Preparation,Characterization and Photocatalytic Activity of Novel Tin Oxide Nanocomposites
Author:Huang Ru Zuo
Supervisor:chen zhi wen
Semiconductor photocatalysis has the outstanding advantages of low energy consumption,low cost,high efficiency and stability,and no secondary pollution.SnO2 nanosheet material is an important semiconductor material with different spatial structure and large specific surface area than one-dimensional materials.The surface of SnO2 has more electron-hole pairs,which shows great potential in the field of photocatalysis.However,due to the wide forbidden band characteristics of SnO2,it can only react to the light in the ultraviolet range of sunlight.At the same time,the photo-generated electron-hole recombination efficiency generated by ultraviolet light excited by tin dioxide is higher,thus the low utilization rate has become a key issue that constrains its application.In order to improve the response range of SnO2 to visible light and reduce the recombination rate of photogenerated carriers,this thesis synthesizes the heterostructured SnS2-SnO2 nanosheets and metal organic framework-derived CO3O4/SnO2 composites by hydrothermal method.For increasing the specific surface area of SnS2-SnO2 heterojunction nanosheets and compensating for the shortcomings of slow electron transport rate,the SnS2-Sn02 heterojunction was introduced by graphene prepared the SnS2-Sn02/graphene composites.In order to further improve the recycling efficiency of SnO2 composite photocatalyst,we selected magnetic narrow band gap spinel iron oxide,and successfully prepared the NiFe2O4-Sn02/graphene nanorods.By studying the related morphologies of these materials and their performances in photocatalysis,the reaction mechanism was deeply explored,which laid a foundation for the application of tin dioxide-based heterostructure in the field of photocatalysis.The research results are as follows:(1)The p-n-type SnS2-SnO2 heterojunction nanosheets were successfully prepared by a simple one-step hydrothermal method at 190℃ for 6 h.Morphological characteristics indicate that the flaky SnS2 is loaded with tiny Sn02 particles to form irregular sheet-like agglomerates.The SnS2-SnO2 heterojunction was treated under different electron beam irradiation doses.The results indicate that the sample after irradiation treatment has better photocatalytic performance than the untreated sample.The photocatalytic performance shows the optimal especially when the irradiation dose was 140 KGy.We believe that the formation of the heterojunction and the modulation of the irradiation dose make the SnS2-SnO2 heterojunction broadened the absorption range of visible light and it shows the better photocatalytic performance than the pure phase materials.(2)Based on the above research results,the SnS2-SnO2/graphene composites with a specific surface area of 107.69 m2/g were synthesized by the introduction of graphene.We studied the effects of hydrothermal reaction time on the morphology and photocatalytic properties of the samples.The formation of SnS2-SnO2/graphene heterojunction was confirmed by X-ray diffractometry(XRD),transmission electron microscopy(TEM)and scanning electron microscopy(SEM).The experimental results indicate that the composite exhibits the better dispersibility and larger specific surface area.Compared with the unsupported graphene sample,it is found that the SnS2-SnO2/graphene heterojunction omposites show the stronger photocatalytic activity.The catalytically active reactant is considered to be mainly the hydroxyl radical.Comparing the samples with different hydrothermal reaction times,it is found that the sample with hydrothermal time of 6 h have the better photocatalytic performance and could degrade 96.5%of rhodamine B in 60 min.In addition,the optical and electrochemical performance tests indicate that the SnS2-SnO2/graphene heterojunction omposites have a larger electron transport rate and higher photo-generated carrier separation efficiency.At the same time,based on various characterization data,we speculated the photocatalytic mechanism of SnS2-SnO2/graphene heterojunction composites under visible light.(3)Considering the large specific surface area and special structural characteristics of the metal organic framework(MOF)materials,we successfully synthesized a MOF material with a diameter between 200 nm and 250 nm by calcination at 300 0C after one step of hydrothermal heating.The Co3O4/SnO2 heterojunction composites can be successfully derivatized and their photocatalytic properties were investigated in detail.The results indicate that the Co3O4/SnO2 heterojunction composites exhibite a larger specific surface area and a wider visible light response range than SnO2.It is found that the addition of Co3O4 could effectively improve the light absorption properties of SnO2,which could be more full use of visible light.Fluorescence spectroscopy and current-time experiments confirmed that the formation of Co3O4/SnO2 heterostructures could inhibit the recombination of photogenerated electrons and holes.The photocatalytic performance of the derivatized Co3O4/SnO2 heterojunction composites could degrade 89.6%of rhodamine B in 60 min,and the photocatalytic hydrogen production of this material was 12.64 mmol/g/h within 3 h,which was obviously better than the pure SnO2.(4)Spinel-type iron oxides were selected as the metal-organic frameworks(MOFs)to synthesize NiFe2O4-SnO2/graphene nanorods.The results indicate that with the addition of NiFe2O4 and graphene,the formed ternary composite NiFe2O4-SnO2/rGO nanorods with a length of 130-150 nm broadened the range of light absorption,especially the absorption of visible light.Through the optical and electrochemical tests,the graphene could be proved to be an excellent charge transport channel which greatly promoted the electron transfer and thus exhibited the greater photogenerated electron-hole separation efficiency.Compared with the photocatalytic performance of SnO2,the photocatalytic activity of NiFe2O4-SnO2/graphene nanorods was obviously improved,the 98.4%of rhodamine B could be degraded in 60 min,which showed the excellent stability.In addition,due to the magnetic characteristics of the photocatalyst,the recovery and reuse efficiency were greatly improved after the reaction.