A method for cold plasma modulation of surface defects and phase states of indium oxide

Abstract

This invention relates to a method for controlling surface defects and phase states of indium oxide (IoA) using cold plasma. The production method primarily involves placing the IoA precursor, indium hydroxide, in a dielectric barrier discharge plasma reactor. Subsequently, a gas is introduced, and a high-voltage electric discharge is applied to break down the gas, generating plasma. The high-energy electrons in the plasma cause the indium hydroxide to decompose, forming IoA of different phase states, while simultaneously allowing oxygen atoms in the IoA lattice to escape, thus creating oxygen defects on the IoA surface. This method is simple to operate, operates under mild conditions, is quick, consumes little energy, and is environmentally friendly, showing promising application prospects in the field of materials science.

Description

Technical Field

[0001] This invention belongs to the field of indium oxide materials, specifically, it relates to a method for controlling surface defects and phase states of indium oxide using cold plasma. Background Technology

[0002] Indium oxide (IO) is an n-type semiconductor functional material with a wide bandgap, low resistivity, and good gas sensitivity, and it has been widely used in optoelectronics and gas sensor materials. The two most common phases of IO are the stable cubic ferromanganese oxide structure and the metastable hexagonal corundum structure.

[0003] Common methods for synthesizing indium oxide include indium hydroxide decomposition, nitrate decomposition, sol-gel method, carbonic acid decomposition, and chemical vapor deposition. While these methods yield indium oxides with diverse morphologies and sizes, they do not effectively control the indium oxide structure. Recently, defective indium oxides have shown high methanol selectivity in the thermocatalytic hydrogenation of carbon dioxide to methanol, and oxygen vacancies, as important active sites for this reaction, have been extensively studied. Traditional methods for synthesizing indium oxide cannot easily and rapidly control oxygen vacancies. Generally, the synthesis of hexagonal indium oxide requires high temperature and pressure conditions, making the synthesis difficult and energy-intensive.

[0004] Numerous reports exist on introducing defects into metal oxides, but reports on controlling surface defects in indium oxide (IoO) are scarce. Examples include CN110534346A, CN107768663A, CN114464807A, and CN115385387A. However, these defect-introducing methods typically require high-temperature calcination or prolonged hydrothermal treatment, which is not only time-consuming and energy-intensive but also makes rapid and effective defect control difficult. Furthermore, reports on phase control of IoO are rare. Currently, there are no reports on controlling surface defects and phase states of IoO using cold plasma.

[0005] The cold plasma method designed in this invention differs from these traditional methods. Although it still obtains indium oxide from the decomposition of indium hydroxide, it does not require high-temperature heating. Instead, it generates a large number of high-energy particles and electrons through gas discharge, exciting electrons and molecules on the sample surface between electrodes, thereby achieving sample decomposition. This invention relates to a method for controlling surface defects and phase states of indium oxide using cold plasma. While achieving sample decomposition, it also allows for the control of oxygen defects and phase states of the product by adjusting the processing time and power. This method has advantages such as high efficiency, simple operation, economic feasibility, and environmental friendliness. Summary of the Invention

[0006] This invention provides a method for cold plasma modulation of surface defects and phase states of indium oxide, so as to achieve precise control of oxygen defects and phase states on the surface of indium oxide under mild conditions, thereby solving the problems of complex processes, long time, poor accuracy, poor controllability and high energy consumption in the prior art.

[0007] This invention provides a method for cold plasma modulation of surface defects and phase states of indium oxide, comprising the following steps:

[0008] Step 1: Place indium hydroxide in a plasma reactor;

[0009] Step 2: Place the reaction vessel between the two electrodes of the plasma generator;

[0010] Step 3: Introduce plasma generating gas from one end of the reactor;

[0011] Step 4: Adjust the voltage and current of the plasma generator to produce high voltage on the working electrode, which breaks down the dielectric gas and generates plasma, which acts on indium hydroxide for 10-60 min. The treatment time is further preferably 10-45 min.

[0012] Preferably, in step 4, the discharge power of the plasma generator is adjustable within a range of 100–2000 V·A. More preferably, in step 4, the operating voltage of the plasma generator is adjustable within a range of 100–500 V; and the operating current is adjustable within a range of 1–4 A.

