溶胶-凝胶法制备多孔晶体材料C12A7-Cl-

利用溶胶-凝胶法制备了多孔晶体材料C12A7-Cl- (Ca12Al14O32Cl2), 制备凝胶的原料是四水合硝酸钙、九水合硝酸铝、氯化钙、尿素和乙二醇. 混合溶液经过搅拌2-3 h形成溶胶, 再经350 ℃热处理后形成凝胶体, 最终在流动氩气气氛中1000 ℃烧结后得到材料. 用X射线衍射, 场发射扫描电子显微镜, 热重分析, 电子顺磁共振和离子色谱等方法表征合成的C12A7-Cl-多孔晶体材料. 结果表明, 利用溶胶-凝胶法成功地生成了C12A7 结构, 氯负离子是材料中存储的主要负离子. 此外, 从C12A7-Cl-晶体材料表面发射的氯负离子也被飞行时间质谱观测到. 上述结果说明溶胶-凝胶法可被用于制备C12A7-Cl-晶体材料.     

低温区CsI掺杂的12CaO·7Al2O3型发射材料负离子的发射特性

本文利用潮湿浸渍法将碘化铯(CsI)掺杂至12CaO·7Al2O3(C12A7)型负离子存储发射材料的表面并对其的结构与存储特性进行了X射线衍射和电子顺磁共振的表征,与此同时还对该材料的发射特性、离子发射分支比以及温度对发射强度的影响等方面进行了研究和分析。将实验和表征结果与未掺杂的C12A7进行对比后发现,C12A7表面上CsI的掺入很大程度上改善了该材料的发射特性。掺杂CsI后,在800 V·cm-1的引出场下,发射温度由570℃降低至470℃,与此同时,在同样的发射条件下,其发射强度也明显增强。低温区(<500℃)氧负离子O-的发射纯度接近100%。以上结果表明掺杂CsI至C12A7表面是一种在低温下获得氧负离子O-源的有效途径。     

掺杂Cs元素的微孔晶体材料C12A7的表征及负离子发射特性

利用浸渍CsI的方法在微孔晶体材料12CaO·7Al₂O₃ (C12A7)表面掺杂Cs元素并对其进行场发射扫描电镜、透射电子显微镜、X射线衍射以及电子顺磁共振的表征. 场发射扫描电镜以及透射电子显微镜的结果均证实CsI沉积在C12A7的表面; X射线衍射证明C12A7的结构并没有被破坏; 电子顺磁共振谱说明了浸渍后C12A7中的O^-和O₂^-浓度也无明显变化. 将浸渍后的同原始的C12A7进行比较发现, 掺杂样品在结构和存储特性上均无明显变化. 此外, 对该材料的发射性能与温度和引出场的关系也进行了研究与分析. 结果表明: 浸渍CsI至C12A7表面不仅降低了氧负离子的发射温度, 还大幅增强了发射强度; 氧负离子发射增强的主要原因归结于浸渍CsI后其表观活化能的降低.     

溶胶-凝胶法制备多孔晶体材料C12A7-C1~-

利用溶胶-凝胶法制备了多孔晶体材料C12A7-Cl~-(Ca_(12)Al_(14)O_(32)Cl_2),制备凝胶的原料是四水合硝酸钙、九水合硝酸铝、氯化钙、尿素和乙二醇.混合溶液经过搅拌2-3 h形成溶胶,再经350℃热处理后形成凝胶体,最终在流动氩气气氛中1000℃烧结后得到材料.用X射线衍射,场发射扫描电子显微镜,热重分析,电子顺磁共振和离子色谱等方法表征合成的C12A7-Cl~-多孔晶体材料.结果表明,利用溶胶.凝胶法成功地生成了C12A7结构,氯负离子是材料中存储的主要负离子.此外,从C12A7-Cl~-晶体材料表面发射的氯负离子也被飞行时间质谱观测到.上述结果说明溶胶-凝胶法可被用于制备C12A7-Cl~-晶体材料.     

