Ormosil Film Research Articles

Exploring electrochemical reactivity toward ametryn of hybrid silicate films with phosphomolybdic acid

This paper describes the synthesis of organically-modified silicates (ormosils) with phosphomolybic acid (HPMo), and their use to detect ametryn. Gold electrodes coated with an ormosil film made of 3-cyanopropyltriethoxysilane (CPTS) and HPMo were used to detect ametryn between 3.5 and 24 µmol L−1 in an acidic medium. There was no evidence of electroreduction of ametryn when ormosils with HPMo and (3-glycidyloxypropyl)trimethoxysilane (GLPTS) or 3-aminopropyltriethoxysilane (APTS) were used. This difference in behavior is ascribed to aggregation in CPTS ormosil, while GLPTS and APTS ormosils displayed homogeneous surfaces, according to scanning electron microscopy. HPMo had its structure preserved in CPTS ormosil as indicated by 31P solid-state nuclear magnetic resonance spectra. Using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), we inferred that the functional group dipole moments in all ormosils are oriented parallel to the interface. Control of morphology thus seems essential for applications of ormosil films, being particularly promising to monitor environmentally-relevant herbicides.

Ormosil-coated conjugated polymers for the detection of explosives in aqueous environments

A fluorescence-based sensor for detecting explosives, based on a conjugated polymer coated with an ormosil layer, has been developed for use in aqueous environments. The conjugated polymer Super Yellow was spin-coated onto glass substrates prior to a further spin-coating of an MTEOS/TFP-TMOS-based ormosil film, giving an inexpensive, solution-based barrier material for ruggedization of the polymer to an aqueous environment. The sensors showed good sensitivity to 2,4-DNT in the aqueous phase at micromolar and millimolar concentrations, and also showed good recovery of fluorescence when the explosive was removed.

A low temperature solution-processed ormosil film for low-voltage organic field-effect transistors

A high performance, low operating voltage organic field effect transistor (OFET) has been fabricated by utilizing organically modified silicate (ormosil) based film as dielectric. The ormosil film is fabricated by a sol-gel method at low temperature (180 °C) and exhibits a high dielectric (k = 33), a smooth surface (Rq = 0.29 nm) and a low leakage current density (5 × 10−9 A cm−2 at −2 V). The ormosil film contains hydrophobic methyl (CH3) functional groups derived from methyltriethoxysilane (MTES) and these groups produce a surface with hydrophobic character and low surface energy for pentacene film growth. The OFET with the ormosil dielectric exhibits excellent performs with high mobility (0.80 cm2 V−1 s−1), low operating voltage (−1.5 V), low threshold voltage (−0.25 V) and low sub-threshold swing (192 mV dec−1). The result demonstrates that the ormosil film can be used as a high performance dielectric for OFETs, and provides a promising way for low power and low cost organic electronics.

Deposition and characterization of a CoHCF nanorod array in a templated ormosil film on an electrode and application to electrocatalysis

Cobalt hexacyanoferrate (CoHCF) was electrodeposited into an organically modified silica (ormosil) film with a nanoarray of parallel, cylindrical channels, which were obtained using 20-nm poly(styrene sulfonate), PSS, beads as a templating agent. The PSS was bound to the electrode surface with 3-aminopropyltriethoxysilane, APTES. Methoxytrimethylsilane was the ormosil precursor. Electrochemically assisted processing at a positive potential where the hydrogen ion catalyst was generated was used to deposit the ormosil film. Subsequently, the PSS and APTES were removed to provide the pores. The CoHCF was deposited in the 20-nm channels by cyclic voltammetry of a freshly prepared K3Fe(CN)6, CoCl2 mixture with 1.0 mol dm−3 KCl as the supporting electrolyte. Limiting the number of electrodeposition cycles to 10–20 resulted in CoHCF nanorods in the pores, whereas with 50 cycles bulk-form CoHCF spilled over the outer ormosil surface. Electrocatalytic oxidation of cysteine was successfully performed on these nanorod arrays, which showed greater catalytic activity than bulk-form CoHCF.

