2017 Vol. 30, No. 3

Article
A combined cavity ringdown (CRD) and laser induced fluorescence (LIF) spectroscopic study on the A1+-X1+ transition of CuH has been presented.The CuH molecule,as well as its deuterated isotopologue CuD,are produced in a supersonic jet expansion by discharging H2(or D2) and Ar gas mixtures using two copper needles.Different profiles of relative line intensities are observed between the measured LIF and CRD spectra,providing an experimental evidence for the predissociation behavior in the A1+ state of CuH.The lifetimes of individual upper rotational levels are measured by LIF,in which the J'-dependent predissociation rates are obtained.Based on the previous theoretical calculations,a predissociation mechanism is concluded due to the strong spin-orbit coupling between the A1+ state and the lowest-lying triplet 3+ state,and a tunneling effect may also be involved in the predissociation.Similar experiments are also performed for CuD,showing that the A1+ state of CuD does not undergo a predissociation process.
A new velocity map imaging spectrometer is constructed for molecular reaction dynamics studies using time-resolved photoelectron/ion spectroscopy method.By combining a kHz pulsed valve and an ICCD camera,this velocity map imaging spectrometer can be run at a repetition rate of 1 kHz,totally compatible with the fs Ti:Sapphire laser system,facilitating time-resolved studies in gas phase which are usually time-consuming.Time-resolved velocity map imaging study of NH3 photodissociation at 200 nm was performed and the time-resolved total kinetic energy release spectrum of H+NH2 products provides rich information about the dissociation dynamics of NH3.These results show that this new apparatus is a powerful tool for investigating the molecular reaction dynamics using time-resolved methods.
As the photo-dissociation product of methanol on the TiO2(110) surface,the diffusion and desorption processes of formaldehyde (HCHO) were investigated by using scanning tunneling microscope (STM) and density functional theory (DFT).The molecular-level images revealed the HCHO molecules could diffuse and desorb on the surface at 80 K under UV laser irradiation.The diffusion was found to be mediated by hydrogen adatoms nearby,which were produced from photodissociation of methanol.Diffusion of HCHO was significantly decreased when there was only one H adatom near the HCHO molecule.Furthermore,single HCHO molecule adsorbed on the bare TiO2(110) surface was quite stable,little photo-desorption was observed during laser irradiation.The mechanism of hydroxyl groups assisted diffusion of formaldehyde was also investigated using theoretical calculations.
To elucidate the nature of low-lying triplet states and the effect of ligand modifications on the excited-state properties of functional cationic iridium complexes,the solventdependent excited-state dynamics of two phosphorescent cationic iridium (III) complexes,namely[Ir (dph-oxd)2(bpy)]PF6( 1 ) and[Ir (dph-oxd)2(pzpy)]PF6( 2 ),were investigated by femtosecond and nanosecond transient absorption spectroscopy.Upon photoexcitation to the metal-to-ligand charge-transfer (MLCT) states,the excited-state dynamics shows a rapid process (τ=0.7-3 ps) for the formation of solvent stabilized 3MLCT states,which significantly depends on the solvent polarity for both 1 and 2 .Sequentially,a relatively slow process assigned to the vibrational cooling/geometrical relaxation and a long-lived phosphorescent emissive state is identified.Due to the different excited-state electronic structures regulated by ancillary ligands,the solvation-induced stabilization of the 3MLCT state in 1 is faster than that in 2 .The present results provide a better sight of excited-state relaxation dynamics of ligand-related iridium (III) complexes and solvation effects on triplet manifolds.
