The study of thermal decomposition kinetics of zinc oxide formation from zinc oxalate dihydrate

This study is devoted to the thermal decomposition of ZnC₂O₄·2H₂O, which was synthesized by solid-state reaction using C₂H₂O₄·2H₂O and Zn(CH₃COO)₂·2H₂O as raw materials. The initial samples and the final solid thermal decomposition products were characterized by Fourier transform infrared and X-ray diffraction. The particle size of the products was observed by transmission electron microscopy. The thermal decomposition behavior was investigated by thermogravimetry, derivative thermogravimetric and differential thermal analysis. Experimental results show that the thermal decomposition reaction includes two stages: dehydration and decomposition, with nanostructured ZnO as the final solid product. The Ozawa integral method along with Coats–Redfern integral method was used to determine the kinetic model and kinetic parameters of the second thermal decomposition stage of ZnC₂O₄·2H₂O. After calculation and comparison, the decomposition conforms to the nucleation and growth model and the physical interpretation is summarized. The activation energy and the kinetic mechanism function are determined to be 119.7 kJ mol^?1 and G(α) = ?ln(1 – α)^1/2, respectively.     

A label-free electrochemical biosensor based on a DNA aptamer against codeine

In order to develop a sensor for opium alkaloid codeine detection, DNA aptamers against codeine were generated by SELEX (systematic evolution of ligands by exponential enrichment) technique. An aptamer HL7-14, which is a 37-mer sequence with K_d values of 0.91 μM, was optimized by the truncation-mutation assay. The specificity investigation shows that HL7-14 exhibits high specificity to codeine over morphine, and almost cannot bind to other small molecule. With this new selected aptamer, a novel electrochemical label-free codeine aptamer biosensor based on Au-mesoporous silica nanoparticles (Au-MSN) as immobilized substrate has been proposed using [Fe(CN)₆]^3−/4− as electroactive redox probe. The linear range covered from 10 pM to 100 nM with correlation coefficient of 0.9979 and the detection limit was 3 pM. Our study demonstrates that the biosensor has good specificity, stability and well regeneration. It can be used to detect codeine.     

Cell-specific internalization study of an aptamer from whole cell selection

Nucleic acid aptamers have been shown many unique applications as excellent probes in molecular recognition. However, few examples are reported which show that aptamers can be internalized inside living cells for aptamer functional studies and for targeted intracellular delivery. This is mainly due to the limited number of aptamers available for cell-specific recognition, and the lack of research on their extra- and intracellular functions. One of the major difficulties in aptamers' in vivo application is that most of aptamers, unlike small molecules, cannot be directly taken up by cells without external assistance. In this work, we have studied a newly developed and cell-specific DNA aptamer, sgc8. This aptamer has been selected through a novel cell selection process (cell-SELEX), in which whole intact cells are used as targets while another related cell line is used as a negative control. The cell-SELEX enables generation of multiple aptamers for molecular recognition of the target cells and has significant advantages in discovering cell surface binding molecules for the selected aptamers. We have studied the cellular internalization of one of the selected aptamers. Our results show that sgc8 is internalized efficiently and specifically to the lymphoblastic leukemia cells. The internalized sgc8 aptamers are located inside the endosome. Comparison studies are done with the antibody for the binding protein of sgc8, PTK7 (Human protein tyrosine kinase-7) on cell surface. We also studied the internalization kinetics of both the aptamer and the antibody for the same protein on the living cell surface. We have further evaluated the effects of sgc8 on cell viability, and no cytotoxicity is observed. This study indicates that sgc8 is a promising agent for cell-type specific intracellular delivery.     

Dual-salts of LiTFSI and LiODFB for high voltage cathode LiNi0.5Mn1.5O4

Journal of Solid State Electrochemistry - The LiNi0.5Mn1.5O4 has been investigated as promising because of its high operating voltage (4.7 V vs. Li+/Li) and decent specific capacity....     

