2016 Vol. 29, No. 6

The outer-valence binding energy spectra of ethanol in the energy range of 9-21 eV are measured by a high-resolution electron momentum spectrometer at an impact energy of 2.5 keV plus the binding energy. The electron momentum distributions for the ionization peaks corresponding to the outer-valence orbitals are obtained by deconvoluting a series of azimuthal angular correlated binding energy spectra. Comparison is made with the theoretical calculations for two conformers, trans and gauche, coexisting in the gas phase of ethanol at the level of B3LYP density functional theory with aug-cc-pVTZ basis sets. It is found that the measured electron momentum distributions for the peaks at 14.5 and 15.2 eV are in good agreement with the theoretical electron momentum distributions for the molecular orbitals of individual conformers (i.e., 8a' of trans and 9a of gauche), but not in accordance with the thermally averaged ones. It demonstrates that the high-resolution electron momentum spectrometer, by inspecting the molecular electronic structure, is a promising technique to identify different conformers in a mixed sample.
The orientation angle is an important parameter that reflects the structure of molecules at interfaces. In order to obtain this parameter, second order nonlinear spectroscopic techniques including second harmonic generation (SHG) and sum frequency generation-vibrational spectroscopy (SFG-VS) have been successfully applied through analysis of the nonlinear signal from various polarizations. In some SHG and SFG-VS experiments, total internal reflection (TIR) configuration has been adopted to get enhanced signals. However, the reports on the detailed procedure of the polarization analysis and the calculation of the orientation angle of interfacial molecules under TIR configuration are still very few. In this paper, we measured the orientation angles of two molecules at the hexadecane-water interface under TIR and Non-TIR experimental configurations. The results measured from polarization analysis in TIR configuration consist with those obtained from Non-TIR configuration. This work demonstrates the feasibility and accuracy of polarization analysis in the determination of the orientation angle of molecules at the interfaces under TIR-SHG configuration.
Ab initio study of the equilibrium structure, spectroscopy constants, and anharmonic force field for several isotopomers of germanium dichloride (70GeCl2, 72GeCl2, and 76GeCl2) have been carried out at the MP2 and CCSD(T) levels of theory using cc-pVTZ basis set. The calculated geometries, rotational constants, vibration-rotation interaction constants, harmonic frequencies, anharmonic constants, quartic and sextic centrifugal distortion constants, cubic and quartic force constants are compared with experimental data. For small mass differences of the Ge isotopes, the isotopic effects for germanium dichloride are much weaker. The agreements are satisfactory for these two methods, but the deviations of CCSD(T) results are slightly larger than that of MP2, because of CCSD(T)'s inadequate treatment of electron correlation in hypervalent Cl atom.
We present a fitting calculation of energy-loss function for 26 bulk materials, including 18 pure elements (Ag, Al, Au, C, Co, Cs, Cu, Er, Fe, Ge, Mg, Mo, Nb, Ni, Pd, Pt, Si, Te) and 8 compounds (AgCl, Al2O3, AlAs, CdS, SiO2, ZnS, ZnSe, ZnTe) for application to surface electron spectroscopy analysis. The experimental energy-loss function, which is derived from measured optical data, is fitted into a finite sum of formula based on the Drude-Lindhard dielectric model. By checking the oscillator strength-sum and perfectscreening-sum rules, we have validated the high accuracy of the fitting results. Furthermore, based on the fitted parameters, the simulated reflection electron energy-loss spectroscopy (REELS) spectrum shows a good agreement with experiment. The calculated fitting parameters of energy loss function are stored in an open and online database at http://micro.ustc.edu.cn/ELF/ELF.html.
A series of Mn-doped K-Co-Mo catalysts were prepared by a sol-gel method. The catalyst structure was well characterized by X-ray diffraction, N2 physisorption, NH3 temperatureprogrammed adsorption, in situ diffuse reflectance infrared Fourier transform spectroscopy, and X-ray absorption fine structure spectroscopy. The catalytic performance for higher alcohol synthesis from syngas was measured. It was found that the Mn-doped catalysts exhibited a much higher activity as compared to the unpromoted catalyst, and in particular the C2+ alcohol selectivity increased significantly. The distribution of alcohol products deviated from the Anderson-Schulz-Flory law. The portion of methanol in total alcohol was suppressed remarkably and the ethanol became the predominant product. Characterization results indicated that the incorporation of Mn enhanced the interaction of Co and Mo and thus led to the formation of Co-Mo-O species, which was regarded as the active site for the alcohol synthesis. Secondly, the presence of Mn reduced the amount of strong acid sites significantly and meanwhile promoted the formation of weak acid sites, which had a positive effect on the synthesis of alcohol. Furthermore, it was found that the incorporation of Mn can enhance the adsorption of linear- and bridge-type CO significantly, which contributed to the formation of alcohol and growth of carbon chain and thus increased the selectivity to C2+OH.
