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

Basic bismuth nitrate Bi6O6(OH)(2)(NO3)(4)center dot 2H(2)O; BiON), alpha- and delta-Bi2O3, or Bi5O7NO3 and beta-Bi2O3 were synthesized from Bi(NO3)(3)center dot 5H(2)O 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 delta-Bi2O3 nanosheets would be obtained if ethylene glycol (EG) instead of EM (pH approximate to 6) was used. The addition of NH3 center dot H2O as a base led to the formation of amorphous nanoparticles in EG-H2O (pH approximate to 6) and EM-H2O (pH range 6-9) solutions or amorphous nanotubes in H2O (pH approximate to 9) solution, which completely converted into highly crystalline beta-Bi2O3 nanoparticles or Bi5O7NO3 nanoplates upon calcination at 300, 350 or 400 degrees 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 alpha-Bi2O3. The studies of the photocatalytic activity of the as-prepared samples indicated that delta-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.