Ag/Co-Ce复合氧化物在O2及NOx气氛中催化燃烧碳烟的性能:Ag的作用

柴油车由于其良好的燃油经济性及强劲的动力得到了广泛应用,但同时柴油车尾气排放中颗粒物(PM)也对环境造成巨大污染,并严重威胁人类健康.与气体污染物相比,PM的处理难度更大,其组分复杂,起燃温度高,是当前柴油车排放问题的瓶颈和难点.颗粒过滤器(DPF)是一种有效消除PM的手段,它需要及时再生以保证其较高的碳烟捕集效率.与其他再生方案相比,连续催化再生系统工艺简单,能耗低,研发一种能够连续催化再生柴油车DPF的催化剂也成为当务之急.Ag是一种比较特殊的贵金属,其工业属性较强,价格也相对低廉.Ag基催化剂在环境催化领域有着广泛应用,已被应用于CO催化氧化、VOC催化去除及甲醛催化氧化等领域.目前的文献报道主要集中于研究Ag基催化剂负载于惰性载体对O2气氛下碳烟起燃性能的影响,并基于此讨论Ag的作用.本文利用柠檬酸络合法合成了高性能低温催化氧化材料体系xAg/Co0.93Ce0.07,探讨了不同Ag负载量对在两种气氛O2及O2+NO中催化性能的影响,并深入分析了引起此现象的原因.结果表明,Ag对Co-Ce复合氧化物的催化性能有显著的促进作用;Ag/Co-Ce复合氧化物在O2气氛下的起燃活性取决于Ag含量,Ag含量最高的样品0.3Ag/Co0.93Ce0.07催化性能最佳.而在NOx气氛下,Ag基催化剂的起燃性能不及在O2中的数值;0.2Ag/Co0.93Ce0.07与0.3Ag/Co0.93Ce0.07催化活性并列最优,其起燃温度可低至226oC.XRD及Raman的表征结果证实了Ag主要以单质形态存在,且其对Co-Ce复合氧化物的晶体结构未产生显著的影响,Ag的晶粒尺寸也未明显变化.H2-TPR则表明了Ag的负载未能提高催化剂的整体氧化还原能力,soot-TPR预示Ag甚至恶化了催化剂在惰性气氛下表面晶格氧及体相晶格氧的活性.NOx-TPD表征结果则证明了Ag对催化剂的NOx吸附有积极作用.此外,Ag/Co-Ce复合氧化物催化剂也具备了优异的耐久性及稳定性.本文还依据催化性能及表征结果剖析了碳烟在不同气氛下的催化氧化机理.在O2气氛下,Ag为反应的活性位,Ag与其表面的氧化物层AgOy之间存在一个自再生的反应循环.Ag吸附解离氧原子后,将其转化为AgOy,这表明此氧化物层不仅能够在低温下贡献表面晶格氧去除碳烟,促进氧分子向超氧物种转化,它在分解后也能将吸附氧解离为过氧物种及超氧物种.在NOx气氛下,催化剂表面硝酸根物种是催化剂催化性能维持稳定的重要因素;反应过程中催化材料表面硝酸盐物种的热稳定性筛查结果也进一步佐证了催化剂表面的AgNO3物种是碳烟起燃的决定性因素,其自身的氧化还原活性及Ag离子移动性均有利于降低碳烟的起燃温度.TGA结果说明了NOx气氛中的活性中间产物AgNO3的氧化还原活性劣于O2气氛下活性中间产物Ag2O,这直接导致催化剂在O2气氛下具备更好的碳烟起燃性能.本文工作有助于启发其他研究者开发高活性催化氧化催化材料.     

Pillararene Host–Guest Complexation Induced Chirality Amplification: A New Way to Detect Cryptochiral Compounds

The contradiction between the rising demands of optical chirality sensing and the failure in chiral detection of cryptochiral compounds encourages researchers to find new methods for chirality amplification. Inspired by planar chirality and the host–guest recognition of pillararenes, we establish a new concept for amplifying CD signals of cryptochiral molecules by pillararene host–guest complexation induced chirality amplification. The planar chirality of pillararenes is induced and stabilized in the presence of the chiral guest, which makes the cryptochiral molecule detectable by CD spectroscopy. Several chiral guests are selected in these experiments and the mechanism of chiral amplification is studied with a non-rotatable pillararene derivative and density functional theory calculations. We believe this work affords deeper understanding of chirality and provides a new perspective for chiral sensing.     

