Fabrication and Adsorptive Performance of Carbon Nanotube/Polypyrrole@poly(acrylonitrile-co-styrene) Nanofibers for Sustainable Removal of Methyl Orange Dye from Aqueous Media

Abstract

This work reports the fabrication and application of electrospun carbon nanotube/polypyrrole@poly(acrylonitrile-co-styrene) (CNT/Ppy@PAN-ST) nanofibers as efficient adsorbents for the removal of methyl orange (MO), a carcinogenic azo dye, from water. SEM analysis confirmed uniform nanofibers with diameters of 191–252 nm, while FTIR, XRD, NMR, and TGA verified successful incorporation of Ppy and CNTs, enhanced stability, and reduced crystallinity favorable for adsorption. Batch experiments revealed strong pH dependence, with ∼93% removal at pH 5. Kinetic modeling followed a pseudo-second-order model (R2 = 0.981), indicating chemisorption, and equilibrium data best fit the Langmuir isotherm (R2 = 0.991), yielding a maximum adsorption capacity of 189.14 mg/g. Thermodynamic parameters (ΔG° = −3.89 to −6.53 kJ/mol, ΔH° = +17.12 kJ/mol, and ΔS° = 72.21 J/mol·K) confirmed spontaneous and endothermic adsorption. The nanofibers exhibited strong reusability across seven cycles, with efficiency decreasing from 92 to 70%. Mechanistic analysis indicated electrostatic interactions, π–π stacking, hydrogen bonding, and van der Waals forces as dominant uptake mechanisms. Furthermore, the adsorption performance under realistic conditions showed that the nanofibers maintained over 90% efficiency across varying salinity levels and above 80% in the presence of coexisting heavy metal ions (Mn(VII), Cr(VI), Fe(II), Cu(II), and Cd(II)), confirming their high tolerance, selectivity, and stability in complex wastewater environments. Optimization via response surface methodology (Box–Behnken design) identified near-neutral pH, moderate contact time, and balanced dosage as optimal, achieving >97% removal. These findings highlight CNT/Ppy@PAN-ST nanofibers as robust, recyclable, and sustainable adsorbents for wastewater remediation.