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 Cs3Bi2Br9 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 Cs3Bi2Br9 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 Cs3Bi2Br9 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-C3N4), 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-C3N4 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-C3N4 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-C3N4 photocatalytic system, leading to the efficacious degradation of pollutants through the contribution of all reactive species (•O2–, •OH, and h+). Overall, this research emphasizes the potential of utilizing material instability as a strategic method to develop advanced and sustainable photocatalysts.