Silica Sol-gel Matrix Research Articles

Spectroscopic Analyses and the Influence of Concentration on the Photoluminescence Characteristics of Sm+3-Doped Silica Sol-Gel matrix

Spectroscopic Analyses and the Influence of Concentration on the Photoluminescence Characteristics of Sm+3-Doped Silica Sol-Gel matrix

Eu-substituted hydroxyapatite/silica sol-gel treatment for corrosion protection of AZ31 magnesium alloy

Europium-hydroxyapatite (Eu-HA) nanocomposite was developed via continuous hydrothermal synthesis. Eu+3 ions partially replaced the Ca+2 ions within hydroxyapatite molecular structure. High quality Eu-HA nanorods of 20 nm width and 6 μm lengths were verified via TEM micrographs. Eu-HA maintained the crystalline structure of HA with minimum change; material studio software confirmed the partial replacement of Ca+2 by Eu+3. XPS analysis demonstrated Eu+3 content of 6.91 atom %. Ca/P ratio was found to be 1.405 and 0.118 for virgin HA and Eu-HA respectively; this was ascribed to the partial replacement of Ca+2 with Eu +3. The EDAX mapping verified the uniform dispersion of Eu ions within Eu-HA structure. Eu-HA nanocomposite was uniformly distributed in silica sol-gel matrix; subsequently it was applied on AZ31 magnesium alloy. The corrosion performance of Eu-HA sol-gel coating nanocomposite (Eu–S) was evaluated using different electrochemical techniques including Potentiodynamic Polarization (PDP), Electrochemical Impedance Spectroscope (EIS), and Electrochemical Noise (EN) in aerated 0.1 M NaCl solution. Corrosion protection was assessed to that of neat silica sol-gel coating (NSG). Pitting was detected over the whole NSG coated sample, after few hours of immersion in the corrosive solution. EuS coated AZ31 withstand up to 144 h without any sign of corrosion or delamination. EIS analysis with PDP parameters suggested the formation of protective layer; that is responsible for the corrosion resistance. Europium has unique ability to form a protective oxide layer acting as a barrier layer that could prevent the penetration of corrosive electrolyte to the underlying metal substrate.

Chromium(III)-substituted hydroxyapatite/silica sol–gel coating: towards novel green coating for corrosion protection of AA2024

A novel Cr-substituted hydroxyapatite (Cr-HA) nanoparticles were synthesized via continuous hydrothermal technique. Moreover, the synthesized material was embedded into a silica sol–gel matrix and applied on an AA2024 substrate to evaluate the corrosion inhibition efficiency of the coating. TEM and SEM micrographs confirmed the development of Cr-HA nanorods of 20 nm width and 6 µm length. XRD diffractograms demonstrated the evolution of a new crystalline structure; the XRD pattern was analyzed by Material Studio software which confirms the replacement of Ca2+ by Cr3+. The EDX mapping revealed a uniform distribution of Ca and Cr ions within the Cr-HA crystal structure. The atomic ratio of Ca2+: Cr3+ was reported to be 4:1 respectively. The Cr-HA nanoparticles were uniformly distributed in a silica sol–gel matrix and applied on an AA2024 substrate. The corrosion performance of the Cr-HA sol–gel coating composite was evaluated using Electrochemical Impedance Spectroscopy (EIS) in an aerated 3.5% NaCl solution and the results compared to those of neat silica sol–gel coating. Whereas pitting corrosion was also observed in the case of a neat sol–gel coated sample within 5 days of immersion, Cr-HA sol–gel coated AA2024 exhibited prolonged pitting resistance over 110 days with no sign of corrosion or delamination. The EIS data fitting suggested the formation of a protective layer that is responsible for the extended corrosion resistance of the Cr-HA-coated sample. The scratch test indicated that the Cr-HA nanocomposite coating might offer short-term self-healing properties in the 3.5% NaCl corrosive media.Graphical

Effect of ZnS nanoparticles on the spectroscopic transitions of Ho3+ ions in sol-gel silica matrix