In this work, pyrolysis photoionization time-of-flight mass spectrometry (Py-PI-TOFMS) was applied to study the behavior of ammonia poisoning on H-form ultra stable Y (HUSY) zeolite for the catalytic pyrolysis of polypropylene (PP). Firstly, ammonia poisoning on HUSY was performed to obtain the suitable catalysts with different strength and amounts of acid sites. Secondly, online photoionization mass spectra for the pyrolysis products of PP and HUSY with various acid strength were recorded at different pyrolysis temperatures. Finally, the formation curves of various pyrolysates of PP/HUSY with the increase of temperature were determined. Our results indicate that the formation temperatures, yields and selectivity of the pyrolysis products of PP demonstrate obvious relationship with the acid strength of HUSY.
We systematically investigated the electrical properties of spiral-type and smooth Bi2Se3 nanoplates through field effect transistor and conductive atomic force microscopy (CAFM) measurement. It is observed that both nanoplates possess high conductivity and show metallic-like behavior. Compared to the smooth nanoplate, the spiral-type one exhibits the higher carrier concentration and lower mobility. CAFM characterization reveals that the conductance at the screw-dislocation edge is even higher than that on the terrace, implying that the dislocation can supply excess carriers to compensate the low mobility and achieve high conductivity. The unique structure and electrical properties make the spiral-type Bi2Se3 nanoplates a good candidate for catalysts and gas sensors.
Developing highly active and durable electrocatalysts for the oxygen reduction reaction (ORR) is crucial to large-scale commercialization of fuel cells and metal-air batteries. Here we report a facile approach for the synthesis of nitrogen and oxygen dual-doped mesoporous layer-structured carbon electrocatalyst embedded with graphitic carbon coated cobalt nanoparticles by direct pyrolysis of a layer-structured metal-organic framework. The electrocatalyst prepared at 800℃ exhibits comparable ORR performance to Pt/C catalysts but possesses superior stability to Pt/C catalysts. This synthetic approach provides new prospects in developing sustainable carbon-based electrocatalysts for electrochemical energy conversion devices.
A nano-Li3V2(PO4)3/C powder was successfully prepared by a thermal polymerization method. The particle sizes of the intermediate product powder and the final product Li3V2(PO4)3 are all less than 200 nm. The carbon is partially coated on the surface of Li3V2(PO4)3 particles and the rest exists between particles with a total carbon content of 4.6wt%. This nano-Li3V2(PO4)3/C sample shows a discharge capacity of 124 mAh/g without capacity fading after 100 cycles at 0.1 C in the voltage rang of 3.0-4.3 V. Excellent rate performance is also achieved with a capacity of 80 mAh/g at 20 C in 3.0-4.3 V and 100 mAh/g at 10 C in 3.0-4.8 V. This study suggests that the thermal polymerization method is suitable to synthesize nano-Li3V2(PO4)3/C materials.
Gamma-ray radiation has always been a convenient and effective way to modify the interfacial properties in polymer blends. In this work, a small amount of trimethylolpropane triacrylate (TMPTA) was incorporated into poly(ethylene terephthalate) (PET)/random terpolymer elastomer (ST2000) blends by melt-blending. The existence of TMPTA would induce the crosslinking of PET and ST2000 molecular chains at high temperatures of blending, resulting in the improvement in the impact strength but the loss in the tensile strength. When the PET/ST2000 blends were irradiated by gamma-ray radiation, the integrated mechanical properties could be enhanced significantly at a high absorbed dose. The irradiated sample at a dose of 100 kGy even couldn't be broken under the impact test load, and at the same time, has nearly no loss of tensile strength. Based on the analysis of the impactfractured surface morphologies of the blends, it can be concluded that gamma-ray radiation at high absorbed dose can further in situ enhance the interfacial adhesion by promoting the crosslinking reactions of TMPTA and polymer chains. As a result, the toughness and strength of PET/ST2000 blend could be dramatically improved. This work provides a facial and practical way to the fabrication of polymer blends with high toughness and strength.
