Study On The Construction Of Visible Light Driven Photocatalyst With Core@shell Structure And Its Photocatalytic Performance

Harmful organic products(such as azo dyes,phenol,and antibiotic)discharge into the environment along with the wastewater due to the improper treatment of industrial wastewater,leading to the deterioration of the landscape ecology,aquatic life loss,human drinking water source pollution,and many other problems.Due to the toxicity of organic pollutants,and they can cause cancer,abnormality and mutation,more and more attention has been paid to the pollution caused by organic pollutants in water.The researchers developed a series of sewage disposal method,such as adsorption method,chemical precipitation method,electrochemical method etc..However,there are many shortcomings and the insufficiency in the practical application for some traditional repair technology,including high energy consumption,complex operation,and prone to cause secondary pollution,more important is that the purification effect is not obvious.Photocatalysis technology,which is using semiconductor photocatalyst as the environmental restoration material,can directly convert solar energy into chemical energy,and then make a thorough oxidative decomposition of organic pollutants.The merits of photocatalytic technology are: Green,energy saving,simple operation,not easy to produce secondary pollution,as well as good reproducibility.Semiconductor photocatalytic technology,therefore,is bound to be the focus of future environmental restoration technology field.Semiconductor photocatalyst is the core of the photocatalytic technology,to enhancing the practical application of photocatalysis technology potential is to improve the photocatalytic efficiency of catalyst.Photocatalyst,however,there are still shortcomings and deficiencies in the actual application:(1)Lower utilization rate of light source;(2)Higher recombination rate of photogenerated electron-hole pairs;(3)Not easy to separation and recycling.This study aimed at the abovementioned shortcomings and deficiencies,three kinds of composite photocatalyst with core-shell structure based on two-dimensional semiconductor materials were prepared,respectively.In the first two parts of the research,two kinds of photocatalysts with hollow core@shell structure were synthesized,the first part of the research content mainly focuses on the photocatalytic oxidation degradation ability of TiO2@g-C3N4 towards organic pollutants.The second parts of the research mainly emphasizes the photocatalytic reduction ability of TiO2@MoS2 by changing the two dimensional semiconductor material.The third part of the research contents for the separation and recycling of photocatalyst difficult,magnetic materials was introduced into the photocatalyst to make it easy to separate and recycle from the system via the additional magnetic field.Azo dyes,phenols and antibiotics are chosen as the simulate pollutants.The prepared photocatalyst materials is evaluated by the material controllable synthesis and characterization,photocatalytic performance research,and cycle performance test.Synthesis conditions of core-shell structure photocatalyst were discussed,relationship between the structure-activity is explored,the electron transfer mechanism during the photocatalytic reaction is discussed,with the help of photoelectric testing method,the relationship between core-shell structure and the migration efficiency of photogenerated charge;verifying the necessity of magnetic for enhancing the recycling ability.Concrete research content is as follows:(1)Controllable synthesis and characterization of TiO2@g-C3N4 core@shell composite photocatalyst and the study of its performance.In this study,hollow TiO2@g-C3N4 core@shell heterojunction was successfully engineered for the first time by in calcining and growing of cyanamide(CY)on the surface of TiO2.It can be found by analyzing of the photocatalytic experiment results that HTCN-1 shows good performance both in microstructure and photocatalytic activity when the volume of CY is up to 1 m L.The photocatalytic experiment results demonstrated that the photocatalytic degradation rate towards CR,Rh B,phenol,and CIP is 97%,100%,71%,74% under simulated sunlight irradiantion,the TOC remove efficiency in each system is 69%,72%,73%,71%,respectively.Take the degradation of CR as the example,the final product was tested by GC/MS,the results indicate that CR was cleaved into nontoxic hydroxyl and alcohol metabolites.By contrasting the degradation efficiency and the results of photoelectric chemical testing,the separation efficiency of photocatalyst with core@shell structure is much higher than that of non-core@shell structure.The above experiments results demonstrated that the TiO2@g-C3N4 shows high application potential in photocatalytic oxidation ability towards organic pollutant in water.(2)For further enhance the practical application of the photocatalyst,on the basis of the first part of the research,with hollow core-shell structure as the starting point,we expand the application of the composite photocatalyst by changing the two-dimensional materials.The TiO2 was encapsulated by flexible and crumpled MoS2 nanosheets through hydrothermal method to form the core@shell TiO2@MoS2 composite photocatalyst.The microstructure and features of the product is regulated by changing the amount of Mo element.It can be found by analyzing of the photocatalytic experiment results that HT@M-0.8 shows good performance both in microstructure and photocatalytic activity when the amount Mo element is up to 0.8 mmol.The BET surface area of HT@M-0.8 is 63.03 m2/g.The experiment results of photocatalytic reduction of 4-NP demonstrated that the 4-NP is completely reduced to 4-AP in 35 min under simulated sunlight irradiation in the presence of Na BH4 act as the sacrificial donor.According to the results of photoluminescence spectrum and photoelectric chemical testing,TiO2@MoS2 with core@shell structure possesses higher separation efficiency of photogenerated electron-hole pairs.TiO2@MoS2 composite photocatalyst was obtained by changing the two-dimensional materials,expanding the application of TiO2@MoS2 photocatalyst.(3)Aiming at the problem of separation and recycling during the photocatalytic reaction,and we introduce the magnetic materials.Firstly,Fe3O4 magnetic nanoparticles(MNPs)were prepared,and then the two-dimensional MoS2 nanosheets coating on the outside of the Fe3O4 MNPs to form a core-shell structure.Subsequently,the Ag3PO4 nanoparticles are deposit on the surface of MoS2,and Fe3O4@MoS2/Ag3PO4 composite photocatalyst are obtained finnally.The photocatalytic performance of the product is regulated by changing the loading amount of Ag3PO4.It can be found by analyzing of the photocatalytic experiment results that FM/A-6% shows good performance both in microstructure and photocatalytic activity when the loading amount of Ag3PO4 is 6%.Photocatalytic degradation experiment results demonstrated that FM/A-6% exhibited degradation efficiency up to 91% for CR and 99% for Rh B after 10 min irradiation under visible light irradiation.The TOC removal efficiency is 84% and 87% for CR and Rh B in 180 min.FM/A-6% also show high photocatalytic activity under simulated sunlight irradiation,with the degradation rate of 85%,92% respectively.Photocatalytic cycling experiments show that the combination of Ag3PO4 and MoS2 can efficiently inhibit the photocorrosion of Ag3PO4,and Fe3O4 MNPs plays vital role during the recycling process.Due to the magnetic effect,photocatalyst can be completely separated from the suspension system without any loss.To sum up,aiming at the limitations of photocatalyst in the applications,three kinds of core@shell visible-light photocatalyst were synthsised and applied them to the purification of organic pollutants in water.From the point view of microstructure and photogenerated carriers transfer across the interfaces,systematic analysis of the advantages of core-shell structure composite photocatalyst:(1)enhanced separation efficiency of photogenerated electron-hole pairs is attribute to the larger interfaces area;(2)Light utilization rate of composite photocatalysts is enhanced with the help of hollow structure;(3)introducing magnetic material makes the light catalyst is advantageous for the magnetic separation and recycling.This study provides a rich theoretical and experimental basis on the synthesis and application of visible light core@shell structure photocatalyst.