Ammonia-Responsive Gelatin/Co-MOF Composite Films Based on Gallic Acid-Derived Metal-Organic Frameworks for...

Ammonia-responsive gelatin-based composite films containing cobalt metal-organic frameworks (Co-MOFs) synthesized using gallic acid as an organic ligand were developed and evaluated as intelligent packaging materials. Co-MOFs were incorporated into gelatin films at concentrations of 2.5, 5.0, 7.5, and 10.0% (w/w, based on gelatin). The effects of Co-MOF incorporation on the physicochemical, structural, thermal, mechanical, and sensing properties of gelatin films were systematically investigated. Increasing Co-MOF content reduced film moisture content (from 14.47 to 13.25-13.58%) and swelling capacity (from 599.37 to 484.88-547.30%), while increasing solubility (from 39.09 to 48.88%), water vapor permeability (WVP; from 1.652 to 2.054 g·mm/m²·h·kPa), and moisture sorption behavior. Sorption isotherm analyses based on the Guggenheim-Anderson-de Boer (GAB) and Brunauer-Emmett-Teller (BET) models confirmed enhanced water adsorption capacity and increased specific surface area in the films (from 356.13 to 455.74 m²/g). Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analyses demonstrated successful incorporation of Co-MOFs into the gelatin matrix, revealing good dispersion at low and moderate concentrations and partial aggregation at higher loadings. The incorporation of Co-MOFs improved the thermal stability of the films, while only a moderate reduction in mechanical strength was observed with increasing filler content. The composite films exhibited rapid and concentration-dependent colorimetric responses toward ammonia vapor. After 120 min of exposure, the color difference (ΔE) increased from less than 1 in the control film to approximately 12, 15, 24, and 27 for G/Co-MOF2.5, G/Co-MOF5, G/Co-MOF7.5, and G/Co-MOF10 films, respectively. Films containing higher amounts of Co-MOF showed faster response kinetics and greater color differences, enabling clear visual detection of ammonia. These findings demonstrate that gelatin/Co-MOF composite films based on gallic acid-derived metal-organic frameworks are promising intelligent packaging materials for monitoring food freshness and spoilage through ammonia detection.