Studies On Assembly Design And Performance Of Molecular Clusters Separation Membranes

With the ever-increasing demand for high-performance separation membrane materials,two-dimensional（2D）layered separation membranes have demonstrated broad application prospects in various fields such as gas,liquid,ion,and even nanoparticle separation due to their unique ultra-thin structure,high permeability,and good selectivity.However,the pursuit of high flux and selectivity in current 2D layered membranes often comes with the compromise of rejection rate,and issues such as easy swelling and poor stability in water also urgently need to be addressed.Therefore,the development of 2D layered separation membranes with high flux,high selectivity,and good stability has become a research hotspot.By exploring more 2D materials suitable for separation membranes,optimizing the nanochannel structure to improve separation efficiency,and deeply understanding the mass transfer behavior in nano-confined channels,it is expected to develop high-performance and widely applicable 2D separation membranes,driving the innovation of separation technology.This study capitalized on the advantages of 2D materials,employing graphene oxide（GO）and MXene as building blocks.By introducing polyoxometalates（POMs）and amino-modified metal-organic zirconium cages（Zr MOC）as nanospacers,precise regulation of 2D nanochannels was achieved.Utilizing the interaction between the intercalated molecules and GO or MXene nanosheets,2D separation membranes with stable layered structures were constructed,and their applications in ion,dye,and nanoparticle separation were thoroughly investigated.The main research contents are summarized as follows:1.A polyoxometalate-assisted in-situ photoreduction strategy was developed to prepare rGO-PW₁₂ membranes with high permeability.The interlayer channels were precisely confined to sub-nanometer sizes,enabling effective rejection of salt ions.The permeance of rGO-PW₁₂membranes for K⁺,Na⁺,Li⁺,Ca²⁺,Mg²⁺,and Al³⁺was only 0.00851,0.00802,0.00611,0.00591,0.00413,and 0.00166 mol m^-2 h^-1,respectively,which was reduced by approximately two orders of magnitude compared to GO membranes.Simultaneously,the strong hydrogen bonding and van der Waals interactions between rGO and PW₁₂ resulted in close interlocking of the rGO sheets,endowing rGO-PW₁₂ with excellent anti-swelling and stability.It maintained good block ability against Na Cl in ion diffusion experiments lasting up to 400 hours.When applied in forward osmosis process,the 270 nm-thick rGO-PW₁₂ membrane exhibited high water flux(0.11790 L m^-2 h^-1 bar^-1),Na Cl rejection rate（98.3%）,and excellent water/salt selectivity,surpassing most 2D nanomaterials reported in the literature.2.Based on the aforementioned strategy,2D rGO-POMs membranes with highly ordered and uniform nanochannels were synthesized by adjusting the size and structure of POMs,which were embedded between the interlayers of rGO membranes.The structure of the rGO-POMs membranes could be altered by adjusting the mass ratio of rGO to POMs.Different sizes of POMs clusters(PMo₁₂,{Mo₁₃₂},and{Mo₃₆₈}with the size of 1.0,2.9 and 3.8 nm,respectively)were employed as nanospacers to precisely regulate the size of nanochannels.The prepared rGO-PMo₁₂,rGO-Mo₁₃₂,and rGO-Mo₃₆₈membranes were used to separate carbon quantum dots and gold nanoparticles,which enabled precise rejection of nanoparticles larger than 1.0 nm,2.9 nm,and 3.8 nm,respectively,through size-exclusion effects.The uniformity and dispersibility of nanoparticles were significantly improved after filtration by rGO-POMs membranes.The cutoff size of the rGO-POMs membrane was in accordance with the size of the intercalated POMs clusters,suggesting that the effectively regulating of the interlayer spacing of the membrane could be achieved by adjusting the size of the intercalated POMs clusters.The sub-nanometer channels constructed by POMs clusters enabled the precise sieving of molecules and small nanoparticles（<5 nm）.3.To realize the efficient screening of two-dimensional layered membranes in the field of molecular separation,an effective multi-dimensional channel design strategy was adopted.MXene-Zr MOC membranes were prepared by intercalating amino-modified Zr MOC between the MXene interlayers as a nanospacer.The enlarged interlayer spacing of MXene layers and the inherent nanopores of Zr MOC enabled the MXene membrane to possess abundant nanochannels,which contributed to improved permeability of the membrane.The assembly of MXene nanosheets and Zr MOC was driven by electrostatic interactions,which facilated the forming of stable layered structure and effectively suppressed the swelling of the MXene-Zr MOC composite membrane in water.The permeability of MXene-Zr MOC membranes with different Zr-MOC loading was carried out.It was demonstrated that the MXene-Zr MOC membrane exhibited excellent separation performance during dye separation.When the mass ratio of the MXene to Zr MOC was 1:1,MXene-Zr MOC membranes exhibited extremely high water permeance(199.16 kg m^-2h^-1bar^-1)while maintaining high dye rejection（～100%）and low salt rejection（<5%）,thus enabling the efficient separation of salt and dye mixtures.