▎ 摘　　要

NOVELTY - Preparing single crystal graphene quantum dots comprises preparing single crystal graphene quantum dots with an average particle diameter of 3.73 nm by hydrothermal carbonization of lignin. USE - The method is useful for preparing single crystal graphene quantum dots. ADVANTAGE - The method: realizes controllable preparation of the particle size of the graphene quantum dots and the different fluorescence emission wavelengths by adjusting reaction conditions. is simple and economical; can utilize large-scale utilization of lignin waste generated by papermaking enterprises and biomass refining enterprises; The single crystal graphene quantum dots: fluorescence performance is closely related to its size and particle size, larger the size, the greater the red shift of the fluorescence emission wavelength, which can be widely used in different fields; quantum yield is as high as 22%, and has up-conversion luminescence properties in the near-infrared region, which has important application value for biological imaging; has optimum pH of 7, which corresponds to potential application value for humans or other mammals; does not change much under the alkaline conditions, but has large change in strength under acidic conditions and can be used in acidic pH response equipment. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for graphene quantum dot, prepared by above method, and comprising lignin raw material, i.e. alkali lignin, lignosulfonate, or sulfate lignin, preferably alkali lignin.