低温制备超细γ-Bi2O3粉末

氧化铋是一种黄色的聚晶粉末,广泛用于化工、医药和釉彩等工业．一般认为,氧化铋具有а,β,γ和δ四种晶型．其中α,δ-Bi2O3是热力学稳定晶体形态．α-Bi2O3以单斜结构在730℃以下稳定存在;立方萤石结构的δ-Bi2O3在730～825℃范围内稳定存在．另外,在650℃下还会出现具有四方结构(β)和体心立方结构(γ)的亚稳相化合物,γ-Bi1O3是一种光学活性立方晶体,可作为电子光学材料。     

Sm对MoO3-Bi2O3催化剂性能的影响

在MoO3-B i2O3催化剂中加入稀土氧化物Sm2O3,在固定床反应器中考查了Sm2O3添加量、反应温度、异丁烯浓度、原料气流量等对异丁烯转化为甲基丙烯醛反应的影响。实验表明,添加Sm2O3可明显提高异丁烯的转化率和甲基丙烯醛的选择性。用XRD技术研究了催化剂的组成,Mo-B i-O催化剂的成分主要是B i2O3和MoO3的混合物,添加Sm后出现了Sm2Mo3O12的衍射峰,且衍射峰的强度随着Sm添加量的增加而增强。     

α-Bi2Mo3O12和γ-Bi2MoO6的水热合成及可见光催化性能

采用水热法经调控nBi/nMo比和pH值,制备了α-Bi2Mo3O2钠米板和γ-Bi2MoO6纳米片2种钼酸铋材料.结果表明:在低pH值和较高的钼浓度下可合成α-Bi2Mo3O2,高pH值和低的钼浓度导致了γ-Bi2MoO6的形成,并对其形成机理进行了探讨;光物理和光催化性能研究表明,Aurivillius结构的γ-Bi2MoO6在可见光区有较强的吸收和较高的光催化性能,同时对影响2种钼酸铋光催化活性的因素进行了讨论.     

Photocatalytic Degradation of 4-Chlorophenol by Gd-Doped β-Bi2O3 Under Visible Light Irradiation

Chlorophenols are known as persistent organic pollutants.Therefore,research on the removal of chlorophenols has attracted widespread attention.Hereto,the photocatalytic degradation of 4-chlorophenol by Gd-doped β-Bi2O3 under visible light irradiation was studied.The results showed that Gd-doped β-Bi2O3 materials are efficient catalysts for the photocatalytic degradation of chlorophenols,and 2%(atomic traction)Gd-doped β-Bi2O3 exhibits the highest photocatalytic activity for 4-chlorophenol degradation,because doping an appropriate amount of Gd^3+ions can effectively reduce the recombination rate of the photogenerated e^-/h^+pairs and then enhance the photocatalytic performance.When the reaction was carried out at 25 ℃ for 6 h using the 2% Gd-doped/β-Bi2O3 micro/nano materials of 200 mg and at air flow rate of 40 mL/min,the degradation rate of 4-chlorophenol reached 92.3%.Additionally based on the analysis of the products,it was speculated that the dominant photocatalytic degradation mechanism of 4-chlorophenol by Gd-doped β-Bi2O3 under visible light irradiation is an oxidative process involving an attack by the hydroxyl radical.     

