Amorphous Silica Matrix Research Articles

The use of a laponite dispersion to increase the hydrophilicity of cobalt-ferrite magnetic nanoparticles

In the literature, several attempts have been made to synthesize and later to modify magnetic nanoparticles to make them feasible for several applications. For biomedical applications, magnetic nanoparticles and clay minerals were combined to form a material that is both stable and biocompatible. In this context, composites with ratios of 4.70, 2.35 and 1.17 (weight/weight) of Cobalt Ferrite and Laponite were synthesized and characterized. These composites were treated with acid, and consequently the laponite was converted into an amorphous silica matrix around the magnetic nanoparticles. This morphology was confirmed using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD). The particle size distribution, obtained by Transmission Electron Microscopy (TEM), was used as an input parameter for the polydispersity function in the Small Angle X-ray Scattering (SAXS) analysis. The latter was also applied to verify the particle shapes and aggregates for each composite. It was demonstrated by Thermal Gravimetric Analysis (TGA), that these materials, except for the composite with the highest ratio, adsorbed at least one order of magnitude more water than pure Cobalt Ferrite nanoparticles. Thus, increasing the hydrophilicity properties of the Cobalt Ferrite - laponite/silica system. A preliminary magnetization experiment corroborated with these findings and showed that a fraction of the system is not in the superparamagnetic regime at room temperature.

A Short Review on Novel Membranes for Gas Separation

The area is a membrane that works faster than any publicly accessible scheme. Membrane technology are more useful than other kinds of membranes for CO2/CH4 separation, which includes both carbon and zeolite molecular sieves and amorphous silica matrix. Besides, there are several related to the membrane system such as insufficient heat and chemical stability and plasticisation sensitivity. The further improve the transmitter system's position in the separation of gas and economic saving are the advantage of membrane technology to the world. Despite centuries of studies on the topic, fewer than ten polymer kinds are currently used for business gas separation, and no polymer specifically intended for this function. New membrane must deliver substantial rises in CO2 permeance and selectivity of CO2 / CH4 relative to current technologies to contend internationally.

Controlling the morphology of copper-silica nanocomposites from laser ablation in liquid

Synthesis of copper-silica nanocomposites with controllable morphology and composition were produced with a one-step femtosecond reactive laser ablation in liquid (fs-RLAL) technique. The composite nanomaterials were generated by focusing femtosecond near-IR laser pulses onto a silicon wafer immersed in an aqueous copper(II) nitrate solution, with the solution pH adjusted using nitric acid or potassium hydroxide. Under acidic conditions (pH 3.0 and 5.4), little copper was incorporated in the predominantly silica product (1.4 and 1.5 wt.%). These acidic conditions yielded large ~30–80 nm silica particles, with some particles consisting of copper core/silica shell. In contrast, increasing the solution pH to 10.4 resulted in extremely high Cu loading of 31.5 wt.% and a composite product consisting of 1.5 nm copper clusters distributed throughout a matrix of amorphous silica and copper phyllosilicate. The relationship between the precursor solution pH and the product morphology and copper loading is attributed to the point of zero charge (PZC) of silica, in which the high solution pH allows for electrostatic adsorption to occur between the deprotonated silica clusters from the ablated silicon wafer and the copper hydroxide dimer formed in solution.

Electrochemistry and Thermal Behavior of SiOx Made by Reactive Gas Milling

SiOx with various oxygen contents were synthesized from Si powder by a simple room-temperature ball milling method by controlling the air exposure time during milling. The resulting SiOx consists of nano and amorphous Si dispersed in an amorphous silicon oxide matrix. The oxygen saturated composition of SiO0.37 is thermally stable up to 800 °C and has improved cycling performance after annealing. The 1st irreversible capacity is reduced by high temperature annealing due to defect healing, while the high reversible capacity (1500–2000 mAh g−1 or 1600–1800 Ah l−1) is well maintained. This work demonstrates the thermal properties of SiOx made by reactive gas milling and how internal defects directly influence its electrochemistry.

