H2SO4-H2O中硝酸铜对脱硫石膏晶须生长的影响

以处理后的脱硫石膏为原料,在H₂SO₄-H₂O体系中以Cu(NO₃)₂为晶形控制剂采用水热法制备脱硫石膏晶须,探讨了Cu(NO₃)₂对脱硫石膏晶须生长的影响机理。结果表明:Cu(NO₃)₂对脱硫石膏有明显促溶作用,其中Cu²⁺可减小溶液中各离子的活度系数,使溶液中的Ca²⁺浓度增大。NO^-₃通过静电作用在Ca²⁺周围聚集并对SO^2-₄产生屏蔽作用,导致脱硫石膏继续溶解并使Ca²⁺和SO^2-₄的浓度处于相对稳定状态,有利于半水脱硫石膏晶体的形核与生长。此外,Cu²⁺还可在晶须的生长过程中选择性吸附在晶须表面,生成CuSO₄,促进了脱硫石膏的结晶生长,最终在Cu(NO₃)₂用量为2.0%(质量分数)时制备的脱硫石膏晶须长径比约为73。     

CRISPR-Cas12a System for Biosensing and Gene Regulation

Clustered regularly interspaced short palindromic repeats (CRISPR) is a promising technology in the biological world. As one of the CRISPR-associated (Cas) proteins, Cas12a is an RNA-guided nuclease in the type V CRISPR-Cas system, which has been a robust tool for gene editing. In addition, due to the discovery of target-binding-induced indiscriminate single-stranded DNase activity of Cas12a, CRISPR-Cas12a also exhibits great promise in biosensing. This minireview not only gives a brief introduction to the mechanism of CRISPR-Cas12a but also highlights the recent developments and applications in biosensing and gene regulation. Finally, future prospects of the CRISPR-Cas12a system are also discussed. We expect this minireview will inspire innovative work on the CRISPR-Cas12a system by making full use of its features and advantages.     

MCNOs/CdS双效光催化剂的制备及其性能研究

水热合成法制备了不同磁性纳米洋葱碳(MCNOs)负载量(0%、1%、3%、5%)的MCNOs/CdS光催化剂。并通过X射线衍射分析(XRD)、扫描电子显微镜(SEM)、傅里叶红外光谱(FT-IR)、X射线光电子能谱(XPS)、紫外可见光光谱(UV-Vis)、磁滞回线测定仪(VSM)对其进行表征,探究了MCNOs负载比例对催化剂在可见光下降解RhB性能及机理的影响。结果表明,MCNOs能有效提高CdS的光催化效果,复合3%MCNOs后降解率为96%,与纯CdS相比降解率提高了30%,磁性分析表明,其具有良好的顺磁性并能实现催化剂的有效回收。MCNOs/CdS在可见光下催化降解RhB的一级反应动力学直线有较好的拟合度,表明制备的催化剂有较好的催化活性。     

埋藏哈密翼龙化石的雅丹风化的光谱分析——以大海道2号水源地雅丹为例

新疆哈密地区翼龙化石具有极高的科学研究价值。哈密翼龙动物群主要埋藏在早白垩世湖相地层形成的雅丹中，富集在风暴沉积层。化石一旦暴露地表，就会发生不同程度的自然风化破碎，尤其是见水或受潮后风化更为严重。哈密大海道2号水源地附近的雅丹底部由于地下水和间歇性地表水的作用，发生了严重的盐碱析出导致的强烈风化现象，造成雅丹下部剥落侵蚀和上层雅丹重力坍塌，从下到上不同地层的风化程度差异较大，底部地层的风化最为剧烈。对大海道雅丹地层剖面取样，利用多种分析方法确定每一层的岩性和可溶盐种类，从微观上揭示雅丹风化的机理。偏光显微观察和X射线衍射（XRD）结果显示每一层都含有石英、长石、方解石和粘土矿物，矿物组成无较大差异，但粘土含量差别较大。精确的可溶盐种类鉴别方法，包括离子色谱（IC）确定出样品中可溶盐离子含量及种类，拉曼光谱（Raman）和傅里叶变换红外光谱（FTIR）鉴别出样品中的硝酸盐和硫酸盐，扫描电子显微镜能谱仪（SEM-EDS）鉴别出氯盐、硝酸盐和硫酸盐。结果显示雅丹各风化层中最底层可溶盐主要是NaCl和Na₂SO₄，第二层是NaCl和CaCl₂，第三层是NaCl，盐种类/含量的差别是此处雅丹从下到上发生不同风化现象的重要原因。结合大海道雅丹所处的气候地理环境（极干旱高盐碱地区、水源地附近），探讨水盐活动规律并关联风化表现，分析该处雅丹风化原因，内因是每层沉积岩的岩性不同，外因是水和盐（NaCl，Na₂SO₄，CaCl₂）的共同作用下，强烈的水盐活动造成了埋藏有哈密翼龙化石的雅丹严重化学风化。这一风化机理也可很好地解释哈密翼龙化石及其围岩层受潮后的强烈风化破碎现象。     

