CO在金属掺杂TiO2纳米管阵列中的吸附及氧化

采用密度泛函理论(DFT)研究了五种不同金属元素V、Cr、Pd、Pt、Au掺杂二氧化钛纳米管阵列(TNTAs)的性质以及CO在这些二氧化钛纳米管阵列中的吸附和氧化.结果表明:金属的掺杂使TNTAs的带隙减小;弱吸附的CO能够和二氧化钛纳米管阵列中的晶格氧通过氧化还原机理生成CO2,这可归因于纳米管阵列的限域效应和金属元素的掺杂.合适的金属掺杂能促进CO氧化,除Cr以外的金属元素的掺杂降低了CO氧化的活化能垒,特别是Pd或Au的掺杂使能垒降低最为明显.贵金属元素Pd或Au掺杂TiO2纳米管阵列具有优良的光催化性能,可用于CO的低温氧化催化剂.     

一氧化碳分子在Pt/t-ZrO2(101)表面的吸附性质

运用广义梯度密度泛函理论(GGA-PW91)结合周期平板模型方法,研究了CO分子在完整与Pt负载的四方ZrO2(101)表面的吸附行为.结果表明:表面第二层第二氧位和表面第二桥位分别为CO分子和Pt原子在完整ZrO2(101)表面的稳定吸附位,且覆盖度为0.25ML(monolayer)时均为稳定吸附构型,吸附能分别为56.2和352.7kJ·mol-1.CO分子在负载表面的稳定吸附模式为C-end吸附,吸附能为323.8kJ·mol-1.考察了CO分子在负载表面吸附前后的振动频率、态密度和轨道电荷布居分析,并与CO分子和Pt原子在ZrO2表面的结果进行比较.结果表明,C端吸附CO分子键长为0.1161nm,与自由的和吸附在ZrO2表面后的CO相应值(0.1141和0.1136nm)相比伸长.吸附后C―O键伸缩振动频率为2018cm-1,与自由CO分子相比发生红移;吸附后CO带部分正电荷,电子转移以Pt5dCO2π的π反馈机理占主导地位.     

CO和H在Pt/WC(0001)表面的吸附

采用密度泛函理论(DFT)和周期平板模型,研究两种WC(0001)表面的几何结构和表面能,并对Pt原子单层(PtML)在两种WC(0001)表面的高对称性吸附位上的吸附能和分离功进行计算.结果发现,终止于W原子的WC(0001)为最稳定的WC(0001)表面,Pt原子单层以hcp位的方式吸附于W终止的WC(0001)表面是PtML/WC(0001)体系最稳定的几何构型.在此基础上研究了CO分子和H原子分别在PtML/WC(0001)表面和具有相似表面结构的Pt(111)表面的吸附行为.在0.25 ML(monolayer)低覆盖度下,与在Pt(111)表面相比,在PtML/WC(0001)表面上的Pt—C间距明显拉长和CO分子吸附能减少,说明PtML/WC(0001)表面抗CO中毒能力比Pt(111)表面高;态密度分析进一步解释了CO分子与不同表面Pt原子的成键机理.在同一覆盖度下,H原子在PtML/WC(0001)表面的最大吸附能等于甚至略高于在Pt(111)表面的,表明Pt/WC对氢气氧化反应具有良好的催化活性,是一种很有前途的质子交换膜燃料电池(PEMFC)阳极催化剂.     

甲醇在Pt-Fe(111)/C表面吸附的理论研究

采用密度泛函理论和周期平板模型相结合的方法, 对CH3OH分子在Pt-Fe(111)/C表面top, fcc, hcp和bridge位的吸附模型进行了构型优化、能量计算, 结果表明bridge位是较有利的吸附位. 掺杂后费米能级的位置发生了右移, 价带和导带均增宽, 极利于电子-空穴的迁移, 这对提高催化活性是非常有利的. 考察抗中毒性发现: CO在Pt(111)/C面上的吸附能比甲醇吸附能要高, CO在Pt-Fe(111)/C的吸附能比甲醇吸附能要低, 可说明CO在Pt(111)/C面上有中毒效应, 而Pt-Fe(111)/C的抗CO中毒能力增强, 是催化氧化甲醇良好的催化剂.     

