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A method based on infrared (IR) micro-reflectance measurements for the structural characterization of glassy nanomaterials is presented. Near-specular reflectance spectra of pressed pellets can be analyzed using a model relating the structure of silicate glasses to their dielectric response and an effective medium approximation to account for the effect of porosity. The integrated intensities of phenomenological bands attributed to Q 2 , Q 3 , and Q 4 structural units allow quantifying their relative populations. These values are in good agreement with those obtained with magic-angle spinning nuclear magnetic resonance, which serves as validation of the method and proves the feasibility of extracting quantitative information about glass structure from IR micro-reflectance experiments. Graphical abstract This is a visual representation of the abstract. [ABSTRACT FROM AUTHOR]

Sol‐gel‐derived silica thin films generated onto electrode surfaces in the form of organic‐inorganic hybrid coatings or other composite layers have found tremendous interest for being used as platforms for the development of electrochemical sensors and biosensors. After a brief description of the strategies applied to prepare such materials, and their interest as electrode modifier, this review will summarize the major advances made so far with composite silica‐based films in electroanalysis. It will primarily focus on electrochemical sensors involving both non‐ordered composite films and vertically oriented mesoporous membranes, the biosensors exploiting the concept of sol‐gel bioencapsulation on electrode, the spectroelectrochemical sensors, and some others. [ABSTRACT FROM AUTHOR]

Foot ulcerations are a disabling complication of diabetes and no treatment is currently available based on disease mechanisms. The protein serpin B3 (SB3) was identified as a positive biomarker of successful diabetic wound healing; therefore, its exogenous administration may promote healing. The topical administration of SB3 is challenging due to its protein nature. Physical entrapment in wet sol–gel silica can stabilize the protein's conformation and permit its sustained delivery. However, irreversible syneresis and poor viscoelastic properties hamper wet sol–gel silica application as a semisolid vehicle. To overcome these limits, a sol–gel silica/hydroxypropylmethylcellulose (HPMC) hydrogel blend was developed. SB3 entrapped in 8% SiO2 wet sol–gel silica preserved its structure, was stabilized against denaturation, and was slowly released for at least three days. Blending a silica gel with an HPMC–glycerol (metolose-G) hydrogel permitted spreadability without affecting the protein's release kinetics. When administered in vivo, SB3 in silica/metolose-G—but not in solution or in metolose-G alone—accelerated wound healing in SB3 knockout and diabetic mouse models. The results confirmed that SB3 is a new pharmacological option for the treatment of chronic ulcers, especially when formulated in a slow-releasing vehicle. Silica–metolose-G represents a novel type of semisolid dosage form which could also be applied for the formulation of other bioactive proteins. [ABSTRACT FROM AUTHOR]

Foot ulcerations are a disabling complication of diabetes and no treatment is currently available based on disease mechanisms. The protein serpin B3 (SB3) was identified as a positive biomarker of successful diabetic wound healing; therefore, its exogenous administration may promote healing. The topical administration of SB3 is challenging due to its protein nature. Physical entrapment in wet sol–gel silica can stabilize the protein’s conformation and permit its sustained delivery. However, irreversible syneresis and poor viscoelastic properties hamper wet sol–gel silica application as a semisolid vehicle. To overcome these limits, a sol–gel silica/hydroxypropylmethylcellulose (HPMC) hydrogel blend was developed. SB3 entrapped in 8% SiO2 wet sol–gel silica preserved its structure, was stabilized against denaturation, and was slowly released for at least three days. Blending a silica gel with an HPMC–glycerol (metolose-G) hydrogel permitted spreadability without affecting the protein’s release kinetics. When administered in vivo, SB3 in silica/metolose-G—but not in solution or in metolose-G alone—accelerated wound healing in SB3 knockout and diabetic mouse models. The results confirmed that SB3 is a new pharmacological option for the treatment of chronic ulcers, especially when formulated in a slow-releasing vehicle. Silica–metolose-G represents a novel type of semisolid dosage form which could also be applied for the formulation of other bioactive proteins.

In the present work, the preparation, characterisation, and efficiency of two different silica nanostructures as release vehicles of Cisplatin are reported. The 1‐hexadeciltrimethyl‐ammonium bromide templating agent was used to obtain mesoporous silica nanoparticles which were later loaded with Cisplatin. While sol–gel silica was very fast prepared using an excess of acetic acid during the hydrolysis–condensation reactions of tetraethylorthosilicate and at the same time the Cisplatin was added. Several physicochemical techniques including spectroscopies, electronic microscopy, X‐ray diffraction, N2 adsorption–desorption were used to characterise the silica nanostructures. An in vitro Cisplatin release test was carried out using artificial cerebrospinal fluid. Finally, the toxicity of all silica nanostructures was tested using the C6 cancer cell line. The spectroscopic results showed the suitable stabilisation of Cisplatin into the two different silica nanostructures. A large surface area was obtained for the mesoporous silica nanoparticles, while low areas were obtained in the silica nanoparticles. Cisplatin was released faster from mesoporous silica channels than from inside of aggregates nanoparticles silica. Cisplatin alone, as well as, cisplatin released from both silica nanostructures exerted a toxic effect on cancer cells. In contrast, both silica structures without the drug did not exert any toxic effect. [ABSTRACT FROM AUTHOR]

