Structural Design Of Polyacrylonitrile Nanofiber/chitosan Composite Forward Osmosis Membrane

Forward osmosis(FO)process owns great potential for many water treatment applications such as seawater desalination,food concentration,wastewater treatment,power generation,medicine and so on.FO without external hydraulic pressure has several unique preponderance including low energy consumption,low operating cost.efficient water recovery,high rejection of small compounds and wide range of feed solutions.The interconnected structure and low tortuosity of nanofiber mats make electrospun nanofiber membrane potential candidate for FO membrane support layers.In this work,we designed a novel composite structure as the support layer for FO membrane and optimized its preparation technique.The composite structure contained electrospun nanofiber mat and a thin chitosan sub-layer.After surface modification of nanifiber.it was found that nanofiber membrane got best performance when the time for hydrolysis reaction was 30 min.In this way,the hydrolysis reaction only took place on the surface of the nanofiber so that the mechanical property of nanofiber remained about the same as the unmodified nanofibers.Moreover,the nanofiber became hydrophilic after hydrolysis reaction and its water contact angle decreased from 95° to 11° which would contribute to the enhancement of the w ater flux and mitigate the internal concentration polarization.The surface roughness of composite support layer got decreased continuously after assembling chitosan sub-layer.And the mechanical property enhanced with the increasing of the concentrate of chitosan casting solution.The tensile strength reached over 30MPa and the Young's modulus reached over 90 MPa.The FO membrane prepared with the composite supported layer showed superior filtration performance.The osmotic water flux reached over 60L/(m2·h)in FO mode(active layer face feed solution).When the concentrate of the chitosan casting solution was 3.5%.the NaCl rejection reached 97%and the reverse salt flux was only 0.93g/(m2·h).According to a series of tests,it was confirmed that the composite nanofiber FO membrane solved the main problems that nanofiber FO membrane had.High water flux and low reverse salt flux was achieved while high mechanical property was retained,which was benefit to improve the service life.