| In the field of heterogeneous photocatalysis,titanium dioxide has attached much attention because of its excellent properties,and has been applied in many aspectss including the solar cell,the development of new energy,pollution degradation,organic transformation and 50 on.However,it could only display its superiorities in the region of UV-light due to its wide band gap.To address the problem mentioned above,multitude of research attention had been focused on the construction of improved photocatalytic system based on TiO2,aiming at broadening the response scope to visible light region.In this thesis,photocatalytic systems constructed by two different strategies were designed based on TiO2,which drove the selective oxidation of organic compounds under visible light irradiation.More detailed research advancements are as follows:1?Inspired by the dye sensitized method,the transformation from the alcohols to the responding products was realized under the green LEDs irradiation.We complexed the 5(6)-carboxyfluorescein[5(6)-FAM]onto the anatase TiO2 to obtain the dye-sensitized photocatalyst 5(6)-FAM-TiO2.In the designed photocatalytic system,the aerobic oxidation of alcohol was undergoing in the present of the new photocatalyst with the aid of CH3O-TEMPO as the cocatalyst,O2 as the terminal oxidant.With visible light irradiation,the fluorescein dye molecule injected the hot electron directly into the conduction band of anatase TiO2.Then,the injected electron goes through the conduction band,subsequently combines with O2 to form superoxide anion radical O2·-on TiO2.Meanwhile,the CH3O-TEMPO is considered as the electron transform mediator,enhancing the catalytic activity.In detail,the generated dye radical cations return to its ground state after driving the transformation from CH3O-TEMPO to CH3O-TEMPO+.Next,the CH3O-TEMPO+preferred to be attack by alcohols to form CH3O-TEMPOH,along with the generation of an intermediate,which would undergo further cleavage to obtain the final product.The produced CH3O-TEMPOH reacted with the ROS O2·-to return to CH3O-TEMPO,achieving the catalytic cycle.2?With the strategy of complexing two different semiconductors,the benzyl amine can be transformed with high conversation and selectivity with visible-light irradiation.We combined the transition metal sulfide CdS with the anatase TiO2 to get the CdS-TiO2 complex.The novel photocatalytic system was applied to the selective oxidation of benzyl amine with air under the green LEDs irradiation.In this catalytic reaction,CdS produced the photo-induced electron and hole under the visible light irradiation,and then the conducting electron transform to the conduction band of TiO2 and finally captured by the oxygen getting O2·-,which played a crucial part in the transformation from the amine to imine.At the moment,the substrate was oxidized by the hole of CdS firstly,subsequently reacted with O2·-to the final product.In conclusion,the heterojunction is constructed in the CdS-TiO2 complex,and each component is vital.In detail,CdS performed as the sensitizer to absorb the visible light,while TiO2 worked as the junction of the electron transfer and reaction platform,which promoted the separation of the electron hole pair and boost the process of amine transformation.Further,this photocatalytic system showed an excellent tolerance to primary amines.Furthermore,CdS-TiO2 displayed another advantage in reusability.In summary,we have developed different strategies,including dye sensitized TiO2 and coupling semiconductor with TiO2 to construct heterogeneous photocatalytic systems to fulfill the selective oxidation of the alcohols or amines to the responding products under moderate conduction,in which oxygen was employed as the oxidant avoiding the toxic by-products.The novel systems attempting to improve the property TiO2 and expanding its application in visible light region,provided new ideas and reference. |
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