Preparation And Properties Of Carbon Quantum Dots And Silver Sulfide Composites

In recent years,carbon quantum dots?CQDs?have attracted more and more attention due to their unique photoluminescence?PL?properties,good water solubility and biocompatibility,high chemical stability,low toxicity,environmental friendliness and light bleaching resistance.These advantages make CQDs have great application prospects in the fields of bacteriostasis and imaging,photocatalysi s,optoelectronic devices,ion detection and so on.In this paper,carbon quantum dots and CQDs-Ag₂S nanocomposites were synthesized by one-step hydrothermal method and used for ion detection,bacteriostatic and adsorption studies.The main contents were as follows:?1?Nitrogen-doped carbon quantum dots?N-CQDs?were prepared using black tea as carbon source and ethylenediamine as nitrogen source and surface modifier.The surface information and structure of N-CQDs were characterized and discussed by XRD,TEM,Raman,FT-IR and other methods.The results show that the prepared N-CQDs have a good hydrophilicity and a low crystalline graphite structure.The particles are spherical and uniformly dispersed,and have no agglomeration phenomenon.The size and diameter of the prepared N-CQDs ranged from 1.0 nm to3.0 nm,and the average particle size was 1.8 nm.At the same time,the PL properties of CQDs were used to study the detection of various ions.The results showed that CQDs has bright green fluorescence,pH sensitivity,excitation wavelength dependence and other properties.With the increase of Pb²⁺ion concentration,the quenching effect on CQDs solution is enhanced,and the quenching efficiency can reach 70.2%,with a low detection limit,which can be used for the trace detection of Pb²⁺ions in practical applications.?2?A new type of CQDs-Ag₂S nanocomposite was successfully prepared by using GO modified with polyethylenimine?PEI?as template and binder to compound CQDs and Ag₂S nanoparticles.The structure of CQDs-Ag₂S nanocomposites was analyzed by TEM,XRD,Raman,SEM,and FT-IR.The synthetic CQDs-Ag₂S nanocomposite material was used to evaluate the antibacterial activity of Escherichia coli,Staphylococcus aureus,Pseudomonas aeruginosa and Enterococcus faecalis.The results showed that CQDs-Ag₂S composite material had obvious bacteriostatic effect on four kind's different strains,and the antibacterial mechanism of the CQDs-Ag₂S composite material was studied.?3?The above synthesized CQDs-Ag₂S nanocomposite was used for the adsorption study of methylene blue dye.The effects of different reaction temperature,initial concentration and solution pH,reaction time on the adsorption process were tested.The thermodynamic,kinetic and adsorption isotherm model of the obtained data were fitted,the parameters were calculated and the adsorption process was analyzed.The results showed that:?1?Under alkaline condition,the adsorption of methylene blue was more favorable.The adsorption reaction temperature and time have a significant effect on the removal rate of methylene blue.When the adsorption reaction temperature is increased,the adsorption performance of the adsorption reaction is correspondingly improved;the adsorption equilibrium was achieved at 60 min,and the adsorption process was more consistent with the pseudo-second order kinetic equation model.?2?The adsorption process was more consistent with the Freundlich isothermal model,and the correlation coefficient of the fitted Langmuir isoth ermal model was also higher.The maximum adsorption capacity was calculated to be 348mg·g^-1.Therefore,chemisorption and physical adsorption co-exist in the process of adsorption.The adsorption process is dominated by chemical adsorption.?3?The?G<0,?H>0 and?S>0 were calculated from thermodynamic model indicate that the adsorption process was a spontaneous endothermic reaction driven by entropy.This work not only enriches the types of CQDs and its composites,but also has theoretical value for the application of CQDs in bacteriostasis and adsorption.