Hydrous ZrO₂ decorated polyaniline nanofibres: Synthesis, characterization and application as an efficient adsorbent...

A new hybrid material comprising hydrous zirconium oxide (HZrO₂) supported onto polyaniline (PANI) nanofibres (HZrO₂@PANI NFs) was prepared via the precipitation of HZrO₂ onto as-synthesized PANI NFs and tested for its defluoridation capabilities. The developed adsorbent (HZrO₂@PANI NFs) was fully characterized by FTIR, BET, XRD, SEM-EDX, TEM-(S)TEM, XPS, and zeta potential measurements. HZrO₂@PANI NFs achieved 2-fold BET surface area ∼86.64 m²/gas compared to PANI NFs ∼44.72 m²/g, implying that the incorporation of HZrO₂ onto the PANI nanofibres enhanced the available surface area for effective fluoride adsorption. Moreover, HZrO₂@PANI NFs was found to be effective over a wide pH range (3-9) as designated by its high pH_pzc ∼9.8. The adsorption kinetics obeyed the pseudo-second-order model well with equilibrium attainment in 30min. Adsorption isotherm was best described by the Langmuir model and the maximum adsorption capacities obtained were 83.23 and 28.77mg/g at pH 3 and 6.5, respectively, which is superior to most ZrO₂ based adsorbents reported in the literature and better than that of native PANI. Furthermore, the developed adsorbent manifested quite a selective fluoride uptake at pH 3 as compared to pH 6.5±0.1 wherein significant chemical affinity competition was presented by phosphate ions followed by bicarbonate and sulfate. The recyclability of HZrO₂@PANI NFs for four cycles and its applicability to fluoride spiked ground water has also been demonstrated. The adsorption mechanism was interpreted with the help of FTIR, XPS and Zeta potential analysis and the results revealed the involvement of both anion exchange and electrostatic attraction in the adsorption of F^- ions. Thus, a new efficient adsorbent with reasonably high adsorption capacity and superior pH tolerance has been developed for fluoride removal.