Sol-gel Composite Materials Research Articles

Comparative experiments on a new CaCl2-based composite material and zeolite 13X inside a thermochemical heat storage reactor

Thermal energy storage includes sensible, latent and thermochemical heat storage. The latter is particularly interesting because the heat is stored as a chemical potential, which reduces heat loss in long-term applications. The viability of thermochemical storage systems strongly depends on the energy density of the storage material. The development of high energy density materials is thus essential to achieve compact systems suitable for a wide range of applications. A new sol-gel composite material is investigated here: it is composed of CaCl2 dispersed within a matrix of silica and PEG-600 polymer. Composite materials containing CaCl2 have the highest storage capacities and seem to be the most promising candidates. The aim is to develop a composite that is both efficient and stable. The suitability of the material depends on the ability of the PEG to stabilise calcium chloride and prevent its deliquescence and leakage. The experimental results are compared to those obtained using zeolite 13X, which is a reference adsorbent material.

LiNbO3-based sol-gel composite ultrasonic transducer poled at low temperatures

A LiNbO3 (LN) based sol-gel composite could be suitable for high temperature ultrasonic transducer application at 700 °C, however, poling requires high temperature above 550 °C and it shows relatively low signal strength. In order to realize the polarization temperature reduction of an LN-based sol-gel composite ultrasonic transducer, alumina (AO) and strontium doped titanium oxide (TO) were chosen as sol-gel phase material, and LN/AO and LN/TO films were fabricated onto Inconel substrates. In each polling process, corona discharge after heat treatment in the furnace at 400 °C and at 200 °C was executed for LN/AO and LN/TO, respectively. Ultrasonic measurements up to 700 °C were performed and both transducers were able to confirm the reflected echoes and ultrasonic performance stability at 700 °C. Especially LN/TO showed the highest signal strength compared to previously developed high temperature lead-free sol-gel composite materials, Bi4Ti3O12 (BiT)/BiT and CaBi2Ta2O9 (CBTa)/BiT.

Polarity effect of corona discharge poling for sol-gel composite-based ultrasonic transducers

Corona discharge was produced in air atmosphere by applying positive and negative high voltage to a needle to investigate the poling effects for two kinds of sol-gel composite materials, Pb(Zr, Ti)O3(PZT)/PZT and Bi4Ti3O12 (BiT)/PZT. Concerning piezoelectric constant d33, only polarity was different. The samples poled by negative corona discharge showed superior temperature durability above certain temperatures even though no significant difference was observed regarding ultrasonic performance characteristics such as center frequency, 6 dB frequency bandwidth. When the pulse voltage supplied by pulser/receiver increased, that difference starting temperature decreased and negative corona poling effect increased. Negative corona discharge poling was effective to improve thermal durability of sol-gel composite ultrasonic transducers when normal pulser/receiver with negative excitation pulse voltage was used for measurements.

Fabrication of Coaxial and Confocal Transducer Based on Sol-Gel Composite Material for Optical Resolution Photoacoustic Microscopy.

We have newly developed coaxial and confocal optical-resolution photoacoustic microscopy based on sol-gel composite materials. This transducer contains a concave-shaped piezoelectric layer with a focus depth of 5 mm and a hole with a diameter of 3 mm at the center to pass a laser beam into a phantom. Therefore, this system can directly detect an excited photoacoustic signal without prisms or acoustic lenses. We demonstrate the capability of the system through pulse-echo and photoacoustic imaging experiments. The center frequency of the fabricated transducer is approximately 7 MHz, and its relative bandwidth is 86%. An ex-vivo experiment is conducted, and photoacoustic signals are clearly obtained. As a result, 2- and 3-dimensional maximum amplitude projection images are reconstructed.

Sol–gel composite material characteristics caused by different dielectric constant sol–gel phases

Ultrasonic transducers prepared by a sol–gel composite method have been investigated in the field of nondestructive testing (NDT). Sol–gel composite materials could be ideal piezoelectric materials for ultrasonic transducer applications in the NDT field, and a new sol–gel composite with desirable characteristics has been developed. Three kinds of sol–gel composite materials composed of different dielectric constant sol–gel phases, Pb(Zr,Ti)O3 (PZT), Bi4Ti3O12 (BiT), and BaTiO3 (BT), and the same piezoelectric powder phase, PbTiO3 (PT), were fabricated and their properties were compared quantitatively. As a result, the PT/BT, sol–gel composite with the highest dielectric constant sol–gel phase showed the highest d33 and signal strength. In addition, only PT/BT was successfully poled by room-temperature corona poling with reasonable signal strength.

