Octahedral magnesium oxide nanomaterial, preparation method and application thereof

Abstract

The present application belongs to the technical field of inorganic material synthesis, and provides an octahedral nano magnesium oxide, a preparation method and application thereof. The preparation raw materials (hydrated magnesium salt and a precipitating agent (including one or more of urea, hexamethylenetetramine and ethanolamine)) are heated at 25-95 DEG C to obtain a reaction liquid, the reaction liquid is subjected to hydrothermal reaction, the obtained gel intermediate is directly calcined to obtain the octahedral nano magnesium oxide. The present application strictly controls the ratio of water to magnesium in the reaction liquid to be ≤130 mL:1 mol, and the one-dimensional nano structure intermediate product can be obtained through hydrothermal reaction; the one-dimensional nano structure intermediate product is calcined to form the octahedral structure [(100) crystal surface] with the lowest energy and the most stable structure; the precipitating agent forms ammonium radical in the hydrothermal reaction, the ammonium radical escapes in the form of nitrogen oxide or ammonia gas, which enriches the pore structure of the octahedral nano magnesium oxide and improves the specific surface area thereof.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic material synthesis, and particularly relates to an octahedral nano-magnesium oxide, a preparation method and application thereof. BACKGROUND

[0002] Magnesium oxide is an important inorganic chemical product, and is widely used. In addition to being used for making refractory materials, antacid and stomach medicine, moisture retention material, etc., it is also widely used in the food industry, plastic board accelerator, plasticizer for glass steel, surface coating paint for silicon steel sheet, paper production, insulating material, ceramics, drying agent and flame retardant, etc.

[0003] There are many methods for the preparation of nano-magnesium oxide, such as coprecipitation method, sol-gel method, hydrothermal synthesis method, solid phase reaction method, template method, etc. By controlling different reaction conditions, many types and structures of nano-magnesium oxide have been obtained. For example, Ashok research team (Ashok A, Kennedy L J, Vijaya J J, et al. Optimization of biodiesel production from waste cooking oil by magnesium oxide nanocatalyst synthesized using coprecipitation method. Clean Technologies and Environmental Policy, 2018, 20(6): 1219-1231.) used Mg(NO)3·6H2O as magnesium source, NaOH as precipitant, and sodium dodecyl sulfate as dispersant to prepare Mg(OH)2precipitate at room temperature and pH value of 13. The precipitate was calcined at 400℃ for 2h to obtain nano-magnesium oxide with an average particle size of 7.86nm. Cui et al. (Cui Z X, Liu J Y, Gao H F, et al. Size and shape dependences of the adsorption kinetics of malachite green on nano-MgO: a theoretical and experimental study. Physical Chemistry Chemical Physics, 2019, 21(25): 13721-13729.) used magnesium acetate tetrahydrate and cetyltrimethylammonium bromide as raw materials to prepare spherical and cubic nano-MgO with different particle sizes by changing the calcination temperature, pH value and amount of magnesium acetate tetrahydrate. Najafi research group (Najafi A. Novel synthesis method of hierarchical mesoporous MgO nanoflakes employing carbon nanoparticles as the hard templates for photocatalytic degradation. Ceramics International, 2017, 43(7): 5813-5818.) used carbon nanoparticles as hard templates to synthesize hierarchical mesoporous MgO nanoflakes for photocatalytic degradation.Li et al. (Li P, Liu C, Zhang L, et al. Enhanced boron adsorption onto synthesized MgO nanosheets by ultrasonic method. Ultrasonics Sonochemistry, 2017, 34: 938-946) prepared magnesium oxide nanosheets with a lateral size of about 200-600 nm and a thickness of about 10 nm by using magnesium nitrate as a magnesium source, potassium carbonate as a precipitant, mixing the solution, standing at 90℃ for 30 min, collecting the white precursor, calcining the white precursor at 500℃ for 2h, then performing ultrasonic treatment at room temperature, and finally calcining at 600℃ for 2h.

