The 1H NMR spectra of CTAB, SDS and Triton x-100 aqueous micellar solutions containing dimethyl phthalate have been determined. The results indicate that dimethyl phthalate in CTAB, SDS and Triton x-100 micellar solutions at a low solubilizing concentration is adsorbed on the micelle-water interface. With the increase of solubilizing concentration, it is preferentially solubilised in both the palisade layer and hardly solubilised in the centre of the micellar core in CTAB micellar solution, and it is preferentially solubilised in both the palisade layer and the micellar core in SDS micellar solution while it is solubilised and uniformly distributed along the hydrocarbon chain of the surfactant in Triton X-100 micellar solution.
Effect of SDS micelles and premicelles on the alkaline fading reversible reaction of malachite green has been studied. Micellar and premicellar catalytic models for the 1-1 type reversible reaction have been proposed.
The rate constants of forward and backward reactions and equilibrium constants of the alkaline fading reversible reaction of malachite greed in micellar phase have been obtained by the micellar model. Under premicellar condition the average number of SDS molecules per substrate molecule with n detergent molecules have been obtained by the premicellar catalytic model.
The results indicate that both SDS micelles and premicelles exhibit an inhibiting effect for the forward reaction. While they exhibit an accelerating effect for the backward reaction. These results were reasonably accounted for with electrostatic interaction.
Graphene, a recently discovered carbon nanomaterial with carbon atoms tightly packed into a two dimensional honeycomb lattice, possesses many novel and unique physical and chemical properties because of its unusual monolayer atomic structure. Graphene has received a great deal of attention in fundamental and applied research. This review presents the current status of graphene synthesis, functionalization, and applications in chemistry. Specifically, the use of graphene for the fabrication of chemically modified electrodes, the preparation of chemical power sources, catalyst and medicinal matrices, and in gas sensors are summarized. Finally, further applications based on graphene are briefly introduced.
A blue-green emitter of iridium(III) complex (ppy)2Ir(pybi), has been synthesized (ppy= 2-phenyridine and pybi=2-(2-pyridyl)benzimdazole) and its structure was characterized by Fourier transform infrared (FT-IR) spectroscopy, proton nuclear magnetic resonance (1H NMR), mass spectroscopy (MS), and elemental analysis. Its photophysical properties and energy-level structure were studied by UV-Vis absorption, excitation and emission spectroscopy, and cyclic voltammetry combining timedependent density functional theory (TD-DFT). The electrophosphorescent performance of (ppy)2Ir(pybi) was characterized by using 4,4'-bis(9-carbazolyl)-1,1'-biphenyl (CBP) as host. The results indicated that the UV-Vis absorption bands were located at 250, 295, 346, and 442 nm, which were in good agreement with the TD-DFT simulation results. The blue-green phosphorescent emission was observed with peaks at 495, 518 nm in CH2Cl2 solution at room temperature. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energy levels and optical gap were -6.11, -3.43, and 2.68 eV, respectively. Theoretical calculation revealed that the HOMO for (ppy)2Ir(pybi) was mainly distributed on the ppy ligand and the iridium ion, whereas the LUMO was centered mainly on the pybi ligand. The device based on the system of (ppy)2Ir(pybi) doped into CBP has an electroluminescence (EL) spectrum with a peak wavelength of 508 nm, a maximum luminance of 8451 cd·m-2, and a maximum current efficiency of 17.6 cd·A-1. These investigations will provide an important experimental basis for the application of (ppy)2Ir(pybi) in the organic electroluminescent field.
Graphene/polyaniline composites (GP) were prepared from aniline and graphite oxide using an electrochemical method. The structure characterization and surface morphology were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), and its electrochemical properties were measured. The results show that the composite keeps the basic morphology of graphene and that the polyaniline particles are uniformly dispersed. The specific capacitances of the composite materials reach 352 and 315 F·g-1 at 500 and 1000 mA·g-1, respectively, higher than those of graphene and polyaniline. The majority (90%) of the capacitance remains after 1000 cycles of charge and recharge at 1000 mA·g-1. The composite shows potential for use in supercapacitors.
Nitrogen-doped graphene was synthesized by the hydrothermal method with graphene oxide (GO) as the raw material and urea as the reducing-doping agent. The morphology, structure, and components of the as-produced graphene were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption analysis, and electrical conductivity measurements. The results showed that nitrogen was doped into the graphene plane at the same time as the GO sheets were reduced, and the nitrogen content was between 5.47%-7.56% (atomic fraction). In addition, the electrochemical performance of the graphene was tested. Nitrogen-doped graphene with a nitrogen content of 7.50% showed excellent capacitive behavior and long cycle life. The first cycle specific discharge capacitance for the material was 184.5 F·g-1 when cycled at 3 A·g-1, and 12.4% losses were found after 1200 cycles in anaqueous electrolyte of 6 mol·L-1 KOH.
