Enhanced adsorption performance of aspartic acid intercalated Mg-Zn-Fe-LDH materials for arsenite.

A series of hydrophobic and hydrophilic amino acid (aspartic acid, phenylalanine, glutamic acid, and proline) intercalated LDH materials were synthesized and characterized. The results of batch experiments showed that Mg7Zn1Fe4-Asp-LDH and Mg7Zn1Fe4-Phe-LDH showed good adsorption performances for both arsenate and arsenite in aqueous solutions. The effects of various experimental conditions have been investigated by the batch test, which included the effects of initial pH, arsenic concentration, contact time and coexisting ions. For Mg7Zn1Fe4-Asp-LDH under the optimal experimental conditions, the maximum adsorption capacity of As(iii) and As(v) reached 94.81 mg g-1 and 57.42 mg g-1, respectively. It showed a higher adsorption capacity for As(iii) than that for As(v), which is of great significance to remove the trivalent arsenic species with higher toxicity. When the dosage of Mg7Zn1Fe4-Asp-LDH was 0.8 g L-1, the concentration of As(iii) in the aqueous solution could be reduced from 2 mg L-1 to below 10 μg L-1.When Mg-Zn-Fe-Asp-LDH was applied in practical water samples with a dosage of 0.2 g L-1, the residual concentrations of arsenic in three actual water samples were all lower than 10 μg L-1 after adsorption. The column test showed that 1.0 g of Mg7Zn1Fe4-Asp-LDH could continuously treat 2.6 L of As(iii) aqueous solution (2 mg L-1) and reduced the concentration of As(iii) to below 10 μg L-1 or handle 0.4 L of arsenic-contaminated (10 mg L-1, As(iii) : As(v) = 1 : 1) water, and the effluent concentration was below 10 μg L-1. Compared with the previously reported hydrophobic amino acid intercalated LDHs, aspartic acid (hydrophilic amino acid) intercalated LDH has a good removal efficiency for arsenic. The synthesized Mg7Zn1Fe4-Asp-LDH is considered to be a potentially functional material that can be used to treat arsenic contamination in water.