Amorphous Silica Matrix Research Articles

Bridging Structural and Dynamical Models of a Confined Sodium Nitroprusside Complex

Sodium nitroprusside (SNP), an active pharmaceutical ingredient, is encapsulated in biocompatible amorphous silica matrices and characterized by solid-state NMR. Through complementary NMR and pair distribution function (PDF) study, we previously showed that when confined in 1–2 nm sized nanopores of an amorphous silica matrix, the complex displays a “liquid like” isotropic motion (NMR) but still retains an associated anion/cation preferential arrangement (PDF). In this study, we present new insights into the physical state of the confined drug to explain the coexistence of these two seemingly contradictory characteristics. By performing temperature-dependent T1 relaxation experiments on the samples with different hydration levels, we retrieve respective motional activation energies for all three guest species inside the pores (sodium cations, nitroprusside anions, and water). For the hydrated samples, we identify a temperature range where results ascertain isotropic but correlated ionic motion of the SNP ...

Ag nanoaggregates as efficient broadband sensitizers for Tb3+ ions in silica-zirconia ion-exchanged sol-gel glasses and glass-ceramics

In this paper we report the study of down-shifting silica-zirconia glass and glass-ceramic films doped by Tb3+ ions and Ag nanoaggregates, which combine the typical spectral properties of the rare-earth-ions with the broadband sensitizing effect of the metal nanostructures. Na-Tb co-doped silica-zirconia samples were obtained by a modified sol-gel route. Dip-coating deposition followed by annealing for solvent evaporation and matrix densification were repeated several times, obtaining a homogeneous crack-free film. A final treatment at 700 °C or 1000 °C was performed to control the nanoscale structural properties of the samples, resulting respectively in a glass (G) or a glass-ceramic (GC), where tetragonal zirconia nanocrystals are surrounded by an amorphous silica matrix. Ag introduction was then achieved by ion-exchange in a molten salt bath, followed by annealing in air to control the migration and aggregation of the metal ions. The comparison of the structural, compositional and optical properties are presented for G and GC samples, providing evidence of highly efficient photoluminescence enhancement in both systems, slightly better in G than in GC samples, with a remarkable increase of the green Tb3+ PL emission at 330 nm excitation: 12 times for G and 8 times for GC samples. Furthermore, after Ag-exchange, the shape of Tb3+ excitation resembles the one of Ag ions/nanoaggregates, with a broad significant absorption in the whole UV-blue spectral region. This broadband enhanced downshifting could find potential applications in lighting devices and in PV solar cells.

Microwave absorption performance of in situ synthesized Fe3O4-SiO2 hybrid fibres with enhanced environmental stability

Fe3O4-SiO2 hybrid fibres were prepared by a combination of sol-gel and electro spinning techniques. The X-ray diffraction peaks of the fibres at 30.5, 35.5, 43.0, 57.0 and 62.6 correspond to the (220), (311), (400), (511) and (440) Fe3O4 planes and confirm the formation of Fe3O4 in the amorphous silica matrix. Si and Fe elemental mappings at the microstructural level were determined by scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS). The results reveal the uniform distribution of Si and Fe in the hybrid fibres. The Fe3O4-SiO2 hybrid fibres are immersed in the test hydrochloric acid solution with pH=1 and still can be magnetized and attracted to an external magnet after 6h in the solution. The heat- and flame-resistant performances of the hybrid fibres are demonstrated. Moreover, the prepared Fe3O4-SiO2 hybrid fibres display good microwave absorption performance in the range of relatively high frequencies. At a thickness of 5mm, the bandwidth corresponding to reflection loss below −10dB reaches approximately 11GHz (7–18GHz), covering the entire X-band (8.0–18.0GHz) and Ku-band (12.0–18.0GHz).

Hydrothermal synthesis of silicon oxide clad uranium oxide nanowires

AbstractA facile method to synthesize silicon oxide clad uranium oxide nanowires is presented. U3Si2, used as a precursor, was oxidized to produce uranium oxide nanocrystallites and amorphous silicon oxide under hydrothermal conditions at 300°C and a pressure of 7.8 × 106 Pa. The growth of uranium oxide nanowires was assisted by silicon oxide via assembling the uranium oxide nanocrystallites in an amorphous silicon oxide matrix. The microstructure and composition of silicon oxide clad uranium oxide nanowires were characterized by XRD, SEM, TEM, and EDS. The uranium oxide in the nanowires was determined as UO2.34 with a fluoride cubic structure.

