Sulfonated graphene oxide as an adsorbent for removal of Pb²⁺ and methylene blue

One of the major challenges encountered in some conventional nano-structured adsorbents such as graphene oxide (GO) and graphene is the structural limits including serious aggregation and hydrophilic surface in water. And the sulfanilic acid functionalized graphene oxide (SGO) can powerfully attract positively charged pollutants. Therefore, the SGO served as an adsorbent to remove dyes and toxic metal ions from aqueous solution were intensively investigated. At the same time the reduced sulfonated graphene oxide (rSGO), reduced graphene oxide (rGO), and graphene oxide (GO) were performed as the comparative samples. The results showed that the maximum adsorption capacities of SGO were 2530 mg/g for methylene blue and 415 mg/g for Pb²⁺, which was much higher than that of the contrast samples and adsorbents reported in literatures. The adsorption of SGO was investigated systematically including the saturated adsorption capacities, isotherm, and kinetic adsorption process. The SGO displayed high adsorption efficiency and superior adsorption capacity toward metal ions and dyes, which is mainly attribute to the good dispersibility and the multiple adsorption sites of SGO. These results are promising not only providing effective adsorbing heavy metal ions and organic dyes, but also gaining insights into adsorption mechanism of graphene materials.