Pt（111）和Pt3Ni（111）表面上CO催化氧化反应的密度泛函理论研究

采用密度泛函理论,对Pt(111)和Pt3Ni(111)表面上CO和O的单独吸附、共吸附以及CO的氧化反应进行了系统的研究. 结果表明, Pt3Ni(111)表面上CO的吸附弱于Pt(111)表面, O的吸附明显强于Pt(111)表面. 两个表面表现出相似的CO催化氧化活性. 表面Ni的存在不但稳定了O的吸附,同时也降低了过渡态O的能量.     

杂原子掺杂的含单空位缺陷BN纳米管的非线性光学性质

采用密度泛函理论(DFT)研究了杂原子M(M=Li, Na, K, Be, Mg, Ca, C和Si)在B/N单空位缺陷处的掺杂对(6,0)BN纳米管体系非线性光学性质的影响. 采用B3LYP方法共得到了14种几何构型, 并采用BHandHLYP方法计算了这些结构的第一超极化率β₀值. 研究结果表明, 单纯的B或N缺陷几乎不影响BN纳米管体系的非线性光学性质; 与B缺陷处掺杂的体系相比, 杂原子在N缺陷处的掺杂更有利于提高BN纳米管体系的第一超极化率β₀值; 对于同周期掺杂原子, 还原性越强的原子掺杂对BN纳米管体系的第一超极化率β₀值的改善越明显, 表现为β₀(Ⅰ族)>β₀(Ⅱ族)>β₀(Ⅳ族); 对比同主族掺杂原子, 第三周期元素Na和Mg的掺杂能更有效地提高体系的第一超极化率β₀值, 原因主要在于原子半径和还原性等因素共同决定其对BN纳米管体系第一超极化率β₀值的改善程度. 本文研究结果为有效提高BN纳米管体系的非线性光学性质提供了一种新思路, 为基于BN纳米管的非线性光学材料设计提供了有价值的理论信息.     

甲醇在Pt-Mo(111)/C表面上的吸附

采用密度泛函理论和周期平板模型相结合的方法, 对CH3OH分子在Pt-Mo(111)/C表面的顶位、穴位和桥位共计9种吸附模型进行了构型优化、能量计算和频率分析, 结果表明top-Pt位是较有利的吸附位. Mo掺杂后价带与导带位置均有不同程度的降低, 电子结构的变化使得Pt-Mo(111)/C的催化活性提高. 并且在考虑催化剂抗中毒性能时发现: CO在Pt(111)/C面上的吸附能比甲醇吸附能要高, CO在Pt-Mo(111)/C上的吸附能比甲醇的要低, 说明CO在Pt(111)/C面上的吸附会阻碍甲醇的吸附, 并影响催化过程的进行, 而Pt-Mo(111)/C的抗CO中毒化能力增强, 是催化氧化甲醇较好的催化剂.     

硅掺杂的氮化硼纳米管对氯化氰吸附性能的理论研究

为了探索氮化硼纳米管(BNNT)在化学传感器件领域的潜在应用,我们利用密度泛函理论研究了(8,0)单壁BNNT和硅掺杂的(8,0)BNNT对毒性气体氯化氰分子(ClCN)的吸附性能.结果表明,硼位或氮位硅掺杂的BNNT,均对ClCN分子存在较强的化学吸附,而纯氮化硼纳米管对ClCN仅有较弱的物理吸附.态密度的计算进一步表明硅掺杂使纳米管费米能级附近的电子结构发生显著变化,由于杂化态的引入,使带隙明显减小,增强了对毒性ClCN分子的吸附敏感性.硅掺杂的BNNT有望成为检测毒性ClCN分子的潜在资源.     