ZnS NPs and Ho3+ co-doped silica matrices are prepared by room temperature sol-gel method. The fabricated matrices are characterized structurally by X-ray diffractometry, Transmission electron microscopy, Energy dispersive X-ray analysis and Fourier transform infrared spectroscopy. Structural studies reveal the presence of ZnS NPs in the Ho3+ co-doped silica matrices. Judd Ofelt analysis of UV–Visible absorption spectra shows that the phenomenological Judd Ofelt intensity parameters Ωt, which illustrate the intensities for transitions in lanthanides and actinides in solids as well as solutions follow the trend Ω2>Ω4>Ω6. Enhancement in the Ω2 parameter with ZnS NP concentration indicates higher asymmetry and a stronger covalent environment of Ho3+ ions in the studied matrix, compared to some popular hosts. The four distinct PL emission bands of Ho3+ observed in the studied matrices show a strong dependence on ZnS NP concentration, with 0.67 M of ZnS as the optimum concentration. The enhancement in the PL emissions with ZnS NPs is attributed to the network modification and sensitization of Ho3+ ions by the NPs. Sensitization through energy transfer also increases the lifetime of the excited state, as observed from the PL decay study. The decrease of PL emission beyond optimum ZnS concentration is most likely due to the self-quenching of ZnS NPs. The upconversion study shows enhancement in Ho3+ luminescence up to 14 times with ZnS co-doping; indicating the viability of the fabricated matrix for their application in UC devices as well.

ZnS NPs enhanced Eu3+ photoluminescence in the sol-gel silica matrix

ZnS co-doped Eu3+ Silica matrices were fabricated by sol–gel route. The fabricated matrices were structurally characterized by XRD and EDX. Optical characterizations were performed by FTIR, UV–Vis Absorption as well as PL Spectroscopy. Structural characterizations show the presence of nanosized ZnS particles (ZnS NPs) embedded in the Eu3+ doped Silica matrix. The study reveals an enhancement in PL intensity with ZnS concentration owing to the structural modification of the Eu3+ environment in the host matrix as well as energy transfer from the ZnS NPs to Eu3+ ions. The observations are elucidated in the light of Judd Ofelt intensity parameters as well as radiative parameters.

Effect of ligands PPIA and TOPO on radiative behaviour of Eu3+ ions in sol-gel silica matrix

Eu3+ singly doped and Eu3+ co-doped with ligands PPIA and TOPO in silica matrix were fabricated via sol-gel route and investigated by structural and spectroscopic techniques. Structural studies reveal the amorphous nature of the silica matrix as well as the presence of the ligands in the matrix. Spectroscopic studies were performed through absorption, excitation, emission and time-correlated decay spectra of the fabricated samples. The phenomenological Judd-Ofelt parameters were calculated from the observed photoluminescence spectra considering the integrated intensity ratio of the allowed electric and magnetic dipole transitions. The dependence of Judd-Ofelt intensity parameters and radiative parameters of Eu3+ ions on the ligands PPIA and TOPO in the studied matrix were evaluated. The radiative efficiency improved significantly with the addition of the ligands and showed the maximum for both PPIA and TOPO co-doped sample. The emission transition 5D0→7F2 observed at 616 nm wavelength of Eu3+ corresponding to the red colour in the present study showed excellent radiative behaviour compared to other popular glass hosts. The study suggests PPIA and TOPO co-doped Eu3+ sol-gel silica matrix as a prospective candidate for optical device applications harnessing the red emissions.

Ag nanoparticle enhanced radiative behaviour of Eu3+ ions in sol-gel silica matrix

AgNP doped Eu SiO2 glasses were prepared by the sol-gel method with fixed Eu3+ and varying Ag concentrations. The samples have been characterized structurally by XRD, SEM, EDX and TEM. The effects of incorporation of AgNPs on the radiative properties of the Eu3+ in SiO2 matrix are studied with the help of Absorption and Photoluminescence Spectroscopy. Various radiative parameters like oscillator strength, Judd Ofelt intensity parameters, spontaneous emission probabilities, branching ratio, radiative lifetime, emission cross-section etc. are calculated from the observed absorption and photoluminescence spectra using Judd Ofelt theory, whereas the experimental lifetime of 5D0 state of Eu3+ ion and colour chromaticity is estimated from lifetime and CIE 1931 colour chromaticity measurements. The observed enhancement in the absorption and emission intensities of Eu3+ ions are elucidated in the light of enhanced local field in the vicinity of the AgNPs due to the LSPR effect and also the network modifying role of AgNPs.

Long term storage of miRNA at room and elevated temperatures in a silica sol-gel matrix.

