Site passivation and structural densification drive long-term low-emissivity MXene films

Functional-group coordination and lamellar structure determine the stability of MXene. • Strong Ti-S bonding passivates active Ti sites and suppresses oxidation. • Functional-group synergy induces ordered and compact MXene lamellae. • Infrared emissivity remains 0.18 after three humid-heat cycles. MXene exhibits intrinsically low infrared (IR) emissivity, making it a promising candidate for IR stealth applications. However, its pronounced oxidation susceptibility constrains long-term stability. Herein, serine (Ser) and glutathione (GSH) were employed to elucidate how functional-group modification regulates active-site passivation and structural densification in MXene films. The coordination affinity of functional groups toward reactive Ti sites plays a key role in environmental stability, with thiol (−SH) moieties preferentially forming strong coordination bonds to passivate active sites, thereby suppressing oxidative degradation. Simultaneously, the synergistic interplay of multiple functional groups promotes nanosheet alignment and structural compaction, effectively hindering oxygen and water penetration. Benefiting from the synergistic effects of active-site passivation and structural densification, the modified MXene film retains low IR emissivity (∼0.18) after three consecutive 24 h humid-heat aging cycles, whereas the emissivity of pristine MXene increases to ∼ 0.34 under the same conditions. This study presents a rational design framework for durable, low-emissivity MXene materials. Download: Download high-res image (199KB) Download: Download full-size image