Silica derived from sol-gel approach was used as co-filler in aluminium hydroxide (ATH) or hydromagnesite (HM) ethylene-vinyl acetate (EVA) formulations. In this bottom-up approach, the silica network is formed inside the extruder in a first process step. The 3D silica structure is investigated by solid-state nuclear magnetic resonance (ssNMR) spectroscopy and a combined TGA-FTIR analysis revealing a partially incomplete reaction to form silica particles. In addition, 29Si CPMAS NMR showed the formation of chemical Si–C bonds between EVA and silica networks. The performance enhancement of the fire retardant properties was established by comparing with composites prepared by a top-down approach, i.e by adding preformed silica. It is confirmed that the preformed silica acts as a synergistic agent with both ATH or HM, increasing the flame retardant properties (limiting oxygen index, UL-94 and cone calorimeter tests) of EVA composites, however, the sol-gel silica shows the best performances in reducing both heat release and smoke production. The role of the sol-gel structure was deeply investigated in correlation with combustion test. • EVA-based flame retarded composites have been successfully prepared with silica as co-filler. • Silica formed in-situ during the extrusion process is compared with preformed silica. • NMR spectroscopy shows that the sol-gel silica lattice is not completely condensed and it reacts with the polymer. • Preformed and in-situ prepared silica does not lead to any change in the polymer degradation mechanism. • In-situ formed silica based composite forms a consistent and compact residue with better flame retardant properties. [ABSTRACT FROM AUTHOR]

Highlights • Stirring assisted sol-gel method is used to insert Ag nanowires in a silica matrix. • The Ag nanowires are aligned in the silica matrix, parallel to the stirring direction. • The aligned silver nanowires in silica matrix show light polarizing properties. • Ag nanowires aligned in silica composite is promising for use as polarizer. Abstract One-directional alignment of Ag nanowires (AgNWs) embedded in silica matrix was achieved by means of the sol-gel fabrication process by stirring the precursor solution consisting of tetramethyl orthosilicate (TMOS) and AgNW during gelation. The parallel orientation of AgNWs along the stirring direction was confirmed in the sliced composite by optical microscopy. The optical function of the obtained composite as polarizer was demonstrated by transmission measurement with polarized light. The polarization response was found to be limited and can be explained with the buckling of AgNWs formed during the condensation reaction. [ABSTRACT FROM AUTHOR]

Mobil Composition of Matter no. 48 (MCM-48) is a promising inorganic particle due to its unique crystal structure and 3-dimensional porous network. Incorporating a discrete amount of nanosized MCM-48 for material development would give significant impact to the material's performance and mechanical robustness. Thus far, the synthesis of MCM-48 in the nanoscale regime has been achieved via chemical modification techniques. However, they are often not reproducible due to limited understanding of surfactant behaviour. On the other hand, physical modification technique is more stable, thereby can reduce the possibility of producing other undesired mesophase. Nevertheless, this technique has not been adapted for nanosized MCM-48 synthesis. In this work, the physical modification technique was adapted to tailor MCM-48 particle size by varying stirring speed (i.e., 1000 rpm, 3000 rpm and 5000 rpm) and using different types of washing medium. Particle size distribution (PSD) studies showed mean particle size of 250 ± 50 nm. XRD analysis displayed several crystalline peaks indexed to cubic crystal mesophase. Transmission electron microscopy (TEM) and Brunauer-Emmett Teller (BET) analyses also showed a unique 3D cubic interconnecting porous network with specific surface area of 1030 m² g-1. It was revealed that the degree of agglomeration increased as relative polarity of alcohol increased, CH3OH > CH3CH2OH. Therefore, particle size and agglomeration state of MCM-48 can be tailored by varying the physical modification techniques while maintaining its intrinsic pore morphology. [ABSTRACT FROM AUTHOR]

Electrospinning was employed to fabricate composite membranes containing perfluorosulfonic acid (PFSA) ionomer, poly(vinylidene fluoride) (PVDF) reinforcement and a sulfonated silica network, where the latter was incorporated either in the PFSA matrix or in the PVDF fibers. The best membrane, in terms of proton conductivity, was made by incorporating the sulfonated silica network in PFSA fibers (Type-A) while the lowest conductivity membrane was obtained when sulfonated silica was incorporated into the reinforcing PVDF fibers (Type-B). A Type-A membrane containing 65 wt.% PFSA with an embedded sulfonated silica network (at 15 wt.%) and with 20 wt.% PVDF reinforcing fibers proved superior to the pristine PFSA membrane in terms of both the proton conductivity in the 30–90% RH at 80 °C (a 25–35% increase) and lateral swelling (a 68% reduction). In addition, it was demonstrated that a Type-A membrane was superior to that of a neat 660 EW perfluoroimide acid (PFIA, from 3M Co.) films with respect to swelling and mechanical strength, while having a similar proton conductivity vs. relative humidity profile. This study demonstrates that an electrospun nanofiber composite membrane with a sulfonated silica network added to moderately low EW PFSA fibers is a viable alternative to an ultra-low EW fluorinated ionomer PEM, in terms of properties relevant to fuel cell applications.

