甲醛分子在羟基化TiO2-B(100)面吸附的第一性原理研究

利用第一性原理研究TiO₂-B表面上甲醛分子（HCHO）与氧桥位羟基（BH）、钛顶位羟基（TH）共吸附时羟基基团对HCHO分子吸附的影响.结果表明：这两种羟基的存在对HCHO在清洁和羟化表面形成多种化学吸附构型产生不同影响.与HCHO分子共吸附时，氧桥位羟基弱化HCHO的吸附；而钛顶位羟基强化HCHO的吸附，且在不同面积超胞上均能显著强化其吸附.利用电子结构分析不同吸附的内在机制，为理解HCHO分子与TiO₂基材料表面的相互作用提供新的视角.     

长链烷烃和醇在石墨表面吸附的扫描隧道显微镜研究

用扫描隧道显微镜（STM）研究了室温下十八醇（1-C18H37OH）和十四烷（C14H30）在石墨表面的吸附行为.十八醇在石墨表面自组装形成条状结构.实验发现了十八醇分子在石墨表面的两种不同的密排方式，它们形成并列的不同宽度的条状结构.还发现，由于溶剂（正十四烷C14H30）的完全蒸发，留下的十八醇分子在石墨表面吸附的自组装结构与固液界面中十八醇分子在石墨表面的吸附形成的结构在分子方向、表面分子晶体的晶格常数及条状结构宽度等方面有很大的不同.此外，实验中也发现溶剂十四烷在某种情况下也能在石墨表面吸附形成可供STM观察的有较长时间稳定性的条状周期结构.实验观察到的十四烷在石墨表面形成的晶体结构与固液界面中观察到的有序结构的晶体结构常数和分子排列方向也是不同的.根据STM图像，提出了十八醇和十四烷在石墨表面吸附的结构模型. 关键词： 十四烷 十八醇 石墨 扫描隧道显微镜     

杂质对CO在Ni（100）表面化学吸附位置的影响

在紧束缚近似下，采用ＥＳ模型和格林函数方法，通过对含杂Ｎｉ（１００）表面ＣＯ分子顶位、桥位和心位化学吸附能的计算，讨论了替位杂质对Ｎｉ（１００）表面ＣＯ化学吸附位置的影响。     

含锰钢表面氢原子/氢分子吸附行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法研究了氢原子和氢分子在纯铁表面和锰原子掺杂表面的吸附与解离行为.研究结果表明,氢原子可在纯铁(001)表面稳定吸附,吸附能按照顶位,桥位和心位依次增强;而溶质原子锰降低了氢原子距离表面的位置并强化了氢原子的吸附行为.氢分子在纯铁表面的吸附解离行为取决于氢分子距离模型表面的初始距离和初始空间构型.氢分子平行于纯铁(001)表面时,距离心位1.2?发生解离,而桥位、顶位均不会发生解离;氢分子垂直放置时,距离桥位0.6?、顶位1.0?发生解离,心位不会发生解离.氢分子平行于锰掺杂纯铁(001)表面时,距离桥位0.6?、顶位0.7?、心位1.2?发生解离;氢分子垂直放置时,距离桥位、心位0.8?发生解离,而顶位放置氢分子不发生解离.归纳可知,锰溶质原子掺杂会增加铁基体表面氢原子和氢分子的吸附作用并促进氢分子发生分解.     

H2O分子在Fe（100）, Fe（110）, Fe（111）表面吸附的第一性原理研究

采用第一性原理研究了H₂O分子在Fe（100）,Fe（110）,Fe（111）三个高对称晶面上的表面吸附.结果表明,H₂O分子在三个晶面上的最稳定结构皆为平行于基底表面的顶位吸附结构.H₂O分子与三个晶面相互作用的吸附能及几何结构计算结果表明H₂O分子与三个晶面的相互作用程度不同,H₂O分子与Fe（111）晶面的相互作用最强,其次是Fe（100）,相互作用最弱的是Fe（110）表面,而这与晶面原子 关键词： 第一性原理 Fe单晶表面 2O分子')" href="#">H₂O分子 分子吸附     

乙烯在Ni（110）表面吸附的几何结构

用理论计算的方法研究了不同覆盖度的乙烯在Ni（110）表面吸附的位置.乙烯的吸附几何结构在团簇计算中进行了局部优化.在低覆盖度下，单个乙烯分子占据了短桥位和顶位之间的中间位置.乙烯分子的C—C轴大致沿衬底的Ni原子链排列（即沿<110>晶向），C—C轴与衬底Ni（110）表面有10°的倾斜角.乙烯分子的C—C键的键长为0151nm.在高覆盖度下(05ML)，乙烯在Ni (110)上形成了有序的c（2×4）相，在一个表面元胞内的两个乙烯分子的吸附位置类似于低覆盖度时的结果，但乙烯分子的C—C 键键长分别为0142和0143nm.     

