AgGaS2-type photocatalysts for hydrogen production under visible light: Effects of post-synthetic H2S treatment

Bulky AgGaS₂ was synthesized as a p-type semiconductor photocatalyst by a conventional solid state reaction under N₂ flow for hydrogen production under visible light. To remove impurity phases involved in the synthesized material and improve crystallinity, the material was treated at various temperatures of 873-1123 K under H₂S flow. Impurity phases were identified as β-Ga₂O₃ and Ag₉GaS₆ with the cell refinements of XRD and the local coordination structure around gallium atom in AgGaS₂ was investigated by EXAFS. As the H₂S-treatment temperature increased, the contribution from impurity phases was diminished. When the temperature reached 1123 K, the impurity phases were completely removed and the material showed the highest photocatalytic activity. Thus, the post-synthetic H₂S treatment could be applied for the synthesis of sulfide-type photocatalysts with high activity.     

Controlled morphology synthesis of β-FeOOH and the phase transition to Fe2O3

The hexagram and arrayed β-FeOOH nanorods were first synthesized free of surfactants through the solvent-thermal method. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectrum (EDAX) and thermal gravimetric analysis (TGA) were used to characterize the as-prepared products. The TEM and FESEM images showed that hexagram β-FeOOH and arrayed rod-like β-FeOOH with an average diameter of 10-15 nm and an average length of 100 nm (aspect ratio is about 10) were prepared. Electrochemical tests show that these nanorods deliver a large discharge capacity of 277 mA h g⁻¹ versus Li metal at 0.1 mA cm⁻² (voltage at 1.5-4.2 V). Treated the as-synthesized rod-like β-FeOOH by annealing, rhombus hematite was obtained.     

ZIF-67/CeO2催化CO2和甲醇直接合成碳酸二甲酯

采用沉淀法将ZIF-67负载到CeO₂上,制备了具有多重活性位点的非均相催化剂ZIF-67/CeO₂,并研究其催化CO₂和甲醇直接反应生成碳酸二甲酯(DMC)的性能。采用 X 射线衍射、N2吸附-脱附、傅里叶变换红外光谱和 X 射线光电子能谱研究了ZIF-67/CeO₂的各种理化性质。结果表明,ZIF-67的引入使ZIF-67/CeO₂催化剂产生更多的氧空位。在考察的ZIF-67/CeO₂系列催化剂中,0.3-ZIF-67/CeO₂(0.3为Co、Ce物质的量之比)在具有高的比表面积的同时还能保持介孔结构,具有丰富的酸碱位点,并且具有较高的CO₂吸附容量,表现出最好的催化性能。在反应温度为140℃、压力为4.5 MPa的条件下反应4 h,DMC收率可达到3.79 mmol_DMC·gcat^-1。     

ZIF-67/CeO2催化CO2和甲醇直接合成碳酸二甲酯

采用沉淀法将ZIF-67负载到CeO₂上,制备了具有多重活性位点的非均相催化剂ZIF-67/CeO₂,并研究其催化CO₂和甲醇直接反应生成碳酸二甲酯(DMC)的性能。采用X射线衍射、N₂吸附-脱附、傅里叶变换红外光谱和X射线光电子能谱研究了ZIF-67/CeO₂的各种理化性质。结果表明,ZIF-67的引入使ZIF-67/CeO₂催化剂产生更多的氧空位。在考察的ZIF-67/CeO₂系列催化剂中,0.3-ZIF-67/CeO₂(0.3为Co、Ce物质的量之比)在具有高的比表面积的同时还能保持介孔结构,具有丰富的酸碱位点,并且具有较高的CO₂吸附容量,表现出最好的催化性能。在反应温度为140℃、压力为4.5 MPa的条件下反应4 h,DMC收率可达到3.79 mmol_DMC·g_cat^-1。     

