SiO2 Matrices Research Articles

Matrix-induced defects and molecular doping in the afterglow of SiO2 microparticles

A deep understanding of how the host matrix influences the afterglow properties of molecule dopants is crucial for designing advanced afterglow materials. Despite its appeal, the impact of defects on the afterglow performance in molecule-doped SiO2 matrices has remained largely unexplored. Herein, we detail the synthesis of monodisperse SiO2 microparticles by hydrothermally doping molecules, such as 4-phenylpyridine, 4,4’-bipyridine, and 1,4-bis(pyrid-4-yl)benzene. Our results demonstrate that hydrothermal reactions induce not only the formation of emissive defects in the SiO2 matrix but also enable molecule doping through SiO2 pseudomorphic transformation. Optical analyses reveal a remarkable afterglow activation of doped molecules, driven by a synergistic interplay of hydrogen bonding and physical fixation. Specifically, 4-phenylpyridine doping leads to an impressive 227- and 271-fold enhancement in fluorescence and afterglow, respectively, and an extraordinary 3711-fold enhancement in the afterglow lifetime of the resulting SiO2 MPs. We also document hybrid states involving molecule dopants and SiO2 defects, explaining energy transfer from molecule dopants to defects in both singlet and triplet states. The robust achievement of molecule doping provides flexibility to tailor excitation-dependent afterglow attributes while preserving angle-dependent structural colors, facilitating the creation of diverse building blocks for multiscale optical platforms for afterglow modulation and information encoding.

Matrix Effect of Properties of Au, ZnO and Eu2O3: Silica, Titania and Alumina Matrices

The composites Au/SiO2, Au/TiO2, Au/Al2O3, ZnO/TiO2, ZnO/TiO2, ZnO/Al2O3 and Eu2O3/SiO2, Eu2O3/TiO2 and Eu2O3/Al2O3 were prepared using a solid-state method. The effect of the polymer precursors was investigated using two precursor polymers, Chitosan and Poly(styrene-co-4vinylpyridine), (PS-co-4-PVP) in the M/MxLy•Chitosan//M’xO’y as well as M/MxLy•PS-co-4-PVP//M’xO’y with M’xO’y = SiO2, TiO2 and Al2O3. The effects on the particle size and morphology were observed. The new composites were characterized using X-ray powder diffraction, SEM-EDS mapping and HRTEM analysis. The distribution of the metallic nanoparticles as well as the metal oxide nanoparticles inside the matrices depend on the matrix. Marked optical and photocatalytic effects of the Au, ZnO and Eu2O3 inside the SiO2, TiO2 and Al2O3 matrices are expected. An experiment is in course.

Effect of synthesis conditions on morphology and spectral properties of SiO2:DAST composites

SiO2:DAST composites based on SiO2 matrices with a porosity of 30–70% saturated with DAST molecules were synthesized both by evaporation from a solution and by lowering the temperature in a crystallizer. X-ray study of the composites showed the absence of DAST crystalline phase. There was only one luminescence band for all the composites with a maximum in the region of 620–640 nm (at their annealing at 100 °C). A hypsochromic shift (590-565 nm) of the luminescence band maxima of the composites was observed with an increase in their annealing temperature to 200 °C. Annealing at 200 °C also led to a change in the structure of the composite – “filling” of the pores of SiO2 matrices. This was probably due to a decrease in the interaction of the adsorbed DAST cations with the surface of SiO2 matrices due to exfoliation of DAST layers from the xerogel surface into the pores.

Magnetic circular dichroism of Co nanoparticles localized in matrices of various types

Magnetic and magneto-optical properties of cobalt nanoparticles (Co-NPs) dispersed in a transparent dielectric SiO2 and semiconductor ZnO matrices have been investigated. Field and temperature dependences of the samples magnetization showed the typical behavior of an ensemble of superparamagnetic particles with a blocking temperature near and below room temperature. The spectroscopy of magnetic circular dichroism (MCD) in the visible and near-infrared light ranges has revealed a significant difference between the behavior of the Co-NPs and a solid Co film. It has been found that the MCD spectrum shape for the Co-NPs does not depend on the matrix type. The room temperature magneto-optical activity of the Co-NPs in the different matrices has been estimated as an indicator for practical applications.

