2014 Vol. 27, No. 3

The photodissociation dynamics of acetaldehyde in the radical channel CH3+HCO has been reinvestigated using time-sliced velocity map imaging technique in the photolysis wavelength range of 275?321 nm. The CH3 fragments have been probed via (2+1) resonance-enhanced multiphoton ionization. Images are measured for CH3 formed in the ground and excited states (v2=0 and 1) of the umbrella vibrational mode. For acetaldehyde dissociation on T1 state after intersystem crossing from S1 state, the products are formed with high translational energy release and low internal excitation. The rotational and vibrational energy of both fragments increases with increasing photodissociation energy. The triplet barrier height is estimated at 3.881±0.006 eV above the ground state of acetaldehyde.
We have investigated the properties of cellulose diacetate in solution by using laser light scat-tering. The cellulose diacetate molecules can form micelles and micellar clusters in acetone besides the individual chains. As the concentration increases, the average hydrodynamic radius h linearly increases, whereas the ratio of gyration radius to hydrodynamic ra-dius g>/h linearly decreases. It indicates that the micelles associate and form micellar clusters due to the intermolecular interactions.
By numerically solving the Maxwell-Bloch equations using an iterative predictor-corrector finite-difference time-domain technique, we investigate propagating properties of a few-cycle laser pulse in a 4,4′-bis(di-n-butylamino) stilbene (BDBAS) molecular medium when a static electric field exists. Dynamical two-photon absorption (TPA) cross sections are obtained and optical limiting (OL) behavior is displayed. The results show that when the static electric field intensity increases, the dynamical TPA cross section is enhanced and the OL behavior is improved. Moreover, both even- and odd-order harmonic spectral components are generated with existence of the static electric field because it breaks the inversion symmetry of the BDBAS molecule. This work provides a method to modulate the nonlinear optical properties of the BDBAS compounds.
The theoretical calculation and spectroscopic experiments indicate a kind of triangu-lar three bonding supramolecular complexes CBr4…X-…H-C, which consist of carbon tetrabromide, halide, and protic solvent molecule (referring to dichloromethane, chloro-form and acetonitrile), can be formed in solution. The strength of halogen and hydro-gen bonds in the triangular complexes using halide as common acceptor obeys the order of iodide>bromide>chloride. The halogen and hydrogen bonds work weak-cooperatively. Charge transfer bands of halogen bonding complexes between CBr4 and halide are observed in UV-Vis absorption spectroscopy in three solvents, and then the stoichiometry of 1:1, for-mation constants K and molar extinction coefficients ? of the halogen bonding complexes are obtained by Benesi-Hildebrand method. The K and ? show a dependence on the solvent dielectric constant and, on the whole, obey an order of iodide>bromide>chloride in the samesolvents. Furthermore, the C-H vibrational frequencies of solvent molecules vary obviously with the addition of halide, which indicates the C-H…X- interaction. The experimental data indicate that the halogen bond and hydrogen bond coexist by sharing a common halide acceptor as predicted by calculation.
The electronic structure of the perovskite LaCoO3 at room temperature structure (293 K) was calculated by using PBE, PBE+U and HSE. Different spin configurations have been considered. Our calculations showed that the choice of the Hubbard U parameter in DFT+U and mixing factor α in HSE significantly influenced the band gap as well as relative energies. For the spin exited states, the optimal value for U and α were 3.0 eV and 0.05, respectively. Our calculation also emphasized that when U≥5.0 eV, PBE+U would lead to unreasonable electronic structure and energy order.
The four-body model has been used to calculate the fully differential cross-sections (FDCS) for the single ionization of helium by 100 MeV/amu C6+ impact in geometries. By compar-ing with experimental data and other theories, we find the results of four-body model are in very good agreement in the scattering plane, but poor agreement out of the scattering plane. Accordingly, the contributions of different scattering amplitudes to FDCS are analyzed. It is found that the cross sections due to the interference of the scattering amplitudes between projectile-target nucleus interaction and projectile-ejected electron interaction almost tend to experimental results around the recoil region in geometries. In particular in the perpen-dicular plane, the cross section originating from interference of the scattering amplitudes between projectile-target nucleus and projectile-ejected electron interactions yields an ex-perimental double-peak structure in the angular distribution. However, this feature could not be presented by the interference of the three amplitudes. Thus, the failure of the four-body model predicting the feature in this geometry may be attributed to an inappropriate weighting of the three amplitudes.
