Fabrication Of Graphene/Molybdenum Disulphide Composite Nanofiltration Membranes And Its Performance Study

With the advancement of industrialization in the world,global water pollution and water shortage have gradually become obstacles to modern economic and social development,posing a serious threat to public health.In this context,a variety of advanced water treatment technologies are gradually being developed and applied in practical research.Membrane separation technology stands out among other water treatment technologies for its low environmental impact,ease of operation and high efficiency.In recent years,with the development of two-dimensional materials,graphene oxide（GO）,a new type of two-dimensional material,has received wide attention from researchers and been applied to membrane separation due to its thin two-dimensional structure,good mechanical properties and other advantages.However,due to the abundance of oxygen-containing functional groups,graphene oxide membranes are prone to hydration in water,resulting in very low water flux and poor stability.In order to improve the water flux and retention performance,this dissertation explores the preparation of new composite membranes by embedding molybdenum disulfide（Mo S₂）and mild hydrothermal reduction of graphene oxide.Its main contents are as follows:（1）Molybdenum disulphide nanosheets were prepared by hydrothermal methods using sodium molybdate and thiourea as raw materials.The morphology and chemical structure of the preparations were analysed using electron microscopy（SEM）,Raman spectroscopy（Raman）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）,and the results showed that the prepared molybdenum disulphide had a structurally stable 2H-type structure.（2）After pretreatment of the clustered molybdenum disulphide,The composite nanofiltration membrane of GO/Mo S₂ was successfully prepared by filtering Mo S₂ and GO on a PES substrate membrane through vacuum filtration.The experimental results showed that the membrane performed best when the GO content was 0.5 mg and the Mo S₂ content was 0.45 mg,and the flux of pure water could be up to 22.5 L/（m²·h·MPa）,which was 6.8 times that of the pure GO membrane,and the retention effect on direct red80（AR）dye and methyl blue（MB）dye was 98.8%and 96.7%respectively,and the retention on different concentrations of MB dye was The retention of different concentrations of MB dyestuff reached more than 95%.The percentages of retention for Na₂SO₄,Mg SO₄,Na Cl and Mg Cl₂ were 64.1%,50.2%,39%and 25%correspondingly,and the retention rules for the four salt solutions were satisfied:R（Na₂SO₄）>R（Mg SO₄）≈R（Na Cl）>R（Mg Cl₂）.At the same time,the composite membrane has good stability performance as it has not been damaged by immersion in pure water for thirty days.（3）On this basis,a mild hydrothermal reduction of GO was carried out to prepare RGO/Mo S₂ composite nanofiltration membranes.It was found that the surface morphology of the composite membranes was observed by using scanning electron microscopy（SEM）and the roughness was found to increase gradually using atomic force microscopy（AFM）.As the Mo S₂ content increases,the d-spacing increases compared to the pure GO film,while the contact angle becomes larger at 84°,which contributes to the stability of the film in water.Composite membranes have a higher electronegativity than GO membranes and have a better retention effect on dyes.The experimental results show that the RGO/Mo S₂ composite nanofiltration membrane can be up to 35 L/（m²·h·MPa）with a favourable retention rate of 86.7%for sodium sulphate,while the different salts also satisfy the retention rate of R（Na₂SO₄）>R（Mg SO₄）>R（Na Cl）>R（Mg Cl₂）.The composite membrane had good retention rates of 97.8%and 98.6%for methyl blue and Congo red,and above 95%for Congo red at different p H values and concentrations.In addition,the composite nanofiltration membranes showed no damage under immersion in different p H environments,and the retention performance of the membranes for dyes remained almost unchanged under staggered flow conditions for 50 h,indicating that the membranes maintain good stability in both static and dynamic conditions.