Study On The High-efficiency Treatment Of Salt-containing Dye Wastewater By GO/GQDs Modified Composite Nanofiltration Membranes

With the increasingly strict emission standards,it is necessary to develop effective methods for wastewater treatment and reuse.Nanofiltration（NF）technology has great development prospects in the treatment and reuse of salt-containing dye wastewater due to its advantages of high efficiency,easy operation,selective separation,no secondary pollution and good effluent quality.In this study,the GO-PCS mixed matrix NF membrane and GQDs doped loose NF membrane with excellent selective-permeability and fouling resistant performance were prepared by cross-linking method and interfacial polymerization method.A series of characterization methods were used to study the morphology,roughness,contact angle,Zeta potential and average effective pore size of the prepared membrane.The separation and fouling resistance performance of the synthetic membrane were evaluated by filtration of synthetic wastewater such as direct black 38,ponceau S,xylenol orange,direct red 80,alcian blue 8GX and the real hairwork dyeing effluent（HDE）.It provides a new reference for the advanced treatment and reuse of salt-containing dye wastewater.The topic mainly includes the following aspects:（1）Study on the preparation and performance of GO-PCS mixed matrix NF membrane:The coating and crosslinking method was adopted to design a one-step method to obtain the ideal skin characteristics and loose support structure.A novel type of GO-PCS NF membrane was prepared by the surface functionalization of graphene oxide（GO）nanosheets.The effects of the amount of GO nanosheets on the physicochemical properties and separation properties of the membranes were studied.The experimental results show that a novel PCS based NF membrane was fabricated via surface functionalization with an appropriate amount of GO nanosheets through forming covalent bonds.It demonstrated superior surface hydrophilicity,smoothness and negative charge（decreasing to 41.9°,18.7 nm and-56.4 m V,respectively）,and showed good anionic dye and salt rejection performance.Due to the disruption of the packing of polymer chains with the two-dimensional layered rigid GO nanoplates,porosity of its surface layer increased by 16.8%concurrently.Compared with the bare PCS membrane,the permeate fluxes of NF₂ membrane to aqueous solutions dissolved with direct black 38,xylenol orange,ponceau S,Na Cl and Na₂SO₄ under steady state were higher by 58.8%,76.3%,75.1%,83.1%and 78.8%,respectively.Also,it exhibited slightly higher anionic dyes and significantly superior salt removal efficiencies.Furthermore,the optimal GO-PCS membrane also exhibited better antifouling property for achieving the outstanding flux decline ratio of 8.67%and especially irreversible fouling ratio of only 0.17%to direct black38.（2）Study on the preparation and performance of graphene quantum dots（GQDs）based TFC/TFN loose NF membrane:The interfacial polymerization method was adopted to customize the loose nanocomposite membrane by after partial alternative doping of4,4’-bipiperidine and continuous incorporating of GQDs to verify the feasibility of its efficient fractionation simulation and real dye/salt mixture.The effects of BP and GQDs on the functional layer properties and removal properties of NF membranes were studied.The results showed that partial alternative doping BP allowing chain extension could only significantly increase the nominal pore size and reduce the crosslinking degree of PA layer,thereby leading to the generation of smoother membrane surface.Nevertheless,in addition to further reinforcing the above positive effects,continuous incorporating of GQDs also endowed the prepared TFN membrane with markedly improved hydrophilicity and charge property.The as-prepared TFN-0.2 membrane displayed the highest water permeance of 56.0L·m^-2·h^-1·bar^-1,retention for all selected dyes（≥99.8%）and salt permeability（≥91.2%）tested by aqueous dye/salt solutions.Besides,the antifouling indexes in terms of R_r and R_ir of TFN-0.2 membrane against HDE solution reduced from 13.0%and 20.6%of bare one to 8.30%and 1.30%,respectively.While FRR prominently increased from 79.4%to 98.7%during the period.Overall,the novel modified loose TFN-0.2 membrane exhibited excellent fractionation and fouling resistance performance for both synthetic and real dye/salt mixtures.