(490d) Sustainable Graphenic Fixed-Bed Hybrid Adsorbents: Green Synthesis and Application

Organic dyes are one of the most common types of pollutants found in urban waterbodies, with potentially serious health hazards. While various technologies including adsorption, precipitation, separation, amalgamation, and ion-exchange are employed to remove such contaminants from water, adsorption proved to be the most economical and efficient. Due to the high surface area and benign nature of activated carbon (AC), it is heavily used in the removal of various pollutants. However, increasing amounts of anthropogenic wastes necessitates the discovery of adsorbents with higher remediation efficacy. Graphene, the newest member of carbon-based nanomaterials, composed of sp2 hybridized carbons arranged in a perfect planar honeycomb lattice, have the highest surface area among the carbon family. Recent research indicated the large utility of graphenic materials in environmental remediation applications. However, the dependence on petroleum-based or high-value precursors for graphene synthesis is one of the challenges in its large-scale utilization for applications such as water purification. In addition, this dependence also limits the sustainability of such adsorbents. Hence, we report, for the first time, an immobilized graphenic adsorbent system prepared from a highly sustainable, naturally abundant, and underutilized bio-product, Lignin. Lignin, the most abundant natural polymer with aromatic monomers, was coated onto inexpensive sand particles. The lignin coated sand was thermochemically converted to graphene coated sand (GCS), leveraging the inherent high density of aromatic rings in lignin. The as-synthesized GCS with a large number of defects or void spaces, that act as the active adsorption sites, were investigated for their utility in removing a variety of dyes from simulated contaminated water. By controlling the process parameters, we engineered the microstructure of the adsorbent to derive highest possible adsorption capacity. To further embellish the adsorption efficacy, a metal-graphene hybrid adsorbent was prepared via a green reduction process. The hybrid system, due to enhanced surface area and activity, demonstrated improved adsorption capacity. It is expected that the completely green process employed for the synthesis and the highly sustainable nature of the product will attract widespread attention and help the push towards the application of graphenic materials for largescale applications such as water purification.