Preparing Ag(Cu)/SBA-15 Nano-composites By Supercritical Fluid Deposition

The synthesis of nanoscale composite materials has attracted a great deal of attention due largely to their unique physical and chemical properties.The control over either particle dimensions,including the particle size and distribution,or metal concentration in the composites remains the major problems for these methods.Supercritical Fluid Deposition has been proved to be a novel and effective approach for the preparation of nanocomposites with mesoporous material as substrate,inorganometallic and organometallic mompounds as precursor.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(SCFD) method in this paper.The experimental results and conclusions are as follow:(1) Inorganic AgNO3 was deposited into the channels of mesporous SBA-15 using SCFD method with ethanol as co-solvent at the pressure of 20-24MPa,temperature of 50℃.After deposition,Ag/SBA-15 nano-composites was prepared by calcining and reduction.The Ag/SBA-15 composites were characterized by means of TEM,XRD and EDX.Ag nanowires with the seze distribution from 5.1 nm to 6.4nm 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 of SBA-15.Furthermore,Highly dispersed Ag nanoparticles with seze distribution from 5nm to 7nm are found to be supported onto the channels of SBA-15 by TEM analysis.And the Ag content of the composites is as high as 19.23%.(2) Cu-Ag/SBA-15 bimetallic nanocomposites was prepared by SCFD with ethanol and glycol as co-solvent at the pressure of 20-24MPa,temperature of 50℃.Cu-Ag/SBA-15 bimetallic nanocomposites were characterized by means of TEM,XRD.Metal nanoparticles and nanowires were found in channels of SBA-15,The maximal uptake of precursor is about 0.168g.(3) The growth mechanism of Ag deposited into channels of SBA-15 was investigated with Ag/SBA-15 nano-composite as example.It is found that growth mechanism of Ag nanoparticles or nanowires were different when co-solvent were differently selected.The morphology of Ag deposited into SBA-15 was as follows with ethanol as co-solvent:small nano-particles,short nanowires and nanoparticles,nanowires,nanowire and nanoparticles,big nanoparticles.When ethanol and glycol were selected as co-solvent,the shape of Ag in SBA-15 was lots of nanowires and nanoparticles.Finally when the deposition time is very long,the morphology of Ag was unconspicuous changes.(4) The effect of selectness of co-solvent,deposition temperature,deposition pressure and the mass ratio of precursor and substrate on morphology of nanophase was investigated in this paper.The bigger solubility of co-solvent was selected,The bigger uptakes of precursor. When the deposition temperature,the deposition pressure and the mass ratio of precursor and substrate increase,uptakes of precursor was bigger and morphology of Ag was most nanoparticles.The maximal uptakes of precursor was 35.1%.(5) With CO oxidation and Selective hydrogenation of cinnamaldehyde to cinnamaylalcohol as model reaction,we investigated the catalytic performance of Ag/SBA-15. CO conversion reached about 100%at 300℃.Cinnamaylaldehyde conversion reached about 92%at 6h.The catalytic performance of nanoscale composite materials is related to the morphology of metal deposited into substrate.(6) Adsorption of the precursor to the substrate from SCCO2 was studied and Langrnuir model,modified Langmuir model,Freundlich model and R-P model were used to fit the adsorption equilibrium data.It is found that the above four traditional adsorption models can fit the adsorption process during SCFD method well.