Showing papers on "Silicon dioxide published in 2019"

Cotransport and Deposition of Iron Oxides with Different-Sized Plastic Particles in Saturated Quartz Sand

Abstract: The present study was designed to investigate the cotransport and deposition of different-sized plastic particle from nano- (0.02 μm) to micrometer-scale (0.2 and 2 μm) with goethite and hematite (two types of representative iron oxides abundant in natural environment) in porous media at both low (5 mM) and high ionic strength (25 mM) in NaCl solutions. We found that through different mechanisms (i.e., modification of surface properties of iron oxides, steric repulsion, or alteration in deposition sites on quartz sand), different-sized plastic particles induced different effects on the transport and deposition behaviors of iron oxides in quartz sand. Likewise, via different mechanisms such as change of surface properties or alteration in deposition sites on quartz sand, different transport behaviors for different sized plastic particles induced by the copresence of iron oxides were also observed. The results of this study suggested that cotransport of iron oxides and plastic particles in porous media is far more complex than those of individual colloid transport. Since both plastic particles and iron oxides are ubiquitous presence in natural environment, it is expected that they would interact with each other and thus alter the surface properties, leading to the change of transport behaviors in porous media.

Electrodeposition of crystalline silicon films from silicon dioxide for low-cost photovoltaic applications

Abstract: Crystalline-silicon solar cells have dominated the photovoltaics market for the past several decades. One of the long standing challenges is the large contribution of silicon wafer cost to the overall module cost. Here, we demonstrate a simple process for making high-purity solar-grade silicon films directly from silicon dioxide via a one-step electrodeposition process in molten salt for possible photovoltaic applications. High-purity silicon films can be deposited with tunable film thickness and doping type by varying the electrodeposition conditions. These electrodeposited silicon films show about 40 to 50% of photocurrent density of a commercial silicon wafer by photoelectrochemical measurements and the highest power conversion efficiency is 3.1% as a solar cell. Compared to the conventional manufacturing process for solar grade silicon wafer production, this approach greatly reduces the capital cost and energy consumption, providing a promising strategy for low-cost silicon solar cells production. The photovoltaics market has been dominated by crystalline silicon solar cells despite the high cost of the silicon wafers. Here Zou et al. develop a one-step electrodeposition process in molten salt to produce high-purity solar-grade silicon films, delivering power conversion efficiency of 3.1%.

The synergistic effect between graphene oxide nanocolloids and silicon dioxide nanoparticles for gallic acid sensing.

Abstract: For the first time, the synergistic effect of graphene oxide nanocolloids (nano-GO) and silicon dioxide (silica) nanoparticles (SiO2-nanoparicles) has been used to modify a glassy carbon electrode (GCE) for the determination of gallic acid (GA). The modified electrode surface was characterised by using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXA) and Fourier transform infrared spectroscopy (FTIR). The electrochemical behaviour of the modified electrode was then studied, using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), showing that the electrode was sensitive to GA in a concentration range of 6.25 × 10−6 to 1.0 × 10−3 mol L−1, with a correlation coefficient R2 of 0.9956 and a limit of detection of 2.09 × 10−6 mol L−1 (S/N = 3). The proposed method was successfully used for the determination of GA in red wine, white wine and orange juice, with recoveries of 102.3, 95.4 and 97.6%, respectively.

Highly Thiolated Dendritic Mesoporous Silica Nanoparticles with High-Content Gold as Nanozymes: The Nano-Gold Size Matters.

Abstract: Thiolated dendritic mesoporous silica nanoparticles (T-DMSNs) with ultrahigh density of thiol groups (284.6 ± 9 μmol g-1) are synthesized and used to load gold nanoparticles with tunable sizes (1.2-2.7 nm) and high content (34.0 wt %). It is demonstrated that the size of gold nanoparticles has a significant impact on their peroxidase-mimicking activity. At an optimized size of 1.9 nm, T-DMSNs@Au exhibits the highest activity. Our contribution provides new insights into the rational design of nanozymes for future applications.

The Effects of Silica-Based Fillers on the Properties of Epoxy Molding Compounds

Abstract: Global design and manufacturing of the materials with superb properties remain one of the greatest challenges on the market. The future progress is orientated towards researches into the material development for the production of composites of better mechanical properties to the existing materials. In the field of advanced composites, epoxy molding compounds (EMCs) have attained dominance among the common materials due to their excellent properties that can be altered by adding different fillers. One of the main fillers is often based on silicon dioxide (SiO2). The concept of this study was to evaluate the effects of the selected silica-based fillers on the thermal, rheological, and mechanical properties of EMCs. Various types of fillers with SiO2, including crystalline silica and fused silica, were experimentally studied to clarify the impact of filler on final product. Fillers with different shape (scanning electron microscope, SEM), along with different specific surface area (specific surface area analyzer, BET method) and different chemical structure, were tested to explore their modifications on the EMCs. The influence of the fillers on the compound materials was determined with the spiral flow length (spiral flow test, EMMI), glass transition temperature (differential scanning calorimetry, DSC), and the viscosity (Torque Rheometer) of the composites.

