On-board phthalocyanine gas sensor microsystem dedicated to the monitoring of oxidising gases level in passenger compartments

International audienceThe monitoring of in-vehicle pollutant concentrations by means of an on-board molecular semiconductor gas sensor microsystem is described in this paper. The main objective is to measure in real time with a high level of accuracy the variations of oxidising gases concentration in bus passenger compartments to inform travellers or commuters and to evaluate the assessment of bus drivers' exposure. A self-contained gas sensor microsystem of which the sensitive element is constituted by a thin layer of copper phthalocyanine has been developed, validated at laboratory under controlled experimental conditions and then implemented in a bus of the urban network of Clermont-Ferrand, France. Preliminary in-car measurements realized with commercial analyzers show that nitrogen dioxide is the major oxidising gas present on urban roads and so is considered as the target gas in this study. Tests realized under artificially polluted atmosphere show the high performances obtained with our microsystem, such as high resolution, low threshold, good reproducibility, satisfying concentration range and real time detection. The calibration curve has been determined at laboratory by experiments made under low NO2 concentrations in the range of those measured in urban atmosphere. The relation between sensor microsystem response and gas concentration is established with accuracy. The validation of our microsystem is illustrated by measurements realized under real conditions, i.e. in an urban bus. It shows that NO2 concentration variations are mainly correlated with the nature of roads and that rates of pollutant measured in traffic are always greater than those measured by the nearest stations of the air quality control network

A Chemical Microsystem for selective detection of polluting gases in vehicle compartments

International audienceThis paper deals with the design of an original microsystem devoted to the real time monitoring of air polluting gases in vehicle compartments. The selective detection is focused on two species, ozone and nitrogen dioxide, because of their specific toxicity. The gas sensing element is made of thin layers of an organic semiconductor provided with a specific chemical filter. A particular methodology of measurement is implemented, witch allows a selective sensing behaviour. On-board tests are presented

An original all-organic sensor with integrated gas filtering layer for selective measurements of NO2

International audienceThe selective and real time monitoring of oxidising gases in atmosphere by semiconductor gas sensors remains a real challenge despite all improvements to reach analyzer performances. Thanks to its insensitivity to reducing species and its high reactivity with oxidising ones, even for low concentrations, copper phthalocyanine (CuPc) is one of the most attractive semiconductor for this application. In recent works, we have shown that selective detection of O3 can be obtained with CuPc based gas sensor, using an appropriate methodology of measurements exploiting the fastest kinetics of response to this gas [1-2]. For the selective detection of NO2 in air, ozone constitutes the most important interfering agent and leads to the irreversible degradation of phthalocyanine molecular units in long term which reduces the sensors lifetime [3]. Thus, to efficient monitoring of NO2 in atmosphere by phthalocyanine gas sensors, it appears necessary to eliminate O3 without altering NO2 concentration, by means of selective filter. Among all the material investigated as ozone filter (MnO2 powder or impregnated grids, charcoal, C60 powder, stainless steel cuttings, indigo powder...), only indigo can be considered as a real selective ozone filter. Moreover, indigo powder being easily sublimed to be deposited as thin layers, this material is really suitable for the realization of integrated selective ozone filter. The structure investigated in this work is constituted by a 300nm-CuPc thin film as sensitive layer and an additional indigo evaporated film as the filter layer. The range of thickness investigated for indigo layer is 10-100nm. The very low intrinsic conductivity of indigo films (Σ = 2.10-107-1.cm-1) makes them insulating, that's avoid bypassing the sensitive layer. Sensor responses measured for the same concentration of NO2 and O3 emphasize that response and recovery times remain high, gas/phthalocyanine interactions are reversible, the response under O3 is negligible and kinetics of response to NO2 is slower than device without indigo filter due probably to the slow diffusion of NO2 species through the filtering layer to reach the sensitive one. The last point is confirmed by experiments made on structures with different thicknesses of indigo: the thicker the layer is, the slower the kinetics of response is. The integrated indigo layer on phthalocyanine sensors makes them selective to NO2 and avoids the fast ageing effect due to the strong and irreversible interaction of O3 on the sensitive layer

