A method for preparing zinc germanate hollow microspheres with controllable size

Abstract

The present invention discloses a method for preparing zinc germanate hollow microspheres with controllable size. The method for preparing zinc germanate hollow microspheres with controllable size disclosed by the present invention includes the preparation of a solvothermal system, the preparation of a crystallization precursor solution, and the steps of crystallization and drying. The method of the present invention has simple process, mild reaction conditions, and the size of the prepared material is controllable. Compared with the zinc germanate prepared by the solid-phase synthesis method, the zinc germanate hollow microspheres prepared by the present invention exhibit more efficient catalytic activity and have high application prospects in the fields of semiconductors and photocatalysis.

Description

Technical Field

[0001] The present invention belongs to the field of material synthesis and relates to a method for preparing zinc germanate hollow microspheres with controllable size. Background Art

[0002] Energy shortage and environmental pollution are two major problems faced by human society today. The reduction of greenhouse gas carbon dioxide emissions and the development of renewable energy to replace traditional fossil energy are extremely urgent. Using photocatalytic technology to convert carbon dioxide into energy that can be utilized by humans through semiconductor catalysts has been put on the agenda. The key technology for photocatalytic reduction of carbon dioxide is to develop photocatalysts with mild conditions and simple processes.

[0003] Zinc germanate is an n-type metal oxide semiconductor material composed of germanium oxygen tetrahedrons and zinc oxygen tetrahedrons. It has many advantages such as good thermal stability and simple processing, and is an ideal electroluminescent material. Generally, it is considered that in the germanium oxygen tetrahedron structure, the germanium atom center deviates from the oxygen atom center and is distorted, which is beneficial to the separation of photo-generated electrons and holes under light illumination, has good photocatalytic performance, and can be used to treat refractory organic compounds, photocatalytic water splitting and photoreduction of carbon dioxide. At the same time, the structure of zinc germanate materials, especially the differences in microscopic morphology and microscopic size, have a significant impact on their applications in photoelectric conversion and photocatalysis.

[0004] At present, the methods for synthesizing zinc germanate materials include solid-phase synthesis method and liquid-phase synthesis method. The solid-phase synthesis method mainly forms bulk zinc germanate by uniformly mixing stoichiometric ratios of zinc oxide and germanium oxide and calcining at high temperature. The prepared zinc germanate has various morphologies and many defects. The liquid-phase synthesis method, especially the traditional hydrothermal synthesis method, is carried out by using the chemical reactions of substances in an aqueous solution under certain temperature and the self-generated pressure brought by a certain temperature. The products prepared by the traditional hydrothermal synthesis method have simple structures, which limit their applications in semiconductor and photocatalytic materials.

[0005] Finding a method for preparing zinc germanate materials with mild conditions, simple preparation and controllable size, especially preparing zinc germanate materials with special morphologies, to meet their uses in photoelectric conversion and photocatalytic conversion, etc., is the research goal of those in this field. Solvothermal reaction, as an extension of hydrothermal reaction, uses organic solvents instead of water as the reaction solvent. By controlling the reaction conditions, it can change the morphology and size of materials in low-dimensional units and synthesize materials with specific structures and morphologies under liquid-phase or supercritical conditions. There has been no report on synthesizing zinc germanate hollow microspheres with controllable size by solvothermal method. Summary of the Invention

[0006] Aiming at the problems of high energy consumption and large size in the solid-phase synthesis method and the need to add surfactants, high cost and single morphology in the liquid-phase synthesis method for the current method of synthesizing zinc germanate materials, the present invention provides a method for preparing zinc germanate hollow microspheres with controllable size.

[0007] The present invention uses a certain proportion of ethylenediamine-water system as the solvent and a small amount of alcohols as the dispersant. Zinc acetate and germanium oxide raw materials with a molar ratio of 2:1 are successively dissolved in the solvent system. By using the solvothermal method and controlling the addition amount of the alcohol dispersant and the crystallization time, zinc germanate hollow microspheres with a particle size of 5-50 μm are synthesized in one step.

[0008] Specifically, a method for preparing zinc germanate hollow microspheres with controllable size provided by the present invention includes the following steps:

[0009] (1) Preparation of the solvothermal system: Measure ethylenediamine (EN) and water with a volume ratio of more than 3:1. While stirring, drop EN into water and stir and dissolve at room temperature to form a homogeneous solution A; Measure 5-10% (for example, 5%, 6%, 7%, 8%, 9%, 10%, or any value or range between any two of these values) of the alcohol dispersant based on the sum of the volume values of ethylenediamine and water, and add it to the homogeneous solution A while stirring and dissolve at room temperature to form a homogeneous solution B;

[0010] (2) Preparation of the crystallization precursor solution: Take zinc acetate dihydrate and germanium oxide with a molar ratio of 2:1 as raw materials. Slowly add germanium oxide powder to the homogeneous solution B while stirring and dissolve at room temperature to form a homogeneous solution C; Slowly add zinc acetate dihydrate powder to the homogeneous solution C while stirring and dissolve at room temperature to form a homogeneous solution D. The homogeneous solution D is the precursor solution of the crystallization system;

