酸化对层状K_2La_2Ti_3O_(10)光催化活性的影响

本文通过高温固相反应合成了一种层状金属氧化物K2La2Ti3O10,利用离子交换反应对其在不同条件下进行酸化.并通过对甲基橙溶液的降解对其光催化活性进行评价,结果发现,酸化后K2La2Ti3O10的光催化活性有显著提高.通过对样品的结构、XRD、DRS分析,对这种现象做出了几种可能的解释.     

可见光下Fe3+掺杂对K2La2Ti3O10分解水制氢性能的影响

采用溶胶-凝胶法制备了Fe3+掺杂的Fe-K2La2Ti3O10光催化剂, 并通过X射线衍射(XRD)、紫外-可见漫反射(DRS)、X射线光电子能谱(XPS)等技术对其进行了表征和分析, 考察了不同掺杂量对K2La2Ti3O10的性质及光催化分解水制氢活性的影响. 结果表明, Fe-K2La2Ti3O10在400-650 nm范围内显示强吸收, 光谱响应扩展到可见光区(λ>400 nm), 掺杂Fe3+后, K2La2Ti3O10的可见光区的光催化制氢活性显著提高, 掺杂量为nFe/nTi=0.04时活性最佳, 当催化剂用量为0.1 g, 反应液为CH3OH(30 mL)+H2O(90 mL)时, 产氢量达到1.92 μmol·h-1, 为未掺杂时的4倍.     

Ce掺杂K_2La_2Ti_3O_(10)催化剂的可见光高效催化制氢的研究

采用高温固相法合成了铈掺杂的K2La2Ti3O10催化剂,利用X射线衍射(XRD)、紫外-可见漫反射(UV-visDRS)、透射电镜(TEM)和X射线光电子能谱(XPS)对催化剂进行了表征.考察了催化剂的可见光催化分解甲醇水溶液制氢的活性,并对可见光催化机理进行了分析.研究表明,铈的掺杂没有改变K2La2Ti3O10的微晶结构,并使催化剂粒径有所减小.紫外可见漫反射分析表明禁带宽度为2.3eV左右,对可见光具有较高吸收.XPS表明La和Ti为+3和+4价,而Ce则是+3和+4的混合价态.担载2wt%Pt后,在可见光下光催化活性大大提高,当铈的掺杂量为0.5mol%(即Ce取代La的摩尔百分量)时,光催化活性达到最大,产氢速率为0.05mmol/h;光照5h后产氢量为0.22mmol,而纯K2La2Ti3O10的产氢量只有0.037mmol.     

微波辅助制备CdS插层K2La2Ti3O10复合物及其光催化制氢的性能

采用微波辅助通过酸交换、胺柱撑、离子交换等步骤制备了CdS插层的K2La2Ti3O10(记做CdS-K2La2Ti3O10)复合光催化剂.利用X射线粉末衍射(XRD),场发射扫描电子显微镜(SEM),紫外-可见漫反射吸收光谱(UV-Vis)和光致发光光谱(PL)等对产物进行表征,考察了CdS-K2La2Ti3O10在紫外光及可见光下催化制氢活性.结果表明,微波辅助法与传统法制备的插层复合催化剂晶型结构相似,同时大大减少了离子交换反应时间,减少了对层间结构的破坏,拓展了催化剂的可见光吸收范围.微波辅助制备的催化剂在紫外光和可见光照射3 h后的产氢量分别为221.53 mmol/(g cat.)和3.23 mmol/(g cat.),并对光催化机理进行了分析.     

Er3+和Yb3+共掺杂La2Ti2O7纳米晶的上转换发光

采用溶胶-凝胶法制备了 Er3+单掺杂A2 Ti2O7(A=La,Y,Gd)和Er3+,Yb3+共掺杂的La2 Ti2O7纳米晶样品.用X射线衍射仪、扫描电子显微镜和紫外-可见-近红外光谱仪分别对样品的结构、形貌和光吸收性质进行了表征;测试了样品在980 nm激光激发下的室温上转换光谱.结果发现,样品都发出了很强的绿光(大约在525和549 nm)和红光(大约660 nm).通过研究这些基质的晶体结构对上转换发光的影响,发现La2 Ti2O7基质中Er3+离子的上转换发射最强.对La2 Ti2O7纳米晶的上转换发光研究表明,Yb3离子能够有效地敏化Er3离子的上转换发射.对上转换发光强度与泵浦功率的依赖分析,发现红光和绿光的发射均属于双光子吸收过程,最后讨论了Er3+和Yb3的上转换发光机制.     

