Kinetic enhancement in photocatalytic oxidation of organic compounds by WO₃ in the presence of Fenton-like reagent

WO₃-mediated photocatalytic oxidation is achievable in the presence of electron acceptors as an alternative to O₂ or co-catalysts enabling O₂ reduction pathway. This study suggests the combination with Fenton-like reagent (Fe(III)/H₂O₂) as a strategy to improve the photocatalytic activity of WO₃. Under neutral pH condition where Fe(III) is present as iron oxide precipitate, photocatalytic degradation of 4-chlorophenol (4-CP) proceeded 3-fold faster in the WO₃/Fe(III)/H₂O₂ system relative to the WO₃/H₂O₂ system, while no noticeable oxidation occurred in the systems of Fe(III)/H₂O₂, WO₃, and WO₃/Fe(III). Such efficacy increase at circumneutral pH was observed in photocatalytic oxidation of diverse organics including phenol, bisphenol A, acetaminophen, and carbamazepine. Compatible with the pH dependence of photocatalytic activity of the WO₃/Fe(III)/H₂O₂ system, hydroxylation of benzoic acid and coumarin as indirect indication for OH radical production was drastically retarded with increasing pH. The pH effect indicates that OH radical as primary oxidant may be responsible for the kinetic enhancement in the WO₃/Fe(III)/H₂O₂ system. In that platinum deposits or Nafion layers as physical barriers possibly inhibit surface Fe(III) precipitation, use of platinized or Nafion-coated WO₃ caused the negligible photocatalytic improvement in the ternary system. Effective oxidative degradation in the presence of the UV cut-off filter corroborated visible light activation of the WO₃/Fe(III)/H₂O₂ system.