Palladium-doped indium oxide composite material, and preparation method and application thereof

Abstract

The application belongs to the field of gas sensors, discloses a kind of indium oxide composite material based on palladium doping and its preparation method and application, its preparation process is to utilize indium nitrate, anhydrous ethanol, ammonia, deionized water to prepare indium oxide material, then doping palladium ion in indium oxide solution to obtain palladium ion doped indium oxide solution, using sodium borohydride reduction, centrifugal to obtain palladium doped indium oxide composite material, then prepare into gas sensor.The application can effectively solve the problems of high activation energy required for pure indium oxide gas sensor reaction and lack of selectivity of pure semiconductor surface to sulfide by improving the design of key process flow of preparation method, and realizes the detection of dimethyl disulfide gas.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation, and more specifically, relates to a palladium-doped indium oxide composite material, its preparation method, and its application. Background Technology

[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 odor threshold (<1 ppm) pose a serious threat to the environment and human health. However, traditional detection methods for DMDS (such as gas chromatography-mass spectrometry and infrared spectroscopy) suffer from drawbacks such as expensive equipment, complex operation, and difficulty in real-time monitoring. Especially in complex gas environments, spectroscopic methods are susceptible to cross-interference from other sulfides (such as H₂S and methanethiol), leading to insufficient sensitivity and specificity. Therefore, the development of low-cost, high-sensitivity, and high-specificity gas sensors is urgently needed.

[0003] Metal oxide semiconductor (MOS) gas sensors, represented by pure indium oxide (In2O3) and tin oxide (SnO2), have advantages such as low cost and fast response, but they have significant bottlenecks in DMDS detection:

[0004] 1. Insufficient sensitivity: DMDS molecules are large (containing two thioether groups), have low adsorption efficiency on pure In2O3 surface, and the reaction requires high activation energy (>200℃), resulting in weak conductivity response.

[0005] 2. Poor specificity: Pure semiconductor surfaces lack selectivity for sulfides and are easily affected by coexisting VOCs (such as ethanol and acetone) or reducing gases (such as CO and H2), making it impossible to distinguish DMDS.

[0006] Therefore, in view of the above situation, improving DMDS adsorption efficiency, reducing reaction activation energy, and increasing selectivity are the decisive factors for achieving high specificity detection of semiconductor gas sensors. Summary of the Invention

[0007] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide a palladium-doped indium oxide composite material, its preparation method, and its applications. The method involves doping an In₂O₃ semiconductor with the noble metal palladium (Pd), reducing it with sodium borohydride, and then centrifuging to obtain the palladium-doped indium oxide composite material. This preparation method overcomes the problems of high activation energy required for the reaction of pure indium oxide (In₂O₃) and the lack of selectivity for sulfides on the pure semiconductor surface. The preparation method of this invention not only utilizes palladium as a highly efficient catalyst, significantly reducing the activation energy for the decomposition of DMDS molecules, but also leverages palladium's strong adsorption properties to improve adsorption efficiency, avoid the influence of other VOCs gases, and achieve ultra-high specificity detection of dimethyl disulfide.

[0008] To achieve the above objectives, one objective of this invention is to provide a method for preparing palladium-doped indium oxide composite materials, comprising the following steps:

[0009] (1) Mix ammonia water and anhydrous ethanol evenly, slowly add it to anhydrous ethanol solution containing indium nitrate, place it in a sealed container, vacuum and heat it in a water bath, then perform solid-liquid separation and washing with ethanol-water solution, centrifuge again, repeat 3 to 10 times, and dry it to obtain pure dry block indium hydroxide.

[0010] (2) Disperse the blocky indium hydroxide material in deionized water, add palladium source and stir for 2-24 h for loading modification, then add 0.1 mol / L of NaBH4 and anhydrous ethanol mixture and stir for 0.5-4 h for solid-liquid separation, washing and drying to obtain palladium particle-doped indium oxide.

[0011] (3) The obtained palladium-doped indium oxide was subjected to air annealing in an air environment to obtain a pure and dry palladium-doped indium oxide composite material.

