Design and simulation of the micromixer with chaotic advection in twisted microchannels

Chaotic mixers with twisted microchannels were designed and simulated numerically in the present study. The phenomenon whereby a simple Eulerian velocity field may generate a chaotic response in the distribution of a Lagrangian marker is termed chaotic advection. Dynamic system theory indicates that chaotic particle motion can occur when a velocity field is either two-dimensional and time-dependent, or three-dimensional. In the present study, micromixers with three-dimensional structures of the twisted microchannel were designed in order to induce chaotic mixing. In addition to the basic T-mixer, three types of micromixers with inclined, oblique and wavelike microchannels were investigated. In the design of each twisted microchannel, the angle of the channels' bottoms alternates in each subsection. When the fluids enter the twisted microchannels, the flow sways around the varying structures within the microchannels. The designs of the twisted microchannels provide a third degree of freedom to the flow field in the microchannel. Therefore, chaotic regimes that lead to chaotic mixing may arise. The numerical results indicate that mixing occurs in the main channel and progressively larger mixing lengths are required as the Peclet number increased. The swaying of the flow in the twisted microchannel causes chaotic advection. Among the four micromixer designs, the micromixer with the inclined channel most improved mixing. Furthermore, using the inclined mixer with six subsections yielded optimum performance, decreasing the mixing length by up to 31% from that of the basic T-mixer.     

A fast passive and planar liquid sample micromixer

A novel microdevice for passively mixing liquid samples based on surface tension and a geometrical mixing chamber is presented. Due to the laminar flow regime on the microscale, mixing becomes difficult if not impossible. We present a micromixer where a constantly changing time dependent flow pattern inside a two sample liquid plug is created as the plug simply passes through the planar mixer chamber. The device requires no actuation during mixing and is fabricated using a single etch process. The effective mixing of two coloured liquid samples is demonstrated.     

Promoting the photoanode efficiency for water splitting by combining hematite and molecular Ru catalysts

Most implementations of the photoanode for water splitting are based on semiconductors and inorganic catalysts, wherein the surface defect and the grain boundary of inorganic materials have been a major barrier hindering the charge transfer between the light absorber and the catalyst. Here we report a new type of photoanode for water splitting, featuring the combination of α-Fe₂O₃ and molecular Ru catalysts. Fabricated by self-assembly, the semiconductor/molecule interface is not only efficient for the light-induced charge separation but also highly catalytic toward the water oxidation reaction. This work opens a new avenue for improving the efficiency of the solar-to-fuel conversion.     

A rationally designed two-dimensional MoSe2/Ti2CO2 heterojunction for photocatalytic overall water splitting: simultaneously suppressing electron–hole recombination and photocorrosion

Electron–hole recombination and photocorrosion are two challenges that seriously limit the application of two-dimensional (2D) transition metal dichalcogenides (TMDs) for photocatalytic water splitting. In this work, we propose a 2D van der Waals MoSe₂/Ti₂CO₂ heterojunction that features promising resistance to both electron–hole recombination and photocorrosion existing in TMDs. By means of first-principles calculations, the MoSe₂/Ti₂CO₂ heterojunction is demonstrated to be a direct Z-scheme photocatalyst for overall water splitting with MoSe₂ and Ti₂CO₂ serving as photocatalysts for hydrogen and oxygen evolution reactions, respectively, which is beneficial to electron–hole separation. The ultrafast migration of photo-generated holes from MoSe₂ to Ti₂CO₂ as well as the anti-photocorrosion ability of Ti₂CO₂ are responsible for photocatalytic stability. This heterojunction is experimentally reachable and exhibits a high solar-to-hydrogen efficiency of 12%. The strategy proposed here paves the way for developing 2D photocatalysts for water splitting with high performance and stability in experiments.

The two challenges of electron–hole recombination and photocorrosion for two-dimensional transition metal dichalcogenides in the application of photocatalytic water splitting are simultaneously suppressed by rational design of heterojunctions.     

A novel 3D Tesla valve micromixer for efficient mixing and chitosan nanoparticle production

Current three-dimensional micromixers for continuous flow reactions and nanoparticle synthesis are complex in structure and difficult to fabricate. This paper investigates the design, fabrication, and characterization of a novel micromixer that uses a simple spatial Tesla valve design to achieve efficient mixing of multiple solutions. The flow characteristics and mixing efficiencies of our Tesla valve micromixer are investigated using a combination of numerical simulations and experiments. The results show that in a wide range of flow rates, viscoelastic solutions with different concentrations can be well mixed in our micromixer. Finally, experiments on the synthesis of chitosan nanoparticles are conducted to verify the practicability of our micromixer. Compared with nanoparticles prepared by conventional magnetic stirring, the size of nanoparticles prepared by micromixing is smaller and the distribution is more uniform. Therefore, our Tesla valve micromixer has significant advantages and implications for mixing chemical and biological reactions.     

