Shell-free three-dimensional graphene-based monoliths for the aqueous adsorption of organic pollutants

Three-dimensional graphene-based monoliths (GBM) are promising materials for pollutant adsorption in aqueous solution. However, the compact shell of GBM blocks mass transfer, reduces the specific surface area and adsorption sites, and reduces overall adsorption performance. To improve the properties of these materials, we used sodium ascorbate (Vc'Na) to reduce graphene oxide (GO) to prepare shell free GBM. The microstructures and properties of the produced Vc'Na-GBM were characterized. Hydrophilic methylene blue (MB) and hydrophobic Bisphenol A (BPA) were used as adsorbates to investigate the adsorption performance of the prepared Vc'Na-GBM. The shell-free Vc'Na-GBM, compared with un-modified Vc-GBM, exhibited a higher BET surface area of 248.3 m(2)/g for an increase of 21.4%, recovered 43.3% of sp(2)-hybridized domains for an increase of 24.4%, showed higher mass transfer efficiency with 1.60 and 2.47-fold increases in the kinetic constants for MB and BPA respectively, and possessed higher saturated adsorption capacities of 154 mg/g and 204 mg/g, for MB and BPA respectively, for an increase of 1.34 and 1.20-fold. We propose that the strong electrostatic repulsion induced by Vc'Na promoted the removal of the shell of GBM. This study provides the theoretical basis for the facile and lowcost preparation of high-performance GBM adsorbents. (C) 2017 Elsevier B.V. All rights reserved.