Adsorption of Cr (VI) on synthetic hematite (α-Fe_2O_3) nanoparticles of different morphologies

摘要

The adsorption of Cr (VI) from aqueous solution onto nanoparticles hematite (α-Fe_2O_3) of different morphologies synthesized by acid hydrolysis, transformation of ferrihydrite, sol gel methods has been investigated. The hematite particle sizes were in the range 15.69-85.84 nm and exhibiting different morphologies such as hexagonal, plate-like, nano-cubes, sub-rounded and spherical. The maximum adsorption capacity of Cr (Ⅵ) was found to be in the range 6.33-200 mgg~(-1) for all hematite samples. The kinetics of sorption was rapid, reaching equilibrium at 45-240 minutes. Sorption kinetics and equilibria followed pseudo-second order and Langmuir adsorption isotherm models. The rate constants were in the range 0.996-2.37 × 10~2 g/mg/min for all samples. The maximum adsorption was attained at pH 3.0, while adsorption decreased as the pH increased from pH 3.0 to 10.0. The study revealed that the hematite with plate-like morphology has the highest adsorption capacity. The sorption process has been found to be feasible following a chemisorption process, and adsorption of Cr (Ⅵ) onto hematite nanoparticles was by inner sphere surface complex-ation due to low desorption efficiency in the range 9.54-53.4%. However, the result of ionic strength revealed that the reaction was by outer sphere complexation. This study showed that morphologies play a vital role in the adsorption capacities of samples of hematite in the removal of Cr (Ⅵ) from aqueous solution.