Synthesis of novel acidic ionic liquid immobilized on silica

A novel acidic ionic liquid immobilized on silica has been synthesized by hydrolyzing tetraethyl orthosilicate (TEOS) and the acidic ionic liquid derived from (3-aminopropyl) trimethoxysilane. The catalytic activities were evaluated in the acetalization and biodiesel synthesis. The results showed that the solid acid was a very efficient catalyst for the traditional acid-catalyzed reactions with the yield over 99.0%. A novel solid acid combined both the high activities inherent to the acidic ionic liquid and the feasibility of separation of the solid catalysts. High acidity, enhanced catalytic activities and improved stability were the key properties of the novel solid acid.     

Synthesis of nanoporous silica aerogel by ambient pressure drying

A crack-free silica aerogel monolith was fabricated from a cheap water glass derived silicic acid solution by adding glycerol, which served as a drying control chemical additive (DCCA). The OH surfaces of the wet gel with glycerol were modified using a TMCS/n-hexane mixture followed by solvent exchange from water to n-hexane. The obtained surface modified wet gel was dried at 75 °C under ambient pressure. The addition of glycerol appears to give the wet gel a more homogeneous microstructure (larger pore size and uniform size distribution) as well as enhanced stiffness. However, glycerol also retards surface modification and solvent exchange. The aerogel synthesized with glycerol added to the silica sol maintained a relatively low bulk density compared with the aerogels aged in a mixed ethanol (EtOH)/TEOS solution. The reproducibility of aerogel production was further improved in the aerogel synthesized with glycerol added to the silica sol and aged in a 70%EtOH/30%TEOS solution.     

Synthesis of novel solid acidic ionic liquid polymer and its catalytic activities

The novel solid acidic ionic liquid polymer has been synthesized through the copolymerization of acidic ionic liquid oligomers and resorcinol-formaldehyde (RF resin). The catalytic activities were investigated through the acetalization. The results showed that the PIL was very efficient for the reactions with the average yield over 99.0%. The procedure was quite simple with just one-step to complete both the reactions. The high hydrophobic BET surface, high catalytic activities and high stability gave the PIL great potential for green chemical processes.     

单分散酸性纳米二氧化硅的合成新方法

非极性有机溶剂中,乙酸和醇在没有酸性催化剂的情况下发生酯化反应,酯化生成的水水解TEOS(硅酸乙酯)合成单分散酸性纳米二氧化硅,粒径从数十纳米到数百纳米。TEM研究表明,溶剂的极性影响二氧化硅的形态,只有在非极性溶剂中才可以得到球形粒子,醇的种类和TEOS的浓度影响粒子的大小和粒径分布,利用FTIR和GC对TEOS的水解和二氧化硅形成过程进行研究。同时,文中提出了有机相在TEOS的酯化水水解、晶核的形成和生长的过程模型。     

Enzyme encapsulation in nanoporous silica spheres

Encapsulating enzymes in mesoporous silica spheres via immobilization, followed by assembling an organic/inorganic nanocomposite shell on the particle surface leads to high loadings, high enzymatic activity and stability, and protection from proteolysis.     

The electrochemical behaviour of the altenuene mycotoxin and its acidic properties

The electrooxidation of altenuene (ALT), one of the mycotoxins of the Alternaria alternata genus, on a glassy carbon disk electrode is studied for the first time by using cyclic and square wave voltammetry. From the electrochemical responses, a complex reaction mechanism could be inferred. Values of 1.06×10⁻⁵ cm² s⁻¹, 1.116 V and 2 were determined for the diffusion coefficient, the apparent formal potential and the electron number, respectively, for the overall electrode process by convolution analysis of linear scan voltammograms. Square wave voltammetry was used to generate I_p versus c_ALT* calibration curves for this fungal metabolite. A detection limit of 4.0×10⁻⁷ M was determined for a 2:1 signal to noise ratio. The acid dissociation constant for ALT was determined from conventional UV–vis spectrophotometric measurements. Experimental variations of absorbance as a function of pH at a given wavelength were fitted by using the exact equation that describes the system. Good agreement between the experimental absorbance versus pH plots and the curves generated by the fitting process was found.     