The enthalpies of dissolution for 1,3,3-trinitroazetidine (TNAZ) in ethyl acetate (EA) and N,N-dimethylformamide (DMF) were measured using a RD496-2000 Calvet Microcalorimeter at 298.15 K under atmospheric pressure. Differential enthalpies (△difH) and molar enthalpies (△solH) were determined for TNAZ in different solvents. The corresponding kinetic equations that describe the two dissolution processes are dα/dt=10-7.26(1-α)0.88 for the dissolution of TNAZ in ethyl acetate and dα/dt=10-7.21(1-α)0.66 for the dissolution of TNAZ in N,N-dimethylformamide.
Conceptual density functional theory (DFT), also called Density Functional Reactivity Theory or Chemical DFT, is the chemical reactivity theory of DFT. Its framework and some recent developments of Conceptual DFT are briefly reviewed in this article. Introduced in more detail are the reactivity indices such as electronegativity, hardness, softness, Fukui function, electrophilicity index, as well as principles derived from them. Two representative recent developments, the dual descriptor and steric effect quantification, are succinctly summarized. A personal prospective on the future of Conceptual DFT is provided at the end.
The construction of TiO2with a special architecture to enhance the photocatalytic property of nano-titanium dioxide (TiO2) was achieved by synthesizing a three-dimensional (3D) network TiO2 nanowire film (W-film) on the surface of Ti foil using a hydrothermal method. Samples were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). Results showed that the three-dimensional network nanowire film was composed of many randomly-oriented anatase nanowires, which had diameters of 10-30 nmand lengths larger than 5 μm. Optical properties of these W-films were studied by UV-Vis spectrophotometry (UV-Vis). The results indicated that the absorbency of the W-film was higher than that of a particulate film (P-film) in the 350-700 nm region and the absorption edge was red-shifted. Meanwhile, the absorbency of the W-film increased as the hydrothermal time increased. After further investigation of the photoelectrochemical properties of the W-film in Na2SO4 solution, we determined that the photoelectrochemical properties of the W-film were better than those of P-film. Methyl orange was used as a target molecule to estimate the photocatalytic activity of the W-film. Under the same testing conditions, the catalytic efficiency of the W-film was found to be 2.3 times as that of the P-film and it, therefore, has a bright future. This kind of composited W-film electrode possesses advantages both in flexibility and implementation of the applied potential, which will increase the application field of this TiO2 film.
A stable hydrosol of graphene was synthesized by oxidation reduction and then a flow assembly of this graphene was used to form a graphene-based membrane by vacuum extraction filtering method. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, particle size analysis, and scanning probe microscopy (SPM) were used to characterize the crystal structure, granularity, and characteristic change of the molecular spectrum of the samples in the reaction. FTIR tests show that the structural layer of graphite during the oxidation process bonds to a large number of functional groups and parts of these stable functional groups remain on the reduced structural layer of graphene. X-ray diffraction results show that the peaks of the graphite oxide shift to lower angles, become broader and the original graphite peak disappears. Suspensions of graphene oxide form condensed matter and graphene flocculating constituent during film deposition. Particle size analysis and SPM tests show that the particle sizes of the graphene oxide sheets that are dispersed in water show a tailing peak and a broad distribution while the graphene sheets show a singlet, narrower distribution, and smaller dimensions. Raman results show that during oxidation and reduction, the D peak and G peak of the samples gradually extend, ID/IG increases gradually and the degree of sample disorder increases. On the basis of the above analyses, the structural characteristics of the samples in the reaction are summarized.
Zinc oxide (ZnO) is a multifunctional material with wide applications in chemical engineering.Hydrothermal synthesis of ZnO under supercritical conditions from salt solutions containing zinc ions is an environmentally safe process. Two reaction steps are involved, zinc hydroxide sol formation and dehydration from the sol. However, little is known about the underlying mechanism. In this study, molecular dynamics simulations were performed to investigate the structural and thermodynamic changes in the zinc acetate hydrolysis process, i.e., Zn(CH3COO)2, in supercritical water (SCW). Our results show that Zn(CH3COO)2 is prone to aggregate in SCW. On average, one Zn2+ ion coordinates with five CH3COO- species and one H2O molecule, forming an octahedral configuration. WHowever, more water molecules bind Zn2+ at the SCW interface to form Zn(CH3COO)2 clusters. The total potential energy of each system decreases after the hydrolysis of Zn(CH3COO)2, suggesting that it is a thermally favorable process in SCW. The OH- reaction product incorporates into the amorphous Zn(CH3COO)2 cluster and CH3COOH is in the SCW phase. Our results provide a general theoretical framework for the Zn(CH3COO)2 hydrothermal synthesis in SCW.
