Doped Silica Sol Research Articles

One‐step flame retardant/hydrophobic finishing on cotton fabric with ammonium salt of hexamethylenediamine ‐ N, N, N′, N′ ‐ tetra (methylphosphonic acid) doped silica sol

AbstractWith the rapid development of textile technology, single‐function textile finishing is difficult to meet the current needs of people for textiles. Textiles with flame retardancy, superhydrophobicity, UV resistance, and other functions are increasingly favored by people. At present, most of the preparation processes of multifunctional textiles are complex and time‐consuming. In this work, a flame retardant hexamethylenediamine tetramethylene phosphate ammonium salt of hexamethylenediamine ‐ N, N, N′, N′ ‐ tetra (methylphosphonic acid) (AHDTMPA) was synthesized using hexamethylenediamine tetramethylene phosphate (HDTMPA) and urea with aqueous solution as solvent. Then AHDTMPA and cetyltrimethoxysilane were added into the solution with methyl trimethoxysilane (MTMOS) and tetraethyl orthosilicate (TEOS) as precursors to obtain a multifunctional sol. Finally, the multifunctional cotton fabric can be obtained by immersing the cotton fabric in the multifunctional sol in one‐step. The limiting oxygen index (LOI) and water contact angle (WCA) value of the finished cotton fabric was 27.6% and 131.4°, respectively. The FT‐IR characterization results and the SEM analysis verified the synthesis of AHDTMPA. The micro calorimeter combustion (MCC) and thermo gravimetric (TG) analysis indicated that the finished samples had less heat release capacity and less weight loss. The smoke density test showed good smoke suppression of the finished cotton fabric. Moreover, the whiteness of finished samples was nearly unchanged. In this work, the flame retardant and hydrophobic multi‐functional cotton fabric was prepared by one‐step, and the method is simple and efficient. The prepared functional cotton fabrics can be widely used in home textile fabrics, automotive interior fabrics, clothing fabrics, flags, tents, and protective clothing.

Doped silica sol layer coatings on evanescent field fiber Bragg gratings for optical detection of nitroaromate based explosives

Evanescent field etched fiber Bragg gratings (eFBG) were prepared with doped and non-doped nanoporous silica sol coatings for optical detection of the nitroaromatic explosives 2,4-dinitrotoluene (DNT), 1,3-dinitrobenzene (DNB) and trinitrotoluene (TNT). We used 3-aminopropyltrimethoxysilane (APTMS) and tetrabutylammonium hydroxide based receptors (TBAH, C16H37NO) as dopants in order to increase the specific identification of the nitroaromates. In nitroaromatic trace gas atmosphere the induced wavelength shift of the Bragg reflection signal was highest for the sensor with TBAH-doped silica sol receptor coating. Within the first two minutes during exposure the change of the signal intensity, reflecting the adsorption dynamics of the nitroaromatic explosives, was most significant and characteristically depending on the type of receptor dopant used. The cross sensitivities of the sensor with TBAH-doped silica sol receptor coating with four common solvents like acetone, ethanol, 2-propanol and tetrahydrofuran (THF) in comparison to the sensitivity of the tested explosives was more than six orders of magnitude (106) lower than that of solvents, indicating a very high selectivity of the sensor. By applying a simplified diffusion model correlated to a series of measurements with different distances to the target we estimated the limit of detection for a sensor coated with TBAH doped silica sol with 35.8 ± 0.9 ppb for DNB and 140.2 ± 1.8 ppb for DNT in air at room temperature. Using a more etched FBG (but mechanically less robust) sensor we were able to detect TNT as well at concentrations about 5 ppb at room temperature in air. A major result of our investigations was to demonstrate, that the nanoporous silica sol host matrix is suited for fast adapting with low technological effort the affinity of the receptor coating for silica-based evanescent field sensors. For future applications a set of sensors of silica-sol coatings with different dopants in combination with pattern recognition of the sensor signals could be used for clear identification of explosives.

