Silica-Based and Transition Metal-Based Inorganic-Organic Hybrid Materials—A Comparison

Organically substituted metal alkoxides can be prepared by reaction of the parent alkoxides with complexing organic compounds. The chemical and structural consequences of such substitutions are discussed in this article. Examples are given showing how functional organic moieties, such as polymerizable groups, can be incorporated into sol-gel materials via the complexing ligands. Major structural differences between silica-based and metal-based hybrid materials originate from the different charge/coordination number ratios of silicon and most metals. This results in a high tendency for the molecular building blocks to aggregate. In many cases, metal oxide clusters are formed which are capped by the organic ligands. Such surface-modified clusters are themselves very valuable condensed matter units for materials syntheses.     

Inorganic—Organic Hybrid 18—Molybdodiphosphate Nanoparticles Bullk—modified Carbon Paste Electrode and Its Electrocatalysis

A kind of inorganic‐organic hybrid 18‐molybdodiphosphate nanoparticles ([(C₄H₉)₄N]₆P₂Mo₁₈Q₆₂·4H₂O) was firstly used as a bulk‐modifier to fabricate a three‐dimensional chemically modified carbon paste electrode (CPE) by direct mixing. The electrochemical behavior of the solid nanoparticles dispersed in the CPE in acidic aqueous solution was characterized by cyclic and square‐wave voltammetry. The hybrid 18‐molybdodiphosphate nanoparticles bulk‐modified CPE (MNP‐CPE) displayed a high electrocatalytic activity towards the reduction of nitrite, bromate and hydrogen peroxide. The remarkable advantages of the MNP‐CPE over the traditional polyoxometalates‐modified electrodes are their excellent reproducibility of surface‐renewal and high stability owing to the insolubility of the hybrid 18‐molybdodiphosphate nanoparticles.     

外循环式耐硫甲烷化反应器分析

建立了耐硫甲烷化循环式反应器的拟均相一维模型，考察了床层直径，循环比，入口气体温度及压力和温度范围对反应器操作的影响，结果表明：循环比和温度操作范围是反应器操作的决定因素，对日产５万标准立方煤气的反应器进行了优化设计分析。     

杂合型全局优化法优化水分子团簇结构

基于遗传算法、快速模拟退火及共轭梯度方法提出了一种快速的杂合型全局优化方法(fast hybrid global optimization algorithm, FHGOA),并将这一方法应用于TIP3P和TIPS2模型水分子团簇(H2O)n结构的优化.在进行TIP3P模型水分子团簇结构的优化过程中,发现了能量比文献值更低的团簇结构,且执行效率有较大提高.把该方法应用到优化TIPS2模型的水分子团簇,发现最优结构和采用TTM2-F模型优化的水分子团簇结构在n < 17时完全相同,为全表面结构;而在n=17、19、22时为单中心水分子笼状结构;在n=25、27时为双中心水分子笼状结构.说明随着团簇中水分子个数的增加,采用TIPS2和TTM2-F势能函数优化的团簇最优结构有相同的变化趋势.     

