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Abstract: An original organic semiconductor gas sensor devoted to the selective monitoring of nitrogen dioxide in air has been successfully developed. This device combines the great sensitivity and the partial selectivity toward oxidizing gases of a molecular organic semiconductor, copper phthalocyanine, with the O3 filtering selectivity of an organic material, indigo. Experimental measurements highlight filtering yield of indigo close to 100% toward O3 and lower than 10% for NO2. Nanometric indigo layers were realized for the first time by thermal evaporation and characterized by FT-IR spectroscopy. Such all-organic device exhibits a high NO2 sensitivity for low concentrations, a resolution better than 20ppb, a threshold of detection to few ppb and a high level of selectivity. The influence of filtering layer thickness and the optimization for real-time measurements are also discussed. Beyond sensor development, such nanostructured indigo layers are relevant as protective element of electronic components against adverse ozone effects. [Copyright &y& Elsevier]

Abstract: In order to achieve the selective detection of NO2 in the environment, a chemical filter is added to a semiconductor gas sensor that is very sensitive to oxidizing gases in the gas flow. The aim is to remove ozone (O3), the main interfering oxidizing gas for NO2 detection before its measurement by a phthalocyanine sensor. The first parameter for the carbon material as a filter is the specific surface area (SSA), which should be high enough to ensure interaction with O3 and low enough to avoid interaction with NO2. The key role of surface oxygenated groups and dangling bonds was underlined by NEXAFS and EPR, respectively. A mixture of nanocones/nanodiscs (20/70%w/w) with SSA of 30m2 g−1 with both structural and electronic defects is found to be the most efficient filter and was used upstream of a phthalocyanine sensor. The lifetime of the chemical filter was investigated and a strategy to increase it is described. Raman spectroscopy, EPR and NEXAFS allow the reactivity of the carbon with NO2 and O3 in the 10–1000ppb concentration range to be studied. [Copyright &y& Elsevier]

Abstract: An original gas sensor system dedicated to the selective monitoring of nitrogen dioxide in air has been successfully developed. This device combines the great sensitivity and the partial selectivity toward oxidizing gases of a molecular organic semiconductor, copper phthalocyanine, with the O3 filtering capability of different carbonaceous nanomaterials located upstream the sensitive layer in the gas flux. The carbonaceous materials are used either as-prepared or modified by physical or chemical treatments. The ability to filter nitrogen dioxide and ozone, has been correlated to both the BET specific surface area determined by N2 adsorption at 77K and the presence of chemical functional groups at the surface. A sensing structure is finally proposed using a chemical filter containing nanocarbons, impermeable to ozone and inert toward nitrogen dioxide, leading to a selective NO2 sensor response. [Copyright &y& Elsevier]

Abstract: This study deals with a sensor system involving a resistive copper phthalocyanine gas sensor and a nanocarbonaceous filter achieving the selective measurement of nitrogen dioxide in an environmental context. The assignments of the interactions between the oxidizing gases, ozone and nitrogen dioxide, and the filtering material selected from the studies developed in Part I are established. Raman spectroscopy, EPR and NEXAFS studies were performed in order to propose chemical mechanisms between gases and nanocarbons. This study allows the working method of the system to be implemented, leading to the improvement of the carbonaceous filter durability. [Copyright &y& Elsevier]

Abstract: In previous reports, we have investigated on the influence of current transport mechanism on the sensitivity of InP Schottky and pseudo-Schottky diodes, for nitrogen dioxide detection. In this paper, the influence of the metal nature and the structure of the rectifying contact on the sensing layer are highlighted. More especially, we will focus on the behavior of these Schottky structures during and after their exposures to nitrogen dioxide (NO2) and ozone (O3). In this context, two types of structures have been studied: the simple Schottky diodes and the more elaborated structures called pseudo-Schottky. These diodes are realized with Au or Pd as metals. First, we will describe samples preparation and electrical characterization of the two types of structures. Then, we will compare sensor responses of these different structures under NO2 and O3. Finally, to better understand the action of these gases on the sensitive layer (the Schottky contact), X-rays photoelectron spectroscopy (XPS) is performed to follow the evolution of the metallic layer. The poisoning effect of active sites, which appears after NO2 and O3 expositions, is illustrated by comparative study of the active layer before and after exposure. [Copyright &y& Elsevier]

This article presents a literature review of sensors for the monitoring of benzene in ambient air and other volatile organic compounds. Combined with information provided by stakeholders, manufacturers and literature, the review considers commercially available sensors, including PID-based sensors, semiconductor (resistive gas sensors) and portable on-line measuring devices as for example sensor arrays. The bibliographic collection includes the following topics: sensor description, field of application at fixed sites, indoor and ambient air monitoring, range of concentration levels and limit of detection in air, model descriptions of the phenomena involved in the sensor detection process, gaseous interference selectivity of sensors in complex VOC matrix, validation data in lab experiments and under field conditions., Competing Interests: The authors declare no conflict of interest. The founding sponsors, EURAMET, had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

The widespread diffusion of sensors, mobile devices, social media and open data are reconfiguring the way data underpinning policy and science are being produced and consumed. This in turn is creating both opportunities and challenges for policy-making and science. There can be major benefits from the deployment of the IoT in smart cities and environmental monitoring, but to realize such benefits, and reduce potential risks, there is an urgent need to address current limitations, including the interoperability of sensors, data quality, security of access and new methods for spatio-temporal analysis. Within this context, the manuscript provides an overview of the AirSensEUR project, which establishes an affordable open software/hardware multi-sensor platform, which is nonetheless able to monitor air pollution at low concentration levels. AirSensEUR is described from the perspective of interoperable data management with emphasis on possible use case scenarios, where reliable and timely air quality data would be essential.

In order to enhance the durability of chemical filters for ozone molecules, devoted to microsystem for the selective detection of NO2 in the environment, the adsorption of indigo molecules onto the surface of carbonaceous nanomaterials (multi-walled carbon nanotubes, a mixture of nanodisks/nanocones, nanofibres) was investigated. The surface of the multi-walled carbon nanotubes was coated by π-stacking with adsorbed indigo molecules. An excess of indigo has resulted in a biphasic sample where nanotubes covered with indigo coexist with free indigo particles. Although similar filtering yields toward O3 (close to 100%) and NO2 (around 0%) were obtained as compared to individual materials, the indigo/MWCNTs samples exhibit enhanced durability as chemical filter at high ozone concentration (1 ppm)., (Copyright © 2013. Published by Elsevier Inc.)

The gas filtering abilities of different nanocarbon materials such as nanocones/nanodiscs, and nanofibres, either as-prepared or modified by physical (annealing, grinding) or chemical (fluorination) treatment are reported. The aptitude to filter nitrogen dioxide and ozone, two of the most significant gaseous pollutants of the atmosphere, have been correlated to both the BET specific surface area studied by N2 adsorption at 77 K, and the presence of chemical functional groups at the surface. Valuable information regarding the mechanisms of gas-nanocarbon interaction has been obtained, in terms of chemisorption and physisorption. A prototype microsystem is proposed for the selective measurement of nitrogen dioxide and ozone concentration by means of organic semiconductor gas sensors.