Regulation Of Micro/nano Structure And Surface Charge Properties Of Graphene-based Aerogels And Its Performance For Removing Pollutants From Water

Graphene-based aerogel(GBA)is a three-dimensional porous material with graphene-based nanosheets as the skeleton.Owing to its unique physical and chemical properties,it has attracted great attention in the environmental field recently,especially it is widely used in the adsorption and catalytic transformation of pollutants in water.GBA possess hierarchical structures,including microscopic micro/nano structures,macroscopic pore structures and surface properties,etc.Many studies have been conducted to regulate their hierarchical structures and optimize their adsorption-catalytic performance through different regulation method.However,the influence of the structure of graphene oxide(GO)on the micro-nano structure,surface charge properties and performance of graphene-based aerogels is still unclear.Especially,the influence of oxidation debris(OD)on the surface of GO on the stability,adsorption,catalytic and separation performance of GBA deserves further explore and providing theoretical guidance for the design and fabrication of GBA functional materials.In this study,we introduce the structural characteristics of graphene oxide in the first place,then summarizes the fabrication methods of graphene-based aerogels,and reviews the hierarchical structure and influence factors of graphene-based aerogels.The research progress of graphene-based aerogels on the adsorption,catalytic conversion and separation of pollutants in water are also summarized.Exploring the influence of the OD nanoparticles on graphene oxide on the structure,loading of noble Pd particles and C-Pd coupling of graphene-based aerogels.The adsorption-catalytic transformation performance of GBA and its Pd-supported composite toward organic pollutants are studied.Aiming at the continuous control of the surface charge properties of graphene-based aerogels,the graphene oxide/polyethyleneimine aerogels are fabricated using polymers and exploring its hierarchical structure characteristics,adsorption-separation performance and device application of organic pollutants.The main original conclusions of this work are drawn as follow:(1)After removing the OD nanoparticles,the structural stability and adsorption performance of graphene oxide aerogels are concurrently improved,and the structure-property relationship and mechanism are clarified.The base-washed GO nanosheets(BGO)without OD possess more wrinkles and conjugatedπareas,which enhances theπ-πinteraction and weakens the electrostatic repulsion between nanosheets,resulting in a more integrated microstructure in prepared 3D BGO.And its structural stability and thermal stability are greatly improved.The increased macroscopic pores and surface wrinkles facilitate the diffusion and transport of pollutants in the 3D BGO,and the increased sp~2 hybrid area and carboxyl groups in the BGO reduce adhered water molecules and increase adsorption sites,improving the adsorption performance of 3D BGO on phthalates in water.For example,the saturated adsorption capacity of diethyl phthalate is 5 times higher than that of 3D GO.(2)OD regulates the size,stability and catalytic performance of palladium nanoparticles loaded on the surface of graphene-based aerogels,revealing the coupling mechanism and confinement effect of the carbon sp~2-hybridized domain-palladium nanoparticles in Pd-loaded aerogels.After removing the OD,the size of the Pd nanoparticles loaded on the aerogel is 4.67 times smaller than that with OD,and the Pd nanoparticles are more uniformly distributed and the catalytic activity is increased by 15 times.The coupling of Pd nanoparticles with sp~2 domain and the spatial confinement effect of the folds on the nanosheets alleviate the agglomeration of Pd nanoparticles,reduce the particle size,and improve the catalytic activity.At the same time,it prevents the Pd nanoparticles from being oxidized,maintaining the stability of the catalyst,and exhibit excellent reusability.(3)Polyethyleneimine(PEI)loading could effectively regulate the surface charge properties,stability and adsorption-separation performance of graphene-based aerogels,and clarify the mechanism of its selective adsorption and separation.Due to the covalent cross-linking between PEI and GO,graphene oxide/polyethyleneimine aerogel(GP)maintain stable structure in p H 2-12 aqueous solution,methanol,acetonitrile,toluene,acetone and N,N-dimethylformamide.By adjusting the PEI loading amount,the surface charge and isoelectric point of GP aerogels could be continuously regulated,and it exhibits excellent adsorption performance for anionic dyes.At p H 2.0,the adsorption capacity of the aerogel for the anionic dye methyl orange is 331.0 mg/g,which is the highest value reported in the literatures.At the same time,it still maintains good adsorption performance for cationic dyes,and the adsorption capacity for methylene blue is 249.6 mg/g under p H 10.5.The adsorption mechanism of GP aerogel to dyes mainly includes electrostatic attraction andπ-πinteraction.GP aerogels with different isoelectric points could be used for the separation of anionic dyes and cationic dyes.GP51 with an isoelectric point of 4 could achieve complete separation of MO and MB when the p H is greater than 8.5.GP55aerogel with an isoelectric point of 10 could absorb 90.99%of MO while retaining 96%of MB under pH 3.3.