In situ FTIR experimental results in the silylation of low-k films with hexamethyldisilazane dissolved in supercritical carbon dioxide

In situ Fourier Transform Infrared Spectroscopy measurements were performed using an innovative equipment to study the surface modification reaction between a functionalized porous MSQ-film and hexamethyldisilazane (HMDS) dissolved in CO₂ at supercritical conditions (scCO₂). scCO₂ was used in the heterogeneous reaction due to enhancing properties, ideal for porous materials. Different infrared signatures, from the gas and solid phases, were observed and identified, implying gas–gas and solid–gas phase reactions. Among the different component signatures observed in the gas phase, carbonic acid was observed as a possible silylating gas phase nucleophilic component, while in the solid phase the predominant reaction mechanism proceeded by forming SiOSi bonds and Trimethylaminosilane (as gas phase product).     

Synthesis and Characterization of Hyperbranched Linear Surfactants

A series of hyperbranched linear surfactants (HLS) was prepared by using oleic acid modifying the first generation hydroxyl-terminated hyperbranched polymer (HBP-1), which was obtained through a step synthesis method using trimethylolpropane and N,N-dihydroxyethyl dodecylamine -3-amine-methyl propionate (AB₂-type monomer). AB₂—type monomer was obtained through the Michael addition reaction of methyl acrylate and diethanol amine. Single-factor experiments were conducted to investigate the influences of reaction conditions such as temperature, oleic acid dosage, and reaction time on the synthesis of HLS. Results indicate that the optimal temperature and time of the esterification reaction were 130 °C and 3 h, respectively. The structures of HLS were characterized by Fourier transform infrared spectrophotometry (FT-IR) and the results indicate that HBP-1 had been successfully modified by oleic acid. Furthermore, the surface tension and the critical micelle concentration (CMC) of the HLS solution show that HLS can significantly reduce the surface tension of water.     

Synthesis and characterization of novel water-based poly(urethane-imide) nanodispersions

Poly(urethane-imide) nanodispersions were synthesized in four steps, as described below. In the first step, polyurethane prepolymer was prepared by the reaction of hexamethylene diisocyanate and polypropylene glycol in the presence of a catalytic amount of dibutyltin dilaurate. In the second step, poly(urethane-imide) prepolymer was prepared by the reaction of synthesized polyurethane prepolymer in the first step with pyromellitic dianhydride in dimethylformamide. In the third step, the prepared poly(urethane-imide) (PUI) reacted with 2,2-bis (hydroxymethyl) propionic acid, and the reaction completed in the last step which involved neutralization and dispersion in water, where acidic poly(urethane-imide) was neutralized by the addition of triethylamine. The prepared poly(urethane-imide) dispersions were characterized by fourier transform infrared spectrometry, proton nuclear magnetic resonance spectroscopy (¹HNMR), thermogravimetric analysis, and dynamic laser scattering. A series of PUI dispersions with 30 wt% solid content, viscosities of 9 ± 1 cps, and particle sizes of 78–133 nm range were prepared and characterized.     

Partial or total silylation of dextran with hexamethyldisilazane

The silylation reaction of dextran with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) in DMSO was studied as the first step of the synthesis of new amphiphilic polyester-grafted dextrans. According to the experimental conditions, i.e. dextran molar weight, medium temperature and reaction time, HMDS/OH ratio, addition of a catalyst and co-solvent, partially or totally silylated dextrans were recovered. The highest silylation yields were obtained with the lowest molecular weight dextrans. The increase in temperature medium and/or reaction time, the presence of catalyst or co-solvent favored the protection yield. Whatever the dextran used, complete silylation of the polysaccharide chain could be achieved by adequate selection of the experimental conditions. The thermal properties of resulting silylated polysaccharides were investigated by temperature modulated DSC. It was observed that T_g values of partially silylated dextran were maintained between 120 and 140 °C, independently of the dextran molecular weight. Interestingly, DMSO proved to behave as an efficient plasticizer of (partially) silylated dextrans. The partially silylated dextrans were efficiently used as multifunctional macroinitiators for the controlled ring-opening polymerization (ROP) of lactone. The ROP was then promoted from the remaining hydroxyl groups in the presence of tin or aluminium activator. After polymerization and ultimate deprotection of the silylated dextran backbone, amphiphilic polyester-grafted dextrans were readily recovered.     

