Dhruvil Virani

I recommend to study the kinetics of sedimentation with periodic measurement of particle sizes in a long glass cylinder. When you find the start time for the nanoparticles to start deposition, this will be the time from which you will need to collect the nanoparticles.

Separating silicon coarse particles from nanoparticles can be challenging due to their size similarity. However, there are a few methods that can be attempted.

- Sedimentation. Silicon nanoparticles are typically much smaller and lighter than coarse particles. By allowing the mixture to settle in a liquid, the larger particles will settle faster due to gravity, while the smaller nanoparticles will remain suspended for a longer period. Carefully decanting the liquid can help separate the coarse particles from the suspended nanoparticles.

- Filtration. Using a fine filter or membrane with a pore size smaller than the nanoparticles, you can pass the mixture through the filter. The coarse particles will be retained on the filter while the nanoparticles pass through. This method may require optimization of filtration parameters to prevent clogging or loss of nanoparticles due to their small size.

- Centrifugation. By subjecting the mixture to high-speed centrifugation, the coarse particles, being heavier, will sediment at the bottom of the centrifuge tube while the nanoparticles will remain in the supernatant. Carefully decanting or pipetting off the supernatant can separate the nanoparticles from the coarse particles.

- Density gradient centrifugation. This method involves creating a density gradient using different concentrations of a gradient medium in a centrifuge tube. When the mixture is centrifuged, the particles will separate based on their density. The coarse particles will move towards the region with higher density, while the nanoparticles will settle at a different position. By carefully collecting the fractions at the desired location, you can separate the coarse particles from the nanoparticles.

It is important to note that the effectiveness of these separation methods will depend on the size difference between the coarse particles and nanoparticles, as well as other properties such as density and surface characteristics. It may be necessary to optimize the parameters and perform multiple separation steps to achieve the desired separation efficiency.