Density functional theory was used to study the NH3 behavior on Ni monolayer covered Pt(111) and WC(001). The electronic structure of the surfaces, and the adsorption and decomposition of NH3 were calculated and compared. Ni atoms in the monolayer behave different from that in Ni(111). More dz2 electrons of Ni in monolayer covered systems were shifted to other regions compared to Ni(111), charge density depletion on this orbital is crucial to NH3 adsorption. NH3 binds more stable on Ni/Pt(111) and Ni/WC(001) than on Ni(111), the energy barriers of the first N-H bond scission were evidently lower on Ni/Pt(111) and Ni/WC(001) than on Ni(111), these are significant to NH3 decomposition. N recombination is the rate-limiting step, high reaction barrier implies that N2 is produced only at high temperatures. Although WC has similar properties to Pt, differences of the electronic structure and catalytic activities are observed for Ni/Pt(111) and Ni/WC(001), the energy barrier for the rate-determined step increases on Ni/WC(001) instead of decreasing on Ni/Pt(111) when compared to Ni(111). To design cheaper and better catalysts, reducing the N recombination barrier by modifying Ni/WC(001) is a critical question to be solved.
Tetraphenyl-porphyrin iron (FeTPP) was chosen to sensitize Cr doped TiO2 (Cr-TiO2) nanoparticles, a novel multimodified photocatalyst FeTPP-Cr-TiO2 with excellent visiblelight photocatalytic activity was successfully synthesized. The FeTPP-Cr-TiO2 microspheres were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electronic microscopy, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectra and N2 adsorption-desorption isotherms. The photocatalytic activity of FeTPP-Cr-TiO2 was evaluated by degradations of methylene blue in aqueous solution under irradiation with Xe lamp (150 W). The results showed that the FeTPP-Cr-TiO2 multimodified photocatalyst was anatase phase with high specific surface area (74.7 m2/g), and exhibited higher photocatalytic degradation efficiency than Cr-TiO2 and FeTPP-TiO2. The photocatalytic degradations of three quinolone antibiotics (lomefloxacin, norfloxacin, and ofloxacin) were further estimated for the feasibility of practical application of catalyst in wastewater treatment. It is desirable that photodegradation of antibiotics with FeTPP-Cr-TiO2 achieved pretty high degradation rates and all followed the pseudo first-order reaction model, and the rate constants k of 3.02×10-2, 2.81×10-2, and 3.86×10-2 min-1 and the half-lifes t1/2 of 22.9, 24.6, and 17.9 min were achieved respectively.
We have prepared polyion complex (PIC) hydrogel consisting of poly(3-(methacryloylami no) propyl-trimethylamonium chloride) and poly(sodium p-styrenesulfonate) polyelectrolytes via a two-step polymerization procedure and have investigated specific ion effects on the selfhealing of the PIC hydrogel. Our study demonstrates that the mechanical properties of the PIC hydrogel are strongly dependent on the type of the ions doped in the hydrogel. The ion-specific effects can be used to modulate the self-healing efficiency of the PIC hydrogel. As the doped anions change from kosmotrops to chaotropes, the self-healing efficiency of the PIC hydrogel increases. A more chaotropic anion has a stronger ability to break the ionic bonds formed within the hydrogel, leading to a higher efficiency during the healing.
Carboxyl graphene modified CuxO/Cu electrode was fabricated. The bare copper electrode was firstly anodic polarized in 1.0 mol/L NaOH solution in order to get CuxO nanoparticles, then the carboxyl graphene (CG) was electrodeposited on the CuxO/Cu electrode by cyclic potential sweeping. The electrocatalytic oxidation behaviors of calcium folinate (CF) at the graphene modified CuxO/Cu electrode were investigated by cyclic voltammetry. A positive scan polarization reverse catalytic voltammetry was used to obtain the pure catalytic oxidation current. The graphene modified CuxO/Cu electrode was served as the electrochemical sensor of CF, a highly sensitivity of 22.0 μA·(μmol/μL)-1cm-2 was achieved, and the current response was linear with increasing CF concentration in the range of 2.0×10-7 mol/L to 2.0×10-5 mol/L, which crossed three orders of magnitude, and the detection limit was found 7.6×10-8 mol/L (S/N=3). In addition, the proposed sensor was successfully applied in determination of CF in drug sample.
