Study On The Photocatalytic Degradation Performance Of VOCs By TiO₂ Structure Regulation And Surface Modification

Photocatalytic oxidation is a promising technology for removing volatile organic compounds?VOCs?from indoors.Titanium dioxide?TiO₂?is widely used in the removal of gaseous pollutants due to its low cost,high stability and excellent photocatalytic ability.However,considering the short lifetime of electrons generated by TiO₂ photo excitation and the forbidden band width required for ultraviolet?UV?excitation,TiO₂ cannot fully meet the required practical requirements.A number of methods for modifying TiO₂ have been studied and reported.A strategy for modifying the TiO₂ crystal plane?exposure active sites?and complexing with other semiconductors to improve the activity of the TiO₂ photocatalyst by loading or doping different metals or nonmetals.These techniques can reduce the electron-hole recombination rate of TiO₂ and broaden the photoresponse range of TiO₂.However,the degradation of VOCs not only requires an increase in the separation efficiency of electron-holes,but also the performance of the photocatalyst for the adsorption and desorption of VOCs.Therefore,our main research contents are as follows:?1?We prepared the{001}and{101}crystal flaky TiO₂ by spray drying method,and obtained the optimal activity of flaky TiO₂ by adjusting the sintering temperature of the precursor.We used different methods to load Pd on the{101}crystal plane of TiO₂.Photoreduction:The electrons generated by TiO₂ under ultraviolet light are enriched in the{101}crystal plane,which causes the Pd metal ions to be reduced and anchored by electrons on the{101}crystal plane.Photoinduced method:The prepared Pd?3-5 nm?particles have a positively charged amino group,which causes the Pd particles to be attracted to the{101}crystal plane enriched in electrons.The Pd particles are prepared to be selectively loaded onto the{101}crystal face.By comparing the two preparation methods,an optimal loading mode of Pd metal is obtained.The photoinduced method makes the Pd particles no longer grow up during the loading process?because the particle size has been fixed at the beginning?,fully utilizing the ability of the noble metal to transfer electrons,and improving the electron-hole separation efficiency.It provides a feasible idea for the specific modification of the carrier by future precious metals.?2?We obtained a carbon-supported porous structure TiO₂ by adjusting the calcination method of Ti-MOF?MIL-125?.During the calcination process,the MOF converts the organic matter into a carbon in situ loading into the porous TiO₂ in the pores,and the carbon can be grown in situ in the pores.And the amount of carbon in the inside of the tunnel is stepped,and as the pores deepen,the amount of carbon is gradually increased.This type of loading is more conducive to the adsorption and diffusion of toluene gas.Comparing the activity with P25 and commercial TiO₂?anatase phase?,it was found that its activity was much higher than both,and it had good stability.?3?Using MOF as a template,a photocatalyst composed of C,Pd,TiO₂ was constructed.Ti-MOF will leave a large amount of carbon after being calcined at700°C by argon gas,and the obtained porous TiO₂ maintains the macrostructure of Ti-MOF,and a large amount of carbon remains inside and on the surface to adsorb toluene gas pollutants well.The Pd particles were loaded into the pores of TiO₂.It was proved by comparison experiments that Pd loading into the pores has better photocatalytic degradation of toluene than on the surface.This is because Pd is not favorable for the adsorption of toluene on the surface of the catalyst,and the internal pores of the porous titanium oxide and the carbon toluene are not sufficiently adsorbed.And Pd will block the pores on the surface,which is not conducive to the catalysis.The Pd particles enhance the contact between the metal and the carrier in the channel and shorten the electron transport distance.Greatly promote the progress of catalytic reaction,and provide ideas for future gas phase catalyzed material design.