Showing papers by "Nanjing Tech University published in 2004"

Synthesis of p-aminophenol from p-nitrophenol over nano-sized nickel catalysts

Abstract: p-Aminophenol was synthesized by catalytic hydrogenation of p-nitrophenol on nano-sized nickel catalysts prepared by a chemical reduction method from aqueous solutions. The catalysts were characterized by XRD, EDS, SEM, HRTEM and Mastersizer 2000. Analysis results show that as-prepared catalysts are pure f.c.c. nickel and are prone to aggregation; the average particle size of nickel catalysts is 57 nm and there are high-density defects on particle surfaces. In hydrogenation reactions of p-nitrophenol, the hydrogenation rate is zero-order dependent on nitro aromatics and increases with increasing of hydrogen pressure. Compared with commercial Raney Ni, catalytic properties (activity, selectivity, and stability) of the as-prepared nickel are superior. The reason proposed for higher catalytic activity of nano-sized nickel is a combination effect of the small particle size and high-density surface defects. The partial sintering of nano-sized nickel might lead to the deactivation of the catalytic activity of nano-sized nickel.

Personal experience with four kinds of chemical structure drawing software: review on ChemDraw, ChemWindow, ISIS/Draw, and ChemSketch.

Abstract: Chemical structure drawing software is specialized in the chemical structural information with regards to processing, storing, rendering, and editing. With the advent of bioinformatics and chemoinformatics explosion, professional chemical informatics software for personal computers developed rapidly. For the complexity and specialty of chemical information, to use general-purpose drawing software in chemical structure drawing was painstaking and inefficient. The result was unsatisfactory even in the case of simple molecular drawings. The expression of three-dimensional molecular structure and the conversion of molecular structure from two-dimensional to three-dimensional (2D to 3D) were unfeasible by common graphic software. More than a dozen years ago, chemical professionals made use of ink-pen and chemical stencil sets to prepare papers or presentations. Freehand chemical drawing was not uncommon in professional publications. Nowadays, people in chemistry get use to a variety of chemical drawing software in dozens-megabits size. The slim and compact software for chemical drawing of the DOS time seems to be a remote memory. If it was a rarity in the DOS time, the chemical drawing software is commonplace now. Chemists use it everyday. There are more than a dozen popular chemical drawing software, 1 such as ChemDraw, ChemWindow, ChemPen, C-Design, ChemFrontier, DrawMol, and MolDraw, which belong to standalone ones, and ISIS/Draw, ChemSketch, and Chemistry 4-D Draw, which work as interfacial software or add-ins. Interfacial software is usually a member of a suite and could be used independently. Powerful standalone software such as ChemDraw and ChemWindow are members of commercial suites. This article is based on the authors’ experiences with ChemDraw, ChemWindow, ISIS/Draw, and ChemSketch; the current version of ours is 5.0 Ultra, 6.0, 2.5, and 5.12, respectively.

Diameter and helicity effects on static properties of water molecules confined in carbon nanotubes

Abstract: The behavior of water in carbon nanotubes has recently received increasing attention since some theoretical work has shown that nanotubes have the potential to be used as proton-conducting pores for a variety of biological applications. The properties of a nanotube strongly depend on its diameter and helicity; therefore, their influences on the behavior of water molecules confined in carbon nanotubes have to be fully examined for a better understanding of nanotube's potential biological applications. In this work, molecular dynamics simulations were performed under ambient conditions for armchair and zigzag type nanotube segments of various diameters submerged in water. The results indicate that single-file water chains as the basis of fast proton conduction can be formed only in narrow nanotubes (0.676–0.811 nm diameter). The formation of ice-like water structures inside nanotubes might be sensitive to potential models and corresponding parameters. Obvious variation in average number of H-bonds per molecule can occur only in narrow carbon nanotubes, which is expected to significantly affect the diffusion rate of confined water. The extent of confinement phenomena is dominated by tube diameter. Tube helicity rarely affects the static properties of confined water.

Highly Efficient Liquid-Phase Photooxidation of an Azo Dye Methyl Orange over Novel Nanostructured Porous Titanate-Based Fiber of Self-Supported Radially Aligned H2Ti8O17·1.5H2O Nanorods

Abstract: Novel nanostructured porous fibers of self-supported, radially aligned H2Ti8O17·1.5H2O nanorods were prepared from layered H2Ti4O9·1.2H2O tetratitanate fibers by novel solvothermal reaction in glycerine at 150−250 °C. The H2Ti8O17·1.5H2O fibers with diameters of 0.5−1.5 μm and lengths of 10−20 μm consist of multi-scale nanopores and nanostructures. They also are of high crystallinity, large surface area of 127 m2 g-1, and stable phase up to 350 °C. Photocatalytic activity of the H2Ti8O17·1.5H2O fibers was evaluated in aqueous photooxidation of an azo dye methyl orange in the presence of UV irradiation and O2, using P-25 as the standard sample. Both the photocatalytic activity and the dispersity−agglomeration property of H2Ti8O17·1.5H2O fibers are pH-controllable. Highly photooxidative activity, superior to that of P-25, occurs at pH 6.0−11.0 due to certain distinguishable material characteristics and to large amounts of adsorbed reactants of surface active OH• free radicals, surface hydroxyl OH, O2•-, O•O...