光催化制氢中助催化剂表面氢氧复合反应的抑制

在光催化分解水产氢的过程中,Pt等助催化剂在催化产生氢的同时也会诱导催化氢气和氧气重新复合为水的逆反应,严重降低了悬浮体系光催化全分解水产氢的效率。本文综述了近年来在逆反应抑制方面的研究进展,总结和对比分析了各种抑制逆反应策略的特点,并对这些方法的应用于悬浮体系光催化全分解水制氢的前景进行了展望。     

On the determination of molecular hyperpolarizabilities by combining data from the Kerr effect and from electrically induced NMR line splitting

It is shown that in the calculation of the contribution to the Kerr effect in polar liquids by the hyperpolarizabilities, the effective field should be taken equal to the sum of the Lorentz field and the reaction field. Calculation of first hyperpolarizabilities on this basis by combining values of the Kerr constant with values of the alignment from electrically induced line splitting in NMR, yields for strongly polar molecules (μ ≈ 4 D) values that are smaller by an order of magnitude than those from previous calculations on the same effects, but that compare more favourably with other data.     

镍铂修饰n型硅电极光电解析氧

本文以n/n^+-Si半导体为基底, 通过碱溶液刻蚀处理和Ni/Pt双层金属膜表面修饰后作为光阳极, 用于1.0mol·dm^-^3KOH溶液中光助电解水析氧。在恒电势1.0V(相对HgO/Hg电极)和90mW·cm^-^2光照射下, 最佳电极的析氧电流达到65.2mA·cm^-^2, 稳定性实验表明, 连续光照不超过200小时, 光电极具有良好的抗腐蚀性。对电极表面进行了X-光电子能谱(ESCA)分析。     

Thermochemical splitting of CO2 on perovskites for CO production: A review

Energy supply dominated by fossil energy has been and remains the main cause of carbon dioxide emissions,the major greenhouse gas leading to the current grave climate change challenges.Many technical pathways have been proposed to address the challenges.Carbon capture and utilization(CCU) represents one of the approaches and thermochemical CO₂ splitting driven by thermal energy is a subset of the CCU,which converts the captured CO₂ into CO and makes it possible to achieve c...     

中低压条件下蛇纹石直接矿物碳酸化隔离CO2的实验研究

对中低压条件下蛇纹石CO₂直接矿物碳酸化隔离进行了一系列实验研究,考察了反应温度、反应压力、缓冲剂的加入、预先热处理、颗粒粒径及不同气氛等因素对蛇纹石矿物碳酸化吸收二氧化碳效率的影响。结果表明,在中低压条件下,蛇纹石可以通过液相直接矿物碳酸化对模拟烟气中的CO₂进行直接固定;随反应温度的升高、反应压力的增大,矿物碳酸化效率随之增加;对蛇纹石进行预先热处理或者在反应体系中引入NaHCO₃缓冲剂以及减小蛇纹石矿石颗粒粒径,可以有效地提高蛇纹石矿物碳酸化隔离二氧化碳的效率。在纯CO₂、t=150℃、p=4 MPa、颗粒粒径30 μm的条件下得到最高矿物碳酸化效率为47.7%;在模拟烟气、t=150℃、p=4 MPa、颗粒粒径30 μm的条件下最高矿物碳酸化效率也可以达到36.3%。     

A scalable divide-and-conquer algorithm combining coarse and fine-grain parallelization

We describe an efficient algorithm for carrying out a “divide-and-conquer” fit of a molecule's electronic density on massively parallel computers. Near linear speedups are achieved with up to 48 processors on a Cray T3E, and our results indicate that similar efficiencies could be attained on an even greater number of processors. To achieve optimum efficiency, the algorithm combines coarse and fine-grain parallelization and adapts itself to the existing ratio of processors to subsystems. The subsystems employed in our divide-and-conquer approach can also be made smaller or bigger, depending on the number of processors available. This allows us to further reduce the wallclock time and improve the method's overall efficiency. The strategies implemented in this paper can be extended to any other divide-and-conquer method used within an ab initio, density functional, or semi-empirical quantum mechanical program. Received: 15 September 1997 / Accepted: 21 January 1998     

A photocatalytic water splitting device for separate hydrogen and oxygen evolution

A two-compartment Plexiglas cell has been set up and tested for separate hydrogen and oxygen production from photocatalytic water splitting on a thin TiO2 layer deposited by magnetron sputtering on a flat Ti electrode inserted between the two cell compartments.     

Transport and recombination dynamics studies of polymer/fullerene based solar cells

We have studied the electron/hole transport and recombination dynamics in blends of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene], (MDMO-PPV) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) at room temperature, as a function of laser excitation density and PCBM concentration. The experimental results of these studies indicate the important role played by hole-trap states in MDMO-PPV. Electron and hole transport are not balanced within the blend. PCBM is a less disordered material than MDMO-PPV and electron transport dominates the response of the solar cell device.     

A soluble hybrid material combining carbon nanohorns and C60

A soluble hybrid nanomaterial that combines fullerenes and carbon nanohorns (CNHs) has been prepared and fully characterized. Electrochemical investigations revealed that the CNHs modify the electron accepting ability of C(60) in the hybrid material.     

