Study Onluminescent And Photocatalytic Properties Of Ca_1-xTiO₃:Pr³⁺

Inrecent years,semiconductor photocatalytic materials have been attracted the attention of scholars as one of the most promising environmental materials due to its low energy consumption,low secondary pollution,easy maintenance,sustainability,etc.Nowadays,it has become a research hotspot in the fields of environmental protection,chemical synthesis and new materials.As a new type of photocatalyst,perovskite-type oxides have attracted more and more attention because of their higher stability,higher structural controllability and larger absorption range than TiO₂.In a recent study,one fluorescent powder,CaTiO₃:Pr³⁺,exhibits visible-light degradation performance,which attracted our attention.After extensive literature search,several studies have not been conducted on this versatile material;hence,a more in-depth study of those materials with both red continuous red photoluminescence properties and ideal photocatalytic activity,is required.CaTiO₃ is a typical representative of the perovskite oxide,its cations at both A and B sites could be substituted by a foreign cation without destruction of the matrix structure.In this work,the perovskite photocatalyst were prepared via the combustion method.The samples were characterized by X-ray diffraction?XRD?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,BET and ultraviolet-visible?UV-vis?diffuse reflection spectroscopy.The results show that a small amount of Ca deficiency did not destroy the structure of calcium titanate crystal.The characteristic diffraction peaks of anatase TiO₂ appeared to become stronger with the increase of x when x > 0.25.The particle size of Ca_1-xTiO₃:Pr³⁺ powder sample is about 20 nm,easy to agglomerate and has low porosity,which is formed by the mesoporous of particle agglomeration.Ca²⁺ deficiency could result in the formation of defective bands in CaTiO₃:Pr³⁺,which is benefit to electron transitions and enlarge the absorption range of the catalyst,leading to decreased band-gap energy.With excitation under 278 nm,all samples exhibited an emission peak at the same position centered at 616 nm,corresponding to the characteristic ¹D₂?³H4 transition of Pr³⁺.When the Pr³⁺ concentration is constant,the luminescence intensity of the material depends on the amount of Ca deficiency.According to the analysis result,the increase of x could improve luminescence properties with x increasing from 0 to 0.15,but it decreased with decreasing calcium content.When the x value is small,the characteristic excitation peak of Pr³⁺ plays the leading role in red light emission,and the Pr³⁺ are all or partially compensated by the Ca vacancy.while the Pr³⁺ are gradually compensated with the increasing Ca vacancy,the excitation peak of Pr³⁺ makes little contribution to the luminescence of the material.Through the analysis and calculation of the fluorescence spectrum of the material,the Ca²⁺ deficiency must be greater than 0.15% to obtain the best luminous intensity.Ca²⁺ deficiency can improve the photocatalytic activity in the MB and MO solutions.For methylene blue solutions,the highest degradation rate was 93.6% under UV irradiation for 7h at x = 0.15,corresponding to 4.93 times greater than that observed for CaTiO₃:Pr³⁺;When x=0.25,the highest degradation rate of methyl orange was 78%.The surface defects caused by the Ca²⁺ vacancy decrease the recombination of photogenerated electrons and holes,which is beneficial to the redox reaction of the catalytic active factors,thus improving the catalytic activity of the materials.And the higher pH is beneficial to photocatalycal reaction.When pH=8.94,the degradation rate of methylene blue by Ca0.85TiO₃:Pr³⁺ reached the highest.Charge compensation agent and sensitizer ions have some influence on the luminescence and photocatalytic properties of CaTiO₃:Pr³⁺.When Li+,Na+,K+,Ag+ were served as charge compensation agents to replace Ca²⁺,materials reached the charge balance,both the luminescence intensity and the photocatalytic performance were improved.Among them,the performance of the CaTiO₃: Pr³⁺,Na+sample is the best.When Bi³⁺ was used as sensitizer,the characteristic excitation peak of CaTi O₃ was enhanced,which showed the energy transfer between Bi³⁺ and CaTiO₃.When the doping concentration of Bi³⁺ is 0.2mol%,the obtained samples exhibits the maximum emission intensity and the best photocatalytic properties.