CN110806431B

CN110806431B - Preparation method and application of ammonia gas sensor based on in-situ polymerization binary nano composite material

Info

Publication number: CN110806431B
Application number: CN201911025632.2A
Authority: CN
Inventors: 张冬至; 樊晓曦; 郭亮; 宫礼坤; 王兴伟
Original assignee: China University of Petroleum East China
Current assignee: China University of Petroleum East China
Priority date: 2019-10-25
Filing date: 2019-10-25
Publication date: 2020-07-07
Anticipated expiration: 2039-10-25
Also published as: CN110806431A

Abstract

The invention discloses a preparation method and application of an ammonia gas sensor based on an in-situ polymerization binary nano composite material, relating to the technical field of nano gas sensors, wherein the preparation steps comprise: 1) preparing a CuFe2O4 nano material by adopting a combustion method; 2) preparing a PANI-CuFe2O4 nano composite material by an in-situ polymerization method; 3) the PANI-CuFe2O4 solution was cast onto an epoxy substrate using interdigitated electrodes to form a sensing film. The ammonia sensor has good responsiveness and selectivity, high response speed and short recovery time, and is obviously superior to a single material film.

Description

Preparation method and application of ammonia gas sensor based on in-situ polymerization binary nano composite material

Technical Field

The invention relates to the technical field of nano gas sensors, in particular to a preparation method and application of an ammonia gas sensor based on an in-situ polymerization binary nano composite material.

Background

Industry has developed rapidly in recent years, but exhaust pollution has become more serious. NH (NH)₃As an alkaline pollution gas, once leaked, the alkaline pollution gas can pollute various fields of human life. Even at low NH concentrations₃It also has serious influence on human health, such as irritation to eyes, respiratory tract and skin, dizziness, nausea and fatigue.

Therefore, there is an urgent need to develop cost-effective, sensitive, and highly selective NH for human health and environmental protection₃A gas sensor. In a metal oxide semiconductor, the electrical properties of the analyte gas can change significantly because there is a reversible interaction between the ammonia gas in air and the previously adsorbed ambient oxygen. However, the response, stability, linearity and sensitivity are still to be improved.

The prior art shows that the sensing performance of the binary oxide semiconductor with a chemically obvious spinel structure is superior to that of a single oxide semiconductor, and the main trend of controlling the doping of the spinel oxide is researched by calculating a large amount of the spinel oxide. However, CuFe in spinel ferrites₂O₄Due to its unique magnetic and dielectric properties, it is difficult to directly apply in devices, in NH₃The prior art in gas sensing has not been studied in detail. The pure copper-based sensor has the defects of poor selectivity, low sensitivity, high power consumption and the like, and the limitation of the pure copper-based sensor on NH is realized₃Application in gas detection.

Improvement of CuFe₂O₄An effective method for the performance of gas sensing materials is primarily to modify them with suitable materials. The conductive polymer Polyaniline (PANI) is a low-cost sensing material and has sensitive chemical property for gas detection. It has excellent properties of fast response, high sensitivity, etc., but there is still much room for improvement in the response of the sensor to ammonia.

Disclosure of Invention

In order to overcome the problems in the prior art, the preparation method and the application of the ammonia sensor based on the in-situ polymerization binary nano composite material are provided, and the ammonia sensor has good responsiveness and selectivity, high response speed and short recovery time, and is obviously superior to a single material film.

The invention provides a method based on in-situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃The preparation method of the gas sensor comprises the following steps:

1) with Cu (NO)₃)₂·3H₂O and Fe (NO)₃)₃·9H₂Preparing CuFe by combustion method with O as cation precursor and citric acid as fuel₂O₄A nanomaterial;

2) in-situ polymerization method for preparing PANI-CuFe₂O₄The nanometer composite material is prepared through ① mixing aniline into acid solution and stirring ② mixing ammonium persulfate and CuFe₂O₄Adding the nanometer materials into water, stirring, mixing the two solutions, stirring at ③ (0-5) deg.C for 1-3 hr to change the color of the solution from white to green, and making PANI-CuFe₂O₄The nanocomposite gradually formed;

3) mixing PANI-CuFe₂O₄The solution is cast on an epoxy substrate by using an interdigital electrode (IDE) to form a sensing film, and the sensing film is dried in vacuum at 60 ℃ for 4 hours to obtain PANI-CuFe₂O₄A gas sensor.