High sensitivity volatile organic compounds (VOCs) sensors based on a tapered small core single mode fiber (TSCSMF) and a microfiber coupler (MFC) are reported. The TSCSMF had a waist diameter of ∼5.1 μm and the MFC had a waist diameter of ∼1.9 μm each and both were fabricated using a customized microheater brushing technique. Silica based materials containing immobilized Nile red prepared by sol-gel method with two different recipes (recipe I and recipe II) are investigated. Initially recipe I based coating materials were applied to the surfaces of the TSCSMF and MFC. The experimental results show that the sensor based on an MFC shows much better sensitivities of −0.130 nm/ppm and −0.036 nm/ppm to ethanol and methanol than those of the TSCSMF based sensor. The corresponding minimum detectable concentration change of the MFC based sensor are calculated to be ∼77 ppb and ∼281 ppb to ethanol and methanol respectively. Both sensors are demonstrated fast response times of less than 5 min, while the recovery times varied from 7 min to 12 min. In addition, another TSCSMF based sample (∼7.0 μm) coated with a mixed layer of sol silica and Nile red prepared by recipe II was fabricated to achieve simultaneous measurement of ethanol and methanol, employing a second-order matrix approach. [ABSTRACT FROM AUTHOR]

Sol–gel silica doped with different amount of sec-octylphenoxyl acetic acid (CA12) was prepared using sol–gel method and characterized by scanning electron microscopy and thermogravimetric analysis. The adsorption behavior of methylene blue (MB) from aqueous solution onto sol–gel silica doped with CA12 (SSC) was studied. Batch experiments were carried out to measure the adsorption as a function of equilibrium time, pH of the solution, initial MB concentration and temperature. The results showed that the contents of CA12 were 0, 4.4%, 5.1% and 7.5% for SSC-0, SSC-1, SSC-2 and SSC-3, respectively. The adsorption equilibrium was reached within 8 h for SSC-0, 5 h for SSC-1, 2 h for SSC-2 and SSC-3. With the increase of the content of CA12, the equilibrium time decreased, which may be due to their increased pore structure. Both the pseudo-first-order and pseudo-second-order kinetics models fitted the data well. The higher adsorption amount was found at neutral and basic conditions, and the lower adsorption amount was found at lower pH. The adsorption data for MB on SSC were consistent with the Langmuir isotherm equation. The maximum adsorption capacities of MB on SSC-0, SSC-1, SSC-2 and SSC-3 were 23.8, 32.4, 46.3 and 65.9 mg g–1, respectively. The thermodynamics properties indicated that the adsorption processes were spontaneous and endothermic nature. [ABSTRACT FROM AUTHOR]

Azobenzene molecules are well known for their photoswitching properties. When incorporated into a polymer film, push−pull azobenzene derivatives such as the DR1 (Dispersed Red 1) confer to the film some remarkable photomechanical properties, allowing for the direct optical inscription of relief patterns. While mainly investigated in the case of organic polymers such as poly(methyl methacrylate) (PMMA), it was shown some years ago that similar photoinduced deformation phenomena could occur in materials using sol‐gel silica as a host matrix. In the present study, the process is revisited, showing that photopatterning can be drastically improved through a careful control of the rheology of the sol‐gel film. Increase in the photoinscribed relief pattern amplitude by up to a factor of three to four is thus achieved. In the second step, it is also shown that sol‐gel silica matrix offers the possibility of removing all organic compounds from the film after photostructuration, without any relaxation of the patterns. This opens the way toward the use of sol‐gel azo/silica films for the elaboration of micro and nanostructured transparent silica coatings that could be used for many applications among which there is light extraction management in light emitting devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Front end to flame atomic absorption system for automatic determination of metals. • On-line column preconcentration method for monitoring Cu(II) and Pb(II) in beers. • Synthesis a new sol–gel functionalized silica-based sorbent for metal determination. • Copper and lead content of beer samples was in the range 1.6–17.6 μg L−1. • The method exhibited sensitivity, simplicity, reusability, high sampling frequency. A novel sol–gel pyridylethylthiopropyl functionalized silica-based sorbent was synthesized and utilized in an on-line column preconcentration system coupled with flame atomic absorption spectrometry for metal determination. The developed platform was used for the determination of Pb(II) and Cu(II) in beer samples, since there are limited automatic methods for routine analysis of alcoholic beverage. For a preconcentration time of 60 s, the calculated enhancement factors were 96 for Cu(II) and 130 for Pb(II). The limits of detection were 0.33 μg L−1 and 1.98 μg L−1 for Cu(II) and Pb(II), respectively. Moreover, the RSDs were less than 2.9% indicating good method precision. The method was successfully employed for the analysis of commercially available beers. The Cu(II) content of the samples was 1.6–21.8 μg L−1 and the Pb(II) content was 7.3–17.6 μg L−1. The developed manifold exhibited operational simplicity and good performance characteristics, indicating its potential utilization for routine analysis in beer industry. [ABSTRACT FROM AUTHOR]

This works reports the structural investigation of homogeneously doped sol–gel-derived silica optical fiber preforms. Crack-free germanosilicate (2.7 wt% Ge) and phosphosilicate (2.5 wt% P) glasses, suitable for optical fiber fabrication, have been prepared using the polymeric sol–gel route combined with the sol-doping technique. Space homogeneity of the doping oxide (GeO 2 or P 2 O 5 ) in the cylindrical preforms has been checked by chemical analysis. The structure of these glasses have been studied using Raman spectroscopy and compared to pure silica glasses. It is shown that phosphorus has a much more sensitive effect on the glassy structure than germanium, both at small and medium scales. Indeed, in the low-wavenumber region (7−100 cm −1 ), the phosphorus-doping was found to affect the intensity of the boson peak, suggesting an enhancement of heterogeneity at the nanometer scale. At a shorter scale, both germanium- and phosphorus-doping were found to reduce the number of three- and four-membered rings in the silica glass network. [ABSTRACT FROM AUTHOR]