Designing and fabricating high-performance photovoltaic devices have remained a major challenge in organic solar cell technologies.In this work,the photovoltaic performances of BTBPD-PC61BM system were theoretically investigated by means of density functional theory calculations coupled with the Marcus charge transfer model in order to seek novel photovoltaic systems.Moreover,the hole-transfer properties of BTBPD thin-film were also studied by an amorphous cell with 100 BTBPD molecules.Results revealed that the BTBPDPC61BM system possessed a middle-sized open-circuit voltage of 0.70 V,large short-circuit current density of 16.874 mA/cm2,large fill factor of 0.846,and high power conversion efficiency of 10%.With the Marcus model,the charge-dissociation rate constant was predicted to be as fast as 3.079×1013 s-1 in the BTBPD-PC61BM interface,which was as 3-5 orders of magnitude large as the decay (radiative and non-radiative) rate constant (108-1010 s-1),indicating very high charge-dissociation efficiency (~100%) in the BTBPD-PC61BM system.Furthermore,by the molecular dynamics simulation,the hole mobility for BTBPD thin-film was predicted to be as high as 3.970×10-3 cm2V-1s-1,which can be attributed to its tight packing in solid state.
A wide range of quantum systems are time-invariant and the corresponding dynamics is dictated by linear differential equations with constant coefficients.Although simple in mathematical concept,the integration of these equations is usually complicated in practice for complex systems,where both the computational time and the memory storage become limiting factors.For this reason,low-storage Runge-Kutta methods become increasingly popular for the time integration.This work suggests a series of s-stage sth-order explicit RungeKutta methods specific for autonomous linear equations,which only requires two times of the memory storage for the state vector.We also introduce a 13-stage eighth-order scheme for autonomous linear equations,which has optimized stability region and is reduced to a fifth-order method for general equations.These methods exhibit significant performance improvements over the previous general-purpose low-stage schemes.As an example,we apply the integrator to simulate the non-Markovian exciton dynamics in a 15-site linear chain consisting of perylene-bisimide derivatives.
A numerical investigation on the co-pyrolysis of 1,3-butadiene and propyne is performed to explore the synergistic effect between fuel components on aromatic hydrocarbon formation.A detailed kinetic model of 1,3-butadiene/propyne co-pyrolysis with the sub-mechanism of aromatic hydrocarbon formation is developed and validated on previous 1,3-butadiene and propyne pyrolysis experiments.The model is able to reproduce both the single component pyrolysis and the co-pyrolysis experiments,as well as the synergistic effect between 1,3-butadiene and propyne on the formation of a series of aromatic hydrocarbons.Based on the rate of production and sensitivity analyses,key reaction pathways in the fuel decomposition and aromatic hydrocarbon formation processes are revealed and insight into the synergistic effect on aromatic hydrocarbon formation is also achieved.The synergistic effect results from the interaction between 1,3-butadiene and propyne.The easily happened chain initiation in the 1,3-butadiene decomposition provides an abundant radical pool for propyne to undergo the H-atom abstraction and produce propargyl radical which plays key roles in the formation of aromatic hydrocarbons.Besides,the 1,3-butadiene/propyne co-pyrolysis includes high concentration levels of C3 and C4 precursors simultaneously,which stimulates the formation of key aromatic hydrocarbons such as toluene and naphthalene.
By the first-principles calculations,most studies indicated that the (11102)-CoO2 termination of LaCoO3 cannot be stabilized,which disagrees with the experimental observation.Besides the crystal structure,we found that the spin states of Co3+ ions could affect surface stability,which previously were not well considered.By examining the different states of Co3+ ions in hexagonal-phase LaCoO3,including low spin,intermediate spin,and high spin states,the surface grand potentials of these facets are calculated and compared.The results show that the spin states of Co3+ ions have an important influence on stability of the LaCoO3 facets.Different from the previous results,the stability diagrams demonstrate that the (11102)-CoO2 termination can stably exist under O-rich condition,which can get an agreement with the experimental ones.Furthermore,the surface oxygen vacancy formation energies (EOv) of stable facets are computed in different spin states.The EOv of these possible exposed terminations strongly depend on the spin state of Co3+ ions:in particular,the EOv of the HS states is lower than that of other spin states.This indicates that one can tune the properties of LaCoO3 by directly tuning the spin states of Co3+ ions.
