Chemical sensors using coated or doped carbon nanotube networks
Inventors
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-7801687-B1
Publication Date
2010-09-21
Expiration Date
2025-07-08
Interested in licensing this patent?
MTEC can help explore whether this patent might be available for licensing for your application.
Abstract
Methods for using modified single wall carbon nanotubes (“SWCNTs”) to detect presence and/or concentration of a gas component, such as a halogen (e.g., Cl2), hydrogen halides (e.g., HCl), a hydrocarbon (e.g., CnH2n+2), an alcohol, an aldehyde or a ketone, to which an unmodified SWCNT is substantially non-reactive. In a first embodiment, a connected network of SWCNTs is coated with a selected polymer, such as chlorosulfonated polyethylene, hydroxypropyl cellulose, polystyrene and/or polyvinylalcohol, and change in an electrical parameter or response value (e.g., conductance, current, voltage difference or resistance) of the coated versus uncoated SWCNT networks is analyzed. In a second embodiment, the network is doped with a transition element, such as Pd, Pt, Rh, Ir, Ru, Os and/or Au, and change in an electrical parameter value is again analyzed. The parameter change value depends monotonically, not necessarily linearly, upon concentration of the gas component. Two general algorithms are presented for estimating concentration value(s), or upper or lower concentration bounds on such values, from measured differences of response values.
Core Innovation
The invention provides chemical sensors for detecting the presence and/or concentration of specific gas components at or near room temperature using modified single wall carbon nanotubes (SWCNTs). The sensor comprises a connected network of SWCNTs between electrodes, which is either coated with selected polymers or doped with transition elements. The invention specifically addresses gases such as halogens, hydrogen halides, hydrocarbons, alcohols, aldehydes, and ketones, where unmodified SWCNTs are substantially non-reactive. Changes in electrical parameters like conductance, current, voltage difference, or resistance are measured and analyzed to detect gas presence.
The detection approach uses two embodiments: one with SWCNT networks coated with polymers such as chlorosulfonated polyethylene or hydroxypropyl cellulose to achieve selectivity towards gases like chlorine and hydrogen chloride, and another with SWCNT networks doped with transition elements like Pd, Pt, Rh, or Au to detect hydrocarbons and carbon oxides. Algorithms are provided to estimate concentration values or bounds from measured electrical response differences, enabling selective sensing and quantitative assessment of gas components.
The problem addressed lies in the limitations of existing sensors, particularly those using single SWCNT field effect transistors which suffer from issues like difficulty in selective growth of semiconducting nanotubes, alignment challenges, cost sensitivity, low yield, and poor reproducibility. Moreover, pristine SWCNT sensors do not respond to certain gases such as chlorine and hydrogen chloride, limiting sensor scope. The invention solves these issues by employing SWCNT networks with polymer coatings or metal doping to enable selective, sensitive, low power, and room temperature detection of a wide range of gases, while also providing scalable fabrication methods suitable for practical use.
Claims Coverage
The patent describes two independent claims directed to methods for providing sensors that detect the presence of selected gas molecules using modified SWCNT networks, focusing on coating and doping strategies and related concentration estimation processes.
Use of coated and doped SWCNT networks for gas detection
Providing interdigitated electrodes connected to a controllable voltage or current source, and forming zeroth order uncoated SWCNT networks and N coated or doped SWCNT networks where at least one SWCNT is loaded with a selected chemical. The networks form electrical paths between electrodes, enabling absorption of gas molecules and measurement of electrical response values associated with these networks.
Algorithmic estimation of gas concentration from sensor responses
Adding known concentration increments of a gas constituent to create augmented gases and measuring response value differences between coated/doped and uncoated networks both before and after augmentation. Estimating concentrations or concentration bounds via error function minimization involving response value coefficients and solving resulting linear equations relating response changes to gas concentrations.
Selective modification of SWCNT networks to target specific gases
Choosing coating chemicals from chlorosulfonated polyethylene, hydroxypropyl, polystyrene, polyvinylalcohol to coat SWCNTs for detecting halogens, hydrogenated halogens, alcohols, aldehydes, and ketones. Alternatively, doping SWCNTs with transition elements such as Pd, Pt, Rh, Ir, Ru, Os, and Au to detect hydrocarbons and oxides of carbon.
Use of ultraviolet light to accelerate sensor recovery
Exposing sensor paths to ultraviolet light to facilitate desorption of gas molecules and recovery of sensor baseline electrical parameters, reducing recovery time between sensing cycles.
The independent claims cover methods of fabricating SWCNT-based gas sensors with coated or doped networks, measuring electrical response changes under controlled gas exposure, and applying algorithms to estimate gas concentrations, thereby enabling selective, sensitive detection of various target gases with improved sensor recovery processes.
Stated Advantages
High sensitivity to target gases including parts per million (ppm) and parts per billion (ppb) detection.
Room temperature operation with low power consumption.
Improved selectivity for gases such as chlorine and hydrogen chloride through polymer coatings.
Faster sensor recovery times facilitated by ultraviolet light exposure.
Scalable and reproducible sensor fabrication methods suitable for mass production.
Documented Applications
Detection of halogens (e.g., Cl2), hydrogen halides (e.g., HCl), hydrocarbons (e.g., CH4), alcohols, aldehydes, and ketones in gas mixtures at or near room temperature.
Use in sensor arrays and pattern recognition systems for selective identification and concentration estimation of gas constituents in industrial or environmental settings.
Environmental monitoring of greenhouse gases such as methane (CH4) and carbon oxides (COx).
Industrial sensing applications requiring rapid, selective, and low-cost gas detection.
Interested in licensing this patent?