[0004] Due to the structural characteristics of magnesium oxide, most of the currently prepared nano-magnesium oxide has a spherical, rod, sheet or block morphology. There are very few reports on the preparation method of octahedral nano-magnesium oxide exposing specific crystal faces. Structure determines performance, and the different morphology of materials is closely related to the advantages and disadvantages of their performance. In the fields of catalysis and heavy metal adsorption, the same material exhibits different adsorption energy barriers and catalytic activity differences due to the so-called crystal face characteristics, so it is of great significance to construct octahedral magnesium oxide. At present, the synthesis of magnesium oxide exposing specific crystal faces mainly depends on structure inducers and organic solvents, and the preparation process is complex and the conditions are harsh. For example, Yan Xirui (Yan Xirui, Preparation and application of nano-octahedral magnesium oxide, Master's thesis, 2020) prepared nano-octahedral magnesium oxide by solvothermal method and single crystal culture method; among them, the solvothermal method uses ethanol as a solvent and urea and magnesium nitrate as solutes to obtain an intermediate by hydrothermal crystallization at 200℃ for 24 hours, and then octahedral magnesium oxide is prepared by calcining at 500℃; the single crystal culture method uses magnesium nitrate, urea and ethanol as raw materials, and after standing for two weeks, colorless block crystals are obtained; then the colorless block crystals are calcined at 500℃. Both the solvothermal method and the single crystal culture method use organic solvent ethanol, and the specific surface area of the obtained octahedral magnesium oxide needs to be further improved. SUMMARY

[0005] Therefore, the purpose of the present application is to provide an octahedral nano-magnesium oxide, a preparation method and application thereof. The octahedral nano-magnesium oxide prepared by the preparation method has a large specific surface area and does not use organic solvents.

[0006] To achieve the above object, the present application provides the following technical solutions.

[0007] The present application provides a preparation method of octahedral nano-magnesium oxide, comprising the following steps:

[0008] The preparation raw material is heated at 25-95℃ to obtain a reaction solution;

[0009] The reaction solution is subjected to hydrothermal reaction;

[0010] After the hydrothermal reaction, the obtained gel intermediate is directly calcined to obtain the octahedral nano-magnesium oxide;

[0011] The preparation raw material comprises a hydrated magnesium salt and a precipitant;

[0012] The precipitant comprises one or more of urea, hexamethylenetetramine and ethanolamine;

[0013] The ratio of water to magnesium in the reaction solution is ≤130 mL:1 mol.

[0014] Preferably, the hydrated magnesium salt comprises one or more of magnesium sulfate heptahydrate, magnesium chloride hexahydrate, magnesium nitrate hexahydrate and magnesium acetate tetrahydrate.

[0015] Preferably, the preparation raw material further comprises water.

[0016] Preferably, the water is deionized water.

[0017] Preferably, the amount of substance of the precipitant is 0.5-3 times the amount of substance of the hydrated magnesium salt.

[0018] Preferably, the temperature of the hydrothermal reaction is 110-140℃, and the holding time is 2-6h.

[0019] Preferably, the temperature of the calcination is 400-800℃, the rate of temperature rise to the temperature of the calcination is 5℃ / min, the holding time is 3-6h, and the atmosphere of the calcination is air.

[0020] The present application further provides the octahedral nano-magnesium oxide obtained by the preparation method described above, and the specific surface area of the octahedral nano-magnesium oxide is 82.5-324.2m 2 / g.

[0021] The present application further provides the application of the octahedral nano-magnesium oxide described above in wastewater treatment and catalysis.

[0022] The application provides a preparation method of octahedral nano magnesium oxide, comprising the following steps: heating preparation raw materials at 25-95 DEG C to obtain a reaction liquid; performing hydrothermal reaction on the reaction liquid; performing calcination on the obtained gel intermediate to obtain the octahedral nano magnesium oxide; the preparation raw materials comprise a hydrated magnesium salt and a precipitating agent; the precipitating agent comprises one or more of urea, hexamethylenetetramine and ethanolamine; the ratio of water to magnesium in the reaction liquid is ≤130 mL:1 mol.