In this work we investigate the effect of different drying control chemical additives (DCCAs) on the sol–gel processing of silica. Formamide, N,N-dimethylformamide, and propylene carbonate were used as DCCAs in this study. The sols were prepared by the hydrolysis and condensation of tetraethyl orthosilicate in the presence of water, nitric acid, and ethanol. After gelation, the samples were heat treated in air at temperatures from 110 to 1150 °C. The structural evolution of these materials was evaluated by Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption tests, and helium pycnometry. The band attributed to silanol groups (≈ 960 cm − 1 ) decreased in intensity and shifted towards larger wavenumbers as reaction time progressed. Bands ascribed to Si–O bonds also shifted towards larger wavenumbers with reaction time. These findings suggest the formation of a more rigid silica framework as time progressed. This behavior was more pronounced for sols prepared using formamide and N,N-dimethylformamide. The heat treatment of DCCA-containing gels at temperatures up to 800 °C gave rise to materials with a strong and interconnected framework, showing a high concentration of silanols on the surface. The presence of such groups could enable the chemical modification of these materials upon a post-synthesis treatment. [ABSTRACT FROM AUTHOR]

The ether-functionalized imidazolium ionic liquids (IL) applied in the silica sol–gel process demonstrated a defined coordination potential. These IL display the capacity to control the system organization from the reactions’ first moments through a dynamic system-assembling ability, being the sum of ionic and physical interactions, i.e. Coulomb forces, H-bonding and London forces. The initial hydrolysis steps of tetraethyl orthosilicate (TEOS) in the presence of these IL were followed by Fourier transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS), both in time-resolved experiments, in an attempt to correlate the structuring and the bonding dynamics of these systems. [ABSTRACT FROM AUTHOR]

The methylotrophic Pichia angusta VKM Y-2559 and the oleaginous Cryptococcus curvatus VKM Y-3288 yeast cells were immobilized in a bimodal silica-organic sol–gel matrix comprised of tetraethoxysilane (TEOS), the hydrophobic additive methyltriethoxysilane (MTES) and the porogen polyethylene glycol (PEG). Under carefully optimized experimental conditions, employing basic catalysts, yeast cells have become the nucleation centers for a silica-organic capsule assembled around the cells. The dynamic process involved in the formation of the sol–gel matrix has been investigated using optical and scanning electron microscopic techniques. The results demonstrated the influence of the MTES composition on the nature of the encapsulation of the yeast cells, together with the architecture of the three-dimensional (3D) sol–gel biomatrix that forms during the encapsulation process. A silica capsule was found to form around each yeast cell when using 85 vol% MTES. This capsule was found to protect the microorganisms from the harmful effects that result from exposure to heavy metal ions and UV radiation. The encapsulated P. angusta BKM Y-2559 cells were then employed as a biosensing element for the detection of methanol. The P. angusta -based biosensor is characterized by high reproducibility (Sr, 1%) and operational stability, where the biosensor remains viable for up to 28 days. [ABSTRACT FROM AUTHOR]

Nafion-SiO 2 hybrid electrolytes were synthesized by sol–gel reaction. The homogeneity, structural properties, and proton conductivity of the hybrid membranes were studied. Small-angle scattering analyses indicate that the Nafion structural matrix was preserved on the nanoscale, and the growth of silica particles occurred both in the ionic and nonionic domains of Nafion, which resulted in hybrids with characteristic morphologies. The water uptake and the weight fraction of the inorganic phase were found to be dependent on the alcohol solvent used for the sol–gel synthesis. Nafion-silica hybrids with homogeneous distribution of the inorganic phase were obtained using methanol as the solvent for the sol–gel reaction. The observed microstructural properties of the Nafion-silica membranes were related to enhanced proton conductivity at high temperatures and low relative humidity conditions. [ABSTRACT FROM AUTHOR]

Ink-jet printing of ionogel for low-cost microbattery is presented. Such an approach allows to provide liquid-like electrolyte performances for all-solid microdevices. Ink-jet printing process is possible thanks to sol precursor of the ionogel. This full silica based ionogels confining ionic liquid are known to be thermal resistant, serving safety and technologies requiring solder reflow. High ionic conductivity and compatibility with porous composite electrodes allow reaching good electrochemical cycling performance: full Li-ion cell with LiFePO 4 and Li 4 Ti 5 O 12 porous composite electrodes shows a surface capacity of 300 μAh cm −2 for more than 100 cycles. Such surface capacities are very competitive as compared to those obtained for microdevices based on expensive PVD processes. [ABSTRACT FROM AUTHOR]

The electroassisted encapsulation of Single-Walled Carbon Nanotubes was performed into silica matrices (SWCNT@SiO2). This material was used as the host for the potentiostatic growth of polyaniline (PANI) to yield a hybrid nanocomposite electrode, which was then characterized by both electrochemical and imaging techniques. The electrochemical properties of the SWCNT@SiO2-PANI composite material were tested against inorganic (Fe3+/Fe2+) and organic (dopamine) redox probes. It was observed that the electron transfer constants for the electrochemical reactions increased significantly when a dispersion of either SWCNT or PANI was carried out inside of the SiO2 matrix. However, the best results were obtained when polyaniline was grown through the pores of the SWCNT@SiO2 material. The enhanced reversibility of the redox reactions was ascribed to the synergy between the two electrocatalytic components (SWCNTs and PANI) of the composite material. [ABSTRACT FROM AUTHOR]

Highlights: [•] A porous layer of MCM-41 type silica sorbent for gas–solid chromatography. [•] Hybrid organic–inorganic sorbents based on silica. [•] Selectivity of sorbents can be changed by varying the VTEOS/TEOS ratio. [Copyright &y& Elsevier]

The article presents the study, offering information on the use of Silica nanoparticles (SNPs) for evaluating risk management measures and comparison of nanoparticle exposures between sol-gel and fumed nano-silica manufacturing facilities. Topics discussed include the measurement of particle size by real-time instrument along with analysis of Airborne nanoparticles, discharge of SNP into the air, and spherical shaped morphology of particles from sol-gel silica nanoparticles process.