O2在Mo(001)表面吸附的第一原理研究

采用第一原理方法计算了O2分子在 Mo(001) 表面的吸附,得到了吸附构型的各种参数,并且计算了O2分子在 Mo(001) 表面4个位置（顶位,桥位,穴位垂直,穴位平行）吸附后的能量,结果表明在顶位吸附能最高。通过对O2分子在 Mo(001) 表面吸附的原子轨道电荷分布与态密度图的分析可以看出在吸附过程中主要是O原子的2p轨道电子与钼的4s和4d轨道电子的相互作用。     

O2在Mo(001)表面吸附的第一原理研究

采用第一原理方法计算了O2分子在 Mo(001) 表面的吸附,得到了吸附构型的各种参数,并且计算了O2分子在 Mo(001) 表面4个位置（顶位,桥位,穴位垂直,穴位平行）吸附后的能量,结果表明在顶位吸附能最高。通过对O2分子在 Mo(001) 表面吸附的原子轨道电荷分布与态密度图的分析可以看出在吸附过程中主要是O原子的2p轨道电子与钼的4s和4d轨道电子的相互作用。     

气体分子在石墨表面的吸附与扩散特性

采用分子动力学方法模拟研究气体分子在石墨表面上的吸附和扩散特性,结果表明气体分子在石墨表面上的吸附强度跟石墨中碳原子和气体分子之间的微观作用力密切相关,不同分子在石墨表面上的吸附强度不同。气体分子在石墨表面上的吸附特性符合Langmuir等温吸附模型,压力越高吸附层内分子的密度越高。通过分子的表面扩散系数随着压力的增加而降低的现象以及特定时间内分子运动距离的正常概率分布,发现石墨表面上分子的扩散主要由分子之间的碰撞控制,趋近于体相扩散。分子在石墨表面吸附层内的密度对表面扩散系数的影响非常显著,导致吸附性强的CO_2和H_2S分子扩散系数要明显低于吸附性弱的CH_4和N_2分子.     

过渡金属Pd掺杂AsP结构及其吸附甲醛和一氧化碳的性能研究

基于第一性原理方法,研究了单层本征磷砷AsP和过渡金属钯（Pd）掺杂磷砷AsP的结构,并对比研究了本征和掺杂后的AsP吸附甲醛（HCHO）和一氧化碳（CO）气体分子的稳定性、能带结构、态密度以及电荷差分密度。研究结果表明：经Pd掺杂后AsP由半导体转变为导体;本征AsP吸附一氧化碳最稳定的位置为P-As键顶上,吸附甲醛最稳定的位置为P原子顶上;本征吸附时气体分子与基底之间的距离在3 Å左右,气体分子与基底之间未形成化学键。过渡金属Pd原子掺杂AsP后形成两种结构,分别为Pd原子替换超胞结构中的As原子或P原子。两种掺杂结构分别吸附一氧化碳或甲醛气体分子时,除了Pd原子替换AsP中的As原子形成的结构吸附甲醛的吸附能未明显增加外,其余掺杂结构吸附一氧化碳或甲醛的吸附能和电荷转移较本征吸附时均显著增强,吸附CO分子时,C原子与Pd原子之间形成了化学键。特别是,Pd原子替换AsP中的P原子形成的结构对一氧化碳和甲醛气体分子的吸附性能明显强于Pd原子替换AsP中的As原子所形成的结构。     

Density functional theory investigation of carbon monoxide adsorption on the kaolinite(001) surface

