Preparation Of Carbon Nanotube-Based Composites And Their Photocatalytic And Electrocatalytic Properties

It is a very important subject to study a new catalyst which can utilize the sunlight effectively or control environmental pollutant efficiently in catalysis because we are undergone the dual pressure of energy crisis and environment pollution at present. Carbon nanotubes (CNTs) exhibit excellent performance when used as a cocatalyst, catalyst support or catalyst because of their unique hollow tubular structure, high specific area, and the remarkable electronic, mechanical, and chemical properties. Until now, only a few studies have been reported that CNTs are used as the photocatalyst support or photocatalyst for application in the treatment of environmental pullutants. In this dissertation, we explored the photocatalytic and electrocatalytic activities of CNTs-based nanocomposites to degrade and detect the environmental pullutants. The work includes five parts:1. Explore the roles of CNTs as the cocatalyst in the photocatalytic oxidation process. Nanocomposites of ZnO and multi-walled carbon nanotubes (MWNTs) were prepared by electrostatic interaction and in situ hydrothermal synthesis approaches. The ZnO/MWNTs nanocomposites display relatively higher photocatalytic activity than ZnO nanoparticles for the degradation of Rhodamine B (RhB). Therein, MWNTs, acting as a photogenerated electron acceptor, retard the recombination of photoinduced electron and hole. The experimental results show that the photocatalytic activity of the ZnO/MWNTs nanocomposites strongly depends on the synthetic route, which is probably due to the difference of surface states resulted from the different preparation processes.2. The aim of this part is to assess the visible light photocatalytic activity of MWNTs, and the roles of MWNTs in removing environmental pollutants were explored. MWNTs were directly used as a visible light photocatalyst for the degradation of methyl orange (MO) and RhB in aqueous solutions. The adsorption and photocatalytic activity tests indicate that the MWNTs serve as both an adsorbent and a visible light photocatalyst. The photocatalytic activity of MWNTs is enhanced when Ag or Pt nanoparticles are loaded on the surface of MWNTs. The enhanced photocatalytic activity may be ascribed to the effective electron transfer between MWNTs and the metal nanoparticles. The visible light photocatalytic activity of Ag/MWNTs depends on the synthetic route. The Ag/MWNTs synthesized with thermal decomposition method display higher photocatalytic activity than that of Ag/MWNTs synthesized with photoreduction method. The Ag/MWNTs are an ideal alternative to Pt/MWNTs for the RhB degradation due to the low cost and high visible light photocatalytic activity.3. The composite photocatalyst (SnP/MWNTs) was prepared from trans-dihydroxy (5,10,15,20-tetraphenylporphyrinato) tin (IV) (SnP) and MWNTs by a sonication-refluxing method. The SnP/MWNTs exhibit high photocatalytic activities for the degradation of RhB or p-nitrophenol (PNP) under visible light irradiation. The high visible light photocatalytic activity of SnP/MWNTs is owed to the high molar absorption coefficient of SnP in the visible region and the strong electron transfer capability of MWNTs.4. Explore the roles of MWNTs in the detection of environmental polluants. Cobalt (Ⅱ) tetrakis (4-sulfonatophenyl) porphyrin (CoTPPS) was axially coordinated with amino-modified multi-walled carbon nanotubes (MWNTs-NH2) to form a MWNTs-CoTPPS composite. The composite was drop-cast on the glassy carbon electrode (GCE) to obtain MWNTs-CoTPPS/GCE. The MWNTs-CoTPPS/GCE exhibits high stability and excellent electrocatalytic activity for the oxidation of NO. The wide linear range (6.6×10-6-2×10-2 mol L-1), short response time (less than 7 s) and low detection limit (6.6×10-6 mol L-1) are achieved. The experimental results imply that the oxidation of NO at the MWNTs-CoTPPS/GCE is an irreversible, diffusion-controlled process with an activation energy of 19.18 kJ·mol-1.5. In addition, a simple route to prepare the high quality Ag film is developed at room temperature by using Ag nanoparticles stabilized by polyvinylpyrrolidone (PVP) as the Ag source. The silver film prepared on the glass substrate is smooth and dense, and exhibits high catalytic activity for the reduction of p-nitroaniline using NaBH4 as a reduction agent. No specialized apparatus and hard experimental conditions are needed in the procedure, which is very attractive for potential applications.