[0011] (3) Crystallization and drying: Load the precursor solution into a crystallization synthesis reactor (such as a stainless-steel reactor with a polytetrafluoroethylene lining), place it in an oven, heat it from room temperature to 160-200 °C (for example, 160, 170, 180, 190, 200 °C, or any value or range between any two of these values) and keep it at a constant temperature for more than 12 h (for example, 12, 24, 48 h, or any value or range between any two of these values) for crystallization reaction. After crystallization is completed, rinse the reactor with tap water; After the reactor is cooled to room temperature, separate the product, rinse it with distilled water until neutral, and then transfer the product to an oven at 80-100 °C for drying to obtain zinc germanate hollow microspheres;

[0012] If the crystallization temperature is too low, germanium oxide in EN cannot fully participate in the reaction, and some will precipitate. If the crystallization temperature is too high, the rate of formation of zinc germanate is too fast, and it is prone to agglomeration. If the crystallization time is too short, there will basically be no products in a complete form. To form a large amount of products, the time needs to be extended. In the present invention, crystallization is carried out at 160 - 200 °C for more than 12 h;

[0013] The so-called room temperature refers to about 25 °C.

[0014] In some embodiments, in the above method, the product is separated by suction filtration or any suitable separation method known in the art.

[0015] In some embodiments, in any of the above methods, the stirring can be magnetic stirring or any suitable stirring method known in the art.

[0016] In some embodiments, in any of the above methods, in step (1), the volume ratio of ethylenediamine to water is 3:1 - 5:1, such as 3:1, 4:1, 5:1, or any value or range between any two of these values, preferably 5:1.

[0017] In some embodiments, in any of the above methods, in step (1), the volume of the alcohol dispersant is 5% of the sum of the volumes of ethylenediamine and water.

[0018] In some embodiments, in any of the above methods, in step (1), the alcohol dispersant is composed of one or more of methanol, ethanol, isopropanol, and ethylene glycol, preferably composed of ethylene glycol and ethanol, more preferably composed of ethylene glycol and ethanol with a volume ratio of 5:1 to 1:5, such as ethylene glycol and ethanol with a volume ratio of 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, or 1:5.

[0019] In some embodiments, in any of the above methods, in step (2), the particle sizes of the zinc acetate dihydrate powder and the germanium oxide powder are 75 - 100 μm.

[0020] In some embodiments, in any of the above methods, in step (2), the concentration of zinc acetate in the homogeneous solution D is 0.2 - 0.4 mol / L (such as 0.2, 0.3, 0.4 mol / L, or any value or range between any two of these values), and the concentration of germanium oxide in the homogeneous solution D is 0.1 - 0.2 mol / L (such as 0.1, 0.2 mol / L, or any value or range between any two of these values);

[0021] If the concentration of the reactants is too high, part of the reactant germanium oxide cannot be completely dissolved in the EN solvent and will become impurities in the product.

[0022] In some embodiments, in any of the above-mentioned methods, in step (2), the concentration of zinc acetate in homogeneous solution D is 0.2 mol / L, and the concentration of germanium oxide in homogeneous solution D is 0.1 mol / L

[0023] In some embodiments, in any of the above-mentioned methods, in step (3), the crystallization temperature is 160 °C and the crystallization time is 24 h.

[0024] In some embodiments, in any of the above-mentioned methods, the particle size of the zinc germanate hollow microspheres is 5 - 50 μm, such as 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 μm.

[0025] The present invention also provides zinc germanate hollow microspheres prepared by any of the above-mentioned methods.

[0026] The present invention adopts a solvothermal synthesis method, utilizes the dispersion effect of alcohol solvents on germanium sources and zinc sources in the synthesis solution, regulates the formation of zinc germanate crystal seeds and the anisotropic growth process, and synthesizes zinc germanate hollow microspheres with controllable particle sizes in one step by changing the ratio of the ethylene glycol and ethanol mixed solution and the crystallization time of the zinc germanate precursor solution.

[0027] The beneficial effects of the present invention are as follows:

[0028] The solvothermal preparation method adopted by the present invention has simple process, mild reaction conditions, and controllable size of the prepared materials. The alcohol solvents used as dispersants are cheap and easily available, and have the potential for large-scale production;

[0029] The zinc germanate hollow microspheres with controllable particle sizes prepared by the present invention have a hollow spherical structure and adjustable particle size, meeting the special requirements of zinc germanate for the size and morphology of semiconductor materials in photoelectric conversion and photocatalytic conversion, and are expected to be applied as luminescent materials and photocatalytic materials;

[0030] The zinc germanate hollow microspheres prepared by the present invention are subjected to a photocatalytic reduction of CO2 experiment with zinc germanate prepared by a solid-phase synthesis method. The prepared microspheres with controllable sizes show more efficient catalytic activity and have high application prospects in the fields of semiconductors and photocatalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the XRD pattern of the zinc germanate prepared in the present invention; among them, 5 - 50 μm represents the zinc germanate hollow microspheres with different particle sizes prepared in the examples, and bulk represents the solid zinc germanate prepared in Comparative Example 1 using the traditional solid-phase synthesis reaction method (SSR).

