CuZnAl mixed-metal oxides prepared by a novel sol–gel route and the application for synthesis of 2- methylpyrazine

Metal (Cu, Zn, Al) nitrates and chlorides were used for preparing CuZnAl xerogels by a sol–gel route with propylene oxide as gelation initiator. The CuZnAl mixed-metal oxides were further obtained by thermal treatment the xerogels at 500 °C for 5 h in air. Thermal decomposition behavior of the CuZnAl xerogels, the microstructures and the reducibility of the calcined xerogels were investigated by thermogravimetry (TG), scanning electron microscope (SEM), powder X-ray diffraction (XRD), N₂ adsorption/desorption (BET, BJH) and temperature-programmed reduction (TPR) techniques. The catalytic activity in dehydrocyclization of ethylenediamine (ED) with 1, 2-propyleneglycol (PG) to 2-methylpyrazine (2-MP) was carried out at 380 °C. The results displayed that the CuZnAl mixed-metal oxides prepared using nitrates as the metal precursors had a higher metallic Cu dispersion and a superior low-temperature reducibility than those prepared by chlorides, which results in a higher catalytic activity for the synthesis of 2-methylpyrazine. Especially when the molar ratio of Cu/Zn/Al = 2:1:2, the catalyst using nitrates as the metal precursors improved the selectivity of 2-MP to 87.5%.     

A simple template-free sol–gel synthesis of spherical nanosilica from agricultural biomass

Mesoporous silica nanoparticles with a spherical morphology have been synthesized from rice husk (agricultural biomass) by a simple, template-free synthetic approach, which was carried out via sol–gel technique at ambient condition. Transmission electron micrographs revealed the formation of spherical silica nanoparticles with an average diameter of 50.9 nm. From the nitrogen adsorption–desorption analysis, the rice husk silica shows a high specific BET surface area of 245 m² g⁻¹. The silica nanoparticles have a narrow pore size distribution of 5.6–9.6 nm.     

A simple sol–gel hydrothermal method for the synthesis of defective TiO2 nanocrystals with excellent visible-light photocatalytic activity

Research on Chemical Intermediates - Defective TiO2 nanocrystals (D-TiO2) were synthesized by a simple, mild and green sol–gel hydrothermal method. The as-prepared sample possesses a high...     

Review of mullite synthesis routes by sol–gel method

The sol–gel method for the mullite synthesis is reviewed, with particular emphasis on the characterization of monophasic and diphasic gels at low, intermediate and high temperatures and the factors that influence the hydrolysis and condensation rate of the sol–gel process, which in turn determine the properties of the final material. A wide range of studies about mullite precursors synthesized via sol–gel is discussed here.     

Microwave-assisted sol–gel synthesis for molecular imprinting

Molecularly imprinted polymers have been the subject of intense research for several decades in both academic and industrial settings. In this paper, we introduce a novel microwave-assisted sol–gel method for molecular imprinting of silica microspheres. The microspheres were characterized, and their adsorption of imprint and non-imprint molecules was investigated. The dye molecules methyl orange and ethyl orange were used as templates. Good molecular imprinting was observed as evaluated by the re-adsorption of dye into the silica matrix followed by the removal of dye from the supernatant solution.     

A novel sol–gel strategy to prepare temperature-sensitive hydrogel for encapsulation of protein

A novel sol–gel strategy was proposed to prepare temperature-sensitive hydrogel including the copolymerization of N-isopropylacrylamide and 3-methacryloxypropyl-trimethoxy silane and then the hydrolysis and condensation of the linear polymers through the sol–gel process under extra-mild conditions. Bovine serum albumin, as a model protein, was loaded into the hydrogel matrix to investigate the encapsulation and release properties. Experimental results indicated that the preparation conditions were valuable for the loading and release of biomacromolecules.     

A study on sol–gel synthesis and characterization of SiC nano powder

Nano sized β-SiC particles were synthesized from sol–gel process. Mono dispersed β-SiC nano particles with semi spherical morphology were obtained by employing APC as a dispersant agent and adjusting pH in the range of 2.5–4. Phenolic resin and TEOS were employed as precursors and heat treatment was conducted up to 1500 °C. Different techniques such as XRD, DTA, FTIR, PSA, SEM and TEM were used to characterize the formation of β-SiC. The (Si–O-C) bonds were formed by hydrolysis and condensation reactions in the gel while the nucleation of crystalline β-SiC was found to be initiated at 1400 °C. The primary particles in the sol were found to be (< 10 nm) while the size distribution in the final product was recorded in the range of 30–50 nm.     

Non-hydrolytic sol–gel synthesis of tantalum sulfides

Non-hydrolytic sol–gel synthesis provides a low temperature solution based approach to solid-state materials. In this work, reactions of TaX₅ (X = F, Cl, Br, I) with the thio-ethers di-tert-butylsulfide and hexamethyldisilathiane were carried out in chloroform or acetonitrile. The influence of synthetic parameters such as temperature, reaction time, starting sulfur to tantalum ratio, and solvent volume were explored, and optimized conditions for the preparation of phase pure crystalline TaS₂ were established. Amorphous powders were recovered for most of the samples, but crystalline 1T- and 3R-TaS₂ modifications could be selectively prepared by heat treatments of the as-recovered precursors at 700 and 800 °C, respectively. The crystallite sizes could be adjusted by tuning the starting sulfur to tantalum ratios, and by choice of solvent. For specific conditions, nanocrystalline 1T-TaS₂ was directly recovered from solution. To our knowledge, this is the first time that crystalline TaS₂ was directly obtained from low temperature solution based routes.     

