ZIF-8衍生的具有可控氧空位的ZnO对光催化去除NO的增强及毒性NO2形成的抑制

氧化锌作为一种半导体材料,具有合适的能带结构位置,高催化效率,低成本和环境可持续性,因而广泛用于光催化领域.然而,由于氧化锌的宽带隙,可见光吸收能力差以及光生电子-空穴对的快速复合,极大地影响了其光催化效率.通过引入氧空位调控光催化剂的结构被证明是一种可以改善光生载流子的分离,从而提高光催化性能的有效方法.本文以ZIF-8为前驱体,采用两步煅烧法合成了具有不同浓度氧空位分布的ZnO纳米光催化剂,通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、紫外-可见漫反射光谱(UV-Vis DRS)、X射线光电子能谱(XPS)、电子顺磁共振(EPR)、荧光光谱仪(PL)等手段系统地分析了合成的光催化剂的理化性质,并评价了它们在可见光下光催化氧化去除NO反应性能.EPR结果表明,样品中氧空位的浓度取决于温度处理的过程.通过两步煅烧法得到氧化锌中氧空位的含量高于一步直接煅烧法所得的样品.此外,随着煅烧温度升高,合成的氧化锌晶格越完好,其氧空位含量越少.UV-Vis DRS结果表明,两步煅烧法合成的ZnO与商业的ZnO及一步法直接煅烧合成的ZnO相比,其吸光范围从紫外光拓展到了可见光,表现出了更加优异的吸光性能.光催化反应结果表明,与商业氧化锌和一步直接煅烧法所得样品相比,两步煅烧法合成的样品表现出了更优异的光催化去除NO性能,并抑制了中间产物毒性NO2的产生,促进了NO的深度氧化.具体反应路径为:在光照过程中,光生电子很容易被氧空位俘获,与O2反应产生更多的超氧自由基(·O2^-),从而将NO氧化成最终的产物硝酸盐.尤其有趣的是,先在350 ℃煅烧2小时再400℃煅烧1小时的两步法样品Z 350-400的NO去除效率分别比一步法样品Z 400(400℃煅烧)和商用ZnO高出1.5和4.6倍.这表明以MOF材料衍生的具有适当量氧空位的金属氧化物为一种高效去除NO的光催化剂具有很好的应用前景.     

加强实验教学环境内涵建设 提高环境育人质量

在实验室里的实验教学过程涉及到教书育人、管理育人、服务育人和环境育人。一个良好的实验环境不仅能够对学生起到潜移默化的教育作用,而且对教书育人、管理育人和服务育人工作的开展和实施也能起到推动和促进作用。本文主要介绍厦门大学化学国家级实验教学示范中心"以学生为中心",在强化实验教学环境内涵建设、提高实验环境育人质量方面的一些做法和体会,以期更好地为实验教学"思政"提供可复制、可推广的建设方案。     

“元素化学实验”中的“异常”现象(一)--Mn元素化学实验中的“异常”现象及其探析

大一学生在“元素化学实验”教学过程中,对反应条件如温度、催化剂、酸度、浓度或试剂用量等因素的影响考虑不周,可能出现某些实验现象和预想的或理论分析的结果不一致的“异常”现象。本文就学生在Mn元素化学实验过程中遇到的一些“异常”现象进行分析和总结,借助生动直观的演示实验,引导学生探究“异常”现象产生的可能原因和直观认识反应条件对反应结果的影响,培养学生的观察、分析、判断、归纳、推理和解决实际问题的能力。     

钯-膦-酸体系催化烯烃氢酯基化反应研究进展

烯烃氢酯基化反应是羰基合成领域的重要分支之一,长期以来一直备受关注。目前已发展了钯基、铑基、钴基、钌基等众多催化体系,其中钯-膦-酸催化体系因具有反应条件温和、底物普适性良好、催化性能优异等优点而得到最广泛、最深入的研究。因此,我们对均相、非均相的钯-膦-酸催化体系在烯烃氢酯基化反应中的研究应用进行了简要综述,并对催化机理、催化剂组成和性能进行讨论,最后指出稳定性高、可回收性好的非均相钯-膦-酸催化体系将是该领域的研究重点。     

基于半刚性配体的柔性超微孔金属有机骨架的合成及其尺度选择性二氧化碳捕获

基于半刚性的配体3′,5′-di(1H-1,2,4-triazol-1-yl)-(1,1′-biphenyl)-3,5-dicarboxylic acid (H₂DTBDA)和硝酸钴制备了一个柔性超微孔的金属有机骨架{[Co(DTBDA)]·4H₂O}_n (FJI-H35),并对该材料的结构进行了系统的表征。FJI-H35活化以后可以发生自适应的结构转变,使得孔径从0.43 nm收缩到0.37 nm。气体吸附测试表明FJI-H35可以从氮气和甲烷中选择性捕获二氧化碳,具有很高的吸附选择性和相对低的吸附焓。突破实验进一步证实FJI-H35可以从二氧化碳/氮气(15∶85,V/V)和二氧化碳/甲烷(50∶50,V/V)混合气中高效选择性捕获二氧化碳。     