[0012] As a further preferred embodiment of the present invention, in step (1), the mass ratio of ammonia to anhydrous ethanol is 1:2 to 5, and the mass ratio of ammonia to indium nitrate is 50 to 100:1.

[0013] 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 0.5-4h.

[0014] 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.

[0015] As a further preferred embodiment of the present invention, in step (2), the centrifugation conditions of the suspension are: centrifugation at 5500-8500 r / min for 5-10 min.

[0016] As a further preferred embodiment of the present invention, in step (3), the palladium source is one of palladium nitrate, palladium tetraammine chloride, and palladium tetraammine nitrate, and the mass ratio of palladium ions to indium hydroxide is 0.001 to 0.02:1.

[0017] When the palladium source material is palladium nitrate, the mass ratio of palladium nitrate to indium hydroxide is 1.66 × 10⁻⁶. -3 ~3.32×10 -2 :1; When the palladium source is palladium tetraamminenitrate, the mass ratio of palladium tetraamminenitrate to indium hydroxide is 2.8 × 10⁻⁶. -3 ~5.6×10 -2:1; When the palladium source is palladium tetraamminechloride, the mass ratio of palladium tetraamminechloride to indium hydroxide is 2.3 × 10⁻⁶. -3 ~4.6×10 -2 :1.

[0018] As a further preferred embodiment of the present invention, in step (3), the mass ratio of NaBH4 to anhydrous ethanol is 1:3 to 10.

[0019] 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.

[0020] Another object of the present invention is to provide a palladium-doped indium oxide composite material, which is prepared by the above-described method for preparing palladium-doped indium oxide composite materials.

[0021] Another object of the present invention is to provide a gas sensor made of the above-mentioned palladium-doped indium oxide composite material for the detection of dimethyl disulfide gas.

[0022] The process of fabricating a gas sensor using palladium-doped indium oxide composite material is as follows: The palladium-doped indium oxide is ground in a mortar, dissolved in deionized water, and the heating stage temperature is controlled at 30–40°C. The palladium-doped indium oxide composite material is then attached to the sensor substrate using a dropper on the heating stage. The substrate is then connected to the sensor electrode via a device to obtain the palladium-doped indium oxide gas sensor. By reacting various VOCs gases with this gas sensor to change its resistance, the differences in the gas response values ​​of the VOCs gases are compared by measuring the voltage. It was found that the gas response value of dimethyl disulfide gas is higher than that of other VOCs gases, thus achieving specific detection.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The palladium-doped indium oxide composite material provided by this invention addresses the defects of pure indium oxide: DMDS molecules have a stable structure (containing two thioether bonds) and require high temperature (>200℃) to dissociate into active intermediates (such as -CH3S· radicals), resulting in a weak response signal (ΔR / R0<15%) and poor selectivity for sulfides such as H2S and methanethiol. This can be improved by palladium doping. The palladium nanoparticles generated by NaBH4 reduction act as a highly efficient catalyst, significantly reducing the activation energy of DMDS decomposition (from 1.2 eV to 0.7 eV), thus lowering the reaction temperature to below 150℃. The DMDS molecules adsorbed on the surface of the palladium nanoparticles rapidly dissociate into active sulfur radicals, which then migrate to the In2O3 surface and react with adsorbed oxygen, increasing the response value by 6-10 times (ΔR / R0 reaches 80-120%). 0The soft acid forms a strong coordination bond (binding energy difference > 0.5 eV) with the disulfide structure (S–C–S bond, soft base) of DMDS. The active sites on the surface of palladium nanoparticles are compatible with the molecular size of DMDS (chain length ~ 0.4 nm), and the selectivity coefficient S for DMDS is much higher than that of pure In2O3.

[0025] (2) The palladium-doped indium oxide composite material provided by the present invention can be used as the sensing material of the resistive gas sensor. It can be directly brushed onto the gas-sensitive test electrode to achieve ultra-high selectivity detection of dimethyl disulfide gas.

