NiO / CdS nanoparticle heterojunction array and preparation method and application thereof

Abstract

The application belongs to the technical field of nano material heterojunction, and particularly relates to a NiO / CdS nanoparticle heterojunction array and a preparation method and application thereof. The application comprises a substrate and a NiO / CdS heterojunction array in-situ grown on the surface of the substrate; the substrate is an Al2O3 gas sensitive substrate; the NiO / CdS heterojunction array is composed of NiO nanosheets and CdS nanoparticles, wherein the NiO nanosheets are in an array structure of vertical interlaced growth, and the CdS nanoparticles are uniformly dispersed on the surface of the NiO porous nanosheets. The preparation process of the application is simple, and the cost is low. The NiO / CdS heterojunction array prepared by the application has good heterojunction interface contact, and the size and distribution density of the CdS nanoparticles in the NiO / CdS heterojunction array can be conveniently regulated. In addition, the NiO / CdS nanoparticle heterojunction array can be applied in room temperature gas sensing, and specifically in high selectivity detection of triethylamine at room temperature under green light excitation.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial heterostructure technology, specifically relating to a NiO / CdS nanoparticle heterostructure array, its preparation method, and its application. Background Technology

[0002] With industrial development and rising living standards, environmental damage has become increasingly severe, and the threat to human health from various toxic, harmful, flammable, and explosive gases is growing daily. In recent years, the detection and management of toxic and harmful gases in industrial production processes has received widespread attention. Compared with detection methods such as fluorescence, colorimetry, and gas chromatography, resistive gas sensors based on semiconductor materials offer advantages such as low cost, ease of use, simple structure, and easy integration. Therefore, researchers have invested significant effort in developing resistive gas sensors based on semiconductor materials. Currently, resistive gas sensors typically require operation at relatively high temperatures (200℃~400℃) to ensure high sensitivity and response characteristics. This not only limits their ability to detect flammable and explosive gases but also requires substantial energy consumption. Furthermore, high temperatures can induce grain growth, reducing sensor stability and lifespan. Therefore, the development of resistive gas sensors with excellent room-temperature gas-sensing performance has attracted considerable interest in the sensor field.

[0003] Besides the optimization of the semiconductor gas-sensitive material itself, the device structure is also a crucial factor affecting the gas-sensing performance of semiconductor sensors. Currently, the fabrication of semiconductor gas sensors typically involves the following steps: First, a powdered semiconductor gas-sensitive material is prepared. Then, the powder is dispersed in a specific solvent, and a gas-sensitive slurry is obtained through ultrasonic or ball milling. Finally, the slurry is assembled onto a gas-sensitive substrate with pre-fabricated electrodes using brush coating or screen printing to obtain a thick-film device. These processes inevitably lead to agglomeration, structural damage, and poor electrical contact of the gas-sensitive material, resulting in a significant reduction in the inherent gas-sensing activity of the semiconductor. Furthermore, this technique makes it difficult to precisely control the thickness and uniformity of the sensing layer, thus hindering the consistency and reliability of the sensor. Therefore, it is essential to fabricate a semiconductor heterojunction gas-sensitive material array that can address these issues. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a NiO / CdS nanoparticle heterojunction array, its preparation method, and its application. Specifically, the following technical solution is adopted:

[0005] A NiO / CdS nanoparticle heterojunction array includes a substrate and a NiO / CdS heterojunction array grown in situ on the surface of the substrate; the substrate is an Al2O3 gas-sensitive substrate; the NiO / CdS heterojunction array is composed of NiO nanosheets and CdS nanoparticles, wherein the NiO nanosheets are arranged in a vertically staggered array structure, and the CdS nanoparticles are uniformly dispersed on the surface of the NiO porous nanosheets.

[0006] This invention constructs a semiconductor gas sensing array in situ on a gas-sensitive substrate. Because the sensing layer is an array constructed in situ on the gas-sensitive substrate, this not only avoids a series of problems caused by thick-film formation processes in traditional methods but also greatly simplifies device manufacturing costs and enables miniaturization. Furthermore, the tight bonding between the sensing film and the gas-sensitive substrate ensures the consistency and reliability of the sensor. Most importantly, since the sensor array is typically porous and has a large specific surface area, this is highly beneficial for the diffusion of the target gas and the surface gas sensing response.

