A facile, green and scalable approach to fabricate hierarchical ZnAl-LDH for efficient removal of hexavalent chromium

Abstract

A convenient, green, and scalable production approach to cost-effective adsorbents with large adsorption capacity is exceedingly desirable yet challenging. Herein, a unique hierarchical zinc–aluminum layered double hydroxide (ZnAl-LDH-D) is obtained through a solid–liquid reaction with only zinc oxide (ZnO) and aluminum nitrate [Al(NO₃)₃] as the feedstocks. The synergistic activation involving hydrolysis of Al³⁺, etching of ZnO, and reconfiguration of LDH results in a fast-kinetic behavior (less than 1 min), and it is quite easy to produce at least 200 g in one batch in lab-scale. In the removal of Cr^VI, ZnAl-LDH-D can function steadily under different pH ranges (4–10) with a high adsorption capacity of 73.4 mg g⁻¹ and a strong removal ability (from 10 mg L⁻¹ to 3.3 μg L⁻¹). Using a deuterated experiment and a series of characterization technologies, we clarified the removal mechanism of Cr^VI and revealed that the hydroxyl groups play a critical role in the removal process, including complexation, replacement, and reduction. Therefore, our work develops a new strategy for convenient scale-up production of ZnAl-LDH-D and provides guidance for exploring efficient adsorbents.