Structural,optical and electric properties of nanocrystalline MgSe thin films deposited by chemical route using triethanolamine as a complexing agent

Semiconducting nanocrystalline thin films of magnesium selenide have been prepared using economic chemical bath deposition technique onto glass substrates at room temperature. The deposition bath consists of magnesium chloride, triethanolamine, hydrazine hydrate and selenium dioxide. The quantity of triethanolamine in the deposition bath was varied to study its effect on growth process as well as on physical properties of MgSe. The deposited films were characterized using X-ray diffraction, scanning electron microscopy and atomic force microscopy techniques. The effect of complexing agent (TEA) on optical and electrical properties is reported. It was found that as the triethanolamine in deposition bath increases, optical band-gap and electrical resistivity decreases. The thermo-emf measurement shows p-type nature of MgSe.     

Light-assisted chemical deposition of highly (0001) oriented zinc oxide film

Highly (0001) oriented zinc oxide (ZnO) films of smooth layer type and hexagonal columns have been prepared on quartz glass substrates at temperature as low as 323 K by UV light assisted chemical deposition from an aqueous solution containing hydrated zinc nitrate and dimethylamine-borane (DMAB).     

Extraction of metal ions using chemically modified silica gel: a PIXE analysis

Organic ligand with carboxyhydrazide functional group was immobilised on the surface of silica gel and the metal binding capacity of the ligand-embedded silica was investigated. The functional group was covalently bonded to the silica matrix through a spacer of methylene groups by sequential reactions of silica gel with dibromobutane, malonic ester and hydrazine in different media. Surface area value of the modified silica was determined. The changes in surface area were correlated with the structural change of the silica surface due to chemical modifications. A mixture solution of metal ions [K(I),Cr(III),Co(II),Ni(II),Cu(II),Zn(II),Hg(II) and U(VI)] was treated with the ligand-embedded silica in 10(-3) M aqueous solution. The measurement of metal extraction capacity of the silica based ligand was done by multielemental analysis of the metal complexes thus formed by using Proton Induced X-ray Emission (PIXE) technique.     

Glass of the past: The degradation and deterioration of medieval glass artifacts

Medieval artifacts made of glass are at a serious disadvantage concerning the chemical stability compared with ancient or common modern glasses. The total amount of silica and other network formers such as alumina is very low and potassium instead of sodium was introduced into the silicate structure by using local raw material. By means of scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS) and nuclear reaction analysis (NRA) a weathering mechanism governed by an ion exchange process could be determined for medieval glass paintings exposed to the ambient air for centuries. Additionally, the leached glass surface of medieval hollow glass artifacts found in a well and exposed to moist earth show a brown discoloring due to the oxidation of Mn(II) to Mn(IV) oxide. That process can be converted by a treatment of the glass objects in an aqueous hydrazine solution.     

Mesopore-free hollow silica particles with controllable diameter and shell thickness via additive-free synthesis

Mesopore-free hollow silica particles with a spherical shape, smooth surface, and controllable diameter (from 80 to 300 nm) and shell thickness (from 2 to 25 nm) were successfully prepared using an additive-free synthesis method. Different from other hollow particle developments, a mesopore-free shell was produced because of the absence of additive. Although common reports pointed out the importance of the additional additive in pasting and growing silica on the surface of a template, here we preferred to exploit the effect of the template charge in gaining the silica coating process. To form the silica, basic amino acid (i.e., lysine) was used as a catalyst to replace ammonia or hydrazine, which is harmless and able to control the silica growth and produce hollow particles with smooth surfaces. Control of the particle diameter was drastically achieved by altering the size of the template. The flexibility of the process in controlling the shell thickness was predominantly attained by varying the compositions of the reactants (i.e., silica source and catalyst). The present mesopore-free hollow particles could be efficiently used for various applications, especially for thermal insulator and optical devices because of their tendency not to adsorb large molecules, as confirmed by adsorption analysis.     

