Structure Regulation And Oil/Water Separation Performances Of Cellulose Acetate Electrospinning Nanofibrous Membranes

With the rapid economic development and continuous industrialization,water pollution has been recognized as an important global challenge for future generations.Offshore crude oil leakage,oil and gas industry,and domestic grease produce a large amount of oily water,which seriously affect the ecological environment,but also cause a huge waste of resources and economic losses.The key strategy to solve this problem is to develop an effective material and technology to treat oily water.Electrospinning nanofiber membrane has the characteristics of high porosity,easy to adjust pore size structure,and interconnected three-dimensional network,which are conducive to the rapid mass transport,and can be used for the purification of oily water.Compared with traditional electrospinning oil/water separation membranes,such as polyacrylonitrile(PAN),polyimide(PI),and polytetrafluoroethylene(PTFE),cellulose acetate(CA)membranes have the advantages of adjustable hydrophilicity,simple preparation,low cost,and biodegradability.Employing the unique surface modification and structure design to improve the surface wettability and adjust the internal pore size structure,CA-based electrospinning nanofiber membranes can be used to achieve the purification of various oily water.The main work of this thesis is as follows:Firstly,the deacetylated CA(d-CA)nanofiber membranes were prepared via a typical electrospinning method,the deacetylation treatment and the removal of polyethylpyrrolidone(PVP).The effects of CA spinning solution concentration,PVP addition,and deacetylation time on the morphologies,hydrophilicity,and oil/water separation properties of nanofiber membranes were investigated respectively.It was found that when the CA spinning solution concentration is 8 wt.%,the PVP addition is 30 wt.%,and the deacetylation time is 24 h,d-CA nanofiber membrane displays the best comprehensive performance.It has a uniform size distribution of nanofibers(the average diameter of 152 nm)and exhibits good hydrophilicity(the water contact angle of 71°).The separation fluxes of the oil/water emulsion without(SFE)and with(SSE)emulsifier(only for gravity)are 1824 L·m-2·h-1 and 1456 L·m-2·h-1,respectively,and the separation efficiencies are 51.87%and 59.55%,respectively.However,pure d-CA nanofiber membranes usually exhibit poor mechanical properties and low oil/water separation efficiency,which limit their application in practical processes.Therefore,we prepared a superwettable CA-based electrospinning nanofibers membrane by the simple dipping of bacterial cellulose(BC)and the crosslinking of citric acid(CCA)to form the voronoi-nets structure spontaneously.The results show that as the BC impregnation concentration is 0.8 mg·mL-1 and the CCA concentration is 3 wt.%,the d-CA/BC@CCA nanofiber membrane exhibits the superhydrophilic and superhydrophobic properties(a water contact angle of 26.60 and a underwater oil contact angle of 155°).Meanwhile,dCA/BC@CCA membrane possesses the best oil/water separation performance,and the flux and separation efficiency for n-hexane/water SFE and SSE are 9259 L·m-2·h-1·bar-1,98.34%and 5418 L·m-2·h-1·bar-1,99.93%,respectively.This is attributed to the introduction of strongly hydrophilic BC and CCA,the construction of cobweb-like structure,and the improvement on the surface wettability of d-CA/BC@CCA nanofiber membrane.In addition,the dCA/BC@CCA nanofiber membranes also exhibit the excellent mechanical properties and good recyclability.Finally,a series of double layer CA nanofiber membrane/MgAl-LDH(DCA/LDH)with multi-scale rough structure had been successfully fabricated via the electrostatic spinning,electrostatic spraying technology,and hydrothermal synthesis method.It can be found that when the spraying concentration of the upper CA layer is 3 wt.%,the spraying time is 3 h,and the LDH growth time is 9 h,the DCA/LDH nanofiber membrane exhibits the outstanding oil/water SSE separation performances with the separation flux of 27346 L·m-2·h-1·bar-1 and separation efficiency of 98.93%.It can be attributed to the strong hydrophilicity of LDH and the construction of multi-scale rough structure,endowing DCA/LDH composite films with good superwettability.In addition,DCA/LDH nanofiber membranes also display high mechanical properties and durability,suggesting the wide application prospect in the purification of oily wastewater.