Patent Application
20230184731
In at least one aspect, the present invention is related to methods and devices for measuring the amount of ammonia in a sample.
Ammonia is not only a ubiquitous environmental pollutant for aquatic eutrophication but also an important component of industrial fertilizer currently manufactured via the Haber-Bosch (H-B) process that supports 50% of the nitrogen element in the human body nowadays. Sensitive ammonia detection has been a Holy Grail for many decades as its application is of great importance to fundamental research areas catalysis and electrochemistry1. Ammonia emission to atmosphere nowadays is fully dominated directly and indirectly by human activity2. Thus it is pivotal for areas that are instrumental and influential to our everyday life—cement3, food industry4, water quality control5, exhaust gas sensing6, 7, chemistry and detection of combustibles8, and many more. The literature on the topic is very rich, and strategies to achieve the goal are highly diverse. This makes it virtually impossible to discuss, review and compare all of the approaches. Most notable conventional methods employ electrochemical9-11 approaches as metal oxides12-19, catalytic polymer20-27, including novel inkjet printing films28 and graphene/polymer hybrid framework29, and optical techniques30-33, fluorescence-labeled metal-organic-framework34, and nonlinear optics35, 36.
Probably, the most widely accepted optical methods are based on colorimetric approaches and its experimental derivatives37. The popular solution employs Berthelot reaction between ammonia, chlorine, and phenolic compounds, resulting in blue coloration of indophenol dye that can be easily detected by conventional spectrometers32. The following approach allows fine sensitivity down to several tens of parts per billion (ppb)32, 33, 38, 39. Though the method probably champions in overall detection limits, the blue indophenol method requires routine and time-consuming sample handling. It requires an aliquot of 2 mL to be taken out of the reactor each time and mix with other toxic reagents, followed by a 20-60 min aging before the final spectrophotometric analysis. In addition to its intrinsic time and materials consuming nature, colorimetric approaches fail to track the tiny change of on-site ammonia evolution and intermediate species, wherein key factors to reaction mechanism and catalyst design might be lost.
Probing samples directly via the intrinsic absorption or emission properties of ammonia molecule are broadly explored as well. The molecule has several UV40 and IR41-43 active bands, allowing non-invasive detection in the liquid or gaseous phase. In UV range, such detection relies on unique laser source and a quite complex optical setup. Moreover, acquisition time is rather long for rapid sample characterization40. These techniques proved to be rather sensitive to total ammonia concentrations. However, many concerns have been raised on results being contaminated from ammonia presence in surrounding laboratory and experimental environment. Due to the fact that IR light has long pathway and it is difficult to isolate it from external contamination, labeling with nitrogen isotope has been utilized44. Such an approach allows one to identify specific absorption modes associated with N15, similarly to the approach used for nuclear magnetic resonance studies. However, such isotope-related approaches make experiments complex and expensive. Emission techniques, like conventional Raman spectroscopy, have also shown some potential35, 36, 45-47, including UV resonant Raman approach48-54. Though Raman scattering can reveal background free chemical contrast, the signals have shown to be weak and with reasonable experimental conditions it cannot be employed for tracking small concentrations of ammonia.
Many efforts have been made towards the creation of a device to allow rapid ammonia detection in both liquid and gaseous forms. Within the most modern approach, a gas sensor with a detection limit of 10 ppm has been demonstrated using paper with perovskite halide as a sensor material55. Another elegant work reports on the fabrication and deployment of a thin film of metal-organic framework (MOF) as a chemical capacitive sensor. MOF is an organic-inorganic crystalline porous material that has unique structural properties compared to conventional porous materials as it allows control of topology and functionality of framework56-58. Detection of level as low as 1 part per million (ppm), with 100 part per billion (ppb) projected limit, has been successfully demonstrated34. Alternative solutions that use metal particles decorated with a graphene-based framework are also of high interest. Such sensors demonstrate a rather short recovery time with a projected detection limit of 45 ppb29.
Although the prior art method works reasonably well, current developments do not allow rapid analysis required for observation of live chemical processes.
Accordingly, there is a need for improved methods and devices for detecting ammonia.
In at least one aspect, a method for detecting and quantifying an amount of ammonia in a sample is provided. The method includes steps of providing a liquid or gaseous sample and positioning the sample proximate to a detection substrate. Incident light is focused onto the detection substrate while it is proximate to the sample. Characteristically, the incident light has an excitation wavelength from about 300 nm to 900 nm. Raman activity is detected from ammonia and/ammonia-containing complexes proximate to the detection substrate.
In another aspect, a method for in situ ammonia detection with comparable or superior sensitivity to the complex or known conventional experiments without sample perturbation, alterations, and modifications.
