Synthesis And Forward Osmosis Properties Of Drew Solutes Based On Functionalized Ferroferric Oxide Nanoparticles

The shortage of fresh water resources seriously affects people’s daily life and social economic development of our society.Therefore,seeking fresh water sources has become the consensus of researchers.Ocean with the most vast water resource is the most ideal place to obtain fresh water.Because of its specific low energy consumption with the no pressure-driven working mode,the forward osmosis（FO）technique has become an ideal technology for seawater desalination.Its key factors include the semi-permeable membrane that only allows water molecules to pass through and the drew solute（DS）with large water flux capability.At present,HTI company has developed a commercially available composite membrane as the FO membrane,while further research is still needed to obtain appropriate drew solutes.The ideal drew solute should not only provide a large water flux but also be easy to separate and recycle at a low cost.Therefore,it is critical to develop drew solutes which can not only desalinate seawater,but also be recovered easily for the potential application of the Forward osmosis technique.To address this problem,magnetic Fe₃O₄ nanoparticles were first synthesized in this study and further modified to obtain functional magnetic nanoparticle drew solutes.Then,their structures,morphologies,magnetic properties,and forward osmosis performance were studied.Finally,the functional magnetic nanoparticle drew solute with the best forward osmosis performance was used for simulated seawater desalination experiment.The main research results are as follows:1.Magnetic Fe₃O₄ nanoparticles with the size of～80 nm were synthesized by a solvothernal process,and then modified by D-Xylose to obtain the Fe₃O₄/D-Xylose sample.XRD,FT-IR and TEM analysis results demonstrated that aldehyde groups（-CHO）of D-xylose were successfully loaded on the Fe₃O₄ surface,which did not change the crystal structure and morphology of the original Fe₃O₄ nanoparticles.The saturation magnetization of the Fe₃O₄/D-Xylose sample decreased from～56 emu/g of the original Fe₃O₄ sample to～37emu/g,which still met the magnetic separation requirement.The water flux values of Fe₃O₄and Fe₃O₄/D-Xylose samples were determined at～0.373 LMH and～2.085 LMH,respectively,when they served as drew solutes with the concentration of 5 g/L and ultrapure water was used as the feed solution.Their stabilities in acidic solution（p H=4.5）were investigated,which demonstrated that Fe³⁺leakage happened for both of them.The Fe³⁺concentrations for Fe₃O₄ and Fe₃O₄/D-Xylose samples reached～0.6 and 1.39 mg/L,respectively,which could cause the secondary iron pollution problem.2.To protect magnetic Fe₃O₄ nanoparticles to avoid the secondary iron pollution problem,carbon and SiO₂ shells were coated on their surface with glucose and tetraethyl silicate as rwa materials,respectively.It was found that the SiO₂ shell could effectively protect magnetic Fe₃O₄ nanoparticles.The Fe³⁺concentrations in acidic solution（p H=4.5）was only～0.07mg/L,which met the drinking water standard.For the C shell,however,it could not protect Fe₃O₄ nanoparticles effectively,and the Fe³⁺concentrations in acidic solution（p H=4.5）still reached～0.64 mg/L.The coating of either shell could enhance the dispersion of these Fe₃O₄nanoparticles,which subsequently improved their forward osmosis performances.When they served as drew solutes with the concentration of 5 g/L and ultrapure water was used as the feed solution,the water flux values of Fe₃O₄@C and Fe₃O₄@SiO₂ samples were determined at～0.893 LMH and～2.98 LMH,respectively.The effect of SiO₂ shell thickness on the water flux of the Fe₃O₄@SiO₂ sample was also investigated.The water flux values of Fe₃O₄@SiO₂-1,Fe₃O₄@SiO₂-2,and Fe₃O₄@SiO₂-3 samples with the SiO₂ shell thicknesses of～10,25 and 50 nm were determined at～2.98 LMH,～2 LMH,and～0.927 LMH,respectively,when their concentrations were fixed at 5 g/L and ultrapure water was used as the feed solution.Due to the good hydrophilicity of silicon oxygen（Si-O）groups,their water flux values with the SiO₂ shell increased by 149%-699%.3.Fe₃O₄@SiO₂/D-Xylose and Fe₃O₄@SiO₂-COOH functional magnetic nanoparticle drew solutes were created by the further modification of the Fe₃O₄@SiO₂-1 sample with the D-Xylose and sodium citrate dihydrate.The existences of hydrophilic aldehyde groups（-CHO）and carboxyl groups（-COOH）on the Fe₃O₄@SiO₂-1 sample surface were verified by FT-IR.The water flux values of Fe₃O₄@SiO₂/D-Xylose and Fe₃O₄@SiO₂-COOH samples were determined at～3.02 LMH and～4.58 LMH,respectively,when they served as drew solutes with the concentration of 5 g/L and ultrapure water was used as the feed solution.Thus,the Fe₃O₄@SiO₂-COOH sample had the best forward osmosis performance among samples we developed.When ultrapure water was used as the feed solution,its water flux values were determined at～4.58 LMH,～8 LMH,～13.69 LMH,and～20.32 LMH,respectively,with the concentration of 5,15,35 and 50 g/L.Finally,a 35 g/L Na Cl solution was used to simulate seawater as the feed solution and the 50 g/L Fe₃O₄@SiO₂-COOH was used as the drew solute to examined its forward osmosis seawater desalination performance.The result demonstrated that the Fe₃O₄@SiO₂-COOH sample could desalinate seawater with the water flux value of～0.75 LMH under current experimental conditions.Its saturation magnetization was～37emu/g,which endowed it an easy magnetic separation capability for recover and reuse.