A preparation method of a Pd / ZnO / g-carbon nitride composite nanomaterial for hydrogen detection

Abstract

The application discloses a preparation method of Pd / ZnO / g-C3N4 composite nanomaterial for hydrogen detection. First, g-C3N4 is formed by heat treatment with urea as raw material, a metal-organic framework material with a MOF structure is formed on the surface of g-C3N4, PdCl2 is used as a noble metal source, PdCl2 molecules are anchored on the surface of the material through impregnation-freeze drying technology, then Pd clusters are formed by in-situ reduction, and finally, the organic part in the metal-organic framework material is removed by heat treatment, a large number of pore structures with specific sizes are formed in the material, the pore structures are beneficial to the preferential adsorption of hydrogen, then the catalytic reaction of Pd clusters to H2 is utilized, and the response sensitivity of the composite material to hydrogen is improved. The method provided by the application is simple in manufacturing and low in cost, and is expected to greatly improve the application of nanomaterials in the field of hydrogen detection.

Description

Technical Field

[0001] This invention relates to the field of gas detection, specifically a method for preparing Pd / ZnO / g-carbon nitride composite nanomaterials for hydrogen detection, which is a method for preparing semiconductor gas sensors. Background Technology

[0002] Metal oxide semiconductor materials have become gas-sensitive materials for detecting various toxic, harmful, flammable, and explosive gases due to their excellent stability and ease of synthesis and surface property control. However, pure semiconductor materials are not satisfactory in terms of selectivity and detection of low-concentration gases. By constructing pore structures of specific sizes during the preparation of nanomaterials, the preferential adsorption of specific gases can be promoted, thereby improving the selectivity of gas-sensitive materials. On the other hand, modifying nanomaterials with noble metals can increase the catalytic reaction of gases, which can further improve their gas response sensitivity. Finally, the constructed nanomaterials have a large number of oxygen vacancies, which is conducive to the adsorption of oxygen in the air to form reactive oxygen species. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing Pd / ZnO / g-carbon nitride composite nanomaterials for hydrogen detection.

[0004] Another objective of this invention is to provide a MEMS gas sensor based on Pd / ZnO / g-carbon nitride composite nanomaterials to achieve highly sensitive detection of hydrogen and improve the selectivity of semiconductor gas-sensitive materials.

[0005] The objective of this invention is achieved through the following method: a method for preparing Pd / ZnO / g-carbon nitride composite nanomaterials for hydrogen detection, wherein the Pd / ZnO / g-carbon nitride is Pd / ZnO / g-C3N4, comprising the following steps:

[0006] Step 1: Take a certain amount of urea, place it in a covered crucible, and heat treat it in a muffle furnace to obtain g-C3N4;

[0007] The heat treatment conditions are as follows: hold at 250 ℃ for 2 hours with a heating rate of 1-2 ℃ / min, then hold at 600-650 ℃ for 1-2 hours with a heating rate of 2-5 ℃ / min.

[0008] Step 2: Take 0.1 g of g-C3N4 powder, grind it and place it in a beaker, add 30 mL of deionized water, sonicate for 1-2 h, add 0.35-0.5 g of zinc nitrate, stir for half an hour, freeze dry at -80 ℃, grind the dried sample to obtain sample A;

[0009] Step 3: Dissolve 0.5 g of 2-methylimidazole in 30 mL of methanol. Take another 0.45 g of sample A and add it to the methanol solution of 2-methylimidazole. Stir for 30 min, then place it in a 50 mL beaker. Cover the mouth of the beaker with plastic wrap and seal it with a rubber band. Place it in a forced-air drying oven for hydrothermal reaction. After cooling to room temperature, centrifuge the sample, dry it at 80 ℃, and grind it. Take 0.5 g of the obtained sample, place it in deionized water and stir. Then add 0.005~0.01 g of palladium chloride, stir evenly, freeze dry at -80 ℃, grind it, and place the sample in a 0.05 M ascorbic acid aqueous solution. After 5 min, centrifuge the sample, dry it at 80 ℃, and heat treat it in a muffle furnace. After heat treatment and cooling to room temperature, Pd / ZnO / g-C3N4 composite nanomaterials are obtained.