In this paper, the liquid-solid equilibrium for the ternary systems composed of 1,2-propanediol, MCl (M=Na, K, Rb, Cs), and H2O were studied at 298.15 and 308.15 K, with the mass fraction of 1,2- propanediol ranging from 0 to 0.9. The solubilities, densities, and refractive indices of the saturated systems, and the densities and refractive indices of the unsaturated solutions are reported herein. The solubilities were determined via a titration method using mercury nitrate as the titrant. Refractive index and density data were measured using an Anton Paar RXA170 refractometer and Anton Paar DMA4500 densimeter, respectively. The experimental values of the solubilities and densities of the saturated solutions decreased with increasing 1,2-propanediol concentration, whereas different trends of increase were observed for the refractive indices. The experimental density and refractive index data for the unsaturated solutions increased with increasing 1,2-propanediol to water ratios. Empirical equations have been provided for these properties as a function of concentration. On the basis of the standard deviations, we concluded that the empirical equations could be satisfactorily used to correlate the solubility, density, and refractive index data of the investigated systems. These values will enrich the thermodynamics data for alkali metals in mixed solvents, and lay a foundation for any subsequent work.
Kinetics of the reactions of ozone with diethylamine (DEA) and triethylamine (TEA) were investigated in a self-made Teflon chamber. Experiments were conducted under pseudo-first-order decay conditions using excess DEAand TEA. Cyclohexane was added to the reactor to quench OHradicals. At (298±1)Kand 1.01×105 Pa, the measured absolute rate constants were (1.33±0.15)×10-17 cm3·molecule-1·s-1 for DEA and (8.20±1.01)×10-17 cm3·molecule-1·s-1 for TEA. Comparing our results with data for the reactions of analogous amines with ozone, we propose that the amines react with ozone probably through an electrophilic reaction mechanism. In addition, the reactions of trialkylamines with ozone are all much faster than those of dialkylamines with ozone, which may explain the intriguing finding in several field studies where higher concentrations of dialkylammoniumwere detected in aerosol samples. The atmospheric lifetimes of DEA and TEA were also estimated based on the measured rate constants and the ambient tropospheric concentration of ozone, which indicates that the reaction with ozone is an important loss pathway for these amines in the atmosphere, especially in polluted areas.
Reactions between transition metal oxide clusters and hydrocarbon molecules were extensively studied to reveal the mechanisms of the related catalytic processes at a molecular level. Compared with transition metal oxide cluster cations, anions are usually much less reactive toward some hydrocarbon molecules and thus much less studied. In this work, vanadium oxide cluster anions (VxOy) were prepared by laser ablation and reacted with alkanes (C2H6 and C4H10) and alkenes (C2H4 and C3H6) in a fast flow reactor under near thermal collision conditions. A time of flight mass spectrometer was used to detect the cluster distribution before and after the reactions. Hydrogen atom-pickup products V2O6H- and V4O11H- were observed in the reactions of VxOy with alkanes while the association products V2O6X- and V4O11X- (X=C2H4 or C3H6) were produced in the cluster reactions with alkenes. Density functional theory calculations predict that V2O-6 reacts with C2H6 and C4H10 by C—H activation and with C2H4 and C3H6 by 3+2 cycloaddition to form a five-membered ring structure (-V-O-C-C-O-) with surmountable reaction barriers. This is in agreement with the experiments. Both the V2O-6 and V4O-11 clusters have the bonding characteristics of oxygen-centered radicals (O·or O-) and these were also identified over the surface of the vanadium oxide based catalysts. This study provides a molecular level mechanismfor the reaction between surface O- species and hydrocarbon molecules.
A series of nanoscale HZSM-5 zeolites modified with different amounts (0-8%, w) of magnesium were prepared by an impregnation method and characterized by X-ray diffraction (XRD), Al solid state magic angle spinning nuclear magnetic resonance (27Al MAS NMR), N2-adsorption/desorption, temperature-programmed desorption of NH3 (NH3-TPD), and pyridine adsorption Fourier transform infrared (FT-IR) methods. The conversion of methanol to propylene was tested in a continuous flow fixed-bed microreactor at atmospheric pressure, 500 ℃, and a methanol space velocity (WHSV) of 1.0 h-1. The results indicated that with an increase in the amount of Mg, the selectivity of propylene and butene increased but those of methane, ethylene and aromatics decreased consistently. With an increase in the amount of Mg the stability of the catalyst was found to increase initially, pass through a maximum at 2% and then decrease with higher amounts of Mg. The effect of modification with magnesium oxide on the catalytic performance of the nanoscale HZSM-5 zeolite for the conversion of methanol to propylene can be attributed to the resultant changes in acidity and texture of the modified nanoscale HZSM-5 zeolites.
