Preparation Of G-C₃N₄ Oxidized And Nitrogendoped Graphene Oxide Quantum Dots Modified Polyamide Reverse Osmosis Membrane And Its Chlorine Resistance

With the continuous development of human society,more and more countries are beginning to face the problem of lack of fresh water resources.Considering that most of the brackish water that cannot be directly used on the earth is seawater,seawater desalination has become the main solution of the problem.About half a century ago,when Sidney Leob and Srinivasa Sourirajan invented the reverse osmosis membrane,the freshwater revolution began.Today,with low energy consumption and high energy efficiency,reverse osmosis?RO?technology has become the most widely used seawater desalination technology in the world,but due to the actual operating environment and the presence of active chlorine in the treatment process will destroy the membrane structure,it leads to the decline of membrane performance,so poor chlorine resistance is one of the key factors affecting the development of reverse osmosis membrane.Currently,improving the chlorine resistance of reverse osmosis membranes and trying to improve their separation performance are hot topics in the field of desalination.This paper uses different nanomaterials and different methods to modify the PA membrane.The graphene oxide?GO?-like structure and characteristics of these materials are utilized.Chemical grafting modification of commercial membranes using oxidized g-C₃N₄?CNO?,nitrogen-doped graphene oxide quantum dots?N-GOQD?,and doping modification of membranes using N-GOQD and N-GOQDT.It has obviously improved the chlorine resistance of the membrane.The specific work is as follows:1.Grafted modification of CNO:Based on previous research on GO,we chose to prepare relatively simple CNO as a modified material.CNO contains rich oxygen-containing functional groups that can effectively improve the activity of the membrane in actual operation.For the degradation of chlorine,the experiment first synthesized CNO,and characterized and analyzed the synthesized materials by means of SEM,TEM and FTIR,which proved the successful synthesis of CNO and the rich oxygen-containing functional groups.The rich oxygen-containing functional groups provide guarantee for the subsequent modification experiments.Through the activation of the carboxyl group by EDC/NHS,the CNO was finally grafted onto the surface of the membrane,a and the morphological structure of the grafted membrane was characterized by SEM,which proved that the successful grafting reaction on the membrane surface,and the separation performance of the pristine membrane and the grafted membrane was tested.In the subsequent chlorine resistance test,after a 120 hour chlorine resistance test,the rejection rate of the pristine membrane decreased by 11.6%,while the rejection rate of the graft modified membrane decreased by only 6.7%.It was verified that CNO grafting played a protective role on the membrane in sodium hypochlorite solution,and the chlorine resistance of the commercial membrane was improved,and the functional groups on the membrane surface were analyzed by FTIR to verify this2.Graft modification of N-GOQD:By synthesizing N-GOQD and characterizing this material using SEM,TEM,FTIR and XPS,it was verified as a graft modification the possibility of using a flexible material was successfully grafted on the surface of a commercial membrane through EDA.After testing the membrane separation performance,it was found that when the N-GOQD solution was 0.002 mg/mL,the grafted membrane showed better performance than the pristine membrane.For example,the water flux of the pristine membrane is 36.4 L/?m²h?,while the water flux of the modified membrane is 40.02L/?m²h?.This indicates that the N-GOQDs.The introduction overcomes the phenomenon that chemical grafting increases the resistance of the membrane to water,not only that,but also deeply explores the effect of grafting time on membrane separation performance,and finally achieves the purpose of regulating membrane separation performance.The membrane surface was characterized by SEM,XPS and FTIR,and the successful grafting of N-GOQD was verified,and the reason why the N-GOQD grafted membrane can improve the membrane flux was proposed.The modified membrane was also tested for chlorine resistance.The results showed that when the concentration of N-GOQD was 0.002 mg/mL,the rejection rate at 280 h was 80.1%,which was much higher than the original membrane of 60.3%.In this study,compared with the pristine commercial membrane,the graft modification of N-GOQD can not only increase the flux of the graft membrane,but also all the modified membranes showed better chlorine resistance than the pristine commercial membrane.3.Bulk-doped N-GOQD to improve the chlorine resistance of polyamide reverse osmosis membranes:In this experiment,N-GOQD was doped into the surface of the membrane by means of bulk doping.Not only that,but also selected a Green and easily available natural polyphenols,tannic acid,it was used to coat N-GOQD in order to increase the flux based on N-GOQD.Two materials were prepared and characterized by TEM and FTIR.The modified films were tested by experiments by adding the two materials to the MPD aqueous solution at different concentrations and interfacial polymerization method.Separation performance.The experimental results show that the water flux of the PA-N-GOQD membrane reaches the maximum when the concentration is 0.002 mg/mL,which is5.2 L/m^-2h^-1,and the water flux of the PA-N-GOQDT membrane is 0.003 mg/mL.The maximum was reached at mg/mL,6.3 L/m^-2h^-1,while the original membrane water flux was only 3.1 L/m^-2h^-1.The experiment also verified the good chlorine resistance of the modified membrane,and analyzed the surface morphology of the membrane before and after chlorine resistance by SEM.