KR102132830B1 - Substrate structure for improved adsorption of NOx, and NOx sensor using the same - Google Patents

Abstract

The present invention relates to a substrate structure having improved NOx adsorption properties, and a NOx sensor using the same. More specifically, the present invention relates to an NOx sensor and an NOx trapping device having excellent NOx measurement sensitivity and responsiveness at room temperature using a SERS substrate structure capable of improving NOx adsorption and NOx desorption.

Description

Substrate structure for improved adsorption of NOx, and NOx sensor using the same}

The present invention relates to a substrate structure having improved NOx adsorption properties, and a NOx sensor using the same. More specifically, the present invention relates to a surface-enhanced Raman spectroscopy (SERS) substrate structure with improved NOx adsorption and NOx desorption, a NOx sensor and a NOx trapping device having excellent NOx measurement sensitivity and responsiveness using the same.

Nitrogen oxides are produced by combining nitrogen in combustion air and fuel with oxygen under the influence of temperature, etc., including nitrogen monoxide (NO), nitrogen dioxide (NO ₂ ), and dinitrogen trioxide (N ₂ O ₃ ). It is expressed as NOx.

Nitrogen monoxide and nitrogen dioxide occupy most of the nitrogen oxide, and the need for measurement of the nitrogen oxide concentration is increasing because it is caused by a lot of transportation such as a vehicle and acts as an air pollution source. In particular, nitrogen dioxide is a toxic and oxidizing action with a reddish-brown irritating odor, and is a gas harmful to the human body because it can worsen asthma.

As a method of measuring the concentration of the existing nitrogen oxide gas, a method using an equilibrium potential, a method using a current sensor, a mixed potential method, or a method using a conversion cell for converting nitrogen oxide gas into one gas type has been proposed. However, these conventional methods have a problem in that measurement accuracy is poor for nitrogen oxide gas in which nitrogen dioxide and nitrogen monoxide are mixed.

In addition, a resistive gas sensor including a conventional metal oxide semiconductor material has low sensitivity at room temperature and has difficulty in identifying signals of target molecules in a mixture of various gas molecules.

Furthermore, the sensor using SERS technology has a problem in measuring NOx at room temperature because gas molecules are difficult to adsorb at room temperature.

Therefore, there is a need for a NOx sensor having excellent NOx measurement sensitivity and responsiveness that can accurately measure NOx at room temperature in real time in the field.

Korean Patent Publication No. 10-2014-0148164 (2014.12.31.) describes a nitrogen oxide sensor device.

The above descriptions as background arts are only for improving understanding of the background of the present invention, and should not be accepted as acknowledging that they correspond to the prior arts already known to those skilled in the art. .

An object of the present invention is to provide a SERS substrate structure in which NOx adsorption power is improved and NOx desorption is possible due to temperature rise.

Another object of the present invention is NOx having excellent measurement sensitivity and responsiveness at room temperature using a SERS substrate structure. It is to provide a SERS sensor. In particular, NOx can be detected up to 0.1 ppm, which is an environmental regulation standard for NOx. It is to provide a sensor.

Another object of the present invention is a NOx capable of accurately measuring NOx at room temperature in real time in the field. It is to provide a sensor.

Another object of the present invention is a NOx capable of efficiently collecting NOx, which is an air pollutant, by using a three-dimensional porous substrate structure having a large surface area. It is to provide a collection device.

Another object of the present invention is a NOx capable of accurately measuring NOx at room temperature in real time using a SERS substrate structure. It is to provide a measurement method.

The objects of the present invention are not limited to the objects mentioned above, and other objects not mentioned will be clearly understood from the description of the detailed description.

According to an aspect, a substrate including a plurality of voids; A metal-containing nanowire laminated on the substrate without passing through the voids; And an Au thin film layer formed on the metal-containing nanowires, wherein the metal-containing nanowires form a nanogap that induces surface plasmon resonance with adjacent metal-containing nanowires and NOx. A substrate structure with improved adsorption properties is provided.

According to an embodiment, the Au thin film layer may be formed with an adjacent Au thin film layer and a nanogap that induces surface plasmon resonance.

According to one embodiment, the substrate may be a filter paper made of glass fiber.

According to an embodiment, the metal of the metal-containing nanowire may be formed of Ag, Al, Co, Cu, Fe, Li, Ni, Pd, Pt, Rh, Ru and alloys thereof.

