An evidence of contact ion pair in β-(acyloxy)alkyl radical heterolysis during copper(I)-mediated synthesis of trisubstituted alkenes

The first evidence for a unified mechanism of heterolysis in β-(acyloxy)alkyl radical involving contact ion pair (CIP) is presented for both fragmentation and rearrangement of the acyloxy group in the reaction of 1-alkoxy-2,2,2-trichloroethyl acetate with 2 mol equiv each of CuCl and bpy in refluxing DCE under a N₂ atmosphere and availed this reaction for the synthesis of Z-stereoselective trisubstituted alkenes. The stereochemistry of the trisubstituted alkenes was assigned by the uniform pattern of the chemical shift values of some relevant signals in ¹H and ¹³C NMR spectra. This assignment was further supported by the X-ray diffraction spectroscopy of Z-1-chloro-2-(4-nitrobenzyloxy)vinyl acetates.     

Comparisons of CIP,compact and CIP‐CSL2 schemes for reproducing internal solitary waves

Six different models were evaluated for reproducing internal solitary waves which occur and propagate in a stratified flow field with a sharp interface. Three stages were used to compute internal solitary waves in a stratified field: (1) first‐phase computation of momentum equations, (2) second‐phase computation of momentum equations, which corresponds to computing the Poisson's equation, and (3) density computation. The six models discussed in this paper consisted of combinations of four different schemes, a three‐point combined compact difference scheme (CCD), a normal central difference scheme (CDS), a cubic‐polynomial interpolation (CIP), and an exactly conservative semi‐Lagrangian scheme (CIP‐CSL2). The residual cutting method was used to solve the Poisson's equation. Three tests were used to confirm the validity of the computations using KdV theory; i.e. the incremental wave speed and amplitude of internal solitary waves, the maximum horizontal velocity and amplitude, and the wave form. In terms of the shape of an internal solitary wave, using CIP for momentum equations was found to provide better performance than CCD. These results suggest one of the most appropriate scheme for reproducing internal solitary waves may be one in which CIP is used for momentum equations and CCD to solve the Poisson's equation. Copyright © 2005 John Wiley & Sons, Ltd.     

Cu2+改性g-C3N4光催化剂的光催化性能

Photocatalytic technology can effectively solve the problem of increasingly serious water pollution, the core of which is the design and synthesis of highly efficient photocatalytic materials. Semiconductor photocatalysts are currently the most widely used photocatalysts. Among these is graphitic carbon nitride (g-C₃N₄), which has great potential in environment management and the development of new energy owing to its low cost, easy availability, unique band structure, and good thermal stability. However, the photocatalytic activity of g-C₃N₄ remains low because of problems such as wide bandgap, weakly absorb visible light, and the high recombination rate of photogenerated carriers. Among various modification strategies, doping modification is an effective and simple method used to improve the photocatalytic performance of materials. In this work, Cu/g-C₃N₄ photocatalysts were successfully prepared by incorporating Cu²⁺ into g-C₃N₄ to further optimize photocatalytic performance. At the same time, the structure, morphology, and optical and photoelectric properties of Cu/g-C₃N₄ photocatalysts were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, UV-Vis diffuse reflectance spectroscopy (DRS), and photoelectric tests. XRD and XPS were used to ensure that the prepared photocatalysts were Cu/g-C₃N₄ and the valence state of Cu was in the form of Cu²⁺. Under visible light irradiation, the photocatalytic activity of Cu/g-C₃N₄ and pure g-C₃N₄ photocatalysts were investigated in terms of the degradation of RhB and CIP by comparing the amount of introduced copper ions. The experimental results showed that the degradation ability of Cu/g-C₃N₄ photocatalysts was stronger than that of pure g-C₃N₄. The N₂ adsorption-desorption isotherms of g-C₃N₄ and Cu/g-C₃N₄ demonstrated that the introduction of copper had little effect on the microstructure of g-C₃N₄. The small difference in specific surface area indicates that the enhanced photocatalytic activity may be attributed to the effective separation of photogenerated carriers. Therefore, the enhanced photocatalytic degradation of RhB and CIP over Cu/g-C₃N₄ may be due to the reduction of carrier recombination rate by copper. The photoelectric test showed that the incorporation of Cu²⁺ into g-C₃N₄ could reduce the electron-hole recombination rate of g-C₃N₄ and accelerate the separation of electron-hole pairs, thus enhancing the photocatalytic activity of Cu/g-C₃N₄. Free radical trapping experiments and electron spin resonance indicated that the synergistic effect of superoxide radicals (O₂^•−), hydroxyl radicals (•OH) and holes could increase the photocatalytic activity of Cu/g-C₃N₄ materials.     

