Comparison of benzene and toluene photodegradation under visible light irradiation by Ba-doped BiFeO3 magnetic nanoparticles with fast sonochemical synthesis.

Bi1-xBaxFeO3 (x = 0.02, 0.04 and 0.07) multiferroic materials with a diameter in the range of 30-40 nm were controllably synthesized by a facile ultrasonic method, with a very short reaction time of 5 min at a low temperature of 30 °C, and the resulting BiFeO3 magnetic nanoparticles (BFO MNPs) exhibited enhanced magnetic and photocatalytic performance. The substitution of Ba2+ ions for Bi3+ ions at the A-site of BFO MNPs, even at only 2%, decreased their particle size and distorted the lattice in the rhombohedral structure of BFO MNPs. Increasing the Ba doping to 7% greatly increased the ferromagnetic properties of BFO MNPs from 3.55 to 6.09 emu g-1. In comparison with pure BFO MNPs, 7% Ba substitution in the Ba-doped BFO MNP samples produced strong absorption in the visible light region, decreasing the band-gap energy from 2.11 to 1.86 eV. Photoluminescence (PL) spectroscopy identified the band-gap emission for BFO MNPs at 587 nm, while for both pure and Ba-doped samples, the other emissions were attributed to the defect states related to oxygen deficiencies inside the band gap. After 50 min of visible light irradiation, Bi1-xBaxFeO3 (x = 7%), with the lowest band gap energy, highest magnetization and smallest particle size, showed almost complete photocatalytic degradation of toluene and benzene (100 mg L-1), with 91 and 81% reduction, respectively, in total organic carbon (TOC). For all irradiation times, the mineralization efficiency of toluene was higher than that of benzene, which demonstrated that toluene is more sensitive to photocatalytic oxidation than is benzene.