Analysis on First-stage Ignition of n-Heptane at Low Temperatures with a Lumped Skeletal Mechanism

Two-stage ignition exists in the low-temperature combustion process of n-heptane and the first-stage ignition also shows a negative temperature coefficient(NTC) phenomenon. To study key reactions and understand chemical principles affecting the first-stage ignition of n-heptane, a lumped skeletal mechanism with 62 species is obtained based on the detailed NUIGMech1.0 mechanism using the directed relation graph method assisted by sensitivity analysis and isomer lumping. The lumped mechanism shows good performance on ignition delay time under wide conditions. The study revealed that the temperature after the first-stage ignition is higher and a larger amount of fuel is consumed at lower initial temperatures. The temperature at the first-stage ignition is relatively insensitive to the initial temperature. Further sensitivity analysis and reaction path analysis carried out based on the lumped mechanism show that the decomposition of RO₂ to produce alkene and HO₂is the most important reaction to inhibit the first-stage ignitions. The chain branching explosion closely related to the first-stage ignition will be terminated when the rate constant for the RO₂ decomposition is larger than that of the isomerization of RO₂ to produce QOOH. The NTC behavior as well as other characteristics of the first-stage ignition can be rationalized from the competition between these two reactions.     

Surface Organometallic Chemistry for Single-site Catalysis and Single-atom Catalysis

Although driven by different research interests, single-site catalysts and single-atom catalysts are both believed to be model systems bridging homogeneous and heterogeneous catalysis. The two concepts are similar but different. In this review, we will first explain the difference between single-atom catalysis and single-site catalysis, in terms of their goals, synthetic methods and coordination structures of corresponding catalysts. Then, we will introduce the surface organometallic chemistry method, a method traditionally used for synthesizing single-site catalyst. We will explain why it might benefit the single-atom catalysis community. At last, the choice of support to accommodate the method for synthesizing single-atom catalysts will be discussed.     

负载无定型钌纳米簇的原子级钴掺杂一维碳纳米笼增强析氢催化性能

析氢反应是电解水产制氢的关键反应之一.在碱性条件下,由于催化剂表面与反应过程中产生的氧物种、氢物种与催化剂的吸附未处于最佳状态,析氢反应动力学往往比较缓慢,比在酸性条件下慢2-3个数量级.目前,铂基纳米催化剂被认为是最优的析氢催化剂,但因价格昂贵、稳定性较差,限制了其在电解水器件上的大规模应用.因此,设计一种价格较为低...     

溶剂热合成可调控氧空位的Bi2MoO6纳米晶及其光催化氧化制喹啉和抗生素降解

近年来,半导体光催化在环境净化和有机合成领域的研究引起了广泛的重视.其中,在有机合成领域中,光催化技术已经应用在醇类、环己烷以及芳香族化合物的选择性氧化研究.而另一类具有特殊结构的有机物——N-杂环芳烃,在药物化学和材料科学中具有重要意义.而传统用于合成N-杂化芳烃的脱氢催化氧化反应通常需要高温高压的苛刻环境,传统方法通常还需要使用贵金属催化剂,这也增加了N-杂化芳烃的合成成本;另外,如果合成是均相催化过程,则催化剂难以实现回收利用.因此,开发室温常压条件下的非贵金属多相光催化技术具有巨大的应用前景.本文以能够被可见光驱动的钼酸铋半导体为催化剂,利用氧缺陷策略来提升钼酸铋的光催化氧化性能.不同于传统氧缺陷制备方法(氢气还原热处理、离子掺杂等),本文采用一种低成本的乙二醛辅助溶剂热的方法合成具有可调控的含氧空位Bi₂MoO₆催化剂(OVBMO).通过X射线粉末衍射(XRD)、扫描电镜、透射电镜、紫外可见漫反射吸收光谱、氮气物理吸附脱附、X射线光电子能谱(XPS)、电子自旋共振光谱、光致发光光谱及电化学测试等技术对制备的OVBMO材料进行了物理化学性质及能带研究.XPS,XRD,Raman和FT-IR结果表明,氧空位存在于[Bi₂O₂]²⁺和MoO₆八面体的层间.紫外可见漫反射结果表明,随着氧空位的引入,Bi₂MoO₆的光吸收范围扩大,带隙变窄.结合莫特肖特基和VBXPS分析获得OVBMO的能带位置,发现氧空位的存在不仅会导致禁带中出现缺陷带能级,还会导致价带顶位置上移,促进光生空穴的迁移.PL和电化学结果表明,氧空位的存在使得载流子浓度、载流子的分离能力与界面电荷迁移能力都有较大提升,这是因为氧空位引入的缺陷能级可以浅势捕获电子,抑制光催化剂中的电子与空穴的复合,改变化学反应的速率.同时,氧空位有助于捕获分子氧,分子氧与捕获的光生电子发生反应,产生更多的超氧自由基(·O₂)和空穴(h⁺),从而极大地提升光催化剂的氧化性能.因此,OVBMO在1,2,3,4-四氢喹啉脱氢氧化产生喹啉及系列抗生素(环丙沙星、四环素、盐酸土霉素)的降解反应中,表现出较好的光催化氧化性能.结合多种表征分析,本文还进一步阐明了OVBMO催化剂将1,2,3,4-四氢喹啉脱氢氧化为喹啉的自由基参与的多相催化反应机理.     

