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Abstract: Novel hollow β-MnO2 polyhedral nanorods have been successfully synthesized by a simple hydrothermal process. The morphology and structure of the samples obtained at different reaction time have been characterized by XRD, TEM and SEM. The results indicate that β-MnO2 nanorods prepared at reaction time 12 h have hollow, polyhedral structure and uniform size with the length of about 2–3 μm. At longer reaction time, the shells of the hollow β-MnO2 polyhedral nanorods were broken. After analyzing the above results, it''s obvious that the reaction time has a great effect on the structure and morphology of the products. The morphology evolution of MnO2 products demonstrates that the growth mechanism of hollow β-MnO2 polyhedral nanorods could be assigned to the cooperation of oriented attachment and Ostwald ripening mechanism. [Copyright &y& Elsevier]

The controlled growth of metallic single-wall carbon nanotubes (m-SWCNTs) is very important for the fabrication of high-performance interconnecting wires, transparent conductive electrodes, light and conductive fibers, etc . However, it has been extremely difficult to synthesize m-SWCNTs due to their lower abundance and higher chemical reactivity than semiconducting SWCNTs (s-SWCNTs). Here, we report the kinetically controlled growth of m-SWCNTs by manipulating their binding energy with the catalyst and promoting their growth rate. We prepared CoRe 4 nanoparticles with a hexagonal close-packed structure and an average size of ∼2.3 nm, which have a lower binding energy with m-SWCNTs than with s-SWCNTs. The selective growth of m-SWCNTs from the CoRe 4 catalyst was achieved by using a low concentration of carbon source feed at a relative low temperature of 760 °C. The m-SWCNTs had a narrow diameter distribution of 1.1 ± 0.3 nm, and their content was over 80%.