Sensors for VOCs

Ogawa T, Kobayashi K, Masuda G, Takase T, Maeda S (2001) Electronic conductive characteristics of devices fabricated with 1,10-decanedithiol and gold nanoparticles between 1-m electrode gaps. Thin Solid Films 393 374-378 Pang P, Guo Z, Cai Q (2005) Humidity effect on the monolayer-protected gold nanoparticles coated chemiresistor sensor for VOCs analysis. Talanta 65 1343-1348 Pileni MP (1993) Reverse micelles as microreactors. J Phys Chem 97 6961-6973... 

Table 14.2 Summary for optical and mass transduction-based sensors for VOCs... 

Three types of materials, metal oxide semiconductors such as ZnO and SnOa, conducting polymers such as polyanUine and polypyrrole, and carbon-based materials such as carbon nanotubes (CNTs) and graphene, have shown significant performance benefit for the development of 1-D- and 2-D-based sensors for VOCs (Table 14.3). Until recently, the development of 1-D nanostructure-based VOC sensor using the abovementioned materials was slow because of challenges in the synthesis and fabrication of these nanostructures with controlled dimensions, morphology, and purity. 

Goelen E, Lambrechts M, Geyskens F, Rymen T 1992) Development and performance characteristics of a capillary dosage unit with an in situ weight sensor for the preparation of known amounts of gaseous VOC s in air. Intern J Environ Anal Chem 47 217-225. 

COz sensors are suitable for living rooms, offices and bedrooms, whereas for bathrooms (main parameter humidity) and kitchens (main parameter smell ) other non-specific sensors may be used. Therefore combinations of different sensors like humidity sensors, smelF-sensors (unspecific VOC-sensors) and presence sensors could be the best solution. A simple movement detector with an additional manual override (ventilation on/off for a predetermined time) could be a low-cost alternative. 

A small 3 cm x 3.5 cm section of the catalyst-coated desiccant wheel (25 cm diameter) was cut and placed in specially made holder shown in Fig. 12.9-6a. The piece of sample was tested in a 0.2 m3 environmental chamber at Chiaphua Industries Ltd. (Fig. 12.9-6b) for reduction of airborne VOC. The chamber was filled with the target VOCs through two stage saturators shown in Fig. 32b. Once the VOC level in the chamber stabilized, the fan was turned on to circulate the air through the sample. Three sets of sensors were located at the inlet and outlet of the holder, as well as in the center of the chamber. The chamber temperature and relative humidity were kept constant during the test. Figure 12.9-6c shows the results for VOC levels of 4000, 2000 and 1000 ppb at room temperature. The reduction rate was slower because of the low VOC concentration and the poor air circulation in the chamber. Also unlike the Prototype Unit, the catalyst was kept at room temperature throughout the test. 

Yoon J, Chae SK, Kim J-M. Colorimetric sensors for volatile organic compounds (VOCs) based on conjugated polymer-embedded electrospun fibers. J Am Chem Soc 2007 129 3038-3039. 

Aggregation as the cause of luminescence was also probed in fluid solutions, since a dilute colorless solution was not emissive, but a concentrated (2 x 10-2 M) solution was weakly emissive a result that is consistent with the aggregation of these units in solution. Undoubtedly, this complex has potential for practical applications as a luminescent sensor for the detection of volatile organic compounds (VOCs). 

The luminescence of a thin film coated with [Re(CO)3(/u.-4,4 -bipyridine)Cl]4 was quenched by nitrobenzene vapor because of electron transfer. Recently, mesoporous thin films of [Re(CO)3(/u.-L)Cl]4 (L = 4,4 -pyrazine or 4,4 -bipyridine) have been utilized as sensors for volatile organic compounds (VOCs). The host-guest interaction between the rhenium cyclophanes and VOCs was confirmed by quartz crystal microbalance studies. 

Tchoupo, G. N. Guiseppi-Elie, A., On padern recognition dependency of desorption heat, activation energy, and temperature of polymer-based VOC sensors for the electronic NOSE, Sensors and Actuators B-Chemical 2005, 110, 81-88. 

J. Garcia-Guzman, N. Ulivieri, M. Cole, and J.W. Gardner, Design and simulation of a smart ratiometric ASIC chip for VOC monitoring, Sensors and Actuators B, 95 (2003) 232-243. 

Rodriguez-Mendez M. L., Souto J., de Saja R., Martinez J., and de Saja J. A., Lutetium bisphathalocyanine thin films as sensors for volatile organic components (VOCs) of aromas, Sens. Actuators B, B58, 544-551, 1999. 

Semiconductor gas sensors for methane, propane, butane, ammonia, alcohol, hydrogen, CO, VOCs, etc. 

