Chiang Mai Journal of Science

     The Zn-Cr layered double hydroxide was intercalated with polyoxometalate ion [α-SiW₁₂O₄₀]⁺ to form Zn-Cr-[α-SiW₁₂O₄₀]. Materials were characterized by X-Ray, FTIR, and nitrogen adsorptiondesorption and pH pzc analyses. Then materials were applied to remove cobalt(II) from in watery phase. Factors that affecting the adsorption included effect of adsorption time, initial concentration of cobalt(II), and adsorption temperature were systematically examined. The performance of Zn-Cr and Zn-Cr-[α-SiW₁₂O₄₀] were studied by regeneration process. The results showed that Zn-Cr layered double hydroxide has interlayer galley 7.53 Å. Zn-Cr-[α-SiW₁₂O₄₀] layered double hydroxide after intercalation has a unique diffraction peak at 8.62o with an interlayer gallery 10.35 Å; thus interlayergallery increase 2.82 Å after the intercalation process. The surface area properties were also increased from 31.638 m²/g to 128 m²/g after intercalation. The pH pzc of Zn-Cr and Zn-Cr-[α-SiW₁₂O₄₀] layered double hydroxides were 7.5 and 8, respectively, and adsorption of cobalt(II) was conducted at these pH media. Adsorption of cobalt(II) on both adsorbents follows the pseudo second-order kinetic model and is categorized as physical adsorption in the range of energy 17.628-64.452 kJ/mol. Zn-Cr-[α-SiW₁₂O₄₀] follow the Langmuir isotherm model with an adsorption capacity is 45.45 mg/L at 303 K. That capacity is higher than Zn-Cr LDH, which has an adsorption capacity 30.39 mg/L at 303 K. Adsorption of cobalt(II) on layered double hydroxide was sharply decreased after three-time cycles due to sprayed and exfoliated of layered double hydroxide structure.