Effect of TiO₂ and Fe₃O₄ Co-loading on the morphology, tensile response, and Cu(II) uptake of electrospun recycled-PET nanofibers

Upcycling post-consumer poly(ethylene terephthalate) (PET) into water-treatment media advances circular-economy goals. We ask whether electrospun recycled-PET (rPET) nanofibers can host titanium dioxide (TiO₂), alone and with magnetite (Fe₃O₄), without sacrificing fiber integrity or Cu(II) uptake. Two formulations — P15T (12 wt% TiO₂ relative to PET) and P15FT (12 wt% TiO₂ + 9 wt% Fe₃O₄) — were electrospun from 15 wt% rPET in TFA/DCM and compared with same-programme neat-rPET (P15) and rPET–Fe₃O₄ (P15F) references tested under identical protocols [4]. Sol–gel TiO₂ was phase-pure anatase (crystallite 9.96 nm; particles 20–53 nm). After heat treatment, FE-SEM showed localized TiO₂ aggregation and surface voids in P15T but a more uniform P15FT surface. P15FT significantly outperformed P15T in ultimate tensile strength (45.3 ± 2.8 vs. 25.3 ± 2.8 MPa, p < 0.001), elastic modulus (631 ± 25 vs. 562 ± 28 MPa, p = 0.033), and toughness (14.8 ± 1.9 vs. 6.7 ± 0.8 MJ m⁻³, p = 0.003); elongation at break did not differ significantly ( p = 0.063). Absolute stress contrasts are indicative given systematically different mat thicknesses. In identical batch tests (1 mM CuSO₄, 5 × 5 cm², 100 mL, 120 min), Cu(II) uptake followed P15F (19.9 [4]) > P15FT (18.0) > P15T (15.6 mg g⁻¹) — surface interaction at oxide–water interfaces under ambient, dark conditions, not photocatalysis. Fe₃O₄ co-loading thus recovers the tensile properties lost with TiO₂ alone at a small uptake cost — a mechanical–adsorptive trade-off positioning co-loaded rPET nanofibers as a candidate multifunctional adsorbent, pending isotherm/kinetic, spectroscopic, and regeneration studies.