富含光诱导氧空位Bi12O17Br2的制备及其高效光催化固氮性能

采用一步水热法制备了Bi₁₂O₁₇Br₂光催化剂,其平均微片尺寸为1.2μm,比表面积约为29 m²·g^-1。Bi₁₂O₁₇Br₂的禁带宽度为2.42 eV,能够响应可见光。值得注意的是,在光照条件下Bi₁₂O₁₇Br₂表面能够产生氧空位;光诱导氧空位不仅能促进氮气在催化剂表面的吸附,而且对吸附的氮气分子的活化起到至关重要的作用。实验结果表明在可见光照射下,Bi₁₂O₁₇Br₂光催化剂上的氨生成速率为337.6μmol·g^-1·h^-1。在可见光的驱动下,Bi₁₂O₁₇Br₂光催化剂能够实现氮气与水反应生成氨的过程。     

Stereochemical patterns in bromofullerenes C60Br2 to C60Br12

The stabilities of different isomers of C₆₀Br_n have been calculated for n = 2 to 12. A general stereochemical pattern which emerges is the tendency to form strings created by the edge sharing of C₆Br₂ hexagonal faces. Stable structures are formed if these strings form loops, thereby eliminating string ends, which may involve the creation of C₆Br₃ hexagonal faces. A particularly stable structure is formed at C₆₀Br₆ in which the loop forms a C₁₀Br₆ fragment with a pentagonal pyramidal arrangement of six bromine atoms. Two isomers of C₆₀Br₁₂ are also particularly stable. One isomer contains two of these Br₆ pentagonal pyramids on opposite sides of the molecule, and the other isomer contains a single large loop wrapped around the middle of the molecule.     

Normal co-ordinate analyses and structural considerations of TeCl4, TeBr4 and TeCl2Br2

The molecular structure of TeCl₂Br₂ in the vapour phase is reconsidered in the light of the recently published X-ray crystal structure for TeCl₄. Normal coordinate calculations are performed on molecular TeCl₂Br₂ in its three possible symmetries using force fields derived from the parent molecules TeCl₄ and TeBr₄. The calculations indicate that the data for molecular TeCl₂Br₂ can best be interpreted as arising from a mixture of at least the two high symmetry conformers rather than just the low symmetry C₁ molecule as previously reported.     

Binary systems of C60 with positional isomers 1,2- and 1,3-C6H4Br2

Thermodynamic properties of binary systems of C₆₀ with 1,2- and 1,3-dibromobenzenes have been studied by means of differential scanning calorimetry (DSC). Solid solvates with the compositions C₆₀3(1,2-C₆H₄Br₂); C₆₀2(1,3-C₆H₄Br₂) and C₆₀0.6(1,3-C₆H₄Br₂) have been found. The solvates have been characterised by their enthalpies and temperatures of incongruent melting transition and in part by X-ray powder data. It has been shown that positional isomers 1,2- and 1,3- of the substituted benzenes formed two series of “typical” phase diagrams. Solubility behaviour of C₆₀ in positional isomers has been discussed.     

Synthesis and molecular structure of the all-trans- and the trans–cis-[UO2Br2(OAsPh3)2] isomers

The all-trans and the trans–cis isomers of [UO₂Br₂(OAsPh₃)₂] have been prepared by reacting UO₂Br₂·xH₂O with OAsPh₃. The molecular structures for both isomers have been established by X-ray diffraction analysis. The all-trans isomer is singular as the two U---OAsPh₃ bonds are very different.     

On structural phase transitions in (i-C4H9NH3)3Bi2Br9: differential scanning calorimetry, dielectric and infrared studies

Two structural phase transitions at 263 and 252 K are detected in a new isobutylammonium crystal (i-C₄H₉NH₃)₃Bi₂Br₉ by means of differential scanning calorimetry (DSC) and dielectric studies. Internal vibrations modes of (i-C₄H₉NH₃)₃Bi₂Br₉ are studied through their phase transitions using the infrared spectrscopy. The infrared studies show that the vibrational state of isobutylammonium cations changes weakly during the phase transition at 252 K. The 263 K phase transition is not reflected in the infrared spectra. The lower temperature phase transition (252 K) is believed to be governed by the reorientational motion of the isobutylammonium cations and may be classified as an ‘order–disorder' type.     

