2015 Vol. 28, No. 2

Content
Content
2015, 28(2): 0-0.
Article
The electronic structure of methanol/TiO2(110) interface has been studied by photoemission spectroscopy. The pronounced resonance which appears at 5.5 eV above the Fermi level in two-photon photoemission spectroscopy (2PPE) is associated with the photocatalyzed dissociation of methanol at vefold coordinated Ti sites (Ti5c) on TiO2(110) surface [Chemical Science 1, 575 (2010)]. To check whether this resonance signal arises from initial or intermediate states, photon energy dependent 2PPE and comparison between one-photon photoemission spectroscopy and 2PPE have been performed. Both results consistently suggest the resonance signal originates from the initially unoccupied intermediate states, i.e., excited states. Dispersion measurements suggest the excited state is localized. Time-resolved studies show the lifetime of the excited state is 24 fs. This work presents comprehensive characterization of the excited states on methanol/TiO2(110) interface, and provides elaborate experimental data for the development of theoretical methods in reproducing the excited states on TiO2 surfaces and interfaces.
We theoretically investigate the Autler-Townes (AT) splitting in the photoelectron spectra of three-level ladder K2 molecule driven by a pump-probe pulse via employing the timedependent wave packet approach. The dependence of AT splitting on two laser intensities and wavelengths are studied in detail. We firstly quantify these effects on peak shift and AT separation. The photoelectron spectra show double splitting with symmetric profiles, but with asymmetric profiles when the wavelength is changed. The magnitude of AT splitting increases with the pump laser intensity, but does not vary with probe intensity. The shifts of the absorption peaks and the splitting between AT doublet are predicted by using an analytical fitting function when the intensity/wavelength of one of the two fields is changed. These novel results are of importance for the molecular spectroscopy and may further stimulate the first principles theoretical studies analytically.
The absorption spectrum of N2+ has been studied using optical-heterodyne velocity mod-ulation spectroscopy in the near-infrared region. The observed spectral lines were assigned to the (3,1), (4,2), (5,3), (8,5) bands of the A2Πu-X2Σ+g system and the line lists were provided. The (5,3) band was studied for the first time. Fourteen rotational-resolved bands in literatures were fitted together with our observed bands and the molecular constants were obtained for υA=0-9 and υX=0-5.
Spin-polarized periodic density functional theory was performed to characterize H2S adsorption and dissociation on graphene oxides (GO) surface. The comprehensive reaction network of H2S oxidation with epoxy and hydroxyl groups of GO was discussed. It is shown that the reduction reaction is mainly governed by epoxide ring opening and hydroxyl hydrogenation which is initiated by H transfer from H2S or its derivatives. Furthermore, the presence of another OH group at the opposite side relative to the adsorbed H2S activates the oxygen group to facilitate epoxide ring opening and hydroxyl hydrogenation. For H2S interaction with -O and -OH groups adsorption on each side of graphene, the pathway is a favorable reaction path by the introduction of intermediate states, the predicted energy barriers are 3.2 and 10.4 kcal/mol, respectively, the second H transfer is the rate-determining step in the whole reaction process. In addition, our calculations suggest that both epoxy and hydroxyl groups can enhance the binding of S to the C-C bonds and the effect of hydroxyl group is more local than that of the epoxy.
Charge compensation plays a very important role in modifying the local atomic structure and moreover the spectroscopic property of an isolated luminescent center, and so has been widely adopted in phosphor designs. In this work, we carry out first principles calculations on various cases of Ce3+ centers in Ca3Sc2Si3O12 by considering the effects of the charge compensations related to N3-, Sc3+, Mn2+, Mg2+, and Na+. Firstly, the local structures around Ce3+ are optimized by using density functional theory calculations with supercell model. The 4f→5d transition energies of Ce3+ are then obtained from the CASSCF/CASPT2/RASSI-SO calculations performed on Ce3+-centered embedded clusters. The calculated energies support the previous assignments of the experimental spectra. Especially, a previously unclear peak is identified to be caused by Sc3+ substituting Si4+. The results show that the first principles calculations can be used as an effective tool for predicting and interpreting spectroscopic properties of the phosphors.