Abstract: The incidence of methicillin-resistant Staphylococcus aureus (MRSA) infection has significantly increased. Generally, the success of this bacterium as a pathogen is attributed to its ability to adhere to surfaces and remain there, under the protection of an extracellular matrix known as biofilm. To combat MRSA with regular doses of vancomycin, efforts are continuously underway to increase its effectiveness. A promising technique is to use combinational therapeutics. In vitro experiments showed that farnesol can be used as an adjuvant with conventional antibiotics. Farnesol is a natural sesquiterpenoid and quorum-sensing molecule. The biggest obstacle to using this concept is that farnesol is highly water insoluble. This compromises its bioavailability if it were to be used along with vancomycin at the site of infection when the treatment needs to be administered in vivo. Herein we designed an efficient therapeutic strategy for the simultaneous delivery of both antibiotic and adjuvant in order to treat MRSA infections. We demonstrate that sufficient quantities of both vancomycin and farnesol can be incorporated into sol–gel silica applied as thin films on an implant surface. The incorporation of the hydrophobic farnesol does not affect the stability of the thin films and neither does it affect the controlled release of vancomycin. The data demonstrate the potent adjuvant effect of farnesol on vancomycin in inhibiting MRSA infection. In vitro experiments show the complete inhibition (106 fold reduction in growth compared to control) of methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) when the ratio of vancomycin to farnesol in the sol–gel silica films is optimized. The local delivery of antibiotics minimizes the need for systemic antibiotics. The incorporation of vancomycin and farnesol into thin sol–gel films represents a new treatment paradigm for the topical delivery of antibiotics with adjuvant. The potential clinical benefits are significant and include avoiding the need for revision surgery, preventing surgical site infection and controlling healthcare costs. [Copyright &y& Elsevier]

Abstract: This work describes the electro-assisted generation of clay-mesoporous silica composite films onto glassy carbon electrodes (GCEs). The method involved the deposition of clay particles by spin-coating on GCE and the subsequent growing of a surfactant-templated silica matrix around these particles by electro-assisted self-assembly (EASA). EASA typically consisted in applying a cathodic potential to the electrode immersed into a hydrolyzed sol (containing tetraethoxysilane, TEOS, as the silica source, and cetyltrimethylammonium bromide, CTAB, as surfactant) in order to generate the necessary hydroxyl catalysts inducing the formation of the mesoporous silica. In such conditions, alongside the silica deposition process, the interlayer distance between the clay sheets was found to increase as a result of CTAB ion exchange. After removal of the surfactant template, the composite film became highly porous (i.e., to redox probes) and the clay recovered its pristine interlayer distance and cation exchange properties. This made it promising for application in preconcentration electroanalysis, as pointed out here using copper(II) as a model analyte, especially because it offered much better long-term operational stability than the conventional (i.e., without silica binder) clay film electrode. [Copyright &y& Elsevier]

Abstract: Ultra high temperature ceramic coatings (UHTCs) have a potential use as thermal protection systems in rocket exhaust cones, insulating tiles for the space shuttle, and engine components. The porous ceramic coatings require a sealing strategy with ceramic nanoparticles to enhance the corrosion resistance and prevent the formation of thermally grown oxides (TGO) at the ceramic/metallic interface. In this context, we report a simple, yet highly versatile sol–gel process to seal the pores in alumina coating with silica nanoparticles. Tetraethylorthosilicate (TEOS) was used as sol–gel precursor. Polysilicate molecules are likely formed inside the coating pores during the sol–gel process. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests were performed to measure the corrosion resistance of alumina coatings before and after treatment with TEOS. A significant enhancement of the corrosion resistance of alumina coating was performed via post-treatment with sol–gel silica which perfectly sealed the open pores and voids in alumina coatings. [Copyright &y& Elsevier]

Abstract: Porous sol–gel silica monoliths are prepared using PMMA nanoparticles, 60nm in diameter, as sacrificial templates. The pore-structure of the calcined pellets is investigated through nitrogen adsorption to assess the evolution of the porosity when varying the amount of porogen. The latex templated monoliths present a well defined spherical extrinsic porosity and an intrinsic microporosity due to preparation process. As a result of a careful analysis of the adsorption hysteresis, we identify a percolation threshold of the spherical porosity around 30% volume fraction. This phenomenon, similar to the percolation previously observed in latex-templated silica films, opens the way to the use of latex-templated porous silica monoliths with a tailorable and reliable pore structure. [Copyright &y& Elsevier]

