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Glucose in water (L 2 O, L = H or D) at pH = 7 (phosphate buffer) is oxidized in presence of Bi 2 WO 6 and light. An unusually large solvent isotope effects, k H 2 O =k D 2 O ¼ 7:8 and 6.8, have been measured using solar light and solar simulator, respectively. These large values come from the contribution of the equilibrium L 2 O ⇄ L + + OL − previous to the rate-limiting step (rls) and the kinetic one (proton transfer) involved at the transition state. The reaction is faster when [L + ] increases; therefore, L + species instead of OL − one participates in the photooxidation. The rls is the 1 e − reduction-adsorption of H + on the Bi 2 WO 6 surface (Bi 2 WO 6 /Bi 2 WO 6 -H, −0.6 V vs NHE). Subsequently, O 2 reduction to L 2 O, as driving force, occurs at the catalyst conduction band (CB). Linear sweep voltammetry when Bi 2 WO 6 is used as cathode shows two reduction processes: H + /H 2 and O 2 /O 2 .− . The last one-electron reduction occurs at −0.2 V vs NHE and the first one at −0.4 V vs NHE. Both show solvent isotope effect, although the i 0H 2 O =i 0D 2 O are 2.4 and 1.9, respectively, quite smaller than the value obtained in the photooxidation due to the influence of the bias on the transition state symmetry in the first case and through water O 2 reduction in the second. Cyclic voltammetry indicates that the reduced and adsorbed H (Bi 2 WO 6 -H 2 ) is oxidized to Bi 2 WO 6 -H at approximately 0.2 V vs NHE. Positive conduction band potential of Bi 2 WO 6 (+0.5 V vs NHE) establishes the difference with other semiconductors where oxidation (L 2 O/L + ,OL . )instead of reduction has been proposed as rls in photooxidation.

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This report discusses the effects of the initial concentration of 4-chlorophenol (4-CP) on its solar light photoinduced oxidation/mineralization kinetics on Bi2WO6catalyst. Photocatalytic degradation followed the Langmuir-Hinshelwood (L-H) mechanism. From the kinetic data the Langmuir adsorption equilibrium constant of 4-CP on the Bi2WO6surface and the L-H maximum reaction rate for 4-CP oxidation have been evaluated. Chromatographic and spectroscopy studies show the presence ofp-benzoquinone and maleic acid as the main reaction products; these compounds first increase and then decay until they disappear. Chemical oxygen demand (COD) and produced CO2measurement show that photocatalytic mineralization of the phenolic compound was readily possible in a wide concentration range.