[0032] Figure 2SEM images of zinc germanate hollow microspheres with different particle sizes prepared in the embodiments of the present invention.

[0033] Figure 3 Schematic diagram of the Labsolar-H2 type photocatalytic CO2 reduction reaction device.

[0034] Figure 4 Using the Labsolar-H2 type photocatalytic reaction system to evaluate the yield of photocatalytic reduction of CO2 to CH4 by the zinc germanate prepared in the present invention.

[0035] Figure 5 XRD patterns of the products prepared in Comparative Examples 1-10 of the present invention.

[0036] Figure 6 SEM images of the products prepared in Comparative Examples 1-10 of the present invention. Detailed implementation manners

[0037] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0038] Unless otherwise specified, the materials, reagents, etc. used in the following examples can all be obtained from commercial channels.

[0039] The following further illustrates the present invention in conjunction with specific examples. It should be understood that the following examples are only used to illustrate the present invention and not to limit the scope of the present invention.

[0040] The endpoints and any values in the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0041] In the following examples, room temperature refers to 25 °C.

[0042] Example 1

[0043] 1. Preparation of zinc germanate hollow microspheres

[0044] (1) Preparation of the solvothermal system: Measure ethylenediamine (EN) and water with a volume ratio of 5:1. While stirring magnetically, add EN dropwise to water and stir at room temperature for 30 min until fully dissolved to form a homogeneous solution A; Measure a mixed solution of ethylene glycol and ethanol with a volume of 5% of the sum of the volume values of ethylenediamine and water as the alcohol dispersant (the volume ratio of ethylene glycol to ethanol is 5:1), and add it to the homogeneous solution A while stirring magnetically, and stir at room temperature for 30 min until fully dissolved to form a homogeneous solution B.

[0045] (2) Preparation of the crystallization precursor solution: Take zinc acetate dihydrate and germanium oxide with a molar ratio of 2:1 as raw materials. Among them, zinc acetate is used as the zinc source and germanium oxide is used as the germanium source. They are respectively ground into fine powders with a particle size of 75 - 100 μm for standby. The ground germanium oxide powder is slowly added to the homogeneous solution B under magnetic stirring, and stirred at room temperature for 30 min until it is fully dissolved to form a homogeneous solution C. The ground zinc acetate dihydrate powder is slowly added to the homogeneous solution C under magnetic stirring, and stirred at room temperature for 60 min until it is fully dissolved to form a homogeneous solution D. The homogeneous solution D is the precursor solution of the crystallization system. The concentration of zinc acetate in the homogeneous solution D is 0.2 mol / L, and the concentration of germanium oxide in the homogeneous solution D is 0.1 mol / L.

[0046] (3) Crystallization and drying: The precursor solution is filled into a stainless - steel autoclave with a polytetrafluoroethylene lining and placed in an oven. It is heated from room temperature to 160 °C and kept at a constant temperature for 24 h for the crystallization reaction. Then, the autoclave is rinsed with tap water. After the autoclave is cooled to room temperature, the product is separated using a suction flask and repeatedly rinsed with distilled water until it is neutral. Then, the product is transferred to an 80 °C oven for drying to obtain zinc germanate hollow microspheres.

[0047] Specific experimental conditions can also be seen in Table 1.

[0048] Figure 1 Among them, the XRD pattern marked with 5 μm is the XRD pattern of the sample prepared in this example. From the positions of the characteristic peaks of the crystal phase structure of this figure, it can be seen that the prepared product is zinc germanate.

[0049] Figure 2 Among them, the photo marked with 5 μm is the SEM photo of the zinc germanate sample prepared in this example. From this figure, it can be seen that the prepared zinc germanate is a hollow microsphere structure. By measuring the sample using the scale in the figure, its particle size is about 5 μm.

[0050] 2. Photocatalytic reaction evaluation

[0051] Use the Labsolar - H2 type photocatalytic reaction system to evaluate the yield of photocatalytic reduction of CO2 to CH4 of the prepared material. The schematic diagram of the Labsolar - H2 type photocatalytic CO2 reduction reaction device is as Figure 3 shown. The specific steps are as follows:

[0052] (1) Place the prepared sample into the reactor, connect it to the system, and adjust the cooling water flow rate. Inject the reactants CO2 - water vapor into the system through the stopcock at the bottom of the reactor connecting to the CO2 - water vapor generating device (first, CO2 in the steel cylinder is injected into the 25°C constant temperature water vapor generating device filled with distilled water through a pressure reducing valve, and then the water vapor generating device is connected to the gas phase reactor). After the injection is completed, discharge the excess carbon dioxide from the system to keep the system pressure balanced with the atmospheric pressure (the vacuum gauge shows 0).

[0053] (2) Turn on the high - speed gas circulation device to make the gas circulation rate in the reaction system reach the maximum.

[0054] (3) Collect the samples. Connect the six - way valve to the sampling panel, evenly disperse the gas - phase products through the high - speed gas circulation device, and then automatically collect the samples in the system through the quantitative tube (1 mL) at fixed time intervals (1 h).

