Preparation And Application Of Sulfide Quantum Dots By High Gravity Liquid-liquid Interface Reaction

As a new generation of semiconductor nanomaterials,quantum dots are widely used in various fields due to their unique quantum size effect and fluorescence properties.Among them,sulfide quantum dots have excellent optical properties and wear resistance,and have great potential in the field of bioluminescent imaging and lubricating materials.At present,the synthesis methods of sulfide quantum dots,such as high-temperature hot injection method and homogeneous precipitation method,generally have the problems of high toxicity of reagent,large product size and easy agglomeration.Liquid-liquid interface synthesis is a new method for preparing nanomaterials,which is developed in recent years.It is usually carried out at a low temperature and has the advantages of simple synthesis process and low cost.At present,reports on liquid-liquid interface synthesis technology are mostly completed in batch reactors.Due to the difficulty in controlling parameters such as temperature,stirring speed and precursor injection location in the reaction process,the repeatability between batches is poor,which makes it difficult to achieve mass production and commercial application.Therefore,the development of a continuous synthesis process that is easy to produce and rapidly scale up is of great significance for the large-scale production of sulfide quantum dotsHigh gravity technology is a kind of technology which provides the centrifugal force field by rotating packed bed(RPB)and uses the unique flow phenomenon of multiphase fluid in the high gravity environment to strengthen the mass transfer and micro mixing between the fluids.Many kinds of nanoparticles with small size and uniform particle size distribution can be synthesized by this technology.In addition,as a continuous reactor,RPB can realize the continuous production of products.Based on it,this paper combines the high gravity technology with the liquid-liquid interface reaction to prepare the sulfide quantum dots,and explores the mechanism of the high gravity liquid-liquid interface reaction.At the same time,the application of the preparation of sulfide quantum dots is studied.My research works and conclusions of this thesis as follow:(1)Firstly,Ag2S quantum dots with near-infrared fluorescence emission were prepared by high gravity liquid-liquid interface reaction.The effects of high gravity level,liquid flow rate and high gravity cycle time on the products were investigated.The results show that when Ag:S=2:1,the high gravity level is 25,the liquid flow rate is 7 mL s-1,and no high gravity cycle,the size of Ag2S quantum dots is the smallest,and the average particle size is about 4.5 nm.Compared with the beaker experiment results,RPB reactor can effectively shorten the reaction time,reduce the particle size of the product,and improve the stability of the dispersion.The mechanism of high gravity liquid-liquid interface reaction was investigated by computational fluid dynamics simulation.The results show that the emulsion droplet size in RPB reactor is small and uniform,which is helpful to accelerate the reaction rate,increase the supersaturation of the solution,and synthesize the small-particle size products.(2)Based on the liquid paraffin solvent system,a green method to prepare ZnS quantum dots was developed in RPB reactor.The effects of the ratio of zinc to sulfur,the amount of oleic acid and the high gravity level on the product were studied.The results show that when the concentration of S2-is slightly higher than the concentration of Zn2+,the amount of oleic acid is 5 mL and the high gravity level is 300,the ZnS quantum dots with better comprehensive performance can be obtained The average particle size of the product is about 2.0 nm,which can be well dispersed in cyclohexane,and fluorescence emission can be detected at 410 nm under the excitation of 306 nm.In addition,in order to solve the problem of serious loss of quantum dots in the washing process,RPB reactor was introduced into the purification stage,which successfully shortened the purification time and improved the yield of the product by 10%.(3)The application of two kinds of sulfide quantum dots was studied.Firstly,the oil-soluble Ag2S quantum dots were surface modified by ligand exchange,the modified products maintain the near-infrared fluorescence characteristics and have great water solubility.The cytotoxicity experiments show that the modified products have lower cytotoxicity and show better application potential in biological systems.The effect of ZnS quantum dots on tribological properties of liquid paraffin was studied.Under the experimental conditions,the effects of ZnS addition and load on the diameter and friction factor were investigated.The results show that when ZnS is 0.3 wt.%and the load is more than 300 N,the liquid paraffin with ZnS added show higher bearing capacity and wear resistance.