[0007] The aforementioned Al2O3 gas-sensitive substrate is a commercially available flat-plate Al2O3 gas-sensitive substrate manufactured by Huachuang Ruike Technology Co., Ltd. This substrate is composed of inexpensive and readily available Al2O3 and has two pairs of Pt interdigitated electrodes on its surface, one pair being heating electrodes and the other pair being resistance signal collection electrodes. Heating the substrate and collecting the resistance signal are very convenient, and the two pairs of electrodes do not interfere with each other. A NiO / CdS heterojunction array serves as a novel gas-sensitive sensing layer for surface gas adsorption and gas-sensitive reactions.

[0008] As a further preferred embodiment, the lateral size of the NiO nanosheets in the above-mentioned NiO / CdS nanoparticle heterojunction array is 5 μm to 10 μm, and the size of the CdS nanoparticles is 10 nm to 100 nm.

[0009] This invention also provides a method for preparing a NiO / CdS nanoparticle heterojunction array, comprising the following steps:

[0010] First, a NiO porous nanosheet array was grown on the surface of an Al2O3 gas-sensitive substrate using a hydrothermal method combined with annealing. Then, CdS nanoparticles were further grown in situ on the surface of the NiO porous nanosheet array using a solvothermal method to obtain the final product, a NiO / CdS nanoparticle heterojunction array.

[0011] As a further preferred embodiment, the above-mentioned hydrothermal method combined with annealing to grow a NiO porous nanosheet array on the surface of an Al2O3 gas-sensitive substrate specifically includes the following steps:

[0012] Nickel nitrate, ammonium fluoride, and urea were dissolved in water and stirred for 0.2-1 h to obtain a reaction solution. An Al₂O₃ gas-sensitive substrate was then added to the reaction solution for a hydrothermal reaction at 100-120 °C for 5-10 h. After the reaction, the Al₂O₃ gas-sensitive substrate was washed, dried, and then annealed at 450-600 °C for 1-3 h, yielding a NiO porous nanosheet array. At a reaction temperature of 100-120 °C, the alkali source urea began to decompose slowly. If the temperature was too low, the urea could not decompose to produce OH⁻. - Ni(OH)2 cannot nucleate and grow; if the temperature is too high, urea decomposes too quickly, and ammonium fluoride cannot regulate the pH value of the reaction system through buffering; when the annealing temperature is 450 ℃~600 ℃, the purpose of annealing is to convert Ni(OH)2 into NiO. This process mainly involves decomposition and dehydration. If the temperature is too low, Ni(OH)2 cannot be completely decomposed and dehydrated into NiO; if the temperature is too high, NiO nanosheets will continue to grow, causing the nanosheets to thicken and stick together.

[0013] As a further preferred embodiment, the molar ratio of nickel nitrate, ammonium fluoride, and urea is 1:3~5:4~6. Urea, as an alkaline source, decomposes to produce OH-. - (CO(NH2)2→NH3↑+HCNO), the metallic Ni ions and OH in nickel nitrate - The compounds combine to form Ni(OH)₂. Ammonium fluoride, as a strong acid-weak base salt, can effectively control the pH of the reaction system, thereby controlling the nucleation and growth of Ni(OH)₂, resulting in ultrathin nanosheet morphology. Through extensive experimental research, we found that the optimal molar ratio of nickel nitrate, ammonium fluoride, and urea is 1:4:5. Too much or too little urea and ammonium fluoride are detrimental to the formation of the optimal nanosheet structure.

[0014] As a further preferred embodiment, the specific steps of the above-mentioned solvothermal method for in-situ growth of CdS nanoparticles on the surface of NiO porous nanosheet array are as follows:

[0015] Cadmium acetate and thiourea were dissolved sequentially in water and ethylene glycol solutions and mixed to obtain a mixed solution. Then, a NiO porous nanosheet array was immersed in the mixed solution for a solvothermal reaction at a temperature of 140℃ to 180℃ for 15h to 30h. After the reaction, the NiO porous nanosheet array was washed and dried to finally obtain a NiO / CdS nanoparticle heterojunction array.

