Fast and efficient removal of Cr(VI) to ppb level together with Cr(III) sequestration in water using layered double hydroxide interclated with diethyldithiocarbamate

It is still a great challenge to find an eco-friendly, easy-to-synthesize, and cheap adsorbent to rapidly remove Cr (VI) to ppb level in the Cr(VI)-polluted water. Herein, a new layered double hydroxide nanocage intercalated with diethyldithiocarbamate (DDTC-LDH) was fabricated via a facile calcination-rehydration method. The DDTC-LDH rapidly decreased Cr(VI) concentration from 5 to <0.05 mg/L within 35 min, and only a few seconds were required to completely remove it at an initial concentration of 0.5-1mg/L, primarily attributed to the effective adsorption-reduction of Cr(VI) to Cr(III) by sulfur atoms in C-S and C=S groups. Attractively, the generated Cr(III) was also quickly removed to below 0.1 mg/L via an opportune Lewis hard-hard interaction with C-SOx groups produced through C-S oxidation. Additionally, Cr(VI) could be removed by DDTC-LDH at a wide pH application range (3.17-10.78) and with weak effects by coexisting anions (Cl-, NO3-, CO32-, SO42-, and PO43-). We systematically analyzed and proposed the mechanisms for Cr(VI) removal by the DDTC-LDH, orderly containing electrostatic attraction, Cr(VI) complexation by sulfur atoms in C-S and C=S groups, reduction of the Cr(VI) to Cr(III) by the C-S and C=S groups, and Cr(III) complexation by sulfur atoms in C-SOx groups. Our results provide new insights into the Cr(VI) removal using organosulfur compounds, that is to say, the organosulfur group Lewis hardness increased (from C-S to C-SOx) as the Cr species Lewis hardness increased (from Cr(VI) to Cr(III)), so as to opportunely ensure fast and efficient capture of both Cr(VI) and Cr(III) via Lewis acid-base interactions. (C) 2020 Elsevier B.V. All rights reserved.