Chemically Modified Graphene-based Sensors

Graphene is a monolayer of two-dimensional(2D)crystal.It has large specific surface area,excellent mechanical property,stable physical and chemical property and high electrical conductivity at room temperature.Therefore,graphene and its composites are ideal active materials for fabricating various sensors.In this dissertation,we investigated the electrochemical active sites of graphene,fabricated several graphene-based gas and strain sensors and characterized their performances.We coated the single-layer graphene sheet region-specifically with a non-conducting thin film,and obtained the edge-electrode and plain-electrode respectively.The electrochemical behavior at the basal plane of a single-layer graphene was compared to that of its edge.The graphene edge showed 4 orders of magnitude higher areal specific capacitances,and much higher electron transfer rate and stronger electrocatalytic activity than those of graphene basal plane.Coupling with the high conductivity of a high-quality graphene basal plane,graphene edge is an ideal material for energy storage and electrocatalysis.Fuctionalized graphene materials,including sulfonated graphene(S-G)or ethylenediamine modified graphene(EDA-G)were prepared through covalent functionalization.The ultrathin sensing sheets were prepared by dip-coating method and applied for chemoresistor-type nitrogen dioxide(NO2)sensors.Compared with the conventional RGO-based sensor,the S-G and EDA-G based sensors exhibited stronger responses.The responses of the sensors also showed good linear relationships in wide NO2 concentration ranges with good repeatability and selectivity.Furthermore,the fuctionalized graphene-based sensors can spontaneously recover to their initial states by flowing N2 gas.Reduced graphene oxide(RGO)sheets were self-assembled onto the surfaces of electrospun polymer nanofibers to form an ultrathin coating.These RGO/polymer composite nanofibers were used to fabricate NO2 sensor.This sensor can be performed at room temperature,and exhibited a high sensitivity of 1.03 ppm-1 with excellent selectivity and good reversibility.The limit of detection was experimentally measured to be as low as 150 ppb.Besides,the response and recovery speed had also been significantly improved.Renewable resource human hairs were employed as elastomer,and GO sheets were assembled onto its surface.After reduction we obtained RGO/hair composites and applied it for strain sensing.The obtained sensors were small,light and robust,which can be shaped into different structures such as fiber,spring and network due to the flexibility of hair.They can be used to detect various deformations including stretching,bending and compression.In practical application,the strain sensors can be used as a part of wearable electronics for the detection of finger motion,or as on-off pressure sensors.