KCl标准溶液的绝对法定值研究

对KCl标准溶液绝对法定值法进行了研究,并考察了绝对法标准装置的稳定性和准确性,评定了KCl标准溶液定值的不确定度.     

Correlations of carbon isotope discrimination with element and ash contents in two Sabina evergreen trees in northwest China: patterns and implications

Foliar carbon isotope discrimination (Δ) is widely used as an integrator of physiological plant responses to environmental change. However, the relationship between foliar Δ and mineral nutrient accumulation is still not well-known. The foliar Δ, K, Ca, Mg, Si and ash contents of S. przewalskii Kom. (SP) and S. chinensis (Lin.) Ant. (SC), two over-winter trees distributed on high altitude plateaux and lower altitude plains, respectively, were measured at monthly intervals over two years under the same growing conditions to examine the genetic and seasonal variation in foliar nutrient concentrations in relation to foliar Δ. The foliar Δ, Mg, K and ash contents were markedly lower in SP than in SC, and the foliar Si content was significantly higher in SP than SC, while the differences in Ca contents between the two Sabina trees were not significant. There was higher foliar Δ in winter than in summer for both Sabina trees. Close negative correlations of foliar Δ with K and Mg content, and significant positive correlations between foliar Δ and Si contents, were observed in SP but not in SC. Thus, higher water-use efficiency of SP than of SC is related to higher Si and lower Mg and K contents that have positive effects on the reduction of transpiration rates or stomatal conductances. The results obtained by the present study will advance the understanding of the adaptive strategies of mineral nutrition and water use in harsh environments.     

带虚设层的抗反射结构导模共振滤波器设计与分析

提出带虚设层的抗反射导模共振滤波器结构及设计方法,该方法适用于任意角度入射带虚设层的抗反射结构导模共振滤波器设计与分析.得到带虚设层的导模共振滤波器抗反射结构所满足的关系式.指出在维持虚设层光学厚度不变的情况下,可以通过不同选材,在低反射旁带中实现等带宽不同波长的选择.此外,由于结构的抗反射特性在低角范围内具有较大的角度容差,改变入射角,可以实现滤波波长及光谱带宽在宽光谱范围内的准线性可调谐.     

透射光栅谱仪测谱不确定度分析

透射光栅谱仪广泛应用于惯性约束聚变和其他激光等离子体相互作用领域. 而辐射光谱的精确测量依赖于测量设备的不确定度. 本文从标定过程出发, 分析了标定实验对透射光栅各级衍射效率带来的不确定度. 结合标定实验带来的不确定度, 分析了实验结果解谱过程带来的不确定度. 给出了0.1-5keV能段测量光谱的不确定度. 关键词： 不确定度 透射光栅 实验标定     

