石墨和纳米碳中缺陷和电子密度随温度的变化

测量了石墨和纳米碳在不同温度下的正电子寿命谱,研究了石墨和纳米碳中缺陷和电子密度随温度的变化.结果表明,纳米碳中缺陷的开空间和缺陷浓度分别大于和高于石墨晶体;纳米碳的平均自由电子密度低于石墨晶体.当温度从25K升至295K时,石墨和纳米碳中的平均自由电子密度随温度的升高而下降:石墨晶体中的自由电子密度随温度的升高变化较小;纳米碳的自由电子密度随温度的升高变化较大.随着温度的升高,石墨和纳米碳中的热空位数量增多,而且这些空位可迁移至微孔洞的内表面使微孔洞的开空间增大.     

接枝羧基的有限长碳纳米管电子结构的第一性原理研究

基于局域密度泛函理论，采用第一性原理方法，建立了对(5,5)型和(9,0)型有限长碳纳米管接枝羧基官能团的原子模型，通过计算其电子分布和态密度的变化，讨论羧基官能团对碳纳米管电子结构和电子输运特性的影响. 计算表明，接枝羧基的碳纳米管,其电子结构明显改变，其费米能级上的电子态密度下降；最高占据轨道上的非定域程度减弱,致使电子输运性能呈下降趋势. 关键词： 碳纳米管 密度泛函理论 电子结构     

脉冲磁场处理对碳纳米管掺杂MgB2线材临界电流密度的影响

对碳纳米管(CNT)掺杂MgB₂超导体磁场处理后的行为进行了研究. 结果表明，CNT掺杂MgB₂超导体经5T脉冲磁场处理后临界电流密度J_c(H)在低磁场下提高了2—3倍，高场下提高一个数量级以上，扫描电镜结果显示CNT沿着处理磁场方向规则排列并且成为MgB₂基体的形核中心和高效的磁通钉扎中心. 关键词： 2')" href="#">MgB₂ 碳纳米管 脉冲磁场处理     

La2Sn2O7/g-C3N4 nanocomposites: Rapid and green sonochemical fabrication and photo-degradation performance for removal of dye contaminations

The deficiency of drinking water sources has become a serious crisis for the future of the world that the photocatalytic process is one of the most favorable methods for removal of artificial dyes and poisonous organic impurities. In the present study, rapid ultrasonic treatment was performed to obtain La₂Sn₂O₇/Graphitic carbon nitrides (LSO/CN) nanocomposites with advanced photo-catalytic performance. Broccoli extract was utilized as a natural surfactant with active surface groups to control nucleation and growth of formed crystals with the creation of spatial barriers around the cations, and finally prevent nano-product agglomeration. Changing experimental parameters in synthesis reaction in turn offers a virtuous control over the nano-products size and shape. The shape and size distribution of particles was considered via diverse characterization techniques of microscopic and spectroscopic. The photocatalytic behaviors along with a kinetic study of the nanoparticles were examined by elimination and degradation of different artificial dyes under the UV waves. Effect of particle size, weight ratio of LSO:CN, type of dye, scavenger kind, dye and catalyst loading was designated on altering proficiency of nano-catalyst function. Also, the probable mechanism of removal dye by photocatalytic function was studied.     

Facile and Scalable Synthesis of Si@void@C Embedded in Interconnected 3D Porous Carbon Architecture for High Performance Lithium-Ion Batteries

Si-based materials possess huge potential as an excellent anode material for Li-ion batteries. However, how to realize scalable synthesis of Si-based anode with a long cycling life and high-performance is still a critical challenge. Here a water-in-oil microemulsion process followed by UV illumination, calcination, and hydrothermal method to produce yolk-shell Si@void@C embedded in interconnected 3D porous carbon network architecture using silicon nanoparticles is reported. As a result, the sample Si@void@C/C-2 electrode has achieved a reversible capacity of 1160 mA h g⁻¹ at 0.2 A g⁻¹ after 300 cycles and a stable long cycling life of 480 mA h g⁻¹ at 1 A g⁻¹ after 1000 cycles. A full battery with the synthesized anode shows a capacity of 128 mA h g⁻¹ at 0.2 A g⁻¹ as well as good cycling stability after 1100th cycles. Such excellent electrochemical performance is ascribed to its unique structure, the yolk-shell void space, highly robust carbon shells and interconnected porous carbon nets that can improve the conductivity of the electrode, buffer the volume expansion, and also suppress Si nanoparticles stress variation. This water-in oil system makes it possible for mass production of environmentally friendly synthesis of core–shell structure.     