Stabilization of β-carotene embedded in a silica matrix and study of its physical properties

This work reports on the behavior of β-carotene within a silica matrix prepared by the sol-gel method. Results show that highly pure β-carotene integrates with the silica to form a silica-based composite. The interaction exhibited between the inorganic matrix and the β-carotene results in a π-d conjugated system that guarantees the development of the protective mechanism of the β-carotene and stabilizes the organic molecule, allowing its preservation at high calcination temperature. The spectroscopic analysis, made through fluorescence emission and infrared spectroscopy, shows the presence of β-carotene within the silica matrix after the composite was calcined at 1000 °C. Furthermore, the structural interactions of the β-carotene with the silica and the protective function of the β-carotene change the crystallization route naturally followed by the silica when exposed to increasing temperature. In this case, the amorphous silica matrix is preserved after high-temperature calcination, which is beneficial for biomedical applications as it allows the release and transport of the β-carotene to take full advantage of its health benefits.

Characterization of Sol-gel Prepared Silica Supported NiO-CuO Composites

Silica (SiO2) supported nickel oxide-copper oxide (NiO-CuO) composites were synthesized through alkoxide route of sol-gel process using tetraethyl ortthosilicate (TEOS), nickel nitrate hexahydrate and copper nitrate trihydrate as precursors. A series of different compositions were prepared varying NiO:CuO molar ratios keeping all other process parameters constant. The gels thus obtained were calcined at a moderate temperature i.e. 500and#186;C for one hour. The crystal structure and thermal stability of metal oxide particles embedded in silica matrix were studied using X-ray diffraction technique (XRD) and differential scanning calorimetry (DSC-TGA) respectively. The purity of the composites was checked by Infrared spectroscopy (IR) whereas the composite formation was confirmed by scanning electron microscopy. The results revealed that crystals of NiO and CuO nanoparticles aggregated to form spheres of variable sizes were successfully embedded in the amorphous silica matrix composed of silica particles agglomerated to form clusters.

Characterization of Sol-gel Prepared Silica Supported NiO-CuO Composites

Silica (SiO2) supported nickel oxide-copper oxide (NiO-CuO) composites were synthesized through alkoxide route of sol-gel process using tetraethyl ortthosilicate (TEOS), nickel nitrate hexahydrate and copper nitrate trihydrate as precursors. A series of different compositions were prepared varying NiO:CuO molar ratios keeping all other process parameters constant. The gels thus obtained were calcined at a moderate temperature i.e. 500and#186;C for one hour. The crystal structure and thermal stability of metal oxide particles embedded in silica matrix were studied using X-ray diffraction technique (XRD) and differential scanning calorimetry (DSC-TGA) respectively. The purity of the composites was checked by Infrared spectroscopy (IR) whereas the composite formation was confirmed by scanning electron microscopy. The results revealed that crystals of NiO and CuO nanoparticles aggregated to form spheres of variable sizes were successfully embedded in the amorphous silica matrix composed of silica particles agglomerated to form clusters.

Size and distribution of the iron oxide nanoparticles in SBA-15 nanoporous silica via SANS study

Structural characteristics of nanocomposite series consisting of iron oxide nanoparticles (NPs) embedded in the regular pores of amorphous silica matrix (SBA-15) were investigated by means of small angle neutron scattering (SANS). By virtue of unique neutron properties, insight into the inner structure and matter organization of this kind of systems was facilitated for the first time. Based on rigorous experimental support, fundamental model describing the neutron scattering intensity distribution was proposed by assuming general composite structural features. Model application to SANS data confirmed the presence of iron oxide NPs in the body of examined matrices, providing additional information on their shape, concentration and size distribution. Scattering superposition principle employed in the model conception allows for tailoring its fundamental characteristics, and renders it a potent and versatile tool for a wide range of applications.

Enhancement the photocatalytic performance of semiconductors through composite formation with Eu-TUD-1