Preferably, CuFe is prepared by combustion method in step 1)₂O₄The nano-material step comprises: 1.21gCu (NO)₃)₂·3H₂O and 4.04g Fe (NO)₃)₃·9H₂O as a cation precursor was dissolved in a beaker containing 80ml of distilled water, and then stirred at 60 ℃ for 2 hours; 3.756g of citric acid is used as fuel, the solution is added, and the mixture is stirred for 2 hours at 60 ℃; the solution was then heated to 80 ℃ to evaporate the water; finally, the beaker is heated in a muffle furnace at 400 ℃ for 2 hours to remove the citric acid and obtain the powdery CuFe₂O₄And (3) nano materials.

The invention also provides PANI-CuFe obtained by the preparation method₂O₄The application of the gas sensor in ammonia gas detection.

Preferably, the PANI-CuFe prepared by in-situ polymerization₂O₄Gas sensor for gas transient response detection to NH₃Response performance detection, response recovery curve detection, and NH₃In response to detecting.

Preferably, in PANI-CuFe₂O₄NH of gas sensor₃In gas detection, in-situ polymerization of PANI-CuFe₂O₄The real-time resistance of the sensor is in a monotonous descending trend; respectively exposed to 5ppm, 30ppm, 50ppm NH₃And in the air for 3 times, the cyclic measurement process has no obvious change; and/or

PANI-CuFe₂O₄Gas sensor pair NH₃Higher response than formaldehyde, ethanol, acetone, methanol, benzene and methane gases; NH at concentrations of 5ppm, 20ppm and 50ppm₃The sensor error is stable within 2 months in the environment.

Further, PANI-CuFe₂O₄Nanocomposite on NH₃In the detection, the interaction of the p-n heterojunction and the synergistic effect of the binary nano composite material play a role together.

Preferably, in PANI-CuFe₂O₄NH of the sensor₃In detection, PANI exhibits characteristics of a p-type semiconductor; due to in situ oxidative polymerization, PANI absorbs protons and forms N-H⁺A key; when in contact with NH₃When gas is present, the sensor adsorbs NH₃Molecule, then N-H group and NH on PANI surface₃Reaction to form NH₃Thereby facilitating NH₃Adsorption of gas; the reversible process is summarized as

Preferably, the sensor is exposed to air, NH₄ ⁺Can be decomposed into NH₃The oxygen molecules in the air capture electrons from the conductive band of the nano composite material through chemical adsorption and are adsorbed on the surface of the nano composite material, so that the concentration of holes is reduced, and the resistance in the air is increased; NH (NH)₃Chemisorbed oxygen molecules with NH upon contact with the sensor surface₃Reacting, electrons are separated from the conductive band of the nano composite material, and the loss layer is reduced; the reaction equation of surface oxygen with ammonia is as follows:

O_2(gas)→O_2(ads)(1)

O_2(gas)+e^-→O₂ ^- _(ads)(2)

NH_3(gas)→NH_3(ads)(3)

4NH_3(ads)+3O₂ ^-→2N₂+6H₂O+3e^-(4)

2NH₄ ⁺+3O₂ ^-→2NO+4H₂O+e^-(5)。

where gas is gas and ads is adsorbate.

Preferably, the p-type PANI nanocapsules are attached to the n-type CuFe₂O₄Forming a p-n junction on the nanosphere; then PANI-CuFe₂O₄The heterojunction establishes a depletion region electron field; at NH₃Upon exposure to gas, the electrons of PANI are removed from the depletion layer, CuFe₂O₄The holes of (a) move in the opposite direction, resulting in a decrease in the depletion layer at the equilibrium point and a decrease in resistance; in this process, the p-n junction amplifies the signal by converting the ammonia concentration into a change in impedance.