A novel apparatus combining polymer extrusion processing and x-ray scattering

A novel apparatus was designed and constructed combining polymer extrusion processing and x-ray scattering. It allows direct, real time monitoring of structure and temperature development in polymer material during extrusion. The apparatus involves a vertical industrial extruder equipped with a four-roll stretching device to mimic the processing environments of uni-axially oriented films or sheets, a simultaneous small and wide angle x-ray scattering system and an infrared thermometer as detection unit. The charging barrel of the extruder and the stretching device can be moved upward and downward precisely. By moving the sample along the center line, structure and temperature development as a function of position can be obtained. The performance of the apparatus was verified by a test experiment, which allows us to establish the relationship between processing parameters and evolution of structure with different length scales, and may lead to a better understanding of the physics in polymer processing.     

A sensitive immunosorbent bio-barcode assay combining PCR with icELISA for detection of gonyautoxin 2/3

In the current study, we developed a nanosphere bio-barcode technology to detect trace gonyautoxin 2/3 (GTX 2/3). GTX 2/3-glucose oxidase (GOX) conjugates were first prepared as the coating antigen in a periodate reaction. Subsequently, gold nanoparticles (NP) dual-labeled with anti-GTX 2/3 monoclonal antibodies (Mab) and DNA oligonucleotides were synthesized via a one-step preparation method. Combining PCR with indirect competitive ELISA (icELISA), a novel immunosorbent bio-barcode assay was established utilizing the Mab-NP-dsDNA complex to convert enzymatic signals to DNA signals. Importantly, the limit of detection of the method was lower than 0.74 μg mL⁻¹. Thus, the immunosorbent bio-barcode assay is a rapid and high-throughput screening tool to detect GTX 2/3 in aquatic products.     

Singlet/triplet exciton dissociation and charge recombination in donor-acceptor ThQs-C60/PDIxCN2 complexes

The donor-acceptor interface plays a critically important role in determining the power conversion efficiency of organic solar cells via controlling charge separation (CS) and recombination (CR) processes. Here, we combine the electronic structure calculations with electron transfer rate theory to clarify the CS and CR processes in ThQs-C₆₀ /PDIxCN₂ donor-acceptor complexes. The results reveal that in ThQs-PDIxCN₂ the CS comes from both the dissociations of photo-induced singlet exciton and singlet fission-induced triplet exciton with a high efficiency, whereas in ThQs-C₆₀ only the singlet exciton dissociation can take place because the triplet exciton lies below the charge-transfer exciton. However, very high CR rates in ThQs-PDIxCN₂ obliterate the benefit of fast CS, inversely leading to the ThQ-C₆₀ complex with a better cell efficiency. The present results are consistent with experimental observation and may furnish a possible patten to improve the overall conversion efficiency. © 2018 Wiley Periodicals, Inc.     

Cu负载TiO_2及其CdS复合物的光解水性能

光解水制氢技术是解决能源环境问题的重要手段.本研究通过负载非贵金属Cu于TiO_2表面,提高光催化活性,并与CdS进行复合从而获得高活性的可见光催化材料.利用X射线衍射、紫外-可见漫反射和高分辨透射电镜手段表征了Cu的物种、催化材料的光吸收性能及复合物的形貌和复合状态.活性测试显示Cu的负载可以显著提高TiO_2的光催化活性,当Cu负载量为2%(质量分数)时光催化活性产氢最高,为未负载的29倍.Cu/TiO_2与CdS复合后,CdS的电子可以快速的传递到TiO_2表面的Cu上,从而达到电子和空穴的分离,提高了CdS在可见光下的产氢活性.     

A charge-transfer challenge: combining fullerenes and metalloporphyrins in aqueous environments

A series of truly water-soluble C(60)/porphyrin electron donor-acceptor conjugates has been synthesized to serve as powerful mimics of photosynthetic reaction centers. To this end, the overall water-solubility of the conjugates was achieved by adding hydrophilic dendrimers of different generations to the porphyrin moiety. An important variable is the metal center of the porphyrin; we examined zinc(II), copper(II), cobalt(II), nickel(II), iron(III), and manganese(III). The first insights into electronic communication between the electron donors and the electron acceptors came from electrochemical assays, which clearly indicate that the redox processes centered either on C(60) or the porphyrins are mutually affected. Absorption measurements, however, revealed that the electronic communication in terms of, for example, charge-transfer features, remains spectroscopically invisible. The polar environment that water provides is likely to be a cause of the lack of detection. Despite this, transient absorption measurements confirm that intramolecular charge separation processes in the excited state lead to rapid deactivation of the excited states and, in turn, afford the formation of radical ion pair states in all of the investigated cases. Most importantly, the lifetimes of the radical ion pairs were found to depend strongly on several aspects. The nature of the coordinated metal center and the type of dendrimer have a profound impact on the lifetime. It has been revealed that the nature/electronic configuration of the metal centers is decisive in powering a charge recombination that either reinstates the ground state or any given multiplet excited state. Conversely, the equilibrium of two opposing forces in the dendrimers, that is, the interactions between their hydrophilic regions and the solvent and the electronic communication between their hydrophobic regions and the porphyrin and/or fullerene, is the key to tuning the lifetimes.