Electro-assisted Molecular Assembly Giving Atomic-Scale Catalytic Active-Site Detection

The artificially accurate design of nonmetal electrocatalysts’ active site has been a huge challenge because no pure active species with the specific structure could be strictly controlled by traditional synthetic methods. Species with a multiconfiguration in the catalyst hinder identification of the active site and the subsequent comprehension of the reaction mechanism. We have developed a novel electro-assisted molecular assembly strategy to obtain a pure pentagon ring on perfect graphene avoiding other reconstructed structures. More importantly, the active atom was confirmed by the subtle passivation process as the topmost carbon atom. Recognition of the carbon-defect electrocatalysis reaction mechanism was first downsized to the single-atom scale from the experimental perspective. It is expected that this innovative electro-assisted molecular assembly strategy could be extensively applied in the active structure-controlled synthesis of nonmetal electrocatalysts and verification of the exact active atom.     

Diffusiophoresis in suspensions of highly charged soft particles

Diffusiophoresis phenomenon of aoft particles suspended in binary electrolyte solutions is explored theoretically in this study based on the spherical cell model, focusing on the chemiphoresis component in absence of diffusion potential. Both the electrostatic and hydrodynamic aspects of the boundary confinement, or steric effect, due to the presence of neighboring particles are examined extensively under various electrokinetic conditions. Significant local extrema are found in mobility profiles expressed as functions of the Debye length in general, synchronized with the strength of the motion-inducing double layer polarization. Moreover, a seemingly peculiar phenomenon is observed that the soft particles may move faster in more concentrated suspensions. The competition between the simultaneous enhancement of the motion-inducing electric driving force and the motion-retarding hydrodynamic drag force from the boundary confinement effect of the neighboring particles is found to be responsible for it. The above findings are also demonstrated experimentally in a very recent study on the diffusiophoretic motion of soft particles through porous collagen hydrogels. The results presented here are useful in various practical applications of soft particles like drug delivery.     

Elastic-inertial separation of microparticle in a gradually contracted microchannel

Separation of microparticle in viscoelastic fluid is highly required in the field of biology and clinical medicine. For instance, the separation of the target cell from blood is an important prerequisite step for the drug screening and design. The microfluidic device is an efficient way to achieve the separation of the microparticle in the viscoelastic fluid. However, the existing microfluidic methods often have some limitations, including the requirement of the long channel length, the labeling process, and the low throughput. In this work, based on the elastic-inertial effect in the viscoelastic fluid, a new separation method is proposed where a gradually contracted microchannel is designed to efficiently adjust the forces exerted on the particle, eventually achieving the high-efficiency separation of different sized particles in a short channel length and at a high throughput. In addition, the separation of WBCs and RBCs is also validated in the present device. The effect of the flow rate, the fluid property, and the channel geometry on the particle separation is systematically investigated by the experiment. With the advantage of small footprint, simple structure, high throughput, and high efficiency, the present microfluidic device could be utilized in the biological and clinical fields, such as the cell analysis and disease diagnosis.     