The thickness of TiO2 film is vital to realize the optimization on photovoltaic performance of dye sensitized solar cells (DSSCs). Herein, the process of charge separation in DSSCs was simulated by using a drift-diffusion model. This model allows multiple-trapping diffusion of photo-generated electrons, as well as the back reaction with the electron acceptors in electrolyte, to be mimicked in both steady and non-steady states. Numerical results on current-voltage characteristics allow power conversion efficiency to be maximized by varying the thickness of TiO2 film. Charge collection efficiency is shown to decrease with film thickness, whereas the flux of electron injection benefits from the film thickening. The output of photocurrent is actually impacted by the two factors. Furthermore, recombination rate constant is found to affect the optimized film thickness remarkably. Thicker TiO2 film is suitable to the DSSCs in which back reaction is suppressed sufficiently. On the contrary, the DSSCs with the redox couple showing fast electron interception require thinner film to alleviate the charge loss via recombination. At open circuit, electron density is found to decrease with film thickness, which engenders not only the reduction of photovoltage but also the increase of electron lifetime.
Catalytic degradation of cellulose to chemicals is an attracting topic today for the conversion of biomass, and the development of novel catalysts is a key point. Since metal-organic frameworks (MOFs) possess uniform, continuous, and permeable channels, they are valuable candidate as catalysts. Here, a new 3D MOF/graphene catalyst was prepared by in situ growth of the zeolitic imidazolate frameworks (ZIF-8) nanoparticles inside the pore of an as-formed 3D reduced graphene oxide (rGO) hydrogel. The ZIF-8/rGO nanocomposite owns both micropores and mesopores with large specific surface area and plenty of acids sites, which is an idea catalyst for biomass degradation. Cellulose was dissolved in alkaline aqueous solution at first, and then it was degraded efficiently over the new catalyst under hydrothermal condition. The conversion reaches 100% while the main products are formic acid with a maximum yield of 93.66%. In addition, the catalyst can be reused with high activity.
We demonstrate a very convenient access to self-suspended pure poly(10,12-pentacosadiynoic acid) (PDA) nanoparticles (NPs) simply by adding the ethanol solution of diacetylene monomer to water, followed by UV irradiation. The as-obtained PDA NPs are of high purity because no any initiator, catalyst or stabilizer was used during the whole process. The stabilizer-free PDA NPs are stable in the aqueous suspension. Due to the high purity and stability, the PDA NPs can respond sensitively and selectively to lysine and arginine among 18 kinds of water soluble natural amino acids; without the competitive interaction from the stabilizer, the sensitivity was enhanced.
Using nonequilibrium molecular dynamics simulations, we study the non-Newtonian rheological behaviors of a monoatomic fluid governed by the Lennard-Jones potential. Both steady Couette and oscillatory shear flows are investigated. Shear thinning and normal stress effects are observed in the steady Couette flow simulations. The radial distribution function is calculated at different shear rates to exhibit the change of the microscopic structure of molecules due to shear. We observe that for a larger shear rate the repulsion between molecules is more powerful while the attraction is weaker, and the above phenomena can also be confirmed by the analyses of the potential energy. By applying an oscillatory shear to the system, several findings are worth mentioning here:First, the phase difference between the shear stress and shear rate increases with the frequency. Second, the real part of complex viscosity first increases and then decreases while the imaginary part tends to increase monotonically, which results in the increase of the proportion of the imaginary part to the real part with the increasing frequency. Third, the ratio of the elastic modulus to the viscous modulus also increases with the frequency. These phenomena all indicate the appearance of viscoelasticity and the domination of elasticity over viscosity at high oscillation frequency for Lennard-Jones fluids.
In this study, 75% and 96% argon diluent conditions were selected to determine the ignition delay time of stoichiometric mixture of C2H4/O2/Ar within a range of pressures (1.3-3.0 atm) and temperatures (1092-1743 K). Results showed a logarithmic linear relationship of the ignition delay time with the reciprocal of temperatures. Under both two diluent conditions, ignition delay time decreased with increased temperature. By multiple linear regression analysis, the ignition delay correlation was deduced. According to this correlation, the calculated ignition delay time in 96% diluent was found to be nearly five times that in 75% diluent. To explain this discrepancy, the hard-sphere collision theory was adopted, and the collision numbers of ethylene to oxygen were calculated. The total collision numbers of ethylene to oxygen were 5.99×1030 s-1cm-3 in 75% diluent and 1.53×1029 s-1cm-3 in 96% diluent (about 40 times that in 75% diluent). According to the discrepancy between ignition delay time and collision numbers, viz. 5 times corresponds to 40 times, the steric factor can be estimated.