Thermal, structural and optical properties of magnetic BiFeO₃ micron-particles synthesized by coprecipitation method: heterogeneous photocatalysis study under white LED irradiation

Abstract

Bismuth ferrite, BiFeO₃ (BFO) prepared via a coprecipitation method, was used as an effective photocatalyst for the degradation of methylene blue (MB) using a white light-emitting diode (LED-50 W) lamp. The as-prepared material was characterized by TGA, XRD, SEM-EDX, FTIR, and UV-vis-DRS techniques. The effects of experimental key parameters such as pH, catalyst dosage, initial dye concentration, and calcination temperature were investigated. Results showed that BFO-600 (calcined at 600 °C/3 h) was a rhombohedrally-distorted perovskite oxide with the R3c space group. The average crystal size and band gap energy for BFO-600 were found to be 24.8 nm and 2.1 eV, respectively. Under optimal operating conditions ([MB]=20 mg.L^-1, BFO-600/dye mass ratio=0.5 g.L^-1, pH=11, and 25 °C), MB/BFO-600/LED process exhibited an efficient photodegradation (up to 94.4%) within 120 min, much higher than the MB sorption process (MB/BFO-600/dark system, 69.4%) and the MB self-photolysis system (MB/LED, 33.9%). The photocatalytic degradation of MB was found to fit well with the pseudo-first-order kinetic model. Thus, the MB photodegradation was attributed to the generation of reactive radicals such as ^•OH, h⁺, H₂O₂, and MB^•+ via direct heterogeneous photocatalysis and mediated by MB through a self-photosensitization process of MB over BFO-600 NPs.

Keywords:
magnetic BiFeO₃; methylene blue; vis-LED; photocatalysis; photosensitization process