Indium oxide composite material based on palladium doping and preparation method and application thereof

Abstract

The invention belongs to the field of gas sensors, and discloses an indium oxide composite material based on palladium doping and a preparation method and application thereof.The preparation method comprises the steps that indium nitrate, absolute ethyl alcohol, ammonia water and deionized water are used for preparing an indium oxide material, then palladium ions are doped in an indium oxide solution to obtain a palladium ion-doped indium oxide solution, and the palladium ion-doped indium oxide solution is subjected to vacuum drying to obtain the palladium ion-doped indium oxide composite material. And reducing and centrifuging by using sodium borohydride to obtain a palladium-doped indium oxide composite material, and then preparing the palladium-doped indium oxide composite material into the gas sensor. The key technological process design of the preparation method is improved, so that the problems that the reaction of a pure indium oxide gas sensor needs relatively high activation energy and the surface of a pure semiconductor lacks selectivity to sulfide can be effectively solved, and the detection of dimethyl disulfide gas is realized.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of composite materials, and more specifically, relates to a palladium-doped indium oxide composite material and a preparation method and application thereof. Background Art

[0002] Dimethyl disulfide (DMDS) is a volatile organic sulfur compound widely used in industrial applications such as petrochemicals, wastewater treatment, and pesticide production. Its high toxicity and low olfactory threshold (<1 ppm) pose a serious threat to the environment and human health. However, traditional DMDS detection methods (such as gas chromatography-mass spectrometry and infrared spectroscopy) are subject to costly equipment, complex operation, and difficulty in real-time monitoring. Especially in complex gas environments, spectroscopic methods are susceptible to cross-interference from other sulfur compounds (such as H2S and methyl mercaptan), resulting in insufficient sensitivity and specificity. Therefore, the development of low-cost, highly sensitive, and highly specific gas sensors is urgently needed.

[0003] Metal oxide semiconductor (MOS) gas sensors, represented by pure indium oxide (In2O3) and tin oxide (SnO2), have the advantages of low cost and fast response, but they have significant bottlenecks in DMDS detection: 1. Insufficient sensitivity: DMDS molecules are large (containing two sulfide groups), and their adsorption efficiency on the pure In2O3 surface is low. In addition, the reaction requires a high activation energy (>200°C), resulting in a weak conductivity response.

[0004] 2. Poor specificity: Pure semiconductor surfaces lack selectivity for sulfides and are easily interfered by coexisting VOCs (such as ethanol, acetone) or reducing gases (such as CO, H2), making it impossible to distinguish DMDS. Therefore, in view of the above situation, how to improve the DMDS adsorption efficiency, reduce the reaction activation energy, and improve the selectivity are the decisive factors for achieving high-specificity detection of semiconductor gas sensors. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvements in the prior art, the present invention aims to provide a palladium-doped indium oxide composite material, its preparation method, and its application. The palladium-doped indium oxide composite material is obtained by doping an In2O3 semiconductor with the precious metal palladium (Pd), reducing it with sodium borohydride, and centrifuging it. This preparation method overcomes the high activation energy required for pure indium oxide (In2O3) and the lack of selectivity for sulfides on the surface of the pure semiconductor. This preparation method not only utilizes palladium as a highly efficient catalyst, significantly reducing the activation energy required for DMDS molecular decomposition, but also leverages palladium's strong adsorption capacity to improve adsorption efficiency, avoid the influence of other VOCs, and achieve ultra-specific detection of dimethyl disulfide.

[0006] To achieve the above objectives, one object of the present invention is to provide a method for preparing a palladium-doped indium oxide composite material, the preparation steps being as follows: (1) Ammonia water and anhydrous ethanol are mixed evenly, and slowly added to an anhydrous ethanol solution containing indium nitrate, placed in a sealed container, evacuated, and heated in a water bath, followed by solid-liquid separation and washing with an ethanol-water solution, centrifuged again, and repeated 3 to 10 times. After drying, pure, dry, blocky indium hydroxide is obtained; (2) Dispersing the bulk indium hydroxide material into deionized water, adding a palladium source and stirring for 2 to 24 hours for loading modification, then adding a mixture of 0.1 mol / L NaBH4 and anhydrous ethanol and stirring for 0.5 to 4 hours, performing solid-liquid separation, washing and drying to obtain palladium particle-doped indium oxide; (3) The obtained palladium-doped indium oxide is subjected to air annealing treatment in an air environment to obtain a pure and dry palladium-doped indium oxide composite material.

