2001 Vol. 14, No. 4

Article
Coupling of methane in the present of hydrogen to C2hydrocarbons operated at atmospheric pressure in order to evaluate a newly-developed plasma reactor with rotating poly-tip electrodes, in which circular glow discharge plasma zone between a stator and a rotor with polytip electrodes is vertical to the way of the stream of flowing reactants. No substantial amount of carbon formation was observed on the surface of the electrodes after a long period of the reaction(>1 h) when the molar ratio of feed flow of CH4∶H2is 1∶1 and the A.C. glow discharge at 20kHz, input power of 856 V(rms). C2hydrocarbons single pass yield is 42.6%, in which C2H2 38.9% and C2H43.5% respectively, with 62.3% methane conversion but with carbon formation when input power is 1010 V(rms)
Photodissociation dynamics of CS2+molecular ions has been investigated by (1+two-photon resonance technique. CS2+were prepared by (3+1) resonance-enhanced multi-photon ionization (REMPI) of CS2molecules at 483. 2nm. The photofragment S+excitati (PHOFEX) spectra were recorded by scanning another laser in the 424~482nm region, and we assigned essentially to CS2+(~A2Πu,3/2(v′=0~4)←~X2Πg,3/2(0,0,0)) and (~A2Πu,1/2(v′=0,4)←~X2Πg,1/2(0,0,0)) (herev′=v1′+(1/2)v2′) transitions. The S+production channel wpreliminarily attributed to, (i) one-photon excitation CS2+from the ground state~X2Πgto texcited state~A2Πu; (ii) vibronic coupling between the~A2Πustate and the high vibrational lev in the~X2Πgstate; (iii) second photon excitation from the coupling vibrational levels to the excied state~B2Σu+and dissociation to produce S++ CS via the repulsive4Σ-state through spin-orb interaction between the~B2Σu+and4Σ-states.
Carbene is a very important reactive intermediate to explain organic reaction mechanism that cannot be considered by generally; on the other hand, the triplet carbene has been considered to the unite of organic magnetic materials owing to its special electronic structure that has a parallel electronic configuration described asσ1ρ1. However the triplet carbene is too reactive to trap, for instance, the lifetime of triplet diphenylcarbene is only 0.002ms. For this reason the stabilization of carbene would be necessary for organ chemistry and advance organic materials. Two basic strategies, i.e., thermodynamic and kinetic stabilization, are possible for the stabilization of reactive species. Studies examining the relationship between structure and reactivity have shown that thermodynamic stabilization (electronic conjugation effect) usually play an important role in stabilizing the singlet state and that the singlet state undergoing the stabilization becomes less reactive due to the contribution of the conjugation to such an extent that the species can be isolated under ambient condition. On the other hand, kinetic stabilization (steric protection) is more effective in stabilizing the triplet counterpart since the introduction of sterically bulky groups around the carbenic center results in an increase in the carbene bond angle and protection the carbenic center attacked by minor impurities in the surrounding medium, i.e., a trace of oxygen. To explorer the stable effect of substituents on the triplet diphenylcarbene, in the preceding paper, we had generated a series of triplet diphenylcarbenes, in which have various substituents at the para- or ortho-position by photolysis of the corresponding diphenyldiazomethane at room temperature, and studied their reactivities with oxygen by laser flash technique. And revealed that the substituents whether para- or ortho-position can cause the stable effect on the triplet diphenylcarbenes, and the steric protective effect in ortho-position is more effective. In order to further investigate the steric protective effect (kinetic stabilization) of substituents on the triplet diphenylcarbene, a series of triplet diphenylcarbenes having a varied size of substituents at orthoand para-positions have been generated by the irradiation of diazo precursors, and observed them directly by UV/vis spectroscopy. And measured the lifetime of the triplet diphenylcarbenes by means of laser flash photolysis in degassed benzene at room temperature. It has been shown that the triplet diphenylcarbenes have farther stabitities with the bigger substituents at ortho- and para-positions, because the steric effect, that the bigger substituents have made carbene have a bigger central bond angle, protect the attack on the carbenic center by minor impurities.