Storage of biospecimens in their near native environment at room temperature can have a transformative global impact, however, this remains an arduous challenge to date due to the rapid degradation of biospecimens over time. Currently, most isolated biospecimens are refrigerated for short-term storage and frozen (−20 °C, −80 °C, liquid nitrogen) for long-term storage. Recent advances in room temperature storage of purified biomolecules utilize anhydrobiosis. However, a near aqueous storage solution that can preserve the biospecimen nearly “as is” has not yet been achieved by any current technology. Here, we demonstrate an aqueous silica sol–gel matrix for optimized storage of biospecimens. Our technique is facile, reproducible, and has previously demonstrated stabilization of DNA and proteins, within a few minutes using a standard benchtop microwave. Herein, we demonstrate complete integrity of miRNA 21, a highly sensitive molecule at 4, 25, and 40 °C over a period of ∼3 months. In contrast, the control samples completely degrade in less than 1 week. We attribute excellent stability to entrapment of miRNA within silica-gel matrices.

Release rate kinetics of corrosion inhibitor loaded halloysite nanotube-based anticorrosion coatings on magnesium alloy AZ91D

Abstract Halloysite nanotubes were used as nanocontainers to hold corrosion inhibitors such as Ce3+-Zr4+, 2-mercaptobenzothiazole and 8-hydroxyquinoline in their lumen. An acid assisted etching of the nanotubes was carried out with a view to increase the lumen diameter and thereby, increase the amount of loading of the corrosion inhibitor. The morphology of as-received and etched halloysite nanotubes was observed using TEM analysis. The loading of corrosion inhibitors was confirmed using SEM-EDS and BET analysis. Polymeric microcapsules were used as capping agents for the ends of the loaded HNTs following which, they were dispersed into a hybrid sol-gel silica matrix. Dip coating method was used to generate coatings on AZ91D substrates followed by heat treatment at 130 °C for 1 h. The release rate kinetics of corrosion inhibitors from as-received and etched nanotubes was investigated in buffer solutions of 3.5 wt% NaCl at different pH. The release mechanism of corrosion inhibitors from the HNT lumen was validated using various semi-empirical models. Coatings were also evaluated for their corrosion protection ability using electrochemical techniques after exposure to 3.5 wt% NaCl solution for 120 h. Coatings generated using Ce3+-Zr4+ loaded into as-received halloysite nanotubes have shown more effective corrosion protection when compared to other corrosion inhibitors after 120 h exposure to the corrosive medium.

Investigation of Thermoluminescence Properties of Potential Fibered-OSL Dosimeter Materials

The luminescence properties of several doped materials are explored in many fields of application, including ionizing radiation dosimetry. These luminescence properties are essentially provided by the doping element. In this article, we report thermally stimulated luminescence (TSL) measurements of the trapping and recombination centers involved in the luminescence process of sol–gel-derived glasses. Three-doped species will be concerned: one transition metal (Cu), one rare-earth element (Ce), and a combination of both in the sol–gel silica matrix. By comparing the performances of these samples according to the criteria required for dosimetry by both TSL and optically stimulated luminescence (OSL) (sensitivity, dose response, and thermal fading), the results show that the simply doped samples really are potential candidates for fibered-OSL dosimetry.

Efficient enzyme encapsulation inside sol-gel silica sheets prepared by poly-L-lysine as a catalyst

ABSTRACT High catalytic activities of enzymes are necessary for the enzyme immobilizing technology for the development of better biocatalysts and biosensors. Basic polypeptide (poly-L-lysine)-templated precipitation of silica synthesized by sol-gel chemistry produced a composite material that allows high enzyme activity. This study investigates the structural properties of the composite material that allow retaining the glucose oxidase (GOx) activity. Scanning (SEM) and transmission (TEM) electron microscopies reveal that the composite has plate- or sheet-type morphologies composed of hexagonal structures that are 0.2–2 µm in diameter. After the encapsulation in a sol-gel silica matrix, encapsulated GOx retained high activity (over 85% of oxidation activity compared with that of free GOx). The relative activity of GOx-encapsulated in SiO2@pLys remained approximately at 50–60% after eight cycles; in addition, the catalytic stability of encapsulated GOx improved under high temperature (60°C) and in several solvents (e.g., HCl, urea, and acetone). Moreover, D-glucose detection was performed in the linear range of 1–400 µM using SiO2@pLys-GOx composites. The obtained results show that SiO2@pLys-GOx composites can be used for enzyme encapsulation with high activity and stability and as biosensor materials with high sensitivity.