SiO2-Coated Ag Nanoparticles for Conversion of Terminal Alkynes to Propolic Acids via CO2 Insertion

Integration of adequate activity, stability, and productivity in a catalyst is of strategical importance to achieve high performance, particularly for inactive reactants, e.g., CO2. Here, using a reversed microemulsion method, ultrafine metallic Ag nanoparticles coated with porous SiO2 can be facilely obtained using micelles as separated nanoreactors for the preparation. Such architectures allowed the rigid SiO2 matrices to act as physical spacers, so that aggregation of the Ag particles could be avoided. Meanwhile, due to the templating effect from the surfactant, large mesopores could be induced in the SiO2 shell, and thus the diffusion barrier of reactants could be minimized. When used as a heterogeneous catalyst for carboxylation of terminal alkynes by CO2 under mild conditions, the prepared x[email protected]2 catalysts showed extraordinary performance in terms of excellent activity, stability, productivity, and wide substrate scope. The knowledge developed here may also enrich the toolbox for performance promotion of metal catalysts via specially fabricated structures.

Organotrialkoxysilane-Functionalized Prussian Blue Nanoparticles-Mediated Fluorescence Sensing of Arsenic(III).

Prussian blue nanoparticles (PBN) exhibit selective fluorescence quenching behavior with heavy metal ions; in addition, they possess characteristic oxidant properties both for liquid–liquid and liquid–solid interface catalysis. Here, we propose to study the detection and efficient removal of toxic arsenic(III) species by materializing these dual functions of PBN. A sophisticated PBN-sensitized fluorometric switching system for dosage-dependent detection of As3+ along with PBN-integrated SiO2 platforms as a column adsorbent for biphasic oxidation and elimination of As3+ have been developed. Colloidal PBN were obtained by a facile two-step process involving chemical reduction in the presence of 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane (EETMSi) and cyclohexanone as reducing agents, while heterogeneous systems were formulated via EETMSi, which triggered in situ growth of PBN inside the three-dimensional framework of silica gel and silica nanoparticles (SiO2). PBN-induced quenching of the emission signal was recorded with an As3+ concentration (0.05–1.6 ppm)-dependent fluorometric titration system, owing to the potential excitation window of PBN (at 480–500 nm), which ultimately restricts the radiative energy transfer. The detection limit for this arrangement is estimated around 0.025 ppm. Furthermore, the mesoporous and macroporous PBN-integrated SiO2 arrangements might act as stationary phase in chromatographic studies to significantly remove As3+. Besides physisorption, significant electron exchange between Fe3+/Fe2+ lattice points and As3+ ions enable complete conversion to less toxic As5+ ions with the repeated influx of mobile phase. PBN-integrated SiO2 matrices were successfully restored after segregating the target ions. This study indicates that PBN and PBN-integrated SiO2 platforms may enable straightforward and low-cost removal of arsenic from contaminated water.

Solventless Preparation of Thoria and Its Inclusion into SiO2 and TiO2: A Luminescence and Photocatalysis Study.

Thoria was prepared using a solid-state method from the macromolecular precursor Chitosan·Th(NO3)4 (chitosan) and PS-co-4-PVP·Th(NO3)4 (PVP). The morphology and the average size of ThO2 depend of the chitosan and PS-co-4-PVP polymer forming the precursor. Their photoluminescent properties were investigated, finding a dependence of their intensity emission maxima, with the nature of the precursor polymer. The photocatalytic activity of ThO2 toward the degradation of methylene blue was measured for the first time, finding a degradation of about 66% in 300 min. The inclusion of ThO2 into SiO2 and TiO2 was achieved by the solid-state pyrolysis of the macromolecular composites Chitosan·Th(NO3)4//MO2 and PS-co-4-PVP·Th(NO3)4//MO2, MO2 = SiO2 or TiO2. The ThO2 exhibits a homogeneous dispersion inside the silica, showing sizes of about 40 and 50 nm for the chitosan and PVP polymer precursors, respectively. The luminescent properties of the ThO2/SiO2 and ThO2/TiO2 composites were also studied, finding a decrease in intensity when introducing the SiO2 or TiO2 matrices. The photocatalytic behavior to methylene blue degradation of ThO2 and their composites ThO2/SiO2 and ThO2/TiO2 was investigated for the first time, with them in the following order: ThO2 > ThO2/TiO2 > ThO2/SiO2.

