Sol Concentration Research Articles

Structural Influence on the Thermal Conversion of Self‐Catalyzed HfB2/ZrB2 Sol–Gel Precursors by Rapid Ultrasonication of Oxychloride Hydrates

Sol–gel precursors to HfB2 and ZrB2 are processed by high‐energy ultrasonication of Hf,Zr oxychloride hydrates, triethyl borate, and phenolic resin to form precipitate‐free sols that turn into stable gels with no catalyst addition. Both precursor concentration and structure (a sol or a gel) are found to influence the synthesis of the diboride phase at high temperature. Decreasing sol concentration increases powder surface area from 3.6 to 6.8 m2/g, whereas heat‐treating a gel leads to residual oxides and carbides. Particles are either fine spherical particles, unique elongated rods, and/or platelets, indicating particle growth with directional coarsening. Investigation of the conversion process to ZrB2 indicates that a multistep reaction is likely taking place with: (1) ZrC formation, (2) ZrC reacts with B2O3 or ZrC reacts with B2O3 and C to form ZrB2. At low temperatures, ZrC formation is limiting, while at higher temperatures the reaction of ZrC to ZrB2 becomes rate limiting. ZrC is found to be a direct reducing agent for B2O3 at low temperature (~1200°C) to form ZrB2 and ZrO2, whereas at high temperatures (~1500°C) it reacts with B2O3 and C to form pure ZrB2.

Synthesis and electrochemical characterization of sol–gel-derived RuO2/carbon nanotube composites

Ruthenium oxide was coated on multiwalled carbon nanotubes (MWCNTs) to obtain nanocomposite electrode which has a good response to the pH. To synthesize this electrode, gold and cobalt were coated on a stainless steel 304 substrates, respectively, and then, vertically aligned carbon nanotubes were grown on the prepared substrates by chemical vapor deposition. Gold reduced activity of the stainless steel, while cobalt served as a catalyst for growth of the carbon nanotube. Ruthenium oxide was then coated on MWCNTs via sol–gel method. At last, different techniques were used to characterize the properties of synthesized electrode including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction, and cyclic voltammetry. SEM results showed that the length of the carbon nanotubes varied with reaction time, and in this research, it was maintained around 9 μm with a diameter about 100 nm. Electrochemical analysis revealed that optimum sol concentration and heat treatment temperature to meet the best pH sensing response were 0.1 M RuCl3 sol and 200 °C, respectively. Moreover, the obtained electrode represented a linear and near-Nernstian response (about −63 mV/pH) throughout the whole pH range (2–12) of Britton–Robinson buffer solutions.

Optical characterization of sol–gel derived Nb2O5 thin films

Abstract The optical properties of thin Nb2O5 films, obtained by spin coating of Nb sol on glass and silicon substrates are investigated. The Nb sol was prepared by a sonocatalytic method using niobium chloride dissolved in ethanol. A calculation procedure for reliable and unambiguous determination of optical constants (refractive index and extinction coefficient) and thickness of films is developed that uses transmittance and reflectance measurements and non-linear curve fitting. By means of the developed procedure, the impacts of the sol ageing and the post deposition annealing on the optical properties and thickness of the films are investigated. It is demonstrated that films with controlled thicknesses and refractive index values in the range from 1.82 to 2.20 (at wavelength of 600 nm) could be obtained using different concentrations of the Nb sol and post deposition annealing in the range 60–650 °C. The possibility of fabrication of single layer anti-reflective coating for silicon is discussed.

Formation of ZnO Nanoparticulate Thin Film: Sol-Gel Synthesis and Characterisation

ZnO thin films have been prepared sol gel dip coating method using zinc acetate dehydrate (Zn(CH3COO)2·2H2O, Merck) as cation source, 2-methoxyethanol (C3H8O2, Merck) as solvent and monoethanolamine, MEA (C2H7NO, R&M) as sol stabilizer. Film deposition was performed by dip-coating technique at a fixed deposition rate on Corning 7740 glass substrate. The effect of sol concentration on the properties of the thin films is discussed. The effect of the sol concentration on produced ZnO films was found to be significant. X-ray analysis showed that thin films were preferentially orientated along the c-axis direction of the crystal. Besides, the films had a transparency of greater than 80% in the visible region for sol–gels with a zinc content of up to 0.8 M and exhibited absorption edges at ~375 nm.