Carbon monoxide(CO) is a gaseous pollutant with adverse effects on human health and the environment. Kaolinite is a natural mineral resource that can be used for different applications, including that it can also be used for retention of pollutant gases. The adsorption behavior of carbon monoxide molecules on the(001) surface of kaolinite was studied systematically by using density-functional theory and supercell models for a range coverage from 0.11 to 1.0 monolayers(ML). The CO adsorbed on the three-fold hollow, two-fold bridge, and one-fold top sites of the kaolinite(001) was tilted with respect to the surface. The strongest adsorbed site of carbon monoxide on the kaolinite(001) surface is the hollow site followed by the bridge and top site. The adsorption energy of CO decreased when increasing the coverage, thus indicating the lower stability of surface adsorption due to the repulsion of neighboring CO molecules. In addition to the adsorption structures and energetics, the lattice relaxation, the electronic density of states, and the different charge distribution have been investigated for different surface coverages.     

Monte Carlo simulation of carbon monoxide,carbon dioxide and methane adsorption on activated carbon

In this study, the adsorption capacity of pure and activated carbon with regard to carbon monoxide (CO), carbon dioxide (CO₂) and methane (CH₄) gases at 298?K and pressure from 0.01 up to 2.0?MPa has been investigated computationally. Computational work refers to Monte Carlo (MC) simulation of each adsorbed gas on a graphite model with varying density of activation sites. The Grand Canonical Monte Carlo (GCMC) simulation technique was employed to obtain the uptake of each adsorbed gas by considering a graphite model of parallel sheets activated by carboxyl and hydroxyl groups, as observed experimentally. The simulation adsorption data for these gases within the examined carbon pore material are presented and discussed in terms of the adsorbate fluid molecular characteristics and corresponding interactions between adsorbate species and adsorbent material. We found that the simulated adsorption uptake of the examined graphite model under these conditions with regard to the aforementioned fluids increases in the order CO?<?CH₄?<?CO₂.     

IR spectroscopic study of surface properties of amorphous water ice

The state of the surface of amorphous ice with a specific surface area of about 160 m²/g obtained by the condensation of water vapor at 77 K is studied by IR spectroscopy. As the temperature increases to 130–160 K, absorption bands of surface hydroxyl groups vanish, whereas changes in bands characteristic of hydroxyl groups in the bulk of ice are indicative of a phase transition of ice from amorphous to the polycrystalline structure. The surface sites of amorphous ice are characterized with low-temperature adsorption of carbon monoxide. It is shown that there are two types of CO adsorption sites, free hydroxyl groups and oxygen atoms of surface coordinately unsaturated water molecules. Upon adsorption of nitrogen, methane, and carbon monoxide, in addition to the perturbation of surface OH groups, reversible changes in the spectrum are observed in the region of vibrations of bulk hydroxyls, which indicate that the strength of hydrogen bonds between water molecules in the surface layer of icy particles increases approaching the strength of these bonds in the crystal and that the ice surface becomes less amorphous. These results indicate that the properties of the ice surface layer substantially depend on the presence of adsorbed molecules.     

First principles study of oxygen adsorption on nickel-doped graphite

Density functional theory is used in a spin-polarized plane wave pseudopotential implementation to investigate molecular oxygen adsorption and dissociation on graphite and nickel-doped graphite surfaces. Molecular oxygen physisorbs on graphite surface retaining its magnetic property. The calculated adsorption energy is consistent with the experimental value of ?0.1?eV. It is found that substituting a carbon atom of the graphite surface by a single doping nickel atom (2.8% content) makes the surface active for oxygen chemisorption. It is found that the molecular oxygen never adsorbs on doping nickel atom while it adsorbs and dissociates spontaneously into atomic oxygens on the carbon atoms which are bound to the nickel. The adsorption energy of ?1.4?eV and zero activation energy barrier indicate that O₂ dissociative adsorption is both thermodynamically and kinetically favoured over the surface. The large electric field near the doping nickel atom along with the excess electrons on the neighbouring carbon atoms, which are bound to the nickel induce molecular oxygen to adsorb and dissociate favourably.     

