Synthesis And Properties Study Of ZnO Quantum Dots

Due to its low toxicity,low cost,high oxidation-reduction potential,optical properties,and environmental protection,it has many excellent properties not found in conventional materials such as magnetism,light,electricity,etc.,making ZnO Concerned in many fields,and the application prospects are broad.In this thesis,ZnO quantum dots were synthesized by sol-gel method,and their fluorescence properties in the visible region and photocatalytic degradation of organic dyes were studied.The main contents are as follows:ZnO quantum dots were prepared by sol-gel method using zinc acetate as raw material.The effects of preparation conditions on the fluorescence properties of ZnO quantum dots were studied by changing the reaction temperature,reaction time and molar ratio of Zn?AC?₂/LiOH.The crystal structure,surface functional group,morphology and fluorescence properties of the prepared ZnO quantum dots were characterized by X-ray diffraction?XRD?,infrared spectroscopy?IR?,transmission electron microscopy?TEM?and fluorescence emission spectroscopy?PL?.The photocatalytic efficiency of rhodamine B solution degraded by ZnO quantum dots was also determined by UV-Vis spectrophotometer.The results show that the ZnO quantum dots prepared by the water bath reaction at 60°C for 4 h and the Zn?AC?₂/LiOH ratio of1/2 have the highest fluorescence intensity,and the structure is a typical spherical hexagonal wurtzite;It exhibits a certain agglomeration phenomenon,its particle size is about 5.26 nm,and the surface contains a large number of hydrophilic groups;In addition,the photocatalytic performance of ZnO quantum dots prepared under this condition is the best,and the degradation rate is the fastest;During the ZnO quantum dot degraded rhodamine B solution,the catalysis of holes is the largest,and the photocatalysis of superoxide radicals is small.The surface modification of ZnO quantum dots was carried out by using ethylenediamine,polyethylene glycol-2000 and oleic acid respectively.At the same time,ZnO quantum dots with Mg²⁺and Eu³⁺as dopants were prepared respectively;The samples were characterized by X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,infrared spectroscopy?IR?,transmission electron microscopy?TEM?,and fluorescence emission spectroscopy?PL?.Studies have shown that the fluorescence intensity of ZnO quantum dots modified by ethylenediamine,oleic acid and polyethylene glycol-2000 is obviously enhanced,and the optimal addition amount is 120?l ethylenediamine,140?l oleic acid and 15%PEG in 40 ml ZnO quantum dots ethanol solution,respectively;The fluorescence properties of Mg²⁺and Eu³⁺doped ZnO QDs are also enhanced,and the optimal doping amount is 15%.The crystal structure of the modified ZnO quantum dots is not distorted,and the Eu³⁺doped ZnO quantum dots weaken the Zn-O bond,the Eu-O-Zn bond exists in the quantum dots structure;while the Mg-O-Zn bond is present in the Mg²⁺doped ZnO quantum dots,the quantum dot particle size distribution is relatively uniform,the shape is irregular,and the agglomeration phenomenon is reduced,the average particle size is about 4.89 nm.Photocatalytic experiments show that the doping of Mg²⁺improves the photocatalytic performance of ZnO quantum dots,while the photocatalytic performance of ZnO quantum dots with PEG modified is reduced.Water-soluble carbon quantum dots were prepared by pyrolysis and hydrothermal methods using L-glutamic acid as carbon source,and the effects of synthesis conditions on their properties were investigated;Carbon quantum dots were added to the ZnO quantum dot degradation methylene blue experiment to investigate the effect of CQDs on the photocatalytic performance of ZnO quantum dots.The results show that the carbon quantum dots prepared by pyrolysis and hydrothermal methods are amorphous carbon structures,and the surface contains a large number of hydrophilic groups,such as—OH,—NH₂,etc.;the CQDs prepared by the pyrolysis method at 200°C for 4 h has the best fluorescence performance,while the hydrothermal method has the highest fluorescence intensity when reacted at 200°C for 6 h.Photocatalytic experiments show that an appropriate amount of carbon quantum dots can enhance the photocatalytic performance of ZnO quantum dots.6 ml of carbon quantum dots is added to 0.06 g ZnO quantum dots photocatalytic degradation 50 mL of 10 mg·L^-1methylene blue,the photocatalytic degradation of methylene blue was the best,and the degradation rate was increased to 96.75%,however,the excess will reduce its photocatalytic performance.