[0016] As a further preferred embodiment, the molar ratio of cadmium acetate to thiourea is 1:1.

[0017] The volume ratio of water to ethylene glycol solution mentioned above is 1:1 to 2. Ethylene glycol and water are two common solvents with different viscosities and polarities. The addition of ethylene glycol can regulate the viscosity and polarity of the reaction solvent, thus facilitating the growth of CdS nanoparticles. Through extensive experimental research, the optimal volume ratio of ethylene glycol to anhydrous ethanol is 1:1.

[0018] The beneficial effects of this invention are as follows: the preparation process of this invention is simple and low in cost; the NiO / CdS heterojunction array prepared by this invention has good heterojunction interface contact; and the size and distribution density of CdS nanoparticles in the NiO / CdS heterojunction array can be easily controlled. In addition, the NiO / CdS nanoparticle heterojunction array can be applied to room temperature gas sensing, specifically to achieve high-selectivity room temperature detection of triethylamine under green light excitation. Attached Figure Description

[0019] Figure 1 The X-ray diffraction (XRD) patterns of the NiO / CdS heterojunction array and the comparison sample are shown.

[0020] Figure 2 The images shown are scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, and elemental distribution maps of the NiO / CdS heterojunction array and the comparison sample NiO.

[0021] Figure 3 The images shown are scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, and elemental distribution maps of the NiO / CdS heterojunction array comparison sample.

[0022] Figure 4 The image shows the kinetic gas-sensitive response of a NiO / CdS heterojunction array and a control sample to 100 ppm triethylamine at room temperature without light.

[0023] Figure 5 The image shows the gas-sensing performance of a NiO / CdS heterojunction array and a comparative sample to triethylamine under room temperature green light excitation. Detailed Implementation

[0024] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with the embodiments and accompanying drawings, so as to fully understand the purpose, solution, and effects of the present invention.

[0025] Example 1

[0026] A NiO / CdS nanoparticle heterojunction array, the preparation method of which includes the following steps:

[0027] Step 1: First, wash the commercial flat Al2O3 gas-sensitive substrate (produced by Huachuang Ruike Technology Co., Ltd.) repeatedly in deionized water and anhydrous ethanol, and then dry it for later use.

[0028] Step 2: Nickel nitrate (Ni(NO3)2·6H2O), ammonium fluoride (NH4F), and urea (CH4N2O) were added to a polytetrafluoroethylene autoclave in a molar ratio of 1:5:6. Deionized water was then added until the inner liner was 72% full. The mixture was continuously stirred magnetically for 0.2 hours to obtain a reaction solution. A washed commercially available flat Al2O3 gas-sensitive substrate was added to the reaction solution, and a hydrothermal reaction was carried out at a temperature of 100 °C for 10 hours. After the reaction, the commercially available flat Al2O3 gas-sensitive substrate was washed and dried, and then annealed in a muffle furnace at a temperature of 450 °C for 2 hours to obtain a NiO nanosheet array.

[0029] Step 3: Cadmium acetate (Cd(CH3COO)2·2H2O) and thiourea (C4H8N2S) were dissolved sequentially in a 1:1 molar ratio in 20 mL of a mixed solution of deionized water and ethylene glycol (volume ratio of deionized water to ethylene glycol was 1:1). After complete mixing under magnetic stirring, the reaction solution was transferred to a 50 mL polytetrafluoroethylene autoclave. A commercially available flat-plate Al2O3 gas-sensitive substrate with a NiO porous nanosheet array was immersed in the solution for a solvothermal reaction. The reaction temperature was set at 170 °C and the reaction time was 20 hours. After the reaction, the commercially available flat-plate Al2O3 gas-sensitive substrate was washed and dried to obtain the final product, a NiO / CdS heterojunction array.

[0030] Example 2

[0031] A NiO / CdS nanoparticle heterojunction array, the preparation method of which includes the following steps:

[0032] Step 1: First, wash the commercial flat Al2O3 gas-sensitive substrate (produced by Huachuang Ruike Technology Co., Ltd.) repeatedly in deionized water and anhydrous ethanol, and then dry it for later use.

