Ethyl acetate gas sensor based on cobalt tungstate nanoparticle modified ferric oxide composite material and preparation method thereof
Technical Field
The invention belongs to the technical field of gas sensors, and particularly relates to a sensor based on cobalt tungstate (CoWO)4) Nanoparticle modified iron sesquioxide (Fe)2O3) An ethyl acetate gas sensor made of composite material and a preparation method thereof.
Background
With the rapid development of industry and science and technology, the problems of production safety and environment are increasingly highlighted while the material wealth is greatly enriched. There is an increasing chance of exposure to hazardous gases such as natural gas based on methane and carbon monoxide, the volatile organic toxic gases formaldehyde, benzene, xylene released from decorative materials, sulfur dioxide and nitrogen oxides in coal combustion, automobile exhaust, etc. Once generated or leaked, the flammable, explosive, toxic and harmful gases can threaten the health and life of people. Therefore, it is necessary to develop a gas sensor having high responsiveness and high detection speed.
Ethyl acetate is an important fuel and raw material, is a flammable and explosive gas, and is often used in metal cutting and welding and organic material synthesis. When the leaked ethyl acetate reaches a certain concentration, the ethyl acetate is easy to explode when meeting open fire, and the life and property safety of people is threatened. If an alarm is given when the concentration is lower than the explosion limit at the initial stage of leakage of ethyl acetate, serious loss can be effectively avoided. Therefore, the development of the ethyl acetate gas sensor with high responsiveness, low detection lower limit and high response speed is of great significance.
When some metal oxide semiconductor nano materials are contacted with certain gases, the electrical properties and the like of the metal oxide semiconductor nano materials are obviously changed, and the detection peripheral circuit can detect the change of the electrical properties (electrical signals) of the materials, so that the gases are monitored. The gas sensor based on the metal oxide semiconductor gas sensitive material has the advantages of high responsiveness, high response recovery speed, low detection lower limit and the like.
The gas-sensitive performance of the metal oxide semiconductor nano material has a great relationship with the surface activity and the surface state of the material, and the morphology, the size and the surface modification of the material can influence the surface activity and the catalytic activity of the material. Generally, the metal oxide semiconductor gas-sensitive material exposed with the crystal face rich in dangling bonds has higher activity and can generate higher response to gas; the nano-scale noble metal has a remarkable catalytic effect and can catalyze the gas-sensitive reaction, so that the gas-sensitive performance of the matrix material is improved. Therefore, the combination of the crystal face rich in dangling bonds and the modification of the noble metal nanoparticles can obviously improve the gas-sensitive performance of the base material and prepare a high-performance gas sensor.
Fe2O3And CoWO4The materials are relatively mature semiconductor gas-sensitive materials, and have good performance in the aspect of detecting ethyl acetate; reasonably modified CoWO4Fe (b) of2O3The sensitivity and stability of the gas sensor in detecting the ethyl acetate gas can be further improved by the sensitive layer.
Disclosure of Invention
The invention aims to provide a CoWO-based material4Nanoparticle modified Fe2O3An ethyl acetate gas sensor made of composite material and a preparation method thereof. The method is simple and easy to implement, few in working procedures, low in cost and low in equipment requirement, can improve the gas-sensitive response of the gas sensor to ethyl acetate, is suitable for mass production, and has important application value.
The invention relates to a CoWO-based material4Nanoparticle modified Fe2O3The preparation method of the ethyl acetate gas sensor made of the composite material comprises the following steps:
1. and (3) processing the Pd metal interdigital electrode:
respectively wiping Al with Pd metal interdigital electrode by using acetone and ethanol cotton balls2O3Cleaning the substrate, and then putting Al with Pd metal interdigital electrode2O3Sequentially placing the substrate in acetone, ethanol and deionized water, respectively ultrasonically cleaning for 5-10 minutes, and finally drying at 100-120 ℃;
the invention uses the silk-screen printing technology to print Al2O3The method for preparing the Pd metal interdigital electrode on the substrate comprises the following steps: mixing the ink [ Jiahua JX07500487]Pd powder and a diluent are mixed according to the proportion of 1: 1: 2, mixing and stirring to prepare paste; then, injecting the paste on a silk screen plate with an interdigital electrode pattern, scraping the paste under the conditions of an inclination angle of 30-45 degrees and a pressure of 5-10 newtons, and adding Al2O3Printing interdigital electrodes on a substrate, drying, and curing by ultraviolet light to finish the preparation of the Pd metal interdigital electrodes, wherein the width and the electrode spacing of the Pd metal interdigital electrodes are 0.15-0.20 mm, the thickness is 100-150 nm, and the number of pairs of interdigital electrodes is 5-10.
