Polyaniline nanofiber–silica composite aerogels

Strong, electrically conducting aerogels were prepared by introducing polyaniline nanofibers to a silica sol just prior to gelation and drying through supercritical carbon dioxide processing. The addition of a few milligrams of polyaniline per cm³ increased the flexural strength of the cylindrical monoliths by 200%. Using preformed polymeric nanofibers avoided filling of microporosity often observed with polymer reinforcement of aerogels and allowed preparation of polyaniline–silica composite aerogels with surface areas over 900 m²/g. Despite the small amount of polyaniline nanofibers (1.3–16.5 wt.%), the composite aerogels were electrically conducting (8.0 × 10^? 8–1.83 × 10^? 5 S/cm) and it was possible to prepare chemiresistor sensors for detection of acidic (HCl) and basic (ammonia) gaseous molecules with response times similar to thin film sensors containing orders of magnitude more polyaniline.     

Novel monolithic mesoporous foamed carbons prepared using micro-colloidal particles as templates

Novel mesoporous foamed carbons were synthesized from carbonization of organic gels templated by polymer micro-colloidal particles. Resorcinol and formaldehyde were allowed to gel in dilute polymethylmethacrylate (PMMA) microemulsion latex, subsequently the water in the gel was solvent exchanged with methanol and the wet gel was dried under ambient pressure. Pyrolysis was carried out at 800 °C to afford carbon xerogels with porous structures similar to those of resorcinol–formaldehyde (RF) carbon aerogels, but of higher density (>1.2 g/cm³), which provide the carbon materials with relatively higher volumetric surface area (up to 918 m²/cm³). Brunauer–Emmett–Teller (BET) adsorption results indicate that PMMA micro-colloid particles with mean diameter 25 nm contributed to the formation of mesopores of mean diameter at 5 nm.     

Development of microporous carbon xerogels by controlling synthesis conditions

Textural properties of carbon gels can be controlled by varying the synthesis and drying process conditions. In this work, the influence of the initial pH and the drying method on the final properties of carbon gels, synthesized using methanol as a solvent, was evaluated. Furthermore, the use of microwaves as a drying method for the synthesis of carbon xerogels was assessed. In the light of the results obtained, in order to synthesize monolithic and microporous carbon gels in a short period of time, the use of a multimode microwave oven is proposed. The use of pH 7 also leads to shorter gelation times and more consistent monoliths. Furthermore, the multimode microwave drying can produce homogeneous microporosity and surface areas of up to 1341 m² g^?1, in a very short time (i.e., only 6 min is required for the drying step).     

Electrochemical properties of conductive filler/carbon aerogel composites as electrodes of supercapacitors

Carbon black, multi-walls carbon nanotube (CNT) and vapor grown carbon nano-fiber with different contents were added to the carbon aerogels (CAs) electrodes as conductive fillers to improve their capacitive properties. The results show that maximum capacitance exists when the content of the conductive filler gets to its percolation threshold. CNT is the most ideal conductive filler. The CA with 1 wt% content of CNT has the best electrochemical performance; its specific capacitances are 141.3 F g^?1 at 5 mV s^?1 and 127.1 F g^?1 at 100 mV s^?1, 1.4 times and 2.2 times as high as that of CA electrode, respectively.     

Silica-doped alumina cryogels with high thermal stability

Alumina cryogels with a dopant of silica in the content range of 0–10 wt% were synthesized from aqueous boehmite sol through the sol-gel technique and subsequent freeze drying. The higher thermal stability was achieved by the addition of 10 wt% silica; a γ-Al₂O₃ phase still remained after heating at 1200 °C for 5 h, and the surface area and pore volume were 47 m² g⁻¹ and 105 mm³ g⁻¹, respectively. The marked stability was ascribed to the synergetic effect of the very low bulk density (0.05 g cm⁻³) and the dopant. The thermal stability was lower for the cryogels than for the corresponding aerogels; however, it was also suggested that cryogel was highly durable in water in contrast to aerogel.     

Preparation and electrochemical characterizations of MnO2-dispersed carbon aerogel as supercapacitor electrode material

The nano-sized amorphous α-MnO₂-dispersed carbon aerogels (CAs) were prepared by liquid phase co-precipitation technique. Different MnO₂ contents and heating temperatures were taken to prepare the composites. The composites prepared were used to make electrodes of electrochemical supercapacitors. Electrochemical properties of the electrodes were studied by cyclic voltammetry and galvanostatic charge–discharge. The specific capacitances of the MnO₂-dispersed CAs and the nano-MnO₂ ingredient in the composite are up to 219 F g^?1 and 401 F g^?1 at 5 mA.cm^?2, 1.6 times and 5.0 times greater than that of neat CA and MnO₂, respectively.     