Structural and Optical-Phonon Properties of InSb Nanocrystals Synthesized in Si and SiO2 Matrices

Interest in creating and studying silicon-based InSb nanocrystals is due to the need for hybrid integrated circuits involving elements with different functional properties. Optical phonons localized in low-dimension crystals can affect both the optical and electrical properties of these crystals. The optical-phonon properties of InSb nanocrystals ion-beam synthesized in silicon and InSb nanocrystals formed in SiO2 layers by ion-beam synthesis and rf magnetron sputtering are compared. The properties of optical phonons in InSb nanocrystals are explained in terms of the effect of the structural properties of the surrounding matrix.

Impact of dielectric environment on the linear and nonlinear optical properties for CdS/ZnS cylindrical core/shell quantum dots

By the mean of the effective mass approximation (E.M.A) and compact density matrix method, the energy eigenvalues, linear and nonlinear dielectric function have been theoretically investigated for CdS/ZnS cylindrical core/shell quantum dot embedded in PVA, PMMA and SiO2 matrices. Simulation results showed that the presence of the dielectric mismatch in the QD-matrix system can lead to a significant enhancement of the nonlinear dielectric function. According to our calculations, peaks of the real and imaginary part of the dielectric function can experience a redshift or a blue shift with the appropriate dielectric environment.

XPS and thermal studies of silver doped SiO2 matrices for plasmonic applications

Silver nanocrystals doped SiO2 matrices were synthesized through sol–gel route using acid catalyst. The prepared silica matrices with different concentrations of silver were annealed at different temperatures and characterized using, XRD, FTIR, Absorption spectroscopy, XPS, thermogravimetric and differential thermal analysis. The XRD data confirm the amorphous nature of silica and crystalline nature of silver nanocrystals. Using the Fourier-transform infrared red spectrum the formation of silica glass was confirmed. The characteristic Surface Plasmon Resonance of silver nanoparticles obtained around 400 nm from the absorption spectrum. The observed blue shift and skewness in SPR with increasing silver concentrations were studied. The 3d doublet state of silver at a binding energy of 368.4 eV with the splitting of 6 eV obtained in XPS confirm the state Ag0 along with the presence of a minor quantity of silver (II) oxide. The thermal stability and nature were analyzed using TGA-DTG and DTA and showed good thermal stability from 400 °C to higher temperatures.

TEMPO-Functionalized Silica as an Efficient and Recyclable Oxidation Catalyst for Conversion of a Lignin Model Compound to Value-Added Products

Catalytic oxidation of a lignin model compound, vanillyl alcohol (VAL), to vanillin (VN), is a promising process for valorizing lignin-based biomass. As research interests in oxidation of alcohols are concentrated on direct usage of O2, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) has been developed as an oxidation catalyst which can be mediated by O2 to cyclically oxidize alcohols. However, as recover of homogeneous TEMPO from reaction media could be an issue, it is necessary to develop a recyclable heterogeneous TEMPO for VAL oxidation. In the present study, a particular heterogeneous TEMPO is fabricated via a simple condensation of OH-TEMPO and tetraethyl orthosilicate to insert TEMPO functional groups into SiO2 matrices. The resulting composite of TEMPO@SiO2 is then employed for the first time for oxidation of VAL to VN. By incorporation with a co-catalyst, Cu+, TEMPO@SiO2/Cu+ successfully and selectively converts VAL to VN, and the corresponding conversion efficiency reaches CVAL = 96% with SVN = 96.5 and YVN = 92.6%. Such a superior conversion efficiency is achieved conveniently at ambient temperature within 30 min, demonstrating that TEMPO@SiO2 is not only a highly active catalyst but also a sustainable oxidation catalyst. The optimum condition of TEMPO@SiO2/Cu+ is 7.5 g/L of TEMPO@SiO2 and 5 g/L of Cu salt. TEMPO@SiO2 can be also reused over multiple cycles for VAL conversion to VN with a stably high selectivity for VN. These features validate that TEMPO@SiO2 is indeed a promising, highly-selective and efficient heterogeneous catalyst for valorization of VAL, the lignin model compound, to the target product, VN.