Characterization of particles created by laser-driven hydrothermal processing

This study aims to identify, using various characterization techniques, the changes suffered by glassy materials as result of being subjected to laser-driven hydrothermal processing (LDHP). The overarching goal of the research was to verify if LDHP was more or less likely to comminute elements such as Fe and Ti. LDHP is an innovative technique used for the dissolution of submerged materials for subsequent chemical analysis. Two naturally occurring glasses, obsidian and tektite, were used as example targets in this study. Characterization of sample materials before and after laser processing was conducted through multiple techniques such as optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. Examination of the untreated base material, in bulk and crushed form, established a baseline for comparison to particles created by laser processing of the same material. The analytical methods employed here provided data on micrometer- and nanometer-sized particles, including their crystal structure, microstructure, and chemical composition. The bulk and crushed obsidian and tektite samples contained inclusions rich in several transition elements, most notably iron or titanium. Analysis of liquid media collected after laser processing of bulk obsidian and tektite samples revealed fine particles rich in the same elements. Qualitative evidence suggests that the laser-driven hydrothermal process preferentially partitions the transition metals in to the submerged liquid from the mostly amorphous silica matrix thus selectively enriching the supernate.

A transmission electron microscopy (TEM) study of silver nanoparticles associated with mine waste from New Caledonian nickel deposits: potential origins of silver toxicity in a World Heritage Site

The nature of silver nanoparticles associated with nickel-laterite ore deposits in New Caledonia (SW Pacific Ocean) is explored using transmission electron microscopy. The silver nanoparticles, dispersed in a matrix of amorphous silica, display complex textures such as linear aggregation and bimodal diameter distributions of 3–12 and 20–60 nm for one sample and 2–30 and 150–650 nm for the other, indicative of Ostwald ripening. These features as well as chemical heterogeneity (31–82% Ag—normalized X-ray energy dispersive spectrum), destructive assemblage interfaces, and amorphous and nanoparticle silica phases are consistent with those observed in epithermal gold deposits, potentially indicating a similar origin. Silver is highly toxic to a wide variety of organisms, and therefore, its significant presence in material directly related to mine runoff is a major threat to the New Caledonian environment, particularly the lagoons, which are listed as a World Heritage Site. Potential exists that the silver nanoparticles observed here provide the key to the origin of the toxic silver accumulation observed in New Caledonian reef organisms.

Existence of cryogenic magnetic entropy change in Gd based nanoparticles

Magnetic nanoparticles with average diameter of 5–7 nm were prepared by nanocasting method inside of the pores of periodic silica matrix of SBA15 type. The uniform size of the pores limited the particles' growth what resulted in formation of nanocomposite consisting of monodisperse nanoparticles of Gd2O3 embedded in amorphous silica matrix. Magnetic properties of the material were examined in magnetic fields up to 5 T and in temperature range 2–52 K. The magnetic entropy change of 29 J/kg K was observed at 2 K for field variation 5 T in the investigated nanocomposite what suggests this material could be feasible for cryomagnetic refrigeration applications.

Highly blue emission of ZnO nanoparticles embedded in a SiO2 matrix

The main drawbacks of fluorescent ZnO nanoparticles in practical optoelectronic applications are fast particle growth and agglomeration in water, causing a periodic decrease of light emission intensity. In this work, ZnO nanoparticles were successfully embedded within a silica matrix to prevent their agglomeration. The ZnO NPs were synthesized by the polyol method, using ethylene glycol and glycerol in sizes ranging from 5–6 nm. The as-obtained ZnO particles were dispersed in an amorphous silica matrix under three different ZnO:SiO2 molar ratios: 20:80, 15:85 and 10:90. With the aim of enhancing the luminescent properties of the ZnO@SiO2 composites, various annealing treatments in the range of 150–210 °C were carried out. The chemical analyses of the bare ZnO and the composites were carried out by Fourier transform infrared spectroscopy, which confirmed the presence of functional groups attached to the ZnO surface. By means of thermogravimetric analysis, it was determined that the evaporation of solvents shifted to lower temperatures (180 °C) when silica was added to the ZnO colloidal solution. By means of photoluminescence, a bright blue emission, centered at 440 nm, was observed in all of the samples, even at high temperatures (i.e., 210 °C); only a red shift of 20 nm was observed. Interestingly, the emission intensity of the sample 20:80, when annealed at 170 °C for 4 h, was enhanced 2.6 times, compared to the bare ZnO.

