I need to disperse Fe304 nanoparticles (25nm) in PVA solution. I tried to do it using a bath sonicator as well as a probe sonicator but the particles seem to agglomerate and settle down at the bottom.

So, I decided to coat the particles with a surfactant and then disperse them, below is the steps I followed for coating:

Step 1: 0.05g Fe304 NMP were added to 2ml of citric acid(0.5g/ml conc) and were left to incubate at 90C for one hour

Step 2: After one hour, the solution was subjected to vigorous stirring for one hour while maintaining the temp at 90C.

Step 3: The black precipitate was washed with deionized water and centrifuged 3 times to remove any remaining citric acid.

Step 4: The particles obtained from centrifugation were dried at 100C to remove any water.

After the above procedure, I tried to check if the coat was successful by seeing if the particles were attracted to a magnet and they were, so the problem of dispersion remains.

Did I miss out a step in the coating process? Can I use another method to successfully disperse the NMP.