2. Pure Fe2O3Nanomaterial, CoWO4Nanoparticle modified Fe2O3Preparing a composite material:
(1)Fe2O3preparing a nano material precursor: dissolving 0.19-0.21 g of terephthalic acid and 0.66-0.68 g of ferric chloride hexahydrate in 15-20 mL of dimethylformamide (analytically pure) at room temperature, and stirring for 2-3 h; then transferring the obtained solution into a reaction kettle, and reacting for 19-21 h at 100-120 ℃; cooling to room temperature, centrifugally cleaning the resultant with deionized water, and drying at room temperature to obtain Fe2O3A nanomaterial precursor powder;
(2) fe prepared in the step (1)2O3Annealing the nano material precursor powder for 2-4 hours at 350-400 ℃ in air to obtain Fe2O3A nanomaterial;
(3)CoWO4nanoparticle modified Fe2O3Preparing a composite material: 0.70 g-0.75 g of Fe prepared in the step (2)2O3Dispersing the nano material in 45-55 mL of deionized water at room temperature, stirring for 20-30 minutes, and then carrying out ultrasonic treatment for 10-20 minutes to enable Fe2O3Uniformly dispersing the nano material in deionized water, and sequentially adding 0.022-0.087 g of cobalt nitrate hexahydrate, sodium tungstate and ammonium fluoride into the obtained suspension, wherein the molar ratio of the cobalt nitrate hexahydrate to the sodium tungstate to the ammonium fluoride is 1: 1: 6; stirring for 2-3 hours at room temperature, transferring the obtained solution into a reaction kettle, and reacting for 5-7 hours at 170-190 ℃; cooling to room temperature, centrifugally cleaning the product with deionized water, and drying at room temperature to obtain CoWO4Nanoparticle modified Fe2O3A composite material;
3. based on CoWO4Nanoparticle modified Fe2O3Preparing an ethyl acetate gas sensor made of the composite material:
mixing CoWO4Nanoparticle modified Fe2O3Putting the composite material into a mortar, and grinding for 20-30 minutes to obtain nano material powder; then, dripping deionized water into the mortar, and continuously grinding for 20-30 minutes to obtain viscous slurry; dipping a small amount of slurry by using a hairbrush, and coating the slurry on Al with Pd metal interdigital electrodes2O3Drying the substrate at 60-80 ℃ to obtain 2-4 mu m CoWO4Nanoparticle modified Fe2O3A composite sensitive layer; finally, aging for 48-72 hours under the direct current of 80-120 mA in the environment with the relative humidity of 20-40% RH and the temperature of 20-35 ℃, thereby obtaining the product based on CoWO4Nanoparticle modified Fe2O3A gas sensor of composite material.
The invention utilizes a CGS-1TP type gas-sensitive performance tester produced by Beijing Elite technology limited to test the gas-sensitive performance of the ethyl acetate.
