Development Of Hyperbranched Polyglycerol Modified Membranes For Pressure Retarded Osmosis:Preparation And Antifouling Properties

The rapid growth of energy consumption and greenhouse gas emissions in the world today has stimulated the exploration of renewable energy as an alternative fuel.Osmotic energy is the energy released by the mixing of different salinity streams.It is a clean,sustainable and largely untapped energy with great prospects.The maturity of the preparation process of membranes for pressure retarded osmosis(PRO)makes osmotic energy generation more and more realistic.However,the porous layer of the PRO membrane is easily contaminated by contaminants in the feed solution,reducing the performance of PRO membrane and the amount of power generation.In order to solve this problem,the polymers with anti-fouling property are grafted onto the membrane porous layer to improve the anti-fouling performance of PRO membrane.The main contents are divided into three chapters.In the first chapter,there is a brief introduction to osmotic energy and PRO process,focusing on the development of PRO membranes,pollution and current strategies for anti-fouling.In the second chapter,negatively charged sulfated hyperbranched polyglycerol(SHPG)was prepared by post-polymerization modification with α-lipoic acid and sulfamic acid of hyperbranched polyglycerol(HPG)prepared a priori by anionic ring-opening polymerization.The SHPG polymer was grafted onto polydopamine(PDA)pretreated poly(ether sulfone)(PES)hollow fiber membrane by Michael addition reaction to obtain the PES-g-SHPG membrane.Then the PES-g-SHPG membrane was tested for anti-bacterial adsorption,anti-protein adsorption and PRO process anti-fouling test,the results show that the antibacterial adsorption and anti-protein adsorption performance of PES-g-SHPG membrane is stronger than that of unmodified PES membrane.In PRO tests under different hydraulic pressures,the SHPG-grafted membranes show a lower flux reduction and a higher flux recovery rate in comparison with the pristine PES membranes than that of the PES hollow fiber membrane before the modification.In the third chapter,considering that some coatings are damaged when the SHPG coating is fouled for a long time.Once the coating is destroyed,microorganisms such as bacteria will adhere and proliferate on the PES porous layer,further destroying the anti-fouling coating.Inspired by the biological system induced by micro-damage-induced autonomic repair process,poly(2-ethyl-2-oxazoline)was first hydrolyzed under sulfuric acid to prepare linear polyethyleneimine,followed by quaternization with bromine hexane to obtain the quaternized linear polyethylenimine(QLPEI),and then the QLPEI was grafted onto the SHPG modified membrane named PES-g-SHPG by Michael addition reaction and electrostatic interaction,to obtain healable coating layers with sufficiently high mobility from electrostatic interaction.The modified membrane named PES-g-SHPG-QLPEI membrane was tested for antibacterial adsorption,anti-protein adsorption and PRO process anti-fouling test.The results prove that the antifouling performance of PES-g-SHPG-QLPEI membrane was better than that of unmodified PES membrane.In order to further confirm the self-healing properties of the PES-g-SHPG-QLPEI membrane,the PES-g-SHPG membrane and the PES-g-SHPG-QLPEI membrane are soaked in sewage for two months to get aged membranes.In the antibacterial,anti-protein test and PRO antifouling test,the anti-fouling performance of the aged PES-g-SHPG membrane is weaker than non-aged memranes and the anti-fouling ability of the aged PES-g-SHPG-QLPEI membrane is basically the same as the non-aged membrane,indicating that the coating is healable.