Fabrication And Modification Of WO₃ Nanoplate Arrays On Stainless Steel Surface For Photoelectrocatalytic Applications

In recent years,photoelectrocatalytic（PEC）degradation of recalcitrant organic pollutants using semiconductor photocatalys is developing rapidly in environmental protection due to its low energy consumption,mild reaction conditions,high efficient removal of organic pollutants and no secondary pollution.Among various photocatalysts,WO₃ holds immense potential applications in PEC field for its relatively narrow band gap of 2.4～2.8 eV that can absorb approximately 12%of solar light and high resistance against photo corrosion.However,WO₃ suffers from its slow charge transfer at the semiconductor/electrolyte interface,and rapid electron-hole recombination,which limits the actual application of WO₃.Besides the photocatalytic activity of photocatalysts,physical properties of the substrate are also important to its practical application for organic pollutants degradation.Stainless steel has advantageous mechanical properties,good conductivity,and acceptable corrosion resistance.Thus,stainless steel appears to be an ideal alternative as a substrate for photocatalyst immobilization.Herein,the vertical alignment of WO₃ nanoplate arrays was fabricated on a stainless steel via hydrothermal method and calcination to improve the electronic transmission performance,and then Zn O modified WO₃ thin films were prepared to promote the separation of photogenerated electron-hole pairs resulting in the promotion of PEC efficiency.In this dissertation,the following several parts of work have been done:（1）The WO₃ nanoplate films were fabricated via hydrothermal method and calcination at 450℃for 1h.The effect of hydrothermal reaction time and temperature on the morphological,photoelectrochemical and PEC properties has been studied.The obtained optimum fabrication technical conditions were 2.5h of hydrothermal reaction time and 120℃of reaction temperature.The WO₃ film was composed of square-shaped plates which were grown vertically on the substrate.The nanoplates exhibited a thickness of 260±40 nm and an edge length of 1.1±0.4μm and a height of 1.35μm of the film.When the initial mass concentration of methylene blue（MB）is 10 mg/L and the applied bias voltage is 0.8V,the removal rates of MB is 98.9%and the rate constant is 0.038min^-1using the WO₃ nanoplate films after 120 min of visible light irradiation.（2）A facile dip-coating-annealing process was employed for Zn incorporated WO₃nanoplate films using a Zn（NO₃）₂ precusor.Results show that Zn（Ⅱ）exists as ZnO nanoparticles and adheres to the surface of WO₃.The ZnO/WO₃ composite material exhibits much improved performance over WO₃ nanoplate films with an enhancement of50%in PEC activity.The Zn O modified WO₃ nanoplate film degraded MB to 95.6%in60 min in PEC process and the rate constant is 0.057 min^-1.The excellent PEC performance should be attributed to the prolonged lifetime of the photogenerated electron-hole pairs on the Zn O/WO₃ nanoplate arrays.Moreover,the stability of ZnO/WO₃ nanoplate films was also studied and no significant reduction in PEC activity was observed after recycling for 5 times.