Preparation of photocatalytic nano-ZnO/TiO2 film and application for determination of chemical oxygen demand

A composite nano-ZnO/TiO2 film as photocatalyst was fabricated with vacuum vaporized and sol–gel methods. The nano-ZnO/TiO2 film improved the separate efficiency of the charge and extended the range of spectrum, which showed a higher efficiency of photocatalytic than the pure nano-TiO2 and nano-ZnO film. The photocatalytic mechanism of nano-ZnO/TiO2 film was discussed, too. A new method for determination of low chemical oxidation demand (COD) value in ground water based on nano-ZnO/TiO2 film using the photocatalytic oxidation technology was founded. This method was originated from the direct determination of the Mn(VII) concentration change resulting from photocatalytic oxidation of organic compounds on the nano-ZnO/TiO2 film, and the COD values were calculated from the absorbance of Mn(VII). Under the optimal operation conditions, the detection limit of 0.1 mg l−1, COD values with the linear range of 0.3–10.0 mg l−1 were achieved. The results were in good agreement with those from the conventional COD methods.