KR20180015369A - Highly reliable complex for detecting gas having independence againt humidity, method for preparing the complex, gas sensor comprising the complex, and method for preparing the gas sensor - Google Patents

Abstract

The present invention relates to a complex for detecting gas, a manufacturing method for the same, a gas sensor including a complex for detecting gas as a gas sensing layer, and a manufacturing method for the same. The complex for detecting gas has stable and reliable detection performance in a moisture environment. Specifically, the complex for detecting gas includes: a nanostructure of an oxide semiconductor selected from a group composed of SnO_2, ZnO, WO_3, and NiO; and a CeO_2 additive soaked in the nanostructure. According to the present invention, the complex for detecting gas can rapidly detect gas to be detected at high sensitivity regardless of concentration and existence of the moisture by using the nanostructure of the oxygen semiconductor in which CeO_2 is evenly added.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a high-reliability gas detection composite, a production method thereof, a gas sensor including the gas detection composite, and a method for preparing the gas sensor,

The present invention relates to a gas detecting complex which exhibits stable and reliable detection ability even in a humid environment, a method for producing the same, and a gas sensor including the gas detecting complex as a gas sensing layer and a method for producing the same.

Oxide semiconductor type gas sensor has been proposed for the first time by Professor Seiyama of Kyushu University in Japan in the 1960s and has advantages such as high sensitivity, small size integration, simple operation circuit and low price, Detection, detection of noxious gas, and the like. In recent years, demand for indoor and outdoor environmental gas detection sensors, gas sensors for disease self-diagnosis, and artificial olfactory sensors that can be mounted on mobile devices have been rapidly increasing as interest in human health and environmental pollution has increased. However, since the oxide semiconductor type gas sensor has a fundamental problem in that it readily reacts with external moisture and greatly degrades performance and reliability, it still has difficulties in commercialization.

The oxide semiconductor type gas sensor detects the gas through a change in resistance that occurs when the reducing gas reacts with the oxygen ions adsorbed on the surface of the oxide. When moisture is present in the atmosphere, the water reacts with oxygen ions The gas sensitivity is greatly reduced and the sensor resistance is changed. However, since the oxide semiconductor type gas sensor operates in the atmosphere, exposure to moisture is inevitable, and the humidity varies greatly due to changes in weather, season, day and night, so that stable gas response It is almost impossible to secure the characteristics. Particularly, since the humidity present in the atmosphere is generally higher than the general concentration (several tens ppm) of the gas to be measured to be measured by the gas sensor in the range of several thousands to ten million ppm, the resistance change and the sensitivity change due to humidity, It should be considered as the most important factor in securing. Such a problem of deteriorating the performance and reliability of the oxide semiconductor gas sensor due to humidity has remained an unresolved problem for about 50 years since the gas sensor was proposed and serves as a main factor hindering commercialization of the sensor. In other words, in order to increase the reliability of the sensor and to utilize it in various applications, it is a priority to develop a highly reliable gas sensor that exhibits constant gas sensitivity and sensor resistance regardless of presence or concentration of moisture.

Specifically, since moisture in the atmosphere causes a reaction similar to a gas to be detected on the oxide semiconductor surface, (1) sensor resistance and gas sensitivity are largely changed by humidity change, (2) gas sensitivity is high in a high humidity atmosphere, - It has a serious problem that it is reduced to several tens of minutes. Recently, the humidity stability of the sensor material is highlighted as the most important issue in the oxide semiconductor type gas sensor field. However, more than 99% of studies on existing oxide semiconductor type gas sensors still evaluate the gas response characteristics in a dry atmosphere, and research on gas sensors in a humidity atmosphere has hardly been conducted. There are only 12 studies on the change in the gas response characteristics due to the humidity reported in the last four years. Except for the research results reported by Kim et al. (Non-Patent Document 1) It is only the level that mentioned the problem.

Furthermore, Kim et al. Also found that the Ni ion penetrates into the SnO ₂ lattice and forms an acceptor level, which greatly increases the resistance of the sensor and lowers the gas sensitivity. And the sensor resistance of the humidity atmosphere becomes very similar to the sensor resistance of the dry atmosphere, which is a long time. Nevertheless, many researches on this important issue have not been made because the fundamental problem is that the more sensitive substances with high gas reactivity, the greater the reactivity with moisture. Therefore, to solve the humidity dependence problem of the gas sensor, it may be more effective to design additives that can reduce or eliminate the humidity dependence rather than finding a new high sensitivity material.

The present inventors have also recognized the above-described problems and have proposed a gas sensor capable of exhibiting ultra-high sensitivity, high selectivity, and high-speed response characteristics without affecting moisture for various reducing gases. A gas detecting complex comprising nanoparticles, a method of producing the same, and the like have been reported (Patent Document 1).

Patent Document 1: Korean Patent Publication No. 10-1594734

Non-Patent Document 1: H.-R. Kim, Adv. Funct. Mater. 21 (2011) 4456-4463

Therefore, in the present invention, gas sensitivity and sensor resistance can be constantly derived in a very short time regardless of the presence or absence of moisture through a gas sensor manufactured by supporting a CeO ₂ additive uniformly on various oxide semiconductor nanostructures A gas sensor including the gas sensing complex as a gas sensing layer, and a method of manufacturing the same.

In order to solve the first problem,

SnO ₂ , ZnO, WO _3, and NiO; And

And a CeO ₂ additive supported on the nanostructure.

According to an embodiment of the present invention, the nanostructure may be a nanostructure having a hollow structure or an egg yolk structure.

According to another embodiment of the present invention, the CeO ₂ additive may be applied to the surface of the nanostructure.

According to another embodiment of the present invention, the CeO ₂ additive may be supported in an amount of 3 wt% to 30 wt% based on the total weight of the gas sensor.

