Photoelectrochemical determination of chemical oxygen demand

Abstract

A method for determining chemical oxygen demand of a water sample comprises the steps of (a) applying a constant potential bias to a photoelectrochemical cell, having a photoactive working electrode (e.g. a layer of titanium dioxide nanoparticles coated on an inert conductive substrate) and a counter electrode, and containing a supporting electrolyte solution; (b) illuminating the working electrode with a light source and recording the background photocurrent produced at the working electrode from the supporting electrolyte solution; (c) adding a water sample, to be analyzed, to the photoelectrochemical cell; (d) illuminating the working electrode with a light source and recording the total photoelectrocurrent produced with the sample; (e) determining the chemical oxygen demand according to the type (exhaustive or non-exhaustive) of degradation conditions employed.

1 . A method of determining chemical oxygen demand of a water sample, comprising the steps of 
 a) applying a constant potential bias to a photoelectrochemical cell, having a photoactive working electrode and a counter electrode, and containing a supporting electrolyte solution;    b) illuminating the working electrode with a light source and recording the background photocurrent produced at the working electrode from the supporting electrolyte solution;    c) adding a water sample, to be analysed analyzed, to the photoelectrochemical cell;    d) illuminating the working electrode with a light source and recording the total photocurrent produced with the sample;    e) determining the chemical oxygen demand of the water sample according to the type of degradation conditions employed.    
     
     
         2 . A method as claimed in  claim 1  wherein the photoactive working electrode is a nanoparticulate semiconductive electrode.  
     
     
         3 . A method as claimed in  claim 2  in which the working electrode is a layer of titanium dioxide nanoparticles coated on an inert conductive substrate.  
     
     
         4 . A method as claimed in  claim 1  in which a reference electrode is also used in addition to the working and counter electrodes.  
     
     
         5 . A method as claimed in  claim 1  in which the chemical oxygen demand is determined under exhaustive degradation conditions, in which all organics present in the water sample are oxidized.  
     
     
         6 . A method as claimed in  claim 1  in which the chemical oxygen demand is determined under non-exhaustive degradation conditions, in which the organics present in the water sample are partially oxidized.  
     
     
         7 . A method as claimed in  claim 1  in which the background photocurrent is deducted from the total photocurrent produced with the sample to obtain the photocurrent due to the oxidation of organic material in the sample.  
     
     
         8 . A method as claimed in claim in  claim 1  in which the sample is diluted with the supporting electrode.  
     
     
         9 . A method as claimed in  claim 1  in which the chemical oxygen demand is determined by measuring charge or current under exhaustive degradation conditions with a stationary or flow cell using different operational modes including batch mode, flow-stopped mode and continuous flow mode.  
     
     
         10 . A method as claimed in  claim 1  in which the chemical oxygen demand is determined by measuring charge or current under non-exhaustive degradation conditions with a stationary or flow cell using different operational modes including batch mode, flow-stopped mode and continuous flow mode.  
     
     
         11 . A photoelectrochemical assay apparatus for determining oxygen demand of a water sample which consists of. 
 a) a measuring cell for holding a sample to be analyzed;    b) a photoactive working electrode and a counter electrode disposed in said cell;    c) a light source adapted to illuminate the photoactive working electrode;    d) control means to control the illumination of the working electrode, the applied potential bias, and photocurrent recording;    e) photocurrent/charge measuring means to measure the photocurrent/charge at the working electrode;    f) analysis means to derive a measure of oxygen demand from the measurements made by the photocurrent/charge measuring means.    
     
     
         12 . Apparatus as claimed in  claim 11  in which the measuring cell is a flow through cell.  
     
     
         13 . Apparatus as claimed in  claim 11  in which a reference electrode is included in the measuring cell.  
     
     
         14 . Apparatus as claimed in  claim 11  wherein the photoactive working electrode is a nanoparticulate semiconductive electrode.  
     
     
         15 . Apparatus as claimed in claim  111  in which the working electrode is a layer of titanium dioxide nanoparticles on an inert substrate.  
     
     
         16 . Apparatus as claimed in  claim 11  which also includes a reservoir for a supporting electrolyte which is used to measure the background photocurrent and to dilute the sample.  
     
     
         17 . Apparatus as claimed in  claim 16  which also includes a sample supply/injection system and a supporting electrolyte supply/injection system.