Synthesis,characterization, and evaluation of unsupported porous NiS submicrometer spheres as a cathode material for lithium batteries

Synthesis of a nanostructured pure phase nickel sulfide in a single step is a challenge. In this work, a new method for direct synthesis of uniform NiS–SiO₂ submicrospheres was developed by ultrasonic spray pyrolysis. Colloidal silica was used as a sacrificial template to create the porous structure. After silica removal, hollow, porous pure phase NiS nanospheres were obtained. The product was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy, and N₂ adsorption/desorption isotherm. The results confirmed the formation of single phase millerite NiS porous nanospheres with a high surface area of 312 m² g^?1. The NiS spheres were tested as cathode for lithium batteries. A discharge capacity of 340 mAh g^?1 with good capacity retention during multiple cycles was obtained.     

Preparation of HMDS-modified silica/polyacrylate hydrophobic hard coatings on PMMA substrates

Colloidal silica nanoparticles synthesized from tetraethoxysiliane via a sol–gel process were surface modified by 3-(trimethoxysilyl)propyl methacrylate (MSMA) and 1,1,1,3,3,3-hexamethyldisilazane (HMDS). MSMA acted both as a C=C provider and a coupling agent, whereas HMDS was used to prevent particle aggregation and engender hydrophobicity. The modified silica particles (HMSiO₂) were UV-cured together with the crosslinking agent, dipentaerythritol hexa-acrylate (DPHA) to form coatings on poly(methyl methacrylate) (PMMA) substrates. Dynamic light scattering of the synthesized sols indicated that the average size of HMSiO₂ was ca. 10 nm, consistent with that obtained from TEM imaging. FTIR spectroscopic analyses demonstrated chemical attachment of HMDS to the silica particles. The cured coatings were characterized in terms of water contact angle, light transmittance, hardness, abrasion resistance, and surface morphology. It was found that hydrophobicity of the coatings increased while light transmittance and hardness decreased with increasing HMDS content. DPHA played the role of providing mechanical strength and adherence; however, the coatings became lightly hazy when the weight ratio of DPHA/silica fell in the range 0.3–0.7. In the optimal case, a hard coating (4H) with water contact angle of 108° and transmittance of ~100% (vs PMMA) had been obtained at the DPHA content of 10 wt%.     

Gas-to-Particle Conversion in the Particle Precipitation–Aided Chemical Vapor Deposition Process I. Synthesis of the Binary Compound Titanium Nitride

Particle precipitation-aided chemical vapor deposition (PP-CVD) is a modification of the conventional CVD process, where an aerosol is formed in the gas phase at an elevated temperature, and particles are deposited on a cooled substrate. The synthesis of titanium nitride (TiN), using titanium tetrachloride vapor (TiCl₄), nitrogen (N₂), ammonia (NH₃), and hydrogen (H₂), by the PP-CVD process is studied. TiN is formed by a heterogeneous reaction, using TiCl₄, N₂, H₂, whereas simultaneously TiCl₄ and NH₃ react to form an aerosol. The activation energy of this homogeneous reaction is on the order of 100 kJ/mol. The powder formation process is determined by the dissociation of a titanium containing intermediate species. At low temperature differences between substrate and gas phase (i.e., < 2 K), only dense columnar microstructures, with growth rates of around 20 μm/h, are observed. At these temperature differences no particle deposition is observed. The layers are formed by a molecular diffusion controlled CVD growth mechanism. Porous coherent layers are found in experiments, where intermediate temperature differences are applied (i.e., approximately 2–10 K). The observed interconnection of the particles has to originate from a heterogeneous reaction. Apparently, under these conditions the heterogeneous reaction is fast enough, with respect to the particle precipitation rate, to interconnect the precipitated particles. A further increase in temperature difference between the susceptor and the gas phase only leads to loose powder deposits. In principle, the PPCVD process is a suitable method for the synthesis of thin porous layers of ceramics. To obtain uniform coherent porous layers two separate reaction mechanisms are required under the same experimental conditions. There should be a homogeneous reaction in the gas phase as well as a heterogeneous reaction, which is controlled by surface kinetics, in order to interconnect precipitated particles to obtain a coherent porous layer. Porous ceramic layers can be formed as long as the particle precipitation rate is slow enough with respect to the heterogeneous reaction rate.     

