Flexible Cu2O-Cu co-doped carbon nanofibrous membrane for efficient solar-driven clean water production

Flexibility is critical to the dimensional stability of photothermal materials during sustainable solar water evaporation. Herein, a flexible Cu 2 O-Cu co-doped carbon (Cu 2 O-Cu@C) nanofibrous membrane was fabricated by carbonization of polyacrylonitrile (PAN)/Cu(CH 3 COO) 2 nanofiber membrane at 400 °C. This process transformed Cu(CH 3 COO) 2 into a mixture of Cu 2 O and Cu. The Cu 2 O-Cu@C membrane achieved a significantly enhanced stress at break of 3.95 MPa—a 14.6-fold enhancement over pure carbon membranes (0.27 MPa). Moreover, the membrane exhibited excellent flexibility, as it recovered its original shape within 40 ms after folding and maintained its dimensional integrity throughout 1000 bending cycles. Raman spectroscopy and molecular dynamics simulations demonstrated that Cu 2 O-Cu co-doping dramatically improves mechanical properties by (1) increasing density, which enhances structural densification, (2) introducing new interatomic energy contributions that strengthen interfacial interactions, and (3) improving stress transfer and crack inhibition to promote external force dissipation. Under one sun illumination, the Cu 2 O-Cu@C nanofibrous membrane achieved evaporation rates of 1.57 kg·m −2 ·h −1 for 3.5 % saline water and 1.61 kg·m −2 ·h −1 for actual dye wastewater. In addition, following hydrophilic hydrogel modification, the Cu 2 O-Cu@C membrane maintained a stable evaporation rate exceeding 1.76 kg·m −2 ·h −1 during 10-h indoor tests. It also showed no salt crystallization in outdoor testing, confirming its salt resistance and long-term stability for practical applications. These findings will encourage research aimed at enhancing the mechanical properties of PAN-based carbon nanofibers, which are intended for applications in flexible photothermal evaporators, wearable electronics, and related devices.