To the best of my knowledge, bulk TiO2 is widely accepted as an n-type semiconductor. What about an TiO2 nanoparticle? Is it also an n-type semiconductor?
Yes. Due to intrinsic defects present in TiO2 i.e. oxygen vacancies and leading to Ti3+ ions (excess electrons), nano TiO2 is also n-type semiconductor.
As the size of nanoparticles decreases the band gap increases and I think thw Fermie level could be affected the potential of the electrode surface in the solution.