Using hypervirial theorem (HVT) and Hellmann-Feynman theorem (HFT), perturbation calculation of successive order approximate values of energy levels in a potential well with power series expansion of the potential energy are processed. Algebraic recursion formulas for calculating energy levels are deduced. We use the exact energy levels for parabolic potential well (one dimensional harmonic oscillator) as zero order approximation, and derive algebraic formulas for successive order approximate energy levels for given potential energy function. The corresponding wave functions can then be written as polynomials in which coefficients are expressed in terms of the energy levels and coefficients in the power series of potential energy. In this way, tedious and cumbersome perturbation calculations in Rayleigh-Schr dinger perturbation method are avoided. Thus the present method is simple, efficient and time saving. Typical examples are illustrated with the algebraic formulas, including: energy levels for Gaussian potential well; for modified P schel-Teller well; potential wells for anharmonic oscillators; Morse potential for vibrational energy levels of diatomic molecules and modified Morse potential for vibrational-rotational energy levels. Formulas for calculation of wave functions corresponding to calculated energy levels are given for anharmonic oscillators and for symmetric potential energy functions. The present method can be extended to two or three dimensional potential well, and can also be used in other mathematically analogous eigenvalue problem
Density functional theory (DFT) andab initiomethods were used to optimize the molecular geometry of 2,3,7,8-TCDD at B3LYP/6-31G, B3LYP/6-31G*, B3LYP/6311G* and MP2/6-31G* levels, respectively. Harmonic vibrational spectrums have been performed at B3LYP/6-31G* and B3LYP/6-311G* levels. The standard thermodynamic parameters such as heats of formation, standard entropy, standard enthalpy, heat capacity at various temperatures have been evaluated using the scaled B3LYP/6-31G* and B3LYP/6-311G* frequencies. Semi-empirical molecular orbital method with the PM3 Hamiltonian at restricted Hartree-Fock level (RHF) was also performed to compare the geometrical optimization and thermodynamic properties with those methods mentioned above. The results show that: (1) 2,3,7,8-tetrachlorinated dibenzo-p-dioxin(TCDD) is a planar molecule, optimal geometries obtained by B3LYP/6-31G, B3LYP/6-31G*, B3LYP/6311G * andMP2 / 6 - 3 1 G* arealmostthesame, thelargestdifferenceinbondlengthbetweenthemis 7.9 pm, the largest difference in bond angle is 0.55o, and the largest difference in rotational constant is 0.03 GHz; (2) There are 60 vibrational frequencies for this molecule, of which there are 10 strongest intensities of vibration bands. The computed frequency scaled by 0.9628 for B3LYP/6-31G* and scaled by 0.9711 for B3LYP/6-311G* have similar frequencies and intensities of vibration bands, both are in good accordance with experimental values. (3) The thermody namic parameters such as standard entropy, standard enthalpy, heat capacity, heats of formation at temperatures from 298~1500K have been calculated, All the thermodynamic parameters increase with the increment of temperature, and the difference between B3LYP/6-31G* and B3LYP/6-311G* is small, PM3 method alsopredictsgood results, and ingood accordancewithother′sworksandexperimen talvalues. (4) The optimal geometry and thermodynamic parameters of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (TCDD) obtained in this paper would be fundamental databases for further research on generation, decomposition and kinetics study of dioxins.
The formulas of inner pressure and inner energy of the liquid are derived using distribution function theory. During the derivation three characters of interaction potential energy of the liquid are assumed. The first is that the interaction force between molecules is the short-range force. The second is that the many-body potential is only relying on the distances between the molecules. The third is that the potential energy of the liquid can be written as the sum of a series of many-body potential . The inner pressure and inner energy can be expressed in the power series of the volume. The coefficients in the series are expressed in many-body potential and radial distribution functions and are only depend on temperature. When onlynth many-body potential is exist, the formula of inner pressure and inner energy are in agreement with the result of perturbation theory obtained by Egelstaff. The results not only give the expressions for parameters but also are suitable for stronger interaction between molecules. Another form of expressions of inner pressure and inner energy is obtained by defining parametersmandα(T). The expressions agreed with the experimental result worked out by Frank. The results give the expressions for parametersmandα(T)and point out that the Frank formulas are tenable only for the liquid which mandα(T)are independent of volume.