According to one embodiment, the Au thin film layer may have a thickness of 1 nm or more.

According to one embodiment, the average diameter of the metal-containing nanowires on which the Au thin film layer is formed may exceed 50 nm.

According to one embodiment, the metal-containing nanowires may be formed by laminating a metal-containing nanowire on the substrate by filtering a solution containing the metal-containing nanowires through a vacuum filtration method through the substrate.

According to another aspect, a NOx sensor is provided, comprising a gas-flow chamber comprising the substrate structure herein.

According to one embodiment, the detection limit of the NOx sensor may be 0.1 ppm.

According to an embodiment, the NOx sensor may detect NOx at room temperature in less than 1 minute.

According to one embodiment, the NOx sensor may further include a heater that desorbs NOx from the gas-flow chamber by heating the gas-flow chamber.

According to an embodiment, the NOx sensor may enable NOx monitoring.

According to another aspect, a NOx trap device is provided that includes a substrate structure herein.

According to an embodiment, the NOx collection device may further include a decomposition device capable of decomposing the captured NOx.

According to an embodiment, the decomposition device may be a plasma device.

According to another aspect, an air purifier comprising a NOx trap device of the present application is provided.

According to another aspect, passing a gas sample through a substrate structure herein; And measuring a Raman signal by irradiating light to the substrate structure.

According to an embodiment, the NOx measurement method may have a NOx detection limit of 0.1 ppm.

According to an embodiment, the method for measuring NOx may further include heating the substrate structure after measuring NOx and re-measuring.

According to one embodiment, the NOx adsorption power is improved, it is possible to provide a SERS substrate structure capable of desorption by temperature rise.

According to one embodiment, it is possible to provide a SERS substrate structure for NOx adsorption with improved optical properties in the visible region.

According to one embodiment, the measurement sensitivity and responsiveness of the NOx sensor may be improved by using the SERS substrate structure. In particular, it is possible to provide an NOx sensor capable of detecting up to 0.1 ppm, which is an environmental regulation standard for NOx.

According to one embodiment, the NOx capture device using the SERS substrate structure can efficiently collect NOx, which is an air pollution source.

According to one embodiment, using the SERS substrate structure, it is possible to accurately measure NOx with high sensitivity at room temperature in real time.

1A is a view showing a part of a method for manufacturing a substrate structure including a 3D porous nanowire according to an embodiment.
1B is a diagram schematically showing a structure of a substrate structure including a 3D porous nanowire according to an embodiment.
2 is a scanning electron microscope (SEM) image showing the structure of a three-dimensional porous nanowire.
Figure 3 is a graph showing the distribution of the average diameter of the three-dimensional porous nanowires.
Figure 4 is a graph showing the optical properties of the SERS substrate structure comprising a three-dimensional porous nanowires.
5 is a schematic view schematically showing a method for measuring NOx using a NOx sensor including a SERS substrate structure including a 3D porous nanowire.
6 is a graph showing the SERS spectrum according to the NO ₂ concentration measured using a SERS substrate structure including a 3D porous nanowire.
7 is a quantitative curve graph showing the change in SERS signal intensity at 810 cm ^-1 according to the NO ₂ concentration prepared based on the results of FIG. 6.
8 is a graph showing NO ₂ gas response characteristics of a SERS substrate structure including a 3D porous Au-Ag nanowire including an Au thin film layer.
9 is a graph showing the NO ₂ gas response (response) characteristics of the SERS substrate structure including a three-dimensional porous Ag nanowires without the Au thin film layer.
10 is a graph showing the results of NO ₂ in the exhaust gas of diesel and gasoline vehicles measured in situ using a SERS substrate structure including a 3D porous Au-Ag nanowire including an Au thin film layer.
11 is a graph showing the change in SERS signal strength over time by placing NO ₂ collected on a 3D porous Au-Ag nanowire on a 100°C hot plate.

The objects, specific advantages and novel features of the present disclosure will become more apparent from the following detailed description and embodiments associated with the accompanying drawings.

Prior to this, the terms or words used in the specification and claims should not be interpreted in a conventional and lexical sense, and the inventor may appropriately define the concept of terms in order to best describe his or her invention. Based on the principle of being present, it should be interpreted as meaning and concept consistent with the technical idea of the present disclosure.