Compared with the prior art, the invention has the advantages and positive effects that:
in the present invention, synthesis of a catalyst from CoWO was achieved by self-sacrificial organometallic framework (MOF) template and catalyst functionalization4Nanoparticle modified porous Fe2O3A nano octahedron. CoWO (cobalt oxide)4Nanoparticle modified Fe2O3The composite material is a heterostructure and is made of black tungstenCobalt tungstate of mineral structure (CoWO)4Band gap of 3.8eV) and iron oxide (Fe)2O3Band gap of 2.2 eV). The synthetic route includes the preparation of Fe using a self-sacrificial template method and a thermal annealing method2O3Octahedron, then in Fe by a one-step hydrothermal process2O3Above all, CoWO4And (4) modifying the nano particles. With pure Fe2O3In contrast, CoWO4Nanoparticle modified Fe2O3The sensing ability of the composite material to ethyl acetate is enhanced due to the three advantages: (i) a large number of surface active sites, (ii) the nature of the heterostructure and (iii) the modification of the nanocatalyst.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1a shows Fe2O3SEM topography of Material (S1), FIG. 1b is CoWO4Nanoparticle modified Fe2O3SEM topography of the composite (S2); from FIG. 1a, Fe2O3The material has a regular octahedral structure, and the particle size is 400-700 nm; from FIG. 1b, it can be seen that CoWO4The nano particles are uniformly and dispersedly modified in Fe2O3Surface of material, CoWO4The size of the nanoparticles is about 30 nm.
FIG. 2a shows Fe2O3TEM topography of the Material (S1), FIG. 2b is CoWO4Nanoparticle modified Fe2O3A TEM topography of the composite material (S2); as can be seen by comparing FIG. 2a and FIG. 2b, CoWO4The nano particles are successfully modified in Fe2O3A surface.
FIG. 3 shows CoWO-based products prepared according to the invention4Nanoparticle modified Fe2O3The structure schematic diagram of the ethyl acetate gas sensor made of the composite material; from bottom to top in the order of Al2O3Substrate 1, Pd metal interdigital electrode 3, Pd metal interdigital electrode and Al coated on2O3CoWO on a substrate4Nanoparticle modified Fe2O3And the composite material sensitive layer 2.
FIG. 4 shows CoWO-based products prepared according to the invention4Nanoparticle modified Fe2O3The responsivity-ethyl acetate concentration characteristic curve of the ethyl acetate gas sensor S2 made of the composite material at the working temperature of 206 ℃; the responsivity (Ra/Rg) of a gas sensor is defined as the ratio of the resistance of the sensor in air, Ra, and the resistance in ethyl acetate, Rg. As shown in FIG. 4, when the gas sensor S2 is operated at 206 ℃, the responsivity of the gas sensor increases with the increase of the ethyl acetate concentration, and the curve shows a good linear relation in the range of the ethyl acetate concentration of 1-1000 ppm.
FIG. 5 is CoWO prepared by the invention4Nanoparticle modified Fe2O3Response curves of the composite material gas sensor (S1, S2, S3 and S4) corresponding to different working temperatures under the condition that the concentration of ethyl acetate gas is 100 ppm; as shown in fig. 5, when the gas sensor S2 was operated at 206 ℃ and the ethyl acetate concentration was 100ppm, the maximum value of the responsivity was reached, and the responsivity of the gas sensor was about 21.07. It is known that the optimum operating temperature of the gas sensor S2 is 206 ℃.
FIG. 6 shows CoWO-based products prepared according to the present invention4Nanoparticle modified Fe2O3The selection characteristic diagram of the composite material ethyl acetate gas sensor under the conditions that the working temperature is 206 ℃ and the ethyl acetate gas concentration is 100ppm is shown. As shown in fig. 6, when the gas sensor is operated at 206 ℃ and the gas concentration is 100ppm, the gas sensors (S1, S2, S3, S4) all have a higher response to ethyl acetate than other detection gases. The gas sensor showed good selectivity.
FIG. 7 shows CoWO-based products prepared according to the present invention4Nanoparticle modified Fe2O3Composite ethyl acetate gas sensorResponse-recovery time curve at working temperature of 206 ℃ and ethyl acetate gas concentration of 100 ppm; as shown in fig. 7, when the gas sensor was operated at 206 ℃ and the ethyl acetate concentration was 100ppm, the responsivity of the device S1 was 4.41, and the response time and recovery time were 9S and 11S; the responsivity of the device S2 was 21.05, and the response time and recovery time were 7S and 9S; the responsivity of the device S3 was 11.49, and the response time and recovery time were 7S and 9S; the responsivity of device S4 was 7.1, and the response time and recovery time were 8S and 9S.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived from the embodiments of the present invention by a person skilled in the art without any creative effort, should be included in the protection scope of the present invention.
