The role of the precipitating agent on the formation of bismuth oxide was carefully evaluated. This research aims to investigate the influence of choice of strong or weak bases as the precipitating agent on the physicochemical properties of bismuth oxide, as regards crystal structure, morphology, bandgap, and photocatalytic activity. Bismuth oxide particles synthesized using NH4OH as the precipitating agent had the form of bright yellow powder with α and β crystal structures, 0.6-5.2 μm size, and bandgaps of 2.51 and 2.88 eV, respectively; while bismuth oxide synthesized using NaOH as the precipitating agent was a pale yellow powder with α, β and δ crystal structures, 2.50-10 μm in size, and bandgap of 2.80 eV. The amounts of OH and NO functional groups as impurities in the particles was decreased by calcination. Furthermore, the photocatalytic activity of BO3 was better than that of BO4 with reaction rate constants 2.38 x 10-5s-1 and 0.68 x 10-5 s-1, respectively, probably because of the different physicochemical properties.
