Assembly,Structure Regulation And Properties Of Graphene Aerogels

Graphene aerogels?GAs?,combined with the unique structure and excellent performance of graphene and aerogel,possesses extremely low density,extremely high specific surface area and porosity,excelent mechanical properties as well as electrical conductivity,and have broad application prospects in many fields such as adsorption,catalysis,energy storage and electromagnetic protection.However,the complex preparation process,high cost and energy consumption and difficulty in controlling the structure and performance greatly limit the large-scale application of GAs.Thus,it is urgent to optimize the preparation process,improve the preparation efficiency and clarify the relationship of structure and performance for GAs.Based on systematic review of the research progress and application status of graphene and its aerogel,this research focuses on the assembly,structure regulation and performance of GAs.Firstly,the GAs with tunable wall thickness and pore size was prepared by ice-template method and the internal relationship between the structure and performance of GAs was revealed,Further,the combination of silver nanowires and graphene was adopted to prepare aerogel composites with superior mechanical and electromagnetic shielding properties.Secondly,a green and rapid preparation method was developed to prepare GAs with unique microstructure and good mechanica l properties,and further Fe-O_x nanoparticles was introduced to prepare Fe-O_x nanoparticles/graphene aerogel composites with good electrocatalytic performance.The green and rapid preparation method,regulation of structure and property built an important theoretical foundation for mass preparation and large-scale application of GAs.Detailed research contents and results are as follows:?1?Intrinsic structure regulation and properties of GAs.Based on ice-template method,GAs with ultra-flyweight(?<1 mg·cm^-3),superelastic?low energy loss factor is 0.80?,and high-strength?the strength and Young'modulus are 264 and 237 kPa,respectively?can be obtained by integrating different wall thicknesses and pore sizes.And it has been found that at the same density,the obtained aerogel with smaler pore size has presented higher mechanical strength and modulus at low freezing temperature,i.e.the grain refinement of ice crystals has a positive impact on the strength and modulus of as-prepared GAs during freezing-drying,which accords with typical Hall-Petch strengthening in fine crystal metal materials.Importantly,the as-prepared GAs with the thinnest wall thickness has the highest geometric specific surface area and the adsorption capacity for oil solvents is 1272 times of its own weight,which is more than these carbon-based adsorption materials in open literature.?2?Preparation and electromagnetic shielding properties of AgNWs/graphene aerogel composites.Silver nanowire?AgNWs?/graphene aerogel composites were prepared by natural y air-drying based on optimized ice template method.The silver nanowires with a high aspect ratio can act as crosslinkers to bridge two-dimensional graphene sheets,and reinforces the network frame of aerogel,which resists high external loading and owns great mechanical properties.Consequently,the aerogel composites exhibits a mechanical strength of 42 kPa,35 times higher than that of the neat GA?1.2 kPa?,which has great ability to resist external damage.More importantly,the silver nanowires increase the carrier concentration and electron transport paths of the aerogel composites,endowing high conductivity and electromagnetic shielding performance as high as 45.2 dB.?3?Green rapid preparation and electromagnetic shielding performance of GAs.A green,time-saving method has been developed for preparing GAs,that is,the solid film can be directly converted into the GAs with continuous and stable internal structure by a foaming technology.The resulting GAs material exhibits a layer-by-layer structure with excelent compressibility,compression resilience and fatigue resistance.The compression cycle repeats 10⁵ times at a strain of 90%,while the structural integr ity is still maintained.Due to its high intrinsic conductivity,layer-by-layer wavy structure and high porosity,the GAs can effectively attenuate electromagnetic waves,and the shielding effectiveness of the as-prepared aerogel can reach to 113.9 dB,mainly derived from electromagnetic absorption.Moreover,specific shielding effectiveness?SSE?can reach to 17188 dB·cm³·mg^-1 and thickness-averaged specific shielding effective ness?TASSE?can reach to 85939 dB·cm²·mg^-1,when normalized the density and thickness.This foaming technique has proposed a new design and approach for the preparation of aerogel monolithic materials.?4?Preparation and electrocatalytic performance of Fe-O_x nanoparticles/graphene aerogel composite.Fe-O_x nanoparticles/graphene aerogel composite was prepared by direct solution impregnation and thermal reduction on the basis of above rapidly prepared GO aerogels.The resultant aerogel composite has high electrical properties,high specific surface area and abundant electrochemical active sites,indicating excelent electrocatalytic performance due to the combination of graphene aerogel and iron.With the increase of iron salt precursor content,the aerogel composites show superior OER performance with overpotential of 259 mV and Tafel slope of 61.7 mV·dec^-1.The OER performance will decrease with the further increase in the iron salt precursor content,which may be caused by the agglomeration of excessive nanoparticles.