Periodicity-dependent long range coulomb on-site repulsion in hydrogen adsorbed graphene:A DFT+U study

The long rang Coulomb on-site repulsion between u electrons in hydrogen (H) adsorbed graphene has been studied based on DFT+U calculations.This study demonstrates that the rigidity of n electronic structure of graphene is partially destroyed in the cases of H adsorption due to the introduction of un-paired electron in this system.The softness of n conjugation is largely depending on the concentrations as well as the periodicity of H adsorption.Due to the destruction of the rigidity of n conjugation,the Coulomb on-site repulsion increases.The results show that the Coulomb on-site repulsion between n electrons is very sensitive to the periodicity of H adsorption.A considerable enhancement of Coulomb on-site repulsion occurs for the systems with 3n×3n peroidcity.More importantly,the strength and the patterns of Coulomb on-site repulsion in the graphene plane are significantly size-dependent,which further induces the band gap opening at Fermi level.Especially for 6 x 6 system,the on-site repulsion induces a stabilized non-ferromagnetic state.Our results reveal for the first time that the considerable long rang Coulomb onsite repulsion between n electrons exists which plays an important role in the electronic characteristics of H adsorbed graphene.The finding in this investigation provides new insight into the many-body interaction between localized impurities with delocalized n electrons in graphene related materials.     

Adsorption recovery of Ag(I) and Au(III) from an electronics industry wastewater on a clay mineral composite

The aim of this work is to investigate the ability of an adsorbent of a clay mineral composite to remove and recover gold and silver ions from wastewater. The composite was prepared by mixing phosphogypsum (PG), obtained from an industrial waste, and a natural clay mineral. The materials were characterized before and after use in adsorption by several techniques. Batch adsorption experiments were carried out, and the effects of the contact time and the pH and temperature of solution on the removal processes were investigated. The optimum pH for the adsorption was found to be 4. The adsorption of these metal ions reached equilibrium after 2 h of contact. The pseudo-first- and the pseudo-second-order kinetic models, as well as the Freundlich and the Langmuir isotherm equations, were considered to describe the adsorption results. The maximum adsorbed amount of 85 mg·g-1 Ag(I) and 108.3 mg·g-1 Au(Ⅲ) was found. The recovery of the adsorbed gold and silver ions from the adsorbent was also analyzed. Strong acids appeared to be the best desorption agents to recover gold and silver ions. The use of aqua regia gave regeneration rates close to 95.3% and 94.3% for Ag(I) and Au(Ⅲ), respectively. Finally, the removal of gold and silver ions from an industrial wastewater was tested in batch experiments, and percentage recoveries of 76.5% and 79.9% for Ag(I) and Au(Ⅲ), respectively, were obtained. To carry out the industrial application of the proposed methodology, an economic viability study is required.     

Highly Sensitive and Portable Gas Sensing System Based on Reduced Graphene Oxide

Graphene has been widely used in gas-sensing applications due to its large specific surface area and strong adsorption ability. Among different forms of graphene used as gas-sensing materials, reduced graphene oxide is one of the most convenient and economical materials to integrate with Si-based electronics, which is very important to graphene-based gas sensors. In addition, the stacking structure of graphene oxide flakes facilitates absorption and detection of gas molecules. Based on reduced graphene oxide, a highly sensitive and portable gas-sensing system was demonstrated here. Solution-based graphene oxide was cast on a chip like a TF memory card and then reduced thermally. A signal acquisition system was designed to monitor resistance variation as a sign of gas concentration. This miniature graphene-based gas sensor array demonstrates a new path for the use of graphene in gas-detection technologies. And the creation of a sensitive and portable graphene gas sensor also shows great potential in fields such as medicine and environmental science.     

Theoretical study of adsorption and dissociation of NH_3 on the Ir{110}(1×2) surface

The adsorption and dissociation of NH3 on Ir{110}(1×2) have been investigated using the densityfunctional calculations at a coverage of 0.25 ML. The adsorption sites, energy, and geometries were obtained for NH3, NH2, and H adsorptions on the surface. The transition state for NH3 dissociation on Ir{110}(1×2) was also identified. It was found that NH3 is adsorbed preferentially at the ridge atop site, while NH2 and H are adsorbed at the ridge bridge site. The activation barrier of NH3 dissociation is 78.4 kJ/mol, which is very close to the NH3 adsorption energy of 90.0 kJ/mol. This indicates that the desorption and dissociation of NH3 on Ir{110}(1×2) are very competitive, which is consistent with the recent experimental results.     

