Efficient solar-driven photodegradation of methylene blue dye and antibacterial activity of Bi₂X₃–TiO₂ (X = S or O?) nanocatalysts

Abstract

Background

Titania (TiO₂) is a widely studied photocatalyst for wastewater treatment, but its efficiency is often limited by rapid charge recombination. Modifying TiO₂ with Bi₂S₃ can enhance visible light absorption and charge separation, improving its photocatalytic potential for pollutant degradation and antibacterial applications.

Methods

Bi₂X₃-TiO₂ (X = S or O?) composites with different Bi₂X₃ to TiO₂ ratios were synthesized via the sol-gel method. The catalysts were characterized using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UV-DRS), Photoluminescence Spectroscopy (PL), Fourier-Transform Infrared Spectroscopy (FT-IR), High-Resolution Transmission Electron Microscopy (HR-TEM), and X-ray Photoelectron Spectroscopy (XPS). Photocatalytic efficiency was evaluated by methylene blue degradation under solar light, and reaction kinetics were analyzed.

Significant Findings

Bi₂X₃-TiO₂ demonstrated superior photocatalytic activity compared to pure TiO₂ and Bi₂X₃, achieving effective methylene blue degradation at pH 5. Superoxide radical anions played the dominant role in the degradation mechanism, followed by holes and hydroxyl radicals, as confirmed by scavenger studies. The addition of electron acceptors like H₂O₂ and K₂S₂O₈ significantly enhanced photodegradation. Chemical oxygen demand (COD) measurements confirmed efficient mineralization of MB, and the catalyst exhibited good reusability. Gas Chromatography–Mass Spectrometry (GC–MS) analysis identified key degradation intermediates, supporting the Langmuir-Hinshelwood kinetic model. Additionally, the Bi₂X₃-TiO₂ composite showed notable antibacterial activity, making it a promising material for both wastewater treatment and antimicrobial applications.