With the help of the phase separation model and the regular solution theory, on the basis of synergism conditions derived by Rubingh and Rosen, some synergism parameters in surface tension reduction effectiveness in binary mixed systems of surfactants are obtained, including the synergism condition (βs-βm<0), the optimum molar fractionα*1, the lowest surface tension of the mixtureγ*cmcand the corresponding critical micelle concentrationcmc12*at the point of maxi mum synergism. Application of these relationships to two binary systems of surfactants, C12NMe3Br~C12SO4Na and C12NMe3Br~C8SO4Na, shows both the systems to be consistent with observed data. This indicates that an easier and more accurate method on the study of synergism in nonideal binary mixed systems of surfactants has been obtained.
For obtaining high quality LEDs, many different contacting schemes have been tried, e.g., using metals, conducting polymers and indium tin oxide. The main goal for these is to produce long life, stable and high efficient photoluminescence (PL)/electroluminescence (EL) from porous silicon at room temperature. A conducting polymer is a very promising contact for making high quality LEDs. Porous silicon-based devices produce stable electro-luminescence (EL) by the deposition of PCDM monolayer, a low band gap conducting polymer, into the nano-structure of PS. The structure of these devices is Au/PCDM/PS/Si/Al. The EL emission is bright, visible by the naked eye under normal daylight, and broad in wavelength, covering the whole visible range with a peak at 650 nm. The emission area of the devices is ~1 cm2. The EL starting voltage is in the range of 4~30V and the current is around 300mA. Since preventing oxygen molecules from approaching the PS surface, PCDM films largely increase the time stability of all the devices tested. After exposure to the air for more than 3 months, the PCDM coated samples show nearly the same emission intensity without increase of external power supplied. When a reversing bias is applied, the device can still emit stable light. There is no obvious change inI~Vcurve within 250h. The SEM image shows that the PCDM covered surface is soomther than that of bare porous silicon surface, which may imply that the PCDM may have penetrated into the nano-structure of PS. The substitution PCDM molecules for unstable molecules on the PS surface may results in theincreasing the lifetime and stability of the LEDs.
A new silicon-based luminescence material—C(film)/Si(SiO2)(nanometer particles)/C(film) has been prepared by sputtering Si(SiO2) nano-particles on amorphous carbon film in Argas, then depositing amorphous carbon film on Si(SiO2) nano-particles in vacuum. The sample consists of 6 layers of carbon films and 5 layers of Si(SiO2) nano-particles. Finally, the sample is annealed at different temperatures(RT-750℃). Its configuration has been studied by means of TEM, SEM, XRD and XPS. TEM image shows that Si(SiO2) nano-particles almost be spherical, whose diameter is about 30nm. SEM images show that the thickness of the sample is about 50μm and the surface of the sample is relatively flat and compact. Hole structure is found on the surface of sample annealed at 400℃, the particles on the surface are well-distributed and compacted after annealed at 650℃, particle aggregations grow after annealed 750℃. XRD spectra shows that the sample is almost composed by SiO2and Si, and the ratio of SiO2/Si alternately changes with the increase of annealing temperature: SiO2are reduced to Si by C atoms at 400℃, so the content of Si is highest, on the contrary, the content of SiO2is lowest. Si nanometer particles are oxidized superiorly beyond 400℃, so the content of Si gradually decreases, the content of SiO2 gradually increases and becomes to highest at 650℃. XPS spectra shows that C atoms diffuse into Si (SiO2) nano-particles layer during annealing, and produce SiC by reacting with Si at 650℃.
Oil soluble lead naphthenate(LN) and lead alkylsalicylate(LAS) were in-situ synthesized by microwave assisted-technique in liquid paraffin. The tribological properties of LN , LAS and corresponding carboxylic acid were evaluated with four-ball tribo-tester under the condition of high speed (r=1500±10rpm) low load (P=196~392N) and low speed (r=300±10rpm)high load(P=800N). The anti-wear and friction-reducing of LN and LAS as additives were also evaluated with reciprocation tribo-tester. The results indicated that LN additive exhibited good anti-wear property, good friction-reducing efficiency and middling extreme pressure property, and all tribological properties of LN as additive was better than LAS. The reason producing the performance difference of tribological behaviors was analyzed for revealing tribological mechanism, and wear scar surface was characterized with photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Analytical results showed that LN and LAS could formed adsorbing film on steel-steel friction pair and part of film transformed oxidic film protecting the rubbing surfaces from wear by means of tribochemical reaction, but the thickness of films was different.