Stable fluorescent CdS:Cu QDs and their hybridization with carbon polymer dots for white light emission

Facile synthesis of a white light emitting colloidal solution and ORMOSIL film, by hybridizing the orange emission of CdS:Cu and the cyan emission of CPD, as a donor–acceptor pair.

Immobilization of nanobeads on a surface to control the size, shape, and distribution of pores in electrochemically generated sol–gel films

Electrochemically assisted deposition of an ormosil film at a potential where hydrogen ion is generated as the catalyst yields insulating films on electrodes. When the base electrode is modified with 20-nm poly(styrene sulfonate), PSS, beads bound to the surface with 3-aminopropyltriethoxysilane (APTES) and using (CH3)3SiOCH3 as the precursor, the resulting film of organically modified silica (ormosil) has cylindrical channels that reflect both the diameter of the PSS and the distribution of the APTES-PSS on the electrode. At an electrode modified by a 20-min immersion in 0.5 mmol dm-3 APTES followed by a 30-s immersion in PSS, a 20-min electrolysis at 1.5 V in acidified (CH3)3SiOCH3 resulted in an ormosil film with 20-nm pores separated by 100 nm. Cyclic voltammetry of Ru(CN)64- at scan rates above 5 mVs-1 yielded currents controlled primarily by linear diffusion. Below 5 mVs-1, convection rather than the expected factor, radial diffusion, apparently limited the current.

Electrochemistry of redox mediators encapsulated within organically modified silicate matrix in the presence of TiO2 and palladium nanoparticles; application on electroanalysis of ascorbic acid

The encapsulation of redox mediators (i.e. ferrocene methanol, potassium ferricyanide) within the nanostructured network of organically modified silicate (ormosil) on a electrode surface is studied. The redox electrochemistry of modified electrodes made by sol–gel processing of 3-aminopropyltrimethoxysialne (3-APTMS) and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane containing aqueous solution of desired redox mediators (potassium ferricyanide or ferrocene methanol) on electrode surface is reported. The synthetic protocol of ormosil film preparation on electrode surface also enables the encapsulation of titania (TiO2) and palladium when suitable precursors of the same are incorporated during sol–gel processing. The ormosil films are characterized by Atomic force spectroscopy, EDX and cyclic voltammetry. The modified electrodes of three different types (Ormosil, Ormosil–TiO2, and Ormosil–TiO2–Pd) together with either ferrocene methanol or potassium ferricyanide are made to understand the redox behaviour of these electron transfer mediators present within nanostructured domain useful in electrochemical sensing with following major findings: (1) the redox electrochemistry of ormosil-encapsulated ferrocene methanol/potassium ferricyanide show gradual improvement in reversible electrochemical behavior in the order of Ormosil–TiO2–Pd>Ormosil–TiO2 and Ormosil; (2) the presence of TiO2–Pd in ormosil shows better catalytic activity as compared to that of made with only TiO2 toward ascorbic acid (AA) oxidation; (3) ferrocene methanol encapsulated ormosil has been found relatively more efficient mediator as compared to that of potassium ferricyanide toward AA oxidation. The findings justify the novel approach on the fabrication of porous chemically modified electrode of suitable nanogeometry for electroanalytical applications.

Development of novel bioelectrocatalytic platform based on in situ generated gold nanoparticles for biomedical applications

ABSTRACTGold nanoparticles (AuNp) formed using alkoxysilane precursors are utilized in the development of thin organically modified silicates (ormosil) films. The resulting films are optically transparent thereby retaining the optical properties of AuNp. Surface morphology shows that the in situ generated AuNp retained their nanogeometry in the ormosil films. An application of the AuNp encapsulated ormosils is shown in electrocatalytic determination of hydrogen peroxide. For this purpose, potassium ferricyanide is chosen as electron transfer mediator and is encapsulated in the films. Results show that the presence of AuNp in the ormosil matrix dramatically improves the electrochemical behavior of potassium ferricyanide. The ormosil films are utilized for electrocatalytic determination of hydrogen peroxide. In order to investigate the biocompatibility of the ormosil film, horseradish peroxidase (HRP) is incorporated resulting in improvement in oxidation and reduction of peroxide.

