吉林长白山硅藻土的红外光谱研究

对长白山硅藻土在 10 0～ 1330℃温度范围进行热处理并开展红外光谱研究 ,结果表明经 5 0 0℃热处理样品开始出现 374 5cm- 1 峰 ,在 90 0℃达到最大 ,12 0 0℃消失 ,此时硅藻土转变成方石英。对 374 5cm- 1 峰所反映的以孤立Si—OH形式存在的水的含量进行了半定量计算 ,表明这种OH除存在于样品表面外 ,还存在于内部的结构缺陷处 ,并推测硅藻土转变成方石英与这种孤立Si—OH的消失有关     

除草剂苄嘧磺隆在针铁矿表面吸附的红外光谱研究

文章用FTIR光谱,探讨了热带、亚热带地区水稻土中普遍存在的针铁矿对近年来广泛使用于水稻田的磺酰脲类除草剂苄嘧磺隆的吸附机理。结果表明:(1)在针铁矿对苄嘧磺隆的吸附过程中,游离羟基(A型)及C型羟基均没有明显作用。(2)针铁矿表面的水合羟基峰在吸附前后的图谱中由3158移到3129cm~(-1),缔合程度增高,表明在该吸附过程中针铁矿表面的水合羟基峰起主要作用。(3)在吸附后的针铁矿图谱中出现了波数增高了的苄嘧磺隆的羰基及磺酰基弱峰。其波数分别由1712和1161cm~(-1)增至1789和1164cm~(-1),由此判断,苄嘧磺隆被针铁矿表面吸附是由该农药分子中的羰基和磺酰基起主要作用。(4)由以上结果推断:苄嘧磺隆在针铁矿表面的吸附是苄嘧磺隆分子中的羰基和磺酰基与针铁矿表面的水合羟基形成了电荷-偶极键以氢键结合的吸附。     

疏水表面上吸附态溶菌酶的DSC和FTIR研究

联合差示扫描量热 (DSC)和傅里叶变换红外吸收光谱(FTIR)分别研究了鸡蛋白溶菌酶(Lyz)在适度疏水吸附剂(PEG-600)表面上吸附和折叠时,不同盐(硫酸铵)浓度、表面覆盖度和变性剂(盐酸胍)浓度对无水环境的吸附态天然和变性溶菌酶构象变化及热稳定性的影响。研究发现：随着硫酸铵浓度和溶菌酶表面覆盖度的增加,吸附态天然和变性溶菌酶的吸热峰温度都逐渐降低,同时在较高温度下的微扰也增多。吸附发生后,α-螺旋结构减少,β-折叠和β-转角结构增多。在FTIR图谱中,吸附态变性溶菌酶在1 400～1 425 cm-1处的C—C拉伸振动峰和1 650～1 670 cm-1处的酰胺Ⅰ带特征峰都能明显观测到。但是,与之相比,相同条件下吸附态天然溶菌酶在1 650～1 670 cm-1处特征峰却几乎看不到。吸附态天然溶菌酶发生了结构丢失,表现得更加不稳定。     

Reactions and structures of water on clean and oxygen covered Pt(111) and Fe(100)

An atom superposition and election delocalization (ASED) technique applied to water adsorption on a small cluster model of Pt(111) shows weak and reversible chemisorption and facile and reversible hydrogen transfer to preadsorbed oxygen atoms as observed by Fisher, Sexton and Gland in EELS and UPS studies. Our theory predicts much stronger adsorption of water to Fe(100) with low barriers to dehydrogenation, in agreement with high temperature LEED-Auger results of Dwyer, Simmons, and Wei and wide temperature range XPS studies of Akimov. We predict a low barrier to transfer of hydrogen from water to adsorbed oxygen atoms, forming hydroxyl groups on the iron surface, and a fairly low barrier to the reverse reaction. On both metals we find hydroxyl groups are strongly held. Our calculations produce a trend toward greater negativity on going from adsorbed water to hydroxyl groups, and to hydroxyl dissociation products on these surfaces. We present reaction mechanisms, transition state geometries, and analysis in terms of molecular orbital theory and the total energy. It is found that the platinum is generally less reactive than iron toward water and hydroxyl species because platinum orbitals are less diffuse and the platinum s-d band lies lower, closer to adsorbate energy levels such that adsorbate-platinum antibonding orbitals are filled.     

加热影响凹凸棒土结构的光谱分析

凹凸棒土含有四种羟基,3 614 cm-1处的吸收峰是与结构内部的四面体结构和八面体之间的Mg,Al相连羟基的伸缩振动;3 552和3 581 cm-1处的吸收峰是与凹凸棒土孔道边缘的Mg,Al八面体相连的结构水的羟基的对称和不对称伸缩振动;3 415 cm-1处的吸收峰是凹凸棒土中结晶水的羟基振动引起的;1 653 cm-1处的吸收峰是沸石水的吸收峰。将凹凸棒土在不同温度恒温30 min,通过不同的恒温温度各粉样的傅里叶红外光谱(FTIR)和X射线衍射光谱(XRD)的实测和比较,发现温度较低时结构内部的沸石水、结晶水、结构水同时减少;经450 ℃恒温30 min后,结构水被除去,凹凸棒土的晶体结构开始改变;结构羟基非常稳定,600 ℃恒温才会被破坏。文章初步探讨了热处理过程中化学变化过程。     

