Effect Of MoS₂ On The Performance Of Forward Osmosis Membranes And The Mechanism

FO desalination is an emerging membrane technology with a range of possible water treatment applications.However,the major obstacle of this technology is the lack of an adequate membrane that possesses high water permeability,high solute rejection,superior antifouling property and good stability.To date,all FO studies with commercial and recently developed membranes showed that ICP and membrane fouling are mainly responsible for decline in water flux.In previous studies,these two problems have been addressed separately.Since ICP and membrane fouling often occur in tandem in FO processes,it is desirable to develop a single solution for both.Today the MoS2 nanosheet is a kind of promising membrane modification materials which holds excellent hydrophilicity,exceptional separation capability,multifunctional and anti-fouling properties.The hydrophilicity of MoS2 is beneficial to decrease the ICP problem.As well as,there is on conjugated structure in MoS2 which could help avoid the organic fouling problem.In this paper,MoS2 is used for the FO membrane modification in order to improve the hydrophilicity of the existing FO membrane and to reduce the structural parameters and ICP.Furthermore modification could increase the water flux and at the same time improve the antifouling performance of the membrane.The main research contents and results of this paper are as follows:(1)MoS2-coated-membranes were prepared by LbL self-assembly method.The SEM and EDS characterization results showed that MoS2 nanosheets have been successfully loaded on the surface of the FO membrane.The surface roughness of the modified membrane is significantly reduced,which helps to reduce the interaction of pollutants with the membrane surface,thereby reducing membrane fouling problems.The contact angle of the MoS2-coated-membrane decreased by 40.25%,indicating that the hydrophilicity of the membrane was significantly improved.In addition,the porosity and the average pore size were increased,which was beneficial to the decrease of structural parameters and ICP,and thus to improve the water flux.All membranes had higher water fluxes and relatively lower reverse salt flux under the four different valence state draw solutions.When the draw solution is 1M NaCl,the water flux of the MoS2-coated-membrane increased by 35.34%,while the reverse salt flux decreased by 26.67%.In the BSA cycle pollution experiment,the MoS2-coated-membrane always maintains the highest water flux.After physical cleaning,the water flux recovery rate also maintains the highest level,exhibits better anti-pollution performance.(2)PES powder was used to synthesize self-made forward osmosis membrane by phase transfer method.MoS2 powder with different concentration gradient was used to modify the membrane material.The lateral SEM results indicate that the porosity and the pore size increases after MoS2 incorporation.This result is consistent with the porosity and average pore size measurements,and the optimum incorporation amount of MoS2 is 1%.This result is beneficial to relieve the ICP problem,thereby greatly reducing the reduction of water flux.In addition,The hydrophilicity at the top of the basal layer increased after merging into MoS2.The increase hydrophilicity of the substrate is conducive to the formation of a thinner finger hole active layer,which avail a high water flux.The smoothness of the MoS2 itself reduces the surface roughness of the modified membrane by 45.46%,which is contribute to alleviate the membrane fouling.In the three different concentrations of NaCl draw solutions,all membranes have high water flux,and the increase of water flux is proportional to the increase of draw solution concentration.However,the reverse salt flux increases significantly as well with the increase of draw solution concentration.Js/Jv result shows that 1 M NaCl solution is a suitable draw solution.Js/Jv tends to stabilization after the incorporation of MoS2.In summary,FO membranes that modified by different methods have high water flux and relatively lower reverse salt flux,and show excellent antifouling property.Consequently,the MoS2 membrane with a wide range of applications prospect provides a new FO membrane for desalination.