Controlled-Phase Synthesis of Bi2Fe4O9 & BiFeO3 by Flame Spray Pyrolysis and their evaluation as non-noble metal catalysts for efficient reduction of 4-nitrophenol

Abstract

Pure phases of Bismuth-Iron-Oxide nanomaterials, i.e. perovskite BiFeO3-phase or mullite-type Bi2Fe4O9-phase have been synthesized, using Flame Spray Pyrolysis (FSP). Based on a systematic study of the phase-formation by XRD diffraction, X-Ray Photoelectron and Raman spectroscopies, FSP protocols are developed for the synthesis of 100% pure phases of either BiFeO3 or Bi2Fe4O9, as well as mixed-phase [BiFeO3: Bi2Fe4O9] at controllable phase-percentages. The materials are shown to be quite efficient in catalytic reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4. Based on an Arrhenius study, the activation energy for the of 4-Nitrophenol catalysis is estimated Ea = 22 kJ mol−1 for BiFeO3 and Ea = 36 kJ mol−1 for Bi2Fe4O9. Thus, the FSP-made BiFeO3-nanophase shows enhanced catalytic reaction of 4-Nitrophenol that is comparable to the, so far reported, best-performing noble-metal nanocatalysts. The catalytic physicochemical mechanism is discussed based on the thermodynamic, in-situ FT-IR, and 4-Nitrophenol adsorption isotherms data for the BiFeO3, Bi2Fe4O9 nanophases.