Stabilization of Ni(I)(1,4,8,11‐tetraazacyclotetradecane)+ in a Sol‐Gel Matrix: It's Plausible Use in Catalytic Processes

AbstractMonovalent nickel is used as a catalyst in a diversity of important chemical systems due to its properties as a strong reducing agent. However, monovalent nickel is unstable in homogeneous systems; its lifetime is very short, and therefore, its efficiency as a catalyst is quite limited. In this article, we demonstrate the catalytic capabilities of Ni(I)(1,4,8,11‐tetraazacyclotetradecane)+ as a reducing and catalytic agent by its entrapment in the silica sol gel matrix. The EPR results indicate that the sol‐gel matrix plays two roles: it inhibits the common mechanism of Ni(I)L+ decomposition in aqueous solutions, and it also facilitates its functionality as a heterogeneous catalyst, by stabilizing it for at least several hours. The activity of Ni(I)L+ which is entrapped within the matrix, was studied by reducing 2,2‐Bis(bromomethyl)‐1,3‐Propanediol and I3−. The results indicate that Ni(I)L+/Ni(III)L−H2+ acts as a good reducing agent. These results have important implications for a variety of essential catalytic reactions by shedding light on a new feature of sol‐gel matrices and their use as active species stabilizers.

Design and Application of an Optical pH Sensor Based on Thionine Doped Modified Sol–Gel Film

An optical chemical sensor was constructed by incorporating the thionine (TN) dye molecules into a sol–gel silica matrix and it was used for determination the pH of the aqueous solutions. Entrapment of TN dye into the silica matrix was made via an acid-catalyzed sol–gel reaction of tetraethyl orthosilicate (TEOS) and the thionine molecules. The thionine molecules in the immobilized form, showed a different spectral behavior than its solution form. After optimizing the experimental conditions, the fabricated optical sensor showed a fast response to pH changes in the range of 11–13 with a response time about one minute. Also, the obtained results indicate that the proposed pH sensor, has a good reproducibility, reversibility, stability and low leaching and a long lifetime of over 7 months.

Preparation of Sol-Gel Derived Anticorrosive Coating on Q235 Carbon Steel Substrate with Long-Term Corrosion Prevention Durability.

Anticorrosive coatings prepared by sol-gel derived approaches have become an emergent research area in the field of corrosion prevention materials. Furthermore, enhanced coating thickness can greatly improve the barrier effect of the sol-gel coatings, thus influencing their service life in industrial applications. Here, we propose the preparation of a two-layer coating system using a low-cost sol-gel derived method. The coating structure was composed of first an underlying layer incorporated with silica and titania powder as filler and pigment materials, and a second translucent topcoat containing a colloidal silica sol-gel matrix crosslinked by methyltrimethoxysilane (MTMS). This coating system was applied on Q235 carbon steel substrate by a two-step spray deposition method, resulting in an enhanced coating thickness of around 35 μm. The physical and morphological properties of the coatings were characterized using multiple techniques, including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). The anticorrosion performance of the sol-gel coatings was studied by a salt spray test, outdoor exposure test and electrochemical impedance spectroscopy (EIS). Results revealed that this two-layer coating system exhibited excellent physical and anticorrosion properties, and that the topcoat played a crucial role in maintaining the barrier effect and preventing water leakage.

Environmentally friendly Zn–Al layered double hydroxide (LDH)-based sol–gel corrosion protection coatings on AA 2024-T3

Zn–Al layered double hydroxide (LDH) intercalated with various corrosion inhibitors namely vanadate (E1), 2-mercapto benzothiazole (E3), molybdate (E7), phytic acid (E8) and 8-hydroxyquinoline (E9) was dispersed in a hybrid sol–gel silica matrix sol. Bilayer coatings with configurations E3|E1, E7|E1, E8|E1 and E9|E1 were generated on aluminum alloy AA 2024-T3 substrates using the inhibitor intercalated LDH modified sols by dip coating technique followed by UV curing and thermal curing at 80°C for 1 h in air. Corrosion resistance of coatings deposited from matrix sol with and without inhibitor intercalated LDH was studied by electrochemical impedance spectroscopy, potentiodynamic polarization after exposure to 3.5% NaCl and salt spray tests, results of which were compared with those of uncoated and chromated substrates. A non-chromated primer was applied on the sol–gel coated substrates. Adhesion of the coatings to the substrate and to the primer was evaluated by peel-off tape test and found to be rank 5. The sol–gel coated substrates did not exhibit corrosion during salt spray tests. Electrochemical tests showed that all the sol–gel coated substrates exhibited superior corrosion resistance when compared to bare and chromated substrates. More specifically, coatings generated using the corrosion inhibitors phytic acid and 8-hydroxy quinoline intercalated Zn–Al LDH were seen to render maximum corrosion protection, exhibiting two orders of magnitude lower corrosion currents than bare substrates and one order lower corrosion current than chromated substrate, after 120-h exposure to 3.5% NaCl solution.