In the current article, two different functionalities were employed to enhance the photocatalytic performance of the two famous semiconductors; ZnO and TiO2, under UV light illumination. Eu3+ incorporated TUD-1 mesoporous material (Si/Eu ratio of 10) was wet deposited with ZnO and TiO2 with a mass ratio of 1 Eu-TUD-1: 1 ZnO or TiO2. The prepared composites were characterized by means of XRD, DR UV-Vis, Raman spectroscopy, SEM, EDX and HR-TEM. Characterization data confirmed the presence of Eu2O3 nanoparticles embedded in amorphous silica matrix that support the nanoparticles of commercial ZnO or TiO2. The photocatalytic performance of the prepared materials was examined in the decolourization reaction of methyl green (MG) dye under black light illumination with a wavelength centered at 367 nm and at ambient temperature. The activity of the prepared materials was almost 3.4-3.6 times higher than neat ZnO or TiO2 and almost 1.2-1.3 times higher than same composites without silica, under the same condition. The prepared composites were recycled successfully for four consecutive reaction without significant loss in the case of Eu-TUD-1/TiO2 composite and 18-20% of loss activity in the case of Eu-TUD-1/ZnO composite. Hence, the results suggest the application of prepared material as photocatalyst under UV illumination with strong adsorption affinity.

Structure and Electrochemistry of SiOx Made By Reactive Gas Milling

SiO x is a promising Li-ion battery negative electrode material because of its high capacity and unique microstructure that leads to good cycle life. However, SiO is typically made by high temperature methods that are expensive and difficult to realize, especially at lab scale. Here, SiO x negative electrode materials were synthesized by ball milling Si in air. This method allows efficient control of oxygen content, as shown in Figure 1a and results in a similar microstructure as a commercially purchased SiO. XRD and TEM results show that the SiOx prepared by ball milling in air are composed of nanocrystalline Si embedded in an amorphous silicon oxide matrix (Figure 1b). The very low initial coulombic efficiency (ICE) of conventionally made SiO (measured here to be ~55% for Aldrich SiO) is one of its major drawbacks. In contrast, reactive gas milled SiO x have much higher reversible capacities (>1500 mAh/g) and higher ICE values (>70%). Reactive gas milled SiO x has a number of attractive features: an inexpensive and simple synthesis process, high capacity, high ICE, high thermal stability (stable microstructure at 800 °C, Figure 1c), and a special microstructure that protects Si from reaction with electrolyte, resulting in excellent cycling performance (Figure 1d). Here a detailed study will be presented describing SiO x synthesis by reactive gas milling, thermal properties, and its electrochemical performance in relation to its composition and microstructure. Figure 1

Preparation and characterization of CuCr2O4/SiO2 and Cu2Cr2O4/SiO2 nanocomposites obtained from carboxylate complex combinations

This study reports the preparation and characterization of CuCr2O4/SiO2 and Cu2Cr2O4/SiO2 nanocomposites. In order to obtain 50 mass% CuCr2O4/SiO2 and Cu2Cr2O4/SiO2 nanocomposites, we have used a method based on the thermal decomposition of the precursors Cu(II) and Cr(III) carboxylate type complexes inside the SiO2 matrix. The precursors were formed inside the gels during the redox reaction between Cu(II) and Cr(III) metal nitrates and 1,3-propanediol (1,3PD). As a result of the gels heating, the precursors decomposed at ~ 300 °C leading to the amorphous metal oxides CuO and Cr2O3+x. Cr2O3+x turned to crystalline α-Cr2O3 (crystalline) at 400 °C which subsequently interacted with CuO. Well crystallized Cu2Cr2O4 was obtained at 1000 °C as a result of the interaction between CuCr2O4 and residual CuO formed at 800 °C. In both samples the oxides were homogenously distributed within the amorphous silica matrix. The nanocomposite samples CuCr2O4/SiO2 and Cu2Cr2O4/SiO2 obtained at different annealing temperatures were characterized by thermal analysis, FT-IR spectrometry and powder x-ray diffraction. The results showed that the silica matrix plays a crucial role for the preparation of the desired chromite nanoparticles.

Synthesis of SiOx/C composite with dual interface as Li-ion battery anode material

A dual interface SiOx/C composite is prepared through a novel, facial, one-step route by redox reaction of organic carbon with silica precursor, using tetraethyl orthosilicate (TEOS) and sucrose as raw material, in which sucrose acts as both a reductant and coated carbon. HRTEM indicates that the composite has a dual interface structure with carbon coating layer and intermediate layer. Crystalline Si approximately 3 nm–20 nm in size is dispersed in amorphous silicon oxide matrix. The SiOx/C is utilized in LIB as anode material and exhibits a high reversible specific capacity of 755 mA h g−1 after 300 cycles at 100 mA g−1 with capacity retention about 91%. Such outstanding cycling stability can be ascribed to the intermediate layer and carbon scaffold, which serve as a buffering to relieve volume change of produced Si upon cycles.