17O excess transfer during the NO2 + O3 → NO3 + O2 reaction

The ozone molecule possesses a unique and distinctive (17)O excess (Δ(17)O), which can be transferred to some of the atmospheric molecules via oxidation. This isotopic signal can be used to trace oxidation reactions in the atmosphere. However, such an approach depends on a robust and quantitative understanding of the oxygen transfer mechanism, which is currently lacking for the gas-phase NO(2) + O(3) reaction, an important step in the nocturnal production of atmospheric nitrate. In the present study, the transfer of Δ(17)O from ozone to nitrate radical (NO(3)) during the gas-phase NO(2) + O(3) → NO(3) + O(2) reaction was investigated in a series of laboratory experiments. The isotopic composition (δ(17)O, δ(18)O) of the bulk ozone and the oxygen gas produced in the reaction was determined via isotope ratio mass spectrometry. The Δ(17)O transfer function for the NO(2) + O(3) reaction was determined to be: Δ(17)O(O(3)?) = (1.23 ± 0.19) × Δ(17)O(O(3))(bulk) + (9.02 ± 0.99). The intramolecular oxygen isotope distribution of ozone was evaluated and results suggest that the excess enrichment resides predominantly on the terminal oxygen atoms of ozone. The results obtained in this study will be useful in the interpretation of high Δ(17)O values measured for atmospheric nitrate, thus leading to a better understanding of the natural cycling of atmospheric reactive nitrogen.     

Determination of the Rate Constants of the Reactions Cr + O2 + M → CrO2 + M and Cr + O2 → CrO + O

Kinetics and Catalysis - The rate constants of the interactions of chromium atoms with molecular oxygen through recombination Cr + O2 + M → CrO2 + M (I) and exchange Cr + O2 → CrO + O...     

Enhanced Charge Separation of α-Bi2O3-BiOI Hollow Nanotube for Photodegradation Antibiotic Under Visible Light

It is highly desirable to exploit semiconductor materials with high photocatalytic degradation activity, especially bismuth oxyhalide semiconductor photocatalysts with special layered structure and suitable bandgap width. The low utilization rate of visible light and high recombination rate of photogenerated electron-hole of BiOI photocatalyst severely restrict its development. Herein, a heterojunction photocatalyst of α-Bi₂O₃-BiOI hollow nanotube was prepared by electrospinning method, solvothermal method and ion-exchange method. The α-Bi₂O₃-BiOI(BB-4, the stirring time of Bi₂O₃ in KI solution was 4 h) exhibited the best photocatalytic performance towards degrading the tetracycline hydrochloride(TC) solution, which could remove 85% of TC(10 mg/L) in 2 h under visible light irradiation. The estimated k_TC of α-Bi₂O₃-BiOI(BB-4) was ca. 3.9 and 1.8 times as much as that of α-Bi₂O₃ and pure BiOI, respectively. It indicated that the formation of α-Bi₂O₃-BiOI heterojunction can significantly improve the separation efficiency of photogenerated electron-hole pairs, therefore the photocatalytic ability was enhanced. Furthermore, a corresponding photocatalytic mechanism was proposed that ^·O₂^- radical and holes are the main active components in the photodegradation through trapping experiment.     

Enhanced visible light photoelectrochemical performance of β-Bi2O3-TiO2/ITO thin films prepared by aqueous sol-gel

Journal of Solid State Electrochemistry - Semiconductor heterojunction of β-Bi2O3-TiO2/ITO thin films was prepared by aqueous sol-gel and their photoelectrochemical and photoelectrocatalytic...     

Boosted photocatalytic efficiency of GQDs sensitized (BiO)2CO3/β-Bi2O3 heterojunction via enhanced interfacial charge transfer

The NO gas is easily oxidized to form toxic by-products (NO₂) during the oxidation process, which are adsorbed on the catalyst surface and inhibit the subsequent reaction. For photocatalytic NO removal, a significant challenge is to achieve catalytic stability while maintaining high conversion efficiency. Here, we fabricated a (BiO)₂CO₃/β-Bi₂O₃ heterostructure that enables efficient charge transfer and promotes the NO removal. We propose that the catalytic stability depends on the heterojunction structure, which is able to generate interfacial charge transfer channels. In addition, we further introduce graphene quantum dots on the heterojunction structure, which further strengthens the interfacial charge transfer dynamics and finally realizes that the NO₂ byproduct could gain electrons and convert to the final product (nitrite or nitrate). This composite structure not only exhibits high activity for NO removal but also maintains long-term stability under visible light.     