Compared with the prior art, the invention has the beneficial effects that:

provides a method based on in-situ polymerization PANI-CuFe₂O₄High quality NH of nanocomposites₃A sensor. The Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) photographs are adopted for representation and display, the nano copper oxide has a nano microsphere structure, and the PANI nano capsule is rod-shaped. The PANI-CuFe was examined at room temperature₂O₄Sensor for different NH concentrations₃NH of (2)₃Gas sensing performance. Experimental results show that the sensor is high in response speed and short in recovery time. PANI-CuFe₂O₄The nanocomposites have excellent ammonia sensitivity and are mainly due to p-n heterojunction interactions and the synergistic effect of binary nanocomposites.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. The invention is based on in-situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃The preparation method of the gas sensor comprises the following steps:

FIG. 1 example is based on in situ polymerization of PANI-CuFe₂O₄NH of binary nanocomposites₃The process schematic diagram of the preparation method of the gas sensor;

FIG. 2 example is based on in situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃Scanning electron micrographs of the material obtained by the gas sensor preparation method (a) PANI and (b) CuFe₂O₄，(c)-(d)PANI-CuFe₂O₄。

FIG. 3 example is based on in situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃XRD pattern of the material prepared by the gas sensor preparation method: PANI, CuFe₂O₄And PANI-CuFe₂O₄；

FIG. 4 example is based on in situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃PANI-CuFe obtained by gas sensor preparation method₂O₄(ii) XPS Spectroscopy of (a) measurement Spectroscopy,(b) an Fe2p spectrum, (c) a Cu 2p spectrum, (d) an N1 s spectrum, (e) an O1s spectrum, and (f) a c1s spectrum.

FIG. 5 example is based on in situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃CuFe (a) of material obtained by gas sensor preparation method₂O₄And (b) TEM image of PANI, (c) HRTEM image of PANI and (d) PANI-CuFe₂O₄Electron diffraction pattern of the SAED selected region.

FIG. 6 example is based on in situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃PANI and CuFe obtained by gas sensor preparation method₂O₄And PANI-CuFe₂O₄A raman spectrum of (a).

FIG. 7 example is based on in situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃PANI-CuFe prepared by in-situ polymerization and physical blending of sensor (a) applied to gas sensor preparation method₂O₄Transient response of the sample; (b) PANI, CuFe₂O₄And in situ polymerized PANI-CuFe₂O₄Sensor pair NH₃(ii) a response of (d); (c) PANI, CuFe₂O₄And in situ polymerization of PANI-CuFe₂O₄Sensor pair NH₃Response and recovery curves of; (d) PANI, CuFe₂O₄And in situ polymerization of PANI-CuFe₂O₄Sensor pair NH₃Is used to generate a gas concentration function response graph.

FIG. 8 example is based on in situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃In-situ polymerization PANI-CuFe applied to sensor prepared by gas sensor preparation method₂O₄Sensor for different NH concentrations₃Resistance measurement of (2); (b) in situ polymerization of PANI-CuFe₂O₄The repeatability of the sensor; (c) in situ polymerization of PANI-CuFe₂O₄The selectivity of the sensor; (d) in situ polymerization of PANI-CuFe₂O₄Sensor pair NH₃5ppm, 20ppm and 50 ppm.

FIG. 9 example is based on in situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃PANI-CuFe applied to sensor prepared by gas sensor preparation method₂O₄Response of the mixed film sensor is plotted as a function of relative humidity.

FIG. 10 example is based on in situ polymerization PANI-CuFe₂O₄NH of binary nanocomposites₃The effect of PANI in ammonia sensitivity in a sensor applied by a gas sensor manufacturing method (a); (b) in situ polymerization of PANI-CuFe₂O₄Hybrid sensor pair NH₃A gas mechanistic diagram; (c) PANI and CuFe₂O₄Schematic of the p-n heterojunction in between.

Detailed Description

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

In industrial production, in order to protect the environment and maintain human health, room temperature detection of ammonia gas is very necessary. To achieve this goal, the present invention uses in-situ polymerized PANI-CuFe₂O₄Nanocomposite, incorporating CuFe₂O₄And PANI sensing capability to exploit high performance NH₃A sensor. The composition, chemical state and morphology of the nano composite material are characterized by a Transmission Electron Microscope (TEM), an x-ray photoelectron spectrum (XPS), a Raman spectrum (Raman), a Scanning Electron Microscope (SEM) and an x-ray diffraction (XRD), and the success and rationality of the preparation are verified. The results of a transmission electron microscope and a scanning electron microscope show that the nano copper oxide product has a nano microsphere structure, and the nanocapsule is rod-shaped. At 25 deg.C, PANI-CuFe was studied₂O₄Sensor for different NH concentrations₃NH of (2)₃Gas sensing performance. The experimental result shows that the film has good responsiveness and selectivity, and is obviously superior to pure PANI and CuFe₂O₄And (3) a membrane.₂₄PANI-CuFe₂O₄The nanocomposite has excellent NH₃Sensitivity, which is due to the p-n heterojunction interaction and the synergistic effect of the binary nanocomposite.