Doping with various impurities is an effective approach to improve the photoelectrochemical properties of TiO2. Here, we explore the effect of oxygen vacancy on geometric and electronic properties of compensated (i.e. V-N and Cr-C) and non-compensated (i.e. V-C and Cr-N) codoped anatase TiO2 by performing extensive density functional theory calculations. Theoretical results show that oxygen vacancy prefers to the neighboring site of metal dopant (i.e. V or Cr atom). After introduction of oxygen vacancy, the unoccupied impurity bands located within band gap of these codoped TiO2 will be filled with electrons, and the position of conduction band offset does not change obviously, which result in the reduction of photoinduced carrier recombination and the good performance for hydrogen production via water splitting. Moreover, we find that oxygen vacancy is easily introduced in V-N codoped TiO2 under O-poor condition. These theoretical insights are helpful for designing codoped TiO2 with high photoelectrochemical performance.
An extensive computational study on the conformations of gaseous dipeptide glycinearginine, GlyArg, has been performed. A large number of trail structures were generated by systematically sampling the potential energy surface (PES) of GlyArg. The trial structures were successively optimized with the methods of PM3, HF/3-21G*, BHandHLYP/6-31G*, and BHandHLYP/6-311++G** in order to reliably find the low energy conformations. The conformational energies were finally determined with the methods of BHandHLYP, camB3LYP, B97D, and MP2 using the basis set of 6-311++G(3df,3pd). The results establish firmly that gaseous GlyArg exists primarily in its canonical form, in sharp contrast with ArgGly that adopts the zwitterionic form. Important data such as the rotational constants, dipole moments, vertical ionization energies, temperature distributions and IR spectra of the low energy conformers are represented for the understanding of the future experiments. Moreover, considering the global minima of all amino acids and many dipeptides, combined with the hydrophobicities of amino acids, a model predicting whether the global minimum configuration of a dipeptide is canonical or zwitterionic is developed.
The traditional quasiharmonic approximation cannot predict the phase diagram of Ti accurately, due to the well-known soften phonon modes of the β-Ti. By means of self-consistent ab initio lattice dynamics (SCAILD) method, in which the effects of phonon-phonon interactions are considered, the phonon dispersion relations at finite temperature for Ti are calculated. From the phonon dispersions, we extrapolat the acoustic velocities and harmonic elastic constants. The dynamical stable regions and phase diagram of Ti are also predicted successfully. The results show that SCAILD method can be designed to work for strongly anharmonic systems where the QHA fails.
The possibilities of magnetism induced by transition-metal atoms substitution in Bi2Te3 system are investigated by ab initio calculations. The calculated results indicate that a transition-metal atom substitution for a Bi atom produces magnetic moments, which are due to the spin-polarization of transition-metal 3d electrons. The values of magnetic moments are 0.92, 1.97, 2.97, 4.04, and 4.98 μB for 4% Ti-, V-, Cr-, Mn-, and Fe-doped Bi2Te3 respectively. When substituting two transition-metal atoms, the characteristics of exchanging couple depend upon the distributions of the Bi atoms substituted. When two transitionmetal atoms substituting for Bi atoms locate at the sites of Bi1 and Bi5, with the distance of 11.52 Å, the Bi1.84TM0.16Te3 system is energetically most stable and exhibits ferromagnetic coupling.
Density functional theory was used to optimize structures of different methylaluminoxane nanotubes with general formula [(AlOMe)2]n, [(AlOMe)3]n and [(AlOMe)4]n cycle unit, where n ranges from 1 to 10. To explore the stability of nanotubes, the binding energies and total energies are calculated. The results indicate that [(AlOMe)3]n and [(AlOMe)4]n have the stable structure of nanotubes. When n is 3, they have the most stable structure in all systems. Moreover, [(Al5O5)]n and [(Al7O7)]n are also considered, but their dimers have irregular and distorted structures. So [(Al5O5)]n and [(Al7O7)]n nanotubes are impossible to exist.
Synthesis of amorphous SiCO nanowires was carried out by means of direct current arc discharge. Free-standing SiCO nanowires were deposited on the surface of a graphite crucible without any catalyst and template. The SiCO nanowires were analyzed by XRD, SEM, TEM, XPS, and FTIR. The SiCO nanowires were typically 20—100 μm in length and 10—100 nm in diameter as measured by SEM and TEM. The XPS and FTIR spectroscopy analysis confirmed that the Si atoms share bonds with O and C atoms in mixed SiCO units. The PL spectrum of the SiCO nanowires showed strong and stable white emissions at 454 and 540 nm. A plasma-assisted vapor-solid growth mechanism is proposed to be responsible for the formation of the SiCO nanowires.
