| Photocatalysis was recognized as one of the most promising strategy to solve current environmental and energy issues.Traditional photocatalytic material,TiO2,with large band gap(about 3.2 eV),can only be excited by ultraviolet light,which greatly limits its practical application.Therefore,it is very important to develop novel visible-light-actived photocatalystst.Bi-based photocatalysts have been paid extensive attention for their unique d10 configuration and 6s2 lone pair of Bi3+ ions in the lattice of crystal.Bismuth oxide.,the simplest Bi-based photocatalyst,can be excited by visible light for its narrow band gap and exhibit apparent visible-light activity in dye degradation.Moreover,Bi2O3 has multiple crystal structures including ?-Bi2O3,?-Bi2O3,?-Bi2O3 and ?-Bi2O3,in which ?-Bi2O3 usually shows the highest photocatalytic activity under visible light irradiation.However,the photocatalytic activity of pure ?-Bi2O3 is not high enough due to the fast recombination of photogenerated carriers in the practical application.In this work,we firstly synthesized nano-spherical ?-Bi2O3 with oxygen vacancies via a new sol-gel method.Then a series of ?-Bi2O3-based photocatalytic materials were prepared by ion doping and heterostructure construction.Various characterization methods were adopted to analyze the properties of the materials,such as structural characteristics,light absorption properties,and photogenerated charge separation efficiency and so on.The photocatalytic activity of the as-prepared photocatalysts was evaluated by the degradation of methylene blue(MB)under visible light,and finally the possible mechanism was also discussed in detail.The main research contents of this thesis are as follows:(1)The nano-spherical ?-Bi2O3 with oxygen vacancies(denoted as OVs-BO)was prepared by a one-pot sol-gel method for the first time.Compared with other Bi2O3 samples,the degradation efficiency of MB reached 70%over OVs-BO under visible light irradiation.The superior photoreactivity of OVs-BO is attributed to the strong visible light absorption and the enhanced charge separation induced by oxygen vancancies.(2)Zn doped OVs-BO nanoparticles have been successfully prepared using OVs-BO as precursor and Zn as a dopant.Compared to pure OVs-BO,all Zn doped OVs-BO catalysts with different Zn content showed higher visible light activity and the optimal molar ratio of Zn to Bi is 0.3:1.The enhancement of photocatalytic activity of Zn doped OVs-BO could be mainly attributed to the efficient mobility of photogenerated holes for the hybridization of O 2p,Zn 3d and Bi 6s orbitals in the valence band,stronger oxidative power of holes and appropriate amount of oxygen vancancies.(3)Cycling experiments indicated that the stability of Zn doped OVs-BO is similar to that of OVs-BO during photocatalytic degradation process.However,the comparison of structure by XRD between ZnBiO-O.3(Zn doped OVs-BO with Zn to Bi molar ratio of 0.3)and pure OVs-BO both stored in air after 11 months illustrated that the stability of Zn doped OVs-BO during long-term storage was much better than that of pure OVs-BO.After stored in air for 11 months,pure OVs-BO almost completely converted into Bi2O2CO3 and its activity greatly declined.While for ZnBiO-0.3 after long-term storage,a small amount of them changed into Bi2O2CO3 to form the ZnBiO-0.3/Bi2O2CO3 heterojunction,improving its photocatalytic activity.The improvement in structural stability is ascribed to the interstitial doping of Zn2+ in OVs-BO lattice.This study demonstrates that Zn doped OVs-BO could be a new promising photocatalyst for its highly efficient and stable visible light activity in the photodegradation of contaminants.(4)A series of Ag2CO3/ZnBiO-0.3 composites using ZnBiO-0.3 as precursor have been prepared by simple chemical precipitation method.As the mass ratio of Ag2CO3 to ZnBiO-0.3 was 0.05:1,the degradation efficiency of MB under visible light irradiation is almost 100%.This improvement in photocatalytic perfomance may be related to the formation of heterojunction between Ag2CO3 and ZnBiO-0.3,which promotes more efficient separation of photogenerated carriers.(5)Novel nano-structured ?-Bi2O3/Bi2O2CO3 heterojunctions with oxygen vacancies(OVs-BO/BOC)using OVs-BO as precursor was firstly synthesized in situ self-growth.The ratio of BO to BOC can be adjusted by the reaction time.And the photocatalytic activities are evaluated by the photodegradation of methylene blue(MB)under visible-light irradiation.The results indicated that,as the reaction time is 45 minutes,the as-prepared OVs-BO/BOC-45 min composites exhibit the highest activity than other samples,which is attributed to the synergistic effect of the ?-Bi2O3/Bi2O2CO3 heterojunction and oxygen vacancies. |
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