Efficient trimethylsilylation of alcohols and phenols in the presence of ZrCl4 as a reusable catalyst

ZrCl₄ can be used as an efficient and reusable catalyst for the conversion of alcohols and phenols to their corresponding trimethylsilyl ethers with hexamethyldisilazane (HMDS). All reactions were performed under mild and completely heterogeneous reaction conditions in good to high yields.     

Hydrothermal Biotemplated Synthesis of Biomorphic Porous CeO2 and Their Catalytic Performance

Biomorphic porous CeO₂ powder was synthesized by the hydrothermal method using stems of clover as biotemplates. Thermogravimetric and differential thermal analysis, X-ray diffraction, N₂ adsorption–desorption, field emission scanning electron microscopy and Fourier transfer infrared spectroscopy were applied to characterize the samples. The oxygen storage/release capacity (OSC) and catalytic oxidation performance of the biomorphic porous CeO₂ for acid magenta were also investigated. Results show that the as-synthesized CeO₂ powders exhibit a cubic phase and have porous structures with pore size ranging from several to dozens of micrometers. The results of N₂ adsorption–desorption measurement suggest that the biomorphic CeO₂ contains a large number of mesopores on the surface of CeO₂ framework; and, the pore diameter is from 15–35 nm. The OSC value of the biomorphic porous CeO₂ is 174.6 μmol O₂/g ceria, which is two-times higher than powdered CeO₂. After catalytic oxidation for 300-min by the biomorphic porous CeO₂, the decolorizing rate of acid magenta is close to 95 %, which is higher than for powdered CeO₂ (64 %).     

Preparation of porous polyvinyl acetate materials using concentrated emulsion templates

This paper is devoted to the preparation of highly porous polyvinyl acetate (PVAc) materials using concentrated emulsion templates. Stable concentrated emulsions were obtained by introducing colloidal silica to the aqueous phase, which was absorbed at the interface of the emulsion preventing the coalescence of the dispersed phase. The prepared samples were characterized by Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption (BET), thermo-gravimetric and differential thermal techniques. SEM measurement revealed that cell diameter of the resulting foams was controlled from 1 to 10 μm by altering the emulsion composition, such as the content of colloidal silica, and the volume fraction of the dispersed phase. FT-IR revealed the presence of SiO₂ and PVAc in the resulting foams. The nitrogen adsorption analysis showed that the samples possessed mesoporous structure with surface areas lager than 62 m² g^?1. Porous PVAc materials, which are biocompatible, will have potential applications in area of life science.     

Synthesis of Poly-L-Lactide for Scaffold Materials by Melt-Solid Polycondensation

Poly-L-lactide (PLLA) with low viscosity average molecular mass for scaffold materials was synthesized by melt-solid condensation polymerization and characterized by IR, XRD, and ¹H-NMR. The influences of catalyst (LaCl₃/C₇H₈SO₃) concentration, polymerization temperature and polymerization time on the viscosity average molecular mass of poly-L-lactide acid (PLLA) were investigated. Poly-L-lactide with a viscosity average relative molecular mass of about 7.2 × 10⁴ was obtained when melt-solid polycondensation was conducted with first preheating at 110°C for 4 h and solid polycondensation at 150°C for 20 h; the catalyst concentration was 0.4 wt. %. PLLA was made into porous materials by using sodium hydrogen carbonate particulates as the porogen to foam. Scanning electron microscope observation indicates that the sample is highly porous and well distributed with good interconnections between pores and the pore size of porous materials in the range of 300–500 μm and it can be used as scaffold for bone tissue engineering.     

