Microwave-assisted synthesis of bismuth oxide

Single phase and ultrafi ne bismuth oxide was synthesized via microwave-assisted hydrothermal synthesis. The effect of reaction parameters (temperature/pressure and pH) on the product phase composition and morphology was discussed. The transformation of bismuth hydroxide into bismuth oxide was controlled by pH value and it was accelerated by time and temperature. The phase composition of reaction products was strongly dependent on pH value. The amorphous products were obtained at acidic pH conditions and the crystalline single phase product α-Bi 2 O 3 phase was obtained at pH ≥12. The particle size was reduced from micrometric to nanometric size in the presence of a chelating agent. The bismuth hydroxides into bismuth oxides transformation mechanism, consisting in polycondensation of Bi – OH bounds to Bi – O – Bi bridges and crystallization of Bi 2 O 3 , was proposed.