<p>Recent advancements in sustainable bio-sourced functional materials have focused on enhancing the valorization of lignin-derived biopolymers through innovative transformation methodologies. This study highlights breakthroughs in lignin-based Z-scheme heterojunction photocatalytic systems, emphasizing extended spectral responsiveness, optimized interfacial photoexcited carrier separation and reduced energy loss mechanisms. Two photocatalysts, Bi₂WO₆ (BWO) and ZnIn₂S₄ (ZIS) were co-engineered via a Z-scheme charge-transfer pathway using coaxial electrospinning and hydrothermal synthesis with lignin-based carbon nanofibers (CNFs), preserving the fibrous skeleton intact. The all-component photocatalytic nanomembrane exhibited superior mechanical strength (Young’s modulus = 20.38 MPa, toughness = 2.48 kJ/m³) under wet conditions along with accelerated stabilization kinetics (1°C/min, representing a 10-fold increase), resulting in significant energy savings. Using methylene blue (MB) as a model pollutant, the CNFs@BWO/ZIS nanomembrane achieved 94.4% degradation efficiency (<i>k</i> = 0.01664 min⁻¹) after 120 min of solar irradiation, while maintaining excellent recyclability through five successive cycles. Furthermore, we elucidated the systematic mechanism of surface charge-carrier migration in the Z-scheme heterojunction and MB decomposition. This photocatalytic system utilizing sustainable biomass functional materials paves the way for wastewater treatment, with the goal of achieving peak carbon emissions and carbon neutrality.</p>