Alkylation of 1-Dodecene with Benzene over H3PW12O40 Supported on Mesoporous Silica SBA-15

Abstract: The SBA-15 supported 12-phosphotungstic acid catalysts were prepared and measured in the alkylation of benzene with 1-dodecene at the atmospheric batch reactor. It is found that the catalysts exhibit much higher catalytic activity, selectivity and stability than HY zeolite in this reaction at the reaction temperature of 80 °C, with the 1-dodecene conversion of nearly 90%, 2-phenyldodecane selectivity of nearly 40%, and monoalkylbenzene selectivity of 100%.

Positional assembly of hybrid polyurethane nanocomposites via incorporation of inorganic building blocks into organic polymer

Abstract: Polyurethane (PU)/silica nanocomposites (PSNs) were synthesized using the “grafting from” technique by incorporation of inorganic nano-sized silica building blocks into a polyurethane matrix. Structurally well-dispersed and stable hybrids were obtained via a two-step functionalized reaction. Firstly, 3-aminopropyltriethoxysilane (APTS) was employed to encapsulate silica as the core surface. Secondly, the PU shell was tethered to the silica core surface via surface functionalization. In order to obtain complete encapsulation of silica with APTS, different ratios of APTS to silica were investigated. The mechanism of the incorporation process was also revealed. PSNs hybrids were characterized by attenuated total reflectance and Fourier transform infrared spectroscopies, differential scanning calorimetry, thermogravimetric analysis, and transmission electron microscopy.

High Quality and Yield in Potassium Titanate Whiskers Synthesized by Calcination from Hydrous Titania

Abstract: Hydrous titanium dioxide (TiO2·n H2O) was used to prepare K2Ti2O5 single crystals, K2Ti4O9 whiskers and K2Ti6O13 whiskers at 820°, 940°, and 1110°C, respectively, by calcination. At T < 820°C, dehydration of hydrous titania, decomposition of potassium carbonate, and reaction between titanate and potassium oxide occurred simultaneously, ending with a crystallization reaction of K2Ti2O5 single crystals at 820°C. Subsequently, K2Ti2O5 single crystals convert into K2Ti4O9 whiskers at 940°C, and K2Ti4O9 whiskers further convert into K2Ti6O13 whiskers at 1110°C. The reaction temperatures for the generations of these types of potassium titanates were all 10°–40°C lower than the corresponding temperatures when anatase was used as the reactant. The whiskers synthesized in the present study exhibited uniform size, good morphology, and a high yield.

Phase equilibria for binary systems of methyl oleate-supercritical CO2 and α-tocopherol-supercritical CO2

Abstract: In order to study the possibility of using supercritical CO 2 to concentrate tocopherols from soybean oil de-odorizer distillate (DOD), the binary phase equilibrium data for methyl oleate–CO 2 and α-tocopherol–CO 2 were measured at 313.15–353.15 K in the pressure ranges of 5–23 MPa for methyl oleate and 5–30 MPa for α-tocopherol, respectively. The measured data were well correlated using the Soave–Redlich–Kwong (SRK) equation of state (EOS) with the Adachi–Sugie (AS) mixing rule. The solubilities and distribution coefficients of methyl oleate and α-tocopherol in CO 2 were investigated. Finally, on the basis of these results, a conclusion was preliminarily drawn, supercritical CO 2 can be used to concentrate natural tocopherols from the esterified DOD in the experimental range investigated. In addition, the critical points of methyl oleate–CO 2 at three temperatures were estimated.

Improved catalytic activity and stability of mesostructured sulfated zirconia by Al promoter

Abstract: Al-promoted mesostructured sulfated zirconia (Al-MSZ-5) has been successfully synthesized from the template of triblock polymer surfactant (P123) in aqueous solution. Mesostructured Al-MSZ-5 shows high thermal stability, and it can preserve its characteristic mesostructures until calcination at 650 °C. In contrast, the mesostructure of mesoporous sulfated zirconia (MSZ-5) will be destroyed during calcination at 600 °C. Catalytic data for n-butane isomerization show that the Al-MSZ-5 exhibits higher catalytic activity and better stability than both MSZ-5 and conventional Al-promoted sulfated zirconia (Al-SZ). The Al-MSZ-5 sample was characterized by XRD, bright-field and dark-field TEM images, N2 adsorption isotherms, NMR, TG–DTA, IR, and numerous other techniques. The results suggest that Al-MSZ-5 has worm-like mesopores, and that the mesostructured walls contain tetragonal crystalline ZrO2. Such unique structural features might be responsible for the observed large surface area, high catalytic activity for n-butane isomerization, and high thermal stability of mesostructured Al-MSZ-5.

