▎ 摘　　要

NOVELTY - Fluorescent graphene quantum dots (GQDs) are prepared by preparing oxidized graphene by adding pre-oxidized graphene in 150-200 ml concentrated sulfuric acid with 95-98% mass fraction at 0-10 degrees C, mechanically stirring for 10-30 minutes, adding 2-6 g sodium nitrate, slowing adding 15-30 g fine powder potassium permanganate at less than or equal to 5 degrees C, low temperature stirring for 1-3 hours, heating to 30-50 degrees C, stirring for 6 hours, keeping temperature and speed overnight, adding 250-400 ml de-ionized water, and adding 1000-1500 ml de-ionized water after 15-30 minutes. USE - Preparation of fluorescent graphene quantum dots for photovoltaic device and sensor used in biomedical imaging. ADVANTAGE - The prepared GQDs exhibit excellent chemical stability, good biocompatibility, and low biotoxicity. DETAILED DESCRIPTION - Fluorescent graphene quantum dots (GQDs) are prepared by preparing oxidized graphene by adding pre-oxidized graphene in 150-200 ml concentrated sulfuric acid with 95-98% mass fraction at 0-10 degrees C, mechanically stirring for 10-30 minutes, adding 2-6 g sodium nitrate, slowing adding 15-30 g fine powder potassium permanganate at less than or equal to 5 degrees C, low temperature stirring for 1-3 hours, heating to 30-50 degrees C, stirring for 6 hours, keeping temperature and speed overnight, adding 250-400 ml de-ionized water, adding 1000-1500 ml de-ionized water after 15-30 minutes, adding 10-30 ml hydrogen peroxide, filtering product, washing product by 1000 ml hydrochloric acid with mass fraction of 6-20%, washing with water, dispersing product into water solution with mass fraction of 2-5%, dialyzing by dialysis bag with molecular weight of 3500-14400, and freeze-drying to obtain oxidized graphene powder, preparing green fluorescent GQDs by dispersing 10-1000 mg of oxidized graphene powder in 10-30 ml N,N-dimethyl formamide, subjecting solution to ultrasound process for 10-120 minutes, transferring to reacting kettle, reacting for 5-20 hours at 80-300 degrees C, taking supernatant, rotary distilling, and drying to obtain dried GQDs with green fluorescence, and preparing fluorescent GQDs with controllable degree of oxidation by subjecting dried GQDs to 2-step gradient column chromatography to obtain fluorescent GQDs with gradually increasing oxidation degree. DESCRIPTION OF DRAWING(S) - The drawings show the visible light absorption spectrum and the fluorescence emission spectrum of GQDs.