Graphene/waste-newspaper cellulose composite aerogels with selective adsorption of organic dyes: preparation, characterization, and adsorption mechanism

Abstract

Eco-friendly graphene oxide (GO)/waste-newspaper cellulose (WCE) and graphene nanosheet (GNS)/WCE composite aerogels were facilely synthesized via the sol–gel and freeze-drying processes. Morphological analysis and structural characterization revealed that the prepared composite aerogels possessed the perfect foam structure. Due to the different interactions between the aerogel and dyes, namely, electrostatic attraction, charge repulsion, and π–π interaction, the composite aerogels exhibited significantly discrepant adsorption capacities for two dyes, namely, methylene blue (MB, cationic) and Congo red (CR, anionic). With the addition of 0.5 w/v% GO, the MB adsorption capacity of WCE obviously improved by 235.6% from 65.4 to 154.1 μmol g⁻¹, while the CR adsorption only increased by 70.2%. On the contrary, the CR adsorption of GNS/WCE was distinctly superior to that of MB. Furthermore, the entire adsorption process was suitable to be modeled by Langmuir isotherm, pseudo-second-order kinetics model, and intraparticle diffusion mechanism. These findings provide guidance for the development of green and efficient adsorbents for the removal of dyes from wastewater.