Synthesis of WS₄^2– Intercalated NiZnAl LDHs as Effective Adsorbents to Remove Copper Ions from Water

Abstract

A series of WS 4 2− intercalated NiZnAl ternary-layered double-hydroxides (LDHs) with various Ni/Zn ratios were synthesized by an ion-exchange method and used as adsorbents to remove Cu 2+ from water. The introduction of Zn produced ZnS on the surface of LDHs. The LDH with the Ni/Zn/Al molar ratio of 0.1/1.9/1 showed the best adsorption ability. Cu 2+ ions are removed via three routes: forming [Cu−WS 4 ] n− complexes via soft acid−soft base interaction between WS 4 2− and Cu 2+ , isomorphic substitution of Zn 2+ in sheets by Cu 2+ , and cation exchange of Cu 2+ , with ZnS on the surface of LDHs. With the increased Cu 2+ concentration, the complexes dominated the adsorption because polynuclear [Cu−WS 4 ] n− complexes with high Cu/W ratios (2−6) may be formed. Cu + is present in such complexes, which is produced by the internal redox. Even at Cu 2+ concentration up to 600 mg•L −1 , neither amorphous CuWS 4 nor decreased interlayer distance was observed. Contrarily, the interlayer distance was slightly enlarged due to forming bigger [Cu−WS 4 ] n− complexes. The adsorption followed the pseudo-second-order kinetics and Langmuir isotherm model. The experimental maximum adsorption capacity reached 555.4 mg•g −1 .