Theoretical study on the supramolecular complexes formed between boron-doped het-erofullerene (C59B) and zinc porphine (ZnP), namely C59B-ZnP and its anion species C59B--ZnP, was performed by density functional theory calculation at wB97XD/6-31G(d)level. Strong interaction between porphyrin and heterofullerene moiety was predicted for these complexes based on geometry and electronic structure analysis. Especially, pseudo-bonding interaction occurring between the B atom of fullerene and the N atom of porphyrin was predicted to occur in C59B-ZnP complex, but be broken in C59B--ZnP complex. Time-dependent density functional theory calculation manifests the redshift of electron absorption for ZnP upon the interaction with heterofullerene.
Rhodamine molecules are one of the most used dyes for applications related to Raman spectroscopy. We have systematically studied Raman spectra of Rhodamine 6G, Rhodamine 123, and Rhodamine B (RhB) molecules using density functional theory. It is found that with BP86 functional the calculated Raman spectra of cationic Rhodamine molecules are in good agreement with corresponding experimental spectra in aqueous solution. It is shown that the involvement of the counter ion, chlorine, and the specific hydrogen bonds has noticeable effects on the Raman spectra of RhB that can partially explain the observed difference between Raman spectra of RhB in solution and on gold surfaces. It also indicates that an accurate description of surface enhanced Raman scattering for Rhodamine moleculeson metal surface still requires to take into account the changes induced by the interfacial interactions.
The elastic property and sound velocity of Fe3C under high pressure are investigated by using the spin-polarized generalized gradient approximation within density-functional theory. It is found that the magnetic phase transition from the ground ferromagnetic (FM) state to the nonmagnetic (NM) state occurs at ~73 GPa. Based on the predicted Hugoniot of Fe3C, we calculate the sound velocities of FM-Fe3C and NM-Fe3C from elastic constants. Compared with pure iron, NM-Fe3C provides a better match of compressional and shear sound velocities with the seismic data of the inner core, supporting carbon as one of the light elements in the inner core.
Cerium (III) tetraphenylporphyrin nitrate Ce(TPP)NO3 was synthesized by using meso-tetraphenylporphyrin (TPP) and Ce(NO3)·6H2O in mixture solution of CHCl3 and C2H5OH (V :V =1:1). The complex was characterized by UV-Vis, FT-IR, conventional uorescence, MALDI-TOF-MS, and 1H NMR spectral techniques. The structure of complex was pro-posed viaSpectral analyses, in which tetraphenylporphyrin was coordinated to a cerium ion in a tetradentate fashion, while one nitrate was coordinated to the same cerium ion. Af-ter bubbling NO to the solution of Ce(TPP)NO3 in CH2Cl2, spectral analyses suggested that Ce(TPP)NO3 could interact with NO to form a novel complex of Ce(TPP)(NO)NO3, and NO was coordinated to the center cerium ion. When nitrogen was poured into the Ce(TPP)(NO)(NO3) solution, the complex could be reduced to Ce(TPP)NO3.
The interaction between N'N0-bis(dimethyldodecyl)-1,6-hexanediammoniumdibromide (G12-6-12) and cetyltrimethylammonium bromide (CTAB) in D2O aqueous medium has been investigated by NMR at 298 K. The measured critical micelle concentration (cmc) of G12-6-12 and CTAB are about 0.773 and 0.668 mmol/L, respectively. The cmc* (cmc of mixture) values are less than CMC* (cmc of ideally mixed solution) in the mixed system, and the interaction parameter βM<0 at different molar fractions α of G12-6-12 in the mixed systems, but just when α≤0.3, cmc* values are much smaller than CMC*, and βM satisfies the relation of |βM|>|ln(cmc1=cmc2)|(cmc1: cmc of pure G12-6-12 and cmc2: cmc of pure CTAB). The results indicate that there exists synergism between G12-6-12 and CTAB, and they can form mixed micelles, which is further proven by 2D NOESY and self-diffusion co-efficient D experiments. There are intermolecular cross peaks between G12-6-12 and CTAB in 2D NOESY, and the radius of micelles in mixed solution is bigger than that in G12-6-12 pure solution in D experiments, indicating there are mixed micelles. However, when α>0.3, we find that cmc*≈CMC*, βM≈0, obviously, the two surfactants are almost ideal mixing fitting the pseudo-phase separation model and regular solution theory.
