Efficient COD Removal Coinciding with Dye Decoloration by Five-Layer Aurivillius Perovskites under Sunlight-Irradiation

Abstract

An absorption edge in the visible region and a slow recombination of photogenerated electron–hole pairs in semiconductors are desirable for efficient sunlight-driven photocatalysis. One of the strategies to harvest visible-light instead of ultraviolet is to identify or develop new semiconductors with a band gap below 3 eV. The five-layer Aurivillius phase perovskites, Bi_6–<i>x</i>La_<i>x</i>Ti₃Fe₂O₁₈ (<i>x</i> = 0, 1), where the band gap ranges from ∼2.02–2.57 eV, have been identified as potential members. The compounds, Bi_6–<i>x</i>La_<i>x</i>Ti₃Fe₂O₁₈ (<i>x</i> = 0, 1), are synthesized by solid state reaction and characterized by PXD, FE-SEM, EDS, UV–vis DRS, and PL spectroscopy. La-substitution into Bi₆Ti₃Fe₂O₁₈ results in a sluggish recombination of photogenerated electron–hole pairs in Bi₅LaTi₃Fe₂O₁₈ as compared to the parent. The compounds showed remarkable photocatalytic performance toward Rhodamine B (RhB) degradation (more than 96%) within 30 min of sunlight-irradiation under mild acidic medium. Dye degradation is found to be coincident with COD removal. Moreover, the photocatalytic cycle test demonstrated the catalysts to be highly stable and reusable after five catalytic cycles without any noticeable decrease in the activity. Because of the fact that reactive oxygen species (ROS) are generated by sunlight-irradiation over the layered perovskite catalysts and that up to 95% COD removal takes place within 30 min, the catalysts may find practical application in dye/organic contaminant degradation or waste treatment that is sustainable without incurring any additional energy cost