Study On Functional Group-Modification Of Graphene And Its Application In Electrochemical Detection

Graphene is a novel 2D carbon nanomaterial with unique physical structure and many excellence properties. Graphene based materials have drawn great attentions in electrochemical detection from its large specific surface area, high electron transfer ability and high electrochemical catalytic activity. However, there are still many unsettled problems such as the methods to functionalize graphene and the interaction mechanism between analyte and functionalized graphene, both hinder the in-depth research and further application of graphene material in electrochemical detection. In order to promote the fundamental research and real application of graphene, this thesis focuses on the modification of graphene with oxygen-, nitrogen- and sulfur-containing functional groups, as well as the impact of modification on the physical and chemical properties and electrochemical detection performance of modified graphene materials. New process and innovative results have been achieved as follows:(1) The species and amount of oxygen-containing groups were efficiently controled by adjusting the reaction time between graphene oxide(GO) and hydrazine hydrate. And the contribution of oxygen-containing functional groups to the electrochemical detection of Cu2+ was further investigated. We found that oxygen-containing functional groups, especially carboxyl, could make graphene material negatively charged from ionization of carboxyl in aqueous solution. The graphene materials with abundant surface negative charges are favourable for detecting positively charged Cu2+, which broadens our horizon in the understanding of graphene materials. We developed an effective method to prepare carboxyl-rich graphene quantum dots(GQDs) based on the coupling oxidation of GO by ozone and hydrogen peroxide under ultrasonic. This method is simple, easy to control and inexpensive, and the as-prepared GQDs are highly purified.(2) We further investigated the influence of different nitrogen-containing functional groups like amino and nitrogen species in the carbon skeleton of graphene on its electrochemical detection performance. Especially, this thesis compared the influence of amino and nitrogen species in the carbon skeleton on the suface potential of graphene material using many characterization methods of batchequilibrium method, Zeta potential and CV. We found that the protonation of amino could make the surface of modified graphene positively charged that could improve the electrochemical detection performance of graphene material towards negatively charged analyte.(3) In this thesis, homogeneous thiophene S-doped graphene had been successfully synthesized through reaction between GO and sulfate. S-containing species and doping level could be easily tuned. Additionally, abundant micropores and some in-plane pores in the surface of graphene were formed during S-doping. The electrochemical behavior of dopamine(DA) on the homogeneous thiophene S-doped graphene electrode was systematacially investigated and thiophene S doped graphene exhibited high selectivity and sensitivity due to its unique physical and chemical structures.(4) We presented the nitrogen- or sulfurmodification and simultaneous electrochemical reduction of GO with a mild electrolysis method, in which nitrogen and sulfur-containing substance was dissolved or dispersed in the electrolyte and reacted with GO or reduced GO in the process of electrolysis. We took electrolyte additive ethylenediamine as an example for further investigation. We found that ethylenediamine was grafted onto GO by nucleophilic substitution with epoxy groups and amidation with carboxyl, and the resulting nitrogen-containing graphene oxide was sequentially reduced by negative electrolysis while amide groups were converted to second amino groups. The as-prepared graphene material showed great conductivity and high electrochemical activity.