GAS SENSOR

Abstract

A gas sensor configured to detect a target gas in a gaseous atmosphere, for example NO.sub.2 or O.sub.3 in air, comprises: a transparent substrate; a gas sensitive detection layer supported by the transparent substrate, the gas sensitive detection layer comprising i) a gas sensitive detection material having an electrical impedance which is sensitive to the target gas and ii) connections configured to allow for detection of electrical impedance of the gas sensitive detection material; and a light source, for example a LED, configured to provide light to the gas sensitive detection layer through the transparent substrate. The gas sensor may operate at room temperature whilst requiring little power.

Claims

1. A gas sensor configured to detect a target gas in a gaseous atmosphere, the gas sensor comprising: a transparent substrate; a gas sensitive detection layer supported by the transparent substrate, the gas sensitive detection layer comprising: i) a gas sensitive detection material having an electrical impedance which is sensitive to the target gas, and ii) connections configured to allow for detection of electrical impedance of the gas sensitive detection material; and a light source configured to provide light to the gas sensitive detection layer through the transparent substrate.

2. A gas sensor according to claim 1, wherein the gas sensitive detection material includes at least one of: i) a metal oxide; ii) graphene and/or graphene oxide; or iii) a combination of a metal oxide with an organic material; wherein the metal oxide includes at least one of a doped metal oxide or a sub-stoichiometric metal oxide, and wherein the metal is selected from at least one of Zn, Sn, W, or Ni.

3. A gas sensor according to claim 1, wherein the transparent substrate is selected from: i) a plastics film; or ii) a glass substrate.

4. A gas sensor according to claim 1, wherein the connections configured to allow for detection of electrical impedance of the gas sensitive detection material comprise a pair of spaced electrodes, each of which is electrically connected to the gas sensitive detection material.

5. A gas sensor according to claim 1, wherein the connections configured to allow for detection of electrical impedance of the gas sensitive detection material are supported by the transparent substrate and overlaid by the gas sensitive detection material.

6. A gas sensor according to claim 1, wherein at least one of: the target gas to be detected includes at least one of NO.sub.2, O.sub.3, H.sub.2, SO.sub.2, H.sub.2S, CO, or VOC gas, or the gaseous atmosphere is air.

7. A gas sensor according to claim 1, wherein the light source comprises a light-emitting diode.

8. A gas sensor according to claim 1, wherein the light source is a monochromatic light source.

9. A gas sensor according to claim 1, wherein the gas sensitive detection material comprises nanoplatelets of the gas sensitive detection material.

10. A gas sensor according to claim 9, wherein the nanoplatelets of the gas sensitive detection material have a thickness of less than 0.3 μm.

11. A gas sensor according to claim 1, further including a gas filter between the gas sensitive detection material and the gaseous atmosphere, the gas filter configured to prevent or reduce the concentration of one or more selected gasses from the gaseous atmosphere from contacting the gas sensitive detection layer.

12. A gas sensor according to claim 1, wherein the gas sensor is configured to detect at least one of: a concentration of the target gas of less than 10 ppm in the gaseous atmosphere; or a change of electrical impedance of the gas sensitive detection layer of at least 500%, in response to a concentration of target gas in the gaseous atmosphere which is less than 1 ppm.

13. A gas sensor according to claim 1, wherein the gas sensor is configured to detect a electrical impedance in the range 1 kΩ to 100 MΩ.

14. A gas sensor according to claim 1, wherein the gas sensor is configured to detect a target gas in the gaseous atmosphere at 20° C.

15. A method of detecting a target gas in a gaseous atmosphere, the method comprising: arranging a gas sensor in accordance with claim 1 in the gaseous atmosphere; providing light to the gas sensitive detection layer through the transparent substrate from the light source; and detecting the presence and/or the concentration of the target gas in gaseous atmosphere by monitoring the electrical impedance of the gas sensitive detection layer.

16. A gas sensor according to claim 3, wherein the plastics film includes at least one of a PET film, a PE film, a PEN film, a polymer film, a non-crystalline polymer film, or a polylactide film.

17. A gas sensor according to claim 1, wherein the light source is a blue light emitting source configured to provide a blue light in the range 460-490 nm.

18. A gas sensor according to claim 9, wherein the nanoplatelets provide hollow microspheres having an external mean diameter of less than 20 μm.