2E3-4 Room Temperature Poling of Sol-Gel Composite Materials with High Coercive Field Piezoelectric Powder Phase

2E3-4 Room Temperature Poling of Sol-Gel Composite Materials with High Coercive Field Piezoelectric Powder Phase

PbTiO3/Pb(Zr,Ti)O3 sol–gel composite for ultrasonic transducer applications

A new sol–gel composite material, PbTiO3 (PT)/Pb(Zr,Ti)O3 (PZT) was developed for ultrasonic transducer applications, especially for high temperature applications, since long-term monitoring is desired for safety assurance. PT was considered as a good piezoelectric powder candidate because of its reasonable piezoelectric constant, high Curie temperature of approximately 760 K, and low dielectric constant. Approximately 50-µm-thick PT/PZT, PZT/PZT, Bi4Ti3O12 (BiT)/PZT, and CaBi4Ti4O15 (CBT)/PZT films were fabricated on 3-mm-thick titanium substrates and their ultrasonic performances were compared at various temperatures. As a result, PT/PZT poled at 470 and 670 K showed higher sensitivity than PZT/PZT, BiT/PZT and CBT/PZT from room temperature to 630 K. Since PT/PZT showed stable thermal cycle results from room temperature to 630 K, PT/PZT could be a good piezoelectric material for ultrasonic transducer application, not only for high temperatures but also a wide temperature range.

Preparation of Durable Emitter of Electrospray Mass Spectrometry by Covalently Coating the Fused‐Silica Capillary Tip with Carbon‐Nanotube Sol‐Gel Composite Material

AbstractA simple approach for the preparation of emitter of electrospray ionization mass spectrometry by covalently coating the fused‐silica capillary tip with the conductive carbon‐nanotube sol‐gel composite material (CNTSCM) is described. The CNTSCM was prepared by dispersing single‐walled carbon nanotubes in the sol composed of a mixture of 3‐glycidoxypropyltrimethoxysilane and 3‐aminopropyltrimethoxysilane, and ethanol. The long‐term stability of the prepared ESI emitters was demonstrated by at least 180 h of continuous use. Signal intensity obtained by the prepared emitter was mass‐flux sensitive when the flow rate was lower than 500 nL/min, while the signal intensity performed a concentration dependence when the flow rate was in the range of 500–800 nL/min. The usefulness of such a prepared emitter was demonstrated by the analysis of various types of samples such as organic small molecular drugs, oligosaccharide, peptide, and protein.

Two-photon polymerization technique with sub-50 nm resolution by sub-10 fs laser pulses

Nanofabrication of structures with a feature size of sub-50 nm with ultrashort-laser based two-photon polymerization (2PP) technique is presented. The spatial resolution of the 2PP structures depends on the characteristics of the polymer material and the laser system used for fabrication. Here we compare the successful creation of sub-100 nm structures with two different few-cycle laser systems and chemically modified zirconium-based sol-gel composite material using cross-linker for resolution enhancement.

Ionic Liquid and Silica Sol-Gel Composite Materials Doped with N,N,N′,N′-tetra(n-octyl)diglycolamide for Extraction of La3+ and Ba2+

Sol-gel processed silica materials, which incorporated ionic liquids and N,N,N′,N′-tetra(n-octyl)diglycolamide (TODGA), were prepared and used as sorbents for extraction of La3+ and Ba2+ from aqueous solutions. Imidazolium-based ionic liquids (ILs), 1-alkyl-3-methylimidazolium bis(trifluoromethane)sulfonimide ([Cnmim][NTf2], n = 2, 4, 6, 8, 10) were entrapped in these monolithic composite sol-gel sorbents. The corresponding extraction efficiencies were found to be dependent on both the volume of IL used in the silica matrix and the alkyl chain length of the IL cation. The silica composite sorbent containing [C8mim][NTf2] exhibited the best extraction efficiency for La3+ and the best separation factor for La3+/Ba2+. The separation results were analyzed by both Langmuir and Freundlich adsorption isotherm models and the Freundlich model was found to give better fit.