Immobilization of horseradish peroxidase and nile blue into the ormosil nanocomposite for the fabrication of hydrogen peroxide biosensor based on MWCNT modified glassy carbon electrode

A novel approach to construct a second-generation amperometric biosensor is described. The classical redox dye nile blue (NB) as mediator and horseradish peroxidase as a base enzyme were coimmobilized into the multiwalled carbon nanotubes (MWCNTs) modified ormosil matrix. Nafion was dispersed into the matrix to enhance the rate of the electron transfer and prevent the cracking of the ormosil film. The surface morphology of MWCNT/NB/NAF/HRP nanocomposite was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry and amperometry measurements were used to study and optimize the performance of the resulting peroxide biosensor. The apparent Michaelis–Menten constant was determined to be 1.1 mM. The effect of pH, applied potential and amount of the HRP enzyme on the electrochemical biosensor has been systematically studied. The fabricated biosensor demonstrated significant electrocatalytic activity for the reduction of hydrogen peroxide with wide linear range from 2 × 10 −7 to 3.8 × 10 −4 M, and low detection limit 1 × 10 −7 M (S/N = 3) with fast response time <3 s. The facile procedure of immobilizing HRP and MWCNTs into the ormosil used in the present work can promote the development of electrochemical research for enzymes, proteins, biosensors, biofuel cells and other bioelectrochemical devices.

Structural insight on organosilica electrodes for waste-free alcohol oxidations

Organic modification of sol–gel catalytic glassy electrodes made of a thin layer of organosilica doped with nitroxyl radical TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) crucially enhances stability in the waste-free oxidation of alcohols to carbonyls in water. Structural comparison between analogous films made of organosilica and unmodified SiO2 shows that the origin of the pronounced stable activity of the ORMOSIL film lies in high hydrophobic and also in the pronounced low degree of hydrophilicity.

Chemically sensitized ormosil-modified electrodes—Studies on the enhancement of selectivity in electrochemical oxidation of hydrogen peroxide

The chemically sensitized ormosil-modified electrodes were made by encapsulating potassium ferricyanide together with organic-ionophore (dibenzo-18-crown-6/Nafion) within ormosil films. The modified electrodes were studied in details from following angles; (1) the effect of variation in potassium ferricyanide concentration in ormosil films; (2) the effect of variation in dibenzo-18-crown-6 concentration in ormosil films; (3) effect of pH on the electrochemistry of ormosil-modified electrodes, and (4) variation in the microstructure of ormosil's films as a function of chemical sensitizers based on atomic force microscopy. Another remarkable contribution of such films based on the bilayer configuration was investigated and the results justified further enhancement in the selectivity for electrochemical sensing of peroxide. Two approaches of bilayer configuration were adopted based on the absence and the presence of chemical sensitizers (Nafion/crown ether) in the upper layer. Excellent results of peroxide sensing were recorded with remarkable finding as given below: (1) introduction of bilayer configuration reduced the sensing of interfering analytes like ascorbic acid, (2) the presence of crown ether in the upper layer caused enhancement in peroxide sensing, (3) the presence of crown ether in the upper layer and Prussian blue in the lower layer increased the detection limit of peroxide sensing to 0.1 μM as compared to that of 0.5 μM recorded in earlier publication, (4) the presence of the bilayer resulted in an increase in the linear range of peroxide sensing, (5) the single layer Prussian blue modified electrode showed electrocatalytic oxidation of ascorbic acid whereas the same with the bilayer containing crown ether reduced the electrochemical sensing of ascorbic acid, followed by an increase in peroxide sensing, and (6) the kinetics of peroxide reduction on the bilayer ormosil-modified electrode was reduced as compared to that on the single layer modified-electrode. The results based on cyclic voltammetry showed a linear increase in cathodic and anodic peak currents with increasing the concentration of ferricyanide within the ormosil film. The results on the effect of pH suggested that lowering of pH caused faster reduction as well as oxidation of peroxide whereas the reverse was recorded with increasing the pH. An increase in dibenzo-18-crown-6 concentration resulted higher oxidation current of peroxide, followed by a decrease in reduction of the same. The results of cyclic voltammery and amperometric measurements were also reported in this communication. The calibration curve of peroxide sensing using the bilayer ormosil-modified electrodes was reported.