[0007] As a further preferred embodiment of the present invention, in step (1), the mass ratio of the ammonia water to the anhydrous ethanol is 1:2-5, and the mass ratio of the ammonia water to the indium nitrate is 50-100:1.

[0008] As a further preferred embodiment of the present invention, in step (1), the water bath heating temperature is 60-90° C., and the heating and stirring time is 0.5-4 h.

[0009] As a further preferred embodiment of the present invention, in step (2), a palladium source is added and stirred for 2 to 24 hours for loading modification.

[0010] As a further preferred embodiment of the present invention, in step (2), the suspension is centrifuged at 5500-8500 r / min for 5-10 min.

[0011] As a further preference of the present invention, in step (3), the palladium source is one of palladium nitrate, tetraamminepalladium chloride, and tetraamminepalladium nitrate, and the mass ratio of palladium ions to indium hydroxide is 0.001 to 0.02:1.

[0012] When the palladium source material is palladium nitrate, the mass ratio of palladium nitrate to indium hydroxide is 1.66×10 -3 ~3.32×10 -2 : 1; When the palladium source is tetraammine palladium nitrate, the mass ratio of tetraammine palladium nitrate to indium hydroxide is 2.8×10 -3 ~5.6×10 -2 : 1; When the palladium source is tetraamminepalladium chloride, the mass ratio of tetraamminepalladium chloride to indium hydroxide is 2.3×10 -3 ~4.6×10 -2 :1.

[0013] As a further preferred embodiment of the present invention, in step (3), the mass ratio of NaBH4 to anhydrous ethanol is 1:3-10.

[0014] As a further preferred embodiment of the present invention, in step (4), the annealing temperature is 350-600°C, the heating rate is 2-10°C / min, and the annealing time is 0.5-5h.

[0015] Another object of the present invention is to provide a palladium-doped indium oxide composite material, which is prepared using the above-mentioned palladium-doped indium oxide composite material.

[0016] Another object of the present invention is to provide a gas sensor prepared from the palladium-doped indium oxide composite material for detecting dimethyl disulfide gas.

[0017] The process for preparing a gas sensor using a palladium-doped indium oxide composite material is as follows: grind the palladium-doped indium oxide in a mortar, dissolve it in deionized water, control the heating plate temperature at 30-40°C, attach the palladium-doped indium oxide composite material to a sensor substrate using a pipette, and then bond the substrate to the sensor electrodes using a device to produce a palladium-doped indium oxide gas sensor. By reacting with various VOCs, the gas sensor changes its resistance, and measuring the voltage to compare the differences in the gas response values of the VOCs, it was found that the gas response value of dimethyl disulfide is higher than that of other VOCs, thus achieving specific detection.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The palladium-doped indium oxide composite material provided by the present invention addresses the defects of pure indium oxide: the DMDS molecular structure is stable (containing two sulfide bonds), and high temperature (>200°C) is required to dissociate into active intermediates (such as -CH3S·free radicals), resulting in a weak response signal (ΔR / R0 <15%) and poor selectivity for sulfides such as H2S and methyl mercaptan. It can be improved by palladium doping. The palladium nanoparticles generated by NaBH4 reduction serve as efficient catalysts, significantly reducing the activation energy of DMDS decomposition (from 1.2 eV to 0.7 eV) and reducing the reaction temperature to below 150°C. The DMDS molecules adsorbed on the surface of the palladium nanoparticles quickly dissociate into active sulfur free radicals, which then migrate to the In2O3 surface to react with adsorbed oxygen, and the response value is increased by 6-10 times (ΔR / R0 reaches 80-120%). 0 (soft acid) forms a strong coordination bond (binding energy difference > 0.5 eV) with the disulfide structure of DMDS (S–C–S bond, soft base), and the active sites on the surface of palladium nanoparticles are adapted to the molecular size of DMDS (chain length ~0.4 nm). The selectivity coefficient S for DMDS is much higher than that of pure In2O3.

[0019] (2) The palladium-doped indium oxide composite material provided by the present invention can be used as a sensing material for a resistive gas sensor and can be directly applied to a gas-sensitive test electrode to achieve ultra-high selectivity detection of dimethyl disulfide gas.