The SrTiO3powders were synthesized from TiO2·nH2O gel under moderate hydrothermal condition. TiO2·nH2O gel was prepared by diluting TiCl4with cold distilled water. The influence of pre-processing of TiO2·nH2O gel and anions (Cl-and NO3-) on the properties of SrTiO3 powders was studied in details by X-ray diffraction (XRD), transition electron microscopy (TEM) and Fourier transform infrared spectrometry (FTIR). The results showed that TiO2·nH2O could be crystallized during the washing and thermal processing. The crystallization of TiO2·nH2O had an important influence on the product particle size and particle size distribution. The SrTiO3powders prepared from amorphous TiO2·nH2O are with big particle size and wide particle size distribution, and those from crystallized TiO2·nH2O are with small particle size and narrow particle size distribution. To get nanometer SrTiO3powders, the suitable crystallization of TiO2·nH2O gel is essential. The chloride and nitrate ions can accelerate the formation of large-grained particles of SrTiO3, but such effect is very small. In a word, the main reason for the effect of washing of TiO2·nH2O on properties of SrTiO3powders is the crystallization of TiO2·nH2O gel during the washing, and the washing process can be substituted by thermal processing neglecting the effect of anions.
Thin poly-hexamethyladisiloxane films on deposited polyster film substrate were successfully prepared with CVD method in a R.F. plasma polymerizing apparatus. Elemental oxygen erosion resistance of the films was measured in an equipment simulated the elemental oxygen environments and the property was good. The films can protect the material surface of the apparatus in space. Property of the films related to the loss of oxygen in the film preparation and deposited density of the films that was tested by AFM was not uniform. Functional groups structure and surface chemical state of the films, which were prepared under different processing parameters were investigated by using XPS in present work in order to obtain films that had good elemental oxygen erosion resistance
Negatively charged colloidal nano-silver particles were successfully prepared by the colloidal chemical method. A 1.7% solution of silver nitrate (2 mL) was diluted with deionized water to 100 mL. A 1% solution of tannic acid (1 mL) was added dropwise to the solution stirring, then a 1% solution of potassium carbonate anhydrous (3~4 drops) was added to the mixed solution. Finally ,a red-brown silver sol was obtainned,which was stable at room temperature for seven months. It has been testified that the silver sol is a negatively charged colloid by experiment of electrophoresis. The sizes of particles were determined by Hitachi H-800 transmisson electron microscope. Absorption spectroscopy and SERS were used to determine of the main properties. Absorption spectroscopy was obtained with UV-1201. Raman spectra were recorded with RENISHAW MIK 1000 Raman micro-spectroscopy. The 514.5 nm line of an argon ion laser with about 3 mW was used. It has been found that the mean diameter of the particles was 11 nm; it had absorption maximum at 422 nm; Strong SERS spectra were observed when cationic molecules of fuchsin basic and methylene blue and neutral molecule of 1,10-phenanthroline were adsorbed on it respectively, but no SERS for the anionic molecule of Indolebutyric acid.
The ultrafine particle films of tin oxide were deposited on glass substrates by gas discharge activating reaction evaporation. The crystal stracture and surface morphology of typical samples prepared in various conditions was studied by X-ray diffraction spectroscopy and scanning electron microscopy. The results show that the average size of particles increased with oxygen pressure increasing. The uniform and amorphous SnO2ultrafine particle films with an average particle size of 40~50 nm were deposited, when the oxygen pressure was 8 Pa. With increase of oxygen pressure and extension of deposition time the films were oxidized enough and crystallized and the crystal grains grew in SnO2(110). When the discharge voltage was raised, the crystal grains obviously grew in SnO(001) and SnO2(200), respectively. The peak from SnO2(200) was specially strong and sharp and the films had a growing tendency toward single crystallinity.
