The effect of acidity on the structural and textural evolution of titania in the presence of primary amine and inorganic precursor

Titania was synthesized from laurylamine hydrochloride (LAHC) and Ti(SO₄)₂ under different acidic conditions. The effect of acidity on the structural and textural evolution of titania has been investigated by X-ray diffraction (XRD), nitrogen adsorption–desorption, transmission electron micrographs (TEM), FTIR spectroscopy and thermogravimetric analysis (TGA). With increasing the pH value in the initial mixture, the obtained samples transformed from nanoparticles with intra-particle mesostructures (pH 0.6 and 2.0) to nanoparticles with nonporous structure (pH 3.7), and finally to worm-like porous materials with inter-particle mesostructures (pH 4.2) resulted from the aggregates of nanoparticles. The obtained mesoporous nanoparticles (pH 0.6 and 2.0) have mean diameter of ca. 25 nm, and the pore size distributions are bimodal with fine intra-particle pores and larger inter-particle pores. The intra-particle mesostructure not only retard the growth of nanocrystallites, but also prevent phase transition of anatase to rutile at high temperature. The BET surface area of the TiO₂ calcined at 300 °C decreased from 212 to 74 m²/g with pH increasing from 0.6 to 4.2.     

Preparation of amorphous carbon nanotubes using attapulgite as template and furfuryl alcohol as carbon source

Amorphous carbon nanotubes were synthesized by vapor deposition polymerization (VDP) method using attapulgite as template and furfuryl alcohol as carbon source. The morphology and microstructure analysis of the as-prepared samples showed that highly pure amorphous carbon nanotubes were obtained, and determined by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SEAD) and energy dispersive X-ray (EDX) spectrum. The Brunauer–Emmett–Teller (BET) surface area analysis indicated that the specific surface area of the as-prepared amorphous carbon nanotubes reaches up to 503.1 m²/g. A hypothesis about the formation mechanism of the amorphous carbon nanotubes was also proposed accordingly.     

The effect of zirconia content on properties of Al2O3–ZrO2 (Y2O3) composite nanopowders synthesized by aqueous sol–gel method

Al₂O₃–ZrO₂ (Y₂O₃) nanopowders containing 5, 10 and 15 wt% ZrO₂ were synthesized by aqueous sol–gel method using aluminum sec-butoxide and zirconium butoxide as precursors. BET analysis shows that, increasing the zirconia content results in a decrease in surface area, 152, 125 and 121 m²/g, and an increase in pore size, 5.63, 9.79 and 11.05 nm for 5, 10 and 15 wt% ZrO₂, respectively. Furthermore, a shift toward higher temperatures is observed for transition of transitional aluminas to stable α-alumina phase through increasing the zirconia content. SEM micrograph of calcined nanopowders revealed nanosize spherical particles in the range of 15–75 nm.     

A novel process to prepare a hollow silica sphere via chitosan-polyacrylic acid (CS-PAA) template

Hollow silica spheres were synthesized by using a chitosan-polyacrylic acid (CS-PAA) template. Polyacrylic acid (PAA) was titrated into the dissolved chitosan solution to form CS-PAA particles. For forming the core-shell particle, colloidal silica which was prepared from homogeneous nucleation was mixed with a solution of CS-PAA particles. Colloidal silica was adsorbed on to the surface of the CS-PAA particles to form a shell structure. CS-PAA could be removed from the core of the core-shell particles by adjusting with HCl to pH < 1 for forming the hollow silica structure. The outside particle size diameter, shell thickness, specific surface, pore diameter and pore volume of the final hollow silica sphere are about 200 nm, 20 nm, 350.95 m²/g, 5.4078 nm and 0.516768 cm³/g, respectively.     

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.     

