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2014-03-16 - Colloque/Présentation - poster - Anglais - 4 page(s)

Lahem Driss, Debliquy Marc , Van Baekel Alexandre, Bouvet Marcel, "Optical NO2 Sensing Based on Mesoporous Sol–gel Impregnated with Lutetium Bis-phthalocyanine" in IMCS 2014 International Conference on Chemical Sensors, Buenos-Aires, Argentina, 2014

  • Codes CREF : Capteurs et périphériques (DI2563), Matériaux optiques (DI1256)
  • Unités de recherche UMONS : Science des Matériaux (F502)
  • Instituts UMONS : Institut de Recherche en Science et Ingénierie des Matériaux (Matériaux)
  • Centres UMONS : Ingénierie des matériaux (CRIM)
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Abstract(s) :

(Anglais) Topic 7. Sensing for Health, Safety and Security Optical NO2 Sensing Based on Mesoporous Sol–gel Impregnated with Lutetium Bisphthalocyanine Driss LAHEMa,*, Marc DEBLIQUYb, Alexandre VAN BAEKELb, Marcel BOUVETc, and Marie-Georges OLIVIERa,b aMateriaNova, Parc Initialis, 1, Avenue Nicolas Copernic, 7000 Mons, Belgique. bService de Sciences des Materiaux, Faculté Polytechnique de Mons, Université de Mons, 56 Rue de l’Epargne, 7000 Mons, Belgique. cService d’Electrochimie, Materiaux Moléculaires et Dispositifs (EMMD), Institut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB), 9 Avenue Alain Savary, 21078 Dijon, France.), driss.lahem@materianova.be Summary In this work we present the results of a sensor using a coating consisting of lutetium bisphthalocyanine (LuPc2) dispersed in a porous silica matrix. LuPc2 shows a strong and reversible gasochromic effect with NO2 in the ppm range. its absorption spectrum strongly changes in contact with NO2 for visible and near-infrared regions. In comparison with LuPc2 layer deposited by sublimation, we showed that the response time is drastically shortened when LuPc2 is grown in a mesoporous matrix. It drops from hours to a few minutes. Although the recovery is very slow at room temperature, we found that a short exposure to UV light of the film leads to a drastic reduction of this recovery time from hours to a few minutes. The changes in the 1200-1600 nm band corresponding to the preferred wavelengths for telecommunication with optical fibres are interesting for the use on optical fibre sensors taking profit of the available low cost components . Keywords: Lutetium bisphthalocyanine, Mesoporous sol-gel, NO2-sensing, Optical sensor Introduction NO2 is an important air pollutant with significant impacts on human health [1] and air quality [2]. There is a general consensus that road traffic is the main source of NO2 in urban areas especially at traffic sites [3]. There exist many laboratory devices able to accurately measure NO2 [4]. However, the complexity, the cost and the environment needed for this type of device do not allow envisaging their systematic use for pollution monitoring in the traffic. For this reason, the need for gas sensors suitable for NO2 monitoring near roadways and in urban areas has been raised. There are lots of efforts on the development of many kinds of NO2 gas sensors [5-6]. Among the different technologies, optical systems based on optical fibers can be very useful in specific applications like the NO2 monitoring in enclosed areas. The idea here is to exploit the optical and chemical properties of lutetium bisphthalocyanine (LuPc2). NO2 can be reversibly bound with LuPc2 resulting in the oxidation of the molecule which can be detected trough a change of the absorption spectrum [ref]. The diffusion of NO2 in LuPc2 crystals is very slow leading to a very long response time if the grain size or the thickness of the layer is important [7]. To avoid this effect, LuPc2 will be immobilized in a mesoporous matrix in such a way that the grain size remains small leading to rapid diffusion and short response time. The sensitive layer was built in two steps: (1) deposition of a mesoporous silica film by dip-coating according to a sol-gel process on flat glass substrates followed by (2) impregnation in a chloroform solution of LuPc2. Results and discussion In Fig. 1, we show the absorption spectra of LuPc2 immobilized in a mesoporous silica layer (trickness~600 nm) in air and in contact with NO2 7 ppm compared to that with a 100 ppm pure LuPc2 film deposited by sublimation. e whole spectrum is modified and the interesting wavelength range 1300-1600 nm is strongly affected. Whereas the dense sublimated film presents a poor and slow response, the mesoporous film shows a big optical change is very big and the response is fairly fast (the response time is shortened to 10 min) (Fig. 2). (Tricher sur les figures pour qu’on voie la réponse sur le film évaporé) It can be seen on Fig. 3, that the sensitive layer needs a long time to recover (more than 24 hours) which is a problem for practical applications. Nevertheless, an appropriate UV treatment of layer after NO2 injection (xxx nm, yyyW/m2) made it possible to break the (LuPc2+NO2-) complex, facilitating a quick return to its initial state (Fig. 3). Conclusions On the basis of the obtained results, LuPc2 immobilized in a mesoporous silica matrix seems to be a promising transducer for the optical NO2 detection in the ppm range. Compared to the sublimated LuPc2 layer, the developed sensitive layer shows a response to NO2 at room temperature with a response time drastically shortened. Moreover, an appropriate UV treatment makes the NO2 reaction with the sensitive layer completely reversible without damaging its properties. As the optical change can appear in the Telecom wavelengths, the sensitive layer reported here could be used on optical fibres to develop distributed sensors. This type of sensors could be interesting for the monitoring of NO2 in closed spaces like road tunnels or undercroft car parks. Acknowledgment This work was carried out in the framework of the NOSens project of Materia Nova and the University of Mons, financially supported by the Walloon Region of Belgium. References [1] U. Latza, S. Gerdes, X.Baur, Int J Hyg Environ Health 212, 271–87 (2009); doi: 10.1016. [2] P.S. Monks, et al., Atmos Environ 43, 5268–5350 (2009); doi:10.1016. [3] Air quality in Europe-2012 report. EEA Report No 4/2012. http://www.eea.europa.eu/publications/air-quality-in-europe-2012. [4] W. A. Simmons, P. W. Seakins, Science of the Total Environment 438, 248–259 (2012); doi: 10.1016. [5] G. F. Fine, L. M. Cavanagh, A. Afonja, R. Binions, Sensors 10, 5469-5502 (2010); doi:10.3390. [6] David L. Vaughn et al., Draft Final Report STI-910112-3958-DFR. Prepared for U.S. Environmental Protection Agency Research Triangle Park, North Carolina, September 28, 2010. [7] M. S. Nieuwenhuizen, A. J. Nederlof, A. Coomans, Fresenius Z Anal Chem 330,123-124 (1988); doi: 10.1007. Figure 1. Absorption spectra of LuPc2 incorporated in the silica matrix on glass substrates before and after 3 min of exposure to NO2 at 7 ppm. Figure 2. Absorbance versus time for λ = 661 nm of LuPc2 immobilized in the silica matrix on glass substrate. Figure 3. Absorption spectra showing the recovery of LuPc2 incorporated in the silica matrix on glass substrate after exposure to NO2 at 7 ppm.