Extraordinary synergetic effect of precursors in laser CVD deposition of SiBCN films

Herein, we report on the synergetic effect of simultaneously using of hexamethyldisilane (HMDS) and trimethylamine borane (TMAB) as precursors for a high-rate laser chemical vapor deposition of SiBCN films. The major components of obtained films were successfully controlled by deposition temperature from B₄C to graphene and β-SiC. In addition, B₄C and graphene/β-SiC films were synthesized from TMAB and HMDS, respectively. The growth rate of SiBCN films was extremely high (up to 1620 μm/h) in contrast to 18 μm/h and 415 μm/h for graphene/β-SiC and B₄C films, respectively. Thermodynamic modeling demonstrated that reactions between nitrogen- and silicon-containing gas species during double-source CVD process could be the possible reason of synergism and growth rate increasing. A mechanical study demonstrated very high hardness (up to 43 ± 7 GPa) and wear resistivity of the SiBCN films. The reported results reveal a significant potential of precursor synergism for the design of new materials with enhanced properties.     

Preparation and characterization of a porous silicate material from silica fume

A porous silicate material derived from silica fume was successfully prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, Thermogravimetry and Differential thermal gravity (TG-DTG), N₂ adsorption and desorption isotherms, and scanning electron microscopy (SEM). Raw silica fume was analyzed by XRD, FT-IR and SEM. The analysis results of silica fume indicated that SiO₂ in silica fume is mainly determined as amorphous state, and that the particles of raw silica fume exhibited characteristic spherical structure with a diameter of from 50 nm to 200 nm. The preparation of the porous silicate material involved two steps. The first step was the extraction of the SiO ₃ ^2? leachate from raw silica fume. The maximum value of SiO ₃ ^2? extraction yield was obtained under the following conditions: reaction temperature of 120 °C, reaction time of 120 min, NaOH concentration of 15%, and alkali to SiO₂ molar ratio of 2. The second step was the preparation of the porous silicate material though the reaction of SiO ₃ ^2? leachate and Ca(OH)₂ suspension liquid. The optimum preparation conditions were as follows: preparation temperature of 90 °C, preparation time of 1.5 h, Si/Ca molar ratio of 1 : 1, and stirring rate of 100 r/min. The BET surface area and pore size of the porous silicate material were 220.7 m²·g^?1 and 8.55 cm³/g, respectively. The porous silicate material presented an amorphous and unordered structure. The spectroscopic results indicated that the porous silicate material was mainly composed of Si, Ca, O, C, and Na, in the form of Ca²⁺, SiO ₃ ^2? , CO ₃ ^2? and Na⁺ ions, respectively, which agreed with the XRD, TG-DSC, and FT-IR data. The N₂ adsorption-desorption isotherm mode indicates that the porous silicate material belonged to a typical mesoporous material. The porous silicate material presented efficiency for the removal of formaldehyde: it showed a formaldehyde adsorption capacity of 8.01 mg/g for 140 min at 25 °C.     

Mesoporous titania/tungstophosphoric acid composites: suitable synthesis of flavones

