Sol-gel Composite Film Research Articles

Synthesis and fluorescent thermal response of sol-gel SiO2 composite film containing nanodiamonds

Fluorescence of negatively charged nitrogen-vacancy color centers in nanodiamond is applied in nanoscale sensing. Here, we generated a stable transparent composite ND-SiO2 film by introducing well-dispersed nanodiamonds into silica sol with sol-gel method and spin coating. The transmission electron microscope, X-ray diffraction and Raman curves all can demonstrate homogeneous dispersion of nanodiamond particles in the silicon dioxide film. The hybrid coating displayed significant temperature dependence by studying the fluorescence behavior from liquid nitrogen temperature to room temperature. With rising temperature, the red shift in zero phonon line position, reduction in intensity, extension in the full width at half maximum and decrease in amplitude were obviously typical characteristics. In addition, the sensitivity was 19 K Hz−1/2 at 80K, while it increased to 28 K Hz−1/2 at 300K.

The role of embedded 2-ABT@Cu-BTC MOF on the anti-corrosion performance of electro-assisted deposited silica sol-gel composite film

Using electro-assisted sol-gel method, composite coatings of silica sol-gel reinforced with metal-organic frameworks are formed on a nickel binary alloy. The metal-organic framework of Cu-1,3,5-tricarboxylate (Cu-BTC MOF) embedded in the sol-gel matrix acts as the reinforcing phase. Cu-BTC MOF loaded with 2-aminobenzothiazol (2-ABT) was prepared by the encapsulation method. The resulting micro-particles were characterized and the encapsulation of the 2-ABT inhibitor was confirmed. Loading capacity was about 10.7 mg of 2-ABT per 100.0 mg of modified Cu-BTC MOF. The release of the inhibitor has been investigated by cyclic voltammetry and it has been determined that 40% of 2-ABT is released after 24 h. The mechanism of release is based on the low electrostatic attraction between inhibitor molecules in the outer layer of Cu-BTC MOF. The effect of Cu-BTC MOF and 2-ABT@Cu-BTC MOF on the corrosion parameters of silica sol-gel coating was investigated by electrochemical experiments in a 3.5 wt% NaCl solution. It was shown that encapsulation of corrosion inhibitor can effectively protect the silica sol-gel composite coating against corrosion. Loading MOFs with 2-ABT inhibitor retards the corrosion process of the coating during storage in the corrosive solution.

H2S gas sensing performance and mechanisms using CuO-Al2O3 composite films based on both surface acoustic wave and chemiresistor techniques

Surface acoustic wave and chemiresistor based gas sensors integrated with a sensing layer of sol-gel CuO-Al2O3 composite film were fabricated and their performance and mechanisms for H2S sensing were characterized and compared. In the composite film, CuO nanoparticles provide active sites for adsorption and reaction of H2S molecules while Al2O3 nanoparticles help to form a uniform and mesoporous film structure, both of which enhance the sensitivity of the sensors by providing numerous active CuO surfaces. Through the comparative studies, the SAW based H2S sensor operated at room temperature showed a lower detection limit, higher sensitivity, better linearity and good selectivity to H2S gas with its concentration ranging from 5 ppb to 100 ppm, compared with those of the chemiresistor sensor, which are mainly attributed to the effective mass sensing properties of the SAW sensor, because a minor change in the mass of the film caused by adsorbed H2S molecules would lead to a significant and monotonous change of the resonant frequency of the SAW devices.

Tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence ethanol biosensor based on ionic liquid doped titania-Nafion composite film

A highly sensitive tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)32+] electrogenerated chemiluminescence (ECL) biosensor for the detection of ethanol based on ADH and NAD+ cofactor with ionic liquid (IL) doped sol-gel titania-Nafion composite film has been developed. Regardless of the type of the ILs, the incorporation of IL in the composite resulted in the enhancement in both the electron transfer and diffusion rates in the composite modified electrode, thus leading to dramatic increase in ECL intensity. Among several ILs tested, 1-butyl-3-methylimidazolium with chloride counter anion was most effective for the construction of the Ru(bpy)32+ ECL biosensor. Two-layer system with the inner layer of Ru(bpy)32+ immobilized in IL-titania-Nafion composite film and the outer layer of ADH immobilized in titania-Nafion composite film has been used to maintain the activity of the enzyme and the overall stability of the ECL biosensor. The present biosensor exhibited linear response towards ethanol with a linear dynamic range of 1.2 × 10−5 M–2.5 × 10−1 M and a detection limit of 5.0 × 10−6 M (S/N = 3). The outstanding dynamic range showed the applicability of the present biosensor for ethanol detection not only in human blood but also in a variety of different fields such as alcoholic beverages or other commercially available products.