Examples 1 to 2:
1. and (3) processing the Pd metal interdigital electrode:
respectively wiping Al with Pd metal interdigital electrode by using acetone and ethanol cotton balls2O3Cleaning the substrate, and then putting Al with Pd metal interdigital electrode2O3Sequentially placing the substrate in acetone, ethanol and deionized water, respectively ultrasonically cleaning for 5 minutes, and finally drying at 100 ℃;
the invention uses the silk-screen printing technology to print Al2O3The method for preparing the Pd metal interdigital electrode on the substrate comprises the following steps: mixing the ink [ Jiahua JX07500487]Pd powder and a diluent are mixed according to the proportion of 1: 1: 2, mixing and stirring to prepare paste; then, the paste was poured onto a screen plate having an interdigital electrode pattern, scraped at an inclination angle of 30 ℃ and under a pressure of 5N, and applied to Al2O3Printing interdigital electrodes on a substrate, drying, and finishing the preparation of the Pd metal interdigital electrodes after ultraviolet curing, wherein the width and the electrode spacing of the Pd metal interdigital electrodes are both 0.15mm, and the thickness is 150nmThe number of pairs of interdigitated electrodes is 5 pairs.
2. Pure Fe2O3Nanomaterial, CoWO4Nanoparticle modified Fe2O3Preparing a composite material:
(1)Fe2O3preparing a nano material precursor: dissolving 0.20g of terephthalic acid and 0.67g of ferric chloride hexahydrate in 15mL of dimethylformamide (analytically pure) at room temperature, and stirring for 2 hours; then transferring the obtained solution into a reaction kettle, and reacting for 20 hours at 110 ℃; cooling to room temperature, centrifugally cleaning the resultant with deionized water, and drying at room temperature to obtain Fe2O3A nanomaterial precursor powder;
(2)Fe2O3preparing a nano material: fe prepared in the step (1)2O3Annealing the nano material precursor powder at 400 ℃ for 2 hours to obtain Fe2O3A nanomaterial;
(3)CoWO4modification of nano particles: 0.75g of ferric oxide (Fe) prepared in the step (2) is added under the condition of room temperature2O3) Dispersing the nano material in 50mL deionized water, stirring for 30 minutes, and then carrying out ultrasonic treatment for 20 minutes to enable Fe2O3Uniformly dispersing the nano material in deionized water, respectively and sequentially adding 0.022g of cobalt nitrate hexahydrate, 0.025g of sodium tungstate and 0.017g of ammonium fluoride into the obtained suspension, and stirring at room temperature for 3 hours; then transferring the obtained solution into a reaction kettle, reacting for 6 hours at 180 ℃, cooling to room temperature, centrifugally cleaning the product with deionized water, and drying at room temperature to obtain CoWO4Nanoparticle modified Fe2O3A composite material;
3. preparing a gas sensor:
(1) based on Fe2O3Preparing a gas sensor made of nano materials: mixing Fe2O3Putting the nano material into a mortar, and grinding for 30 minutes to obtain nano material powder; then, dropping deionized water into the mortar, and continuing to grind for 30 minutes to obtain viscous slurry; dipping a small amount of slurry by using a hairbrush, and coating the slurry on Al with Pd metal interdigital electrodes2O3Drying the substrate at 80 deg.C to obtain Fe with thickness of 2 μm on the surface of the Pd metal interdigital electrode2O3A nanomaterial sensitive layer; finally aging the mixture for 48 hours under the direct current of 100mA in an environment with the relative humidity of 30 percent RH and the temperature of 25 ℃, thereby obtaining the Fe-based alloy2O3Nanomaterial gas sensor, labeled S1 (example 1).
