An Emerging Strategy in Sequential Synthesis of Catalyst and Carbon Nanotube Foams by Employing a Chemical Vapor Deposition Procedure: Structural Evaluation and Growth Mechanism

Abstract

In an effort to further expand the simplification of the bulk production of carbon nanotube (CNT) foams, herein, a new approach based on one-step synthesis procedure is developed, where the production of the catalyst is followed by CNT foam growth in a chemical vapor deposition (CVD) furnace during acetylene decomposition over three various mole ratios of Fe: Mo: MgO: PEG (polyethylene glycol) sol-gel viscous precursor catalyst (viz., 1: 0.5: 13: 4.8, 1: 1: 13: 5, and 1: 1: 50: 17.3) under Ar/H₂ atmosphere at various reaction conditions. The growth of multi-walled CNT foams was directly carried out, i.e., without preceding any reduction and oxidation phases over viscous gels. The various parameters such as molar ratio, reaction temperature, and acetylene flow rate were optimized individually for the production of ultra-lightweight foamed CNTs. The CNT foams grown from the optimized reaction conditions were discussed by using various physicochemical characterization studies, such as XRD, FT-Raman, SEM, TEM, FE-SEM with EDX, N₂ sorption isotherms, and thermal analysis. The issues regarding the growth mechanism of high specific surface area CNT foams are taken in the present approach. Such a mechanism has been proposed for the carbo-thermal reduction of acetylene over the optimized viscous catalyst precursors gel at 800 °C in a CVD furnace.