A novel approach for the synthesis of monodispersed porous silica microspheres with high surface area

Monodispersed porous silica microspheres are synthesized by the hydrolysis and condensation of tetraethoxysilane (TEOS) in a water–ethanol mixed solution containing 1-alkylamine as a template and hydrolysis catalyst. The as-prepared products were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), small angle X-ray diffraction (SAXRD), Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption, respectively. It was found that the alkyl chain length of 1-alkylamine and calcination temperature have an obvious influence on the particle size, morphology, specific surface area and pore structure of the as-prepared silica powder. The specific surface area, porosity and pore volume increased with increasing calcination temperature. Further observation showed that at 600 °C, with increasing the alkyl chain length of template from C₁₂ to C₁₈, the specific surface area decreased and the pore size, porosity and pore volume increased. This research may provide new insight into the control of morphology and pore structures of oxide materials.     

Synthesis of hybrid mesoporous spheres using the chitosan as template

Hybrid mesoporous spheres of Al and Si oxides were synthesized for the mixture of organic material (chitosan) with inorganic material (aluminum and silicon hydroxide). It was observed that chitosan with larger polymerization degree, resulted in a larger mechanical resistance of the spheres. The oxides were characterized by the following: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), as well as, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and adsorption isotherms of N₂ (BET). Highly uniform oxide sphere diameters were obtained (average of 1.0 mm). The results of the adsorption isotherms indicated that the material is mesoporous. The surface area of the materials ranged between 620 and 245 m²/g, and the pore volume varied between 0.82 and 0.28 cm³/g, depending on the molar ratio of the organic and inorganic materials.     

Characteristics of p-type nanocrystalline silicon thin films developed for window layer of solar cells

Different rf-power and chamber pressures have been used to deposit boron doped hydrogenated silicon films by the PECVD method. The optoelectronic and structural properties of the silicon films have been investigated. With the increase of power and pressure the crystallinity of the films increases while the absorption decreases. As a very thin p-layer is needed in p–i–n thin film solar cells the variation of properties with film thickness has been studied. The fraction of crystallinity and thus dark conductivity vary also with the thickness of the film. Conductivity as high as 2.46 S cm⁻¹ has been achieved for 400 Å thin film while for 3000 Å thick film it is 21 S cm⁻¹. Characterization of these films by XRD, Raman Spectroscopy, TEM and SEM indicate that the grain size, crystalline volume fraction as well as the surface morphology of p-layers depend on the deposition conditions as well as on the thickness of the film. Optical band gap varies from 2.19 eV to 2.63 eV. The thin p-type crystalline silicon film with high conductivity and wide band gap prepared under high power and pressure is suitable for application as window layer for Silicon thin film solar cells.     

Morphological and mechanical properties of hybrid matrices of polysiloxane–polyvinyl alcohol prepared by sol–gel technique and their potential for immobilizing enzyme

Hybrid matrices of polysiloxane–polyvinyl alcohol (POS–PVA) were prepared by sol–gel technique using different concentrations of the organic component (polyvinyl alcohol, PVA) in the synthesis medium. The goal was to prepare carriers for immobilizing enzyme by taking into consideration properties as hardness, mean pore diameter, specific surface area and pore size distribution. The matrices were activated with sodium metaperiodate to render functional groups for binding the lipase from Candida rugosa, used here as a study model. Results showed that low proportion of PVA gave POS–PVA with low surface area and pore volume, although with higher hardness. The chemical activation decreased the pore volume and increased the pore size with a decrease on the surface area of about 60–75%. The matrices for enzyme immobilization were chosen considering the best combination of high surface area and hardness. Thus, the POS–PVA prepared with 5.56 × 10^?5 M of PVA with a surface area of 123 m²/g and hardness of 71 HV (50 gf 30 s) was shown to be suitable to immobilize the lipase, with an immobilization yield of about 40%.     