Comparative study on ciprofloxacin removal in sulfur-mediated biological systems

The removal of ciprofloxacin(CIP) in sulfur-mediated bio processes,e.g.,sulfate-reducing bacteria(SRB)-mediated process and sulfur-oxidizing bacteria(SOB)-mediated process,was examined for the first time.The results showed that the SRB-mediated process had more efficient CIP removal than that in SOB-mediated process.Adsorption was the primary removal pathway of CIP in SRB-mediated process and SOB-mediated process with the specific adsorption removal rate of 131.4±1.1 μg/g-SS/d and30.1±1.4 μg/g-SS/d,respectively,at influent CIP concentration of 500 μg/L.In addition,extracellular polymeric substances(EPS) also played an important role on CIP migration and removal in both types of sludge.Further study was conducted to specify the different adsorption of CIP in these two sludge systems from the perspective of sludge properties.The results indicated that there are more potential adsorption sites exist on the SRB-mediated sludge for CIP adsorption than SOB-mediated sludge since the higher protein(PN) content and more kinds of aromatic amino acid substances in EPS,more negative zeta-potential and stronger and more numbers of functional groups in SRB-mediated sludge compared to SOB-mediated sludge.The findings of this study provide insights into the sludge properties affecting CIP removal in sulfur-mediated bioprocesses,and are of guiding significance to employ sulfur-mediated biological systems for treating CIP-containing wastewaters.     

Numerical modeling of wave interactions with coastal structures by a constrained interpolation profile/immersed boundary method

A high‐order difference method based multiphase model is proposed to simulate nonlinear interactions between water wave and submerged coastal structures. The model is based on the Navier–Stokes equations using a constrained interpolation profile (CIP) method for the flow solver, and employs an immersed boundary method (IBM) for the treatment of wave–structure interactions. A more accurate interface capturing scheme, the volume of fluid/weighed line interface calculation (VOF/WLIC) scheme, is adopted as the interface capturing method. A series of computations are performed to verify the application of the model for simulations of fluid interaction with various structures. These problems include flow over a fixed cylinder, water entry of a circular cylinder and solitary waves passing various submerged coastal structures. Computations are compared with the available analytical, experimental and other numerical results and good agreement is obtained. The results of this study demonstrate the accuracy and applications of the proposed model to simulate the nonlinear flow phenomena and capture the complex free surface flow. Copyright © 2015 John Wiley & Sons, Ltd.     

Comments on a CIP rule conundrum: Why I think I’m right

A question is raised as to how the CIP rules as related to a certain class of 2,1-benzothiazines should be applied. There are two subtle rules among the better known ones that seem to work in opposition, thus creating problems for assignments. It appears that one rule has been give precedence over the other at CAS and in programs like Chemdraw. Whether that is appropriate and true to the original rules is called into question.     

A fully conservative high‐order upwind multi‐moment method using moments in both upwind and downwind cells

We propose a fully conservative high‐order upwind multi‐moment method for the conservation equation. The proposed method is based on a third‐order polynomial interpolation function and semi‐Lagrangian formulation and is a variant of the constrained interpolation profile conservative semi‐Lagrangian scheme with third‐order polynomial function method. The third‐order interpolation function is constructed based on three constraints in the upwind cell (two boundary values and a cell average) and a constraint in the downwind cell (a cell center value). The proposed method shows fourth‐order accuracy in a benchmark problem (sine wave propagation). We also propose a less oscillatory formulation of the proposed method. The less oscillatory formulation can minimize numerical oscillations. These methods were validated through scalar transport problems, and compressible flow problems (shock tube and 2D explosion problems). Copyright © 2016 John Wiley & Sons, Ltd.     

液面冲击引起液滴飞溅问题的CIP方法数值模拟

利用自主研发的CIP-ZJU（Constrained Interpolation Profile Method in Zhejiang University）高精度数学模型研究强非线性自由表面流动问题.模型在直角坐标系统下建立,采用紧致插值曲线CIP方法作为流场的基本求解器,通过多相流的方式实现固-液-气耦合同步求解,采用平衡格式的VOF（VOF/WLIC：Volume of Fluid/Weighted LineInterface Calculation）自由面捕捉方法改进了原模型,利用浸入边界方法处理运动物体.利用改进的CIP模型开展了不同类型的物体冲击液面引起的液滴飞溅现象的数值模拟,重点分析液滴飞溅过程中的自由液面变形、作用荷载和物体位置等.通过数值结果与实验结果的比较验证模型的可靠性.结果表明：平衡格式的VOF自由面捕捉方法能更精确地重构自由面,本文的数学模型可精确预测强非线性自由表面流动问题.