[0010] This invention first uses urea as a raw material to form g-C3N4 through heat treatment. A metal-organic framework (MOF) material with a MOF structure is then formed on its surface. PdCl2 is used as a noble metal source, and PdCl2 molecules are anchored to the material surface through impregnation-freeze-drying technology. Then, Pd clusters are formed through in-situ reduction. Finally, the organic portion of the MOF material is removed through heat treatment, forming a large number of pores of a specific size inside the material. This pore structure facilitates the preferential adsorption of hydrogen. The catalytic reaction of H2 by the Pd clusters is then utilized to enhance the composite material's response sensitivity to hydrogen. The method provided by this invention is simple to prepare and low in cost, and is expected to significantly improve the application of nanomaterials in the field of hydrogen detection.

[0011] Based on the above scheme, in step three, the hydrothermal reaction temperature is 60 ℃ and the reaction time is 8~12 h;

[0012] Furthermore, in step three, the heat treatment temperature is 600~650 ℃, the time is 1~2 h, and the heating rate is 2~5 ℃.

[0013] The prepared Pd / ZnO / g-C3N4 composite nanomaterial was used to fabricate a MEMS device for gas sensing performance testing. The specific steps were as follows: a MEMS device with Pt interdigitated electrodes was taken, ultrasonically cleaned with deionized water and ethanol, dried with a nitrogen gun, and the obtained Pd / ZnO / g-C3N4 composite nanomaterial sample was made into a slurry, uniformly coated on the surface of the MEMS device, dried, and then placed in a muffle furnace for heat treatment at a temperature of 400 ℃, a holding time of 1 h, and a heating rate of 2 ℃ / min. After the chamber cooled to room temperature, it was taken out to obtain a MEMS gas sensor based on Pd / ZnO / g-C3N4 composite nanomaterial.

[0014] The advantage of this invention lies in the fact that the Pd / ZnO / g-C3N4 composite nanomaterial obtained by the method of this invention forms a large number of pore structures of specific sizes inside. These pore structures are conducive to the preferential adsorption of hydrogen, and the catalytic reaction of H2 by Pd clusters enhances the response sensitivity of the composite material to hydrogen. The method provided by this invention is simple to prepare and low in cost. The Pd / ZnO / g-C3N4 composite nanomaterial prepared by this method can achieve highly sensitive detection of hydrogen and can also improve the selectivity of semiconductor gas-sensitive materials. Detailed Implementation

[0015] Example 1:

[0016] A Pd / ZnO / g-carbon nitride composite nanomaterial for hydrogen detection, wherein the Pd / ZnO / g-carbon nitride is Pd / ZnO / g-C3N4, is prepared according to the following steps:

[0017] Step 1: Weigh a certain amount of urea, place it in a covered crucible, and heat treat it in a muffle furnace. The heat treatment conditions are: 250 ℃ for 2 hours, heating rate 2 ℃ / min, then 650 ℃ for 2 hours, heating rate 2 ℃ / min, to obtain g-C3N4.

[0018] Step 2: Take 0.1 g of g-C3N4 powder, grind it and place it in a beaker. Add 30 mL of deionized water, sonicate for 1-2 h, add 0.35 g of zinc nitrate, stir for half an hour, freeze dry at -80 ℃, grind the dried sample to obtain sample A;

