Chromium adsorption from aqueous solution using novel green nanocomposite: Adsorbent characterization, isotherm, kinetic and thermodynamic investigation

In this study, Peganum harmala seed was used as a precursor for the preparation of powdered activated carbon (PAC). In addition, the plant extract was used for the synthesis of zero-valent iron nanoparticles (GnZVI). Then GnZVI was loaded on PAC and used as a novel green nanocomposite to adsorb hexavalent chromium from aqueous solutions. In order to synthesize activated carbon and nanoparticles, ultrasonic waves were used as a new tool for carbon activation and nanoparticle preparation. TEM images were used to show the synthesis of iron nanoparticles with a size of <60 nm. Based on the results of FESEM test, it was found that the surface of the produced activated carbon had many pores which indicated the effective role of ultrasonic waves in the process of activation. EDAX analysis was used to confirm the loading of GnZVI on PAC; based on the results, Fe was present on PAC after loading GnZVI. In addition, the FTIR range confirmed the role of hydroxyl groups generated by organic compounds in the synthesis of nanoparticles. BET test showed that after the loading of Iron nanoparticles the specific surface area of activated carbon reduced from 442 m(2)/ g to 107 m(2)/g. The results of adsorption tests showed that the loading of GnZVI resulted in an increase in the adsorption capacity of hexavalent chromium. Equilibrium adsorption test showed that laboratory data were well-fitted with Langmuir model and kinetic experimental data were consistent with Ho pseudo-second order model; moreover, intraparticle diffusion and film diffusion were the mechanisms involved in the adsorption process. Thermodynamic data on adsorption showed that the adsorption process was endothermic and spontaneous; furthermore, with increasing the temperature, the removal efficiency of chromium increased too. (C) 2018 Elsevier B.V. All rights reserved.