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.     

掺杂碳纳米管对五氯酚吸附作用的理论研究

为了寻找检测高毒性、持久性有机污染物五氯酚(PCP)的新型材料,应用密度泛函理论研究了(8,0)和(5,5)单壁碳纳米管(SWCNT)以及相应的Si、B和N掺杂的SWCNT对PCP分子的吸附性能.计算结果表明,(8,0)和(5,5)SWCNT与PCP分子之间为物理吸附;Si原子掺杂(8,0)和(5,5)SWCNT,引起了碳纳米管掺杂部位六元环的畸变,增强了SWCNT的反应活性,掺杂后的SWCNT对PCP分子形成化学吸附,其几何结构和电子性质发生了显著变化;B和N原子掺杂的SWCNT对PCP分子的吸附没有明显增强.Si原子掺杂的SWCNT最有潜力用于检测PCP分子.     

铂掺杂氮化硼纳米管及CO在其表面的吸附行为的理论研究

采用基于密度泛函理论的PBEPBE方法对铂(Pt)掺杂的氮化硼(BN)纳米管进行了理论研究. 计算结果表明, Pt原子突出BN纳米管表面, Pt的d轨道暴露到外面, 使它更容易和外来分子发生相互作用, 提高了纳米管的反应活性. Pt取代掺杂缩小了纳米管的能隙, 从而提高BN纳米管的导电性. 一氧化碳(CO)在Pt掺杂BN纳米管上的吸附行为表明, 2个CO能化学吸附到纳米管表面, 更多的CO分子吸附是物理吸附.     

Mn掺杂TiO_2(101)提高锂空电池阴极催化活性的第一性原理研究

本文基于密度泛函理论对TiO_2(101)和Mn_xTi_(1-x)O_2(101)作为锂空电池阴极催化材料进行了研究,发现其表面能够生成两种不同结构的Li_2O_2,进一步地研究了其中最稳定的生成结构并通过计算锂空电池首次充放电过程中的过电势来评价催化性能.结果表明,Mn掺杂进入Ti O_2(101)对充放电的过电势均有降低作用,深入分析发现掺杂Mn对TiO_2促进阴极催化反应的本质因素源于掺杂原子Mn的d态轨道的分布以及其平均能量.掺杂原子的d态轨道在费米能级处的峰态诱导了附近O的p态轨道,二者共同作用在Mn_xTi_(1-x)O_2(101)的总态密度的费米能级处形成多个新峰,改变了催化剂的导电方式.此外,由于掺杂原子Mn的d态轨道的平均能量高于Ti原子,使得O的p态轨道受到更多的激发,促使在Mn掺杂原子附近的氧空位形成能降低,为放电过程阴极催化反应的氧还原提供了更多的活性位点并且有利于氧气的吸附与还原.     

氢原子在Pt及Pt系双金属催化表面吸附的密度泛函理论研究

采用密度泛函理论(dFT)考察了Pt(100)、(110)、(111)三种表面氢原子的吸附行为, 计算了覆盖度为0.25 ML时氢原子在Pt 三种表面和M-Pt(111)双金属(M=Al, Fe, Co, Ni, Cu, Pd)上的最稳定吸附位、表面能以及吸附前后金属表面原子层间弛豫情况. 分析了氢原子在不同双金属表面吸附前后的局域态密度变化以及双金属表面d 带中心偏离费米能级的程度并与氢吸附能进行了关联. 计算结果表明, 在Pt(100), Pt(110)和Pt(111)表面, 氢原子的稳定吸附位分别为桥位、短桥位和fcc 穴位. 三种表面中以Pt(111)的表面能最低, 结构最稳定. 氢原子在不同M-Pt(111)双金属表面上的最稳定吸附位均为fcc 穴位, 其中在Ni-Pt 双金属表面的吸附能最低, Co-Pt 次之. 表明氢原子在Ni-Pt 和Co-Pt 双金属表面的吸附最稳定. 通过对氢原子在M-Pt(111)双金属表面吸附前后的局域态密度变化的分析, 验证了氢原子吸附能计算结果的准确性. 掺杂金属Ni、Co、Fe 的3d-Pt(111)双金属表面在吸附氢原子后发生弛豫, 第一层和第二层金属原子均不同程度地向外膨胀. 此外, 3d金属的掺入使得其对应的M-Pt(111)双金属表面d带中心与Pt 相比更靠近费米能级, 吸附氢原子能力增强, 表明3d-Pt系双金属表面有可能比Pt具有更好的脱氢活性.     

