Portable Photoelectrochromic Visualization Sensor for Detection of Chemical Oxygen Demand.

Chemical oxygen demand (COD) is an important parameter to estimate water quality, and many methods have been developed to measure COD. However, these methods are not satisfying because of the use of hazardous materials, the interference of chloride, and complicated operations. Meanwhile, the development of portable sensors for field testing COD is still at an early stage. In this work, we propose a new portable COD sensor based on the photoelectrochromic principle. The whole detection can be conducted with a small indium tin oxide (ITO) electrode modified with photocatalytic material TiO2/g-C3N4 and the electrochromic material Prussian blue. Under light illumination, organic pollution can be photocatalytically oxidized by TiO2/g-C3N4 and photogenerated electrons are transferred to Prussian blue, which will be reduced to colorless Prussian white. So the COD value can be obtained through the color change of the ITO electrode. By adjusting the electrode size, the detection range is flexible from 0.025 to 750 mg/L, and this sensor has a good repeatability and stability. Meanwhile, this portable visualization PEC sensor has been successfully applied in actual wastewater sample detection, which has a good prospect in COD monitoring.