▎ 摘　　要

NOVELTY - Preparing graphene quantum dots under coupling action of magnetic field and ultrasonic field, comprises e.g. (1) preparing graphene oxide, adding graphene oxide to deionized water, and using high-speed shearing machine and ultrasonic dispersing instrument to process to obtain graphene oxide aqueous solution; where preparation of graphene oxide comprises e.g. (i) adding graphite powder to concentrated sulfuric acid, heating; cooling, placing in centrifuge tube, centrifuging, washing with deionized water, and drying to obtain pre-oxidized graphite; (ii) keeping temperature of ice bath at 3-5 degrees C, mixing the pre-oxidized graphite with sodium nitrate, adding concentrated sulfuric acid under magnetic stirring; controlling the temperature of ice bath at below 20 degrees C, adding potassium permanganate in three portions, and stirring; (iii) removing the ice bath, placing it for 24 hours, transferring to beaker, adding deionized water, heating; adding deionized water and 30% sodium peroxide solution. USE - The method is useful for preparing graphene quantum dots under coupling action of magnetic field and ultrasonic field. ADVANTAGE - The quantum dot: has excellent electrochemical performance. DETAILED DESCRIPTION - Preparing graphene quantum dots under coupling action of magnetic field and ultrasonic field, comprises (1) preparing graphene oxide, adding graphene oxide to deionized water, and using high-speed shearing machine and ultrasonic dispersing instrument to process to obtain graphene oxide aqueous solution; where the preparation of graphene oxide comprises (i) adding 1 g graphite powder to 1 ml concentrated sulfuric acid, heating at 100-120 degrees C for 12-24 hours; cooling, placing in centrifuge tube, centrifuging, washing with deionized water, and drying to obtain pre-oxidized graphite; (ii) keeping the temperature of ice bath at 3-5 degrees C, mixing the pre-oxidized graphite with 2 g sodium nitrate, adding 50 ml concentrated sulfuric acid under magnetic stirring; controlling the temperature of the ice bath at below 20 degrees C, adding 6 g potassium permanganate in three portions, and stirring; (iii) removing the ice bath, placing it for 24 hours, transferring to beaker, adding 100 ml deionized water, heating at 100-120 degrees C for 10-15 minutes; adding 300 ml deionized water and 10 ml 30% sodium peroxide solution, stirring and centrifuging for 15-20 minutes; (iv) washing the supernatant with hydrochloric acid according to 1:10 to remove sulfate ions, and then washing with deionized water to neutral; and (v) washing with absolute ethanol, centrifuging at 10000-11000 revolutions/minute, and drying in vacuum at 60-80 degrees C for 24-28 hours to obtain graphene oxide; (2) adding nitric acid solution and concentrated sulfuric acid to the graphene oxide aqueous solution obtained in step (1), stirring and mixing uniformly, adding to sealed container containing 100 ml polytetrafluoroethylene, and carrying out microwave reaction; where the conditions for the oxidation reaction of the graphene oxide aqueous solution, nitric acid solution, and concentrated sulfuric acid comprises: taking 10 ml graphene oxide aqueous solution, 5 ml 65% nitric acid solution, 5 ml 98% concentrated sulfuric acid and mixing, and carrying microwave reaction for 5-10 minutes; (3) after completing reaction, cooling to room temperature, adding sodium carbonate powder, performing ultrasonic treatment with ultrasonic analyzer, simultaneously applying AC magnetic field, controlling the use of magnetic and ultrasonic fields to influence the reaction process of graphene quantum dots until the end; and (4) using microporous membrane to decompress and filter to obtain a coarse quantum dot solution, taking the supernatant, using ultrafiltration membrane to ultrafilter in deionized water for 24-28 hours, obtaining high-concentration dark brown graphene quantum dot solution.