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In this study, the adsorption of Ni2+ and Fe3+ metal ions from aqueous solutions onto graphene oxide (GO) have been explored. The effects of various experimental factors such as pH of the solution, initial metal ion concentration and temperature were evaluated. The kinetic, equilibrium and thermodynamic studies were also investigated. The adsorption rate data were analyzed using the pseudo-first-order kinetic model, the pseudo-second-order kinetic model and the intraparticle diffusion model. Kinetic studies indicate that the adsorption of both ions follows the pseudo-second-order kinetics. The isotherms of adsorption data were analyzed by adsorption isotherm models such as Langmuir and Freundlich. Equilibrium data fitted well with the Langmuir model. The maximum adsorption capacities of Ni2+ and Fe3+ onto GO were 35.6 and 27.3 mg g-1, respectively. In addition, various thermodynamic parameters, such as enthalpy (ΔHO), entropy (ΔSO) and Gibbs free energy (ΔGO), were calculated. [ABSTRACT FROM AUTHOR]

The adsorption of cationic dyes Basic Yellow 28 (BY28) and Basic Red 46 (BR46) from an aqueous solution by graphene oxide (GO) as adsorbent is presented. Graphene oxide is prepared using a modified Hummers’ method and characterized by Fourier Transform-Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Atomic Force Microscopy (AFM), Raman spectroscopy, Transmission Electron Microscopy (TEM) and zeta potential measurements. Adsorption properties of cationic dyes using GO were studied in different dye concentrations (10–50 mg L −1 ), pH of the solutions (3.0–11.0), and temperature range of 20–60 °C. The Langmuir and Freundlich isotherm models were applied to fit the adsorption data. Equilibrium data fitted very well with the Langmuir isotherm model. The maximum monolayer adsorption capacity of BY28 and BR46 onto GO was 68.5 and 76.9 mg g −1 , respectively. The experimental kinetics data were analyzed using pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models. The kinetic studies showed that the adsorption data followed the pseudo-second-order kinetics model. In addition, various thermodynamic parameters, such as the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were calculated and it was revealed that the adsorption of BY28 and BR46 was spontaneous and endothermic. [ABSTRACT FROM AUTHOR]

In the present study, graphene oxide (GO) was used for the adsorption of anionic azo-dyes such as Acid Orange 8 (AO8) and Direct Red 23 (DR23) from aqueous solutions. GO was characterized by Fourier Transform-Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetric Analysis (TGA), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HRTEM) and zeta potential measurements. The influence of dye initial concentration, temperature and pH on AO8 and DR23 adsorption onto GO was investigated. Equilibrium data were analyzed by model equations such as Langmuir Freundlich, Temkin, Dubinin-Radushkevich and Redlich-Peterson isotherms and were best represented by Langmuir and Redlich-Peterson isotherm model. Kinetic adsorption data were analyzed using the pseudo-first-order kinetic model, the pseudo-second-order kinetic model and the intraparticle diffusion model. The adsorption kinetics well fitted using a pseudo-second-order kinetic model. Thermodynamics parameters, ΔG°, ΔH° and ΔS°, were calculated, indicating that the adsorption of AO8 and DR23 onto GO was spontaneous process. The adsorption process of AO8 onto GO was exothermic, while the adsorption of DR23 onto GO was endothermic in nature. [ABSTRACT FROM AUTHOR]