[0019] Step 3: Dissolve 0.5 g of 2-methylimidazole in 30 mL of methanol to obtain a methanol solution of 2-methylimidazole; separately, take 0.45 g of sample A and add it to the methanol solution of 2-methylimidazole. After stirring for 30 min, place it in a beaker, cover the mouth of the beaker with plastic wrap and seal it with a rubber band. Place it in a forced-air drying oven and hydrothermally react at 60 ℃ for 8 h. After cooling to room temperature, centrifuge the sample, dry it at 80 ℃, and grind it into powder; take 0.5 g of the obtained powder, place it in deionized water and stir, then add 0.005 g of palladium chloride, stir evenly, freeze dry at -80 ℃, grind it, place the sample in a 0.05 M ascorbic acid aqueous solution, centrifuge the sample after 5 min, dry it at 80 ℃, place it in a muffle furnace and heat at 600 ℃ for 2 h at a heating rate of 2 ℃, then cool it to room temperature to obtain Pd / ZnO / g-C3N4 composite nanomaterials.

[0020] The prepared Pd / ZnO / g-C3N4 composite nanomaterial was used to fabricate a MEMS device for gas sensing performance testing. The specific steps were as follows: a MEMS device with Pt interdigitated electrodes was taken, ultrasonically cleaned with deionized water and ethanol, dried with a nitrogen gun, and the obtained Pd / ZnO / g-C3N4 composite nanomaterial was made into a slurry and uniformly coated on the surface of the MEMS device. After drying, it was placed in a muffle furnace for heat treatment at a temperature of 400 ℃, a holding time of 1 h, and a heating rate of 2 ℃ / min. After the chamber cooled to room temperature, it was removed to obtain a MEMS gas sensor based on Pd / ZnO / g-C3N4 composite nanomaterial.

[0021] The MEMS gas sensor obtained in this embodiment has a sensitivity of 4.5 to hydrogen gas with a concentration of 200 ppb at an operating temperature of 100 ℃.

[0022] Example 2:

[0023] A Pd / ZnO / g-carbon nitride composite nanomaterial for hydrogen detection is prepared according to the following steps:

[0024] Step 1: Take a certain amount of urea, place it in a covered crucible, and heat treat it in a muffle furnace. The heat treatment conditions are: 250 ℃ for 2 hours, heating rate 1 ℃ / min, then 650 ℃ for 1 hour, heating rate 2 ℃ / min, to obtain g-C3N4.

[0025] Step 2: Take 0.1 g of g-C3N4 powder, grind it and place it in a beaker, add 30 mL of deionized water, sonicate for 2 hours, add 0.4 g of zinc nitrate, stir for half an hour, freeze dry at -80 ℃, grind the dried sample to obtain sample A;

[0026] Step 3: Dissolve 0.5 g of 2-methylimidazole in 30 mL of methanol to obtain a methanol solution of 2-methylimidazole; separately, add 0.45 g of sample A to the methanol solution of 2-methylimidazole, stir for 30 min, place in a beaker, cover the mouth of the beaker with plastic wrap and seal with a rubber band, place in a forced-air drying oven at 60 ℃ for hydrothermal reaction for 10 h, after cooling to room temperature, centrifuge the sample, dry at 80 ℃ and grind into powder; take 0.5 g of the obtained powder, place in deionized water and stir, then add 0.008 g of palladium chloride, stir evenly, freeze dry at -80 ℃, grind, place the sample in a 0.05 M ascorbic acid aqueous solution, centrifuge after 5 min, dry at 80 ℃, place in a muffle furnace for heat treatment at 650 ℃ for 2 h with a heating rate of 2 ℃, after cooling to room temperature, obtain Pd / ZnO / g-C3N4 composite nanomaterials.

[0027] The prepared Pd / ZnO / g-C3N4 composite nanomaterial was used to fabricate a MEMS device for gas sensing performance testing. The specific steps were as follows: a MEMS device with Pt interdigitated electrodes was taken, ultrasonically cleaned with deionized water and ethanol, dried with a nitrogen gun, and the obtained Pd / ZnO / g-C3N4 composite nanomaterial was made into a slurry and uniformly coated on the surface of the MEMS device. After drying, it was placed in a muffle furnace for heat treatment at a temperature of 400 ℃, a holding time of 1 h, and a heating rate of 2 ℃ / min. After the chamber cooled to room temperature, it was taken out to obtain a MEMS gas sensor based on Pd / ZnO / g-C3N4 composite nanomaterial.

