The synthesis of tannin-based graphene aerogel by hydrothermal treatment for removal of heavy metal ions

Tannin (complex polyphenol) is commonly obtained from the bark and fruits. Its ortho-phenolic hydroxyl groups can adsorb heavy metal ions from wastewater by chelation. However, the adsorption performance to heavy metals (especially Pb) of the tannin-based materials is unsatisfactory. Herein, the tannin-reduced graphene aerogel (TRGA) was prepared by a one-step method for Pb(II) and Cd(II) adsorption. Results indicated that TRGA with a three-dimensional porous structure, low density, large specific surface area (122.2 m2/g) and high porosity, can facilitate the adsorption of metal ions. The maximum Pb(II) adsorption capacity of TRGA reached 803.84 mg/g at pH 4, which was much higher than that of precious tannin based adsorbents. Besides, the maximum adsorption capacity for Cd(II) is 395.80 mg/g at pH 4 when the optimal initial concentration of Cd(II) is 160 mg/L. Overall, the high capability and large efficiency of TRGA display widespread potentials for heavy metals adsorption.