Surface-Induced Silica Scaling during Brackish Water Desalination: The Role of Surface Charge and Specific Chemical Groups

Abstract: Silica scaling of membranes used in reverse osmosis desalination processes is a severe problem, especially during the desalination of brackish groundwater due to high silica concentrations. This problem limits the water supply in inland arid and semiarid regions. Here, we investigated the influence of surface-exposed organic functional groups on silica precipitation and scaling. A test solution simulating the mineral content of brackish groundwater desalination brine at 75% recovery was used. The mass and chemical composition of the precipitated silica was monitored using a quartz crystal microbalance, X-ray photoelectron spectroscopy, and infrared spectroscopy, showing that surfaces with positively charged groups induced rapid silica precipitation, and the rate of silica precipitation followed the order -NH2 ∼ -N+(CH3)3 > -NH2/-COOH > -H2PO3 ∼ -OH > -COOH > -CH3. Force vs distance AFM measurements showed that the adhesion energy between a silica colloid glued to AFM cantilever and the studied surfaces increased as the surface charge changed from negative to positive. Thus, for the first time direct measurements of molecular forces and specific chemical groups that govern silica scaling during brackish water desalination is reported here. The influence of the different functional groups and the effect of the surface charge on silica precipitation that were found here can be used to design membranes that resist silica scaling in membrane-based desalination processes.

Formation of Si/SiO2 Luminescent Quantum Dots From Mesoporous Silicon by Sodium Tetraborate/Citric Acid Oxidation Treatment.

Abstract: We propose a rapid, one-pot method to generate photoluminescent (PL) mesoporous silicon nanoparticles (PSiNPs). Typically, mesoporous silicon (meso-PSi) films, obtained by electrochemical etching of monocrystalline silicon substrates, do not display strong PL because the silicon nanocrystals (nc-Si) in the skeleton are generally too large to display quantum confinement effects. Here we describe an improved approach to form photoluminescent PSiNPs from meso-PSi by partial oxidation in aqueous sodium borate (borax) solutions. The borax solution acts to simultaneously oxidize the nc-Si surface and to partially dissolve the oxide product. This results in reduction of the size of the nc-Si core into the quantum confinement regime, and formation of an insulating silicon dioxide (SiO2) shell. The shell serves to passivate the surface of the silicon nanocrystals more effectively localizing excitons and increasing PL intensity. We show that the oxidation/dissolution process can be terminated by addition of excess citric acid, which changes the pH of the solution from alkaline to acidic. The process is monitored in situ by measurement of the steady-state PL spectrum from the PSiNPs. The measured PL intensity increases by 1.5- to 2-fold upon addition of citric acid, which we attribute to passivation of non-radiative recombination centers in the oxide shell. The measured PL quantum yield of the final product is up to 20%, the PL activation procedure takes <20 min, and the resulting material remains stable in aqueous dispersion for at least 1 day. The proposed phenomenological model explaining the process takes into account both pH changes in the solution and the potential increase in solubility of silicic acid due to interaction with sodium cations.

Orientation effects on the nanoscale adsorption behavior of bone morphogenetic protein-2 on hydrophilic silicon dioxide

Abstract: Bone Morphogenetic Protein-2 (BMP-2) is a growth factor associated with different developmental functions in regenerative medicine and tissue engineering. Because of its favorable properties for the development of bone and cartilage tissue, BMP-2 promotes the biocompatibility of medical implants. In this research, molecular dynamics simulations were implemented to simulate the interaction of BMP-2 with a flat hydrophilic silicon dioxide substrate, an important biomaterial for medical applications. We considered the influence of four orthogonal protein orientations on the adsorption behavior. Results showed that arginine and lysine were the main residues to interact with the silicon dioxide substrate, directly adsorbing onto the surface and overcoming water layers. However, between these charged residues, we observed a preference for arginine to adsorb. Orientations with the α-helix loop closer to the surface at the beginning of the simulations had greater loss of secondary structure as compared to the other configurations. Among all the orientations, the end-on B configuration had favorable adsorption characteristics with a binding energy of 14 000 kJ mol−1 and retention of 21.7% β-sheets as confirmed by the Ramachandran plots. This research provides new insights into the nanoscale interaction of BMP-2 and silicon dioxide substrate with applications in orthopedic implants and regenerative medicine.

