Preparation of Fe(II)–Al layered double hydroxides: Application to the adsorption/reduction of chromium

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 516; pp. 362 - 374
• Main Authors: He, Xin, Qiu, Xinhong, Chen, Jinyi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05-03-2017
• Subjects: Adsorption; Layered double hydroxides; Reduction; Reduction; Adsorption; Cr; Layered double hydroxides
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2016.12.053

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•Fe–Al LDH showed good performances in the adsorption and reduction of Cr(VI).•The sorption mechanism of by Fe–Al LDH was explored and proposed.•A competitive adsorption between Cr(VI) and humic acid was observed.
Chromium is highly toxic and readily soluble in water. Herein, Fe(II)–Al layered double hydroxides (LDH) with Fe:Al ratios of 2:1 (LDH-2) and 3:1 (LDH-3) were synthesized by a hydrothermal synthesis method. The resulted products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) measurements, scanning electron microscopy (SEM), thermogravimetric analysis coupled with differential scanning calorimetry (TG/DSC), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Highly crystalline forms with sheet structure were revealed by XRD and TEM results, while the BET surface area of the LDH-2 and LDH-3 materials were 46.85 and 53.22m2/g, respectively. In addition, both products showed good performances in the removal of Cr(VI), although the removal efficiency of LDH-2 was higher than that of LDH-3. Based on the characterization results, two different removal mechanism involving both adsorption and reduction processes were proposed. The Fe2+ ions in LDH were involved in reducing Cr(VI) to Cr(III) while simultaneously being oxidized to Fe3+. pH was found to influence the adsorption of Cr(VI), with higher pH values being beneficial to the removal process. Common anions present in the environment such as SO42−, NO3−, and CO32− showed minor influence in the adsorption performance of the LDH materials. A competitive adsorption between Cr(VI) and humic acid (HA) was observed. The crystalline structure of LDH-2 collapsed after adsorption of very high concentrations of Cr(VI), thereby demonstrating once again that Fe involved in the lamination of LDH-2 was dissolved out to a large extent promoting the Cr(VI) to Cr(III) process.