La-Ce对PbTiO3陶瓷气相扩渗生成La2Ti6O15和CeTi21O38的陶瓷材料及其电性能

报道了采用气相法对PbTiO3陶瓷扩渗La-Ce混合稀土元素的研究. 在气相扩渗过程中, La, Ce与PbTiO3陶瓷组元发生了复杂反应,生成了稀土化合物La2Ti6O15和CeTi21O38, 制备出未见报道的La2Ti6O15-CeTi21O38-PbTiO3陶瓷材料, 经测试其导电性能发生了十分显著的变化. La2Ti6O15-CeTi21O38-PbTiO3陶瓷材料的室温电阻率从2.0 ×1010??@m下降为0.248 ?@m,而且随着温度的变化, 晶粒电阻呈现明显的PTCR效应,而晶界电阻随着温度的升高,呈急剧连续降低状态,总电阻的变化规律与晶界电阻的变化相一致, 试样总电阻的PTCR效应已不存在, 近趋导体. 经XPS测试分析, 进一步证实了La2Ti6O15-CeTi21O38-PbTiO3陶瓷材料中铅、钛等元素均有变价, 因而导致了La2Ti6O15-CeTi21O38-PbTiO3陶瓷材料电阻率的降低, 测试结果还首次给出了La2Ti6O15-CeTi21O38-PbTiO3陶瓷材料中各元素结合能位置的峰值. TG-DTA热分析表明La2Ti6O15-CeTi21O38-PbTiO3陶瓷材料具有较好的高温热稳定性.     

La2M2O7(M=Ti,Zr)多晶粉末的低温水热合成及表征

低温水热合成是水热化学一个活跃的研究方向,在氧化物粉末的合成方面具有潜在的应用价值.La2M2O7(M=Ti,Zr)陶瓷材料的优良特性使其多晶粉末的合成倍受关注[1,2].     

La2O3对钛合金表面镍基喷焊涂层组织和性能的影响

采用火焰喷焊技术在钛合金基体上制备了不加La2O3和加4％(质量分数)La2O3两种镍基涂层，分析了它们的显微组织、合金元素的扩散、显微硬度以及耐磨性能。结果表明：La2O3的加人，改善了涂层合金的流动性和显微组织的均匀性，并使涂层与基体的熔合更加明显，结合性能得到进一步提高；虽然一定程度上减弱了基体Ti元素对喷焊层的强化作用，使表层显微硬度略有下降，但磨损失重却较未加La2O3的喷焊涂层下降了20％。     

硼族元素掺杂对K2La2Ti3O10光催化产氢性能的影响

通过溶胶.凝胶法制备了层状钙钛矿结构的K2La2Ti3O10及硼族元素掺杂的K2La2Ti3O10,采用X-射线衍射(XRD)、紫外可见漫反射光谱(DRS)等对K2La2Ti3O10及硼族元素掺杂K2La2Ti3O10进行表征.以I-为电子给体、分别在紫外和可见光辐射下研究了K2La2Ti3O10及硼族元素掺杂K2La2Ti3O10光催化分解水的产氢活性;采用第一性原理,计算了硼族元素掺杂对K2La2Ti3O10半导体能带结构和态密度的影响.从电子结构的变化揭示了掺杂引起光催化活性差异的原因.研究结果表明,硼族元素的掺入能够改善和提高K2La2Ti3O10的光解水产氢活性;在B,Al,Ga,In与Ti的物质的量的比为0.01:1的情况下,K2La2Ti3O10紫外光催化分解水产氢速率分别为151.7、119.6、155和119.2 umol·L-1·h-1,比K2La2Ti3O10掺杂改性前产氢速率分别提高了166%、110%、172%和109%,可见光分解水的产氢速率为67.0、60.5、55.0和50.0umol·L-1·h-1,分别为K2La2Ti3O10掺杂改性前产氢速率的4、3.7、3.3和3倍.     

MC尼龙-纳米La2O3复合材料的制备及性能研究

用原位分散聚合法制备了一系列MC尼龙／纳米La2O3复合材料，研究了纳米La2O3用量对复合材料力学性能的影响，用SEM观察了La2O3粒子在MC尼龙基体中的分散情况，用XRD对复合材料的晶体结构进行了表征。SEM观察结果表明，当纳米La2O3用量小于1％时，纳米La2O3均匀分散于MC尼龙基体中，团聚情况很少，当纳米La2O3用量大于1％时，纳米La2O3开始团聚；XRD研究结果表明，纳米La2O3没有改变MC尼龙的结晶形态；力学性能的研究结果表明，随着纳米La2O3用量的增加，复合材料的拉伸强度、断裂伸长率、缺口冲击强度、弯曲强度和弯曲模量都呈先升后降的趋势，当纳米La2O3用量为0．5％时，复合材料的拉伸强度和断裂伸长率达到最大值，分别比MC尼龙提高17．9％和52．1％，当纳米La2O3的用量为1．0％时，复合材料的缺口冲击强度、弯曲强度和弯曲模量达到最大值，分别比MC尼龙基体提高36，6％．12．7％和16．3％。     

Sc2MgGa2 and Y2MgGa2

Scandium magnesium gallide, Sc₂MgGa₂, and yttrium magnesium gallide, Y₂MgGa₂, were synthesized from the corresponding elements by heating under an argon atmosphere in an induction furnace. These intermetallic compounds crystallize in the tetragonal Mo₂FeB₂‐type structure. All three crystallographically unique atoms occupy special positions and the site symmetries of (Sc/Y, Ga) and Mg are m2m and 4/m, respectively. The coordinations around Sc/Y, Mg and Ga are pentagonal (Sc/Y), tetragonal (Mg) and triangular (Ga) prisms, with four (Mg) or three (Ga) additional capping atoms leading to the coordination numbers [10], [8+4] and [6+3], respectively. The crystal structure of Sc₂MgGa₂ was determined from single‐crystal diffraction intensities and the isostructural Y₂MgGa₂ was identified from powder diffraction data.     