In the present specification, when a component such as a layer, part, or substrate is described as being "on", "connected" to, or "coupled" with other components, it is directly "on" or "on" other components. It may be "connected" or "coupled", and may also be interposed between one or more other components. In contrast, if a component is described as being “directly on”, “directly connected” to, or “directly coupled” to other components, no other component may be interposed between both components. .

The terms used in this specification are only used to describe specific embodiments, and are not intended to limit the present disclosure. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this specification, terms such as “include” or “have” are intended to indicate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, and that one or more other features are present. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

In the present specification, when a part “includes” a certain component, it means that the component may further include other components, not to exclude other components, unless otherwise stated. In addition, in the entire specification, "top" means that it is located above or below the target part, and does not necessarily mean that it is positioned above the center of gravity.

Since the present disclosure can apply various transformations and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present disclosure to specific embodiments, and it should be understood to include all conversions, equivalents, and substitutes included in the spirit and scope of the present disclosure. In describing the present disclosure, when it is determined that a detailed description of related known technologies may obscure the subject matter of the present disclosure, the detailed description will be omitted.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, and in describing with reference to the accompanying drawings, identical or corresponding components will be given the same reference numbers and redundant description thereof will be omitted. do.

1A is a view showing a part of a method of manufacturing a substrate structure including a 3D porous nanowire according to an embodiment. 1B is a diagram schematically showing a structure of a substrate structure including a 3D porous nanowire according to an embodiment.

1A and 1B, a substrate structure 100 according to an embodiment includes a substrate 110, a metal-containing nanowire 120, and an Au thin film layer 130.

The substrate 110 is formed with a number of pores so that the solution 122 containing the metal-containing nanowire 120 can be filtered. In the plurality of pores included in the substrate 110, the solvent 124 excluding the metal-containing nanowire 120 is filtered when the solution 122 containing the metal-containing nanowire 120 is filtered through the substrate 110. To be able to.

As the substrate 110, any one of alumina, polytetrafluoroethlylene (PTFE), polycarbonate (PC), glass fiber, cellulose, and paper may be used, but is not limited thereto. The substrate 110 may be used as long as it has a filtration function regardless of material.

In one embodiment, a filter paper using glass fiber was used as the substrate 110. Glass fiber can be used in a variety of organic solvents, the signal noise is not large, there is an advantage of low cost. In addition, when using glass fibers, it is possible to secure heat resistance that can withstand high temperatures in a process such as heat treatment of the substrate 110.

In the metal-containing nanowire 120, the metal may be any one of Ag, Al, Co, Cu, Fe, Li, Ni, Pd, Pt, Rh, Ru, and alloys thereof, but is not limited thereto.

The metal-containing nanowires 120 stacked on the substrate 110 may be formed by vacuum filtration of the solution 122 including the metal-containing nanowires 120 such as nanowire ink on the substrate 110. Can. 1A shows a filtration device using a vacuum filtration method.

Since the metal-containing nanowires 120 have a length that does not pass through the pores of the substrate 110, most of them do not pass through the substrate 110 during vacuum filtration and are stacked with a dense density on the substrate 110 Accumulate. The solution 122 containing the metal-containing nanowire 120 is filtered on the substrate 110 and collects the filtered solvent 124 in a collection device at the bottom.

The metal-containing nanowires 120 are stacked in an irregular direction on the substrate 110 to form a plurality of cross points. A nanogap is formed near the crossing point and becomes a hot spot that causes strong plasmon resonance, so it can make the greatest contribution to the enhancement of the Raman signal during light irradiation.

Hot spots can be formed both vertically and horizontally. As the metal-containing nanowires 120 are thickly stacked, the Raman signal may be enhanced, but the Raman signal is not significantly increased above a certain thickness. In this specification, this is expressed as the thickness at which the increase of the Raman signal is saturated. If the thickness of the Raman signal does not increase significantly, it can be used in the manufacturing process. That is, the thickness at which the Raman signal does not start to be increased is recorded and set, and the thickness at which the metal-containing nanowires 120 are stacked can be set based on this. In this way, when analyzing the Raman signal, there is little dependence on the laser focal length.

In addition, since the metal-containing nanowires 120 do not have a certain orientation and have an irregular direction, there is an advantage that there is little difference in results according to the orientation of the laser during analysis using a Raman signal.