In another aspect, a surface-enhanced Raman spectroscopy (SERS) method to detect on-site ammonia concentration down to single-digit ppm level is provided. It is demonstrated that the method is reversible under different ammonia environments. Moreover, the potential of this method to study the evolution of surface-intermediate species during ENRR and other heterogeneous reactions for ammonia generation is computationally explored. Such low cost, high sensitivity, and feasible method is essential to environmental monitoring and fundamental research on ammonia synthesis and even other nitrogen-related reactions.
In another aspect, a method allowing in situ ammonia detection is provided.
In another aspect, a method allowing revisable ammonia detection is provided.
In another aspect, a method allowing the detection of ammonia in closed environments is provided.
In still another aspect, a device for in situ observation of chemical/catalytic reaction through ammonia release is provided.
In still another aspect, a new elegant yet simple method of sensitive ammonia detection using surface-enhanced Raman scattering (SERS) is provided. This detection method is a non-contact technique that does not rely on the complex chemical design of the sensor or alteration of the sample and solution. The devices implementing this method provide high-speed in-situ detection, with concentrations of 10 ppm concentration of ammonia in water easily observed with a potential 400 ppb projected detection limit. Advantageously, the device is a re-usable closed system, allow detection of both decrease and increase of ammonia concentration without worrying of contamination from the surrounding laboratory environment. Moreover, the described approach is based on very modest experimental conditions, using excitation powers available with most LED light sources (<3 mW) and commercially available plasmonic structures. Since the approach does not rely on complex instrumentation, analysis, or labeling, it is expected to fully democratize ammonia detection, thus drastically boosting the research in many areas of chemistry and surrounding disciplines.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
For a further understanding of the nature, objects, and advantages of the present disclosure, reference should be made to the following detailed description, read in conjunction with the following drawings, wherein like reference numerals denote like elements and wherein:
Reference will now be made in detail to presently preferred compositions, embodiments, and methods of the present invention, which constitute the best modes of practicing the invention presently known to the inventors. The Figures are not necessarily to scale. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for any aspect of the invention and/or as a representative basis for teaching one skilled in the art to variously employ the present invention.
Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary: the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; the first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation; and, unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.
It must also be noted that, as used in the specification and the appended claims, the singular form “a,” “an,” and “the” comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components.
As used herein, the term “about” means that the amount or value in question may be the specific value designated or some other value in its neighborhood. Generally, the term “about” denoting a certain value is intended to denote a range within +/−5% of the value. As one example, the phrase “about 100” denotes a range of 100+/−5, i.e. the range from 95 to 105. Generally, when the term “about” is used, it can be expected that similar results or effects according to the invention can be obtained within a range of +/−5% of the indicated value.
As used herein, the term “and/or” means that either all or only one of the elements of said group may be present. For example, “A and/or B” shall mean “only A, or only or both A and B”. In the case of “only A”, the term also covers the possibility that B is absent, i.e. “only A, but not. B”.
It is also to be understood that this invention is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular embodiments of the present invention and is not intended to be limiting in any way.
The term “comprising” is synonymous with “including,” “having,” “containing,” or “characterized by.” These terms are inclusive and open-ended and do not exclude additional, unrecited elements or method steps.
The phrase “consisting of” excludes any element, step, or ingredient not specified in the claim. When this phrase appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.
The phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps, plus those that do not materially affect the basic and novel characteristic(s) of the claimed subject matter.
The phrase “composed of” means “including” or “consisting of.” Typically, this phrase is used to denote that an object is formed from a material.
With respect to the terms “comprising,” “consisting of,” and “consisting essentially of,” where one of these three terms is used herein, the presently disclosed and claimed subject matter can include the use of either of the other two terms.
The term “one or more” means “at least one” and the term “at least one” means “one or more.” The terms “one or more” and “at least one” include “plurality” as a subset.
The term “substantially,” “generally,” or “about” may be used herein to describe disclosed or claimed embodiments. The term “substantially” may modify a value or relative characteristic disclosed or claimed in the present disclosure. In such instances, “substantially” may signify that the value or relative characteristic it modifies is within ±0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or 10% of the value or relative characteristic.
It should also be appreciated that integer ranges explicitly include all intervening integers. For example, the integer range 1-10 explicitly includes 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Similarly, the range 1 to 100 includes 1, 2, 3, 4 . . . 97, 98, 99, 100. Similarly, when any range is called for, intervening numbers that are increments of the difference between the upper limit and the lower limit divided by 10 can be taken as alternative upper or lower limits. For example, if the range is 1.1. to 2.1 the following numbers 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2.0 can be selected as lower or upper limits. In the specific examples set forth herein, concentrations, temperature, and reaction conditions (e.g. pressure, pH, etc.) can be practiced with plus or minus 50 percent of the values indicated rounded to three significant figures. In a refinement, concentrations, temperature, and reaction conditions (e.g., pressure, pH, etc.) can be practiced with plus or minus 30 percent of the values indicated rounded to three significant figures of the value provided in the examples. In another refinement, concentrations, temperature, and reaction conditions (e.g., pH, etc.) can be practiced with plus or minus 10 percent of the values indicated rounded to three significant figures of the value provided in the examples.
