Since their discovery, carbon nanotubes and carbon nanofibers (CNTs or CNFs) have exhibited potential in a wide range of physical and chemical applications 1,2. For applications in gas phase catalysis, loose CNTs or CNFs are unsuited because they limit the catalyst-reactant transport properties and they are difficult to handle when filling in the reactor tubes. In addition, there is a health risk associated with loose CNTs or CNFs 3. Immobilizing CNTs or CNFs on a supporting material is thus highly desirable. CNFs or CNTs have previously been grown on carbon materials, particularly on CNT or CNF support 4-7. Activated carbon (AC) has been widely used as an efficient adsorbent for the purification of water, air and many fluid synthetic and natural products 8. Previously we have reported that CNFs nested inside and immobilized onto modified AC exhibit an excellent adsorption behavior for hcteropolymolybdate compared to metal cations 9. The productivity of CNFs and CNTs is a function of the preparation conditions, such as nature of the substrate and of the catalyst, temperature, gas composition and time on stream 10,11 . In this work, a systematic study was conducted of the parameters for the synthesis of CNFs from C_2H_4 on modified AC. The productivity, porosity and morphology of the CNF/AC composites can be controlled with iron salt precursors, the ratio of C_2H_4/H_2, the reaction temperature and the reaction time.
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