| With the development of society,the demand for energy has rapidly increased,thus the exploitation,transportation and production of petroleum have significantly developed.However,the leakage of various oils caused by natural or human factors has caused great harm to the ecological environment.The existence of oils in water will isolate the exchange of water with air and forbid the incidence of sunlight,which may cause fatal damages to the aquatic organisms.Moreover,most of the oils contain carcinogenic or toxic hydrocarbon compounds,and they will be passed on through the aquatic plants and animals'food intake and finally be concentrated in human body,which is a serious threat to human health.Therefore,it is a global issue to efficiently purify the oily sewage.Generally,the oils in water present as floating oil,dispersed oil,emulsified oil,and dissolve oil.Among which,the floating oil and dispersed oil are easy to be removed from water because of their larger particle size making them agglomerate into oil film;the formed oil film can be easy removed by using traditional separation methods such as adsorption,sedimentation and mechanical skimming.Whereas,the emulsified oil?oil-in-water emulsions?is relatively difficult to be separated due to the good stability of the oil water mixtures.Although the present demulsification techniques including sedimentation method,biological method,super/microfiltration membrane separation and so on,are able to separate the emulsions to some degree,but several critical limitations still remain,such as high energy consumption,low efficiency,and the relative low efficiency of demulsification.Therefore,it is urgent to develop new and high efficient oil/water separation materials.Electrospun nanofibers possess several advantages with small fiber diameters,good continuity,and adjustable structures,thus the corresponding nanofibrous porous membranes exhibit high specific surface area,high porosity,and good pore connectivity.In addition,with the merit of easy to be functionalized,the surface wettability of the membranes could be effective regulated through the surface physical and chemical modification of the fibers,which ensure an elaborate design of the membrane according to different properties of oil-water mixture.Moreover,the high porosity and connected channel of nanofibrous membranes can guarantee a high flux,which ensure the continuously oil-water separation with high efficiency.Consequently,electrospun nanofibrous membranes are considered as promising materials for the oily sewage purification.In this article,we developed a variety of material process technologies and surface/interface modification strategies to cooperatively regulate the pore structures and surface wettability of the electrospun nanofibrous membranes.As a result,the separation efficiency and fouling resistance of the membranes for various oil-in-water emulsions were significant improved.Additionally,we also explore a new type of porous carbon nanofibrous membranes for the application of oil-in-water micro-emulsions separation.Besides,the structure-activity relationship of the membrane material was studied,and a preliminary analysis of the separation mechanism of the membranes for oil-in-water emulsions was carried out,which could provide a theory and practice foundation for the development of electrospun nanofibrous membranes for the purification of oily sewage.The specific research works are concluded as below:?1?For the first time,we used electrospray method to regulate the surface wettability of the electrospun nanofibrous membranes,and prepared a composite membrane with microspheres layer/nanofibers,which exhibited intriguing superhydrophilicity and underwater superoleophobicity.The influence of PAN concentration and the content of SiO2 NPs on the morphology of microspheres layer and its surface wettability was carefully investigated;meanwhile,the selective transport mechanism of oil and water in the membrane was also revealed.Based on which,we explored the application of the obtained membrane for the separation of oil-in-water type emulsions.The results demonstrate that the hierarchical structured microspheres layer significantly enhanced the separation efficiency and the fouling resistance of the composite membrane with tiny influence on the permeation flux,thus the composite nanofibrous membrane can effectively separate the micron sized oil droplets from water solely under the driven of gravity?equivalent driven pressure is about1 kPa?,and the related membrane also possessed robust reusability.?2?Inspired by the multi-layered structure of the surface filter layer of earth,we fabricated a multi-layer composite nanofibrous membrane by combing the electrospinning technology with suction deposition method.Owing to the high porosity of the electrospun fibrous substrate,the honeycomb like nanofibers middle layers with small pore size,and the superhydrophilic and underwater superoleophobic SiO2 nanofibrous surface layer,the composite membrane exhibited excellent selective wettability,submicron pore structures,and the stable anti-oil-fouling property.On this basis,we studied the influence of SiO2 nanofibrous layer on the oil-fouling resistance and the oil-in-water emulsions separation performance of the composite membrane,the results showed that when the loading amount of SiO2 nanofibers reach to 0.2 mg cm-2,the corresponding composite membrane exhibited satisfactory separation performance and good anti-oil-fouling property.As a result,the composite membrane was able to effectively separate various oil-in-water emulsions with submicron oil droplets solely under the driven of gravity,and it also possessed good reusability.?3?Our approach,for the first time,fabricate a superhydrophilic and underwater superoleophobic skin with lotus leaf like surface structures and submicron pores via elaborately tuning a transient state of electrospraying and electrospinning.With the synergistic effect of biomimetic micro-/nanostructures and superior hydrophilicity of the hydrated polymer matrix,the obtained nanofibrous skin exhibited intriguing superhydrophilicity and underwater superoleophobicity,and a plausible mechanism was firstly proposed to explain the superwetting ability of the nanofibrous membrane.Benefiting from the superwettability,high porosity,and submicron pore size,the obtained superwettable nanofibrous skin in situ constructed on a common electrospun membrane could effectively separate both highly emulsified surfactant-free and surfactant-stabilized emulsions with numerous micron and nano-sized oil droplets;and ultrahigh separation flux was obtained at quite low driving pressures along with desired anti-fouling and reusability.?4?We demonstrate a facile strategy to construct a highly porous CNFs membrane with excellent mechanical flexibility and intriguing functionality based on a novel carbon source of polybenzoxazine?PBZ?via combing the multicomponent electrospinning and in-situ polymerization.We synthesized an flexible CNFs membranes with excellent durability and ultrahigh specific area(1415 m2 g-1)based on the precursor of PBZ without subsequently activation process.The effective influence of the doped precursor salt on the spinning ability and thermal stability of the precursor fibers was investigated.Moreover,a probable plasticizing mechanism of the heterogeneous nanostructures was proposed to reveal the principle for the enhancement of mechanical flexibility and durability of CNFs membranes.With their integrated properties of extraordinary mechanical property,high porosity,larger surface area,and good underwater superoleophilicity,the as-prepared CNFs membrane exhibited superior adsorption performance for the oil-in-water microemulsions compare with the commercial activated carbon,indicating a good potential for the deep treatment of oily sewage. |
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