Imaging Photodissociation Dynamics of MgO at 193 nm

In this work, we used time-sliced ion velocity imaging to study the photodissociation dynamics of MgO at \mbox{193 nm}. Three dissociation pathways are found through the speed and angular distributions of magnesium. One pathway is the one-photon excitation of MgO(X\begin{document}$^1\Sigma^+$\end{document}) to MgO(G\begin{document}$^1\Pi$\end{document}) followed by spin-orbit coupling between the G\begin{document}$^1\Pi$\end{document}, 3\begin{document}$^3\Pi$\end{document} and 1\begin{document}$^5\Pi$\end{document} states, and finally dissociated to the Mg(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{u}$\end{document})+O(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{g}$\end{document}) along the 1\begin{document}$^5\Pi$\end{document} surface. The other two pathways are one-photon absorption of MgO(A\begin{document}$^1\Pi$\end{document}) state to MgO(G\begin{document}$^1\Pi$\end{document}) and MgO(4\begin{document}$^1\Pi$\end{document}) state to dissociate into Mg(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{u}$\end{document})+O(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{g}$\end{document}) and Mg(\begin{document}$^1$\end{document}S\begin{document}$_\textrm{g}$\end{document})+O(\begin{document}$^1$\end{document}S\begin{document}$_\textrm{g}$\end{document}), respectively. The anisotropy parameters of the dissociation pathways are related to the lifetime of the vibrational energy levels and the coupling of rotational and vibronic spin-orbit states. The total kinetic energy analysis gives \begin{document}$D_0$\end{document}(Mg\begin{document}$-$\end{document}O)=21645\begin{document}$\pm$\end{document}50 cm\begin{document}$^{-1}$\end{document}.     

Fast Fabrication and Judgement of Tip-Enhanced Raman Spectroscopy-Active Tips

The quality of the scanning tip is crucial for tip-enhanced Raman spectroscopy (TERS) experiments towards large signal enhancement and high spatial resolution. In this work, we report a controllable fabrication method to prepare TERS-active tips by modifying the tip apex at the atomic scale, and propose two important criteria to in-situ judge the tip's TERS activity for tip-enhanced Raman measurements. One criterion is based on the downshift of the first image potential state to monitor the coupling between the far-field incident laser and near-field plasmon; the other is based on the appearance of the low-wavenumber Raman peaks associated with an atomistic protrusion at the tip apex to judge the coupling efficiency of emissions from the near field to the far field. This work provides an effective method to quickly fabricate and judge TERS-active tips before real TERS experiments on target molecules and other materials, which is believed to be instrumental for the development of TERS and other tip-enhanced spectroscopic techniques.     

一步法高通量可控制备生物相容水/水微囊及其响应释放

生物相容水/水微囊在药物递送、 医学治疗等领域具有重要应用. 本文通过设计同轴微流控器件, 结合数值模拟优化和流动阻力分析, 实现一步法高通量可控制备大小均匀、 尺寸可控、 壁厚可调、 生物相容的水/水微囊. 采用实验研究和数值模拟相结合的方式, 研究了微流控器件结构、 内相流速、 外相流速、 外相/空气界面张力、 内相/外相界面张力、 内相黏度和外相黏度等参数对水/水微囊直径和壁厚的调控规律. 通过微通道流动阻力分析, 设计多通道平行放大微流控器件, 实现尺寸均匀可控水/水微囊的高通量制备. 验证了生物相容水/水微囊作为活性物质的理想载体, 可以通过改变pH或溶解囊壁释放载体, 进而实现活性物质的pH响应释放, 为其实际应用奠定了基础.     

Influence of Atomistic Protrusion on the Substrate on Molecular Luminescence in Tunnel Junctions

Scanning tunneling microscope (STM) induced luminescence can be used to study various optoelectronic phenomena of single molecules and to understand the fundamental photophysical mechanisms involved. To clearly observe the molecule-specific luminescence, it is important to improve the quantum efficiency of molecules in the metallic nanocavity. In this work, we investigate theoretically the influence of an atomic-scale protrusion on the substrate on the emission properties of a point dipole oriented parallel to the substrate in a silver plasmonic nanocavity by electromagnetic simulations. We find that an atomic-scale protrusion on the substrate can strongly enhance the quantum efficiency of a horizontal dipole emitter, similar to the situation with a protrusion at the tip apex. We also consider a double-protrusion junction geometry in which there is an atomic-scale protrusion on both the tip and the substrate, and find that this geometry does provide significantly enhanced emission compared with the protrusion-free situation, but does not appear to improve the quantum efficiency compared to the mono-protrusion situation either at the tip apex or on the substrate. These results are believed to be instructive for future STM induced electroluminescence and photoluminescence studies on single molecules.     

Chemoselective hydrogenolysis of tetrahydrofurfuryl alcohol to 1,5-pentanediol over Ir-MoOx/Si02 catalyst

In this work, MoOx promoted Ir/SiO2 catalysts were prepared and used for the selective hydrogenolysis of tetrahydrofurfuryl alcohol （THFA） to 1,5-pentanediol in a continuous flow reactor. The effects of different noble metals （Ir, Pt, Pd, Ru, Rh）, supports and Ir contents were screened. Among the investigated catalysts, 4 wt%Ir-MoOx/SiO2 with a Mo/Ir atomic ratio of 0.13 exhibited the best catalytic performance. The synergy between Ix particles and the partially reduced isolated MoOx species attached on them is essential for the excellent catalytic performance of Ix-MoOx/SiO2. The catalyst exhibited a better hydrogenolysis efficiency of THFA with the selectivity of 1,5-pentanediol of 65%-74% at a conversion of THFA of 70%-75% when the initial THFA concentration is ranging from 20 wt% and 40 wt%. And higher system pressure was also in favor of the conversion of THFA. During a stability test, the conversion of THFA and 1,5-pentanediol yield over Ix-MoOz/SiO2 decreased with reaction time, which can be explained by the leaching of Mo species during the reaction.