Characterization of nickel–alumina aerogels with high thermal stability

The characterization of NiO–Al₂O₃ aerogels prepared from nickel nitrate and aluminum iso-propoxide through a sol–gel processing and subsequent supercritical drying was performed. The UV–visible, XPS and FT–IR investigations revealed that nickel ions were incorporated into alumina spinel structure as nickel aluminate form, not as nickel oxide, after calcination. TEM observations after the subsequent reduction exhibited uniform and fine nickel particles less than 6 nm diameter throughout the alumina aerogel support with high dispersion, by which not only high thermal stability of the metal at elevated temperatures but also high reforming activity and stability should be brought about. The large surface area and pore volume also provided the catalyst stability through the improvement of the thermal stability of alumina support.     

Improved method for preparation of anhydrous silica by microwave irradiation with spectroscopic characterization and toxicity assay

Amorphous anhydrous silica SiO_{2 (mw)} (99.99%) is successfully synthesized through microwave irradiation technique and time of reaction is reduced up to 1 h. The dehydration phase study of Si–water, Si–OH, Si–O–Si networking, elemental analysis and surface morphology was carried out by FTIR, FTNIR, SEM and EDAX spectroscopic techniques. The broad absorption stretching and bending of Si–OH and H₂O at 3695.38–2832.96 cm^? 1, 1638 cm^? 1 and 1191.20–1017.14 cm^? 1 completely disappeared and appearance of new bands at 946.93 and 797.63 cm^? 1 confirmed the amorphous anhydrous silica with Si–O–Si networking. The SEM images of SiO_{2 (mwc)} described the smooth and fine particle texture and confirmed 99.99% Si–O–Si networking of anhydrous silica. The 99.99% purity was verified by EDAX spectra which exhibited sharp signals only for oxygen and silicon. Toxicity against Monomorium minimum and Tribolium castaneum with 100% mortality and LT₅₀ 91 min and 7.5 h respectively is being reported. It can be used for long storage of grains in the future.     

Growth and characterization of nanostructured CdS/Polyaniline/CuInSe2 thin films for solar cell applications

In the present paper, we report about synthesis of nanostructured organic–inorganic heterojunction of CdS/Polyaniline/CuInSe₂ thin films by cost effective chemical route at room temperature, for solar cell application. As such obtained thin films are characterized for structural, compositional, morphological, optical and electrical properties by X-ray diffraction (XRD) pattern, energy dispersive X-ray (EDAX) analysis, scanning electron microscopy (SEM), optical absorbance spectra and I–V response respectively. The XRD reveals the polycrystalline nature of the thin films having tetragonal crystal structure and a crystallite size of 19 nm. The presence of observed and expected elements in the EDAX spectra confirms the elemental compositions in CdS/Polyaniline/CuInSe₂ thin films. From SEM images it can be inferred that the surface morphology of the Polyaniline thin films exists like clothing fibers, while CdS/CuInSe₂ shows granular shape particles distributed over the substrate and the SEM of CdS/Polyaniline/CuInSe₂ represents mixing and attachment of circular particles to fiber like structure. The optical absorbance spectra have shown red shift in absorbance strength and energy band gap value of CdS/CuInSe₂ from ~ 1.36 eV to ~ 1.62 eV upon formation of CdS/Polyaniline/CuInSe₂ thin film. The I–V response of CdS/CuInSe₂ and CdS/Polyaniline/CuInSe₂ measured under dark and illumination to 100 mW/cm² light, exhibited the solar characteristics from these graphs and the conversion efficiency calculated is observed to be 0.26 and 0.55% for CdS/CuInSe₂ and CdS/Polyaniline/CuInSe₂ thin films respectively.     