Grand canonical Monte Carlo and molecular dynamics simulations were used to study the adsorption and diffusion of oxygen in polypropylene (PP). It is found that at roomtemperature, the loading of oxygen in PP increases and the diffusion coefficient of oxygen in PP decreases as the polymerization degree of PP increases. The loading and diffusion coefficient reach platform values when the polymerization degree of PP is relatively high. The loading of oxygen decreases and the diffusion coefficient of oxygen in PP increases as the temperature increases. The oxygen diffusion mechanism in PP is also discussed according to free volume theory. Oxygen molecules firstly oscillate inside one cavity of PP and then jump from this cavity to another one through a channel formed by the thermal motion of PP chains. In general, simulation results indicate that polymer materials with a high degree of polymerization used at room or low temperatures should be preferred in food reservation technology. This work provides some guidance and basis for developments in food packing materials.
The ion-pairs of the anionic surfactants (dodecyl sulfonate, dodecyl carboxylate) and the cations (Na+, Ca2+, Mg2+) were optimized using density functional theory (DFT) at the B3LY/6-31G level and the interaction between the surfactants and ions were studied at the molecular level. The results showed that: i) a 2:1 type of ion-pair was formed in which two oxygen atoms from the polar group in the surfactant bound with one ion; ii) the α-methylene nearest the headgroup should be classified as the part of the polar head because of its negative charge before ion bonding; iii) the charge of the α-methylene group can be converted from a weak negative into a weak positive charge by the cations, which decreased the effect of the polar headgroup. This calculation also showed that the tail chain had a weak positive charge in the micelle resulting in the core of the micelle having polarity. This core polarity of the micelle is somewhere between the oil phase polarity and the water phase polarity, which favors surfactant aggregation in solution.
Gold nanoparticles were covalently attached to the thiol-terminated surface, which was created by aqueous silanization of the single crystal silicon substrate with 3-mercaptopropyl-trimethyl-silane(3-MPTMS). This paper reports the first evidence for Au-S bonding between the gold particles and the surface thiol-groups given by the angle resolved XPS measurements.
WO3/TiO2 samples were prepared by sol-gel process and characterized by means of XRD、LRS、TEM、DRS、BET、XPS.It has been shown that the mean crystal diameter and mean particle diameter of WO3/TiO2 samples decreased while the percent of anatase and specific surface area increased owing to the doping of WO3.New LRS peaks presented at 797,967 and 969cm-1,respectively,when the concentration of doped WO3 was 2%,5%and 8%.The reflectance percentate of WO3/TiO2 samples was less than that of pure TiO2 in the range of 380-460nm.The XPS fitting analyses showed that there were W6+、W5+、W4+ and Ti4+、Ti3+ in the lattice of WO3/TiO2.Being a model reaction,the photo-catalytic degradation of methylene blue was investigated in TiO2 and WO3/TiO2 nanopowder suspension irradiated by high-pressure mercury lamp.As a result,the addition of WO3 to TiO2 greatly enhanced its photo-catalytic behavior,and the optimum concentration of WO3 in TiO2 was 2%(molar percent).Moreover,the relationship between photo-activity and the physical and chemical properties of the samples have been discussed.
We treated carbon nanotubes (CNTs) with hydrazine hydrate and diethylenetriamine separately and characterized them using scanning electron spectroscopy (SEM) and X-ray photoelectron spectroscopy (XPS). SEM indicated that the treated CNTs retained the length/diameter ratio of the pure CNTs and XPS showed that nitrogen was doped in the CNTs. XPS analysis also indicated that the carbon/nitrogen atomic ratio of the CNTs treated by hydrazine hydrate was 95/2, which was much higher than the 96/0.5 for the CNTs treated by diethylenetriamine. The hydrophilicity of the CNTs was found to be much higher after N-doping and it increased with an increase in the N content. Therefore, the water dispersibility of the N-doped CNTs treated by hydrazine hydrate was better than that of the N-doped CNTs treated by diethylenetriamine. As electrode materials for electrochemical capacitors, nitrogen functional groups contribute to the pseudo-Faradic capacitance but their cyclic performance still needs to be improved. Because of the good hydrophilicity of the N-doping CNTs, which improves the wettability of the CNTs for the electrolyte, the specific capacitance of the N-doping CNT electrode is still slightly higher than that of the pure CNT electrode after cycling.