苯环共价功能化碳纳米管电性理论研究

通过4种键连方式将苯环共价连接到超晶胞为1×1×3的锯齿型单壁碳纳米管CNT(8,0)上.在密度泛函理论基础上,通过Siesta软件计算苯环共价功能化碳纳米管的几何结构、能带结构、态密度和波函数,分析键连方式对碳纳米管电性的影响.结果表明苯环通过4种键连方式共价功能化的碳纳米管都是在Γ点具有直接带隙的半导体.其中直接键连和酰胺键连得到的苯环功能化碳纳米管在费米能级附近产生杂质带,比纯CNT带隙减小约0.4e V.而通过2个亚甲基键连和吡咯烷键连2种方式功能化的碳纳米管,其带隙仅比纯CNT带隙减小0.1~0.15e V.     

氮化硼纳米管热输运性能的分子动力学模拟

采用基于声子散射理论的Boltzmann-Peierls声子传输方程(BTE)和非平衡态分子动力学模拟(NEMD)方法研究了氮化硼纳米管(BNNT)的热输运性能.分析了BNNT的热力耦合效应,通过BTE与NEMD两种方法相结合,分析了温度和长度对BNNT热输运性能的影响,并应用量子修正扩大了NEMD的研究范围.结果表明:随着拉伸或压缩应变的增加,BNNT热输运性能均呈降低的趋势.通过计算声子态密度(PDOS)在理论上分析了以上结果,发现在拉伸状态下,声子模式的变化是决定BNNT热输运性能变化的主要因素;在压缩状态下,热导率变化是由于模型发生明显的屈曲变形引起的.在低温段,BNNT的热输运性能受量子效应影响最初有一个线性增加的过程,当温度超过一定值时,其开始显著地降低;当BNNT长度小于120nm时,随着长度的增加,其弹道性能逐渐减弱,但仍主要体现为弹道特征,其热导率(κ)与长度(L)基本满足κ∝Lα这一关系.     

氮化硼纳米管气敏特性的理论研究

采用密度泛函理论计算研究了氮化硼纳米管及碳掺杂氮化硼纳米管对CH4, CO2, H2, H2O, N2, NH3, NO2, O2, F2等十余种气体小分子的气敏特性. 研究结果表明: 氮化硼纳米管对CH4, CO2, H2, H2O, N2, NH3等气体分子不敏感, 而对O2, NO2, F2等气体分子比较敏感. 虽然碳掺杂氮化硼纳米管可以明显地改变其表面的化学反应活性, 增强了气体分子与氮化硼纳米管之间的相互作用, 但是并不能明显地改变其对所研究气体分子的敏感性.     

β-环糊精修饰的壳聚糖对氯酚吸附的动力学和热力学

制备了β-环糊精(β-CD)修饰的壳聚糖(CS)—β-环糊精-6-壳聚糖(CS-CD), 并用傅里叶变换红外(FT-IR)光谱仪, 扫描电镜(SEM), X 射线衍射(XRD)仪和比表面分析仪(BET)进行了表征. 详细研究了其对2-氯酚(2-CP)、2,4-二氯酚(DCP)和2,4,6-三氯酚(TCP)的吸附行为和机理. 研究表明其吸附较好地满足Langmuir 和Freundlich 吸附模型, β-环糊精的引入能够较大地提高吸附效率, 2-CP、DCP和TCP在CS-CD上吸附的最大吸附量分别为14.51、50.68和74.29 mg·g^-1. 动力学研究表明其吸附速率快, 在1 h内能达到吸附平衡, 并符合假二级动力学模型. 计算出了热力学参数ΔG⁰、ΔH⁰和ΔS⁰的值, ΔG⁰为负值表明吸附剂对氯酚的吸附是一个自发的过程. 电解质和溶液pH值对吸附的影响说明在吸附过程中主要是氯酚与吸附剂之间形成了氢键, 并进一步讨论了可能的吸附机理. 改性吸附剂易重复利用, 重复使用六次后的质量和吸附效率与初次相比分别保持在90%和82%以上, 然而CS的质量有较大的损失, 吸附效率也明显降低.     

Li掺杂ZnO的电子结构与电性能的研究

采用密度泛函理论平面波超软赝势方法研究了p型Li掺杂的纤锌矿结构ZnO的能带结构、态密度和电荷分布,并分析了Li掺杂ZnO的电输运性能.结果表明,Li掺杂ZnO具有1.6eV的直接带隙,且为p型半导体,体系费米能级附近的态密度大大提高,在导带和价带中都出现了由Li电子能级形成的能带,其费米能级附近的能带主要由Li的s态、Zn的p态、Zn的d态和O的p态电子构成,且他们之间存在着强相互作用.电输运参数和电输运性能分析结果表明,Li掺杂的ZnO氧化物价带和导带中的载流子有效质量均较大;其载流子输运主要由Li的s态、Zn的p态和O的p态电子完成;Li掺杂有望改善ZnO的电输运性能.     

