Structural Adjustment Of Self-supporting Graphene-based Composite Aerogels And Their Adsorption Properties Towards Organic Pollutants In Water

Graphene aerogel(GA),as a new type of three-dimensional(3D)carbon-based material,has broad application prospects in wastewater treatment because of its excellent physical and chemical properties,such as large specific surface area,good chemical stability and strong conductivity.However,due to the?-? interaction between graphene nanosheets,it is easy to stack and difficult to disperse,which brings obstacles to the functional modification of graphene materials and the preparation of their assemblies.Meanwhile,GA is usually assembled by the electrostatic,hydrogen bonding,?-? stacking and other effects between graphene oxide(GO)nanosheets.It is difficult to maintain its 3D structure during the process of functionalization,and the prepared GA is quite brittle.Moreover,its pore structure is prone to irreversible collapse or deformation,which limits its practical application.Therefore,constructing GA with a 3D structure and self-supporting macro body,that is,self-supporting GA,can obtain GA with the structural characteristics of‘hierarchical skeleton,channel,and component',which is imperative for the treatment of increasingly serious water pollutants.To obtain a functionalized graphene-based composite aerogel with easy recovery,high adsorption capacity and strong reproducibility and realize its application in water pollution treatment,three composite GAs,including magnetic graphene-based composite aerogel(MCNS/NGA),amino-functional graphene oxide aerogel(MGOA)and hollow carbon nanosphere graphene-based composite aerogel(HCNS/NGA),were prepared in this paper.Magnetic carbon nanospheres(MCNS)and hollow carbon nanospheres(HCNS)were introduced into GA by using the graphene derivative GO as the matrix material.After surface modification,the comprehensive performance of functionalized graphene-based composite aerogels is greatly improved.This research provides a new way for the development of advanced sewage purification materials.The research contents and results are as follows:(1)Preparation and adsorption property of MCNS/NGA.In order to improve the recovery capacity of bulk adsorbents,alkaline ammonium citrate as reducing agent and nitrogen source,MCNS/NGA was fabricated under weakly alkaline condition by one-step hydrothermal in-situ electrostatic self-assembling strategy.The aerogel has low density(12.07 mg cm-3),super-elasticity(up to 95%compression),high specific surface area(787.92 m2 g-1)and good magnetic property(22.47 emu g-1).Therefore,it exhibits an adsorption capacity in the range of 187-537 g g-1 towards various organic solvents and oils,which is superior to most reported materials to date.The aerogel not only has excellent solid-liquid separation advantage,but also can be regenerated by squeezing,distillation and combustion.More importantly,the magnetic control technology can be adopted to realize an oriented adsorption and facilitate the recycling of organic solvents and oils in extreme environments.(2)Preparation and adsorption property of MGOA.In order to improve structural stability and adsorption performance of GA,a novel 3D MGO A was prepared by an acid induction strategy,which triggers the esterification and amidation of GO nanosheets and ammonium citrate.At 298 K,pH=7,and initial quinoline concentration of 50 mg L-1,the adsorption capacity(103 mg g-1)and distribution coefficient(PC,0.689 mg g-1?M-1)of MGOA towards quinoline are better than those reported in most literatures.The adsorption results show that the adsorption of quinoline on MGOA is exothermic and spontaneous,which conforms to the pseudo-second-order kinetic equation and Langmuir-Freundlich model.Thomas and Yoon-Nelson models can well describe the adsorption behavior of quinoline on MGOA in fixed-bed column adsorption.More importantly,in the column adsorption system,corresponding to 10%breakthrough time(BT),PC is 14.16 mg g-1 ?M-1,which is the highest level reported in the current literatures.This means that MGOA has great potential in practical application.Furthermore,after eight adsorption-desorption cycles,about 89.54%of the original adsorption capacity is still retained,suggesting the excellent structural stability and good reusability of MGOA.(3)Preparation and adsorption property of HCNS/NGA.In order to further strengthen the adsorption performance,HCNS were encapsulated by 3D graphene networks to obtain composite GA.The hierarchical nanocomposite of HCNS/NGA with large surface area,ideal pore structure and high conductivity was successfully synthesized,which show outstanding adsorption ability towards quinoline.When initial quinoline concentration is 50 mg L-1,the adsorption capacity of HCNS/NGA towards quinoline is as high as 138.37 mg g-1 at 298 K,and the PC value is 2.11 mg g-l?M-1),which is better than that of most adsorbents reported.The adsorption process conforms to the pseudo-first-order kinetic model and Langmuir-Freundlich model.In the column adsorption system,corresponding to 10%BT,PC is up to 35.19 mg g-1 ?M-1,which means that HCNS/NGA has great potential in practical industrial application.Thomas and Yoon-Nelson models can well describe the adsorption behavior of quinoline by HCNS/NGA in fixed-bed column adsorption.More importantly,HCNS/NGA can not only easily realize solid-liquid separation,but also rapidly regenerated in situ by electrochemical assisted regeneration device.In conclusion,the introduction of MCNS into GA has greatly improved the mechanical properties of GAs,and endowed them with excellent magnetism,which can realize directional adsorption,rapid separation,recovery and reuse through external magnetic field.Amino-functionalization can strengthen the 3D network structure of GA and provide abundant adsorption sites,while can promote the hydrophilicity of the material and significantly improve its adsorption capacity for organic pollutants.The introduction of HCNS into GA enables composite GAs to produce a hierarchical porous network structure,resulting in higher specific surface area,which greatly facilitates internal mass transfer and further enhances their adsorption properties.Three functionalized graphene based composite aerogels exhibit excellent structural properties and potential applications as adsorbent.These findings have an important theoretical and actual guidance for the development and design of highly efficient adsorbent materials.