奥硝唑在TiO_2(101)晶面上吸附特征的理论研究

奥硝唑残留是一种新兴污染物,对环境和人类健康具有巨大的威胁.采用密度泛函理论,研究了奥硝唑在锐钛矿TiO_2(101)晶面的吸附特性.优化了奥硝唑在锐钛矿TiO_2(101)晶面的吸附结构,计算了最佳吸附位点,吸附能,态密度,电子结构图.结果表明,当咪唑环上N(3)原子吸附在TiO_2的Ti(5)原子上时,吸附能最大,为最稳定的吸附构型.通过对吸附构型的分析,我们发现C(2)-N(3)键呈现变弱趋势,我们推测奥硝唑在TiO_2表面降解的可能性以及反应活性位点就是咪唑环上C-N键.     

第一性原理研究五氯硝基苯在TiO_2表面吸附

采用基于密度泛函理论的Materials Studio(MS)程序包中的CASTEP程序优化了TiO_2(101)晶面、五氯硝基苯(PCNB)结构和TiO_2(101)对五氯硝基苯的16种吸附结构.计算了最佳吸附位点,吸附能,以及稳定吸附模型的电子结构.研究结果表明:五氯硝基苯中硝基的对位上Cl原子被垂直吸附在TiO_2(101)表面的O原子时吸附能最大,吸附结构最稳定,是TiO_2吸附PCNB的最佳吸附方式,吸附后五氯硝基苯的C-Cl键长变短,其它C—Cl键和C—N键增长,吸附过程为化学吸附.     

第一性原理研究O2和H2O在ZnO (101 ̅0)表面上的吸附行为

运用基于密度泛函理论(DFT)的第一性原理方法研究了O2和H2O单分子在ZnO (101 ̅0)表面上的吸附行为。吸附位点主要考虑了表面的Zn顶位和Zn桥位,同时也考虑了其它可能的吸附行为。对于O2在ZnO (101 ̅0)表面上的吸附设计了9个模型,H2O在ZnO (101 ̅0)表面上的吸附设计了12个模型。通过形成能计算发现,O2在表面上的吸附为正值,H2O的吸附为负值。O2和H2O单分子在表面上发生分子吸附,未见解离形态。对于O2吸附最稳定的结构是O2分子与表面相邻的Zn原子形成了Znslab1-Oads1-Oads2-Znslab2桥连键。其它较为稳定的结构是Oads1原子迁移到下一个表面重复晶胞的O原子位置附近,在表面上形成了Znslab1-Oads1键,同时Oads2原子扩散至表面沟渠上方。对于H2O吸附,不论以何种方式吸附结构都比较稳定。其中最稳定的构型是Oads迁移到下一个表面重复晶胞的O原子位置附近,形成了Znslab1-Oads键以及Oslab3-H氢键。另外较稳定的构型是Oads迁移到ZnO (101 ̅0)表面台阶上方,形成了Znslab1-Oads键以及Oslab1-H氢键。     

酸碱环境对TiO2吸附替硝唑的影响

基于密度泛函理论,研究了酸碱性条件下替硝唑在TiO2(101)和(001)晶面上的吸附特性.优化了替硝唑在TiO2(101)和(001)晶面的吸附结构,计算了最佳吸附位点,吸附能以及态密度.结果表明,当咪唑环上N(3)原子吸附在TiO2的Ti(5)原子上时,吸附能最大,为最稳定的吸附构型.通过对吸附构型的分析,我们发现C(2)-N(3)成键性质被削弱,且光催化反应中各构型价带与导带间电子跃迁均在可见光范围内.     

表面非金属掺杂对锐钛矿相TiO_2(101)面吸附NH_3特性的影响

采用基于密度泛函理论(DFT-D)体系下的第一性原理平面波超软赝势方法,研究了被不同非金属(B、C、N、F)掺杂的TiO_2(101)表面吸附NH_3的特性与作用机理.研究发现:被非金属掺杂后的表面对NH_3的吸附效果要优于未掺杂表面.不同元素掺杂对比发现:C掺杂后的表面吸附能最大,稳定后吸附距离最小,为最稳定吸附结构.通过Mulliken电荷分布和分态密度的分析,得到了不同吸附条件下NH_3在TiO_2掺杂表面的催化氧化还原作用机理,并发现各模型吸附能的不同是由于掺杂(X)位原子与NH_3分子的相互作用强弱不同所造成.掺杂原子在费米面附近的电子态密度贡献越强,掺杂原子与NH_3分子电荷转移的净值越小,吸附距离越小,吸附能越大,吸附更稳定.     

