Highly dispersed metal nanoparticles on carbon nanotubes: synthesis, characterization, and application

• Main Authors: Yong-Ming Dai, 戴永銘
• Other Authors: 鄭紀民
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/51384850619565353540

博士 === 國立中興大學 === 化學工程學系所 === 99 === Abstract Synthesis of highly dispersed metal nanoparticles (NPs) on the supports with uniform NPs size still remains a challenge. Loaded the carbon nanotube (CNTs) with metal, could improve the functionality, compatibility and reactivity of the surface, further endow the spheres with specific catalytic. In this thesis, there are three major research parts: A) high-yield synthesis of CNTs over a metal alloy catalyst by thermal chemical vapor deposition; B) purification and functionalization of the CNTs; C) synthesis of highly dispersed metal NPs onto CNTs and the catalytic performances of these new materials. Part A: High-yield synthesis of CNTs over a metal alloy catalyst by thermal chemical vapor deposition In Chapter Two, Synthesis of CNTs by the catalytic decomposition of methane over various alloy catalysts (polyol process method prepared). Characterization of the catalysts and the products was performed by chemical analyses, X-ray diffraction (XRD), and transmission electron microscopy (TEM). CNTs were grown by thermal chemical vapor deposition (TCVD) of CH4 by using the alloy catalyst. The optimum carbon yield for growing CNTs in MgNi alloy in this study is determined by using MgNi alloy catalyst to perform the CH4 pyrolysis. The highest yield of CNTs growth can reach up to about 932 % for the pyrolysis of CH4 at 923K for 30 min with the presence of hydrogen in the reaction stream. Part B: Purification and functionalization of the CNTs In Chapter Three, CNTs were grown by TCVD of CH4 by using NiMg as the catalyst. High-purity CNTs were achieved after the purification procedures with the air oxidation at 450 oC and hydrochloric acid (HCl) treatments, the final purified yield and purity of CNT reach to 78% and 100% respectively. The CNTs was treated with HNO3 to increase their surface area and improve their properties. Cyclic voltammetry (CV) was used to evaluate the optimize conditions of the modified CNT for the higher specific capacitance. The FTIR results show that after the activated treatment by HNO3, CNTs possess -CO and -OH functional groups, where as the HRTEM results show that the surface of the CNTs becomes rough. After the activity treatments, the CNTs surface area increases to 145m2/g. The CV performance of the modified CNT has shown that the specific capacitance increases from 8.9 to 22.6 F/g. Thus, the modification of the CNT improves the surface properties and increases their capacitance. Part C: Synthesis of highly dispersed metal NPs onto CNTs and the catalytic performances of these new materials. In Chapter Four, The Pt/ PCNTs were synthesized by the polyol process as a function of sodium dodecyl sulfate (SDS) concentration to control the Pt NPs size. The Pt NPs size and the extent of dispersion were strongly dependent on the SDS concentration. The physical properties and structural information of the Pt/PCNTs were further characterized by TGA, XRD, and TEM. The results of TEM and XRD have revealed that the Pt/PCNT prepared by the polyol process at The Pt/PCNTs catalyst prepared of SDS concentration of 0.5 wt% possessing a uniform dispersion and particle size within the range of 4nm. The Pt/PCNTs catalyst prepared of SDS concentration of 0.5 wt% exhibited better exhibits higher activity with regard to CO oxidation reaction compared to the other preparation SDS concentration catalysts. In Chapter Five, A simple and easy method has applied to prepare a highly dispersed Ag (NPs) on modified carbon nanotubes (MCNTs). The Ag NPs were easily attached to the MCNT support by anchoring them to the functional groups. Oxygen functionalities on the HNO3-activated MCNT surface provide nucleation centers for metal ions and can stabilize metal NPs on the support surface. This is an essential process for obtaining highly dispersed Ag NPs on MCNTs due to the presence of surface oxygen-containing functional groups. In addition, the Ag NP active sites with a smaller particle size and higher dispersion rate exhibit higher activity for CO oxidation at low reaction temperatures. The catalytic results suggest that the Ag/MCNTs catalysts have a high potential for application in low-temperature CO oxidation.