无表面活性剂条件下一锅法制备金属/氧化锌复合材料用于催化二氧化碳加氢制甲醇反应

Catalytic hydrogenation of CO₂ to methanol is an important chemical process owing to its contribution in alleviating the impacts of the greenhouse effect and in realizing the requirement for renewable energy sources. Owing to their excellent synergic functionalities and unique optoelectronic as well as catalytic properties, transition metal/ZnO (M/ZnO) nanocomposites have been widely used as catalysts for this reaction in recent years. Development of size-controlled synthesis of metal/oxide complexes is highly desirable. Further, because it is extremely difficult to achieve the strong-metal-support-interaction (SMSI) effect when the M/ZnO nanocomposites are prepared via physical methods, the use of chemical methods is more favorable for the fabrication of multi-component catalysts. However, because of the requirement for an extra H₂ reduction step to obtain the active metallic phase (M) and surfactants to control the size of nanoparticles, most M/ZnO nanocomposites undergo two- or multi-step synthesis, which is disadvantageous for the stable catalytic performance of the M/ZnO nanocomposites. In this work, we demonstrate facile one-pot synthesis of M/ZnO (M = Pd, Au, Ag, and Cu) nanocomposites in refluxed ethylene glycol as a solvent, without using any surfactants. During the synthesis process, Pd and ZnO species can stabilize each other from further aggregation by reducing their individual surface energies, thereby achieving size control of particles. Besides, NaHCO₃ serves as a size-control tool for Pd nanoparticles by adjusting the alkaline conditions. Ethylene glycol serves as a mild reducing agent and solvent owing to its capacity to reduce Pd ions to generate Pd crystals. The nucleation and growth of Pd particles are achieved by thermal reduction, while the ZnO nanocrystals are formed by thermal decomposition of Zn(OAc)₂. X-ray diffraction patterns of the M/ZnO and ZnO were analyzed to study the phase of the nanocomposites, and the results show that no impurity phase was detected. Transmission electron microscopy (TEM) was used to study the morphology and structural properties. In addition, X-ray photoelectron spectroscopy analysis was performed to further confirm the formation of M/ZnO hybrid materials, and the results confirm SMSI between Pd and ZnO. Inductively coupled plasma mass spectrometry was used to check the actual elemental compositions, and the results show that the detected atomic ratios of Pd/Zn were consistent with the values in the theoretical recipe. To investigate the effects of the Pd/Zn molar ratios and the added amount of NaHCO₃ on Pd size, the average sizes of Pd particles were calculated, and the results were confirmed by TEM observation. The Cu/ZnO/Al₂O₃ composite is a widely known catalyst for hydrogenation of CO₂ to methanol, and other M/ZnO composites are also catalytic for this reaction. Therefore, different M/ZnO hybrids were further studied as catalysts for hydrogenation of CO₂ to methanol, among which Pd/ZnO (1 : 9) demonstrated the best performance (30% CO₂ conversion, 69% methanol selectivity, and 421.9 g_methanol·(kg catalyst·h)^-1 at 240 ℃ and 5 MPa. The outstanding catalytic performance may be explained by the following two factors: first, Pd is a good catalyst for the dissociation of H₂ to give active H atoms, and second, SMSI between Pd and ZnO favors the formation of surface oxygen vacancies on ZnO. Moreover, most M/ZnO composites exhibit excellent performance in methanol selectivity, especially the Au/ZnO catalyst, which has the highest methanol selectivity (82%) despite having the lowest CO₂ conversion. Hopefully, this work would provide a simple route for synthesis of M/ZnO nanocomposites with clean surfaces for catalysis.     

利用ZnO@ZIF-8核壳结构构建高选择性、高稳定性的Pd/ZnO催化剂用于CO2加氢制甲醇

Catalytic CO₂ hydrogenation to methanol is a promising route to mitigate the negative effects of anthropogenic CO₂. To develop an efficient Pd/ZnO catalyst, increasing the contact between Pd and ZnO is of the utmost importance, because "naked" Pd favors CO production via the reverse water-gas shift path. Here, we have utilized a ZnO@ZIF-8 core-shell structure to synthesize Pd/ZnO catalysts via Pd immobilization and calcination. The merit of this method is that the porous outer layer can offer abundant "guest rooms" for Pd, ensuring intimate contact between Pd and the post-generated ZnO. The synthesized Pd/ZnO catalysts (PZZ8-T, T denotes the temperature of calcination in degree Celsius) is compared with a ZnO nanorod-immobilized Pd catalyst (PZ). When the catalytic reaction was performed at lower reaction temperatures (250, 270, and 290 ℃), the highest methanol space time yield (STY) and highest STY per Pd achieved by PZ at 290 ℃ were 0.465 g g_cat^-1 h^-1 and 13.0 g g_Pd^-1 h^-1, respectively. However, all the PZZ8-T catalysts exhibited methanol selectivity values greater than 67.0% at 290 ℃, in sharp contrast to a methanol selectivity value of 32.8% for PZ at the same temperature. Thus, we performed additional investigations of the PZZ8-T catalysts at 310 and 360 ℃, which are unusually high temperatures for CO₂ hydrogenation to methanol because the required endothermic reaction is expected to be severely inhibited at such high temperatures. Interestingly, the PZZ8-T catalysts were observed to achieve a methanol selectivity value of approximately 60% at 310 ℃, and PZZ8-400 was observed to maintain a methanol selectivity value of 51.9% even at a temperature of 360 ℃. Thus, PZZ8-400 attains the highest methanol STY of 0.571 g g_cat^-1 h^-1at 310 ℃. For a better understanding of the structure-performance relationship, we characterized the catalysts using different techniques, focusing especially on the surface properties. X-ray photoelectron spectroscopy (XPS) results indicated a linear relationship between the methanol selectivity and the surface PdZn : Pd ratio, proving that the surface PdZn phase is the active site for CO₂ hydrogenation to methanol. Furthermore, analysis of the XPS O 1s spectrum together with the electronic paramagnetic resonance results revealed that both, the oxygen vacancy as well as the ZnO polar surface, played important roles in CO₂ activation. Chemisorption techniques provided further quantitative and qualitative information regarding the Pd-ZnO interface that is closely related to the CO₂ conversion rate. We believe that our results can provide insight into the catalytic reaction of CO₂ hydrogenation from the perspective of surface science. In addition, this work is an illustrative example of the use of novel chemical structures in the fabrication of superior catalysts using a traditional formula.     