乙烷在Ni(111)表面的吸附和分解

研究了乙烷在Ni(111)表面解离的可能反应机理, 使用完全线性同步和二次同步变换(complete LST/QST)方法确定解离反应的过渡态. 采用基于第一性原理的密度泛函理论与周期平板模型相结合的方法, 优化了C2H6裂解反应过程中各物种在Ni(111)表面的top, fcc, hcp和bridge位的吸附模型, 计算了能量, 并对布居电荷进行分析, 得到了各物种的有利吸附位. 结果表明, 乙烷在Ni(111)表面C—C解离的速控步骤活化能为257.9 kJ·mol-1, 而C—H解离速控步骤活化能为159.8 kJ·mol-1, 故C—H键解离过程占优势, 主要产物是C2H4和H2.     

基于质谱的六硝基六氮杂异伍兹烷热分解动力学

采用低能电子轰击质谱研究了六硝基六氮杂异伍兹烷(HNIW)的裂解过程, 建立了质谱中离子强度曲线的非等温动力学处理方法, 根据产物离子的Arrhenius曲线解释了HNIW热分解的机理. 结果表明, HNIW质谱裂解的表观活化能为145.1 kJ·mol-1. 在130-150 ℃范围内, HNIW质谱的离子产物主要是电子轰击产生的, 其活化能在28-41 kJ·mol-1之间; 在213-228 ℃范围内, 离子主要是热分解产生的, 其活化能在143-179 kJ·mol-1之间. HNIW在213-228 ℃的热分解动力学参数存在良好的动力学补偿效应, 补偿效应公式为lnA=0.252Ea-0.645. HNIW 热分解的主要反应为HNIW.438→6NO2+2HCN+HNIW.108, HNIW.438→6NO2+3HCN+HNIW.81, HNIW.438→6NO2+4HCN+HNIW.54.     

星际媒介H2NCH2CN与H2O反应中的H2O分子偶合质子转移机理和氢隧道效应

H2NCH2CN+H2O→H2NCH2C(OH)NH是一个重要的反应, 涉及到星际媒介中甘氨酸的形成, 与早期地球上的氨基酸起源有关. 如果没有考虑氢隧道效应, 在MP2/6-311+G(d,p)级别上计算反应能垒是254.7 kJ·mol-1, 在星际媒介中该气相反应很难进行. 在星际媒介冰颗粒表面上, 水分子催化反应增强了该化学反应的活性. H2NCH2CN与(H2O)3反应中的两个水分子作为催化剂降低活化能77.5 kJ·mol-1和活化自由能70.9 kJ·mol-1, 并且通过氢键桥协同传递质子. 量子氢隧道对于该反应进行至关紧要,采用小弯曲隧道(SCT)近似和正则变分过渡态理论(CVT)方法研究. 温度50 K时, 速率常数kSCT/CVT为1.86×10-23 cm3·molecule-1·s-1, 表明在星际媒介中通过质子隧道机理该反应容易进行. 研究结果与地球上的氨基酸起源于地球本身物质的观点相一致.     

Pd催化甲醇裂解制氢的反应机理

基于密度泛函理论(DFT), 研究了甲醇在Pd(111)面上首先发生O—H键断裂的反应历程(CH3OH(s)→CH3O(s)+H(s)→CH2O(s)+2H(s)→CHO(s)+3H(s)→CO(s)+4H(s)). 优化了裂解过程中各反应物、中间体、过渡态和产物的几何构型, 获得了反应路径上各物种的吸附能及各基元反应的活化能数据. 另外, 对甲醇发生C—O键断裂生成CH3(s)和OH(s)的分解过程也进行了模拟计算. 计算结果表明, O—H键的断裂(活化能为103.1 kJ·mol-1)比C—O键的断裂(活化能为249.3 kJ·mol-1)更容易; 甲醇在Pd(111)面上裂解的主要反应历程是: 甲醇首先发生O—H键的断裂, 生成甲氧基中间体(CH3O(s)), 然后甲氧基中间体再逐步脱氢生成CO(s)和H(s). 甲醇发生O—H键断裂的活化能为103.1 kJ·mol-1, 甲氧基上脱氢的活化能为106.7 kJ·mol-1, 两者均有可能是整个裂解反应的速控步骤.     

