Synthsis of carbon nanohorns hybridized with palladium nanoparticles by gas-injected arc discharge technique

Abstract

The objective of this research to develop a method for synthesizing single-walled carbon nanohorns (SWCNHs) hybridized with palladium nanoparticles (Pd) in a single step by using gas-injected arc-in-water method (GI-AIW). A deep insight into GI-AIW reaction system has been examined. An influence of water temperature on synthesis of SWCNHs has been experimentally studied. It is revealed that the yield of SWCNHs significantly decreases with the increase in water temperature although the purity of SWCNHs is independent on the temperature change. A mathematical model of relevant reactions in GI-AIW system was proposed by accounting the emission of carbon vapor, formation of SWCNHs and diffusion of water vapor in three zones inside cathode hole, which are arc plasma zone, quenching zone and downstream zone. A side reaction between H[subscript 2]O and C produces H[subscript 2] gas and consumes a certain amount of carbon vapor, resulting in the hindered SWCNH formation. Moreover the observation of the optical spectra emitted from the arc plasma zone strongly supports an expected mechanism that the H[subscript 2] generating reaction does not occur in the arc plasma zone since N[2] flow can purge H[subscript 2]O out. The model proposed in this study can precisely explain the correlation between H[subscript 2] gas production and water temperature. By using the GI-AIW method, SWCNHs/Pd nanocomposite can be synthesized by using Pd wire inserted inside anode hole as a precursor. Pd nanoparticles with spherical shape are embedded inside SWCNHs aggregates. The diameter of Pd nanoparticles is in the range of 3-6 nm when Pd wire diameters of 0.1 and 0.3 mm are employed. Meanwhile, the mean diameter and the size distribution of Pd nanoparticles tend to increase when Pd wire diameters of 0.5 and 0.8 mm are used. Additionally Pd nanoparticles tend to expose outside SWCNHs aggregates when larger diameter of Pd wire is employed. The total surface area of the composite dominantly depended on the surface area of SWCNHs. Based on thermogravimetric analysis, the amount of Pd nanoparticles in the composite increases with the increase in Pd wire diameter.