Density Functional Theoretical Study on SERS Chemical Enhancement Mechanism of 4-Mercaptopyridine Adsorbed on Silver

基于密度泛函理论计算和拉曼光谱理论分析,我们研究了对巯基吡啶(4MPY)分子的拉曼光谱和其在银上的表面增强拉曼光谱(SERS),并进一步探讨了S; ERS与界面吸附结构、异构化、质子化和氢键作用以及低能激发态的关系。首先,我们对两种分子异构体的相对稳定性和拉曼光谱进行了理论分析。在此基础上,; 进而研究了该分子与不同银簇作用时的拉曼光谱,结果表明,4MPY以巯基硫与银簇作用形成强的Ag-; S键,导致拉曼光谱的线型不依赖于所选银簇的大小。接着我们考虑了吡啶氮端作用的两种情况。(1)当4MPY-银簇复合物同时以吡啶氮与水簇或水合质子簇; 形成氢键时,结果表明吡啶环的部分振动频率随氢键和质子化发生蓝移。(2)当考虑吡啶氮与银簇作用时,吡啶环三角畸变振动发生蓝移。上述情况不仅解释了实; 验观测的振动频率变化,而且表明了化学环境改变对相对拉曼强度的影响。最后,我们计算了当对巯基吡啶分子以单端或双端与银簇作用,在考虑激发光与低能激发; 态的能量匹配时,拉曼光谱强度与低能激发态的关系。计算结果表明,在双端吸附构型下,与吡啶氮成键的银簇受激发产生电荷转移态,不仅导致吡啶环v_(12; )、 v_1和v_(8a)振动的拉曼信号增强,而且选择性地增强吡啶环C-H面内对称弯曲振动v_(9a)的拉曼信号。Surface-enhanced Raman spectroscopy (SERS) is one of the most powerful techniques for obtaining fingerprint information on molecules adsorbed on coinage metal surfaces. Its detection sensitivity has reached the single-molecule level. On the basis of density functional theoretical (DFT) calculations and Raman scattering theory, we investigated the normal Raman spectra of two isomers and surface-enhanced Raman scattering (SERS) spectra of 4-mercaptopyridine (4MPY) adsorbed on silver. The results aided us in uncovering the relationships between normal Raman spectra and SERS spectra and adsorption configuration, tautomerization, protonation, and hydrogen bonding interactions as well as low-lying excited states. First, we compared the relative stability and normal Raman spectra of two isomers of 4MPY in the gas phase and aqueous solution with a solvent model similar to the solvation model of density (SMD). We then studied the Raman spectra of 4MPY interacting with silver clusters. Our results indicate that the Raman spectra were not dependent on the size of the silver clusters, owing to the formation of strong Ag-S bonds. We also considered two cases of N-end interaction in the 4MPY-Ag-5 complex. (1) For the hydrogen bond interaction between the nitrogen in 4MPY and water clusters or hydrated proton clusters, the theoretical results indicated that the vibrational frequencies of the pyridine ring increase. (2) For the interaction of the 4MPY-Ag-5 complex with a silver cluster Ag-4 through the lone-paired orbital in nitrogen of the pyridine ring, the theoretical results further revealed that the vibrational frequency shift is in good agreement with SERS peaks reported in the literature. Finally, our calculated results focused on the relationship between the Raman spectra and the charge transfer mechanism when the excitation photonic energy matches the transition energy of low-lying excited states in single-end and double-end adsorption configuration. Particularly for the case of the double-end adsorption configuration, the charge transfer states from the excitation from the silver cluster binding to the pyridine ring not only enhance the Raman signals of v(12), v(1), and v(8a) modes, but also selectively enhance the Raman signal of the v(9a) mode associated with the symmetric C-H in-plane bending vibration.国家自然科学基金（21273182,21533006,21373172）资助项

Effects of Pre-Deformation on Electrochemical Behavior of AISI304 Stainless Steel

AbstractEffect of pre-deformation on corrosion behavior of AISI 304 stainless steel was investigated by electrochmeical measurements, and the influence factors were chacterized by microstructural analysis and electron backscattering diffraction (EBSD). The results of polarization curves and electrochemical impedance spectroscopy indicated that corrosion resistance decreased 15%-20% after 20% pre-deformation. The reason may be due to the martensite transformation and the pile-up of dislocation according to the change of the microstructure. EBSD displays that an increase in grain orientation of austensite and martensite is another factor leading to the decrease of corrosion resistance. Besides corrosion resistance can also be reduced by the increase of the variety and fractions of texture. While corrosion resistance increases because of the increase of low angle boundaries

Preparation and characteristic of poly(piperazine-amide) hollow fiber composite nanofiltration membrane and the effect of additives

纳滤膜技术作为现代分离技术的重要手段之一，其分离特性介于超滤膜和反渗透膜之间，独特的分离性能赋予纳滤膜技术在工业领域中广泛应用，尤其是在水处理、脱盐、食品工业、生物医药等方面。有许多的制备纳滤膜的方法，如L-S相转化法、合金共混法、复合法等，其中复合法又分为涂覆法、表面接枝改性法、层层自组装法、界面聚合法，界面聚合法是目前商业化纳滤膜的主要制备方法。 本课题采用界面聚合法，在聚醚砜（PES）中空纤维超滤膜上制备复合纳滤膜，选用制备商业化复合纳滤膜广泛使用的聚合单体哌嗪（PIP）和均苯三甲酰氯（TMC）。根据单因素法确定最佳制膜工艺参数：水相晾置时间15min，PIP为1.5wt%，TMC为0...The separation property of nanofiltration(NF) membrane is between ultrafiltrati- on(UF) membrane and reverse osmosis(RO) membrane, this special separation performance endows NF membrane technology with extensive application in industrial areas, especially in water treatment, desalination, food industry, biological medicine etc.There are lots of methods to prepare NF membrane, such as L-S phase in...学位：理学硕士院系专业：材料学院_高分子化学与物理学号：2072012115006

“一带一路”背景下拉日铁路在中印铁路外交中的影响

“铁路外交“作为中国外交的一翼,有利于进一步扩大中国在世界的影响力。青藏铁路的延伸线——拉日铁路,是我国经济社会发展战略向西倾斜的表现,有利于实现与南亚邻国,尤其是印度的交流与合作。在通路的基础上通商,形成和平与发展新常态,这有利于将政治互信、地缘毗邻、经济互补等优势转化为务实合作,是启动“铁路外交“的目的和意义。因此,拉日铁路的开通,将会对中印铁路外交在经济、政治等方面产生重要影响,为“一带一路“战略在中亚和南亚的实施做出重大贡献