[0023] The application takes full advantage of the inherent crystal water and low melting point characteristics of the hydrated magnesium salt, and by controlling the ratio of water to magnesium in the reaction liquid, i.e., the ratio of water to magnesium in the reaction liquid is ≤130 mL:1 mol, one-dimensional nanostructured intermediate products can be obtained through hydrothermal reaction without adding a surfactant or a structure inducer; the one-dimensional nanostructured intermediate products are calcined to form an octahedral structure [(100) crystal surface] with the lowest energy and the most stable structure; the precipitating agent produces by-products ammonium ions during the hydrothermal reaction, which escape in the form of nitrogen oxides or ammonia gas, and promote the dispersion of the octahedral nano magnesium oxide particles and enrich the pore structure of the octahedral nano magnesium oxide at the same time. The application strictly controls the ratio of water to magnesium in the reaction liquid, significantly reduces the hydrogen bond network between the crystal grains, avoids agglomeration, and promotes the high dispersion of the octahedral nano magnesium oxide. During the hydrothermal reaction, the by-product ammonium ions and the one-dimensional nanostructured intermediate products form a gel intermediate, no wastewater is produced, the environmental pressure and the preparation cost are greatly reduced, and green preparation is realized; the gel intermediate can be directly calcined without washing, and no water washing is needed, thereby avoiding the ammonia-nitrogen wastewater caused by water washing and being more environmentally friendly. During the calcination process, the by-product ammonium salt escapes in the form of gas, so that the synthesized magnesium oxide has a large specific surface area and a rich pore structure, the exposed active crystal surface promotes its catalytic ability and heavy metal adsorption ability, and is more conducive to subsequent application in the fields of catalysis and heavy metal adsorption; at the same time, the escaped ammonia gas can be recycled. In summary, the preparation method provided by the application does not introduce organic solvents, inducers, dispersants, etc., reduces the raw material cost, does not need to add water or only needs a small amount of water during the synthesis process, is extremely beneficial to saving water resources, the required equipment is simple, and the synthesis conditions are mild.

[0024] Specifically, taking magnesium nitrate hexahydrate as an example, the mass fraction of water in 1 mol of magnesium nitrate hexahydrate is 6*18 / 246*100% = 43.9%, i.e. the mass of water in 246 g of magnesium nitrate hexahydrate is 108 g. In the case of using urea as a precipitant, the solubility of urea in water at 20℃ is 108 g / 100 mL, and it increases obviously with the increase of temperature. Therefore, when the magnesium salt containing crystal water reaches its melting point (the melting point of magnesium nitrate hexahydrate is about 95℃), the magnesium nitrate is dissolved into its own crystal water to form a liquid state. Since the content of crystal water is high and the solubility of urea is also high, the crystal water of the molten magnesium nitrate hexahydrate can completely act as a solvent to dissolve the precipitant such as urea without adding deionized water as a solvent. In this case, the molar concentration of magnesium ions and the precipitant is very high, which promotes the sufficient contact between magnesium ions and the precipitant, reduces the reaction energy barrier, and enables the reaction to occur rapidly at a lower temperature to form the intermediate product with one-dimensional nanostructure. With the decomposition of the precipitant such as urea into ammonium and hydroxyl, the alkalinity of the reaction system gradually increases. Compared with the conventional synthesis conditions such as co-precipitation, hydrothermal reaction and gel-sol, the concentration of reactants (magnesium salt and precipitant) in the reaction solution of the present application is extremely high, so that the primary crystal grains of the product are closely arranged during the hydrothermal reaction to form the intermediate product with one-dimensional nanostructure. In addition, since no water is added or a very small amount of water is added during the whole reaction process, the intermediate product with one-dimensional nanostructure formed after the hydrothermal reaction forms a high-density gel intermediate with ammonium without generating waste water; the formed ammonium is wrapped in the gel intermediate. During the calcination process, the intermediate product with one-dimensional nanostructure forms an octahedral structure [(100) crystal surface] with the lowest energy and the most stable structure, and the by-product ammonium escapes in the form of nitrogen oxide or ammonia gas, which promotes the dispersion of the octahedral nano-magnesium oxide particles and enriches the pore structure of the octahedral nano-magnesium oxide. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A digital photo of the intermediate product A prepared in Example 1;