高催化活性2D/2D Ti3C2/Bi4O5Br2纳米片异质结的构建及其可见光催化去除NO

This study concentrated on the production of a two-dimensional and two-dimensional (2D/2D) Ti₃C₂/Bi₄O₅Br₂ heterojunction with a large interface that applied as one of the novel visible-light-induced photocatalyst via the hydrothermal method. The obtained photocatalysts enhanced the photocatalytic efficiency of the NO removal. The crystal structure and chemical state of the composites were characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that Ti₃C₂, Bi₄O₅Br₂, and Ti₃C₂/Bi₄O₅Br₂ were successfully synthesized. The experimental results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the prepared samples had a 2D/2D nanosheet structure and large contact area. This structure facilitated the transfer of electrons and holes. The solar light absorptions of the samples were evaluated using the UV-Vis diffuse reflectance spectra (UV-Vis DRS). It was found that the absorption band of Ti₃C₂/Bi₄O₅Br₂ was wider than that of Bi₄O₅Br₂. This represents the electrons in the Ti₃C₂/Bi₄O₅Br₂ nanosheet composites were more likely to be excited. The photocatalytic experiments showed that the 2D/2D Ti₃C₂/Bi₄O₅Br₂ composite with high photocatalytic activity and stability. The photocatalytic efficiency of pure Bi₄O₅Br₂ for the NO removal was 30.5%, while for the 15%Ti₃C₂/Bi₄O₅Br₂ it was 57.6%. Moreover, the catalytic reaction happened in a short period. The concentration of NO decreased exponentially in the first 5 min, which approximately reached the final value. Furthermore, the stability of 15%Ti₃C₂/Bi₄O₅Br₂ was favorable: the catalytic rate was approximately 50.0% after five cycles of cyclic catalysis. Finally, the scavenger experiments, electron spin resonance spectroscopy (ESR), transient photocurrent response, and surface photovoltage spectrum (SPS) were applied to analyze the photocatalytic mechanism of the composite. The results indicated that the 2D/2D heterojunction Ti₃C₂/Bi₄O₅Br₂ improved the separation rate of the electrons and holes, thus enhancing the photocatalytic efficiency. In the photocatalytic reactions, the photogenerated electrons (e⁻) and superoxide radical (·O₂⁻) were critical active groups that had a significant role in the oxidative removal of NO. The in situ Fourier-transform infrared spectroscopy (in situ FTIR) showed that the photo-oxidation products were mainly NO₂⁻ and NO₃⁻. Based on the above experimental results, a possible photocatalytic mechanism was proposed. The electrons in Bi₄O₅Br₂ were excited by visible light. They jumped from the valence band (VB) of Bi₄O₅Br₂ to the conduction band (CB). Then, the photoelectrons transferred from the CB of Bi₄O₅Br₂ to the Ti₃C₂ surface, which significantly promoted the separation of the electron-hole pairs. Therefore, the photocatalytic efficiency of Ti₃C₂/Bi₄O₅Br₂ on NO was significantly improved. This study provided an effective method for preparing 2D/2D Ti₃C₂/Bi₄O₅Br₂ nanocomposites for the photocatalytic degradation of environmental pollutants, which has great potential in solving energy stress and environmental pollution.     

Synthesis and structure of a new selenium-bridged tungsten cluster, [W3Se7(S2P(OEt)2)3]Br

[W₃Se₇(S₂P(OEt)₂)₃]Br was prepared by reacting (Et₄N)₂W₃Se₇Br₆ with KS₂P (OEt)₂ in CH₃CN and its crystal structure determined. In the [W₃(μ₃-Se)(μ₂-Se₂)₃]⁴⁺ core the W---W bond length is 2.755(5)-2.764(6) Å and the Se---Se bond length is 2.32(1)- 2.34(4) Å.     

