| With the progress of society and the rapid development of industry and agriculture,a lot of pollutants have been discharged into the nature,posing a serious threat to human’s living environment and health.Among them,water pollution has become a key concern of people.There are more than 100,000 commercial dyes in the world with an annual output of more than 700,000 tons,of which about 10%are discharged into the environment during production and use.And these organic dyes are usually toxic,carcinogenic and teratogenic,etc.Photocatalytic degradation of organic pollutants in wastewater is undoubtedly an environment-friendly technology owing to its many advantages,such as high degradation efficiency,simple operation,low cost,strong oxidation capacity,good stability,energy saving and environmental protection.At present,the research of nano-photocatalyst is mainly focused on solving the following problems to improve their photocatalytic activity and practical application:First,to reduce the band gap width of the catalyst and make the photoabsorption range of the catalyst red shift;The second is to accelerate the transfer of photogenerated carriers and restrain the recombination rate of electron holes;The third is to improve the adsorption of organic pollutants in wastewater catalyst,improve the photocatalytic degradation efficiency;The fourth is to make the catalyst simple,rapid separation and recovery,to achieve reusable use,reduce the use cost of photocatalyst.Therefore,a composite nano-photocatalyst with magnetic core-shell structure was constructed to reduce the band gap by using semiconductor Fe3O4 nanospheres as magnetic carriers,studying and designing a simple and novel synthesis method of anatase type TiO2.Under UV light irradiation,it can efficiently catalyze the degradation of the simulated target pollutant methylene blue(MB),and achieve simple,rapid separation and recycling under the external magnetic field.By doping Ru4+ ions with a similar radius to Ti4+ ions,the light absorption range of the catalyst was widened and the photocatalytic degradation activity of MB was improved.Taking advantage of the excellent optical and electrical properties and large specific surface area of rGO,it was supported on the surface of the catalyst to enhance its ability to adsorb the target organic pollutants,inhibit the recombination of electron holes,and effectively reduce the band gap energy of the catalyst to achieve catalytic degradation of MB in the visible light region.The photocatalytic performance of precious metal Ru was further investigated.Ru nanoparticles with small particle size(～5 nm)were loaded on the magnetic Fe3O4@C surface by reducing RuCl3·3H2O with hydrazine hydrate,and the electron hole separation efficiency was significantly improved.Therefore,the photocatalytic activity of the catalyst was significantly enhanced.Additionally,the increase of the specific surface area also increased the active sites on the surface of the catalyst,thus enhancing its ability to adsorb MB.Under sunlight irradiation,it can efficiently catalyze the degradation of MB,realizing the purpose of energy saving,environmental protection and low cost.The research content of this paper was mainly composed of the following five parts:1.Study on the synthesis of magnetic Fe3O4 nanospheres and their catalytic degradation performance in photo-Fenton reactionThe spherical magnetic Fe3O4 particles were prepared by water(solvent)thermal method and the degradation performance and kinetics of them to MB were studied through different degradation experiments.The results showed that the use of photo-Fenton reaction system of MB had the best catalytic degradation of performance,and the first order kinetics by fitting calculation kphoto-Fenton reaction rate constant was 6.96×10-3 min-1,which was 7.2 times that of Fenton degradation reaction,indicating the synthesized core-shell magnetic Fe3O4 catalyst had good photo-Fenton catalytic activity.The possible mechanism of photo-Fenton catalytic degradation was discussed in detail.Through five cycle recovery experiments,it is proved that the catalyst can realize convenient and fast separation and recovery under the external magnetic field,and has a relatively stable catalytic activity.Through 5 cycle recovery experiments,it was proved that the catalyst can be separated and recovered conveniently and quickly under the external magnetic field,and had a relatively stable catalytic activity.2.Study on the synthesis of magnetic core-shell Fe3O4@TiO2 composites and