Synthesis And Research On The Properties Of Large-size Graphene Sponge

Graphene is a novel nano-material with outstanding properties such asexcellent mechanical, thermal, electrical performances and so on, which make it hasmany promising applications in various fields. Preparation of macroscopic structurebased on self-assembled grephene has greatly promoted the large-scale applicationsof graphene. Nano-porous material, a new type of porous material, has high porosity,high specific surface area and possess distinct mechanical, optical and electricalproperties. These properties make nano-porous materials play an important role inmaterials scientific research, economic construction and other fields. The engineeredporous structures based on graphene will offer combined excellent properties ofgraphene on the micro-scale and porous materials on the macro-scale. Hence, it is ofgreat significance to assemble graphene into macro-sized graphene networks withporosity structure. In this thesis, a new type of macroscopic structure based on threedimensional, high porous, large-size graphene networks, namely graphene sponge,ware prepared in a controllable way. Firstly, graphene oxide was prepared as the rawmaterials for the preparation of graphene sponge. Secondly, we made a study of thecontrollable preparation of large-size graphene sponge and its basic performanceespecially for the sorption properties of graphene sponge for organic solvents and thefiltering capabilities of trapping dye molecules from water, aiming at laying afoundation for the practical application of graphene sponge.Large-size graphene sponge is controlled synthesized by directionalsolidification freeze-drying method with graphene oxide as raw materials andhydrazine hydrate as reductant respectively. The maximum size of the preparedgraphene sponge can reach400×600×15mm3. On the micro-level, the graphenesponge consists of many graphene pieces, which intertwine with each other and self-assemble into a porous, highly interconnected and three-dimensional framework. Onthe macro-level, freestanding graphene sponge has many performances that thetraditional porous materials are very difficult to have, such as low densities of2.4±0.2mg/cm3, porosity of larger than99%, hydrophobic,conductive,low thermalconductivity,uniform structure, high stability and so on. The apparent density,porosity and microstructure of the graphene sponge can be controlled by modulatingthe freeze-drying process parameters and the concentration of the solution ofgraphene oxide. The sorption properties of graphene sponge for organic solvents have beenstudied. Compared with traditional oil-absorbing materials，the graphene sponge issuper-hydrophobic, lipophilic and active to a wide range of solvents with fastsorption rate, large sorption capacity and excellent recyclability. The sorptioncapacity is up to226~567times the sponge weight for the organic solvents withdensities of0.788~1.595g/cm3and the sorption capacity increases with the decreaseof the organic solvents. After adsorption, the organic solvents can be removed simplyby combustion, and the graphene sponge can be used for multiple times. After5cycles of absorption and desorption tests, the saturated adsorption amount of petrolwas up to80g/g and the desorption rate was still over96%. We have also studied thefiltering capabilities of graphene sponge for trapping dye molecules from water, Itturns out that when the filter amount was less than0.35L/g, the filter efficiency ofMO was as high as100%. Thus the graphene sponge has very broad applicationprospects in the field of sewage treatment.