Fabrication And Modification Of Nanoporous Anodic WO₃ And Their Applications In Photocatalysis And Ion Detection

In 1972,Fujishima and Honda first discovered the photocatalytic splitting of water on TiO₂ electrodes.Since then a lot of research work has focused on understanding the fundamental processes and on enhancing the photocatalytic efficiency of semiconductor catalysts. However,as a practical solar-light application,TiO₂ presents some intrinsic limitation:its large band-gap energy(3.0-3.2 eV) covers only a marginal part of the solar spectrum.Since WO₃ has received considerable recognition because of its excellent photochromic/ electrochromic properties,gas sensing properties and catalytic properties that have potential applications for electrochromic devices,"smartwindows" and displays,chemical sensors, biomimetic switch,photocatalysts.Nanoerystalline WO₃ photoelectrodes can utilize the most intense region of the solar spectrum because of most nanoerystalline WO₃ films' band gap in the range of 2.5-3.0 eV,corresponding absorption edges are in the range of 410-500 nm, which is more beneficial to utilize sunlight than TiO₂.It can achieve unique properties and superior performance of materials by fabrication of ordered nanodimensional structure,which impetus toward fabricating nanodimensional materials.In this dissertation,we pay much attation to fabricate ordered tungsten oxide nanomaterials by electrochemical anodization and modify the prepared tungsten oxide nanomaterials further.Based on these,their properties and application are investigated primarily.Firstly,according to detailed investigations on various anodization conditions,chemical environment of self-assembled growth comes true by adjusting the equilibrium of field-enhanced oxidation growth at the metal/oxide interface and field-enhanced oxide dissolution at the oxide/electrolyte interface,and therefore,self-assembled nanoporous tungsten oxide(WO₃) with preferential orientation(002) planes was successfully synthesized on the tungsten sheet by anodization.The pore sizes of the highly ordered self-assembled nanoporous tungsten oxide are turntable.The relationship between the nanocrystalline tungsten oxide with specific preferential orientation of crystal faces and photocatalytic activities are investigated.The results indicate that the nanoporous WO₃ with preferential orientation of(002) planes are possibly more favourable in photoresponse and photocatalytic degradation pollutants than the WO₃ film with preferential orientation of(020) planes. Furthermore,to improve photoresponse to UV/visible light,we have successfully fabricated N-doped nanoporous tungsten oxide photoelectrode with different N-doping species,which facilities our research on how the N-doping species influence the photocatalytic activities of catalysts.Photoelectrochemical measurements,energy-band research together with photoeatalytie activity demonstrated that interstitial N-doping obviously heightened photoelectric activity and photocatalytic capability under UV illumination over that of the undoped WO₃;while the substitutional N-doping evidently increased photocurrent response and photocatalytic activity under Vis light(λ＞400 nm) than do the undoped WO₃.Finally,we modify the self-assembled nanoporous WO₃ electrode with CdS quantum dots and fabricate differently functional CdS/WO₃ electrode for selective detection of metal ions and photo to electric conversion.The results show that a simple,rapid and specific method for Zn²⁺ or Pb²⁺ determination was proposed using the CdS/WO₃ electrode prepared in low concentration of organic reactants.In addition,the photocurrent density obtained by the CdS/WO₃ electrode prepared in high concentration of organic reactants is 60%higher than the nanoporous WO₃ electrode under artificial sunlight illumination.