Hydroxyapatite nanofibers fabricated through electrospinning and sol–gel process

For the replacement and regeneration of hard tissues, hydroxyapatite (HA) has been considered to be one of the most promising biomaterials. To develop new potential HA-based nanofibers, microfibrous composite membranes were first prepared by electrospinning from gelatin–calcium phosphate (CaP) sol blend solutions of various concentrations of CaP sol. The resulting fibers exhibited a fully interconnected porous structure and their average diameter varied from 1.09±0.24μm to 1.44±0.17μm according to the CaP sol content. For the fabrication of HA nanofibers, the thermal treatment of microfibrous composite membrane was carried out. After the thermal treatment at 800°C, the average fiber diameter of GECP20 composite membrane significantly reduced from 1.21±0.21μm to 400±52nm, which may be caused by the elimination of gelatin due to the thermal treatment. ATR-FTIR, EDX, XRD and XRF analyses confirmed that the HA nanofibers could be produced by combining the electrospinning and thermal treatment methods in the sol–gel process. These HA nanofibers showed the same crystalline phase with that of the stoichiometric HA. In addition, the results from simulated body fluid immersion (SBF) test and cell viability assay showed the improved in vivo bone bioactivity of HA nanofibers.

Hierarchical sol–gel derived porous titania/carbon nanotube films prepared by controlled phase separation

Titania/carbon nanotube (CNT) composite films containing hierarchical interconnected porous structure have the advantages of high surface area of mesoporous structure and micro-channels of titania as well as high conductivity and charge separation properties of CNTs. In this research, the composites were prepared with controlled phase separation of titania sol. The main parameters to control the phase separation and macroporous morphology of the films including water content, stabilizer content, polyethylene glycol content, sol concentration, and deposition speed were investigated. X-ray diffraction and Raman spectroscopy confirmed the presence of CNTs together with anatase titania phase. Transmission electron microscopy showed that a very thin layer of titania was formed on CNT surface which improved interface of TiO2/CNT. It was found that macropores grew either with increasing water or polyethylene glycol content. However, stabilizer content and deposition speed had an inverse effect on macropores formation. Furthermore, sol concentration caused binodal decomposition and hence widened the pore size distribution. Although CNTs were ineffective in macropores formation, they strongly affected the transparency and charge separation of the composite films.

Preparation of an anti-oxidative SiC/SiO2 coating on carbon fibers by a sol–gel method

A SiC/SiO2 ceramic coating on carbon fibers was prepared by a sol–gel method followed by heat treatment at high temperature. The structure and the morphology of the SiC/SiO2 coating were characterized by X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. The oxidation resistant properties of the carbon fibers with and without the coating were compared by thermogravimetric analysis. Results indicate that a uniform and continuous coating can improve the oxidation resistance of carbon fibers. The oxidation resistance of the coated carbon fibers increased with increases in the sol concentration and heat treatment temperature. A coating of thickness 300 nm increased the onset oxidation temperature by about 200 ° C and the single fiber tensile strength was decreased by 37.7% compared with the pristine carbon fibers. After isothermal oxidation at 700 ° C for 90 min, the single fiber tensile strength of the coated carbon fibers was decreased to 1.37 GPa. The oxidation resistance of the fibers was decreased when the coating thickness exceeded 400 nm due to the spallation of the coating. [New Carbon Materials 2013, 28(3): 208–214]

A novel sol-gel multi-layer approach for cotton fabric finishing by tetraethoxysilane precursor

The way of producing functional textile finishings by the sol-gel process using a multistep approach, consisting of consecutive depositions of sol layers on cotton fabric, for obtaining architectures with a different number of layers (namely, 1, 3 or 6 layers) is discussed. To this aim, tetraethoxysilane (TEOS) has been used as a precursor and the role of such architectures has been deeply investigated and correlated with the sol concentration and with the presence of the condensation catalyst DBTA (Dibutyltindiacetate). The multi-layer coatings were applied by padding using sols containing appropriate molar ratios of the precursor, anhydrous ethanol, catalyst and hydrochloric acid. The effects of the catalyst during the alkoxide reaction and the silica amount applied by sol-gel treatment on the thermo-oxidative behavior of the treated fabrics were deeply studied. FT-IR ATR spectroscopy, SEM analysis, thermal and thermo-oxidative stability, washing fastness, flammability and mechanical properties of the sol-gel treated cotton fabrics have been also investigated. The results obtained should be interpreted according to the properties investigated. The higher the concentration and the number of layers of the inorganic matrix, the higher the heat protection of textile samples. However, the resulting coating was so rigid that it modified the mechanical properties and particularly it decreased the wear resistance according to Martindale test. To improve the mechanical properties the best results were obtained by modulating a lower concentration of the matrix using a layered approach. In all cases, high adhesion of the coating to the textile fabrics was observed.