Thermal behavior and effect of SiO2 and PVA-SiO2 matrix on formation of Ni–Zn ferrite nanoparticles

The paper presents the synthesis of ZnFe2O4/SiO2, NiFe2O4/SiO2, Ni0.4Zn0.6Fe2O4/SiO2 and Ni0.4Zn0.6Fe2O4/PVA-SiO2 nanocomposites by a modified sol–gel method. The influence of matrix type on the formation of Ni-, Zn- and Fe-succinate precursors and their decomposition into ferrites within the pores of SiO2 or PVA-SiO2 matrices was investigated by thermal analysis. The decomposition processes, formation of crystalline phases and mass changes during samples annealing at different temperatures were also assessed by thermal analysis. The formation and decomposition of succinates and the formation of the matrix were studied by Fourier transform infrared spectroscopy, while the formation of main (ZnFe2O4, NiFe2O4) and secondary phases (SiO2) was studied by X-ray diffraction analysis. The influence of matrix type on the formation of the crystalline phases was also investigated. Transmission electron microscopy revealed spherical-shaped ferrite particles with particle size of 4–50 nm. The particle size increases with increasing Zn content and annealing temperature. The coloring properties and the potential ceramic applications of the obtained dark-brown–black powders were tested by their incorporation in opaque tile glazes and application on ceramic tile.

The Germanium “Halo”: Visualizing Ge interstitial dynamics in nanocrystallite formation

We report the ability to image distributions of Ge interstitials within amorphous SiO2 matrices using conventional transmission electron microscopy and energy dispersive X-ray spectroscopy mapping. While previous, established methods have only been able to indirectly infer the presence of interstitials within materials, our direct “visualization” approach allows the ability to study and better understand the dynamics of several interesting phenomena occurring within the Ge–Si–O system during processing at temperatures greater than 700 °C which has not been described in any previously published work. Experimental observations by TEM of the Ge interstitial dynamics has allowed us to clarify the various operating mechanisms for Ge nanocrystallite growth within these SiO2 matrices. These phenomena include Ostwald ripening, migration of Ge nanocrystallites through amorphous SiO2 and Si3N4 matrices, Ge incorporation in Si-rich materials such as Si3N4 and Si, and finally, morphological changes in the Ge nanocrystallites themselves.

Optical properties of high photoluminescence silicon nanocrystals embedded in SiO2 matrices obtained by annealing hydrogen silsesquioxane

Thin films of silicon nanocrystals embedded in SiO2 matrices were prepared by annealing a photoresist of hydrogen silsesquioxane. As compared to films made by a common method of annealing SiOx (1 < x < 2), significant enhancement on photoluminescence intensity was observed. Spectroscopic ellipsometry was applied to figure out optical properties of nc-Si made from HSQ. High-resolution tunneling electron microscopy, photoluminescence and absorption spectra were taken to either confirm the fitting results of SE or characterize structural, morphological and photoluminescent properties of all samples. The deduced refractive indices of nc-Si:SiO2 films made from HSQ were given. The influence of particle size and spatial distribution of nc-Si on the extinction coefficient K and PL spectra was observed and discussed.

Amorphous silicon dioxide-based composites for high-performance Li-ion battery anodes

To design high performance SiO2-based anodes for Li-ion batteries (LIBs), an amorphous SiO2-FeSi-graphite (a-SiO2/FeSi/G) composite was synthesized by a simple solid state synthetic method using SiO, Fe, and graphite powders. The a-SiO2/FeSi/G composite was comprised of well dispersed amorphous SiO2 and tiny (5–10 nm sized) FeSi inactive matrices within the graphite buffering matrices. The a-SiO2/FeSi/G composite electrode showed excellent electrochemical performance featuring high initial charge capacity of 729 mAh g−1, with high initial Coulombic efficiency of approximately 74%, and long capacity retention of 93.7% after 200 cycles, with a highly reversible capacity of 683 mAh g−1.

Tubular and Spherical SiO₂ Obtained by Sol Gel Method for Lipase Immobilization and Enzymatic Activity.