[0020] (3) The preparation method of the palladium-doped indium oxide composite material provided by the present invention is simple, fast and efficient. Since conventional reducing agents (such as H2, NaH) require high temperature or long reaction time, Pd is easily agglomerated into micron-sized particles, and the active sites are reduced. Therefore, the key role of the sodium borohydride reduction process is required: NaBH4 (reduction potential -1.24 V) reduces Pd within 10 minutes at room temperature. 2+ Completely reduced to Pd 0 , preventing the growth of intermediate particles and ensuring uniform dispersion of palladium nanoparticles (particle size distribution ±1 nm). At the same time, the ethanol solvent forms hydrogen bonds with the Pd precursor through hydroxyl groups (-OH), inhibiting the aggregation of palladium nanoparticles caused by local excessive concentration and increasing the density of active sites.

[0021] In summary, the present invention not only obtains a palladium-doped indium oxide composite material, but can also be used as the sensing layer of a resistive metal oxide gas sensor to achieve specific detection of dimethyl disulfide gas. Moreover, it does not require expensive detection equipment, has low detection cost, is simple to operate, and is fast and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a test chart of the selectivity of palladium-doped indium oxide composite materials with a mass ratio of palladium ions to indium hydroxide of 0.001:1 to different gases. Figure 2 This is a test chart of the selectivity of a palladium-doped indium oxide composite material with a mass ratio of palladium ions to indium hydroxide of 0.005:1 to different gases.

[0023] Figure 3 This is a test chart of the selectivity of a palladium-doped indium oxide composite material with a mass ratio of palladium ions to indium hydroxide of 0.02:1 to different gases.

[0024] Figure 4 This is a test chart of the selectivity of pure indium hydroxide material to different gases. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0026] Example 1 The palladium-doped indium oxide composite material is prepared in the following steps: Step a1, 20 mL of ammonia water and 60 mL of anhydrous ethanol were mixed evenly, and the mixture was slowly added to a solution containing 266 mg of indium nitrate solid. The mixture was placed in a sealed container, heated in a water bath at 80° C. and stirred for 0.5 h, followed by solid-liquid separation and washing, and centrifugation again. The mixture was repeated 5 times, and dried to obtain pure, dry, bulk indium hydroxide. Step b1, dispersing 100 mg of blocky indium hydroxide into 50 mL of deionized water, then adding 0.166 mg of palladium nitrate, stirring for 24 h, and then adding a mixture of 0.1 mol / L of NaBH4 and anhydrous ethanol, stirring for 0.5 h, performing solid-liquid separation, washing and drying to obtain palladium particle-doped indium oxide; Step c1: air annealing the obtained palladium particle-doped indium oxide at an annealing temperature of 600° C., a heating rate of 10° C. / min, and an annealing time of 3 h to obtain a palladium-doped indium oxide composite material.

[0027] Example 2 The palladium-doped indium oxide composite material is prepared in the following steps: Step a2: 10 mL of aqueous ammonia and 30 mL of anhydrous ethanol were mixed evenly, and the mixture was slowly added to a solution containing 266 mg of indium nitrate solid. The mixture was placed in a sealed container, heated in a water bath at 80° C. and stirred for 0.5 h, followed by solid-liquid separation and washing, and centrifugation again. The mixture was repeated 5 times, and dried to obtain pure, dry, bulk indium hydroxide. Step b2: 100 mg of indium hydroxide was dispersed in 50 mL of deionized water, and then 0.83 mg of palladium nitrate was added, stirred for 20 h, and then a mixture of 0.1 mol / L of NaBH4 and anhydrous ethanol was added, stirred for 0.5 h, and solid-liquid separation, washing, and drying were performed to obtain palladium particle-doped indium oxide; Step c2: air annealing the obtained palladium particle-doped indium oxide at an annealing temperature of 500° C., a heating rate of 8° C. / min, and an annealing time of 2 h to obtain a palladium-doped indium oxide composite material.

[0028] Example 3 The palladium-doped indium oxide composite material is prepared in the following steps: Step a3, 10 mL of ammonia water and 30 mL of anhydrous ethanol were mixed evenly, and the mixture was slowly added to a solution containing 133 mg of indium nitrate solid. The mixture was placed in a sealed container, heated in a water bath at 80° C. and stirred for 0.5 h, followed by solid-liquid separation and washing, and centrifugation again. The mixture was repeated 5 times, and dried to obtain pure, dry, bulk indium hydroxide. Step b3, 50 mg of indium hydroxide was dispersed in 30 mL of deionized water, and then 0.14 mg of tetraammine palladium nitrate was added, and the mixture was stirred for 22 h. Then, a mixture of 0.1 mol / L of NaBH4 and anhydrous ethanol was added, and the mixture was stirred for 0.5 h. The mixture was subjected to solid-liquid separation, washing, and drying to obtain palladium particle-doped indium oxide; Step c3: air annealing the obtained palladium particle-doped indium oxide at an annealing temperature of 500° C., a heating rate of 5° C. / min, and an annealing time of 3 h to obtain a palladium-doped indium oxide composite material.