Fiber-optic glucose biosensor based on glucose oxidase immobilised in a silica gel matrix

A monolithic silica gel matrix with entrapped glucose oxidase was constructed as a bioactive element in an optical biosensor for glucose determination. Physicochemical and biochemical characterizations of the catalytic matrix were performed, and the intrinsic fluorescence of immobilised glucose oxidase (GOD) was investigated in the UV and visible range by performing steady state and time course measurements. In all cases, the silica gel matrix proved to be a suitable support for optical biosensing owing to its superior optical properties (e.g., high transmittance and reliable fluorescence and GOD absorption spectra after immobilisation). From steady state measurements, calibration curves were obtained as a function of glucose concentration. When time course measurements were performed, the silica gel support displayed a larger linear calibration range and higher sensitivity than other immobilisation systems. In addition, a glucose optical biosensor was developed and characterised using as catalytic element GOD immobilised on a gel disk bound to a bundle of optical fibres.     

Silica-stabilized gold island films for transmission localized surface plasmon sensing

Ultrathin gold films prepared by evaporation of sub-percolation layers (typically up to 10 nm nominal thickness) onto transparent substrates form arrays of well-defined metal islands. Such films display a characteristic surface plasmon (SP) absorption band, conveniently measured by transmission spectroscopy. The SP band intensity and position are sensitive to the film morphology (island shape and inter-island separation) and the effective dielectric constant of the surrounding medium. The latter has been exploited for chemical and biological sensing in the transmission localized surface plasmon resonance (T-LSPR) mode. A major concern in the development of T-LSPR sensors based on Au island films is instability, manifested as change in the SP absorbance following immersion in organic solvents and aqueous solutions. The latter may present a problem in the use of Au island-based transducers for biological sensing, usually carried out in aqueous media. Here, we describe a facile method for stabilizing Au island films while maintaining a high sensitivity of the SP absorbance to analyte binding. Stabilization is achieved by coating the Au islands with an ultrathin silica layer, ca. 1.5 nm thick, deposited by a sol-gel procedure on an intermediate mercaptosilane monolayer. The silica coating is prepared using a modified literature procedure, where a change in the reaction conditions from room temperature to 90 degrees C shortened the deposition time from days to hours. The system was characterized by UV-vis spectroscopy, ellipsometry, XPS, HRSEM, AFM, and cyclic voltammetry. The ultrathin silica coating stabilizes the optical properties of the Au island films toward immersion in water, phosphate buffer saline (PBS), and various organic solvents, thus providing proper conditions where the optical response is sensitive only to changes in the effective dielectric constant of the immediate environment. The silica layer is thin enough to afford high T-LSPR sensitivity, while the hydroxyl groups on its surface enable chemical modification for binding of receptor molecules. The use of silica-encapsulated Au island films as a stable and effective platform for T-LSPR sensing is demonstrated.     

Catalytic reduction of U(VI) to U(IV) using hydrogen with platinum loaded on alumina and silica

During the reprocessing of spent nuclear fuel, uranium (U) and plutonium (Pu) are together extracted by employing tri-n-butyl phosphate (TBP)/dodecane mixture and their partitioning is achieved by adding uranous nitrate. The partitioning agent, uranous is conventionally produced by the electrolytic reduction of uranyl nitrate. An alternate route for the reduction of U from (VI) to (IV) using hydrogen (H₂) as reductant was developed using platinum (Pt) based catalyst. Improvements in the development of the catalyst have been carried out in order to reduce the requirement of Pt without affecting the reduction performance. Experiments using 2 wt% Pt loaded on alumina beads and alumina powder have been performed and results are discussed. As the catalyst supported on alumina was found to be unstable in acidic environment, Pt loaded on silica powder has also been developed. Pt loaded on alumina and silica substrates have been tried to envisage the reduction behaviour using H₂ as reductant in presence of hydrazine nitrate which acts as U(IV) stabiliser as well as reductant. Parametric studies have been carried out to optimise the process parameters namely pressure, temperature, U concentration, free acidity, hydrazine concentration and catalyst to U (C/U) ratio. 2 wt% Pt loaded on silica has been selected for further scale up studies for making uranous.     

Gel-silica optics: Theory and application

A new generation of silica optics has resulted from alkoxide-based sol-gel processing of silica including: net shape transmissive optical elements, surface diffractive optics, inorganic doped GRIN optics, organic impregnated optical composites such as dye lasers and scintillators, optics with internal diffraction gratings, laser densified microoptical lenses and arrays, and laser densified waveguides. Processing control of the ultrastructure of the monolith at the time of gelation and during aging is essential to producing the optical devices together with chemical and thermal stabilization of the surface of the pore network prior to densification or impregnation. The process control variables for gel-silica optics are summarized together with spectroscopic analysis and molecular orbital calculations that explain how and why the thermal-chemical processing controls work at a molecular level.     