Molecular engineering for micro-systems in urban air quality control applications

2-7 Juillet 200

Molecular semiconductors based gas sensors dedicated to selective oxidizing pollutants evaluation

Mainly originated from industrial emissions and car exhausts, air pollutants are responsible for environmental problems and harmful effects on human health. Measurements of pollutant gas concentrations (Nitrogen dioxide, Ozone, Volatile Organic Compounds ...) are collected by urban air quality control networks. The devices used by pollutant monitoring networks are commercial gas analyzers which principle of measurements is based on spectroscopic analysis. Despite of their good performances, their high cost and their uneasy implementation make them unadapted for sporadic campaigns of measurement or to realize a cartography of pollution with high special resolution. The monitoring of atmospheric pollution using chemical gas sensors is a challenge due to the lack of selectivity of most existing devices. The great reactivity of phthalocyanines towards oxidizing species and especially strong oxidizing species, such as NO2 or O3, induced many studies on sensors using those molecular semiconductors as sensitive elements. But, phthalocyanine based sensors suffer from a lack of selectivity, from too slow kinetics of response, due especially to diffusion process of gaseous molecules into the layer, and from long-term stability problems. Metrological characteristics improvements can be achieved by adapted methodologies of measurements. The poster presentation deals with methodologies dedicated to reach : • selective and real time detection of ozone in air based on response kinetics study of copper phthalocyanine sensor during short times under pollutants. The methodology implemented is based on cyclic sensor recalibrations by thermal cleaning of the sensitive membrane, and on pollutant concentration quantification according to the kinetics of the sensor response. Results of laboratory experiments for various NO2 and O3 concentrations, in the range of 10-200 ppb, illustrate the selectivity of CuPc sensors towards ozone, obtained by our methodology. • selective detection of nitrogen dioxide using an indigo filtering system achieving the removal of ozone while preserving nitrogen dioxide

Noncovalent Functionalization of Single-Wall Carbon Nanotubes for the Elaboration of Gas Sensor Dedicated to BTX Type Gases: The Case of Toluene

International audienceSingle-wall carbon nanotubes (SWNTs) have been noncovalently functionalized, using a dispersion technique, and the resulting hybrid materials are used for a gas sensing purpose. The functionalization entities are macrocycles (MCs) of phthalocyanines (Pc's) and porphyrin (Por) derivatives. These MCs exhibit a highly delocalized π-system which can be used as a target for π-π interaction but also for monitoring of the functionalization process. Raman spectroscopy, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) analysis of the hybrid materials revealed the occurrence of the functionalization. The obtained hybrids are used as sensing layers for the detection of toluene. Two transduction modes (resistive and QCM (quartz crystal microbalance) type mass sensors) have been simultaneously used in order to understand the gas/material interaction. An improvement of the sensor responses due to the high surface area of the hybrid material has been observed. Desorption of the gas molecules from the free CNT surfaces sites happens faster than desorption from the MC-occupied CNT surface sites

Elaboration of single wall carbon nanotubes-based gas sensors: Evaluating the bundling effect on the sensor performance

International audienceIn this article, carbon nanotube (CNT)-based sensors have been prepared using dispersion techniques. Sensors are obtained from a dispersion of CNTs using either chloroform as a solvent or sodium dodecylbenzene sulfonate as a surfactant. These sensors are prepared by drop-cast deposition of the solutions on interdigitated electrodes. The organic solvent processing leads to CNT layers where carbon nanotubes are obtained as larger bundles, whereas smaller bundles and individual tubes are predominantly formed in the surfactant processing. Under gas exposure (NO2), both sensors respond to low gas concentrations; however, the sensing layers composed of larger bundles of CNTs present a slightly different behaviour (in terms of rapid stabilisation and sensitivity) compared to those made of individual CNTs