Preparing Nano-composites By SFD (Supercritical Fluid Deposition) Method

Nano-composites are the focus of many researches in material fields. Limiting of metallic nanoparticles into confined space of mesoporous material has been proved to be a novel and effective approach for the preparation of nanocomposites.The feasibility, experiment parameters, mechanism and the model of supercritical adsorption were investigated about preparing supported metal nanoparticles and nanowires into the channels of mesoporous material SBA-15 via Supercritical Fluid Deposition (SFD) method. The main experiments and results are as follows:(1) Organic metallic compound Cu(acac)₂ was deposited into the channels of mesporous SBA-15 using SFD method at the pressure of about 25MPa,temperature of 50℃, followed by calcinations and hydrogen reduction. Highly dispersed Cu nanoparticles with an average particle size of 4.7nm are found to be supported onto the channels of SBA-15 by TEM analysis. And the particles have a size distribution from3.3nm to 6.0nm.(2) To reduce the cost of preparation of nano-composites,developing a cheap precursor and making a short deposition time are supposed to be an effective way. Inorganic Cu(NO₃)₂ was deposited into the channels of mesporous SBA-15 using SFD method with ethanol as co-solvent at the pressure of 20-26MPa,temperature of 50℃.Supported Cu nanowires and nanoparticles were obtained after calcinations and hydrogen reduction of Cu(NO₃)₂/SBA-15. The Cu/SBA-15 composites were characterized by means of TEM, XRD and ICP. The Cu content of the composites is as high as 7.97%. Cu nanowires with the mean diameter 5.5-6nm were found filling the channels of SBA-15 and their lengths varied from several nanometers to several micrometers. What's more, the nanowires grew and curved along the channels. Highly dispersed Cu nanoparticles with the mean particle size of 4-5nm.The particles size ,size distribution and the metal content of the nano-composites prepared using Cu(NO₃)₂ have no distinct differences with those prepared using Cu(acac)₂, but as far as the deposition time is concerned, the former(Cu(NO₃)₂) is much shorter than the latter(Cu(acac)₂).(3) To discuss the metal loading of the nano-composites, adsorption of the precursor to the substrate from SCCO₂ was studied and Langmuir model and Freundlich model were used to fit the adsorption equilibrium data. The two traditional adsorption models can fit the adsorption process during SFD method well.(4) The morphology of Cu in the composites was controllable by changing the experiment conditions. Mechanism model of the nanowires or nanoparticles growing during SFD process are put forward based on the experiment result. The precursor concentration and deposition time influence the morphology of the nano-phase a lot. When the precursor concentration and the ratio of precursor to substrate are fixed, the formation of the nano-phase can be divided into four stages based on the deposition time. The first stage small nano-particles are formed, during the second stage nanowires appear and small nanoparticles vanish, nanowires break during the third stage and big nanoparticles as well as short nanowires appear. Finally when the deposition time is very long, all nanowires disappear and big nanoparticles are found instead.