Examples

In-situ polymerization-based PANI-CuFe₂O₄NH of binary nanocomposites₃The preparation method of the gas sensor comprises the following steps:

Preparation of CuFe by combustion method in step 1)₂O₄The nano-material step comprises: 1.21gCu (NO)₃)₂·3H₂O and 4.04g Fe (NO)₃)₃·9H₂O as a cation precursor was dissolved in a beaker containing 80ml of distilled water, and then stirred at 60 ℃ for 2 hours; 3.756g of citric acid is used as fuel, the solution is added, and the mixture is stirred for 2 hours at 60 ℃; the solution was then heated to 80 ℃ to evaporate the water; finally, the beaker is heated in a muffle furnace at 400 ℃ for 2 hours to remove the citric acid and obtain the powdery CuFe₂O₄And (3) nano materials.

Powdery CuFe₂O₄And (3) performance characterization of the nano material:

the surface morphology of the composite material is characterized by using a Scanning Electron Microscope (SEM): the SEM pictures are shown in fig. 2. FIG. 2(a) shows PANI nanocapsules in the shape of a rod, and FIG. 2(b) shows CuFe₂O₄The Nanos, FIGS. 2(c) and (d) show PANI-CuFe₂O₄SEM image of nanocomposite material. Visible PANI and CuFe₂O₄The contact is good, and a porous structure is formed.

PANI and CuFe by using Cu K α radiation x-ray diffractometer with wavelength of 1.5418a₂O₄And PANI-CuFe₂O₄The sample was subjected to XRD characterization, and the results are shown in FIG. 3. The diffraction peak scanning range of the nano composite material is 10-80. The XRD pattern of PANI showed that there were three dominant peaks at 2 θ of 14.8, 20.2, and 25.4, consistent with the (011), (020), and (200) planes of PANI. The peak between 10 and 30 is caused by the parallel and vertical periodicity of the PANI chains. These peaks indicate that the crystallinity of the conductive polymer is low due to the repetition of benzene and quinone rings on the PANI chain. CuFe₂O₄The XRD spectrum of the crystal shows that 2 peaks corresponding to the planes (111), (220), (311), (222), (400), (422), (511), (440) and (533) are respectively 18.3, 30.4, 35.7, 37.2, 43.4, 53.7, 57.3, 62.4 and 74.7, and the crystal meets the standard card JCPDS: 77-0010. PANI-CuFe₂O₄The XRD patterns of the nano composite material are mainly original PANI and original CuFe₂O₄Superposition of peaks proves PANI and CuFe₂O₄Is present.

The XPS measurement spectrum of the nanocomposite is shown in FIG. 4(a), and the main constituent elements are Fe, Cu, N, O and C. In the Fe2p XPS spectrum shown in fig. 4(b), 5 different peaks are located at 710.63, 713.71, 718.52, 723.43 and 726.04eV, respectively. The highest peak at 710.63eV is attributable to Fe ³⁺2p of_3/2. 713.71 and 723.43eV Peak sum Fe ²⁺2p of_1/2And 2p_3/2The binding energy of (c). The peak at 726.04eV is Fe³⁺And Fe ²⁺2p of_1/2The last peak appearing at 718.52eV can be considered a satellite of the four peaks described above, illustrating PANI-CuFe₂O₄Fe in nanocomposites³⁺And Fe²⁺Good coexistence of (a). As shown in FIG. 4(c), the peak at 932.27eV in the Cu 2p XPS spectrum correlates with the Cu (I) species. The peak is at 933.36eV, corresponding to 2p_3/2Cu (II) of (1). Its peak value is 953.68eV, its oscillation satellite is 961.60eV, and copper2p_1/2Are connected. The N1 s XPS spectrum in fig. 4(d) has two main peaks at 399.01 and 399.63eV, belonging to ═ NH respectively₂ ⁺-and-N ═ groups. The two lower peaks of 397.97 and 400.49eV are represented by the amine group (-NH3-) and the cation group (-NH), respectively⁺-) indicating successful aniline polymerization. For the O1s XPS spectrum in FIG. 4(e), the lattice oxygen of Fe-O and Cu-O contributed two peaks with binding energies of 531.84 and 529.85 eV. The C1s XPS spectrum in FIG. 4(f) is due to C-C (sp)²Carbon) shows a dominant peak at 284.12eV, followed by sp³The presence of hybridized carbon with two lower peaks appearing at 286.09 and 285.07 eV.