Mn-Doped CaBi4Ti4O15/Pb(Zr,Ti)O3 Ultrasonic Transducers for Continuous Monitoring at Elevated Temperatures

Continuous ultrasonic in-situ monitoring for industrial applications is difficult owing to the high operating temperatures in industrial fields. It is expected that ultrasonic transducers consisting of a CaBi4Ti4O15(CBT)/Pb(Zr,Ti)O3(PZT) sol-gel composite could be one solution for ultrasonic nondestructive testing (NDT) above 500 °C because no couplant is required and CBT has a high Curie temperature. To verify the high temperature durability, CBT/PZT sol-gel composite films were fabricated on titanium substrates by spray coating, and the CBT/PZT samples were tested in a furnace at various temperatures. Reflected echoes with a high signal-to-noise ratio were observed up to 600 °C. A thermal cycle test was conducted from room temperature to 600 °C, and no significant deterioration was found after the second thermal cycle. To investigate the long-term high-temperature durability, a CBT/PZT ultrasonic transducer was tested in the furnace at 600 °C for 36 h. Ultrasonic responses were recorded every 3 h, and the sensitivity and signal-to-noise ratio were stable throughout the experiment.

Highly sensitive electrochemical capsaicin sensor based on graphene-titania-Nafion composite film

A highly sensitive electrochemical capsaicin sensor utilizing graphene-doped sol-gel titania-Nafion composite film modified glassy carbon electrode (GCE) is presented. The composite modified GCE is characterized by scanning electron microscopy and its electrochemical properties by electrochemical impedance spectroscopy and cyclic voltammetry. The composite modified GCE facilitates the direct adsorption of capsaicin on the electrode surface via π-π interaction between capsaicin and graphene. Furthermore, the present composite modified electrode not only significantly enhances the oxidation peak current, but also decreases its oxidation peak potential, indicating that the graphene in the titania-Nafion composite clearly exhibits good electocatalytic ability to oxidize capsaicin. Under the optimized conditions, the present electrochemical sensor shows a linear response to capsaicin from 0.03 to 10.0μM with a remarkably low detection limit of 8.6nM (S/N=3), which is much lower compared to those obtained with previously reported electrochemical sensors. The recovery tests performed for spiked capsaicin in real samples such as Korean hot pepper and red pepper flakes are satisfactory. Thus, the present capsaicin electrochemical sensor could be implemented as a replacement for the human-subjective Scoville organoleptic test, and can also be further developed as a sensitive portable electrochemical sensor for the determination of capsaicin in food and pharmaceuticals.

Frequency control of sol–gel composite films fabricated by stencil printing for nondestructive testing applications

Ultrasonic transducers made of sol–gel composites have been developed for nondestructive testing (NDT) applications in various industrial fields. Stencil printing of sol–gel composite films has been developed for the reduction of fabrication time and cost. However, it was necessary to develop low frequency (<10 MHz) ultrasonic transducers for inspecting industrial structures under severe high-temperature conditions, because high-frequency components suffer attenuation effect caused by high temperature. To realize this, increasing the thickness of Pb(Zr,Ti)O3 (PZT)/PZT films fabricated by stencil printing was attempted in this study. The samples were fabricated by single-layer stencil printing with a thick stencil mask and multilayer pure stencil printing with prespraying and postspraying. The film thicknesses were 150–185 µm, and the center frequencies of ultrasonic responses were 6.0–6.4 MHz. Throughout three thermal cycles of up to 370 K, the ultrasonic performance was stable, and the frequency characteristics were not markedly different from the beginning to the end of the test. Therefore, low-frequency ultrasonic transducers were successfully manufactured using a stencil-printing-based technique.

Piezoelectric Sol-Gel Composite Film Fabrication by Stencil Printing.

