A colorimetric ammonia sensor based on interfacially assembled porous polymer membrane: coupled hydrogen-bonding and electronic structure modulation

Abstract

Real-time, low-power, and selective detection of ammonia (NH₃) is of critical importance in semiconductor manufacturing, environmental monitoring, and occupational safety. However, current sensing technologies often fall short in achieving a balance between sensitivity, stability, device integration, and user accessibility. In this work, we introduce a structurally asymmetric porous organic polymer membrane, synthesized via a liquid–liquid interfacial acylhydrazone condensation reaction, that enables rapid (∼1 s), reversible, and visually perceptible colorimetric sensing of NH₃. The membrane exhibits dynamic keto–enol tautomerism and a well-defined anisotropic morphology—featuring a dense organic-phase side and a highly porous, fibrous aqueous-phase side—that collectively enhance molecular diffusion and optical responsiveness. Upon exposure to NH₃, the disruption of intramolecular hydrogen bonding within the membrane backbone induces a pronounced absorption red-shift and a visible color transition from pale yellow to orange. Building on these molecular-level interactions, we engineer a laminated optical sensor that leverages UV-vis absorption changes for device-level signal transduction, achieving a quantification limit as low as 1 ppm. Additionally, we implement a smartphone-assisted RGB extraction method to enable semi-quantitative and user-friendly data analysis, highlighting the potential of the membrane for intelligent, field-deployable sensing. This work establishes a new paradigm in porous organic polymer-based gas sensors by uniting dynamic covalent chemistry, interfacial nanostructuring, and accessible device engineering to meet the demands of next-generation ammonia monitoring.