A sensor for detecting and estimating the concentration of methane gas has been developed using single wall carbon nanotubes (SWCNT). The SWCNTs has been employed as the sensing element in the proposed gas sensor. A sensor test cell has been developed and tested for the performance of the sensing element. The resistance of the sensor element has been found to be increasing linearly with increase in the volume of the methane gas and 11.3% change in the resistance has been recorded for 20mL volume of methane gas.
I.INTRODUTION
Chemical sensors especially gas sensors have wide range of application in hospital, industries and also for environmental monitoring. Hydrocarbon gases which constituents mostly inflammable fuel are difficult to be detected as these are colorless and odorless. So development of Gas sensor is necessary. In this report we have developed gas sensor for methane using SWCNT. SWCNT has been extensively used as sensor.
Sensors have many important roles in various fields of scientific and engineering applications, such as for controlling and monitoring the chemical process, biomedical, machining process etc [1]. Methane is globally produced gas, since it is colorless and combustible it is necessary to detect the methane gas during chemical reactions. Before, methane can be detected by different methods like semiconductor sensors, electrochemical cell, optical detectors etc. Since the detection is limits to few tens of ppm here we are using Single Wall Carbon nanotubes (SWCNT) as an active material for methane gas sensors [2]. SWCNT is used as a sensing element now a days due to its extraordinary physical, chemical and mechanical properties [3-4]. Carbon nanotubes can be classified into two main subdivisions: Single Wall Carbon Nanotubes (SWCNTs) and Multiwall Carbon Nanotubes (MWCNTs). SWCNT is a single layer of rolled graphene [5].
Here we represented a chemo resistive sensor which is able to detect the sub-ppm concentration of methane gas with high selectivity. The sensing mechanism is based on the high sensitivity towards the resistance of the single wall carbon nanotube. This principle is used in the variety of sensing application [6]. We used Copper (I) complex for the selective detection of methane gas, where Cu(I) is an essential to receptor[7]. The detection technique is based on an intimate mixture of SWCNT with copper (I) complex, which is able to interact with the atoms of the single wall carbon nanotubes. Hence influencing the conductivity. The choice of copper(I) complex is based on the fact that when the copper complex is interact with the gas, it does not easily oxidized under ambient condition and is also very stable in high vacuum[8].
II.EXPERIMENTAL DETAILS
A. Preparation of Silver electrode
A 2.5cm X 2.5cm glass slide was cleaned with acetone was patterned with the Silver electrode by Silver nano conductive ink using screen printing method ( electrode width 1mm , 2mm of inter electrode gap and thickness of 100??m ),measured using AFM. The glass slide was placed in an hot air oven for 1 hour at 120?? C to make it dry.
B. Decoration of SWCNT on the glass slide
A Cuprous chloride (CuCl) with molecular weight of 98.99g is made into a 0.1 molar concentration solution by mixing 10ml of double distilled DI water
with 98.99mg of CuCl, Stirred the mixture for 20 minutes until it fully dissolves without any precipitation. Then 0.5??l of CuCl solution is mixed well with 1ml of SWCNT. The solution is heated in a heater until all the water get evaporated and the volume of the solution is reduced to ?? of its volume. The thick SWCNT solution is coated on the electrode using brush with hands and then sintered it for 45 minutes in the hot air oven to get dried. Then we made the silver contacts connected with silver leads over electrode and sintered it for one hour at 70?? C. now our sensor is ready. As Shown in Figure 1.
Figure 1. Decoration of SWCNT on glass slide with silver electrode,
C. Sensing measurements
For the testing of the gas, we need to put our entire sensor inside a 30.6cm3 air tight sealed test cell (gas flow chamber of size 4cm x 4cm x 3cm) made up of acrylic material. As shown in figure 2.
Figure 2. Test cell in which gas sensor is fitted inside.
In which the silver electrodes of the device is soldiered with connection to the outside of the test cell with the silver coated copper wire. As shown in figure 3.
Figure 3. soldiering in outside of test cell with the silver electrode with silver coated cupper wire.
The test cell consists of two hole, one for the gas inlet positioned over the chip and other for the gas outlet which is air tightened. During measurement, a continuous stream of gas with constant flow rate, is injected inside the test cell directed over the device. And thus methane gas at different concentrations are to be measured.
III. RESULT AND DESCUSSION
The device is tested at the room temperature, atmospheric air is injected inside the test cell, the device resistance value is recorded as 1.0874 K’ (Rair). Then methane gas of 20ml volume is injected inside test cell, the reaction took place between the sensor and injected gas and recorded an increase in resistance value up to 1.210 k’ (Ranalyte).The percentage change in resistance can be calculated by equation 1.
= — (1)
Thus change in resistance percent with respect to volume is 11.3%.similarly for 15ml volume of methane gas, it shows 8% change in resistance, and for 10 ml volume of gas it shows 4.8% change in resistance, respectively as shown in the figure 4.
Figure.4 Percentage change in resistance of the sensor with increasing gas volume.
The result shows the required time for sensor to achieve steady state is 60 sec. And after few minutes the device is regaining its original resistance value on the application of nitrogen gas as well as for the cleaning of sensor. The device is showing exactly reversible reaction. And the response of the sensor is approximately linear with 1% of tolerance.
IV. CONCLUSION
In summery, this study reports the fabrication of gas sensor using random dispersions of SWCNT doped with 10wt% of CuCl on silver IDT electrodes. CuCl markedly increases the devices sensitivity and selectivity towards methane. The device is showing the exactly reversible reaction under the influence of methane gas at different concentrations when the nitrogen gas is applied to the sensor to neutralize the reaction. So the response, recovery, sensitivity, linearity and stability of fabricated sensor is favorable.