Study of hexane adsorption in nanoporous MCM-41 silica

We study here the adsorption of hexane on nanoporous MCM-41 silica at 303,313, and 323 K, for various pore diameters between 2.40 and 4.24 nm. Adsorption equilibria, measured thermogravimetrically, show that all the isotherms, that are somewhat akin to those of type V, exhibit remarkably sharp capillary adsorption phase transition steps and are reversible. The position of the phase transition step gradually shifts from low to high relative pressure with an increase in the temperature as well as the pore sizes. The isosteric heats of adsorption derived from the equilibrium information using the Clapeyron equation reveal a gradual decrease with increasing adsorbed amount because of the surface heterogeneity but approach a constant value near the phase transition. A decrease in the pore size results in an increase in the isosteric heat of adsorption because of the increased dispersion forces. A simple strategy, based on the Broekhoff and De Boer adsorption theory, successfully interprets the hexane adsorption isotherms for the different pore size MCM-41 samples. The parameters of an empirical expression, used to represent the potential of interaction between the adsorbate and adsorbent, are obtained by fitting the monolayer region prior to capillary condensation and the experimental phase transition simultaneously, for some pore sizes. Subsequently, the parameters are used to predict the adsorption isotherm on other pore size samples, which showed good agreement with experimental data.     

Synthesis of tris(β-diketonato) technetium(III) and its adsorption behaviour on silica gel

Tris (benzoylacetonato) technetium(III) and tris (2-thenoyltrifluoroacetonato) technetium(III) were synthesized by the direct reduction of pertechnetate with dithionite in the presence of excess ligands. The geometrical isomers of the benzoylacetonate were further separated by means of a silica gel column chromatography. In the silica gel system, the adsorption distribution coefficient of the tris (-diketonato) technetium(III) decreases in the order of Tc(acac)₃>fac-Tc(bzac)₃>mer-Tc(bzac₃)>Tc(tta)₃.     

Synthesis and mesomorphic behaviour of novel light-emitting liquid crystals

We report the results of a systematic study of the structure-mesomorphic behaviour relationships of a diverse range of light-emitting liquid crystals, but especially nematic 2,7-disubstituted-9,9-dialkylfluorenes. The dependence of the mesomorphic behaviour and transition temperatures on the nature and length of the terminal chains, the nature, position and number of lateral substituents and the number and nature of aromatic rings with and without heteroatoms in the central core is studied. The results of these studies are used to design polymerizable, light-emitting crystals (reactive mesogens) with a nematic phase having a high clearing point and a melting point below room temperature for facile OLED fabrication.     

Preparation and thermal properties of chemically prepared nanoporous silica aerogels

This work focuses on the dependence preparation conditions—structure—physical properties of hydrophobic silica aerogels, all of them prepared under subcritical drying conditions (70 °C and 0.4 atm.), thus aiming at potential application as case insulation filling in heat pumps. The so prepared, millimeter scaled nano-porous hydrophobic silica aerogel granules were analyzed with standard electron microscope and atomic force microscopy, IR spectroscopy, UV/Vis spectroscopy, differential scanning calorimetry and thermal conductivity measurements. The physical properties of the aerogels were compared with commercial aerogel granules. A method for contact angle measurement of micro-droplets situated on the silica granules was proposed to quantify the level of their hydrophobicity.     

Fabrication of lotus-leaf-like nanoporous silica flakes with controlled thickness

Lotus-leaf-like silica flakes with a three-dimensionally (3D) connected nanoporous structure and controllable thickness have been facilely synthesized; the flakes produced exhibited superior performance in adsorbing enzymes to their microspheric analogues.     

