From the current transients (inset in Figure 3), all films show anodic photocurrents upon illumination, corresponding to the n-type photoresponse of TiO2. For TiO2-1 film, the initial anodic photocurrent spike is very strong and subsequently decays quickly. Simultaneously, a cathodic overshoot appears immediately when the light is switched off. The anodic current spike and cathodic
overshoot are occasionally observed selleck chemicals in many cases, and which is generally regarded as the indication of the surface recombination of photogenerated charges [24–26]. A decay of anodic current immediately after the initial rise of the signal when the light is switched on is attributed to photogenerated electron transfer to the holes trapped at the surface states or the intermediates which originated from the reaction of holes at the semiconductor surface. With the accumulation of the intermediates, the electrons are trapped by the surface states, resulting in an anodic current spike. Owing to the same reason, the intermediates or trapped holes would induce a cathodic overshoot when switching off the light. The obvious strong spike for the illuminated TiO2-1 film suggests the slow consumption see more of holes and the corresponding oxidation process, which is related to the activity of the surface
TiO2 layer. The poor crystallinity, Buspirone HCl large TiO2 particles, and the small amount of TiO2 in the directly oxidized film would result in the poor photoelectrochemical performance. However, the transient of NP-TiO2 film is different, displaying much smaller anodic current spike and more stable photocurrent. The photocurrent density is calculated as the difference of the current density upon illumination at the center time and in the
dark, which is shown as a graph in Figure 3. NP-TiO2 film possesses the highest photocurrent density, which is about 1.2 mA/cm2, significantly higher than the corresponding TiO2-1 and TiO2-2 films. The efficient photoelectrochemical performance can be attributed to the porous structure of NP-TiO2 film, in which the interaction time between TiO2 and light would be increased due to the trapped photons inside the pores, corresponding to its enhanced optical absorption. Figure 3 A comparison of photocurrent density of various films. The inset shows a comparison of the current transients (applied potential: 0.2 V vs. Ag/AgCl). The performance of the NP-TiO2 film was further tested by photoelectrocatalytic degradation of RhB solutions. The decolorization of RhB by photolysis is low, only 5.2% reduction observed after 2 h of irradiation (Figure 4). Without an applied bias, by illuminating the solution with the NP-TiO2 film, the decolorization efficiency only improved to about 11%.