Steroid glycosides as potential analytes for Cu-doping on TiO2 for photocatalytic water treatment

The kernel of Thevetia peruviana, a toxic ornamental shrub, is rich in cardiac glycosides and, its concentration could be as high as 4.8%. This work aimed for the functionalization of a photocatalyst support, TiO2 by Cu-doping using a facile bio-mediated green methodology. Herein, the mechanism of Cu-doping on TiO2 mediated by cardiac glycosides present in the bioextract is proposed. Cu(II) was first immobilized on TiO2 and, then the aqueous kernel extract of T. peruviana was used to dope Cu(II) on TiO2 at room temperature. The loading of Cu doped on TiO2 was found to be about 99% of the initial amount of Cu(II) taken in the immobilization stage. With the increase in Cu loading, there was a gradual redshift in the optical absorbance but the optimal dopant concentration was found to be 1.5% (true loading). The polydispersity index was increased by 1.8-folds due to the transformation of the rutile phase to the anatase phase (maximum 8.48%) and increase in the crystallite size (17.7-24.5 nm). Cu-doped TiO2 exhibited as high as 75% trypan blue dye degradation in 120 min at the optimal dopant concentration under the visible light irradiation by the combined effect of photocatalysis and photosensitization which was originated in the presence of trypan blue dye. However, the photosensitization effect due to the adsorption of pigments present in the bioextract was also insignificant as evidenced from the decomposition of a colorless pharmaceutical compound. The electron spin resonance spectra confirmed that O2 center dot- radicals primarily caused the dye decomposition. (c) 2018 American Institute of Chemical Engineers Environ Prog, 37: 1901-1907, 2018