In this study, we developed a new chemi-resistive, flexible and selective ammonia (NH₃) gas sensor. The sensor was prepared by depositing thin film of polyaniline-cobalt ferrite (PAni-CoFe₂O₄) nanocomposite on flexible polyethylene terephthalate (PET) through an in situ chemical oxidative polymerization method. The prepared PAni-CoFe₂O₄ nanocomposite and flexible PET-PAni-CoFe₂O₄ sensor were evaluated for their thermal stability, surface morphology and materials composition. The response to NH₃ gas of the developed sensor was examined thoroughly in the range of 1–50 ppm at room temperature. The sensor with 50 wt% CoFe₂O₄ NPs content showed an optimum selectivity to NH₃ molecules, with a 118.3% response towards 50 ppm in 24.3 s response time. Furthermore, the sensor showed good reproducibility, ultra-low detection limit (25 ppb) and excellent flexibility. In addition, the relative humidity effect on the sensor performance was investigated. Consequently, the flexible PET-PAni-CoFe₂O₄ sensor is a promising candidate for trace-level on-site sensing of NH₃ in wearable electronic or portable devices.

Purpose: The purpose of this paper is to prepare and optimize the preparation conditions of some new hydrogels and in addition, evaluate their water absorbance at different mediums and their ability to remove ions from aqueous solutions.Design/methodology/approach: Cellulose was extracted from depithed bagasse at two different pulping conditions; 3 and 6 hours cooking times, pulp (I) and (II), respectively. These pulps, in addition to cotton linter for comparison, were grafted with acrylamide followed by cross‐linking with glutaraldehyde. The networks were partially hydrolyzed and the structures of products (before and after hydrolysis) were studied using FTIR, SEM, TGA and X‐ray. The optimum preparation conditions were identified, before and after hydrolysis, to achieve maximum absorbance and the ability of prepared hydrogels to remove ions from solutions was investigated.Findings: Maximum level of absorption was recorded using hydrogels prepared with monomer concentration =0.8 mol/l, cross‐linker concentration =0.01 mol/l, reaction time =2 hours and temperature =65°C. Hydrogels prepared using pulp (I) showed the best absorbance behavior and a tendency to remove ions from water.Research limitations/implications: The ability of the prepared gels to remove ions from water could be further investigated to evaluate the ability of their use in a multi‐filtration system for water treatment.Practical implications: This piece of work has suggested a simple way to convert an agricultural waste to hydrogel able to remove metal ions from water.Social implications: Consuming this type of waste reduces the risks resulting from its burning in some countries, such as Egypt, that produce large amounts of it.Originality/value: In this paper, low cost hydrogels, with expected value in water treatment, were prepared using agricultural wastes. They have shown better reactivity than gels prepared using pure cellulosic materials (cotton linter).