甲壳素对铅(Ⅱ)的吸附研究

进行了铅离子在甲壳素上的吸附行为实验,结果表明在pH=4.46时吸附最佳。测得静态饱和吸附容量为478mg.g-1(树脂);用0.5mol.L-1HCl可洗脱,洗脱率达98.8%;测得表观速率常数k298=8.53×10-5s-1;表观活化能Ea=16.54kJ.mol-1;等温吸附服从Freundlich经验式;吸附热力学参数△H=8.70kJ.mol-1,△S=41.7J.mol-1.K-1,△G=-3.71kJ.mol-1。     

HCOO在Cu(110)、Ag(110)和Au(110)表面的吸附

采用密度泛函理论(DFT)以及广义梯度近似方法(GGA)计算了甲酸根(HCOO)在Cu(110)、Ag(110)和Au(110)表面的吸附. 计算结果表明, 短桥位是最稳定的吸附位置, 计算的几何参数与以前的实验和计算结果吻合. 吸附热顺序为Cu(110)(-116 kJ·mol-1)>Ag(110)(-57 kJ·mol-1)>Au(110)(-27 kJ·mol-1), 与实验上甲酸根的分解温度相一致. 电子态密度分析表明, 吸附热顺序可以用吸附分子与金属d-带之间的Pauli 排斥来关联, 即排斥作用越大, 吸附越弱. 另外还从计算的吸附热数据以及实验上HCOO的分解温度估算了反应CO2+1/2H2→HCOO的活化能, 其大小顺序为Au(110)>Ag(110)>Cu(110).     

Features and mechanism of H- anion emission from 12 CaO x 7 Al2O3 surface

The hydrogen anion (H-) and other anionic species (O-, OH-, e-) in the gas phase, emitted from the synthesized crystal surface of 12 CaO x 7 Al2O3-H- (C12A7-H-), have been observed. The emission intensity of all the anionic species strongly depends on the sample surface temperature and the extraction field. H- has the highest emission branch ratio, and the extraction field can reduce its apparent activation energy. H- emission current at a microA/cm2-level has been achieved, which is about 4 orders of magnitude higher than that obtained from the thermal desorption process of CaH2. The observed anions of H- and OH- are attributed to their migration from the C12A7-H- cages onto the surface [i.e., Y-(cages) --> Y-(surface) --> Y-(gas phase) (Y = H, OH)]. The weak O- and electron emission would both arise from the dissociation of O2-: O2-(surface) --> O-(surface) + e-(surface) --> O-(gas phase) + e-(space).     

Preparation and Characterization of Storage and Emission Functional Material of Chlorine Anion: Ca24Al28O644+·(Cl-)3.80(O2-)0.10

A storage and emission functional material of Ca₂₄Al₂₈O₆₄⁴⁺·(Cl^-)_3.80(O^2-)_0.10(C12A7-Cl^-), was prepared by the solid-state reactions of CaCO₃, γ-Al₂O₃, and CaCl₂ in Cl₂/Ar mixture atmosphere. The anionic species stored in the C12A7-Cl^- material were dominated by Cl^-, about (2.21±0.24)×10²¹ cm^-3, accompanied by a small amount of O^2-, O^-,, and O^2-, measured via ion chromatography, electron paramagnetic resonance, and raman spectra measurements. These results also corroborate identification of time-of-flight mass spectroscopy—the anionic species emitted from the C12A7-Cl^- surface were dominated by the Cl^- (about 90%) together with a small amount of O^-and electrons. The structure and morphological alterations of the material were investigated via X-ray diffraction and field emission scanning electron microscope, respectively.     