Theoretical study of adsorption and dissociation of NH3 on the Ir{110}（1×2） surface

The adsorption and dissociation of NH3 on Ir{110}（1×2） have been investigated using the density- functional calculations at a coverage of 0.25 ML. The adsorption sites, energy, and geometries were obtained for NH3, NH2, and H adsorptions on the surface. The transition state for NH3 dissociation on Ir{110}（1×2） was also identified. It was found that NH3 is adsorbed preferentially at the ridge atop site, while NH2 and H are adsorbed at the ridge bridge site. The activation barrier of NH3 dissociation is 78.4 kJ/mol, which is very close to the NH3 adsorption energy of 90.0 kJ/mol. This indicates that the desorption and dissociation of NH3 on Ir{110}（1×2） are very competitive, which is consistent with the recent experimental results.     

Potential Dependence of the Raman Spectra and the Study of Adsorption Model for 4, 4-Bipyridine on A Silver Electrode

The study of the adsorption properties and adsorption model of molecules or ions on substrates is an important part of surface enhanced Raman scattering (SERS) experimental investigations. In this paper, we will present the findings of our research work with regard to the potential dependence of the SERS spectra for 4, 4' -bipyridine (bpy) on the silver electrode and the adsorption model for bpy adsorbed on the silver electrode surface. We find the intensities of the SERS spectra with all Raman shifts can be changed by changing the applied potentiat and reach maxima when the applied potential is ca. -0.70 V (Vs. SCE). The experimental study also indicates that the pyridine ring of bpy adsorbs directly on the silver electrode surface via the N-atom.     

The first-principles study on the doping effect of Re in Ni3Al

Using first-principles density function for molecules method （DMol） and discrete variational method （DVM） based on the density functional theory, we studied the doping effect of Re in Ni3Al. The structure relaxation and the alloying energy show that Re has a strong Al site preference and leads to the local deformation, which is in agreement with the experimental results and other theoretical results. In addition, the charge density difference and the bond order show that Re can strongly enhance the interatomic interaction between the nearest neighbor atoms. From the density of states and the Pauli spectrum, we find that resonance states and localized states are induced by doping Re, and the doped Re atom forms the hybridized bond with the nearest neighbor atoms.     

Molecular dynamics simulations of atomic-scale friction in diamond-silver sliding system

Molecular dynamics simulations have been performed to explore the atomic-scale sliding friction, especially the stick-slip friction, in a system consisting of a diamond slider and a silver substrate. The mechanisms of the stick-slip behavior are investigated by considering sliding speeds between 10 m/s and 200 m/s.The analyses of the shear distance between the upmost layer and the downmost layer and displacements of a column of atoms in the slider show that shearing deformation of the slider is the main cause of the stick-slip phenomenon. Our simulations also present that a commensurate fit between the two contact surfaces is unimportant for the stick-slip friction.     

THE STUDY OF ADSORPTION MODEL FOR 4,4''''-BIPYRIDINE ADSORBED AT THE CHEMICALLY DEPOSITED SILVER FILM BY SERS

This paper presents the SERS spectru spectrum of 4,4'-bipyridine adsorbed at the chemically deposited silver film. Comparing with the normal Raman spectra of 4,4'-bipyridine in the solid state and in 0.5 mol/L methanol solution, we have studied the SERS spectrum and further discussed the adsorption model for 4,4'-bipyridine adsorbed at the chemically deposited silver film, and also explained the experimental results with image field mode. Experimental results show that 4,4'-bipyridine adsorbed at the chemically deposited silver film via N-atom of pyridinering (Upright).     

