Utilizing the Water Instability of Cs₃Bi₂Br₉ Perovskite for In Situ Growth of BiOBr Nanosheets on g-C₃N₄ toward Enhanced Photocatalytic Activity

The growing attention to lead-free Cs 3 Bi 2 Br 9 perovskites underscores its considerable potential in light-based applications. However, the propensity of bismuth-based halide perovskites to hydrolyze and form bismuth oxyhalides upon exposure to water can pose major challenges. Therefore, to address this issue it is crucial to conduct a comprehensive investigation to understand the underlying factors and interactions involved. Herein, we explore the phase stability, reversibility, decomposition mechanisms, and various properties of Cs 3 Bi 2 Br 9 when subjected to water over different time intervals ( t = 3, 10, 30, and 120 min). Our findings confirm the formation of BiOBr nanosheets after 120 min of Cs 3 Bi 2 Br 9 hydrolysis, accompanied by continuous surface precipitation. Conversely, we view this phenomenon as a unique opportunity for the in situ growth of BiOBr nanosheets on other semiconductors, such as graphitic carbon nitride (g-C 3 N 4 ), without requiring additional chemicals and expensive equipment, aimed at sustainable photocatalytic applications. Various characterization techniques, such as X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and elemental mapping analysis, affirm the successful synthesis of BiOBr/g-C 3 N 4 photocatalysts. A combination of optical, electrochemical, band structure, and radical-related tests reveals the construction of S-scheme heterojunctions by effective interfacial charge transfer. The optimal 20% BiOBr/g-C 3 N 4 photocatalyst attains superior degradation rates of 93.7, 100, and 95.6% of 4-nitrophenol (4-NP), tetracycline, and methyl orange, respectively, under simulated solar light irradiation. Our results demonstrate that the S-scheme charge-transfer mechanism provides the maximum redox potential for the BiOBr/g-C 3 N 4 photocatalytic system, leading to the efficacious degradation of pollutants through the contribution of all reactive species ( • O 2 –, • OH, and h + ). Overall, this research emphasizes the potential of utilizing material instability as a strategic method to develop advanced and sustainable photocatalysts.