I have been trying to stabilise the pre-synthesised (commercial) iron (II,III) oxide nanoparticles using sodium citrate (anhydrous). I have tried different concentrations of citrate to prepare and stabilise 1 and 3 mg/mL iron oxide by sonicating them at high temperatures (60-80 deg), however, the particles still settle at the bottom of the flask. I have tried washing them after magnetic separation with DI water, and they start settling at the bottom within minutes. I tried to check if the citrate had stabilised the NP by UV-Vis spectroscopy as citrate shows a characteristic peak at ~220 nm, however, it failed to show any distinct peak.

I realised that many papers have used sodium citrate dihydrate instead of anhydrous salt. I believe it should not make a huge difference, but would it? Am I missing something on how to stabilise the particles with citrate?

/Thanks