One-step synthesis of barium hexaferrite nano-powders via microwave-assisted sol–gel auto-combustion

Single phase barium hexaferrite nano-powders have been innovatively one-step synthesized via a microwave-assisted sol–gel auto-combustion in a specially designed quartz vessel using citric acid and ethylene diamine tetraacetic acid as composite chelating agents and freeze-drying technique to remove sols’ moisture. The auto-combustion product powder is characterized by fluffy particle aggregates with the crystallites ranging from 50 to 100 nm in diameter and containing single magnetic domains for each with a low apparent coercive field of 260 Oe and a high saturation magnetization of 64.1 emu/g. The direct formation of barium hexaferrite is believed to result from the effective improvement in the spatial distribution homogeneity of metal ions and oxidant in the gels. Moreover, the quartz vessel with barium hexaferrite ceramic pad on sample's support and film-strips on its interior wall can effectively build up a favorable temperature environment to promote the direct formation of barium hexaferrite with microwave assistance during the gel's uniform auto-combustion.     

Hydrothermal synthesis of potassium–sodium niobate powders

Potassium–sodium niobates (K_xNa_1−xNbO₃, 0 < x < 1, KNN) were hydrothermally synthesized under varying alkaline ratios (K⁺/Na⁺), total hydroxide concentration, reaction temperature, and time. Compositional surveys were developed by using Rietveld analyses derived quantitative volume fractions. The data demonstrated that phase pure KNN synthesis can be achieved by reacting the niobium source with the hydroxide solution having 6 M total hydroxide concentration, cation ratio (K⁺/Na⁺) of above 6 at temperatures ≥200°C for 24 h. Dissolution–precipitation events through intermediate products including hexaniobates were postulated as a plausible formation mechanism. It was shown also that the single-phase KNN approaching the morphotropic phase boundary (MPB) could be obtained by further incorporation of sodium ions into the crystal via post-annealing at 800°C/2 h, following the hydrothermal synthesis.     

A new route for the synthesis of functionalized benzothiadiazine 1,1-dioxide derivatives via intramolecular C–H activation reactions of N,N′,N′′-trisubstituted guanidines and benzenesulfonylchloride

ABSTRACT

In this study, a simple and appropriate procedure for the synthesis of functionalized benzothiadiazine 1,1-dioxide with good yields via the Cu-catalyzed intramolecular C–H activation reaction from benzenesulfonylchloride and N,N′,N′′-trisubstitutedguanidines, generated by copper(II) oxide-catalyzed hydroamination of carbodiimides, is reported.     

A new method of bimodal support preparation and its application in Fischer–Tropsch synthesis

A simple preparation method of bimodal silica was developed by introducing SiO₂ sol into large pores of SiO₂ gel pellet directly. Cobalt supported on this kind of bimodal silica support, exhibited remarkably high activity in liquid-phase Fischer–Tropsch synthesis, which was attributed to its bimodal structure having not only a higher surface area but also a larger pore size. The support with a large surface area allowed highly dispersed cobalt particle and its large pore size improved the diffusion of reactants and products.     

Conventional and microwave-assisted synthesis of hyperbranched and highly branched polylysine towards amphiphilic core–shell nanocontainers for metal nanoparticles

Hyperbranched amphiphilic polymeric systems with core–shell architecture can be used as versatile nanocontainers and templates with great potential in application fields ranging from medicine to organic coatings. In order to explore an alternative to the already widely used and established synthetic macromolecules, we synthesized new polymers based on hyperbranched polylysine. Polylysine was prepared with classical heating and microwave-assisted heating, respectively. While, the synthesis at 160 °C resulted in hyperbranched polylysine with degrees of branching (DB) between 0.50 and 0.54, the microwave-assisted heating at 200 °C resulted in highly branched polymers with DB values of 0.30–0.32. The molecular weight M_n could be controlled in a range of 5000–12,000 g/mol. The hyperbranched polylysine was hydrophobized via polymer-analogue reactions using a mixture of stearoyl/palmitoyl chloride and glycidyl hexadecyl ether, respectively. These reactions yielded in high degrees of modification (80% and 90%, respectively). The synthesized polymers are soluble in non-polar organic solvents, such as toluene and chloroform, and take up metal salts to up to 25 wt.%. They support the formation of Ag, Au, and Pd nanoparticles and nanocrystals in organic solvents and stabilize them. Thus, the here presented macromolecules are a promising readily achievable alternative to existing core–shell systems.     

