| Organic dyes and heavy metal ion are important components of pollutants in water,which have seriously threatened human health and ecological balance.Graphene aerogel(graphene aerogel,GA)is a three-dimensional(3D)macroscopic material,which is regarded as one of the most promising adsorbent because of its high specific surface area and porosity.However,the 3D structure of GA is prone to collapse due to its brittleness,which may cause secondary pollution to the water environment and greatly limit the adsorption capacity and recycle ability of GA.Therefore,improving the structural stability and adsorption efficiency of GA is the focus of current research.In this paper,a functional graphene aerogel(PVA-N/GA)was synthesized by one-step hydrothermal and freeze drying methods.The obtained samples were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),Raman spectroscopy(Raman),X-ray photoelectron spectroscopy(XPS),automatic specific surface area meter(BET)and uv-vis absorption spectroscopy(UV-Vis).Under different conditions(initial concentration of solution,amount of adsorbent,pH of solution,adsorption time,temperature),the effects of PVA-N/GA on the adsorption properties of methylene blue(MB),methyl orange(MO)and heavy metal ions(Cr(VI))and the adsorption mechanism were investigated.And the cycle performance of the samples was analyzed.The mainly conclusions are shown as follows:(1)PVA-N/GA with three-dimensional porous structure was successfully prepared using GO as the precursor,urea as the nitrogen source and polyvinyl alcohol(PVA)as the crosslinking agent.The addition of nitrogen element and crosslinking agent effectively prevented the aggregation of graphene sheets,which not only enhanced the structural stability of PVA-N/GA but also provided more adsorption sites,offerring the possibility of effective capture of contaminants.(2)The adsorption properties of PVA-N/GA on MB and MO were investigated at 25 ?.The results showed that the adsorption was the best under the condition of the solution concentration of 20 mg/L,5 mg of adsorbent and the pH value of 8 and 2.The adsorption equilibrium was reached after 4 h.The maximum adsorption capacities were 236.83 mg/g and 192.57 mg/g,respectively.And the adsorption reached equilibrium after 4 h.The adsorption process were endothermic and spontaneous,and fitted the pseudo-second-order kinetic model.The adsorption isotherms conformed to the Langmuir model and Freundlich model,respectively.The adsorption mechanism analysis showed that the removal ability of PVA-N/GA to organic dyes mainly depended on electrostatic force and ?-? bond between them.(3)The adsorption performance of PVA-N/GA for Cr(VI)was analyzed at 25 ?.Research showed that the PVA-N/GA had the optimal adsorption capacity(176.13 mg/g)for Cr(VI)under 20 mg/L,pH=2,5 mg adsorbent dosage,and the adsorption reached equilibrium after 4 h.The adsorption kinetic model of adsorption fitted pseudo-second-order kinetic model.The adsorption isotherm was described by Langmuir model.Adsorption thermodynamics indicated that the adsorption process was endothermic and spontaneous.It could be inferred that the adsorption of heavy metal ion was attributed to the electrostatic force and hydrogen bond interactions.(4)The cycling property of PVA-N/GA after adsorption was tested.The results showed that the structure of PVA-N/GA had no change significantly before and after adsorption,which proved the interactions between PVA-N/GA and adsorbates.Loading experiments showed that PVA-N/GA had good mechanical property.After five cycles of adsorption,the removal rates of MB,MO and Cr(VI)by PVA-N/GA still reached 98.66%,94.95% and 73.87%,exhibiting prominent repeatability.Therefore,PVA-N/GA is a candidate for effective treatment of water pollution. |
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