N-doped polymeric resin-derived porous carbons as efficient ammonia removal and detection media

Abstract

Nitrogen-containing polymeric resin-derived carbons were prepared and used as ammonia adsorbents at dynamic conditions in dry air. For their preparation different combinations of melamine/urea and phenol/resorcinol/formaldehyde were selected as the nitrogen and carbon sources, respectively. Surface structural and chemical features of the carbons were further modified by oxidizing the samples in air at 350 °C. The adsorption capacity significantly increased after this process, reaching 73 mg/g, which, to the best of our knowledge, is higher than those reported in the literature for other carbon materials. It was found that the specific surface chemistry, arising from the type of the nitrogen source used for the preparation of the carbons, governs the ammonia adsorption mechanism. Nitrogen located in six-membered rings in the form of pyridines, pyridine-N-oxides and quaternary nitrogen, rather than other peripheral nitrogen species (amines, amides), was found to enhance ammonia adsorption. The air-oxidized samples also showed high sensitivities as ammonia sensors. A linear correlation between the sensor response and the number of weakly acidic groups was observed. The material with the highest adsorption capacity showed the optimal electrical performance. Melamine-phenol-urea was found to be the best combination of precursors leading to the highest ammonia uptake and sensitivity in the application as a gas sensor.