Preparation Of Functional Nylon-based Forward Osmosis Membrane And Investigation On Its Forward Osmosis Properties

In recent years,forward osmosis water treatment technology has received extensive research attention in the field of water treatment because it requires no additional driving force,and has a relatively low membrane fouling tendency and high water recovery rate.Among the forward osmosis membranes,thin film composite forward osmosis(TFC-FO)membranes have been investigated by researchers for their classic double-layer structure and ease of modification.At present,TFC-FO membranes have been used in water desalination,wastewater treatment,power generation,food industry,pharmaceutical industries,etc.,showing the great application potential.However,in practical applications,it still faces challenges such as concentration polarization,membrane fouling and reverse solute diffusion.In this paper,in view of the main problems faced by the TFC-FO membranes,two different modification methods were applied onthe nylon-based FO membranes to improve the membrane’s forward osmosis performance and antibacterial property.The main research results of this thesis are as follows:(1)TFC-FO membranes with typical double-layer structure were prepared on polyethersulfone(PES),polyvinylidene fluoride(PVDF),and nylon-based membranes using traditional interfacial polymerization(IP)methods,with the FO performance and mechanical strength tested and compared.It was found that the commercial nylon membranes have the highest mechanical strength and good FO performance.On this basis,the interfacial polymerization conditions based on the nylon membrane were further explored.The results showed the best interfacial polymerization conditions with the MPD concentration of 6 wt.%and the TMC concentration of 0.6 wt.%.Then,a novel thin-film nanocomposite(TFN)forward osmosis(FO)membrane was fabricated by embedding bovine serum albumin(BSA)and gold nanoparticles(GNPs)to the cockscomb-like nylon supporting membrane.The influence of BSA/GNPs incorporation was investigated on the surface morphology,surface roughness,surface charge,and FO performance of TFN-FO membrane.The water flux of the modified FO membrane was up to 55.2±5.4 LMH in AL-DS(active layer facing the draw solution)mode,which was about five times as high as that of the pristine FO membrane,and the value of J_s/J_w reached as low as 0.034 g/L indicating a high selectivity.BSA/GNPs located between the nylon supporting membrane and the polyamide(PA)skin layer provided passage for water transport and increased the roughness as well as compactness of the PA layer,thus increasing the effective area on which the osmotic pressure would act and decreasing the reverse salt flux.In addition,BSA/GNPs located at the bottom of the supporting layer provided a nearly electroneutral membrane surface in solution and alleviated the dilutive concentration polarization.In this study,the nylon membrane with the special cockscomb-like surface structure was chosen as the supporting layer to load BSA/GNPs nanoparticles,providing a simple and effective modification method for preparing high separation performance TFN-FO membranes.(2)The macroporous supporting layer of the forward osmosis(FO)membrane favoring the water transport would also constitute a challenge for the preparation of the flawless and uniform skin layer,due to the easy collapse of the skin layer at the macroporous structure.In this study,the porous nylon supporting layer(pore size of 5μm)was partially filled with the calcium alginate hydrogel(CA-gel)and the silver nanowires were fixed at the bottom.The CA-gel on the surface of the supporting layer favored the formation of a more uniform and cross-linked PA skin layer during the interfacial polymerization(IP)process,resulting in a low reverse salt flux and a high rejection of heavy metal ions.In addition,the three-dimentional network CA-gel located in the supporting layer swelled and provided transport channels for water permeation.Furthermore,the silver nanowires fixed on the bottom of the supporting layer endowed the membrane with antibacterial properties.The novel FO membrane showed a high selectivity with a significant increase in water flux,almost 3 times that of the original FO membrane with no addition of the CA-gel.In addition,the water flux maintained at more than85%of the original water flux after four cycles of FO tests(compared to 65%for the original FO membrane),indicating a good antifouling performance.Furthermore,an excellent heavy metal rejection of 99%was achieved in the FO process,and significant zone of inhibition was observed due to the fixed silver nanowires and the hydrophilicity of the supporting layer in the bacterial-containing solution,indicating a significantly-enhanced antibacterial performance of modified FO membrane.