Flexible and Porous Gasochromic Film Based on Polyoxomolybdate‐Loaded Cellulose Acetate for Ultra‐Sensitive Hydrazine Detection

Hydrazine (N 2 H 4 ) is widely recognized as an environmental pollutant due to its high toxicity, flammability, and explosiveness, necessitating rapid, sensitive, and portable on‐site detection technologies. This study presents a high‐performance gas‐sensitive film based on a cellulose acetate (CA) and polyoxometalate (POM) composite for spectral detection of hydrazine vapor. A Keggin‐type phosphomolybdic acid modified by solvated [Bi(DMF) 8 ] 3+ (Bi‐PMo 12 ) was used as the active component and uniformly loaded onto a CA porous membrane via solution blending and phase inversion to form a flexible, porous CA/Bi‐PMo 12 film. The film features a well‐developed pore structure, impressive mechanical flexibility, superior film‐forming ability, and inherent degradability, significantly boosting its adsorption capabilities and mass transfer capacity for hydrazine vapor. Upon exposure to hydrazine vapor, Mo(VI) in Bi‐PMo 12 is reduced to Mo(V), resulting in a color change and an increase in the UV‐Vis absorption peak at 720 nm. The sensor shows a linear detection range from 1 × 10 −1 to 1 × 10 −7 ppm. Mechanistic analysis confirms a four‐electron redox reaction between hydrazine and the CA/Bi‐PMo 12 film, leading to coloration of the reduced POMs. This work provides a new practical strategy for developing low‐cost and highly sensitive hydrazine vapor sensors.