A study of electrolytic coagulation of gold sols by the method of localized surface plasmon resonance spectroscopy

Surface plasmon resonance spectroscopy has been employed to study the aggregation of gold sols with average nanoparticle sizes of 15–35 nm under the action of an indifferent electrolyte (NaCl). The structure of resulting aggregates has been established as depending on the coagulation regime. In the regime of fast coagulation, anisotropic aggregates with branched structure are initially formed; then, they are transformed into denser aggregates with a lower degree of anisotropy. The change of the aggregate structure accelerates with an increase in hydrosol concentration. At the same time, slow coagulation obviously yields denser aggregates, the structure of which is independent of the sol concentration and particle size. A procedure has been proposed for estimating the critical coagulation concentration of gold hydrosols based on the analysis of variations in their extinction. It has been found that the critical coagulation concentration increases with a reduction in the sol concentration and gold nanoparticle size.

Antimicrobial films containing lysozyme for active packaging obtained by sol–gel technique

Antimicrobial packaging is a promising form of active packaging that refers to the incorporation of antimicrobial agents into packaging systems with the aim to extend the product shelf life maintaining its quality and safety. In our work an antimicrobial active packaging based on poly(ethylene terephthalate) (PET) was prepared by sol–gel route, incorporating as antimicrobial agent lysozyme with the aim to obtain packaging films with controlled release properties. The fine tuning of the sol concentration and viscosity as well as the dip-coating extraction rate, allowed to deposit on the external surface of the PET support uniform coatings with controllable thickness at the sub-micron scale. FTIR microspectroscopic and tapping mode-Atomic Force Microscopy (TM-AFM) measurements were used to characterize the prepared coatings.The antimicrobial activity of the obtained surface modified films was tested on agar plates against Micrococcus lysodeikticus. Furthermore, the stability of the coating was evaluated in order to verify a possible migration of lysozyme to a liquid media (buffered solution at pH 6.2), due to a possible release from the plastic substrate. The quantitative determination of the released lysozyme in the buffered solution was performed by HPLC UV-DAD. Results show that the incorporation of lysozyme into the sol–gel modified PET do not lead to a loss of activity of the enzyme, and suggest a significant potential for the use of these packaging materials.

Randomly organized and self-assembled Na0.5Bi0.5TiO3 nanodots elaborated by sol–gel and pulsed laser deposition routes

This work reports for the first time on the elaboration, by both chemical (sol–gel) and physical (pulsed laser deposition) routes, of lead-free ferroelectric Na0.5Bi0.5TiO3 nanodots deposited on bare c-sapphire single crystal substrates presenting a 5° miscut angle along the [110] direction. Prior to any deposition, the sapphire substrates were treated at 1350°C, during 24h in air, in order to increase the height of the surface steps, reaching by this way ~8nm. The experimental parameters adjusted for the growth of Na0.5Bi0.5TiO3 dots were the concentration of sols and the number of laser pulses (50 and 100) for the sol–gel and pulsed laser deposition routes, respectively. Whereas the sol–gel route leads to randomly organized Na0.5Bi0.5TiO3 nanodots in respect to the surface steps, the pulsed laser deposition route provokes the self-assembly for some important proportion of these dots along the same surface steps. Despite the lack of organization for the sol–gel dots, the latter present a much more regular distribution in size (~100 and ~10–20nm as an average lateral dimensions and height, respectively) compared to dots deposited by laser ablation, where three different populations of grains can be observed. In each case, the dots do not seem to be epitaxially grown.

Growing parameters and quality of ZnO seed-layer film. Part 2

The results of deposition of ZnO seed-layer on the silicon substrate, Al-coated silicon and Al-coated lithium niobate substrates by sol-gel method at sol concentration of 0,8 and 1,2 M were introduced. It was shown that film roughness and grain size had increased with increasing of the sol concentration. The new results of synthesis of ZnO vertically oriented nanorods on the obtained thin seed-layer on the silicon substrate by hydrothermal method were presented. The diameter and density of synthesized ZnO nanorods were defined, the dependence between such geometrical parameters and seed-layer properties was shown. The obtained results could be applied for design of acoustic wave sensors and nanoscale devices.References 5, figures 5

Soil humic acid aggregation by dynamic light scattering and laser Doppler electrophoresis