A wide range of hybrid biomaterials has been designed in order to sustain bioremediation processes by associating sol-gel SiO2 matrices with various biologically active compounds (enzymes, antibodies). SiO2 is a widespread, chemically stable and non-toxic material; thus, the immobilization of enzymes on silica may lead to improving the efficiency of biocatalysts in terms of endurance and economic costs. Our present work explores the potential of different hybrid morphologies, based on hollow tubes and solid spheres of amorphous SiO2, for enzyme immobilization and the development of competitive biocatalysts. The synthesis protocol and structural characterization of spherical and tubular SiO2 obtained by the sol gel method were fully investigated in connection with the subsequent immobilization of lipase from Rhizopus orizae. The immobilization is conducted at pH 6, lower than the isoelectric point of lipase and higher than the isoelectric point of silica, which is meant to sustain the physical interactions of the enzyme with the SiO2 matrix. The morphological, textural and surface properties of spherical and tubular SiO2 were investigated by SEM, nitrogen sorption, and electrokinetic potential measurements, while the formation and characterization of hybrid organic-inorganic complexes were studied by UV-VIS, FTIR-ATR and fluorescence spectroscopy. The highest degree of enzyme immobilization (as depicted from total organic carbon) was achieved for tubular morphology and the hydrolysis of p-nitrophenyl acetate was used as an enzymatic model reaction conducted in the presence of hybrid lipase–SiO2 complex.

A composite material with CeO2-ZrO2 nanocrystallines embedded in SiO2 matrices and its enhanced thermal stability and oxygen storage capacity

A simple hydrothermal procedure is introduced, which leads to the successful synthesis of a new composite material with fine CeO2-ZrO2 nanocrystallites embedded in amorphous and porous SiO2 matrices. The composite material possesses an extraordinary high thermal stability. After being calcined at 1000 °C, it retains CeO2-ZrO2 nanocrystallites of the size around 5 nm, a BET-specific surface area of 165 m2/g, and an oxygen storage capacity of 468 μmol/g. No phase segregation for CeO2-ZrO2 nanocrystallites is detected and the SiO2 matrices remain not crystallized. The composite material shows a great potential as a support of three-way catalyst, as evidenced in catalytic tests with supported Pt.

Matrix and element dependences of useful yield in Si and SiO2 matrices using laser-ionization sputtered neutral mass spectrometry

The element and/or material dependence of the useful yield in laser-ionization sputtered neutral mass spectrometry (SNMS) using a high-photon-flux laser was investigated. Useful yields obtained from Si, B, As, and O in Si and SiO2 matrices using both secondary ion mass spectrometry (SIMS) and SNMS were compared, and the possibility of the accurate analysis of impurities in multilayers was investigated in terms of tunnel ionization. The behavior of atoms released from the surface by ion bombardment was calculated, and it was considered that the flying speed of sputtered atoms depends on the mass and that this causes the elemental difference in the fractions of laser-irradiated atoms. In the case of SNMS, excluding O, whose ionization probability is considered to be much lower than for the other elements, the useful yields of Si, B, and As are within 1 order of magnitude in both the Si and SiO2 matrices, and the difference between the matrices for each element is within a factor of two. These differences are much smaller than in the result of SIMS. It was confirmed that the distribution of B in a SiO2/Si stacked layer can be analyzed more accurately by SNMS than by SIMS. SNMS with a high-photon-density laser is considered to be effective for the analysis of more than one element in multilayers.

Growth morphology and structure of PdCu ion-plasma condensate in the pores of SiO2 and Al2O3 amorphous matrices

The features of the growth morphology and structure of ion-plasma palladium-copper condensate both on the surface and in the pores of amorphous SiO2 and Al2O3 matrices were studied by scanning electron microscopy and high resolution transmission electron microscopy. Differences in the morphology and crystal structure of the metallic ion-plasma condensate obtained by magnetron sputtering deposition of the PdCu alloy on the surface and in a limited pore volume were shown and substantiated. The main regularities of the ion-plasma condensates formation on a developed surface with a high open porosity were discussed.

Enhanced emission of Nile Red on plasmonic platforms

Strongly enhanced fluorescence of Nile Red deposited in the vicinity of silver nanoparticles and gold semitransparent mirror was observed. The properties of three different plasmonic platforms based on TiO2, TiO2-GLYMO (1:1) and SiO2 matrices were studied with spectroscopic and microscopic techniques. Significant differences of Nile Red spectroscopic properties in both matrices were observed. In particular, the sensitivity of Nile Red fluorescence enhancement and its peak location to the polarity of local surrounding was found.