Strategically tailored double S-scheme heterojunction in h-MoO3 doped Bi7O9I3 decorated with Cr–CdS quantum dots for efficient photocatalytic degradation of phenolics

Abstract

Phenolic compounds are widely used in various industrial processes, but they can be harmful to the environment if released without proper treatment. In this study, we developed a ternary nanocomposite (NCs) consisting of molybdenum trioxide, bismuth oxoiodide, and chromium-doped cadmium sulphide quantum dots h-MoO3/Bi9O7I3/Cr–CdS QDs (MBC) nanocomposite (NCs) to enhance the photocatalytic degradation of p-chlorophenol (p-CP). The nanomaterial morphology, distribution of depositing material, and heterojunction formation were investigated using SEM, TEM, SAED, and elemental mapping. Further, the structural characterization was done by XRD, XPS, and Raman spectroscopy which confirmed its purity, chemical states, bonding nature, and the presence of oxygen vacancies (OVs) and sulphur defects. The 30-MBC NCs exhibited the highest surface area of 354.5 m2/g and pore volume of 0.76 cm3/g, with the H3 hysteresis loop indicating their mesoporous nature. The Kubelka-Munk plot determined the band gap of the NCs to be 2.22 eV and ensured successful visible-light sensitization. PL and ESR studies revealed that 30-MBC NCs had the lowest charge carrier recombination and highest ROS production. The photocatalytic degradation of p-CP by 30-MBC NCs achieved 94% in 300 min. The highest efficiency was observed at 75 mg/L NCs, 150 mg/L p-CP, and pH 6. Additionally, NCs retained activity in the presence of different ions and degraded 82% p-CP even after six consecutive cycles. •O2− was the dominant ROS involved in the degradation process, while OVs and sulphur defects played a crucial role in ameliorating charge transfer in the 30-MBC NCs. GC-MS/MS analysis identified the possible degradation pathways of p-CP, and ECOSAR showed that less toxic by/end products were produced. Overall, this study highlights the promising potential of 30-MBC NCs for extensive wastewater treatment.