The photoionization and dissociation photoionization of toluene have been studied using quantum chemistry methods.The geometries and frequencies of the reactants,transition states and products have been performed at B3LYP/6-311++G (d,p) level,and single-point energy calculations for all the stationary points were carried out at DFT calculations of the optimized structures with the G3B3 level.The ionization energies of toluene and the appearance energies for major fragment ions,C7H7+,C6H5+,C5H6+,C5H5+,are determined to be 8.90,11.15 or 11.03,12.72,13.69,16.28 eV,respectively,which are all in good agreement with published experimental data.With the help of available published experimental data and theoretical results,four dissociative photoionization channels have been proposed:C7H7++H,C6H5++CH3,C5H6++C2H2,C5H5++C2H2+H.Transition structures and intermediates for those isomerization processes are determined in this work.Especially,the structures of C5H6+ and C5H5+ produced by dissociative photoionization of toluene have been defined as chain structure in this work with theoretical calculations.
Oxygen vacancy (Ov) has significant influence on physical and chemical properties of TiO2 systems,especially on surface catalytic processes.In this work,we investigate the effects of O v on the adsorption of formaldehyde (HCHO) on TiO2(110) surfaces through firstprinciples calculations.With the existence of Ov,we find the spatial distribution of surface excess charge can change the relative stability of various adsorption configurations.In this case,the bidentate adsorption at five-coordinated Ti (Ti5c) can be less stable than the monodentate adsorption.And HCHO adsorbed in Ov becomes the most stable structure.These results are in good agreement with experimental observations,which reconcile the long-standing deviation between the theoretical prediction and experimental results.This work brings insights into how the excess charge affects the molecule adsorption on metal oxide surface.
Hydrogen generation from formic acid (FA) has received significant attention.The challenge is to obtain a highly active catalyst under mild conditions for practical applications.Here atomic layer deposition (ALD) of FeOx was performed to deposit an ultrathin oxide coating layer to a Pd/C catalyst,therein the FeOx coverage was precisely controlled by ALD cycles.Transmission electron microscopy and powder X-ray diffraction measurements suggest that the FeOx coating layer improved the thermal stability of Pd nanoparticles (NPs).X-ray photoelectron spectroscopy measurement showed that deposition of FeOx on the Pd NPs caused a positive shift of Pd3d binding energy.In the FA dehydrogenation reaction,the ultrathin FeOx layer on the Pd/C could considerably improve the catalytic activity,and Pd/C coated with 8 cycles of FeOx showed an optimized activity with turnover frequency being about 2 times higher than the uncoated one.The improved activities were in a volcanoshape as a function of the number of FeOx ALD cycles,indicating the coverage of FeOx is critical for the optimized activity.In summary,simultaneous improvements of activity and thermal stability of Pd/C catalyst by ultra-thin FeOx overlayer suggest to be an effective way to design active catalysts for the FA dehydrogenation reaction.
Two-dimensional transition metal dichalcogenides heterostructures have stimulated wide interest not only for the fundamental research,but also for the application of next generation electronic and optoelectronic devices.Herein,we report a successful two-step chemical vapor deposition strategy to construct vertically stacked van der Waals epitaxial In2Se3/MoSe2 heterostructures.Transmission electron microscopy characterization reveals clearly that the In2Se3 has well-aligned lattice orientation with the substrate of monolayer MoSe2.Due to the interaction between the In2Se3 and MoSe2 layers,the heterostructure shows the quenching and red-shift of photoluminescence.Moreover,the current rectification behavior and photovoltaic effect can be observed from the heterostructure,which is attributed to the unique band structure alignment of the heterostructure,and is further confirmed by Kevin probe force microscopy measurement.The synthesis approach via van der Waals epitaxy in this work can expand the way to fabricate a variety of two-dimensional heterostructures for potential applications in electronic and optoelectronic devices.
