Catalytic Growth of Carbon Nanotubes Using a Single Molecule Catalyst Precursor

[摘要] Controlled growth of carbon nanotubes (CNTs) is of interest for numerous applications due to the superlative properties they exhibit as consequence of their structure. As such, controlled CNT growth may be possible using uniform critically-sized catalysts under tightly controlled reaction conditions. To this end, the uniform single molecule nanocluster [HxPMo12O40H4Mo72Fe30(O2CMe)15O254(H2O)98-y(EtOH)y] (FeMoC) appears to be an ideal catalyst for CNT growth. However, it was found necessary to add catalyst promoters to FeMoC at undesirably high growth temperatures (T > 900 °C) to enable CNT growth. To understand these disappointing results a systematic investigation of the catalytic chemical vapor deposition conditions employed in CNT growth was conducted revealing temperature-dependent growth behavior. Further experimentation aimed at unraveling this thermal behavior reveals the ;;activation” mechanism for CNT growth to be the sufficient reduction of the metal oxide components in FeMoC. By ensuring FeMoC reduction prior to introduction of growth gases, we demonstrate unprecedented CNT growth at temperatures as low as 600 °C without the aid of catalyst promoters. Furthermore, the role of the catalyst promoters used in prior work was revealed to serve two key roles, 1) to replenish the number of metal atoms lost to sublimation, and 2) to reduce the reduction temperature required to ;;activate” FeMoC. Prompted by the critical role reduction plays in ;;activating” FeMoC for CNT growth, and the desire for a predictive tool, reduction kinetics studies were undertaken. In this aim, model free isoconversional kinetic analysis studies were performed with kinetic results being validated by isothermal experimentation. This work cautions the conditions employed in earlier literature and provides an initial framework for optimizing CNT growth using FeMoC and related catalyst systems in the aim of controlled CNT growth.

[发布机构] Rice University

[效力级别] nanotubes