[0026] Figure 2 An XRD pattern of the octahedral nano-magnesium oxide prepared in Example 1;

[0027] Figure 3 An SEM pattern of the octahedral nano-magnesium oxide prepared in Example 1;

[0028] Figure 4 An SEM pattern of the intermediate product A prepared in Example 2;

[0029] Figure 5 An XRD pattern of the octahedral nano-magnesium oxide prepared in Example 2;

[0030] Figure 6SEM image of octahedral nano-magnesium oxide prepared in Example 2;

[0031] Figure 7 XRD image of octahedral nano-magnesium oxide prepared in Example 3;

[0032] Figure 8 SEM image of octahedral nano-magnesium oxide prepared in Example 3;

[0033] Figure 9 SEM image of octahedral nano-magnesium oxide prepared in Example 4;

[0034] Figure 10 XRD image of magnesium oxide prepared in Comparative Example 1;

[0035] Figure 11 SEM image of magnesium oxide prepared in Comparative Example 1.

[0036] Figure 12 SEM image of magnesium oxide prepared in Comparative Example 2. DETAILED DESCRIPTION

[0037] The present application provides a preparation method of octahedral nano-magnesium oxide, comprising the following steps:

[0038] The preparation raw material is heated at 25-95℃ to obtain a reaction solution;

[0039] The reaction solution is subjected to hydrothermal reaction;

[0040] After the hydrothermal reaction, the obtained gel intermediate is directly calcined to obtain the octahedral nano-magnesium oxide;

[0041] The preparation raw material comprises a magnesium hydrate and a precipitating agent;

[0042] The precipitating agent comprises one or more of urea, hexamethylenetetramine and ethanolamine;

[0043] The ratio of water to magnesium in the reaction solution is ≤130 mL:1 mol.

[0044] In the present application, the raw materials used in the present application are preferably commercially available products, unless otherwise specified.

[0045] The preparation raw material is heated at 25-95℃ to obtain a reaction solution.

[0046] In the present application, the preparation raw material comprises a magnesium hydrate and a precipitating agent.

[0047] In the present application, the hydrated magnesium salt preferably comprises one or more of magnesium sulfate heptahydrate, magnesium chloride hexahydrate, magnesium nitrate hexahydrate and magnesium acetate tetrahydrate, and is further preferably magnesium chloride hexahydrate or magnesium nitrate hexahydrate.

[0048] In the present application, the precipitant comprises one or more of urea, hexamethylenetetramine and ethanolamine. In the present application, the amount of the precipitant is preferably 0.5-3 times, and is further preferably 1-2 times, the amount of the hydrated magnesium salt.

[0049] In the present application, the preparation raw material preferably further comprises water, which is preferably deionized water.

[0050] In the present application, the heating temperature is preferably 30-90℃, and is further preferably 40-80℃, and is more preferably 50-70℃. In the present application, the heating is preferably carried out under stirring. In the present application, the heating is preferably carried out in a closed device. In the present application, the heating is preferably carried out in a closed device, which can avoid water loss during the heating.

[0051] In the present application, the heating of the preparation raw material at 25-95℃ preferably comprises: heating the hydrated magnesium salt and the precipitant at 25-95℃ to obtain a reaction liquid; or heating the hydrated magnesium salt and the precipitant at 25-95℃, and then adding water to obtain a reaction liquid; or heating the hydrated magnesium salt at 25-95℃, and then adding the precipitant to the obtained clear liquid to obtain a reaction liquid.

[0052] In the present application, the ratio of water to magnesium in the reaction liquid is ≤130 mL:1 mol, i.e. at most 130 mL of water is used to dissolve 1 mol of magnesium.

