Eco-friendly, non-toxic and super adsorbent hydrogels based on graphene.

This work aimed to develop three-dimensional materials based on graphene by a simple, low-cost, and environmentally friendly method, evaluating its toxicity and capacity for the cationic dye safranin removal from water. 3D-rGO materials were obtained by reducing graphene oxide (GO) in one step and through a sustainable route. The materials were obtained over 2 h, showing a self-supporting three-dimensional structure. The effect of ascorbic acid amount as a reducing agent for this material was evaluated. It was observed that variations in the reaction promoted significant morphological changes. The results showed that the greater the reducing agent amount used in the synthesis, the more compact the three-dimensional structure, the smaller the pores and specific surface area, and the lower the number of oxygenated sites. The pH of the zero charge point (pH ZCP) ranged between 2 and 2.37, indicating that the material must efficiently adsorb cationic dyes at neutral pH. Adsorption studies for the cationic dye safranin showed materials capable of adsorbing the dye quickly, with a kinetic equilibrium time of only 10 min, and a high adsorption capacity (937,841 mg g−1), in the equilibrium isotherm studies. The changes in the surface area and the compaction of the structure directly influence intraparticle diffusion and adsorption mechanisms. In addition, the materials did not present significant toxicity in D. melanogaster fly, indicating the absence of immediate toxicological risk in a situation of possible contamination. [Display omitted] • Materials with different degrees of oxidation were obtained in a one-step route. • The route is eco-friendly and produces materials with a cohesive structure. • None of the materials showed toxicity to Drosophila melanogaster. • One 3D-rGO material had an adsorptive capacity of 937.841 mg g−1 for safranin. • Another 3D-rGO material was able to remove 100% of safranin in just 10 min. [ABSTRACT FROM AUTHOR]