Removal of Noxious Cr (VI) and Cr (III) Ions by Hierarchically Tailored Pseudo-Monolithic Silica/Activated Carbon Composite

Abstract

In the present study, 2.34 m (average) silica particles with large pore size (363 Å) have been prepared from bulk monoliths by using sol–gel method and were then chemically modified by reaction with a C-18 and was used for the adsorption of Cr (VI) and Cr (III) ions from wastewater. The prepared adsorbent was characterized by Scanning electronic microscope (SEM) and X-ray Diffraction (XRD) analysis before and after the adsorption of Cr (III) and Cr (VI) ions. The amount of Cr (III) and Cr (VI) adsorbed was detected by Atomic Absorption spectroscopy (AAS). The 90 % Cr (VI) and 98 % Cr (III) were achieved at pH3 and, 6 respectively. The process followed pseudo 2 nd order kinetics, Langmuir and Freundlich isotherms well. The ΔG values were -50.02 and -49.62 kJ mol −1 , for Cr(VI) ions and Cr(III) ions respectively, which show spontaneous adsorption of Cr(VI) and Cr(III) ions on to AC surface. ΔH was 44.18 kJ mol -1 for Cr(VI) and 39.55 kJ mol −1 “for Cr(III) ions, are showing the endothermic nature of adsorption. The ΔS (152 J mol -1 K -1 for Cr(VI) and 139.88 mol -1 K -1 for Cr(III) ions) showing sorbate/sorbent complex stability.