H MAS and H[Na] double resonance NMR studies on the modification of surface hydroxyl groups of γ-alumina by sodium

The modification of surface hydroxyl groups with sodium in a series of Na₂CO₃-γ-Al₂O₃ catalysts was investigated as a function of both the Na₂CO₃ loading and the calcination temperature by means of ¹H magic angle spinning (MAS) and ¹H[²³Na] spin-echo double resonance NMR techniques. The ¹H NMR experiments revealed that sodium ions are homogeneously distributed over the alumina surface and closely coordinated with the surface hydroxyl groups. In the catalysts calcined at 250 °C, the acidic hydroxyl groups (with a chemical shift of 2.0 ppm) are preferentially associated with sodium ions at low Na₂CO₃ coverages (5 and 10%), while both the acidic and the basic (0 ppm) hydroxyl groups are accessible for sodium ions at high coverages (15 and 20%). The coordination causes a low-field shift of about 2 ppm in the ¹H MAS spectra, and a broad signal at 4.5 ppm appears. It is interesting that the 4.5 ppm signal is completely suppressed in the ¹H[²³Na] MAS experiments, providing direct evidence that a strong interaction exists between adsorbed sodium ions and the surface hydroxyl groups. Increasing the calcination temperature to 450 °C results in preferential removal of the acidic hydroxyl groups, and only the most basic hydroxyl groups remain when the calcination temperature is raised to 600 °C. This is attributed to the formation of the coordinated species which enhances the acidity of the surface hydroxyl groups and prompts their dehydroxylation, especially at high calcination temperature. Correlation of the ¹H MAS NMR results and catalytic activity measurements indicates that the basic hydroxyl groups are essential for the carbonyl sulfide hydrolysis reaction.     

基于芯-电子结合能偏移的碱金属中的表面、尺寸和热效应

还原氧化石墨烯是大规模生产石墨烯的前体;然而迄今为止,还原氧化石墨烯的电子结构还没有达成共识. 本文运用从头分子动力学方法研究羟基在石墨烯表面的吸附过程. 在吸附过程中,OH基团首先在位于两个碳原子桥位上方形成物理吸附络合物,然后翻越过渡态,最终被吸附在一个碳原子的顶位位点. 结果显示5×5石墨烯表面最多可以吸附6个羟基,表明石墨烯表面羟基的覆盖率约为12%. 计算结果还显示,负吸附能随着羟基吸附数目的增加而线性增加,带隙也随着羟基吸附数目的增加而线性增加.     

The adsorption of water on clean and oxygen covered Cu(110)

The water adsorption on clean and oxygen precovered Cu(110) surfaces is studied by means of UPS, LEED, work function measurements and ELS. At 90 K on the clean surface molecular water adsorption is indicated by UPS. The H₂O molecules are bonded at the oxygen end and the H-O-H angle is increased as compared with the free molecule. In the temperature range between 90 and 300 K distorted H₂O molecules and adsorbed hydroxyl species (OH) are detected, which are desorbed at room temperature. On an oxygen covered surface hydroxyl groups are formed by dissociation of adsorbed water molecules at a lower temperature than on the clean surface. Multilayers of condensed water are found below 140 K in both cases.     

An infrared study of the surface chemistry of lithium titanate spinel (Li4Ti5O12)

While there are numerous studies examining the performance of lithium titanate spinel (LTS) as a lithium-ion battery, little is known about the surface chemistry of this material. In this paper, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy spectroscopy was used to study the type of surface groups present on LTS as a function of temperature. The surface was found to contain isolated and hydrogen-bonded TiOH groups and the dehydroxylation behavior with thermal treatment was similar to that of TiO₂. In addition, hexamethyldisilazane (HMDZ) and pyridine were used to probe the reactivity of surface hydroxyl groups and the presence of Lewis acid sites, respectively. The reaction of HMDZ occurred with both LiOH and TiOH groups to form Li-O-Si and Ti-O-Si. In addition, the reaction of gaseous CO₂ with the Li⁺ ions resulted in the formation of surface carbonate ions. The carbonate ions are removed by heating at 400 °C in air.     

Surface-adsorbate-induced fluorescence-type Raman background of Pb(Zr0.4Ti0.6)O3 nanotubes

We report the effects of adsorbates on the Raman spectra of Pb(Zr_0.4Ti_0.6)O₃ nanotubes (PZT-NTs). PZT-NTs with adsorbates were prepared by exposing PZT-NTs to air for 1 day. We found that the presence of surface adsorbates can cause an intense and broad Raman background that hinders the observation of the Raman vibrational modes of the PZT-NTs. This background can be suppressed by adjusting the Raman excitation wavelength from 514.5 nm to 414.6 nm. It can also be removed by post-annealing the PZT-NTs at 500 °C, but it returns readily after re-exposure to air. X-ray photoelectron and Fourier transform infrared spectroscopies show that hydroxyl and carbonate groups are adsorbed onto the surfaces of the PZT-NTs during exposure to air. Moreover, dispersive Raman spectra reveal that the background is a tail of a very broad band from 1000 to 4000 cm^?1, which corresponds to hydroxyl groups. These results suggest that the main contribution to the Raman background of the PZT-NTs is that of surface hydroxyl groups rather than carbonate groups.