[0055] (4) Detect the samples. Blow the gas - phase components in the quantitative tube into the gas chromatograph through the back - flushing system, continuously enter the thermal conductivity detector and the hydrogen flame detector, measure the gas - phase products of the photocatalytic reaction, and use the internal standard method to calculate the content of the photocatalytic reaction products through the chromatographic software.

[0056] (5) After the experiment is over, first turn off the Xe lamp light source, then open the vent valve to balance the air pressure inside and outside the system, and at the same time stop the magnetron air pump and the circulating water; turn off the automatic sampling and back - flushing systems. When the temperatures of the chromatographic column oven and the conversion furnace are lower than 80°C, turn off the chromatograph and the carrier gas.

[0057] Figure 4 Among them, the curve marked with 5 μm represents the cumulative yield of CH4, the photocatalytic reaction product of the sample prepared in this example.

[0058] Example 2

[0059] 1. Preparation of zinc germanate hollow microspheres

[0060] Repeat step 1 of Example 1, with the only difference being that in step (1), in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 4:1.

[0061] Specific experimental conditions can also be seen in Table 1.

[0062] Figure 1 Among them, the spectrogram marked with 10 μm is the XRD pattern of the sample prepared in this example. From the positions of the characteristic peaks of the crystal phase structure of this figure, it can be known that the prepared product is zinc germanate.

[0063] Figure 2Among them, the SEM photograph of the zinc germanate sample prepared in this example is marked with 10 μm. It can be seen from this figure that the prepared zinc germanate is a hollow microsphere structure. By measuring the sample with the scale in the figure, its particle size is about 10 μm.

[0064] 2. Photocatalytic reaction evaluation

[0065] Repeat step 2 of Example 1, with the only difference being that the sample is replaced with the sample prepared in this example to evaluate the yield of photocatalytic reduction of CO2 to produce CH4 by the prepared material.

[0066] Figure 4 Among them, the curve marked with 10 μm represents the cumulative yield of the photocatalytic reaction product CH4 of the sample prepared in this example.

[0067] Example 3

[0068] 1. Preparation of zinc germanate hollow microspheres

[0069] Repeat step 1 of Example 1, with the only difference being that in step (1), in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 3:1.

[0070] The specific experimental conditions can also be seen in Table 1.

[0071] Figure 1 Among them, the spectrogram marked with 15 μm is the XRD pattern of the sample prepared in this example. From the positions of the characteristic peaks of the crystal phase structure of this figure, the prepared product is zinc germanate.

[0072] Figure 2 Among them, the SEM photograph of the zinc germanate sample prepared in this example is marked with 15 μm. It can be seen from this figure that the prepared zinc germanate is a hollow microsphere structure. By measuring the sample with the scale in the figure, its particle size is about 15 μm.

[0073] 2. Photocatalytic reaction evaluation

[0074] Repeat step 2 of Example 1, with the only difference being that the sample is replaced with the sample prepared in this example to evaluate the yield of photocatalytic reduction of CO2 to produce CH4 by the prepared material.

[0075] Figure 4 Among them, the curve marked with 15 μm represents the cumulative yield of the photocatalytic reaction product CH4 of the sample prepared in this example.

[0076] Example 4

[0077] 1. Preparation of zinc germanate hollow microspheres

[0078] Repeat step 1 of Example 1, with the only difference being that in step (1), in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 2:1.

[0079] The specific experimental conditions can also be seen in Table 1.

[0080] Figure 1 In, the spectrogram marked with 20μm is the XRD spectrogram of the sample prepared in this example. From the positions of the characteristic peaks of the crystal phase structure of this figure, it can be known that the prepared product is zinc germanate.

[0081] Figure 2 In, the photo marked with 20μm is the SEM photo of the zinc germanate sample prepared in this example. From this figure, it can be known that the prepared zinc germanate is a hollow microsphere structure; by measuring the sample with the scale marked in the figure, its particle size is about 20μm.

[0082] 2. Photocatalytic reaction evaluation

[0083] Repeat step 2 of Example 1, with the only difference being that the sample is replaced with the sample prepared in this example to evaluate the yield of photocatalytic reduction of CO2 to produce CH4 of the prepared material.

[0084] Figure 4 In, the curve marked with 20μm represents the cumulative yield of the photocatalytic reaction product CH4 of the sample prepared in this example.

[0085] Example 5

[0086] 1. Preparation of zinc germanate hollow microspheres

[0087] Repeat step 1 of Example 1, with the only difference being that in step (1), in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 1:1.

[0088] The specific experimental conditions can also be seen in Table 1.

[0089] Figure 1 In, the spectrogram marked with 25μm is the XRD spectrogram of the sample prepared in this example. From the positions of the characteristic peaks of the crystal phase structure of this figure, it can be known that the prepared product is zinc germanate.

[0090] Figure 2 In, the photo marked with 25μm is the SEM photo of the zinc germanate sample prepared in this example. From this figure, it can be known that the prepared zinc germanate is a hollow microsphere structure; by measuring the sample with the scale marked in the figure, its particle size is about 25μm.

