Gas-sensitive nano material based on single-layer ordered tin oxide nano bowl branched zinc oxide nanowire structure, preparation process and application thereof
Technical Field
The invention relates to the technical field of semiconductor nano material preparation, in particular to a gas-sensitive nano material based on a single-layer ordered tin oxide nano bowl branched zinc oxide nanowire structure, a preparation process and application thereof.
Background
In recent years, gas sensors capable of monitoring various toxic, harmful, flammable and explosive gases, with high sensitivity and high selectivity, have become an urgent need for public health and environmental monitoring. The common product hydrogen sulfide in industrial production is one of dangerous harmful gases, which has great harm to human body, and trace amount of hydrogen sulfide can destroy respiratory system of human body, causing involuntary nerve sequelae and cardiovascular related diseases. In view of this, it is of great significance to effectively monitor the hydrogen sulfide content in the surrounding living environment. To date, various chemical sensors based on different mechanisms for detecting trace amounts of hydrogen sulfide have been widely researched and developed, including chemiresistive sensors, electrochemical sensors, and optical sensors. The chemical resistance type gas sensor based on the semiconductor metal oxide material has the irreplaceable advantages of low cost, convenient manufacture, good integrated circuit compatibility and the like, and has attracted great research interest.
Among various semiconductor metal oxide materials, n-type semiconductor tin oxide has the advantages of high carrier mobility, high stability, low cost and the like, and is a promising candidate material for a high-performance gas sensor. In order to improve the performance of the tin oxide-based gas sensor, a great deal of research has been focused on the design and fabrication of different nanostructures having a large specific surface area, such as nanoparticles, nanowires, nanoflowers, and the like. However, these nanomaterials are typically printed or drop-coated onto ceramic tubes or micro-electromechanical systems (MEMS), greatly limiting the reliability and repeatability of the sensor. Therefore, a fabrication technology capable of seamlessly integrating the nano-sensing material and the micro-heating platform is very important for developing a high-performance gas sensor with high stability and low power consumption. The hard mask method for synthesizing the single-layer macroporous material in situ, which is developed in recent years, can better meet the requirements. The in-situ preparation process is not only suitable for wafer-level preparation, but also can effectively reduce contact resistance and further improve the performance of the device.
Gas sensors made of a single tin oxide material often have the problems of poor selectivity, long response/recovery time and the like, so methods such as noble metal doping, multilevel structure construction, composite heterostructure design and the like are provided to effectively improve the device performance. The multilevel structure construction is favorable for increasing the specific surface area of the material, and simultaneously more homogeneous/heterojunction can be formed on the interface between the parent body and the secondary nanostructure, so that the multilevel structure is widely considered as one of the gas-sensitive performance improvement methods with great prospect, and great research interest is aroused. In addition, considering the synergistic effect of different properties among different materials, the gas-sensitive property of the nano multilevel composite material with the heterostructure is superior to that of a homogeneous multilevel nanostructure.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a gas-sensitive nano material based on a single-layer ordered tin oxide nano bowl branched zinc oxide nanowire structure, a preparation process and application thereof. The invention provides a brand new synthesis route for preparing a multi-stage nano material of a single-layer ordered tin oxide nano bowl branched zinc oxide nano wire in a large scale, which specifically comprises three processes of preparing a single-layer ordered tin oxide nano bowl by a hard mask method, preparing a zinc oxide seed layer film with controllable thickness by an atomic layer deposition technology and preparing a branched zinc oxide nano wire by a hydrothermal method. The method adopts an advanced atomic layer deposition technology, accurately controls the thickness of the film at an atomic layer level, has excellent conformal covering capability, has the advantages of strong repeatability, high yield, high preparation efficiency and the like, and provides a brand new thought for large-scale preparation of the multi-level heterogeneous gas-sensitive nano material. The single-layer ordered tin oxide nanometer bowl branched zinc oxide nanowire material prepared by the invention has the characteristics of high specific surface area, high sensitivity, high selectivity and excellent stability as a gas sensitive material.
In the invention, the preparation of the single-layer ordered tin oxide nanometer bowl material adopts a hard template method with simple synthesis conditions, and the branched zinc oxide nanometer wire adopts a process of combining an atomic layer deposition technology and a hydrothermal method. The technical solution of the present invention is as follows.
