Study Of Preparation Of Nanoparticles For Catalytic Ecomaterials Using W/O Microemulsion

The catalyst made of precious metal Pt is applied to many different areas, such aschemical industrial, environmental protection, material science and so on. It is veryimportant to study the chemical and physical properties of the supported Ptnano-cataylst which have high catalytic activity.Water-in-oil (W/O) microemulsion in which water disperses in oil medium,provides the very microscopic environment for the formation of nanoparticles in themicro-water pool sized between 10-7-10-9m. In this system, the growth of the particlesis suppressed. Surfactants adsorbed on the particles' surface prevent the particles fromconverging into masses. So the nanoparticles prepared by W/O microemulsion arecharacteristic of small size, good dispersing capability, and high purity. Moreover, thistechnique is relatively simple and requires only a few apparatus. It's hopefully apromising way to prepare nanoparticles.A systematic study of the characteristics of W/O microemulsion and preparationof nanoparticles are presented in the dissertation. Dynamic behaviors for thepreparation of nanoparticles and carbon-based Pt nano-catalyst also are investigated.The properties of W/O microemulsion, including phase activities andconductance activities affect preparation of nanoparticles. The effects of different ofcategories surfactants, the proportion of surfactant and cosurfactant (alcohol), thechain lengths of alcohol and alkane, temperatures and pH values on the W/Omicroemulsion phase areas are systematically studied in the dissertation. SEM andlaser scatting techniques are used to verify particles' sizes of W/O microemulsion.Consequently, a system TritonX-100/ n-C₅H₁₁OH(weight ratio 1:1)/C₆H₁₂/H₂O isobtained which is a stable system with relatively large W/O microemulsion phase area.Chemicals used in this system are very inexpensive and easily obtained. Meanwhile,this system is not sensitive to temperature and pH value. By investigating theconductance of W/O microemulsion, a percolation threshold was found whenconcentration of water is 0.33 by weight. That imply the water concentration must belower than 0.33 by weight in this W/O system. Only under this condition, themicrowater pool is spherical. The formation of the W/O microemulsion based onthermodynamics principles are studied. The results show that when n-C5H11OH movesfrom solution to interface, ΔG=-3208 J·mol-1,ΔH=57588 J·mol-1, ΔS=203J·mol-1·K-1, which means that n-C5H11OH facilitates the formation of W/Omicroemulsion.Pt, Cu, Ag nanoparticles by adopting the system TritonX-100/ n-C5H11OH(weightratio 1:1)/C6H12/H2O W/O microemulsion are made successfully. TEM tests showedthat their average particle diameters are 10nm, 22nm, 18nm, respectively. In thisdissertation, investigation is made on a number of factors affecting the size of Ptnanoparticles, such as the categories of surfactants, the molar ratio of water andsurfactant(ω0), concentration of surfactants, H2PtCl6 and reductants, and the pH etc..Experimental results show that sizes of nanoparticles are positively proportional toω0and concentration of H2PtCl6, while the sizes are little affected by concentration ofsurfactants and reductants especially when reductants concentration reach a saturatedlevel.There are primarily four steps to undertake in order to obtain the nanoparticles byW/O microemulsion: (1) the exchange;(2) the chemical reaction;(3) the nucleation;(4) growth of particles. As for the investigated system, the substance exchange andchemical reaction are finished within one minute when two W/O microemulsions areblended. Around three minutes immediately after the chemical reaction is the step ofnucleation 3-20 minutes, after that it is the growth step. Chemical reactions are ratecontrol step. When the reductant is excessively used, the reaction is pseudo-first ratereaction, the pseudo-first rate constant k=0.056s-1. At the steps of the nucleation andgrowth, particle sizes are negatively proportional to the number of the nucleation.Three approaches are investigated to prepare carbon-based Pt nano-catalyst. Sizeof Pt nanoparticles made from the macerating and microemulsion integraled methodare comparatively small, about 7nm. Catalyst's surface area increases when treatedwith washing and heating, while its granularity increases too.