A series of carbon nanotubes-supported K-Co-Mo catalysts were prepared by a sol-gel method combined with incipient wetness impregnation.The catalyst structures were characterized by X-ray diffraction,N2 adsorption-desorption,transmission electron microscopy and H2-TPD,and its catalytic performance toward the synthesis of higher alcohols from syngas was investigated.The as-prepared catalyst particles had a low crystallization degree and high dispersion on the outer and inner surface of CNTs.The uniform mesoporous structure of CNTs increased the diffusion rate of reactants and products,thus promoting the reaction conversion.Furthermore,the incorporation of CNTs support led to a high capability of hydrogen absorption and spillover and promoted the formation of alkyl group,which served as the key intermediate for the alcohol formation and carbon chain growth.Benefiting from these characteristics,the CNTs supported Mo-based catalyst showed the excellent catalytic performance for the higher alcohols synthesis as compared to the unsupported catalyst and activated carbon supported catalyst.
Metal-free catalysts are preferred during these days in organic synthesis or in polymerizations.Sulfonic acid is reported to be efficient in catalyzing reactions between isocyanates and alcohols.In this work,synthesis of sulfonic acid immobilized organic nanoparticles (nanoacid) and its application in catalyzing urethane formation,are elaborated.The nanoacid can be simply prepared by miniemulsion polymerization with a reactive surfactant,namely sodium 4-((perfluoronon-8-en-1-yl) oxy) benzenesulfonate,followed by an acidification.From the images of scanning electron microscope,the nanoacid obtained is found to be narrowly dispersed and the average diameter is around 90 nm.The measured sulfur content is 0.5%,from which the content of sulfonic acid in the nanoparticles is calculated to be 0.16 mmol/g.When catalyzing urethane formation based on hexamethylene diisocyanate and n-butanol,the nanoacid catalyst exhibits considerable efficiency.
Using 3D Langevin dynamics simulations,we investigate the effects of the shape of crowders on the dynamics of a polymer chain closure.The chain closure in spherical crowders is dominated by the increased medium viscosity so that it gets slower with the increasing volume fraction of crowders.By contrast,the dynamics of chain closure becomes very complicated with increasing volume fraction of crowders in spherocylindrical crowders.Notably,the mean closure time is found to have a dramatic decrease at a range of volume fraction of crowders 0.36-0.44.We then elucidate that an isotropic to nematic transition of spherocylindrical crowders at this range of volume fraction of crowders is responsible for the unexpected dramatic decrease in the mean closure time.
Cumene is an important intermediate and chemical in chemical industry.In this work,directional preparation of cumene using lignin was achieved by a three-step cascade process.The mixture aromatics were first produced by the catalytic pyrolysis of lignin at 450℃ over 1% Zn/HZSM-5 catalyst,monocyclic aromatics with the selectivity of 85.7 wt% were obtained.Then,the catalytic dealkylation of heavier aromatics resulted in benzene-rich aromatics with 93.6 wt% benzene at 600℃ over Hβ catalyst.Finally,the cumene synthesis was performed by the aromatic alkylation,giving cumene selectivity of 91.6 C-mol% using the[bmim]Cl-2AlCl13 ionic liquid at room temperature for 15 min.Besides,adding a small amount of methanol to the feed can efficiently suppress the coke yield and enhance the aromatics yield.The proposed transformation potentially provides a useful route for production of cumene using renewable lignin.
Biochar is a massively produced by-product of biomass pyrolysis to obtain renewable energy and has not been fully used.Incomplete separation of sludge and effluent and insufficient denitrification of sewage are two of main factors that influence the efficiency of activated sludge process.In this work,we proposed a new utilization of biochar and investigated the effect of biochar addition on the performance of settleability and denitrification of activated sludge.Results show that the addition of biochar can improve the settleability of activated sludge by changing the physicochemical characteristics of sludge (e.g.,flocculating ability,zeta-potential,hydrophobicity,and extracellular polymeric substances constituents).Moreover,the dissolved organic carbon released from biochar obtained at lower pyrolysis temperature can improve the nitrate removal efficiency to a certain extent.