Comparative study on photocatalytic performances of crystalline α- and β-Bi2O3 nanoparticles under visible light

α- and β-Bi2O3 nanoparticles were synthesized in the presence of either urea or polyethylene glycol. The XRD, TEM, and Raman analysis indicated that α-(monoclinic) Bi2O3 nanoparticles were obtained using either sol–gel or hydrothermal method in the presence of urea; however β-(tetragonal) phase of Bi2O3 was formed using hydrothermal method in the presence of polyethylene glycol. The β-Bi2O3 nanoparticles exhibited higher photocatalytic activity than α-Bi2O3. MB was completely photodegraded after 6 h of visible light illumination using β-Bi2O3 photocatalyst whereas only 30% was photodegraded using α-Bi2O3. The photodegradation rate of β-Bi2O3 was 5.7 times greater than that α-Bi2O3 nanoparticles.