Designed Synthesis Of Asymmetric Graphene Oxide Membrane For Decolorization And Desalting

Due to the water as the human survival resource,its separation has attracted tremendous attention.The industrial pollution of water contained various toxic chemicals such as metal ions and organic pollutes,which caused serious harm to human health and environment.Among all water treatment methods,membrane technology is a popular alternative for its high efficiency,low cost,and the fact that it is environmentally friendly.Therefore,the key factor is the design and synthesis of high-performance membrane.However,presently available membrane shows varying degrees of limitations regarding poor mechanical properties and low selective performance and so on.It is also important to further understand the interrelationship between membrane structure and separation performance.Considering the characteristics of graphene oxide（GO）such as lamellar structure,high specific surface area as well as abundant oxygen-containing groups,these advantages promote the application of GO as a membrane separation material.In addition,the GO flake size is controllable and has different physical and chemical properties.Herein,we have designed and synthesized a series of novel graphene oxide membrane（GOM）with gas phase and solvent filter method.Furthermore,we also studied the relationship between the structure of membrane and selective performance of water treatment.Specifically,the work includes the following aspects:（1）Most GOM studies focus on the impact of oxygen-containing functional groups,ignoring the influence of GO inherent structure.Therefore,this work prepared different GO flake sizes by ultrasonic and centrifugation methods,and constructed asymmetric GO membrane（asy-GOM）with heterojunction in a very direct way.Remarkably,the mechanism of ion transport in asy-GOM was systematically studied by controlling electrolyte concentration and scanning rate.The results show that asy-GOM exhibits asymmetric ion transport under external electric field.This represents a new model to understand the role of the asymmetric cation-anion ratio at the nano-contacting interfaces,which might inspire other transport devices or structures for targeted applications.In addition,asy-GOM shows blocked ion transport behavior under the electric field,which has the prospect of seawater desalination application.（2）Aiming to address the issue of the swelling of GO in water,we have designed and synthesized a polymer-GO composite membrane.In this synthesis,the l-asparagine is regarding as bridging agent and formaldehyde was introduced into the interlayer by gas phase method to induce in situ polymerization reaction.And then,the performance of the composite membrane was systematically studied by controlling the ratio of polymer doping.At the same time,polymer-GO composite membrane with vertical heterostructure were obtained by changing the assemble modes of different GO flake sizes,based on the above heterostructure GO system.The results show that the rejection of composite membrane for methylene blue can reach 92%,the permeance can reach 161 LMH bar^-1,and the composite membrane has good stability in water.The preparation strategy was based on the gas phase method,and the composite membrane with vertical heterostructure was synthesized by layer by layer,which significantly improved the rejection of the composite membrane for dyes.