| Water environment is an important component of ecosystem.However,with the continuous development of economy,water environment security is facing severe challenges,showing the characteristics of high concealment and variety of pollutants.Among them,the situation that water contains both heavy metals and organic pollutants,which are difficult to degrade naturally,is becoming more and more frequent,which should attract enough attention.Therefore,the development of a technology that can effectively remove heavy metals and organic pollutants in wastewater has become one of the important topics in the field of environmental protection.Photocatalytic technology is an environmentally friendly advanced oxidation technology.Semiconductor materials can generate strong oxidizing groups and strong reducing electrons after being excited by light,which can realize the simultaneous oxidation reaction and reduction reaction,thus degrading heavy metals and organic pollutants.Ti O2 is one of the most widely used catalysts in photocatalytic technology,but its wide band gap and easy recombination of photogenerated electron-hole pairs limit its photocatalytic performance.In this paper,Ti O2 with different physical and chemical properties and different microstructure were prepared by solvothermal method by controlling the reaction conditions.Bi2 Mo O6-Ti O2 core-shell composite photocatalyst was obtained by loading Bi2 Mo O6 on the surface of three-dimensional(3-D)coreshell Ti O2 by constructing heterojunction to improve the photocatalytic performance of Ti O2.The effects of different reaction conditions on the degradation performance of Bi2 Mo O6-Ti O2 coreshell structure were studied by using Bi2 Mo O6-Ti O2 core-shell structure photocatalyst as the research object and Cr(Ⅵ)and tetracycline combined pollution as the target pollutant,and the photocatalytic reaction mechanism was studied.The main conclusions of this paper include the following aspects :(1)When the reaction temperature is 90°C and the reaction time is 12 h,the core-shell structure Ti O2 with the best performance can be obtained.The removal rates of Cr(Ⅵ)and TCH were 49.3% and 72.4%,respectively.Under the reaction temperature and time,the rod-like and spherical Ti O2 were prepared by changing the water-alcohol ratio of the reaction solvent and the dosage of the precursor titanium sulfate(Ti OSO4).The core-shell structure Ti O2 was used as a modified basic material to further improve its photocatalytic performance.Bi2 Mo O6-Ti O2 composite photocatalysts with different molar ratios(n(Bi2Mo O6):n(Ti O2))were prepared by solvothermal method.The microstructure,elemental composition and photoelectric properties of the composite photocatalyst were characterized by SEM,TEM,XRD,UV-vis/DRS,XPS and EDS.It is proved that the Bi2 Mo O6-Ti O2 core-shell structure photocatalyst has good crystallinity,dispersibility and stable chemical properties,and the photocatalytic activity of the composite material is significantly increased.(2)The photocatalytic reaction conditions(initial composite pollutant concentration ratio,different Bi2 Mo O6 loading,different catalyst dosage,initial p H value,common inorganic anions,reaction background water quality,etc.)had a significant effect on the treatment effect of pollutants.It was found that reducing the concentration ratio of Cr(Ⅵ)to TCH was beneficial to the reduction of Cr(Ⅵ).When the concentration ratio of Cr(Ⅵ)to TCH was 10: 10mg/L,the comprehensive removal efficiency of the two was the highest.For Ti O2 catalysts with different Bi2 Mo O6 loadings,1% Bi2 Mo O6-Ti O2 was the best.The neutral environment is beneficial to the simultaneous degradation of TCH and Cr(Ⅵ),and the acid and alkaline environment will significantly inhibit the removal effect of the system.The composite material still has a good treatment effect on the Cr(Ⅵ)-TCH pollutant system under different background water quality;in addition to tetracycline,the combined pollution of Cr(Ⅵ)and other organic pollutants such as bisphenol A and acetaminophen can still be effectively removed simultaneously.(3)The possible mechanism of photocatalytic degradation of Cr(Ⅵ)-TCH composite pollution by Bi2 Mo O6-Ti O2 was analyzed.The photocatalytic reaction mechanism of simultaneous removal of TCH and Cr(Ⅵ)by Bi2 Mo O6-Ti O2 core-shell structure under visible light was speculated by semiconductor band structure theory,free radical capture experiment and high performance liquid chromatography mass spectrometry.The specific reaction process is as follows : under the drive of visible light,the photogenerated electrons on the conduction band of Bi2 Mo O6 undergo charge transfer under the action of heterojunction,transfer to the conduction band of Ti O2 and diffuse to the surface of core-shell Ti O2.Cr(Ⅵ)is similar to electron capture agent,which can quickly contact the electrons on core-shell Ti O2.The reduction reaction is converted to Cr(III);due to the excellent specific surface area of the core-shell structure,another part of the electrons react with O2 in water to form superoxide radicals,which contact with tetracycline and decompose it into small molecules such as H2 O and CO2. |
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