Adsorptive Behavior Of 3D Nitrogen-doped Graphene Gels For Organic Dyes

Dye wastewater has become a serious threat to human health and ecological balance.Adsorption is the most cost-effective method for the treatment of dye wastewater,the choice of adsorbent is crucial.Recently,graphene has attracted great attention due to its economic,green,and excellent performance.In particular,three-dimensional heteroatom doped graphene gels not only exhibit all the advantages of graphene materials,but also present a rich three-dimensional pore structure,which display excellent adsorption capacity and have an application prospect in dye wastewater treatment.In this work,a series of 3D nitrogen doped graphene(NG)hybrids was designed and synthesized by hydrothermal method.The structure and properties of NG were regulated by changing the nitrogen source.Among them,NG-6 hybrid prepared from 1,6-hexanediamine showed excellent adsorption capacity for acid red B(AR)and methyl orange(MO),while NG-2 hybrid prepared by ethylenediamine was the best choice for methylene blue(MB)and rhodamine B(RhB).Characterization results indicated that the properties of the adsorbents are affected by the nitrogen and oxygen functional groups on NG surface.Among them,pyridinic N is beneficial to the adsorption for AR and MO,while oxygen functional groups are conducive to the adsorption ability of NG materials for MB and RhB.In addition,the adsorption process and kinetics of the adsorbents are in accordance with the Langmuir model and the pseudo-first-order kinetic model,respectively.In order to further explore the adsorption behavior and mechanism of the adsorbents.NG-2 was pyrolyzed at different temperatures and applied to the adsorption for methylene blue.The results show that the pyrolysis temperature has an important effect on the adsorption properties of NG adsorbents.With the increase of pyrolysis temperature,the maximum adsorption capacity and the adsorption rate of dyes were increased gradully,and the adsorption dynamic behaviors of pyrolytic NG hybrids for MB were in accordance with the pseudo-first-order kinetic models.The adsorbent pyrolzed at 1000 ? showed the best adsorption performance.However,when the pyrolysis temperature reached 1200 ?,the adsorption capacity of the material slightly decreases.Moreover,the adsorption dynamic behavior of pyrolytic NG hybrid for MB is changed to fit for the pseudo-second-order kinetic model.The above results are possibly attributed to the synergistic effect between specific surface area and the functional groups on the surface of adsorbents.