The metal-containing nanowire 120 may control the size and density of the metal-containing nanowire 120 so as to form a nanogap that induces surface plasmon resonance with the adjacent metal-containing nanowire 120.

Adjustment of the density or thickness of the metal-containing nanowires 120 may be achieved by various factors, and in one embodiment, the concentration of the metal-containing nanowires 120 in the solution 122 and the solution 122 Adjustment was made using excess.

The solvent 124 may include a coating material such as polyvinylpyrrolidone (PVP) for securing dispersion stability of the metal-containing nanowire 120. The coating material may be removed through heat treatment, but it may also be used to control the nanogap. That is, when the density of the metal-containing nanowires 120 is increased, the nanogaps are gradually reduced from each other, so that the metal-containing nanowires 120 may be in contact with each other, so that the nanogaps may disappear. It is possible to exist in a minimized state.

The coating material as described above may act as noise when analyzing a Raman signal using a substrate for surface-enhanced Raman spectroscopy. In this case, only the distance between the metal-containing nanowires 120 is secured as described above using the coating material, and then the coating material is removed and the analyte is adsorbed to be used for Raman signal analysis.

2 is a scanning electron microscope (SEM) image showing the structure of a three-dimensional porous nanowire. Figure 2 (a) is a scanning electron microscope image showing a three-dimensional porous Ag NWs structure, Figure 2 (b) is a Au-Ag bimetal (bimetal) when 15 nm coating Au on the three-dimensional porous Ag NWs structure It is a scanning electron microscope image showing the structure of NWs. Figure 2 (c) is an image showing that the three-dimensional porous Au-Ag bimetal (bimetal) NWs structure is formed on the lower substrate made of glass fiber, (d) is a three-dimensional porous Au-Ag bimetal (bimetal) NWs This is a cross-sectional scanning electron microscope image of the structure. It can be seen that the three-dimensional porous metal nanowire structure is well stacked on the micron scale. When measuring the SERS, the depth of the laser beam is 200 nm. For the application of the SERS sensor, if the metal nanowire of 40 nm level is divided into 5 layers, it is advantageous to increase the thickness of the 3D porous metal nanowire to increase the amount of gas trapping. Do. The 3D porous Au-Ag bimetal NWs structure can be prepared by forming an Au thin film layer (130 in FIG. 1B) on the 3D porous Ag NWs structure.

Referring to FIG. 1B, in the three-dimensional porous Au-Ag bimetal NWs structure, a nanogap may be formed near the intersection of the metal-containing nanowires 120 and between the metal-containing nanowires 120.

As described above, since the substrate structure 100 according to an embodiment forms a nanogap at various points, the intensity and uniformity of the Raman signal according to an increase in hot spot density during light irradiation is improved.

In addition, when analyzing the analyte using the substrate structure according to an embodiment, it is possible to allow the analyte to be adsorbed on the various nanogaps described above, which is advantageous for analyzing a large amount of low concentration analyte.

In particular, Au-Ag bimetal (bimetal) NWs structure is remarkably the detection sensitivity for NO ₂ by improving the adsorption of the NO ₂ by having the Au thin film layer 130 formed in the binding energy with the NO ₂ is -27.0 kcal / mol Au Can be improved. The bond energy between the NO ₂ is about -7.2 kcal / mol of Ag NWs 3D porous structure formed of Ag is 0.1 environmental regulation standards for NO ₂ in a relatively low adsorption property, the minimum detection concentration of 0.3 ppm for NO ₂ Up to ppm NO ₂ cannot be detected.

The Au thin film layer 130 may be formed by vacuum deposition of Au, and the vacuum deposition may use any one of sputtering, evaporation, and chemical vapor deposition, but is not limited thereto. .

The thickness of the Au thin film layer 130 may be controlled by controlling conditions such as deposition time and deposition rate during vacuum deposition.

