Preparation And Photocatalytic Activity Of Silver-based Composite Structures

Nowadays,the excessive use of textile dyes,surfactants,insecticides and heavy metals has caused pollution in rivers,lakes,underground aquifers and the sea.However,the traditional water treatment methods have disadvantages such as high cost and low efficiency.Therefore,green,efficient and low-cost wastewater treatment technologies need to be developed urgently.Semiconductor photocatalytic technology has received more and more attention due to its excellent activity and stability.Recently,metal oxide,sulfide and nitride semiconductor photocatalysts which were used for photocatalytic water splitting and degradation of dyes have become a research hotspot.However,most semiconductor photocatalysts have problems such as low solar energy utilization and fast carrier recombination,which still has a large room to exploration.In this thesis,Ag-based metal-semiconductor heterostructure photocatalysts have been designed and prepared,which enhance the light absorption intensity,broaden the light response range through the surface plasmon resonance?SPR?effect of Ag and increase the separation efficiency of photogenerated carriers through the heterojunction of Ag-based metal-semiconductor structure.The specific research content and results are as follows:1.Ag dendrites with a central stem size about 50 nm was synthesized by electrochemical deposition,subsequently Ag₂S was grown on Ag dendrites surface by in-situ sulfidation.The Ag-Ag₂S heterostructure photocatalyst exhibited the best photocatalytic activity after Ag dendrites were sulfided for 4 hours.Under the simulated solar light irradiation for 50 minutes,the degradation efficiency of the 10 ppm methylene blue?MB?solution reached 98%and the rate of photodegradation of the sample was 7 times more than the pure Ag₂S.UV-Vis-NIR diffuse reflectance spectroscopy and electrochemical impedance spectroscopy show that the the SPR effect of Ag is combine with the narrow band gap,high absorption coefficient of Ag₂S.The light absorption intensity was enhanced and the range of light absorption has been broadened from visible to infrared.In addition,in-situ sulfided Ag₂S and Ag are closely integrated,so the coated heterostructures are facilitates the transport of photogenerated electrons from Ag₂S to Ag dendrites,which reduce the recombination of the carriers.2.The Ag-Ag₂S was loaded onto the carbon cloth?CC?substrate through a simple two-step method,forming Ag nanospheres-Ag₂S nanosheets/CC composite structure material.The sample which were sulfided for 3 hours showed the highest photocatalytic activity.Compared to the same quality of Ag-Ag₂S dendrites,the rate of photodegradation is increased by 10 times.The reasons for the enhancement of photocatalytic activity of the composite structure are investigated:the appropriate proportion of Ag/Ag₂S in the photocatalyst not only broadens the photoresponse range,enhances the intensity of light absorption,but also facilitates the separation and transport of carriers.More importantly,the good conductivity of carbon cloth substrate can further promote transfer of photoelectron,and its high specific surface area is conducive to the adsorption of dyes.In addition,the flexibility of the carbon cloth makes the system have good stability in use,and the efficiency of photocatalyst shows almost no decay after 10 cycles.3.On the basis of as-prepared Ag nanospheres/CC structure,a series of Ag-AgCl/CC composite photocatalysts were prepared through the successive ionic layer adsorption and reaction?SILAR?method,in which cetyltrimethylammonium chloride?CTAC?and AgNO₃were used as Cl^-source and Ag⁺source,respectively.MB was chosen as the organic pollutant to test the photocatalytic activity.Among them,the sample which has reacted for 4 times showed the best photocatalytic activity.The degradation of 10 ppm MB solution took only 30minutes,and the rate of photodegradation of the sample was 12 times more than the pure AgCl nanoparticles.The enhancement of photocatalytic activity is due to the the appropriate proportion of Ag/AgCl which guarantee the high intensity and wide range of light absorption of photocatalyst.Simultaneously,the photogenerated electron which produce in AgCl can be transferred to the carbon substrate in time through the Ag nanospheres,so that the photogenerated carriers can be separated,migrated and participate in the photocatalytic reaction,rapidly.At the same time,the fast electron transfer can prevent the AgCl from photocorrosion and improve the stability of photocatalytic materials.