[0029] Example 4 The palladium-doped indium oxide composite material is prepared in the following steps: Step 4: 15 mL of ammonia water and 45 mL of anhydrous ethanol were mixed evenly, and the mixture was slowly added to a solution containing 266 mg of indium nitrate solid. The mixture was placed in a sealed container, heated in a water bath at 80° C. and stirred for 0.5 h. The mixture was then subjected to solid-liquid separation and washing, and centrifuged again. This was repeated 5 times, and then dried to obtain pure, dry, bulk indium hydroxide. Step b4: 100 mg of indium hydroxide was dispersed in 60 mL of deionized water, and then 5.6 mg of tetraammine palladium nitrate was added, and the mixture was stirred for 24 h. Then, a mixture of 0.1 mol / L of NaBH4 and anhydrous ethanol was added, and the mixture was stirred for 0.5 h. The mixture was subjected to solid-liquid separation, washing, and drying to obtain palladium particle-doped indium oxide; Step c4: air annealing the obtained palladium particle-doped indium oxide at an annealing temperature of 450° C., a heating rate of 8° C. / min, and an annealing time of 4 h to obtain a palladium-doped indium oxide composite material.

[0030] Example 5 The palladium-doped indium oxide composite material is prepared in the following steps: Step a5: 10 mL of aqueous ammonia and 30 mL of anhydrous ethanol were mixed evenly, and the mixture was slowly added to a solution containing 133 mg of indium nitrate solid. The mixture was placed in a sealed container, heated in a water bath at 80° C. and stirred for 0.5 h. The mixture was then subjected to solid-liquid separation and washing, and centrifuged again. This was repeated 5 times, and then dried to obtain pure, dry, bulk indium hydroxide. Step b5: 50 mg of indium hydroxide was dispersed in 30 mL of deionized water, and then 0.575 mg of tetraamminepalladium chloride was added, and the mixture was stirred for 18 h. Then, a mixture of 0.1 mol / L of NaBH4 and anhydrous ethanol was added, and the mixture was stirred for 0.5 h. The mixture was subjected to solid-liquid separation, washing, and drying to obtain palladium particle-doped indium oxide; Step c5: air annealing the obtained palladium particle-doped indium oxide at an annealing temperature of 550° C., a heating rate of 6° C. / min, and an annealing time of 5 h to obtain a palladium-doped indium oxide composite material.

[0031] Example 6 The palladium-doped indium oxide composite material is prepared in the following steps: Step a6: 20 mL of aqueous ammonia and 60 mL of anhydrous ethanol were mixed evenly, and the mixture was slowly added to a solution containing 266 mg of indium nitrate solid. The mixture was placed in a sealed container, heated in a water bath at 80° C. and stirred for 0.5 h. The mixture was then subjected to solid-liquid separation and washing, and centrifuged again. This was repeated 5 times, and then dried to obtain pure, dry, bulk indium hydroxide. Step b6: 100 mg of indium hydroxide was dispersed in 50 mL of deionized water, and then 4.6 mg of tetraamminepalladium chloride was added, and the mixture was stirred for 22 h. Then, a mixture of 0.1 mol / L of NaBH4 and anhydrous ethanol was added, and the mixture was stirred for 0.5 h. The mixture was subjected to solid-liquid separation, washing, and drying to obtain palladium particle-doped indium oxide; Step c6: air annealing the obtained palladium particle-doped indium oxide at an annealing temperature of 350° C., a heating rate of 5° C. / min, and an annealing time of 5 h to obtain a palladium-doped indium oxide composite material.

[0032] The palladium-doped indium oxide composite materials prepared in the above examples were fabricated into gas sensors using the following process: the palladium-doped indium oxide was ground in a mortar and dissolved in deionized water. The temperature of the heating plate was controlled at 35°C. The palladium-doped indium oxide composite material was then attached to a sensor substrate using a pipette on the heating plate. The substrate was then bonded to the sensor electrodes using a device to produce a palladium-doped indium oxide gas sensor. The gas sensor was exposed to various VOCs, causing changes in its resistance. The voltage response was then measured to compare the differences in the VOC response values. The gas response value for dimethyl disulfide was found to be higher than that for other VOCs, thus achieving specific detection.