[0091] 2. Photocatalytic reaction evaluation

[0092] Repeat step 2 of Example 1, with the only difference being that the sample is replaced with the sample prepared in this example to evaluate the yield of photocatalytic reduction of CO2 to produce CH4 of the prepared material.

[0093] Figure 4Among them, the curve marked with 25 μm represents the cumulative yield of the photocatalytic reaction product CH4 of the sample prepared in this example.

[0094] Example 6

[0095] 1. Preparation of zinc germanate hollow microspheres

[0096] Repeat step 1 of Example 1, with the only difference being that in step (1), in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 1:2.

[0097] Specific experimental conditions can also be seen in Table 1.

[0098] Figure 1 Among them, the spectrogram marked with 30 μm is the XRD spectrogram of the sample prepared in this example. From the positions of the characteristic peaks of the crystal phase structure of this spectrogram, it can be seen that the prepared product is zinc germanate.

[0099] Figure 2 Among them, the photo marked with 30 μm is the SEM photo of the zinc germanate sample prepared in this example. From this photo, it can be seen that the prepared zinc germanate is a hollow microsphere structure; by measuring the sample with the scale marked in the figure, its particle size is about 30 μm.

[0100] 2. Photocatalytic reaction evaluation

[0101] Repeat step 2 of Example 1, with the only difference being that the sample is replaced with the sample prepared in this example to evaluate the yield of photocatalytic reduction of CO2 to CH4 of the prepared material.

[0102] Figure 4 Among them, the curve marked with 30 μm represents the cumulative yield of the photocatalytic reaction product CH4 of the sample prepared in this example.

[0103] Example 7

[0104] 1. Preparation of zinc germanate hollow microspheres

[0105] Repeat step 1 of Example 1, with the only difference being that in step (1), in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 1:3; in step (3), the constant temperature time in the oven at 160 °C is 12 h.

[0106] Specific experimental conditions can also be seen in Table 1.

[0107] Figure 1 Among them, the spectrogram marked with 35 μm is the XRD spectrogram of the sample prepared in this example. From the positions of the characteristic peaks of the crystal phase structure of this spectrogram, it can be seen that the prepared product is zinc germanate.

[0108] Figure 2Among them, the SEM photograph marked with 35 μm is the SEM photograph of the zinc germanate sample prepared in this example. It can be seen from this figure that the prepared zinc germanate is a hollow microsphere structure; by measuring the sample with the scale in the figure, its particle size is about 35 μm.

[0109] 2. Photocatalytic reaction evaluation

[0110] Repeat step 2 of Example 1, with the only difference being that the sample is replaced with the sample prepared in this example to evaluate the yield of photocatalytic reduction of CO2 to produce CH4 of the prepared material.

[0111] Figure 4 Among them, the curve marked with 35 μm represents the cumulative yield of the photocatalytic reaction product CH4 of the sample prepared in this example.

[0112] Example 8

[0113] 1. Preparation of zinc germanate hollow microspheres

[0114] Repeat step 1 of Example 1, with the only difference being that in step (1), in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 1:4; in step (3), the oven temperature is 200 °C.

[0115] The specific experimental conditions can also be seen in Table 1.

[0116] Figure 1 Among them, the spectrogram marked with 40 μm is the XRD pattern of the sample prepared in this example. It can be known from the positions of the characteristic peaks of the crystal phase structure of this figure that the prepared product is zinc germanate.

[0117] Figure 2 Among them, the photograph marked with 40 μm is the SEM photograph of the zinc germanate sample prepared in this example. It can be seen from this figure that the prepared zinc germanate is a hollow microsphere structure; by measuring the sample with the scale in the figure, its particle size is about 40 μm.

[0118] 2. Photocatalytic reaction evaluation

[0119] Repeat step 2 of Example 1, with the only difference being that the sample is replaced with the sample prepared in this example to evaluate the yield of photocatalytic reduction of CO2 to produce CH4 of the prepared material.

[0120] Figure 4 Among them, the curve marked with 40 μm represents the cumulative yield of the photocatalytic reaction product CH4 of the sample prepared in this example.

[0121] Example 9

[0122] 1. Preparation of zinc germanate hollow microspheres

[0123] Repeat step 1 of Example 1, with the only difference being that in step (1), the volume ratio of ethylenediamine to water is 3:1, and in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 1:5.

[0124] The specific experimental conditions can also be seen in Table 1.

[0125] Figure 1 Among them, the spectrogram marked with 45μm is the XRD spectrogram of the sample prepared in this example. From the positions of the characteristic peaks of the crystal phase structure in this figure, it can be known that the prepared product is zinc germanate.

[0126] Figure 2 Among them, the photo marked with 45μm is the SEM photo of the zinc germanate sample prepared in this example. From this figure, it can be known that the prepared zinc germanate is a hollow microsphere structure; by measuring the sample with the scale in the figure, its particle size is about 45μm.