Atom Probe Tomography for 3D Structural and Chemical Analysis of Individual Proteins.

Determination of the 3D structure of proteins and other biomolecules is a major goal in structural biology, to provide insights to their biological function. Such structures are historically unveiled experimentally by X-ray crystallography or NMR spectroscopy, and in recent years using cryo-electron microscopy. Here, a method for structural analysis of individual proteins on the sub-nanometer scale using atom probe tomography is described. This technique offers a combination of high-resolution analysis of biomolecules in 3D, and the chemical sensitivity of mass spectrometry. As a model protein, the well-characterized antibody IgG is used. IgG is encapsulated in an amorphous solid silica matrix via a sol-gel process to provide the requisite support for atom probe analysis. The silica synthesis is tuned to resemble physiological conditions. The 3D reconstructions show good agreement with the protein databank IgG crystal structure. This suggests that the silica-embedding strategy can open the field of atom probe tomography to the analysis of biological molecules. In addition to high-resolution structural information, the technique may potentially provide chemical information on the atomic scale using isotopic labeling. It is envisaged that this method may constitute a useful complement to existing tools in structural biology, particularly for the examination of proteins with low propensity for crystallization.

A Seedless Method for Gold Nanoparticle Growth inside a Silica Matrix: Fabrication of Materials Capable of Third-Harmonic Generation in the Near-Infrared.

A composite in which gold nanoparticles (AuNPs) approximately 10 nm in size are embedded in amorphous transparent silica matrix has been produced. The synthetic protocol uses HAuCl4 as the Au ion source, tetraethoxysilane (TEOS) as the SiO2 precursor, and l-ascorbic acid (AA) as the reducing agent. AA is employed before the sol-gel process in an amount sufficient only for reduction of Au3+ ions to Au+ . By using a cationic surfactant, benzylcetyldimethylammonium chloride hydrate (BDAC) and/or cetyltrimethylammonium bromide (CTAB), the Au+ ions are encapsulated within metalomicelles, which prevents them from being reduced to Au0 and enables their homogeneous distribution in the gel. Reduction of Au+ to Au0 and the growth of the AuNPs occurs at room temperature during the gelation, and arises from the release of EtOH during the hydrolysis of TEOS. The composites contain 0.027 wt % of Au. They exhibit nonlinear optical behavior characterized by the third-order nonlinear refraction index, n2 , in the range 3.6-5.7×10-16 cm2 W-1 at λ=1.030 μm. The composites are capable of effective third-harmonic generation of ultrashort near-IR (210 fs, 1.030 μm) laser pulse through a direct third-order mechanism.

Study of Dielectric properties for porous silicon prepared by Anodization

The nanostructure for porous silicon (PS) films is produced by anodization of p-type silicon chip with current consistency (15 mA/cm2), etching time about 10 min and HF concentration (32%) to the formation nanosized pore order with a dimension of around few hundreds nanometric. The films were featured by the measurement of atomic force microscopy (AFM) in the Baghdad university, X-Ray diffraction (XRD) and FTIR spectroscopy characteristics in the technological university. I am having appraising crystallites size from XRD about nanoscale for porous silicon and AFM proves the nanometric size. Chemical fictionalizations through the electrochemical etching clear on superficies chemical structure of PS. The etching possess disproportionate microstructures that include Si-H clusters in (Si3-SiH), sparse in amorphous silica matrix and Si-H2 scissor mode. From the FTIR testing appeared that the Si suspending bonds of the as- produced PS layer have massive quantities of Hydrogen to form weak Si–H bonds related to Si–H stretch (Si3-SiH) and Si-H stretch (Si2-SiH). The AC electrical properties were measured with LCR meter analyzer the frequency between 50 Hz and 5 MHz. for capacitance, dielectric and loss tangent (tan δD) to balk silicon and porous silicon have been done in the ministry of science and technology.