Consolidation analysis of a cross-anisotropic homogeneous elastic soil using a finite layer numerical method

Abstract: This paper presents a finite layer procedure for Biot's consolidation analysis of layered soils using a cross-anisotropic elastic constitutive model. The program is first verified using published results. Then, using this program, the influences of cross-anisotropy on the immediate settlement, the final settlement, and the consolidation behaviour are investigated by changing one model parameter at one time. The results obtained using the cross-anisotropic elastic model are compared with results using an isotropic elastic model. It is found that the cross-anisotropy has very large influences on the immediate settlement, the final settlement, and the consolidation behaviour. Curves or tables of the immediate settlement coefficients, the final settlement coefficients, and the average degree of consolidation are obtained and presented in the paper. These curves or tables can be easily used to estimate the immediate settlement, the final settlement, and the consolidation settlement of a cross-anisotropic soil. Copyright © 2004 John Wiley & Sons, Ltd.

The synthesis of boron nitride nanotubes by an extended vapour?liquid?solid method

Abstract: An extended vapour?liquid?solid (VLS) growth method, which is the reaction of a mixture of nitrogen and ammonia gas over nanoscale Fe?B 'catalyst' particles at 1100??C, has been developed. With this method, BN nanotubes of diameter about 20?nm have been prepared and well characterized by high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy. In contrast to traditional VLS growth, the boron component in the BN nanotubes comes from the Fe?B 'catalyst' itself, rather than from the vapour precursor. A growing mechanism has been discussed accordingly.

A controllable approach for the synthesis of titanate derivatives of potassium tetratitanate fiber

Abstract: Three types titanate derivatives, K2Ti6O13 fiber, K2Ti8O17 fiber and anatase TiO2 fiber, were synthesized by ion-exchange reaction from potassium tetratitanate fiber (K2Ti4O9) based on the hydrate conditions predicted by a thermodynamic model. These products were formed by a heat treatment of the corresponding hydrate intermediates K1.33H0.67Ti4O9·H2O, KHTi4O9·0.5H2O and H2Ti4O9·1.2H2O which were quantitatively obtained by controlling the pH value and the equilibrium concentration of potassium ion. The mole ratio of Ti/K in solid phase (R) of the target products was taken as the controlling aim in the hydrate process. The temperature for heat treatment of hydrate intermediates was determined by thermogravimetry (TG) and differential scanning calorimetry (DSC). All products retained fibrous morphology similar to that of K2Ti4O9 used as the starting material.

Room temperature solid-state reaction?a convenient novel route to nanotubes of zinc sulfide

Abstract: Nanotubes of zinc sulfide (ZnS) have been synthesized conveniently by a simple route of solid-state reaction at room temperature and were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), x-ray powder diffractometry (XRD) and transmission electron microscopy (TEM). XRD showed the product obtained to be crystalline sphalerite (cubic ZnS) and TEM clearly demonstrated the nanotubes of ZnS with average diameters of about 90 nm and lengths of up to 10 µm.

Low-temperature controllable calcination syntheses of potassium dititanate

Abstract: Thermodynamic calculations were used to estimate the free energy for reactions of anatase and TiO2·nH2O with K2CO3 to generate potassium dititanate at 25–1200°C, and the results showed that amorphous TiO2·nH2O with reaction activity higher than that of anatase can decrease the lowest generation temperature of potassium dititanate. The precise temperatures of 300°C for TiO2·nH2O and 500°C for anatase were determined by experiments. The crystal growth of potassium dititanate was studied experimentally. It was found that potassium dititanate hydrate is first formed from TiO2·nH2O at 300°C, and converts into K2Ti2O5·0.35H2O at 640°C. The dehydration of K2Ti2O5·0.35H2O occurs at 660–820°C, ending with the generation of K2Ti2O5 single crystals at 820°C. Potassium dititanates with a diversity of morphologies, sizes, water contents, and crystallinities, showing various abilities for optical absorption/reflex, were fabricated from TiO2·nH2O under control, whereas only K2Ti2O5 was prepared from anatase at 500–850°C, which indicate that reaction processes and properties of products are determined according to the type of reactants and the reaction temperature. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1568–1577, 2004

Non-destructive determination of carbohydrate content in potatoes using near infrared spectroscopy

Abstract: The performance of near infrared spectroscopy as a simple technique for the non-destructive determination of carbohydrate content in potatoes was examined. An interactance method was adopted to measure near infrared spectra (700–1100 nm). A good calibration model with reasonable accuracy (correlation coefficient of 0.93 and standard error of prediction of 0.98%) was developed using partial least square (PLS) regression. The PLS calibration model utilised effectively two characteristic absorption bands of 990 nm and 916 nm, assigned to potato starch. The plots of the regression coefficients were thought to be useful for understanding the calibration model structure.