An eco-friendly and effective flame retardant coating for cotton fabric based on phytic acid doped silica sol approach

The high flammability of cellulosic materials somewhat limits their practical application. The introduction of an environmentally benign flame retardant coating for cotton fabric was achieved by hydrolyzing tetraethoxysilane and doping the silica sol with phytic acid in the presence of sodium alginate. The hybrid silica sol had high condensation degree and the modified silica particles had a spherical structure. The coated cotton fabrics with the hybrid PA/silica sol systems showed enhanced thermal stability at high temperatures, and displayed significantly suppressed heat and smoke generation ability, compared with the uncoated one. The hybrid silica sol coatings influenced the combustion performance of cotton via a charring action, and endowed the cotton fabrics with self-extinguishing ability during the vertical flammability test, demonstrating the improvement in fire resistance. The coated cotton fabrics displayed enhanced char yields, whilst maintained their texture structures after burning. Besides, the silicon- and phosphorus-containing components were also found to have a synergistic flame retardant action on cotton.

Few layer deposition and sol-gel finishing of organic-inorganic compounds for improved flame retardant and hydrophilic properties of polyamide 66 textiles: A hybrid approach

A hybrid methodology, including a few layer deposition of bio-based polyelectrolytes, chitosan (CS) and phytic acid (PA), along with a sol-gel treatment from (3-Aminopropyl) triethoxysilane (APTES) and boron doped APTES sol solutions, was followed in constructing a flame retardant and hydrophilic coating onto polyamide 66 (PA66) fabric surfaces. Layer by layer (LbL) assembled and simultaneously sol-gel treated PA66 fabric samples (i.e., PA66-5BL-APTES and PA66-5BL-B-d-APTES) could be able to stop the melt-dripping in vertical burning test. The boron doped APTES sol treated fabric samples with a 2–5 bi-layers deposition showed a reduced peak heat release rate (pHRR) (i.e., 22–30 % reduction) in cone calorimetry test and revealed improved thermal stability in thermogravimetric analysis test. More interestingly, the boron doped silica sol could boost up the hydrophilicity of the treated fabrics significantly compared to only LbL and simultaneously LbL deposited and silica sol treated fabric samples. Furthermore, only the 5 bi-layers deposited and concurrently sol-gel treated fabric samples exhibited durable flame retardant behavior after laundering.

Kinetically Doped Silica Sol–Gel Optical Biosensors: Expanding Potential Through Dip-Coating

Kinetic doping has previously been shown to be an effective method of doping silica sol–gel thin films with an enzyme to construct biosensors. Until now, kinetic doping has only been applied to films produced through the spin-coating method. In this study, we present the use of dip-coating to produce thin films kinetically doped for biosensor development. In this way, kinetically doped biosensors may benefit from the increased range of substrate material shapes and sizes that may be easily coated through dip-coating but not spin-coating. The biosensors produced through dip-coating continue to show enhanced performance over more conventional enzyme loading methods with horseradish peroxidase and cytochrome C samples, showing an increase of 2400× and 1300× in enzyme concentration over that in their loading solutions, respectively. These correspond to enzyme concentrations of 5.37 and 10.57 mmol/L all while preserving a modest catalytic activity for the detection of hydrogen peroxide by horseradish peroxidase. This leads to a 77% and 88% increase in the total amount of horseradish peroxidase and cytochrome C, respectively, over that from coating the same glass coverslip via spin-coating methods.

High Efficiency Raman Lasers Based on Zr-Doped Silica Hybrid Microcavities

Raman lasers form a particularly unique and versatile class of optically pumped laser. Because they rely on stimulated Raman scattering (SRS), which is governed by the vibrational frequency of the gain material and not electronic transitions, the emission wavelength is determined by the pump wavelength, enabling broad tunability. Ultrahigh quality factor (Q) silica optical resonators are an ideal platform for Raman lasers because the long photon lifetime results in large circulating optical intensities. Previous work has demonstrated extremely low thresholds using these devices. However, only moderate Raman lasing efficiencies have been achieved in silica devices. In the present work, we demonstrate that a zirconium (Zr)-doped silica sol–gel coating can improve the performance of a silica microcavity Raman laser. Several concentrations of Zr-doped sol–gel are synthesized. The intrinsic Raman gain of the Zr-doped silica is measured using Raman spectroscopy, and the values show a clear dependence on Zr dopa...