Electronic structures of nitrogen(N)/fluorine (F)-doped and N-F-codoped TiO2 anatase (101) surfaces were investigated by density functional theory (DFT) plane-wave pseudopotential method. Since DFT calculations performed on transition metal oxides always lead to a severe underestimation of the band gap, DFT+U (Hubbard coefficient) method was also adopted to calculate the electronic structures. DFT results demonstrated that mixing of N 2p states with O 2p and Ti 3d valence band (VB) states contributes to the band gap reduction of TiO2 whereas F doping and the introduction of oxygen vacancies have no obvious effect on the electronic structure. However, from DFT+U, no obvious band gap narrowing was observed by N-doping except for the isolated N 2p states lying in the gap. In DFT+U calculation, F-doping as well as the introduction of oxygen vacancies leads to an obvious band gap narrowing. Results from DFT+U calculations accord well with some experimental results.
We studied the effect of Pluronic F127 micelle solution on the solubility of ibuprofen (IBU). The critical micelle concentration (cmc) of F127 in both water and 0.01 mol·L-1 pH 7.4 phosphate buffer salt (PBS) solution at different temperatures was determined by the pyrene fluorescence method. The concentration of the solubilized IBU was determined using high-performance liquid chromatography (HPLC). We calculated the solubility descriptors (molar solubilization capacity, χ, and micelle-water partition coefficient, K). The influences of temperature, medium properties, and additional copolymer F68 on the micellization of F127 and the solubilization of IBU were also investigated. The results showed that the solubility of IBU increased linearly with an increase in the F127 mass fraction. With an increase in temperature, a significant decrease in the cmc was apparent and a less polar microenvironment was present in the micelle core. Slight increases in χ and K were found with an increase in temperature. The cmc of F127 in PBS solution was much less than that in water, χ was essentially the same and K decreased significantly in PBS solution. F127 micelle property and the solubilization capacity of the F127 micelles were only slightly affected in the presence of F68. An analysis of the solubility descriptors indicates that the K is particularly unique for the drug IBU, and the χ is useful in determining the solubility effectiveness of copolymer F127. We also demonstrated that IBU was predominantly in the micelle core and core-corona interface.
Solubilities of methane in binary mixtures of water and t-butyl alcohol (TBA) have been measured in the temperature range from 303.15 K to 333.15 K and at pressures up to 6 MPa. The mole fraction of t-butyl alcohol(x_(TBA)) in the mixed solvents varied from 0.0 to 1.0. The dependence of the solubilities on temperature and the composition of the mixed solvents can be explained by clathrate structure in the mixed solvents. The Henry s Law constans, the partial mole volumes of methane in the solvents, and the standard thermodynamic functions (ΔG°, ΔH°, ΔS°) have been calculated and discussed.
The mechanisms of all the addition reaction paths of 1,3-cyclohexa-diene with propylene have been studied by using ab initio UHF/6-31G* method. All geometries of the stationary points have been optimized. Stepwise and concerted processes are both possible for the reaction. The stepwise processes are most favorable in all reaction paths. The exo and endo products of the reaction can be formed through two mechanisms, i.e. the terminal double-bonded carbon of propylene attacks 1,3- cyclohexa-diene at first step or so do the center double-bonded carbon. The stepwise processes contain four reaction paths involving biradical intermediates. The calculated activation barriers of the rate determining steps of these paths are about 102~114 kJ•mol-1. Based on microcanonical transition state theory the canonical rate constants for the four stepwise paths have been computed by using data calculated at UHF/6-31G* level. The computational results show that the canonical rate constants for the reaction paths of forming endo product are larger than that for exo ones, and that the canonical rate constants for the reaction paths with the terminal double-bonded carbon of propylene attacking 1,3- cyclohexa-diene at first step are larger than that with the center carbon atom. The canonical rate constants of four stepwise paths are close to each other, so they are competing reactions.
Core-shell photocatalysts of hierarchical porous nanospheres (HP-Fe2O3@TiO2) have been designed and prepared using solvothermal and sol-gel methods. Transmission electron microscopy (TEM) images confirm that the obtained samples a hierarchical porous structure, which results from both the macroporous structure of the core (Fe2O3) and the mesoporous structure of the shell (TiO2). X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption-desorption isotherms were employed to characterize the structure and properties of HP-Fe2O3@TiO2 nanospheres. We investigated the photocatalytic degradation (in the presence of H2O2) of methylene blue (MB) irradiated under visible and ultraviolet light. The observed photocatalytic performance of HP-Fe2O3@TiO2 nanospheres is attributed to the synergetic effects of the core-shell structure, which indicates that the TiO2 shell enhances the photocatalytic performance of α-Fe2O3. HP-Fe2O3@TiO2 (1 mL Ti(OC4H9)4 (TBT)) possesses the highest photodegradation reaction constant among all samples under visible light irradiation. Moreover, HP-Fe2O3@TiO2 (4 mL TBT) has an optimal monodisperse morphology and achieves high photocatalytic activity under ultraviolet light irradiation.