g-C3N4/Bi2O2CO32D纳米片复合材料的制备及可见光催化性能研究

采用自组装和化学沉淀法分别制得两种可见光驱动复合材料石墨相氮化碳/碳酸氧铋(g-C_3N_4/Bi_2O_2CO_3).采用X射线衍射光谱(XRD),紫外可见光谱、扫描电镜(SEM)、N_2吸附、电化学阻抗谱(EIS)和X射线光电子能谱(XPS)等分析手段对制备的催化剂进行了表征.结果表明,制备方法对纳米复合材料的晶相、形态及光学性能没有影响,但是影响g-C_3N_4和Bi_2O_2CO_3之间的相互作用力,导致光生电子-空穴对的分离速率存在显著差异.以可见光驱动苯酚和罗丹明B的降解实验为探针反应检测催化剂的光催化性能.实验结果表明自组装法得到的异质结催化剂中相互作用力更强,催化效果最高.O_2-是罗丹明B降解反应的主要活性物种,染料的光敏化、Bi_2O_2CO_3与g-C_3N_4综合效应,导致光生载流子电荷分离效率更高.     

Cp2TiCl2 catalyzed one-pot synthesis of n-Bu3GeH from GeCl4

The reaction of GeCl₄ with n-BuMgCl in presence of a catalytic amount of Cp₂TiCl₂ gives n-Bu₃GeH and n-Bu₄Ge in ca. 70 and 25% yield, respectively. This method provides an industrially feasible one-pot synthesis for Bu₃GeH and Bu₄Ge. The reaction temperature and stoichiometry seem to be important in the distribution of the products. Apart from elemental analysis these compounds have been characterized by comparing their boiling points, NMR spectral data and GC assay with that of the authentic samples.     

Preparation of ZrO2-TiO2-CeO2 and Its Application in the Selective Catalytic Reduction of NO with NH3

TiO₂,ZrO₂-TiO₂,andZrO₂-TiO₂-CeO₂ were prepared by co-precipitation method and characterized by X-ray diffraction (XRD), specific surface area measurements (BET), temperature programmed desorption (NH₃-TPD), oxygen storage capacity (OSC), and temperature programmed reduction (H₂-TPR). The results showed that ZrO₂-TiO₂-CeO₂ exhibited large number of surface strong acid, possessed some oxygen storage capacity, and strong redox property. The three materials were used as supports and the monolith catalysts were prepared with 1% (w) V₂O₅ and 9% (w)WO₃ for selective catalytic reduction (SCR) of NO with ammonia in the presence of excessive O₂, and the results of catalytic activity showed that the catalyst used ZrO₂-TiO₂-CeO₂ as support yielded nearly 100% NO conversion at 275 °C at a gas hourly space velocity (GHSV) of 10000 h⁻¹, and it had the best catalytic activity and showed great potential for practical application.     

Ion-beam irradiation of lanthanum compounds in the systems La2O3-Al2O3 and La2O3-TiO2

Thin crystals of La₂O₃, LaAlO₃, La_2/3TiO₃, La₂TiO₅, and La₂Ti₂O₇ have been irradiated in situ using 1 MeV Kr²⁺ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La₂O₃ remained crystalline to a fluence greater than 3.1×10¹⁶ ions cm⁻² at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (T_c) of 647 K for LaAlO₃, 840 K for La₂Ti₂O₇, 865 K for La_2/3TiO₃, and 1027 K for La₂TiO₅. The T_c values observed in this study, together with previous data for Al₂O₃ and TiO₂, are discussed with reference to the melting points for the La₂O₃-Al₂O₃ and La₂O₃-TiO₂ systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between T_c and melting temperature (T_m) in the two systems. More complex relationships exist between T_c and crystal structure, with the stoichiometric perovskite LaAlO₃ being the most resistant to amorphisation.     

Cr2(WO4)3和Cr2(MoO4)3的负热膨胀特性研究

用液相反应-前驱物烧结法制备了Cr₂(WO₄)₃和Cr₂(MoO₄)₃粉体。298～1 073 K的原位粉末X射线衍射数据表明Cr₂(WO₄)₃和Cr₂(MoO₄)₃的晶胞体积随温度的升高而增大, 本征线热膨胀系数分别为(1.274±0.003)×10^-6 K^-1和(1.612±0.003)×10^-6 K^-1。用热膨胀仪研究了Cr₂(WO₄)₃和Cr₂(MoO₄)₃在静态空气中298～1 073 K范围内热膨胀行为，即开始表现为正热膨胀，随后在相转变点达到最大值，最后表现为负热膨胀，其负热膨胀系数分别为(-7.033±0.014)×10^-6 K^-1和(-9.282±0.019)×10^-6 K^-1。     