[0028] The gas sensor of the device obtained in this embodiment has a sensitivity of 5.1 for hydrogen gas with a concentration of 200 ppb at an operating temperature of 100 ℃.

[0029] Example 3:

[0030] A Pd / ZnO / g-carbon nitride composite nanomaterial for hydrogen detection is prepared according to the following steps:

[0031] Step 1: Take urea, place it in a covered crucible, and heat treat it in a muffle furnace. The heat treatment conditions are: 250 ℃ for 2 hours, heating rate 2 ℃ / min, then 600 ℃ for 2 hours, heating rate 5 ℃ / min, to obtain g-C3N4.

[0032] Step 2: Take 0.1 g of g-C3N4 powder, grind it and place it in a beaker. Add 30 mL of deionized water, sonicate for 2 hours, add 0.5 g of zinc nitrate, stir for half an hour, freeze dry at -80 ℃, grind the dried sample to obtain sample A;

[0033] Step 3: Dissolve 0.5 g of 2-methylimidazole in 30 mL of methanol to obtain a methanol solution of 2-methylimidazole; separately, take 0.45 g of sample A and add it to the methanol solution of 2-methylimidazole. After stirring for 30 min, place it in a beaker, cover the mouth of the beaker with plastic wrap and seal it with a rubber band, and place it in a forced-air drying oven for hydrothermal reaction at 60 ℃ for 10 h. After cooling to room temperature, centrifuge the sample, dry it at 80 ℃, and grind it into powder; take 0.5 g of the obtained powder, place it in deionized water and stir, then add 0.01 g of palladium chloride, stir evenly, freeze dry at -80 ℃, grind it, place the sample in a 0.05 M ascorbic acid aqueous solution, centrifuge the sample after 5 min, dry it at 80 ℃, and then heat treat it in a muffle furnace at 650 ℃ for 2 h with a heating rate of 5 ℃. After cooling to room temperature, Pd / ZnO / g-C3N4 composite nanomaterials are obtained.

[0034] The prepared Pd / ZnO / g-C3N4 composite nanomaterial was used to fabricate a MEMS device for gas sensing performance testing. The specific steps were as follows: a MEMS device with Pt interdigitated electrodes was taken, ultrasonically cleaned with deionized water and ethanol, dried with a nitrogen gun, and the obtained Pd / ZnO / g-C3N4 composite nanomaterial was made into a slurry and uniformly coated on the surface of the MEMS device. After drying, it was placed in a muffle furnace for heat treatment at a temperature of 400 ℃, a holding time of 1 h, and a heating rate of 2 ℃ / min. After the chamber cooled to room temperature, it was taken out to obtain a MEMS gas sensor based on Pd / ZnO / g-C3N4 composite nanomaterial.

[0035] The gas sensor of the device obtained in this embodiment has a sensitivity of 4.8 to hydrogen gas with a concentration of 200 ppb at an operating temperature of 100 ℃.