NH＋O3→ONH＋O2反应热力学和动力学研究

在量子化学对NH自由基与臭氧O3反应计算的基础上，应用统计热力学方法研究了100～1600 K温度范围内NH和O3反应过程的各热力学量的变化及平衡常数，用经Wigner校正的Eyring过渡态理论计算了不同温度下该反应两不同反应通道的活化热力学量、反应速率常数及频率因子.计算表明，相对于反应通道II，反应通道I不仅有很强的反应自发性，而且在动力学上也是较容易实现的反应.     

NH+O3→ONH+O2反应热力学和动力学研究

在量子化学对 NH自由基与臭氧 O3反应计算的基础上,应用统计热力学方法研究了 100～ 1600 K温度范围内 NH和 O3反应过程的各热力学量的变化及平衡常数,用经 Wigner校正的 Eyring过渡态理论计算了不同温度下该反应两不同反应通道的活化热力学量、反应速率常数及频率因子.计算表明,相对于反应通道 II,反应通道 I不仅有很强的反应自发性,而且在动力学上也是较容易实现的反应.     

Crystal structure determination of α, β and γ-Bi4V2O11 polymorphs. Part I: γ and β-Bi4V2O11

Using combined X-ray single crystal and neutron powder thermodiffraction data, the crystal structure of the high temperature γ-form of Bi₄V₂O₁₁ was confirmed and accurately refined in the I4/mmm space group and that of the β-form was entirely determined in the centrosymmetric Amam space group. The two-fold superlattice characterising the β structure is the result of an ordering process involving corner-sharing V–O tetrahedra and disordered trigonal bipyramids. A possible scheme for the γ↔β phase transition is proposed.     

β-Bi2O3修饰Bi2WO6光催化降解苯酚及其可能机理

采用简单混合法制备了一系列Bi₂O₃/Bi₂WO₆复合光催化剂. 在紫外光降解水中苯酚的过程中, Bi₂O₃/Bi₂WO₆的光催化活性随Bi₂O₃含量的增加呈现先增大后减小的趋势. 当Bi₂O₃最佳负载量等于12.5% (质量分数, w)时, 该复合光催化剂的活性大约是单一Bi₂WO₆的4 倍. 固体样品表征表明, Bi₂O₃主要以β-Bi₂O₃存在, 复合光催化剂是Bi₂O₃和Bi₂WO₆的简单混合物. 此外, 在电催化氧化水的过程中, β-Bi₂O₃/Bi₂WO₆薄膜电极的光电流远大于β-Bi₂O₃和Bi₂WO₆薄膜电极的光电流之和. Bi₂O₃对Bi₂WO₆光催化的促进作用是由于前者接受后者的光生空穴, 提高Bi₂WO₆光生载流子的分离效率, 从而加快了O₂的还原和苯酚的降解.     

TG Study of the Dispersion Threshold of Mn2O3 on γ-Al2O3

Mn₂O₃/-Al₂O₃ catalysts were prepared by the impregnation method, and the maximum monolayer dispersion capacity or dispersion threshold value of Mn₂O₃ on the surface of -Al₂O₃ was determined to be 13.08% from the decomposition mass loss of supported Mn(NO₃)₂ in the monolayer state. This was compared with the values estimated from a close-packed monolayer model and an interaction model. It was confirmed that the high activities and selectivities of the catalysts for benzoic acid hydrogenation to benzaldehyde are due to the monolayer dispersion of the Mn₂O₃ on the surface of -Al₂O₃.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nonadiabatic collision model calculations of ion-pair formation cross sections of Cs+O2→Cs++O2-

This paper has improved Hickman's nonadiabatic collision model by substituting Hickman's constant velocity classical straight line trajectory approximation with the solution of motion equation mR=-dV(R)/dR, and has calculated the cross sections of ion-pair formation Cs+O2 -Cs++O2- with the improved nonadiabatic collision model (INCM). A comparison of our results with other theoretical and experimental results has been made.     