A modified multiscale model of a sol-gel silica drying process is presented that treats first-shell substitution effects and unlimited four-membered ring cyclization. The inclusion of four-membered (8-atom) rings allows the model to simulate the formation of the tetrasiloxane rings and cubic silsesquioxane cages known to be prevalent components of sol-gel silica systems, as well as a full range of other ring-containing structures. The polymerization process is treated using a dynamic Monte Carlo method where a discrete population of one million monomers evolves according to kinetic rules, including unimolecular-like closure of three-bond blocks. Compared with prior simulations with extensive cyclization that allowed only three-membered rings, the molecular structures formed with unlimited four-membered ring are more complex, and the occurrence of 'skinning' (the rapid formation of a gel only at the surface of the film) is more pronounced and leads to more severe structure gradients. © 2012 American Institute of Chemical Engineers AIChE J, 59: 707-718, 2013 [ABSTRACT FROM AUTHOR]

Abstract: Sol–gel silica/nanoclay composites were prepared through sol–gel polymerization technique using tetraethylorthosilicate precursor and montmorillonite (MMT) clay in aqueous media. In this study, both montmorillonite-K+ and organically modified MMT (OMMT) clays were used. The prepared composites were coated on glass substrate by making 1wt% solution in ethyltrichlorosilane. The incorporation of nanoclay does not alter the intensity of characteristic Si–O–Si peak of silica network. Thermogravimetric studies show that increasing clay content increased the degradation temperature of the composites. Differential scanning calorimetry (DSC) results of organically modified MMT nanoclay incorporated composite show a shift in the melting behavior up to 38°C. From DSC thermograms, we observed that the ΔH value decreased with increasing clay loading. X-ray diffraction patterns prove the presence of nanoclay in the composite and increase in the concentration of organically modified nanoclay from 3 to 5wt% increases the intensity of the peak at 2θ =8° corresponds to OMMT. Morphology of the control silica gel composite was greatly influenced by the incorporation of OMMT. The presence of nanoclay changed the surface of control silica gel composite into cleaved surface with brittle in nature. Contact angle measurements were done for the coatings to study their surface behavior. These hybrid coatings on glass substrate may have applications for hydrophobic coatings on leather substrate. [Copyright &y& Elsevier]

This study investigated the effects of different additives and precursors on the catalytic activity of laccase entrapped in sol-gel silica. It was found that the laccase catalytic activity and stability of sol-gel laccase could be enhanced if the entrapment was performed in the presence of additives such as PVA, PEG and APTS. The use of TEOS as a precursor showed slightly higher laccase catalytic activity compared to TMOS. The PVA as an additive showed a better catalytic activity enhancement compared to the PEG and APTMS with the optimum PVA concentration of 0.03 mg/mL. The optimal temperatures of sol-gel laccase without and with additives were found to be at 40 and 27°C, respectively. After 70 days of storage at 27°C, the catalytic activity of the immobilized sol-gel laccase with additives maintained its catalytic activity compared to only 30% of its original catalytic activity for the sol-gel laccase without additives. [ABSTRACT FROM AUTHOR]

Abstract: Copper nanoparticles were formed by photoirradiation of doped sol–gel silica, which was prepared by mixing Cu2+ ions, ethylenediaminetetraacetic acid (EDTA), and riboflavin into sol–gel solutions of tetramethoxysilane. The doped silica exhibited broad absorption bands at 442nm due to riboflavin and 740nm due to Cu2+-EDTA complexes. After photoirradiation, the sol–gel silica showed a reddish brown color and the absorption peak around 580nm due to the plasmon band of copper nanoparticles. Copper nanoparticles were also formed from other sol–gel silica doped with lumichrome or lumiflavin. The photostability of the flavins dyes obtained from the fluorescence intensities was in the order of lumichrome>lumiflavin>riboflavin in the sol–gel silica without Cu2+ ions. On the other hand, the fluorescence intensities were considerably reduced by photoirradiation of the sol–gel silica doped with Cu2+ ions, irrespective of the flavin dyes doped. Considering the absorption and fluorescence spectral changes during the photoirradiation, we concluded that copper nanoparticles are produced by the photoinduced electron transfer from the flavin dyes in the sol–gel silica. [Copyright &y& Elsevier]

In vivo suppression of glioblastoma multiforme (GBM) in Wistar rats using silica-shelled biocatalytic Pt(NH3)4Cl2 nanoparticles is reported. These nanoparticles were synthesized by a sol-gel technique and characterized by SEM and HRTEM imaging. We confirmed morphological uniformity (30 nm) and surface acidity of the nanoparticles, respectively, by TEM imaging and FTIR spectral analysis. Interestingly, treatment of Wistar rats intraperitoneally inoculated with C6 cells using the biocatalysts resulted in considerable tumor shrinkage. Efficiency of the biocatalyst to shrink a tumor is superior to that by the commercial cytotoxic agent cisplatin. The tumor suppression property of Pt(NH3)4Cl2 nanoparticles is attributed to catalytic damage of DNA in C6 cells. [ABSTRACT FROM AUTHOR]

Abstract: A one-step procedure without heat-treatment was carried out to yield the space-selective growth of gold nanoparticles inside a transparent silica matrix. A silica porous monolith was prepared via a sol–gel route and then post-doped with an aqueous solution of hydrogen tetrachloroaurate (HAuCl4) as a gold precursor, in the presence of sodium carbonate as an additive. Direct and local precipitation of gold nanoparticles inside the deep volume of the silica matrix was induced by a femtosecond laser irradiation at room temperature. Gold nanoparticles with size of about 50–60nm were evidenced by absorption spectroscopy and transmission electron microscopy. The additive is assumed to be involved in a photo-electrochemical mechanism including redox reactions, which is necessary to the formation of gold nanoparticles. [Copyright &y& Elsevier]

