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871.
Weihong Wu Shufang Lv Xin Liu Hongqiang Qu Hongchao Zhang Jianzhong Xu 《Journal of Thermal Analysis and Calorimetry》2014,118(3):1569-1575
Three typical metal hypophosphite flame retardants La(H2PO2)3·H2O (LHP), Ce(H2PO2)3·H2O (CHP), and Al(H2PO2)3 (AHP) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction, scanning electron microscopy, thermogravimetric analysis (TG), derivative thermogravimetric analysis, and differential thermal analysis. The thermal degradation products from the synthesized metal hypophosphites were also investigated using thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR) and thermogravimetry coupled with mass spectrometry (TG–MS). The synthesized metal hypophosphites were also used as flame retardants for poly (1,4-butylene terephthalate) (PBT), and the combustion properties of flame-retarded PBT were evaluated using the limiting oxygen index and UL-94 tests. The results showed that the metal hypophosphites LHP, CHP, and AHP can be used as effective flame retardants for PBT, and these compounds can be obtained through a simple precipitation method. TG–FTIR and TG–MS results showed that the degradation process of AHP involves two steps, corresponding to the removal PH3 reaction and the further dehydration reaction of the hydrogen phosphate aluminum. While LHP and CHP have three degradation steps, the additional step is due to that LHP and CHP which will loss the crystal water at lower temperature. 相似文献
872.
Jianming Lan Wenming Xu Qiping Wan Xi Zhang Jia Lin Jinghua Chen Jianzhong Chen 《Analytica chimica acta》2014
The proposed palladium nanoparticles (Pd NPs), which with the catalytic activity similar to the horseradish peroxidase (HRP) mimic enzyme, can effectively catalyze the H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine sulfate (TMB) accompanied with a color change from colorless to blue in solution. And as a result, the sensitive detection of sarcosine can be realized by the naked eye observation and ultraviolet spectrophotometry, using Pd NPs as catalyst and TMB as the substrate of the simulation enzyme catalytic reaction. Under the optimal condition, the catalytic system of Pd NPs mimic enzyme can be used for the detection of sarcosine. It has been found that the color change could be clearly observed with the naked eyes, and the absorbance intensity at 653 nm showed a fine linear fitting with the concentration of sarcosine in the range from 0.01 μM to 50 μM, and the detection limit (3σ/S) for sarcosine was calculated to be 5.0 nM. In order to evaluate the feasibility and reliability, the method was also used for analyzing concentrations of sarcosine in human urine samples from diagnosed prostate cancer patients and healthy donors. It is expected to provide a convenient and efficient method for indirect evaluation for the diagnosis of prostatic carcinoma (PCa). 相似文献
873.
The bleaching action of ozone on indigo and related compounds is well known. We describe sensitive automated instrumentation for measuring ambient ozone. Air is sampled around a porous polypropylene tube filled with a solution of indigotrisulfonate. Light transmission through the tube is measured. Light transmission increases as O(3) diffuses through the membrane and bleaches the indigo. Evaporation of the solution, a function of the RH and the air temperature, can, however cause major errors. We solve this problem by adding an O(3)-inert dye that absorbs at a different wavelength. Here we provide a new algorithm for this correction and show that this very inexpensive instrument package (controlled by a BASIC Stamp Microcontroller with an on-board data logger, total parts cost US$ 300) provides data highly comparable to commercial ozone monitors over an extended period. The instrument displays an LOD of 1.2ppbv and a linear span up to 300ppbv for a sampling time of 1min. For a sampling time of 5min, the respective values are 0.24ppbv and 100ppbv O(3). 相似文献
874.
Jing Guan Dr. Jianzhong Chen Yicong Luo Lisen Guo Prof. Dr. Wanbin Zhang 《Angewandte Chemie (International ed. in English)》2023,62(35):e202306380
A highly chemoselective earth-abundant transition metal copper catalyzed asymmetric hydrogenation of C=O bonds of exocyclic α,β-unsaturated pentanones was realized using H2. The desired products were obtained with up to 99 % yield and 96 % ee (enantiomeric excess) (99 % ee, after recrystallization). The corresponding chiral exocyclic allylic pentanol products can be converted into several bioactive molecules. The hydrogenation mechanism was investigated via deuterium-labelling experiments and control experiments, which indicate that the keto-enol isomerization rate of the substrate is faster than that of the hydrogenation and also show that the Cu−H complex can only catalyze chemoselectively the asymmetric reduction of the carbonyl group. Computational results indicate that the multiple attractive dispersion interactions (MADI effect) between the catalyst with bulky substituents and substrate play important roles which stabilize the transition states and reduce the generation of by-products. 相似文献
875.