A preparation process of a gas-sensitive nano material based on a single-layer ordered tin oxide nano bowl branched zinc oxide nanowire structure comprises the following specific steps:
(1) taking PS (polystyrene) balls or PMMA (polymethyl methacrylate) ball powder, ultrasonically dispersing the PS balls or PMMA balls with deionized water to prepare a dispersion liquid with the mass fraction of 1-4 wt%, and adding absolute ethyl alcohol to dilute the obtained dispersion liquid by 1-2 times;
(2) preparing a stannic chloride solution with the concentration of 0.05-0.20 mol/L;
(3) dropwise adding the dispersed solution of the PS balls or the PMMA balls diluted by the absolute ethyl alcohol prepared in the step (1) into the stannic chloride solution prepared in the step (2), and then dropwise adding a few drops of surfactant to obtain single-layer PS balls or PMMA balls floating on the surface of the precursor solution;
(4) fishing the single-layer PS balls or PMMA balls floating on the surface of the precursor solution in the step (3) by using the cleaned substrate, and putting the sample into a muffle furnace for calcination after the single-layer PS balls or PMMA balls are completely dried at room temperature or in an oven; after calcining and sintering, naturally cooling to room temperature to obtain a single-layer tin oxide nano bowl material;
(5) placing the single-layer tin oxide nanometer bowl material obtained in the step (4) into an atomic layer deposition system to deposit a zinc oxide film and provide a seed crystal layer for the branching of the subsequent nanowires;
(6) and (3) branching the zinc oxide nanowire structure of the sample prepared by the atomic layer deposition in the step (5) by a hydrothermal method, washing with deionized water after the branching, and drying to obtain the multilevel heterogeneous gas-sensitive nanomaterial of the single-layer ordered tin oxide nanometer bowl-branched zinc oxide nanowire.
In the step (3), after the surfactant (e.g., sodium dodecyl sulfate) is dropped, the densely arranged (e.g., hexagonal close-packed) single-layer ordered PS spheres or PMMA spheres floating on the surface of the tin tetrachloride solution can be obtained.
In the step (4), different substrates, such as a silicon wafer, a quartz wafer, or other substrates, may be selected as required.
In the step (4), when the drying oven is adopted for drying, the setting temperature of the drying oven is not higher than 80 ℃.
In the step (4), the calcining temperature of the muffle furnace is 450-600 ℃, and the calcining time is 1-3 h.
In the step (5), DEZ (diethyl zinc) is selected as a zinc source and deionized water is selected as an oxygen source in the process of depositing the zinc oxide film by the atomic layer, the reaction temperature is set to be 180-220 ℃, and finally the growth rate of the zinc oxide film is 0.20-0.30 nm/cycle.
In the step (5), the thickness of the atomic layer deposition zinc oxide film is 10-30 nm.
In the step (6), the precursor for hydrothermal growth is a mixed solution of zinc nitrate and HMT (hexamethylenetetramine) in an equal molar ratio of 10-50 mmol/L, the growth temperature is 60-80 ℃, and the growth time is 3-8 hours.
The invention also provides a gas-sensitive nano material based on the single-layer ordered tin oxide nano bowl branched zinc oxide nano wire structure prepared by the preparation process. The average pore diameter of the gas-sensitive nano material with the single-layer ordered tin oxide nano bowl branched zinc oxide nanowire structure is determined by the diameter of a PS ball or a PMMA ball of a hard template, and the average diameter of the branched nanowire is about 10-200 nm.
The invention further provides an application of the gas-sensitive nano material based on the single-layer ordered tin oxide nano bowl branched zinc oxide nanowire structure in the aspect of selectively detecting hydrogen sulfide gas; the concentration of hydrogen sulfide can be as low as 1ppm to 3 ppm.
Compared with the prior art, the invention has the beneficial effects that:
1. the multistage nano structure based on the heterojunction is constructed, compared with a single tin oxide structure, the sensitivity is greatly improved when the multistage nano structure is applied to gas sensing, the response time and the recovery time are greatly shortened, and more excellent gas-sensitive performance is shown.
2. Compared with a thin film structure, the single-layer ordered nano bowl structure effectively increases the specific surface area of the material, and the branched nano line structure further increases the specific surface area, so that the gas-sensitive performance of the material can be effectively improved.
3. The multi-stage heterogeneous gas-sensitive nano material with the single-layer ordered tin oxide nano bowl branched zinc oxide nanowire structure can realize ultra-sensitive and high-selectivity detection on 1 ppm-stage trace hydrogen sulfide; meanwhile, the sensor responds to other gases, can detect the organic volatile gas at a relatively high concentration (such as 10 ppm), and provides a solid technical support for developing a gas sensor with high sensitivity and high stability in the field of gas monitoring.
4. The preparation process combines the atomic layer deposition technology, the hydrothermal method and the hard template method with simple synthesis conditions, can realize large-scale preparation on various substrates, and has the advantages of strong repeatability, high yield, high preparation efficiency, suitability for large-scale preparation, compatibility with silicon substrates and the like compared with the traditional preparation process.
Drawings
FIG. 1 is a flow diagram of a preparation process of a multi-stage heterogeneous gas-sensitive nano material based on a single-layer ordered tin oxide nano bowl branched zinc oxide nanowire structure.
FIG. 2 is an SEM representation of the monolayer ordered tin oxide nanobowl obtained in example 1.
FIG. 3 is an SEM representation of the single-layer ordered tin oxide nano-bowl branched zinc oxide nanowire obtained in example 1.
FIG. 4 is a TEM representation of the single-layer ordered tin oxide nano-bowl branched zinc oxide nanowire obtained in example 1.
