3D nitrogen-doped graphene gels as robust and sustainable adsorbents for dyes

Herein, a series of 3D nitrogen-doped graphene gels (NG) were synthesized for the removal of dyes from wastewater. Their structures were characterized by XRD, SEM, TEM, elemental analysis, BET analysis, and XPS. It was found that the distribution of functional groups on the NG surface could be significantly affected using different nitrogen sources, which could further influence their adsorption behaviors. Among them, the hybrid prepared from hexamethylenediamine as the nitrogen source shows best adsorbability for acidic dyes, whereas the hybrid obtained from ethylenediamine displays largest adsorption capacity for basic dyes. Adsorption isotherms and kinetics were also investigated. The results indicate that the best interpretation is provided by the Langmuir isotherm equation, and the adsorption dynamic behavior is fit for the pseudo-first-order model. In addition, intra-particle diffusion kinetics manifest rate-controlling steps including external diffusion and intra-particle diffusion. Moreover, all adsorbents exhibit excellent reusability. Therefore, NG adsorbents show potential applicative value in the treatment of dye wastewater.