The structure-property relationship of Fe-doped SrCoO3-δ was studied. With increase of Fe content in SrCo1-xFexO3-δ from x=0 to x=0.2, the phase composition changed progressively in the order of hexagonal→brownmillerite (main)+hexagonal→cubic (main)+brownmillerite→single cubic phase. Transition between the hexagonal/brownmillerite phase and the cubic phase took place with variation of the operating conditions, and was associated with remarkable changes in the electrical conductivity and oxygen permeation flux.
Novel hollow Fe3O4 nanoparticles for drug delivery were synthesized via a one-step templatefree approach. These nanoparticles were obtained by modifing the Fe3O4 nanoparticles with 3-aminopropyltrimethoxy silane, and then grafting alginate onto the surface of amine magnetic. The hollow structure of Fe3O4 spheres was characterized by TEM, XRD, and XPS. The M-H hysteresis loop indicated that the magnetic spheres exhibit superparamagnetic characteristics at room temperature. Daunorubicin acting as a model drug was loaded into the carrier, and the maximum percent of envelop and load were 28.4% and 14.2% respectively. The drug controlled releasing behaviors of the carriers were compared in different pH media.
Hydroxylamine sulfate (HAS) and sodium nitrite are used as the accelerators for zinc phosphate coating on high carbon steel. Phase evolution of phosphate coating was investigated by X-ray diffraction. It is found that the phosphating coatings are mainly composed of hopeite Zn3Fe(PO4)2·4H2O and phosphophyllite Zn2Fe(PO4)2·4H2O. The microstructural changes of the phosphate coating, as a function of phosphating time, were evaluated by scanning electron microscopy. Four-ball friction experiments reveal that hydroxylamine sulfate instead of sodium nitrite can effectively reduce the friction coefficient of lubricated phosphating coating. Therefore, it may be expected that HAS will be widely used as a fast and ECO-friendly accelerator in phosphate industry.
The poisoning effect of CO2 on the oxygen surface exchange kinetics of BSCF (Ba0.5Sr0.5Co0.8Fe0.2O3-δ) is investigated with a novel pulse isotopic exchange technique. The surface exchange rate of BSCF severely decreases after in situ exposure to CO2, which is ascribed to carbonate formation on the material surface. The detrimental effect of CO2 starts at a low temperature of 375 oC and concentration as low as 1%, and becomes more pronounced at higher temperatures. Degradation of the surface exchange kinetics is associated with a rapid loss of oxygen permeation performance of BSCF in CO2.
Nickel nanowire and nanotube arrays as supports for Pt-Pd catalyst were prepared by electroless deposition with anodic aluminum oxide template. Pt-Pd composite catalyst was deposited on the arrays by displacement reaction. SEM images show that the nickel nanowires have an average diameter of 100 nm and the nickel nanotubes have an average inner diameter of 200 nm. EDS scanning reveals that elemental Pt and Pd disperse uniformly on the arrays. Cyclic voltammetry study indicates that the nickel nanotube array loaded with Pt-Pd possesses a higher electrochemical activity for ethanol oxidation than the nickel nanowire array with Pt-Pd.
The metal-acid bifunctional catalysts have been used for bio-oil upgrading and pyrolytic lignin hydrocracking. In this work, the effects of the metal-acid bifunctional catalyst properties, including acidity, pore size and supported metal on hydrocracking of pyrolytic lignin in supercritical ethanol and hydrogen were investigated at 260 oC. A series of catalysts were prepared and characterized by BET, XRD, and NH3-TPD techniques. The results showed that enhancing the acidity of the catalyst without metal can promote pyrolytic lignin polymerization to form more solid and condensation to produce more water. The pore size of microporous catalyst was smaller than mesoporous catalyst. Together with strong acidity, it caused pyrolytic lignin further hydrocrack to numerous gas. Introducing Ru into acidic catalysts promoted pyrolytic lignin hydrocracking and inhibited the polymerization and condensation, which caused the yield of pyrolytic lignin liquefaction product to increase significantly. Therefore, bifunctional catalyst with high hydrocracking activity metal Ru supported on materials with acidic sites and mesopores was imperative to get satisfactory results for the conversion of pyrolytic lignin to liquid products under supercritical conditions and hydrogen atmosphere.