According to another embodiment of the present invention, the gas may be a reducing gas selected from the group consisting of acetone, formaldehyde, ethanol, carbon monoxide and mixtures thereof.

Further, in order to solve the second problem,

a) at least one salt selected from the group consisting of an Sn salt, a Zn salt, a W salt and a Ni salt; Ce salt; And a solution comprising an organic acid or a sugar;

b) spraying the solution through a spray pyrolyzer to perform a spray pyrolysis reaction; And

c) obtaining a fine powder as a result of the spray pyrolysis reaction.

According to an embodiment of the present invention, the Sn salt is SnC ₂ O ₄ , SnCl ₄ .xH ₂ O (x is 2 or 5), Sn (CH ₃ COO) ₄ And mixtures thereof; Wherein the Zn salt is selected from the group consisting of Zn (NO ₃ ) ₂ .6H ₂ O, ZnCl ₂ , Zn (CH ₃ COO) ₂ .2H ₂ O and mixtures thereof; Wherein said W salt is selected from the group consisting of WO ₃ , (NH ₄ ) ₁₀ H ₂ (W ₂ O ₇ ) ₆ and mixtures thereof; Wherein the Ni salt is selected from the group consisting of Ni (NO ₃ ) ₂ .6H ₂ O, NiCl ₂ .6H ₂ O, Ni (CH ₃ COO) ₂ .4H ₂ O and mixtures thereof; Wherein the Ce salt is selected from the group consisting of Ce (NO ₃ ) ₃ .6H ₂ O, Ce (SO ₄ ) ₂ 4H ₂ O, CeCl ₃ 4H ₂ O and mixtures thereof; The organic acid is selected from the group consisting of citric acid, ethylene glycol and mixtures thereof; The sugar may be selected from the group consisting of sucrose, glucose and mixtures thereof.

According to another embodiment of the present invention, the spray pyrolysis reaction in step b) is carried out by injecting the solution into an electric furnace heated at 600 ° C to 1100 ° C at an injection rate of 2 L / m to 50 L / m .

Further, in order to solve the second problem,

a) preparing a dispersion in which at least one salt selected from the group consisting of an Sn salt, a Zn salt, a W salt and a Ni salt is dispersed in a solvent;

b) adding and reducing Ce salt to the dispersion; And

and c) obtaining a fine powder as a result of the reduction.

According to an embodiment of the present invention, the Sn salt is SnC ₂ O ₄ , SnCl ₄ .xH ₂ O (x is 2 or 5), Sn (CH ₃ COO) ₄ And mixtures thereof; Wherein the Zn salt is selected from the group consisting of Zn (NO ₃ ) ₂ .6H ₂ O, ZnCl ₂ , Zn (CH ₃ COO) ₂ .2H ₂ O and mixtures thereof; Wherein said W salt is selected from the group consisting of WO ₃ , (NH ₄ ) ₁₀ H ₂ (W ₂ O ₇ ) ₆ and mixtures thereof; Wherein the Ni salt is selected from the group consisting of Ni (NO ₃ ) ₂ .6H ₂ O, NiCl ₂ .6H ₂ O, Ni (CH ₃ COO) ₂ .4H ₂ O and mixtures thereof; The Ce salt may be selected from the group consisting of Ce (NO ₃ ) ₃ .6H ₂ O, Ce (SO ₄ ) ₂ 4H ₂ O, CeCl ₃ 4H ₂ O, and mixtures thereof.

According to another embodiment of the present invention, the reduction reaction in step b) may be performed by adding a material selected from the group consisting of NaBH ₄ , hydrazine, and mixtures thereof as a reducing agent.

The present invention also provides a gas sensor gas for gas detection comprising the gas sensing complex as a gas sensing layer.

Further, according to the present invention,

Preparing a solution comprising the gas sensing complex and a binder; And

And coating, drying and heat treating the solution on a substrate.

According to one embodiment of the present invention, the coating is performed by a drop-coating process, wherein the drying is performed at 70 ° C to 120 ° C for 12 to 24 hours and the heat treatment is performed at 500 ° C to 900 ° C for 1 hour To 6 hours.

According to the present invention, there is provided a gas detection complex capable of rapidly detecting a gas to be detected with a high sensitivity regardless of the presence or concentration of moisture using an oxide semiconductor nanostructure in which CeO ₂ is uniformly added, , A gas sensor including the gas sensing complex as a gas sensing layer, and a manufacturing method thereof.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic process diagram of a method for manufacturing a hollow structure gas sensor according to Examples 1-1 and 1-2 using an ultrasonic spray pyrolysis method. FIG.
FIG. 2 is a schematic process diagram of a method for manufacturing an egg yolk structure gas sensor according to Examples 2-1 and 2-2 using ultrasonic spray pyrolysis. FIG.
3 is a schematic flow diagram of a method of manufacturing a gas sensor according to Example 3 using a solution stirring method.
FIG. 4 is a graph showing the relationship between the pure SnO ₂ (Comparative Example 1-1, a) and ZnO (Comparative Example 1-2, c) hollow structure fine powder synthesized through ultrasonic spray pyrolysis; WO ₃ (Comparative Example 2-1, e) and NiO (Comparative Example 2-2, g) egg yolk structure fine powder; And Examples 2-1 (b), 1-2 (d), 2-1 (f) and 2-2 (h).
5 is an SEM photograph of Example 3 (b) synthesized using a solution stirring method and a commercial SnO ₂ fine powder (Comparative Example 3) (a).
Fig. 6 is a graph showing the results of the comparison between the results of Example 1-1, Comparative Example 1-1, Example 1-2, Comparative Example 1-2, Example 2-1, Comparative Example 2-1, Example 2-2 and Comparative Example using XRD This is the result of phase analysis for 2-2.
FIG. 7 shows phase analysis results for Example 3 and Comparative Example 3 using XRD.
Fig. 8 shows the results of comparison between the dry atmosphere of Comparative Examples 1-1 and 1-1 and the 20 ppm acetone gas sensitive transient and the gas sensitivity in an atmosphere of 80% relative humidity measured at 450 ° C.
FIG. 9 is a graph showing the results of the comparison of Comparative Examples 1-1, 1-1, 1-2, 1-2, 2-1, 2-1, 2-2, The results are compared with the dry atmosphere of Example 2-2 and the acetone gas sensitivity of 20 ppm at 20, 50 and 80% relative humidity.
FIG. 10 is a graph showing the results of the comparison of Comparative Examples 1-1, 1-1 and 1-2, Example 1-2, Comparative Example 2-1, Example 2-1, Comparative Example 2-2, The results of the sensor resistance comparison in the dry atmosphere of Example 2-2 and the relative humidity of 20, 50, and 80% atmosphere.
11 shows the results of comparing the sensitivity of the gas sensors of Comparative Example 3 and Example 3 measured at 450 ° C with the sensitivity of acetone gas at 20 ppm in a dry atmosphere and a relative humidity of 20, 50 and 80%.