The Au thin film layer 130 may have a thickness of 1 to 100 nm, but is not limited thereto. If the thickness of the Au thin film layer 130 is less than 1 nm or more than 100 nm, plasmonic characteristics may be deteriorated. If the thickness of the Au thin film layer 130 is more than 100 nm, it is difficult to induce a plasmonic coupling phenomenon between the metal-containing nanowires 120 and/or between the Au thin film layers 130, and the plasmonic synergistic effect ( synergistic effect) can be difficult to expect. Although not limited thereto, the thickness of the Au thin film layer 130 is 1 to 100 nm, 1 to 90 nm, 1 to 80 nm, 1 to 70 nm, 1 to 60 nm, 1 to 50 nm, 1 to 40 nm, 1 To 30 nm, 1 to 20 nm, 5 to 100 nm, 5 to 90 nm, 5 to 80 nm, 5 to 70 nm, 5 to 60 nm, 5 to 50 nm, 5 to 40 nm, 5 to 30 nm, 5 to It may be 20 nm, and 5 to 20 nm may be suitable.

Herein, the Au thin film layer 130 means a substantial thin film layer, but does not exclude the partially deposited Au deposition layer.

Figure 3 is a graph showing the distribution of the average diameter of the three-dimensional porous nanowires. The white bar in the graph shows the number of three-dimensional porous Ag NWs structures, and the hatched bar shows the diameter distribution of the Au-Ag bimetal NWs structure when 15 nm of Au is deposited on the three-dimensional porous Ag NWs structure.

Referring to FIG. 3, the average diameter of the porous nanowires of the 3D porous Ag NWs structure is 45.8 nm, and when the Au thin film layer 130 is deposited to 15 nm, the porousness of the 3D porous Au-Ag bimetal NWs structure It can be seen that the average diameter of the nanowires is 62.6 nm.

Figure 4 is a graph showing the optical properties of the SERS substrate structure comprising a three-dimensional porous nanowires.

Referring to Figure 4, the substrate structure of the three-dimensional porous Ag NWs significantly decreases light absorption at a long wavelength of 550 nm or more, but the substrate structure of the three-dimensional porous Au-Ag bimetal NWs has light absorption at a long wavelength. Appeared relatively high. In particular, when the coating thickness of Au is 15 nm, it can be seen that the light absorption of the three-dimensional porous Au-Ag bimetal is significantly increased. This shows that the substrate structure of the 3D porous Au-Ag bimetal NWs increases the interaction of light and metal in visible light compared to the substrate structure of the 3D porous Ag NWs, and the light and metal interaction when 15 nm is deposited. You can see that the action is greatest. For example, when the wavelength of the laser used to measure the SERS is 550 nm or more, it can be determined that the sensitivity of the NOx sensor of the substrate structure including 3D porous Au-Ag bimetal NWs deposited with Au 15 nm will be the best. .

5 is a schematic view schematically showing a method for measuring NOx using a NOx sensor including a SERS substrate structure including a 3D porous nanowire.

Referring to FIG. 5, the NOx sensor 200 includes a gas-flow chamber 210 in which the substrate structure 100 of the present application is centrally located. The gas-flow chamber 210 may be provided with a quartz window on the upper surface.

In addition, the NOx sensor 200 may include a gas inlet 220 and a gas outlet 230, and a Raman spectroscopy device 300 that introduces or discharges sample gas containing NOx into the gas-flow chamber 210. have.

Among the sample gases introduced through the gas inlet 220, NOx is chemically adsorbed to the surface of the Au thin film layer 130 of the substrate structure 100 in the gas-flow chamber 210. At this time, the NOx sensor 200 may further include a suction device (not shown) that accelerates the inflow of the sample gas.

Light is irradiated to the Raman spectroscopy device 300 through the quartz window of the gas-flow chamber 210 to measure the Raman signal of NOx.

At this time, as described above, Au has a binding energy with NO ₂ of -27.0 kcal/mol, thereby improving adsorption power to NO ₂ and preventing desorption. Thus, NO ₂ sensor of the present application can detect up to high optical (or plasmonic) Characteristics and 0.1 ppm NO ₂ of the US Environmental Protection Agency regulations basis of NO ₂ according to the increase of the attraction force substrate assembly.

The NOx sensor 200 can measure NO ₂ at room temperature, thereby overcoming the limitations of the high operating temperature of the existing resistance change type gas sensor and immediately NOx in the field. It is possible to measure and improve usability.

When the NOx sensor 200 is used, NOx measurement can be performed in less than 1 minute, thereby improving the speed of NOx measurement (see FIG. 10 ).