Enhanced near-infrared emission from erbium and cerium oxide codoped silica nanocomposite

Er3+-doped CeO2-SiO2 nanocomposite was successfully fabricated by a sol-gel route. The homogeneous distribution of CeO2 nanocrystals among amorphous silica matrix was evidenced by the X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. The incorporation of Er3+ ions into CeO2 nanocrystals was revealed by emission spectra and luminescence decay curves. Increasing CeO2 content and raising annealing temperature lead to the enhancement of the 1532 nm Er3+ emission, because CeO2 nanocrystals can efficiently sensitize the emission of Er3+, provide a low phonon energy environment, and defend them from hydroxyl quenching. It is expected that the investigated nanocomposite might be a promising candidate for optical fiber communication.

Mechanism and crucial parameters on GaN nanocluster formation in a silica matrix

The formation of wurtzite GaN nanoclusters in an amorphous silica matrix, via gallium and nitrogen ion implantation and rapid thermal annealing, is identified using Extended X Ray Absorption Fine Structure analysis. The mechanism and the crucial parameters that rule the formation of the nanoclusters are established by the use of molecular dynamics simulations. The dominant structural parameters are found to be the concentration of the silicon and oxygen vacancies that are formed during the implantation and the annealing temperature. It is concluded that annealing at 1400 K and 8% Ga/Si and 12% N/O ratios are needed for the formation of GaN nanoclusters. In addition to that, the GaN nanocluster formation is accomplished only when the vacancy concentrations of silicon and oxygen atoms are equal to 10% and 20%, respectively. Finally, the observation of various snapshots upon an increase of the annealing duration indicates the coalescence of smaller GaN nuclei towards larger ones, designating that the Ostwald ripening is a dominant mechanism.

Influence of anatase titania nanoparticles content on optical and structural properties of amorphous silica

In this work, the influence of TiO2 NPs content on optical and structural properties of amorphous SiO2 is investigated. Amorphous SiO2/TiO2 thin films were wet-mixed and then deposited onto glass substrate by spin coating technique. The homogeneity distribution of anatase titania nanoparticles within amorphous silica matrix was evidenced by the results of X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and field emission scanning electron microscope (FE-SEM). The crystallite size of the mixed phase increased significantly upon increment of TiO2 NPs content. The results of emission and photoluminescence excitation (PLE) confirmed the defects creation in the SiO2 matrix. The trapped electrons and the presence of oxygen vacancies at the TiO2/SiO2 interface enhanced the emission intensity of SiO2/TiO2 nanocomposite thin films.

Hydrothermal Stability of Ru/SiO2–C: A Promising Catalyst for Biomass Processing through Liquid-Phase Reactions

In this work, structural and morphological properties of SiO2–C composite material to be used as support for catalysts in the conversion of biomass-derived oxygenated hydrocarbons, such as glycerol, were investigated in liquid water under various temperatures conditions. The results show that this material does not lose surface area, and the hot liquid water does not generate changes in the structure. Neither change in relative concentrations of oxygen functional groups nor in Si/C ratio due to hydrothermal treatment was revealed by X-ray photoelectron spectroscopy (XPS) analysis. Raman analysis showed that the material is made of a disordered graphitic structure in an amorphous silica matrix, which remains stable after hydrothermal treatment. Results of the hydrogenolysis of glycerol using a Ru/SiO2–C catalyst indicate that the support gives more stability to the active phase than a Ru/SiO2 consisting of commercial silica.

Study of association of Eu(III) β-diketonato-1,10-phenanthroline complexes in silica-based hybrid materials

Hybrid organic-inorganic materials based on silica and mixed-ligand complexes of Eu(III) with β-diketones and 1,10-phenanthroline with covalent and non-covalent attachment to matrix were obtained by a sol-gel route. Luminescent study of obtained systems allowed to propose spectral criteria for estimation of the uniformity of complex distribution in amorphous silica matrix. Thus, such criteria are the broadening of Eu(III) 4f-luminescence bands, emission decay and the shape of plot of the emission intensity vs. concentration of complex in the materials. Full width of 5D0→7F2 band at its half maximum and the ratio of the 5D0→7F2 and 5D0→7F1 bands intensities were used as quantitative measures of spectral changes and the bands broadening in Eu(III) emission spectra.