Influence of the synthesis parameters on the mesoporous structure and adsorption behavior of silica xerogels fabricated by sol–gel technique

Abstract: Silicon dioxide xerogels with controlled mesoporosity were produced by sol–gel technique. The mesoporosity and adsorption behavior of methylene blue (MB) were evaluated for the fabricated silica materials. This study is supported by several characterizations, including FTIR, TEM, SEM, and N2 sorption. The adsorption kinetics of MB on the prepared samples was evaluated at room temperature over time. It was demonstrated that the pore structure and adsorption performance of silica are closely dependent on the pH of the sol–gel solution, H2O:TEOS molar ratio, the addition of F127 template, and heat treatment performed. The present study shows that for the adsorption parameters used in this work, the control of sol–gel parameters can give rise to silica xerogels with higher adsorption capacities than SBA-16 silica molecular sieve used as the reference and already recognized as an efficient dye adsorbent. The highest adsorption capacities were measured for silica structures obtained without the use of acidic catalyst, heat treatment or F127 template. As the pore volume of the studied materials is much larger than the amount of MB captured in the adsorption tests, such results seem to be related to the specific surface area and pore size obtained in the sol–gel synthesis. Therefore, it appears that large surface areas and pore sizes accelerate the adsorption kinetic and increase the amount of MB able to stay in equilibrium in the pore structure of silica. As a matter of fact, the work developed here underlines the advantages regarding the simplicity, safety, environmental preservation and cost saving of the synthesis methodology developed herein when compared with the other methodologies commonly used to fabricate silica adsorbents.

Sonochemically-Promoted Preparation of Silica-Anchored Cyclodextrin Derivatives for Efficient Copper Catalysis

Abstract: Silica-supported metallic species have emerged as valuable green-chemistry catalysts because their high efficiency enables a wide range of applications, even at industrial scales. As a consequence, the preparation of these systems needs to be finely controlled in order to achieve the desired activity. The present work presents a detailed investigation of an ultrasound-promoted synthetic protocol for the grafting of β-cyclodextrin (β-CD) onto silica. Truly, ultrasound irradiation has emerged as a fast technique for promoting efficient derivatization of a silica surface with organic moieties at low temperature. Three different β-CD silica-grafted derivatives have been obtained, and the ability of β-CD to direct and bind Cu when CD is bonded to silica has been studied. A detailed characterization has been performed using TGA, phenolphthalein titration, FT-IR, diffuse reflectance (DR), DR UV-Vis, as well as the inductively-coupled plasma (ICP) of the β-CD silica-grafted systems and the relative Cu-supported catalysts. Spectroscopic characterization monitored the different steps of the reaction, highlighting qualitative differences in the properties of amino-derivatized precursors and final products. In order to ensure that the Cu-β-CD silica catalyst is efficient and robust, its applicability in Cu(II)-catalyzed alkyne azide reactions in the absence of a reducing agent has been explored. The presence of β-CD and an amino spacer has been shown to be crucial for the reactivity of Cu(II), when supported.

Direct nanomechanical measurements of boron nitride nanotube-ceramic interfaces.

Abstract: Boron nitride nanotubes (BNNTs) are a unique class of light and strong tubular nanostructure and are highly promising as reinforcing additives in ceramic materials. However, the mechanical strength of BNNT-ceramic interfaces remains largely unexplored. Here we report the first direct measurement of the interfacial strength by pulling out individual BNNTs from silica (silicon dioxide) matrices using in situ electron microscopy techniques. Our nanomechanical measurements show that the average interfacial shear stress reaches about 34.7 MPa, while density functional theory calculations reveal strong bonded interactions between BN and silica lattices with a binding energy of -6.98 eV nm-2. Despite this strong BNNT-silica binding, nanotube pull-out remains the dominant failure mode without noticeable silica matrix residues on the pulled-out tube surface. The fracture toughness of BNNT-silica ceramic matrix nanocomposite is evaluated based on the measured interfacial strength property, and substantial fracture toughness enhancements are demonstrated at small filler concentrations.

Design and Optimization of Piezoresistive Materials Based Microbridge for Electro-osmosis Pressure Sensor

Abstract: Diabetes is a metabolic disorder which is due to high sugar levels. Symptoms of diabetes are frequent urination, increased hungry and increased thirst. Here we are using electro-osmotic pressure sensor to measure the change in glucose concentration levels. Silicon dioxide, aluminium nitride and silicon nitride are suitable for microbridge membrane, among them SiO2 is considered as membrane material due to minimum young’s modulus. Silicon, liquid crystal polymer and glass (quartz) are used for substrate materials, owing to its high cost LCP and glass (quartz) is not much preferable for substrate materials. By using FEM tool, the mechanical behavior of microbridge and electrical response of the Piezo resistors are analyzed based on the non-linearity and sensitivity.