High Purity Glass Forms by a Colloidal Sol-Gel Process

Novara Technology (NTECH) has developed its own process for bulk silica glass based on Sol-Gel chemistry. The process is characterized by its thermomechanical ideal isotropy of the aerogel and the glass it forms. Remarkable glass properties are: ultrapurity up to 1 ppb or better for single metal contaminant, optical compatibility with high-temperature treatments up to 2000°C, precision mouldability without intrinsic dimensional limitations.The process, that makes large use of the fumed silica Aerosil® in combination with TEOS, is characterized by the synthesis of monolithic material, i.e. a chemically manufactured body with shape and dimensions defined at reaction time, when the whole material is generated as a unit. Process implementation was achieved with the operation of a pilot plant. The road to industrialization besides volume scale-up, readily achieved for the chemical and hypercritical drying sector of the plant, was focused on getting a cost effective procedure.     

Anodic oxidation of hydrazine and its methylderivatives on bare Pt and Pt electrode surfaces modified by underpotential metal adsorbates in acetonitrile

The electrooxidation of hydrazine and its methylderivatives (methylhydrazine and 1,1-dimethylhydrazine) on bare Pt and Pt electrode surfaces modified by underpotential metal adsorbates was studied in acetonitrile. On bare Pt, one-third of the molecules of the substances under examination undergo a two-electron oxidation to the corresponding diimides, while the remaining number of molecules act as the required proton acceptors in neutral acetonitrile. In alkaline solutions, hydrazine undergoes a quantitative four-electron oxidation process, while its methyl derivatives are oxidized quantitatively to the corresponding diimides in the same media. The pronounced inhibition effects on hydrazine oxidation caused by underpotential T1 and Pb adsorbates were interpreted in terms of a change in the chemical interaction of hydrazine molecules and the electrode surface modified by the underpotential metal adsorbates.     

Synthesis and characterization of monodispersed core-shell spherical colloids with movable cores

Gold nanoparticles have been conformally coated with amorphous silica (using a sol-gel method) and then an organic polymer (via surface-grafted, atom transfer radical polymerization) to form spherical colloids with a core-double-shell structure. The thickness of silica and polymer shells could be conveniently controlled in the range of tens to several hundred nanometers by changing the concentration of the reagent and/or the reaction time. Selective removal of the silica layer (through etching in aqueous HF) led to the formation of hollow polymer beads containing movable gold cores. This new form of core-shell particles provides a unique system for measuring the feature size and transport property associated with hollow particles. In one demonstration, we showed that the thickness of a closed polymer shell could be obtained by mapping the electrons backscattered from the core and shell. In another demonstration, the plasmon resonance band of the gold cores was used as an optical probe to follow the diffusion kinetics of chemical reagents across the polymer shells.     

Nuclear Waste Storage in Gel-Derived Materials

For long life nuclear wastes (essentially actinides) research is in progress to propose new matrices with an improvement of the chemical durability. High silica content glasses present high chemical durability, and we describe a process to prepare silica glass embedding the nuclear waste. Porous silica (gel) is used as a host matrix for nuclear waste. Neodymium oxide and cerium oxide are used to simulate the actinide oxides. The gel is soaked in a solution containing the simulant in nitrate salt form.We investigate the effect of the porous network features (pore size distribution) on the ability of the material to soak up the simulating salts. A new kind of gel (composite aerogel) is proposed owing to its large permeability. After drying and nitrate decomposition, the composite material is fully sintered trapping the nuclear waste.The glass-ceramic materials (silica glass + simulating oxide) have been synthesized with simulant content close to 20 weight percent. We show that the 2 simulant oxides behave differently because of their ability to form silicate phases. The chemical durability of the glass-ceramics is investigated. The large improvement of the chemical durability (60 times) compared to the classical borosilicate glasses shows that this containment process can be a suitable way to confine actinides and long life nuclear wastes.     