Fig. 5 is a diagram showing the results of gas-sensitive performance tests of trace hydrogen sulfide for two devices, namely the single-layer ordered tin oxide nanometer bowl and the single-layer ordered tin oxide nanometer bowl branched zinc oxide nanometer wire obtained in example 1.
FIG. 6 shows five types of reducing gases (hydrogen sulfide (H) in two devices, namely the single-layer ordered tin oxide nano-bowl and the single-layer ordered tin oxide nano-bowl branched zinc oxide nano-wire obtained in example 12S), ammonia (NH)3) Acetone (CH)3OCH3) Toluene (C)7H8) And formaldehyde (HCHO)) are shown.
FIG. 7 is an SEM representation of the single-layer ordered tin oxide nano-bowl branched zinc oxide nanowire obtained in example 2.
Detailed Description
The invention is described in further detail below with reference to the figures and examples.
The flow block diagram of the preparation process of the multilevel heterogeneous gas-sensitive nano material based on the single-layer ordered tin oxide nano bowl branched zinc oxide nano wire structure is shown in figure 1.
Example 1
(1) Taking PS ball (with the average diameter of 800 nm) dispersion liquid with the mass fraction of 2 wt%, and adding absolute ethyl alcohol to dilute by 1 time;
(2) preparing a stannic chloride solution with the concentration of 0.15 mol/L;
(3) dropwise adding 0.15 mol/L stannic chloride solution into PS sphere dispersion liquid diluted by absolute ethyl alcohol, and then adding 1 drop of surfactant lauryl sodium sulfate to obtain a single-layer PS sphere floating on the surface of the stannic chloride solution;
(4) directly taking the MEMS micro-heater as a substrate, fishing out the single-layer PS ball in situ, and calcining the sample in a muffle furnace for 2 hours at 500 ℃ after the sample is completely dried at room temperature; after calcining and sintering, naturally cooling to room temperature to obtain the single-layer ordered tin oxide nano bowl MP-SnO2The SEM representation is shown in FIG. 2, which shows that the single-layer tin oxide bowl-packed nano structure with close-packed ordered arrangement is visible, and the diameter of the nano bowl is about 700 nm;
(5) putting the sample obtained in the step (4) into an atomic layer deposition system, depositing a zinc oxide film with the thickness of 20 nm on the surface of the single-layer ordered tin oxide nano bowl, carrying out hydrothermal treatment at the temperature of 80 ℃ for 5 hours to branch the zinc oxide nanowire, wherein hydrothermal precursors are 25 mmol/L zinc nitrate and 25 mmol/L hexamethylenetetramine, washing with deionized water after the hydrothermal treatment is finished, and drying to obtain the single-layer ordered tin oxide nano bowl branched zinc oxide nanowire MP-SnO2@ ZnO NWs, whose SEM and TEM images are shown in FIGS. 3 and 4, respectively, it can be seen that zinc oxide nanowires were crystallized on the ordered single-layer tin oxide nanobowls, and that the branched zinc oxide nanowires had an average length of about 340 nm and a diameter of about 30 nm.
In the embodiment, the single-layer ordered tin oxide nanometer bowl branched zinc oxide nanowire MP-SnO obtained by separation and utilization2@ ZnO NWs and single-layer ordered tin oxide nano bowl MP-SnO2And carrying out a gas sensing test on 1-3 ppm of hydrogen sulfide gas.
The test results were as follows: for 1ppm of hydrogen sulfide gas, MP-SnO2Response value of @ ZnO NWs (defined as R)a/RgWherein R isaIs resistance in air, RgResistance in gas to be measured) of 6.24, and MP-SnO2The sensitivity of (a) is 3.03, and the result shows that the branched nanowire structure of the invention improves the sensing sensitivity of 1ppm hydrogen sulfide gas by more than 2 times, and improves the sensitivity of hydrogen sulfide gas at other concentrations to different degrees (as shown in fig. 5).
In addition, for the obtained MP-SnO2The selectivity test was carried out with @ ZnO NWs, i.e., the gas-sensitive sensing test was carried out for hydrogen sulfide, ammonia, acetone, toluene and formaldehyde at the same concentrations (1 ppm), respectively. As shown in figure 6, the single-layer ordered tin oxide nanometer bowl branched zinc oxide nanowire MP-SnO of the invention2@ ZnO NWs exhibits extremely excellent selectivity for hydrogen sulfide gas.
Example 2
Similar to example 1, except that the hydrothermal growth time was 3 hours when branching zinc oxide nanowires. An SEM representation picture of the obtained single-layer ordered tin oxide nanometer bowl-branched zinc oxide nanowire is shown in figure 7, the average length of the branched zinc oxide nanowire is about 300 nm, the diameter of the branched zinc oxide nanowire is about 32 nm, and it is known that when the hydrothermal growth time of the branched zinc oxide nanowire is reduced compared with that of example 1, the average length of the branched zinc oxide nanowire is correspondingly shortened.
The embodiments of the present invention have been described in detail in the above examples, but the present invention is not limited to the specific details in the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.