The alkali hypophosphites KH2PO2, RbH2PO2 and CsH2PO2

The structures of the hypophosphites KH₂PO₂ (potassium hypophosphite), RbH₂PO₂ (rubidium hypophosphite) and CsH₂PO₂ (caesium hypophosphite) have been determined by single‐crystal X‐ray diffraction. The structures consist of layers of alkali cations and hypophosphite anions, with the latter bridging four cations within the same layer. The Rb and Cs hypophosphites are isomorphous.     

Zur Kenntnis der Dialkalimetalldichalkogenide β-Na2S2, K2S2, α-Rb2S2, β-Rb2S2, K2Se2, Rb2Se2, α-K2Te2, β-K2Te2 und Rb2Te2

On Dialkali Metal Dichalcogenides β-Na₂S₂, K₂S₂, α-Rb₂S₂, β-Rb₂S₂, K₂Se₂, Rb₂Se₂, α-K₂Te₂, β-K₂Te₂ and Rb₂Te₂ The first presentation of pure samples of α- and β-Rb₂S₂, α- and β-K₂Te₂, and Rb₂Te₂ is described. Using single crystals of K₂S₂ and K₂Se₂, received by ammonothermal synthesis, the structure of the Na₂O₂ type and by using single crystals of β-Na₂S₂ and β-K₂Te₂ the Li₂O₂ type structure will be refined. By combined investigations with temperature-dependent Guinier-, neutron diffraction-, thermal analysis, and Raman-spectroscopy the nature of the monotropic phase transition from the Na₂O₂ type to the Li₂O₂ type will be explained by means of the examples α-/β-Na₂S₂ and α-/β-K₂Te₂. A further case of dimorphic condition as well as the monotropic phase transition of α- and β-Rb₂S₂ is presented. The existing areas of the structure fields of the dialkali metal dichalcogenides are limited by the model of the polar covalence.     

Electrochemical study of (NEt4)2Cl2FeS2MoS2 and (NEt4)2Cl2FeS2MoS2FeCl2

Summary The ability of [MoS₄]^2–, anions to be used as ligands for transition metal ions has been widely demonstrated, especially with Fe²⁺. The present study has been restricted to linear complexes such as (NEt₄)₂ [Cl₂FeS₂MoS₂] and (NEt₄)₂[Cl₂FeS₂MoS₂FeCl₂]. Their electrochemical properties are described: upon electrochemical reduction, these compounds yield MoS₂, as a black precipitate, and an iron complex in solution, assumed to be [SFeCl₂]^2–. The electrochemical reduction goes through two electron transfers, coupled with the breakdown of the molecular skeleton: a DISPl and an ECE mechanism. Depending on the solvent, the following equilibrium may be observed: [Cl₄Fe₂MoS₄]^2–[Cl₂FeMoS₄]^2–+FeCl₂. The equilibrium constant, K_D, was evaluated by differential pulse polarography. K_D is tightly related to the donor number of the solvent.     

Formal [(2+2)+2] and [(2+2)+(2+2)] nonconjugated dienediyne cascade cycloadditions

[reaction: see text] Fluoranthene 2 and heptacycle 3 are easily accessible from the reaction of diyne 1 and norbornadiene (NBD) in the presence of the rhodium catalyst. The unusual [(2+2)+(2+2)] adduct 3 was confirmed by the X-ray crystal structure analysis.     

The bivalent metal hypophosphites Sr(H2PO2)2, Pb(H2PO2)2 and Ba(H2PO2)2

The structures of isomorphous monoclinic strontium and lead bis­(di­hydrogenphosphate), Sr(H₂PO₂)₂ and Pb(H₂PO₂)₂, and orthorhombic barium bis­(di­hydrogen­phos­phate), Ba(H₂PO₂)₂, consist of layers of hypophosphite anions and metal cations exhibiting square antiprismatic coordination by O atoms. The Sr and Pb atoms are located on sites with point symmetry 2, and the Ba atoms are on sites with point symmetry 222. Within the layers, each anion bridges four metal cations.     

Thermal decomposition of Me3SnO2PCl2, Me2Sn(O2PCl2)2 and Ph3SnO2PCl2

TG and DTA studies on Me₃SnO₂PCl₂, Me₂Sn(O₂PCl₂)₂ and Ph₃SnO₂PCl₂ were carried out under dynamic argon atmosphere. The results show that the decomposition proceeds in different stages leading to the formation of Sn₃(PO₄)₂ as a stable product. This compound was characterized by IR spectroscopy. Decomposition schemes involving reductive elimination reactions were proposed.