Sulfate radical-based photo-Fenton reaction derived by CuBi2O4 and its composites with α-Bi2O3 under visible light irradiation: Catalyst fabrication, performance and reaction mechanism

Abstract

Sulfate radical-based photo-Fenton (SR-photo-Fenton) reaction, assisted by visible light irradiation, was achieved by CuBi2O4 and its composites with α-Bi2O3 for refractory chemical degradation in aqueous solution. Herein, this catalyst was fabricated by a sol-gel method and the fabrication conditions, including calcination temperature and molar ratio of Cu/Bi, were optimized according to the crystal phase composition, catalytic activity and toxic copper ion leaching. The optimal calcination temperature was 500 °C and molar ratio of Bi to Cu was 2.0. The catalyst containing CuBi2O4 and α-Bi2O3 showed a higher density of surface OH which might be the key surface active site than pure CuBi2O4. The influence of initial solution pH, PMS concentration, catalyst dosage and catalyst reuse on rhodamine B (RhB) degradation was investigated. Importantly, calcination at 500 °C reverted the catalytic activity of catalyst. Results of electron paramagnetic resonance, competitive radical experiments and surface chemical property characterization demonstrated that the reaction mechanism of this novel SR-photo-Fenton reaction is a combination of interface and solution reactions. In the interface reaction, the transfer of photogenerated electron/hole pairs drives the decomposition of PMS to produce SO4− and OH. Furthermore, the cycling of Cu(I)/Cu(II) facilitated effective PMS activation to generate free radical that was responsible for the degradation of RhB. The second order reaction rate constant between RhB and SO4− was determined to be 0.595–6.436 × 1010 M−1 S−1 based on the chemical reaction kinetics of radical, which was a first and important report for SO4− chemistry.