Application Of Polycationic Liquid/PVDF Blend Membrane In Water Treatment

Global freshwater resources are in short supply,and water pollution is becoming increasingly serious.Compared with traditional water treatment methods,membrane separation technology has been widely used in wastewater treatment because of its low cost,high efficiency and no secondary pollution.Among the membrane materials,polyvinylidene fluoride（PVDF）is widely concerned because of its good thermal stability,chemical stability and high mechanical properties.The membrane materials prepared by blending have the advantages of uniform membrane structure,consistent chemical composition and good separation effect.Among the organic blending modified materials,poly ionic liquid（PIL）is a kind of polymer with ionic liquid（IL）monomer in its structure,which has the dual characteristics of ionic liquid and polymer.The blended membrane containing polycationic ionic liquid can enhance the positive charge of the base membrane,and the pollutants in water can be efficiently removed by physical screening and electrostatic action.In this study,a series of P（BVIm Br₁-co-PEGMA₁）/PVDF blend membranes with different composition of casting solution and coagulation bath were prepared by blending the synthesized polyionic liquid P（BVIm Br₁-co-PEGMA₁）with PVDF.A series of characterization methods（FTIR,SEM,zeta potential analysis,pure water flux analysis,water contact angle analysis,mechanical strength analysis,etc.）show that compared with pure PVDF membrane,the modified P（BVIm Br₁-co-PEGMA₁）/PVDF membrane has significantly enhanced hydrophilicity,increased water flux and enhanced surface positive charge,but decreased mechanical strength.Through the above-mentioned performance characterization,the better blend membranes were selected,and the removal of different pollutants（oil-water emulsion,bovine serum albumin,dyes and heavy metal ions）in water was further studied.The experimental results showed that the blend membranes showed good anti-fouling performance and high rejection rate in filtering n-hexadecane oil-water emulsion and BSA solution,among which M5 membrane（PVDF:P（BVIm Br₁-co-PEGMA₁）=8:2）The flux recovery rate of casting solution with concentration of 22 wt%is as high as 97.3%and95.5%respectively,and M4(PVDF:P（BVIm Br₁-co-PEGMA₁）=9:1;The rejection rates of casting solution with a concentration of 22 wt%are as high as 99.4%and 87.2%,respectively,and the flux recovery rate and rejection rate both decrease in the third cycle filtration.In the experiment of filtering different types of dyes（methylene blue and methyl orange）with different concentrations,it was found that M5 membrane had a high rejection rate（87.33%）for low concentration（5 mg/L）of methyl orange.After filtering,it was ultrasonically cleaned with 5 g/L sodium nitrite methanol solution,and it was found that the flux recovery rate was higher than 90%.The experiment of filtering heavy metals found that M10（PVDF:P（BVIm Br₁-co-PEGMA₁））=8:2;The concentration of casting solution is 24 wt%.The composition of coagulation bath is VH20:VDMF=95:5.The removal effect of bivalent copper ions and bivalent cadmium ions is not ideal,and the highest rejection rates are only 19.4%and 24%.Under the conditions of p H=1 and membrane pressure of 0.02 MPa,the removal efficiency of divalent mercury ions is good,and the rejection rate is as high as 89%.The research results show that different P（BVIm Br₁-co-PEGMA₁）/PVDF blend membranes have strong anti-fouling performance,and have good retention effect on oil-water emulsion,BSA,dye and divalent mercury ions.