achieved due to the bi-modal porous structure and nitrogen doping effect.

Enhanced oxygen reduction reaction of Pt deposited Fe/N-doped bimodal porous carbon nanostructure catalysts

For commercialization of proton exchange membrane fuel cells (PEMFCs), the loading amount of Pt-based cathode catalysts for oxygen reduction reaction (ORR) needs be significantly reduced. In this study, we propose Pt catalysts supported by an iron/nitrogen-doped porous carbon (FeNC) nanostructure having a catalytic activity for ORR in order to significantly reduce the utilization of Pt. The FeNC nanostructure was prepared using a template method with 50 and 500 nm SiO2 beads and phthalocyanine as a dopant and carbon source. The nanosized Pt catalysts with different loading weights (5, 10, 20, 30 wt%) were uniformly deposited on the FeNC with a bimodal porous crystalline doped carbon nanostructure using an electron beam radiation method. In particular, the cathode catalyst having 5 wt% Pt on FeNC (Pt5/FeNC) exhibited enhanced ORR mass activities of 2.19 and 2.58 A mgPt−1 at 0.9 V measured by electrochemical half cells in acidic and alkaline media, respectively, compared to a commercial Pt(20 wt%)/C (Pt20/C). Furthermore, Pt5/FeNC showed a higher mass activity of 18.76 A mgPt−1 at 0.6 V as a unit cell performance than that of the commercial catalyst. The improved ORR activity of Pt/FeNC might be synergistically attributed to the homogeneous dispersion of Pt nanoparticles on the bimodal porous doped carbon nanostructure, the interaction (electronic effect) between the metallic catalyst and the doped support, and the dual catalytic effect of both Pt and the doped carbon nanostructure.

Easily separated and recyclable amino-functionalized porous SiO2 beads with 3D continuous meso/macropore channels

Amino-functionalized porous SiO2 beads with a diameter of 200—800 μm(PSB-NH2) have been success-fully synthesized by grafting 3-aminopropyl-triethoxysilane onto meso/macroporous silica beads(PSB), in which the PSB was prepared by hydrothermal synthetic method with a porous hard template anion-exchange resin. The as-prepared materials were characterized by means of nitrogen sorption and transmission electron micrographs(TEM), showing the presence of 3D interconnected and continuous large mesopores and macropores inside. The beads were used to catalyze Knoevenagel condensation and proved to be highly active and selective due to the high accessibility of the reactants to the amino groups via the continuous 3D meso/macopores. Notably, such material in bead format facilitates the extremely straightforward separation from reaction solution without any centrifugation or filtration. Moreover, PSB-NH2 proved to be a stable catalyst via leaching experiment test, and can be easily recovered and reused without significant loss of activity in successive catalytic cycles.

Photocatalytic disinfection of sporulating Bacillus subtilis using silver-doped TiO2/SiO2

The efficiency of TiO2 supported on porous SiO2 beads (TiO2/SiO2), and Ag-doped TiO2/SiO2 for the photocatalytic disinfection of Bacillus subtilis in aqueous medium was investigated. The photocatalytic activity of Ag-doped TiO2/SiO2 for the disinfection of B. subtilis was larger than that of non-doped TiO2/SiO2 under UV irradiation. B. subtilis, a gram-positive bacterium, has specific features that enable it to form a tough spore to protect itself from extreme environmental conditions. Sporulating B. subtilis is resistant to UV irradiation, desiccation, high temperature, extreme freezing, and chemical disinfectants. While it has no known toxicity, this bacterium is difficult to disinfect. Approximately 5 weeks were required to cultivate the sporulating bacteria, and the presence of spores was subsequently confirmed using the Wirtz method. Typical vegetative B. subtilis was disinfected using both TiO2/SiO2 and Ag-doped TiO2/SiO2 photocatalysts under UV irradiation. However, the sporulating bacteria were only disinfected when using the Ag-TiO2/SiO2 photocatalyst. Although sporulating B. subtilis is a hardy organism, it can be disinfected using an Ag-doped TiO2/SiO2 photocatalyst.

Synthesis of SiC nanonecklaces via chemical vapor deposition in the presence of a catalyst

SiC nanonecklaces were synthesized on a large scale on as-prepared Si–SiC ceramic substrates via chemical vapor deposition with ferrocene as a catalyst. Structural, morphological, and elemental analyses showed that the as-synthesized nanonecklaces consisted of 3C–SiC stems up to several hundreds of micrometers in length with diameters of 200–400 nm, and SiO2 beads with diameters of 0.3–1 μm. On the basis of the experimental and theoretical characterizations, a combination of growth mechanism of a vapor–liquid–solid-stem and modulation-bead was proposed as the growth mode of the SiC nanonecklaces.