| In recent years,along with large-scale production and the rapid development of our society,a shortage of non-renewable energy resource and the environmental problem become more and more stern,thus destructing natural ecological balance is also harmful to human life and profit.Therefore,it is imperative to develop clean energy resource and to promote the sustainable development.Semiconductor photocatalytic technology is a new-style and one of the most perspective techniques applied to solve energy and environmental problems,so it has aroused more and more attention.A high redox potential,a direct band-gap of 3.37 eV at room temperature,and superior physical and chemical stability were identified as the main reasons for the wide acceptability of ZnO materials compared to the other semiconductor photocatalysts.Alkaline earth metal ions can be taken as the candidate dopants to regulating and controlling the photocatalytic properties.However,there are few reports on the visible light photocatalytic properties of strontium doped Zinc Oxide.Hence,the research on visible light photocatalytic performance of strontium-doped ZnO photocatalyst is of great significance.In this work,a series of Sr-doped ZnO(SZO)powders with different strontium doping levels were prepared by sol gel method.XRD results indicate that all synthesized powders are of hexagonal wurtzite structure of ZnO.XPS spectra confirm that the chemical state of Sr ions in the powders is Sr2+.SEM images show that the morphologies of SZO powders are significantly different from the pure ZnO.The enhanced absorption in the visible-light region for SZO powders can be observed by DRS,this result can be attributed to the charge transfer between the ZnO valence or conduction band and the Sr2+ ion 5s level as well as more visible-light is absorbed via active defect sites.Obvious lower emission peak can be observed in the room-temperature PL spectra of F5 and F7 samples.Photocatalytic experiments show that SZO powders exhibits higher photocatalytic activity than that of undoped ZnO.F1 sample with a Sr/Zn ratio of 1 at%in precursor solution exhibits the highest photocatalytic activity under visible light,which can decolorize about 97.61%Rhodamine B(RhB)within 70 min.Considering it is difficult to remove ZnO powdes from water,ZnO films with different Sr doping concentrations were also fabricated on glass substrates with ultrasonic assisted spray pyrolysis method at the temperature of 400 ?.XRD results indicate that all samples are of hexagonal wurtzite structure and no impurity(such as Sr,SrO and ZnSrO2)diffraction peaks were detected.The typical EDS Mapping analysis for S5 sample with a Sr/Zn ratio of 5 at%in precursor solution show that the Sr element has been uniformly distributed in the film.UV-Vis absorption spectra show that the optical absorption properties of the SZO films in the visible region were enhanced compared with that of pure ZnO.Ultraviolet emission peaks at around 380 nm and green emission peaks at around 500 nm were observed in the room-temperature PL spectra of ZnO and SZO films.Obvious enhanced green emission peak related to a singly ionized oxygen vacancy in ZnO can be observed in the SZO films with the increase of Sr doping.Photocatalytic experiments show that the SZO films exhibit higher photocatalytic activity than that of undoped ZnO film,it means that Sr2+ on the surface of ZnO film may act as an electron scavenger and O-vacancy benefits the efficient separation of the generation of the(e-/h+)pairs,which favors the decolorization of RhB.The S3 sample exhibits the highest visible-light photocatalytic activity.PL spectra of SZO thin films as-grown and annealed at different temperatures confirm that a green emission is related to a singly ionized oxygen vacancy in ZnO. |
PDF Full Text Request