The morphology of the nanocomposite was obtained by TEM characterization and the image is shown in figure 5. FIGS. 5(a-b) show CuFe₂O₄And PANI structures, consistent with corresponding SEM images. Fig. 5(c) depicts HRTEM images of PANI nanocapsules with 0.25nm lattice fringes, which are consistent with the (311) plane. As can be seen from fig. 5(d), the annular structure of the nanocomposite is clear and the crystallinity is high.

The Raman spectrum is utilized to research the PANI-CuFe₂O₄CuFe in nanocomposite₂O₄Interaction with the electronic potential between PANI. As can be seen from FIG. 6, PANI and PANI-CuFe₂O₄The main bands are present in the nanocomposites. The Raman spectrum of pure PANI is shown at 1478.36cm^-1In the form of strips, and PANI-CuFe₂O₄Strips of nanocomposite material at 1491.44cm^-1There is a band indicating that the product is due to CuFe₂O₄The disorder of the surface increases and the band has a small drift.

PANI-CuFe obtained by the preparation method₂O₄The application of the gas sensor in ammonia gas detection.

The PANI-CuFe prepared by in-situ polymerization₂O₄Gas sensors are used for gas transient response detection:

PANI-CuFe prepared by physical blending and in-situ polymerization₂O₄Transient response of the sample as shown in FIG. 7(a), with the gas sensor at NH₃Gas and dry airThe gases were moved at 150 second intervals and polymerized PANI-CuFe in situ as the concentration of ammonia increased in parts per million₂O₄The response of the sensor is higher than that of PANI-CuFe obtained by physical blending₂O₄A sensor. Thus, PANI-CuFe₂O₄The nanocomposite is prepared by an in situ polymerization process.

The PANI-CuFe prepared by in-situ polymerization₂O₄Gas sensor for measuring NH₃Response performance detection of (2):

at room temperature of 25 ℃, polyaniline and CuFe are carefully compared₂O₄And in situ polymerization of polyaniline-CuFe₂O₄NH of the sensor₃Gas sensing performance. In situ polymerized PANI/CuFe as shown in FIG. 7(b)₂O₄Sensor at NH₃At concentrations of 1ppm,5ppm,10ppm,20ppm,30ppm,40ppm and 50ppm, respectively, the sensor response was about 12.55%, 27.37%, 40.55%, 48.94%, 63.56%, 71.60% and 81.93%. In-situ polymerization of PANI-CuFe in three sensors₂O₄The response of the sensor is highest.

FIG. 7(c) shows polyaniline and CuFe₂O₄And in situ polymerization of polyaniline-CuFe₂O₄Three sensors at 5ppm NH₃The following response and recovery curves. In situ polymerization of PANI-CuFe₂O₄The response time and recovery time of the sensors are 84s and 54s, respectively, which are shorter than the other sensors.

Response curves of three sensors as a function of NH₃The change in concentration is shown in FIG. 7 (d). PANI, CuFe₂O₄And in situ polymerization of PANI-CuFe₂O₄The fitting function of the sensor is Y ═ 6.60X^0.53,Y＝6.81X^0.32And Y ═ 12.71X^0.47. Coefficient of correlation R²0.9870, 0.9802, and 0.9924, respectively.

Table 1 shows CuFe₂O₄PANI, PANI-CuFe₂O₄Sensor performance in terms of recovery time, response time and response value of the sensor, at 5ppm and 30ppm NH, respectively₃And (6) measuring. PANI-CuFe₂O₄The sensor is one in which the performance is optimalIn (1).