Microdischarge-Induced Decomposition of Ammonia and Reduction of Silver Ions for Formation of Two-Dimensional Network Structure

Microdischarge-induced reaction processes working at atmospheric pressure create fractal-like network structure of metal nano-particles which shows variable electric and optical properties. Due to their smallness, microdischarges or microplasmas can be installed in a gas-tubing system, and they enable us to create a compact chemical reduction reactor which includes decomposers of molecules, gas flows, and aqueous solutions with metallic ions at atmospheric pressure. Ammonia (NH₃) gas is successfully decomposed in this reactor, and its products which include mainly hydrazine (N₂H₄) and flow in the downstream induce reduction reactions for AgNO₃ solution. Various parameters in the reactor trigger formation of functional patterns of silver nano-particles like partially transparent layers whose conductivity is variable. Optical properties of this equivalent films show some absorption spectra coming from structure resonances, which can be an optical metamaterials in this self-assembly process.     

Acetylferrocene Modified Carbon Paste Electrode; A Sensor for Electrocatalytic Determination of Hydrazine

The electrocatalytic oxidation of hydrazine at a carbon paste electrode spiked with acetylferrocene as a mediator was studied by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In contrast to other ferrocenic compounds, acetylferrocene exhibits a chemical irreversible behavior, but it can act as an effective mediator for electrocatalytic oxidation of hydrazine, too. The heterogeneous electron transfer rate constant between acetylferrocene and the electrode substrate (carbon paste) and the diffusion coefficient of spiked acetylferrocene in silicon oil were estimated to be about 3.45×10^?4 cm s^?1 and 4.45×10^?9 cm² s^?1, respectively. It has been found that under the optimum conditions (pH 7.5) the oxidation of hydrazine occurs at a potential of about 228 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak current of hydrazine was linearly dependent on its concentration and the obtained linear range was 3.09×10^?5 M–1.03×10^?3 M. The detection limit (2σ) has been determined as 2.7×10^?5 M by cyclic voltammetry. Also, the peak current was increased linearly with the concentration of hydrazine in the range of 1×10^?5 M–1×10^?3 M by differential pulse voltammetry with a detection limit of 1×10^?5 M. This catalytic oxidation of hydrazine has been applied as a selective, simple, and precise new method for the determination of hydrazine in water samples.     

化学反应-顶空气相色谱法测定气相二氧化硅表面硅羟基

建立了一种基于化学反应-顶空气相色谱测定气相二氧化硅表面硅羟基含量的新方法.实验取气相二氧化硅放入顶空瓶中于105℃烘箱中加热2 h去除水分,将甲苯稀释的格氏试剂注入密闭的顶空瓶中,格氏试剂与气相二氧化硅表面硅羟基快速反应产生甲烷(CH4),甲烷量与气相二氧化硅表面硅羟基含量成正比.经过气相色谱-氢火焰离子化检测器测定...     

Surface modification of P(EMA-co-HEA)/SiO2 nanohybrids for faster hydroxyapatite deposition in simulated body fluid?

P(EMA-co-HEA)/SiO₂ nanocomposites with 0, 15 and 30 wt% of silica were obtained by copolymerization of ethyl methacrylate, EMA, and hydroxyethyl acrylate, HEA, during the simultaneous acid-catalyzed sol–gel polymerization of tetraethoxysilane, TEOS. A surface modification treatment was applied in order to reduce the induction time for hydroxyapatite (HAp) nucleation, combining a previous NaOH attack to increase the number of surface nucleating sites, and an alternate soaking process in Ca and P solutions to form apatite precursors, prior to the immersion in a simulated body fluid (SBF). The NaOH treatment was not effective by itself in shortening the HAp induction time. It introduced sodium carboxylates in the copolymer but hydrolyzed the silica network excessively, thus reducing the surface nucleating potential of its boundary silanols. Therefore, bioactivity was only due to the surface carboxylate groups of the organic phase. Maybe a controlled dissolution extent of the silica network so as to improve bioactivity could be attained by reducing the duration of the NaOH-treatment. This would be interesting in the hybrid with 30 wt% of silica, because its dense silica network is not able to hydrolyze in SBF without any previous treatment, whereas the silica network in the hybrid with 15 wt% of silica hydrolyzes at the surface promoting the deposition of HAp. The CaP treatment was able to coat the surfaces of the samples with a calcium phosphate layer within minutes. This amorphous calcium phosphate acted as HAp precursor, skipping the induction period in SBF.     