Role of palladium in the redox electrochemistry of ferrocene monocarboxylic acid encapsulated within ORMOSIL networks.

We report herein the effect of palladium on the redox electrochemistry of ferrocene monocarboxylic acid encapsulated within an organically modified sol-gel glass network (ORMOSIL). It has been found that amount of palladium and its geometrical distribution significantly alter the redox electrochemistry of FcMCA. The geometrical distribution of palladium has been controlled by two methods: (i) palladium is allowed to link within nanostructured network of the ORMOSIL which was subsequently availed from the reactivity of palladium chloride and trimethoxysilane; (ii) palladium powder is encapsulated together FcMCA thus allowing the presence of palladium within the nanoporous domain. The content of palladium is varied by controlling the reaction dynamics of palladium chloride and trimethoxysilane interaction. For this we initially allowed to trigger hydrolysis, condensation and poly-condensation of trimethoxysilane and dimethyldiethoxysilane in acidic medium and subsequently partially dried ORMOSIL film was allowed to interact with palladium chloride. Even with partially dried ORMOSIL derived from trimethoxysilane and dimethyldiethoxysilane undergoes rapid interaction with palladium chloride and the transparent color of ORMOSIL changed to a black colour due to the formation of palladium silicon linkage. The palladium-silicon linkage has been identified by NMR, UV-VIS and transmission electron spectroscopy. The electrochemistry of FcMCA encapsulated within such an ORMOSIL matrix has been studied. Excellent redox electrochemistry of ferrocene monocarboxylic acid having peak potential separation tending to 0 for a multilayered electrode was investigated. The palladium content has been found to affect the redox electrochemistry of ferrocene as well as electrocatalytic efficiency of new ORMOSIL material. The electroanalysis of NADH is reported. The modified electrode is very sensitive to NADH with lowest detection limit of < 1 μM.

Differential selectivity in electrochemical oxidation of ascorbic acid and hydrogen peroxide at the surface of functionalized ormosil-modified electrodes

Functionalized ormosil-modified electrodes have been developed for electroanalytical applications. The functionalized ormosil-modified electrodes are made by encapsulating potassium ferricyanide/potassium ferrocyanide within ormosil film derived from an optimum composition of 3-aminopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and phenyltrimethoxy silane in acidic medium in absence of Nafion/crown ether (system 1), in the presence of Nafion (system 2) and in the presence of dibenzo-18-crown-6 (system 3). Another modified electrode (system 4) is also developed using the reaction product of potassium ferricyanide, 3-aminopropyltrimethoxysilane and either tetrahydrofuran (THF) or cyclohexanone followed by ormosil formation in the presence of 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and phenyltrimethoxy silane in acidic medium. The electrochemical oxidation of hydrogen peroxide and ascorbic acid conducted at the surface of these four types of functionalized electrodes shows very interesting observations on the selective sensing of ascorbic acid and peroxide. The results based on cyclic voltammetry justify the relative performances on the kinetics of hydrogen peroxide oxidation and reduction. System 3 shows relatively much better oxidation kinetics of hydrogen peroxide as compared to other three systems with relatively weak reduction kinetics whereas system 4 shows relatively faster reduction kinetics of hydrogen peroxide as compared to other three systems. Similarly system 4 shows excellent response to ascorbic acid whereas system 3 shows insensitivity to ascorbic acid under similar experimental conditions. Typical response curve for the analysis of hydrogen peroxide and ascorbic acid using system 3 and system 4 respectively are reported. The results show that system 3 is the best for probing hydrogen peroxide with lowest detection limit of 0.5 μM without any interference from ascorbic acid as commonly encountered using many conventional and chemically modified electrodes.