Synthesis and application of multi-walled carbon nanotubes–molecularly imprinted sol–gel composite material for on-line solid-phase extraction and high-performance liquid chromatography determination of trace Sudan IV

A novel composite material of multi-walled carbon nanotubes (MWNTs)–Sudan IV molecularly imprinted polymers (MIPs) was prepared by surface molecular imprinting technique in combination with sol–gel technology. The MWNTs–MIPs were evaluated by scanning electron micrograph (SEM), Fourier transform infrared spectroscopy (FT-IR), and adsorption experiments. The results showed that the MWNTs–MIPs exhibited good selective recognition to Sudan IV. The maximum saturated binding capacity ( Q max) is 63.2 μmol g −1. Applied as sorbent, the MWNTs–MIPs were used for the determination of trace Sudan IV in chilli powder by on-line solid-phase extraction–high-performance liquid chromatography (SPE–HPLC). The results showed that an enrichment factor of 741 was achieved with a loading flow rate of 1.0 mL min −1 for sampling 50 mL. The MWNTs–MIPs provided a fast and convenience determination platform for Sudan IV in real samples.

Synthesis and characterization of particle loaded sol–gel composite material for microfluidic chip system

Sol–gel immobilization provides a simple method for introducing different functions into microfluidic devices. In this study, sol–gel was employed for the immobilization of C4 modified silica particles in microfluidic channels, which were etched in quartz using photolithography and wet etching. The effect of variation in sol–gel synthesis conditions was evaluated by preparing a variety of composite materials. Sol–gel syntheses were carried out under both acidic and basic conditions. The effect of additives was also evaluated by introducing formamide and urea into the sol–gel precursor solutions. Composite materials prepared under different conditions were characterized using SEM visualization, nitrogen adsorption experiments, conductivity ratio of packed to empty channels, and separation experiments. SEM visualization provided qualitative information about the overall morphology of the composite material. In addition, more quantitative characterization was obtained by calculating pore size distributions and by measurements of conductivity ratios. Separation experiments were employed in order to evaluate the accessibility of the C4 functional group in the materials prepared under different sol–gel synthesis conditions. While acidic conditions promoted accessibility of the C4 functional group and improved separations, other conditions lead to reduced accessibility and separation efficacy.

Monolithic silica with bimodal pore size distribution fabricated by self-separated sol–gel composite materials

The sol–gel process of tetraethoxysilane involving the simultaneously occurring cationic polymerization of furfuryl alcohol has been used to fabricate large amounts of monolithic silica having hierarchical bimodal pore size distribution with regular arrayed mesopores. In the key step of the sol–gel polymerization a phase separation on micrometer scale takes place and two different poly(furfuryl alcohol)/silica composite material portions are formed. Each phase consists of a poly(furfuryl alcohol)/silica composite of different quantitative elemental compositions as determined by electron probe microanalysis. The final step involves the thermal decomposition of the poly(furfuryl alcohol)/silica composite material at 900 °C. The discovery of the phase separation among the sol–gel process demonstrates that morphological control can be achieved without additional templates, but under limited molar ratio of tetraethoxysilane/furfuryl alcohol used. The specific advantage of this synthesis is that large amounts in the 100 g scale can be produced using this procedure.

Nanostructured porous sol‐gel materials for applications in solar cells engineering

Two nanostructured Sol-Gel composite materials for application in solar cells engineering were created and studied: the TiO 2 /SiO 2 films for antireflecting coatings of cells, and PMMA/SiO 2 insulating layers on metal substrate for efficient heat extraction from a cell. Structural and optical investigation of the first composite proved that its parameters are adequate to serve the purpose; when doped with the dye absorbing UV light and emitting in the visible, it could also increase quantum yield of a cell. The second composite is designed for use in a hybrid PV/Thermal system, where it could optimize the heat exchange between a cell and solar plane collector, which also leads to an increase of efficiency of the system.

An optical biosensor for multi-sample determination of biochemical oxygen demand (BOD)

An optical biosensor for parallel multi-sample determination of biochemical oxygen demand (BOD) in wastewater samples has been developed. The biosensor monitors the dissolved oxygen (DO) concentration in water through an oxygen sensing film immobilized on the bottom of glass sample vials. The oxygen sensing film contains the tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) dye (Ru(dpp)) the luminescence intensity of which varies with oxygen concentration. A computer-controlled moving optrode head with four blue light emitting diodes (LEDs) was scanned sequentially under each sample vial. The luminescence signal was collected by an optical cable and transmitted to a photomultiplier tube (PMT) and processed by a microcomputer. The microbial samples (activated sludge and Bacillus subtilis were immobilized in a sol–gel composite material of silica and poly(vinyl alcohol)-grafted-poly(vinylpyridine) on the oxygen sensing film. The performance of the microbial film as a function of cell loading, thickness, temperature and pH and in the presence of heavy metals as well as its stability and service life have been investigated. The BOD value was determined from the rate of oxygen consumption by the microorganisms in the first 20 min. The BOD values obtained from this biosensor correlates well with the results of the conventional 5-day BOD test.

