A Study On Preparation Of GQDs Catalyzed By Solid Acid And Their Performance

Graphene quantum dots not only have the low toxicity,excellent mechanical strength,and excellent electrical properties of graphene,but also overcome the problems of poor electronic transmission performance of traditional quantum dots and the inability of graphene to emit light due to zero band gap.Graphene quantum dots have good application prospects in the field of photoelectricity,sensor,biological imaging.For a long time,people can quickly produce graphene quantum dots by one-step hydrothermal synthesis,but most of the catalysts used are concentrated acids that are not friendly to the environment,and it is difficult to separate the catalyst from the product after the reaction.Based on this,this article uses solid acid instead of the original liquid acid to prepare graphene quantum dots,and explores the influence of different preparation conditions on the optical properties of graphene quantum dots,and also makes a simple performance test.First,in this paper,SO₄^2-/ZrO₂solid super acid was prepared by a two-step sol-gel method,and SO₄^2-/ZrO₂solid super acid was used as catalyst in the preparation of graphene quantum dots with a fluorescence quantum which has a yield of 8.63%.The preparation method is as follows:SO₄^2-/ZrO₂solid super acid,deionized water and glucose were added in a polytetrafluoroethylene lining,and then the mixture was stirred and sonicated for 10 minutes,and reacted at 200°C for 3 hours.The electron microscope was transmitted by the product which showed a graphene structure with a high crystal lattice,and its lateral size was 4-6nm.A considerable part of the graphene quantum dots was discovered to be only 1-3 layers of graphene thick（less than 3nm）,and to be365nm thick under the ultraviolet lamp.These quantum dots emitted blue fluorescence light under irradiation.Based on this,this article draws the following conclusions based on experimental methods:（1）The effects of reaction conditions on graphene quantum dots are:1.Increasing the amount of SO₄^2-/ZrO₂can produce higher quality graphene quantum dots.When the amount of SO₄^2-/ZrO₂increases from 0.2g to 0.4g,the fluorescence quantum yield increases from 2.93%to 8.63%,followed by the increase in the amount of SO₄^2-/ZrO₂to0.6g,the fluorescence quantum yield decreases to 6.121%;2.The increase in temperature can effectively reduce the oxygen-containing functional groups in the graphene quantum dots.Too high temperature（greater than 240°C）will generate a large amount of graphene quantum dots and increase the tendency of transferring graphene quantum dots to agglomerate,resulting in a decrease in the fluorescence quantum yield of graphene quantum dots.Therefore,under 240°C reaction conditions,the highest fluorescence quantum yield（10.511%）is obtained and the extension of 3 times will increase the amount of oxygen-containing functional groups in GQDs.As the reaction time increases from 2h to 6h,the corresponding fluorescence quantum yield gradually decreases from 8.82%to 4.02%;4.The increase of glucose concentration will change the structure of graphene quantum dots,but when the amount of glucose is 1g,the structure of graphene quantum dots does not change with the increase of the amount of glucose;5.In order to explore the effect of different solid super acid catalysts on graphene quantum dots.The SO₄^2-/Ti O₂solid super acid is prepared when the nano Ti O₂（this article directly uses the nano Ti O₂purchased from Aladdin Chemicals.com）is immersed in 1M sulfuric acid（solid-to-liquid ratio is 1:5）for 2h,and the filtered solid is kept at 600℃for 3h.By comparing the graphene quantum dots prepared by SO₄^2-/ZrO₂and SO₄^2-/Ti O₂catalysis,it is observed that the surface of the graphene quantum dots obtained by SO₄^2-/Ti O₂catalysis contains less oxygen-containing functional groups,but it is worth noting that SO₄^2-Graphene quantum dots prepared by Ti O₂catalysis can emit rare ultraviolet fluorescence;（2）The performance of graphene quantum dots:1.The acidity makes the fluorescence emission peak of graphene quantum dots shift toward blue region,alkalinity makes the fluorescence emission peak shift toward red region,acid and alkali will reduce the fluorescence intensity,and the greater the acid and alkali concentration,the biger the effect;2,0.4g SO₄^2-/ZrO₂,1.5g glucose and 20m L deionized water reacted at 260℃for 3h,the graphene quantum dots prepared by catalysis have a strong response to Fe³⁺.It can reach 100umol/L,and 500umol/L Fe³⁺can also be detected in the mixed ion solution;3.Compared with pure ZnO nanowires,ZnO nanowires loaded with graphene quantum dots photocatalytically the degrade rhodamine performance has been significantly improved.