Preparation and Characterization of Storage and Emission Functional Material of Cs2O-doped 12CaO·7Al2O3

We provides a novel approach to generate low-temperature atomic oxygen anions (O^-) emis-sion using the cesium oxide-doped 12CaO·7Al₂O₃ (Cs₂O-doped C12A7). The maximal emis-sion intensity of O^- from the Cs₂O-doped C12A7 at 700 oC and 800 V/cm reached about 0.54 μA/cm², which was about two times as strong as that from the un-doped C12A7(0.23 μA/cm²) under the same condition. The initiative temperature of the O^- emission from the Cs₂O-doped C12A7 was about 500 oC, which was also much lower than the initiative temperature from the un-doped C12A7 (570 oC) in the given field of 800 V/cm. High pure O^- emission close to 100% could be obtained from the Cs₂O-doped C12A7 under the lower temperature (<550oC). The emission features of the Cs₂-doped C12A7, including the emis-sion distribution, temperature effect, and emission branching ratio have been investigated in detail and compared with the un-doped C12A7. The structure and storage characteristics of the resulting material were also investigated via X-ray diffraction and electron paramag-netic resonance. It was found that doping Cs₂ to C12A7 will lower the initiative emission temperature and enhance the emission intensity.     

Mechanistic features for hydroxyl anion emission from the modified 12CaO.7Al2O3 surface

OH(-), O(-), and H(-) emissions from the [Ca(24)Al(28)O(64)](4+).4(OH(-)) (defined as C12A7-OH(-)) surface were investigated by time-of-flight (TOF) spectrometry. The emission intensities were sensitive to surface temperature and extraction field. The apparent activation energies of anions decreased with the increase of applied extraction field. At an extraction field of 800 V/cm, the emission ratio of OH(-) to total anions is 0.98-0.65 in the temperature range of 870-1075 K. The OH(-) emission from C12A7-OH(-) was described by the following kinetic processes: the OH(-) anions in the cages migrated onto the sample surface by field enhanced thermal diffusion, and then desorbed to form the gas-phase anions of OH(-). The O(-) emission originated from the dissociation of O(2-) and OH(-). Similarly, H(-) emission was also attributed to the dissociation of OH(-) on the C12A7-OH(-) surface.     

Characterization of C12A7-O- Catalyst and Mechanism of Phenol Formation by Hydroxylation of Benzene

The benzene conversion and phenol selectivity from C6H6/O2/H2O over Ca24Al28O644+·4O-(C12A7-O-) catalyst were investigated using a flow reactor. The benzene conversion increases with the increase of temperature, and the phenol selectivity mainly depends on both reaction temperature and the composition of the mixtures. The changes of the catalyst structure before and after the reactions and the intermediates on the catalyst surface and in the bulk were investigated by XRD, EPR and FT-IR. The catalytic reactions do not cause any damage to the structure of the positively charged lattice framework C12A7-O-, but part of the O- and O2- species in the bulk of C12A7-O- translate to OH- after the reactions. The neutral species and anion intermediate were investigated by Q-MS and TOF-MS respectively. It is suggested that the active O- and OH- species played a key role in the process of phenol formation.     

Na2O掺杂C12A7材料的结构及其抗菌性能

本文利用溶胶-凝胶方法制备了Na2O掺杂的C12A7(12CaO.7Al2O3-Na2O)材料,通过X-射线衍射(XRD)、电子顺磁共振(EPR)、电感等离子体耦合-原子发射光谱(ICP-AES)和飞行时间质谱(TOF-MS)研究了材料结构与性能。选用金黄色葡萄球菌和大肠杆菌为受试菌种,研究了C12A7-Na2O的抗菌性能。结果表明,Na2O掺杂对C12A7的晶体结构以及材料中的氧负离子的浓度没有显著的影响,且C12A7-Na2O材料具有较高的抗菌性能。利用扫描电镜(SEM)对杀菌前后的金黄色葡萄球菌和大肠杆菌的菌体形态进行了观测,初步探讨了C12A7-Na2O的抗菌机理。