[0026] (3) The method for preparing palladium-doped indium oxide composite materials provided by this invention is simple, fast, and efficient. Conventional reducing agents (such as H2 and NaH) require high temperatures or long reaction times, which easily leads to Pd agglomeration into micron-sized particles, reducing the number of active sites. Therefore, the key role of the sodium borohydride reduction process is crucial: NaBH4 (reduction potential -1.24 V) reduces Pd within 10 minutes at room temperature. 2+ Completely restored to Pd 0 This avoids the growth of intermediate-state particles and ensures 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 excessively high local concentrations and increasing the density of active sites.

[0027] In summary, this invention not only yields palladium-doped indium oxide composite material, but also serves as the sensing layer of a resistive metal oxide gas sensor, enabling specific detection of dimethyl disulfide gas. Moreover, it eliminates the need for expensive detection equipment, has low detection costs, and is simple, fast, and efficient to operate. Attached Figure Description

[0028] Figure 1 The graph shows the selectivity of a palladium-doped indium oxide composite material with a palladium ion to indium hydroxide mass ratio of 0.001:1 to different gases.

[0029] Figure 2 This is a test graph showing the selectivity of a palladium-doped indium oxide composite material with a palladium ion to indium hydroxide mass ratio of 0.005:1 to different gases.

[0030] Figure 3 This is a test graph showing the selectivity of a palladium-doped indium oxide composite material with a palladium ion to indium hydroxide mass ratio of 0.02:1 to different gases.

[0031] Figure 4 This is a test chart showing the selectivity of pure indium hydroxide material to different gases. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be 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 illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Example 1

[0034] The preparation steps of palladium-doped indium oxide composite material are as follows:

[0035] Step a1: Mix 20 mL of ammonia water and 60 mL of anhydrous ethanol evenly, and slowly add it to a solution containing 266 mg of indium nitrate solid. Place it in a sealed container, heat it in a water bath at 80 °C and stir for 0.5 h. Then perform solid-liquid separation and washing, centrifuge again, repeat 5 times, and dry it to obtain pure dry block indium hydroxide.

[0036] Step b1: Disperse 100 mg of indium hydroxide in 50 mL of deionized water, then add 0.166 mg of palladium nitrate, stir for 24 h, then add a mixture of 0.1 mol / L NaBH4 and anhydrous ethanol, stir for 0.5 h, and perform solid-liquid separation, washing and drying to obtain palladium-doped indium oxide.

[0037] Step c1: The obtained palladium-doped indium oxide particles are subjected to air annealing at a temperature of 600℃, a heating rate of 10℃ / min, and an annealing time of 3h to obtain a palladium-doped indium oxide composite material.

[0038] Example 2

[0039] The preparation steps of palladium-doped indium oxide composite material are as follows:

[0040] Step a2: Mix 10 mL of ammonia water and 30 mL of anhydrous ethanol evenly, and slowly add it to a solution containing 266 mg of indium nitrate solid. Place it in a sealed container, heat it in a water bath at 80 °C and stir for 0.5 h. Then perform solid-liquid separation and washing, centrifuge again, repeat 5 times, and dry it to obtain pure dry block indium hydroxide.

[0041] Step b2: Disperse 100 mg of indium hydroxide in 50 mL of deionized water, then add 0.83 mg of palladium nitrate, stir for 20 h, then add a mixture of 0.1 mol / L NaBH4 and anhydrous ethanol, stir for 0.5 h, and perform solid-liquid separation, washing and drying to obtain palladium-doped indium oxide.

[0042] Step c2: The obtained palladium-doped indium oxide particles are subjected to air annealing at a temperature of 500℃, a heating rate of 8℃ / min, and an annealing time of 2h to obtain palladium-doped indium oxide composite material.

