Preparation And Modification Of TiO₂ Nanotubes And Application In The Chemical Oxygen Demand Determination

With the development of society,environmental pollution,especially water pollution is becoming more and more serious.Chemical oxygen demand?COD?has been extensively employed as one of the most important indicators of the organic contamination of water.At present,the standard method?potassium dichromate method?for determination of COD involves reflux over a long period of time to achieve adequate oxidation,but this method consumes a long time,highly corrosive and toxic?Cr2O7-?chemicals,expensive reagents?Ag+?.So it's very necessary to find a fast,environmentally friendly detection methods.Other alternative assay?photoelectrocatalytic?has been developed based on TiO₂ nanotubes.However,the specific surface area of TiO₂ nanotubes is smaller than that of nanoparticles,and only a small fraction of visible light is used,which limits the practical application of photoelectrocatalytic detection of COD.The photocatalytic degradation of organic compounds and photocatalytic capacity of TiO₂ nanotubes are improved by the preparation and modification of the nanotubes.?1?The titanium dioxide nanotubes were obtained on the titanium foil by anodic oxidation,and then the titania nanotubes were hydrothermally treated in the titanium trichloride solution to obtain the hierarchical TiO₂ nanotubes.The pore size of the nanotubes became smaller,and the surface of the nanotubes were attached with many small particles of titanium dioxide,resulting in the increase of the specific surface area and the absorbance of the nanotubes.Most photoinduced electrons generated on the isolated TiO₂ NPs,were easily extracted to the TNT layer and transported through the TNTs.In other words,H-TNTs could suppress the recombination of the photogenerated electronhole pairs which contributes to the improvement of photocurrent.?2?The microchannel was carved out on the PMMA plate according to the pre-designed pattern.The TiO₂ nanotubes were fixed in the working electrode position.The device was finally integrated with inlet,outlet,reference electrode and counter electrode by the reserved hole.It was easily concluded that the inet had a good liner relationship with the COD concentration of all the investigated organic compounds.The linear range of 0-300 mg L-1 COD and the detection limit of 1 mg L-1 COD were achieved.?3?Citric acid?CA?was used as a carbon precursor to synthesize Graphene quantum dots under hydrothermal processes.These GQDs are uniform in size ranging from 4 to 8 nm in diameter.The graphene quantum dots were compounded on the TiO₂ nanotubes by hydrothermal and subsquently heat treatment.The incorporation of GQDs not only extends the photoresponses of the complexes to the visible region,but also the GQDs/TiO₂ heterojunction can absorb more O₂ than pure TiO₂ on the surface,and then produce more O₂-species for organic degradation.Therefore,compared with TiO₂ nanotubes,GQDs/TiO₂ composites exhibit better visible-light-driven photocatalytic properties.The GQDs/TiO₂ composite electrode was used as a COD detector to quantify COD by photoelectrocatalytic degradation of organic matter in water and recording the generated photocurrent.It was easily concluded that the inet had a good liner relationship with the COD concentration of all the investigated organic compounds.The linear range of 0-288 mg L-1 COD and the detection limit of 1 mg L-1 COD were achieved.?4?The tantalum oxynitride composite nanotube arrays were prepared by drop coating basing on titanium dioxide nanotubes.The results showed that a thin film of tantalum oxynitride was successfully deposited on the surface of TiO₂ nanotubes.Tantalum oxynitride absorbs visible light and can produce carriers,which are rapidly separated at the interface due to the energy level difference at the interface.In addition,tantalum oxynitride can effectively passivate the surface defects of titanium dioxide nanotubes and reduce the recombination probability of electron holes.So the photocatalysis of Ta ON-deposited TiO₂ nanotubes in visible light increases a lot.The tantalum oxynitride composite electrode exhibited excellent photoelectrocatalytic degradation ability in the photoelectrocatalytic methylene blue test.And the Ta ON-TNTs composite electrode was used as COD detection.COD was quantitated by photoelectrocatalytic degradation of organic matter in water and the photocurrent was recorded.It was easily concluded that the inet had a good liner relationship with the COD concentration of all the investigated organic compounds.