Claims

1. A method for preparing Pd / ZnO / g-carbon nitride composite nanomaterials for hydrogen detection, wherein the Pd / ZnO / g-carbon nitride is Pd / ZnO / g-C3N4, characterized in that, It includes the following steps: Step 1: Take urea, place it in a covered crucible, and heat treat it in a muffle furnace to obtain g-C3N4; Step 2: Take 0.1 g of g-C3N4 powder, grind it and place it in a beaker, add 30 mL of deionized water, sonicate for 1-2 h, add 0.35-0.5 g of zinc nitrate, stir for half an hour, freeze dry at -80 ℃, grind the dried sample to obtain sample A; Step 3: Dissolve 0.5 g of 2-methylimidazole in 30 mL of methanol to obtain a methanol solution of 2-methylimidazole; separately, take 0.45 g of sample A and add it to the methanol solution of 2-methylimidazole. After stirring for 30 min, place it in a beaker, cover and seal the mouth of the beaker with plastic wrap, and place it in a forced-air drying oven for hydrothermal reaction. After cooling to room temperature, centrifuge the sample, dry it at 80 ℃, and grind it into powder; take 0.5 g of the obtained powder, place it in deionized water and stir, then add 0.005~0.01 g of palladium chloride, stir evenly, freeze dry at -80 ℃, grind it, place the sample in a 0.05 M ascorbic acid aqueous solution, centrifuge the sample after 5 min, dry it at 80 ℃, heat treat it in a muffle furnace, and then cool it to room temperature to obtain Pd / ZnO / g-C3N4 composite nanomaterials.

2. The method for preparing Pd / ZnO / g-carbon nitride composite nanomaterials for hydrogen detection according to claim 1, characterized in that: In step one, hold at 250 ℃ for 2 hours with a heating rate of 1-2 ℃ / min, then hold at 600-650 ℃ for 1-2 hours with a heating rate of 2-5 ℃ / min.

3. The method for preparing Pd / ZnO / g-carbon nitride composite nanomaterials for hydrogen detection according to claim 1, characterized in that: In step three, the hydrothermal reaction temperature is 60 ℃ and the reaction time is 8~12 h.

4. The method for preparing Pd / ZnO / g-carbon nitride composite nanomaterials for hydrogen detection according to claim 1, characterized in that: In step three, the heat treatment temperature is 600~650 ℃, the time is 1~2 hours, and the heating rate is 2~5 ℃.

5. A method for preparing a Pd / ZnO / g-carbon nitride composite nanomaterial for hydrogen detection according to any one of claims 1 to 4, characterized in that: Prepare according to the following steps: Step 1: Weigh a certain amount of urea, place it in a covered crucible, and heat treat it in a muffle furnace. The heat treatment conditions are: hold at 250℃ for 2 hours, heating rate 2℃ / min, then hold at 650℃ for 2 hours, heating rate 2℃ / min, to obtain g-C3N4. Step 2: Take 0.1 g of g-C3N4 powder, grind it and place it in a beaker. Add 30 mL of deionized water, sonicate for 1-2 h, add 0.35 g of zinc nitrate, stir for half an hour, freeze dry at -80 ℃, grind the dried sample to obtain sample A; Step 3: Dissolve 0.5 g of 2-methylimidazole in 30 mL of methanol to obtain a methanol solution of 2-methylimidazole; separately, take 0.45 g of sample A and add it to the methanol solution of 2-methylimidazole. After stirring for 30 min, place it in a beaker, cover the mouth of the beaker with plastic wrap and seal it with a rubber band. Place it in a forced-air drying oven and hydrothermally react at 60 ℃ for 8 h. After cooling to room temperature, centrifuge the sample, dry it at 80 ℃, and grind it into powder; take 0.5 g of the obtained powder, place it in deionized water and stir, then add 0.005 g of palladium chloride, stir evenly, freeze dry at -80 ℃, grind it, place the sample in a 0.05 M ascorbic acid aqueous solution, centrifuge the sample after 5 min, dry it at 80 ℃, place it in a muffle furnace and heat at 600 ℃ for 2 h at a heating rate of 2 ℃, then cool it to room temperature to obtain Pd / ZnO / g-C3N4 composite nanomaterials.

