Improving optical and charge separation properties of nanocrystalline TiO2by surface modification with vitamin C

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 .