Corrosion resistance properties of Ormosil coatings on 2024-T3 aluminum alloy

The corrosion resistance behavior of organically modified silane (Ormosil) thin films on 2024-T3 aluminum alloy substrates was investigated using electrochemical impedance spectroscopy (EIS) and accelerated salt spray analysis techniques. Coatings were prepared containing 0–16.6 vol.% alkyl-modified silane, X n Si(OR) 4− n , where X=methyl, dimethyl, n-propyl, n-butyl, i-butyl, n-hexyl, n-octyl, or i-octyl. Coating thicknesses were measured to be in the 6–16 μm range, with the thickest coatings being observed for the highest concentrations of alkyl-modified silane. Contact angle measurements showed an enhancement in hydrophobicity of the Ormosil film imparted by increasing size and concentration of the alkyl-modifiers in the coating. In general, corrosion resistance characteristics, as determined using EIS and salt spray techniques, were found to increase with increasing alkyl-modified silane concentration and alkyl chain length. The best overall corrosion resistance was observed for coating systems containing ≥10.4 vol.% alkyl-modified silane; the hexyl-modified films exhibited corrosion resistance properties superior to the other Ormosil coatings. Immersion studies conducted in 0.5 M K 2SO 4 indicated that coating degradation occurs via hydration of the dense linear chain silicate network leading to the formation of porous cyclic structures.

Characterization of ormosil film for dissolved oxygen-sensing

An organically modified silicate (ormosil) as a matrix for the fabrication of dissolved oxygen-sensing film was produced. The process included taking tetramethoxysilane (TMOS) and dimethyldimethoxysilane (DiMe-DMOS) as precursor and running a reaction at 60 °C in an open vial, which accelerates hydrolysis and condensation and results in the formation of emulsion. The film doped with tris-(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) ([Ru(dpp) 3] 2+) as an oxygen indicator exhibited a good linear relationship, fast response time, long-term stability and enhanced sensitivity to dissolved oxygen after optimizing the sol–gel processing parameters. The properties and the oxygen-sensing behavior of the film were investigated. The results presented here emphasized the significance of ormosil as a matrix for dissolved oxygen-sensing.

Spectroscopic and corrosion resistance characterization of GLYMO–TEOS Ormosil coatings for aluminum alloy corrosion inhibition

Corrosion resistance properties of spray- and dip-coated 3-glycidoxypropyltrimethoxysilane (GLYMO)–tetraethoxysilane (TEOS) Ormosil films have been investigated using salt spray analysis. 1 H– 13 C and 1 H– 29 Si CP/MAS NMR analyses indicate that organic content and hydrolysis water ratio affect the Ormosil structure, and in turn, the corrosion resistance properties of the Ormosil film. For spray-coated samples, films derived from the 11 mol% GLYMO Ormosil prepared using hydrolysis water content ( W=2 and 4) provided good corrosion protection, as this combination of organic content, water ratio, and deposition method produced films of the appropriate thickness, hydrophobicity, and density for good corrosion protection. Films prepared from high organic contents (25 and 67 mol% GLYMO) and low hydrolysis water content values ( W=1 and 2) exhibited the best corrosion resistance for films prepared by dip coating. Presumably, these films comprise a dense network structure with organic groups dispersed throughout the film, providing a hydrophobic barrier coating capable of repelling water and corrosion initiators.