A sensitive electrochemical chlorophenols sensor based on nanocomposite of ZnSe quantum dots and cetyltrimethylammonium bromide

In this work, a very sensitive and simple electrochemical sensor for chlorophenols (CPs) based on a nanocomposite of cetyltrimethylammonium bromide (CTAB) and ZnSe quantum dots (ZnSe–CTAB) through electrostatic self-assembly technology was built for the first time. The composite of ZnSe–CTAB introduced a favorable access for the electron transfer and gave superior electrocatalytic activity for the oxidation of CPs than ZnSe QDs and CTAB alone. Differential pulse voltammetry (DPV) was used for the quantitative determination of the CPs including 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP). Under the optimum conditions, the peak currents of the CPs were proportional to their concentrations in the range from 0.02 to 10.0 μM for 2-CP, 0.006 to 9.0 μM for 2,4-DCP, and 0.06 to 8.0 for PCP. The detection limits were 0.008 μM for 2-CP, 0.002 μM for 2,4-DCP, and 0.01 μM for PCP, respectively. The method was successfully applied for the determination of CPs in waste water with satisfactory recoveries. This ZnSe–CTAB electrode system provides operational access to design environment-friendly CPs sensors.     

The effect of gas adsorption on the field emission mechanism of carbon nanotubes

We have investigated systematically the effects of various gas adsorbates (H2, N2, O2, and H2O) on the electronic structures and the field emission properties of open edges of single-walled carbon nanotubes by density functional calculations. All of the molecules, except N2, dissociate and chemisorb on open nanotube edges with large adsorption energies. The Fermi levels are moved toward the valence (conduction) bands for O2 (H2, H2O) adsorption induced by the Mulliken charge transfer on the tube edge. The Fermi level shift for N2 adsorption is negligible. Adsorption of H2O enhances the field emission current, whereas H2 adsorption does not affect the field emission current much because of the absence of the density of states near the Fermi level. The correlation of the electronic structures and the field emission current is further discussed.     

The activity and selectivity of catalytic peroxide oxidation of chlorophenols over Cu-Al hydrotalcite/clay composite

Liquid phase catalytic oxidation of chlorophenols (CPs) was carried out over Cu-Al hydrotalcite/clay composite at ambient temperature and pressure using hydrogen peroxide as oxidant. The results showed that the catalyst had high catalytic activity, with complete oxidation of 4-CP within 40 min at 40 °C. The content and position of chlorine on the aromatic ring had significantly different effects on the oxidation rate of CPs, with the rate sequence of phenol > monochlorophenol (MCP) > dichlorophenol (DCP) > trichlorophenol (TCP), 3-CP > 2-CP > 4-CP, and 3,5-DCP > 3,4-DCP > 2,5-DCP > 2,4-DCP > 2,6-DCP. This was ascribed to the interactions among σ-electron withdrawing conductive effect, π-electron donating conjugative effect, and steric hindrance effect of chlorine. It was evidenced that the catalytic peroxide oxidation of CPs in the first step was selective and rate-limiting, where chlorinated 1,4-benzoquinones formed.     

Studies on the encapsulation of F- in single walled nanotubes of different chiralities using density functional theory calculations and Car-Parrinello molecular dynamics simulations

In this study, the encapsulation of F(-) in different nanotubes (NTs) has been investigated using electronic structure calculations and Car-Parrinello molecular dynamics simulations. The carbon atoms in the single walled carbon nanotube (CNT) are systematically doped with B and N atoms. The effect of the encapsulation of F(-) in the boron nitride nanotube (BNNT) has also been investigated. Electronic structure calculations show that the (7,0) chirality nanotube forms a more stable endohedral complex (with F(-)) than the other nanotubes. Evidence obtained from the band structure of CNT calculations reveals that the band gap of the CNT is marginally affected by the encapsulation. However, the same encapsulation significantly changes the band gap of the BNNT. The density of states (DOS) derived from the calculations shows significant changes near the Fermi level. The snapshots obtained from the CPMD simulation highlight the fluctuation of the anion inside the tube and there is more fluctuation in BNNT than in CNT.     