19. A gas sensor according to claim 10, wherein the nanoplatelets of the gas sensitive detection material have a thickness in the range 50-100 nm.

20. A gas sensor according to claim 12, wherein the change of electrical impedance of the gas sensitive detection layer of at least 10000%.

Description

[0032] An embodiment of the invention will now be described, by way of example only with reference to the accompanying drawings of which:

[0033] FIG. 1 is a schematic cross-section (not to scale) of a gas sensor; and

[0034] FIGS. 2 to 4 are graphs showing responses of the gas sensor.

[0035] The gas sensor 1 shown in FIG. 1 comprises a flexible transparent PET film 12 having a thickness of about 100 μm having on one of its surface printed gold electrodes 11 having a thickness of about 200 nm and a gas sensitive detection material 10 comprising hollow spheres of WO.sub.3 having an external mean diameter of about 2 μm. This thickness of the gas sensitive detection material 10 is about 20 μm. On the opposite surface of the PET film, a LED 13 is arranged to provide light towards the gas sensitive detection material 10 and electrodes 11 through the PET film 12.

[0036] The gas sensor 1 is manufactured by [0037] Printing a negative image of the electrodes on the PET film 12 with a laser printer (HP colour laser Jet CP1515) to provide a printed substrate; [0038] Depositing a gold layer of about 200 nm on the printed substrate by sputtering (Leica EM SCD 500, 10-2 mbar air); [0039] Revealing the golden electrodes 11 by a lift off in an acetone bath which removes the ink of the negative drawing; [0040] Screen printing the WO.sub.3 powder 10 on the front side of the substrate 12; [0041] Installing a LED lamp 13 on the back side of the substrate 12.

[0042] The tungsten oxide (hereinafter written as WO.sub.3) powder of the gas sensitive detection material 10 was prepared according to the following process: about 2 mmol Pb(Ac).sub.2 and about 2 mmol Na.sub.2WO.sub.4 (2 mmol) were dissolved in about 25 mL of distilled water, respectively, and then the two solutions were mixed under vigorous magnetic stirring at room temperature. Precipitates were formed quickly, and after that the mixture was transferred into a Teflon-lined stainless steel autoclave at about 160° C. for about 5 h. After cooling to room temperature, the product was filtered, washed several times with distilled water, and then dried in air at about 70° C. Subsequently, the product was immersed in about 4M HNO.sub.3 solution for about 48 h to transform PbWO.sub.4 to WO.sub.3.H.sub.2O. Then the products were filtered, washed with distilled water, and dried in air. Next, the acid-treated products were calcined in a furnace at about 500° C. for about 2 h in air to obtain the WO.sub.3 powder. Afterwards, about 3 g of as-synthesized WO.sub.3 powder was dissolved in the 2.5 mL terpineol solution to form a homogenous paste. Subsequently, the obtained paste was screen-printed on the sensor substrate and the printed sensor was calcined in a furnace at about 400° C. to remove terpineol.

[0043] FIG. 2 illustrates the sensing response of the sensor towards 100-700 ppb of NO.sub.2 gas. The sensor exhibits an excellent response to ppb-level of NO.sub.2 gas. The detection limit is very low, and the sensor response is about 14.3 even for 100 ppb of NO.sub.2 gas. The response time is about 1.5 min; the recovery time is 3 min. The sensing property of the sensor is comparable to prior art sensors working at high temperatures.

[0044] FIG. 3 shows a repeatability test of the sensor towards about 400 ppb of NO.sub.2 gas at room temperature. The result demonstrates that the sensor possesses a good repeatability at room temperature. For high temperature gas sensors, humidity is not a problem because water molecules will evaporate at elevated temperatures. In contrast, water vapour may be present on the material surface at room temperature and thus humidity variation might affect the sensing behaviour in this case. Light illumination may be used to eliminate the influence of any water molecules.

[0045] FIG. 4 shows the effect of humidity on the sensing performance towards 400 ppb NO.sub.2 in the humidity range of 0-80% at room temperature and shows that the effect of humidity on the sensitivity is insignificant. The base resistance decreases when humidity increases, especially from 0 to 20%. When it further increases, the decrease in base resistance becomes not obvious. As a result, the prepared sensor is substantially insensitive to humidity variations.