MgO、SnO_2、TiO_2表面氧空位性质对气体光学传感特性的影响

光学气敏传感器是当今研究领域的一个热门方向.文章采用密度泛函理论(DFT)体系下广义梯度近似(GGA)第一性原理平面波超软赝势方法,分析和计算了光学气敏材料岩盐型MgO、金红石型SnO_2和锐钛矿型TiO_2表面氧空位的特性.以CO作为吸附分子进行微观机理研究,研究不同氧化物表面吸附气体分子的机理.对氧化物表面的几何结构、吸附能、态密度、差分电荷密度、电荷布居、电荷转移、光学性质等进行分析.研究发现:含有氧空位缺陷的MgO(001)、SnO_2(110)和TiO_2(101)能稳定的吸附CO分子,吸附后造成了材料光学性质的变化,可作为光学气敏传感材料.分析发现:氧空位氧化能力的大小是光学性质改变的核心原因.表面吸附CO分子后,发现SnO_2(110)表面对分子的吸附能最大,分子与表面的吸附距离最短.通过差分电荷密度和电荷布居数发现,表面与CO分子间存在电荷转移,其转移电子数目大小为:SnO_2(110)TiO_2(101)MgO(001),由此得出不同氧化物表面氧化性的大小为:SnO_2(110)TiO_2(101)MgO(001);通过对比吸收谱和反射谱发现:吸附气体分子后SnO_2(110)表面的光学性质变化最为明显,是一种较好的光学气敏传感材料.     

CH_4/H_2O/CO_2在β-SiO_2(100)面吸附的第一性原理研究

多孔介质中的吸附直接影响页岩气赋存、运移.基于密度泛函理论从量子力学角度研究CH_4/H_2O/CO_2在页岩储层主体矿物成分SiO_2上的吸附构型和吸附特性,计算并分析了吸附能与态密度等特征.研究表明:CH_4、H_2O和CO_2在β-SiO_2(100)面的吸附能分布在-0.2 eV～-0.1eV区间内,为物理吸附;最小吸附能大小依次为:CH_4 H_2O CO_2,即,CO_2的吸附能力最强,H_2O次之,CH_4最弱;各吸附质处于吸附能最大与最小时的键长键角变化均小于1%,最大吸附能对应的吸附质键长键角变化率均大于吸附能最小时的,吸附质的物理结构变化微弱表明其所受作用力微弱;基底处于最稳定吸附位时态密度基本重合,表明各吸附质与β-SiO_2表面相互作用相似且差异较小;CH_4、H_2O、CO_2的态密度均出现不同程度偏移,且CO_2在能量更低的区域具有态密度分布,更易优先吸附.     

甲烷在多孔硅表面物理吸附特征研究(英文)

在密度泛函理论耦合超软贋势第一性原理的平台上,研究了甲烷在Si(111)表面的物理吸附特性.通过建立硅晶胞的不同吸附位置(top、bridge、fcc)模型,对比分析了甲烷在相应位置吸附界面变化的键结构、吸附能和态密度,获得了相应吸附点的吸附特征.对比分析的结果表明,甲烷只有在fcc位置物理吸附状态较为理想.分析态密度、键长及键角等数据揭示fcc位甲烷吸附对体系硅晶胞有很大的影响,其体系的键能最低,即此时体系结构最稳定.本文所得研究成果可用于Si表面对甲烷气体的敏感性分析及气体传感器领域.     