In this paper, the dissolution and dissociation enthalpies of benzoic acid in ethanol water and isopropanol-H2O mixtures have been determined by two kinds of microcalorimeters respectively. Combined with the corresponding Gibbs function changes existing in the literature, the dissolution and dissociation entropies have been calculated. Great efforts have been made to interpret the characteristic variations of the transfer enthalpies and entropies according to the skin phase model for solute solvent interactions and the structure alteration of the mixed solvents.
Ground state geometries of a series of 1, 8-naphthalimide derivatives were calculated by density functional theory (DFT). Their UV-Vis absorption spectra in gaseous, C6H12 (cyclohexane) and CH2Cl2 environments were calculated by the time dependent-DFT (TDDFT) method and the conductor polarizable continuummodel-TDDFT (CPCM-TDDFT) method. We found that theoretical values were in good agreement with X-ray geometric parameters. The addition of various substituents (H, methyl, phenyl, and naphthyl) to the 4 and 5 positions of the naphthalic ring's amines lengthened the (N—C) bond length between the amine and the naphthalimide moiety. This bond lengthening resulted in more intramolecular charge transfer and a lower energy gap. Both the bathochromic effect and the frontier orbital electron cloud density showed that the absorption maximum corresponds to a π-π* transition. By comparison to the maximumabsorption peak of UV-Vis absorption spectrumof the B isomer, that of the A isomer was red shifted and this was mainly attributed to more intramolecular charge transfer and a lower energy gap.
Ordered zinc (Zn) nanowire arrays embedded in anodic aluminum oxide (AAO) templates were prepared by an effective electrodeposition method. Oxygen was used to oxidize the electrodeposited zinc nanowire arrays in the AAO templates. By thermal treatment in an oxygen atmosphere at 800 °C for 2 h, the deposited Zn was completely oxidized. The microstructures and optical properties of the synthesized zinc oxide (ZnO) nanowire arrays were investigated by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and photoluminescence (PL) spectrum analytic apparatus. We found that large scale polycrystalline ZnO nanowire arrays were uniformly assembled in the nanochannels of the AAO template. The nanowires have a very high aspect ratio of about 1000:1 with the length equaling the template thickness and a diameter of about 80 nm. PL measurements of the ZnO/AAO assembly showed a strong green emission at 504 nm, which was attributed to the oxygen vacancy defects of the ZnO nanowires. These results can be used in further studies of the structural and functional properties of electroluminescence devices based on the ZnO/AAO assembly.
A highly efficient and environmentally friendly method for the resolution of racemic 1,1'-bi-2-naphthol (BINOL) was developed by inclusion complexation with the cheap and readily accessible (R)/(S)-N,N,N-trimethyl-1-hydroxyl-3-methyl-2-butanaminiumiodide resolving agents, which were prepared by a simple two-step reaction starting with D/L-valinol. The X-ray structural analysis was carried out for the inclusion complex of the (R)-quaternary ammoniumsalt with (R)-BINOL in CH3OH. This showed that the O—H…I- hydrogen bonds among the bridged iodide anions with the alcoholic hydroxyl of the host (resolving agent) and the phenolic hydroxyls of the guests (BINOL) together with the C—H…O hydrogen-bond interactions between the host and guest molecules from the adjacent layers are responsible for the chiral recognition in the inclusion complex formation. In addition, the solution and solid-state circular dichiroism(CD) spectra of a pair of inclusion complexes were also carefully investigated.
We systematically studied the heats of formation (HOFs) for a series of 3,3′-azobis-1,2,4, 5-tetrazine derivatives by density functional theory (DFT). The results show that the —N3 group plays a very important role in increasing the HOFs for these derivatives. An analysis of the bond dissociation energies for the weakest bonds indicates that the attachment of —NH2 or —N3 group to 3,3′-azobis-1,2,4, 5-tetrazine is favorable in enhancing its thermal stability. The calculated detonation velocities (D) and pressures (p) indicates that —NO2 or —NF2 largely enhances the detonation performance of the derivatives. Considering the detonation performance and the thermal stability, the three derivatives may be regarded to be promising candidates for high-energy density materials (HEDMs).
Oleic acid was used in low-temperature hydrothermal reaction of tetrabutyl titanate (TBOT) to control the growth direction of TiO2 particles. TiO2 nano-crystallines in the shapes of needle and spindle were synthesized. The morphology and structure of these TiO2 particles were confirmed by means of TEM and XRD. The FT-IR spectrum analysis proved that oleic acid molecule was absorbed onto the surface of TiO2 particles through electrostatic interaction. The band-gap energies of TiO2 nano-crystallines were calculated according to their UV-Vis spectra. In the photocatalytic reaction, the spindle TiO2 particles showed higher activity, and 90% rhodanmine B was degraded in 60 min.