Preparation of thick,crack-free germanosilicate glass films by polyvinylpyrrolidone and study of the UV-bleachable absorption band

With addition of polyvinylpyrrolidone (PVP) transparent, stable GeO₂–SiO₂ sols containing up to 60–80 mol% GeO₂ were synthesized using tetraethyl orthogermanate (TEOG) and tetraethylorthosilicate (TEOS) as precursors for germania and silica, respectively. It was shown by TEM analyses that the PVP can be absorbed onto the colloidal particles providing steric hindrance for the combination and aggregation of particles. These sols were observed showing rapid increase in viscosity within both the early period and the end period of sol aging time, but exhibiting a viscosity value of about 28 mPa s within the rest aging time (45–90 h) satisfying well the requirements for the deposition of thick films by cycles of dip-coating operation. It was determined by TG-DTA and SEM analyses that the densification of GeO₂–SiO₂ gel material with PVP was much more retarded than the gel without PVP resulting in crack-free germansilicate films with a thickness of 3 μm. The crystallization behavior of germansilicate films was enhanced with the increase of GeO₂ content but glass films with a composition of 60GeO₂ · 40SiO₂ was obtained by sintered at 700 °C for 1 h and annealed at 550 °C under a flowing H₂/N₂ atmosphere for 2 h. FT-IR analyse showed that the heat treatment at 700 °C for 60 min was effective to remove the organics and hydroxyl groups in the germansilicate film. An intense 5 eV absorption band was distinctly observed in films. The intensity of this absorption band was found to be effectively bleached by UV illumination. Weak photoluminescence emission bands which originated from the neutral oxygen di-vacancy (NODV) were detected near 375 and 276 nm. Therefore, the 5 eV absorption band observed in this work was mainly caused by the neutral oxygen monovacancy (NOMV). A saturated absorptivity change of the UV-bleachable band after prolonged illumination was found to be 256 cm⁻¹ for the 60GeO₂ · 40SiO₂ films implying the NOMV concentration in the films reached about 3.8 × 10¹⁸ cm⁻³.     

Molecular design of polymer precursors for controlling microstructure of organic and carbon aerogels

Organic and carbon aerogels were prepared by sol–gel polymerization of phenol, melamine and formaldehyde, followed by supercritical drying and pyrolysis. The effect of the mole ratio of melamine/phenol (M/P) on microstructure of organic and carbon aerogels was investigated by N₂ adsorption, SEM and TEM. Coordination M/P could change the hydrophilicity and cross-linking density of polymer framework, thereby affecting polymer colloid nanoparticle nucleation and growth, and ultimately determine the 3-dimensional network of the gels. The bulk densities of organic and carbon aerogels have maxima at M/P of 0.1, which are inversely proportional to volume shrinkage of gels during drying and pyrolysis. The size of the nanoparticles could be adjusted by varying M/P in the range from 10 to 22 nm. The mesopore volumes of organic and carbon aerogels are tailored in the range of 1.4–2.9 and 0.8–2.5 cm³/g, respectively. The average mesopore diameter has experienced a decreasing first and increasing afterward tendency with the increase of M/P, and exhibit a minimum at M/P of 0.1.     

Cadmium ions adsorption in simulated wastewater using structured alumina–silica nanoparticles

Some results on the removal of cadmium ions from simulated industrial wastewater using sol–gel structured nanoparticles of silica and alumina are presented. Two different core-shell nanoparticles were prepared: Al–Si particles (alumina core surrounded by a silica shell) with a molar composition Al:Si of 1:5, and Si–Al particles (silica core and alumina shell) with a molar composition Si:Al of 1:5. Different amounts of cadmium ions were added and the flocculation process of these particles, induced by the ions adsorption, was followed using dynamic light scattering. The efficiency of the ions adsorption was determined using atomic absorption spectroscopy. The results show that it is possible to reduce the cadmium concentration from 140 ppm to less than 5 ppb using Si–Al particles, meeting some international regulations for this contaminant (New European Directive 98-83). The Al–Si particles were not so efficient because the cadmium was only reduced from 125 ppm to less than 90 ppb. The sol–gel technique allows to synthesize model nanoparticles with different morphologies to be used as a prototypes, allowing to choose the better morphology and scaling this knowledge to an industrial level using commercially available silica and alumina nanoparticles chemically modified on the surface.     

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.     

