Electrospun chitosan/polyvinyl alcohol nanocomposite holding polyaniline/silica hybrid nanostructures: An efficient adsorbent of dye from aqueous solutions

Abstract

In this work, the addition of a novel polyaniline (PANI)/silica (SiO2) nanostructure (PSn) in chitosan/polyvinyl alcohol nanofibers (CP) was evaluated to enhance the dye removal capacity of CP. Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) results confirmed the chemical grafting of SiO2 on PANI nanoparticles. Brunauer-Emmett-Teller (BET) results showed a specific surface area of 61 m2 g−1 for the PSn filled CP nanofiber (CP-PSn). FE-SEM and EDS-elemental mapping results showed the uniform dispersibility of PSn in CP nanofibers. After the addition of PSn into CP, the adsorption capacity of CP increased from 48 to 110 mg g−1 (from 0.069 to 0.158 mmol g−1), 40 to 90 mg g−1 (from 0.122 to 0.274 mmol g−1), and 31 to 45.2 mg g−1 (from 0.097 to 0.141 mmol g−1) for Congo red (CR), methyl orange (MO), and methylene blue (MB) dyes, respectively. The optimum anionic dye (CR and MO) uptake was observed at pH 5, while for the cationic dye (MB), the optimum uptake was detected at pH 9. The isotherm experiments results showed that the Sips isotherm model could well describe the adsorption process (R2 > 0.98). Thermodynamic studies at 298 and 328 K verified that the adsorption process is spontaneous with ΔG ranging between −10.44 and − 2.83 kJ mol−1. Also, ΔH was found to be 34.16, 22.25, and 17.05 kJ mol−1 for CR, MO, and MB adsorption, respectively. The highest recovery after 5 cycles was observed for a sodium hydroxide solution (NaOH, 0.1 M), which were 74, 68, and 55% of the adsorption capacity of the first cycle for CR, MO, and MB dyes, respectively.