Removal of hexavalent chromium from aqueous solution by mesoporous α-FeOOH nanoparticles: Performance and mechanism

The present work is aimed at studying the properties of α-FeOOH adsorption for removing Cr(VI) from aqueous solution. Batch adsorption experiments were carried out to measure the influences of various parameters (contact time, pH of the medium and adsorbent dosage) for Cr(VI) adsorption taking place on the α-FeOOH nanoparticles surface. Results showed that the process of Cr(VI) adsorption was strongly dependent on the pH, displaying that the adsorption efficiency of Cr(VI) reached the maximum in the pH 3 at an initial Cr(VI) load of 15 mg/L. The thermodynamic parameters such as enthalpy change (ΔH0), entropy change (ΔS0), Gibbs free energy (ΔG0) and Isosteric heat of adsorption were also estimated. The negative value of ΔG0 and positive value of ΔH0 indicated a spontaneous and an endothermic thermodynamically adsorption process, respectively. The values of ΔHx demonstrated that the interaction between α-FeOOH nanoparticles and Cr(VI) was primarily physical adsorption. The adsorption process of Cr(VI) could be simulated by the pseudo-second-order kinetic equation. Intra-particle diffusion model showed that the overall adsorption rate of α-FeOOH for Cr(VI) was dominated by the film diffusion process with some degree of intra-particle diffusion. [Display omitted] •The as-prepared α-FeOOH nanoparticles possessed mesoporous structures and high Cr(VI) adsorption capacity.•The Cr(VI) ions adsorption onto the α-FeOOH was an integrated physico-chemical process.•The XPS analysis demonstrated that a portion of Cr(VI) was reduced to Cr(III) by the α-FeOOH at pH 3.0.