Ammonia-sensing ability of differently structured hydroxyapatite blended cellulose nanofibril composite films

Abstract

Fully bio-based, flexible and lightweight nanocomposite films of different porosity/density were fabricated by integrating variable weight percentages of hydroxyapatite (HAp) nanoparticles within a matrix of cellulose nanofibrils (CNFs) using the one-directional freeze-drying technique, and utilised for study as ammonia sensors. Structural, morphological and thermal-stability characterizations of the samples were assessed by using X-ray diffraction and Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The sensing ability of the films was studied at low operating temperature (25 °C) in the presence of ambient air and 5 ppm of ammonia vapour by two probe electrodes. The results for gas sensing characteristics revealed that the amount and morphology of HAp, its distribution within the micro-porous CNF matrix, and doping on its surface, are the most important parameters which influence the gas sensing performance. It was observed that the film with integrated 5 wt% of HAp exhibited the detection limit of ammonia at a concentration as low as 5 ppm, remarkable high sensitivity (up to 575%) and fast response/recovery (210/30 s) as compared to the HAp (160%, 720/120 s) or CNF (382%, 540/160 s) samples. The designed nanocomposite sensors may be used as gas filters in technological applications using ammonia as indicators for freshness in smart and biodegradable food packaging materials or in high-tech protection clothing.