Band‐Engineered Encapsulation of Lead‐Free Halide Perovskite Nanoplatelets for Multifunctional Aqueous Photocatalysis
Subhajit Bhattacharjee, Kamal Manna, Mohammad Ubaid, Sonu Pratap Chaudhary, Koushik Pal, Sayan BhattacharyyaThe moisture sensitivity of halide perovskites necessitates their encapsulation with a secondary layer that has suitable energy band alignment to enable efficient photocatalysis in aqueous or semi‐aqueous media. We have utilized Cs 3 Bi 2 I 9 (CBI) nanoplatelets as photoabsorber in aqueous media by designing CBI|Ag 2 S and CBI|TiO 2 photocatalyst panels, featuring type‐I and type‐II band alignments, respectively. The Ag 2 S and TiO 2 secondary layers endow the 12.7 ± 3.8 µm thick CBI layer with multifunctional photocatalytic capabilities and help slow the penetration of water into the perovskite. Theoretical calculations show a direct correlation between electronic structure and photocatalytic activity. CBI|Ag 2 S heterojunction promotes carrier localization and enhanced CO 2 photoreduction (CO 2 R), while CBI|TiO 2 heterojunction facilitates charge separation, resulting in superior Cr 6+ photoreduction. For photocatalytic remediation of Cr 6+ and its reduction to Cr 3+ , CBI|TiO 2 exhibits a Cr 6+ reduction of 76.1 ± 2.6% after 4 h in comparison to 68.6 ± 1.7% for CBI|Ag 2 S. In case of photocatalytic CO 2 R, CBI|Ag 2 S system achieves a CO yield of 10 ± 3 µmol g cat ‒1 and areal activity of 104 ± 27 µmol CO m irr ‒2 h ‒1 after 4 h, whereas CBI|TiO 2 produces 8 ± 2 µmol CO g cat ‒1 . The photocatalyst panels retain their structural integrity for 100 h, with minimal alterations in band alignment and negligible degradation.