Novel adsorbent nanoscale zero-valent iron supported on graphene for the removal of diazo Direct Red 81 from aqueous solution: Isotherm, kinetics, and thermodynamic studies

In this study, nanoscale zero-valent iron-graphene (nZVI-G) composite was synthesized and applied for the removal of diazo Direct Red 81 from aqueous solution. The prepared nanocomposite was characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), and Fourier-transform infrared spectroscopy (FTIR). The particle size was in the range of 20 to 35 nm. The effect of influential experimental variables on dye removal such as contact time, pH, adsorbent dosage, initial dye concentration, and the temperature was investigated. In optimum conditions, including contact time of 10 min, pH = 3, the adsorbent dosage of 0.05 g, and initial dye concentration=10 mg/l, dye removal was achieved 92%. Different adsorption isotherm models (Langmuir and Freundlich) were used and adsorption followed Langmuir isotherm well (R2= 0.9773). The maximum Langmuir adsorption capacity of nZVI-G was obtained 29.07 mg g-1. The pseudo-first-order kinetic model with R2=0.9838 fitted well to the experimental data. The thermodynamic parameters (∆G,∆H,∆S) were calculated and the results revealed that the adsorption of dye was spontaneous and exothermic. The nZVI-G composite was found to be a low-cost potential candidate with high adsorption capability to be applied as an adsorbent for the removal of Direct Red 81 from the aqueous media. Reduction degradation reaction which rapidly produces radicals has a major effect on reaction time. This nanoadsorbent has the ability to adsorb, reduction and degradation of pollutants, so the dye was removed efficiently.