Oxygen storage capacity of substituted YBaCo4O7+δ oxygen carriers

Depletion of non-renewable energy sources are at elevated manner due to the rapid growth of industrialization and transportation sector in last few decades and leads to further energy demand. Biodiesels especially second-generation fuels from non-edible oil resources are alternate sources for replacement of diesel fuel in CI engines due to their considerable environmental benefits. In the present work, non-edible feedstock of Calophyllum inophyllum seed oil (tamanu oil) is used for biodiesel production. Transesterification method is used for preparation of biodiesel in the existence of methanol with NaOH as catalyst. The copper nanoparticles are synthesized by electrochemical method, and it is characterized by using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). XRD and SEM results confirm the presence of copper nanoparticle and size of around 30 nm. This paper aims to investigate the effects of the copper additive nanoparticles with biodiesel blends on the engine performance, combustion and emission characteristics of single-cylinder direct-injection diesel engine and compared that with diesel fuel. The results showed that the addition of nano-additives enhances brake thermal efficiency and reduces specific fuel consumption compared to biodiesel blends but slightly lower than diesel. Combustion characteristics also are enhanced by improved oxidation reaction inside the combustion chamber which resulted in higher heat release rate. The emissions of HC, NO_x and O₂ are significantly reduced for nano-additive blends compared to diesel but increased CO₂ emission was observed. It is noticed that higher CO₂ emission and substantial reduction of unused O₂ emissions from engine fueled with nano-additive are evident for enhanced oxidation and better combustion. Energy and exergy analysis of the diesel engine is carried out to estimate the effect of using nanoparticle additive with biodiesel.

     

Uranium(VI) adsorption on montmorillonite colloid

Journal of Radioanalytical and Nuclear Chemistry - Montmorillonite colloid was synthesized and characterized and the adsorption of U(VI) on colloid as a function of contact time, temperature,...     

Synthesis and characterization of CTAB-modified bentonite composites for the removal of Cs+

Journal of Radioanalytical and Nuclear Chemistry - An organic compound adsorbent is prepared by modifying acid-activated bentonite with cetyltrimethylammonium bromide (CTAB). The physical and...     

Asymmetric Syntheses of the Sex Pheromones of Pine Sawflies,Their Homologs and Stereoisomers

We describe efficient and flexible enantioselective syntheses of the active enantiomers of the pheromones of pine sawflies, including the species Diprion jingyuanensis, their homologs and, stereoisomers, as well as those identified from the Chinese species Diprion jingyuanensis, i.e., 126 . A total of 48 compounds, including acetates 78 – 101 and propanoates 102 – 125 , have been synthesized. Our general approach towards these compounds originated from the commercially available chirons diethyl (S)‐ and (R)‐malates, as well as ethyl (R)‐3‐hydroxybutanoate. The Seebach asymmetric methylation was employed in a key step to control additional configuration.