Development of PVDF/SrFe₁₂O₁₉/g-C₃N₄ nanocomposite films for VOC sensing at room-temperature

PVDF/SrFe₁₂O₁₉/g-C₃N₄ composite films were fabricated by the solution casting method by varying the strontium hexa ferrite (SrFe₁₂O₁₉) content from 10 to 20 wt% and keeping g-C₃N₄ content fixed at 5 wt% in the polyvinylidene fluoride (PVDF) matrix. XRD, FT-IR, FE-SEM, and EDAX analyses confirmed the structural, compositional, and morphological characteristics of the fillers and composite films. The results showed that the SrFe₁₂O₁₉ particle was of hexagonal structure with an average crystallite size of 27 nm and g-C₃N₄ of layer-like structure. Furthermore, the composite films were characterized by differential scanning calorimetry (DSC), UV-Vis spectroscopy and I-V analysis. DSC confirmed the thermal stability, whereas optical characterization depicted the broadband absorption of the composite films in the UV-Vis region. I-V analysis revealed the presence of leakage current in the composite films. XPS showed that the material has 39.1% surface oxygen vacancy defects and 55.4% oxygen adsorption sites, which is favourable to sensing the vapours of different volatile organic compounds. These surface defects act as active adsorption centres, enhancing gas-surface interaction and facilitating efficient charge transfer. The resistance variation and corresponding sensitivity toward different test analytes at varying concentrations were systematically studied at room temperature. The sensitivity of composite films toward ethanol (C₂H₅OH) was found to be better than ammonia (NH₃), tetrachloroethylene (C₂Cl₄), toluene (C₆H₅CH₃), formaldehyde (CH₂O) and hexane (C₆H₁₄). The sensing mechanism involves ethanol interacting with surface-adsorbed oxygen species, leading to electron transfer that modulates the electrical resistance of the film. All the composite films exhibited the ability to sense ethanol even at 1 ppm concentration at room temperature. The film with 20 wt% SrFe₁₂O₁₉ loading exhibited the highest sensitivity of 34.7% for 1 ppm ethanol, along with excellent repeatability, a low detection limit of ~ 24 ppb, and a quantification limit of 75 ppb. It also exhibits maximum sensitivity of 7.69 per ppm in the range 0-2 ppm. These findings highlight the potential of these flexible nanocomposite films for low ppm, real-time VOC detection in environmental and industrial settings.