Removal of Metanil Yellow from water environment by amino functionalized graphenes (NH2-G) – Influence of surface chemistry of NH2-G

In this paper, amino functionalized graphenes (NH2-G) were synthesized for the efficient removal of an acid dye, Metanil Yellow (MY). The morphology, physical structure and chemical properties of the NH2-G were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD) and N2 adsorption–desorption isotherms, respectively. Batch experiments were conducted on the adsorption of MY by the prepared modified graphenes to investigate the effect of several parameters such as pH, dye concentration, adsorption time and temperature. Optimal conditions for the adsorption system were as follows: pH of 7, 0.4 g L−1 adsorbent and contact time of 120 min with the maximum adsorption capacity of 71.62 mg g−1. The adsorption mechanism was investigated by (on the basis of) adsorption isotherms, adsorption kinetic and adsorption thermodynamics. MY adsorption by NH2-G was better fitted by both Langmuir isotherm among five different equilibrium models and pseudo-second-order kinetic model. Furthermore, the thermodynamic experiments results with the values of activation parameters such as free energy (ΔG, −4.729 to −5.592 kJ mol−1), enthalpy (ΔH, 8.120 kJ mol−1) and entropy (ΔS, 43.08 J mol−1 K−1) illustrated that the adsorption process of MY onto NH2-G was endothermic and spontaneous in nature. The results obtained in this study suggest that NH2-G is an excellent adsorbent for effective removal of Metanil Yellow from water.