Statistic characteristics of severe convective storm during Warm-Season in the Beijing-Tianjin region and its vicinity

This study analyzed the climatological characteristics of severe convective storms in the Beijing and Tianjin region and its vicinity based on the Doppler radar data of Tanggu during May-August of 2003-2007. The climatological characteristics, e.g. storm area, volume, top height, max reflectivity, life time and motion, are analyzed. The results include： 75% of all storms in the Beijing-Tianjin region last no more than 30 minutes, and most storms have a volume less than 400 kin3; most storms move from southwest to northeast while the speed is between 10-30 km/h; the mean storm top height is about 6 km, but some strong convective storms can have a top height larger than 15 kin; finally, storm area and volume have a similar geographical distribution character showing increasing trends from west to east. Compared with the statistic results based on the conventional surface meteorological observations, the results based on the radar data can present not only 3D spatial statistic results of convective storms （e.g., volume and top height）, but also the quantitative climatological characteristics, such as the lifetime and speed distributions. These statistical results are useful for studying the climatic characteristics of convective storms in the Beijing-Tianjin region and its vicinity.     

Al,Si,P掺杂对Ge在石墨烯上吸附的影响

利用基于密度泛函理论的第一性原理计算方法研究了Al、Si和P掺杂对Ge在石墨烯上吸附的影响.Ge原子在完整石墨烯上吸附的最稳定位置为桥位,Ge的吸附改变了石墨烯中C原子的电子自旋性质;Al、Si和P掺杂石墨烯使衬底C原子发生了移动,且Si,P原子掺杂比Al掺杂石墨烯容易;杂质类型对Ge在石墨烯上的吸附位置有较大的影响,...     

Ag/石墨烯复合涂层的制备及抗菌性能

首先用改进的Hummers法制备氧化石墨烯（GO）; 其次用原位还原法将银氨溶液中的Ag纳米粒子通过还原剂葡萄糖和GO复合, 获得Ag/GO胶体; 最后在真空干燥条件下得到Ag/GO涂层, 并用真空阶梯热还原技术制备Ag/还原氧化石墨烯(rGO)涂层. 利用X射线衍射、 扫描电子显微镜、 透射电子显微镜等方法对膜样品结构形貌进行表征, 并用润湿角测量仪和抑菌环方法分别检测样品的亲/疏水性和抗菌性能. 实验结果表明: 石墨烯基膜材料与基底结合较好, Ag纳米粒子在石墨烯片层间呈球形均匀分布, 粒径为20~50 nm; 纯GO和rGO膜表面未见菌落, 大肠杆菌与金黄色葡萄球菌均未出现有效抑菌环; 复合Ag纳米粒子后, 涂层的抑菌效果得到显著提高; 与Ag/GO复合膜相比, Ag/rGO复合膜呈更强的抗菌活性, 即低温退火有助于提高石墨烯基复合涂层的抗菌性能.     

Ag/graphene composite based on high-quality graphene with high electrical and mechanical properties

A simple and effective process has been reported to prepare the silver (Ag)/graphene composite with excellent mechanical and electrical properties based on high-quality graphene (HQG). The HQG was fabricated via hot pressing of reduced graphene oxide (RGO) from chemical exfoliation, while the Ag/HQG composite was obtained by using spark plasma sintering (SPS) treatment under high temperature (1500 °C) and moderate pressure (40 MPa). With low oxygen-containing functional groups and defect density, the HQG dispersed homogeneously in the composite after high-energy ball milling. In comparison to pure Ag, the as-prepared Ag/RGO composite exhibited a great enhancement of 11% electrical conductivity and 42% micro-hardness with an optimal RGO adding content (1 wt%). The Ag/HQG composite is expected to open up a new way for the novel Ag-based electrical contact materials, and further to broaden its applications in micro-electronics and switching power.     

金属表面Mo(W)-S彩色簇合物膜的光谱研究

Mo（W）S4^2-与金属M（M=Cu、Fe、Zn、Ag、Ni、Sn）表面发生配位化学反应，得到不溶性且具有装饰效果的Mo（W）-S彩色簇合物膜。随着反应时间或加热时间的变化，膜呈现不同的具有金属光泽的颜色。这种膜层属于功能性修饰层，不仅赋予金属表面以美观的外表，而且提高表面的光洁度和清洁度，增强金属＇一的抗腐蚀性能。本文采用加速腐蚀实验、LSV、CV、FT-IR、FT—Raman、XPS和AES研究了Mo（W）S4^2-在金属表面的成键特征和波谱变化，探讨了簇合物膜的组成、性能、结构、化学状态和形成机理。结果表明，膜层中存在桥基Mo（W）-S—M键、端基Mo（W）-S和Mo（W）-O键。膜为多分子层组成的复杂体系，其颜色是各组分统计分布的结果。     