Photocatalytic behavior of α-Bi2Mo3O12 prepared by the Pechini method: degradation of organic dyes under visible-light irradiation

Nanoparticles of α-Bi₂Mo₃O₁₂ were prepared by the Pechini method. The process of formation of the bismuth molybdate was followed by simultaneous thermogravimetric and differential thermal analysis (TGA/DTA). Different samples of α-Bi₂Mo₃O₁₂ were obtained at 400, 450, and 500 °C, and characterized by X-ray powder diffraction (XRD), nitrogen physisorption (BET), and scanning electron microscopy (SEM). When observed by SEM, the morphology of the sample obtained at the lowest temperature consisted of semi-spherical particles with an average diameter of 150 nm. On the other hand, the highest calcination temperature led to the formation of sintered particles of 500–600 nm. The photocatalytic activity of α-Bi₂Mo₃O₁₂ was tested by photodegradation of the organic dyes rhodamine B (rhB) and indigo carmine (IC) under visible-light irradiation. The bismuth molybdate nanoparticles were able to bleach aqueous solutions of both organic dyes. The sample obtained at 400 °C was the best photocatalyst with half-lives, t _1/2, of 108 and 154 min for rhB and IC, respectively.     

O(3P)+O2H→OH+O2反应机理的密度泛函理论研究

用密度泛函理论方法研究了O(3P)与O2H反应生成羟基和氧分子的反应机理. 在PW91/6-31+G水平上用梯度解析技术全自由度优化上述反应物、产物和反应路径上的中间体及过渡态几何构型, 并通过频率振动分析加以确认, 计算IRC反应路径及中间体异构化过程, 确定了此反应的可能反应通道. 结果表明: 该反应是多通道多步骤的强放热反应. 首先形成顺式或反式O3H富能中间体, 此过程无能垒; 然后跨过一个能垒分解成产物OH和O2. 通道IM1→TS1比IM2→TS2克服的能垒要大, 反应放热372.822 kJ*mol-1. IM1TS3IM2 可相互转化.     

Time-sliced ion-velocity imaging study of the reaction Y + O2 → YO + O

The oxidation reaction dynamics of the gas-phase yttrium atoms by oxygen molecules was studied under crossed-beam conditions. The product YO was detected using a time-of-flight mass spectrometer combined with laser single-photon ionization. An acceleration lens system designed for the ion-velocity mapping conditions, a two-dimensional (2-D) detector, and a time-slicing technique were used to obtain the velocity and angular distributions of the products. Two ionization wavelengths were used for the internal (vibrational and/or electronic) energy selective detection of YO. The single photon of the shorter wavelength (202.0 nm) can ionize all states of YO(X?(2)Σ, A'?(2)Δ, and A?(2)Π), while electronically excited YO(A' and A) are dominantly ionized at a longer wavelength (285.0 nm). Time-sliced images were converted to the velocity and angular distributions in the center-of-mass frame. The general features of the velocity distributions of YO, determined at two wavelengths, were well represented by those expected from the statistical energy disposal model. The forward-backward symmetry was also observed for two images. These results suggest that the reaction proceeds via long-lived intermediates, and that this mechanism is consistent with previous chemiluminescence/LIF studies.     

Kinetics of nonisothermal crystallization of Cs2O–Fe2O3–P2O5 glasses

The crystallization kinetics of Cs₂O–Fe₂O₃–P₂O₅ glasses containing 12.5–27 mol% Cs₂O were studied by using differential scanning calorimetry under nonisothermal conditions. Strong dependence of activation energy with temperature was observed, indicating the complex nature of the crystallization process. The various crystallization products were identified by X-ray diffraction technique. CsFeP₂O₇ was found to be the major crystalline phase in all cases. The overall activation energy obtained by classical model-free kinetic method was compared with that of isoconversional method; and from the results, the dependence of activation energy on extent of reaction and average temperature was delineated.