Nitridation of SiO2–B2O3 aerogels

SiO₂–B₂O₃ aerogels have been prepared by drying wet gels at a supercritical condition for ethanol in an autoclave. Aerogels have been nitrided for 6 h in flowing ammonia at the temperature of 1200 °C. It has been found that the amount of nitrogen incorporated in these aerogels always exceeds 20 wt%. This is a much higher value compared with the amount of nitrogen incorporated in a pure silica aerogel nitrided at the same conditions. The specific surface area of SiO₂–B₂O₃ aerogels has been between 312 and 359 m²/g. After nitridation some shrinkage of aerogels has been observed and the surface area decreases about 20%. In FTIR spectra of SiO₂–B₂O₃ aerogels a typical bands for SiO₂ are observed. After nitridation a shift and broadening of 1100 cm^?1 band to lower wavenumbers indicates that Si–N and B–N bonds are formed in nitrided aerogels.     

Synthesis of bulky mesoporous silica (FSM) by hydrothermal hot-pressing method

In this study, we successfully synthesized the bulk of dense mesoporous silica (FSM) bodies by a short-term hydrothermal hot-pressing (HHP) method. It was thought that these dense bodies were achieved by solution/precipitation mechanism during HHP. Bulk pieces with the dimension in the range of centimeters in diameter possessed a high surface area of over 1000 m²/g and sharp distribution of mesopores with an average diameter of approximately 2.4 nm. This successful synthesis of bulky mesoporous silica will expand the capabilities of application to various fields, for example, gas separation (CO₂ and H₂ etc.) and catalysis.     

Preparation of super hydrophobic silica aerogel and study on its fractal structure

The experimental results on silica aerogels with super hydrophobic property are reported. Silica alcogels were prepared via a two-step acid/base process by keeping the molar ratio of tetraethyoxysiliane (TEOS), ethanol (EtOH), water (H₂O), hydrochloric acid (HCl) and ammonia (NH₄OH) constant at 1:6:8:1.0 × 10^?3:1.1 × 10^?2, respectively, and varying the molar ratio of N,N-dimethylformamide (DMF)/TEOS (G) from 0 to 1.2. After two aging treatment steps, they were modified by isopropyl alcohol (IPA)/trimethylchlorosilane (TMCS)/n-hexane solution at 60 °C. It was found that G value at 0.8 resulted in low density (～0.2 g cm^?3) and the minimum volume shrinkage (～6%), with the total water adsorption ratio ～5.1% when exposed to water for 3 months and the contact angle θ ≈ 178°. Besides, the aerogels (G = 0.8) had higher volume fractal dimension (～1.8), which indicted that it possessed better connectivity and more uniform particle sizes.     

Growth of CdSiP2 single crystals by self-seeding vertical Bridgman method

Using a high purity CdSiP₂ polycrystalline charge synthesized in a single-temperature zone furnace, a CdSiP₂ single crystal with dimensions of 8 mm in diameter and 40 mm in length was successfully grown by the vertical Bridgman method. The quality of the crystal was characterized by high resolution X-ray diffraction and the full width at half maximum (FWHM) of the rocking curve for the (200) face is 33″. Thermal property measurements show that: the mean specific heat of CdSiP₂ between 300 and 773 K is 0.476 J g^?1 K^?1; the thermal conductivity of the crystal along the a- and c-axes is 13.6 W m^?1 K^?1 and 13.7 W m^?1 K^?1 at 295 K, respectively; and the thermal expansion coefficient measured along the a- and c-axes is 8.4×10^?6 K^?1 and ?2.4×10^?6 K^?1, respectively. The optical transparency range of the crystal is 578–10,000 nm, and there is no absorption loss in the spectrum from 0.7 to 2.5 μm, as often exists with ZnGeP₂ crystals grown from the melt.     

Thermal,vibrational and Ac impedance studies on proton conducting polymer electrolytes based on poly(vinyl acetate)

Proton conducting polymer electrolytes based on poly(vinyl acetate) (PVAc) and perchloric acid (HClO₄) have been prepared by solution casting technique with various compositions. The X-ray diffraction analysis confirms the polymer–HClO₄ complex formation. FTIR spectra analysis reveals the interaction between proton and ester oxygen of poly(vinyl acetate) (PVAc). The shift in T_g towards the lower temperature indicates that the polymer salt interaction takes places in the amorphous phase of the polymer matrix. Ac impedance spectroscopy reveals that 75 mol% PVAc:25 mol% HClO₄ exhibits maximum conductivity, 3.75 × 10^? 3 S cm^? 1 at room temperature (303 K). The increase in conductivity with increase in dopant concentration and temperature may be attributed to the enhanced mobility of the polymer chains, number of charge carriers and rotations of side chains. The temperature dependence of conductivity shows non-Arrhenius behavior at higher temperatures.     