[0127] 2. Photocatalytic reaction evaluation

[0128] Repeat step 2 of Example 1, with the only difference being that the sample is replaced with the sample prepared in this example to evaluate the yield of photocatalytic reduction of CO2 to CH4 of the prepared material.

[0129] Figure 4 Among them, the curve marked with 45μm represents the cumulative yield of the photocatalytic reaction product CH4 of the sample prepared in this example.

[0130] Example 10

[0131] 1. Preparation of zinc germanate hollow microspheres

[0132] Repeat step 1 of Example 1, with the only difference being that in step (1), in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 1:5, and the addition amount of the alcohol dispersant is 10% of the sum of the volume values of ethylenediamine and water; in step (2), the concentration of zinc acetate in the homogeneous solution D is 0.4mol / L, and the concentration of germanium oxide in the homogeneous solution D is 0.2mol / L; in step (3), the constant temperature time of the oven at 160°C is 48h.

[0133] The specific experimental conditions can also be seen in Table 1.

[0134] Figure 1 Among them, the spectrogram marked with 50μm is the XRD spectrogram of the sample prepared in this example. From the positions of the characteristic peaks of the crystal phase structure in this figure, it can be known that the prepared product is zinc germanate.

[0135] Figure 2 Among them, the photo marked with 50μm is the SEM photo of the zinc germanate sample prepared in this example. From this figure, it can be known that the prepared zinc germanate is a hollow microsphere structure; by measuring the sample with the scale in the figure, its particle size is about 50μm.

[0136] 2. Photocatalytic reaction evaluation

[0137] Repeat step 2 of Example 1, except that: replace the sample with the sample prepared in this example to evaluate the yield of photocatalytic reduction of CO2 to CH4 by the prepared material.

[0138] Figure 4 In, the curve marked with 50 μm represents the cumulative yield of the photocatalytic reaction product CH4 of the sample prepared in this example.

[0139] Comparative Example 1

[0140] 1. Preparation of zinc germanate

[0141] Prepare solid zinc germanate by solid-state synthesis method (SSR). The specific process is as follows: After uniformly mixing zinc oxide and germanium oxide in a stoichiometric ratio (molar ratio 2:1), calcine at 1200 °C for 6 h under an air atmosphere. Wash the obtained product with a large amount of distilled water and ethanol, filter, and dry overnight at 80 °C, and collect for use.

[0142] Specific experimental conditions can also be seen in Table 1.

[0143] Figure 1 In which, the spectrum marked with bulk or Figure 5 In which, the XRD pattern of the sample prepared in this comparative example is the spectrum marked with C1. It can be seen from the characteristic peaks of zinc germanate that the sample is zinc germanate.

[0144] Figure 6 In, the photo marked with C1 is the SEM photo of the zinc germanate sample prepared in this comparative example. It can be seen from this figure that the prepared zinc germanate is in the form of irregular particles of 0.2 - 2 μm, without rod-like aggregation morphology and without forming a spherical hollow structure.

[0145] 2. Photocatalytic reaction evaluation

[0146] Repeat step 2 of Example 1, except that: replace the sample with the sample prepared in this comparative example to evaluate the yield of photocatalytic reduction of CO2 to CH4 by the prepared material.

[0147] Figure 4 In, the curve marked with bulk represents the cumulative yield of the photocatalytic reaction product CH4 of the sample prepared in this comparative example.

[0148] Comparative Example 2

[0149] Repeat step 1 of Example 1, except that: in step (3), the constant temperature time in the oven is 6 h at 160 °C.

[0150] Specific experimental conditions can also be seen in Table 1.

[0151] Figure 5 Among them, the spectrogram marked with C2 is the XRD pattern of the sample prepared in this comparative example. From the positions of the characteristic peaks of the crystal phase structure in this figure, it can be seen that the prepared product is zinc germanate, but the peak intensity indicates that the crystallinity of the prepared product is not high.

[0152] Figure 6 Among them, the photograph marked with C2 is the SEM photograph of the zinc germanate sample prepared in this comparative example. From this figure, it can be seen that the structure of the prepared zinc germanate microspheres is not yet complete.

[0153] Comparative Example 3

[0154] Repeat Step 1 of Example 1, with the only difference being that: in Step (3), the oven temperature is 140 °C.

[0155] The specific experimental conditions can also be seen in Table 1.

[0156] Figure 5 Among them, the spectrogram marked with C3 is the XRD pattern of the sample prepared in this comparative example. From the positions of the characteristic peaks of the crystal phase structure in this figure, it can be seen that there are characteristic peaks of unreacted germanium oxide (circled in dotted line) in the prepared product, and the purity of the prepared product is not high.

[0157] Figure 6 Among them, the photograph marked with C3 is the SEM photograph of the zinc germanate sample prepared in this comparative example. From this figure, it can be seen that the prepared sample shows a rod-like stacking morphology, but no spherical hollow structure is formed.

[0158] Comparative Example 4

[0159] Repeat Step 1 of Example 1, with the only difference being that: in Step (3), the oven temperature is 230 °C.

[0160] The specific experimental conditions can also be seen in Table 1.

