Adsorption of an Azo Dye on Graphene Nanosheet: A Molecular Dynamics Simulation Study

Molecular dynamics simulation was used to investigate the adsorption of a typical azo dye on a graphene nanosheet (GNS). The influence of temperature on the adsorption process was studied in the temperature range of 288.15 to 338.15 K. The structural, transport, and thermodynamic properties of dye and GNS were investigated during adsorption. The results showed that the potential of mean force becomes more negative by reaching dye molecule to GNS surface which reflects the spontaneous adsorption of dye molecule on GNS. The structural studies showed that π-π stacking between benzene rings of dye and GNS surface plays a key role for an efficient adsorption. The results showed that after adding GNS to the dye solution the diffusion coefficient of dye decreased from 2.718×10-8 m2 s-1 to 1.755×10-8 m2 s-1 owning to adsorption. Both radial distribution function and density profile analysis showed that the interaction between water and dye weakens due in the presence of GNS. The isochoric heat capacity was calculated as 24.85 J mol-1 K-1. By increasing the temperature from 288.15 to 338.15 K, the adsorption energy decreased from -2.5070 to -1.7302 kJ mol-1. The negative and low adsorption energies indicate that the dye was physically adsorbed on GNS.