[0013] In any of the above-mentioned preferred embodiments, in step 1, the indium hydroxide is prepared by precipitation using indium nitrate as a precursor. Experimental verification by this invention shows that indium hydroxide prepared by precipitation using indium nitrate as a precursor is more advantageous for obtaining indium oxide products with different defect concentrations and phases using the technical solution of this invention.

[0014] Preferably, in step 1, the plasma reactor is a plate-type or tubular reactor.

[0015] In any of the above-mentioned preferred embodiments, in step 2, the plasma generating device is a dielectric barrier discharge device.

[0016] In any of the above-mentioned preferred embodiments, in step 3, the plasma generating gas is either air or argon.

[0017] In any of the above-mentioned preferred embodiments, in step 3, the operating temperature is room temperature and the operating pressure is atmospheric pressure.

[0018] The technical solution of this invention is as follows:

[0019] A method for cold plasma modulation of surface defects and phase states of indium oxide is characterized by comprising the following steps:

[0020] (1) Indium hydroxide is placed in a plasma reactor;

[0021] (2) Place the reaction vessel between the two electrodes of the plasma generator;

[0022] (3) Introduce plasma generating gas from one end of the reactor;

[0023] (4) The discharge power of the plasma generator is adjustable from 100 to 2000 V·A. It generates high voltage on the working electrode, breaks down the medium gas, generates plasma, and acts on indium hydroxide for 10-45 min to obtain indium oxide products with different defect concentrations and phases.

[0024] This invention controls the defect concentration and phase state of the obtained indium oxide product by controlling the discharge power and action time of the plasma generator in step 4:

[0025] The phase state of the obtained indium oxide product is controlled by the discharge power (voltage-current (V·A)). A discharge power of 100-500 V·A yields a hexagonal indium oxide product; a discharge power of 1200-2000 V·A yields a cubic indium oxide product; and a discharge power greater than 500 V·A and less than 1200 V·A yields a mixture of cubic and hexagonal indium oxide products. When the indium oxide product with surface oxygen defects obtained by this invention is applied to the thermocatalytic reaction of CO2 hydrogenation to methanol, the cubic indium oxide product exhibits better catalytic performance in the CO2 hydrogenation to methanol reaction.

[0026] The discharge time, or reaction time, controls the concentration of oxygen defects on the surface of the obtained indium oxide product. After 15 minutes of discharge, the oxygen defect concentration on the surface of the indium oxide product exceeds 51%. Compared with the indium oxide obtained by existing methods, the indium oxide obtained by this invention has a significantly higher surface oxygen defect concentration. When applied to the thermocatalytic reaction of CO2 hydrogenation to methanol, its catalytic effect is significantly improved.

[0027] The significantly improved catalytic effect of this invention is mainly reflected in higher CO2 conversion rate and higher methanol selectivity.

[0028] Furthermore, the indium hydroxide mentioned in step (1) is prepared by precipitation method using indium nitrate as a precursor.

[0029] The preferred steps for preparing indium hydroxide using indium nitrate as a precursor via precipitation are as follows:

[0030] In(NO3)3•4H2O was dissolved in deionized water to form a 0.186 M In(NO3)3 solution. Na2CO3 solution was added dropwise to the In(NO3)3 solution with continuous stirring at 80 °C until the pH reached 7. After stirring for 3 h, the solution was cooled to room temperature. The precipitate was collected and washed several times with deionized water. After centrifugation, the precipitate was dried overnight in an oven at 60 °C. The product was then ground into powder to obtain In(OH)3 (precipitation method reference: JOURNAL OF ENERGY CHEMISTRY, 2021, 50, 409-415).

[0031] Furthermore, the plasma reactor described in step (1) is a plate-type or tubular reactor.

[0032] Furthermore, the plasma generating device mentioned in step (2) is a dielectric barrier discharge device.

[0033] Furthermore, the plasma generating gas mentioned in step (3) is argon or a gas in the air.

[0034] Furthermore, the operating temperature and operating pressure mentioned in step (3) are ambient temperature and ambient pressure, respectively.

[0035] The advantages and beneficial effects of this invention are:

[0036] 1. In this invention, cold plasma is used to control the surface defects and phase state of indium oxide, realizing the direct decomposition of indium hydroxide into indium oxide. Compared with other methods in the prior art, the processing time is shortened from 3 hours to less than 1 hour, which is more efficient and easier to operate.

[0037] 2. In this invention, the process does not introduce other chemical reagents and does not require high-temperature heating. The operating conditions are mild, and compared with other methods in the prior art, it achieves environmental friendliness and economic feasibility.