Probing the microenvironment of an oligo-(p-phenylene vinylene) derivative encapsulated in polymer-impregnated sol-gel silica matrix

Polymer-impregnated silica sol-gel composite materials are hosts for organics in advanced optics application. An oligo-phenylene vinylene derivative 4,4′-(1,4-phenylene dithenylene)-bis-(N-methyl pyridinium iodide) (OPVD) was introduced to poly(hydroxyethyl methacrylate) (PHEMA)-impregnated silica composite film by the sol-gel process. By comparing the X-ray diffraction, UV-visible spectra, steady-state and time-resolved fluorescence spectra of OPVD in three solid matrices (PHEMA/silica composite film, pure PHEMA film, and pure silica film), the similar results of PHEMA/silica composite film and pure PHEMA film demonstrate that the OPVD is primarily surrounded by a PHEMA-like environment in the composite matrix. The model of such structure is presented, which is useful for further understanding and optimizing of properties of doped sol-gel materials.

The synthesis, characterization and application of Ag–SiO 2–Al 2O 3 sol–gel composites

A new type of tertiary Ag–SiO 2–Al 2O 3 sol–gel composite with various silver concentrations has been prepared and characterized using combined spectroscopic techniques of XRD, XPS, TPR, UV–VIS, DRS and SEM. It was found that the homogeneous Ag–SiO 2–Al 2O 3 glass composites with transparent appearance could be obtained when the silver content is controlled below 20 wt.%. The silver ion species are found to be highly dispersed in the framework of the glass composites and exhibited a unique thermal stability in air. In addition, the use of the Ag–SiO 2–Al 2O 3 sol–gel composite material as promising silver catalysts for the catalytic oxidation of methanol to formaldehyde was demonstrated.

Applications of a versatile sol-gel derived renewable electrode for capillary electrophoresis.

A new electrode has been developed and applied for amperometric detection in capillary electrophoresis (CE), comprised of carbon sol-gel composite material. The versatility of the sol-gel technique permits the flexible configuration of the electrode. The performance of such a sol-gel carbon composite electrode (CCE) is first evaluated in a typical CE application for the detection of purine-based compounds. Application of the CCE is also demonstrated for the detection of phenolic compounds in a micellar system. Separation resolution for non-ionic phenolic compounds can significantly be enhanced by introducing sodium dodecyl sulfate (SDS) at a concentration above its critical micelle concentration (cmc) to the buffer. Another design of the CCE incorporating the electrocatalyst Cu2O is employed for the analysis of sugars and organic acids based on dynamic modification with cetyltrimethylammonium bromide (CTAB). It has been found that the presence of surfactant in the separation buffer does not adversely influence the electrochemical detection using a sol-gel derived carbon electrode.

Single element high frequency (<50 MHz) PZT sol gel composite ultrasound transducers

A sol gel composite process has been used to produce lead zirconate titanate coatings in the thickness range of 3 to 100 microm on aluminum substrates. The complex permittivity (epsilon(33)(S )), elastic stiffness (c(33)(D)), and the piezoelectric constant (h(33)) of the coating and the complex elastic stiffness (c(33)(D)) of the substrate have been determined using impedance measurements and a commercially available software program [Piezoelectric Resonance Analysis Program PRAP 2.0, TASI Technical Software, Kingston, Ontario, Canada]. The complex components of the material parameters account for the losses within the film and the substrate. Sol gel composite films on aluminum have a dielectric constant of 220 with an imaginary component of 1% and an electromechanical coupling coefficient of up to 0.24 with an imaginary component of 3%. These films are applied to the fabrication of a high frequency transducers suitable for ultrasound biomicroscopy (UBM). By combining the sol gel composite material with existing transducer fabrication techniques, single-element focusing transducers have been produced that operate in the frequency range of 70 to 160 MHz. Devices have -6-dB bandwidths up to 52% and minimum insertion losses ranging from -47 to -58 dB. Real-time images of phantom materials and ex vivo biological samples are shown.

Mutually interpenetrating inorganic-organic networks. New routes into nonshrinking sol-gel composite materials

Mutually interpenetrating inorganic-organic networks. New routes into nonshrinking sol-gel composite materials