A hybrid sol–gel synthesis of mesostructured SiC with tunable porosity and its application as a support for propane oxidative dehydrogenation

Porous silicon carbide (SiC) is of great potential as catalyst support in several industrially important reactions because of its unique thermophysical characteristics. Previously porous SiC was mostly obtained by a simple sol–gel or reactive replica technique which can only produce a material with low or medium surface area (< 50 m2 g(?1)). Here we report a new hybrid sol–gel approach to synthesize mesostructured SiC with high surface area (151–345 m2 g(?1)) and tunable porosity. The synthesis route involves a facile co-condensation of TEOS and alkyloxysilane with different alkyl-chain lengths followed by carbothermal reduction of the as-prepared alkyloxysilane precursors at 1350 °C. The resulting materials were investigated by X-ray diffraction, N2 adsorption-desorption, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. A mechanism for the tailored synthesis of mesostructured SiC was tentatively proposed. To demonstrate the catalytic application of these materials, vanadia were loaded on the mesostructured SiC supports, and their catalytic performance in oxidative dehydrogenation of propane was evaluated. Vanadia supported on the mesostructured silicon carbide exhibits higher selectivity to propylene than those on conventional supports such as Al2O3 and SiO2 at the same propane conversion levels, mainly owing to its outstanding thermal conductivity which makes contributions to dissipate the heat generated from reaction thus alleviating the hot spots effect and over-oxidation of propylene.     

Comparative study of the thermal behavior of Sr–Cu–O gels obtained by sol–gel and microwave-assisted sol–gel method

Journal of Thermal Analysis and Calorimetry - In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu2O2 (SCO) having possible applications...     

Aqueous sol–gel synthesis and thermoanalytical study of the alkaline earth molybdate precursors

The preparation and characterization of the M′–Mo–O nitrate–tartrate (M′ = Mg, Ca, Sr, and Ba) gels, which were produced by the simple aqueous sol–gel method and calcined at 500, 600, 700, 800, 900, and 1,000 °C temperatures are reported. The crystalline alkaline earth metal molybdates (MgMoO₄, CaMoO₄, SrMoO₄, and BaMoO₄) and as-prepared M′–Mo–O nitrate–tartrate gels investigated by thermal analysis (TG/DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). TG/DSC analysis showed the possible decomposition mechanism of synthesized gels. XRD studies allowed the identification of main types of crystalline structures in the MgMoO₄, CaMoO₄, SrMoO₄, and BaMoO₄ systems. Moreover, SEM analysis revealed the changes of surface morphology of the final compounds depending on annealing temperatures.     

A simple route to obtain TiO2 nanowires by the sol–gel method

In this work, titanium dioxide (TiO₂) nanowires were synthesized by the sol–gel method, without using any kind of templates, instead of that acetic acid was used as morphological modifier. In order to control crystalline phases and crystal size, TiO₂ was calcinated at 400, 500 and 600 °C during 1 h. The resulting morphology was nanowires, which diameter was maintained constant after calcination at different temperature (about 76 nm). Moreover, crystalline phases in order of predominance were anatase, anatase–rutile and rutile–anatase at 400, 500 and 600 °C, respectively. Additionally, the crystallite size increases with respect to temperature from 13 to 75 nm.     

Synthesis of mesoporous γ-alumina by sol–gel process and its characterization and application for sorption of Pu(IV)

Mesoporous γ-alumina samples were prepared by the sol–gel process from the boehmite sol having different template solutions. Copper doped material was also prepared from sol containing template solution along with copper nitrate. Studies were performed to understand the influence of templates on the morphology of the synthesized samples particularly with respect to specific surface area and porosity. Synthesized samples were used to study sorption of Pu(IV) from nitric acid–oxalic acid solutions. Distribution ratios (D) for Pu(IV) were determined using the γ-alumina samples with an objective to employ these for the recovery of Pu.     

Carbon supported electrocatalysts prepared by the sol–gel method and their utilization for the oxidation of methanol in acid media

One of the key objectives in fuel-cell technology is to improve the performance of the anode catalyst for the alcohol oxidation and reduce Pt loading. Here, we show the use of six different electrocatalysts synthesized by the sol–gel method on carbon powder to promote the oxidation of methanol in acid media. The catalysts Pt–PbO _x and Pt–(RuO₂–PbO _x ) with 10% of catalyst load exhibited significantly enhanced catalytic activity toward the methanol oxidation reaction as compared to Pt–(RuO₂)/C and Pt/C electrodes. Cyclic voltammetry studies showed that the electrocatalysts Pt–PbO _x /C and Pt–(RuO₂–PbO _x )/C started the oxidation process at extremely low potentials and that they represent a good novelty to oxidize methanol. Furthermore, quasi-stationary polarization experiments and cronoamperometry studies showed the good performance of the Pt–PbO _x , Pt–(RuO₂–PbO _x )/C and Pt–(RuO₂–IrO₂)/C catalysts during the oxidation process. Thus, the addition of metallic Pt and PbO _x onto high-area carbon powder, by the sol–gel route, constitutes an interesting way to prepare anodes with high catalytic activity for further applications in direct methanol fuel cell systems.