Mercury(II) halide adducts of an olefinic double betaine: [{Hg2L2X4·6HgX2}n] [X = Cl, Br; L = cis-(p-Me2NC5H4N)2C2(COO)2]

Two polymeric mercury(II) halide adducts of an olefinic double betaine, cis-(p-Me₂NC₅H₄N⁺)₂C₂(COO⁻)₂ (L), have been prepared and characterized by X-ray crystallography. [{Hg₂L₂Cl₄·6HgCl₂}_n] (1) crystallizes in the monoclinic space group C2/c with Z = 4, and [{Hg₂L₂Br₄·HgBr₂}_n] (2) in the triclinic space group P with Z = 1. Complexes 1 and 2 are structurally similar, being composed of centrosymmetric fourteen-membered rings and nearly linear HgX₂ (X = Cl, Br) moieties that are further inter-linked by weak HgX [HgCl = 2.930–3.136(9) Å, HgBr = 3.057–3.310(6) Å] and HgO [2.64, 2.75(3) Å] bonds to generate a two-dimensional polymeric network.     

Synthesis, characterisation and reactivity of trans-[Ru(L)(PPh3)Br2]; L=2-pyridyl-N-(2′-methylthiophenyl)methyleneimine: Crystal structure of trans-[Ru(L)(PPh3)Br2]

Reaction of Ru(PPh₃)₂Br₂ with the NNS chelating tridentate ligand 2-pyridyl-N-(2′-methylthiophenyl)methyleneimine (L) led to the isolation of the ruthenium(II) complex [Ru(L)(PPh₃)Br₂]. Reactivity of this complex with different bidentate chelating ligands revealed that the products are quite different from those obtained by reacting Ru(L)(PPh₃)Cl₂ (the corresponding cis dichloro complex) with the same ligands under comparable conditions. The mixed chelates were isolated and characterised by elemental analysis, magnetic moment measurement and by different spectroscopic methods along with their precursor. Electrochemistry of the complexes was examined by cyclic voltammetry using a platinum working electrode and a Ag/AgCl electrode as reference. The crystal structure of [Ru(L)(PPh₃)Br₂] disclosed that, unlike Ru(L)(PPh₃)Cl₂, the two bromo ligands are in trans position and this explained the difference in its reactivity pattern from the corresponding chloro complex.     

The pure rotational Raman spectra of cyanogen, C2N2 and C2N2

The pure rotational Raman spectra of C₂¹⁴N₂ and C₂¹⁵N₂ have been recorded photographically using a 3-metre spectrograph with a reciprocal linear dispersion of 1.4 cm⁻¹ mm⁻¹ at 488.0 nm and analysed to give the rotational and centrifugal distortion constants for both species. Corrections were applied to compensate for the effect of molecules in excited vibrational states on the pure rotational spectra. Comparisons are made with previous infrared vibration—rotational studies on these species and with previous Raman studies on C₂¹⁴N₂. The following bond lengths were calculated: r₀(C---N) = 116 ± 1 pm; r₀(C---C) = 138 ± 2 pm.     

Theoretical calculational studies on the mechanism of thermal dissociations for RN3 (R=CH3, CH3CH2, (CH3)2CH, (CH3)3C)

Mechanisms of RN₃ (R=CH₃, CH₃CH₂, (CH₃)₂CH, (CH₃)₃C) dissociations are proposed based on CAS, MP2 and B3LYP methods. The energy gaps between the ground-state reactants RN₃ and the intersystem crossing (ISC) points are only a little lower than respective potential energy barriers of the spin-allowed reactions, ¹RN₃ → ¹RN + ¹N₂. The ISC point, therefore, is considered as a transition state of the spin-forbidden reactions, ¹RN₃ → ³RN + ¹N₂. The methods of IRC and topological analysis of electron density are used to explain and predict the thermal dissociation pathways of the reactions studied.     

Lifetime measurements of the excited states of N2 AND N2 by laser-induced fluorescence

Absorption and fluorescent scattering of nitrogen laser radiation by a low-pressure RF laboratory plasma (n_e = 10¹² cm⁻³) has been observed for the first negative system of N₂⁺. A 67±1 ns lifetime of N₂⁺ (B ²Σ_u⁺) was experimentally measured from the laser-induced fluorescence. In addition, enough collisionally excited N₂ (B ³Π_g) was produced to observe laser-induced fluorescence for the second positive system of N₂. The lifetime of N₂ (C ³Π_u) was found to be 41±2 ns. The measured lifetimes are in good agreement with published values calculated from theory.     

