If you dry in an oven in air, your sample is likely to oxidise, and thus be significantly altered. If you can dry in argon or nitrogen, this will be avoided (e.g. in a glovebox or under a stream of nitrogen if it is not possible in an oven). Freeze drying should also avoid oxidation of the particles as much as drying in air.

If you are dealing with a stable oxide, such as magnetite, then an additional oxidation during drying is not happened.

Before measuring the saturation magnetization You will need to know the exact weight of your iron oxide, because then it would have to divide the saturation moment by it. It is important to ensure that there are no other phases on the surface of particles adsorbed during the drying process .

My opinion is that you should use some fluid like alcohol to disperse the NPs in. Apart from dehydrating the NPs by alcohol you may add some capping agent so that after drying in an oven you get your NPs capped to avoid agglomeration and vapor adsorption.

I precipitate my Fe3O4 NPs out with methanol and just pull a vacuum over them to dry them and pack the powder into the SQUID cap. Are you having trouble crashing them out?

vacuum drying or drying in argon or nitrogen are fine as rightly suggested by Christop and Joana. If you don't have both these facilities in your lab simply dry it and do the measurements. During this process, Fe3O4 is partially converted gamma Fe2O3, whose Ms is slightly different from Fe3O4.

Do a thermogravimetric analysis to find out the amount of surfactant (and moisture if any), which should be taken into consideration in the weight correction. If the particles are capped with a surfactant, depending on the particle size, the amount of non-magnetic component could be 5-15%.

I really appreciate all the valuable suggestions.

cheers

i facing the similar problem. after drying, my Fe3O4-silica core shell particle can not be

suspended in water anymore.

Dears please can anyone help?

I have dried mine, Fe3O4 nanoparticles solution of 75 ml volume, as received using an oven 90 degree for 24 hours. They are stick to the bottom of the flask used and I can not take them out. Can anyone advice what I did wrong?

Thanks...

Iam having trouble for the separation of magnetite nanoparticles from the solution stabilized by oleic acid. Is freeze drying a recommended technique for the separation of the particles?