Selective adsorption of Mo(VI) ions from aqueous solution using a surface-grafted Mo(VI) ion imprinted polymer

Abstract

In this study, a novel Mo(VI) ion-imprinted polymer (Mo(VI)-IIP) was prepared by surface imprinting method. For this purpose, molybdenum (VI), isonicotinic acid (IN) and silica gel were used as the template ion, functional monomer and support, respectively. An acidified solution was used to remove the template ions from the polymer matrix. Different properties of the synthesized adsorbent were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) analysis. The adsorption behavior was investigated in detail by batch experiments. The results showed that the maximum adsorption capacity was 126.06 mg g−1, which was observed at pH 3 and at 25 °C. The equilibration time for adsorption of Mo(VI) and the optimum solid/liquid ratio were found to be 10 min and 1 g L−1, respectively. According to kinetics studies, the adsorption process follows pseudo-second order kinetics with a correlation coefficient R2 = 0.99. Also, the adsorption equilibrium data fitted well with the Langmuir isotherm model and the maximum adsorption capacity of the synthesized adsorbent was 131.75 mg g−1, which was very close to the experimental value obtained under optimal conditions. Selectivity investigations demonstrated that Mo(VI)-IIP had a high selectivity coefficients towards Mo(VI) ions in the presence of competing ions. Furthermore, thermodynamics studies defined the adsorption process as an exothermic (ΔH < 0) and spontaneous (ΔG < 0) process. Finally, Mo(VI)-IIP can be reused for at least six cycles with negligible loss of its adsorption capacity.