Xiaoan Li Jianzhong Jia Tao Li Zefeng Zhao Haijing Liu Na Song Jin Pei 《Journal of separation science》2023,46(22):2300196
After medicinal market research, it was found that the harvest time of Ligustri Lucidi Fructus (LLF) was chaotic in practice. In order to determine the optimal harvest period of LLF to ensure its pharmacological activity, metabolomics analysis of LLF at different harvest times based on ultra-high-performance liquid chromatography-triple quadrupole-(linear ion trap)-tandem mass spectrometry was established. In this study, 166 differential metabolites (DMs) in 448 metabolites at different harvest times were screened out based on variable importance in projection value, and among them, 94 DMs with regular trends of change in relative content (59 increased and 35 decreased with the growth period) were chosen to further research. The result of the multivariate statistical analysis showed that November was the optimal harvest period of LLF. Additionally, 10-hydroxyligustroside, oleoside 11-methyl ester, and salidroside were screened out to be used as the evaluation indicators of immature LLF, while specnuezhenide, nuezhenoside G13, and neonuezhenide were the evaluation indicators of mature LLF. This study provides fundamental insight for metabolite identification and proposes the best harvest period of LLF to avoid confusion in the medicinal market. 相似文献
876.
Xiaowei Liu Weihong Wu Jianhong Sun Jianzhong Xu 《Journal of Macromolecular Science: Physics》2016,55(2):115-127
The effects of hydrophobic magnesium hydroxide (Mg(OH)2) particles, prepared by a surface modification method with oleic acid, on the flame-retarding and mechanical properties of polyvinyl chloride (PVC) were investigated. Comparison between the use of modified and unmodified Mg(OH)2 in the preparation of PVC composites showed that the former could provide excellent optical and flame-retarding properties. The dispersion of the modified Mg(OH)2 particles in the PVC matrix was investigated through scanning electron microscopy. Compared with a composite containing unmodified Mg(OH)2, the rheological and impact strength properties of that containing the modified Mg(OH)2 filler were found to be significantly improved. These improvements were mostly attributed to the better dispersion of the modified Mg(OH)2 particles and the strong adhesion between the filler and matrix. 相似文献
877.
基于由光子晶体光纤飞秒激光器产生的高重复频率飞秒激光搭建了飞秒激光微加工系统,利用LabVIEW编写程序精密控制三维移动平台的移动路径和高速快门,在加工功率为1.5W、移动速率为1mm/s时,利用直写技术在无胶铬版上得到了微米量级的任意形状的平面衍射光栅。利用CCD相机对光栅制备过程进行实时监视,保证了光栅的加工质量。制备的光栅在显微镜下观察,条纹边缘清晰、线纹粗细均匀。使用He-Ne激光照射加工的光栅,可以获得清晰、稳定、与理论符合很好的夫琅和费(Frauhofer)衍射图样,显示了所加工的光栅具有良好的光学性能。实验结果也表明了光子晶体光纤飞秒激光在光栅制作过程中所具备的良好的加工性能。 相似文献
878.
879.
Chong Li Shujie Li Zhaoli Liu Jianzhong Pan 《Journal of Differential Equations》2008,244(10):2498-2528
In this paper, we study the structure of the Fucík spectrum of −Δ, the set of points (b,a) in R2 for which the equation
880.
Guo J Chen S Liu L Li B Yang P Zhang L Feng Y 《Journal of colloid and interface science》2012,367(1):61-66
Multifunctional magnetic-fluorescent nanohybrids were successfully fabricated by a facile layer-by-layer (LBL) self-assembly of in situ generated Eu, Gd co-doped LaF(3) nanocrystals (LaF(3):Eu:Gd) on the surface of multi-walled carbon nanotubes (MWNTs). Photoluminescence (PL) quenching occurred when LaF(3):Eu:Gd nanoparticles were directly coated on the surface of MWNTs. By growth of a SiO(2) shell spacer between MWNTs and LaF(3):Eu:Gd nanocrystals, we circumvented the PL quenching and achieved the magnetic-fluorescent MWNTs. Moreover, the nanohybrids showed powerful T(1) and T(2)-weighted magnetic resonance imaging (MRI) signal in water and could be used as MRI contrast agents. As a result, the nanohybrids can be expected to act as a promising multimodal MRI/optical imaging probe. 相似文献