The inhibition of steel corrosion in hydrochloric acid solutions by limonene, which was extracted from citrus and orange fruit, was studied using measurements of mass loss, electrochemical polarisation and electrochemical impedance spectroscopy (EIS) methods. Naturally, the substance reduced the rate of corrosion. The linearity of the cathodic curves for all concentrations indicated that the law of Tafel was followed. The effectiveness of inhibition increased with the increase in concentration of limonene and this exceeded 72% at 0.220 g·L-1. The inhibition efficiency is temperature independent in the temperature range of 298-328 K. Adsorption of the substance on the surface of steel obeys the Frumkin isothermmodel.
The catalytic performance of Ni/α-Al2O3 catalysts with different nickel content was investigated for the partial oxidation of methane to syngas in O2 at atmospheric pressure and very high space velecity of 5×105h-1. Optimal CH4 conversion of 91%, CO and H2 selectivity of 94%and 96%, respectively were obtained over 8%(mass fraction) N1 catalyst at 800 ℃, XRD (X-ray Diffraction) analysis indicated that oxidic nickel is the main surface species on Ni/α-Al2O3 catalyst calcinated at 800℃ under atmosphere. TPR (Temperature Programmed Reduction) suggested a bimodel nature of oxidic nickel that are "fixed" to the support. The "free" oxidie nickel, which is responsible for the serious carbon deposition on catalyst, appeared as the nickel content was increased up to 12%. Promoter effects of lanthanide oxide (CeO2) were also investigated. The results showed that addition of CeO2 was beneficial to CH4 conversion and CO selectivity. An excellant conversion (96.5%) and CO selection (96%) were achieved on NiCe(1%Ce)/α-Al2O3 at 800 ℃ with a space velecity of 5×105h-1. Furthmore, CeO2 significantly improved the stability of nickel under critical reaction conditions. No carbon deposition was found over NiCe(1%Ce)/α-Al2O3 after nine hours at 900℃. The promoting mechanism of CeO2 was discussed on the basis of XPS, TPR and XRD results.
Molecular dynamics method has been used to study NaCl-NaBr molten salt mixture, as one of the simplest examples of common cation molten salt systems. It has been found that some Cl- and Na+ ions in NaCl-NaBr mixture tend to form denser ionic clusters, while the Br- ions distribute in the spaces between the Nam+Cln- clusters. The number of ions with No ≤3 increases in the mixing process between NaCl and NaBr melts. The internal energy data of NaCl, NaBr and NaCl-NaBr (1:1) melts estimated by the molecular dynamics are in agreement with the "experimental data" estimated by Born-Haber cycle. These internal energy data indicate that the mixing process between NaCl and NaBr melts is slightly endothermic. This is chiefly due to the increase of the short-range repulsion energy between Na+ ions and halide anions.
The pendent drop or standing bubble method is applied to measure the interfacial tensions between water and nonpolar fluids (n-hexane, n-heptane, nitrogen, oxygen and methane) up to 473K and 220MPa. The high pressure autoclave with t wo visual windows and the auxiliary equipment are described. The sizes(ca 2mm) and shapes of drops or bubbles are recorded with microscope and video camera. The use of digital image permits fast, precise determination of the contour parameters. The densit y values of the liquids or gases have been chosen from literature. A special program is proposed to calculate the interfacial tensions automatically from drop shape at given temperature and pressure. The interfacial tensions σ12 increase with pr essure for the two liquid-liquid systems, but decrease with pressure for the three gas-liquid systems.
Adsorption and oxidation of CO on a CeO2(111) surface terminated by bridging oxygen atoms were systematically investigated using density functional theory (DFT). We found that O2 adsorption on a clean CeO2(111) surface was weak physisorption; while strong chemical adsorption occurred and the O—O bond was activated with a bond length of 0.143 nmin the present of surface oxygen vacancy. CO adsorption onto a clean CeO2(111) surface and a surface with oxygen vacancies occurred through physisorption with both adsorption energies being less than 0.42 eV. With O2 adsorption onto a surface with oxygen vacancies (O2/Ov), CO might absorb strongly on the surface to form a bidentate carbonate intermediate or directly produce CO2 without an energy barrier. The carbonate intermediate might desorb as CO2 with an energy barrier of 0.28 eV using a climbing nudged elastic band (CNEB). We also found that the values of the Hubbard U parameter affected the CO adsorption energy in the presence of surface oxygen vacancies. Our results indicate that a possible effect of the ceria support on catalytic oxidation consists of O2 adsorbing onto the CeO2(111) surface with oxygen vacancies which can be easily activated to form reactive oxygen species and then take part in the CO oxidation reaction.
