碱活化多孔碳用于分离甲苯及活化/吸附机理

采用生物质木质素磺酸钠(SLS)为碳源, 先与硬模板NaCl混合预碳化, 再加入活化剂NaOH在氮气保护下升温至850 ℃碳化, 得到SLS基碱活化的多孔碳吸附剂(SPCN). 将SPCN用于吸附液体石蜡中芳香烃甲苯, 对比研究了不同活化剂加入量对SPCN结构、 性质及吸附效果的影响. 结果表明, SPCN表面具有丰富的官能团和发达的微/介孔结构, 活化剂加入量对比表面积的影响为先增大后减小, 碱/碳质量比为1∶1时比表面积达到最大值(710.4 m ²/g); 吸附量与比表面积呈正相关, 样品SPCN-1的最大吸附量为2875.17 mg/g, 远高于商业吸附剂, 经5次吸附-解吸循环后仍保持92.5%的吸附效率. 探究了活化机理, NaOH、 碳质和气体发生氧化还原反应释放气体留下孔隙, 经充分酸洗、 水洗后得到永久孔道. 最后, 结合扫描电子显微镜(SEM)、 透射电子显微镜(TEM)、 拉曼光谱(Raman)、 X射线衍射(XRD)、 傅里叶变换红外光谱(FTIR)和比表面积分析等结果证明了吸附机理主要是孔隙填充效应、 范德华力、 π-π相互作用及电子供/受体作用的共同作用. 首次报道了SPCN应用的新方向并探究了活化与吸附机理, 制备方法简易、 经济, 产品循环稳定性好、 无污染, 有望用于工业化生产.     

Phonon spectrum boron nitrideof single-wallednanotubes

Based on a force constant model, we investigated the phonon spectrum and then specific heat of single-walled boron nitride nanotubes. The results show that the frequencies of Raman and infrared active modes decrease with increasing diameter in the low frequency, which is consistent with the results calculated by density functional theory. The fitting formulae for diameter and chirality dependence of specific heat at 300K are given.     

单壁纳米碳管的声子谱研究

通过五步旋转操作方便地得到了不同位置原子间的力常数矩阵，从而可以使对各种不同类型管的声子谱的计算变得简便. 计算表明，非螺旋的扶手椅型（n, n）管与锯齿型(n, 0)管的非简并和二重简并模式数分别为12和6(n-1)，这与从群论等方法所得结果相符. 关键词： 纳米碳管 声子谱 振动模式密度 动力学矩阵     

Codoping of Potassium and Bromine in Carbon Nanotubes： A Density Functional Theory Study

We investigate the co-doping of potassium and bromine in single-walled carbon nanotubes （SWCNTs） and doublewalled carbon nanotubes （DWCNTs） based on density functional theory. In the co-doped （6,0） SWCNTs, the 4s electron of potassium is transferred to nanotube and Br, leading to the n-type feature of SWCNTs. When potassium is intercalated into inner tube and bromine is put on outer tube, the positive and negative charges reside on the outer and inner tubes of the （7,0）@（16,0） DWCNT, respectively. It is expected that DWCNTs would be an ideal candidate for p-n junction and diode applications.     

Electronic transport properties of metallic single-walled carbon nanotubes

We have calculated the differential conductance of metallic carbon nanotubes by the scatter matrix methon.It is found that the differential conductance of metallic nanotube-based devices oscillates as a function of the bias voltage between the two leads and the gate voltage.Oscillation period T is directly proportional to the reciprocal of nanotube length.In addition,we found that electronic transport properties are sensitive to variation of the length of the nanotube.     

Lattice Dynamics of Potassium－Doped Single－Walled Carbon Nanotubes

We calculate the vibrational properties of potassium-doped single-walled carbon nanotubes within lattice dynamical theory. The results show that the frequency of high-frequency Raman mode E29 for K5C40 downshifts to 1553cm^-1, which is in agreement with the value for highly doped samples with effective composition KC8.Moreover, the specific heat curves have a turnover at 22 K, originating from the saturation of K atoms vibrational modes at low energy.     

