of Rtn@TiO2 is even lower (2.0). A high level of aggregation of
nanomaterials was observed at pH close to IEP values (Fig. 6).
Hydrodynamic diameters measured for Trn@TiO2 reached the
highest values (up to 330 nm) at pH within 4–6. When pH increased
to 7 a sudden drop of the average hydrodynamic diameter
to ca. 40 nm was observed. The same pattern of diameter change
close to IEP was observed for other modified and unmodified
TiO2 colloids. At pH = 7 hydrodynamic diameters of all modified
materials were within 10–40 nm.
3.2. Photoelectrochemical measurements
The IPCE (incident photon to current efficiency) profiles for
unmodified and surface modified TiO2 colloids casted on ITO electrodes
are presented in Fig. 7. At electrode potentials of 200 mV
vs. Ag/AgCl cathodic photocurrents were observed. Surface modifi-
cation extends the spectral activity to visible light (up to 550–
650 nm), but also improves the efficiency of interfacial electron
transfer when compared to the processes taking place at neat
TiO2 material [23]. This reflects in a significant increase of photocurrents,
particularly in the case of Trn@TiO2 and Asc@TiO2. Rutin,
as a larger molecule, improves IPCE values less significantly. All
IPCE profiles follow the absorption spectra of nanomaterials. Oxygen
sensitive response proves the role of O2 as an electron acceptor,
being reduced to superoxide radical anion. This process plays
a crucial role in photocatalytic reactions leading to generation of
other reactive oxygen species.
3.3. Coatings on glass
Nanocrystalline TiO2 was successfully used for preparation of
thin films on glass substrates. Coatings obtained by spin-coating
technique were characterized by a good homogeneity and