Coffee Ground-Derived Carbon Dots Reinforced Zein/pvdf Electrospun Nanofiber Membranes with Antioxidant and Photodynamic Antibacterial Activities

Coffee grounds were utilized as a sustainable biomass precursor to synthesize carbon dots (CG-CDs), providing a value-added route for agro-industrial waste reutilization. The as-prepared CG-CDs were incorporated into a zein/polyvinylidene fluoride (PVDF) matrix, and multifunctional composite nanofiber membranes were fabricated by electrospinning. The influences of CG-CDs incorporation on membrane morphology, thermal behavior, mechanical performance, surface wettability, antioxidant activity, and photodynamic antibacterial properties were systematically evaluated.. The results indicated that the incorporation of CG-CDs increased fiber diameter while maintaining a continuous fibrous morphology. In addition, the composite membranes exhibited improved thermal stability and increased hydrophilicity, while mechanical testing revealed a clear strength–flexibility trade-off, characterized by decreased tensile strength and increased elongation at break. More importantly, CG-CDs significantly strengthened the radical-scavenging activity of the membranes and enhanced the light-responsive antibacterial activity against E. coli and S. aureus. ESR spin-trapping analysis further confirmed the light-induced generation of O₂•− and •OH by CG-CDs, providing direct evidence for their ROS-generating capability. These findings indicate that coffee ground-derived carbon dots can simultaneously modulate the physicochemical and functional properties of Zein/PVDF electrospun membranes, providing a resource-valorization strategy for the development of multifunctional fibrous materials.