Baylis-Hillman reactions in aqueous acidic media

The Baylis-Hillman reaction has been successfully performed under aqueous acidic conditions at pH 1, using a range of substrates and tertiary amines as catalysts.     

Synthesis and formation of hierarchical mesoporous silica network in acidic aqueous solutions of sodium silicate and cationic surfactant

Synthesis and formation of hierarchical mesoporous silica network in acidic aqueous solutions of commercial sodium silicate and cationic surfactant were studied by SEM, TEM, XRD and nitrogen adsorption-desorption methods. The formation process occurs through several steps, involving (1) formation of mesoporous silica nanoparticles; (2) aggregation of mesoporous silica nanoparticles into blocks; (3) growth of silica nanorods in closely-packed arrays by merging of silica nanoparticles; (4) separation of the nanorods to form 3D silica network; and (4) shrinking of the mesoporous silica network. The as-prepared 3D silica network exhibits bimodal morphology constituting mesoporous and macroporous phases.     

Synthesis and characterization of positively capped CdTe quantum wires that exhibit strong luminescence in aqueous media

The novelty of the current work lies in the versatile synthesis of highly luminescent water-soluble CdTe quantum rods (QR) which to the best of our knowledge are the first known water-soluble QR carrying positively charged stabilizer.     

Synthesis and comparative behaviour study of fluorocarbon and hydrocarbon cationic surfactants in aqueous media

A series of perfluorinated cationic surfactants and their corresponding hydrocarbon ones whose general formula is C_nX_2n+1-C(O)NH-(CH₂)₃-N⁺Me₃, I⁻, with X = F, H and n = 9, 11, have been synthesized via two steps. Their aggregative and surface-active properties were studied in aqueous solution using tensiometry and conductimetry. The critical micelle concentrations and the molecular areas at the air/water interface of fluorinated surfactants are lower than those of their hydrocarbon homologues. Micellar aggregation numbers and geometric packing parameters have been investigated. The results indicated that fluorocarbon surfactants tend to form lamellar aggregates while the hydrocarbon ones associate into spherical aggregates.     

Synthesis,luminescence and cyclic voltammetric studies of several novel carboxylato diruthenium complexes

New nonpolymeric diruthenium (II, III) carboxylates of the type [Ru₂(μ-O₂CR)₄Cl] [R = 9-methyl-9H-carbazole, 9-phenyl-9H-carbazole, 9-(4-vinylphenyl)-9H-carbazole] were obtained by reaction of HO₂CR with [Ru₂(μ-O₂CCH₃)₄Cl] in MeOH–H₂O. All complexes were characterized by TG, electron spectroscopy, cyclic voltammetry, and ESR spectra. The solvent influence on fluorescence was also discussed. Simultaneously, the electrochemical properties of these complexes were discussed in terms of the most probable electronic configuration of the complexes in solution. The frozen-solution e.s.r. spectra at 110 K give g = 1.94, 1.99, 1.95 for Ru₂(L⁰)₄Cl, Ru₂(L¹)₄Cl and Ru₂(L²)₄Cl, respectively. The complexes in DMF solution exhibited strong two-photon absorption (t.p.a.) at 532 nm nanosecond laser pulse. Their t.p.a. coefficient β, t.p.a. cross-section δ have been determined by the Z-scan technique.     

Transformations of unsymmetrical N-hetarylformazans in acidic media

1-Aryl-3-phenyl-5-hetarylformazans undergo acid cleavage to give benzaldehyde hetarylhydrazones, whereas 1-hetaryl-3-phenyl-5-(4-nitrophenyl)formazans undergo acid cleavage to give benzaldehyde 4-nitrophenylhydrazones. 1-Aryl-3-phenyl-5-(6-oxo-4-methyl-2-pyrimidinyl)-formazans undergo cyclization to 1,2,4-triazolo[4,3-a]pyrimidine derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1268–1270, September, 1977.