Study On Preparation And Dye Separation Performance Of Graphene Oxide Membranes

Graphene oxide?GO?,as a typical two-dimensional material,has become an emerging separation membrane material due to its unique laminar structure and tunable physical and chemical properties.The separation membranes assembled by GO have received extensive attention in recent years owing to its remarkable molecular separation performance in areas such as water purification,desalination and gas separation.In this paper,GO was modified by hydrothermal reduction and filling with MoS₂ and V2O₅ nanometer materials,and the separation membranes with layered structure were prepared on polyvinylidene fluoride?PVDF?substrate by vacuum filtration.The changes of chemical properties and interlayer structure characteristics of modified GO membranes were analyzed,and the influence of modification on its separation mechanism and separation performance were studied systematically.The primary results are as follows:The reduced graphene oxide?rGO?was synthesized by a green hydrothermal reduction method,and the rGO membranes was prepared on polyvinylidene fluoride?PVDF?supporting membranes by vacuum filtration.By controlling the hydrothermal time to adjust the reduction degree of GO,the influence of reduction degree on its interlayer structure and properties was investigated in detail,and then the permeability of rGO membranes with different reduction degrees was evaluated.The results show that with the increase of hydrothermal time,the water flux increased continuously.When the hydrothermal time was performed for 9 h,the pure water flux of the rGO membrane was26.08 L m^-2 h^-1 bar^-1,which was about 4 times that of the GO membrane,and the rejection for methyl blue was 98.92%.The hydrothermally reduced membrane had both mechanical stability and long-term stability,which had high rejection for various dyes.Two-dimensional MoS₂ nanosheets,prepared by a facile liquid-phase exfoliation method,were decorated onto rGO by physical blending.Then MoS₂-rGO membrane was prepared by vacuum filtration.The effects of MoS₂ loading on the interlayer structure and properties of rGO were explored,and the effects of the introduction of MoS₂ on rGO nanochannels and the transport mechanism of water molecules in the membrane were analyzed and explained.The results show that MoS₂ promotes the formation of nanochannels and improves the hydrophilicity of the membrane,which facilitates the transport of water molecules in the membrane.With the increase of MoS₂ loading,the water flux of MoS₂-rGO membrane gradually increased,but its rejection gradually decreased.When the MoS₂ loading was 33.33%,the water flux of MoS₂-rGO membrane was 118.21 L m^-2 h^-1bar^-1,which is about 4.4 times that of rGO membrane and 18.1 times that of GO membrane,and MB rejection is 88.72%.V₂O₅ was intercalated in rGO by two distinct methods,blending and in-situ synthesis.Then V₂O₅-rGO and V₂O₅@rGO membranes were prepared by vacuum filtration.The differences in chemical properties,hydrophilicity,structure and micro-morphology of the as-prepared membranes were analyzed,and the superiority of their separation properties was explored.The results show that during in-situ synthesis of V₂O₅@rGO,V₂O₅ and rGO were closely stacked to form a uniformly distributed lamellar structure with almost no agglomeration,which effectively adjusted the interlayer spacing and optimized the structure and properties of rGO.However,the simple blending of V₂O₅-rGO was uncontrollable and non-uniform,which was prone to agglomeration.The water flux of V₂O₅-rGO membrane increased significantly with the increase of V₂O₅ nanowires loading,but the rejection significantly decreased.V₂O₅@rGO membrane showed excellent separation performance without sacrificing the retention rate.Its water flux was 158.05 L m^-2 h^-1 bar^-1?about 5.4 times that of rGO membrane?,and the MB rejection was 99.41%.In addition,V₂O₅@rGO membrane has better long-term stability than V₂O₅-rGO membrane,and its rejection retains nearly 100%for various dyes.