Preparation and photocatalytic activity of Sb2S3/Bi2S3 doped TiO2 from complex precursor via gel-hydrothermal treatment

Sb₂S₃/Bi₂S₃ doped TiO₂ were prepared with the coordination compounds [M(S₂CNEt)₃] (M=Sb, Bi; S₂CNEt=pyrrolidinedithiocarbamate) as precursors via gel-hydrothermal techniques. The doped TiO₂ were characterized by XRD, SEM, XPS and UV-vis diffuse reflectance means. The photocatalyst based on doped TiO₂ for photodecolorization of 4-nitrophenol (4-NP) was examined. The optimal Bi₂S₃/Sb₂S₃ content, pH and different doped techniques have been investigated. Photocatalytic tests reveal that M₂S₃ doped TiO₂ via the gel-hydrothermal route performs better photocatalytic activity for photodegradation reaction of 4-nitrophenol (4-NP).     

A fast synthesis for Zintl phase compounds of Na3SbTe3, NaSbTe2 and K3SbTe3 by microwave irradiation

The microwave irradiation technique was used to prepare three Zintl phase compounds Na₃SbTe₃, NaSbTe₂ and K₃SbTe₃. The as-prepared products were analyzed and characterized by XRD, EDX and SEM techniques. Higher microwave oven power and shorter irradiation time are required for the synthesis of Na₃SbTe₃, whereas lower oven power and longer irradiation time are needed for NaSbTe₂. Moderate microwave irradiation conditions facilitate the formation of pure K₃SbTe₃. Pure phase of Na₃SbTe₃ are directly obtained by this technique for the first time. Compared with the traditional high-temperature solid-state synthesis, the microwave reaction required a considerable shortened reaction time for the preparation of the three Zintl compounds. The initial driving force for these reactions originates from the interaction of microwave electric field with alkali metals (Na and K) and Sb powders.     

Template synthesis of heterostructured polyaniline/Bi2Te3 nanowires

Heterostructured polyaniline/Bi₂Te₃ nanowires have been prepared by chemical and electrochemical reactions on a porous alumina template. Its morphology and structure have been studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron probe microanalysis. The microscope analysis reveals that Bi₂Te₃ is well enveloped in polyaniline tubules in pores of alumina template. This microscopic material shows possible application in microthermoelectric device.     

Non-centrosymmetric Ba3Ti3O6(BO3)2

The compound previously reported as Ba₂Ti₂B₂O₉ has been reformulated as Ba₃Ti₃B₂O₁₂, or Ba₃Ti₃O₆(BO₃)₂, a new barium titanium oxoborate. Small single crystals have been recovered from a melt with a composition of BaTiO₃:BaTiB₂O₆ (molar ratio) cooled between 1100°C and 850°C. The crystal structure has been determined by X-ray diffraction: hexagonal system, non-centrosymmetric space group, a=8.7377(11) Å, c=3.9147(8) Å, Z=1, wR(F²)=0.039 for 504 unique reflections. Ba₃Ti₃O₆(BO₃)₂ is isostructural with K₃Ta₃O₆(BO₃)₂. Preliminary measurements of nonlinear optical properties on microcrystalline samples show that the second harmonic generation efficiency of Ba₃Ti₃O₆(BO₃)₂ is equal to 95% of that of LiNbO₃.     