[0053] In the present application, water can not be additionally added under the condition that the magnesium salt is completely dissolved in water. The method of the present application uses less water.

[0054] The present application strictly controls the ratio of the amount of water to the amount of magnesium in the reaction liquid, significantly reduces the hydrogen bond network between the crystal grains, avoids agglomeration, and promotes the high dispersion of the octahedral nanometer magnesium oxide.

[0055] After obtaining the reaction liquid, the present application directly carries out hydrothermal treatment without any operation.

[0056] After obtaining the reaction liquid, the present application carries out hydrothermal reaction on the reaction liquid.

[0057] In the present application, the temperature of the hydrothermal reaction is preferably 110-140℃, and is further preferably 120-130℃; and the holding time is preferably 2-6h, and is further preferably 3-5h.

[0058] In the present application, because the concentration of the substance amount of magnesium and the precipitant in the reaction solution is very high, the magnesium ions are fully contacted with the precipitant, the reaction energy barrier is reduced, the reaction can be rapidly carried out at a lower temperature, the primary crystal grains are closely arranged, and then the intermediate product with one-dimensional nanostructure is formed; at the same time, the precipitant is decomposed into ammonium and hydroxyl in the hydrothermal reaction, the intermediate product with one-dimensional nanostructure and the ammonium combine to form a high-density gel intermediate, the formation of the gel intermediate can directly carry out the subsequent calcination, and water washing is not necessary, thereby avoiding the ammonia-nitrogen wastewater caused by water washing and being more environmentally friendly.

[0059] After the hydrothermal reaction, the gel intermediate obtained in the present application is directly calcined to obtain the octahedral nano-magnesium oxide.

[0060] In the present application, the temperature of the calcination is preferably 400-800℃, further preferably 500-700℃, and more preferably 600℃; the rate of temperature rise to the temperature of the calcination is preferably 5℃ / min; the holding time is preferably 3-6h, and further preferably 4-5h; and the atmosphere of the calcination is preferably air. In the present application, the calcination is preferably carried out in a muffle furnace.

[0061] After the calcination, the octahedral nano-magnesium oxide can be obtained by cooling.

[0062] In the present application, in the process of calcination, the intermediate product with one-dimensional nanostructure in the gel intermediate forms the octahedral structure [(100) crystal surface] with the lowest energy and the most stable structure, the by-product ammonium escapes in the form of nitrogen oxide or ammonia gas, and at the same time promotes the dispersion of the octahedral nano-magnesium oxide particles and enriches the pore structure of the octahedral nano-magnesium oxide, thereby increasing the specific surface area of the magnesium oxide.

[0063] The present application also provides the octahedral nano-magnesium oxide obtained by the preparation method of the above technical solution, and the specific surface area of the octahedral nano-magnesium oxide is 82.5-324.2m 2 / g.

[0064] The present application also provides the application of the octahedral nano-magnesium oxide of the above technical solution in wastewater treatment and catalysis.

[0065] The present application does not make specific limitation to the application mode of the octahedral nano-magnesium oxide, and the operation of the resin of the person skilled in the art can be adopted.

[0066] The octahedral nano-magnesium oxide, the preparation method and the application thereof provided by the present application will be described in detail below in combination with examples, but they should not be understood as the limitation to the protection scope of the present application.

[0067] Example 1

[0068] Take 20.3 g (0.1 mol) of magnesium chloride hexahydrate, 12 g (0.2 mol) of urea, and place them in a 200 mL beaker. After continuously stirring at 60°C until a clear solution is formed, continue stirring for 30 minutes, then pour into an autoclave. Crystallize at 120°C for 3 hours, and then take out the intermediate product A in gel form after natural cooling.

[0069] Place the intermediate product A in a muffle furnace, and heat to 400°C at a heating rate of 5°C / min in an air atmosphere. Keep at this temperature for 3 hours, and then take out the octahedral nano-magnesium oxide after natural cooling.