ZnO-SiO2 based nanocomposites prepared by a modified sol-gel method

This paper presents a study on nanocomposites formation in ZnO-SiO2 systems with different ZnO:SiO2 molar ratios (1:4, 1:1, and 4:1), prepared employing a sol-gel method modified by an original procedure. The evolution of ZnO-SiO2 systems depending on the composition and temperature was studied by thermal analysis, Fourier transform infrared spectroscopy, X-ray diffractometry and transmission electron microscopy. Zn(II) carboxylate was synthesized in situ in hybrid silica gels by redox reaction between zinc nitrate and 1,3-propanediol. Its thermal decomposition at low temperatures led to ZnO dispersed in the pores of silica matrix. Only for the 4:1 system, at 400 and 600 °C, ZnO nanocrystallites (average size ∼9 nm) embedded in the amorphous silica matrix were obtained, the other systems being amorphous. Whatever the mixture composition is, above 600 °C, ZnO reacts with SiO2 to form zinc silicate. At 800 °C, for both 1:4 and 1:1 systems, poor crystallized β-Zn2SiO4 and α-Zn2SiO4 phases embedded in silica matrix were formed. Increasing the temperature, at 1000 °C, only for 1:1 system, β-Zn2SiO4 phase turned into single phase α-Zn2SiO4 (average crystallites size 28.3 nm). For 4:1 composition, at 800 and 1000 °C, systems consisting of ZnO and α-Zn2SiO4 nanocrystallites dispersed in silica were obtained.

Structure and magnetic properties of CoFe2O4/SiO2 nanocomposites obtained by sol-gel and post annealing pathways

The influence of the CoFe2O4 nanoparticles concentration in silica matrix on the structural and magnetic properties of xCoFe2O4/(100−x)SiO2 nanocomposites with x=10, 30, 50, 70 and 90 was studied. Magnetic CoFe2O4 nanoparticles dispersed in silica matrix was obtained by sol-gel method, followed by annealing at 1100°C. The X-ray diffraction pattern and FT-IR spectra revealed the single spinel ferrite structure for all samples. The FT-IR spectra also suggested the formation of the amorphous silica matrix. The results showed that the increase of cobalt ferrite concentration (x) in the silica matrix leads to high crystallinity, specific surface area and particle size. The magnetic CoFe2O4 nanoparticles have spherical shapes and size in the 6–35nm range. The Mössbauer measurements were fitted with two Zeeman sextets, indicating that all the samples were completely magnetically ordered. The vibrating sample magnetometer studies showed that the saturation magnetization (Ms) and coercivity (Hc) of the CoFe2O4 nanocrystals embedded in silica matrix possessed a linear relationship with the mean crystallite size. Also, the saturation magnetization of the studied nanocomposites increases with the increase of cobalt ferrite concentration (x) in the silica matrix.

Ion‐beam synthesis and thermal behaviour of luminescent Zn2SiO4 nanoparticles in silica glasses and films

In the present study, the temperature‐dependent photoluminescence (PL) spectra of Zn2SiO4 nano‐crystalline phases formed in glassy and thin‐film SiO2 matrices by means of ion implantation and annealing are studied. Pure willemite ceramics were used as a reference. The green and yellow light emission observed is associated with point defects inside α‐ and β‐Zn2SiO4 nanoparticles. Different PL excitation mechanisms were distinguished for implanted silica. The electronic states of point defects are localised to dimensions much smaller than the nanocrystal size, so the PL band positions are similar to those of bulk material. Conversely, the vibrational states are extended and therefore subjected to the effects of confinement, surface defects and disorder of the host matrix. Hence, the PL intensity quenching (different laws for α‐phase and β‐phase) and line broadening shed light to the PL emission mechanism and reveal the influence of the amorphous silica matrix. The results obtained may be used to tailor the optical properties of the nanocomposite over a wide temperature range.

Synthesis of Aluminosilicates Containing a Ba(Sr)-O-Al-O-Si Arrangement of Natural Feldspar Mineral.

We report a facile route to multicomponent complexes of [M{(μ-ddbfo)2Al(OSiR3)2}2] (M = Ba, Sr; ddbfoH = 2,3-dihydro-2,2-dimethylbenzofuran-7-ol; R = Ph, OtBu) as new efficient single-source routes to barium and strontium celsian feldspar Ba(Sr)Al2Si2O8. The resulting complexes were characterized by elemental analysis, IR and NMR spectroscopy, and single-crystal X-ray diffraction. These compounds calcined at 1100 °C to give porous material Ba(Sr)Al2Si2O8·2SiO2 as an amorphous silica matrix containing spherical oxide nanocrystals of celsian feldspar of ca. 5 nm diameter, as evidenced by transmission and scanning electron microscopies.