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

The present invention provides a gas sensing complex based on an oxide semiconductor nanostructure in which CeO ₂ is uniformly added in order to solve the problems of the prior art as described above. Here, the oxide semiconductor nanostructure plays a role as a main gas sensor for the detection gas, and the added CeO ₂ selectively absorbs and removes the moisture introduced from the outside.

CeO ₂ is an ion conductor that transports lattice oxygen and oxygen ions at a very high rate through its excellent atomic conversion ability. It has recently been reported that PEMFC can perform a role of eliminating the hydroxyl groups generated on the PEM surface by driving for a long time There is a bar (V. Prabhakaran, PNAS (2012) 109, 1029-1034). In the present invention, when the CeO ₂ nanoparticles are applied to the surface of the gas sensitive material, it is determined that the reverse reaction of the following reaction formula 1, which is a moisture adsorption reaction, can be induced. As a result, the humidity dependency of the sensor is actually reduced to a negligible level .

<Reaction Scheme 1>

_{^{O - + H 2 O → 2OH}} + e -

At this time, it is judged that the CeO ₂ nanoparticles remove the humidity dependence according to the following reaction equations. In other words, Ce ^{4 +} in CeO ₂ nanoparticles is converted to Ce ^{3 +} by reaction with moisture and generates hydrogen ions and oxygen (Reaction 2). In this case, the generated Ce ^{3 +} and hydrogen ions react with the hydroxyl group formed on the surface of the gas sensor through the reaction formula 3, so that Ce ^{3 +} is oxidized to Ce ^{4 +} , and water is generated and desorbed (Scheme 4). Finally, the oxygen generated in Reaction Scheme 2 reacts with the electrons injected into the surface of the gas sensor in Reaction Scheme 3 and is regenerated again as oxygen ions (Scheme 5).

<Reaction Scheme 2>

4Ce ^{4 +} + 2H ₂ O - &gt; 4Ce ^{3 +} + 4H ⁺ + O ₂

<Reaction Scheme 3>

^{_{O (M) - + H 2}} O → 2OH (M) + e (M) -

<Reaction Scheme 4>

OH _(M) + Ce ^{+ 3} + H ⁺ → Ce ^{+ 4} + H ₂ O

<Reaction Scheme 5>

1/2 O ₂ + e _(M) ^- &gt; O _(M) ^-

This series of processes occurs repeatedly due to the excellent transition properties of CeO ₂ (L. Xu, Inorg. Chem. 49 (2010) 10590-10597), thereby preventing the sensor surface from being poisoned by moisture.

Through a series of the above processes, CeO ₂ The nanoparticles protect oxide semiconductor nanostructures such as SnO ₂ , ZnO, WO ₃ , and NiO, which are the main sensitizing materials, from a large amount of moisture continuously supplied from the outside, thereby minimizing or eliminating the humidity dependence of the sensor. In order to protect most of the surface of the gas sensitive body from moisture, a certain amount of CeO ₂ nanoparticles should be applied to the surface of the gas sensitive body, since such a reaction occurs only in the interface region between the portion where CeO ₂ and the gas sensitive body contact each other. However, when excessive CeO ₂ is applied, CeO ₂ The nanoparticles may be connected to each other to change the resistance of the sensor or obstruct conduction through the gas sensitive body. Therefore, in order to effectively remove moisture supplied from the outside while CeO ₂ minimally affects the resistance change and the gas response of the sensor, it is essential that the proper concentration of CeO ₂ is discontinuously and uniformly present in most of the gas sensitized bodies to be.

Thus, in the present invention,

SnO ₂ , ZnO, WO _3, and NiO; And

And a CeO ₂ additive supported on the nanostructure.

As described later, the nanostructure may be a nanostructure having a hollow structure or an egg yolk structure. When a SnO ₂ or ZnO oxide semiconductor is used, a hollow structure is used. When WO ₃ or NiO oxide semiconductor is used, .

In addition, the CeO ₂ additive may be applied to the surface of the nanostructure in order to minimize the effect of moisture on the effective protection and gas response.

Further, the CeO ₂ additive may be supported in an amount of 3 to 30 wt% based on the total weight of the gas sensor. When the CeO ₂ additive is less than 3 wt%, the effect of protecting the gas sensor from moisture is insufficient And when it exceeds 30% by weight, CeO ₂ There is a problem that the nanoparticles are connected to each other to change the resistance of the sensor or obstruct conduction through the gas sensitive body.

Meanwhile, the gas sensing complex according to the present invention can be used for the detection of various reducing gases selected from the group consisting of acetone, formaldehyde, ethanol, carbon monoxide and mixtures thereof.