[0033] Step 2: Nickel nitrate (Ni(NO3)2·6H2O), ammonium fluoride (NH4F), and urea (CH4N2O) were added to a polytetrafluoroethylene autoclave in a molar ratio of 1:4:5. Deionized water was then added until the inner liner was 72% full. The mixture was continuously stirred magnetically for 0.5 hours to obtain a reaction solution. A washed commercially available flat Al2O3 gas-sensitive substrate was added to the reaction solution, and a hydrothermal reaction was carried out at a temperature of 100 °C for 8 hours. After the reaction, the commercially available flat Al2O3 gas-sensitive substrate was washed and dried, and then annealed in a muffle furnace at a temperature of 500 °C for 2 hours to obtain a NiO nanosheet array.

[0034] Step 3: Cadmium acetate (Cd(CH3COO)2·2H2O) and thiourea (C4H8N2S) were dissolved sequentially in a 1:1 molar ratio in a 25 mL mixture of deionized water and ethylene glycol (volume ratio of deionized water to ethylene glycol was 1:1). After complete mixing under magnetic stirring, the reaction solution was transferred to a 50 mL polytetrafluoroethylene autoclave. A commercially available flat-plate Al2O3 gas-sensitive substrate with a NiO porous nanosheet array was immersed in the solution for a solvothermal reaction. The reaction temperature was set at 180 °C and the reaction time was 15 hours. After the reaction, the commercially available flat-plate Al2O3 gas-sensitive substrate was washed and dried to obtain the final product, a NiO / CdS heterojunction array.

[0035] Example 3

[0036] A NiO / CdS nanoparticle heterojunction array, the preparation method of which includes the following steps:

[0037] Step 1: First, wash the commercial flat Al2O3 gas-sensitive substrate (produced by Huachuang Ruike Technology Co., Ltd.) repeatedly in deionized water and anhydrous ethanol, and then dry it for later use.

[0038] Step 2: Nickel nitrate (Ni(NO3)2·6H2O), ammonium fluoride (NH4F), and urea (CH4N2O) were added to a polytetrafluoroethylene autoclave in a molar ratio of 1:4:5. Deionized water was then added until the inner liner was 80% filled. The mixture was continuously stirred magnetically for 0.5 hours to obtain a reaction solution. A washed commercially available flat Al2O3 gas-sensitive substrate was added to the reaction solution, and a hydrothermal reaction was carried out at a temperature of 110 °C for 10 hours. After the reaction, the commercially available flat Al2O3 gas-sensitive substrate was washed and dried, and then annealed in a muffle furnace at a temperature of 500 °C for 2 hours to obtain a NiO nanosheet array.

[0039] Step 3: Cadmium acetate (Cd(CH3COO)2·2H2O) and thiourea (C4H8N2S) were dissolved sequentially in a 1:1 molar ratio in 22 mL of a mixed solution of deionized water and ethylene glycol (volume ratio of deionized water to ethylene glycol was 1:1). After complete mixing under magnetic stirring, the reaction solution was transferred to a 50 mL polytetrafluoroethylene autoclave. A commercially available flat-plate Al2O3 gas-sensitive substrate with a NiO porous nanosheet array was immersed in the solution for a solvothermal reaction. The reaction temperature was set at 170 °C and the reaction time was 25 hours. After the reaction, the commercially available flat-plate Al2O3 gas-sensitive substrate was washed and dried to obtain the final product, a NiO / CdS heterojunction array.

[0040] Comparative Example 1

[0041] The preparation of the CdS nanoparticles, the comparative material, was carried out according to the following steps: Cadmium acetate (Cd(CH3COO)2·2H2O) and thiourea (C4H8N2S) were dissolved sequentially in a 1:1 molar ratio in 20 mL of a mixed solution of deionized water and ethylene glycol (volume ratio of deionized water to ethylene glycol was 1:1). After complete mixing under magnetic stirring, the reaction solution was transferred to a 50 mL polytetrafluoroethylene autoclave, and the reaction temperature was set at 170 °C for 20 hours. After the reaction was completed, the CdS nanoparticles were washed and dried to obtain the final product.

