Preparation And Characterization Of Double-skinned Forward Osmosis Membrane Based On PAN Nanofiber Support Layer

After entering the 21 st century,the shortage of water resources has become one of the biggest challenges facing the sustainable development of mankind in the future.Forward osmosis(FO)technology has the advantages of low energy consumption,low pollution,high separation efficiency,and can be used in sewage and wastewater treatment,seawater desalination,and industrial liquid separation and concentration.It is considered to be the most promising solution to the water crisis technology.In FO technology,the preparation of highly permeable selective FO membrane is the key to affecting the efficiency of FO process.In order to utilize the high flux of the single-skin FO membrane in AL-DS mode and reduce internal pollution,the researchers developed a double-skin FO membrane.Since the introduction of the second polyamide(PA)layer increases the mass transfer resistance,the improvement effect of the water flux is not ideal.At present,researchers have done a lot of research on the selective layer when improving the permeability of the double-skin FO membrane,and there is a lack of research on the support layer.The support layer also has a great influence on the flux of the membrane during the osmosis process.This study optimizes the permeability of the double-skin FO membrane from the perspective of the support layer,and uses electrospinning technology to produce a hydrophilic thin nanofiber support layer with high porosity,large pore size,and interconnected pore structures.The porosity and large pore size also bring challenges to the preparation of the PA layer.By using the surfactant-assisted interfacial polymerization(IP)method,a PA layer with excellent performance was prepared on the nanofiber membrane,and its morphology,physical and chemical properties and the influence on the permeability selectivity of the FO membrane were studied.On this basis,the characteristics of the traditional phase inversion support layer and the nanofiber support layer were compared.Subsequently,a double-skinned FO film was prepared on the two carriers using an improved IP process,and the performance was compared and analyzed.In the process of preparing the PA layer on the polyacrylonitrile nanofiber membrane by using the IP method,an economical surfactant-sodium dodecylbenzene sulfonate(SDBS)is added to the water phase,which can further improve the support layer Hydrophilicity improves the residual amount of the water phase in the support layer and makes the water phase interface on the surface of the carrier,thereby forming a complete and defect-free PA layer on the support layer.The study found that adding SDBS will not affect the contact angle and chemical composition of the PA layer.In addition,as the concentration of SDBS increases,the thickness and roughness of the PA layer also increase,while the degree of crosslinking increases first and then decreases.When 0.10 wt% SDBS,3.0 wt% MPD,0.15 wt% TMC are used to prepare the PA layer,the water flux of the membrane reaches the maximum(24.03 LMH),the reverse salt flux is the smallest(4.1 g MH),and the special salt flux is the lowest(0.17),showing excellent selective permeability performance.It provides a simple and economical new method for preparing a PA layer with good performance on a large pore support layer.Compared with traditional phase inversion membranes,PAN nanofiber membranes have the advantages of large specific surface area,high porosity,perforated pore structure,low mass transfer resistance and high mechanical properties.As the support layer of the double-skin FO membrane,it is more helpful to reduce internal concentration polarization effect and improved membrane durability.The flux of the double-skinned FO membrane prepared with the nanofiber support layer is about twice that of the phase-inversion double-skinned FO membrane,and its reverse salt flux is also reduced,showing excellent selective permeability.In addition,the nanofiber double-skinned FO membrane also has excellent mechanical properties and anti-pollution capabilities.This work provides a new development direction for the preparation of double-skin FO membranes with high permeability selectivity.