(2) Based on CoWO4Nanoparticle modified Fe2O3Preparing an ethyl acetate gas sensor made of the composite material: mixing CoWO4Nanoparticle modified Fe2O3Putting the composite material into a mortar, and grinding for 30 minutes to obtain powder of the nano material; then, dropping deionized water into the mortar, and continuing to grind for 30 minutes to obtain viscous slurry; dipping a small amount of slurry by using a hairbrush, and coating the slurry on Al with Pd metal interdigital electrodes2O3Drying the substrate at 80 deg.C, and coating on Al with Pd metal interdigital electrode2O3CoWO with a thickness of 2 μm is obtained on a substrate4Nanoparticle modified Fe2O3A composite sensitive layer; finally, aging the mixture for 48 hours under the direct current of 100mA in an environment with the relative humidity of 30 percent RH and the temperature of 25 ℃, thereby obtaining the CoWO-based material4Nanoparticle modified Fe2O3Composite ethyl acetate gas sensor, labeled S2 (example 2).
After the gas sensor was prepared, the gas sensor was subjected to a test for the gas-sensitive performance of ethyl acetate (CGS-1 TP type gas-sensitive performance tester by ericsson technologies ltd, beijing).
Example 3
The Pd metal interdigital electrode is processed in the same way as in example 2.
Preparation of Fe by solvothermal method2O3The composite material was prepared in the same manner as in example 2.
CoWO4And (3) a nanoparticle modification process: dispersing 0.75g ferric oxide in 50mL deionized water at room temperature, stirring for 30 minutes, and performing ultrasonic treatment for 20 minutes to enable Fe2O3Uniformly dispersing the nano materialIn deionized water, respectively and sequentially adding 0.044g of cobalt nitrate hexahydrate, 0.050g of sodium tungstate and 0.033g of ammonium fluoride into the obtained suspension, and stirring for 3 hours at room temperature; then transferring the obtained solution into a reaction kettle, reacting for 6 hours at 180 ℃, cooling to room temperature, centrifugally cleaning the product with deionized water, and drying at room temperature to obtain CoWO4Nanoparticle modified Fe2O3A composite material;
CoWO4nanoparticle modified Fe2O3Preparing a composite material gas sensor: the experimental procedure was as in example 2, and a device prepared based on this material was labeled as S3.
Example 4
The preparation process of the Pd metal interdigital electrode is the same as that of the example 2.
Preparation of Fe by solvothermal method2O3The composite material comprises the following components: the procedure was as in example 2.
CoWO4And (3) a nanoparticle modification process: dispersing 0.75g ferric oxide in 50mL deionized water at room temperature, stirring for 30 minutes, and performing ultrasonic treatment for 20 minutes to enable Fe2O3Uniformly dispersing the nano material in deionized water, then respectively and sequentially adding 0.087g of cobalt nitrate hexahydrate, 0.099g of sodium tungstate and 0.055g of ammonium fluoride into the suspension, and stirring for 3 hours at room temperature; then transferring the obtained solution into a reaction kettle, reacting for 6 hours at 180 ℃, cooling to room temperature, centrifugally cleaning the product with deionized water, and drying at room temperature to obtain CoWO4Nanoparticle modified Fe2O3A composite material;
CoWO4nanoparticle modified Fe2O3Preparing a composite material gas sensor: the experimental procedure was as in example 2, and a device prepared based on this material was labeled as S4.
CoWO prepared in the above examples4Nanoparticle modified Fe2O3The gas-sensitive performance of the gas sensor taking the composite material as the sensitive layer and Pd as the metal Pd interdigital electrode is tested by a CGS-1TP type gas-sensitive performance tester of Elite technologies, Inc. of Beijing.
After the gas sensor is prepared, the ethyl acetate gas-sensitive performance of the gas sensor is tested.
At 206 deg.C, device S1 had a response of 4.41 to 100ppm ethyl acetate and response and recovery times of 9S and 11S. The responsivity of device S2 to 100ppm ethyl acetate was 21.05, and the response time and recovery time were 7S and 9S. The responsivity of device S3 to 100ppm ethyl acetate was 11.49, with response and recovery times of 7S and 9S. The responsivity of device S4 to 100ppm ethyl acetate was 7.1, and the response time and recovery time were 8S and 9S.
The above description is only an embodiment of the present invention, and the scope of the present invention should not be limited thereto, but all equivalent changes and modifications made within the scope of the present invention should still fall within the scope covered by the present invention.