Calcium Bismuthate (CaBiO3): A Potential Sunlight-Driven Perovskite Photocatalyst for the Degradation of Emerging Pharmaceutical Contaminants

This study reports the photocatalytic efficiencies of CaBiO3 (CBO) towards the degradation of contaminants of emerging concern (CEC), such as ciprofloxacin and tetracycline, under solar light irradiation. CaBiO3 was synthesized using glycine-complexation (GC) and ion-exchange (IE) methods. The structural difference of materials obtained by these different methods was evidenced from XRD and XPS results, and were due to the induced dual oxidation state of Bi (Bi3+/5+) in CaBiO3. The CBO synthesized by the GC method (CBO-GC) showed a broad UV/Vis absorption range from 200 to 550 nm and a band gap energy of 2.30 eV, while it was found to be 200 to 450 nm and 2.65 eV for the CBO synthesized by the IE method (CBO-IE). The VB potential of CBO-IE is shifted towards more positive potentials (+2.45 eV) as compared to the CBO-GC (+1.90 eV), and thereby the calculated CB potential of CBO-GC and CBO-IE was found to be -0.40 and -0.20 eV, respectively. Such positioning of the VB and CB favored the generation of highly reactive radicals towards the effective degradation of pollutants. These relative alignments of the bands could be mediated by the oxygen vacancy defects in the systems owing to the dual oxidation state of Bi. The photocurrent and impedance measurements demonstrated excellent charge separation and lower resistivity in CBO-GC as compared to the CBO-IE. Accordingly, the CBO-GC showed enhanced photocatalytic degradation efficiency, improved photostability and reusability as compared to that of the CBO-IE.