Novel synthesis of a clay supported amorphous aluminum nanocomposite and its application in removal of hexavalent chromium from aqueous solutions

Abstract

A bentonite supported amorphous aluminum (B–Al) nanocomposite was synthesized by the NaBH₄ reduction method in an ethanol–water interfacial solution and characterized with SEM, TEM, XRD, FT-IR and XRF. Surface morphology and line scans obtained from TEM imaging suggest the successful synthesis of the nanocomposite while XRF data shows a drastic change in Al concentration in the synthesized nanocomposite with respect to raw bentonite. This synthesized nanocomposite was further utilized for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. The very high removal efficiency of the composite for Cr(VI) (i.e. 49.5 mg g⁻¹) was revealed by the Langmuir sorption isotherm. More than 90% removal of Cr(VI) in just 5 minutes of interaction suggests very fast removal kinetics. Inner sphere complexation and coprecipitation of Cr(VI) can be concluded as major removal mechanisms. No influence of ionic strength suggests inner sphere complexation dominated in Cr(VI) uptake. pH of the solution didn't influence the sorption much but comparatively the removal was higher under alkaline conditions (99.4%) than under acidic conditions (93.7%). The presence of humic acid and bicarbonate ions reduced the sorption significantly. The final product, Cr–Al(OH)₃ results in precipitation by forming alum which indicates that clay supported amorphous aluminum nanocomposites can be considered as potential sorbents for toxic metal ions in the environment.