Preparation Of Functional Forward Osmosis Membrane And Its Application In Water Filtration And Heavy Metal Removal

In recent years,due to the advantages of low energy consumption,high removal efficiency and high water recovery efficiency,the forward osmosis technology has attracted extensive attention.The forward osmosis technology has shown great potential application value in water desalination and heavy metal ion removal.At present,a large number of scholars have made relevant studies on the forward osmosis technology.However,the preparation of high-performance and multifunctional forward osmosis membrane still remains a challenge.Traditional TFC-type FO separation membranes have small flux,poor selectivity,and are vulnerable to the effects of membrane fouling.In this paper,the support layer and the skin layer of the TFC-type FO were surface modified,which can effectively promote the permeability,separation performance,pollution resistance and ability for the removal of heavy metal ions.In the first part of this thesis,the porous polysulfone?PSf?supporting layer was surface-modified via the UV-initiated grafting polymerization technology,and the hydrophilic poly?3-sulfopropyl methacrylate potassium salt??PSMP?polymer brush was grafted on the pore wall and surface.The prepared FO membrane showed high permeability,high separation selectivity and high anti-fouling ability.In the second part of this thesis,the PEG derivatives?Jeffamine?was further grafted on the polyamide skin layer of the FO membrane prepared in the first part of this thesis,which enhanced its anti-fouling ability and showed excellent heavy metal removal ability.The specific content and research results are as follows.?1?A novel hydrophilic thin-film composite?TFC?-type forward osmosis?FO?membrane was fabricated showing a macroporous surface-functionalized polysulfone?PSf?supporting layer with large open pores at the bottom.Poly?3-sulfopropyl methacrylate potassium salt??PSMP?polymer brush was grafted on the bottom and the internal wall of the PSf supporting layer via the simple UV-initiated grafting polymerization method.The optimum TFC-type FO membrane?g-FO-3?showed a remarkable forward osmosis and anti-fouling performance.The water flux of g-FO-3?43.0 L/m²h?was nearly 2.6 times the conventional TFC-type PSf-based FO membrane?16.8 L/m²h?and 1.8 times the TFC-type FO membrane with macroporous PSf supporting layer but without polymer grafting?24 L/m²h?in AL-DS mode,with water as the feed solution and 2 M NaCl as the draw solution.In addition,the low Js/Jw value of g-FO-3indicated an excellent separation selectivity.Furthermore,the FO membrane kept a water flux of 90%after eight-cycle fouling tests,and the recovery rate of water flux after cleaning is95%.Therefore,the hydrophilic polymer brush-grafted PSf macroporous supporting layer of the FO membrane provides a convenient and efficient means to improve the forward osmosis and the anti-fouling performance of the TFC-type FO membranes.?2?A FO membrane with hydrophilic polymeres brush grafted onto both skin layer and supporting layer was prepared.On the basis of the g-FO-3 membrane prepared in the first part of the thesis,the skin layer was further surface-grafted with Jeffamine polymer brush.The prepared TFC-type FO membrane showed high water permeability,good anti-fouling and high ability to remove heavy metals.Compared to the membrane with the skin layer not grafted with Jaffamine,Water permeability of Jeffamine grafted membrane can still be maintained at the same level as g-FO-3?40⁴3 L/m2h,AL-DS mode,2 mol/L NaCl solution?,and the anti-organic pollution performance has been significantly improved.After eight cycle experiments,the water flux can still maintain 95%of the original water flux.In addition,the FO membrane grafted by Jeffamine has a good ability to remove heavy metal ions in both AL-FS and AL-DS modes.When the pH value is 4 and 2 g/L heavy metal ions in the feed solution,the heavy metal retention rate exceeds 94.2%and 98.8%,respectively,The mechanism of heavy metal ion rejection for the prepared multi-functional TFC-type FO membrane with the functional groups of-NH₂ and-SO₃^-was discussed.Hence,the prepared high-performance TFC-type FO membrane shows the optimized the separation performance and extend the application field of the forward osmosis process.