[0043] Example 3

[0044] The preparation steps of palladium-doped indium oxide composite material are as follows:

[0045] Step a3: Mix 10 mL of ammonia water and 30 mL of anhydrous ethanol evenly, and slowly add it to a solution containing 133 mg of indium nitrate solid. Place it in a sealed container, heat it in a water bath at 80 °C and stir for 0.5 h. Then perform solid-liquid separation and washing, centrifuge again, repeat 5 times, and dry it to obtain pure dry block indium hydroxide.

[0046] Step b3: Disperse 50 mg of indium hydroxide in 30 mL of deionized water, then add 0.14 mg of palladium tetraamminenitrate, stir for 22 h, then add a mixture of 0.1 mol / L NaBH4 and anhydrous ethanol, stir for 0.5 h, and perform solid-liquid separation, washing and drying to obtain palladium-doped indium oxide.

[0047] Step c3: The obtained palladium-doped indium oxide particles are subjected to air annealing at a temperature of 500℃, a heating rate of 5℃ / min, and an annealing time of 3h to obtain palladium-doped indium oxide composite material.

[0048] Example 4

[0049] The preparation steps of palladium-doped indium oxide composite material are as follows:

[0050] Step 4: Mix 15 mL of ammonia water and 45 mL of anhydrous ethanol evenly, and slowly add it to a solution containing 266 mg of indium nitrate solid. Place the solution in a sealed container, heat it in a water bath at 80 °C and stir for 0.5 h. Then perform solid-liquid separation and washing, centrifuge again, repeat 5 times, and dry it to obtain pure, dry block indium hydroxide.

[0051] Step b4: Disperse 100 mg of indium hydroxide in 60 mL of deionized water, then add 5.6 mg of palladium tetraamminenitrate, stir for 24 h, then add a mixture of 0.1 mol / L NaBH4 and anhydrous ethanol, stir for 0.5 h, and perform solid-liquid separation, washing and drying to obtain palladium-doped indium oxide.

[0052] Step c4: The obtained palladium-doped indium oxide particles are subjected to air annealing at a temperature of 450°C, a heating rate of 8°C / min, and an annealing time of 4 hours to obtain palladium-doped indium oxide composite material.

[0053] Example 5

[0054] The preparation steps of palladium-doped indium oxide composite material are as follows:

[0055] Step a5: Mix 10 mL of ammonia water and 30 mL of anhydrous ethanol evenly, and slowly add it to a solution containing 133 mg of indium nitrate solid. Place it in a sealed container, heat it in a water bath at 80 °C and stir for 0.5 h. Then perform solid-liquid separation and washing, centrifuge again, repeat 5 times, and dry it to obtain pure dry block indium hydroxide.

[0056] Step b5: Disperse 50 mg of indium hydroxide into 30 mL of deionized water, then add 0.575 mg of tetraamminepalladium chloride, stir for 18 h, then add a mixture of 0.1 mol / L NaBH4 and anhydrous ethanol, stir for 0.5 h, and perform solid-liquid separation, washing and drying to obtain palladium-doped indium oxide.

[0057] Step c5: The obtained palladium-doped indium oxide particles are subjected to air annealing at a temperature of 550°C, a heating rate of 6°C / min, and an annealing time of 5 hours to obtain palladium-doped indium oxide composite material.

[0058] Example 6

[0059] The preparation steps of palladium-doped indium oxide composite material are as follows:

[0060] Step a6: Mix 20 mL of ammonia water and 60 mL of anhydrous ethanol evenly, and slowly add it to a solution containing 266 mg of indium nitrate solid. Place it in a sealed container, heat it in a water bath at 80 °C and stir for 0.5 h. Then perform solid-liquid separation and washing, centrifuge again, repeat 5 times, and dry it to obtain pure dry block indium hydroxide.

[0061] Step b6: Disperse 100 mg of indium hydroxide in 50 mL of deionized water, then add 4.6 mg of tetraamminepalladium chloride, stir for 22 h, then add a mixture of 0.1 mol / L NaBH4 and anhydrous ethanol, stir for 0.5 h, and perform solid-liquid separation, washing and drying to obtain palladium-doped indium oxide.