Study on the gel casting of fused silica glass

Slip casting process is usually applied for the forming of fused silica products. Segregation always occurs and it will results in density deviation. By using gel casting process, green is fabricated by means of in situ polymerization with a three-dimensional network, holding the particles together and eliminating the tendency of migration. To prepare gel casting slurries, premix solutions were composed of acrylamide and N,N′-methylenebisacrylamide. Solid loading was kept 60% and the average particle size of silica powder 8–8.5 μm. Lactic acid was introduced as a dispersant to regulate the pH value 3–4. Mechanism of the dispersant was investigated by studying ζ-potential at different pH. Ammonium persulfate (NH₄)₂S₂O₄ was added as an initiator. Gelation took place with the help of initiator at 50–60 °C. Nanometer silica was introduced to boost sinterability so that the density and bending strength of fused silica ceramics have been increased to 2.1 g/cm³ and 40 Mpa, respectively.     

Transparent SiO2 aerogels prepared by ambient pressure drying with ternary azeotropes as components of pore fluid

Transparent SiO₂ aerogels were prepared by two-step sol–gel processing followed by ambient pressure drying at temperatures from 70 to 250 °C. The wet gels were synthesized via acid–base catalysis using tetraethyl orthosilicate as a silica precursor and isopropanol as a solvent. Isopropanol was exchanged with n-butanol, and the gel surface was modified using a trimethylchlorosilane solution in n-butanol. Next, the solvent was exchanged in several steps with saturated hydrocarbon in order to obtain pore fluids containing azeotropic mixtures of water, n-butanol and a corresponding hydrocarbon (hexane, heptane, octane, nonane). Ambient pressure drying was performed in two steps, at the boiling points of the ternary azeotropes and hydrocarbons, respectively. In this way, transparent, crack-free aerogels of different shapes, with a specific surface area of 1000 m²/g, average pore diameter of ～40–55 Å and density in the range 0.4–0.57 g/cm³ were obtained.     

Sol–gel derived organic–inorganic hybrid electrolytes for thin film electrochromic devices

Sol–gel derived, lithium ion conducting organic–inorganic hybrid electrolytes for ambient temperatures applications, have been synthesized from tetraethyl orthosilicate (TEOS), poly(ethylene oxide) (PEO), propylene carbonate (PC), propylene oxide, butyl acrylate, butyl methacrylate, ethyl acetoacetate and LiClO₄ precursors. Mass fractions of the organic additions in the gels were of ca 30 mass% for gels 0/B, F–H and 40 mass% for gel J. The colorless transparent or translucent hybrid materials obtained in this work were aged at room temperature for at least three weeks and then dried at 80 °C for 3 h. The morphology and structure of all compositions were investigated by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM/EDX), Fourier transform infrared spectroscopy and ²⁹Si MAS nuclear magnetic resonance. Amorphous nature of the hybrids was confirmed by X-ray diffraction. SEM, FTIR and NMR analysis showed structural properties and [SiO₄] tetrahedrons poly-condensation process to be strongly influenced by organic additives have been employed. Room temperature ionic conductivities of the hybrid electrolytes were in a range of 9.84 × 10⁻⁴–1.56 × 10⁻³ Ω⁻¹ cm⁻¹.     

Synthesis and bioactive properties of macroporous nanoscale SiO2–CaO–P2O5 bioactive glass

A macroporous nanoscale bulk bioactive glass (SiO₂–CaO–P₂O₅ system) was prepared by sol–gel co-template method. Porosimeter analysis showed that the as-synthesized bioactive glasses (BGs) had a porosity of 85% and exhibited a multimodal pore size distribution, nanopores (10–40 nm) and macropores (100 nm–10 μm). Morphological and structural characterizations showed the pores were interconnected with pore walls of about 250 nm in width and 1 μm in length. In vitro bioactivity test indicated that the as-synthesized bulk BGs exhibited faster apatite layer formation capability than the conventional sol–gel BGs. Additionally, the deposited layer was identified as hydroxycarbonate apatite, which is similar to the inorganic part of human bone.