Photocatalytic Performance Of Polyoxometalates/semiconductor Composite Film For NO₂ Removal

In recent years,in order to solve some critical problems which including energy crisis and environmental pollution,and to achieve a sustainable development strategy,using semiconductor materials to achieve the conversion between solar energy,electrical energy and chemical energy has become a popular strategy.Among them,TiO₂ nanorod arrays?TNRs?are popular owning to their stable properties,low price and environmental performance.TaON has also attracted much attention due to its suitable band gap and good response to visible light.However,TiO₂ could only respond to ultraviolet light and the photogenerated carriers of TaON are easy to recombine,which causes their application to be restricted.As a good electron acceptor,polyoxometalates?POMs?could effectively transfer and capture photo-generated electrons.Therefore,it is beneficial for POMs to promote the separation of photo-generated charges thus improve the photovoltaic performance of semiconductor materials that need to be modified.In this paper,we have prepared a series of semiconductors and their composite film electrodes,and performed photocatalytic removal of NO₂.The main research contents are as follows:1.The composite membrane electrodes of TiO₂ nanorod arrays with a series of POMs were prepared by hydrothermal method and spin coating method.And after testing their photoelectrochemical properties and photocatalytic activity,the results suggested that all aspects of performance for TNRs/POMs has been improved than pure TNRs.Among them,the membrane electrode through the modification of K₆SiW₁₁O₃₉Co?II??H₂O?(SiW₁₁Co)exhibited the most obvious improvement in the photoelectric performance.Moreover,TNRs/SiW₁₁Co membrane electrode showed the strongest photocatalytic activity for NO₂ removal.After 4 h light irradiation,the removal efficiency reached about 80.9%.2.SiW₁₁Co and Ag nanoparticles were successfully introduced into TNRs to prepare TNRs/SiW₁₁Co/Ag composite membrane electrodes though spin-coating and chemical bath deposition methods.Compared to the electrode only modified with SiW₁₁Co,the co-modification of SiW₁₁Co and Ag has significantly enhanced the photocatalytic performance of the membrane electrode and greatly improved the NO₂ removal efficiency.This result is mainly attributed to the fact that Ag nanoparticles not only could effectively promote the light absorption of membrane electrodes,but also their good electrical conductivity could facilitate the migration of photo-generated electrons.In addition,we have verified the above explanation through a series of photoelectrochemical tests.3.CdS was successfully deposited on the TaON membrane electrode by successive ionic layer adsorption and reaction method?SILAR?,and ZnS passivation treatment was conducted using the same method.As a result,we found that TaON/CdS/ZnS film displayed highly efficient NO₂ removal rate under visible light irradiation owing to its stronger visible light response,photocorrosion preventive capacity and the high separation efficiency of photo-induced electrons and holes.Furthermore,we also put forward the feasible NO₂ photocatalytic removal mechanism for TaON/CdS/ZnS film.In addition,we found that the active species ?O₂^-and h⁺ both played an important role in photocatalytic removal of NO₂ from capture experiments.