My experience is that metal oxides are NOT soluble in organic solvents.  Ferric salts are notoriously insoluble in both water and organic solvents.

Do you need to solubilize the ferric oxide or just contact it with hexane?  Ferric oxide will be stable in hexane so  surface modification by silane may be possible..

Hi Andrea

Thanks for your answer. I may try something different using a ferric chloride solution.

I was just experimenting with a new novel way to modify the surface of silica substrate.

Dear Don Wilson,

I think, that using of organo-metallic compounds (such as Ferric acetate (CAS Number 3094-87-9), or Iron pentacarbonyl (CAS Number: 13463-40-6)) much convenient as inorganic (FeCl3). Due to many factors: low pH, high ability to hydrolysis, very hygroscopic e.t.c.

Ferric acetate - soluble in ethanol. 

By my opinion you should select precursor taking in to account work media - polar/non polar, and precursor of silica. I do not know your problem in details, but running reaction in liquid media: with first step obtaining SiO2 by precipitation, and in the same reactor/media doping (coating) with Fe2O3 looks very attractive and not complicate. pH. polarity of solvents and precursors and H2O concentration (even changing this parameters in a time) are playing key role in this syntheses. For more details take a look to Sol-gel approach.

Obtaining SiO2 and Fe2O3 in situ you can get bigger surface area, instead of using powders. 

In my profile you can find a similar research: Gas sensitivity of stoichiometric and excess-iron Ni-Zn ferrite prepared by sol-gel auto-combustion

Best regards Andrew