Abstract
Bismuth ferrites have been prepared using a hydrothermal method in a reaction solution containing a mineralizer with various ratios of KOH/NaOH. The phases and morphology of the bismuth ferrites were examined for reaction systems with two different molar ratios of Bi 3+ /Fe 3+ , 1 and 1/2. For the reaction system of Bi 3+ /Fe 3+ = 1, we were able to tune the mean thickness of Bi 2 Fe 4 O 9 plates by varying the ratios of KOH/NaOH. For the reaction system of Bi 3+ /Fe 3+ = 1/2, the main phase transferred from mixed BiFeO 3 and Fe 2 O 3 to Bi 2 Fe 4 O 9 when the ratio of KOH/NaOH decreased to less than 1. The morphology of Bi 2 Fe 4 O 9 , in this case, is more rectangular and block-like with dominating {001} facets. The relatively faster kinetics of the Bi 2 Fe 4 O 9 formation triggered by the presence of sodium ions determines the available concentration of Fe 3+ ions for further growth which, in turn, affects the mean thickness of Bi 2 Fe 4 O 9 plates. The energy bandgaps of Bi 2 Fe 4 O 9 plates, which increase from 2.18 eV to 2.27 eV with decreasing thicknesses, lie in the range of visible-light spectra and are suitable for the application of visible-light photocatalyst. © 2012 The Royal Society of Chemistry.