In addition, the NOx sensor 200 may further include a heater (not shown) capable of desorbing NOx from the gas-flow chamber 210 by heating the gas-flow chamber 210. For example, when the gas-flow chamber 210 is heated at 100° C. for 10 minutes, adsorbed NO ₂ may be removed (see FIG. 11 ). According to the above configuration, monitoring of NOx may be possible using the NOx sensor 200. Therefore, the NOx sensor 200 can be used for monitoring the environment, indoor air, and healthcare.

As described above, the SERS substrate structure of the present application has improved adsorption and capture power for NOx. Accordingly, there is provided a NOx collecting device capable of efficiently collecting NOx, which is an air pollution source, including the substrate structure of the present application.

The NOx collection device may further include a decomposition device capable of decomposing the captured NOx. Although not limited thereto, the decomposition device may be a plasma device.

An air purifier capable of removing NOx after adsorption may be provided, including the NOx capture device and the NOx decomposition device herein.

According to one embodiment, passing a gas sample through a substrate structure described herein; And measuring a Raman signal by irradiating light to the substrate structure. Provided is a method for measuring NOx, comprising:

As described above, it is possible to accurately measure NOx with high sensitivity at room temperature in real time in the field by using adsorption and capture characteristics of NOx of the SERS substrate structure of the present application.

Therefore, the NOx measurement method can measure NO _{2 up} to 0.1 ppm which is an environmental regulation standard.

In addition, the NOx measurement method may further include a step of re-measurement after heating the substrate structure after the NOx measurement.

Hereinafter, the present invention will be described in more detail through examples.

[ Example ]

Substrate structure manufacturing

Comparative example

A filter paper for filtration of 0.7 µm made of glass fiber was used as the substrate 110. As the metal-containing nanowire 120, a nanowire ink including silver (Ag) nanowires having a diameter of 45.8 nm and a length of 50 μm was used, and the substrate of the silver (Ag) nanowire was vacuum filtered. It was laminated on (110) to prepare a substrate structure.

The nanowire ink was a 3 mL aqueous solution containing 0.3 wt% Ag NWs.

Examples 1 to 5

In Examples 1 to 5, the Au thin film layer 130 on the substrate structure manufactured in the same manner as in Comparative Example 1 was 5 nm (Example 1), 10 nm (Example 2), 15 nm (Example 3), and 20 nm ( Example 4) and formed to a thickness of 25 nm (Example 5).

The Au thin film layer 130 formed on the substrate 110 on which the nanowires 120 are stacked was formed by vacuum deposition under the following conditions.

-Heat deposition process

, Vacuum deposition operations the degree of vacuum: 9.8 x 10 ^{- 6} torr

Au deposition rate: 0.3 Å/s

Au deposition thickness: 5 nm to 25 nm

Experimental Example

Optical properties investigation

The optical properties of the substrate structures prepared according to Comparative Examples and Examples 1 to 5 were investigated. The results are shown in FIG. 4.

Referring to FIG. 4, the substrate structure including the porous three-dimensional Ag NWs, which is a comparative example, exhibited an extinction peak near 320 nm by an interband transition (3.8 eV) of Ag. On the other hand, as the thickness of the Au thin film layer increased, as in Examples 1 to 5, which are substrate structures including porous three-dimensional Au-Ag bimetal NWs, the band-to-band transition was shifted to a long wavelength toward 400 nm (red-shift).

In addition, as shown in Figure 4, the substrate structure of the three-dimensional porous Ag NWs is significantly reduced light absorption at a wavelength of 500 nm or more, the substrate structure of the three-dimensional porous Au-Ag bimetal (bimetal) NWs at a long wavelength Light absorption was relatively high. This means that the substrate structure of 3D porous Au-Ag bimetal NWs can increase the sensitivity of the NO ₂ sensor by increasing the interaction between light and metal materials in visible light compared to the substrate structure of 3D porous Ag NWs. do.

NO ₂ Analysis of SERS characteristics according to concentration

Since the optical properties of the SERS substrate structure including the three-dimensional porous nanowires prepared in Example 3 are the best, SERS characteristic analysis according to the NO ₂ concentration was performed (see FIG. 5 ).

The concentration of NO ₂ was adjusted by adjustment of the respective flow rates (flow rate ratio) of the mixed gas of NO ₂ and N _2.

As shown in Fig. 5, a portable Raman spectroscopy device was placed on the quartz window of the NO ₂ sensor, and the focus of the 785 nm laser was focused on the top surface of the 3D SERS substrate structure.

