Application of eco-friendly multifunctional porous graphene oxide for adsorptive sequestration of chromium in aqueous solution.

Abstract

Graphene oxide (GO) was functionalized using two silanes ((3-aminopropyl)-triethoxysilane and (3-mercaptopropyl)-triethoxysilane) to obtain, separately, the eco-friendly amine-functionalized GO (GONH) and thiol-functionalized GO (GOSH). Both silanes were also used together to obtain the amine-thiol dual functionalized GO (GOSN). Various physicochemical characterizations were obtained including spectra from using Fourier transform infrared (FTIR) spectrometer, Thermo-gravimetric analyzer and X-ray diffractometer. The adsorbents were used for a comparative study of Cr adsorption from aqueous solution. The obtained data were fitted to Pseudo-First Order (PFO) and Pseudo-Second Order (PSO) models, the homogeneous Fractal Pseudo-Second Order (FPSO) and the Weber-Morris intraparticle diffusion (IPD) kinetics models. Model parameters of the Langmuir and Freundlich adsorption isotherm models, as well as the thermodynamics were calculated. Characterization results showed successful functionalizations. The GONH, GOSH and GOSN exhibited alkaline, acidic and neutral pH, respectively, in water. Amine and thiol functional groups were observed in the new adsorbents, as well as reduced orderliness. The adsorbents had higher density per unit weight and better thermal stability than pristine GO. Equilibrium Cr adsorption was attained within 60 min for all adsorbents. The PSO and FPSO described the rate data better. The Cr adsorption decreased as solution pH increased; optimum adsorption was recorded at pH 2. Equilibrium adsorption data fitted the Langmuir adsorption isotherm model for the GONH, while it fitted the Freundlich for both GOSH and GOSN. The adsorption process was theoretically exothermic process that was spontaneous processes. The Cr adsorption capacities of these adsorbents are 114, 89.6 and 173 mg/g for GONH, GOSH and GOSN, respectively, and these were better than several reported graphene based adsorbents, and suggests the potential of these adsorbents for water treatment.