铂催化氧还原反应过程中磷酸的影响及抑制磷酸吸附策略

与低温(<100oC)质子交换膜燃料电池相比,磷酸掺杂PBI膜燃料电池可工作于100–200 oC,工作温度的提高有利于提高电极反应动力学速率、增加Pt催化剂对CO等毒物的耐受性,以及简化电池水管理等.然而,磷酸在Pt催化剂表面吸附较强,这将造成Pt一定程度的毒化.基于“第三体效应”,即在Pt表面预吸附某些小分子,可在一定程度上抑制磷酸吸附,然而预吸附分子同时也将占据Pt表面部分活性位点,因而Pt的催化性能最终由两个因素决定：磷酸抑制程度和预吸附分子在Pt表面的覆盖度.
　　本文系统考察了Pt表面预吸附分子覆盖度和预吸附分子链长对其催化氧还原反应(ORR)活性的影响.首先,通过控制预吸附了胺类分子的Pt电极的电位,得到表面具有不同覆盖度的Pt电极,考察了0.1 mol/L H3PO4电解液中Pt电极对ORR的催化活性随预吸附分子覆盖度的变化规律;为分离磷酸吸附和修饰分子吸附本身对Pt催化活性的影响,对比了0.1 mol/L HClO4电解液中Pt电极对ORR的催化活性随预吸附分子覆盖度的变化规律.进一步对比研究了不同链长胺分子——正丁胺(BA)、正辛胺(OA)及十二胺(DA)等作为修饰分子对Pt/C催化剂电催化ORR活性的影响.结果表明,随修饰分子在Pt表面覆盖度提高,在0.1 mol/L HClO4溶液中,由于预吸附分子占据Pt部分活性位,修饰后光滑Pt电极表面的本征活性单调下降;而在0.1 mol/L H3PO4中,修饰后光滑Pt电极表面的ORR活性呈现先升高后降低的趋势,当预吸附分子覆盖度约为20%时,其ORR活性最高,为未修饰的光滑Pt电极表面的1.67倍.这表明预吸附分子有效抑制了磷酸的吸附,且当预吸附分子覆盖度约为20%时,预吸附分子对Pt表面的占据与其抑制磷酸吸附的作用达到最佳平衡点.然而,当修饰分子BA, OA和DA在Pt表面覆盖度分别为38.6%,26.1%和26.1%时, Pt/C在0.1 mol/L H3PO4中的ORR催化活性接近,分别为未经修饰Pt/C电催化剂的1.7,1.8和2.0倍,这表明预吸附分子链长对ORR催化活性影响较小,表面预吸附分子抑制磷酸吸附的策略对Pt/C催化剂也同样适用.同时, Pt/C电极经BA, OA和DA修饰后,其在0.1 mol/L HClO4中的比表面活性分别为未经修饰Pt/C电催化剂的1.0,1.1和1.3倍,与修饰后光滑Pt电极表面本征ORR活性变化规律不一致.然而,与Pt在HClO4电解质中的ORR活性相比, ORR的半波电位仍有大约123 mV的差距,今后还需继续从催化剂的角度,如调控Pt表面的吸附特性,或从创新电解质的角度,如有机磷酸电解质等出发解决磷酸毒化的问题.     

光照对Pt/Al2O3光热CO2加氢反应的增强作用（英文）

在传统热催化材料的研究领域中,光照技术已经得到了广泛的应用,从而使传统热催化剂的催化反应活性和选择性得到优化.然而,在光热协同催化反应过程中,光照因素对催化反应过程的影响尚未得到很好地研究和理解.本文通过浸渍法制得Pt/Al2O3催化剂,并应用于光热协同催化CO2加氢反应.结果证明,在光热协同CO2加氢催化反应中, Pt/Al2O3催化剂表现出光热协同效应.本文结合原位漫反射红外光谱(operandoDRIFTS)和密度泛函理论计算(DFT)对光照因素对该催化反应过程的作用机制进行了进一步深入研究.结果表明, CO气体分子从Pt纳米颗粒上的脱附过程为CO2加氢反应的重要步骤;CO气体分子在Pt纳米颗粒上脱附的位置包含台阶位置(Ptstep)和平台位置(Ptterrace).结果表明,反应过程中CO气体分子从Pt表面的脱附有利于催化剂暴露出Pt反应活性位点.值得注意的是,在光热协同催化CO2加氢反应过程中,光照和温度因素对CO气体分子的脱附过程具有不同影响.吸附能的计算结果证明, CO气体分子吸附在Ptstep和Ptterrace上的吸附能分别为-1.24和-1.43eV.由此可见, CO气体分子与Pt纳米颗粒上的Ptstep吸附位点之间相互作用更强.在无光照作用的条件下对催化剂进行加热, CO气体分子更容易从Ptterrace吸附位点发生脱附;但是在对应的温度下加入光照作用后,吸附在Ptstep位点上的CO气体分子会先转移到Ptterrace吸附位点上,随后脱附,从而促进CO2加氢反应的进行.     

