Controlled Preparation Of Graphene Oxide Membranes And Its Application In Gas Separation

Membrane separation technology has become one of the most important methods in separation science because of its low energy consumption,high operating efficiency and little impact on the environment.Conventional gas separation membranes are mainly composed of polymer membranes,however,their performance is limited by Robeson upper limit,and the balance between selectivity and gas permeability is needed in the application.Recently,two-dimensional?2D?layered materials have attracted the interest of many researchers in advocating new separation membranes.Among these two-dimensional layered materials,graphene oxide?GO?membranes have a layered structure and sub-nano-pore size,and have large molecular sieve properties,so they have become the focus of the research field of separation membranes.However,there are still many problems in the application of GO in the separation field,such as poor mechanical strength and structural control,which are the key factors affecting its application.In order to further promote the application of GO in the field of gas separation membranes,we have done the following work:?1?The mechanical strength of pure GO membranes is poor,and the structure of GO membranes is not controllable enough,which also affects the separation and permeability of GO membranes.In order to improve its mechanical strength,the GO@Al₂O₃ composite membranes were prepared successfully by GO membrane supported by vacuum assisted suction filtration,and high strength porous hollow fiber ceramic membranes based on Al₂O₃ phase inversion method were used as the substrate to improve the overall strength of the membranes in this thesis.?2?In order to control the structure of GO membranes,the size and oxidation degree of GO membranes were controlled firstly.In this thesis,the flake size of GO was controlled by selecting natural flake graphite with different mesh number?50 mesh,325mesh?,and the oxidation degree of GO was controlled by controlling different oxidation conditions?oxidation temperature or time?during the preparation of GO.Separation membranes were prepared from different GO samples,and then the performance of gas separation was tested.The results show that the larger the size of GO lamellae and the higher the oxidation degree,the better the selectivity of GO@Al₂O₃ composite membrane.?3?In the aspect of structure control of GO membranes,the structure of GO membranes was controlled by adding different surfactants.In this thesis,different surfactants,such as sodium dodecylbenzene sulfonate?SDBS?,trisodium citrate?SC?,cetyltrimethylammonium bromide?CTAB?,were selected to modify GO and composite with porous Al₂O₃ hollow fiber membranes.The relationship between the additions of different surfactants and the structural changes of GO membranes was analyzed.It was found that in a selected surfactant,the separation ratio of H₂/N₂ and H₂/CO₂ was improved obviously by SDBS modified GO composite membranes,especially for H₂ and CO₂.The SDBS can effectively adjust that lay spacing of the GO membrane due to the?-?and hydrophobic interaction between the SDBS and the GO membrane.At the same time,the addition of SDBS can also improve the surface wettability of the membrane,which the-SO₃-can effectively increase the adsorption capacity of CO₂,thus improving the separation ratio of H₂/CO₂.At room temperature,the selectivity of H₂/CO₂ and H₂/N₂ was323 and 28 respectively.H₂ permeability was 8.1×10^-8 mol m^-22 s^-11 Pa^-1?H₂ kinetic diameter was 0.29 nm?,N₂ and CO₂ permeability was 1.83×10^-9mol m^-22 s^-11 Pa^-1 and 2.4×10^-10 mol m^-22 s^-11 Pa^-1,respectively.At the same time,the composite membrane can maintain good separation performance at high temperature?100??.In this thesis,GO@Al₂O₃ composite membranes were prepared to improve the mechanical strength of GO membranes,and the structure of GO separation membranes was controlled by controlling the size,oxidation degree and surfactant of GO.The method of preparing GO separation membranes in this thesis is simple and effective,and can be used for macroscopic preparation.This method provides some theoretical and technical support for promoting the application of GO in separation membranes.