Key Role of a-Top CO on Terrace Sites of Metallic Pd Clusters for CO Oxidation

Pd-based catalysts are the most widely used for CO oxidation because of their outstanding catalytic activity and thermal stability. However, fundamental understanding of the detailed catalytic processes occurring on Pd-based catalysts under realistic conditions is still lacking. In this study, we investigated CO oxidation on metallic Pd clusters supported on Al₂O₃ and SiO₂. High-angle annular dark-field scanning transmission electron microscopy revealed the formation of similar-sized Pd clusters on Al₂O₃ and SiO₂. In contrast, CO chemisorption analysis indicated a gradual change in the dispersion of Pd (from 0.79 to 0.2) on Pd/Al₂O₃ and a marginal change in the dispersion (from 0.4 to 0.24) on Pd/SiO₂ as the Pd loading increased from 0.27 to 5.5 wt %; these changes were attributed to differences in the metal-support interactions. Diffuse reflectance infrared Fourier-transform spectroscopy revealed that fewer a-top CO species were present in Pd supported on Al₂O₃ than those in Pd supported on SiO₂, which is related to the morphological differences in the metallic Pd clusters on these two supports. Despite the different dispersion profiles and surface characteristics of Pd, O₂ titration demonstrated that linearly bound CO (with an infrared signal at 2090 cm⁻¹) reacted first with oxygen in the case of CO-saturated Pd on Al₂O₃ and SiO₂, which suggests that a-top CO on the terrace site plays an important role in CO oxidation. The experimental observations were corroborated by periodic density functional calculations, which confirmed that CO oxidation on the (111) terrace sites is most plausible, both kinetically and thermodynamically, compared to that on the edge or corner sites. This study will deepen the fundamental understanding of the effect of Pd clusters on CO oxidation under reaction conditions.     

Experimental study on synchrotron radiation photoionization of secondary organic aerosol derived from styrene ozonolysis

Secondary organic aerosol (SOA) produced by ozonolysis of styrene and other alkene compounds is a major part of fine particles in urban atmospheres. The atmospheric ozonolysis process of styrene is simulated in a smog chamber, and the formed SOA particles are detected on-line by a synchronous radiation vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) in this study. Through molecular ion peaks in the photonionization mass spectra of SOA and the corresponding photoionization efficiency curve, combined with off-line measurement verification of ultraviolet visible and infrared absorption spectra, it is determined that formaldehyde, formic acid, benzene, phenol, benzaldehyde, and benzoic acid are the main constituents of styrene SOA. These provide new information for studying the atmospheric ozonolysis oxidation mechanism of styrene. VUV-PIMS can get over complicated sample preparation procedures, secondary pollution, and other shortcomings of the off-line method and is a useful instrument to measure constituents and unveil the formation process of SOA particles.     

三核过渡金属配合物在催化反应中的研究进展

多核过渡金属配合物作为一类广泛应用的均相催化剂,其设计灵感往往来自天然酶的多金属活性位点所发挥的重要作用.目前,三核金属配合物作为活化小分子的多金属催化剂受到了广泛的关注.为深入理解三核过渡金属配合物在催化反应中作用特点,对近年报道的代表性三核过渡金属配合物按金属中心进行分类,并对配体环境形成特点及催化应用进行综述.从金属中心出发,讨论了三核过渡金属配合物的几何结构和电子特征;从配体环境出发,总结了关联三个独立的金属位点的配位环境特征;在催化应用方面,重点综述了三核过渡金属配合物在涉及特定化学键活化反应的催化作用机制,最后对三核过渡金属配合物的催化应用前景进行展望.     

Metadynamics simulations of R–NHC reductive elimination in intermediate palladium complexes of cross-coupling and Mizoroki–Heck reactions

Exploring the free energy surface of the R–NHC coupling reaction in the key intermediates of the Mizoroki–Heck and cross-coupling catalytic cycles has been conducted by the methods of biased and unbiased molecular dynamics. Molecular dynamics simulations were carried out both in vacuum and in a polar solvent, with the following main observations on the influence of the media: (1) the solvent prevents the dissociation of the solvate ligand, so the R–NHC coupling proceeds in a four-coordination complex (rather than in a three-coordination one, as in the case of a gas-phase reaction); (2) in the condensed phase, the potential barrier of the reaction is significantly higher compared to the same process in vacuum (17.7 vs. 21.8 kcal mol^-1); (3) polar solvent stabilizes the R–NHC coupling product. The reaction in a polar medium is exergonic (ΔG = −3.9 kcal mol^-1), in contrast to the in vacuum modeling, where the process is endergonic (ΔG = 0.4 kcal mol^-1).     

土壤胶体迁移行为及其介导污染物迁移模拟与研究进展

本文综述了土壤多孔介质中胶体迁移的释放与沉积机制、影响胶体迁移的多种因素以及土壤中胶体与各种污染物的协同迁移作用,总结了模拟胶体迁移的数学模型以及计算机软件的应用。研究表明,胶体在土壤中的迁移主要受应变、附着、薄膜应变等迁移机制的影响,多孔介质的性质、流体的性质以及胶体自身的性质也会影响胶体的迁移。此外,胶体能有效吸附地下水多孔介质中的有机或无机污染物,并对其在地下环境中的迁移产生显著影响。目前已有许多学者通过数学模型来模拟胶体在土壤中的迁移过程,而计算机技术的进步也将促进更加先进的软件模型应用到胶体迁移的模拟中。     

高比能锂离子电池层状富锂正极材料改性策略研究进展

层状富锂材料具有超过250 mAh∙g⁻¹的高可逆比容量,被认为是下一代高比能锂离子电池最具商业化前景的正极材料之一。然而,层状富锂材料在实际应用之前仍需解决诸多挑战,如高电压氧释放、层状到岩盐相的结构变化、过渡金属离子迁移等结构劣化,并由此带来了较低的初始库伦效率、电压/容量的衰减以及循环寿命的不足。针对以上问题,进行层状富锂材料改性无疑是一种行之有效的方法。本综述全面介绍了层状富锂材料的结构、组分以及电化学性能,在此基础上对材料改性策略进行了系统阐述,详细介绍了体相掺杂、表面包覆、缺陷设计、离子交换和微结构调控等一系列改性策略的现状以及发展趋势,最终提出了高容量和长循环层状富锂材料和高比能锂离子电池的设计思路。