Enhanced photocatalytic degradation of Rhodamine B dye over novel BiOCl/Bi₂O₃-intercalated bentonite nanocomposites under UV-B and visible light

Abstract

Developing efficient and sustainable photocatalysts for dye-contaminated water treatment remains a major environmental challenge. In this work, novel BiOCl/Bi₂O₃/bentonite (Bi/bentonite) nanocomposites with different bismuth loadings (5%, 12%, and 16%) were successfully synthesized through an intercalation method and applied for Rhodamine B (RhB) degradation under UV-B and visible light irradiation. Structural and optical analyses confirmed the effective incorporation of BiOCl and Bi₂O₃ within the bentonite framework, promoting enhanced charge separation and improved light absorption. Structural analysis by XRD confirmed the successful incorporation of BiOCl and Bi₂O₃ nanoparticles into the montmorillonite layers without altering the original clay framework. FTIR further supported the preservation of the aluminosilicate structure, while SEM–EDS and TEM revealed homogeneous dispersion of Bi-based nanocrystals within the clay structure. Optical characterization by UV–Vis DRS showed a significant red-shift in light absorption with increasing Bi content, with band-gap energies decreasing from 3.1 eV (raw bentonite) to 2.21 eV and 1.95 eV (12% and 16 wt% Bi/bentonite catalysts respectively). The 12% Bi/bentonite sample exhibited the highest photocatalytic performance under UV-B light (99.88% removal), while the 16% Bi/bentonite achieved 99.68% degradation under visible light. Notably, both catalysts operated efficiently at a near-neutral pH of 5.7 without pH adjustment, emphasizing their practicality and environmental compatibility. Kinetic studies followed a pseudo-first-order model, with hydroxyl radicals (•OH) and photogenerated holes (h⁺) identified as the dominant reactive species. The photocatalysts maintained excellent stability and reusability over repeated cycles. Compared with reported systems, these Bi/bentonite composites deliver high efficiency using low-energy light sources, underscoring their potential as cost-effective, eco-friendly photocatalysts for sustainable wastewater remediation.