Further, the present invention provides a method for producing the above-described gas sensing complex,

a) at least one salt selected from the group consisting of an Sn salt, a Zn salt, a W salt and a Ni salt; Ce salt; And a solution comprising an organic acid or a sugar;

b) spraying the solution through a spray pyrolyzer to perform a spray pyrolysis reaction

A step; And

and c) obtaining a fine powder as a result of the spray pyrolysis reaction.

The Sn salt may be SnC ₂ O ₄ , SnCl ₄ .xH ₂ O (x is 2 or 5), Sn (CH ₃ COO) ₄ And mixtures thereof; Wherein the Zn salt is selected from the group consisting of Zn (NO ₃ ) ₂ .6H ₂ O, ZnCl ₂ , Zn (CH ₃ COO) ₂ .2H ₂ O and mixtures thereof; Wherein said W salt is selected from the group consisting of WO ₃ , (NH ₄ ) ₁₀ H ₂ (W ₂ O ₇ ) ₆ and mixtures thereof; Wherein the Ni salt is selected from the group consisting of Ni (NO ₃ ) ₂ .6H ₂ O, NiCl ₂ .6H ₂ O, Ni (CH ₃ COO) ₂ .4H ₂ O and mixtures thereof; The Ce salt is selected from the group consisting of Ce (NO ₃ ) ₃ .6H ₂ O, Ce (SO ₄ ) ₂ 4H ₂ O, CeCl ₃ 4H ₂ O and mixtures thereof.

At this time, when CeO ₂ is added to the nanostructure having a hollow structure by using the Sn salt or the Zn salt, the organic acid is added to the solution of step a), and the organic acid is citric acid, ethylene glycol, Lt; / RTI &gt;

In the case of the addition of CeO ₂ nano-structure having a yolk structure using the W salt or Ni salt, the sugar can be selected from sucrose, glucose and mixtures thereof.

Meanwhile, the spray pyrolysis reaction may be performed under the condition that the solution prepared from the step a) is injected into the electric furnace heated at 600 ° C to 1100 ° C at an injection rate of 2 L / m to 50 L / m .

The gas-detecting complex according to the present invention can be produced by the spray pyrolysis reaction described above, but it can also be produced by a liquid-phase stirring method,

a) preparing a dispersion in which at least one salt selected from the group consisting of an Sn salt, a Zn salt, a W salt and a Ni salt is dispersed in a solvent;

b) adding and reducing Ce salt to the dispersion; And

c) obtaining a fine powder as the reduction product.

In the case of the liquid stirring method, the Sn salt, the Zn salt, the W salt, the Ni salt and the Ce salt are the same as those described in the spray pyrolysis reaction.

On the other hand, in the case of the liquid-phase stirring method, a step of reducing the mixed solution must be carried out in order to prepare the nanostructure to which CeO ₂ is added, wherein the reducing agent is selected from the group consisting of NaBH ₄ , hydrazine and mixtures thereof .

The present invention also provides a gas sensing gas sensor comprising the gas sensing complex as a gas sensing layer,

Preparing a solution comprising the gas sensing complex and a binder; And

Drying, and heat treating the solution on a substrate.

Here, the coating is performed by a drop-coating process, and the drying is performed at 70 ° C to 120 ° C for 12 to 24 hours, and the heat treatment may be performed at 500 ° C to 900 ° C for 1 hour to 6 hours have.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are intended to assist the understanding of the present invention and are not intended to limit the scope of the present invention.

Acetone is a biomarker gas that is detected both in indoor and outdoor environment pollution gas and in the exhalation of people suffering from diabetes. Therefore, it is very important to selectively detect acetone, regardless of presence or concentration of moisture. Therefore, in the following examples, acetone was selected as the main measurement gas, and the influence of external moisture on the gas sensitivity and sensor resistance of the sensor was analyzed.

In the present invention, pure SnO ₂ hollow structure fine powder (Comparative Example 1-1), pure ZnO hollow structure fine powder (Comparative Example 1-2), pure WO ₃ egg yolk structure fine powder (Comparative Example 2-1), and pure NiO 2-2) A gas sensor according to a comparative example was prepared using egg yolk structure fine powder. In addition, the hollow structure of 3 SnO ₂ wt% CeO ₂ is added (Example 1-1), ZnO hollow structure of the 5 wt% CeO ₂ is added (Example 1-2), 12 wt% CeO ₂ is the addition of WO ₃ yolk structure (example 2-1), and a 30 wt% CeO ₂ is added to the egg yolk structure NiO (example 2-2), the synthesis using ultrasonic spray pyrolysis, and then use this gas The sensor was fabricated. For the gas sensors manufactured as described above, the humidity dependency of the sensor, the gas sensitivity, and the sensor resistance were compared. In addition, the gas sensor (Example 3) was manufactured using the SnO ₂ hollow structure fine powder added with the 3 wt% CeO ₂ nanoparticles prepared by the liquid stirring method, and the difference in humidity dependence and gas sensitivity characteristics Respectively. 1 to 3 are a process chart (Fig. 1) for producing a hollow structure gas sensor according to Examples 1-1 and 1-2, respectively, by ultrasonic atomization pyrolysis, ultrasonic atomization pyrolysis (FIG. 2) for a method of manufacturing an egg yolk structure gas sensor according to Examples 2-1 and 2-2, and a method for manufacturing a gas sensor according to Example 3 using a solution stirring method (Fig. 3).