The optical properties of three linear conjugated oligomers (F-P, F-P-F, and P-F-P-F-P),where phenothiazine (P) and fluorene (F) groups arrange alternately, are investigated. With the enhancement of the π-conjugated system, their absorption and emission bands both gradually red shift, and their two-photon properties are also improved. Meanwhile, their flu-orescence dynamic traces are analyzed with continuous rate distribution model, exhibiting that their decay rates gradually accelerate and the rate distribution width become narrower. The quantum chemical calculation offers their molecular structures and transition mecha-nism, showing that the enhancement of π-conjugated system should be responsible for the improvement of two-photon properties.
TiO2 nanocrystals/graphene (TiO2/GR) composite are prepared by combining flocculation and hydrothermal reduction technology using graphite oxide and TiO2 colloid as precursors. The obtained materials are examined by scanning electron microscopy, transition electron microscopy, X-ray diffraction, N2 adsorption desorption, and ultraviolet-visible diffuse spec-troscopy. The results suggest that the presence of TiO2 nanocrystals with diameter of about 15 nm prevents GR nanosheets from agglomeration. Owing to the uniform distribution of TiO2 nanocrystals on the GR nanosheets, TiO2/GR composite exhibits stronger light absorption in the visible region, higher adsorption capacity to methylene blue and higher efficiency of charge separation and transportation compared with pure TiO2. Moreover, the TiO2/GR composite with a GR content of 30% shows higher photocatalytic removal efficiency of MB from water than that of pure TiO2 and commercial P25 under both UV and sunlight irradiation.
A facile impregnation method under mild condition is designed for synthesis of highly dis-persed Pt nanoparticles with a narrow size of 4-7 nm on nitrogen-doped carbon nanotubes(CNx). CNx do not need any pre-surface modification due to the inherent chemical activ-ity. The structure and nature of Pt/CNx were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy spectrum. All the experimental results revealed that the large amount of doped nitrogen atoms in CNx was virtually effective for capturing the Pt(IV) ions. The improved surface nitrogen functionalities and hydrophilicity contributed to the good dispersion and immobi-lization of Pt nanoparticles on the CNx surface. The Pt/CNx served as active and reusable catalysts in the hydrogenation of allyl alcohol. This could be attributed to high dispersion of Pt nanoparticles and stronger interaction between Pt and the supports, which prevented the Pt nanoparticles from aggregating into less active Pt black and from leaching as well.
A simple and green approach to synthesize highly active electro-catalysts for methanol oxidation reaction (MOR) without using any organic agents is described. Pt nanoparticles are directly deposited on the pre-cleaned and pre-oxidized multiwall carbon nanotubes (MWCNTs) from Pt salt by using CO as the reductant. MOR activity has been characterized by both cyclic voltammetry and chronoamperometry, the current density and mass specific current at the peak potential (ca. 0.9 V vs. RHE) reaches 11.6 mA/cm2 and 860 mA/mgPt, respectively. After electro-deposition of Ru onto the Pt/MWCNTs surface, the catalysts show steady state mass specific current of 20 and 80 mA/mgPt at 0.5 and 0.6 V, respectively.
The self-assembly behavior of ABC star triblock copolymers can lead to a large number of nanostructures. Indeed, many new and interesting structures have already been discovered and proven to be hotspot in soft matter physics research. In this work, we introduce different phase diagrams of core-shell-cylinder-forming ABC star triblock copolymers under different conditions, including in-bulk and pore geometries with different sizes. The relation between the pore size geometries and their corresponding structures are also revealed. The different properties of the surface potential field that significantly affect the self-assembly process ofABC star triblock copolymers are investigated as well.