Spectroscopic and corrosion resistance characterization of amine and super acid-cured hybrid organic–inorganic thin films on 2024-T3 aluminum alloy

Primary aliphatic amines (diethylenetriamine, triethylenetetramine, tetraethylenepentamine) and super acids (CF 3SO 3H, HPF 6) have been investigated as room temperature curing agents for hybrid organic–inorganic thin films. 1 H- 13 C CP/MAS NMR analysis indicates that the curing mechanisms promoted by amines and super acids are different, producing Ormosils (organically modified silicates) with different structures. Amine-cured Ormosils were found to be highly crosslinked, dense, and adherent to the underlying aluminum alloy (AA) substrate; analogous super acid-cured Ormosils were oligomeric, exhibiting poor adhesion properties to the underlying metal substrate. The choice of the curing agent was found to affect the Ormosil film corrosion resistance characteristics as indicated by results of potentiodynamic polarization curves and accelerated corrosion tests. Amine-cured films provided corrosion protection, with R corr=37–157 kΩ cm 2, the magnitude of which depended on several processing parameters including stir time prior to amine addition and amine chain length. Super acid-cured films provided poor corrosion resistance, R corr=1–2 kΩ cm 2.

Comparison of single and multilayer coatings based on ormosil and conversion layers for aluminum alloy corrosion inhibition

Corrosion resistance behavior of single and multilayer coatings based on ormosil, trivalent chromium conversion coating (tccc) and hexavalent chromium conversion coatings (hccc) on the surface of 2024-T3 aluminum alloy (AA) was investigated using potentiodynamic polarization curves and accelerated salt spray testing. The magnitude of the corrosion resistance for single layer coatings increased tccc < ormosil < hccc. Multilayer ormosil/ormosil coatings are subject to phase separation, leading to poor performance in the electrochemical and accelerated salt spray testing. The presence of either hccc or tccc in the multilayer film was found to augment the inherent corrosion resistance of the ormosil barrier film. Multilayer coatings composed of either tccc/ormosil or hccc/ormosil were found to exhibit Rcorr values in the range 158–177 kΘcm2. This implies that the environmentally-benign and nontoxic trivalent chromium conversion coating used in combination with an ormosil film may be a potential alternative for hexavalent chromium conversion coatings.

Spin-on-glass thin films prepared from a novel polysilsesquioxane by thermal and ultraviolet-irradiation methods

New dielectric films are prepared by both pyrolytic and photolytic conversion of β-chloroethyl-silsesquioxane (BCESSQ). Film thickness, refractive index, composition, density and morphology are characterized using a palette of techniques including ellipsometry, Rutherford backscattering and forward recoil spectrometry, X-ray reflectivity, and atomic force and electron microscopies. After annealing at 350°C, BCESSQ films, initially 200 nm thick reach about 55% of their original thickness after 20 min. For films heated in air for 4 h, the atom fractions of carbon and hydrogen monotonically decrease to 10 and 30%, respectively, as annealing temperature increases from 225 to 450°C. The BCESSQ reactivity is reflected in the loss of chlorine at 400°C. At 450°C, the film density is 1.88 g/cm3, or 84% of thermally-grown silicon oxide. Upon exposure to ultraviolet ozone radiation, films ranging from ca. 200 to 700 nm are found to convert to ormosil films within 30 min. Surprisingly, the chlorine concentration is found to decrease more quickly than the hydrogen and carbon concentrations, suggesting that the ormosil film evolves HCl leaving a vinyl group of SiCHCH2. This reaction pathway differs from the thermal case. For films prepared by pyrolytic and photolytic methods, atomic force and electron microscopy studies show that the surface is smooth and featureless, the bulk is void free when view at a magnification of 50 000×, and the ormosil/substrate interface is continuous.