Flame retardance and thermal stability of wool fabric treated by boron containing silica sols

Abstract In order to improve flame retardance and thermal stability of wool fabric, a series of boron doped silica sols were prepared from a tetraethyl silicate inorganic precursor and applied to wool fabric as a flame retardant finish through the sol–gel process. Boric acid, zinc borate and ammonium borate were used as flame retardant additives. The effect of the boron containing flame retardant doped sol coatings on flammability, combustion behavior and thermal property of treated wool fabric was investigated via limited oxygen index (LOI) test, vertical burning test, thermogravimetric (TG) analysis, micro-calorimeter combustion (MCC) and smoke density test. It was found that the coatings on wool fabric acted as a heat insulation barrier, increasing the carbon residue and slowing down the spread of flame when burning, thus improving the flame retardance and thermal stability of the treated fabric. Meanwhile, the smoke density result indicated that the NH 4 HB 4 O 7 doped silica sol treated fabric had good smoke suppression property. Furthermore, the result of mechanical properties showed that there was no damage on tensile strength and air permeation of treated wool fabric.

Combustion properties of cotton fabric treated by boron doped silica sol

Cotton fabric was treated with pure silica sol and boron doped partner through sol-gel method in order to improve its thermal and combustion properties. The results of thermo-gravimetric analysis, micro combustion calorimeter, and smoke density test of control showed that the finished cotton fabric had excellent thermal stability and mild combustion behavior with lower heat release rate. Furthermore, the smoke density test also indicated the safety performance of the boron doped silica sol treated cotton fabric in the fire.

Preparation of Fe<sup>2+</sup>-Doped Silica Sol and its Application in Silk Modification

Fe2+ doped silica sol was prepared using tetraethoxysilane (TEOS) as precursor, ethanol as solvent, hydrochloric acid as catalyst and aqueous solution of ferrous iron by sol-gel method under the follow condition: [TEO:n [EtO:n [H2=1:6:11, reacted at 70°C for 120 min with stirring. Through characterization of the prepared silica sol using particle size analyzer, X-ray diffraction (XRD) and UV-visible spectrum, it could be concluded that even and stable silica sol with nanosize and color was prepared. The prepared Fe2+ doped silica sol was applied in silk modification to endow silk with multifunctional properties and color. X-ray Photoelectron Spectroscopy (XPS) and atomic force microscopy (AFM) indicated that Fe2+-doped silica sol was treated onto the surface of silk fabric. The results showed that the Fe2+ doped silica sol treated silk had good flame retardance, water repellence and antistatic property. At the same time, silk fabric treated by the Fe2+-doped silica sol was also endowed with color.

Thermal properties of wool fabric treated by phosphorus-doped silica sols through sol-gel method

Wool fabric was treated with silica sol and phosphorus doped silica sol by sol-gel method in order to improve its thermal properties and flame retardance. The thermal stability, combustion behavior, and smoke suppression of the control and finished wool fabric were analyzed using thermogravimetric analysis, limited oxygen index, micro combustion calorimeter, and smoke chamber. The results showed that wool fabric treated by phosphorus doped silica sol had excellent thermal properties and flame retardance with higher final char residue and LOI value. Furthermore, heat release rate and smoke density results indicated the safety performance of the treated wool fabric on fire.

Time evolution of samarium doped silica sol–gel materials followed by optical spectroscopy

Sol–gel preparation conditions and optical spectra between 220 and 900 nm of Sm3+ doped silica materials are discussed. It is demonstrated that the intensity of the O2− → Sm3+ charge transfer transition at 285 nm depends on gelation conditions due to samarium related defects in the silica matrix. The room temperature sol–gel transformation and drying of Sm3+ doped samples is followed using UV/Vis spectroscopy. The rate of densification of samarium doped silica materials at room temperature is calculated from increase of the intensity of Sm3+ f–f absorption transitions during time.