特定位点上CO_2与(TiO_2)_n团簇相互作用的第一性原理研究（英文）

本文基于密度泛函理论系统地研究了(TiO_2)_n团簇上二氧化碳(CO_2)的吸附和活化性质.计算结果表明,CO_2更倾向于吸附在(TiO_2)_n团簇的桥氧原子上,形成"化学吸附"碳酸盐络合物.而CO更倾向于吸附到末端Ti-O的Ti原子上.发现计算得到的碳酸盐振动频率值与实验获得的结果非常吻合,这表明配合物中CO_2的几何构型与其线性型相比,有微小的弯转.通过对电子结构、电荷密度、电离势、HOMO-LUMO以及态密度的分析,证实了CO_2与团簇之间的电荷转移以及相互作用.从预测的能量分布图来看,(TiO_2)_n团簇上的CO_2活化与结构密切有关,相比于块体的TiO_2,CO_2在团簇结构上更易于吸附和活化.     

三氧化钨表面氢吸附机理的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法,在广义梯度近似下,研究了立方WO_3,WO_3(001)表面结构及其氢吸附机理.计算结果表明立方晶体WO_3理论带隙宽度为0.587 eV.WO_3(001)表面有WO终止(001)表面和O终止(001)表面两种结构,表面结构优化后W—O键长和W—O—W键角改变,从而实现表面弛豫;WO终止(001)表面和O终止(001)表面分别呈现n型半导体特征和p型半导体特征.分别计算了H原子吸附在WO终止(001)表面和O终止(001)表面的H—O_(2c)—H,H—O_(2c)…H—O_(2c),H—O_(1c)—H和H—O_(1c)…H—O_(1c)四种吸附构型,其中H—O_(1c)—H吸附构型的吸附能最小,H—O键最短,H失去电子数最多,分别为-3.684 eV,0.0968 nm和0.55e,此吸附构型最稳定.分析其吸附前后的态密度,带隙从吸附前的0.624 eV增加到1.004 eV,价带宽度基本不变.H的1s轨道电子与O的2p,2s轨道电子相互作用,在-8和-20 eV附近各形成了一个较强的孤立电子峰,两个H原子分别与一个O_(1c)原子形成化学键,最终吸附反应生成了一个H_2O分子,同时产生了一个表面氧空位.     

First-principles study on anatase TiO2（101） surface adsorption of NO

In this paper, the stable structure and the electronic and optical properties of nitric oxide （NO） adsorption on the anatase TiO2 （101） surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV （N end adsorption）, 2.6770 eV （O end adsorption）, and 4.1437 eV （horizontal adsorption）. The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 （101） surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 （101） surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.     

第一性原理研究H_2O分子在CaCO_3(104)表面吸附

基于密度泛函理论的第一性原理方法模拟研究H_2O在CaCO_3(104)表面的吸附特征.首先,研究H_2O分子在CaCO_3(104)表面的顶位、桥位(短桥位、长桥位)和穴位上垂直和平行表面两种类型下的8种高对称吸附结构模型,结合吸附能和稳定吸附构象确定最优吸附位.而后,基于H_2O/CaCO_3(104)最优吸附结构模型,研究吸附前后H_2O和CaCO_3(104)表面的物理结构、电子结构(Mulliken电荷布居数、态密度、电子局域函数)的特征,分析H_2O/CaCO_3(104)表面之间的相互作用以及成键机理.研究结果:吸附能和体系稳定构象显示H_2O分子/CaCO_3(104)表面的最稳定吸附结构为穴位-平行.在穴位-平行位吸附后,H_2O分子的O-H键长和H-O-H键角均发生改变; CaCO_3晶体平行和垂直(104)表面方向上原子位置均发生改变,表面层变化最大;即吸附作用对H_2O分子和CaCO_3晶体的物理结构均产生较大影响; H_2O/CaCO3(104)最优吸附体系的Mulliken电荷布居数、电子态密度、电子局域函数的研究均说明H_2O分子与CaCO3(104)之间存在电子的转移形成化学键.其中,Ca-O(H_2O)形成离子键,H(H_2O)-O(CaCO_3)之间存在氢键作用.本文研究揭示了方解石表面水湿性的原因,同时为方解石润湿性的深入研究奠定基础.     