The reactivity of dimethylaluminum hydride with the aminoarsines Me2AsNMe2, MeAs(NMe2)2, and As(NMe2)3

The reactions of (Me₂AlH)₃ with Me₂AsNMe₂, MeAs(NMe₂)₂, and As(NMe₂)₃ were investigated as a function of time at room temperature and over the temperature range −90 to 24°C by use of ¹H and ¹³C NMR spectroscopy. (Me₂AlH)₃ was found to be very reactive toward the aminoarsines, even at −90°C, and no stable Me₂AlH-aminoarsine adducts were observed. Instead, the initial stages of the reactions involved AS---N bond cleavage with the generation of highly reactive AlN- and AsH-bonded species. The subsequent course of each reaction and the final arsenic-containing product distribution depended upon the original AL:N stoichiometric ratio and the respective aminoarsine. When the Al:N ratio was 1:1, the reactions were straightforward for each aminoarsine. However, in every case, [Me₂AlNMe₂]₂ was the final AlN-containing product. Independent reactions were carried out to verify many of the proposed decomposition pathways that lead to thermodynamically stable products. The results of this study are compared with those of the analogous, previously reported (Me₃Al)₂-aminoarsine systems. Additionally, a new synthetic route to [Me₂AlAsMe₂]₃ has been established from the reaction of (Me₂AlH)₃ with Me₂AsH.     

A study of the B2 excited state geometries of the metal-metal quadruply bonded compounds Mo2X4(PMe3)4 (X = Cl, Br or I)

The excited state geometries of the metal-metal quadruply bonded compounds Mo₂X₄(PMe₃)₄ (X = Cl, Br or I) have been studied by means of resonance Raman and absorption spectroscopy. A fit of the parameters of a simple theoretical model to the experimental data indicates that the metal-metal bond increases some 10 pm on excitation to the ¹B₂ (δδ^*) state, whereas other geometric changes are small. Furthermore, the phenomenological lifetime factor of the excited state, Γ, is found to be dependent on the vibrational quantum number, ν, of this state.     

Dissociative excitation of SiH4, SiD4, Si2H6 and GeH4 by 0–100 eV electron impact

We have measured emission cross sections of various electronically excited fragments produced by electron-impact dissociation of SiH₄, SiD₄, Si₂H₆ and GeH₄. At low impact energy (10–20 eV), the measured appearance potentials are correlated to specific dissociation processes. Below 22 eV superexcited states of SiH₄ play a dominant role in the formation of neutral excited fragments. In agreement with the results obtained on alkanes, the cross sections for fragment emission from Si₂H₆ are lower than those for SiH₄. On the other hand, the comparison of cross sections at 100 eV for fragment emission, dissociation and ionization on going from CH₄ to SiH₄ and GeH₄ shows an increase of the probability for production of neutral ground-state fragments at the cost of excited or ionic fragments. Both effects can be explained by a growing probability for internal conversion among the decay channels of superexcited states with increasing number of atoms or electrons in the parent molecule. For each molecule, the H Balmer-emission cross sections at 100 eV are proportional to n^−b, where n 3 is the principal quantum number of the upper state of H and 3 < b < 5 is a parameter characteristic of the parent molecule. Finally, a detailed analysis of the isotopic effect between SiH₄ and SiD₄ on both fragment emission and ionization cross sections from 0 to 100 eV gives strong evidence of the competition between dissociation and autoionization in the decay of superexcited states.     

