I have synthesized Au-Ag alloy NPs in colloidal form by reducing HAuCl4 and AgNO3 using NABH4 with ATP as capping agent. I want to add a support, Silica MCM-41 to the prepared NPs. What should be the procedure ?
Unfortunately you have to start again, IMHO...
You dry the silica first and measure the pore volume. You then make a solution of your bimetallic salts in the requisite amount of water to just saturate the pores of a known mass of silica. You then reduce the absorbed salts with an appropriate reducing agent. This could be gaseous e.g. H2 or in liquid form (e.g. diluted hydrazine hydrate). A method as I describe will provide a sterically stabilized system.
As Alan mentioned, the deposition of the active components must be on the support. The later is either in powder form, as preferred in laboratory, or in preformed shape as preferred in industry.
The use of diluted solution of the active components salts is recommended in the case of preformed support in order to prevent the blockage of the pores.
Dear Alan
I would perform the reaction from the start. But, currently I have prepared Au, Au25Ag75, Au50Ag50, Au75Ag25 and Ag NPs. So, I would like to use these samles to incorporate SiO2 support. The method you mentioned is incipient impregnation. Can I try wet impregnation in which we can add support to the colloidal NPs?
How can I measure the pore volume of SiO2. I have purchased it from sigma. Please find the link for the SiO2. https://www.sigmaaldrich.com/catalog/product/aldrich/643645?lang=en®ion=IN
They are showing a pore volume of 0.98 ml/g cat. Can I verify it?
Dear Imad
The NP solution is very diluted, around 1 mg in 15 ml milli-Q water. According to the pore volume of SiO2, I should at ~ 10 µl of the sample. Will not it make the colloid NPs even more dilute once I pore this volume on 10 mg of silica support?
Hello Irfan I think you are very confused. What is the reason for preparing these alloy materials and why do you need them on a support? What concentration on the support do you want your metallic particles? Concentrations such as 1, 2, or 5 wt% are common. When I prepared such materials for catalyst applications in the 1970's I was using around 20 - 50 g of support and the corresponding volume (~ 25 - 50 mL) of liquid with the appropriate metal concentrations to give a 5 wt% metal loading after reduction. A pore volume of around 1mL/g support is common for this type of material. You can check it by drying thoroughly a known mass of the silica and 'titrating' it against water in a beaker with vigorous stirring. As soon as the pores saturate then the particles will start to stick to the side of the beaker. However, I would be happy to accept the stated value (0.98 mL/g) from the supplier.
Working with 10 mg of material and 10 µL of sample just isn't feasible and prone to large errors.
I am studying the surface arrangement of Au ang Ag in the alloy NP. For this, I need to anneal the sample. To avoid sintering, I want to add a support.
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