The effect of bernard-marangoni convection on percolation threshold in amorphous polymer-multiwall carbon nanotube composites

The electrical conductivity of amorphous polymer/multiwall carbon nanotube (MWCNT) composite films strongly depends on the Bernard-Marangoni (B-M) instability during solvent evaporation. We demonstrate that the films exhibit the lowest surface resistivity and the highest light transmittance near the onset point of B-M instability. The polymer/MWCNT composite films exhibit three-dimensional behavior in spite of the B-M instability. The percolation threshold for PC/MWCNT composite films at stable, onset, and unstable condition is 3.3 × 10⁻³, 2.75 × 10⁻³, and 5.15 × 10⁻³ vol.%, respectively.     

Evaluation of residual iron in carbon nanotubes purified by acid treatments

A detailed analysis by X-ray photoelectron spectroscopy was carried out on multi-walled carbon nanotube (MWCNT) surfaces after non-oxidative and oxidative purification treatments in liquid-phase. The MWCNT were produced by pyrolysis of camphor and ferrocene, that provides a high yield but with high iron contamination (∼15% wt). The elimination and/or oxidation of iron nanoparticles were monitored by Fe2p and O1s core level. Oxygen-based functional groups attachment was also investigated by C1s fitting. The effectiveness of each treatment in iron removal was evaluated by thermogravimetric analysis (TGA) and atomic absorption spectroscopy (AAS). The integrity of the MWCNT structure was verified by Raman spectroscopy (RS) and transmission electron microscopy (TEM). A purity degree higher than 98% was achieved only with non-oxidative treatments using sonification process.     

不同参数多壁碳纳米管的拉曼光谱研究

拉曼光谱是进行碳材料结构与性质研究的有力手段,为了研究多壁碳纳米管(MWCNT)的管径和长度对其拉曼光学性质的影响,本研究对一系列不同管径和长度的多壁碳纳米管进行拉曼光谱的测试和分析。研究发现: 与高取向的石墨相比,多壁碳纳米管一阶拉曼光谱的G峰中心和D峰中心都会向低波数发生不同程度的红移;MWCNT两个主要特征峰(G峰和D峰)峰强在其他条件相同的情况下,与MWCNT的管径成正比,与长度成反比;G峰的频移与MWCNT的管径和长度两个因素密切相关,与管径成反比关系(这与单壁碳纳米管的径向呼吸模有着一致的结果),与管长成正比关系,而D 峰的频移受MWCNT的管径和长度的影响很弱,并对此现象进行了初步分析。在此基础上,我们以MWCNT的长径比为横坐标,G峰频移为纵坐标作图,进行线性拟合,得到了G峰频移与长径比成一定的线性递增关系。采用同样的分析方法,我们将G峰和D峰强度分别对MWCNT的长径比作图,进行线性拟合,得到了G峰和D峰强度分别与MWCNT的长径比成一定的线性递减关系。     

Ni修饰碳纳米管促进合成气高效制甲醇Cu基催化剂研究

利用化学还原沉积法,制备一类Ni高度分散/修饰的多壁碳纳米管基新型材料y%Ni/MWCNT(y%为质量百分数),并用其作为促进剂,制备共沉淀型y%Ni/MWCNT促进的合成气高效合成甲醇Cu-ZnO-Al₂O₃催化剂,Cu₆Zn₃Al₁-x%(y%Ni/MWCNT)(x%为质量百分数).实验发现,Ni对MWCNT的预修饰能明显地提高单纯MWCNT促进的Cu-ZnO-A1₂O₃催化剂对合成气转化为甲醇的催化活性.在2.0 MPa,493 K,V(H₂):V(CO):V(CO₂):V(N₂)=62:30:5:3,GHSV=2700 mL(STP)·h^-1·(g-cat.)^-1的反应条件下,所观测CO转化率达34%,相应甲醇时空产率为442 mg·h^-1·(g-cat.)^-1,分别是非促进的基质催化剂Cu₆Zn₃Al₁[最佳操作温度513 K时为320 mg·h^-1·(g-cat.)^-1]和单纯MWCNT促进的催化剂Cu₆Zn₃Al₁-12.5%MWCNT[最佳操作温度503 K时为378 mg·h^-1·(g-cat.)^-1]的1.38和1.17倍.在反应温度≤503 K时产物中甲醇的选择性≥98%;当反应温度＞503 K时有可观量CH₄的生成,其选择性随催化剂中M含量及反应温度上升而增加.为兼获较高的CO转化率及相应甲醇选择性,催化剂的组成以Cu₆Zn₃Al₁-12.5%(8%Ni/MWCNT)为佳,反应温度以～493 K为宜.结合催化体系的表征(XRD,TPR,TPD)等结果,讨论了y%Ni/MWCNT促进剂的作用本质.     

Characterization of carbon nanotubes and analytical methods for their determination in environmental and biological samples: A review

In the present paper, a critical overview of the most commonly used techniques for the characterization and the determination of carbon nanotubes (CNTs) is given on the basis of 170 references (2000–2014). The analytical techniques used for CNT characterization (including microscopic and diffraction, spectroscopic, thermal and separation techniques) are classified, described, and illustrated with applied examples. Furthermore, the performance of sampling procedures as well as the available methods for the determination of CNTs in real biological and environmental samples are reviewed and discussed according to their analytical characteristics. In addition, future trends and perspectives in this field of work are critically presented.