H-ZSM-5 Materials Embedded in an Amorphous Silica Matrix: Highly Selective Catalysts for Propylene in Methanol-to-Olefin Process

H-ZSM-5 materials embedded in an amorphous silica were successfully synthesized with three different Si/Al ratios (i.e., 40, 45, and 50). The presence of the MFI structure in the synthesized samples was confirmed by X-ray diffraction (XRD), Fourier transform infra-red (FT-IR), and solid state-nuclear magnetic resonance (SSNMR) techniques. The morphology and textural properties of the samples were investigated by scanning electron microscopy (SEM), TEM, and N2-physisorption measurements. Furthermore, acidic properties of the synthesized catalysts have been studied by NH3-TPD and FT-IR spectroscopy of CO adsorption studies. Variation of the Si/Al ratio affected the crystal morphology, porosity, and particle size, as well as the strength and distribution of acid sites. The synthesized zeolite materials possessed low acid-site density and exhibited high catalytic activity in the methanol-to-olefin (MTO) reaction. To study the intermediate species responsible for catalyst deactivation, the MTO reaction was carried out at high temperature (500 °C) to accelerate catalyst deactivation. Interestingly, the synthesized catalysts offered high selectivity towards the formation of propylene (C3=), in comparison to a commercial microporous crystalline H-ZSM-5 with Si/Al = 40, under the same reaction conditions. The synthesized H-ZSM-5 materials offered a selectivity ratio of C3=/C2= 12, while it is around 2 for the commercial H-ZSM-5 sample. The formation of hydrocarbon species during MTO reaction over zeolite samples has been systematically studied with operando UV-vis spectroscopy and online gas chromatography. It is proposed that the strength and type of acid sites of catalyst play a role in propylene selectivity as well as the fast growing of active intermediate species. The effective conversion of methanol into propylene in the case of synthesized H-ZSM-5 materials was observed due to possession of weak acid sites. This effect is more pronounced in H-ZSM-5 sample with a Si/Al ratio of 45.

Effect of ZnS nanoparticles on the Judd-Ofelt and radiative parameters of Sm3+ ions in sol-gel silica matrix

Sm3+ singly doped and Sm3+ co-doped with varying concentration of ZnS nanoparticles (ZnS NPs) in silica matrix were fabricated via sol-gel route and investigated by various structural, thermo-gravimetric and spectroscopic techniques. Structural characterizations were done by XRD, EDX, TEM and FTIR whereas thermo-gravimetric characterization was performed by TGA/DTG technique. The structural studies reveal the presence of nanosized ZnS particles in the amorphous silica matrix. Spectroscopic studies were performed through absorption, excitation, emission and decay spectra of the fabricated samples. The dependence of Judd-Ofelt and various radiative parameters of Sm3+ on the concentration of ZnS NPs in the studied matrix were evaluated. Significantly high value of Ω2 obtained for the present system reveals effective network modifying nature of the ZnS NPs. The PL behaviour showed strong concentration dependence on ZnS NPs and showed optimum for the ZnS concentration of 0.5 M. The emission transition 4G5/2 → 6H9/2 of Sm3+ corresponding to the red colour observed at 642 nm for silica matrix in the present study showed excellent radiative behaviour compared to other popular glass hosts. This indicates ZnS NPs co-doped Sm3+ sol-gel silica matrix to be a prospective candidate for laser and other optical device applications.

The formation of spinel-group minerals in contaminated soils: the sequestration of metal(loid)s by unexpected incidental nanoparticles

