| In recent years,frequent oil spills and the release of industrial and domestic oily wastewater have imposed a catastrophic impact on our ecosystem,as well as have caused huge economic losses.For example,the floating oil on the ocean could form a dense film,which would induce a serious oceanic anoxic event resulting in unhealthy growth of plankton and the disturbance of the ecosystem.Besides,in the process of oil extraction,transportation,and storage,water would mix with oil in different ways,thus causing deterioration of oil quality and imposing a threat to the normal operation of the car.To address the above issues,the separation of oil and water could not only avoid the waste of petroleum and reduce economic losses,but also solve the harm caused by oil pollutes,thereby protecting the marine ecological environment.Generally,oil/water mixtures exist as free,dispersed,and emulsified states.Among them,the separation of emulsified oil/water mixtures is always difficult and challenging due to their small size and strong stability.The traditional method for the separation of oil/water emulsions,including sedimentation,centrifugation,and chemical methods usually suffered from high energy consumption and low separation efficiency.Recently,membrane separation technology has drawn much attention due to its energy-efficient and simple operation.Electrospun nanofibrous membranes have aroused the broad interest of researchers due to the advantageous features,such as rich raw materials,tunable pore size,high porosity,and good pore connectivity.In this thesis,we pointed out that the synergic regulation of pore structure and surface/interface wettability of membrane is the key to solve the challenges based on the summarization of the research status in the field.Here,we finely combine the electrospinning and post-modification method to realize the high integration of good connective submicron pores and the selective wettability in the nanofibrous membrane,thus achieving a simultaneous improvement of permeation flux and separation efficiency.The main research results obtained are as follows:(1)Three injection modes of charged fluid in the electrohydrodynamic process,including electrospraying(droplet mode),transition mode(jet/droplet mode),electrospinning(jet mode)were finely controlled by optimization of the properties of the poly(vinylidene fluoride)(PVDF)solution.On this basis,a thin film was constructed on the surface of the conventional PVDF nanofibrous membrane.After that,we investigated the influence of different jet modes on the membrane properties,such as surface morphology,pore size,and roughness.Consequently,we achieved a composite membrane with micro/nano roughness,submicron pore size(0.63?m),and interconnective pore.The results showed that the hierarchical structure imposed a significant influence on improving the membrane hydrophobicity and reducing the underoil water adhesion.And the membrane achieved a underoil water contact angle of 162o,an underwater water adhesion force of 4.6?N,and an underoil water rolling angle of 3o.Meanwhile,the submicron pore size of the as-prepared composite membranes could effectively intercept the micron and sub-micron-sized emulsified water droplets.These findings established the design criteria of emulsion separation membranes.Consequently,the PVDF composite membrane could separate various water-in-oil emulsions,achieving an oil permeation flux of 12994 Lm-2 h-1 and high separation efficiency(water content in the filtrate<50 ppm),as well as good anti-fouling property.(2)We utilized Plateau-Rayleigh instability of the liquid film to construct micron-sized polyamide 66(PA66)spindle-knots on the SiO2 nanofibers.The effects of PA66 solution concentration on the morphology structure,roughness,porosity,and pore size were systematically investigated.Then we use in situ chemical oxidation polymerization to construct a layer of polyaniline(PANI)with nanoscale roughness and positive potential on the SiO2/PA66 membrane derived from 0.5 wt%PA66 solution.The resultant SiO2/PA66/PANI nanofibrous membrane could achieve superhydrophilicity and underwater superoleophobicity with a water contact angle(WCA)of 0o and an underwater oil contact angle(UWOCA)of?151o,as well as submicron-sized pores.The membranes can separate various oil-in-water emulsions with a remarkable permeation flux of5403 Lm-2 h-1 and a high separation efficiency(total organic carbon content<5 mgL-1)under the gravity of 1 k Pa.Besides,by virtue of the Laplace pressure difference and positive potential of the spindle-knotted nanofibers,the nanofibrous membranes could remove the filter cake during separation by coalescence,thus ensuring a stable permeation flux,which is of great significance for practical applications.(3)By the combination of chemical oxidation polymerization and successive ionic layer adsorption and reaction(SILAR)method,we developed a heterostructured nanofibrous membrane,in which Bi OBr nanosheet-based microspheres anchored on electroconductive SiO2/PANI core-shell nanofibers.By virtue of the hierarchical roughness,enclosed cells,and the intrinsic hydrophilicity of PANI and BiOBr,the SiO2/PANI/BiOBr membrane achieved promising superhydrophilic and underwater superoleophobic property with water contact angle of 0o and underwater contact angle of 161o as well as low oil adhesion.Meanwhile,the SiO2/PANI/BiOBr membrane possessed submicron pore size(?0.62?m),high porosity(85%),and good pore interconnectivity.Besides,fluorescence spectra and electrochemical analysis showed that the PANI/BiOBr heterojunction and PANI conductive network could effectively promote the separation of electron-hole pairs and inhibit the recombination of charge carriers.After irradiation for 1h under sunlight,the fouled SiO2/PANI/BiOBr membrane could restore its underwater oleophobicity.The SiO2/PANI/BiOBr membrane exhibited desirable capability for separating highly emulsified oil-in-water emulsions with a remarkable permeation flux of 6140 Lm-2 h-1 and a high separation efficiency(total organic carbon content<5 mgL-1).Importantly,the presence of PANI/BiOBr heterojunction arrays with visible light catalytic activity and 3D PANI electroconductive networks could endow good self-cleaning property,maintaining a high flux recovery ratio of over 98%.(4)By employing PANI as the nitrogen-containing carbon source,we developed a flexible SiO2/C core-shell nanofibrous membrane with SiO2 nanofibers as the core layer and nitrogen-containing carbon matrix with a nanoscale roughness as the shell.The effect of calcination temperature on the graphitization degree,nitrogen content,and nitrogen species of the carbon shell was investigated.It is found that the carbon shell could not only improve the membrane mechanical strength but also reduce the membrane pore size(0.85?m).By virtue of the reversible behavior of carbon shell for hydrocarbons,that is adsorption at low temperature and desorption at high temperature,the SiO2/C nanofibrous membranes could achieve superhydrophilic/underwater superoleophobicity(WCA=0°and UWOCA=161°)and hydrophobicity/superoleophilicity(WCA=?150°and OCA=0°)through heat treatment.The as-prepared SiO2/C nanofibrous membranes could separate emulsified oil/water mixtures on demand.We used SiO2/C membranes with superhydrophilic/underwater superoleophobic property to separate oil-in-water emulsions with permeation flux of 2813 Lm-2 h-1 and TOC<5 mgL-1.Meanwhile,we used SiO2/C membranes with superhydrophobic/superoleophilic property to separate water-in-oil emulsions with permeation flux of 10250 Lm-2 h-1 and water content<30 ppm.Also,the membrane could reduce oil fouling on the membrane by calcination,achieving flux recovery rate FRR of 98.3%. |
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