硼或氮掺杂的锯齿型石墨烯纳米带的非共线磁序与电子输运性质

基于非共线磁序密度泛函/非平衡格林函数方法,研究了硼或氮掺杂的锯齿型石墨烯纳米带的非共线磁序与电子透射系数.未掺杂的石墨烯纳米带的计算结果表明磁化分布主要遵循类似于Neel磁畴壁的螺旋式磁化分布.相比于未掺杂的情况,硼/氮掺杂的石墨烯纳米带的磁化分布出现了双区域的特征,即杂质原子附近的磁化较小,杂质原子左(右)侧区域的磁化分布更接近于左(右)电极的磁化方向,这为通过掺杂手段在石墨烯纳米带边缘上构建不同磁畴壁提供了可能性.与未掺杂的透射系数不同的是,硼/氮掺杂的石墨烯纳米带的透射系数在费米面附近随着磁化偏转角增大而减小,表明非共线磁序引起的自旋翻转散射占据主导地位.而在E=±0.65 eV处,出现了一个较宽的dip结构,投影电子态密度的分析表明其来源于杂质原子形成的束缚态所引起的背散射.我们的研究结果对于理解石墨烯纳米带中的非共线磁序与杂质散射以及器件设计具有一定的意义.     

Thermal conductivity of GaAs／A1As superlattices： The Umklapp process

The thermal conductivity of GaAs/AlAs superlattices limited by the three-phonon Umklapp process and boundary scattering has been studied theoretically based on the model of lattice dynamics with force constant matrix. It was found that the Umklapp relaxation rate approximates BTω^2/n with a fitting parameter B. The thermal conductivity increases with the increase of temperature at low temperatures, and would show a peak behaviour at about 60K before falling off at high temperatures. In addition, the thermal conductivity increases with the increase of period thickness of the superlattices.     

Stability, defect and electronic properties of graphane-like carbon-halogen compounds

We perform first-principles total energy calculations to investigate the stabilities and the electronic structures of graphane-like structures of carbon-halogen compounds, where the hydrogen atoms in the graphane are substituted by halogen atoms. Three halogen elements, fluorine (F), chlorine (Cl) and bromine (Br), are considered, and the graphane-like structures are named as CF, CCl and CBr, respectively. It is found that for the single-atom adsorption, only the F adatom can be chemically adsorbed on the graphene. However, the stable graphane-like structures of CF, CCl and CBr can form due to the interaction between the halogen atoms. The carbon atoms in the stable CF, CCl and CBr compounds are in the sp³ hybridization, forming a hexagonal network similar to the graphane. The electronic band calculations show that CF and CCl are semiconductors with band gaps of 3.28 eV and 1.66 eV, respectively, while CBr is a metal. Moreover, the molecular dynamics simulation is employed to clarify the stabilities of CF and CCl. Those two compounds are stable at room temperature. A high temperature (≥1200 K) is needed to damage CF, while CCl is destroyed at 700 K. Furthermore, the effects of a vacancy on the structure and the electronic property of CF are discussed.     

The influence of electronic transport across interface junction between Si substrate and the root of ZnO micro-prism on field emission performance

ZnO micro-prisms are prepared on the p-type and n-type Si substrates, separately. The $I$--$V$ curves analysed by AFM show that the interface junctions between the ZnO micro-prisms and the p-type substrate and between the ZnO micro-prisms and the n-type Si substrate exhibit p--n junction behaviour and ohmic contact behaviour, respectively. The formation of the p--n heterojunction and ohmic contact is ascribed to the intrinsic n-type conduction of ZnO material. Better field emission performance (lower onset voltage and larger emission current) is observed from an individual ZnO micro-prism grown on the n-type Si substrate. It is suggested that the n-Si/n-ZnO interfacial ohmic contact benefits the electron emission; while the p-Si/n-ZnO interface heterojunction deteriorates the electron emission.