Mineralogical studies of contaminated soils affected by smelter emission and dust from mining activities indicate that minerals of the spinel group are one of the common hosts of metal-bearing contaminants. Spinel group minerals typically originate from high temperature processes, but an increasing number of studies indicate that metal-bearing spinel group minerals can also form under ambient Earth surface conditions in surficial soils. In this contribution to honor Donald Sparks, we show that the spinels Zn-bearing magnetite (Zn0.5Fe2.5O4) and minium (Pb3O4) form during low temperature alteration of Pb-bearing silica glass in surficial organic rich soils in proximity to a former Cu-smelter in Timmins, Ontario, Canada. The glass most likely formed during high-temperature processes and has been either emitted by the smelter or wind-blown from waste rock piles to near-by soils. The alteration of the glass by percolating pore solutions has resulted in the formation of large micrometer-size dendritic etch features and in nanometer-size dendritic alteration halos composed of nano-size prismatic crystals of Zn-rich magnetite and spherical nanoparticles of minium. Both spinel-type phases are embedded in an amorphous silica matrix which formed during the alteration of the glass at low temperature. A review on the occurrence of spinel-group minerals in smelter-affected soils or mine tailings indicates that the formation of these minerals under ambient Earth surface conditions is quite common and often results in the sequestration of contaminants such as Cu, Ni, Zn and Sb. The pedogenic spinels often occur as euhedral crystals in nano-size mineral assemblages within alteration features such as dendritic etch patterns, mineral surface coatings and mineralized organic matter. Their well-developed crystal forms indicate that (a) they have not formed during a rapid cooling process in a smelter or refinery which typically creates spherical particulate matter, and (b) they have not been part of particulate matter added via fluvial or Aeolian processes which most commonly yield anhedral morphologies. The formation of nano-size spinel-group minerals in low temperature environmental settings may lead to the long-term storage of metal(loid)s in mineral phases and their transport over vast distances via fluvial, alluvial and Aeolian processes.

One-step femtosecond laser ablation synthesis of sub-3 nm gold nanoparticles stabilized by silica

We report the synthesis of silica-gold nanoparticles (silica-Au NPs) using a one-step femtosecond-reactive laser ablation in liquid (fs-RLAL) technique by focusing femtosecond laser pulses onto a silicon wafer immersed in an aqueous KAuCl4 solution. Characterization of the silica-Au NPs revealed two populations of Au NPs: (i) larger, isolated Au NPs with diameter 7.0 ± 2.0 nm, and (ii) smaller Au NPs (1.9 ± 0.7 nm) stabilized by an amorphous silica matrix, along with new species of silicon observed from XPS analysis. The silica-Au NPs were catalytically active towards the model reaction of para-nitrophenol reduction by NaBH4. The formation of the two populations of silica-Au NPs is ascribed to reaction dynamics occurring on two distinct timescales. First, the dense electron plasma formed within tens of femtoseconds of the laser pulse initiates reduction of the [AuCl4]− complex, leading to the formation of larger isolated Au NPs. Second, silicon species ejected from the wafer surface hundreds of picoseconds or later after the initial laser pulse reduce the remaining [AuCl4]− and encapsulate the growing clusters, forming ultrasmall Au NPs stabilized by the silica matrix. The morphologies of the silica-Au NPs generated from fs-RLAL are distinct from those reported in recent RLAL experiments with nanosecond lasers, reflecting distinct mechanisms occurring on the different pulse duration timescales.

Colored amorphous silica‐based powder with TiN nanocrystals precipitated by ammonolysis of Ti–Si–O ternary glass

AbstractColoration of amorphous silica powder containing titania was investigated by nitridation in an ammonia flow. The oxide precursors were obtained by the hydrolysis of a mixture of tetraethyl orthosilicate (TEOS) and tetrabutoxy titanium (TBT). The color changed with the amount of TBT in the mixture, the hydrolysis pH and the ammonolysis temperature. The original white color of the 8 mol% TBT powder hydrolyzed under basic pH conditions changed to pale goldenrod at 700°C, then to dark olive green at 800°C, and further darkened with increasing ammonolysis temperature. A steel‐blue color appeared at 900°C for the powder obtained with 3 mol% TBT, and increased in darkness at 1000°C. A similar bluish color was observed for powders obtained by acidic hydrolysis after ammonolysis above 900°C, and this was independent of the amount of titania, although the chroma decreased with increasing firing temperature for the powder with 3 mol% TBT. The ammonolysis powder products were characterized using X‐ray diffraction (XRD), electron probe micro analysis (EPMA), transmission electron microscopy‐electron energy‐loss spectroscopy (TEM‐EELS), scanning transmission electron microscopy‐high‐angle annular dark‐field imaging (STEM‐HAADF) and Ti–K edge X‐ray absorption fine structure (XAFS). The color change was related to both precipitated TiN nanocrystals and residual titanium in the amorphous silica matrix. The TiN exhibited a goldish reflection and also plasmonic absorption from light blue to gray depending on the TiN crystallite size. The plasmonic absorption and resonance of nanocrystalline TiN will be useful similarly to that of gold in nanotechnology for various kinds of energy application.