Synergetic enhancement of the photocatalytic activity of TiO₂ with visible light by sensitization using a novel push-pull zinc phthalocyanine

A new one-pot synthesis of a novel A₃B-type asymmetric zinc phthalocyanine (AZnPc) was developed. The phthalocyanine complex was characterized unambiguously and used to prepare a TiO₂ hybrid photocatalyst to enhance its photocatalytic activity in the visible range. Different compositions of the phthalocyanine dye were tested in order to find the optimum amount of sensitizer to get the highest activity during the photocatalytic tests. The hybrid photocatalyst was characterized by UV-Vis diffuse reflectance (DRS) and Fourier transform infrared spectroscopy (FT-IR) and its photocatalytic activity was compared with that of the individual components considering the effects of sensitization on their efficiency to degrade Rhodamine B as a model reaction. A synergic improvement of the photocatalytic activity for the hybrid system was explained in terms of an improved electron injection from the photo-activated phthalocyanine to the TiO₂. Considering the structural features of the phthalocyanine sensitizer and their effect on aggregation, some mechanistic aspects of its binding to TiO₂ are suggested to account for the photocatalytic activity enhancement. Finally, the inhibitory effect on the sprouting of chia seeds (Salvia hispanica) was evaluated in order to test the toxicity of the water effluent obtained after the photodegradation process. According to our growth inhibition assays, it was found that the Rh-B degradation by-products do not lead to an acute toxicity.