After exposing the SERS substrate containing the 3D porous nanowires with NO ₂ gas of various concentrations for 3 minutes, SERS measurement was performed with a 785 nm laser excitation wavelength.

6 is a graph showing the SERS spectrum according to the NO ₂ treatment at a concentration of 0 to 3.0 ppm measured using a SERS substrate structure including 3D porous nanowires.

At 0 ppm (N ₂ only for 3 minutes), the Raman characteristic peaks of polyvinylpyrrolidone (PVP) molecules used as stabilizers of Ag NWs solutions are 750 cm ^-1 and 940 cm ^-1 The Raman band appeared.

At 0.1 ppm, Raman bands appeared at 810 cm ^-1 and 1280 cm ^-1 , depending on the symmetric and asymmetric stretch mode of the NO ₂ molecule.

As shown in FIG. 6, it is clear that the PVP Raman signal is the same even when the NO ₂ concentration increases, while the intensity of the two NO ₂ Raman peaks continues to increase as the concentration increases.

7 is a quantitative curve graph showing the change in SERS signal intensity at 810 cm ^-1 according to the NO ₂ concentration prepared based on the results of FIG. 6. The NO ₂ concentration and the size of the SERS signal follow a typical Hill equation, and the Hill equation is as follows.

In the above equation, V is a constant, Θ is the NO ₂ surface coverage, c is the NO ₂ concentration, k is the equilibrium constant, and n is the value of the slope of the quantitative curve. The values of k and n are 0.39 ppm and 1.73, respectively, which means that the relationship between I _SERS (SERS signal strength) and c is linear at concentrations below k, meaning that reliable quantitative analysis is possible (internal graph in FIG. 7 ). ). The k value was calculated to be higher than 1 with 1.73. The high k value means that the adsorption force between the SERS substrate and the NO ₂ gas is very strong.

8 is a graph showing NO ₂ gas response characteristics of a SERS substrate structure including a 3D porous Au-Ag nanowire including an Au thin film layer. The NO ₂ SERS signal strength was used as measured at 810 cm ^-1 . While continuously injecting NO ₂ gas of each concentration, the SERS signal was continuously measured every 4 seconds. As soon as 0.1 ppm is injected, it can be confirmed that 810 cm ^-1 of the NO ₂ Raman characteristic band is analyzed within 5 seconds. That is, it can be confirmed that it is possible to implement a sensor capable of monitoring NO _{2 in} real time. Although the injection of 0.1 ppm of NO ₂ gas is stopped and the intensity of the Raman signal detected at 810 cm ^-1 gradually decreases even when only N ₂ carrier gas is injected, NO ₂ gas adsorbed on the Au surface cannot be desorbed. , It can be inferred that the NO ₂ gas adsorbed on the Ag surface formed under the substrate is slowly desorbed. Even in the case of 0.3 ppm of NO ₂ gas injection, the increase of the SERS signal was analyzed in real time within 5 seconds after the gas injection, and the intensity of the Raman signal detected at 810 cm ^-1 gradually decreased even when only the N ₂ carrier gas was injected. can confirm. Even in a high concentration situation, there is a tendency of an immediate increase in SERS signal (with NO ₂ gas injection) and a gradual decrease (desorption situation).

9 is a graph showing the NO ₂ gas response (response) characteristics of the SERS substrate structure including a three-dimensional porous Ag nanowires without the Au thin film layer. Although it is possible to analyze NO ₂ gas as quickly as a substrate containing Au, in a desorption experiment in which only N ₂ carrier gas is injected, the intensity of the Raman signal detected at 810 cm ^-1 continuously decreases to 0 and eventually It can be confirmed that NO ₂ gas is not analyzed. That is, it can be experimentally confirmed that the NO ₂ molecules adsorbed by the low bonding force between Ag and NO ₂ are desorbed from the Ag surface by the N ₂ carrier gas.

