Study On Photocatalytic Properties Of SrMoO₄ Prepared By High Temperature Thermal Decomposition

SrMoO4,as a representative scheelite-structured compound,has a tetragonal crystal symmetry with space group I41/a.Each Mo site is surrounded by four equivalent O sites in nearly tetrahedral configuration,and each Sr site is surrounded by eight O sites in nearly octahedral configuration,forming a highly stable structure.It has caused a wide range of attention for its strong stability,pollution-free,and properties to be synthesized easily.In addition,similar to PbMoO4,SrMoO4 has potential application in the field of Photocatalysis.However,its large band gap width(3.9-4.4 eV),small spectral response range,and large SrMoO4 particle size(often on the micron level)make catalytic degradation activity not high.In response to the above problems,we have used a new and simple technology for synthesizing SrMoO4—high temperature thermal decomposition.This technique allows the size of SrMoO4 nanoparticles to be controlled in the nanometer range with a small band gap width.Meanwhile it can modify the SrMoO4 nanoparticles by doping of elements and dilution of SiO2 to broaden the photoresponse range of SrMoO4 in visible light and improve the utilization of sunlight for obtaining better photocatalytic activity.Main tasks as follows:(1)Study on photocatalytic properties of Dy-doped SrMoO4:Dysprosium(Dy)-doping SrMoO4(with different molar ratio of Dy/Sr = 0/100,10/100,15/100 and 20/100)have been synthesized by high temperature thermal decomposition of metal-organic salt in organic solvent with a high boiling point Their structures,morphology,and optical properties were characterized by X-ray diffraction(XRD),X-ray photo-electron spectroscopy(XPS),high-resolution tuning electron microscopy((HR)TEM),and UV-vis diffuse reflectance spectroscopy(UV-vis DRS).Using this method,the pure phase,nano-size,and low band gap of SrMoO4 sample are obtained.The results show that the size of as-synthesized SrMoO4 nanoparticles was about 6nm.The band gap of Dy-doped SrMOO4 ranges from 3.76-3.90 eV,and decreases with increasing Dy concentration.The photocatalytic performance of as-syntheszied products were determined from the degradation of methylene blue(MB)by UV-vis light irradiation.The 15 mol%Dy-doped SrMoO4 sample shows the best performance for photocatalytic degradation of methyl blue of nearly 100%in 120 min under visible irradiation,which is higher than most of those reported before.The present work is meaningful for revealing the underlying mechanism in photocatalyst and improving the photocatalytic performance.(2)Study on photocatalytic properties of Mn-doped SrMoO4:Mn-doped SrMoO4 nanocrystals were synthesized by thermal decomposition of metal-organic salt in the organic solvent with the doping content in the range of 0-12 mol%.The structures,morphologies,and optical properties were characterized by X-ray diffraction(XRD),X-ray photo-electron spectroscopy(XPS),high-resolution tuning electron microscopy((HR)TEM),and UV-vis diffuse reflectance spectroscopy(UV-vis DRS).The results suggest that Mo sites in SrMoO4 lattice are substituted by the Mn dopant,the adsorption band are also found to be shifted toward the visible light region and the band gap become narrower correspondingly.The photocatalytic performance of as-synthesized products was determined by the degradation of methylene blue(MB)by visible light irradiation.The photocatalytic performance is enhanced with Mn doping,and the optimal degradation rate for methyl blue is 85%in 140 min for 5 mol%Mn doping.The enhanced photocatalytic activity with Mn doping may be ascribed to the energy band adjustment and effective photo-generated electron-hole separation caused by the Mn doping.The possible photocatalytic mechanism has also been discussed.(3)Study on photocatalytic properties of SiO2 diluted SrMoO4:0.1Eu:In the present work,mono-dispersed and uniform SrMoO4:0.1Eu nanoparticles were synthesized using thermal decomposition technique.The prepared SrMoO4:0.1Eu nanoparticles have narrower size distribution than the particles synthesized previously using other preparation techniques.In order to improve the photocatalytic performance of SrMoO4-based materials,the SrMoO4:0.1Eu nanoparticles were also diluted in amorphous SiO2 matrix with different concentrations of SrMoO4:0.1Eu nanoparticles.Although,crystalline SiO2 is an insulator and has no photocatalytic activity due to its intrinsic properties,the results suggested that the current SrMoO4:0.1Eu nanoparticles,which are diluted in amorphous SiO2,exhibited enhanced photocatalytic performance in the degradation process of methyl blue.The large absorption in the visible and ultraviolet light is observed by the UV-vis absorbance spectra.The smallest energy gap in these samples was found to be 2.0 eV.In particular,the photodegradation efficiency of methyl blue over SrMoO4-based samples was up to ca.80%in 60 minutes when the quantitative ratio of SrMoO4:0.1Eu and SiO2 was fixed to be 1:2,respectively.By synthesizing the undiluted and SiO2 diluted SrMoO4:0.1Eu samples,this work provides an effective technique to improve the photocatalytic activity of SrMoO4-based materials,especially the SrMoO4:0.1Eu nanoparticles.