[0070] Figure 1 The SEM image of the intermediate product A is shown in Figure 1. Figure 1 It can be seen that the intermediate product is white and in gel form, and there is no solution residue in the autoclave, indicating that the byproduct ammonium salt formed in the reaction process is integrated with the intermediate product, and there is no wastewater residue.

[0071] Figure 2 The XRD pattern of the obtained octahedral nano-magnesium oxide is shown in Figure 2. Figure 2 It can be seen that the prepared substance exhibits characteristic diffraction peaks of magnesium oxide, and there are no obvious impurity peaks, indicating that the prepared substance is magnesium oxide.

[0072] Figure 3 The SEM image of the obtained octahedral nano-magnesium oxide is shown in Figure 3. Figure 2 It can be clearly seen that the prepared magnesium oxide is of octahedral structure.

[0073] The specific surface area of the obtained octahedral nano-magnesium oxide was determined by nitrogen adsorption-desorption, and the result was 228.4 m 2 / g.

[0074] Example 2

[0075] Take 20.3 g (0.1 mol) of magnesium chloride hexahydrate, 12 g (0.2 mol) of urea, and place them in a 200 mL beaker. After continuously stirring at 60°C until a clear solution is formed, continue stirring for 30 minutes, then pour into an autoclave. Crystallize at 120°C for 3 hours, and then take out the intermediate product A in gel form after natural cooling.

[0076] Place the intermediate product A in a muffle furnace, and heat to 400°C at a heating rate of 5°C / min in an air atmosphere. Keep at this temperature for 3 hours, and then take out the octahedral nano-magnesium oxide after natural cooling.

[0077] Figure 4 The SEM image of the intermediate product A is shown in Figure 1. Figure 4 It can be seen that the intermediate product is one-dimensional fibrous.

[0078] Figure 5 The XRD pattern of the obtained octahedral nano-magnesium oxide is shown in Figure 1. Figure 5 It can be seen that the prepared substance exhibits characteristic diffraction peaks of magnesium oxide and no obvious impurity peaks, indicating that the prepared substance is magnesium oxide.

[0079] Figure 6 The scanning electron microscope pattern of the obtained octahedral nano-magnesium oxide is shown in Figure 2. Figure 6 It can be clearly seen that the prepared magnesium oxide is of octahedral structure.

[0080] The specific surface area of the obtained octahedral nano-magnesium oxide was determined by nitrogen adsorption-desorption, and the result was 153.7 m 2 / g.

[0081] Example 3

[0082] 25.6 g (0.1 mol) of magnesium nitrate hexahydrate and 14 g (0.1 mol) of methenamine were weighed into a 200 mL beaker, continuously stirred at 60°C until a clear solution was formed, and then stirred for another 30 minutes before being poured into an autoclave. Crystallization was carried out at 110°C for 3 hours, and the intermediate product A in gel form was taken out after natural cooling.

[0083] The intermediate product A was placed in a muffle furnace, heated to 400°C at a heating rate of 5°C / min in an air atmosphere, and kept at this temperature for 3 hours. The obtained octahedral nano-magnesium oxide was obtained after natural cooling.

[0084] Figure 7 The XRD pattern of the obtained octahedral nano-magnesium oxide is shown in Figure 1. Figure 7 It can be seen that the prepared substance exhibits characteristic diffraction peaks of magnesium oxide and no obvious impurity peaks, indicating that the prepared substance is magnesium oxide.

[0085] Figure 8 The scanning electron microscope pattern of the obtained octahedral nano-magnesium oxide is shown in Figure 2. Figure 8 It can be clearly seen that the prepared magnesium oxide is of octahedral structure.

[0086] The specific surface area of the obtained octahedral nano-magnesium oxide was determined by nitrogen adsorption-desorption, and the result was 298.2 m 2 / g.

[0087] Example 4

[0088] 25.6 g (0.1 mol) of magnesium nitrate hexahydrate was weighed into a 200 mL beaker, continuously stirred at 75°C until a clear solution was formed, and then 12.2 g (0.2 mol) of ethanolamine was added. The mixture was stirred for another 60 minutes before being poured into an autoclave. Crystallization was carried out at 130°C for 2 hours, and the intermediate product A in gel form was taken out after natural cooling.

