The Properties And The Anti-fouling Behavior Of MWCNTs Modified CA Forward Osmosis Membrane

In this paper,the MWCNTs/CA modified forward osmosis membrane was fabricated by phase inversion method,with cellulose acetate(CA)as membrane material,polyester screen mesh as supporting materials,acidified multi-walled carbon nanotubes(MWCNTs)as additive.The effects of MWCNTs on the forward osmosis membrane were discussed,including structure,hydrophilic,the pure water flux and reverse salt flux,the interception effect of conventional pollutants,etc.And the anti-fouling property of the MWCNTs/CA modified forward osmosis membrane was emphatically investigated.Firstly,quartz crystal microbalance with dissipation monitoring(QCM-D)was used to measure the adsorption of sodium alginate(SA)on the surface of different membrane,research the structure characteristics of adsorption layer under the condition of simulated seawater,and explore the SA fouling of forward osmosis membrane under different ionic conditions.Secondly,the adsorption of bovine serum albumin(BSA),humic acid(HA)and sodium alginate(SA)on the surface of membrane and the interaction which was between those typical organic pollutants and the membrane were measured by QCM-D and atomic force microscopy(AFM).Membrane fouling tests explored the adsorption mechanism of different organic pollutants on the surface of membrane.The main conclusions were showed as follows:(1)Effects of MWCNTs on FO membrane’s surface properties and internal structure: Based on the FT-IR spectra analysis,after adding MWCNTs,more hydrophilic functional groups like carboxyl and hydroxyl groups were introduced into membrane surface,and significantly enhanced hydrophilicity of the membrane.Through SEM analysis of the membrane surface morphology and sectional shape,with the increasing of MWCNTs,the modified membrane’s surface became rough and aggregate;fingerlike pore in cross section of the membrane increased,and the membrane’s pore structure got more open and macroporous.(2)Effects of MWCNTs on the permeability of FO membrane: With the increasing of MWCNTs(from 0% to 1%),the pure water flux of the modified membrane increased firstly and then decreased,while the reverse salt flux showed an opposite trend.When MWCNTs content was up to 0.5%,the membrane permeability was best,its hydrophilicity contact angle was 65.05°,and the pure water flux was 14.2 L/m2 h.,reverse salt flux was 8.54 g/m2 h.(3)Effects of MWCNTs on rejection of conventional pollution.The static forward osmosis experiment on artificial simulated sewage showed that every content of modified MWCNTs/CA membrane presented well on the removal of conventional pollutants(such as TDS,TP,TN,organics and so on)with no obvious difference.It meant that MWCNTs had little influence on retention performance of FO membrane.(4)Effects of different ionic conditions on SA fouling of the modified membranes under the condition of simulated seawater: The membrane flux declined quickly,and membrane fouling became aggravated when adding Ca2+,furthermore,SA adsorption rate and adsorption amount on the membrane surface increased,and the structure of SA adsorbed layer got more compact.Therefore,controlling the Ca2+ content in seawater is the key to solving the problem of membrane pollution during the process of desalination.(5)Effects of SA fouling with different content of MWCNTs on the modified membranes under condition of simulated seawater,SA adsorption amount and membrane flux decline rate became dropped with the increasing of MWCNTs(from 0% to 0.5%),Accordingly,SA adsorption layer structure becomes more loose and soft.However,when the MWCNTs content increased to 1%,the amount of SA adsorption on the membrane surface and membrane fouling rate increased,while the structure of SA adsorption layer tended to be dense.(6)The analysis and comparison of three kinds of typical organic membrane fouling(HA,BSA,SA)indicated that the adhesion between HA and membrane surface was the strongest,membrane fouling which HA caused was the most serious,and the adsorption rate and the adsorption amount on membrane surface was the maximum,while it formed loose soft adsorbed layer;SA second;the adhesion between BSA and membrane surface was the weakest,and the membrane fouling was the lightest.The adsorption rate and the adsorption amount on membrane surface was the minimum,while it formed compact adsorbed layer.