Fabrication Of A Novel Nickel-based,Metal-organic Material@Graphene Two-dimensional Heterostructure For Water Desalination

Compared with thermal evaporation methods,membrane separation technologies have the advantages of low energy consumption and simple process,and thus,are considered to be one of the most important directions for water desalination.The separation membranes based on two-dimensional materials have been extensively studied in water desalination due to their unique layered structures and adjustable interlayer spacing.Graphene oxide(GO)is one of the most commonly used twodimensional materials.It contains rich oxygenated functional groups,is highly hydrophilic and easy to disperse in aqueous solutions.Meanwhile,the prepared membranes have sub-nanometer interlayer spacing,which can achieve high rejection rate to hydrated ions.However,the interlayer spacing of GO membranes is unstable,easy to swell,and has relatively low water flux because of the oxygenated functional groups that can block the water flow,resulting in their unsatisfactory overall performance in water desalination.In order to solve these problems,this project is aimed to modify GOs with Ni-p-phenylenediamine(Ni-PPD)and fabricate NiPPD@rGO 2D heterostructured materials to replace GO nanosheets in improving the desalination performance.Based on this,the La3+-intercalated Ni-PPD@rGO membranes were also carried out by vacuum-filtration method with adjustable interlayer spacing,in order to optimize the performance of the Ni-PPD@rGO membranes further.The main contents are as follows,(1)Fabrication of 2D Ni-PPD@rGO heterostructured materials for water desalination.A Ni-PPD@rGO material was prepared by in-situ reduction of GO from Ni-PPD with Ni as the core and p-phenylenediamine as the ligand.It reduces the oxygenated functional groups on GO lamellas and increases the graphitic region in the lamellas,so that the newly synthesized Ni-PPD@rGO membranes has improved resistance to swelling and high water flux.Meanwhile,the re-stack of Ni-PPD on the rGO lamellas introduces about 2.6 ? sub-nanometer channel between the layers,which improves the separation performance towards various hydrated ions.Hydrated Mg2+and hydrated Ca2+ were almost completely separated.The smaller monovalent hydration Na+and hydration K+permeation rate were only 0.0015 mol.m-2 h-1 and 0.0013 mol.m-2 h-1.(2)Fabrication of La3+-intercalated Ni-PPD@rGO composite membrane for water desalination.The Ni-PPD rearrangement in interlayer introduces sub-nanometer channels in Ni-PPD@rGO membranes,which greatly improves the membrane separation performance,but the small layer spacing results in a relatively low water flux.In order to improve the water flux of Ni-PPD@rGO membranes and sustainably improve the separation performance of the membranes,the La3+ was inserted stably between restacked layers through a simple vacuum-filtration method,and the sub-nanometer channels of the composite membranes are adjusted,increasing the water flux by 6-7 times and retaining the ion separation property so as to achieve excellent overall performance of the novel membranes.