Using acetone-water as medium and potassium persulfate(KPS) as initiator, emulsifier-free emulsion co-polymerization of styrene with co-monomers: methyl methacrylate (MMA), butyl methacrylate(BMA), ethyl acrylate(EA) and maleic anhydride(BDA) under microwave irradiation have been investigated. The influence of each co-monomer′s content and hydrophilicity on the hydrodynamic radius of the synthesized copolymer nanoparticles was discussed in detail. The results show that the increase in ratio of hydrophilic copolymer causes an increase in consumption of initiator in the initiation reaction, so an increase in the concentration of the surface -SO3-groups and the stability of the latex, which gives rise to the formation of smaller micelles. The nano-particle′s radius will increase again when the co-monomer′s content increase to a certain degree. The curve of the particle hydrodynamic radius vs. the co-monomer′s content has a minimum point. It can also be found that the size of the particle will be smaller when the solubility of the co-monomer is larger. But the ionic co-monomer has little effect on the stability of the latex though it also could cause the particle′s radius decrease. So nano-particles with a narrow size distribution could be obtained under microwave irradition through emulsifier-free emulsion polymerization in acetone-water medium.
Fish gelatin is extracted from the skin of deep water fish. It is different from general bovine gelatin in conformation, components and physical characters. It is characteristic for fish gelatin conformation thatαchains are major in which the content ofα2component with lower molecular weight is much more than that ofα1one;γcomponent which exists in general bovine gelatin is not found here. Fish gelatin contains less of proline and hydroxyproline, which results in lower gelling temperature. However, the amount of methionine residues in fish gelatin is obviously more than that in bovine gelatin. These properties of fish gelatin is favorable for preparation of photographic emulsion containing AgBrI nanoparticles. Besides, it is found that more sulfur containing components occur and dominant state of iron is one with +3 valence in fish gelatin. In the present study of fish gelatin as the silver halide carrier, AgBrI nanoparticles with average size of 14 nm are made over a wide range of ratio of gelatin to silver from 8∶1 to 4∶1. These particles possess satisfactory monodispersity and thermostability. The sulfur-plus-gold sensitization causes the photosensitivity of this nanoparticle AgBrI emulsion to rise. It is especially interesting that increases of sensitizer amount and prolongation of sensitizing time enhance this synergistic sensitization.
CdFe2O4and its Ag+-doped nano-powders were prepared by sol-gel method, the preparation conditions, phase constituents, microstructures, conductance and gas-sensing properties were also investigated. The results show that Cd1-xAgxFe2O4(0≤x≤0.04) solid solution nano-materials can be obtained when gel powder is calcined for 2h at 800℃, which is made from preheating gels at 350℃for 2hr and gets rid of surviving lemon acid. Measuring conductance shows that the material assumes behavior of the surface-resistance-controlled n-type semiconductor because of ionization of defect AgCd×(→AgCd′+ h·). The positive holes nullify free electrons (h·+ e′→null). The conductance of Ag+-doped solid solution is much lower than that of pure CdFe2O4at same temperature; Sensitivity of the element made from Cd0.98Ag0.02Fe2O4to 45μmol/L C2H5OH is 11 times larger than the petrol interfering gas of same concentration at 330℃. It is hoped to develop a new type information sensitive material of C2H5OH.
A complex oxide Fe-Mo-O was prepared by the coprecipitation mathod. The surface composition and structure, the chemsorption properties and the behaviors of Laser stimulated isobutane selective oxidation have been investigated by the techniques of XRD, IR, TPD and micro-reactor. There are both Lewis basic sites, O2-in the surface Mo=O or Mo-O-Fe bonds, and Lewis acid site Fe3+appeared on the surface of complex oxide. Two methyl hydrogens in isobutane molecule can be chemisorbed on the terminal oxygen of neighboring Mo=O bonds on the surface of complex oxide. Under the conditions of 0.1MPa and 200℃with the 995cm-1 Laser photons exited the Mo=O bonds 1000 times, the conversion of isobutane is about 5.8%, the reaction products are isobutene, MAL and MAA with the selectivity of MAA over 80%. Based on the experiment results, a mechanism of LSSR has been proposed for the isobutane selective oxidation to MAA.