Example  1-1 and Comparative Example  1-1

To 300 mL of tertiary distilled water was added 0.05 M Tin oxalate (SnC ₂ O ₄ , 98%, Sigma-Aldrich, USA) and 0.15 M citric acid monohydrate (C ₆ H ₈ O ₇ .H ₂ O, ≥99.0% Sigma-Aldrich, USA) and stirred for 30 minutes to prepare a spray solution. Ce nitrate hexahydrate (Ce (NO ₃ ) ₃ .6H ₂ O, 99.99%, Sigma-Aldrich, USA) was added to the prepared spray solution so that the weight ratio of Ce / Followed by ultrasonic atomization. Micro-sized droplets formed through ultrasound were annealed at a flow rate of 5 L · min ^-1 (O ₂ ) at 900 ° C and immediately annealed to form a SnO ₂ hollow structure uniformly doped with 3 wt% CeO ₂ (Example 1-1). The pure SnO ₂ hollow structure without CeO ₂ was synthesized by the same procedure without addition of Ce source (Comparative Example 1-1).

The synthesized fine powder was mixed with tertiary distilled water, dropped on an alumina substrate having Au electrode formed thereon, and heat treated at 500 ° C for 2 hours to prepare a gas sensor. I) the air in a dry atmosphere, ii) the air in a relative humidity atmosphere of 20, 50, 80%, iii) the air in a dry atmosphere + 20 ppm acetone, and iv) the 20, 50, The change in resistance was measured by alternately injecting air + 20 ppm acetone in a humid atmosphere. Acetone was pre-mixed and then rapidly changed in concentration using a 4-way valve. The total flow rate was fixed at 100 SCCM so that the temperature difference did not occur when the gas concentration was changed.

Example  1-2 and Comparative Example  1-2

In the distilled water of 600 mL 0.15 M of _{Zinc nitrate hexahydrate (Zn (NO 3} ) 2 · 6H 2 O, 99.0%, Sigma-Aldrich, USA) and 0.1 M of Citric acid monohydrate (HOC (COOH) (CH 2 COOH ) ₂ · H ₂ O, 99.0%, Sigma-Aldrich, USA) was added thereto and stirred for 30 minutes to prepare a spray solution. Ce nitrate hexahydrate (Ce (NO ₃ ) ₃ .6H ₂ O, 99.99%, Sigma-Aldrich, USA) was added to the prepared spray solution so that the weight ratio of Ce / Zn was 5/95. Followed by ultrasonic atomization. Micro-sized droplets formed through ultrasonic waves were subjected to a heat treatment at a flow rate of 10 L · min ^-1 (O ₂ ) at 900 ° C. in a reaction furnace to prepare a ZnO hollow structure uniformly doped with 5 wt% CeO ₂ (Example 1-2). The pure ZnO hollow structure without CeO ₂ was synthesized by the same procedure without addition of Ce source (Comparative Example 1-2). The production of the gas sensor was carried out in the same manner as in Example 1-1.

Example  2-1 and Comparative Example  2-1

(WO ₃ , 99.9%, Sigma-Aldrich, USA) was added to a mixed solvent of 540 mL of tertiary distilled water and 60 mL of ammonia hydroxide solution (NH ₄ OH, 28.0-30.0%, Sigma-Aldrich, USA) And 0.5 M sucrose (C ₁₂ H ₂₂ O ₁₁ , 99.5%, Sigma-Aldrich, USA) were added to the solution and stirred for one day to prepare a spray solution. Ce nitrate hexahydrate (Ce (NO ₃ ) ₃ .6H ₂ O, 99.99%, Sigma-Aldrich, USA) was added to the prepared spray solution so that the weight ratio of Ce / After stirring, ultrasonic atomization was performed. Micro-sized droplets formed through ultrasound were subjected to a heat treatment at a flow rate of 5 L · min ^-1 (O ₂ ) at 900 ° C., and a WO ₃ egg yolk structure with 12 wt% CeO ₂ uniformly added (Example 2-1). The pure WO ₃ egg yolk structure without CeO ₂ was synthesized by the same procedure without addition of Ce source (Comparative Example 2-1). The production of the gas sensor was carried out in the same manner as in Example 1-1.

Example  2-2 and Comparative Example  2-2

To 600 mL of tertiary distilled water, 0.2 M of nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O, 99.999%, Sigma-Aldrich, USA) and 0.7 M Sucrose (C ₁₂ H ₂₂ O ₁₁ , 99.5% Sigma-Aldrich, USA) and stirred for 30 minutes to prepare a spray solution. Ce nitrate hexahydrate (Ce (NO ₃ ) ₃ .6H ₂ O, 99.99%, Sigma-Aldrich, USA) was added to the prepared spray solution so that the weight ratio of Ce / Ni was 30/70. Followed by ultrasonic atomization. Micro-sized droplets formed through ultrasound were subjected to a heat treatment at a flow rate of 5 L · min ^-1 (O ₂ ) through a reactor at 900 ° C. to synthesize a NiO egg yolk structure uniformly doped with 30 wt% of CeO ₂ (Example 2-2). The pure NiO egg yolk structure without CeO ₂ was synthesized by the same procedure without addition of Ce source (Comparative Example 2-2). The production of the gas sensor was carried out in the same manner as in Example 1-1.

Example  3 and Comparative Example  3

0.04 g of SnO ₂ phase powder (SnO ₂ ,%, Sigma-Aldrich, USA) was added to 40 mL of tertiary distilled water and sonicated for 30 minutes to disperse. The dispersed slurry was stirred for 1 hour and then the weight ratio of Ce / Sn was calculated to be 3/97. Ce nitrate hexahydrate (Ce (NO ₃ ) ₃ .6H ₂ O, 99.99%, Sigma-Aldrich, Followed by stirring for 4 hours. 10 mL (2 g / L) of fresh sodium borohydride (NaBH ₄ , 99.99%, Sigma-Aldrich, USA) solution was added to the prepared slurry and further stirred for 3 hours. After centrifugation, Respectively. The remaining slurry after washing was placed in an oven at 70 ° C and dried for two days to synthesize a SnO ₂ precursor added with CeO ₂ . The obtained precursor was heat-treated at 500 ° C for 3 hours to synthesize a SnO ₂ fine powder to which 3 wt% of CeO ₂ was uniformly added (Example 3). In the case of the pure SnO ₂ fine powder, the commercial SnO ₂ fine powder was heat-treated at 500 ° C. for 3 hours without a separate synthesis process (Comparative Example 3). The production of the gas sensor was carried out in the same manner as in Example 1-1.