6. A method for preparing a Pd / ZnO / g-carbon nitride composite nanomaterial for hydrogen detection according to any one of claims 1 to 4, characterized in that: Prepare according to the following steps: Step 1: Take a certain amount of urea, place it in a covered crucible, and heat treat it in a muffle furnace. The heat treatment conditions are: 250 ℃ for 2 hours, heating rate 1 ℃ / min, then 650 ℃ for 1 hour, heating rate 2 ℃ / min, to obtain g-C3N4. Step 2: Take 0.1 g of g-C3N4 powder, grind it and place it in a beaker. Add 30 mL of deionized water, sonicate for 2 h, add 0.4 g of zinc nitrate, stir for half an hour, freeze dry at -80 ℃, grind the dried sample to obtain sample A; Step 3: Dissolve 0.5 g of 2-methylimidazole in 30 mL of methanol to obtain a methanol solution of 2-methylimidazole; separately, add 0.45 g of sample A to the methanol solution of 2-methylimidazole, stir for 30 min, place in a beaker, cover the mouth of the beaker with plastic wrap and seal with a rubber band, place in a forced-air drying oven at 60 ℃ for hydrothermal reaction for 10 h, after cooling to room temperature, centrifuge the sample, dry at 80 ℃ and grind into powder; take 0.5 g of the obtained powder, place in deionized water and stir, then add 0.008 g of palladium chloride, stir evenly, freeze dry at -80 ℃, grind, place the sample in a 0.05 M ascorbic acid aqueous solution, centrifuge after 5 min, dry at 80 ℃, place in a muffle furnace for heat treatment at 650 ℃ for 2 h with a heating rate of 2 ℃, after cooling to room temperature, obtain Pd / ZnO / g-C3N4 composite nanomaterials.

7. A method for preparing a Pd / ZnO / g-carbon nitride composite nanomaterial for hydrogen detection according to any one of claims 1 to 4, characterized in that: Prepare according to the following steps: Step 1: Take urea, place it in a covered crucible, and heat treat it in a muffle furnace. The heat treatment conditions are: 250 ℃ for 2 hours, heating rate 2 ℃ / min, then 600 ℃ for 2 hours, heating rate 5 ℃ / min, to obtain g-C3N4. Step 2: Take 0.1 g of g-C3N4 powder, grind it and place it in a beaker, add 30 mL of deionized water, sonicate for 2 h, add 0.5 g of zinc nitrate, stir for half an hour, freeze dry at -80 ℃, grind the dried sample to obtain sample A; Step 3: Dissolve 0.5 g of 2-methylimidazole in 30 mL of methanol to obtain a methanol solution of 2-methylimidazole; separately, take 0.45 g of sample A and add it to the methanol solution of 2-methylimidazole. After stirring for 30 min, place it in a beaker, cover the mouth of the beaker with plastic wrap and seal it with a rubber band, and place it in a forced-air drying oven for hydrothermal reaction at 60 ℃ for 10 h. After cooling to room temperature, centrifuge the sample, dry it at 80 ℃, and grind it into powder; take 0.5 g of the obtained powder, place it in deionized water and stir, then add 0.01 g of palladium chloride, stir evenly, freeze dry at -80 ℃, grind it, place the sample in a 0.05 M ascorbic acid aqueous solution, centrifuge the sample after 5 min, dry it at 80 ℃, and then heat treat it in a muffle furnace at 650 ℃ for 2 h with a heating rate of 5 ℃. After cooling to room temperature, Pd / ZnO / g-C3N4 composite nanomaterials are obtained.

8. A MEMS gas sensor based on Pd / ZnO / g-carbon nitride composite nanomaterials, characterized in that, MEMS devices are fabricated using the Pd / ZnO / g-carbon nitride composite nanomaterials prepared by any one of claims 1 to 7, following the steps below: A MEMS device with Pt interdigitated electrodes was ultrasonically cleaned with deionized water and ethanol, and dried with a nitrogen gun. The prepared Pd / ZnO / g-C3N4 composite nanomaterial was then made into a slurry and uniformly coated onto the surface of the MEMS device. After drying, the device was placed in a muffle furnace for heat treatment at a temperature of 400 ℃, a holding time of 1 h, and a heating rate of 2 ℃ / min. After the chamber cooled to room temperature, the device was removed to obtain a MEMS gas sensor based on the Pd / ZnO / g-C3N4 composite nanomaterial.