Hierarchically structured polyacrylonitrile nanofiber mat as highly efficient lead adsorbent for water treatment

Hierarchical nanofiber mat (polyacrylonitrile/polypyrrole/manganese dioxide, PAN/PPy/MnO2) was prepared by electrospinning and followed by in situ polymerization of pyrrole monomer, and subsequently treated with KMnO4 solution to deposit MnO2. The obtained nanofiber mats were used as adsorbent for Pb(II) removal from aqueous solution. Fourier transform infrared (FTIR) results confirmed the presence of polypyrrole (PPy) and manganese dioxide (MnO2) layers on the surface of PAN nanofiber. The morphology and structure of the PAN/PPy/MnO2 nanofiber mat were studied by scanning electron microscopy (SEM) and transmission electron microscope (TEM). The hierarchical structures can be clearly seen from the SEM and TEM results. Thermo-gravimetric analysis (TGA) results showed that MnO2 accounts for about 9.25 wt.% in the PAN/PPy/MnO2 nanofiber. Adsorption results indicated that the adsorption performance for Pb(II) increased as the initial solution pH increased. The adsorption equilibrium reached within 120 min, and the process can be better described using the pseudo-second-order model. Isotherm data fitted well to the Langmuir isotherm model. Thermodynamic study revealed that the adsorption process is endothermic and spontaneous in nature. Desorption results showed that the adsorption performance can remain up to 80% after 5 times usage. The adsorption mechanism was also studied by XPS.