Harnessing multi-frequency ultrasound and visible-light for enhanced bisphenol (A/F) mineralization in presence of ultra-small Bi/Bi₂MoO₆/MXene/g-C₃N₄ nanocomposites – energy consumption and toxicity analyses

In this study, highly efficient surface-modified nanocatalyst comprising of ultra-small bismuth nanoparticles (US-Bi NPs) supported with Bi₂MoO_6, MXene and g-C₃N₄ (Bi@Bi₂MoO₆/Ti₃C₂/g-C₃N₄, BMTG) was synthesized using the multi-frequency ultrasound-assisted hydrothermal approach. The BMTG nanocomposites were employed for the degradation of bisphenol A (BPA), bisphenol F (BPF) and BPA + BPF under the multi-frequency ultrasound-assisted sonophotocatalytic environment (MFUSE). The advanced analytical characterisations confirmed the surface characteristics, morphology, crystallinity, and various features of the synthesized nanocomposites. The electron-beam induced current (EBIC) effect demonstrated the successive coating of US-Bi nanoparticles are ~7 nm in size with uniform distribution as evidenced by high resolution transmission electron microscopy (HR-TEM) analysis. The optimization of catalyst dosage, operational parameters and superior degradation kinetics were evaluated and the ternary BMTG nanocomposites (5.1 × 10⁻²) exhibited approximately 8.7-fold enhanced rate of degradation when compared to the commercial TiO₂ (P25). Notably, the complete degradation of BPA was achieved within 60 min under MFUSE conditions in the presence of BMTG nanocomposites. The overall degradation efficiency followed the order: BMTG > BMO > BMG > P25 > g-C₃N₄ > BMT > Ti₃C₂. The frequency driven- and heterojunction-driven- synergistic effects and enhanced production of hydroxyl radicals were evaluated with different approaches. The optimized MFUSE conditions were further applied for the concurrent removal of structural analogues of BPs (BPA-BPF). During the sonophotocatalytic degradation, 15 intermediates were identified via ESI-HRMS/QToF, and in silico toxicity evaluations were conducted to confirm the toxic nature of BPs and their derivatives. Finally, the degradation pathway of BPA and the mechanistic approach for the charge migration in the BMTG nanocomposites were portrayed.