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

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.