Method for preparing self-supporting composite nanofiltration membrane

A method for preparing a self-supporting composite nanofiltration membrane, comprising the following steps:

• (1) a preparation of amino graphene quantum dots:
• dispersing a predetermined amount of graphene oxide in distilled water by ultrasonic shaking to obtain a graphene oxide dispersion, adding a predetermined amount of ammonia solution to the graphene oxide dispersion, mixing the graphene oxide dispersion and the ammonia solution to obtain a uniform mixture and transferring the uniform mixture to a reaction kettle;
• sealing and placing the reaction kettle in a muffle furnace and heating the reaction kettle to conduct a chemical cleavage reaction, and after a completion of the chemical cleavage reaction, cooling, filtering to obtain a filtrate, distilling the filtrate at a reduced pressure, freeze drying to obtain amino graphene quantum dots powder, re-dissolving the amino graphene quantum dots powder to obtain the re-dissolved amino graphene quantum dots solution, filtering the re-dissolved amino graphene quantum dots solution, and freeze drying to obtain the amino graphene quantum dots, wherein:
• a concentration of the graphene oxide dispersion is 0.01-1 w/v %, and a volume ratio of the ammonia solution to the graphene oxide dispersion is (1-4):1;
• and a temperature in the muffle furnace is 100-140° C., and a reaction time is 4-6 h;
• (2) a preparation of a porous graphene-based two-dimensional sheet material:
• using a substrate membrane as a base membrane, first rinsing the substrate membrane with distilled water and then placing the rinsed substrate membrane at a bottom of a sand core funnel;
• preparing the amino graphene quantum dots obtained in the step (1) into an aqueous solution of the amino graphene quantum dots with a concentration of 0.01-1 w/v % to obtain an aqueous solution of the amino graphene quantum dots and then adjusting the pH of the aqueous solution of the amino graphene quantum dots to 11-13 to obtain a pH-adjusted aqueous solution of the amino graphene quantum dots, sequentially adding, in turn, first the pH-adjusted aqueous solution of the amino graphene quantum dots and then a polyacyl chloride organic solution with a concentration of 0.01-1 w/v % into the sand core funnel, thereby contacting the pH-adjusted aqueous solution of the amino graphene quantum dots with the polyacyl chloride organic solution at an interface in the sand core funnel and allowing an interfacial polymerization reaction to occur at the interface for a predetermined time to obtain the porous graphene-based two-dimensional sheet material;
• and
• (3) a preparation of a composite nanofiltration membrane:
• immediately after the step (2), injecting an aqueous solution of polyamine at a uniform speed into the aqueous phase solution in the sand core funnel obtained after the interfacial polymerization reaction in the step (2) by an injector to continue the interfacial polymerization reaction between the polyamine and the polyacyl chloride, wherein a polyamide formed by the continued interfacial polymerization reaction encapsulates the porous graphene-based two-dimensional sheet material in situ to obtain a porous graphene/polyamide separation layer, removing an aqueous phase solution and an organic phase solution from the sand core funnel, loading the porous graphene/polyamide separation layer onto the substrate membrane, and subjecting to a heat treatment to prepare the self-supporting composite nanofiltration membrane.