The adsorption behaviors of O and O2 on charged and neutral Au19 and Au20 clusters were systematically investigated by density functional theory (DFT) with Dmol3 program. Our results indicate that the adsorption energies of O on the hollow sites of Au19 are higher than those on Au20; while those on the side-bridge sites of the Au19 and Au20 clusters are similar. For negatively charged clusters, the adsorption energies of O and O2 are higher than those for neutral and positive clusters. The O―O bond lengths of the adsorbed O2 on the Au19 and Au20 clusters with different charges show a similar trend to the adsorption energy, that is, the O―O bond lengths on Au19- are longer than those on the Au19 and Au19+ clusters. Population analysis shows that more electrons transfer to the adsorbed O and O2 from the Au19- and Au-20 clusters, which indicates stronger interactions compared with the neutral or positive clusters. Charge density difference (CDD) analysis for O2 on the Au19 and Au20 clusters suggests that electrons of the Au19 and Au20 clusters transfer to the π* orbital of O2, upon which the O―O bonds are activated. The dissociation reaction barrier of O2 on Au19- is 1.33 eV, which is lower than those on Au19 (1.86 eV) and Au19+ (2.27 eV).
We developed a low temperature solvothermal approach to synthesize single crystal silver nanoplates with edge lengths of 1-4 μm, thicknesses of 50-100 nm and aspect ratios ≥10 in a large-scale. In this solvothermal approach, N,N-dimethyllformamide (DMF) was used as a main reducing agent and as a solvent, polyvinylpyrrolidone (PVP) was used as a supplementary reducing agent and capping agent, and silver nitrates were used as precursors. The as-obtained silver products of high-purity were characterized by powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). We investigated the impact of different solvents on the morphologies of these silver nanostructures and proposed a possible growth mechanism for the as-synthesized silver nanoplates with large edge lengths and high aspect ratios. The current work provides a new reliable kinetic approach to tune the edge lengths and aspect ratios of silver nanoplates. The as-obtained silver nanoplates with large edge lengths and high aspect ratios have potential important application in polymer-based conductive composites and electromagnetic shielding materials.
【Abstract】 In order to study the aldol condensation of 2.15-hexadecanedione on the surface of aluminium, the intermolecular condensation mechanism of acetone occurring on aluminum was simulated by using semi-empirical AM1 method embodied in MOPAC 6.0 program package. The optimized structures and geometry parameters of 5 transition complexes and 4 intermediates were given. First, 2 molecules of acetone coordinated with aluminum by electrostatic attraction. One atom of hydrogen of acetone migrated to aluminum because of the pulling of the negative oxygen of aluminum, and then aldol condensation occured. Some aluminum containing complex substances may be generated according to the energy variation of intermediates.
Na2MnPO4F/C composites were synthesized by wet ball milling and in situ pyrolytic carbon coating. Stearic acid, citric acid, poly(ethylene glycol) 6000, and β-cyclodextrin were used as carbon sources in the synthesis process. The structures, morphologies, and electrochemical performances of the as-synthesized Na2MnPO4F/C composites were further investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller surface area analysis, and galvanostatic chargedischarge tests. Distinct differences were observed in the morphologies and sizes of the Na2MnPO4F/C particles obtained from different carbon sources, and this significantly affected their electrochemical performances. It was found that the primary particle size of the Na2MnPO4F/C material is a key factor in the electrochemical performance. The sample synthesized using citric acid as the carbon source had a micro-nano structure, with the smallest primary particle size of 10-40 nm, and displayed the best electrochemical properties. It delivered an initial discharge capacity of 80 mAh·g-1 under a current density of 5 mA·g-1 in the voltage range of 1.5-4.8 V, and displayed good cycling performance.
A niobium oxide thin film was obtained by oxidizing Nb(110). UPS was used to characterize the adsorption of methanol, water and ethylene on this film at different temperatures. The results show that at 140K, methanol and water chemisorb associatively at all coverages, while ethylene chemisorbs at low coverages and physisorbs at high coverages. At 300K, these molecules adsorb dissociativelly. The adsorption on surface defect centers is stronger: molecules are adsorbed on these sites first, and are also more affected by the adsorption. Nb5+ is the main adsorption centers on the surface, but oxygen ions on the surface are also adsorption centers.
The dilution enthalpies of N,N-dimethylformamide (DMF) in pure water and aqueous sodium chloride solutions were determined by using flow microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients in the range of sodium chloride concentration from 0 to 0.6 mol·kg-1 were calculated according to the McMillan-Mayer theory. It was found that enthalpic pairwise interaction coefficients (h2) of DMF were all positive in aqueous sodium chloride solutions and became larger with increasing the concentration of sodium chloride. The results were discussed in terms of the solute-solute and solute-solvent interactions.