[0161] Figure 5 Among them, the spectrogram marked with C4 is the XRD pattern of the sample prepared in this comparative example. From the positions of the characteristic peaks of the crystal phase structure in this figure, it can be seen that the prepared product is zinc germanate and has a relatively high crystallinity.

[0162] Figure 6 Among them, the photograph marked with C4 is the SEM photograph of the zinc germanate sample prepared in this comparative example. From this figure, it can be seen that the prepared sample is a hollow microsphere structure, but shows a certain degree of agglomeration morphology.

[0163] Comparative Example 5

[0164] Repeat Step 1 of Example 1, with the only difference being that: in Step (1), the volume ratio of ethylenediamine to water is 2:1.

[0165] The specific experimental conditions can also be seen in Table 1.

[0166] Figure 5 Among them, the spectrogram marked with C5 is the XRD pattern of the sample prepared in this comparative example. From the positions of the characteristic peaks of the crystal phase structure in this figure, it can be seen that there are characteristic peaks of unreacted germanium oxide (circled in dotted line) in the prepared product, and the purity of the prepared product is not high.

[0167] Figure 6 Among them, the photograph marked with C5 is the SEM photograph of the zinc germanate sample prepared in this comparative example. From this figure, it can be seen that the prepared sample presents a rod-like stacking morphology, but no spherical hollow structure is formed.

[0168] Comparative Example 6

[0169] Repeat Step 1 of Example 1, with the only difference being that: in Step (2), the concentration of zinc acetate in homogeneous solution D is 0.6 mol / L, and the concentration of germanium oxide in homogeneous solution D is 0.3 mol / L.

[0170] The specific experimental conditions can also be seen in Table 1.

[0171] Figure 5 Among them, the spectrogram marked with C6 is the XRD pattern of the sample prepared in this comparative example. From the positions of the characteristic peaks of the crystal phase structure in this figure, it can be seen that there are characteristic peaks of unreacted germanium oxide (circled in dotted line) in the prepared product, and the purity of the prepared product is not high.

[0172] Figure 6 Among them, the photograph marked with C6 is the SEM photograph of the zinc germanate sample prepared in this comparative example. From this figure, it can be seen that the prepared sample presents a rod-like stacking morphology of incomplete spheres, and a partial hollow structure is formed.

[0173] Comparative Example 7

[0174] Repeat Step 1 of Example 1, with the only difference being that: in Step (1), the addition amount of the alcohol dispersant is 0.5% of the sum of the volume values of ethylenediamine and water.

[0175] The specific experimental conditions can also be seen in Table 1.

[0176] Figure 5 Among them, the spectrogram marked with C7 is the XRD pattern of the sample prepared in this comparative example. From the positions of the characteristic peaks of the crystal phase structure in this figure, it can be seen that the characteristic peaks of zinc germanate in the prepared product are basically complete, but there are impurity peaks (circled in dotted line), and it is speculated that other crystal forms are formed during the synthesis process.

[0177] Figure 6 Among them, the photograph marked with C7 is the SEM photograph of the zinc germanate sample prepared in this comparative example. From this figure, it can be seen that the prepared sample presents a spherical thick rod stacking morphology, the spherical particle size is about 20 μm, and the structure is relatively rough.

[0178] Comparative Example 8

[0179] Repeat step 1 of Example 1, with the only difference being that in step (1), the addition amount of the alcohol dispersant is 15% of the sum of the volume values of ethylenediamine and water.

[0180] The specific experimental conditions can also be seen in Table 1.

[0181] Figure 5 In, the spectrogram marked with C8 is the XRD spectrogram of the sample prepared in this comparative example. From the positions of the characteristic peaks of the crystal phase structure of this figure, it can be seen that the characteristic peaks of the prepared zinc germanate sample are obvious and the crystalline structure is clear.

[0182] Figure 6 In, the photo marked with C8 is the SEM photo of the zinc germanate sample prepared in this comparative example. From this figure, it can be seen that the prepared sample is in a disordered rod shape and no spherical structure is formed.

[0183] Comparative Example 9

[0184] Repeat step 1 of Example 1, with the only difference being that in step (1), in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 6:1.

[0185] The specific experimental conditions can also be seen in Table 1.

[0186] Figure 5 In, the spectrogram marked with C9 is the XRD spectrogram of the sample prepared in this comparative example. From the positions of the characteristic peaks of the crystal phase structure of this figure, it can be seen that the characteristic peaks of the prepared zinc germanate are obvious and the crystalline structure is clear.

[0187] Figure 6 In, the photo marked with C9 is the SEM photo of the zinc germanate sample prepared in this comparative example. From this figure, it can be seen that the prepared sample has a stacked morphology of rod-shaped crystals, the rod-shaped crystals are incomplete, and no hollow structure is observed to form.

[0188] Comparative Example 10

[0189] Repeat step 1 of Example 1, with the only difference being that in step (1), in the alcohol dispersant, the volume ratio of ethylene glycol to ethanol is 1:6.

[0190] The specific experimental conditions can also be seen in Table 1.