[0038] 3. In this invention, indium oxide with different concentrations of oxygen defects can be obtained by adjusting the processing time, which is highly controllable.

[0039] 4. In this invention, different phases of indium oxide can be obtained by adjusting the processing power, thus achieving control of the phase state of indium oxide under mild conditions.

[0040] 5. In this invention, the cubic indium oxide material with abundant oxygen vacancies prepared by cold plasma can effectively activate CO2 and exhibit high methanol selectivity in the thermocatalytic reaction of CO2 hydrogenation to methanol. Attached Figure Description

[0041] Figure 1X-ray powder diffraction patterns of indium oxide with different crystalline phases obtained by cold plasma decomposition of indium hydroxide;

[0042] Figure 2 Thermogravimetric curve of cubic indium oxide obtained by cold plasma decomposition of indium hydroxide;

[0043] Figure 3 The relative oxygen vacancy concentration on the surface of cubic indium oxide varies with plasma treatment time.

[0044] Figure 4 Comparison of CO2 hydrogenation reaction performance of indium hydroxide with different crystal phases and defects obtained by cold plasma decomposition. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] Figure 1 The images show X-ray powder diffraction patterns of indium oxide with different crystalline phases obtained by cold plasma decomposition of indium hydroxide, where h-In2O3-1 is the product of Example 1, h-In2O3-2 is the product of Example 2, c-In2O3-1 is the product of Example 4, and c-In2O3-2 is the product of Example 3.

[0047] Figure 2 The figure shows the thermogravimetric curve of cubic indium oxide obtained by decomposing indium hydroxide by cold plasma; the figure shows the thermogravimetric change of the indium oxide product obtained in Example 3. Examples 4-6 have similar technical effects, and the thermogravimetric changes are all about 5%.

[0048] Figure 3 To investigate the change in relative oxygen vacancy concentration on the surface of cubic indium oxide with plasma treatment time, the changes in relative oxygen vacancy concentration on the surface of cubic indium oxide with plasma treatment time were compared under discharge conditions of 0 min, 15 min (Example 3), 30 min (Example 5), and 45 min (Example 4). Figure 3 Here are the oxygen defect changes for samples 3, 4, and 5 in Examples: 15 min corresponds to Example 3, 30 min corresponds to Example 5, and 45 min corresponds to Example 4.

[0049] Figure 4 To compare the CO2 hydrogenation reaction performance of indium hydroxide with different crystal phases and defects obtained by cold plasma decomposition, h-In2O3-1 is the product of Example 1, h-In2O3-2 is the product of Example 2, c-In2O3-1 is the product of Example 4, and c-In2O3-2 is the product of Example 3.

[0050] Example 1

[0051] Indium hydroxide was placed in a plate-type plasma reactor, and argon gas was introduced as the discharge gas at room temperature. The power supply of the dielectric barrier discharge plasma generator was turned on and adjusted to 200 V·A. Discharge was performed at room temperature for 15 min. The resulting product was analyzed by XRD, TG, and XPS, yielding a hexagonal indium oxide product (h-In₂O₃⁻¹) with 51% surface oxygen defects. In the reaction of carbon dioxide hydrogenation to methanol (reaction conditions: pressure 5 MPa, total reaction gas flow rate 70 ml·min⁻¹),... -1 (H2 / CO2 = 4:1, reaction temperature 260 ℃), carbon dioxide conversion rate 6%, methanol selectivity 75%.

[0052] Example 2

[0053] Indium hydroxide was placed in a plate-type plasma reactor, and air was introduced as the discharge gas at room temperature. The power supply of the dielectric barrier discharge plasma generator was turned on and adjusted to 500 V·A. Discharge was performed at room temperature for 30 min. The resulting product was analyzed by XRD, TG, and XPS, yielding a hexagonal indium oxide product (h-In₂O₃⁻⁂) with 53% surface oxygen defects. In the reaction of carbon dioxide hydrogenation to methanol (reaction conditions: pressure 5 MPa, total reaction gas flow rate 70 ml·min⁻¹),... -1 (H2 / CO2 = 4:1, reaction temperature 260 ℃), carbon dioxide conversion rate 7.4%, methanol selectivity 84%.

