On the photocatalytic degradation of phenol and dichloroacetate by BiVO4: The need of a sacrificial electron acceptor

The photodegradation of phenol and dichloroacetic acid (DCAA) by \ce{BiVO4} was studied in the absence as well as presence of selected electron scavengers. The experiments were performed under the visible (vis) irradiation of aqueous solutions over a wide pH range (1--13). Phenol was photocatalytically degraded by \ce{BiVO4} into \emph{p}-benzoquinone below pH~3 and into an open-ring structure at pH~13. Methylene blue (MB) accelerated the reaction below the isoelectric point of \ce{BiVO4} and did not undergo significant degradation. In presence of \ce{H2O2}, phenol was rapidly degraded up to pH~9. The degradation rates are two orders of magnitude higher than in absence of electron scavenger. The degradation of dichloroacetic acid was only possible in presence of \ce{H2O2}. High initial concentrations of \ce{H2O2} inhibit the reaction and its consumption is very fast. Sequential additions of this sacrificial electron acceptor (SEA) enables the total degradation of a 1~mM DCAA solution.