AbstractHumic acids (HAs), similar to other fractions of humic substances (HSs), have a large number of reactive functional groups enabling them to aggregate in solutions. Regardless of the origin of humic acid (aqueous or soil), this aggregation process is dependent on environmental conditions and strongly influences the mobility of soluble ionic and molecular pollutants. The aim of this work was to monitor the aggregation process of two humic acids isolated from different mineral soils (IHSS Elliot soil HA standard and Rendzic Leptosol HA) in the 2–11 pH range. Changes in aggregate size in HA sols were followed up using dynamic light scattering (DLS), while zeta potential (ZP) measurements in the same pH range were performed applying laser Doppler electrophoresis (LDE) technique. The effect of HA sol concentration and soil source on aggregation was examined as well. Besides, HA samples were characterized using Fourier transform infrared (FT‐IR) spectroscopy. By inspecting HA‐particle‐size dependence on pH, it can be concluded that both HAs in corresponding sols behave as molecular aggregates or supramolecular structures, formed from small individual moieties (sizes < 10 nm) at higher pH values. The ZP vs. pH curve for both HAs revealed the ZP minimum in the 5–7 pH range, caused most likely by dissociation of acidic functional groups prevailing at lower pH values and deaggregation predominating over dissociation at higher pH values.

45S5 bioactive glass–ceramic coated AZ31 magnesium alloy with improved corrosion resistance

To control the biodegradation rate, 45S5 glass–ceramic coatings were prepared on the commercial AZ31 magnesium alloy substrates by dip-coating method from a synthesized sol–gel. Sol concentration, calcination temperature and dip-coating cycle have been optimized to prepare the compact coatings. The results showed that homogeneous and crack-free coatings with a thickness of 0.48–1.00μm, consisting of amorphous phase and Na2Ca2Si3O9, were successfully fabricated on AZ31 magnesium alloys. The effects of these coatings on the corrosion behavior of the magnesium alloy substrates have been investigated in vitro by soaking samples into modified simulated body fluid (m-SBF) for different periods. It was found that optimized 45S5 glass–ceramic coatings could slow down the degradation rate and decrease the mass loss of the magnesium alloy substrate from 78.04% to 2.31% in the 7th day test, showing a good anti-corrosion property in a certain period. Meanwhile, calcium-deficient hydroxyapatite deposition was observed on the surface of sample 3A500, indicating its biomineralization property in m-SBF. Nevertheless, cracking of the coating during the immersion test is the major factor for 45S5 glass–ceramic coatings to fail to protect the magnesium alloy substrates in the later immersion period.

Effect of Tetraethoxysilane (hybrid sol) on chemical and abrasion resistance, and dyeability of nano polyamide mat

This work deals with the application of inorganic–organic sol–gel layer on polyamide nanofabrics to protect nanofibres against chemical and mechanical damages. To this aim, fabric specimens with different silica concentration (1, 5, 10, 20 and 40 %) have been prepared. Layers were deposited on polyamide nanofabrics by pad-dry-cure technique. Permeability was defined as the rate of airflow perpendicular to a test sample under specified conditions for the test area, pressure gradient, and time according to DIN EN ISO 9237. Abrasion resistance testing was performed for determining the weight loss of samples before and after sol–gel treatment. For chemical resistant measurement, Formic Acid was used. Infrared spectroscopy was also used for investigation of the chemical structure of the treated polyamide nano mats. The morphology of the fabrics was observed using a Scanning Electron Microscope. Also both untreated and sol–gel treated samples were dyed using cationic dyestuff and dyeability of polyamide nanomats after treating by hybrid sol were compared with untreated one. The results indicate that the K/S value of CI. Basic Red 46 are enhanced by increasing the concentration of Tetraethoxysilane based sol, respectively. Also by increasing the concentration of sol–gel to 50 %, the greatest resistance to formic acid was achieved.

Synthesis and structural characterization of Ga-ZnO nanodisk/nanorods formation by polymer assisted hydrothermal process

Abstract Synthesis and characterization of Ga-doped ZnO nanodisk and the formation of nanodisk/nanorod hybrid morphologies on AlN/Si substrate by polymer assisted one-pot hydrothermal process have been studied. The low concentration of Ga-ZnO sol (0.2 M) and optimized concentration (0.5 M) of Zinc sol is used to vary the morphology and physico-chemical properties. Varying amounts of Ga (1%–3%) doped ZnO nanodisks have also been synthesized and characterized. The morphology and structural properties were determined by field emission scanning electron microscopy (FESEM) and X-ray diffraction techniques. Ga-ZnO nanodisk shows major intense X-ray diffraction peak at ZnO (101). X-ray photoelectron spectroscopy (XPS) confirms the effect of gallium doping and variation in their surface property after Ga doping in ZnO. FESEM images clearly confirm the pure nanodisk formation for Ga-ZnO (0.5) at optimized ZnO concentration and hybrid nanodisk/nanorod formation obtained for Ga-ZnO (0.2) at lower ZnO concentration. The pure Ga-ZnO (0.5) nanodisk on AlN/Si thin film substrate showed effective response and fast recovery time towards UV light sensing in dark condition compared to low concentration route prepared Ga-ZnO (0.2)/AlN/Si sample.