Abstract: Stability, defined as the reproducible behavior of a device upon its storage, is an important issue in pharmaceutical formulation. Silica xerogels obtained through the sol–gel route are relatively new as matrices for the controlled release of drugs. In some cases, it was observed that their behavior changes upon storage, so that they cannot always be defined as “stable”. This occurs especially when gel processing is performed at mild temperatures, a procedure that may have to be used to prevent degradation of the embedded drug. This work investigated the use of inorganic catalysts as potential xerogel stability inducers when gel curing by heating is not applicable. Three compounds known to accelerate sol–gel polymerization, namely ammonia, sodium fluoride and sodium carbonate, were introduced during the polymerization of low-temperature processed inorganic and organically modified gels, and the effect of each compound on xerogel stability and drug release was monitored. The use of carbonate leads to formulations with good retention properties, as opposed to ammonia and NaF, which lead to poorly retentive xerogels in accordance with their known ability to increase porosity. Ammonia was shown to be a poor stability promoter independently of gel composition, as opposed to fluoride and carbonate, which both displayed stabilizing properties in a dose-dependent manner. No correlation was found between xerogel stability and drug release properties. An attempt was also made to correlate stability data with polymerization rates and wet gel syneresis time evolution with the purpose of identifying one or more synthesis parameters that could act as stability predictors for pre-formulation studies. No correlation was found between stability and syneresis data. A similar trend in the curve of gel time vs. catalyst concentration was observed for the two stabilizing catalysts, which was different for the non-stabilizing ammonia. It was concluded that the trend of this curve could potentially provide an indicator of catalyst stabilizing efficacy. [Copyright &y& Elsevier]

Abstract: The extraction and separation of Cu(II), Ni(II) and Zn(II) from aqueous sulfate–acetate solution were carried out using solid phase sol–gel silica containing immobilized Cyanex 272 {bis(2,4,4-trimethylpentyl)phosphinic acid, HA} (SGSIC). Characterisation of SGSIC by FT-IR, EDX, SEM, TG-DTA and BET proved the presence of Cyanex 272 in the sol–gel silica. It was found that SGSIC can extract about 95% Zn(II) at equilibrium pH 3.0, 99% Cu(II) at pH 5.3 and 91% Ni(II) at pH 6.2 from synthetic solutions containing 20 mg/L of each metal ion. Various parameters such as pH of the aqueous solution, ratio of solid to liquid, Cyanex 272 to silica, initial Cu(II) concentration and temperature were studied. The adsorption data fitted the Langmuir adsorption model, but at higher Cu(II) concentrations (8.9–82 mM), it followed the Freundlich adsorption model. The maximum adsorption capacity of Cu(II) was found to be 20.9 mg/g (0.33 mmol/g). SGSIC was easily regenerated and reused in the subsequent removal of Cu(II) in five cycles. By varying the aqueous pH and solid to liquid ratio, the separation and recovery of Cu(II), Zn(II) and Ni(II) from a dilute leach solution of printed circuit board was demonstrated. [Copyright &y& Elsevier]

Insufficient bonding between multi-wall carbon nanotubes (MWCNTs) and the matrix reduces the effectiveness of MWCNT reinforcements in sol–gel silica dielectric composites. This paper investigates the efficacy of various surfactants in improving the bonding through morphological and mechanical characterization of MWCNT-reinforced sol–gel silica dielectric films. It is found that use of some surfactants while dispersing MWCNTs improves the modulus and hardness. The improved mechanical properties possibly reduce the delamination problem of Cu/low-k films during flip-chip packaging and wirebonding. [Copyright &y& Elsevier]

Three types of silica particles modified with vinyl groups were obtained: (i) xerogel formed by hydrolytic polycondensation of the mixture of tetramethoxysilane (TMOS) and 1,1,1,7−tetramethoxy-3,5,7-trimethyl-3,5,7-trivinyltetrasiloxane, (ii) mesoporous silica obtained from the same precursors in the presence of the cetyltrimethylammonium bromide (CTAB), and (iii) commercial Fluka silica gel 60A with a vinyltriethoxysilane-treated surface. Vinyl groups on these silica materials were transformed into silyl chloride by hydrosilylation with HMeSiCl. These groups were used to graft living polysiloxane that was synthesized by anionic ring-opening polymerization of 2,4,6-tri(3-chloropropyl)-2,4,6-trimethylcyclotrisiloxane and initiated by BuLi. Chloropropyl groups on the grafted polymer were used to quaternize N,N-dimethyl- n-octylamine. Silica particles with grafted polysiloxane having quaternary ammonium salt (QAS) groups pendant to polymer chains were obtained. Silica material with QAS groups directly attached to the surface were generated by the action of N,N-dimethyl- n-octylamine on particles obtained by the sol-gel process involving tetraethoxysilane (TEOS) with 3-chloropropyltriethoxysilane. The bacteriocidal properties of all these materials were tested in water suspension against five representative strains for Gram-positive and Gram-negative bacteria. Some of the silica-polysiloxane hybrid materials have good antibacterial properties against Gram-positive strains, but not as good as the non-tethered QAS-substituted polysiloxane in water solution. The QAS groups that are directly bonded to the silica material surface are inactive. [ABSTRACT FROM AUTHOR]