Mesoporous TiO₂/H₃PW₁₂O₄₀ composites were synthesized by sol–gel reactions using urea as a low-cost template, and adding tungstophosphoric acid (TPA) at the same time as the template. The TPA concentration was varied in order to obtain TPA contents of 0, 10, and 20 (w/w) in the solid. The samples presented mesopores with a diameter higher than 3.0 nm. The specific surface area of the solids decreased with both the increase of the TPA content and the calcination temperature. From Fourier transform infrared and ³¹P magic angle spinning-nuclear magnetic resonance studies it was observed that the main heteropolyoxometallate species present in the composites is the [PW₁₂O₄₀]^3? anion, which was partially transformed into the [P₂W₂₁O₇₁]^6? and [PW₁₁O₃₉]^7? anions during the synthesis and drying step. The X-ray diffraction patterns of the modified samples only exhibited the characteristic peaks of the anatase phase of titanium oxide. The point of zero charge decreased with both the increase of TPA content in the solids and the calcination temperature. The materials were found to be efficient and recyclable catalysts for the synthesis of a series of flavones. The reaction was carried out in different reaction media: heterogeneous and solvent-free conditions. The solvent-free conditions represent the best green conditions. Initially, we optimize the reaction condition to obtain 6-chloroflavone by direct reaction of the cyclodehydration of 1-(2-hydroxy-5-chlorophenyl)-3-phenyl-1,3-propanodione in the presence of a catalytic amount of mesoporous titania modified with tungstophosphoric acid catalyst. Reactions were performed in two conditions: low volume of toluene, at 110 °C, typically 24 h, and solvent-free at the same temperature, 1 h. In all cases the product (6-chloroflavone) was obtained with high selectivity. Conversions up to 76 and 92 % were obtained respectively, using the supported catalyst (TiTPA10). Optimal reaction conditions were applied to the preparation of six substituted flavones in both conditions.      

Mechanistic Aspects of Os(VIII)/Ru(III) Catalysed Oxidation of L-phenylalanine by Ag(III) Periodate Complex in Aqueous Alkaline Medium

The kinetics of oxidation of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalysed oxidation of L-phenylalanine (L-Pal) by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at 27 °C and a constant ionic strength of 0.25 mol dm^?3 was studied spectrophotometrically. The involvement of free radicals was observed in the reactions. The reaction between DPA and L-Pal in alkaline medium exhibits stoichiometry as [L-Pal]:[DPA] = 1:1. The reaction is of first order in [Os(VIII)], [Ru(III)] and [DPA] and has negative fractional order in [IO₄ ^?]. It has less than unit order in [L-Pal] and [OH^?]. However, the order in [L-Pal] and [OH^?] changes from first order to zero order as their concentrations increase. The main oxidation products were identified by spot test and spectral studies. The probable mechanisms were proposed and discussed. The catalytic constant (K _c) was also calculated for Os(VIII) and Ru(III) catalysis at different temperatures. The activation parameters with respect to slow step of the mechanisms were computed and discussed and thermodynamic quantities were also calculated. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The active species of catalyst and oxidant have been identified.     

Fabrication of self-ordered nanoporous alumina with 500–750 nm interpore distances using hard anodization in phosphoric/oxalic acid mixtures

A hard anodization (HA) technique is employed using different mixtures of phosphoric/oxalic acid for fast fabrication of alumina nanopore arrays in voltages higher than 200 V. The mixtures enable to avoid the breakdown of porous anodic alumina (PAA) in the high voltages. It is revealed for the first time that continuously tunable pore intervals (D_int) from 500 to 750 nm can be controlled by varying the concentrations of oxalic acid at anodization voltages (U_anod) from 230 to 360 V, far beyond the U_anod in the single electrolyte of phosphoric acid or oxalic acid. The ratios of interpore distance, pore diameter and barrier layer thickness to anodization voltage are in the range of conventional HA process for each acid mixture. In this approach, the PAA film growth rate is 26 µm/h, being 7 times larger than that in typical mild anodization.     

Useful experimental technique for the study of heterogeneous reactions

The heterogeneous CaO/SO₂ reaction has been thoroughly investigated by developing a series of new experimental techniques including the TGA reactor, the volulmetric reactor and the entrained flow reactor. The heterogeneous system is designed in such a way that most of the gas film and pore diffusion resistances are reduced. The modelling of each step related to the reaction is discussed while the chemical reaction and product layer diffusion are emphasized as the main influences on the SO₂removal. The unchanging size shrinking core model is used to describe the reaction progress with a two stage assumption which has been confirmed in the TGA reactor: first, a very fast surface reaction, followed by a product layer diffusion controlled reaction. It was found from the experiments that the SO₂-partial pressure aat the very beginning is very important for a high removal efficiency during the initial reaction period.     

