Facile preparation of nitrogen and sulfur co-doped graphene-based aerogel for simultaneous removal of Cd 2+ and organic dyes

Abstract

The need in simultaneous removal of heavy metals and organic compounds dictates the development of synthetic adsorbents with tailor-made properties. A nitrogen (N) and sulfur (S) co-doped graphene-based aerogel (GBA) modified with 2,5-dithiobisurea was synthesized hydrothermally for simultaneous adsorption of Cd²⁺ and organic dyes—safranin-O (SO), crystal violet (CV), and methylene blue (MB). 2,5-Dithiobisurea was used as nitrogen and sulfur sources to introduce N and S-containing functional group onto graphene oxide. The adsorption mechanism of GBA towards Cd²⁺ and organic dyes was studied by Dumwald-Wagner models and the results showed that surface and intraparticle diffusion was the key factor in controlling the rate of adsorption. The maximum adsorption capacities of GBA towards Cd²⁺, SO, CV, and MB comprised 1.755, 0.949, 0.538, and 0.389 mmol/g in monocomponent system, respectively. Adsorption synergism was observed with respect to Cd²⁺ in presence of the dyes. The performance of GBA with respect to Cd²⁺ removal from binary solutions, Cd²⁺-SO, Cd²⁺-CV, and Cd²⁺-MB, was enhanced by the presence of the dyes significantly, while the adsorption capacities towards the dyes were not affected by the presence of Cd²⁺.