FIG. 10 is a measurement of NO ₂ in the exhaust gas of diesel vehicles (Tucson) and gasoline vehicles (K5) having the same displacement using a SERS substrate structure including a 3D porous Au-Ag nanowire including an Au thin film layer. It is a graph showing the results. After starting each vehicle and maintaining it at 1000 rpm, the 2 inch SERS substrate structure was dropped about 5 cm from each exhaust port and the exhaust gas was collected for 10 seconds. Then, a SERS analysis was performed using a portable Raman analyzer (laser wavelength: 785 nm). As shown in FIG. 10, it can be seen that the same NO ₂ SERS peak appears in the two vehicles, but the intensity of the SERS signal can confirm that the diesel vehicle is much larger. Since the diesel car has two exhaust ports, the diesel engine directly measured spectroscopically that the NO ₂ gas emission was 10.4 times to 17.0 times that of the gasoline car. It is generally known that diesel vehicles have 16 times more emission of NO ₂ gas than gasoline vehicles.

11 is a graph showing the change in intensity of the NO ₂ SERS signal over time after placing the SERS substrate collected by the diesel vehicle on a hot plate at 100° C. for a predetermined time. It can be seen that the strong SERS signal that appeared at 810 cm ^-1 disappeared after 10 minutes. That is, it can be determined that the NO ₂ molecule adsorbed on the Au surface is completely desorbed by external thermal energy.

Although the present disclosure has been described in detail through specific embodiments, the present disclosure is intended to specifically describe the present disclosure, and the present disclosure is not limited thereto, and will be understood by those skilled in the art within the technical spirit of the present disclosure. It is clear that the modification and improvement are possible. All simple modifications and changes of the present disclosure belong to the scope of the present disclosure, and the specific protection scope of the present disclosure will become apparent by the appended claims.

100: substrate structure
110: substrate
120: nanowire
130: Au thin film layer
200: NOx sensor
210: gas-flow chamber
220: gas inlet
230: gas outlet
300: Raman spectroscopy

Claims (20)

A substrate including a plurality of voids;
A metal-containing nanowire laminated on the substrate without passing through the voids; And
Including; Au thin film layer formed on the metal-containing nanowire;
The metal-containing nanowires form a nanogap that induces surface plasmon resonance with adjacent metal-containing nanowires, and includes a gas-flow chamber including a substrate structure with improved NOx adsorption,
A NOx sensor further comprising a heater that heats the gas-flow chamber to desorb NOx from the gas-flow chamber. According to claim 1,
The Au thin film layer is formed with a nanogap that induces surface plasmon resonance with an adjacent Au thin film layer, a NOx sensor. According to claim 1,
The substrate is a filter paper made of glass fiber, NOx sensor. According to claim 1,
The metal of the metal-containing nanowire is Ag, Al, Co, Cu, Fe, Li, Ni, Pd, Pt, Rh, Ru or an alloy thereof, NOx sensor. According to claim 1,
The Au thin film layer has a thickness of 1 nm or more, NOx sensor. According to claim 1,
NOx sensor, the average diameter of the metal-containing nanowires on which the Au thin film layer is formed is greater than 50 nm. According to claim 1,
The metal-containing nanowire is formed by depositing a metal-containing nanowire on the substrate by filtering a solution containing the metal-containing nanowire through a vacuum filtration method through the substrate. delete The method according to any one of claims 1 to 7,
The detection limit of the NOx sensor is 0.1 ppm, NOx sensor. The method according to any one of claims 1 to 7,
The NOx sensor is a NOx sensor capable of detecting NOx at room temperature. The method according to any one of claims 1 to 7,
NOx sensor that can detect NOx in less than 1 minute. delete The method according to any one of claims 1 to 7,
NOx sensor, capable of NOx monitoring. A substrate including a plurality of voids;
A metal-containing nanowire laminated on the substrate without passing through the voids; And
Including; Au thin film layer formed on the metal-containing nanowire;
The metal-containing nanowires form a nanogap that induces surface plasmon resonance with adjacent metal-containing nanowires, and the NOx trapping device includes a gas-flow chamber including a substrate structure with improved NOx adsorption. The method of claim 14,
Further comprising a decomposition device capable of decomposing the captured NOx, NOx capture device. The method of claim 15,
The decomposition device is a plasma device, NOx capture device. An air purifier comprising the NOx trapping device according to claim 14. Passing a gas sample through the NOx sensor according to claim 1; And
Measuring a Raman signal by irradiating light to the NOx sensor;
Including, NOx measurement method. The method of claim 18,
A method for measuring NOx, wherein the NOx detection limit is 0.1 ppm. 19. The method of claim 18, further comprising the step of heating the gas-flow chamber of the NOx sensor and re-measurement after measuring NOx.

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