Preparation of cresol–formaldehyde carbon aerogels via drying aquagel at ambient pressure

Carbon aerogels were prepared from mixed cresol (Cm) and formaldehyde (F) via the sol–gel process followed by drying at ambient pressure and carbonization. The inexpensive feedstock of mixed cresol and the simple drying process could be as an alternative economical route to the classical resorcinol–formaldehyde synthesis process. In our process, organic precursor gels were synthesized via polycondensation of cresol with formaldehyde in an aqueous alkaline (NaOH) solution. After gelation the solvent was removed via drying at ambient pressure to obtain organic aerogels that exhibit a drying shrinkage below 5% (linear). Upon carbonization of the organic aerogels at 1173 K, monolithic carbon aerogels (denoted as CmF carbon aerogels) can be produced. Nitrogen adsorption results showed that the CmF carbon aerogels have abundant mesopores and micropores with a dominant pore diameter of 25–40 nm. An increase of the BET surface area and a modification of the pore size distribution of CmF can be realized by a CO₂ activation. The images of scanning electron microscopy (SEM) indicated that the microstructure of carbon aerogels can be effectively controlled and tailored by varying the synthetic conditions during the initial sol–gel process.     

A large core microstructured fluoride glass optical fibre for mid-infrared single-mode transmission

A microstructured optical fibre based on an alumino-zirco-chloro-fluoride glass has been fabricated in which the light-guiding structure comprises a single ring of air-holes, machined directly into the preform rod using an ultrasonic drill around a large effective solid core. The objective was single-moded transmission of longer mid-infrared wavelengths at high laser power without causing radiation damage to the fibre material. It has been demonstrated that this fibre preserves high laser beam quality and can transmit wavelengths between 2.1 and 4.7 μm, single-moded in an effective core of diameter 79 μm. Optical fibre transmission losses from 1.4 to 10.3 dB m^?1 have been measured over this wavelength range. No damage was observed in the fibre at peak pulse power, setting a lower limit of >1 GW cm^?2 for the laser damage threshold. Brightness was preserved at wavelengths longer than 4 μm.     

Kerr studies of several tellurite glasses

Estimates of Kerr electrooptical sensitivity of several tellurite glasses are presented. The highest value of Kerr coefficient B ～ 190 × 10^?16 m V^?2 is registered for 0.6TeO₂–0.3TlO_0.5–0.1ZnO glass. This evidences the prospects of thallium–tellurite glass system for electrooptical applications. A gradual decrease of B from 41 × 10^?16 to 26 × 10^?16 m V^?2 in (1 ? x) TeO₂ – xNbO_2.5 system is revealed for x increasing from 0.1 to 0.15. No crystalline phase was found in that system, thus allowing attributing its Kerr sensitivity to the intrinsic properties of the glass matrix. The Kerr coefficient variation from 66 to 81 × 10^?16 m V^?2 was observed for 0.85TeO₂–0.15WO₃ glasses co-doped with small amounts of silver and cerium. The analysis of optical absorption spectra of several silver-containing tellurium–tungsten oxide glasses makes it possible to think that introducing cerium provokes formation of new mid-range orderings.     

Microstructural and photocatalytic properties of sol–gel-derived vanadium-doped mesoporous titanium dioxide nanoparticles

The vanadium (V)-doped mesoporous titanium dioxide (TiO₂) nanoparticles at low V/Ti ratios ranging from 0 to 2 wt% were prepared using hydrolytic sol–gel method in the presence of tri-block copolymer Pluronic F127. The microstructures of TiO₂ in terms of morphology, crystallization, chemical states of species, surface area, and band gap were characterized by SEM, TEM, XRPD, XPS, surface area analyzer, and UV–Vis spectrophotometer, respectively. SEM images showed that the V-doped TiO₂ nanoparticles were porous structures, and the surface areas and pore sizes ranged from 86 ± 9 to 96 ± 15 m²/g and from 12 ± 4 to 15 ± 2 nm, respectively. The XRPD patterns indicated that V-doped mesoporous TiO₂ after calcination at 500 °C was mainly anatase phase, and the crystallite sizes were in the range 14–16 nm, which are consistent with the results obtained from SEM images. XPS spectra and HRTEM images showed that vanadia was doped both on the surface and in the lattice of anatase TiO₂. A slight red-shift in wavelength absorption was observed when V/Ti ratio increased from 0 to 2 wt%. Methylene blue (MB) was further used as the target compound to examine the photocatalytic activity of V-doped mesoporous TiO₂ nanocatalysts under illumination of solar simulator or UV light. Addition of vanadium ions slightly decreased the photocatalytic activity of TiO₂ toward the decolorization of MB under the illumination of UV light at 305 nm. However, a 1.6–1.8 times increase in rate constants for MB photodegradation was observed when 0.5–1.0 wt% V-doped TiO₂ was illuminated with sunlight at AM 1.5.     

