Controlled synthesis of bismuth-containing compounds (α-, β- and δ-Bi2O3, Bi5O7NO3 and Bi6O6(OH)2(NO3)4·2H2O) and their photocatalytic performance

Abstract

Basic bismuth nitrate (Bi₆O₆(OH)₂(NO₃)₄·2H₂O; BiON), α- and δ-Bi₂O₃, or Bi₅O₇NO₃ and β-Bi₂O₃ were synthesized from Bi(NO₃)₃·5H₂O using a facile solution crystallization route or a subsequent calcination procedure by adjusting growth parameters such as the base and solvent. When hexamethylenetetramine (HMT) was used as a base, distorted hexagonal BiON prisms could be prepared in a mixed solution of 2-methoxyethanol (EM) and H₂O (pH range 2.5–6), whereas δ-Bi₂O₃ nanosheets would be obtained if ethylene glycol (EG) instead of EM (pH ≈ 6) was used. The addition of NH₃·H₂O as a base led to the formation of amorphous nanoparticles in EG–H₂O (pH ≈ 6) and EM–H₂O (pH range 6–9) solutions or amorphous nanotubes in H₂O (pH ≈ 9) solution, which completely converted into highly crystalline β-Bi₂O₃ nanoparticles or Bi₅O₇NO₃ nanoplates upon calcination at 300, 350 or 400 °C for 2 h, respectively. Analogous to previous work, NaOH as a base in H₂O or NaOH/EM–H₂O solution (pH > 13) induced the formation of α-Bi₂O₃. The studies of the photocatalytic activity of the as-prepared samples indicated that δ-Bi₂O₃ nanosheets and Bi₅O₇NO₃ nanoplates exhibited the highest degradation efficiency for Rhodamine (RhB) under visible light irradiation due to their sheet or plate-like morphology and the associated high surface areas.