Corrosion resistance performance of cerium doped silica sol–gel coatings on 304L stainless steel

The aim of this work is the synthesis and investigation of silane based organic–inorganic hybrid coatings, which can be used to improve the corrosion performance of steel structures subjected to a marine environment. The silane based sol–gel coatings were prepared by dip coating 304L stainless steel in a solution of organically modified silica sol made through hydrolysis and condensation of 3-glycidoxypropyl-trimethoxysilane (GPTMS) as precursor and bisphenol A (BPA) as a cross-linking agent in an acid catalyzed condition. The influence of the addition of cerium and the use of bisphenol A as a cross-linking agent on the microscopic features and morphology as well as on the corrosion resistance of the coatings were examined using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), neutral salt spray tests, potentiodynamic polarization and electrochemical impedance techniques. Results show that cerium modified nano-hybrid coatings exhibit a superior corrosion inhibition performance to that displayed by silica hybrid coatings. Additionally, data showed that the bisphenol A as a cross-linking agent has a significant effect on the morphology and corrosion resistance of the cerium doped silica coating. Omitting the use of bisphenol A causes the creation of defects/cracks in the coating, thereby promoting diffusion of the aggressive electrolyte toward the substrate and decreasing the corrosion resistance of the coating.

A disposable amperometric immunosensor for chlorpyrifos-methyl based on immunogen/platinum doped silica sol–gel film modified screen-printed carbon electrode

A disposable amperometric immunosensor for sensitive detection of chlorpyrifos-methyl (CM) has been developed by combining dual signal amplification of platinum colloid with an enzymatic catalytic reaction. The immunosensor was fabricated by modification of the screen-printed carbon electrodes (SPCE) with nanocomposites made by skillful doping of bovine serum albumin conjugated chlorpyrifos-methyl antigen (BSA-Ag) and platinum colloid into silica sol–gel. The scanning electron microscope (SEM) images and electrochemical measurements showed that platinum colloid domains in the nanocomposite material could enhance electron transfer and change the brittleness of the silica sol–gel. The immobilisation of BSA-Ag on the nanocomposite retained its immunoactivities, which allowed the immobilised BSA-Ag to effectively capture unbound Ab-HRP in the detection solution. A linear response to CM concentration was exhibited, ranging from 0.4 to 20ng/mL. Detection of CM with the presented method in soil or grape samples treated with CM matched the reference values well, which indicated that the proposed disposable immunosensor hold promising applications in environmental and food monitoring.

TiO2, ZnO and nanobimetallic silica catalyzed photodegradation of methyl green

The present works describes a method for degradation and decolorization of methyl green (MG) on semiconducting oxides and nanobimetal (Ag/Pt) doped silica sol–gel powder by using UV and solar light. Bimetallic nanoparticles are the recent research interest because of the high catalytic activity and tunable surface plasmon resonances. In this study the nanobimetal (Ag/Pt) doped silica sol–gel powder were prepared and characterized. Silica sol–gel powder was characterized by FT-IR spectroscopy, SEM with EDX, TEM, DRS and XRD analysis. The results of photodegradation of methyl green on TiO2, ZnO and nanoAg/Pt bimetal doped silica sol–gel powder were presented and compared.

Raman spectroscopic investigations on the kinetics of gelation and densification of Cd 2+- and Pb 2+-doped silica glasses under basic conditions

In the present work, the evolution of the gelation of undoped and Cd 2+-and Pb 2+-doped silica sols has been studied. Tetramethyl orthosilicate and cadmium and lead nitrates were selected as suitable precursors for the synthesis of nanoporous undoped and doped silica systems. Raman spectroscopy was used both to follow the different species formed and the structural changes occurring at various stages of the sol–gel transformation. The combination of information obtained from Raman spectra and from textural measurements using nitrogen adsorption–desorption served to investigate the effects of doping metal ion on the structure of both the gels and on the resulting nanoporous silica glasses. Results showed that doping silica materials with different concentrations of Cd 2+ or Pb 2+ makes it possible both to decrease the densification time and to control the porosity of the resulting gels and glasses.

Preparation and characterization of cerium doped silica sol–gel coatings on glass and aluminum substrates

Chromates are among the most common substances used as corrosion inhibitors. However, these compounds are highly toxic, and an intense effort is being undertaken to replace them. Cerium compounds seem to fulfil the basic requirements for consideration as alternative corrosion inhibitors. The aim of this work was to study the effect of the incorporation of cerium ions in silica sol–gel coatings on aluminum alloys as potential replacement of chromate treatments. The main idea was to combine the ‘barrier’ effect of silica coatings with the ‘corrosion inhibitor’ effect of the cerium inside the coatings. Thin (below 1μm for a single layer) and transparent cerium doped silica sol–gel coatings were prepared by dipping 3005 aluminum alloys in sol–gel solutions. Ultra-violet–visible spectra (UV–vis) show that cerium ions, Ce3+ and Ce4+, always are present in the coatings, independently of the cerium salt or firing atmosphere used. Active protection with single and two layer coatings prepared with Ce (IV) salt seems to improve corrosion protection of the coated aluminum while coatings prepared with Ce(III) salt only entails a protection when applied as a two layer, possibly due to sealing of pre-existent defects in the first layer. The improvement of active protection with immersion time would imply that corrosion is inhibited by cerium ions that migrate through the coating to the site of the attack (a defect in the coatings) and then react to passivate the site.