A series of Ce, H3PW12O40 co-doped TiO2 hollow fibers photocatalysts have been prepared by sol-gel method using ammonium ceric nitrate, H3PW12O40 and tetrabutyltitanate as pre-cursors and cotton fibers as template, followed by calcination at 500 oC in N2 atmosphere for 2 h. Scanning electron microscopy, X-ray diffraction, nitrogen adsorption-desorption mea-surements, and UV-Vis spectroscopy are employed to characterize the morphology, crystal structure, surface structure, and optical absorption properties of the samples. The photo-catalytic performance of the samples has been studied by photodegradation phenol in water under UV and visible light irradiation. The results show that the TiO2 fiber materials have hollow structures, and the co-doped TiO2 hollow fibers exhibit higher photocatalytic activi-ties for the degradation of phenol than un-doped, single-doped TiO2 hollow fibers under UV and visible light. In addition, the recyclability of co-doped TiO2 fibers is also confirmed that the TiO2 fiber retains ca. 90% of its activity after being used four times. It is shown that the co-doped TiO2 fibers can be activated by visible light and may be potentially applied to the treatment of water contaminated by organic pollutants. The synergistic effect of Ce and H3PW12O40 co-doping plays an important role in improving the photocatalytic activity.
ZnO bicrystalline nanosheets have been synthesized by using AgxAu1-x alloy catalyst via the vapor transport and condensation method at 650 oC. High resolution transmission electron microscopy characterization reveals a twin boundary with {01-13} plane existing in the bicrystalline. A series of control experiments show that both AgxAu1-x alloy catalyst and high supersaturation of Zn vapor are prerequisites for the formation of ZnO bicrystalline nanosheet. Moreover, it is found that the density of ZnO bicrytalline nanosheets can be tuned through varying the ratio of Ag to Au in the alloy catalyst. The result demonstrates that new complicated nanostructures can be produced controllably with appropriate alloy catalyst.
The adsorption of fibrinogen can be used as a quick indicator of surface haemocompatibility because of its prominent role in coagulation and platelet adhesion. In this work the molec-ular interaction between flbrinogen and a modified titanium oxide surface/platelet has been studied by quartz crystal microbalance with dissipation (QCM-D) in situ. In order to further characterize the conformation of adsorbed flbrinogen, αC and γ-chain antibody were used to check the orientation and denaturation of flbrinogen on solid surface. QCM-D investiga-tions revealed the flbrinogen have the trend to adsorb on hydrophilic surface in a side-on orientation by positively charged αC domains, which would reduce the exposure of platelet bonding site on γ chain and enable less platelet adhesion and be activated. These obser-vations suggest that certain conformations of adsorbed flbrinogen are less platelet adhesive than others, which opens a possibility for creating a non-platelet adhesive substrates.
Biomass is a nature renewable resource which can be used for the production of high value chemicals and bio-fuels. In the present work, the transformation of sawdust into aromat-ics such as benzene, toluene and xylenes was investigated over a series of zeolite catalysts (NaZSM-5, HZSM-5, ReY and HY catalysts). Among the tested catalysts, the HZSM-5 catalyst shows the highest activity for the production of aromatics. The yield and carbon selectivity of aromatics reached about 26.5% and 62.5C-mol%, respectively over the HZSM-5 catalyst under the optimal condition of T=450 oC, f(N2)=300 cm3/min, and catalyst/lignin ratio of 2. The e ects of the reaction conditions including temperature, gas ow rate, and catalyst/sawdust ratio on the production of aromatics were investigated in detail and the formation of aromatics from lignocellulosic biomass was also addressed.
A systematic study was conducted on current efficiency (CE), corrosion and structural changes in SnO2-based inert anodes (made of 96wt%SnO2+2wt%Sb2O3+2wt%CuO) on a laboratory Hall-Heroult aluminium cell. The influence of operating parameters and elec-trolyte composition on the CE and corrosion process were evaluated. The CE was found to be more than 90% and catastrophic corrosion took place at low percent of Al2O3, high percent of LiF, low cryolite ratio and high current densities. From all the structural changes that took place in the SnO2-based inert anodes, we assumed that the most important contri-bution was due to the migration of CuO towards the outer limits of the constituent grains of SnO2 based ceramic. The complex process occurred during the formation of various phases and their sintering ability both directly depended on Cu/Sb molar ratio.
Chinese abstract