用XANES研究Ga_(1-x)Mn_xN稀磁半导体的Mn原子的局域结构

利用基于实空间多重散射的XANES研究了Ga1-xMnxN(x=0.01,0.25,0.10)稀磁半导体中Mn原子的局域结构.结果表明在低Mn含量(摩尔浓度)的Ga0.990Mn0.010N样品中,Mn原子替代了GaN中的Ga,以替位形式存在.当Mn含量增加到0.025时,部分Mn原子处于被4个Ga所包围的间隙位,并与替位Mn原子形成了MnGa-MnI二聚体.当Mn含量进一步增加到0.100时,样品中的Mn原子主要以Mn团簇形式存在.     

掺杂对Al(111)面氧分子吸附性能影响

为了揭示掺杂对Al(111)面O2吸附性能影响规律。采用基于密度泛函理论（Density Functional Theory, DFT）的第一性原理计算方法,通过构建模型以及设置计算参数,计算得到了不同O原子覆盖度下Ni、Mn、Si掺杂对应Al(111)面吸附O2的吸附能、功函、Bader电荷、差分电荷密度、以及态密度。研究表明：当氧原子覆盖度较低情况下,纯铝表面吸附能绝对值最大,转移电子数最多,原子之间存在相互作用并主要由最外层电子轨道决定。当氧原子覆盖度增大至3/8时,掺杂表面吸附能大于纯铝表面,掺杂促进了Al(111)面吸附氧分子。结果表明：Al(111)面吸附氧分子的能力不仅与掺杂元素有关,还与各表面O原子的覆盖度有关,当O原子覆盖度较低时,Mn、Si、Ni掺杂抑制了O2吸附,当覆盖度较高时,Ni、Mn、Si掺杂促进了O2吸附。     

GaN（0001）表面吸附TiO2的DFT研究

建立了GaN(0001)2×2表面吸附模型,采用基于DFT动力学赝势方法,对TiO2分子的吸附进行了理论计算.研究了TiO2分子在GaN(0001)表面的吸附成键过程、成键方位及表面化学键特性.计算结果表明吸附过程经历了物理吸附、化学吸附与稳定态形成的过程,化学结合能达到7.184～7.423 eV.不同初始位置的TiO2分子吸附后,Ti在fcc或hcp位置,两个O原子分别与表面两个Ga原子成键,Ga—O化学键表现出共价键特征,O—O连线与GaN[11-20]方向平行,与实验观测(100)[001]TiO2//(0001)[11-20]GaN一致.     

氧原子在金属银（211）（410） （997）台阶表面吸附和解离的理论研究

笔者利用原子与表面簇合物相互作用的5参数Morse势（5- MP）的理论方法,对氧-银（211）（410）（997）台阶体系进行了研究,并获得了全部临界点性质.通过对（211） （997）台阶面吸附的研究,表明实验上在Ag（111）平坦表面所测得的27.3meV,30 meV为反常的低频振动;对（410）台阶面的研究,推测在Ag（410）台阶缺陷表面存在三类四个氧原子吸附位,其中位于台阶底部的四重LB位是最稳定的吸附位.     

石墨烯吸附材料的制备与应用研究进展

石墨烯具有独特的结构、优异的性能,在诸多领域有广泛的应用.石墨烯层的原子均为表面原子,其表面积非常大,是天然的吸附材料.其易于制备、成本低廉等优势使得石墨烯吸附材料成为水处理研究中的热点.石墨烯及其复合材料已经在重金属、染料、杀虫剂、抗生素、石油等污染物的治理方面得到应用.综述了石墨烯吸附材料的制备方法以及其在污水处理方面的应用.分析了污染物在石墨烯吸附材料上的吸附行为,并讨论了石墨烯与污染物的相互作用.着重关注官能团对石墨烯吸附材料性能的影响,从化学视角提出了设计高效石墨烯吸附剂的思路.     

席夫碱化合物在银溶胶上的吸附状态研究

合成了系列席夫碱化合物,研究了它们的表面增强拉曼光谱,傅立叶变换拉曼光谱,探讨了它们在银溶胶上的吸附状态和表面增强机理,发现这类化合物以化学吸附模式为主,为进一步研究它们在生物体系中的作用方式提供依据。