2014 IEEE 3rd Global Conference on Consumer Electronics (GCCE)
Indoor Air Quality Monitoring System Based on Polymer/Functionalized-SWNT Gas Sensors Treenet Thepudom2, Satetha Siyang2, Thara Seesaard2 and Teerakiat Kerdcharoen1,3,* 1
Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand Materials Science and Engineering Programme and Center of Intelligent Materials and Systems (CIMS), Faculty of Science, Mahidol University, Bangkok 10400, Thailand 3 NANOTEC Center of Excellence at Mahidol University, National Nanotechnology Center, Thailand
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Corresponding author:
[email protected]
of such material, we have developed gas sensing material based on polymer composited with functionalized singlewalled carbon nanotube (SWNT). This type of gas sensing material provides a capability to interact with gas molecules at the surface of the material. In our development, such gas sensors were used as an array to increase the functionality of the monitoring device. Our device has been tested with various types of gases such as toluene, formaldehyde, acetone and ammonia which are commonly volatile contaminants found in the ambient air. The size and power consumption were the issues seriously concerned in this work. Thus, our device was designed for easy installation at various points in a home as shown in Fig. 1. We hope that this work will provide more choices in healthcare technology to the consumer healthcare market.
Abstract—Recently, people pay more attention to healthy living conditions. Such changing lifestyle leads to demand for wearable health monitoring, new medical technology, healthy food and clean air. Thus, indoor air monitoring and control will be an emerging industry with a huge market size. In this paper, we have developed an indoor air monitoring system with ability to observe volatile contaminants, especially related to household origin. This system consists of an array of chemical gas sensor based on polymer/functionalized single-walled carbon nanotubes (SWNT) with ability to detect different gases. A microcontroller was used for data processing and alarming when the concentration of a target gas becomes danger. This system was developed based on consumer-friendly having a compact size and using low-cost technologies. From the experiment, it was demonstrated that such indoor air monitoring device provides an ability to detect contaminated gases in ambient air. The results imply a possibility appropriate for indoor air monitoring in general home and even in factory as well.
II.
A. Indoor Air Monitoring Configurations
Keywords—air monitoring; electronic nose; chemical sensor; polymer/SWNT sensor; pollution
I.
This device was designed and developed based on lowcost technology with compact size as shown in Fig. 2(a). The sensor system was encapsulated within a plastic box (10×12.5×10 cm), with a small exhaust fan on the top of the box to carry the gas into the sensor system and eliminate humidity from the system as well. A power supply was used to generate 5V into the system. Fig. 2(b) shows the schematic diagram of this device that can be divided into 3 parts as
INTRODUCTION
Healthcare technologies have been regarded a prominent role in this era, especially in advanced countries. To support this emerging trend, various innovative healthcare technologies have been developed, for example, wearable health monitoring devices. This technology provides real time access to electronic health records with compact size products. With less popularity as compared to the wearable technology, the awareness in the indoor air quality have become increasing of interest, especially in the factory and urban living spaces. In fact, air pollutants are around us all the time, not excluding the home indoor [1]. Unhealthy volatiles can emanate from household emission, which means that the residents are at risk all the time. To avoid such issue, indoor air monitoring technology should be considered to prevent inhaling the inhouse polluted gas [2]. In fact, many research groups have investigated this issue and tried to develop smart devices to alleviate such problems. Despite incredible improvements in this area, there are still a number of challenges. Gas sensing material is the most important component in a gas monitoring system. The challenge for this development was inevitably the cost and its efficiency [3, 4]. In the recent years, polymer-based gas sensing materials have become increasingly popular due to its practical applications with a low cost. Due to the advantages
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MATERIALS AND METHODS
Fig. 1. Wireless gas sensor devices to measure air quality in home.
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Fig. 2. The indoor air monitoring system and schematic diagram of this device.
follows. (1) Gas sensing material consists of four types of polymer composited with functionalized-SWNT. (2) Voltage divider circuit and microcontroller board were used for data processing to evaluate gas concentration in order to notify when the undesirable gas concentration is critical. (3) Notification LED was used to displays the status of the ambient air, thereby the red light indicating an abnormality of the air whereas the green light implying the opposite situation.
Fig. 4. Radar plots of the average of percent change in resistance of each sensor when exposed to four volatiles at 30 ppm and PCA plots that discriminate four types of target gas.
molecules to carbon nanotube. Principal component analysis (PCA) was performed to discriminate the target gases. Data analysis by PCA can identify 4 groups of data as shown in Fig. 4(b). Based on this result, it implies that all sensors are sufficient to discriminate these samples.
B. Gas Sensing Materials
IV.
The polymer mixed functionalized-SWNT was used as gas sensing material in this work due to low power consumption and easy fabrication. Fig. 3 shows four types of gas sensing materials namely PSE/SWNT-COOH, PSE/SWNT-OH, PVE/SWNT-COOH and Poly (acrylic acid)/SWNT-COOH. Such materials were prepared by spin coating the solution onto interdigitated electrodes with a suitable spin-speed of 1000 rpm. Then the gas sensing response could be obtained by measuring resistance change when the target gas interacts with the surface of the material [5]. III.
CONCLUSIONS
A wireless gas sensor system was developed for indoor air monitoring. It was designed to be suitable for the measurement of volatile pollutants in home. It consists of four types of chemical gas sensors which are able to interact with commonly contaminated gas, namely formaldehyde, acetone, toluene and ammonia. The results reveal the potential of the device to detect volatiles commonly released from household chemicals. Further development such as data access using smart phone or tablet is in progress.
RESULT AND DISCUSSION
ACKNOWLEGEMENT
To test the ability of gas sensors, four types of sample gases were used in the experiment such as acetone, ammonia, formaldehyde and toluene. Fig. 4(a) displays the radar plot of percent average gas sensing response of four sensors with 30 ppm of target gases. It can be seen that the sensor number 1 - 4 exhibit high response to the formaldehyde, toluene, ammonia and acetone respectively. The sensing response can be accounted by two factors; the swelling capability of the polymer matrix and the electron-donating capability of the gas
This project was supported by Mahidol University, National Nanotechnology Center (NANOTEC grant no. P-1201157) and Research and Researcher for Industry (RRI). REFFERENCE
Fig. 3. An array of polymer/functionalized SWNT gas sensors.
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