Self-polymerization magnetic hydrogel for Cu and Pb adsorption from aqueous solutions: theoretical insight and implication

In this work, the polyacrylic acid/carboxymethyl starch/Fe3S4 (PAA/CMS/Fe3S4) magnetic hydrogel was prepared. Pb and Cu in aqueous solution were as targeted pollutants for PAA/CMS/Fe3S4. Fe3S4 as the magnetic factor was added to the hydrogel. The hydrogel that composed by PAA and CMS can prevent Fe3S4 from oxidization. And, Fe3S4 not only had magnetic properties but also promoted the adsorption capacity of PAA/CMS/Fe3S4. In addition, the Fe(II) that in Fe3S4 served as the activator of potassium persulfate to produce SO4-· and triggered polymerization without the traditional method that need extra energy including heating and UV lighting, which can simplify the material preparation process. PAA/CMS/Fe3S4 exhibited adsorption stability in the pH from 3.0 to 6.0. The adsorption process fitted to pseudo-second-order and Langmuir-Freundlich models. The functional groups of C=O/Metal-O-C and O-C=O in PAA/CMS/Fe3S4 were identified by FTIR and XPS, which will adsorb Pb and Cu through complexation. The XRD results showed that the Pb and Cu can also be adsorbed by the formation of PbS and CuS, which due to the present of Fe3S4. The Density-functional theory analysis showed that the orbital hybridization between Pb and Fe3S4 was stronger than that of Cu and Fe3S4, which result in Fe3S4 had a stronger interaction with Pb than Cu. PAA/CMS/Fe3S4 magnetic hydrogel is a novel magnetic hydrogel and have a good adsorption performance for Pb and Cu from water. This work provides a new method for Fe3S4 application in magnetic adsorbent.