Theoretical Study of Adsorption Behavior of Vemurafenib Drug over BNNT(5,5-9) as a Factor of Drug Delivery: a DFT Study

In this research, a density functional theory(DFT) calculation was performed for investigation adsorption behavior of the anticancer drug Vemurafenib on BNNT(5,5-9) by using the M06-2X/6-31 G* level of theory in the solvent water. The electronic spectra of the Vemurafenib drug, BNNT(5,5-9) and complex BNNT(5,5-9)/Vemurafenib in solvent water were calculated by Time Dependent Density Functional Theory(TD-DFT) for the study of adsorption effect. The non-bonded interaction effects of the Vemurafenib drug with BNNT(5,5-9) on the electronic properties, natural charges and chemical shift tensors have been also detected. The results display the change in title parameters after process adsorption. According to the natural bond orbital(NBO) results, the molecule Vemurafenib and BNNT(5,5-9) play as both electron donor and acceptor at the complex BNNT(5,5-9)/Vemurafenib. On the other hand, the charge transfer occurs between the bonding, antibonding or nonbonding orbitals in two molecules drug and BNNT. As a consequence, BNNT(5,5-9) can be considered as a drug delivery system for the transportation of Vemurafenib as anticancer drug within the biological systems.     

Mixed hemimicelles solid-phase extraction based on cetyltrimethylammonium bromide-coated nano-magnets Fe3O4 for the determination of chlorophenols in environmental water samples coupled with liquid chromatography/spectrophotometry detection

Mixed hemimicelles solid-phase extraction (SPE) based on cetyltrimethylammonium bromide (CTAB)-coated nano-magnets Fe3O4 was investigated for the preconcentration of four chlorophenols (CPs) in environmental water samples prior to HPLC-spectrophotometry determination in this paper. By the rapid isolating (about 5 min) of Fe3O4 nanoparticles (NPs) through placing a Nd-Fe-B strong magnet on the bottom of beaker, the time-consuming preconcentration process of loading large volume sample in conversional SPE method with a column can be avoided. The unique properties of Fe3O4 NPs such as high surface area and strong magnetism were utilized adequately in the SPE process. This novel separation method produced a high preconcentration rate and factor. A comprehensive study of the adsorption conditions such as the Fe3O4 NPs zeta-potential, CTAB added amounts, pH value, standing time and maximal extraction volume was also presented. Under optimized conditions, four analytes of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP) were quantitatively extracted. The method was then used to determine four CPs in five real environmental water samples. High concentration factors (700) were achieved for each of the analytes, with observed detection limits ranging between 0.11 and 0.15 microg L(-1). The accuracy of method was evaluated by recovery measurements on spiked samples. Good recovery results (83-98%) with satisfactory relative standard deviation (RSD) were achieved. It is important to note that satisfactory preconcentration factors and extraction recoveries for the four CPs were obtained with only a little amount of Fe3O4 NPs (0.1g) and CTAB (60 mg). To the best of our knowledge, this was the first time a mixed hemimicelles SPE method based on Fe3O4 NPs magnetic separation had been used for the pretreatment of environmental water samples.     

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.     

Theoretical prediction of encapsulation and adsorption of platinum-anticancer drugs into single walled boron nitride and carbon nanotubes

In this research, the adsorption and encapsulation of cisplatin, nedplatin, oxaliplatin and carbaplatin as Pt-anticancer drugs into the (7,7) boron nitride nanotube (BNNT) and carbon nanotube (CNT) are investigated using density functional theory. The different orientation modes of drug molecules onto the outer and inner surfaces of BNNT and CNT are studied. Analysis of the adsorption energy reveals that the complex formation process is favorable. The calculated adsorption energies indicate that the encapsulation of drugs inside the nanotubes is more favorable than the adsorption of drugs outside of the nanotubes. On the other hand, the results show that the BNNT/oxaliplatin(in) system is more stable than the others. The stabilization of nanotube/drug complexes results in electronic and structural properties change in the nanotubes. The natural bond orbital calculations show that the van der Waals forces, hydrogen bonding and electrostatic interactions are the major factors contributed to the overall stabilities of the complexes. The predicted electronic and structural properties of BNNT compared to the CNT towards Pt-anticancer drugs, suggest that BNNT can act as drug delivery vehicles.     

Ferrocene-1,1'-dithiol as molecular wire between Ag electrodes: the role of surface defects

The interaction of ferrocene-1,1(')-dithiol (FDT) with two parallel Ag(111) surfaces has been theoretically studied at density-functional level. The effect of surface defects on the energetic and electronic structure was investigated. The electronic transport properties are studied with the nonequilibrium Green's function approach. The adsorption geometry has a strong effect on the electronic levels and conductivity. The presence of point defects strongly enhances the molecule-surface interaction but has a surprisingly small effect on the density of states near the Fermi energy. The FDT-surface bond is particularly strong near terraces or steps and leads to significant shifts of the molecular orbitals relative to the gas phase. For all considered defect types except the single adatom the electronic conductivity through the FDT molecule is decreased compared to adsorption on perfect surfaces.