Anchoring of Copper(II) Schiff Base Complex into Aminopropyl-Functionalised MCM-41: A Novel,Efficient and Reusable Catalyst for Selective Oxidation of Alcohols

A copper(II) complex containing tetradentate N₂O₂ Schiff base ligand immobilized into aminopropyl-functionalised MCM-41 (mobile crystalline material number 41), was prepared and characterized by Fourier-transform infrared, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, N₂ adsorption–desorption and inductively coupled plasma analysis techniques. The novel heterogeneous catalyst, MCM-41-pr-NH₂-CuL, can be successfully applied for efficient and selective oxidation of different primary and secondary alcohols to the corresponding carbonyl compounds using hydrogen peroxide as an oxidant in acetonitrile at 60 °C. The effect of reaction parameters such as solvent, amount of catalyst, temperature and kind of oxidant on the oxidation of benzyl alcohol was also studied. The prepared catalyst could be recovered and reused four times without important loss of its catalytic performance. The heterogeneous MCM-41-pr-NH₂-CuL catalyst was found to be catalytically more active in the oxidation of alcohols compared to the similar type of copper(II) Schiff base complex in homogeneous media under the same reaction conditions.     

Osmium(VIII) catalyzed oxidation of a sulfur containing amino acid—a kinetics and mechanistic approach

The kinetics of osmium (VIII) catalyzed oxidation of DL-methionine by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm^?3 was studied spectrophoto-metrically. The reaction between hexacyanoferrate(III) and DL-methionine in alkaline medium exhibits 2:1 stoichiometry (2HCF:DL-methionine). The reaction is of first order each in [HCF] and [Os(VIII)], less than unit order in [alkali] and zero order for [DL-methionine]. The decrease in dielectric constant of the medium increases the rate of the reaction. The added products have no effect on the rate of reaction. The main products were identified by spot test. A free radical mechanism has been proposed. In a prior equilibrium step Os(VIII) binds to OH^? species to form a hydroxide species and reacts with [Fe(CN)₆]^3? in slow step to form an intermediate species(C₁). This reacts with a molecule of DL-methionine in a fast step to give the sulfur radical cation of methionine and yields the sulfoxide product by reacting with another molecule of [Fe(CN)₆]^3?. The rate constant of the slow step of the mechanism is calculated. The activation parameters with respect to slow step of the mechanism are evaluated and discussed.     

Influence of the matrix porosity on the synthesis and adsorption behavior of dithiocarbamate styrenic resins toward zinc(II) and cadmium(II) ions

The dependence of the adsorption behavior toward Zn²⁺ and Cd²⁺ on the synthesis conditions of dithiocarbamate styrenic resins was investigated. We synthesized styrene–divinylbenzene copolymers with different kinds of porous structures by varying the divinylbenzene (DVB)‐to‐styrene ratio and the dilution degree of the monomers with n‐heptane. The porous structure of these materials was characterized. The introduction of the dithiocarbamate moiety on the copolymers followed a synthetic pathway based on the nitration reaction, reduction of the nitro group to the amino one, and finally, the addition of the amino group to CS₂. All of the synthesis steps were monitored by Fourier transform infrared spectroscopy. Only the addition reaction to CS₂ was greatly influenced by the copolymer porosity. The effect of the dilution degree on the reaction extension was more pronounced than the effect of the DVB content. The more porous materials with higher dithiocarbamate contents adsorbed a higher amount of ions in a faster way, with Zn²⁺ being preferable over Cd²⁺ ions. The difference between the Zn²⁺ and Cd²⁺ adsorption rates was enhanced with the copolymer porosity, and also enhanced was the difference between the amounts of ions adsorbed by the copolymer; this suggested that the selectivity toward these ions could be controlled by the copolymer porous structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010