[0042] Figure 1 The images show the X-ray diffraction (XRD) patterns of the NiO / CdS heterojunction array and the comparative sample in this invention. It can be seen that the NiO nanosheets are pure-phase NiO (JCPDS No. 47-1049), while the comparative sample's CdS nanoparticles are pure-phase CdS (JCPDS No. 41-1049). The resulting NiO / CdS heterojunction array exhibits both NiO and CdS phases, verifying the synthesis of the heterojunction. Specifically, NiO / CdS-1 is a sample with approximately 1% (molar ratio) of CdS nanoparticles, and NiO / CdS-2 is a sample with approximately 5% (molar ratio) of CdS nanoparticles. It can be observed that as the CdS composite content increases, the XRD characteristic peaks become significantly enhanced.

[0043] Figure 2 These are scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, and elemental distribution maps of the NiO / CdS heterojunction array (NiO / CdS-1) and the comparative sample NiO in this invention. Figure 3 These are scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, and elemental distribution maps of the NiO / CdS heterojunction array comparison sample (NiO / CdS-2) in this invention. Figure 2 Images a and b show SEM images of the NiO porous nanosheet array. It can be seen that the array assembled from porous NiO nanosheets was synthesized uniformly. The surface of the nanosheets is clean. After the growth of CdS nanoparticles, the surface of the NiO nanosheet array is uniformly covered with CdS nanoparticles. This can be clearly seen from the TEM images of NiO / CdS-1. Figure 2 (e and d), a large number of CdS nanoparticles with a diameter of about 20 nm are dispersed on the surface of NiO nanosheets. High-resolution TEM (HRTEM) images revealed lattice fringes with spacings of 0.322 nm and 0.234 nm, which correspond to the (101) crystal plane of CdS and the (111) crystal plane of NiO, respectively. Figure 2 g). Typical diffraction spots of NiO and diffraction rings of CdS are shown in selected area electron diffraction (SAED). Therefore, it can be inferred that a good heterojunctional contact is formed between NiO nanosheets and CdS nanoparticles, which is crucial for ensuring effective charge transfer between the heterojunctions. EDX elemental spectrum of NiO / CdS-1 ( Figure 2 The image (jm) revealed the uniform dispersion of O, Ni, S, and Cd in the nanosheet array, further confirming the successful growth of CdS nanoparticles on the NiO nanosheet array. SEM and TEM images of NiO / CdS-2 (jm) were also shown. Figure 3 The results show that NiO / CdS-2 has a similar morphology and structure to NiO / CdS-1, and the particle size of CdS in NiO / CdS-2 is larger than that in NiO / CdS-1. The EDX elemental spectrum of NiO / CdS-2 (Figure S1e-h) also shows that O, Ni, S, and Cd elements are uniformly distributed in the nanosheet array.

[0044] Triethylamine, a volatile organic compound, is a common and toxic compound that can cause coughing, expiratory headache, and coma. Numerous reports exist on the detection of triethylamine using semiconductor gas sensors. However, these sensors typically require operation at high temperatures (>200°C). Given that triethylamine is flammable and explosive, operating sensors at high temperatures poses safety hazards. Therefore, developing semiconductor gas sensors capable of effectively detecting triethylamine at room temperature is of great significance for human health and safety.

[0045] Based on this, we used the prepared array to detect triethylamine at room temperature. It can be seen that, without photoexcitation at room temperature, the responses of NiO, NiO / CdS-1, and NiO / CdS-2 to triethylamine (100 ppm) are all very limited (<2). Figure 4However, NiO / CdS1 exhibits excellent room-temperature gas sensitivity to triethylamine under low-power (0.06W) green LED light excitation, responding immediately to different concentrations of triethylamine (10-2000ppm) and recovering upon exposure to air. Figure 5 a-5c). Figure 5 Figure d-5e shows the material's response to several consecutive gas in-and-out cycles, confirming the reproducibility of the sensor's response to triethylamine at room temperature. The resistance essentially recovers to its original value after each gas in-and-out cycle. Notably, photoexcitation significantly enhances the gas-sensitive response of NiO / CdS-1, but its enhancement effect on NiO and CdS is less pronounced. Figure 5 f presents the sensing selectivity of the NiO / CdS1 heterojunction array for triethylamine. It can be seen that NiO / CdS-1 exhibits a significant response to triethylamine among various volatile organic compounds (formaldehyde, ethanol, acetone, ethyl acetate, etc.), indicating its excellent selectivity.

