Preparation Of Graphene-based Electrode Materials And Characteristics Study On Its Electrosorption Of Pb²⁺

Heavy metal pollution poses a serious threat to environment and human health.Therefore,it has important practical significance to remove heavy metals from water and wastewater in terms of protecting public health and environment.Electrosorption has advantage of high adsorption capacity and electrode regeneration in removal of heavy metal ions in water,and it has good application prospect in the treatment of heavy metal polluted water.The selection of electrode material is the key to electrosorption.High specific surface area and stable electrochemical performance are favorable for electrosorption.Graphene,a two-dimensional structure carbon material,has attracted a great deal of attention.Owing to its unique properties,graphene holds great promise for electrosorption field.In this paper,graphene hydrogels(GS)were prepared by hydrothermal reduction of graphene oxide(GO)suspensions.Aniline and ethylenediamine were respectively combined with GO suspensions and the mixtures were hydrothermally treated to form the self-assembled functional graphene hydrogels(CN-GS1 and CN-GS2).The morphologies,crystalline structure,surface functional groups,elemental composition,specific surface area and pore size distribution of GS,CN-GS1 and CN-GS2 were characterized by FE-SEM,XRD,FT-IR,Raman,XPS and BET&BJH.And electrochemical properties of GS,CN-GS1 and CN-GS2 are tested by electrochemical workstation.Electrodes for electrosorption were obtained via compresstion of GS,CN-GS1 and CN-GS2.The kinetics and thermodynamics of the electrosorption of Pb2+ on GS,CN-GS1 and CN-GS2 electrodes and GS,CN-GS1 and CN-GS2 electrodes reusability were investigated as well.The results showed that GS,CN-GS1 and CN-GS2 have the interconnected 3D networks pore structure.The specific surface area of GS,CN-GS1 and CN-GS2 were 291 m2 g-1,268 m2 g-1 and 198 m2 g-1,respectively.GS,CN-GS1 and CN-GS2 were all mesoporous and macroporous coexistence,the main pore size distribution of GS was about 5 nm,the main pore size of CN-GS1 was about 70 nm,and the main pore size of GS-GS2 distributed around 5 nm and 70 nm.The interconnected 3D networks of GS,CN-GS1 and CN-GS2 offer an opportunity to optimize the electroactive surface for capacitance and provide well-defined diffusion channels for ion transport.CN-GS1 and CN-GS2 samples were successfully blended with nitrogen,and the nitrogen content was 4.42%and 3.26%,respectively.The nitrogen in CN-GS1 is mainly present in the form of pyridine nitrogen,and the nitrogen in CN-GS2 is mainly present in the form of pyrrole nitrogen.GS,CN-GS1 and CN-GS2 showed different specific capacitances in Na2SO4 and H2SO4 electrolytes.In the H2SO4 electrolyte,the oxygen-containing functional group and the nitrogen-containing functional group can react with the hydrogen ion to generate additional pseudopotential for the material.Compared with the capacitances in Na2SO4 electrolyte,the capacitances of GS,CN-GS1 and CN-GS2 electrode in H2SO4 electrolyte increased by 50.90%(from 132.8 F g-1 to 200.4 F g-1 at 1.0 A g-1),17.97%(from 218.2 F g-1 to 257.4 F g-1 and 1.0 A g-1)and 20.07%(from 174.4 F g-1 to 209.4 F g-1 at 1.0 A g-1).In addition,the electrochemical performance of the three-dimensional graphene hydrogel was further enhanced by the functionalization of the carbon-nitrogen compound and CN-GS1 has the highest capacitance.The content and morphology of nitrogen affect the electrochemical properties of the electrode material.The electrosorption performance of GS indicated high voltage was favored for the removal of Pb2+,and the highest removal efficiencies of Pb2+ on GS,CN-GS1 and CN-GS2 electrodes reached 96.4%,96.0%and 95.0%respectively when the voltage value was-1.2 V.The GS,CN-GS1 and CN-GS2 electrodes could regenerate after electrosorption when the voltage value was +1.2 V and the removal efficiencies of Pb2+ were all still maintained above 90%after electrosorption-desorption for 15 cycles.The electrosorption capacities for Pb2+removal on GS,CN-GS1 and CN-GS2 electrodes were found to be 461.20 mg g-1 196.81 mg g-1 and 485.29 mg g-1,while the saturated adsorption capacities of GS,CN-GS1 and CN-GS2 were only 224.12 mg g-1,102.16 mg g-1 and 256.67 mg g-1,respectively.CN-GS2 had the highest electrosorption adsorption capacity of Pb2+.Electrosorption properties are related to the morphology of nitrogen and the pore size distribution of the material.Pyrrole nitrogen is more likely to react with Pb2+,and mesoporous(～5 nm)is favorable for Pb2+ electrosorption.