Study On The Preparation Of NGO-PDA-DAG Composite Modified Membrane And Its Anti-fouling Performance

In order to solve the problem of membrane fouling,this paper modified the conventional organic membranes to improve the hydrophilicity and antibacterial properties of the membrane and improve its anti-fouling performance.First,the graphene oxide?GO?was modified by ethylenediamine to prepare aminated graphene oxide?NGO?,which with high hydrophilicity and nucleophilic reactivity.Then,using polydopamine?PDA?,1,3-diaminoguanidine hydrochloride?DAG?,and NGO as modifiers,the PVDF membrane was hydrophilic and antibacterial modified by oxidative deposition and surface grafting to prepare the NGO-PDA-DAG modified membrane,and the optimal preparation conditions of the modified membrane were determined.The surface characteristics of the modified membrane such as chemical structure,morphological structure characteristics,hydrophilic properties,mechanical strength and other characteristics are characterized,and test its selective permeability?pure water flux,organic fouling rejection rate?,anti-organic fouling performance and its stability,long-lasting antibacterial performance,and study the anti-fouling characteristics of the modified membrane.The results show:?1?The amination modifier NGO has-NH₂,-CO-NH,-OH and other hydrophilic functional groups,and the chemical element composition is C?70.58%?,O?18.67%?,H?3.62%?,N?7.13%?.?2?The average NGO sheet thickness is 1.12nm,which is a nano-scale single-layer sheet structure.The NGO dispersion is positively charged?+20.4m V?,under the effect of electrostatic repulsion,the NGO dispersion will not aggregate deposition after standing for24 hours,and has excellent dispersion stability.?3?The best preparation conditions of NGO-PDA-DAG modified membrane are:DA concentration 1.5mg·ml^-1,NGO concentration 2mg·ml^-1,DAG mass concentration 1wt%,DA oxidation deposition time 4h,NGO grafting time 1h.?4?The NGO-PDA-DAG modified layer was successfully attached to the surface of the PVDF membrane.In addition to the C-F,C-H and other characteristic functional groups of the original membrane,the modified membrane surface also carries-NH₂,C=N,C=O and other characteristic functional groups from PDA,DAG and NGO.The content of O and N elements on the modified membrane surface were 21.25%and 7.07%?there was no O or N element on the the original membrane surface?,and the O/C ratio was increased to 0.30.At the same time,the modified layer covers the pores of the original membrane,which reduces the average roughness of the modified membrane surface from 46.5nm to 18.3nm.The reduction of roughness can reduce the accumulation of fouling,reduce the probability of bacteria growing on the modified membrane,and effectively improve the anti-fouling performance of the modified membrane.?5?Compared with the PVDF membrane,the hydrophilic performance of the NGO-PDA-DAG modified membrane is significantly improved.hydrophilic functional groups such as-NH₂,C=N,-OH,and C=O were added to the surface of the membrane,which reduced the static contact angle of the modified membrane from 68.7°to 38.7°of the original membrane.?6?NGO-PDA-DAG modified membrane has higher mechanical strength than PVDF membrane.The tensile strength and Young's modulus of the modified membrane were 22.83MPa and 376.25 MPa respectively,which were 39.72%and 13.57%higher than the original membrane's 16.34 MPa and 331.30 MPa,respectively.?7?Compared with the PVDF membrane,the selective permeability of NGO-PDA-DAG modified membrane is significantly improved.The pure water flux of the modified membrane is similar to the original membrane,but the rejection rate of the modified membrane to BSA is 92.16%,which is increased by 18.64%on the basis of the original membrane rejection rate?73.52%?,the modified membrane has better selective permeability.?8?The anti-organic fouling performance of NGO-PDA-DAG modified membranes is significantly enhanced.The original membrane pure water flux recovery rate is only30.56%,and the modified membrane pure water flux recovery rate is 64.64%,which is34.08%higher than the original membrane.Moreover,the total fouling rate of the modified membrane is 56.61%,which is 20.67%less than the original membrane.Among them,the reversible fouling rate increased by 13.41%,and the irreversible fouling rate decreased by34.08%.?9?The NGO-PDA-DAG modified membrane has more stable anti-organic fouling performance than the PVDF membrane,and can be reused after cross-flow cleaning.After three filtration-cleaning cycles,the original membrane pure water flux is only 24.14%before the test,while the modified membrane pure water flux can recover 60.76%.The modified layer on the membrane surface does not fall off,the anti-fouling performance is stable and lasting.?10?Compared with the PVDF membrane,the surface of the NGO-PDA-DAG modified membrane has a stronger antibacterial ability,and the antibacterial effect is lasting.The original membrane does not have any antibacterial ability,and the antibacterial rate of the modified membrane long-lasting antibacterial performance test is 92.3%,88.5%,87.9%,and 85.6%,respectively.The modified membrane can exert antibacterial effect for a long time,and effectively prevent the occurrence of biofilm fouling.