First-principles study on the catalytic role of Ag in the oxygen adsorption of LaMnO3(0 0 1) surface

In the present paper, the catalytic role of Ag in the oxygen adsorption of LaMnO₃(0 0 1) surface has been theoretically investigated using first-principles calculations based on the density functional theory (DFT) and pseudopotential method. The O₂ adsorption energy is larger for the vertical adsorption and the covalent bond was formed between O₂ molecule and surface Mn. The calculation of electronic properties of interaction between Ag atom and LaMnO₃(0 0 1) surface demonstrates that the most stable position for Ag adsorption is hollow site. The O₂ adsorption energy dramatically increased from 0.298 eV to 1.108 eV due to Ag pre-adsorbed. It is Ag pre-adsorbed that facilitates O₂ adsorption on surface. The bond length and bond population of O₂ molecule indicate that Ag atom facilitates O₂ molecule dissociative adsorption. The Ag atom strengthens LaMnO₃(0 0 1) substrate activity and activity center was formed on surface, which enhances the electrocatalytic activity of LaMnO₃ as solid oxide fuel cells cathode material at low temperature.     

Adsorption of Al on the Si(0 0 1) surface

The first-principles calculations have been presented to study the adsorption of aluminum (Al) on the Si(0 0 1)(2×1) surface. We have investigated the optimized geometries and electronic structures of the adatom-substrate system. The adsorption energy of the system has been calculated. The most stable adsorption sites were consequently determined to be HH site and T3+T4. It is shown that the Si-Si dimer is asymmetric on the reconstructed bare surface and become symmetric upon Al adsorption. In addition, the bond length of Si-Si was found to be considerably elongated in the adsorption system. It is found that the work function change obtained in our work is different from other previous results on the adsorption of alkali metals on the Si(0 0 1) surface. In order to investigate the relative stability of phases at different coverages, the surface formation energy of the adsorption system was calculated. To shed light on the nature of the Al-Si bond and the character of silicon surface, the density of states (DOS) and difference charge density of the system were evaluated.     

MoSi_2(001)表面的氧吸附行为

运用第一原理密度泛函理论方法,首先计算了MoSi_2各清洁表面的表面能,(001)Si-|-Si断面具有较低的表面能,是MoSi_2最可能的解理面;通过生成能及键布居分析研究了单氧原子、双氧原子及氧分子在(001)Si-|-Si断面的吸附行为,发现单氧原子在空位处吸附最稳定,此时O极易与Si结合,得到的Si-O-Si键长及键角与SiO_2的非常接近,表明低浓度下O极易与表面的Si结合生成SiO_2;双氧原子发生空位+顶位吸附时O原子除与Si有强作用外,可与Mo有一定相互作用;氧分子以平行的方式接近空位最有利于吸附,此时氧分子最易分解为氧原子,发生氧原子在空位的吸附.     

Surface defects on ZnO nanowires: implications for design of sensors

Surface defects are commonly believed to be fundamentally important to gas-sensor performance. We examine the effect of gas coverage and ethanol orientation on its adsorption on the stoichiometric and oxygen deficient (101(-)0) nanowire surface. Our density functional theory calculations show that ethanol adsorbs in multiple stable configurations at coverages between 1/4 and 1 ML, highlighting the ability of ZnO to detect ethanol. Ethanol prefers to bind to a surface Zn via the adsorbate oxygen atom and, if a surface oxygen atom is in close proximity, the molecule is further stabilized by formation of a hydrogen bond between the hydrogen of the hydroxyl group and the surface oxygen. Two primary adsorption configurations were identified and have different binding strengths that could be distinguished experimentally by the magnitude of their OH stretching frequency. Our findings show that ethanol adsorbed on the oxygen deficient ZnO(101(-)0) surface has a reduced binding strength. This is due to either the lack of a hydrogen bond (due to a deficiency in surface oxygen) or to surface reconstruction that occurs on the defect surface that weakens the hydrogen bond interaction. This reduced binding on the oxygen deficient surface is in contrast to the defect enhanced gas-sensor interaction for other gases. Despite this difference, ethanol still acts as a reducing gas, donating electrons to the surface and decreasing the band gap. We show that multiple adsorbed ethanol molecules prefer to be orientated parallel to each other to facilitate the hydrogen bonding to the defect-free surface for enhanced interaction.