Review

As a result of evaluating the gas sensitivity characteristics, the sensor was manufactured using the fine powder synthesized in the same manner as described above. As a result, it was found that Comparative Example 1-1, Example 1-2, Example 2-1, Example 3, In Examples 1-2, Comparative Examples 2-1 and 3, n-type semiconductor characteristics exhibiting a high resistance state in the air and decreasing resistance at the time of introduction of acetone were exhibited, and in Example 2-2 and Comparative Example In the case of 2-2, the p-type semiconductor exhibited a low resistance state in the air, while increasing acetone and increasing resistance. Accordingly, in the case of the n-type oxide semiconductor gas sensitivity R _a / R _g ( R _a : sensor resistance in air, R _g : sensor resistance in gas), and in the case of p-type oxide semiconductor, gas sensitivity is defined as R _g / R _a . Acetone sensitivity of each sensor was measured in dry atmosphere and compared with acetone sensitivity and sensor resistance measured at 20, 50 and 80% relative humidity. The detailed measurement method is as follows.

After 300 seconds after the resistance of the sensor was fixed in air in a dry atmosphere, the atmosphere was changed to the test gas (acetone 20 ppm) suddenly and exposed to the gas for 300 seconds, and then the atmosphere was changed to air in the dry atmosphere to maintain 1100 seconds And the gas sensitivity in a dry atmosphere was measured. Thereafter, the atmosphere was suddenly changed to air of 20, 50, and 80% relative humidity for 300 seconds, and then exposed to the test gas containing relative humidity of 20, 50, and 80% for 300 seconds, And the response characteristics were evaluated. The same procedure was repeated 3 times to measure changes in gas sensitivity characteristics with time of exposure to moisture. In addition, the value obtained by dividing the gas sensitivity at 20, 50, and 80% relative humidity by the gas sensitivity at the dry atmosphere was defined as the rate of change in gas sensitivity. The sensor resistance at 20, 50, and 80% Divided by the sensor resistance change rate. Therefore, it can be understood that when the gas sensitivity and the change rate of the sensor resistance are 1, the humidity dependency of the sensor is hardly present.

FIG. 4 is a graph showing the relationship between the pure SnO ₂ (Comparative Example 1-1, a) and ZnO (Comparative Example 1-2, c) hollow structure fine powder synthesized through ultrasonic spray pyrolysis; WO ₃ (Comparative Example 2-1, e) and NiO (Comparative Example 2-2, g) egg yolk structure fine powder; And Examples 2-1 (b), 1-2 (d), 2-1 (f) and 2-2 (h).

Referring to FIG. 4, it can be seen that Comparative Example 1-1 and Comparative Example 1-2 are hollow hollow structures (a, c). In Comparative Example 2-1 and Comparative Example 2-2, (E, g) of the egg yolk structure in which a hollow structure is additionally present. In the case of the fine powder according to Example 1-1, Example 1-2, Example 2-1 and Example 2-2 synthesized through the same process by adding CeO ₂ of 2, 5, 12, 30 wt% (B, d) and the egg yolk structure (f, h), regardless of the presence or absence of CeO ₂ addition and concentration.

5 is an SEM photograph of Example 3 and a commercial SnO ₂ fine powder (Comparative Example 3) synthesized using a solution stirring method. 5, the size of the commercial SnO ₂ fine powder was as small as a few nanometers (a), and exhibited almost the same structure even after the addition of CeO ₂ without increasing the size or agglomerating (b).

Fig. 6 is a graph showing the results of the comparison between the results of Example 1-1, Comparative Example 1-1, Example 1-2, Comparative Example 1-2, Example 2-1, Comparative Example 2-1, Example 2-2 and Comparative Example using XRD This is the result of phase analysis for 2-2. Referring to FIG. 6, the X-ray diffraction pattern of Comparative Example 1-1 shows a tetragonal structure of SnO ₂ (a1). In addition, the X-ray diffraction pattern of Example 1-1 did not reveal a diffraction pattern related to CeO ₂ even though CeO ₂ of 2 wt% was added (a 2). This is because the amount of added CeO ₂ is very small and it is beyond the analytical limit of XRD or the CeO ₂ nanoparticles are uniformly distributed throughout the SnO ₂ hollow structure.

On the other hand, the diffraction pattern of Comparative Example 1-2 shows a hexagonal structure of ZnO (b1). In addition, although the amount of CeO ₂ added in Example 1-2 was higher than that of XRD (5 wt%), no diffraction pattern related to CeO ₂ was found (b2). This shows that the added CeO ₂ is dispersed very uniformly over the entire ZnO hollow structure to several nm.

Furthermore, the diffraction pattern of Comparative Example 2-1 was confirmed to be WO ₃ of a monoclinic structure (c1). In addition, in the diffraction pattern of Example 2-1 in which 12 wt% of CeO ₂ was added, it was confirmed that the diffraction pattern of CeO ₂ having a fluorite cubic structure was correlated with the dispersion degree of CeO ₂ nanoparticles (12 wt%) of cerium oxide (CeO ₂₎ added without any additives (c2). Example 2-1 showed a diffraction pattern of NiO having a cubic system structure in the case of Example 2-2 (d1), shown with the diffraction pattern of NiO and CeO ₂ (d2).

On the other hand, in the phase analysis results of each fine powder, no secondary phase was found between the gas sensitizer (SnO ₂ , ZnO, WO ₃ , NiO) and CeO ₂ , and thus, the added CeO ₂ was in the form of nanoparticles, Of the total population.

