Rapid and selective separation of molybdenum ions using a novel magnetic Mo(vi) ion imprinted polymer: a study of the adsorption properties

Abstract

In this work, we have developed a convenient method for the rapid and selective separation of Mo(VI) from aqueous solution by using a novel magnetic Mo(VI) ion imprinted polymer (Mo(VI)-MIIP) as the sorbent. This sorbent was synthesized using methacrylic acid (MAA) as the functional monomer, the Mo⁶⁺ anion as a template, ethylene glycol dimethacrylate (EGDMA) as a cross-linker, and Fe₃O₄@SiO₂ as the magnetic component. The template Mo⁶⁺ ions were removed from the polymer using a solution containing 10% (v/v) methanol in HCl (0.5 mol L⁻¹). The thermal stability, chemical structure, and magnetic properties of the synthesized sorbent were characterized using different techniques. Various parameters which affect the adsorption efficiency were evaluated in a batch system to determine the optimal adsorption conditions and reduce non-specific interactions. The results showed that the maximum adsorption capacity was 28 mg g⁻¹, which was observed at 25 °C. The equilibrium time for the adsorption of the Mo(VI) analyte was determined over 30 min, and the amount of adsorbent which gave the maximum adsorption capacity was 1 g L⁻¹. The kinetic data, obtained under optimum conditions, could be fitted with a pseudo-second order kinetic model with a high correlation coefficient (R² = 0.9971). The adsorption isotherm data could be well described using Langmuir adsorption isotherms, and the maximum adsorption capacity calculated from the Langmuir isotherm was 31.08 mg g⁻¹. This was very close to the maximum adsorption capacity obtained under optimal conditions. The selectivity studies indicated that the synthesized sorbent had a high single selectivity sorption for the Mo⁶⁺ anion in the presence of competing ions. The values of the thermodynamic parameters proved that the adsorption process of molybdenum onto the synthesized sorbent was exothermic (ΔH < 0) and spontaneous (ΔG < 0). In addition, the spent MIIP can be reused several times without a significant decrease in adsorption capacity.