Research On Adsorption Of Hexavalent Chromium And Congo Red In Aqueous Solutions By Functionalized 3D Graphene Aerogel

Cr(Ⅵ)is one of the toxic heavy metal pollution and congo red(CR)is a typical representative of azo dyes.Both Cr(Ⅵ)and CR are highly toxic and difficult to be degraded,seriously endangering the water ecosystem and human health.Therefore,it is urgent to adopt reasonable methods to solve the problem of Cr(Ⅵ)and CR pollution.Adsorption is one of the commonly used and effective methods,which has the advantages of low input cost,simple equipment requirements,simple operation and good treatment effect.Graphene aerogel,also known as carbon sponge,has the advantages of rich pore structure and good mechanical strength.It is widely used for adsorbing organic pollution,heavy metal pollution and separating oil from water.However,The surface of graphene aerogel contains insufficient active groups,which limits its practical application.Therefore,in order to increase the content of active groups,graphene aerogels are usually modified to improve the adsorption capacity.In this study,graphene oxide(GO),pyrrole monomer and disodium ethylenediaminetetraacetic acid(EDTA-2Na)were used as raw materials to synthesize functionalized graphene aerogel(EPGA)by one-step hydrothermal self-assembly method.During the synthesis process,both pyrrole and EDTA-2Na acted as a nitrogen source and crosslinking agent.The doping of Ppy and EDTA-2Na not only facilitated the formation of three-dimensional structure,but also increased the content of active groups in graphene composite aerogels.EPGA was characterized by various characterization methods such as scanning electron microscope(SEM),fourier transform infrared spectroscopy(FT-IR),raman spectroscopy(Raman),X-ray photoelectron spectroscopy(XPS)and X-ray diffraction(XRD)analysis.In addition,the adsorption of Cr(Ⅵ)and CR in solution by EPGA was studied.The influence of p H,coexisting ions,reaction time and temperature on adsorption behavior and adsorption mechanism were also discussed.The results show that polypyrrole(Ppy)and EDTA-2Na have been successfully doped into graphene aerogel,and the aerogel has a well-developed pore structure.EPGA was used to remove Cr(Ⅵ)from the solution.At p H=2.0,the adsorption effect was the best.The maximum adsorption capacity reached 361 mg/g.EPGA showed good anti-interference ability and stability in the adsorption process.the adsorption process can be fitted with thepseudo-second-order kinetic model and Freundlich adsorption isotherm model.The mechanisms involved in the Cr(Ⅵ)adsorption process mainly include electrostatic interaction,complexation,ion exchange and redox.EPGA was used to remove CR from the solution.At p H=4.0,the adsorption effect was the best,and the maximum adsorption capacity reached242.2 mg/g.The pseudo-second-order kinetic model and Langmuir adsorption isotherm model can better explain the adsorption process.The adsorption process was a spontaneous endothermic reaction process,and the adsorption capacity increased with increasing temperature.The removal mechanisms may be weak electrostatic attraction,complexation,π-π interaction and hydrogen bonding.