Fabrication of graphene-oxide/Β-Bi₂O₃/TiO₂/Bi₂Ti₂O₇ heterojuncted nanocomposite and its sonocatalytic degradation for selected pharmaceuticals

A graphene-oxide (GO)/β-Bi₂O₃/TiO₂/Bi₂Ti₂O₇ heterojuncted nanocomposite, designated as GBT, was synthesized via a two-step hydrothermal process. The sonocatalytic activity of the GBT was evaluated at several frequencies (28, 580, and 970 kHz) and compared with Bi-doped GO (GB) and Ti-doped GO (GT). Transmission electron microscopy images showed heterojuncted crystal structures of Bi and Ti on GO, and X-ray diffraction patterns verified that the crystal structures consisted of β-Bi₂O₃, TiO₂, and Bi₂Ti₂O₇ nanocomposites. Energy-dispersive X-ray spectroscopy revealed a higher proportion of metal on GBT surfaces compared with GB and GT surfaces. The energy band gaps of GT, GB, and GBT were 3.0, 2.8, and 2.5 eV, respectively. Two pharmaceuticals (PhACs; carbamazepine [CBZ] and acetaminophen [ACE]) were selected and treated under sonolytic conditions at frequencies of 28, 580, and 970 kHz at a power level of 180 W L⁻¹. The selected pharmaceuticals, present at initial concentrations of 20 μM, were reduced by over 99% by ultrasonic irradiation in the presence of GBT. The 580 kHz treatment achieved the most rapid organic removal among the frequencies tested. The removal kinetic of CBZ was higher than that of ACE owing to its relatively high hydrophobicity. High sonocatalytic activity of GBT was observed through measurement of H₂O₂ in solution. Because of its low band gaps and high surface activity, GBT exhibited higher sonolytic activity in removing selected PhACs than GT or GB.