Preparation and characterization of chitosan-poly(vinyl alcohol)/bentonite nanocomposites for adsorption of Hg(II) ions

Chitosan-poly(vinyl alcohol)/bentonite (CTS-PVA/BT) nanocomposites with high adsorption selectivity for Hg(II) ions were synthesized by introducing BT into the CTS-PVA polymer matrix. The structure and morphology of the nanocomposites were characterized by XRD, FTIR and SEM, etc. The BT content has great influence on microstructure of the nanocomposites. BT is in the exfoliated state in the polymer matrix when the BT content is less than 7%. Whereas some of BT tends to be intercalated by CTS and an intercalate-exfoliated nanostructure is formed as the BT content is beyond 7%. Some of BT particles disperse as tactoids in the polymeric matrix and a flocculated-intercalated nanostructure is formed with further increasing the BT content. The nanocomposites possess a mesoporous structure with a narrow size distribution and BT can effectively enhance the thermal stability. The nanocomposites have high adsorption capacity and selectivity for Hg(II) ions. The adsorption capacities for Hg(II) ions with a BT content of 0%, 10%, 30% and 50% are 460.18, 455.12, 392.19 and 360.73 mg/g, respectively, which are much higher than that for Cu(II), Cd(II) and Pb(II) ions. Interestingly, BT can improve the adsorption selectivity of the nanocomposites for Hg(II) ions. In addition, the nanocomposites can effectively remove Hg(II) of different mercuric salts with various initial concentrations and pH.