Refolding Effect of MgAl Layered Double Hydroxides (MgAl-LDHs) for Removal of Toxic Anion in Aqueous Solution

Abstract

The layered double hydroxides (LDHs) are anionic clay with positively charged layers and counter-anions found in the interlayer spaces. The excellent intercalation and anion-exchange property of LDHs make it a promising material in many practical applications such as catalysis, anion adsorption, pharmaceutics, photochemistry, electrochemistry, and other fields. Cyanide (CN-) and tetracyanonickelate ([Ni(CN)4]2-) ions in wastewater are known to be major toxic substances. And then these toxic anions can be easily removed through the anion exchange capacity of MgAl-LDHs. And When LDHs are mixed in the cement curing process, it is used as an additive that prevented the penetration of chloride ion that cause concrete corrosion.

In this study, after high-temperature calcination of LDHs, the anion layer removed to form a cationic layer oxide, which material is defined as calcined LDHs (C-LDHs). After adding this substance to an aqueous solution, the anions of the aqueous solution are intercalated between the cation layers to form a layered double hydroxides structure again. This phenomenon is “Refolding Effect” and “Memory Effect”. LDHs calcined under heat treatment conditions have a specific surface area that is 3 times higher than that of pristine LDHs. After performing anion adsorption test with C-LDH and analyzing the solution after adsorption, it was confirmed that CN- 99.9% was removed, [Ni(CN)4]2- 98% was removed, and Cl- 77% was removed. After adsorption, the solution was analyzed by ion chromatography, ICP, and UV-vis to optimize the high-performance adsorption capacity of C-LDHs.