ZnSe晶体气相生长输运剂Zn(NH_4)_3Cl_5的热分解行为及动力学

发展了一种新的ZnSe晶体气相生长输运剂Zn(NH4 ) 3Cl5;用非等温TG DTG技术 ,在 5 0、10 0、15 0和 2 0 0℃ /min 4个不同线性升温条件下 ,研究了其热行为和热分解过程的非等温动力学。结果表明 ,分解过程分 2步完成 ,讨论了与ZnSe晶体生长实验有关的第 1步分解过程。第 1步分解机理为随机成核与生长 ,机理函数为Avrami Erofeev方程 ,f(α) ={ 12 ( 1-α) [-ln ( 1-α) ]-1} ,G(α) =[-ln ( 1-α) ]2 。表观活化能E =16 2 94kJ/mol,指前因子A =10 11 75s-1,动力学方程为 dαdt =10 11.75{ 12 ( 1-α) [-ln ( 1-α) ]-1}exp( - 195 98.3T )。研究表明 ,Zn(NH4 ) 3Cl5具有良好的热稳定性 ,是一种适合气相生长ZnSe晶体的输运剂 ;报道了应用此输运剂生长出ZnSe体单晶的最新结果。

ZnSe单晶气相生长输运剂Zn(NH_4)_2Cl_4的制备工艺研究

为了获得高质量的ZnSe单晶气相生长输运剂Zn(NH4)2Cl4,采用3种工艺因素和4个水平的16组正交试验设计方法对Zn(NH4)2Cl4输运剂的工艺过程进行了设计和分析研究.通过观察不同工艺下的结晶形貌,进行了物相和热重分析.研究结果表明:最合理的工艺因素为ZnCl2和NH4Cl的摩尔比为1∶1,烘干温度为130℃,结晶条件为室温静置.Zn(NH4)2Cl4的热分解过程分为3步完成,产物是ZnCl2.

以Zn(NH_4)_3Cl_5为输运剂气相生长ZnSe单晶

以化合物Zn(NH_4)_3Cl_5为气相输运剂,ZnSe多晶为原料,用化学气相输运技术(CVT)在封闭石英管中生长出直径9mm、长度25mm的Zn_(1+o.031)Se单晶。晶体生长区的温度为898～915℃,温度梯度为1.5℃·cm^(-1),生长周期为21d。晶体生长端由{111}和{100}单形包围。用RO-XRD技术研究了晶体的结晶质量,Znse(111)的RO-XRD谱的FWHM为24s。光致发光特性研究表明,Zn_(1+0.031)Se单晶体的PL谱由F_x(439nm)和BBT(418nm)等发光峰组成,晶体的短波吸收限位于465nm处,腐蚀点密度为(5～7)×10~4cm^(-2)。化合物Zn(NH_4)_3Cl_5具有较高的热稳定性,是一种适合气相生长ZnSe单晶的新型输运剂。

碘输运剂对CVT法制备ZnSe单晶的性能影响研究

采用I2作为输运剂，以单质Zn和Se为原料运用化学气相输运法制备了ZnSe晶体。比较了不同I2含量下所生长ZnSe晶体的性能，借助XRD、SEM和EDS检测方法分析了ZnSe晶体的结构、形貌和成分。结果表明：I2含量对ZnSe晶体性能具有重要的影响，通过比较3组I2含量所制备的ZnSe晶体，确定出当I2含量为4mg／cm3时，所生长的ZnSe晶体具有较好的结晶质量，其晶格常数为5．668nm。测定ZnSe中Zn与Se的原子分数比为1：0．99，且只有1个衍射峰（2θ=-27．2°），其晶面指数为（111）。SEM图像表面比较平滑，没有明显气孔。在此条件下，ZnSe晶体的红外透过性能最好，红外透过率为53．07％-62．61％。其他两种I2含量下所生长的ZnSe晶体结晶质量较差，XRD图谱显示有多个衍射峰，SEM图像表面凹凸不平，有明显气泡和孔洞，并且其红外透过率较低。

ZnSe单晶的气相生长及光学性质

用改进的化学气相输运技术(CVT),以Zn(NH4)3Cl5为新的气相输运剂,直接从单质Zn和Se一步在封密管中生长了ZnSe单晶,升华温度1001～1020℃,管内温差<4℃。经过两周生长,得到8mm×7mm×0.8mm的绿色ZnSe晶体。XRD表明晶体表面为(111)面;受气固界面形貌影响,双晶衍射半高峰宽为50s;PL谱由DPA和SA两个发光峰组成;并研究了晶体片的吸收光谱、荧光光谱、反射光谱和红外透过等光学性质。