Vaishanv, V. S., Patel, P. D. and Patel, N. G. (2006) Indium tin oxide thin-fihn sensor for detection of volatile organic compounds (VOCs). Materials and Manufacturing Processes 21,257-61. 

T. Itoh, I. Matsubara, W. Shin, and N. Izu, Synthesis and characterization of layered organic hybrid thin films based on molybdenum trioxide with poly(N-methylanihne) for VOC sensor. Mater. Lett., 61, 4031 034 (2007). 

The response of the four sensors of e-nose for a cookie sample was determined from the (AR/R) value which is the change in the resistance of metal oxide gas sensor due to the VOCs of cookies (with or without clove extract) with respect to the base value [lOOJ.Thebase value of control cookies is the resistance shown by the sensors due to VOCs of freshly prepared cookies (without antioxidant) whereas, base value of antioxidant-rich cookies is the resistance shown by the sensors due to VOCs of freshly prepared cookies with encapsulated clove extract. The representation of sensor responses in terms of (AR/R) value is reported for different food matrices. While, Mildner-Szkudlarz et al. [1] used (AR/R) value of e-nose sensors for monitoring the autoxidation of rapeseed oil, Bhattacharyya et al. [100] used the same in assessing optimum fermentation time of black tea. 

Up to 7 channels, incl. PID sensor for direct reading of toxic VOCs... 

There are a number of techniques that can be used in the field. These include electrochemical sensors for gases such as O2 and SO2 and diffusive samplers containing immobilized reagents that produce a visible color change with visual detection on exposure to a specific chemical. Passive diffusion tubes can also be used for analyte preconcentration. Subsequent laboratory analysis is usually undertaken by thermal desorption coupled with GC. This approach is particularly useful for trace organic compounds such as polyaromatic hydrocarbons (PAHs) and VOCs. Spec-trometric techniques such as Fourier transform infrared (FTIR) spectrometry, correlation spectrometry, and the laser based LIDAR (light detection... 

G460 Multi-gas detector from GfG Instmmentation is a mgged, compact instrument for simultaneous detection of up to 6 gases. 02, LEL, CO and H2S sensors are warranted for three full years. Additional sensor choices include a wide selection of toxic as well as infrared (NDIR) sensors for combustible gas and PID for toxic VOCs. GfG Instrumentation, www.gfg-inc.com. Circle 332... 

Schollhorn et al. 1998 Ceyhan et al. 2006) (see Table 10.2). For explanation of MPc gas sensitivity the approach based on gas molecule interaction with the Ti-electron network of the phthalocyanines is normally used (Roisin et al. 1992). For example, in the case of VOCs sensors the VOCs would play an electron acceptor role. When the VOC molecules interact with the 7i-electron network of the phthalocyanines, it causes the transfer of an electron from the phthalocyanine ring to the VOC molecule (Schollhorn et al. 1998). Thus, the induced positive holes on the film surface give rise to an increase in the p-type conductivity of the film. 

Hand-held monitoring techniques for VOC and gases flame ionization detection (FID), photoionization detector (PID). thermal conductivity detector (TCD). infrared sensor (IR). see Figure 3. 

SWCNTs-porphyrin nanosensors have been fabricated for monitoring toxic substances in the enviromnent [215], Free-base, Ru and Fe octaethyl-and tetraphenyl-substituted porphyrins provided good selectivity and sensitivity to various VOCs tested (acetone, butanone, methanol, ethanol). Nonco-valently functionalized SWCNTs with iron tetraphenylporphyrin were used for benzene detection [216], SWCNTs noncovalently functionalized with copper phthalocyanine and free-base porphyrins were used as sensing layers for the detection of toluene [217]. Also, MWCNTs were used as sensors for benzene, toluene, and xylene, when fnnctionalized with metal tetraphenyl porphyrins [218], SWCNTs-poly(tetraphenylporphyrin) hybrid was prepared and tested as a low-power chemiresistor sensor for acetone vapor [219]. A chemiresistive sensor array was fabricated from SWCNTs noncovalently functionalized with metallo mcxo-tetraphenylporphyrins (Cr(III), Mn(III), Fe(III), Co(III), Co(n), Ni(n), Cu(II), and Zn(II)) [220]. Its responses were treated by statistical analyses and allowed to classify VOCs into five classes alkanes, aromatics, ketones, alcohols, amines. Amines detection as an indicator of meat spoilage was achieved by the same group with the same sensor array [221]. 

Shirsat MD, Sarkar T, Kakoullis J Jr, Myung NV, Konnanath B, Spanias A, Mulchandani A. Porphyrin-functionalized single-walled carbon nanotube chemiresistive sensor arrays for VOCs. J Phys Chem C 2012 116 3845-50. 

---