| Graphene,which is a two-dimensional(2D)crystal material arranged in a close-packed honeycomb(hexagonal)lattice with sp2 hybridization of carbon atoms,has received world-wide attention since it was discovered in 2004.Both professor AndreGeim and Konstantin Novoselov successfully isolated free-standing graphene from graphite in the University of Manchester.Due to this novel discovery,they won the Nobel Prize in physics in 2010.From then on,research on graphene based materials ushered in a boom.Graphene has various unique and excellent properties,such as good transparency,high electrical and thermal conductivities,inherent flexibility,great mechanical strength and an extremely high theoretical specific surface area(2630 m2g-1).These properties have made it as an ideal candidate for a broad range of application including optoelectronic devices,energy storage,environmental protection and biomedicine.However,driven by multiple non-covalent intermolecular forces such as π-π interaction,hydrogen bonding and van der Waals force,irreversible agglomeration or restacking often occurred.And this can bring about chemical inertness,poor dispersion and serious low conductivity,mechanical strength and accessible surface area,giving certain restrictions on the scale-up of application in the practical life.How to maximize the intrinsic properties of monolayer graphene and expand its practical application is still a great challenge.An effective way to solve the above-mentioned problem is functionalizing or assembling individual graphene sheets into hierarchical porous three dimensional(3D)network materials.In this paper,we focus on how to solve the scientific problem of graphene in the preparation and application.Through the functionalization or self-assembly of individual graphene sheets,we finally gained three different multi-functional graphene hybrid aerogels using graphene oxide(GO)precursor.Then the formation mechanism of graphene aerogels was systematically analyzed.Meanwhile,the performance and practical application of the graphene composite aerogel were further investigated.The main results of this dissertation are summarized as follows:1.Hydrothermal self-assembly mechanism of graphene aerogelMacroscopic three dimensional(3D)hierarchical porous graphene aerogels were successfully fabricated by the self-assembly of individual GO sheets combining the hydrothermal reduction and freeze-drying technology.According to handling the concentration of GO,reaction time and temperature,corresponding graphene aerogels could be obtained.Also,the morphology and microstructure of these aerogels were characterized.It is demonstrated that the above three experimental parameters played an important role in the self-assembling process of graphene hydrogels.And they were in the critical state when the concentration of GO,reaction tme and temperature were 2.5 mg mL-1,6h and 110℃,respectively.Especially,the reaction temperature was crucial in the formation of hydrogel.In addition,the introduction of nanoparticles was beneficial to the hydrogel.Finally,the theories of solution-sol-gel and thermodynamic equation were used to give a rational explanation for the formation of graphene hydrogels during the hydrothermal reaction.2.Study on the performance of three-dimentional reduced graphene oxide/gold nanoparticle aerogel(3D rGO/Au NPA)A three-dimensional(3D)porous structure called reduced graphene oxide/gold nanoparticle aerogel(rGO/Au NPA)was built by individual GO sheets and HAuCl4 through the reduction of trisodium citrate dihydrate(Na3Cit)involving hydrothermal,freeze-casting and annealing treatment.The results of FESEM and TEM demonstrated that large amounts of gold nanoparticles with an average diameter of 31.6nm were well immobilized on the surface of graphene.To a certain extent,they could prevent the graphene sheets from restacking and aggregating.Series of characterization techniques indicated that the 3D rGO/Au NPA exhibits many excellent properties such as ultralow density(35.18 mg cm-3),huge specific surface area(37.8325 m2 g-1),high porosity and good thermal stability.In the presence of NaBH4,the material showed an outstanding catalytic activity(96.9%)within 18 min and good reusability towards the reduction of 4-nitrophenol(4-NP).And the 3D rGO/Au NPA was not only mechanically flexible(Young’s modulus of 30.8 kPa)but also the ideal candidate as adsorbent with high uptake capacity for removing organic pollutants.Moreover,it showed a high specific capacitance of 363F g-1.Interestingly,the GO sheets and gold nanorods could not assemble into 3D aerogels due to the opposite charges,as proved by the results of Zeta potential.3.Research on the preparation and performance of graphene/cadmium sulfide nanowire aerogel(RGO/CdS aerogel)A binary composite with interconnected networks named graphene/cadmium sulfide nanowire aerogel(RGO/CdS aerogel)was obtained after ultrasonication,hydrothermal and freeze-drying stratigies.The abundant CdS NWs with an average diameter of-43 nm and length in 4-6 μm range could be easily incorporated into the layers of graphene.A sery characterization results demonstrated that GO could capture the free nanoparticles in the solution during the self-assembly process.The obtained RGO/CdS aerogel showed excellent thermal stability,large specific surface area(47.6723 m2 g-1),rich porosity and extremely high absorption capacities toward organic liquids.Also,the efficiency for degradation of methylene blue(MB)and Rhodamine B(RhB)was 96.60%and 96.58%,respectively.The as-prepared aerogel not only exhibited fluorescence quenching and a high specific capacitance of 255F g-1,but also possessed an outstanding conductivity of 2.694x1 0-3 S/cm,which is an attractive property for potential application in flexible conductor.4.Synthesis,properties and application of graphene/titanium dioxide nanospindle aerogel(T1O2/RGO aerogel)We developed a synergistic assembly strategy for the fabrication of interconnected 3D structure named graphene/titanium dioxide nanospindle aerogel(TiO2/RGO aerogel)integrating with hydrothermal reduction,freeze-drying and annealing treatment.Large number of TiO2 Nanospindles with an average length of 206 nm could be evenly coated on the surface of graphene and regarded as separate layers.Both reaction time and temperature had an important effect on the internal structure and morphology of the products during the hydrothermal reaction.According to series of characterization techniques,TiO2/RGO aerogel also offered the integrated properties of high porosity,low density(23.61 mg/cm3)and large specific surface area(63.7162 m2 g-1).It also performed more superior organic solvents adsorption capacity and specific capacitance(345.2 F g-1)compared with pure graphene monolith and P25/RGO aerogel.The ultraviolet-light-driven photocatalytic efficiency of MB and RhB were 97.95%and 98.26%,respectively.In addition,the as-prepared material was fluorescence quenching and electrically conductive with a conductivity of 3.82×10-3 S/cm.In the end,the TiO2/RGO aerosol could be used as skeleton for fabrication of flexible electronic skin model after injection of PDMS.5.Application of graphene aerogels and their composites in supercapacitors3D rGO/Au NPA,RGO/CdS and TiO2/RGO aerogels,as well as other graphene aerogels obtained at different temperature were investigated as the electrode materials for supercapacitors by using cyclic voltammetry(CV).The experimental results showed that excellent electrical conductivity,high porosity and large specific surface area of graphene aerogels were responsible for the enhancement of capacitive performance.The graphene aerogels with highly open porous structures provided abundant paths for the transmission of electrons and ions,which was beneficial to allowing electrolytes access to the surface of internal frameworks.Meanwhile,the incorporation of nanoparticles into graphene sheets not only stopped the layers from re-stacking,but also increased the number of pores,giving a potential application in supercapacitors. |
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