Comparative approach towards the adsorption of Reactive Black 5 and methylene blue by n-layer graphene oxide and its amino-functionalized derivative

Abstract

N-layer graphene oxide (nGO) was synthetized from graphite oxidation via the modified Hummers method and then functionalized with diethylenetriamine to obtain the novel n-layer amino-functionalized graphene oxide [nGO-(NH)R]. Scanning electron and atomic force microscopies, thermogravimetric analysis, Raman and infrared spectroscopies and X-ray diffraction were employed to characterize nGO and nGO-(NH)R. This nanosorbent was then evaluated through the sorption of anionic Reactive Black 5 (RB5) and cationic methylene blue (MB). pH effect analysis showed that adsorption of anionic RB5 were not influenced by pH changes; on the other hand, cationic MB adsorption was higher at pH 12.0. Langmuir isotherm best fitted the adsorption of both dyes onto nGO-(NH)R and showed maximum monolayer adsorption capacity of 3036.43 and 335.86 mg g−1 for MB and RB5, respectively. Adsorption kinetics indicated that the system reached the equilibrium state within 5 min for MB, and after 90 min for RB5, with adsorption capacity at equilibrium (qe) of 977.06 and 177.85 mg g−1 and kinetic constant (kS) of 3.17 × 10−2 and 2.40 × 10−3 g mg−1 min−1, for MB and RB5 respectively. Additionally, pseudo-second-order model was better fitted to the experimental data for the adsorption of both dyes in nGO and nGO-(NH)R. Thermodynamic parameters exhibited the following values: ΔHo, − 150.01 kJ mol−1, 92.83 kJ mol−1 and ΔGo (at 298 K), − 37.94 and − 22.86 kJ mol−1, for MB and RB5 removal onto nGO-(NH)R respectively, which evidenced the spontaneous adsorption of both dyes and chemisorption behavior of RB5. Recycling experiments showed that the nGO-(NH)R maintained the MB and RB5 removal rate above 95% and 58%, respectively, after ten cycles. Experiments with raw textile effluent showed a decrease of 55% in chemical oxygen demand (in mg O2 L−1) and 90% of its concentration after adsorption by nGO-(NH)R.