Mineralization of Phenol and 4-Chlorophenol Induced by Visible Light and Assisted by Semiconducting β-Bi2O3

Intensely yellow β -bismuth trioxide in the form of about 41 nm large crystallites has been prepared by thermal decomposition of (BiO)2CO3 at 400 ◦C. From the band gap energy of 2.3 eV obtained under the assumption of an indirect band-to-band transition and the quasi-Fermi level of −0.28± 0.02 V (vs. NHE) a valence band edge position of 2.02 V is calculated. This semiconducting oxide assists a Vis light (λ ≥ 455 nm) aerial mineralization of the aqueous model pollutants phenol and 4-chlorophenol exhibiting maximum rates at a bismuth oxide concentration of 2.0 g L−1. In the absence of oxygen no degradation occurs indicating that β -Bi2O3 does not act as oxidizing agent. The mineralization suffers from photocorrosion of β -Bi2O3 generating a mixture of α-Bi2O3 and various bismuth carbonates as observed upon multiple use of the oxide in the mineralization of phenol.