Detection Of Chemical Oxygen Demand Based On Photocatalytic Digestion And Micro-spectrometer

Chemical Oxygen Demand is defined as a measure of the oxygen equivalent of the organic matter content of a sample susceptible to oxidation by a strong chemical oxidant, to a certain, it could reflect the origanic pollution extent of the water,and it is a most important index which is employed to estimate organic pollutant level in waters. If the concentration of chemical oxygen demand exceede standard, it will cause a decline in the quality of the water surface and different degrees of threat to the survival of biologial communities in water.Therefore, the study of the method on the determination of COD is so valuable for the monitoring and controlling to industrial wastewater and domestic sewage. The existence methods has some shorts such as needing a long time to the process of oxidation and digeation, weaking in resistance to the interference on the chloride ion, or needing to mix, heat, centrifugal separation of photocatalyst, is difficult to make films, are not suitable for on-sit rapid determination. So it is significance and imperative to develop a method of a simple, rapid, sensitive for detecting the chemical oxygen demand. The paper will tell us something about the study on the methods for detecting the COD were based on the principle of the photocatalytic oxidation, it mainly include:The concentration of chemical oxygen demand (COD) was directly determined and the effect of COD photocatalytic degradation was examined by three-wavelength spectrophotometry in the titania (TiO₂)suspension systems. The three optimum wavelengths,420nm,476 nm,and516 nm,were obtained by the program of Matlab which based on the theory of three-wavelength spectrophotometry,calculated out the value of A, and determined the value of COD for the samples.Results showed that the linear range of the method is 1～35mg/L, and the detection limit is 0.9mg/L.This method was applied to determine the COD value of actual water samples, the RSD is less than 5%, the recovery is 98.7%～103.4%,and the result is coincide with government standard,the difference have no sense of statistics, the results are satisfactor.P25 and cerium sulfate were made to homodisperse mixture,a single time was used to add the reagent to the sample,the oxidation and digestion of the organic matter are based on the principle of the photocatalysis,a sensitive spectrophotometry for rapid determination of chemical oxygen demand(COD) was proposed. In order to ensure the method to be highly reliable and accurate, the spectral data was processed with dual-wavelength method for deducting background interference. This method has the advantages of accurate, sensitive, simple, rapid, and ultra strong anti-interference to chloride. Results showed that the linear range of the method is 1～20mg/L, and the detection limit is 0.4mg/L.This method was applied to rapidly determine the COD value of actual water samples, the RSD is less than 5%, the recovery is 96.2%～103.5%,and the result is coincide with government standard,the difference have no sense of statistics, the results are satisfactory.Determination of chemical oxygen demand was based on micro-spectrometer, the mixture solution of nano titania and cerium sulfate was used to be the reagent and the micro-spectrometer was used to be the instrument. A series of parameters related on the chemical oxygen demand were determined, such as standard curve, sensitivity, recovery, and so on. The results are coincided with the data determined by UV-2450. The linear range of this method is up to 1～20mg/L, and the detection limit is 0.74mg/L.When this method was applied to determine the COD of actual water samples rapidly, the RSD is less than 5%, the recovery is 99.6%～97.1%,and the results conformed to the government standard,so the results are satisfactory. In addition, this method has the advantages of accurate, sensitive, simple, rapid, and the volume of detecting instrument is small, which meets the requirement for the rapid determination on COD.In this research, nano-titamia-P25 power was used to raw material and Acetylacetone or EDAT was used to disperser, prepared two kinds of nano-titania films. The film doped Ag ion by dip coating technique, it brought about the result of inhibiting the recombination of electron-hole pair, even to increase the efficiency of photodegradation. Two kinds of nano-TiO₂ thin films were characterized the photocatalytic efficiency by degradation of rhodamine B solution as a model and the experiment results showed that the Ag-P25-2 film which EDTA was used to dispersant exhibited a higher photocatalytic activity and stability than the Ag-P25-1 film which acetylacetone was used to dispersant.So the Ag-P25-2 film was used to photocatalyst, determination of COD in the water by spectrophotometry. Results showed that the linear range of the method is 1～15mg/L, and the detection limit is 0.1mg/L.This method was applied to determine the COD value of low concentration of COD in actual water samples, the RSD is less than 5%, the recovery is 96.5%～100.6%,and the result is coincide with government standard,the difference have no sense of statistics, the results are satisfactor. This method has the advantages of strong anti-interference to chloride.