Abstract: In this study, palladium silicide was formed on the sol–gel derived SiO2 supported Pd catalysts when they were prepared by ion-exchange method using Pd(NH3)4Cl2 as a palladium precursor. No other palladium phases (PdO or Pd0) were evident after calcinations at 450°C for 3h. The Pd/SiO2 catalysts with Pd silicide formation were found to exhibit superior performance than commercial SiO2 supported ones in liquid-phase semihydrogenation of phenylacetylene. From XPS results, the binding energy of Pd 3d of palladium silicide on the Pd/SiO2 catalyst shifted toward larger binging energy, indicating that Pd is electron deficient. This could probably result in an inhibition of a product styrene on the Pd surface and hence high styrene selectivities were obtained at high phenylacetylene conversions. The formation of Pd silicide, however, did not have much impact on specific activity of the Pd catalysts since the TOFs were quite similar among the various catalysts with or without palladium silicides if their average particle sizes were large enough. The TOFs decreased by an order of magnitude when palladium dispersion was very high and their average particle sizes were smaller than 3–5nm. [Copyright &y& Elsevier]

A new concept in optical-fiber chemical sensors, the active fiber core optical sensor (AFCOS), is presented. In this sensor, the fiber core acts as a transducer. The sensitivity of an AFCOS sensor is compared with that of an active coating [evanescent wave (EW)] based optical-fiber sensor. Requirements for a fiber core to act as a chemical sensor are discussed. Novel techniques for making a porous sol-gel silica fiber, doping chemical reagents into the fiber, and constructing a chemical sensor using the porous fiber as a transducer have been developed. The microstructure of the fabricated sol-gel silica fiber and the effect of the fiber's microstructure on the capability of the porous sol-gel silica fiber for guiding light are discussed. A humidity sensor employing a CoCl2-doped porous sol-gel fiber as a transducer has been constructed as an example. The test results for the humidity sensor verified a theoretical analysis indicating that an optical-fiber chemical sensor using an active fiber core as a transducer has a much higher sensitivity than that of an EW-based sensor. [ABSTRACT FROM PUBLISHER]

The electrochemical behavior of riboflavin (RF) adsorbed on different surfaces of inorganic matrices was investigated using modified carbon paste electrodes. Silica gel and sol–gel silica modified with niobium oxide were denominated as (SN) and (SNsol–gel), respectively. These materials were treated with a H3PO4 solution to graft phosphate groups and were denominated as (SNP) and (SNPsol–gel). The immobilization of RF on these materials indicated a high electrode stability, avoiding leaching out of the electroactive species (RF) from the electrode surface. The values of formal potential (E0′) of the adsorbed RF on the different matrices changed from −283 (SNRF) up to −165 mV (SNPRFsol–gel) vs SCE in 0.1 mol l−1 NaNO3 solution at pH 7.0. Compared to the E0′ for soluble RF, the values are shifted 183 up to 305 mV toward more positive potentials. The stability of the electrodes and the formal potential of the adsorbed RF on different matrices remained constant upon changing the solution pH from 3 to 8. Some kinetic parameters were estimated; indicating that all systems studied presented a good electron transfer rate. [Copyright &y& Elsevier]

A novel and efficient method for molecular engineering of the pore size and porosity of microporous sol–gel silica membranes is demonstrated in this communication. By adding a suitable organic template (e.g. tetraethyl- or tetrapropylammonium bromide) in polymeric silica sols, otherwise known to result in microporous membranes with pores in the range 3–4 A˚, we can ‘shift’ the pore size to 5–6 A˚, as judged by single-component gas and vapor permeation results with probe molecules of increasing kinetic diameter (dk). The templated membranes exhibit permeances as high as 10−7 to 10−6 mol m−2 s−1 Pa−1 for molecules with dk<4.0 A˚ (e.g. CO2, N2, CH4), coupled with single-component selectivities of 100–1800 for N2/SF6, 20–40 for n-butane/iso-butane, and 10–20 for para-xylene/ortho-xylene. The transport properties of the templated membranes are distinctly different from those of the respective silica membranes prepared without templating, and resemble somewhat the transport properties of polycrystalline zeolite MFI membranes prepared by the lengthy, batch hydrothermal synthesis approach, using tetrapropylammonium bromide as a structure directing agent. [Copyright &y& Elsevier]

Cobalt acetylacetonate encapsulated in sol–gel silica is shown to be a very efficient bifunctional acidic and redox catalyst, giving 2,5-furandicarboxylic acid with 99% selectivity directly from fructose at a conversion of 72%. A cooperative effect of the functions of the catalyst is operative, as the same reaction performed in two consecutive steps gives much lower conversions. [Copyright &y& Elsevier]

A new approach to assemble reagentless amperometric biosensors is presented. The mediators (ferrocene and its derivatives) and the enzyme (glucose oxidase, GOD) are co-immobilized in a sol–gel derived silica (SGS) matrix containing polyelectrolyte (PE) to produce highly stable and sensitive glucose sensors on different base electrodes. The effective immobilization of the enzyme and the mediators comes from the co-operative entrapment by the PE and the three-dimensional interpenetrating network of the (SGS) membrane. The featured PE–SGS membrane provides a favorable environment and functional ligand ‘locking’ mechanism for the immobilized enzyme to remain in its active conformation for high biological activity, and shuttles electrons efficiently from electrode to enzyme via the immobilized mediator without mediator leaching even after long periods of operation. Important sensing parameters such as the catalytic rate constant (k), the apparent Michaelis–Menten constant (KMapp) and the substrate specificity factor (k/KMapp) are evaluated and discussed. The fabricated biosensors demonstrated a useful working range up to 80 mM with fast response time less than 10 s, and a detection limit around 0.3 mM. [Copyright &y& Elsevier]