Thermal and optical properties of TeO2–ZnO–BaO glasses

We report the results of a systematic study of the thermal and optical properties of a new family of tellurite glasses, TeO₂–ZnO–BaO (TZBa), as a function of the barium oxide mole fraction and compare them with those of TeO₂–ZnO–Na₂O (TZN). The characteristic temperatures of this new glass family (glass transition, T_g, crystallization, T_x, and melting, T_m) increase significantly with BaO content and the glasses are more thermally stable (greater ΔT = T_x ? T_g) than TZN glasses. Relative to these, Raman gain coefficient of the TZBa glasses also increases by approximately 40% as well as the Raman shift from ~ 680 cm^? 1 to ~ 770 cm^? 1. The latter shift is due to the modification of the glass with the creation of non-bridging oxygen ions in the glass network. Raman spectroscopy allows us to monitor the changes in the glass network resulting from the introduction of BaO.     

Changing poisson’s ratio of mesoporous silica monoliths with high temperature treatment

The elastic moduli of mesoporous (fractal pore structure with a statistical pore size distribution with a maximum in the mesopore region) silica monoliths (silica aerogels) were measured in situ during calcination using the resonant beam technique. Above a temperature of approximately 573 K, a significant increase of the elastic moduli with increasing heat treatment temperature was observed, which was attributed to the rearrangement and completion of the network. Poisson’s ratio is close to zero up to this temperature and then increases to a positive value typical for isotropic bodies.     

Effect of OH-content on thermal and chemical properties of SnOP2O5 glasses

Glasses with 55–60 mol% SnO and 40–45 mol% P₂O₅ have shown extremely large differences in the chemical and thermal properties depending on the temperature at which they were melted. Glasses prepared at low melting temperature, 450–550 °C, had low T_g, 150–200 °C, and low chemical stability. Glasses prepared at high melting temperature, 800–1200 °C, had much higher T_g, 250–300 °C, and much higher chemical stability. No significant differences were found by ¹¹⁹Sn Mössbauer and ³¹P Nuclear Magnetic Resonance spectroscopy. Large differences in the OH-content could be detected as the reason by infrared absorption spectroscopy, thermal analyses, and ¹H Nuclear Magnetic Resonance spectroscopy. In samples with low T_g, a broad OH – vibration band around 3000 nm with an absorption intensity >20 cm^?1, bands at 2140 nm with intensity ～5 cm^?1, at 2038 nm with intensity ～2.7 cm^?1, and at 1564 nm with intensity ～0.4 cm^?1 were measured. These samples have shown a mass loss of 3–4 wt% by thermal gravimetric analyses under argon in the temperature range 400–1000 °C. No mass loss and only one broad OH-band with a maximum at 3150 nm and low absorption intensity <4 cm^?1 could be detected in samples melted at high temperature, 1000–1200 °C, which have much higher T_g, ～300 °C, and much higher chemical stability.     

Synthesis and structure–property relations in xCuO–(1 − x)Bi2O3 (0.5 ⩽ x ⩽ 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses

Synthesis of the xCuO–(1 ? x)Bi₂O₃ (0.5 ? x ? 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses was done via nitrate–citrate gel route. Glassy phase is ascertained by XRD studies. Magnetic susceptibility results in the range 4.2–400 K show weak paramagnetic nature with exchange integrals ～0.024–0.13 eV in the glasses. The electron paramagnetic resonance (EPR) in the range 4.2–363 K shows g ≈ 2.0 and the trend of the g-matrix elements g_|| > g_⊥ > g_e for the glasses C1–C5 at 4.2 K are due to the Cu²⁺ (3d⁹) paramagnetic site in the glasses which is in a tetragonally elongated octahedron [O_1/2–CuO_4/2–O_1/2] having D_4h symmetry. IR spectroscopic results show the presence of octahedron [BiO_6/2]^3? and [CuO_6/2]^4? units and pyramidal [BiO_2/2O]^? unit in the glasses.     

Hydrophobic and thermal insulation properties of silica aerogel/epoxy composite

Silica aerogel/epoxy composite was prepared by dry mixing hydrophobic aerogels with epoxy powders and heat pressing method. The composite materials show a serviceability temperature up to 250 °C with low thermal conductivity (0.11–0.044 W/m k) and hydrophobic property (water contact angle of 117–140°). Transmission electron microscope photos proved that part of silica aerogels nanopores had been immersed by epoxy. Based on this phenomenon, an immersion model was build up to study the effect of immersion on the thermal insulation and hydrophobic properties. In addition a thermal conductivity prediction equation of aerogel/polymer system was obtained and confirmed by comparing the experimental data.