▎ 摘　　要

NOVELTY - Preparation of aqueous polyurethane coating involves adding carbon nitride nanosheets to concentrated sulfuric acid and nitric acid to obtain a mixed solution, stirring the mixed solution, ultrasonically processing to obtain carbon nitride quantum dot mixed solution, adding hydrogen peroxide solution to the mixed solution, centrifuging, filtering to obtain carbon nitride quantum dot aqueous solution, adding quantum dot aqueous solution to graphene aqueous dispersion, ultrasonically mixing to form carbon nitride quantum dot/graphene composite aqueous solution, drying composite aqueous solution to obtain carbon nitride quantum dot/graphene composite powder, stirring isocyanate and diol, refluxing to obtain solution (A), adding a chain extender, hydrophilic chain extender and diluent to solution (A), stirring, adding neutralizer to obtain solution (B), adding composite powder to deionized water, ultrasonically processing, adding the mixture to solution (B) and removing the diluent. USE - Preparation of aqueous polyurethane coating. ADVANTAGE - The method produces aqueous polyurethane coating having excellent antibacterial and self-cleaning properties by a simple method. The coating is resistant to high temperature and UV rays, and utilizes carbon nitride quantum dots as stabilizer which is economically prepared by a simple method to disperse graphene uniformly and stably in aqueous polyurethane coatings, and effectively avoids agglomeration of graphene with no precipitation and flocculation, and can be stored for a long period of time. The polyurethane coating effectively absorbs and shields UV rays, enhances the anti-UV and anti-aging properties, and the loading of photocatalyst carbon nitride quantum dots further enhances the absorption of UV light. The graphene reduces the diffusion coefficient of chloride ions and improves the corrosion resistance of the coating. DETAILED DESCRIPTION - Preparation of aqueous polyurethane coating involves adding 2-6 g carbon nitride nanosheets to 80-240 mL concentrated sulfuric acid having concentration of 18 mol/L and concentrated nitric acid having concentration of 16 mol/L in a volume ratio of 1:1-2:1 to obtain a mixed solution, stirring the mixed solution at 60-80 degrees C for 2-8 hours in a water bath, cooling to room temperature, ultrasonically processing for 12-24 hours to obtain carbon nitride quantum dot mixed solution, adding 40-100 mL of 30 wt.% hydrogen peroxide solution to carbon nitride quantum dot mixed solution, stirring for 24-48 hours, centrifuging at a speed of 10000 rpm for 10 minutes, washing, filtering to obtain carbon nitride quantum dot aqueous solution having concentration of 0.01-1 mg/mL, adding 4-12 g carbon nitride quantum dot aqueous solution to 10-30 g graphene aqueous dispersion having concentration of 0.1-5 mg/mL, ultrasonically mixing to form a carbon nitride quantum dot/graphene composite aqueous solution, drying the carbon nitride quantum dot/graphene composite aqueous solution at 80-180 degrees C by an atomization drying method to obtain a carbon nitride quantum dot/graphene composite powder, stirring 35-65 g isocyanate and 35-60 g diol, refluxing at 70-90 degrees C under nitrogen protection for 1-2 hours to obtain solution (A), adding 5-20 g chain extender, 0.5-3 g hydrophilic chain extender and 80-100 g diluent to solution (A), stirring at 40-60 degrees C for 2-4 hours, adding 1.5-5 g neutralizer, stirring for 10-30 minutes to obtain solution (B), adding 0.01-5 g carbon nitride quantum dot/graphene composite powder to 250-300 g deionized water, ultrasonically processing for 30-60 minutes, adding the mixture to 50-80 g solution (B), dispersing, emulsifying and removing the diluent by rotary evaporation.