[0191] Figure 5 In, the spectrogram marked with C10 is the XRD spectrogram of the sample prepared in this comparative example. From the positions of the characteristic peaks of the crystal phase structure of this figure, it can be seen that the characteristic peaks of the prepared zinc germanate are obvious and the crystalline structure is clear.

[0192] Figure 6 In, the photo marked with C10 is the SEM photo of the zinc germanate sample prepared in this comparative example. From this figure, it can be seen that the prepared sample presents a disordered rod shape.

[0193] Table 1

[0194]

[0195] Result analysis:

[0196] From Figure 4 It can be seen that among the zinc germanate samples with particle sizes of 5μm, 10μm, 15μm, 20μm, 25μm, and 30μm prepared in the embodiments of the present invention, the cumulative yield (cumulative output divided by time, reflected as a slope trend in the figure) of the zinc germanate hollow microspheres with a particle size of 5μm prepared in Example 1 for photocatalytic reduction of CO2 to CH4 is the highest. The cumulative yields of CH4 generated by photocatalytic reduction of CO2 in the samples with particle sizes of 35μm, 40μm, 45μm, and 50μm are not much different. Under the same reaction conditions, the cumulative yield of CH4 generated by photocatalytic reduction of CO2 in the zinc germanate samples prepared by the solid-phase synthesis method is the lowest.

[0197] From Figure 5 and Figure 6 it can be known that there are problems such as impurity generation, formation of agglomerated morphologies, incomplete spherical structures, and unformed hollow structures in the samples prepared in the comparative examples; among them, the shorter crystallization time in Comparative Example 2 is not conducive to the formation of the zinc germanate sphere structure; the lower crystallization temperature in Comparative Example 3 is not conducive to the crystallization process; the too high crystallization temperature in Comparative Example 4 will lead to the formation of aggregates; the too low content of ethylenediamine in Comparative Example 5 is not conducive to the dissolution of germanium oxide; the too high concentration of germanium oxide in Comparative Example 6 is not conducive to dissolution; the insufficient addition amount of the alcohol dispersant in Comparative Example 7 is not conducive to the dispersion of the product; the increase in the usage amount of the alcohol dispersant in Comparative Example 8 does not form a spherical morphology; the increase in the proportion of ethylene glycol in Comparative Example 9 results in an incomplete structure of the prepared product; the increase in the proportion of ethanol in Comparative Example 10 fails to form a spherical morphology.

Claims

1. A method for preparing zinc germanate hollow microspheres with controllable size, comprising the following steps: (1) Preparation of the solvothermal system: Measure ethylenediamine and water with a volume ratio of more than 3:

1. While stirring, add ethylenediamine dropwise to water and stir to dissolve at room temperature to form a homogeneous solution A; Measure 5-10% of an alcohol dispersant based on the sum of the volume values of ethylenediamine and water, and add it to the homogeneous solution A while stirring and dissolve at room temperature to form a homogeneous solution B; The alcohol dispersant is composed of ethylene glycol and ethanol with a volume ratio of 5:1 to 1:5; (2) Preparation of the crystallization precursor solution: Take zinc acetate dihydrate and germanium oxide with a molar ratio of 2:1 as raw materials. While stirring, add germanium oxide powder to the homogeneous solution B and stir to dissolve at room temperature to form a homogeneous solution C; Add zinc acetate dihydrate powder to the homogeneous solution C while stirring and stir to dissolve at room temperature to form a homogeneous solution D. The homogeneous solution D is the precursor solution of the crystallization system; The concentration of zinc acetate in the homogeneous solution D is 0.2-0.4 mol / L, and the concentration of germanium oxide in the homogeneous solution D is 0.1-0.2 mol / L; (3) Crystallization and drying: Load the precursor solution into a crystallization synthesis reactor, carry out a crystallization reaction at a constant temperature of 160-200 °C for more than 12 h. After crystallization is completed, wait for the reactor to cool to room temperature, separate the product, and rinse it with distilled water until it is neutral, then transfer the product to an oven at 80-100 °C for drying to obtain zinc germanate hollow microspheres.

2. The method according to claim 1, wherein: In step (1), the volume ratio of ethylenediamine to water is 3:1 to 5:

1.

3. The method according to claim 2, wherein: In step (1), the volume ratio of ethylenediamine to water is 5:

1.

4. The method according to any one of claims 1-3, characterized in that: In step (1), the volume of the alcohol dispersant is 5% of the sum of the volume values of ethylenediamine and water.

5. The method according to claim 1, characterized in that: In step (2), the particle sizes of the zinc acetate dihydrate powder and the germanium oxide powder are 75-100 μm.

6. The method according to claim 1 or 5, characterized in that: In step (2), the concentration of zinc acetate in the homogeneous solution D is 0.2 mol / L, and the concentration of germanium oxide in the homogeneous solution D is 0.1 mol / L.

7. The method according to claim 1, characterized in that: In step (3), the crystallization temperature is 160 °C and the crystallization time is 24 h.

8. The method according to claim 1, characterized in that: The particle size of the zinc germanate hollow microspheres is 5-50 μm.

9. Zinc germanate hollow microspheres prepared by the method according to any one of claims 1-8.

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