Preparation And Performance Study Of Polypyrrole Hollow Microspheres Modified Polypiperazinamide Composite Nanofiltration Membrane

Recently,nanofiltration（NF）membranes have been widely used in many fields,especially in the water treatment.Therefore,the requirements for NF membrane performance have become more and more important,such as permeability,selectivity,thermal stability and chemical stability,especially permeability.As we all know,traditional polypiperazinamide（PA）nanofiltration membranes remain have limitations in terms of performance.Low permeation flux is one of the disadvantages of NF membranes.In order to overcome the difficulty of low nanofiltration membrane flux,in this study we incorporated the hollow nano-microspheres into the ultra-thin polyamide layer by using interface polymerization to improve flux of the nanofiltration membranes.In this work,Polysulfone membrane was used as the substrate membrane,and piperazine（PIP）and trimesyl chloride（TMC）were used as the polymerization monomers.The effects of monomer concentration and interface polymerization time during interfacial polymerization were investigated.The results showed that the optimal polymerization conditions were PIP solution 0.8%（w/v）,0.1%（w/v）TMC/n-hexane solution,and the interfacial polymerization was performed at room temperature for 60 s.Then we investigated the effects of the content of PPy hollow nanospheres on the properties of PA nanofiltration membranes.The PPy/PA nanofiltration composite membrane was characterized by infrared,scanning electron microscopy,atomic force microscope,water contact angle,X-ray photoelectron spectrometer and Zeta potential,etc.The results showed that the membrane performance was best when the PPy content is 0.01%（w/v）.As the hollow PPy nanospheres increases,the roughness of the PPy/PA composite nanofiltration membrane increased and the hydrophilicity,the pure water permeation flux increased and from 43.9 L·m^-2·h^-1to 90.1 L·m^-2·h^-1,the rejection of divalent salts remained above 98%,and the rejection order for several common salt solutions was Mg SO₄>Na₂SO₄>Mg Cl₂>Na Cl.However,the long-term running stability of the composite NF membrane was not ideal.Then hollow PPy nanospheres were modified with polypyrrole-3-carboxylic acid（PPy-3-COOH）,We synthesized PPy-3-COOH/PPy hollow composite nonamicrospheres by chemical oxidation.Through a series of characterizations,we concluded that the diameter of PPy-3-COOH/PPy porous hollow composite nanorospheres was about 30 nm,the thickness of the outer layer of the microspheres is5 nm,and the diameter on the microsphere shell is 0.8736 nm.In addition,we also investigated the effect of PPy-3-COOH/PPy content on the performance of PA composite NF membranes.The results showed that when the content of PPy-3-COOH/PPy hollow nano-composite microspheres was 0.01%（w/v）,the membrane showed the best performance,too.The AFM results showed that the roughness of the composite NF membrane first increased and then decreased,compared with 0.01%（w/v）PPy/PA composite NF membrane,the water contact angle value was smaller which a value of 16.23°,hydrophilicity got a more increase.Pure water flux was also higher than 0.01%（w/v）PPy/PA composite NF membrane(90.1 L·m^-2·h^-1)with a value of96.8 L·m^-2·h^-1.At the same time,the rejection of divalent salts has always remained above 97%.The rejection order of several common salt solutions was Na₂SO₄>Mg SO₄>Mg Cl₂>Na Cl,the stability and antifouling ability of PPy-3-COOH/PPy/PA composite NF membranes have been improved significantly.