Adsorption properties of manganese oxides prepared in aqueous-ethanol medium toward Sr(II) ions

Abstract

In this study, nanostructured manganese oxides were synthesized using sol–gel method by reduction of KMnO4 with ethyl alcohol. Firstly, the effect of K+, Na+, Ca2+, and Mg2+ ions as templates on their structure and adsorption properties was studied. According to X-ray diffraction analysis, all samples were identified as amorphous phases. Fourier-transform infrared spectroscopy confirmed that prepared sorption materials had a band around 760 cm−1, characteristic for the tunnel-type manganese oxides. The BET surface area of the obtained samples was 188–293 m2 g−1, the sorption volume of 0.431–1.136 m3 g−1, and the average pore size of 6–20 nm. The maximum Sr2+ sorption capacity of 120 mg g−1 was observed for the non-templated manganese oxide sorbents synthesized at 25 °C during 5 h. The calculated isotherm parameters and corresponding correlation coefficients revealed that the Sr2+ uptake process followed the Freundlich and Redlich-Peterson models for metal ion-templated manganese oxides. The increase in temperature and time of synthesis, as well as the application of K+, Na+, Ca2+, and Mg2+ ions as templates led to the decrease of sorption capacity down to 40–60 mg g−1 and 60–80 mg g−1, respectively. The highest sorption efficiency of metal ion-templated manganese oxides in Na+, K+, and Ca2+-form was shown for 90Sr, its Kd being (3.8–5.1) × 103 cm3 g−1. For Na+ ion-templated sample, as typical, the Kd values were 2.0 × 10−1–8.6 × 104 cm3 g−1 in the pH range of 0.5–12.0 and 3.5 × 102–6.2 × 101 cm3 g−1 for Ca2+ ion concentration varied from 10 to 80 mM, respectively.