Ab initio theoretical study of non-covalent adsorption of aromatic molecules on boron nitride nanotubes

We have studied non-covalent functionalization of boron nitride nanotubes (BNNTs) with benzene molecule and with seven other different heterocyclic aromatic rings (furan, thiophene, pyrrole, pyridine, pyrazine, pyrimidine, and pyridazine, respectively). A hybrid density functional theory (DFT) method with the inclusion of dispersion correction is employed. The structural and electronic properties of the functionalized BNNTs are obtained. The DFT calculation shows that upon adsorption to the BNNT, the center of aromatic rings tend to locate on top of the nitrogen site. The trend of adsorption energy for the aromatic rings on the BNNTs shows marked dependence on different intermolecular interactions, including the dispersion interaction (area of the delocalized π bond), the dipole-dipole interaction (polarization), and the electrostatic repulsion (lone pair electrons). The DFT calculation also shows that non-covalent functionalization of BNNTs with aromatic rings can give rise to new impurity states within the band gap of pristine BNNTs, suggesting possible carrier doping of BNNTs via selective adsorption of aromatic rings.     

Single‐wall Boron Nitride Nanotube with Various Diameters under the Influence of Electric Field,A Computational Investigation

Structural and electrical response of the (4, 0), (5, 0) and (6, 0) zigzag model of single‐walled boron nitride nanotube (BNNT) with H‐terminated at the open ended, have been investigated under the external electric field (EF) with intensities 0–1.6 × 10^?2 a.u. using the DFT B3LYP/6‐31G* level of theory. Results of this study show that with increasing BNNTs diameter, the HOMO‐LUMO gap (HLG) values increase, and with increasing the EF intensity, the HLG values decrease. In both cases with increasing EF intensity and the BNNT diameters, the electric dipole moment is increased significantly. Also the calculated natural bond orbital (NBO) atomic charges on the atoms of the BNNT show that the separation of the center of the positive and the center of the negative electric charges of the boron nitride nanotubes are increases in both case. We have found that the properties of the BNNTs are dependent on their diameters and can be tuned by applied electric fields intensity.     

NBO,AIM, and TD-DFT assisted screening of BNNT optimum diameter on ethyl phosphorodimethylamidocyanidate sensor design

A computational study based on DFT calculations was performed to investigate the effect of phosphorodimethylamidocyanidate (PDMAC) molecule adsorption on the surface of pure and Ga-doped (4,0), (5,0), (6,0), (7,0), and (8,0) zigzag boron-nitride nanotubes (BNNTs). Our results reveal that the interactions between PDMAC molecule and (5,0), (6,0), (7,0), and (8,0) BNNTs are weak. However, according to the AIM and NBO analysis the PDMAC exhibits strong affinity towards the (4,0) BNNT with appreciable adsorption energy (?111.03 kJ/mol). The adsorption of PDMAC molecule onto the (4,0) BNNT affect the electronic conductance, hypsochromic, and hyperchromic shifts in the calculated UV-Visible spectrum. Based on the obtained results, it is expected that the pristine and Ga-doped (4,0) BNNT could be promising candidates in gas sensor devices for detecting the PDMAC molecule.     

Synthesis of boron nitride nanotube films with a nanoparticle catalyst

Boron nitride nanotube (BNNT) films were synthesized by combining ball milling and thermal chemical vapor deposition (CVD) using nano-Fe₃O₄ as a catalyst. The as-produced BNNTs have a bamboo-like structure and have a diameter in the range of 50~200 nm with an average length of more than 40 mm. Moreover, BNNT nanojunction structures were synthesized. The structure and morphology of the BNNTs were characterized by XRD, SEM, TEM and HRTEM. The possible growth mechanism of BNNTs and BNNT nanojunction structures were proposed. Though the BNNT films were observed, out of our expectation, BNNTs with thin tube wall and small average diameter have not been achieved, and this could be mainly ascribed to the aggregation of the nanoparticle catalyst, resulting in greater catalyst particles during the process of BNNT growth. This result will provide a promising approach to obtain the desired shape of BNNTs and produce branched junctions of BNNTs.     

