Influence of halogen substitution in double perovskite Rb2Sn(Br0.75I0.25)6 on the photocatalytic degradation of methylene blue dye under visible light irradiation

In this research work, we reported the preparation of lead-free undoped [Rb2SnBr6] and halogen-doped Rubidium tin bromide [Rb2Sn(Br0.75I0.25)(6)] double perovskite materials using the wet chemical method and they were used for photocatalytic degradation of methylene blue dye (MB) in water solution under visible light irradiation. The structural, optical, thermal, surface morphological analyses and the presence of oxidation state of the prepared samples were characterized by XRD, Raman, UV, PL, TGA/DTA, FESEM-EDAX and XPS, respectively. The UV studies revealed that the bandgap values were tuned from 2.07 eV to 1.80 eV, resulting in a redshift of emission peak which was confirmed by PL studies. TGA/DTA studies showed that the thermal stability slightly improved for doped perovskite over undoped perovskite material. The photocatalytic experiment showed that the degradation (78%) ability of halogen-doped perovskite material is slightly enhanced over undoped perovskite after 120 min irradiation of visible light. Hence, this defect-ordered doped double perovskite is considered to be a potential material for the degradation of similar dyes mainly due to their bandgap values in the visible light region. In addition, it was found from the elemental trapping experiment using different scavengers, the primary active species were hydroxyl radicals (center dot OH) and holes (h(+)) during the photodegradation of MB dye. Charge transfer and recombination processes between electrons and holes of the synthesized double perovskite materials are analysed using electrochemical impedance spectroscopy (EIS) studies. We also illustrated the possible photocatalytic reaction mechanism diagrammatically using band positions of double perovskite materials estimated using Mott-Schottky plots, and this study implies that the synthesized double perovskite material has N-type semiconductor nature.