Investigation On Preparation And Photocatalytic Performance For TiO₂-SnO₂ Based Composite Materials

The unique structure and catalytic performance of TiO2-SnO2 composite,as an efficient,stable and environmental friendly photocatalyst,has been widely used in the field of green technology and environmental governance.According to the preparation method,phase composition,coupling with narrow bandgap semiconductor and mechanism for the TiO2-SnO2 based composite,it mainly focuses on the design and synthesis of composites,photocatalytic performance and stability assessment,and mechanism investigation.It is anticipated to provide some theoretical basis for improving the photocatalytic performance of TiO2-SnO2 based composites in the field of the environmental management.The main research contents and achievements are as follows:(1)Influence of preparation methods on the structure and performance of TiO2-SnO2 photocatalysts.TiO2-SnO2 composites are successfully prepared by five different methods,and the effects of different preparation methods on the structure,crystalline,dispersibility,and light absorption properties are investigated.The photocatalytic performance evaluation shows that the TiO2-SnO2 catalyst prepared by the sol-hydrothermal method displays higher photocatalytic activity than others.The reason may be ascribed to the advantages of the sol-hydrothermal method,which is helpful to form uniform dispersion of particles,high crystalline and good light absorption performance for TiO2-SnO2 catalyst.In this work,a straightforward and mild sol-hydrothermal method is developed,it is anticipated to provide some helpful reference for preparing other similar semiconductor composites.(2)Synthesis and investigation for photocatalytic properties of two-phase symbiotic&coexisting TiO2-SnO2 composites.Based on previous work,a series of TiO2-SnO2 composite with superior photocatalytic performance are successfully synthesized by sol-hydrothermal method.It aims at designing TiO2-SnO2 composites with controllable phase of anatase and rutile by changing the doped concentration of SnO2.The results show that only a small amount of SnO2 is needed to promote the conversion of anatase to rutile,resulting in a two-phase coexistence composite.The microstructure shows that the particle size of the two-phase coexistence composite is only 8 nm and the particles are highly dispersed,which further confirms the superiority of the sol-hydrothermal method.The photocatalytic performance evaluation shows that the catalytic activity and the stability of the TiO2-SnO2 catalyst are excellent.The enhancement of the catalytic activity is attributed to the two-phase symbiotic&coexisting and quantum size effect of TiO2-SnO2 composite.The investigation for the mechanism reveals that the catalytic reaction of the TiO2-SnO2 composite follows the mechanism of "double carrier transfer".(3)Synthesis and investigation for visible light/solar photocatalytic performance of TiO2-SnO2 modified by g-C3N4 with narrow bandgap.The g-C3N4@TiO2-SnO2 ternary composite is prepared by one-step hydrothermal method.The results show that the g-C3N4@TiO2-SnO2 ternary composite is formed by coupling the ? electron of g-C3N4 hybrid with the TiO2-SnO2 composite,rather then by coupling the single C or N atom,which could facilitate the forming of heterojunction by the from the way of coupling.The absorption for visible light improves and broadens by forming the heterojunctions and the unique structure of the composites.Meanwhile,the electron-hole separation rate is enhanced,resulting in the increase of visible/solar photocatalytic activity.The investigation for the mechanism indicates that the catalytic reaction on the visible-driven-light g-C3N4@TiO2-SnO2 composite is a photosensitizing mechanism,while it follows the traditional "double carrier transfer" mechanism under sunlight irradiation(4)Preparation and investigation photocatalytic activity for TiO2 based composite coupling with narrow bandgap CdS Quantum Dots and g-C3N4.CdS/g-C3N4/TiO2 ternary composite photocatalyst is prepared by a simple and mild hydrothermal method.The results display that the absorption for visible light is further improved by simultaneously introducing narrow bandgap g-C3N4 and CdS.Meanwhile,the two-dimensional g-C3N4 nanosheets can act as a support for CdS and TiO2 nanoparticles,which effectively inhibit the aggregation of CdS and TiO2 particles.The microstructure result suggests that the average particle size of CdS and TiO2 is just 4 nm,and they uniformly disperse resulting in a large specific surface area of 201 m2·g-1.There exists a strong interaction among CdS,g-C3N4 and TiO2,which promotes the formation of heterojunctions,effectively reducing the recombination rate of photogenerated electron-hole pairs,and significantly improving the photocatalytic activity and sta'bility of the catalyst.The investigation for the mechanism suggests that both of the visible-driven-light and solar-driven-light CdS/g-C3N4/TiO2 catalyst follow the Z-scheme mechanism.(5)Design and investigation for the performance of a Z-scheme CdS-g-C3N4@TiO2-SnO2 composite.Based on the preliminary result,the Z-scheme-type CdS-g-C3N4@TiO2-SnO2 composite is successfully synthesized via hydrothermal method.The results show that g-C3N4 can not only be used as an active component in the composites,but also as a support,which can effectively decrease the surface energy of CdS and CdS@TiO2-SnO2,inhibiting the agglomeration of the particles and facilitating the particles disperse evenly.Compared with CdS and CdS@TiO2-SnO2,the specific surface areas of CdS-g-C3N4@TiO2-SnO2 composite are increased by 27 and 1.5 times,respectively.The photocatalytic performance and stability evaluation results indicate that CdS-g-C3N4@TiO2-SnO2 has excellent visible/natural photocatalytic activity,the visible-driven-light performance for the degradation of phenol is increased by about 3 times,in comparison with the CdS/g-C3N4/TiO2 obtained in our previous chapter work.The results of repetitive cycle experiments show that the overall stability of the catalyst is good,although the activity of the second cycle is decreased somewhat due to the presence of a small amount of impurities in the fresh sample of CdS-g-C3N4@TiO2-SnO2 catalyst(20%CdS).No photocorrosion behavior occurs on CdS in the composite.In this work,a novel Z-scheme CdS-g-C3N4@TiO2-SnO2 composite photocatalyst is developed,and it is anticipated that it could provide the scientific basis for designing more efficient and stable photocatalytic materials.