[0089] The intermediate product A was placed in a muffle furnace, and heated to 400℃ at a temperature increasing rate of 5℃ / min in air atmosphere, and kept at the temperature for 3 hours, and the octahedral nano magnesium oxide was obtained after natural cooling.

[0090] Figure 9 The scanning electron microscope (SEM) image of the obtained octahedral nano magnesium oxide is shown in Fig. 1. Figure 9 It can be obviously seen that the prepared magnesium oxide has an octahedral structure.

[0091] The specific surface area of the obtained octahedral nano magnesium oxide was determined by nitrogen adsorption-desorption, and the result was 324.2m 2 / g.

[0092] Example 5

[0093] The difference from Example 1 is that 20.3g (0.1mol) of magnesium chloride hexahydrate was replaced by 24.6g (0.1mol) of magnesium sulfate heptahydrate, and the heating temperature was 90℃.

[0094] The specific surface area of the obtained octahedral nano magnesium oxide was determined by nitrogen adsorption-desorption, and the result was 106.8m 2 / g.

[0095] Example 6

[0096] The difference from Example 1 is that 20.3g (0.1mol) of magnesium chloride hexahydrate was replaced by 21.4g (0.1mol) of magnesium acetate tetrahydrate, and the heating temperature was 55℃.

[0097] The specific surface area of the obtained octahedral nano magnesium oxide was determined by nitrogen adsorption-desorption, and the result was 193.8m 2 / g.

[0098] Comparative Example 1

[0099] The difference from Example 1 is that 20mL of deionized water was added in the preparation process, and the other preparation processes were completely consistent, as follows:

[0100] 20.3g (0.1mol) of magnesium chloride hexahydrate and 12g (0.2mol) of urea were weighed and placed in a 200mL beaker, 20mL of deionized water was added, and then the mixture was continuously stirred at 60℃ until a clear solution was formed. After stirring for another 30 minutes, the intermediate product A in the form of gel was poured into a hydrothermal kettle and crystallized at 120℃ for 3 hours. The octahedral nano magnesium oxide was obtained after natural cooling.

[0101] The intermediate product A was placed in a muffle furnace, and heated to 400℃ at a temperature increasing rate of 5℃ / min in air atmosphere, and kept at the temperature for 3 hours, and the octahedral nano magnesium oxide was obtained after natural cooling.

[0102] The intermediate product A was placed in a muffle furnace, and heated to 400℃ at a temperature increasing rate of 5℃ / min in air atmosphere, and kept at the temperature for 3 hours, and the octahedral nano magnesium oxide was obtained after natural cooling.Figure 10 The XRD pattern of the obtained magnesium oxide was obtained from Figure 10 It can be seen that the prepared substance exhibits the characteristic diffraction peaks of magnesium oxide and has no obvious impurity peaks, indicating that the prepared substance is magnesium oxide.

[0103] Figure 11 Here is a scanning electron microscope image of the obtained magnesium oxide, from... Figure 11 It is evident that the prepared magnesium oxide has an irregular, plate-like structure.

[0104] By comparing with Example 1, it can be further clarified that the amount of water added is crucial to whether the resulting magnesium oxide has an octahedral structure.

[0105] Comparative Example 2

[0106] The difference from Example 1 is that 20.3g (0.1mol) magnesium chloride hexahydrate was replaced with 9.5g anhydrous magnesium chloride and 10.8g water.

[0107] The obtained magnesium oxide is as follows Figure 12 As shown, from Figure 12 It can be seen that magnesium oxide has an irregular blocky structure.