In the examples set forth herein, concentrations, temperature, and reaction conditions (e.g., pressure, pH, flow rates, etc.) can be practiced with plus or minus 50 percent of the values indicated rounded to or truncated to two significant figures of the value provided in the examples. In a refinement, concentrations, temperature, and reaction conditions (e.g., pressure, pH, flow rates, etc.) can be practiced with plus or minus 30 percent of the values indicated rounded to or truncated to two significant figures of the value provided in the examples. In another refinement, concentrations, temperature, and reaction conditions (e.g., pressure, pH, flow rates, etc.) can be practiced with plus or minus 10 percent of the values indicated rounded to or truncated to two significant figures of the value provided in the examples.
Throughout this application, where publications are referenced, the disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains.
Ammonia in this context generally means molecular ammonia in the chemical format of NH3, ammonium cations in a chemical format of NH4+, and other ammonia-containing complexes such as ammonia dimer, ammonia water complex, etc. It also means any ammonia-related molecule or complex with intrinsic intermolecular and intramolecular vibration Raman signals characteristic of ammonia.
Abbreviations:
“PEEK” means polyether ether ketone.
“PTFE” means polytetrafluoroethylene.
“SERS” or “SERAS” means surface-enhanced Raman spectroscopy.
In an embodiment, a method for detecting and quantifying an amount of ammonia in a sample by surface-enhanced Raman spectroscopy is provided. The method includes a step of providing a liquid or gaseous sample and then positioning the sample proximate to (e.g., within 10 nm to the substrate) to a detection substrate. In a refinement, the sample is at a distance of 0 to 10 nm from the substrate. In another refinement, the sample contacts the substrate. Incident light is focused on the detection substrate while it is proximate to the sample. The incident light has an excitation wavelength from about 300 nm to 900 nm (e.g., 532 nm). As set forth below, the incident light is focused on the sample with a single lens or lens system. The single lens or lens system can be a Raman objective (e.g., a water immersion objective) that also collects Raman scattered light. Raman activity from ammonia proximate to the detection substrate is then detected.
In one variation, Raman activity from ammonia is detected at 700 wavenumbers to 2000 wavenumbers spectral region. In another refinement, Raman activity from ammonia is detected at 2800 wavenumbers to 4000 wavenumbers spectral region. In a refinement, Raman activity can be detected in both these spectral regions for detecting and quantifying the amount of ammonia.
Characteristically, the detection substrate can have a structured surface that includes a structure size that is comparable to or smaller than a wavelength of excitation. In a refinement, the structured surface has nano-sized structures having dimensions less than 500 nm. In a further refinement, the structured surface has nano-sized structures having dimensions from 50 nm to 200 nm. In a refinement, nano-structured means that the structure has at least one dimension less than 500 nm or within the range 50 nm to 200 nm. In one example, the structured surface includes a plurality of pillars. In a refinement, the pillars are composed of silicon or another semiconductor or a dielectric or metal. Typically, the detection substrate includes a base substrate and a metal layer disposed over the base substrate such that the metal layer (e.g., a silver-containing layer) is proximate to the sample. The metal layer is a signal enhancement “hot-spot.” The base substrate can be virtually, any material such as dielectrics, semiconductor, and metals and nanostructures thereof.
The methods set forth herein can detect and quantify the amount of ammonia as a sample. For example, the concentration of ammonia or an ammonia-containing complex can be determined by measuring the amount of Raman scattered light at a wavelength or range of wavelengths that correspond to vibrational modes of ammonia or the ammonia-containing complex. In particular, a calibration curve can be determined from calibration samples of known ammonia or ammonia-containing complex concentrations. Such a calibration curve allows the determination of the concentration of liquid or gaseous samples of unknown concentration by extrapolation or interpolation as needed.
In some variations, device 10 is operated in a static mode in which the sample is introduced into the closed chamber for at static measurement and then withdrawn after measurement. In other variations, device 10 is operated in a flow mode in which the sample flows through the closed chamber while Raman activity is measured.
Referring to
The following examples illustrate the various embodiments of the present invention. Those skilled in the art will recognize many variations that are within the spirit of the present invention and scope of the claims.
