T. Rajh et al., Improving optical and charge separation properties of nanocrystalline TiO2by surface modification with vitamin C, J PHYS CH B, 103(18), 1999, pp. 3515-3519
The structural and electrochemical properties of nanoparticles were found t
o be different from those of the corresponding bulk semiconductors. Due to
the specific binding of modifiers to "corner defects", the optical properti
es of small titania particles were red shifted 1.6 eV compared to unmodifie
d nanocrystallites. It was found using electron paramagnetic resonance (EPR
) that, as with organic charge transfer superconductors, these novel nanocr
ystallites operate with a charge-transfer mechanism, and exhibit semiconduc
ting properties through both constituents (large band gap semiconductor and
organic modifier). The EPR spectra were consistent with hole trapping on t
he surface modifier and electron trapping on shallow interstitial and parti
ally delocalized Ti sites. These systems have an important feature in that
charge pairs are instantaneously separated into two phases-the holes on the
donating organic modifier and the electrons in the conduction band of TiO2
.