Enhancing the sensitivity of chemiresistor gas sensors based on pristine carbon nanotubes to detect low-ppb ammonia concentrations in the environment

Abstract

The possibility of using novel architectures based on carbon nanotubes (CNTs) for a realistic monitoring of the air quality in an urban environment requires the capability to monitor concentrations of polluting gases in the low-ppb range. This limit has been so far virtually neglected, as most of the testing of new ammonia gas sensor devices based on CNTs is carried out above the ppm limit. In this paper, we present single-wall carbon nanotube (SWCNT) chemiresistor gas sensors operating at room temperature, displaying an enhanced sensitivity to NH3. Ammonia concentrations in air as low as 20 ppb have been measured, and a detection limit of 3 ppb is demonstrated, which is in the full range of the average NH3 concentration in an urban environment and well below the sensitivities so far reported for pristine, non-functionalized SWCNTs operating at room temperature. In addition to careful preparation of the SWCNT layers, through sonication and dielectrophoresis that improved the quality of the CNT bundle layers, the low-ppb limit is also attained by revealing and properly tracking a fast dynamics channel in the desorption process of the polluting gas molecules.

Synthesis of carbon nanofibers by thermal conversion of the molecular precursor 5,6;11,12-di-o-phenylenetetracene and its application in a chemiresistive gas sensor

“…27,28,30,44,45 Yet, one-dimensional single-walled carbon nanotubes detect amounts as low as 125 ppt NO 2 24 and 3 ppb NH 3 . 46 A comparison of sensor data of different carbon materials is given in Table S1 in ESI. † To the best of our knowledge, detection of sulfur dioxide using chemiresistors made of carbon nanobers has not been analyzed yet.…”

Semiconducting Carbon Nanotubes: Properties, Characterization and Selected Applications

“…Recently, low-cost CNT-based layers prepared on plastic substrates have been produced to monitor the presence of ammonia in the environment, where the NH 3 concentrations in the low-ppb range are expected [68]. A systematic monitoring of ammonia concentrations [69] is mandatory to reduce the hazard for human health and vegetation determined by the widespread use of ammonia and its derivatives as agricultural nitrogen fertilizers, which is known to determine a severe environmental problems, such as the eutrophication of semi-natural ecosystems, acidification of soils, formation of fine particulate matter in the atmosphere, and alteration of the global greenhouse balance.…”

“…However, little attention has been paid to the capability of these sensors to measure sub-ppm [NH 3 ] in air. In fact, ppt sensitivity of pristine CNTs to ammonia has been demonstrated, in inert Ar atmosphere under UV irradiation [71], a detection limit (DL) of 50 ppb has been achieved for ammonia diluted in Ar using CNTs functionalized with polianyline [72], and finally a detection limit of 30 ppb has been demonstrated for CNT layers on plastic substrates operating in ambient air [68].…”

Highly efficient Ceramic-SWCNT based free standing films for gas sensing application

“…Since then various types of techniques were proposed for fabrication of CNT based gas sensors like dip coating [17], spray coating [18], dielectrophoresis [19] and chemical vapor deposition (CVD) technique [20]. Even after making nanocomposite films the sensing performance has not been improved to an expected level.…”