Researches On The Preparation Of Carbon Nanotubes/Chitosan/Metal Nanoparticles Composites And Their Catalytic Performance

Carbon nanotubes，as one-dimensional scale of nanostructured carbon materials，haveintrinsic properties, such as high surface area, unique physical properties and morphology,high electrical conductivity, and their inherent size and hollow geometry, which makes themextremely attractive as supports for heterogeneous catalysts. However, carbon nanotubespossess both hydrophobic nature and oleophobic nature, so that it is difficult to disperse insolution. Then it is unfavorable to modify catalyst on it. In order to improve the dispersivityof carbon nanotube, the traditional method was strong acid oxidation method to make carbonnanotube surface with carboxyl and hydroxyl groups, which was advantageous to thenanometer catalyst load. But this method not only caused pollution to the environment, butalso it was long time-consuming and cumbersome process.Chitosan is the natural polymerwith biocompatibility. It has lots of amino and hydroxyl groups, which can make chitosanmodified on carbon nanotube surface because of the uncovalent bond between the chitosanand carbon nanotubes. The technological proces is simple, and friendly to environment. Inthis work, we dedicated to the preparation of carbon nanotubes material modifying chitosan,which loaded different nano metal particle （Ni, Ag） particles. Also we explored thepreparation process of the carbon nanotubes/chitosan/nano metal composites.and theircharacteristics of morphology and structure. At last, the catalytic performance of carbonnanotubes/chitosan/nano metal composites was evaluated by catalytic hydrogenationreduction of p-nitrophenol. At the same time, in order to increase the recyclability of carbonnanotubes/chitosan/nano metal composites, we use cotton to load the composite and study thefeasibility. These results will lay a theoretical and practical basis for developing a newtechnology for carbon nanotubes composites with short process, low cost and less pollution.The specific research contents and results were as follows:1. Carbon nanotube/chitosan composites were prepared by blending carbon nanotubewith chitosan-acetic acid solution by ultrasonic technique, then filtering and drying. ThenNi2+was adsorbed on carbon nanotubes modifying chitsoan, by the reduction of NaBH₄, thuswe got the composite material of CNT-CS-Ni. The morphology, element and structure ofCNT-CS-Ni composites were characterized using XRD, IR,SEM and EDS. The catalysisactivity of CNT-CS-Ni was studied by reduction of p-nitrophenol with sodium borohydride（NaBH₄） solution. The influencing factors on the amount of sodium borohydride, reaction temperature, the amount of catalyst and recycle ability were discussed. The results show thatthe activation energy of CNT-CS-Ni is50.28kJ mol^-1, the activation enthalpy is47.66kJ mol^-1and entropy of activation is-99.84J mol K-1. The CNT-CS-Ni immobilized oncotton avoided the difficulty on separating the catalyst from solution.2. CNT-CS-Ag composites were prepared by firstly adsording Ag+on CNT-CS, thenreducting with amino and hydroxyl groups to nano Ag particle, which were characterized byXRD,IR, and SEM. The catalysis activity of CNT-CS-Ag was studied by reduction ofp-nitrophenol with sodium borohydride （NaBH4） solution. The influencing factors of thereaction activity on the amount of sodium borohydride, reaction temperature, the amount ofcatalyst and recycle ability were discussed. The results show that Ag nanoparticles onCNT-CS were well-distributed and the particle size was5-10nm. The activation energy ofCNT-CS-Ag is89.27kJ mol^-1, the activation enthalpy is86.44kJ mol^-1and entropy ofactivation is29.23J mol K-1. The CNT-CS-Ag composites immobilized on cotton show goodcatalytic performance, and can improve their recyclability.