[0108] Application Example 1

[0109] Removal of cadmium from wastewater: Weigh 0.1g of the octahedral nano-magnesium oxide prepared in Example 1 into a 500mL beaker, and add 100mL of Cd-containing... 2+ An aqueous solution containing Cd 2+ The concentration was 500 mg / L. After magnetic stirring at room temperature for 5 minutes, the supernatant was collected, filtered through a 0.22 μm filter membrane, and Cd was determined by ICP-MS. 2+ The concentration was determined. The results showed that the prepared magnesium oxide achieved a cadmium removal rate of 99.9%, demonstrating excellent application prospects.

[0110] Comparative Application Example 1

[0111] This comparative application example refers to the use of commercially available magnesium oxide with irregular morphology, as in Comparative Example 1, for cadmium removal, compared to Application Example 1. All other processes are completely identical, as detailed below:

[0112] Removal of cadmium from wastewater: Weigh 0.1 g of the random magnesium oxide prepared in Comparative Example 1 into a 500 mL beaker, and add 100 mL of Cd-containing... 2+ An aqueous solution containing Cd 2+ The concentration was 500 mg / L. After magnetic stirring at room temperature for 5 minutes, the supernatant was collected, filtered through a 0.22 μm filter membrane, and Cd was determined by ICP-MS. 2+The results show that the removal rate of cadmium by the prepared magnesium oxide reaches 92.1%, compared with the application example 1, which further proves the excellent performance of the prepared octahedral nano-magnesium oxide.

[0113] Application example 2

[0114] Catalysis on glucose: 0.1 g of the prepared octahedral nano-magnesium oxide in example 2 was weighed in a 500 mL beaker, and 100 mL of an aqueous solution containing glucose was added, wherein the mass fraction of glucose was 4%, and after magnetic stirring at 50 ℃ for 30 minutes, the upper solution was taken and filtered by a 0.22 μm filter membrane, and then the concentration of formic acid therein was measured by HPLC. The results show that the selectivity of the prepared octahedral nano-magnesium oxide for the conversion of glucose into formic acid is 69.8%, which shows very good application prospect.

[0115] As a comparison, the commercial magnesium oxide with irregular morphology was used as a catalyst, and other processes were completely consistent. The results show that the selectivity of the commercial magnesium oxide with irregular morphology for the conversion of glucose into formic acid is only 49.8%, which further proves that the octahedral nano-magnesium oxide provided by the present application has better catalytic activity.

[0116] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing octahedral nanosized magnesium oxide, characterized in that, The method comprises the following steps: heating the preparation raw material at 25-95℃ to obtain a reaction solution; carrying out a hydrothermal reaction on the reaction solution; directly calcining the obtained gel intermediate to obtain the octahedral nano magnesium oxide; the preparation raw material comprises a hydrated magnesium salt and a precipitant; the precipitant comprises one or more of urea, hexamethylenetetramine and ethanolamine; the ratio of water to magnesium in the reaction solution is ≤130 mL:1 mol.

2. The production method according to claim 1, characterized by, the hydrated magnesium salt comprises one or more of magnesium sulfate heptahydrate, magnesium chloride hexahydrate, magnesium nitrate hexahydrate and magnesium acetate tetrahydrate.

3. The preparation method according to claim 1, characterized in that, the preparation raw material further comprises water.

4. The preparation method according to claim 3, characterized in that, the water is deionized water.

5. The preparation method according to claim 1, characterized in that, the amount of substance of the precipitant is 0.5-3 times the amount of substance of the hydrated magnesium salt.

6. The method of claim 1, wherein, the temperature of the hydrothermal reaction is 110-140℃, and the holding time is 2-6 h.

7. The preparation method according to claim 1, characterized in that, the temperature of the calcination is 400-800℃, the rate of temperature rise to the temperature of the calcination is 5℃ / min, the holding time is 3-6 h, and the atmosphere of the calcination is air.

8. The octahedral magnesium oxide nanoparticles obtained by the production process according to any one of claims 1 to 7, characterized in that, The specific surface area of the octahedral nanometer magnesium oxide is 82.5-324.2 m 2 / g.

9. The use of the octahedral nano magnesium oxide of claim 8 in wastewater treatment and catalysis.

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