Fabrication Of High-efficient TiO₂-based Materials For Photocatalytic Oxidation Of Toluene Under Visible Light

The problem of indoor volatile organic compounds（VOCs）pollution has attracted a lot of attention.Photocatalytic technology has become the most promising control technology because of its environmental protection and suitable for the treatment of low-concentration VOCs that are continuously released.TiO₂ is the most commonly used photocatalyst,but its large-scale application is restricted due to the following shortcomings:First,the band structure limits its light absorption range,making it difficult to adapt to indoor visible light environment;Second,the photo-generated electron-hole recombination rate is fast,resulting to poor performance;Third toxic intermediate products are easy to accumulate on its surface,which will lead to catalyst deactivation.In order to solve these shortcomings above,this paper uses inexpensive Cu O and urea to modify the TiO₂ catalyst,systematically study the influence of the amount of modifier on the catalyst performance,explore the structure-activity relationship between the catalyst structure characteristics and the photocatalytic oxidation performance of toluene,in order to provide theoretical guidance for the design and development of high-performance titanium dioxide-based photocatalystsIn this thesis,a series of Cu T catalysts were obtained by loading Cu O on TiO₂;a series of UT catalysts were obtained by thermal modification of TiO₂ with urea by co-thermal decomposition method;and on this basis,XRD、TEM、XPS、UV-Vis DRS、PL、in-situ DRIFTS、GC-MS、ESR and other characterization techniques are used to explore structure-activity relationship of the catalyst.The main research conclusions are as follows:（1）In the study of Cu modified TiO₂ catalyst,we found that Cu has better catalytic activity than Mn,Fe,Ni modified TiO₂ catalysts.Copper acetylacetonate as a precursor salt has higher catalytic activity than copper chloride,copper nitrate,and copper acetate.The catalyst has the best activity when the Cu loading is 3 wt%,and the best CO₂ selectivity when the Cu loading is 1 wt%.However,Cu modification only increased the conversion rate of toluene,but did not significantly promote the selectivity of CO₂.In the photoelectric characterization,it is found that the photocurrent can partially explain the difference in catalyst activity,but the electrochemical impedance and PL cannot be consistent with the activity.In the structural characterization,it is found that the catalyst with better activity has a smaller crystal size under the XRD characterization.It is found in the FT-IR,water contact angle,XPS that Cu⁺and hydrophilic may be important factors affecting the activity of the catalyst.（2）In the study of urea thermal decomposition modified TiO₂,we found that when the mass ratio of urea/TiO₂ is 2:1（UT2）,the catalyst activity is the best,the toluene conversion rate is higher than 80%,and the CO₂ selectivity is higher than 75%.Through various characterizations of the catalysts,it was found that the urea modified samples,a small amount of N atoms were doped into the TiO₂ lattice in the form of interstitial nitrogen,which caused the TiO₂ lattice to be slightly distorted,thereby providing the doped energy level and enhancing the visible light absorption of TiO₂.It is one of the main factors to increase the conversion rate of toluene.In the study of the reaction path and TiO₂ deactivation mechanism,we found that the C and N triple bonds and accumulate double bonds and the surface C and N heterocycles in the UT2 sample can provide additional adsorption sites for VOCs and oxidation intermediates.With more active oxygen species,more intermediate products can be deeply oxidized into benzoic acid which is easier to open the ring,which improves the activity of toluene oxidation and CO₂ selectivity;while the surface intermediate products of TiO₂accumulate with benzaldehyde and benzoic acid Mainly,and the high ring-open energy barrier of benzaldehyde makes it difficult to degrade,which leads to the ultimate inactivation of TiO₂.