Absorption and emission behavior of bis(2,2′-bipyridine)[2-(2-pyridyl)benzimidazole]ruthenium(ii) doped in silica gel matrices

Silica gels doped with bis(2,2′-bipyridine)[2-(2-pyridyl)benzimidazole]ruthenium(II), [Ru(bpy)2(pbimH)]2+, which dissociates a proton from the imino group upon light irradiation, were prepared by the sol–gel method under both acidic and basic conditions. Changes in the absorption spectra of the [Ru(bpy)2(pbimH)]2+-doped silica sols and gels prepared under basic conditions with the transition from sols to wet gels were similar to those of [Ru(bpy)2(pbimH)]2+ in methanol–water solution with a change from basic to acidic conditions. Therefore, the acid–base equilibrium is shifted from the deprotonated form, [Ru(bpy)2(pbim)]+, to the protonated form, [Ru(bpy)2(pbimH)]2+, during the sol–gel transition. At the gelation point, the wavelength of the emission maximum under basic conditions was shorter than that under acidic conditions, indicating that the mobility of the Ru complex in silica gels was more strongly restricted under basic conditions than under acidic conditions.

Diffusion Coefficients of Redox Probes Encapsulated within Sol−Gel Derived Silica Monoliths Measured with Ultramicroelectrodes

The diffusional mobilities of potassium ferricyanide (Fe(CN)63-) and ferrocene methanol (FcCH2OH) encapsulated within silica monoliths have been investigated using cyclic voltammetry and chronoamperometry at an ultramicroelectrode. In this work, a 13-μm-radius Pt microdisk working electrode and a silver chloride coated silver wire (r = 0.5 mm) reference electrode were inserted into doped silica sols prepared by the sol−gel process. The resultant gels were aged and slowly dried under a relative humidity atmosphere of 60−70% to minimize gel cracking. Fast-scan voltammetry (up to 100 V/s) confirmed that the gel−electrode interface remained intact throughout the duration of the drying period (typically 20−50 days). During this time frame, an ca. 30% loss in mass and ca. 50% reduction in volume of the gels were observed. The diffusion coefficients of gel-encapsulated Fe(CN)63- and FcCH2OH were measured without prior knowledge of dopant concentration via normalization of the chronoamperometric response with the steady-state limiting current obtained from a 2 mV/s potential sweep. For gel-encapsulated FcCH2OH, the diffusion coefficient dropped from ca. 4 × 10-6 cm2/s to less than 0.6 × 10-6 cm2/s as the gel dried, whereas for gel-encapsulated Fe(CN)63-, a near constant value of 2 × 10-6 cm2/s was obtained. These results suggest that transport in these solids is influenced by both gel structure and by the nature of the entrapped reagent.

Effects of Zn2+Doping on the Sol-Gel Transition and Optical Properties of Gels in Alkoxide-derived Silica

Doped silica sols were prepared via hydrolysis and poly-condensation reactions involving Si(OC2H5)4 and water in which 0.5–10 mol% equivalent of ZnO was added through Zn(NO3)2.6H2O. Gelation was found to be progressively accelerated with increasing amount of Zn2+ which was suggested to link the silicate polymeric clusters via terminal SiO− groups. Activation energies of the overall process of gelation (calculated from gelling times at 10°, 30°, 40° and 50°C) showed significant drop with increasing dopant content. Optical absorption edges of the gels obtained after heating at 500° and 700°C showed progressive shifts towards longer wavelengths with Increasing Zn2+; the optical band gap recorded a corresponding decrease, suggesting this to be an effect of formation of non-bridging Si-O-Zn groups. Another kind of non-bridging group, namely Si-OH, was found by Infrared spectroscopy to decrease in amount with increase In the temperature of heating.