[0046] Although the description of the invention has been quite detailed and particularly of several described embodiments, it is not intended to limit it to any of these details or embodiments or any particular embodiment, but should be considered as providing a broad possible interpretation of the claims by referring to the appended claims and taking into account the prior art, thereby effectively covering the intended scope of the invention. Furthermore, the invention has been described above with respect to embodiments foreseeable by the inventors in order to provide a useful description, and non-substantial modifications to the invention that have not yet been foreseen may still represent equivalent modifications.

Claims

1. An application of a NiO / CdS nanoparticle heterojunction array in room temperature gas sensing, characterized in that, The NiO / CdS nanoparticle heterojunction array exhibits high room-temperature selectivity for triethylamine under green light excitation. The NiO / CdS nanoparticle heterojunction array includes a substrate and a NiO / CdS heterojunction array grown in situ on the surface of the substrate; the substrate is an Al2O3 gas-sensitive substrate; the NiO / CdS heterojunction array is composed of NiO nanosheets and CdS nanoparticles, wherein the NiO nanosheets are arranged in a vertically staggered array structure, and the CdS nanoparticles are uniformly dispersed on the surface of the NiO porous nanosheets. The NiO nanosheets in the NiO / CdS nanoparticle heterojunction array have a lateral size of 5 μm to 10 μm, and the CdS nanoparticles have a size of 10 nm to 100 nm.

2. A method for preparing a NiO / CdS nanoparticle heterojunction array as described in claim 1, characterized in that, Includes the following steps: First, a NiO porous nanosheet array was grown on the surface of an Al2O3 gas-sensitive substrate using a hydrothermal method combined with annealing. Then, CdS nanoparticles were further grown in situ on the surface of the NiO porous nanosheet array using a solvothermal method to obtain the final product, a NiO / CdS nanoparticle heterojunction array.

3. The preparation method according to claim 2, characterized in that, The growth of NiO porous nanosheet arrays on the surface of Al2O3 gas-sensitive substrates using a hydrothermal method combined with annealing includes the following steps: Nickel nitrate, ammonium fluoride, and urea were dissolved in water and stirred for 0.2 h to 1 h to obtain a reaction solution. Then, an Al2O3 gas-sensitive substrate was added to the reaction solution for a hydrothermal reaction at a time of 5 h to 10 h and a temperature of 100 ℃ to 120 ℃. After the reaction, the Al2O3 gas-sensitive substrate was washed, dried, and then annealed at a temperature of 450 ℃ to 600 ℃ for 1 h to 3 h. After annealing, a NiO porous nanosheet array was obtained.

4. The preparation method according to claim 3, characterized in that, The molar ratio of nickel nitrate, ammonium fluoride, and urea is 1:3~5:4~6.

5. The preparation method according to claim 3, characterized in that, The specific steps for further in-situ growth of CdS nanoparticles on the surface of NiO porous nanosheet array using the solvothermal method are as follows: Cadmium acetate and thiourea were dissolved sequentially in water and ethylene glycol solutions and mixed to obtain a mixed solution. Then, a NiO porous nanosheet array was immersed in the mixed solution for a solvothermal reaction at a temperature of 140 ℃ to 180 ℃ for 15 h to 30 h. After the reaction, the NiO porous nanosheet array was washed and dried to finally obtain a NiO / CdS nanoparticle heterojunction array.

6. The preparation method according to claim 4, characterized in that, The molar ratio of cadmium acetate to thiourea is 1:

1.

7. The preparation method according to claim 4, characterized in that, The volume ratio of water to ethylene glycol solution is 1:1 to 2.

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