FIG. 7 shows phase analysis results for Example 3 and Comparative Example 3 using XRD. Referring to FIG. 7, Comparative Example 3 shows a diffraction pattern of SnO _{2 having} a tetragonal structure (a 1). In the case of Example 3, the diffraction pattern of CeO ₂ together with the diffraction pattern of SnO ₂ together (a 2) was observed, although the addition amount of CeO ₂ (2 wt%) was the same as in Example 1-1. This shows that when the CeO ₂ -metal oxide nanostructure is synthesized by the solution stirring method without using the ultrasonic spray pyrolysis method, the CeO ₂ nanoparticles are not uniformly distributed throughout the gas sensitive body as compared with the ultrasonic spray pyrolysis method .

Fig. 8 shows the results of comparison between the dry atmosphere of Comparative Examples 1-1 and 1-1 and the 20 ppm acetone gas sensitive transient and the gas sensitivity in an atmosphere of 80% relative humidity measured at 450 ° C. Referring to FIG. 8, in Comparative Example 1-1, the sensitivity was as high as 20 ppm of acetone in a dry atmosphere, but when exposed to an atmosphere of relative humidity of 80%, the sensitivity of acetone was greatly decreased. At the same time, (A1 and a2). This is a general phenomenon that occurs when an n-type oxide semiconductor gas sensor such as SnO ₂ is exposed to moisture, which is a main factor causing deterioration of sensor performance and malfunction. On the contrary, in case of Example 1-1, acetone sensitivity and resistance were almost similar to those in a dry atmosphere (FIG. 8B1) even though the relative humidity was suddenly exposed to 80% atmosphere in a short time (<300 s). The results show that, when CeO ₂ is added to SnO ₂ , unlike a general oxide semiconductor type gas sensor, it is possible to obtain high reliability and constant gas sensitivity characteristic regardless of the presence or absence of external moisture (b 2).

FIG. 9 is a graph showing the results of the comparison of Comparative Examples 1-1, 1-1, 1-2, 1-2, 2-1, 2-1, 2-2, The results are compared with the dry atmosphere of Example 2-2 and the acetone gas sensitivity of 20 ppm at 20, 50 and 80% relative humidity. Referring to FIG. 9, in the case of Comparative Example 1-1, Comparative Example 1-2, Comparative Example 2-1, and Comparative Example 2-2, as the concentration of the external relative humidity supplied increases, (A, c, e, and g), the gas sensitivity tended to decrease gradually. On the other hand, in Example 1-1, Example 1-2, Example 2-1 and Example 2-2 in which CeO ₂ was added, almost constant acetone sensitivity was exhibited regardless of the presence or the concentration of the relative humidity ( b, d, f, h). This shows that the added CeO ₂ serves to prevent the surface of the gas sensitive body from poisoning due to hydroxyl groups. As a result of calculating the gas sensitivity change rate, which is an index for evaluating the reliability of the sensor sensitivity, at the relative humidity 80% atmosphere, the gas sensitivity change rates of the gas sensors according to the comparative examples were 0.81 (Comparative Example 1-1) and 0.49 1-2), 0.66 (Comparative Example 2-1), and 0.84 (Comparative Example 2-2), while the gas sensors according to the embodiments were 1.03 (Examples 1-1) and 0.97 1-2), 0.98 (Example 2-1), and 1.03 (Example 2-2). This shows that the addition of CeO ₂ as a water absorbing agent to the oxide semiconductor exhibiting humidity dependence can substantially eliminate the humidity dependence of the gas sensitivity.

FIG. 10 is a graph showing the results of the comparison of Comparative Examples 1-1, 1-1 and 1-2, Example 1-2, Comparative Example 2-1, Example 2-1, Comparative Example 2-2, The results of the sensor resistance comparison in the dry atmosphere of Example 2-2 and the relative humidity of 20, 50, and 80% atmosphere. Referring to FIG. 10, in the case of the gas sensor according to Comparative Example 1-1, Comparative Example 1-2, and Comparative Example 2-1 which is an n-type oxide semiconductor, as the relative humidity increases, (A, c, and e). In this case, the amount of electrons is increased and the sensor resistance is decreased. On the other hand, since the gas sensor according to Comparative Example 2-1 is a p-type oxide semiconductor, the electrons generated by the reaction with moisture decrease the concentration of holes in the NiO, so that the sensor resistance gradually increases as the humidity increases g). The change in the sensor resistance according to the humidity of the gas sensor according to the comparative examples is similar to the resistance change occurring when the sensor reacts with the gas (n type: resistance decrease in gas response; p type: resistance increase in gas response ), Which is a major cause of sensor malfunction. On the other hand, gas sensors according to embodiments in which CeO ₂ was added showed almost constant sensor resistance (b, c, f, h) regardless of the presence or concentration of external moisture. The sensor resistance change rate, which is an index for evaluating the reliability of the sensor calculated on the basis of the relative humidity of 80% atmosphere, is 0.61 (Comparative Example 1-1), 0.46 (Comparative Example 1-2) , 0.73 (Comparative Example 2-1) and 0.93 (Comparative Example 2-2, dry atmosphere sensor resistance / humidity atmosphere sensor resistance), while in the case of the gas sensors according to the embodiments, 0.97 ), 0.99 (Example 1-2), 1.0 (Example 2-1), and 1.0 (Example 2-2). When the CeO ₂ nanoparticles are added to the gas sensitive material as a water absorbing agent, not only the gas sensitivity but also the humidity resistance stability of the sensor resistance can be secured at the same time, and the high reliability gas exhibiting a constant gas sensitivity characteristic regardless of the presence or concentration of moisture Sensor can be implemented.