Piezoelectric films using sol-gel composites could be useful as ultrasonic transducers in various industrial fields. For sol-gel composite film fabrication, the spray coating technique has been used often because of its adaptability for various substrates. However, the spray technique requires multiple spray coating processes and heating processes and this is an issue of concern, especially for on-site fabrication in controlled areas. Stencil printing has been developed to solve this issue because this method can be used to fabricate thick sol-gel composite films with one coating process. In this study, PbTiO3 (PT)/Pb(Zr,Ti)O3 (PZT) films, PZT/PZT films, and Bi4Ti3O12 (BiT)/PZT films were fabricated by stencil printing, and PT/ PZT films were also fabricated using the spray technique. After fabrication, a thermal cycle test was performed for the samples to compare their ultrasonic performance. The sensitivity and signal-to-noise-ratio (SNR) of the ultrasonic response of PT/PZT fabricated by stencil printing were equivalent to those of PT/PZT fabricated by the spray technique, and better than those of other samples between room temperature and 300°C. Therefore, PT/PZT films fabricated by stencil printing could be a good candidate for nondestructive testing (NDT) ultrasonic transducers from room temperature to 300°C.

3P3-1 Selective Sintering of Sol-Gel Composite Films by Commercial Microwave Oven

3P3-1 Selective Sintering of Sol-Gel Composite Films by Commercial Microwave Oven

Electrochemical co-deposition of conductive polymer–silica hybrid thin films

Conductive polymers, such as polypyrrole (ppy), have been the subject of numerous studies due to their promising applications in organic solar cells, flexible electronics, electrochromic devices, super capacitors, etc. Yet, their application is still limited as a result of poor processability. Silica has been reported to improve the mechanical strength and adhesion of conductive polymer films. In this work, we propose a controllable electrochemical approach for preparing ppy-silica hybrid thin films from a solution containing both pyrrole and silane monomers. It is known that pyrrole can be electropolymerised using anodic potentials, while silica can be electrodeposited under cathodic potentials. Thus, we studied the formation of ppy-silica hybrid thin films on a stainless steel surface by applying alternating potentials, i.e. cathodic followed by anodic pulses (denoted C + A) or anodic followed by cathodic pulses (denoted A + C). We show that by controlling the deposition potential and time for the cathodic and anodic pulses, the film thickness and composition can be manipulated well as analysed using profilometry and EDX. The element depth profile of the films was characterized using secondary ion mass spectroscopy (SIMS). In essence, for the C + A process, pyrrole diffuses through the cathodically electrodeposited wet silica gel layer and undergoes anodic polymerisation on the substrate, while for the A + C process, silane can be electrodeposited both on top of the anodically electrodeposited conductive ppy films as well as on the stainless steel through the pinholes in the ppy film. This offers a simple approach for tuning the structure of conductive polymer-sol-gel composite films.

Functionalized Ionic Liquid and Sol-Gel Composite Film for the Electrochemical Reduction and Determination of Nitrite without Interference from Dissolved Oxygen

Functionalized Ionic Liquid and Sol-Gel Composite Film for the Electrochemical Reduction and Determination of Nitrite without Interference from Dissolved Oxygen

Electrochemical Sensor for Sensitive Determination of Ga(III) Ion Based on β‐Cyclodextrin Incorporated Multi‐walled Carbon Nanotubes and Imprinted Sol‐gel Composite Film

AbstractA novel sensor for detection of trace gallium ion [Ga(III)] was created by stepwise modification of a gold electrode with β‐cyclodextrin (β‐CD)/multi‐walled carbon nanotubes (MWCNTs) and an ion imprinted polymer (IIP). The sensor surface morphology was characterized by scanning electron microscopy. The electrochemical performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The sensor displayed excellent selectivity towards the target Ga(III) ion. Meanwhile, the introduced MWCNTs displayed noticeable catalytic activity, and β‐CD demonstrated significant enrichment capacity. A linear calibration curve was obtained covering the concentration range from 5.0×10−8 to 1.0×10−4 mol·L−1, with a detection limit of 7.6×10−9 mol·L−1. The proposed sensor was successfully applied to detect Ga(III) in real urine samples.

Selective Amperometric Response to Hydrogen Peroxide at a Protein-incorporated Sol-Gel Hybrid Film-modified Platinum Electrode

A protein-incorporated silica-based sol-gel composite film was chemically modified onto the surface of an anodized platinum (Pt) wire electrode. The organic/inorganic hybrid sol-gel film was composed of 3-aminopropyl triethoxy silane (APTES), tetraethoxy silane (TEOS) and bovine serum albumin (BSA). The incorporation of BSA was found to be effective to enhance the permselectivity of hydrogen peroxide (H2O2) against possible electrochemical interferents, such as ascorbic acid (AA) and uric acid (UA), probably due to the size-exclusion molecule cut-off mechanism. The anodic current responses of the APTES-TEOS-BSA-based sol-gel film-modified Pt electrode to AA and UA (0.1 mM) were suppressed to less than 1/170 and 1/90 of that to H2O2 (0.1 mM), respectively, suggesting the potential possibility of this film for applications to interference-free oxidase-based amperometric biosensors (e.g., glucose, lactate and glutamate biosensors).