Raman spectra of ammonia solution in water is presented in
There are several distinctive features in the broad region from 3000 cm−1 to 3500 cm−1. The main contributors are a rather sharp line around 3300 cm−1 and low and high-frequency sidebands to it (
Using GF matrix approach, Yeo et al. demonstrated the complexity of spectral information in this region with spectral overlap of all discussed above contributions—ammonia monomer (˜3300 cm−1) and dimer (˜3250 cm−1) of ammonia molecule and ammonium complex (˜3400 cm−1)64. Similar calculation accompanied with experimental studies has been done by Ujike et al.36 The calculated modes appear too close for a given line broadening and experimental resolution, thus only comparison of spectral mass shift for signals from liquid ammonia and water solution leads to some conclusions on lines origins. In spectral regions associated normally with bending modes, so-called, fingerprint region, NH3 and NH3-H2O contributions vary drastically and can be more easily distinguished. However, signals strength appears to be three orders of magnitude smaller, preventing the use of these spectral lines for fine ammonia detection. Please, see experimental observation chapter for further discussions on fingerprint region.
As of now, surface-enhanced Raman spectroscopy (SERS) is a well-used and broadly accepted technique for fine detection down to a single molecule limit. Several mechanisms have been proposed, including electromagnetic67 and charge transfer effects68. The broadly accepted electromagnetic theory for enhancement relies on excitation of localized surface plasmons—confined surface plasmon polariton when the structure size is comparable or smaller than the wavelength of excitation. The ability of a molecule to come in close proximity to LSP, the so-called “hot spot,” is crucial for the enhancement factor.
Surprisingly, SERS has not been a method of choice for ammonia detection since it has been demonstrated in 1984 in work by Sanchez et al.69. Studies on the detection on ammonium nitride reveal great detection limits in fingerprint region70. This work used a rather simple experimental approach based on conventional Au-coated Klarite™ substrates71. However, all the observed lines are attributed to the symmetric stretch of NO3, and no NH3 related signals were detected or discussed.
Raman spectroscopy
All Raman experiments have been done in conventional epi-geometry and schematically represented in
SERS Substrate
For experiments with conventional substrates, we used commercially available SERS substrate (SERStrate, Silmeco). The substrates comprise Si-nanopillars coated with the metal of choice. In current work, all detection of ammonia has been demonstrated with Ag coated Si-nanopillars. Similar specification, but Au-coated substrate did not demonstrate any ammonia sensitivity. The following is probably associated with the different capability of ammonia to be attracted to the hot spots of different metals. Prior to experiments, the drop of Millipore water has been deposited on the substrate surface to lean the Si structures in order to increase the interaction area72.
For simple homemade substrate, a simple colloidal silver paste and colloidal Ag ink (Sigma Aldrich) deposited on mica coverslip has been used.
Sample Preparation
Ammonia chloride power and ammonia water were used to make various concentrations of ammonium and ammonia solutions, respectively. Due to the different molecular weight of NH4Cl (NH3·HCl) and NH3·H2O, the concentration of ammonia (in ppm unit) refers to the quantity of NH3 species as compared to the water background. In this way, for dilute ammonia solution, the molar concentration of NH4Cl and NH3·H2O solutions are consistent.
Typical SERS spectra of ammonia solution in water (50 ppm ammonia solution in water) are shown in FIGS. 4A and 4B. The distinctive peak at 3260 cm−1 corresponds to the previously discussed NH3 dimer signal (
Substrate demonstrated rather homogeneous enhancement throughout its surface with signal variation not to exceed a factor of 2 (
Additional experiments demonstrated that there is no need to employ a specifically designed substrate with complex geometry, rather having uniform Ag coverage of the inert surface with a roughness of the order of 100 nm-200 nm. For such demonstration, commercially available silver paste (Sigma Aldrich) has been deposited on microscopy mica glass coverslip. The resultant cheap substrate demonstrated clear detection of 1000 ppm ammonia concentration (
Technical Description of Device Design
In order to strictly demonstrate the sensitivity, reversibility, and in-situ nature of the methods set forth herein, a flow cell as depicted in
In a typical analysis, Millipore pore water is flowed through the whole cell, and 5*5 data points are collected at different spots on SERS, which allows to fully evaluate the water background. The water enters through inlet 14 and exits through outlet 16. Then, certain concentrations of ammonia solutions (pH=pKa, pKa±2) are flow through the cell for 10 min to replace the water, and then analysis with different Raman parameters is conducted. Finally, the chamber is washed with Millipore water again to evaluate the reversibility of the whole process.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.
References:
This application claims the benefit of U.S. provisional application Ser. No. 63/021,912 filed May 8, 2020, the disclosure of which is hereby incorporated in its entirety by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/031109 | 5/6/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63021912 | May 2020 | US |