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.

Modulation of the electrocatalytic performance of PEDOT-PSS by reactive insertion into a sol-gel silica matrix

Poly(3,4-ethylenedioxythiophene) doped with poly-(styrenesulfonate), PEDOT–PSS, films synthesized by electrochemical methods can be considered as poor electrocatalyst for the oxidation of ferrocene in aqueous solution. The rate of electron transfer to that redox probe decays progressively as the amount of deposited polymer increases and the true electroactive area available for the electrochemical reaction shows quite modest figures. We present here an alternative, simple way to enhance the properties of this material which uses, exclusively, electrochemical synthesis methods. The electrocatalytic performance can be significantly improved by inserting the polymer within a pre-deposited, three-dimensional porous silica matrix forming an interpenetrating hybrid material. On the one hand, the modified PEDOT-PSS shows doping levels which trebles the unmodified material. On the other, the electron transfer constant and the true electroactive area for ferrocene oxidation increased by a factor of 2 and 4, respectively.

Post-synthesis annealing of coprecipitated CoFe2O4 nanoparticles in silica matrix

Cobalt ferrite nanoparticles (d ∼ 11 nm, σd = 0.5) produced by coprecipitation at room temperature are heat treated up to 1000 °C after a preliminary dispersion in a sol-gel silica matrix to avoid aggregation and coarsening. This protected annealing allows for a significant increase of the crystallinity of the particles, as demonstrated by combined x-ray diffraction and transmission electron microscopy experiments. A large increase in the coercive field value is reported, from 1.0 to 1.6 Tesla after annealing at 600 °C. This enhanced coercivity can be explained by the cumulative effect of an increased magnetic anisotropy and of a decreased saturation magnetization (Ms). Mössbauer spectroscopy experiments show that these evolutions of the Ms and anisotropy constant (K) values originate from a small increase in canting angles and in inversion degree, i.e. a displacement of Co2+ ions from tetrahedral to octahedral sites of the spinel lattice. This study emphasizes the little impact of an improved crystallinity on saturation magnetization and canting angle values in coprecipitated CoFe2O4 nanoparticles and highlights that the main source of magnetic disorder is associated with the distribution of Co and Fe within the cationic sites.

Novel Smart Hydroxyapatite/Silica Sol–Gel Nanocomposite Hybrid Coating for Corrosion Protection of AA2024

A coating system adherent to aluminum alloy (AA2024) substrates based on hydroxyapatite nano-platelets dispersed in a silica sol–gel matrix is presented. Using EIS and EN, the coating demonstrates excellent corrosion protective performance with high corrosion resistance during 50 days of immersion in artificial sea water while a neat silica sol–gel coating fails after 14 days. This performance of HA/sol–gel coating (HEX) is not only correlated to reductions in the rate of electrolyte permeation through the coating but also, it offered an active buffering effect to the local acidity of Al/electrolyte interaction.

Multienzymatic Cholesterol Nanobiosensor Using Core–Shell Nanoparticles Incorporated Silica Nanocomposite

The silica sol–gel matrix was prepared with tetraethyl orthosilicate as a precursor by sol–gel method besides functionalized with bovine serum albumin to minimize cracking and to stabilize enzymes for biosensing. Core–shell Fe3O4@C@Ag NPs are prepared using a facile method and applied to enhance electron transfer between enzymes and electrode surface. The Fe3O4 NPs prepared by modifying co-precipitation method; subsequently depositing carbon and silver on Fe3O4 NPs core by the facile green approach. Fe3O4@C@Ag NPs and silica/Fe3O4@C@Ag nanocomposite have been characterized by Fourier Transform Infra-Red spectroscopy, UV–visible spectroscopy, and X-ray diffraction technique. The surface topographies of the nanomaterials were investigated by Scanning electron microscopy and Transmission electron microscopy. Cyclic voltammetry employed to study the electrochemical behavior of nanobiosensor. The sensitivity of modified electrode is 0.0346 µAmM−1cm−1 with detection limit 0.5 mM. The high sensitivity of the biosensor is attributed to the large surface area of Fe3O4@C@Ag NPs for effective loading of HRP besides its high electron communication capability with the aid of enhanced selectivity and anti-interference ability due to the silica sol–gel matrix immobilized with ChOx.