A combined photocatalytic determination system for chemical oxygen demand with a highly oxidative reagent

This study focuses on the proposal and validation of a combined photocatalytic (PC) system and a three-parameterized procedure for the determination of chemical oxygen demand (COD; PcCODcombined), with a highly oxidative reagent utilized as a photoelectron scavenger and signal indicator. The PcCODcombined was the functional combination of photon-efficient thin-layer photocatalytic oxidation, conventional bulk-phase photocatalytic oxidation and photocarrier-efficient high-activity photocatalytic reduction in one single photodigestion system, and consequently, this system possessed high photon-utilization efficiency, automatic stirring function and satisfactory determination characteristics. In comparison with the conventional one-parameterized procedure, the three-parameterized procedure introduces the blank and total photocatalytic reduction responses as two of the three significant analytical parameters. Under the optimized pH value of 3.0–4.5 and a rotating rate of 40 rpm, the representative KMnO4 species was used for the PcCODcombined system as the combined high-activity oxidant, and a narrow and reliable analytical linear range of 0–260 mg L−1 was achieved during the 10 min duration of the determinations. No observable interference of Cl− was found at concentration of the ion up to 2000 mg L−1. A real sample analysis indicated that the measured values for the PcCODcombined were all within a relative deviation below 5% of CODCr of the standard method, which further validates the practical feasibility of the proposed PcCODcombined system.