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.     

Strain Induced Insulator-Metal Transition in Single Wall Carbon Nanotubes

In terms of a single-π orbital model, an analytical expression of the lowest-lying conduction-band and the highestlying valence-band is derived for single wall carbon nanotubes under both the uniaxial and torsional strains. We observe not only semiconductor-metal transitions in primary metallic tubes, but also insulator-metal transitions     

Conformational change-modulated spin transport at single-molecule level in carbon systems

Controlling the spin transport at the single-molecule level, especially without the use of ferromagnetic contacts, becomes a focus of research in spintronics. Inspired by the progress on atomic-level molecular synthesis, through first-principles calculations, we investigate the spin-dependent electronic transport of graphene nanoflakes with side-bonded functional groups, contacted by atomic carbon chain electrodes. It is found that, by rotating the functional group, the spin polarization of the transmission at the Fermi level could be switched between completely polarized and unpolarized states. Moreover, the transition between spin-up and spin-down polarized states can also be achieved, operating as a dual-spin filter. Further analysis shows that, it is the spin-dependent shift of density of states, caused by the rotation, that triggers the shift of transmission peaks, and then results in the variation of spin polarization. Such a feature is found to be robust to the length of the nanoflake and the electrode material, showing great application potential. Those findings may throw light on the development of spintronic devices.     

基于反应力场的分子动力学方法研究氢在钯表面的分解

基于二阶矩近似反应力场方法构建的全维度势能面研究了氢分子及其同位素分子在钯表面的分解过程.在构建势能面的过程中数据库中只包含了氢分子与钯（111）表面相互作用的相关信息,该势能面在研究氢分子在钯（100）表面上的分解过程中表现出了非常好的可转移性.结果表明,氢分子及其同位素分子在钯（111）与钯（100）表面上的分解系数S₀均随着入射能量的增加呈现非单调变化,并且通过固定分子取向的方法发现同核分子（H₂、D₂和T₂）最有利分解取向角为90°,而异核分子（HD、HT和DT）受质心偏移的影响,其最有利分解取向角向大角度偏移.     

Magnetotransport in a dual waveguide coupled by a finite barrier： Energy filter and directional coupler

We propose in this paper that a dual waveguide coupled by a finite barrier be able to serve as an energy filter under a perpendicular magnetic field. In the waveguide direction, the conductance exhibits a periodic square-wave pattern in which the miniband is controlled by the magnetic and potential modulation. The electrons with energies in the miniband can completely transfer along one waveguide while the other electrons undergo filtration. Compared with the coupled waveguide without magnetic modulation, the structure under magnetic field is found to be a good directional coupler. By adjusting the potential barrier and magnetic field, the electrons input from one port of waveguide can transfer to any other ports.     

Ground state properties of a Bose－Einstein condensate confined in an anharmonic external potential

In light of the interference experiment of Bose－Einstein condensates, we present an anharmonic external potential model to study ground state properties of Bose－Einstein condensates. The ground state energy and the chemical potential have been analytically obtained, which are lower than those in harmonic trap. Additionally, it is found that the anharmonic strength of the external potential has an important effect on density and velocity distributions of the ground state for the Thomas－Fermi model.     

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.     

考虑次近邻相互作用下一维单原子链中的孤立波

利用多重尺度法结合准不连续性近似,研究了涉及次近邻相互作用下的一维单原子链中的波动问题,得到了其新的色散关系.结果表明,在同时考虑次近邻相互作用和非谐相互作用的情况下,一维单原子链中不仅存在包络孤立波、扭状和反扭状孤立波,而且存在另一种孤立波形式的元激发——呼吸子. 关键词： 一维单原子链 非谐相互作用 孤立波     

纳米结构链的hopping电导实空间重正化群方法

基于Miller-Abrahams理论,发展了一种重正化群方法,研究了一维纳米结构体系的hopping电导.研究表明在纳米结构体系中晶粒种类、晶粒尺寸对hopping电导有显著的调制作用,界面结构及晶格畸变等对hopping电导也有不同程度的影响.     

多Nb原子掺杂氮化碳与H离子协同作用促进氮高效还原

电化学合成氨因其可以低能耗产氨而备受关注.目前,迫切需要一种稳定、无污染、活性好和选择性高的催化剂来促进电化学合成氨.石墨相氮化碳由于制备简单且具有较好的物理化学性质,是一种有广阔应用前景的基底材料.研究表明,纯石墨相氮化碳不具有电化学合成氨的性能,因此需要对其进行改性.元素掺杂是一种常见的改性方式,其中过渡金属元素因...