Investigation and optimization of photocurrent transient measurements on nano-TiO2

Chronoamperometry with chopped light has been applied to commercial and homemade TiO2 nanopowders, both doped and undoped, to gain information on the charge recombination processes which take place in the oxide and affect its photocatalytic performance. The photocurrent transients can be attributed to photoinduced electron-hole separation, trapping, recombination, and scavenging. In order to evaluate what mainly affects the shape of the transients and the transient time constants (tau) which can be derived, the type and concentration of the electrolyte, the irradiation source (UV or visible light), and the presence of a hole acceptor (oxalate) were varied. The reproducibility of quantitative measurements was best when an inert electrolyte (NaClO4) has been employed under an N-2-saturated atmosphere. Under these conditions, both Pr-TiO2 and N-TiO2 samples show a definitely higher tau than the undoped oxide, which indicates a slower recombination kinetics, both under UV and visible irradiation. Therefore, these are promising as photocatalysts.