Preparation And Photocatalytic Properties Of Red Emissive Carbon Dots/SnS₂ Nanosheets Composites

With the rapid development of industrialization,the problem of pollution is becoming more and more serious,especially water pollution.As a clean,economic and environmental protection"green"technology,photocatalysis has been widely concerned in solving the problem of water pollution;The design and development of efficient photocatalytic materials is the key of photocatalytic technology.Tin disulfide（SnS₂ ）,as a non-toxic,low-cost,visible light responsive semiconductor,has been developed and proved to be a relatively effective and stable visible light driven photocatalyst.Although tin disulfide has great potential as a visible light driven photocatalyst,the narrow band gap structure and limited visible light absorption limit the photocatalytic performance of SnS_2.In order to improve the photocatalytic activity of SnS₂ ,the ultra-thin hexagonal SnS₂ and red carbon dots prepared by high temperature solution heating method were selected to form composite materials,and the photocatalytic characteristics and related mechanism of red carbon dots enhancing SnS₂ were studied.In this dissertation,the ultra-thin hexagonal layered SnS₂ nanosheets were synthesized by crystalline tin tetrachloride and thiourea.The morphology,crystallinity,composition,optical properties and band gap of the nanosheets were analyzed.It is found that SnS₂ is hexagonal phase with a band gap of 2.25 e V.Secondly,red carbon dots with both down conversion and up conversion characteristics were synthesized by high temperature solvothermal method.The morphology,crystallinity,composition and optical properties of the red carbon dots were studied.It was found that the red carbon dots had uniform particle size of about 2-3 nm,which could be described as nanoscale framework/carbon core with graphite structure,The surface is covered with spherical particles with rich nitrogen and oxygen functional groups.Moreover,the carbon dots have full band absorption characteristics,as well as down conversion and up conversion photoluminescence characteristics.R-CDs/SnS₂ composite photocatalyst was synthesized by one-step hydrothermal method.Its morphology,particle size,chemical composition,optical properties,catalytic performance,cycle stability and photocatalytic mechanism were studied by various characterization techniques.Through a series of characterization means,it is confirmed that the red carbon point and tin disulfide are successfully combined,and the influence of the introduction of red carbon point on tin disulfide is explored.The results show that the introduction of red carbon dots can effectively improve the photoresponse range,specific surface area and charge separation ability of tin disulfide.The photocatalytic properties of R-CDs/SnS₂ composite photocatalyst were evaluated by catalyzing organic solutions under simulated sunlight.The results showed that R-CDs/SnS₂ composite photocatalyst with 10 wt%showed the best photocatalytic performance,the degradation degree of organic dyes was up to 98%,and the optimal reaction rate constant was 0.418.Finally,the stability and recyclability of R-CDs/SnS₂ composite photocatalyst were investigated,and the degradation efficiency of R-CDs/SnS₂ composite photocatalyst could still reach more than 80%after five times of recycling,indicating that R-CDs/SnS₂ composite photocatalyst has great potential in the field of photocatalysis.