Near-IR absorption transition of H4 to F2 for UCl6 complex in M2ZrCl6 host crystals (M = K, Rb, and Cs): an experimental and theoretical study

The near-IR electronic transition from ground-state Г₁ of ³H₄ to the excited-state Г₃ of ³F₂ for the UCl₆²⁻ complex in three M₂ZrCl₆ host crystals (M = K⁺, Rb⁺, and Cs⁺) has been investigated experimentally and theoretically. The vibration frequency of the excited state is found to be sensitive to the alkaline ion substitution and the frequency variation follows the trend predicted by the ‘counterion effect’. In contrast to previous studies, the apparent anomaly in the intensity ratio of the two vibronic peaks from the prediction of a Boltzmann distribution relationship is attributed to the vibration frequency difference between the ground and the excited state. This new interpretation is supported by computer simulation of the experimental optical spectra.     

Ab initio MRD-CI study of GaAs, GaAs2(±), Ga2As2(±) and As4 clusters

Using pseudopotentials and double zeta basis sets with s, p diffuse functions and two sets of d functions, MRD-CI calculations were performed on As₂^(±), As₄⁽⁺⁾, GaAs⁻, GaAs₂^(±) and Ga₂As₂^(±). This study complements previous theoretical investigations on Ga^(±) to Ga₄^(±) and GaAs⁽⁺⁾. For As₄ tetrahedral symmetry was assumed, and Re of X¹A₁ determined as 4.73a₀. Vertical ionization potentials to several states of As₄⁺ were calculated. For GaAs₂, GaAs₂⁺ and GaAs₂⁻, ground and one low-lying state were geometry-optimized, both in C_2v (Ga-As-As), and linear symmetry (GaAsAs, C_∞h and AsGaAs, D_∞h). The lowest state of GaAs₂ is ²B₂ in C_2v. For Ga₂As₂, the lowest state and low-lying excited states were optimized in various geometries. The most stable state has rhombic structure (¹A_g in D_2h), but T-form and other forms (C_2v, C_∞v, D_∞h) are only 1–2 eV less stable. In D_2h symmetry, several low-lying excited states of Ga₂As₂ were studied. The ground states of Ga₂As₂⁺ and Ga₂As₂⁻ were found to be ²B_2u, and ²B_2g, respectively. Trends in ionization potentials (IP), electron affinities (EA), atomization energies and fragmentation energies for the molecules Ga_xAs_y and the pure compounds Ga_n and As_n up to 4 atoms, were studied. Ga_xAs_y clusters, with x + y even, have higher IP's than odd-numbered clusters. An experimentally observed alternation of EA, whereby an odd number of atoms have higher EA than their even neighbors, is confirmed. The mixed compounds Ga_xAs_y have atomization energies between those of Ga_n and As_n (x + y = n), usually closer to those of Ga_n. Fragmentation of Ga_xAs_y occurs such that As----As bonds are retained, and if possible, also Ga----As bonds, since the dissociation energy of As₂ is higher than that of GaAs, which in turn is higher than that of Ga₂. Calculated fragmentation energies agree qualitatively with experimental observations about the composition of 3-atomic and 4-atomic clusters Ga_xAs_y.     

Matrix-isolation spectroscopy of Pb2

Fluorescence and Raman scattering were observed from Pb₂ isolated in neon and argon matrices. Two new excited states were observed by two-photon stepwise excitations, which involve low-lying electronic states of Pb₂. Most spectroscopic constants of the states observed could be given and complement previous results. Two resonance Raman progressions with ω_c = 112.5 and 123.1 cm⁻¹ and a single Raman signal at 80 cm⁻¹ were observed in argon matrices. The ω_c = 123.1 cm⁻¹ Raman signal which had recently been assigned to a larger Pb cluster was shown to arise from Raman scattering within the electronically excited A state of Pb₂ at 5500 cm⁻¹.     

Solvent effects on non-resonant vibrational deactivation: N2(ν = 1) deactivated by CH4 in liquid Ar/liquid N2 mixtures

New measurements have been made of rate constants for the vibrational deactivation of N₂(ν = 1) by CH₄ in liquid Ar/liquid N₂ mixtures. The ratio of the liquid phase rate constants, k_L,M for the liquid mixture over k_L,Ar for liquid argon solution, varies non-linearly with composition. The results imply a saturation effect which occurs when one solvent N₂ molecule is present in the first solvation shell of the excited molecule. It is proposed that this is due to the formation of a N₂(ν = 1) … N₂ collision complex.