▎ 摘　　要

NOVELTY - Preparation of nitrogen-doped carbon quantum dot comprises performing hydrothermal reaction to uniformly mixed reaction system of citric acid, histidine and solvent at 180-300 degrees C for 3-8 hours, and post-treatment processing. USE - Nitrogen-doped carbon quantum dot is used in dispersing graphene in water for aqueous epoxy resin coating (claimed). ADVANTAGE - The method provides simple synthesis of nitrogen doped carbon quantum dot being non-toxic and harmless and having good water-solubility. The carbon quantum dot is simple to use in dispersing graphene in water by ultrasonication and effectively improves corrosion resistance of aqueous epoxy resin coating at low dosage, being safe and environment-friendly. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for: (1) a nitrogen-doped carbon quantum dot having size of 3-5 nm, and constituent elements comprising carbon, nitrogen and oxygen; (2) an environment-friendly graphene dispersant comprising the nitrogen-doped carbon quantum dot; (3) a graphene dispersing method comprising uniformly mixing graphene dispersant, graphene material including graphene, graphene oxide and/or reduced graphene oxide, and water, at graphene dispersant and graphene material mass ratio of 1:1-3 to obtain graphene dispersion liquid; and (4) an aqueous epoxy resin coating including filler comprising graphene dispersion, and having graphene material content of 0.1-0.5 wt.%.