Keggin-type polyoxometalates supported on PANI-coated CuS: Synthesis, characterization and application as the efficient adsorbents for selective dye removal

In this work, Keggin type polyoxometalates H₃PW₁₂O₄₀ (PW₁₂), H₃PMo₁₂O₄₀ (PMo₁₂) and H₄SiW₁₂O₄₀ (SiW₁₂), were supported on polyaniline (PANI)-coated CuS nanoparticles by a facile stepwise modification method. These novel nanohybrids 1–3 (denoted as CuS@PANI/PW₁₂ (1), CuS@PANI/PMo₁₂ (2), and CuS@PANI/SiW₁₂ (3)) were fully characterized. The adsorption efficiency of these novel nanohybrids were evaluated for removing methylene blue (MB) and methyl orange (MO) that exhibited high selectivity and high adsorption rate for cationic MB rather than anionic MO. The adsorption results demonstrated a good ability to remove 25 mg L⁻¹ MB with the removal rates of ≥93%. The efficiency of nanohybrid 1 for the removal of MB was evaluated by several factors, such as pH, adsorbent dose, initial dye concentration and temperature. The adsorption isotherms and adsorption kinetic can be well described by the Langmuir isotherm model and the pseudo second order kinetic for MB, respectively. Moreover, the maximum adsorption capacity of MB reached 83.3 mg g⁻¹ in the study of the Langmuir adsorption isotherm, respectively. Thermodynamic studies show that the MB adsorption is a spontaneous endothermic process. The nanohybrids can be easily separated and reused without any change in performances and structures.