theirphotocatalytic degradation performance A simple method for the synthesis of magnetic Fe3O4@TiO2 photocatalyst(FT)with core-shell structure in acetone solvent at room temperature was presented.The properties of the materials and so on were characterized and tested by TEM,HRTEM,VSM,SEM,XRD,BET,XPS and UV-Vis DRS,respectively.The degradation performance and reaction kinetics of FT photocatalytic composites with different TiO2 loads,and Fe3O4 and TiO2 for the photocatalytic degradation of MB under UV irradiation were compared and studied.The results showed that the FT composites had good photocatalytic activity for MB.The kinetic constant k of Fe3O4@TiO2(0.8mL)photocatalyst(FT4)for MB was 4.15×10-2 min-1,the catalytic degradation rate reached 97.56%,which was higher than that of commercial P25 TiO2.The possible mechanism of photocatalytic degradation of MB by FT composites was discussed by contrast experiment and free radical capture experiment.After 5 times of recovery cycle experiments,the photocatalyst can achieve convenient and fast magnetic separation and recovery and good stability under the action of external magnetic field.3.Study on the synthesis of magnetic Fe3O4@Ru-TiO2 composites and their photocatalytic degradation performanceA magnetic Fe3O4@Ru-TiO2(FRT)nano photocatalyst material with a narrow band gap was synthesized by doping Ru4+ ions with a similar radius to Ti4+ ions.The related properties of FRT were tested and characterized by TEM,HRTEM,VSM,SEM,XRD,BET,XPS,UV-vis DRS and PL,respectively.The catalytic degradation rates and kinetics of photocatalytic degradation of MB with different doping amounts of FRT catalysts were studied under simulated sunlight irradiation.The results showed that the band gap energy of the photocatalyst doped TiO2 with Ru4+was narrowed and its light absorption range was widened.Compared with FT catalyst without Ru4+doping,the degradation rate of MB by FRT4 increased by 3.82 times and the kinetic constant k of the first order reaction was 9.84×10-3 min-1.The possible mechanism of photocatalytic degradation was also discussed.The photocatalytic activity and recovery rate of FRT did not decrease significantly after 5 cycle recovery experiments,which proved its stable catalytic activity and high recovery rate.4.Study on the synthesis of magnetic rGO/Fe3O4@Ru-TiO2 composites and their photocatalytic degradation performancerGO/Fe3O4@Ru-TiO2(GFRT)photocatalyst with strong adsorbability was synthesized by using rGO to load Fe3O4@Ru-TiO2.The related properties of GFRT were tested and characterized by TEM,HRTEM,VSM,SEM,XRD,BET,XPS,UV-vis DRS and PL,respectively.Under visible light irradiation(λ>420 nm),the catalytic degradation rate and kinetics of photocatalytic degradation of MB by GFRT catalysts with different rGO loads were studied comparatively.The results showed that the catalytic degradation activity of GFRT was significantly higher than that of unsupported rGO.The photocatalytic degradation rate of MB by rGO(15%)/Fe3O4@Ru-TiO2(GFRT4)reached 97.4%,and the first-order reaction kinetic constant k was 4.93 ×10-2 min-1.The possible mechanism of photocatalytic degradation of MB was also discussed.The photocatalytic activity and recovery rate of GFRT did not decrease significantly after 5 cycle recovery experiments,which proved its stable catalytic activity and high recovery rate.5.Study on the synthesis of magnetic Fe3O4@C@Ru composites and their photocatalytic degradation performanceBy reducing RuCl3·6H2O with hyzine hydrate,small size Ru nanoparticles(～5 nm)was loaded in situ on the surface of magnetic Fe3O4@C nanoparticles,so the Fe304@C@Ru(FCR)photocatalyst was synthesized.TEM,HRTEM,VSM,SEM,XRD,BET,XPS,UV-vis DRS and PL were used to test and characterize the related properties,respectively.Under simulated sunlight irradiation,the catalytic degradation performance and kinetics of MB were studied by using FCR composite photocatalysts with different Ru loads.The results showed that 92.1%of MB can be degraded when the mass ratio of Fe3O4@C to RuCl3·3H2O was 1:1,and the kinetic constant k value of photocatalytic degradation was 1.76×10-2 min-1,which indicated that it had high photocatalytic degradation activity.The possible degradation mechanism was also discussed.After 5 cycles of recovery experiments,FCR was proved to be convenient and fast in separation and recovery under the action of external magnetic field,and had good stability in photocatalytic degradation activity of MB. |
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