11 shows the results of comparing the sensitivity of the gas sensors of Comparative Example 3 and Example 3 measured at 450 ° C with the sensitivity of acetone gas at 20 ppm in a dry atmosphere and a relative humidity of 20, 50 and 80%. 11, in the case of the commercial SnO ₂ powder (Comparative Example 3), there was a large difference between the acetone sensitivity and the sensor resistance in a dry atmosphere and an 80% relative humidity atmosphere (a, c: gas sensitivity change ratio: 0.84 ; Sensor resistance change rate: 0.75). (B, d: gas sensitivity change ratio: 0.89; sensor resistance change ratio: 0.93) in the case where CeO ₂ was added through the solution stirring method (Example 3), the acetone sensitivity and the sensor resistance of the sensor resistance were improved ) And the same amount of Ce was added, it did not show high reliability against moisture as in Example 1-1 (gas sensitivity change ratio: 1.03; sensor resistance change rate: 0.97). This is to uniformly coating the order at the same time, showing that it is also possible to reduce the humidity dependency of the sensor by simply adding the CeO ₂ in the oxide semiconductor to maximize the water absorption and the removal effect of CeO ₂ CeO ₂ to the entire gas-sensitive body It is very important.

Claims (14)

SnO ₂ , ZnO, WO _3, and NiO; And
And a CeO ₂ additive supported on the nanostructure. The method according to claim 1,
Wherein the nanostructure is a nanostructure having a hollow structure or an egg yolk structure. The method according to claim 1,
Wherein the CeO ₂ additive is applied to the surface of the nanostructure. The method according to claim 1,
Wherein the CeO ₂ additive is supported in an amount of 3 wt% to 30 wt% based on the total weight of the gas sensor. The method according to claim 1,
Wherein the gas is a reducing gas selected from the group consisting of acetone, formaldehyde, ethanol, carbon monoxide and mixtures thereof. a) at least one salt selected from the group consisting of an Sn salt, a Zn salt, a W salt and a Ni salt; Ce salt; And a solution comprising an organic acid or a sugar;
b) spraying the solution through a spray pyrolyzer to perform a spray pyrolysis reaction
A step; And
c) obtaining a fine powder as a result of the spray pyrolysis reaction. The method according to claim 6,
The Sn salt may be SnC ₂ O ₄ , SnCl ₄ .xH ₂ O (x is 2 or 5), Sn (CH ₃ COO) ₄ And mixtures thereof; Wherein the Zn salt is selected from the group consisting of Zn (NO ₃ ) ₂ .6H ₂ O, ZnCl ₂ , Zn (CH ₃ COO) ₂ .2H ₂ O and mixtures thereof; Wherein said W salt is selected from the group consisting of WO ₃ , (NH ₄ ) ₁₀ H ₂ (W ₂ O ₇ ) ₆ and mixtures thereof; Wherein the Ni salt is selected from the group consisting of Ni (NO ₃ ) ₂ .6H ₂ O, NiCl ₂ .6H ₂ O, Ni (CH ₃ COO) ₂ .4H ₂ O and mixtures thereof; Wherein the Ce salt is selected from the group consisting of Ce (NO ₃ ) ₃ .6H ₂ O, Ce (SO ₄ ) ₂ 4H ₂ O, CeCl ₃ 4H ₂ O and mixtures thereof; The organic acid is selected from the group consisting of citric acid, ethylene glycol and mixtures thereof; Wherein the saccharide is selected from the group consisting of sucrose, glucose and mixtures thereof. The method according to claim 6,
Wherein the spray pyrolysis reaction in step b) is carried out by injecting the solution into an electric furnace heated at 600 ° C to 1100 ° C at an injection rate of 2 L / m to 50 L / m. &Lt; / RTI &gt; a) preparing a dispersion in which at least one salt selected from the group consisting of an Sn salt, a Zn salt, a W salt and a Ni salt is dispersed in a solvent;
b) adding and reducing Ce salt to the dispersion; And
c) obtaining a fine powder as a result of the reduction. 10. The method of claim 9,
The Sn salt may be SnC ₂ O ₄ , SnCl ₄ .xH ₂ O (x is 2 or 5), Sn (CH ₃ COO) ₄ And mixtures thereof; Wherein the Zn salt is selected from the group consisting of Zn (NO ₃ ) ₂ .6H ₂ O, ZnCl ₂ , Zn (CH ₃ COO) ₂ .2H ₂ O and mixtures thereof; Wherein said W salt is selected from the group consisting of WO ₃ , (NH ₄ ) ₁₀ H ₂ (W ₂ O ₇ ) ₆ and mixtures thereof; Wherein the Ni salt is selected from the group consisting of Ni (NO ₃ ) ₂ .6H ₂ O, NiCl ₂ .6H ₂ O, Ni (CH ₃ COO) ₂ .4H ₂ O and mixtures thereof; Wherein the Ce salt is selected from the group consisting of Ce (NO ₃ ) ₃ .6H ₂ O, Ce (SO ₄ ) ₂ 4H ₂ O, CeCl ₃ 4H ₂ O and mixtures thereof. 10. The method of claim 9,
Wherein the reduction reaction in step b) is carried out by adding a material selected from the group consisting of NaBH ₄ , hydrazine and mixtures thereof as a reducing agent. A gas sensor for gas detection comprising a gas sensing complex according to any one of claims 1 to 5 as a gas sensing layer. A process for producing a gas sensing composite, comprising: preparing a solution containing the gas sensing complex and the binder according to any one of claims 1 to 5; And
And coating, drying and heat treating the solution on a substrate. 14. The method of claim 13, wherein the coating is performed by a drop-coating process, wherein the drying is performed at 70 DEG C to 120 DEG C for 12 to 24 hours, and the heat treatment is performed at 500 DEG C to 900 DEG C for 1 to 6 hours &Lt; / RTI &gt;

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