Modification Of CdS And TiO₂ For Photocatalytic Air Purification

The rapid development of industrialization not only caused convenience to our daily life,but also produced pollution,which is harmful to the health.The discharged nitrogen oxide（NO_x）in air not only destroys the ozone layer,but also the source of photochemical smog and acid rain.Some volatile organic compounds（VOCs）have a great impact on human health,which are easy to induce blood diseases and even cancer.Compared with other methods,semiconductor photocatalysis provides a sustainable way to solve the environment-related problems.CdS and TiO₂are typical visible-and UV-light responsive semiconductor photocatalyst.However,both of them have shortcomings.Although CdS is visible-light-responsive,it suffers from photocorrosion.TiO₂is a stable photocatalyst,but it can only absorb ultraviolet light.In addition,as for both photocatalysts,the quick recombination of photo-generated carriers cause poor photocatalytic activity.In this dessert,we tried to modify CdS and TiO₂to improve the photoreactivity.Specific research contents are as follows:（1）Modification of CdS nanorods with metallic Bi to improve the photoreactivity towards NO oxidation.On considering that the SPR effect of metal Bi can be used to inhibit the photocorrosion and promote the separation of the charge carriers,in this part,chemical reduction of Bi（NO₃）₃by sodium borohydride was used to deposit Bi nanoparticles on the surface of 1D CdS nanorods（CdS-NRs）.It was found that the photoreactivity of CdS-NRs toward NO oxidation in a continuous reactor can increase32%after modification with Bi nanoparticles.The SPR effect of Bi can not only inhibit the photocorrosion,but also improve the photoreactivity of CdS-NRs.The results of fluorescence,surface photocurrent,surface photovoltage and electrochemical impedance spectroscopy（EIS）further indicated that metallic Bi could inhibit the recombination of photo-generated carriers.ESR characterization result showed that superoxide free radicals,hydroxyl free radical and singlet oxygen free radical are the typical reactive oxygen species（ROSs）that are responsible for the oxidation of NO.（2）Introduction of oxygen vacancies on the surface of TiO₂to increase the photoreactivity towards acetone oxidation.The large band gap makes TiO₂only UV-sensitive,and the quick recombination of charge carriers causes poor photoreactivity.To solve these problems,oxygen vacancies were used to modify TiO₂.At first,TiO₂precursors were synthesized by hydrothermal reaction using Ti（OC₄H₉）₄as titanium source and NH₄F as shape-directing reagent.The effects of calcination of temperature on the structure and photocatalytic activity of TiO₂were systematically studied.It was found that 600^oC-calcined TiO₂photocatalyst exhibits the highest photoreactivity for acetone oxidation.More than 80%of the acetone was decomposed after irradiation for 2 h,and almost 100%of X3B in solution was bleaching with 25 min.The production of oxygen vacancies was confirmed by UV-visible light absorption and EPR spectra.In addition,the 600 ^oC-calcined TiO₂photocatalyst exhibits the highest signals in surface photovoltage spectrum（SPS）and photocurretent,indicating that oxygen vacancies can stimulate the separation of charge carriers and retarding the recombination,therefore causing enhanced photoreactivity towards acetone oxidation and X3B dye degradation.