Ferroelectric-assisted BaTiO ₃ /Cr-Zr-HMS (5, 10 & 20) catalysts for efficient visible-light removal of bromocresol green: structure–activity relationship and process optimization

In this study, BaTiO₃/Cr-Zr-HMS (BTCZH<i>x</i>) photocatalysts with different Si/Zr molar ratios were successfully synthesized and evaluated for the visible-light-driven photodegradation of bromocresol green dye. The catalysts were characterized and tested under varying operational parameters, and their performance was optimized using response surface methodology based on central composite design. Three key factors-pH of the dye solution, process time, and Si/Zr molar ratio-were systematically investigated for their influence on the photodegradation efficiency. Statistical analysis confirmed the adequacy of the quadratic model (<i>R</i> ² = 0.97), with pH identified as the most significant factor, followed by Si/Zr ratio and process time. The optimal conditions (pH = 3, <i>t</i> = 35 min, <i>x</i> = 20) yielded a maximum PDE of over 95%. The proposed photocatalytic mechanism suggests that under visible-light irradiation, photogenerated electron-hole pairs initiate the formation of highly reactive species (˙OH and ˙O₂ ^-), which synergistically degrade the dye molecules. Furthermore, reusability and stability tests revealed that the BTCZH20 catalyst maintained nearly 90% of its initial activity after five successive cycles, demonstrating excellent structural robustness and practical applicability. These findings highlight the potential of BaTiO₃/Cr-Zr-HMS composites as efficient and durable photocatalysts for wastewater treatment under visible-light conditions.