In situ real-time study buckling behavior of boron nitride nanotubes with axial compression by TEM

The real time analysis structure evolution of BNNT with compression showed that the formation of V-shape in the post-buckling before BNNT fracture was reversible.     

HPLC Characterization of the Association Mechanism of Organic Compounds with β Cyclodextrin Using a Novel Boron Nitride Nanotube Particulate Stationary Phase

In this paper, a simple homogeneous coating of silica spherical particles with pristine boron nitride nanotubes (BNNTs) was described. BNNTs dissolved in dimethylacetamide (DMAc) were mixed with amino-functionalized silica particles having a 5 μm diameter. Favorable interaction between the amino group and the BNNT surfaces induces the absorption of the BNNTs on the silica. The BNNT-coated silica particles were used as stationary phase for HPLC. For the first time, it was demonstrated that this new particulate BNNT stationary phase can be used for the study of the complexation of solute molecules (terpene molecules used as test drugs in this work) with β cyclodextrin (βCD). The apparent formation constants Kf of terpene derivative/βCD were in the same magnitude as those reported in the literature. The plot of Kf versus the water fraction in the methanol/water mobile phase showed that the BNNT surface played an active role in the complex formation due to terpene/BNNT-specific polar interactions. This work demonstrated that our novel particulate BNNT HPLC stationary phase was an efficient tool to study molecular recognition mechanism and more specifically the association between a drug substance and a target molecule with the aim of reaching biopharmaceutic and clinical applications.     

Electronic structures of organic molecule encapsulated BN nanotubes under transverse electric field

The electronic structures of boron nitride nanotubes (BNNTs) doped by different organic molecules under a transverse electric field were investigated via first-principles calculations. The external field reduces the energy gap of BNNT, thus makes the molecular bands closer to the BNNT band edges and enhances the charge transfers between BNNT and molecules. The effects of the electric field direction on the band structure are negligible. The electric field shielding effect of BNNT to the inside organic molecules is discussed. Organic molecule doping strongly modifies the optical property of BNNT, and the absorption edge is redshifted under static transverse electric field.     

A first principles study on organic molecule encapsulated boron nitride nanotubes

The electronic structures of boron nitride nanotubes (BNNTs) doped with organic molecules are investigated using density functional theory. An electrophilic molecule introduces acceptor states in the wide gap of BNNT close to the valence band edge, which makes the doped system a p-type semiconductor. However, with typical nucleophilic organic molecules encapsulation, only deep occupied molecular states but no shallow donor states are observed. There is a significant electron transfer from a BNNT to an electrophilic molecule, while the charge transfer between a nucleophilic molecule and a BNNT is negligible. When both electrophilic and nucleophilic molecules are encapsulated in the same BNNT, a large charge transfer between the two kinds of molecules occurs. The resulting small energy gap can strongly modify the transport and optical properties of the system.     

Nitrogen monoxide storage and sensing applications of transition metal–doped boron nitride nanotubes: a DFT investigation

The structural properties, electronic properties, and adsorption abilities for nitrogen monoxide (NO) molecule adsorption on pristine and transition metal (TM = V, Cr, Mn, Nb, Mo, Tc, Ta, W, and Re) doping on B or N site of armchair (5,5) single-walled boron nitride nanotube (BNNT) were investigated using the density functional theory method. The binding energies of TM-doped BNNTs reveal that the Mo atom doping exhibits the strongest binding ability with BNNT. In addition, the NO molecule weakly interacts with the pristine BNNT, whereas it has a strong adsorption ability on TM-doped BNNTs. The increase in the adsorption ability of NO molecule onto the TM-doped BNNTs is due to the geometrical deformation on TM doping site and the charge transfer between TM-doped BNNTs and NO molecule. Moreover, a significant decrease in energy gap of the BNNT after TM doping is expected to be an available strategy for improving its electrical conductivity. These observations suggest that NO adsorption and sensing ability of BNNT could be greatly improved by introducing appropriate TM dopant. Therefore, TM-doped BNNTs may be a useful guidance to be storage and sensing materials for the detection of NO molecule.