A visible light assisted photocatalytic system for determination of chemical oxygen demand using 5-sulfosalicylic acid in situ surface modified titanium dioxide

Titanium dioxide (TiO2) nanoparticles were in situ surface modified by the chemisorption of 5-sulfosalicylic acid as non-sacrificial organics and then used as a visible light active photocatalyst (5-SA-TiO2). Based on the photodegradation of organic pollutants, a new system, 5-SA-TiO2–KMnO4, was used for the first time for the determination of chemical oxygen demand (COD). A linear correlation was observed between the amount of oxidizable dissolved organic matter and the amount of MnO4− consumed by the coupled reduction process. Thus, COD could be determined by the depletion of MnO4−. After TiO2 was surface modified by 24.82 μg/mg of 5-SA, the working calibration range was extended from 2–12 mg/L and 50–300 mg/L to 0.3–400 mg/L and the disadvantages of pure TiO2 for COD detection techniques were overcome, including UV irradiation and low oxidation percentage. Without any sample pretreatment and toxic reagents, the COD values of nature water and real wastewater could be successfully determined by achieved technique. Excellent agreement between our proposed method and conventional dichromate method was achieved.