单质直接气相生长ZnSe单晶

本文直接以高纯Zn、Se单质为原料，加入少量碘单质作为反应输运剂，用化学气相输运（CVT）的方法一步成功的生长出了ZnSe单晶。采用XRD、EDS、紫外可见分光光度计和光致发光（PL）技术研究了生长的ZnSe晶体的结构、成份以及光学特性。结果表明，生长的ZnSe单晶具有较好结晶性能，成份接近理想的化学计量比，在500—2000nm范围内透过率达到65％～70％，在1．9—2．5eV范围内存在与Zn空位和杂质能级相关的发光带。由Zn和Se单质在输运剂I2的辅助下一步直接生长ZnSe单晶是可行的。

Zn-Mg-Se-I_2系统生长ZnMgSe单晶及其特征

以高纯的Zn、Mg以及Se2单质为生长原料,加入高纯的碘单质作为反应输运剂,采用化学气相输运(CVT)方法成功制备了ZnMgSe单晶,并且分别采用X射线衍射、双晶衍射、紫外可见分光光度计、红外光谱仪以及光致发光(PL)技术研究了晶体的结构、结晶质量以及光学性质。结果表明,制备的单晶结晶性能良好,在500～1500 nm波长范围内的透过率接近50%,在400～4000 cm-1波长范围内的透过率达到42%,在2.0～2.6 eV范围内有三个明显的空位与杂质发光带。以Zn、Mg及Se2单质为生长原料,在输运剂I2的帮助下可以实现ZnMgSe单晶的生长。

Selective Removal of Nitrogen-Containing Heterocyclic Compounds from Transportation Diesel Fuels with Reactive Adsorbent

This paper presents a new selective adsorbent to remove nitrogen-containing heterocyclic compounds from model and commercial transportation diesel fuels based on characteristic reaction designed to occur in the pores of substrate.This reactive adsorbent is composed of formaldehyde,phosphotungstic acid and Santa Barbara USA(SBA)-15.The experiment was based on assumed hydroxymethylation reaction of nitrogen-containing heterocyclic compounds with formaldehyde using phosphotungstic acid as catalyst in batch and fixed-bed systems.The nitrogen concentration in the model fuel was 237.33 ng.μl-1,carbazole and toluene were used as model nitrogen-containing heterocyclic compound and solvent,respectively.The effectiveness of reactive adsorbent for removal of nitrogen-containing heterocyclic compounds from commercial 0# diesel fuel containing 224.86 ng.μl-1 nitrogen was examined in a fixed-bed reactor at 70 ℃.The results showed that nitrogen in the model fuel was very low and the nitrogen concentration in the commercial diesel reduced to 2.44 ng.μl-1.The demand for transportation fuel with ultra-low nitrogen is satisfied.

Transport of Indium, Gallium and Thallium Metal Ions Through Chromatographic Fiber Supported Solid Membrane in Acetylacetone Containing Mixed Solvents

The transport of metal ions of indium, gallium and thallium from source solution to receiving phase through the chromatographic fiber supported solid membrane in the acetylacetone （HAA） containing mixed solvent system has been explored. The fibers supported solid membranes were prepared with chemical synthesis from cellulose fibers and citric acid with the carboxylic acid ion exchange groups introduced. The experimental variables, such as concentration of metal ions （10^-2 to 10^-4 mol.L^-1） in the source solution, mixed solvent composition [for exampl, e, acetylacetone, （2,4-pentanedione）, （HAA） 20% （by volume）, 1,4-dioxane 10% to 60% and HC1 0.25 to 2 mol.L^-1] in the receiving phase and stirring speed （50-130 r.min ） of the bulk source and receiving phase, were explored. The efficiency of mixed solvents for the transport of metal ions from the source to receiving phase through the fiber supported solid membrane was evaluated. The combined ion exchange solvent extraction （CIESE） was observed effective for the selective transport of thallium, indium and gallium metal ions through fiber supported solid membrane in mixed solvents. The oxonium salt formation in the receiving phase enhances thallium, indium and gallium metal ion transport through solid membrane phase. The selective transport of thallium metal ions from source phase was observed from indium and gallium metal ions in the presence of hydrochloric acid in organic solvents in receiving phase. The separation of thallium metal ions from the binary mixtures of Be（II）, Ti（IV）, AI（III） Ca（II）, Mg（II）, K （I）, La（III） and Y（III） was carried out in the mixed solvent system using cellulose fiber supported solid membrane.