The paper describes the preparation of the TiO2thin film photocatalyst by power-solmethod. The photocatalytic activity of the catalyst was evaluated by measuring the decomposition of gaseous acetone under weak UV light illumination. The result showed that the photocatalytic activity was remarkably enhanced by the addition of the TiO2powder in the TiO2film. And the weight of the PS-TiO2film is 5 times less than that of the SG-TiO2film system. According to the SEM pictures, the reason maybe as that: The film via power-sol (PS-TiO2film) is more coarse than the film via sol-gel(SG-TiO2film), so the surface area is big and it is good for the photoefficent of UV light and reaction rate. Furthermore, adding TiO2powders into the starting solution induces much defect on the film and this is also benefit for the reaction rate. Last, the SG- TiO2film is so thick that it maybe has exceeded the best thickness of the film. Moreover, adding acid into the film can improve the photoreactivity of the film. Because acid can prevent the producing of Ti3+and it is benefit for the separation of photoelectron and photohole. Furthermore, decreasing the amount of Ti3+can increase the amount of O2-. O2-is also good for the photoreactivity of the film.
The NOxstorage catalyst Pt/Ba-Al-O was prepared by co-precipitation method. The sample was characterized by XRD, NO-TPD and NSC. The barium in the sample mainly exists as BaAl2O4except few BaCO3phase. Two kinds of Pt sites seem to operate. The NO-TPD peak at about 270℃corresponds to sites 1 and the other peak at about 500℃corresponds to sites 2. Sites 1 are responsible for NO adsorption and sites 2 are responsible for nitrate and nitrite formation. When the sample adsorbed NO at 300℃with 1.3% O2, the NO desorption from the sample reached the maximum. When the adsorption was carried out over a prereduced surface, the sample had a much better NOxstorage capacity than that over a preoxidized surface. The NSC results indicate that the optimum temperature region for NOxstorage is 300~450℃.
Composite particles of iron red with styrene -butylacrylate with a diameter of the order ofμm were prepared by suspension technology. In the preparation process, initiator, iron red and other additives were put into blend of styrene with butyacrylate firstly, then the mixture is added into water which has dissolved dispersantes. After being ultrasonic agitated 5 min, that mixture of oil with water was pre-dispersed at high speed and then moved to reactor where polymerization occurred at 70℃for 6h.The test data showed that energy at interface between oil and water was lower than both in oil and in water, so the iron red particles should move to interfacial zone automatically. It was lain on which state the whole energy would be the lowest that the iron red particles mostly projected into whether the oil or the water in the interfacial zone. To compare the interfacial energy between the oil and monomer with that between iron red and water, we transformed some known equation related interfacial energy to a expressionγFe/water-γFe/oil=γwatercosθwater+γoilcosθoil. By introducing test data of surface tension and contact angle we obtained a result thatγFe/water<γFe/oil, which indicated that the iron red particles will mostly project into the water .The observational phenomena under microscope confirmed the theoretical discussion above. When the temperature was elevated from room temperature to polymerization temperature, surface tension and viscosity of the water solution increased. The surface tension and viscosity of the oil increased along with polymerization process, while the surface tension and viscosity of the water solution was almost unchangeable at the same time. The experimental results showed that the value of cosθoilhad risen along with polymerization. So it was theoretically probable after a period of polymerization thatγFe/water>γFe/oil, namely, the iron red particles should remove into the oil. However, even ifγFe/water>γFe/oil, it were difficult for iron red particles to return to oil again actually because the viscosity of oil was very high after a period of polymerization. As a result, the iron red particles were embedded in the polymer. The photograph of SEM of composite particles clearly showed that the iron red particles existed on the surface of composite particles. During the polymerization, the iron red particles, whose surface contained Fe3+, always contacted with oil where original free radical, monomer free radical and chain free radical coexisted. The FTIR of iron red extracted from composite proved that iron red had reacted with original free radical while no evidence for other free radical having reacted with iron red.