Photocatalytic activity
The water soluble dye RB5 was selected as a model pollutant because it has been extensively used for dyeing cotton fabrics. Reactive Black 5 dye has two reactive vinylsulfonil groups and two azo groups (Figure 2). The dye is not degradable by direct photolysis and by TiO2 in dark. Decoloration by TiO2 adsorption under dark conditions did not exceeded 10% for all treatments (data not shown), determining that decoloration was conducted primarily by the photocatalytic process.
The changes in RB5 dye concentration C/Co (Co initial concentration and C reaction concentration of the dye) by the synthesized samples with the time of UV and visible radiation are shown in Figures 6 and 7. As can be seen, the iron content is an essential factor to define the photocatalytic activities of the samples. The preparations containing 0.5% Fe showed higher photocatalytic activities than pure TiO2 either under UV or visible light irradiation. On the other hand, doping with higher concentrations of Fe3+ ions led to marked decrease in photocatalytic activity.
It is believed that Fe3+ ions can act as shallow traps in the titania lattice although their role during photooxidation processes remains controversial [37]. Introducing of small amounth of dopant ion