Study On The Photocatalytic Activity Of The Modified Strontium Ferrite

With the rapid development of industry,the problem of environmental security has been paid close attention to by governments and academia all over the world.In fact,in the field of environmental security issues,the research of water environment security has been promoted to the national strategic level,the pollution of waste water from dye industry directly affects the life of human beings.The photocatalytic technology can make full use of the visible light from the sun in order to deal with organic pollutants in the contaminated water,which is conducive to solving the problem of water security.At present,titanium dioxide is one of the representative semiconductor photocatalytic materials,but it can not be widely applied.Because the band gap widths of titanium dioxide and the similar structure semiconductor photocatalytic materials are larger,the photogenerated electrons and holes to fusion.So,in order to make more effective use of the solar light,developing with high photocatalytic material with visible light response is an inevitable trend.After photocatalytic reaction,the photocatalyst could not be recycled completely,which possibly caused the second pollution.Therefore,there is need to exploit magnetic photocatalyst.According to the above analysis,some magnetic photocatalysts were synthesized using strontium ferrite as magnetic substrate by doping and modifying.The substitution mechanism of ios and magnetic properties were investigated.Meanwhile,we prepared p-n-type magnetic heterojuncton SrTiO3-SrFe12O19,BiOCl-SrFe12O19,n-n-type magnetic heterojunction BiVO4-SrFe12O19,ZnFe2O4-SrFe12O19.The corresponding strcture and catalyst performance were characterized.The SrFe12-xSmxO19(x=0.1~0.5)powders were prepared by one-step chemical coprecipitation method.The magnetic analysis indicated in SrFe12-xSmxO19 system,when x=0.1,0.3,and 0.5,the Sm3+ ions would replace Fe3+ ions at 12k(?)sites.The Sm3+ ions would replace Fe3+ ions at 4f2(?)and 2a(?)sites as x=0.2.As x=0.4,the Sm3+ ions would substitute 4f2(?)sites for Fe3+ ions.The Ms of SrFe12-xSmxO19(x=0.4)was the largest,and it was 46.2 emu/g.While,the Hc of SrFe12-xSmxO19(x=0.2)was the largest,and it was 5194.3 G.The photocatalytic performance of the composite was studied by the degradation of methylene blue under visible light irradiation.The degradation rate of methylene blue was 96% when using SrFe12-0.4Sm0.4O19 as a photocatalyst.The experimental results revealed that the degradation rate was still more than 80% when the composite was reused for four times.The activity of the prepared sample was stable in the process of pollutant degradation.Doped Sm3+ ions as trapped center could prevent photoproduced electron-hole pairs from recombining,i.e.,enhancement of electron-hole separation efficiency,which could enhance photocatalytic activity.For comparison,we prepared SrFe12-xSmxCoxO19(x=0.1~0.5)using the same chemical synthesis method.The intrinsic crystal structure of M-type strontium ferrite didn't changed as Sm3+ and Co2+ was doped.When x=0.1,the Ms,Ms and Hc of SrFe12-xSmxCoxO19 were the lagest,and were respecyively 28.05 emu/g,16.10 emu/g and 3064 G.The degradation rate of methylene blue was 99% when using SrFe12-0.1Sm0.1Co0.1O19 as a photocatalyst,and the degradation rate was still more than 80% when the composite was reused for four times.The p-n-type heterojunction SrTiO3-SrFe12O19 was synthesized by chemical synthesis method using SrFe12O19 as magnetic substrate.X-ray diffraction(XRD)investigation revealed that the heterojunction were definitely composed of SrFe12O19 and SrTiO3.The experiment test showed that the photocatalytic activity of SrTiO3-SrFe12O19 was far beyond that of pure component.Three main reasons for the increase in photocatalytic activity were following.The first,the formation of p-n type heterojunction.The second,magnetic field effect stemming from SrTiO3-SrFe12O19.At last,as a sensitizer absorbing visible light,Sr Fe12O19 could help SrTiO3 absorb more incident photons and then produce more photo-excited electron-holes pairs.A novel p-n type magnetic heterojunction BiOCl-SrFe12O19 was synthesized by hydrolysis with medium temperature sintering method.The results showed [001] facet of BiOCl with high photocatalytic activity was exposed in the BiOCl-SrFe12O19.The heterostructured BiOCl-SrFe12O19 had better magnetic properties(Ms=15.13 emu/g,Mr=9.01 emu/g,Hc=5043.20 G),conducing to its reuse and improvement of photocatalysis.Moreover,the composite was blessed with excellent photocatalytic activity and stability.In the BiOCl-SrFe12O19 system,SrFe12O19 acted as sensitizer absorbing light irradiation.The magnetic field generating from Sr Fe12O19 made BiOCl under light radiation produce more photo-induced electrons and holes and simultaneously hampered their recombination.BiVO4-SrFe12O19 was synthesized by chemical coprecipitation method using tartaric acid as complexant.X-ray diffraction(XRD)investigation revealed that the introduction of SrFe12O19 did not change the crystal orientation of monoclinic architecture BiVO4.Micro-morphology study indicated that BiVO4 molecules uniformly distributed on the surface of hexagonal SrFe12O19 particles.BiVO4-Sr Fe12O19 has a good magnetic properties,which was conducive to its separation and reuse.Ms of BiVO4-SrFe12O19 and used five times BiVO4-SrFe12O19 are 16.5 emu/g and 20.0 emu/g,respectively.Mr of BiVO4-SrFe12O19 and used five times BiVO4-SrFe12O19 are 10.1 emu/g and 12.4 emu/g,respectively.Hc of BiVO4-SrFe12O19 and used five times BiVO4-SrFe12O19 are 3900.0 G and 3758.0 G,respectively.The test results indicated that the MB degradation rate was 93.3% using BiVO4-SrFe12O19(15 wt%)after 5h reacton.Magnetic heterjounction photocatalyst BiVO4-Sr Fe12O19 possessed great magnetic properties,which was in favour of its recovery after reaction using a extra magnet.The recovery rate after using five times was reached 92.3%.Meanwhile,the MB degradation rate using the recycled photocatalyst was 62.0%.