Photocatalytic degradation mechanism of benzene over ZnWO4: Revealing the synergistic effects of Na-doping and oxygen vacancies

Metal ion doping and vacancy-engineering are effective strategies to promote photocatalytic performance. ZnWO4 is an important inorganic photocatalytic material. Herein, ZnWO4 with Na-doping and oxygen vacancies (OVs) was prepared by a facile one-step hydrothermal strategy via adding Na2WO4. Due to the synergistic effects of Na-doping and OVs, the photocatalytic benzene removal rate of the ZnWO4 samples is much higher than that of pure ZnWO4. According to the characterization results, the Na-doping and OVs not only promote the migration of electrons but also activate H2O and O-2 molecules to generate a large number of reactive radicals. The results of in situ DRIFT spectroscopy and DFT calculations clearly demonstrate that the Na-doping and OVs enhance the adsorption and activation of reactants and intermediates. The photocatalytic benzene oxidation mechanism is proposed. Benzene is completely oxidized following the order of phenol, catechol (quinol), benzoquinone, and small molecule organics such as acetic acid, eventually producing H2O and CO2. The work could provide new mechanistic understanding for photocatalytic VOCs decomposition.