Synthesizing Red Fluorescent Carbon Dots from Rigid Polycyclic Conjugated Molecules: Dual-Mode Sensing and Bioimaging in Biochemical Applications

Red fluorescent carbon dots (R-CDs) are special desirable for biochemical analysis due to good biological compatibility and deep penetration; however, they remain as bottlenecks due to difficulties in expanding the sp² domain, especially those are fused from rigid polycyclic conjugated molecules (RPCMs) with heteroatom substituents due to huge steric hindrance and heteroatom blockage toward graphic lattice. Here, an RPCM with heteroatom substituents, 1,5-diamino-4,8-dihydroxyanthraquinone (DDAQ), based self-doped R-CDs with PL emission at 635 nm is reported. Further investigations reveal that the expanding, hybrid sp² domain with indanthrone tannin structure from DDAQ is mainly responsible for the obtained red fluorescence of R-CDs. Taking advantage of optical properties, R-CDs are considered to construct a colorimetric/fluorescent dual mode sensing array for quantifying trace levels of Fe³⁺ and glyphosate based on the static quenching, and a biomarker for cell imaging. The CD-based sensors exhibit outstanding recovery, high selectivity, and sensitivity, also facilitated dual-mode detection with the naked-eye. The R-CDs have low cytotoxicity, good cell membrane penetration for rapid cell entry, and high resolution, demonstrating their potential for biolabeling and bioanalytic applications.     

Cyclodextrin Functionalized Carbon Dots Using IFE and FRET Dual Mechanism for Sequential Detection of Morin and Al3+

Carbon dots (CDs) are emerging photoluminescent materials with excellent optical properties. However, the lack of active sites in primitive CDs has limited their development applications. Herein, functionalized carbon dots (Z-CDs) are successfully prepared by surface modification of CDs with mono (6-amino-6-deoxy) cyclodextrin (β-CD). The introduction of β-CD increases the spatial potential resistance between CDs, which effectively reduces the self-quenching effect. Moreover, the conjugated domains of Z-CDs are expanded, which improves the optical properties with a quantum yield of 48.74%. Z-CDs are able to be used in the sequential detection of morin and Al³⁺, and the fluorescence mechanisms are confirmed to be internal filtration effect and fluorescence resonance energy transfer, respectively. The limits of detection are 0.817 and 0.231 × 10⁻⁶ m . This study not only provides an idea to solve the problem of self-quenching of CDs but also enriches the detection means of flavonoids and ions, which is expected to be applied to biosensing and environmental monitoring.     

Assessment of dispersion corrections in DFT calculations on large biological systems

The performance of empirical dispersion corrections in DFT calculations has been assessed for several large, genuine biological systems that include MbAB, H64L(AB), and V68N(AB) (AB?=?CO, O₂), where Mb stands for a wild-type myoglobin, H64L is the (histidine64?→?leucine) mutated myoglobin, and V68N is the (valine68?→?asparagine) mutated myoglobin. The effects of the local protein environment are accounted for by including the five nearest surrounding residues in the calculated systems and they are examined by comparing the binding energies of AB to the myoglobin and to the porphyrin (Por) without residues. Three versions of Grimme's dispersion correction methods, labeled as DFT-D1, DFT-D2, and DFT-D3, were all tested. In the first version (-D1), the dispersion correction (E_disp) is calculated only for noncovalent interactions between molecular fragments and E_disp within a covalent molecule is not calculated. For the DFT functionals, for which the calculated Por–AB binding energies are already too large, only further overestimation occurs when a dispersion correction is made. The geometry optimizations show that the DFT-D2 and DFT-D3 approaches give too short distances between the residues and the heme moiety in the myoglobins and their calculated relative binding energies ΔE_bind(myoglobin-AB/Por–AB) are in poor agreement with experiment in most cases. DFT-D1 performs very well, ensuring structural and energetic features in close agreement with experiment.