[0033] The selectivity of the composite materials for dimethyl disulfide prepared under the conditions of the mass ratio of palladium ion to indium hydroxide being 0.001:1, the mass ratio of palladium ion to indium hydroxide being 0.005:1, and the mass ratio of palladium ion to indium hydroxide being 0.02:1 are as follows: Figure 1 、 2 , as shown in 3.

[0034] Figure 1 、 2 As can be seen from Figure 3, the palladium-doped indium oxide composite material exhibits a very high gas response value to dimethyl disulfide, but has a smaller response to carbon disulfide and methyl sulfide, and almost no response to other gases, proving that the composite structure has ultra-high selectivity for dimethyl disulfide.

[0035] Palladium is a crucial raw material in the composite material. If pure indium hydroxide material is used, the selectivity for dimethyl disulfide is as Figure 4 As shown, it can be seen that pure indium hydroxide material has no selectivity for dimethyl disulfide.

[0036] In summary, the palladium-doped indium oxide composite material prepared in the embodiment of the present invention can be used as the sensing layer of a resistive metal oxide gas sensor to achieve specific detection of dimethyl disulfide gas, without the need for expensive detection equipment, with low detection cost, simple operation, and fast and efficient operation.

[0037] In the above examples, the palladium source material is not only palladium nitrate, but also tetraamminepalladium chloride or tetraamminepalladium nitrate for verification, and the technical effects produced are the same. The various raw materials used in the present invention are all commercially available materials.

[0038] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a palladium-doped indium oxide composite material, characterized in that: Here are the steps: (1) Ammonia water and anhydrous ethanol are mixed evenly, and slowly added to an anhydrous ethanol solution containing indium nitrate, placed in a sealed container, evacuated, and heated in a water bath, followed by solid-liquid separation and washing with an ethanol-water solution, centrifuged again, and repeated 3 to 10 times. After drying, pure, dry, blocky indium hydroxide is obtained; (2) Dispersing the bulk indium hydroxide material into deionized water, adding a palladium source and stirring for loading modification, then adding a mixture of 0.1 mol / L NaBH4 and anhydrous ethanol and stirring evenly, performing solid-liquid separation, washing and drying to obtain palladium particle-doped indium oxide; (3) The obtained palladium-doped indium oxide is subjected to air annealing treatment in an air environment to obtain a pure and dry palladium-doped indium oxide composite material.

2. The method for preparing a palladium-doped indium oxide composite material according to claim 1, wherein In the step (1), the mass ratio of the ammonia water to the anhydrous ethanol is 1:2-5, and the mass ratio of the ammonia water to the indium nitrate is 50-100:

1.

3. The method for preparing a palladium-doped indium oxide composite material according to claim 1, wherein: In the step (1), the water bath heating temperature is 60-90° C., and the heating and stirring time is 0.5-4 h.

4. The method for preparing a palladium-doped indium oxide composite material according to claim 1, wherein: In the step (2), a palladium source is added and stirred for 2 to 24 hours to perform loading modification.

5. The method for preparing the palladium-doped indium oxide composite material according to claim 1, wherein In the step (2), the suspension is centrifuged at 5500-8500 r / min for 5-10 min.

6. The method for preparing the palladium-doped indium oxide composite material according to claim 1, wherein: In the step (3), the palladium source is one of palladium nitrate, tetraamminepalladium chloride, and tetraamminepalladium nitrate, and the mass ratio of palladium ions to indium hydroxide is 0.001 to 0.02:

1.

7. The method for preparing a palladium-doped indium oxide composite material according to claim 1, wherein: In the step (3), the mass ratio of NaBH4 to anhydrous ethanol is 1:3-10.

8. The method for preparing a palladium-doped indium oxide composite material according to claim 1, wherein: In the step (4), the annealing temperature is 350-600°C, the heating rate is 2-10°C / min, and the annealing time is 0.5-5h.

9. A palladium-doped indium oxide composite material, characterized in that: The composite material is prepared by the method for preparing the palladium-doped indium oxide according to any one of claims 1 to 8.

10. The palladium-doped indium oxide composite material according to claim 9 is prepared into a gas sensor for detecting dimethyl disulfide gas.

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