Low power mixed gas sensor
The invention is directed to a chemically robust, highly-selective, low power sensor that can be used for the direct electrical detection of mixed gases. In particular, metal-organic frameworks (MOFs) offer exceptional chemical and structural tunability as mixed-gas capture materials. As an example of the invention, the influence of interfering gases on trace NO 2 detection in a simulated flue gas stream was investigated. The unique interaction of NO 2 with the MOF's metal center leads to orders of magnitude decrease in MOF resistance. More broadly, the coadsorption of specific gases (e.g., H 2 O, SO 2 ) can be beneficial to the electrical detection of the target gas (e.g., NO 2 ), and careful electrical measurements can discern their presence independent of the target gas.
1. A low power mixed gas sensor, comprising:
an electrically insulating substrate;
a pair of interdigitated electrodes disposed on the substrate;
a mixed-gas-capture film that absorbs two or more target gases in a multi-gas environment, wherein the mixed-gas-capture film comprises a metal-organic framework material disposed on the pair of interdigitated electrodes and the substrate, and wherein the metal-organic framework (MOF) material comprises M-MOF-74, wherein M is cobalt, magnesium, zinc, or nickel, or RE-DOBDC, where RE is a rare-earth element and DOBDC is dihydroxyterephthalic acid; and
a frequency response analyzer configured to measure the impedance response of the mixed-gas-capture film when the two or more target gases are absorbed in the mixed-gas-capture film and an alternating voltage is applied to the pair of interdigitated electrodes.
2. The sensor of claim 1 , wherein the mixed-gas-capture film has a thickness of less than 100 μm.
3. The sensor of claim 2 , wherein the mixed-gas-capture film has a thickness of less than 10 μm.
4. The sensor of claim 1 , wherein the substrate comprises a silica glass substrate.
5. The sensor of claim 1 , wherein the alternating voltage has a frequency between 1 mHz and 1 MHz.
6. The sensor of claim 1 , further comprising a high impedance interface connected in series with the frequency response analyzer.
7. The sensor of claim 1 , wherein the mixed-gas-capture film absorbs the two or more target gases comprising NO x , SO x , CO x , and H 2 O from the multi-gas environment.
8. A method for detecting individual gases in a mixed gas stream, comprising:
providing a low power mixed gas sensor, comprising:
an electrically insulating substrate,
a pair interdigitated electrodes disposed on the substrate;
a mixed-gas-capture film that absorbs two or more target gases in a multi-gas environment, when the mixed-gas-capture film comprises a metal-organic framework material disposed on the pair of interdigitated electrodes and the substrate, and wherein the metal-organic framework (MOF) material comprises M-MOF-74, wherein M is cobalt, magnesium, zinc or nickel, or RE-DOBDC, where RE is a rare-earth element and DOBDC is dihydroxyterephthalic acid; and
a frequency response analyzer configured to measure the impedance response of the mixed-gas-capture film when the two or more target gases are absorbed in the mixed-gas-capture film and an alternating voltage is applied to the pair of interdigitated electrodes; exposing the mixed gas sensor to a mixed gas stream; and measuring the impedance response of the mixed-gas-capture film.
9. The method of claim 8 , wherein the step of exposing comprises exposure to the mixed gas stream for a sufficient time for the mixed-gas-capture film to equilibrate with the mixed gas stream, so that the measuring step provides a steady state impedance response.
10. The method of claim 8 , wherein the measuring step provides a transient impedance response.
11. The method of claim 8 , wherein the mixed-gas-capture film absorbs the two or more target gases comprising NO x , SO x , CO x , and H 2 0 from the multi-gas environment.