Preparation And Applications Of Graphene Aerogel

Graphene aerogel, as a unique three-dimensional nano carbon material, is formed by the crimping and stacking of nanosheets based on the two dimensional graphene as a building block. It has ultralow density, high specific area and porosity, and high conductivity and shows great potential in many fields, such as absorption, catalyst support, energy storage and conversion, environment, sensors and so on.In this thesis, compressible 3D graphene aerogel with uniform structure, rich porosity, and excellent mechanical property was prepared by a simple and efficient method. The work focuses on:1. Graphene oxide(GO) was successfully prepared by modified Hummers’ method and characterized by means of AFM, XRD, Raman spectra and TGA. GO shows single layered structure with a sheet thickness 1.2 nm. Oxygen-containing groups were introduced into the sheets resulting in the decrease of thermal stability. The weight loss at 600 oC in N2 atmosphere was 38%.2. Graphene arogel(GA) was prepared by one-step reduction and self-assembly of GO with urea as reducing agent and then freeze-drying. We studied the effects of urea content, reduction time and temperature on the structure and properties of GA. With the increasing of urea content and reaction time, the volume of GO hydrogel decreased and tended to be stable with 1:5 mass ratio of GO to urea and a reaction time of 24 h.3. The density of GA decreased with the increase of reduction temperature. At 85 oC, the density of GA was only 4.7mg/cm3, which belongs to ultra-light material. SEM analysis revealed that rich porous structure formed in GA, and honeycomb structure with uniform porous diameter of 60 μm were constructed in GA reduced at 90 oC. After reduction with urea, the thermal stability of GA was improved compared with GO, the weight loss at 600 oC was 23%. The GA showed excellent mechanical property with stress of 6.34 kPa at 50% strain.4. 3D rich porous GAs with different density were prepared successfully by regulated the concentration of GO water solution. The density of GA can be adjusted from 6.3 mg/cm3 to 9.9 mg/cm3. During the reduction and self-assembly process, parts of oxygen-containing groups were removed and a little amount of nitrogen element was introduced into GA. GA had relative smooth surface, porous inner structure, and excellent compressible property. After 100 cycles of compressing-recovery tests, the mechanical property rarely decreased and the maximum stress reached 19.3 kPa at 70% strain.5. The absorption-desorption property of GA was studied by using chloroform, n-hexane, and pump oil as absorbate by means of absorption-distillation, absorption-combustion, and absorption-squeezing, respectively. After 10 cycles of absorption-desorption, the absorbing capacity and dimensional stability can be well reserved, showing excellent absorbing property. The first absorbing quantity of GA for chloroform, n-hexane, and pump oil were 105.2g/g, 126.5g/g and 178.6g/g respectively, indicating relatively high absorbing capacity.6. The effects of heat treatment on the structure and property of GA were studied under nitrogen atmosphere. After heat treatment at temperature from 400 to 800 oC, the graphitic degree was improved, the hydrophobicity was enhanced by increasing contacting angle from 130 o to 142 o, the electrical resistivity and the resistance was decreased from 2542.5Ω·m to 1.2Ω·m, 11.4 kΩ to 0.98 kΩ, respectively. Under different compressing status the resistance of GA changed with strain, which can be used as strain-controlling resistance sensors.7. The oxygen reduction reaction of heat-treated GA using as catalyst was studied. With the increment of heat-treating temperature, the shape and intensity of oxygen reduction peak, the peak potential and peak current density changed obviously. The results indicated that GA showed oxygen reduction capacity in fuel cell cathode.