Glucose biosensor based on covalent immobilization of enzyme in sol–gel composite film combined with Prussian blue/carbon nanotubes hybrid

A novel electrochemical glucose biosensor was developed based on in situ covalent immobilization of glucose oxidase (GOx) by one-pot chitosan (CS)-incorporated sol–gel process in the presence of Prussian blue deposited multi-walled carbon nanotubes hybrids (PB/MWNTs) using 3-isocyanatopropyltriethoxysilane (ICPTES) as both a sol–gel precursor and a covalent coupling agent for GOx and CS. The electrode modified with the PB/MWNTs-GOx-CS-ICPTES sol–gel composite film showed good electrical conductivity and effective low-potential electron transfer mediation toward H 2O 2 reduction attributed to the incorporation of PB/MWNTs. The biosensor exhibited a linear response to glucose in the concentration range from 2.5 × 10 −5 to 1.3 × 10 −3 M with a correlation coefficient of 0.9998, a detection limit of 7.5 × 10 −6 M, a low response time (10 s), good sensitivity and high anti-interference ability. Compared with the control biosensor based on the traditional tetraethoxysilane derived sol–gel composite film, the biosensor showed a similarly small apparent Michaelis–Menten constant of 3.67 mM but much higher electrochemical and biosensing stability.

Fabrication of superhydrophobic sol–gel composite films using hydrophobically modified colloidal zinc hydroxide

A superhydrophobic sol–gel composite film was fabricated by incorporating hydrophobically modified colloidal zinc hydroxide (CZH) in sol–gel matrix. CZH was prepared by controlled precipitation and modified by treatment with stearic acid. The concentration of stearic acid and stirring time were optimized to obtain modified CZH with very high water contact angle (WCA) of 165° and sliding angle (SA) < 2°. X-ray diffraction (XRD) analysis has shown that the crystal structure of CZH was mainly composed of ε-zinc hydroxide and the modified CZH indicated the presence of zinc stearate. The modified CZH film exhibited a microstructure which resembled clusters of interconnected rods creating roughness on the film surface. The modified CZH suspension was dispersed in an acid-catalyzed sol of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS) and spray-coated on glass slides to prepare sol–gel composite coatings. The concentration of CZH in the composite film was optimized to obtain superhydrophobic surfaces. FTIR spectrum also confirmed the presence of zinc stearate in the composite film. The method is simple and cost-effective and does not involve any expensive chemicals or equipments.

Direct electrochemistry and electrocatalysis of myoglobin based on silica-coated gold nanorods/room temperature ionic liquid/silica sol–gel composite film

A novel biosensor based on the silica-coated gold nanorods (GNRs@SiO 2) and hydrophilic room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluroborate ([bmim][BF 4]) was fabricated for the determination of hydrogen peroxide (H 2O 2) and nitrite. GNRs@SiO 2 can not only act as a binder to hinder [bmim][BF 4] (RTIL) leaking from the electrode surface, but also provide a favorable microenvironment for direct electrochemistry of myoglobin (Mb). A pair of well-defined and quasi-reversible redox peaks of Mb was obtained at the GNRs@SiO 2–Mb/RTIL–sol–gel composite film modified GCE (GNRs@SiO 2–Mb/RTIL–sol–gel/GCE) through direct electron transfer between Mb and the underlying electrode. This biosensor showed an excellent electrocatalytic activity towards hydrogen peroxide and nitrite. The linear range for the determination of H 2O 2 was from 0.2 to 180 μM with a detection limit of 0.12 μM based on the signal-to-noise ratio of 3. In addition, the biosensor also exhibited high selectivity, good reproducibility, and long-term stability. Therefore, this kind of composite film can provide an ideal matrix for protein immobilization and biosensor fabrication.