Direct dynamics studies for the reactions of CF3CHFCF3 and CF3CF2CHF2 with H atoms

The rate constants of the hydrogen abstraction reactions of CF₃CHFCF₃ + H (R1) and CF₃CF₂CHF₂ + H (R2) have been calculated by means of the dual-level direct dynamics method. Optimized geometries and frequencies of stationary points and extra points along the minimum-energy path (MEP) are obtained at the MPW1K/6-311+G(d,p) level, and the classical energetic information is further corrected with the interpolated single-point energy (ISPE) approach by the G3(MP2) level of theory. Using the canonical variational transition state theory (CVT) with small-curvature tunneling corrections (SCT), the rate constants are evaluated over a wide temperature range of 200-2000 K. The calculated CVT/SCT rate constants are in good agreement with available experimental values. It is found that the variational effect is very small and almost negligible over the whole temperature region. However, the small-curvature tunneling correction plays an important role in the lower temperature range. Furthermore, the heats of formation of species CF₃CF₂CHF₂ (SC₁ or SC₂) and CF₃CF₂CF₂ are studied using isodesmic reactions to further elucidate the thermodynamic properties.     

Hydrothermal synthesis and luminescent properties of Sb-doped Sr3(PO4)2

Sb³⁺-doped Sr₃(PO₄)₂ crystals has been synthesized using phosphoric acid, strontium hydroxide and antimony powder as the raw materials through a hydrothermal reaction method. The crystallinity and the microstructure were investigated using X-ray diffraction and scanning electron microscopy. The photoluminescent property was investigated using luminescent spectrometer. Phase pure Sr₃(PO₄)₂ crystal was obtained and it has a shape of hexagonal rod. It showed the emission and excitation peaks at 396, 250, and 215 nm, respectively, indicating that the emission is attributed to ³P₁-¹S₀ transition and the excitation is attributed to ¹S₀-³P₁ and ¹S₀-¹P₁ transition. It was also observed that the intensity of photoluminescence is thermally stable up to 673 K.     

The release of TiO2 and SiO2 nanoparticles from nanocomposites

There is a growing interest in the development of nanocomposites consisting of organic polymers and TiO₂ or amorphous SiO₂ nanoparticles. These nanoparticles may be released from nanocomposites. There is evidence that amorphous SiO₂ and TiO₂ nanoparticles can be hazardous. Thus, in the design of nanocomposites with such nanoparticles, hazard reduction extending to the full nanocomposite life cycle would seem a matter to consider. Options for hazard reduction include: changes of nanoparticle surface, structure or composition, better fixation of nanoparticles in nanocomposites, including persistent suppression of oxidative damage to polymers by nanoparticles, and design changes leading to the release of relatively large particles.     

Synthesis and characterization of MgF2 and KMgF3 nanorods

MgF₂ nanorods with diameters of 60-100 nm were synthesized by a microemulsion method. Subsequent hydrothermal reaction of as-synthesized MgF₂ nanorods and KF at 240°C for 3 days or 140°C for 7 days resulted in KMgF₃ nanorods, which retained the rod-like morphology of the source material MgF₂ in the reaction process. The morphology of as-synthesized MgF₂ strongly depended on the molar ratio between water and the surfactant CTAB and the concentration of CTAB.     

Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.     

三维花状Fe_2(MoO_4)_3微米球的水热制备及电化学性能

以Fe Cl3·7H2O和Na2Mo O4为原料,采用水热合成法制备三维花状Fe2(Mo O4)3微米球。探讨不同合成温度对样品形貌的影响,利用XRD、SEM和EDS等分析技术对样品的结构、形貌进行了表征,对该材料的电化学性能进行了测试。结果表明:Fe2(Mo O4)3微米球是由二维纳米片自组装而成的花状结构,合成温度为160℃时,制备的样品具有良好的电化学性能,当电流密度为100 m A·g-1,首次放电比容量为1 431 m Ah·g-1;并具有较好的循环性能和倍率性能。并对160℃合成样品表现较好电化学性能的原因进行了探讨。     

磁场诱导下Fe3S4向FeS2转化速率的增加

以FeCl₃和CH₄N₂S为主要原料，在0.2～0.4 T的外加磁场强度下，温度为170 ℃的反应体系中研究了磁场对前驱物Fe₃S₄转化成FeS₂过程的影响。结果表明，Fe₃S₄到FeS₂的转化率是与磁场强度有关的。Fe₃S₄的硫化过程可能是通过溶解-再结晶机理。外加磁场的存在可以促进物质的传输过程，从而加速前驱物的溶解和再结晶过程，导致和没有外加磁场相比Fe₃S₄到FeS₂的转化率的增加。