Understanding the ammonia sensing behavior of filter coffee powder derived N-doped carbon nanoparticles using the Freundlich-like isotherm

We report the synthesis of nitrogen-doped carbon nanoparticles (N-CNPs) with different nitrogen at% from coffee powder as a single precursor (that serves as both carbon and nitrogen sources) using a hydrothermal route and the ammonia sensing with N-CNPs as a chemiresistive material. We show that ammonia sensing is possible at room temperature for which the presence of oxygen is essential and the sensing mechanism is similar to that for semiconductor oxides. We also show improved performance in terms of the range of detection, sensitivity and response time with N at%. Furthermore, it has been shown that the dependency of sensitivity on ammonia concentration can be expressed by the Freundlich equation. Interestingly, the sensitivity and Freundlich constant (adsorption capacity) show similar exponential enhancement which advocates the improvement in the low detection limit with N at% as observed experimentally. Finally, the Freundlich exponent (adsorption intensification) is shown to increase linearly with N at%.