Ni/CuO-ZrO2-CeO2-Al2O3 catalysts were prepared by co-precipitation method at pH=9 and using Na2CO3 as the precipitant. The Ni loading (mass fraction) of the catalysts was 10%. The catalysts were characterized by X-ray diffraction, temperature-programmed oxidation (TPO), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). The effects of calcined temperature of support on coke deposition were studied. TPO, SEM and XPS results indicated there was no peak of higher temperature oxygen consumption on Ni/CuO-ZrO2-CeO2-Al2O3catalyst (support was calcined at 800 oC), which could lead to the deactivation of the catalyst. The carbon species were carbonate and inactive carbon (filamentous carbon species) on the surface of catalyst reacting for 40 h which perhaps led to the deactivation of the catalyst.
Triethanolamine monolaurate ester was synthesized by lauric acid and triethanolamine (TEA) with a molar ratio around 1:1 and the esterification process was investigated and optimized. The esterification product of lauric acid with TEA was characterized by infrared spectra and nuclear magnetic resonance. The surface tension (γCMC) at the critical micelle concentration (CMC) was determined, and the antifogging properties of triethanolamine laurate ester on low-density polyethylene (LDPE) films were also measured. The results indicated that the yield of triethanolamine monolaurate ester was more than 69% under optimized esterification condition, the CMC value and γCMC of esterification product was 0.91 μg/mL and 22.1 mN/m in aqueous solution at 25 oC, respectively. The first-drop time and ten-drop time was 257 and 86 s, respectively, and the antifogging duration of triethanolamine laurate ester on the surface of LDPE film at 60 oC was more than 150 h.
Biomass-derived hexose sugars, the most abundant renewable resources in the world, have potential to be the sustainable resources for production of platform chemicals. Here, conversion of glucose is investigated by using sulfonated graphene (rGO-SO3H) as solid acid catalyst in water without any organic solvent. At first, graphene functionalized with sulfonic acid groups is prepared by using NaH and propane sultone, and then it is characterized by means of XPS, FT-IR, and TEM to confirm the existence of the sulfonic acid groups. The catalytic activity of rGO-SO3H in the conversion of glucose to valuable chemicals is studied under different reaction conditions. The maximum yield of 5-hydroxymethylfurfural (HMF) is 28.8%, and the total yield of formic acid, lactic acid and HMF is 51.94% when the reaction is conducted at the optimized reaction condition. In addition, the rGO-SO3H gives a relatively high total yield of the three kinds of products after five run experiments, indicating that the catalyst shows good thermal stability.
A new 3,4-disubstituted-1,8-naphthalimide derivative H1 was designed and synthesized as a selective fluorescent probe for Cu2+ over miscellaneous metal ions in aqueous media. Upon mixing with Cu2+ in CH3OH:H2O (1:1, volume ratio), the increase of fluorescence intensity and a bathochromic shift of absorbance of H1 could be observed with a notable color response (changing from yellow to pink). Furthermore, Cu2+ coordinates to the probe H1 and a 1:1 metal-ligand complex was formed.
We herein report two crystals based on 2-(imidazo[1,2-a]pyridin-2-yl)-2-oxoacetic acid radical and its perchlorate, and investigate the relationship between magnetic properties and crystal stacking structures or supramolecular interactions. 2-(Imidazo[1,2-a]pyridin-2-yl)-2-oxoacetic acid radical in two crystals mainly exist as diamagnetic dimer formed via short atomic contacts or supramolecular interactions (hydrogen bonds, anion-π or lonepair-π interactions), leading to low magnetic susceptibilities. 2-(Imidazo[1,2-a]pyridin-2-yl)-2-oxoacetic acid radical crystal exhibits quasi-one-dimensional columnar stacking chain and weak antiferromagnetism. However, its perchlorate crystal possesses one-dimensional doublestranded chain structure assembled through double hydrogen bonds and anion-π interactions, and reveals weak ferromagnetism.
Chinese abstract
Chinese Abstracts
2015, 28(2): 245-245.