Visible light active photocatalysts for the degradation of drug residues in polluted waters

Removal of pharmaceuticals and their residues from water and wastewater streams is an important environmental issue which has gained a huge amount of attention over the past decades. Photocatalysis is one of the remediation approaches to be considered in this regard in the field of water and wastewater treatment. Hence, solar- or visible light- driven photocatalytic processes and visible light-absorbing materials have recently been the focus of many scientific studies. In the current work, two members of the phenothiazine group of antipsychotic pharmaceuticals, namely, methylene blue and chlorpromazine are considered as model pollutants. Within the scopes of this doctoral thesis, initially, the photocatalytic conversion of methylene blue in the presence of seven self-prepared zinc ferrite semiconducting powders is evaluated. Herein, the zinc ferrite samples are characterized and the impact of different synthetic methods on their properties including the crystalline size and purity, the surface area, the flat band potential and the bandgap energy is determined. Moreover, the reported visible light-activity of zinc ferrite as well as the usefulness of methylene blue to determine the activity of this semiconducting material are investigated through a series of detailed wavelength dependent measurements for the photocatalytic conversion of methylene blue. The experimental results reveal that the observed photobleaching of methylene blue under visible light irradiation in the presence of zinc ferrite is rather contributed to the electron transfer from the photo-excited methylene blue molecules adsorbed at the surface of zinc ferrite into the latter’s conduction band. In addition, the photocatalytic conversion of chlorpromazine, another very important member of the phenothiazine group of antipsychotics is studied. Since very little is known about the possibility of the photocatalytic conversion of chlorpromazine and its metabolites under visible light irradiation, this issue is assessed in detail in the current study. ...