Rapid qualitative profiling and quantitative analysis of Juglandis Mandshuricae Cortex and seven flavonoids by ultra-high performance liquid chromatography–quadrupole/orbitrap high-resolution mass spectrometry

Juglandis Mandshuricae Cortex is the bark of Juglans mandshurica Maxim., which has been used as a folk medicine plant in China and India. In this study, an ultra-high performance liquid chromatography–quadrupole/orbitrap high-resolution mass spectrometry method was developed to clarify and quantify the chemical profiling of Juglandis Mandshuricae Cortex rapidly. A total of 113 compounds were characterized. Among them, seven flavonoids were simultaneously quantified in 15 min, including myricetin, myricetrin, taxifolin, kaempferol, quercetin, quercitrin, and naringenin. The method was validated for accuracy, precision, and the limits of detection and quantification. All calibration curves showed a good linear relationship (r > 0.9990) within test ranges. The intra- and inter-day relative standard deviations were less than 2.16%. Accuracy validation showed that the recovery was between 95.6 and 101.3% with relative standard deviation values below 2.85%. The validated method was successfully applied to determine the contents of seven flavones in Juglandis Mandshuricae Cortex from seven sources and the contents of these places were calculated respectively. This method provides a theoretical basis for further developing the medicinal value of Juglandis Mandshuricae Cortex.     

Pharmacokinetics,hepatic disposition,and heart tissue distribution of 14 compounds in rat after oral administration of Qi-Li-Qiang-Xin capsule via ultra-high-performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry

In the present study, a specific and sensitive approach using ultra-high-performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry was developed and validated for the quantitative analysis of 14 constituents in rat plasma, liver, and heart. The method was fully validated and successfully applied to pharmacokinetic, hepatic disposition, and heart tissue distribution studies of 14 compounds after the oral administration of Qi-Li-Qiang-Xin capsule. Ginsenoside Rb1, alisol A, astragaloside IV, and periplocymarin were found to be highly exposed in rat plasma, while toxic components such as hypaconitine, mesaconitine, and periplocin had low circulation levels in vivo. Moreover, sinapine thiocyanate, neoline, formononetin, calycosin, and alisol A exhibited significant liver first-pass effects. Notably, high levels of alisol A, periplocymarin, benzoylmesaconine, and benzoylhypaconine were observed in the heart. Based on high exposure and appropriate pharmacokinetic features in the systemic plasma and heart, astragaloside IV, ginsenoside Rb1, periplocymarin, benzoylmesaconine, benzoylhypaconine, and alisol A can be considered as the main potentially effective components. Ultimately, the results provide relevant information for discovery of effective substances, as well as further anti-heart failure action mechanism investigations of Qi-Li-Qiang-Xin capsule.     

Highly Efficient Ir(III)-Coumarin Photo-Redox Catalyst for Synergetic Multi-Mode Cancer Photo-Therapy

Four photo-catalysts of the general formula [Ir(CO6/ppy)₂(L)]Cl where CO6=coumarin 6 ( Ir1 – Ir3 ), ppy=2-phenylpyridine ( Ir4 ), L=4′-(3,5-di-tert-butylphenyl)-2,2′ : 6′,2′′-terpyridine ( Ir1 ), 4′-(3,5-bis(trifluoromethyl)phenyl)-2,2′ : 6′,2′′-terpyridine ( Ir2 and Ir4 ), and 4-([2,2′ : 6′,2′′-terpyridin]-4′-yl)-N,N-dimethylaniline ( Ir3 ) were synthesized and characterized. These photostable photo-catalysts ( Ir1 – Ir3 ) showed strong visible light absorption between 400–550 nm. Upon light irradiation (465 and 525 nm), Ir1 – Ir3 generated singlet oxygen and induced rapidly photo-catalytic oxidation of cellular coenzymes NAD(P)H. Ir1 – Ir3 showed time-dependent cellular uptake with excellent intracellular retention efficiency. Upon green light irradiation (525 nm), Ir2 provided a much higher photo-index (PI=793) than the clinically used photosensitizer, 5-aminolevulinicacid (5-ALA, PI>30) against HeLa cancer cells. The observed necro-apoptotic anticancer activity of Ir2 was due to the Ir2 triggered photo-induced intracellular redox imbalance (by NAD(P)H oxidation and ROS generation) and change in the mitochondrial membrane potential. Remarkably, Ir2 showed in vivo photo-induced catalytic anticancer activity in mouse models.