Preparation Of Graphene Quantum Dots By Mechanical Ball Milling And Its Application In Supercapacitor

The graphene quantum dots(GQDs)are a new type of carbon nanomaterials with dimensions below 10 nm.Since the GQDs exhibit fluorescence characteristics,most applications focus on areas related to photoluminescence.In the recent study,due to its large surface area,it was used as an electrode for supercapacitors and batteries.In this paper,a new preparation method of GQDs was studied.The GQDs were obtained by mechanochemical method,and hexachlorobenzene as precursors of carbon.The properties,morphology,application of GQDs and so on were explored,The main research content is as follows:In the first part,to hexachlorobenzene as raw material,adding magnesium powder for ball milling reaction.The results show that when the rotational speed of the ball mill is 180 r/min,the milling time is 16 h and the molar ratio of the metal magnesium powder to HCB is 9: 1,We got the highest yield GQDs.The removal rate of hexachlorobenzene was determined by GC-MS,and the removal rate of hexachlorobenzene was linearly related to the time,which accorded with the quasi-first order reaction kinetics.The preparation method is rarely reported in the literature,there is a certain innovation,through this method can achieve the mass production of GQDs.In the second part,the GQDs were characterized by XRD,TEM,TT-IR,XPS,Raman,Zeta potential and PL.The results show that the average size of GQDs prepared by this method is 2.5 nm,and the surface contains a large number of hydroxyl groups,carboxyl groups and other groups,can be displayed blue fluorescence under the UV lamp(365 nm).The GQDs was made into an electrode material,and its capacitance was tested by cyclic voltammetry,AC impedance,constant current charge and discharge,and cycling stability.The results show that the impedance of the GQDs is 0.05 Ω,the specific capacitance is 128 F/g under 6M KOH electrolyte,and has excellent cycle stability.In the third part,The layer-by-layer selfassembly technology was adopted to prepare GQDs@NiAl-LDH composite.The results show that the effect of GQDs on the capacitance of composites is analyzed.The electrochemical data indicate that when the content of GQDs is 10 %,the composite have highest specific capacitance and excellent large current charge and discharge characteristics.The specific capacitance of composite reaches to 869 F/g at the current density of 1 A/g.Moreover,the capacitance retention at 1 A/g discharge current condition is 69.6 % after 2000 cycles.The composite exhibits a higher specific capacitance and excellent cycle stability.