Pulverized coal plasma gasification

A number of experiments on the plasma-vapor gasification of brown coals of three types have been carried out using an experimental plant with an electric-arc reactor of the combined type. On the basis of the material and heat balances, process parameters have been obtained: the degree of carbon gasification (_c), the level of sulfur conversion into the gas phase (_s), the synthesis gas concentration (CO+Hz) in the gaseous products, and the specific power consumption for the gasification process. The degree of gasification was 90.5-95.0%, the concentration of the synthesis gas amounted to 84.7–85.7%, and the level of sulfur conversion into the gas phase was 94.3–96.7%. Numerical study of the process of plasma gasification of coals was carried out using a mathematical model of motion, heating, and gasification of polydisperse coal particles in an electric-arc reactor of the combined type with an internal heat source (arc). The initial conditions for a conjugate system of nonlinear differential equations of the gas dynamics and kinetics of a pulverized coal stream interacting with the electric arc and oxidizer (water vapor) agree with the initial conditions of the experiments. The computation results satisfactorily correlate with the experimental data. The mathematical model can be used for the determination of reagent residence time and geometrical dimensions of the plasma reactor for the gasification of coals.Nomenclature c _i volume concentration of components (kmol m^–3) - x longitudinal coordinate (m) - f _i source members, determined by variation of the ith component due to chemical reactions in unit volume in unit time (kmol m^–3s^–1) - velocity (m s^–1) - M _s ash mass in one particle (kg) - C _D particle drag coefficient - 3.14 - r _s particle radius (m) - d particle diameter (m) - density (kg m^–3) - C _p heat capacity of components (J mol^t– K^–1) - Q _j thermal effect of reaction (J kmol^–1) - E_j activation energy of reaction - N _l volume concentration of particles of thelth fraction (m^–3) - T temperature (K) - emissivity factor of coal particles - 5.67 × 10^–8, blackbody emissivity coefficient (W m^–2 K^–4) - P pressure (Pa) - S reactor cross section (m²) - D reactor diameter (m) - V reactor volume (m³) - L _R reactor length (m) - F _W friction force on the wall (N) - f _g friction coefficient - residence time (s) - Nu Nusselt number - Re Reynolds number - Pr Prandtl number - thermal conductivity of gas (J m^– s^–1 K^–1) - R 8.3 × 10³, universal gas constant (J kmol K^–1) - µ _i molecular mass of component (kg kmol^–1) - dynamic viscosity coefficient of gas (kg m^–1 s^–1) - thermal efficiency of plasma reactor - q_arc specific heat flow from arc (W m^–3) - P ₁ heat supplied in vapor at T = 405 K (W) - P ₂ heat loss to wall (W) - P ₃ heat loss in the gas and slag separator chamber (W) - P ₄ heat loss in the synthesis gas oxidation chamber (W) - P ₅ heat loss in the slag catcher (W) - P ₆ heat carried away in the off-gas (W) - P heat input of arc (W) - P _arc electric power of arc (W) - Q_sp specific power consumption (kw Hr kg^–1) - d _w specific heat flow to wall (W m^–2) - _c degree of carbon gasification (%) - _s level of sulfur conversion into gas phase (%)     

Sugar-anionic clay composite materials: intercalation of pentoses in layered double hydroxide

The intercalation of non-ionized guest pentoses (ribose and 2-deoxyribose) into the Mg-Al and Zn-Al layered double hydroxides (LDHs) was carried out at 298 K by the calcination-rehydration reaction using the Mg-Al and Zn-Al oxide precursors calcined at 773 K. The resulting solid products reconstructed the LDH structure with incorporating pentoses, and the maximum amount of ribose intercalated by the Mg-Al oxide precursor was approximately 20 times that by the Zn-Al oxide precursor. The ribose/Mg-Al LDH was observed to have the expanded LDH structure with a broad (003) spacing of 0.85 nm. As the thickness of the LDH hydroxide basal layer is 0.48 nm, the interlayer distance of the ribose/Mg-Al LDH is 0.37 nm. This value corresponds to molecular size of ribose in thickness (0.36 nm), supporting that ribose is horizontally oriented in the interlayer space of LDH. The maximum amount of ribose intercalated by the Mg-Al oxide precursor was approximately 5 times that of 2-deoxyribose. Ribose is substituted only by the hydroxyl group at C-2 position for 2-deoxyribose. Therefore, the number of hydroxyl group of sugar is essentially important for the intercalation of sugar molecule into the LDH, suggesting that the intercalation behavior of sugar for the LDH was greatly influenced by hydrogen bond between hydroxyl group of the intercalated pentose and the LDH hydroxide basal layers.     

Diamond synthesis by DC thermal plasma CVD at 1 atm

Diamond crystals and films have been success full y synthesized by DC thermal plasma jet CVD at a pressure of I atrn. A novel triple torch plasma reactor has been used to generate a convergent plasma volume to entrain the participating gases. Three coalescing plasma jets produces! by this reactor direct the dissociated and ionized gaseous species onto ( 100) silicon wafer substrates where the diamond grows. In a typical 10-min run, depending on the method of .substrate preparation, either microcrystals with sizes up to 8 m or continuous films with thicknesses of 1–2 m have been obtained. X-ray diffraction, scanning electron microscopy, and Raman spectroscopy have been used for the characterization of the crystals and of the films.     

SYNTHESIS OF MESOPOROUS POLY(STYRENE-co-MALEIC ANHYDRIDE)/SILICA HYBRID MATERIALS VIA A NONSURFACTANT-TEMPLATED SOL-GEL PROCESS*

Mesoporous poly (styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis wasachieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydride copolymerin the presence of 3-aminopropyl triethoxysilane (APTES) as a coupling agent and citric acid as a nonsurfactant template orpore-forming agent, followed by ethanol extraction. Characterization results from nitrogen sorption isotherms and powder X-ray diffraction indicate that polymer-modified mesoporous materials with large specific surface areas (e.g. 900 m~2/g) andpore volumes (e.g. 0.6 cm~3/g) could be prepared. As the citric acid concentration is increased, the specific surface areas, porevolumes and pore diameters of the hybrid materials increase.