Sorption, Transport and Transformation of Atrazine in Soils,Minerals and Composts: A Review

Atrazine is a widely used herbicide for controlling weeds on both agricultural and nonagricultural land,which is equally detected in water supplies beyond safe concentrations.Although the presence of atrazine metabolites is an indication of herbicide degradation,some of them still exhibit toxicity,greater water solubility and weaker interaction with soil components than atrazine.Hence,studies with atrazine in the environment are of interest because of its potential to contaminate drinking water sources.Data on atrazine availability for transport,plant uptake,and microbial degradation and mineralization are therefore required to perform more comprehensive and realistic environmental risk assessments of its environmental fate.This review presents an account of the sorption-desorption phenomenon of atrazine on soil and other sorbents by revisiting the several mechanisms of atrazine-sorbent binding reported in the literature.The retention and transport of atrazine in soils;the influence of organic matter on atrazine sorption;the interactions of atrazine with humic substances,atrazine uptake by plants,atrazine bioccumulation and microbial degradation;atrazine transformation in composting environments;and finally atrazine removal by biosorption are discussed.

Solvent-molecule interaction induced gating of charge transport through single-molecule junctions

To explore solvent gating of single-molecule electrical conductance due to solvent-molecule interactions, charge transport through single-molecule junctions with different anchoring groups in various solvent environments was measured by using the mechanically controllable break junction technique. We found that the conductance of single-molecule junctions can be tuned by nearly an order of magnitude by varying the polarity of solvent. Furthermore, gating efficiency due to solvent–molecule interactions was found to be dependent on the choice of the anchor group. Theoretical calculations revealed that the polar solvent shifted the molecular-orbital energies, based on the coupling strength of the anchor groups. For weakly coupled molecular junctions, the polar solvent–molecule interaction was observed to reduce the energy gap between the molecular orbital and the Fermi level of the electrode and shifted the molecular orbitals. This resulted in a more significant gating effect than that of the strongly coupled molecules. This study suggested that solvent–molecule interaction can significantly affect the charge transport through single-molecule junctions.

Regulation of excitation transit ons by molecular design endowing full-color-tunable emissions with unexpected high quantum yields for bioimaging application

Organic fluorophores are indispensible in chemical/biological imaging. The conjugated fluorescent molecules simultaneously possessing highly tunable emission, high quantum yield in solvents of different polarities, and large Stokes shift are quite rare. Herein, we report a new category of fluorophores based on diarylated thieno[3,4-b]thiophenes efficiently synthesized by direct C-H arylation reaction. TbT-Fluors showed full-color-tunable emissions with large Stokes shifts. Intriguingly,the fluorescence quantum yields of TbT-Fluors are barely sensitive to solvent polarities, approaching 100%. Based on photophysical and theoretical investigations, we found that the enhanced oscillator strength of the S_1-S_0 transition and increased T2-S1 energy difference can sufficiently compensate the negative effect from the decreased energy gap and increased reorganization energy in dimethyl sulfoxide(DMSO). Bioimaging applications revealed that some TbT-Fluors can penetrate the cell membrane and are superior for imaging in terms of high photochemical stability and low cytotoxicity. Furthermore, TbT-PhF exhibits specific colocalization with mitochondria in living cells.

Influence of Copper on Transport and Dissipation of Lambda-Cyhalothrin and Cypermethrin in Soils

Repeated applications of bordeaux mixture （a blend of copper sulfate and calcium hydroxide） and pyrethroid insecticides （Pys） have led to elevated copper （Cu） and Pys concentrations in vineyard surface soils. To understand the potential influence of Cu on the fate of Pys in the soil environment, we selected two Pys, cypermethrin （CPM） and lambda-cyhalothrin （A-CHT）, and two typical Chinese vineyard soils, Haplic Acrisol and Luvic Phaeozem, as experimental samples. The dissipation experiment was conducted at room temperature in the dark, and the transport of both Pys through the soils was investigated using soil thin-layer chromatography. The results showed that the transport of Pys in both soils increased as the Cu2＋ concentration increased from 0 to 100 mg L-1, and Pys were more transportable in Haplic Acrisol （HA） than in Luvic Phaeozem （LP） under the same experimental conditions. For CPM, only 100 mg L-1 of Cu2＋ significantly （P 〈 0.05） increased Pys transport through both soils relative to water. Lambda-CHT was significantly （P〈0.05） transported through HA by all the Cu2＋ concentrations compared to water, and all but the 1 mg L-1 of Cu2＋ significantly （P 〈 0.05） increased the transport of A-CHT through LP relative to water. However, the dissipation rates of CPM and λ-CHT decreased with the addition of Cu to soils. Our findings suggest that the risk of groundwater contamination by Pys increases in the soils with elevated Cu concentrations.