Exploring the superior adsorption capacity of multi-layer graphene/alginate granules for the removal of methylene blue dye from water

Graphene-based materials are gaining increasing attention towards their use in manufacturing and environmental applications. In this context, multi-layer graphene (MG) has been recently applied for the adsorption of contaminants from water resulting in promising results. However, the extreme lightness of this material often makes it difficult to handle due to its potential dispersion in the surrounding environment as well as to its transport and loss with the effluent. In this study, a novel granular material was synthesized by embedding MG into an alginate matrix, resulting in the so-called granular MG (GMG). This material was tested for the adsorption of methylene blue (MB) from water, which is a typical dye used in textile industries and must be removed from the effluent. GMG materials with different MG contents (5 and 20 %) were compared with MG and a commercial adsorbent to assess their adsorption capacity and the most performing material was selected for in-depth physical and chemical characterization. The structural, surface, kinetic, isotherm, and thermodynamic properties, the pH and temperature dependence, as well as the regeneration and reuse of GMG 5% were investigated through batch adsorption tests under different operating conditions. The study reveals that GMG 5% has a superior adsorption capacity compared to the tested materials and can be considered as a promising alternative to commercial carbon-based materials according to techno-economic considerations.