Structure of Highly Porous Silicon Dioxide Thin Film: Results of Atomistic Simulation

Abstract: The high-energy glancing angle deposition of silicon dioxide films with alternation of deposition angle is studied using classical atomistic simulation. Both slow and fast alternations are investigated. The growth of vertical tree-like columns and chevron-like regular structures is demonstrated under fast and slow alternations, respectively. Due to high porosity, the density of the deposited silicon dioxide films is reduced to 1.3 ÷ 1.4 g/cm3. This results in reduction of the refractive index to 1.3, which agrees with known experimental data. For slow continuous substrate rotation, formation of a helical structure is demonstrated.

Nanostructured silver decorated hollow silica and their application in the treatment of microbial contaminated water at room temperature

Abstract: The present study describes the synthesis of mesoporous silicon dioxide (silica) spheres decorated with silver nanoparticles and the investigation of their antimicrobial properties. The sol–gel method was used for the synthesis of mesoporous hollow silica spheres using tetraethyl orthosilicate (TEOS) as the silica source. Uniform hollow spheres (∼300 nm) with a thin shell of silica (∼40 nm) and a high surface area (516 m2 g−1) were obtained after calcination at 550 °C. Furthermore, silver nanoparticles were decorated on the surface of the hollow structure of silica by the adsorption of silver ions at various concentrations followed by reduction using sodium borohydride. Microscopic studies showed that metallic silver was uniformly distributed over the surface of the hollow silica. The as-obtained silver decorated hollow silica exhibited an excellent antibacterial activity against Escherichia coli (E. coli) compared to that of bare hollow silica, which makes them suitable candidates for the economical treatment of bacteria-contaminated water.

Crystallinity and electrical properties of silicon dioxide (SiO2) from rice straw

Abstract: Rice straw is agro-waste that contain celluloses (32–47%), hemicelluloses (19–27%), lignin (5-24%) and ash (13–20%). The ash of rice straw has a high component of silicon dioxide (SiO2). This study aims to determine the effect variation of temperature on the extraction process, to assess crystallinity and electrical properties of silicon dioxide from rice straw. Based on the results and analysis, the influence of the combustion shown that the increase in temperature, will reduce the purity of the silicon dioxide. The composition of each treatment still contained the impurities at 3% of HCl solution consisted of carbon, calcium, and potassium. The structural characteristics obtained are samples in the amorphous phase. The electrical components of the sample are semiconductors and have the best dielectric constant at a temperature treatment of 800 C.

Experimental study on CO2 hydrate formation in the presence of TiO2, SiO2, MWNTs nanoparticles

Abstract: A series of experiments on CO2 hydrate formation were carried out in the presence of titanium dioxide (TiO2), silicon dioxide (SiO2), multi-walled carbon nanotubes (MWNTs) nanoparticles. Th...

Effect of Graphene on the Sunlight Absorption Rate of Silicon Thin Film Solar Cells

Abstract: The electromagnetic property of graphene is studied by finite-difference time-domain (FDTD) method. As the graphene has excellent electrical conductivity and high transparency, it has certain advantages as a transparent electrode for solar cells. This paper designs a three-layer film structure composed of graphene, silicon, and silicon dioxide (SiO2). Then, the effects of the chemical potential and the scattering rate of the graphene on the light absorption of the film are studied. The study found that the electromagnetic property of graphene is relatively stable, which is not easily influenced by the external environment. After changing its chemical potential, scattering rate, and other parameters, it is found that the film absorption rate is less affected unless the large range of chemical potential changes; it will lead to a decline in the absorption rate of light.

Surface deep profile synchrotron studies of mechanically modified top-down silicon nanowires array using ultrasoft X-ray absorption near edge structure spectroscopy.

Abstract: Atomic, electronic structure and composition of top-down metal-assisted wet-chemically etched silicon nanowires were studied by synchrotron radiation based X-ray absorption near edge structure technique. Local surrounding of the silicon and oxygen atoms in silicon nanowires array was studied on as-prepared nanostructured surfaces (atop part of nanowires) and their bulk part after, first time applied, in-situ mechanical removal atop part of the formed silicon nanowires. Silicon suboxides together with disturbed silicon dioxide were found in the composition of the formed arrays that affects the electronic structure of silicon nanowires. The results obtained by us convincingly testify to the homogeneity of the phase composition of the side walls of silicon nanowires and the electronic structure in the entire length of the nanowire. The controlled formation of the silicon nanowires array may lead to smart engineering of its atomic and electronic structure that influences the exploiting strategy of metal-assisted wet-chemically etched silicon nanowires as universal matrices for different applications.