Toughening of ethylene-propylene random copolymer/clay nanocomposites: Comparison of different compatibilizers

Ethylene/propylene-random-copolymer(PPR)/clay nanocomposites were prepared by two-stage melt blending. Four types of compatibilizers,including an ethylene-octene copolymer grafted maleic anhydride(POE-g-MA) and three maleic-anhydride-grafted polypropylenes(PP-g-MA) with different melt flow indexes(MFI),were used to improve the dispersion of organic clay in matrix.On the other hand,the effects of organic montmorillonite(OMMT) content on the nanocomposite structure in terms of clay dispersion in PPR matrix,thermal behavior and tensile properties were also studied. The X-ray diffraction(XRD) and transmission electron microscopy(TEM) results show that the organic clay layers are mainly intercalated and partially exfoliated in the nanocomposites.Moreover,a PP-g-MA compatibilizer(compatibilizer B) having high MFI can greatly increase the interlayer spacing of the clay as compared with other compatibilizers.With the introduction of compatibilizer D(POE-g-MA),most of the clays are dispersed into the POE phase,and the shape of the dispersed OMMT appears elliptic,which differs from the strip of PP-g-MA.Compared with virgin PPR,the Young’s modulus of the nanocomposite evidently increases when a compatibilizer C(PP-g-MA) with medium MFI is used.For the nanocomposites with compatibilizer B and C,their crystallinities(X_c) increase as compared with that of the virgin PPR. Furthermore,the increase of OMMT loadings presents little effect on the melt temperature(T_m) of the PPR/OMMT nanocomposites,and slight effect on their crystallization temperature(T_c).Only compatibilizer B can lead to a marked increases in crystallinity and T_c of the nanocomposite when the OMMT content is 2 wt%.     

Modification of the Interlayer in HTiNbO5 and its Physicochemical Characterization

Abstract

A layered titanoniobate, in which the interlayer of the metal oxide based on octahedral framework is pillared with silica, has been prepared from HTiNbO₅ by employing alkylamines (C_nH_2n+1NH₂, n = 4, 6, 8, 10) and tetraethylorthosilicate as interlayer exchange guests and a pillar precursor, respectively. The incorporated amine had bilayer arrangements in the interlayer space and their ammonium head groups pointed to the host (TiNbO5₅ ^?) layers. While the basal spacing of the compounds increased with the chain length of alkylamine. the inclination angle also increased. The intercalated structure facilitated the incorporation of tetraethylorthosilicate into the interlayers, and silica-pillared layered titanoniobate was obtained after calcination. The physicochemical properties of the resultant pillared compounds were characterized on the interlayer microstructure, nitrogen adsorption and UV-VIS absorption spectra.     

扫频光学相干层析成像系统的波数校正与相位测量研究

相位敏感光学相干层析成像(OCT)系统可以用于高灵敏度的相位探测,在细胞分析、材料检测等方面具有重要应用,但扫频光源的不稳定性会影响扫频OCT系统的相位测量精度.本文提出了一种基于马赫-曾德尔干涉仪(MZI)时域相位信息的波数校正方法.利用MZI时域包裹相位的互相关运算确定各采集波数序列的相对偏移量,鉴于时域包裹相位的非严格周期特征,可确定偏移量的大小不受限制.依据相对偏移量对各序列信号进行时域同步,并基于同步后的MZI时域解包裹相位实施待测干涉信号在位相域的等间隔重采样.基于所提出的波数校正方法,实施了各扫频序列波数偏移量的校正,开展了基于位相信息的光程重复性测量实验.结果表明,即使在不稳定扫频光源的前提下,也能获得高精度的相位测量结果.     

A friction contact stiffness model of fractal geometry in forced response analysis of a shrouded blade

To investigate the nonlinear vibration behavior of a shrouded blade with friction dynamic contact interface, a friction contact stiffness model is proposed to describe the friction force at different rough interfaces and different normal loads. In the proposed model, the friction contact interface is discretized to a series of friction contact pairs and each of them can experience stick, slip, or separate states. Fractal geometry is used to simulate the topography of contact surfaces. The contact stiffness is calculated using the Hertz contact theory and fractal geometry, which is related to contact interfaces parameters including normal load, roughness, Young??s modulus, and Poisson??s ratio. The trajectory tracking method is used to predict the friction force and it is not necessary to judge the transition condition among stick, slip, and separate states. It is suitable for complicated periodic motion of the contact interfaces. The forced response of a real shrouded blade is predicted using the proposed model and the multi-harmonic balance method. The effect of surface roughness, initial normal load, and contact area on the forced response of a shrouded blade is studied. It is shown that contact stiffness increases with normal load and fractal dimension. The resonant amplitude is sensitive to the initial normal load and contact surface roughness. The response can be influenced by the contact area, which is an important parameter for blade designers.