A new and efficient catalytic system for synthesis of diphenyl carbonate with W–Mo-heteropolyacids as a cocatalyst

A new catalytic system, which consists of Pd(OAc)₂ as the catalyst and W–Mo-containing heteropolyacids (HPAs)/Mn(OAc)₂ as the bicomponent cocatalysts, has been found to be very efficient in the oxidative carbonylation of phenol to diphenyl carbonate at low pressure in the absence of solvent. The efficiency of the catalytic system is dependent on the ratio of W/Mo in the HPAs, being best in a ratio of 6/6. The synergistic effect between W–Mo-containing HPAs and Mn(OAc)₂ has been observed in the catalysis. This revised version was published online in July 2006 with corrections to the Cover Date.     

A study of sodium promotion in Fischer–Tropsch synthesis: electrochemical control of a ruthenium model catalyst

Sodium supplied to the surface of a ruthenium thin film catalyst by electro‐pumping from a solid electrolyte (Na–β″‐alumina) strongly alters the activity and selectivity of the latter in Fischer–Tropsch synthesis. Thus the range of utility of electrochemical promotion has been broadened, this being the first application to a C–C bond forming reaction. The methanation rate is strongly suppressed resulting in a marked increase in selectivity towards C₂–C₄ hydrocarbons, accompanied by an increase in the alkene : alkane ratio. The results obtained with this model system, including the “C₂ anomaly”, are in close agreement with those found for classically promoted conventional dispersed catalysts. Alkali substantially increases the probability of chain growth and CO dissociation is not rate controlling; mechanistic implications are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of nanocrystalline gadolinium doped ceria via sol–gel combustion and sol–gel synthesis routes

Gadolinium doped ceria (GDC) has been investigated as a promising material for application as an electrolyte in intermediate temperature solid oxide fuel cells (IT-SOFC). In this work, 10GDC powders (Gd_0.1Ce_0.9O_1.95) were synthesized by sol–gel combustion and sol–gel synthesis routes using the same complexing agents in both procedures. The thermal behavior of Gd–Ce–O precursor gels was investigated by TG–DSC measurements. X-ray diffraction (XRD) analysis was used for the characterization of phase purity and crystallinity of synthesized samples. Scanning electron microscopy (SEM) was employed for the estimation of surface morphological features. Nitrogen adsorption–desorption (BET model) was used for evaluation of specific surface area. The surface composition was determined by X-ray photoelectron spectroscopy (XPS). Electrical properties of synthesized ceramic samples were studied by means of impedance spectroscopy.     

Direct and facile synthesis of Li–Sr–Zn ferrites via low temperature solution combustion route

Li–Sr–Zn nanoferrites i.e. Li_0.25Sr_0.5–xZn_xFe_2.25O₄, where ‘x’ varies from 0–0.5, have been synthesized using a low temperature solution combustion method which proves to be an efficient and economical technique for synthesizing these type of nanoferrites. The as-synthesized nanoferrites have cubic spinel structure as characterized by X-ray powder diffraction. Powder XRD and TEM (Transmission Electron Microscopy) characterization also evidence that the crystallite and particle size are in close agreement to each other. Mössbauer spectroscopy studies demonstrate that there is a gradual transition from ferrimagnetic to superparamagnetic character, which is also supported by the saturation magnetization and coercivity values. At room temperature, the nanoferrites were found to be superparamagnetic with negligible coercivities approaching towards zero while saturation magnetization values were found to be in the range 6.87–30.10 emu g⁻¹. The frequency dependent dielectric constant and loss values are in accordance with Koop׳s model. These nanoferrites show great potential in high density recordings, magnetic nanodevices and biomagnetic applications.     

Three-component hybrid catalyst for direct synthesis of isoparaffin via modified Fischer–Tropsch synthesis

Direct isoparaffin synthesis method from syngas was developed by using a hybrid catalyst composed of Fischer–Tropsch synthesis catalyst, ZSM-5 zeolite, and Pd/SiO₂, where normal paraffin from Fischer–Tropsch synthesis was hydrocracked in situ on ZSM-5 and Pd/SiO₂ stabilized zeolite activity effectively even at pressurized steam atmosphere mainly via spillover effect.     

Sulfated tungstate: A green catalyst for synthesis of thiomorpholides via Willgerodt–Kindler reaction

Use of sulfated tungstate as an efficient, green and reusable catalyst for preparation of thiomorpholides via Willgerodt–Kindler reaction pathway is presented. The reaction proceeds under solvent free condition. The advantages of this method are high yields, short reaction times, ease of product isolation and recyclability of catalyst for a number of times without significant loss of activity.     

