I've been doing adsorption of heavy metals using nanoparticles as adsorbant. Typically, there are two ways of adding the adsorbant(i.e. the nanoparticles). One is to add the suspension of well-dispersed NPs, while the other is to add the solid powder of NPs directly.
I was wondering that will the NPs aggregate after freeze vacuum dried leading to a decrease of specific surface, which will influence the adsorption amount? Can the dried solid powder of NPs re-disperse well?
I heard someone says that the aggregation of NPs have a small influence of the specific surface area as long as the NPs dispersed well after synthesis. I just want to hear about how people think of this according to your experiences.
Regards
Thank you
It is possible that specific surface area measured in dry form by BET gas sorption will not be significantly impacted by aggregation. It depends to a large extent on the shape of the particles. Spheres touch only at points and therefore most of the surface is available to the gas. It is also possible for the surface to be accessible to the gas, but not to your adsorbates in solution.
You have described an experiment. Do it both ways and actually see if there is a difference in uptake. Keep in mind that simply "adding" a powder to the medium does not necessarily mean it will disperse well. Control of pH and use of ultrasonic energy may be necessary to obtain a good dispersion. Depending on the particle size, shape and material, you may never be able to obtain complete dispersion. But if this has an acceptably low impact on your process, then it may not matter.
If the nanoparticles are not well dispersed the available surface area will be reduced, given that the particles will be interacting with each other adsorption will be reduced. You should evaluate that redispersion after drying actually occurs.
Aggregation is nothing but tightly binding of nanoparticles. If there is aggregation it is going to affect the surface area indirectly adsorption. The dried powder can be dispersed well in suitable medium avoiding aggregation.
With the aggregation of nano-particles , the specific surface area will be reduced which may affect the adsorption. As suggested, drying powder can be dispersed well resulted minimal aggregation.
It is possible that specific surface area measured in dry form by BET gas sorption will not be significantly impacted by aggregation. It depends to a large extent on the shape of the particles. Spheres touch only at points and therefore most of the surface is available to the gas. It is also possible for the surface to be accessible to the gas, but not to your adsorbates in solution.
You have described an experiment. Do it both ways and actually see if there is a difference in uptake. Keep in mind that simply "adding" a powder to the medium does not necessarily mean it will disperse well. Control of pH and use of ultrasonic energy may be necessary to obtain a good dispersion. Depending on the particle size, shape and material, you may never be able to obtain complete dispersion. But if this has an acceptably low impact on your process, then it may not matter.
As Dr.Hackley said you can check the effect of these two types of addition of NPs on the
adsorption amount.However, I think any aggregation will lower the surface area because on aggregation the number of atoms on the surface of the NPs will decrease. The less surface atoms with their free valence, the less activity of the NPs for many interactions such as catalytic, adsorption and so on.
Easy redispersion after storing in dried form is mostly a myth. Formation of chemical bonds between particles (e.g. in case of silica) and aggregate formation by interdiffusion of surface atoms or molecules between particles, is a common observation. Therefore even with high mechanical input 'full' redispersion is only possible in case of adding chemical agents. If feasible one should prefer to keep nanoparticles stabilized in liquid dispersion. Nevertheless, as pointed out already overall accessible surface area may not change too much.
Surface area depends on the pore size, size and shape of the particulates, if the surface area is determined by BET method. In your experiment you are adding a solution containing the NP the adsorption depends on the surface charge of the nanoparticles and this depends on the isoelectric point of the solid ( depends on pH) and adhesion on the surface. The aggregation of the powder on freeze dried powder depends on the dispersing agents and enegy used to dispersed. Once well dispersed and dried, the powder can be redispersed without any issue.
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