TABLE 1 Ammonia sensor response values, response times, and recovery times

In-situ polymerized PANI-CuFe₂O₄Sensor for different NH concentrations₃The resistance of (a): as can be seen from FIG. 8(a), following NH₃Increasing the concentration, in situ polymerizing PANI-CuFe₂O₄The real-time resistance of the sensor is in a monotonous descending trend.

As can be seen from FIG. 8(b), the in situ polymerized PANI-CuFe₂O₄The sensors were exposed to 5ppm, 30ppm, 50ppm NH, respectively₃And 3 times in the air, the cycle measurement process has no obvious change, and the sensor has good repeatability.

FIG. 8(c) shows in situ polymerization of PANI-CuFe₂O₄Sensor pair 5ppm NH₃Formaldehyde (HCHO), ethanol (CH)₃CH₂OH), acetone (CH)₃COCH₃) Methanol (CH)₃OH), benzene (C)₆H₆) And methane (CH)₄) Selectivity of the gas. In situ polymerization of PANI-CuFe₂O₄Sensor pair NH₃The response of the polymer is far higher than that of other gases, which indicates that the PANI-CuFe is polymerized in situ₂O₄Sensor pair NH₃Has good selectivity in detection.

FIG. 8(d) shows in situ polymerization of PANI-CuFe₂O₄Sensor NH concentrations of 5ppm, 20ppm and 50ppm₃Long term stability in the environment. The error of two months is small, which indicates that the PANI-CuFe is polymerized in situ₂O₄The sensor has good stability.

When NH is present₃At 10ppm, PANI-CuFe₂O₄The response of the sensor to relative humidity is shown in fig. 9 and can be written as-0.03 +0.101 RH. This shows that the sensor is not sensitive to humidity, but can compensate errors caused by different relative humidity for high-precision ammonia nitrogen measurement.

Table 2 shows PANI-CuFe₂O₄NH of gas sensor in comparison with prior art₃The performance of the sensors was compared. The response time, response value, response time and operating temperature are shown in Table 2, which illustrates PANI-CuFe₂O₄The sensor has short response time, long response time and high response degree. The result shows that the PANI-CuFe₂O₄The sensor has excellent sensing performance and can be used as ppm-level room temperature NH₃An ideal sensor for detection.

TABLE 2 comparison of the performance of the sensor of this example with that of the ammonia sensor of the prior art

FIG. 10(a) shows PANI in PANI-CuFe₂O₄NH of the sensor₃In detection, PANI exhibits characteristics of a p-type semiconductor; due to in situ oxidative polymerization, PANI absorbs protons and forms N-H⁺A key; when in contact with NH₃When gas is present, the sensor adsorbs NH₃Molecule, then N-H group and NH on PANI surface₃Reaction to form NH₃Thereby facilitating NH₃Adsorption of gas; the reversible process is summarized as

The sensor being exposed to air, NH₄ ⁺Can be decomposed into NH₃The oxygen molecules in the air capture electrons from the conductive band of the nano composite material through chemical adsorption and are adsorbed on the surface of the nano composite material, so that the concentration of holes is reduced, and the resistance in the air is increased; NH (NH)₃Chemisorbed oxygen molecules with NH upon contact with the sensor surface₃Reacting, electrons are separated from the conductive band of the nano composite material, and the loss layer is reduced; watch (A)The reaction equation of surface oxygen with ammonia is as follows:

O_2(gas)→O_2(ads)(1)

O_2(gas)+e^-→O₂ ^- _(ads)(2)

NH_3(gas)→NH_3(ads)(3)

4NH_3(ads)+3O₂ ^-→2N₂+6H₂O+3e^-(4)

2NH₄ ⁺+3O₂ ^-→2NO+4H₂O+e^-(5)。

where gas is gas and ads is adsorbate.

FIG. 10(c) shows that p-type PANI nanocapsules (4.49eV) adhere well to n-type CuFe₂O₄On the nanosphere, a p-n junction is formed. Then PANI-CuFe₂O₄The heterojunction establishes a depletion region electron field. At NH₃Upon exposure to gas, the electrons of PANI are removed from the depletion layer, CuFe₂O₄The hole(s) in the opposite direction causes a depletion layer at the equilibrium point to decrease and the resistance to decrease. In this process, the p-n junction can amplify the signal by converting the ammonia concentration into a change in impedance.

