Fabrication And Application Of Graphene Oxide Based Humidity Sensors And Actuators

Graphene,as a two-dimensional carbon crystal with one-atom thickness,is the basic unit of carbon materials including graphite and carbon nanotubes.Since graphene was successfully prepared in 2004,researchers have conducted extensive researches on it.Due to the unique physical and chemical properties,graphene has become a rising star in various fields.As a derivative of graphene,graphene oxide attracts the attention to fabricate graphene-based devices because of mass production,solution-processing,and controllable physical/chemical properties.We summarized the properties,preparation,reduction,and device fabrication and applications of graphene oxide.However,we found that the development of graphene-based devices through graphene oxide reduction technology still faces problems,such as(1)less methods to control the properties of graphene oxide;(2)the reduction of graphene oxide and preparation of device are not compatible;(3)complex procedures for fabricating graphene-based devices;(4)limited applications.As we known,there is a strong interaction between graphene oxide and water molecules,which has advantages in humidity sensors and humidity actuators.We can tailor the type,quantity,and distributions of oxygen containing groups by tailoring the surface and interface properties,which is helpful to tailor electrical and mechanical properties.However,it fails to control properties of graphene oxide by thermal reduction,chemical reduction,and photo reduction.There still exists barriers to develop humidity sensors and humidity actuators based on graphene oxide.Therefore,we fabricated reduced graphene oxide-based humidity sensors and humidity actuators by tailoring of the surface and interface properties of graphene oxide.The main results are as follows:1.The humidity sensors based on reduced graphene oxide prepared by sunlight.The sunlight reduction of graphene oxide can tailor the micro/nano-structure,oxygen containing groups content,and electricity of reduced graphene oxide.Furthermore,we control the sensitivity and response/recovery time by this method.Sunlight-reduced graphene oxide enables humidity sensors,which does not need complex experimental procedures or special instruments.The entire preparation process is very simple and green.Our humidity sensor shows good humidity stability.Finally,we used our humidity sensors to control circuit(such as: human finger recognition,moisture controller,moisture detector,and electronic harmonica).2.The humidity responsive graphene oxide paper prepared by self-controlled photoreduction.The transmittance decrease of graphene oxide is related to the thickness increase.The oxygen containing groups on the surface/interface of graphene oxide are effectively tailored by the controlled photoreduction technology.Consequently,the anisotropic graphene oxide/reduced graphene oxide bilayer structure can be easily prepared by tuning the photoreduction gradient.Due to the different adsorption capacities of water molecules on both sides,the film will bend to reduced graphene oxide side when the humidity increases.The stimuli-responsive film prepared by this method is based on a solo carbon material,which overcomes the problem of poor interlayer adhesion and poor stability during the frequent bending.In addition,through the rational design,we prepared graphene oxide/reduced graphene oxide with specific bending angles and various reduced graphene oxide patterns.Finally,we developed humidity responsive claw,orientable transporter,crawler paper robot,cilia,and tendril.3.The graphene oxide-based humidity responsive actuator with an asymmetric structure.We prepared graphene oxide-based humidity responsive actuator with an asymmetric structure based on the phenomenon that the interaction between water molecules and graphene oxide initiates the increase in the distance between the graphene oxide layers and the slippage between graphene oxide layers.Due to the asymmetric structure,the film can bend when humidity increases,which shows larger deformation and shorter response/recovery time.Besides,directional bending,spiral bending and chiral bending can be realized by cutting size,cutting angle and cutting direction.Finally,an asymmetric structure of graphene oxide humidity responsive films can be used to capture ladybugs and prepare humidity responsive windmills and crawl centipede.4.The humidity responsive slippery liquid infused porous surface.The slippery liquid infused porous surface was used as the non-responsive layer in the graphene oxide humidity responsive film,which contributes to enlarging the difference in the adsorption capacity of water molecules between the bilayer.The curvature of humidity response of the film increases,and the humidity response/recovery time is shorter.Finally,we used this humidity responsive slippery liquid infused porous surface to realize droplet slipping by humidity changes.In summary,we start with the interaction between water molecules and graphene oxide,which influences the electrical and mechanical properties of graphene oxides.The reduction degree of the graphene oxide is controlled by sunlight.The oxygen containing groups on the surface/interface of graphene oxide are effectively tailored by the controlled photoreduction technology.The microstructure tailored graphene oxide interface properties.Slippery liquid infused porous surface tailored graphene oxide surface properties.Besides,we developed humidity sensors based on reduced graphene oxide,humidity responsive graphene oxide/reduced graphene oxide bilayer film,graphene oxide-based humidity responsive actuator with an asymmetric structure,and humidity responsive slippery liquid infused porous surface.Finally,we explored their potential applications in electronics,materials,biomimetic and mechanical fields.