The Influence of Solution pH on the Self-Assembly Structure and Properties of Oxidized Graphene Films
Compared to graphene,graphene oxide(GO)has advantages in stability,solubility,functional modification,and application as a carrier,making it more practical and valuable in catalysis,separation and filtration,sensing,energy storage,and other fields.In the macroscopic assembly process of GO,the acidity and alkalinity of the solution strongly affect the self-assembly process of GO,but the rules of its influence are not yet clear.Therefore,by adjusting the pH of high concentration GO solution,GO thick films were prepared,and the effects of changes in the interaction force between GO and dispersion medium on GO assembly and macroscopic assembly material properties were studied.The research results show that the various properties of thick GO membranes vary significantly with the change of solution pH value.When the pH of the GO solution is weakly alkaline(pH=9),the film forms,and the tensile strength of the GO film reaches 229.29 MPa,which is more than 7 times the strength of the GO film at pH=4.At the same time,when the pH of the GO solution is 9,the film forms,and the conductivity of the GO film is 27800 S/m,which is more than 1.7 times the pH=4.A series of analysis results indicate that when the solution pH is weakly alkaline,some hydroxyl and carboxyl groups on the surface of GO are reduced,resulting in the presence of both oxidation and sp2 carbon regions on the layer.Hydrogen bonding and electrostatic repulsion forces induce the surface arrangement of the layer,while π-π forces drive the tight stacking of the layer.When the proportion of sp2 carbon regions approaches the oxidation region,the assembly driving force shifts from hydrogen bonding interaction to hydrogen bonding and π-π interactions.It was ultimately found that when the ratio of the two forces differs significantly,it can lead to a larger interlayer stacking distance(greater hydrogen bonding force)or a decrease in stacking arrangement order(greater π-π interaction).Therefore,when preparing macroscopic materials with GO as the main component,the acid-base environment of the solution will greatly affect the orderliness and application performance of the assembled structure.This study has certain inspirational significance for the structural design and performance improvement of graphene based macroscopic materials.Graphene films have excellent thermal conductivity and conductivity,flexibility and robustness,and can be used as candidates for electronic products.
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