Therefore, the PANI-CuFe₂O₄The nano composite material sensor can easily detect low-concentration NH₃。

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. In-situ polymerization-based PANI-CuFe₂O₄PANI-CuFe of binary nano composite material₂O₄The application of the gas sensor in ammonia gas detection is characterized in that: the preparation method of the gas sensor comprises the following steps:

1) at 1.21g of Cu (NO)₃)₂·3H₂O and 4.04g Fe (NO)₃)₃·9H₂Preparing CuFe by combustion method with O as cation precursor and citric acid as fuel₂O₄A nanomaterial;

3) mixing PANI-CuFe₂O₄The solution is cast on an epoxy substrate by using an interdigital electrode (IDE) to form a sensing film, and the sensing film is dried in vacuum at 60 ℃ for 4 hours to obtain PANI-CuFe₂O₄A gas sensor;

PANI-CuFe₂O₄nanocomposite on NH₃In detection, the interaction of the p-n heterojunction and the synergistic effect of the binary nano composite material play a role together;

p-type PANI nanocapsule attached to n-type CuFe₂O₄Forming a p-n junction on the nanosphere; then PANI-CuFe₂O₄The heterojunction establishes a depletion region electron field; at NH₃Upon exposure to gas, the electrons of PANI are removed from the depletion layer, CuFe₂O₄The holes of (a) move in the opposite direction, resulting in a decrease in the depletion layer at the equilibrium point and a decrease in resistance; in this process, the p-n junction amplifies the signal by converting the ammonia concentration into a change in impedance.

2. Use according to claim 1, characterized in that: preparation of CuFe by combustion method in step 1)₂O₄The nano-material step comprises: 1.21gCu (NO)₃)₂·3H₂O and 4.04gFe (NO)₃)₃·9H₂O as a cation precursor was dissolved in a beaker containing 80ml of distilled water, and then stirred at 60 ℃ for 2 hours; 3.756g of citric acid is used as fuel, the solution is added, and the mixture is stirred for 2 hours at 60 ℃; the solution was then heated to 80 ℃ to evaporate the water; finally, the beaker is heated in a muffle furnace at 400 ℃ for 2 hours to remove the citric acid and obtain the powdery CuFe₂O₄And (3) nano materials.

3. Use according to claim 1, characterized in that: the PANI-CuFe prepared by in-situ polymerization₂O₄Gas sensor for gas transient response detection to NH₃Response performance detection, response recovery curve detection, and NH₃In response to detecting.

4. Use according to claim 1, characterized in that: in PANI-CuFe₂O₄NH of gas sensor₃In gas detection, in-situ polymerization of PANI-CuFe₂O₄The real-time resistance of the sensor is in a monotonous descending trend; respectively exposed to 5ppm, 30ppm, 50ppm NH₃And in the air for 3 times, the cyclic measurement process has no obvious change; and/or

5. Use according to claim 1, characterized in that: in PANI-CuFe₂O₄NH of the sensor₃In detection, PANI exhibits characteristics of a p-type semiconductor; due to in situ oxidative polymerization, PANI absorbs protons and forms N-H⁺A key; when in contact with NH₃When gas is present, the sensor adsorbs NH₃Molecule, then N-H group and NH on PANI surface₃Reaction to form NH₃Thereby facilitating NH₃Adsorption of gas; the reversible process is summarized as:

6. use according to claim 5, characterized in that: the sensor being exposed to air, NH₄ ⁺Can be decomposed into NH₃The oxygen molecules in the air capture electrons from the conductive band of the nano composite material through chemical adsorption and are adsorbed on the surface of the nano composite material, so that the concentration of holes is reduced, and the resistance in the air is increased; NH (NH)₃Chemisorbed oxygen molecules with NH upon contact with the sensor surface₃Reacting, electrons are separated from the conductive band of the nano composite material, and the loss layer is reduced; the reaction equation of surface oxygen with ammonia is as follows:

O_2(gas)→O_2(ads)(1)

O_2(gas)+e^-→O₂ ^- _(ads)(2)

NH_3(gas)→NH_3(ads)(3)

4NH_3(ads)+3O₂ ^-→2N₂+6H₂O+3e^-(4)

2NH₄ ⁺+3O₂ ^-→2NO+4H₂O+e^-(5)；

where gas is gas and ads is adsorbate.