A two-step synthesis of ordered mesoporous resorcinol–formaldehyde polymer and carbon

A new two-step method is developed for the synthesis of resorcinol–formaldehyde polymer and carbon with highly ordered mesoporous structures. For this method, resorcinol and formaldehyde is pre-polymerized in the first step under the presence of a basic catalyst to produce resorcinol–formaldehyde resol. Then, the resorcinol–formaldehyde resol is mixed with Pluronic F127 solution followed by the addition of an acid catalyst to allow the rapid self-assembly and condensation in the second step. Compared with the early reported evaporation-induced self-assembly method as well as the one-step liquid phase self-assembly method, in the present two-step liquid method the self-assembly and condensation process can be carried out rapidly by using low amount of base and acid catalysts at room temperature. After the activation by CO₂, the carbon materials maintained ordered mesostructure, and the BET surface area enlarged to 2660 m²/g and total pore volume increased to 2.01 cm³/g. The CO₂ activation not only creates micropores within the carbon frameworks but also enlarges the mesopores by elimination of the carbon pore walls.     

Size-controlled synthesis of mesoporous silica nanoparticles using rice husk by microwave-assisted sol–gel method

Mesoporous silica nanoparticles with distinct characteristics like particle size, tunable pores, and high surface area have received much interest for environmental remediation, energy conversion, and biological applications. In this work, we synthesized spherical silica nanoparticles with tunable particle size and mesoporous properties using a low-cost silica source (rice husk) and polyethylene glycol (PEG) via microwave-assisted sol–gel synthesis. The formation of an amorphous silica structure was found using XRD and FTIR analysis. FESEM analysis showed that altering the PEG concentration from .01 to .005 M produced spherical silica nanoparticles with 100–500 nm in size. Nitrogen adsorption–desorption demonstrated that silica nanoparticles obtained with .005, .007, and .01 M of PEG had unique pore sizes and distributions, with specific surface areas of 51.475, 62.367, and 84.251 m²/g, respectively. These results might be due to PEG molecules’ capping effect, which acts as a soft template to regulate particle size, pore size, and dispersion by interacting with sodium silicate precursor. Hence, this approach can be a facile and cost-effective method to prepare mesoporous silica nanoparticles with controllable nanoscale characteristics for suitable applications.     

A new procedure for the synthesis of α-acyloxy aldehydes from ketones via α,β-epoxy sulfides

α-Acyloxy aldehydes, as O-protected α-hydroxy aldehydes, have been prepared in good yields via a new procedure involving the sequence: (1) reaction of ketones with sulfur ylides to give α,β-epoxy sulfides, (2) ring opening with carboxylic acids, (3) oxidation of the α-acyloxy-β-hydroxy sulfide products by mCPBA to the corresponding sulfones; and (4) acyl migration followed by elimination of the sulfinate group. The last transformation was readily accomplished, in very good yields, by equivalent amounts of triethylamine in dichloromethane at room temperature (method A); or by acyl migration assisted by complexation of the liberated alkanthiol accomplished in the α-acyloxy-β-hydroxy sulfides by Ag₂O in acetonitrile to give the same α-acyloxy aldehydes (method B). The presented procedure, compared to alternative procedures, has advantages including easily available key intermediates (α,β-epoxy sulfides), mildness of the reactions conditions, more general procedure (applied to different types of α-hydroxy aldehydes).     

Influence of ambient gas on microwave-assisted combustion synthesis of CuO–ZnO–Al2O3 nanocatalyst used in fuel cell grade hydrogen production via methanol steam reforming

The effect of different ambient gases for preparation of CuO-ZnO-Al₂O₃ nanocatalysts by the microwave assisted solution combustion method was studied. Air, nitrogen and carbon dioxide as the ambient atmospheres were injected during the solution combustion synthesis method. The fabricated nanocatalysts were characterized by various techniques such as XRD, FESEM, TEM, EDX, FTIR and BET analyses. It was understood that injection of nitrogen during synthesis of nanocatalysts led to high dispersion of Cu crystallites as the active sites for the steam methanol reforming reaction. Moreover, appropriate interaction between CuO and ZnO particles was achieved due to better morphology of the nanocatalyst synthesized by N₂ as the ambient gas than other samples. Finally, high methanol conversion with proper products selectivity were achieved by the nanocatalyst synthesized by injection of N₂ during the microwave assisted combustion synthesis method due to significant superiority in its physicochemical properties.     

