Graphene Oxide–Cellulose Nanowhisker Hydrogel Nanocomposite as a Novel Adsorbent for Methylene Blue

In this research work, methylene blue (MB) was removed by an as-synthesized graphene oxide-cellulose nanowhisker hydrogel (GO–CNW) nanocomposite as an adsorbent. Adsorption experiments were conducted under different MB concentrations, temperatures, shaking rates, ionic strengths, and alkalinities. Maximum adsorption capacities (q_e,max) of the adsorbent at 308, 318, and 328 K were 34.5, 35.3, and 34.8 mg·g^–1, respectively. The structural character of the adsorbent, analytical instrumental analyses, and adsorption models and equations showed that there were two adsorption sites on the surface of GO–CNW-adsorbed MB molecules. These adsorption sites were carboxylate and phenoxide groups of the GO portion of GO–CNW, which were named the CA and Ph adsorption sites, respectively. An analysis of adsorption isotherms by the ARIAN model showed that MB molecules were adsorbed at first on the CA and then on the Ph sites. The interaction of MB molecules with CA sites was stronger than that with Ph sites. On the other hand, the study of kinetic curves by the KASRA model and the KASRA, intraparticle diffusion, and the ISO equation showed that CA sites adsorbed MB molecules more rapid than did Ph sites. Furthermore, the adsorption on both CA and Ph sites was reaction-controlled. Finally, the used adsorbent samples were recycled using acidic solutions.