Influences of dopant concentration in sol–gel derived AZO layer on the performance of P3HT:PCBM based inverted solar cell

Organic solar cells based on P3HT:PCBM bulk heterojunction with an inverted structure have been fabricated using aluminum doped ZnO (AZO) as their electron transport layer, which was prepared by sol-gel route with 2-methoxyethanol as the solvent. The influences of Al concentration on the surface morphology and electrical properties of AZO layer were investigated by atomic force microscopy, X-ray diffraction and Hall effect measurements. The experimental results indicate that Al concentration has major influence on the grain size and only minor influence on crystallite size, leading to different surface morphology for different doping concentrations. Doping at high concentration produces higher charge carrier density, but not for charge carrier mobility and its electrical conductivity, which may be also influenced by the surface morphology. The effects of Al concentration in AZO layer were also observed in the J–V (current density–voltage) and small AC impedance characteristics of the fabricated solar cells. The resistance increases with Al concentration, but the capacitance decreases. The solar cell using AZO layer with doping concentration of 0.5wt% shows the smallest impedance and the best J–V characteristics with the highest conversion efficiency. These characteristics seem to be correlated with the properties of AZO layer and its interface with the active layer.

Preparation of AZO Thin Films by Level Sedimentation and its Optical and Electrical Properties

AZO precursor solution was prepared with dihydrate zinc acetate as raw materials, ethylene glycol monomethyl ether and ethanol as solvent, ethanolamine as a stabilizer, hexahydrate aluminum chloride as the dopant. The AZO thin films were prepared on glass substrates by using homemade liquid level settlement device. The orthogonal design of the experimental conditions was made to optimize the conditions of this method for the preparation of AZO thin films. The films were analyzed by XRD, UV-Vis, AFM, four-probe, step profiler and other methods. The results show that the optimal conditions for preparation of AZO thin films were as follows: the sol concentration was 0.5mol/L, the Al3+/Zn2+ concentration ratio was 4 at%, the drying temperature was 100 °C for 10 minutes, the pretreatment temperature was 450 °C, the coating layers were 20, the level settling velocity was 5 cm/min, the pretreatment time was 10 minutes, the annealing temperature was 550 °C for 2 h. The average transmittance in visible light and the sheet resistance of the AZO thin films were 88% and 536Ω/□, respectively.

Spraying Silicon and/or Cerium Sols Favorably Mediated Enhancement of Cd/Pb Tolerance in Lettuce Grown in Combined Cd/Pb Contaminated Soil

A field experiment of foliar application of silicon sol, cerium sol and silicon-cerium composite sol of different concentrations on Lettuce in field mildly combined Cd/Pb contaminated soil, was conducted to study effects of the application on yield, quality, antioxidant enzymes (SOD, POD) activities and Cd/Pb absorption, and hence to determine optimum concentration of the silicon sols and cerium sols to be sprayed for relieving toxicity of Cd/Pb. Results showed that spraying silicon and cerium sols could promote growth of Lettuce, increase contents of vitamin C and soluble sugar, and reduce nitrite content, enhance activities of SOD and POD, and inhibit the absorption of Cd/Pb and decrease the content and accumulation of Cd/Pb in shoots and roots, and reduce the risk of Cd/Pb to human body through food chain, while spraying silicon-cerium composite sol of 0.50 g·kg-1 silicon sols (SiO2) and 0.20 g·kg-1 cerium sols (CeO2) was the most significant in effect.

Fabrication and antibacterial properties of silver-coated glass substrate against Escherichia coli, Salmonella typhimurium, and Campylobacter jejuni

The antibacterial effects of silver ion containing film against Escherichia coli, Salmonella typhimurium and Campylobacter jejuni were investigated. Silver nitrate was as used silver source. 0.1, 0.5 and 1.0 mol% concentrations of silver sol were prepared with different amounts of silver nitrate. The silver sol was deposited by spin coating method. The roughness of the film surface was confirmed by atomic force microscopy. Antibacterial experiments demonstrated that silver ion containing film was effective against Escherichia coli, Salmonella typhimurium and Campylobacter jejuni. The morphological changes in the cell wall exposed to silver ion were observed by scanning electron microscope. The transmittance of silver ion containing film on glass substrate decreased as the concentrations of silver ion increased. The mechanical strengths of silver coated glass were slightly enhanced by defect-filling effect of the film. There are lots of bacteria that can cause serious food poisoning in the military equipment and environments. So, the antimicrobial activity of the silver ion containing film showed its potential for use as a coating for medical devices and military equipment.