[0054] Example 3

[0055] Indium hydroxide was placed in a plate-type plasma reactor, and argon gas was introduced as the discharge gas at room temperature. The power supply of the dielectric barrier discharge plasma generator was turned on and adjusted to 1200 V·A. Discharge was performed at room temperature for 15 min. The resulting product was analyzed by XRD, TG, and XPS, yielding a cubic indium oxide product (c-In₂O₃⁻⁂) with 52% surface oxygen defects. In the reaction of carbon dioxide hydrogenation to methanol (reaction conditions: pressure 5 MPa, total reaction gas flow rate 70 ml·min⁻¹),... -1 (H2 / CO2 = 4:1, reaction temperature 260 ℃), carbon dioxide conversion rate 8.6%, methanol selectivity 76%.

[0056] Example 4

[0057] Indium hydroxide was placed in a plate-type plasma reactor, and air was introduced as the discharge gas at room temperature. The power supply of the dielectric barrier discharge plasma generator was turned on and adjusted to 1200 V·A. Discharge was performed at room temperature for 45 min. The resulting product was analyzed by XRD, TG, and XPS, yielding a cubic indium oxide product (c-In₂O₃⁻¹) with 57% surface oxygen defects. In the reaction of carbon dioxide hydrogenation to methanol (reaction conditions: pressure 5 MPa, total reaction gas flow rate 70 ml·min⁻¹),... -1 (H2 / CO2 = 4:1, reaction temperature 260 ℃), carbon dioxide conversion rate 12%, methanol selectivity 77%.

[0058] Example 5

[0059] Indium hydroxide was placed in a plate-type plasma reactor, and air was introduced as the discharge gas at room temperature. The power supply of the dielectric barrier discharge plasma generator was turned on and adjusted to 1200 V·A. Discharge was performed at room temperature for 30 min. The resulting product was analyzed by XRD, TG, and XPS, yielding a cubic phase indium oxide product with 53% surface oxygen defects. In the reaction of carbon dioxide hydrogenation to methanol (reaction conditions: pressure 5 MPa, total reaction gas flow rate 70 ml·min),... -1 (H2 / CO2 = 4:1, reaction temperature 260 ℃), carbon dioxide conversion rate 9.5%, methanol selectivity 76%.

[0060] Example 6

[0061] Indium hydroxide was placed in a plate-type plasma reactor, and air was introduced as the discharge gas at room temperature. The power supply of the dielectric barrier discharge plasma generator was turned on and adjusted to 2000 V·A. Discharge was performed at room temperature for 30 min. The resulting product was analyzed by XRD, TG, and XPS, yielding a cubic phase indium oxide product with 55% surface oxygen defects. In the reaction of carbon dioxide hydrogenation to methanol (reaction conditions: pressure 5 MPa, total reaction gas flow rate 70 ml·min),... -1 (H2 / CO2 = 4:1, reaction temperature 260 ℃), carbon dioxide conversion rate 8%, methanol selectivity 75%.

[0062] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for cold plasma modulation of surface defects and phase states of indium oxide, comprising the following steps: Step 1: Place indium hydroxide in a plasma reactor; Step 2: Place the reaction vessel between the two electrodes of the plasma generator; the plasma generator is a dielectric barrier discharge device. Step 3: Introduce plasma generating gas from one end of the reactor; Step 4: Adjust the discharge power of the plasma generator to generate high voltage on the working electrode, which breaks down the dielectric gas and generates plasma, which acts on indium hydroxide for 10–60 min; control the phase state of the obtained indium oxide product by adjusting the discharge power. When the discharge power is 100–500 V·A, the obtained indium oxide product is hexagonal indium oxide; when the discharge power is 1200–2000 V·A, the obtained indium oxide product is cubic indium oxide.

2. The method as described in claim 1, characterized in that, In step 4, the discharge power of the plasma generator is adjusted within the range of 100–2000 V·A.

3. The method as described in claim 1, characterized in that, In step 1, the indium hydroxide is prepared by precipitation method using indium nitrate as a precursor.

4. The method as described in claim 1, characterized in that, In step 1, the plasma reactor is a plate-type or tubular reactor.

5. The method as described in claim 1, characterized in that, In step 3, the plasma generating gas is either air or argon.

6. The method as described in claim 1, characterized in that, In step 3, the operating temperature is room temperature and the operating pressure is atmospheric pressure.

7. The application of the method according to any one of claims 1 to 6 in the preparation of a catalyst for the thermocatalytic reaction of CO2 hydrogenation to methanol.

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