Vibrational characterization of carbon monoxide oxidation on the Pt(111) surface

The surface reaction between coadsorbed carbon monoxide and atomic oxygen has been characterized using high resolution electron energy loss spectroscopy, coupled with temperature programmed reaction spectroscopy on a Pt(111) surface characterized using Auger electron spectroscopy and low energy electron diffraction. Preferential oxidation of bridge bonded CO is not observed despite the fact that bridge bonded CO is adsorbed less vigorously than linearly bound CO. Saturation of the Pt(111) surface with one quarter of a monolayer of atomic oxygen completely suppresses the adsorption of bridge bonded CO. However, substantial coverages of bridge bonded CO can be coadsorbed if the Pt(111) surface is only partially saturated with atomic oxygen. The vibrational data for reaction of coadsorbed CO and atomic oxygen is consistent with a reaction mechanism involving reaction of mobile CO along oxygen island perimeters.     

Carbon monoxide and hydrogen coadsorption on polycrystalline platinum

The coadsorption of carbon monoxide and hydrogen was studied on a polycrystalline platinum foil. In a comparison with single crystal surfaces, the desorption kinetics of the individual species most closely resemble those on Pt(110). In coadsorption there is competition between CO and H₂. Carbon monoxide completely blocks hydrogen adsorption, but on a hydrogen-saturated surface only two-thirds of the carbon nomoxide adsorption is blocked. Shifts in peak temperatures for hydrogen desorption indicate that repulsive interactions between adsorbed CO and H₂ are important, and lead to segregated islands of the two adsorbates. Under some conditions there is also a new low temperature desorption peak for hydrogen which indicates that there are regions on the surface where carbon monoxide and hydrogen are intermixed.     

Role of adsorption on surface composition of Pd–Cu nanoparticles

Monte-Carlo (MC) simulation is used to study the role of adsorption of hydrogen, oxygen and carbon monoxide (CO) on the surface composition and surface bond geometry of Pd–Cu nanoparticles. For clean particles the surface is found to be enriched in Cu. But in the presence of adsorbed hydrogen and CO there is a segregation reversal from Cu segregation at low coverage to Pd segregation at high coverage. In the presence of adsorbed oxygen, on the contrary, the extent of Cu segregation increases with coverage. For a 586-atom nanoparticle with 50% Pd in the bulk the corner sites are found to be occupied by Cu atoms up to one monolayer adsorption. But, while the occupancy of 7, 8 and 9-coordinated sites by Cu atoms decreases with increase of H and CO coverage, for oxygen adsorption this occupancy increases with coverage. The relevance of such results in catalysis studies is discussed.     

Adsorption of Zn(II) and Cd(II) ions onto magnesium and activated carbon composite in aqueous solution

Magnesium and coconuts shell activated carbon composite was prepared to selectively remove heavy metals ions in aqueous solution. Zinc(II) and cadmium(II) ions were used to clarify the adsorption capacity of the composite in comparison with no magnesium containing activated carbon. Influence of the initial heavy metal concentration, time course and solution temperature on the adsorption amounts were examined for the two adsorbents, and surface chemistry of the adsorbents was also characterized using Boehm titration. The magnesium composite adsorbed greater amount of Zn(II) and Cd(II) ions than the no magnesium counterpart. The adsorption amount of Cd(II) was not influenced with rise in solution temperature for the composite, whereas decrease in adsorption was observed for the counterpart. The loaded magnesium was estimated to be combined with carbon surface via oxygen bridge. Cadmium(II) was adsorbed onto the composite surface by ion exchange process with releasing equivalent amount of Mg(II) from the carbon surface, while Zn(II) would adsorb onto the composite by not only the ion exchange, but also the electrostatic interaction with the Cπ electrons on the graphite surface from the experimental results.     

Poisoning and non-poisoning oxygen on Cu(410)

We have investigated ethene and oxygen co-adsorption on Cu(410) by high resolution electron energy loss spectroscopy. We find that these two species compete for the adsorption sites and that pre-exposure to oxygen affects ethene adsorption more or less strongly depending on oxygen coverage and the kind of occupied sites. The c(2 × 2) O overlayer is inert with respect to ethene adsorption, while when some oxygen is removed by thermally induced subsurface incorporation, ethene chemisorption is restored. The latter species also adsorbs on the disordered oxygen phase formed when O(2) is dosed at low crystal temperature. Contrary to the bare surface case, most of the ethene ends up in a π-bonded configuration. Dehydrogenation occurs, too, albeit as a minority channel. The so-produced carbon reacts already at low temperature with adsorbed oxygen to yield carbon monoxide, which desorbs around 190 K.