Structure and photochromic properties of molybdenumphosphoric acid/TiO2 composite films

TiO2 sol-gel composite films with dropping molybdenumphosphoric acid (PMoA) have been prepared by sol-gel method. The structure and constitute of composite thin films were studied with Fourier transforms infrared spectroscopy (FT-IR) atomic force microscopy (AFM), and X-ray diffraction (XRD) patterns, respectively. The photochromic behavior and mechanism of composite thin films were investigated with ultraviolet-visible spectra (UV-vis) and electron spin resonance (ESR). FT-IR results showed that the Keggin geometry of PMoA was still preserved inside PMoA/TiO2 composite thin films, and a charge transfer bridge was built at the interface of PMoA and TiO2 through the Mo-O-Ti bond. Surface topography of the composite film showed obvious changes before/after adding PMoA, and the surface topography of composite films showed obvious changes before/after irradiating as well. Composite thin film had reversible photochromic properties. Irradiated with UV light, transparent films changed from colorless to blue and they can bleach completely with ambient air in the dark. ESR results showed that TiO2 were excitated by UV light to produce electrons, which deoxidized PMoA to produce heteropolyblues. The photochromic process of PMoA/TiO2 system was carried through electron transfer mechanism.

Ionic liquid and nanogold-modified immunosensing interface for electrochemical immunoassay of hepatitis B surface antigen in human serum

A mediator-free electrochemical immunoassay protocol based on a disposable immunosensor for the detection of hepatitis B surface antigen (HBsAg) in human serum was developed. To fabricate such an immunosensor, a layer of sol–gel composite film containing room temperature ionic liquid and chitosan was initially formed on a glassy carbon electrode. Nanogold particles were then adsorbed onto the membrane via the amine groups of chitosan molecules, and then horseradish peroxidase (HRP)-labeled hepatitis B surface antibodies (HRP-anti-HBs) were immobilized onto the nanogold surface. With a non-competitive immunoassay format, the antibody–antigen complex could be formed by a simple one-step immunoreaction between the immobilized HRP-anti-HBs and HBsAg in sample solution. The formed immunocomplex inhibited partly the active center of the HRP, which decreased the immobilized HRP toward the reduction of H2O2. The performance and factors influencing the performance of the immunosensor were evaluated. Under optimal conditions, the current change obtained from the carried HRP relative to H2O2 system was proportional to HBsAg concentration in the range of 1.5–400 ng/mL with a detection limit of 0.5 ng/mL (at 3δ). The reproducibility, selectivity, and stability of the proposed immunosensor were acceptable. Moreover, the proposed immunosensors were used to analyze HBsAg in human serum specimens. Analytical results of clinical samples suggested that the developed immunosensor has a promising alternative approach for detecting HBsAg in the clinical diagnosis.

Shape control synthesis of spheroid and rod-like silver nanostructures in organic–inorganic sol–gel composite

The synthesis of a variety of spheroid and rod-like silver nanoparticles in hybrid organic–inorganic sol–gel composite films was examined. The sol–gel matrix used in this work involves urethane terminated silica network which acts as a stabilizing and coupling agent and can complex with silver atoms through its secondary amine functionality and form stable colloid dispersions. The parameters determining the particles size and shape are the starting concentrations of silver ions, the coordination and reduction abilities of the solvent and the reaction kinetics and temperature. In this work the reduction process of silver ion was performed by DMF in sol–gel polyurethane precursor solution at two reaction temperatures: (a) 40 ∘C and (b) reflux at boiling temperature. The effects of concentration and temperature of solution on the morphology and uniformity of silver nanorods were investigated by UV–VIS spectroscopy, SEM and TEM. Spheroid nanoparticles size was as 10–12 nm. Electron diffraction shows that all nanoparticles have a silver face-centered cubic crystal lattice. The silver nanoparticles obtained in composite films exhibit a strong characteristic extinction peak, due to surface plasmon resonance occurring nearly 420–440 nm.

Influence of powder preparation process on piezoelectric properties of PZT sol-gel composite thick films

In this work, piezoelectric PbZr0.52Ti0.48O3 (PZT) thick films were deposited onto silicon and alumina substrates using sol-gel composite slurry. Thick films prepared with rough and attrited powders are compared. A time stable polymeric PZT sol was first synthesised as the binder. It was then used as a precursor for PZT powder fabrication. Powder attrition ball milling was optimised to reduce the particles size to 200 nm. Composite slurries were obtained by mixing PZT sol with attrited or rough powders and thick films were deposited by dip-coating. The film thickness, roughness and microstructure were studied as a function of powder content, particle size, sol concentration and slurry ageing. Electromechanical measurements were performed. By strictly controlling each step of the thick film fabrication, high coupling factor (thickness mode, kt) can be obtained using both types of powder. Nevertheless, with attrited powder, better and more reproducible effective coupling coefficients in thickness mode (kt up to 46%) were reported on silicon and alumina substrates.