Sol–gel synthesis and characterization of lithium aluminate (L–A–H) and lithium aluminosilicate (L–A–S–H) gels

Hydrous lithium aluminosilicate (L–A–S–H) and lithium aluminate (L–A–H) gels are candidate precursors for glass-ceramics and ceramics with potential advantages over conventional processing routes. However, their structure before calcination remained largely unknown, despite the importance of precursor structure on the properties of the resulting materials. In the present study, it is demonstrated that L–A–S–H and L–A–H gels with Li/Al ≤ 1 can be produced via an organic steric entrapment route, while higher Li/Al ratios lead to crystallization of gibbsite or nordstrandite. The composition and the structure of the gels was studied by thermogravimetric analysis, X-ray diffraction, ²⁷Al and ²⁹Si magic-angle spinning nuclear magnetic resonance, and Raman spectroscopy. Aluminium was found to be almost exclusively in six-fold coordination in both the L–A–H and the L–A–S–H gels. Silicon in the L–A–S–H gels was mainly in Q⁴ sites and to a lesser extent in Q³ sites (four-fold coordination with no Si–O–Al bonds). The results thus indicate that silica-rich and aluminium-rich domains formed in these gels.     

Effect of synthesis methods and aging on synthesis of uvarovite garnet by ceramic and sol–gel processes

Abstract

The uvarovite garnet (CaO)₃ (Cr₂O₃ )(SiO₂ )₃ has been synthesised (mineralised with borax to facilitate diffusion of precursors) by several sol–gel methods. Two routes for uvarovite formation have been observed: where CaCrO₄ forms as an intermediate phase; and where metastable pseudowollastonite (α-CaSiO₃ ) forms as an intermediate phase. Synthesis via CaCrO₄ appears to be more reactive in unaged samples. The reactivity of samples can be directly related to the chemical homogeneity of raw powders, and two methods of synthesis, Pechini and alkoxide, were found to stand out for their reactivity. Aging of raw powders for 6 months inhibits nucleation. Consequently, samples without nucleating agents (i.e. chlorides), such as gels from alkoxides, lead to the stabilisation of amorphous material or metastable phases (α-CaSiO₃ ) and, as a result, hinder uvarovite formation. In contrast, aged samples involving heterogeneous nucleation agents, as in the Pechini method with CaCl₂ as precursor, enhance reactivity.     

Rapid synthesis of a novel cadmium imidazole-4,5-dicarboxylate metal–organic framework under microwave-assisted solvothermal condition

A novel three-dimensional (3D) coordination polymer, [Cd(μ₃-HIDC)(bbi)_0.5]_n (1) (H₃IDC = 4,5-imidazoledicarboxylic acid, bbi = 1,1’-(1,4-butanediyl)bis(imidazole)), has been synthesized under microwave heating solvothermal conditions and characterized by elemental analysis, IR, TG, and single crystal X-ray diffraction. The crystal structure reveal that compound 1 consists of 2D brickwall-like networks of [Cd(μ₃-HIDC)]_n, which are further linked through μ₂-bbi to generate a 3D structure. Compound 1 is stable up to 330 °C and displays strong blue fluorescent emission at room temperature. This work demonstrates that microwave-assisted solvothermal synthesis method is an efficient and fast way to prepare metal coordination polymers.     

Copolymers of ε-caprolactam and polypropylene oxide via anionic polymerization: synthesis and properties

Copolymers with an elastic polypropylene oxide (PPO), middle block in the main chain of poly(ε-caprolactam) were synthesized via activated anionic ring opening polymerization of ε-caprolactam (CL) in the presence of a basic initiator sodium salt of CL (Na-CL) and effective bifunctional polymeric activators (PACs). By varyng the molecular weight, two types of PACs were synthesized based on carbamoyl derivatives of hydroxyl terminated PPO with isophorone diisocyanate and were blocked with CL. The formation of copolymers has been confirmed by proton nuclear magnetic resonance spectroscopy (¹H–NMR) and Fourier transform infrared spectroscopy (FT-IR). The influence of the molecular weight of the PACs, the CL/PAC ratio and polymerization conditions on the conversion, intrinsic viscosity and polymerization kinetics, was investigated. The calorimetric, wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), notched impact test and dynamic mechanical thermal analysis (DMTA) were performed to estimate the influence of the composition ratio and the type of PACs on the physical, thermal, and mechanical properties of the copolymers. The use of the synthesized PACs reduced the polymerization time to several minutes. The copolymers showed improved impact resistance up to more than two times higher than those of the polyamide 6 (PA-6) homopolymer, without significant changes in their high melting temperatures.