[0062] Step c6: The obtained palladium-doped indium oxide particles are subjected to air annealing at a temperature of 350°C, a heating rate of 5°C / min, and an annealing time of 5 hours to obtain palladium-doped indium oxide composite material.

[0063] The palladium-doped indium oxide composite materials prepared in the above embodiments were used to fabricate a gas sensor. The specific process is as follows: The palladium-doped indium oxide was crushed in a mortar, dissolved in deionized water, and the heating stage temperature was controlled at 35°C. The palladium-doped indium oxide composite material was then attached to the sensor substrate using a dropper on the heating stage. The substrate was then connected to the sensor electrode using a device to obtain the palladium-doped indium oxide gas sensor. Various VOCs gases were reacted with the gas sensor to change its resistance. The differences in the gas response values ​​of the VOCs gases were compared by measuring the voltage. It was found that the gas response value of dimethyl disulfide gas was higher than that of other VOCs gases, thus achieving specific detection.

[0064] The selectivity of the composite material for dimethyl disulfide prepared under the conditions of palladium ion to indium hydroxide mass ratio of 0.001:1, 0.005:1, and 0.02:1 are as follows: Figure 1 , 2 As shown in Figure 3.

[0065] 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, while it 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.

[0066] Palladium is a crucial raw material in this composite material. If pure indium hydroxide is used, the selectivity for dimethyl disulfide is as follows: Figure 4 As shown, pure indium hydroxide material has no selectivity for dimethyl disulfide.

[0067] In summary, the palladium-doped indium oxide composite material prepared in the embodiments 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. Moreover, it does not require expensive detection equipment, has low detection cost, is simple to operate, and is fast and efficient.

[0068] In the above embodiments, in addition to palladium nitrate, tetraamminepalladium chloride or tetraamminepalladium nitrate were also used as palladium source materials for verification, and the resulting technical effects were the same. All raw materials used in this invention are commercially available.

[0069] Those skilled in the art will readily understand 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 within the scope of protection of the present invention.

Claims

1. A method for preparing a palladium-doped indium oxide composite material, characterized by, The steps are as follows: (1) Mix ammonia water and anhydrous ethanol evenly, slowly add to anhydrous ethanol solution containing indium nitrate, place in a sealed container, vacuum and heat in a water bath, then perform solid-liquid separation and washing with ethanol-water solution, centrifuge again, repeat 3 to 10 times, and dry to obtain pure dry block indium hydroxide; the mass ratio of ammonia water to anhydrous ethanol is 1:2 to 5, and the mass ratio of ammonia water to indium nitrate is 50 to 100:1; (2) Disperse the blocky indium hydroxide material in deionized water, add palladium source and stir for loading modification, then add 0.1 mol / L of NaBH4 and anhydrous ethanol mixture and stir evenly, then perform solid-liquid separation, washing and drying to obtain palladium particle-doped indium oxide. (3) The obtained palladium-doped indium oxide was subjected to air annealing 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, characterized by, In step (1), the water bath heating temperature is 60-90℃, and the heating and stirring time is 0.5-4h.

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

4. The method for preparing a palladium-doped indium oxide composite material according to claim 1, characterized by, In step (2), the palladium source is one of palladium nitrate, palladium tetraammine chloride, and palladium tetraammine nitrate, and the mass ratio of palladium ions to indium hydroxide is 0.001 to 0.02:

1.

5. The method for preparing palladium-doped indium oxide composite material according to claim 1, characterized in that, In step (2), the mass ratio of NaBH4 to anhydrous ethanol is 1:3 to 10.

6. The method for preparing a palladium-doped indium oxide composite material according to claim 1, wherein In step (3), the annealing temperature is 350-600℃, the heating rate is 2-10℃ / min, and the annealing time is 0.5-5h.

7. A palladium-doped indium oxide composite material, characterized by, The indium oxide composite material based on palladium doping is prepared using the preparation method described in any one of claims 1-6.

8. The gas sensor prepared from the palladium-doped indium oxide composite material as described in claim 7 is used for the detection of dimethyl disulfide gas.

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