Constructing Two-dimensional Laminar Membranes Based On MoS₂

Water is an essential resource for human life.Nowadays,the problems of water pollution and water resources shortage are becoming more and more serious.The application of membrane separation technology to separation processes such as wastewater treatment and seawater desalination is expected to solve those problems.Although two-dimensional（2D）laminar membranes have important prospects in organic solvent nanofiltration,seawater desalination and other application fields,they still face huge challenges to realize industrial application,mainly due to the permeation flux and separation performance.Based on the above descriptions,how to precisely control the stacking behavior of these 2D materials,regulate the channels between 2D layers,optimize the structure of 2D laminar membranes,and improve the permeability,selectivity and stability of the 2D laminar membranes are all the problems that 2D laminar membranes need to face in the future development.This dissertation focuses on 2D laminar membranes.The laminar Mo S₂ based membrane was applicable to organic solvent nanofiltration and desalination separation processes.The specific research content is as follows:（1）The ultrathin 2D lamellar nanofiltration membranes were fabricated by layer-by-layer stacking Mo S₂ nanosheet building blocks.Mo S₂ based membranes have highly ordered and regular transport channels with narrowly distributed sizes,which enable high permeances and favorable rejections to be achieved.The D-Mo S₂membrane in the dry state with a thickness of 20 nm exhibits an exceptional water and acetonitrile permeance of 458 and 1371 L m^-2 h^-1 bar^-1respectively.The higher permeance of water and acetonitrile was gained by the S-Mo S₂ membrane in the solvated state with a thickness of 36 nm,which can reach 1881 and 5207 L m^-2 h^-1 bar^-1respectively.Both of D-Mo S₂ and S-Mo S₂ membranes give rise to good separation efficiency,e.g.,evans blue and methylene blue rejections of 100%.In addition,Mo S₂derived membranes show quite high stability toward high pressure,acid,base,and oxidative environments.（2）Polyvinyl alcohol（PVA）was used to regulate the interlayer channels of Mo S₂membranes to achieve high desalination rate.The incorporated PVA can occupy the interlayer channel of Mo S₂ membranes,thus inhibiting the penetration of various salts through the Mo S₂/PVA membrane.In ion permeation measurements,the Mo S₂/PVA membrane exhibits excellent ion exclusion performance compared with the pure Mo S₂membrane,which reduces the penetration rate of ions of different sizes by about 10-30times.In addition,Mo S₂/PVA membranes also maintain excellent long-term structural stability and cycling stability.In the forward osmosis seawater desalination process,the Mo S₂ membrane exhibited a water flux of 0.1 L m^-2 h^-1 and a Na⁺permeation rate of0.41mol m^-2 h^-1.However,Mo S₂/PVA membrane exhibited an extremely high water flux and low Na⁺permeation rate(0.15 mol m^-2 h^-1)compared with the pure Mo S₂membrane.