i have synthesized nickel zinc ferrite nanoparticles, particles size is around 20 nm, calculated using TEM. and is coated with polymer. suspension remain in good condition for like a month. however when i try to filter these nanoparticles using 200nm filter paper, only water filtered through the paper but no nanoparticles, and all the particles remain on the paper. is it the same everywhere, or just me. Thanks
I am afraid that it is the same everywhere. I have had the same problem with filtration of Fe3O4 (20-30nm in size) nanoparticles suspension in water. Simply, the pores of the filter were too large compared with the size of nanoparticles. You can use a laboratory centrifuge or magnetic field to separate your nanoparticles.
@Bartlomiej Andrzejewski I am saying that all nanoparticles were filtered and i got no nanoparticles in solution obtained after filtering, it was clear water. though partile size were only 20 nm. i want to seprate big particles from small ones, but i got no nanoparticles at all.
The particles are not 20 nm - you have a collection of fused/aggregated post and sub-micron particles whose transport size is much larger than 200 nm. See:
Nov 11th, 2008. Dispersion and nanotechnology http://tinyurl.com/hpywsge
Dear Khan, after wet processing, your particles have some weak bonds such as van der waals, which hold together particles. So it is not so easy task to separate particles as a function of size.
Please check:
https://www.researchgate.net/post/How_to_separate_nanoparticles_of_two_different_sizes2
Dear A. Khan
First of all, TEM is not a reliable technique to quantify exact particle size. There might be small particles in nano-size or and there might be micron-level particles present in your sample. My suggestion is to use PSD (particle size distribution) analysis to quantify the exact sizes of synthesised particles.
Second, the filter paper allows few particles to pass through and rest of them trap inside the pores due to agglomeration. You can easily collect particles using filter paper. Another method to use a centrifuge and then separate the solids from the liquid and then dry them using vacuum dryer.
Dear Khan,
Most probably you need to agitate your sample before filtering through paper, Ultrasonic agitation might help. It seems like your nanoparticles aggregated and relatively act like large particles. Therefore I would try to increase the colloidal stability by favoring the pH in the direction that will lead to decrease in aggregation and agitation.
Thanks
Regards
Engin
Freeze drying of your sample will allow you to retain your nanoparticles, however, un-reacted salts will also be present. Depending on your application, this may be acceptable. The use of dialysis can aid in removing un-reacted salts but as your sample contains iron, this may prematurely age your nanoparticles.
Hi! The material that your filter is made from is also important. Particles can stick to it and thus will be retained in the filter. You can use a centrifuge filters with small pore sizes if you are trying to concentrate them. Is it what you are trying to do? I also agree with one of the previous comments - TEM would allow you to semi-quantitatively measure the metal core size, but for more accurate measurement of the size of the particles in suspension another method should be used. Considering the small size of your particles I would suggest DLS. Nanoparticle tracking analysis is also useful to do if you find in DLS analysis that you have a broad peak and the median size in more than 50 nm. with NTA you will know the concentration of your particles and more accurate size distribution.
The article in the link may help with your method, to stabilize your nanoparticles. Dynamic light scattering should work, if the nanoparticles are not stuck together.
http://www.tf.uns.ac.rs/publikacije/PAC/pdf/PAC%2034%2011.pdf
beside possible causes already mentioned there might be also attraction between stabilizing polymers and filter paper. You may try a PTFE filter instead.
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