Protoporphyrin IX nanoparticle carrier: preparation, optical properties, and singlet oxygen generation

The present study is focused on developing a nanoparticle carrier for the photosensitizer protoporphyrin IX for use in photodynamic therapy. The entrapment of protoporphyrin IX (Pp IX) in silica spheres was achieved by modification of Pp IX molecules with an organosilane reagent. The immobilized drug preserved its optical properties and the capacity to generate singlet oxygen, which was detected by a direct method from its characteristic phosphorescence decay curve at near-infrared and by a chemical method using 1,3-diphenylisobenzofuran to trap singlet oxygen. The lifetime of singlet oxygen when a suspension of Pp IX-loaded particles in acetonitrile was excited at 532 nm was determined as 52 micros, which is in good agreement with the value determined for methylene blue in acetonitrile solution under the same conditions. The Pp IX-loaded silica particles have an efficiency of singlet oxygen generation (eta Delta) higher than the quantum yield of free porphyrins. This high efficiency of singlet oxygen generation was attributed to changes on the monomer-dimer equilibrium after photosentisizer immobilization.     

Surface patterned graft copolymerization of hydrophilic monomers onto hydrophobic polymer film upon UV irradiation

A random copolymer [p(MMA/DMAB)] composed of methyl methacrylate (MMA) and 2,2‐dimethoxy‐1,2‐di(4‐methacryloyloxy)phenylethane‐1‐one (DMAB), which can simultaneously act as a photoradical initiator and crosslinkable monomer, was prepared by free radical random copolymerization. A hydrophobic film on quartz glass was prepared using p(MMA/DMAB) by a spin‐coating technique. Hydrophilic methacrylic acid (MA) and 2‐methacryloyloxyethyl phosphorylcholine (MPC) were graft‐copolymerized from the hydrophobic p(MMA/DMAB) film in water by photo‐cleavage of the DMAB unit. The graft copolymer of MA and MPC was characterized by infrared and X‐ray photoelectron spectroscopies and contact angle measurements. To confirm that MPC can be grafted onto the surface of the film selectively at only UV‐irradiated sites, photoinduced graft copolymerization of MPC using a photomask was performed to prepare a pMPC patterned p(MMA/DMAB) film. The film was stained using a rhodamine 6G dye that can absorb specifically to pMPC to confirm the pMPC pattern. The p(MMA/DMAB) film can be applied to various fields including photolithography and biomedical applications, because the film surface properties can be controlled using various vinyl monomers selectively on UV‐irradiated sites. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2822–2829     

PEDOT-supported Pd nanoparticles as a catalyst for hydrazine oxidation

Composite poly-3,4-ethylenedioxythiophene (PEDOT)/palladium (Pd) films were obtained by chemical deposition of dispersed palladium nanoparticles into PEDOT conducting polymer matrix. The amounts of palladium particles incorporated into PEDOT films were estimated by electrochemical quartz crystal microbalance measurements. It was shown that palladium loading depends on the time a PEDOT film is exposed in the solution, containing Pd(II)-ions, on the concentration of Pd(II) ions and the film thickness. X-ray photoelectron spectroscopy data have confirmed the presence of metallic palladium in the polymer. The morphology of pristine and composite films as well as the size of Pd nanoparticles and their distribution were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From SEM images, it was found that Pd particles decorated PEDOT globular structures as quasi-spherical particles, and their mean size was dependent on synthesis conditions. The nanoparticles were non-uniformly dispersed on the polymer surface. The comparison of TEM images of composite PEDOT/Pd films obtained for different times of metal loading was made. The remarkable effect of loading time on the size of particles has been established: the mean size of dominating palladium particles was close to 6–10 nm for 30 s of metal deposition, and it was getting larger with the increase of deposition time (close to 15–30 nm for 120 s). It is most likely that with prolongation of synthesis time, the deposition of palladium predominantly proceeds on the already deposited palladium clusters, resulting in the extension growth of their size. Catalytic properties of PEDOT/Pd composite films were studied in respect to hydrazine oxidation by cyclic voltammetry and voltammetry on rotating disk electrode. The obtained data allow to conclude that the process of hydrazine oxidation on PEDOT/Pd composites takes place predominantly on palladium particles, located on the surface or in the near-surface layers of the polymer. The diffusion nature of the limiting current of hydrazine oxidation on composite PEDOT/Pd film in phosphate buffer solution рН = 6.86 was confirmed, and hydrazine diffusion coefficient was calculated. The increase of the limiting currents of hydrazine oxidation with the increase of Pd deposition time was observed, resulting from the increase of the active surface area of palladium particles, acting as microelectrodes. The electroanalytical applications of these nanocomposite materials for the determination of hydrazine were demonstrated.