Structure and magnetic properties of Co3O4/SiO2 nanocomposite synthesized using combustion assisted sol-gel method

This paper reports on novel cobalt oxide nanoparticles (NPs) embedded in an amorphous silica (SiO2) matrix, synthesized using a modified sol-gel method. SEM and TEM images show as-synthesized particles to aggregate in the shape of spheres and less than 5nm in size, while XRD and SAED analysis both point to well crystallized cubic spinel cobalt oxide phase with an average crystallite size of about 4.6nm. Raman analysis confirms the formation of cobalt (III) oxide (Co3O4) NPs. As-synthesized Co3O4 single-nanocrystallite has magnetic properties that correlate with finite size effects and uncompensated surface spins. Temperature dependence of ZFC-FC magnetization curves reveals a sharp peak around 10K which corresponds to the blocking temperature. A Curie-Weiss behavior of magnetization above 25K shows lower Néel temperature of the sample compared with its bulk counterpart TN=40K (possibly due to crystal defects and nano-dimensionality of the particles). The magnetic measurements exhibit high magnetization at low temperatures (MS=54.3emu/g) which can be associated with random canting of the particles’ surface spins and uncompensated spins in the core which tends to interact ferromagnetically at low temperatures. The initial magnetization curve falls out from the hysteresis loop at 5K, which could be also the effect of surface spins.

The removal of mercury (II) from water by Ag supported on nanomesoporous silica.

In this study, the synthesis of SBA-15/Ag nanocomposite materials with different amounts of silver (2.5, 5, and 10%) has been investigated under acidic conditions by using P123 as a template via the direct method. The nanocomposites of SBA-15 were synthesized by the same method andby the addition of silver salt. Finally, the nanocomposite materials were examined for the removal of mercury ions from wastewater as an adsorbent by the reverse titration method. Characterization was carried out through x-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption (Brunauer-Emmett-Teller). XRD spectra confirmed the presence of silver nanoparticles within the amorphous silica matrix of SBA-15. The Barrett-Joyner-Halenda analysis showed that SBA-15 and SBA-15/Ag have a narrow pore size distribution. SEM images demonstrated that the morphology of the matrix of SBA-15 is in spherical state. Furthermore, wavelength dispersive x-ray spectroscopy identified the presence and distribution of silver nanoparticles inside the pore channels and outside of them. Typical TEM images of SBA-15 and SBA-15/Ag (5wt.%) indicated a regular hexagonal pore structure with long-range order and long channels. In SBA-15/Ag (5wt.%) sample, the nanoparticles of silver was found into the pores and outside of them. The removal of mercury ions from wastewater using mesoporous silica nanocomposite containing silver nanoparticles was studied by the reverse titration analysis. The best capacity of adsorption of mercury ions from wastewater was obtained for SBA-15/Ag (5wt.%) sample, which was equal to 42.26mg/g in 20min at pH of 7. The Freundlich model was used to explain the adsorption characteristics for the heterogeneous surface, and [Formula: see text] (adsorption capacity) and n (adsorption intensity) were determined for Hg (II) ion adsorption on SBA-15/Ag nanocomposite materials with different amounts of silver (2.5, 5, and 10%). The value of R2 was about 0.99, 0.99, 0.98, and 0.98 and Kf was about 42, 48, 58, and 58mg/g for SBA-15/Ag, SBA-15/Ag (2.5%), SBA-15/Ag (5%), and SBA-15/Ag (10%), respectively. Furthermore, the values of n >1 show a favorable adsorption process for Hg (II) ion adsorption on SBA-15/Ag nanocomposite materials. Moreover, the Langmuir isotherm model evaluation showed that the correlation coefficients for all concentrations were R2 >0.99, indicating that Hg (II) ions were adsorbed on the surface of SBA-15/Ag via chemical and physical interaction. Additionally, the analytic hierarchy process (AHP) and Technique of Order Preference Similarity to the Ideal Solution (TOPSIS) methods that depend on the criteria of the surface area, amount of adsorbent, pore volume, and cost of synthesis were used. The evaluation of results showed that the best sample was SBA-15/Ag (5wt.%). Furthermore, the research work highlighted the antibacterial nanocomposite with suitable adsorption of Hg (II) ions from water solutions and supported its potential for environmental applications. This nanocomposite can be used in the absorption domain of Hg (II) ions from water solutions.

Shrinking of silicon nanocrystals embedded in an amorphous silicon oxide matrix during rapid thermal annealing in a forming gas atmosphere

We report the effect of hydrogen on the crystallization process of silicon nanocrystals embedded in a silicon oxide matrix. We show that hydrogen gas during annealing leads to a lower sub-band gap absorption, indicating passivation of defects created during annealing. Samples annealed in pure nitrogen show expected trends according to crystallization theory. Samples annealed in forming gas, however, deviate from this trend. Their crystallinity decreases for increased annealing time. Furthermore, we observe a decrease in the mean nanocrystal size and the size distribution broadens, indicating that hydrogen causes a size reduction of the silicon nanocrystals.