Efficient antibacterial nano magnesium oxide and preparation method thereof

Abstract

The invention discloses efficient antibacterial nano magnesium oxide and a preparation method thereof, and relates to the technical field of inorganic nano powder synthesizing.The method comprises the steps that industrial magnesium sulfate heptahydrate, urea and a surfactant are mixed, a magnesium carbonate intermediate is synthesized through a hydrothermal precipitation reaction, and then nano magnesium oxide powder is prepared through high-temperature calcination of a muffle furnace. The antibacterial rate of the nano magnesium oxide prepared by controlling the morphology to staphylococcus aureus reaches up to 99.11%, and the nano magnesium oxide has great potential in the field of antibacterial materials. Meanwhile, the nano magnesium oxide with high specific surface area is also widely applied to the fields of inorganic flame retardants, heavy metal adsorption materials, high-efficiency catalysts and the like. The process is based on low-cost bulk raw materials, has the advantages of being simple in process, green and environment-friendly (production waste liquid is converted into agricultural ammonium sulfate), controllable in morphology and the like, and provides a breakthrough technical scheme for large-scale industrial production of nano magnesium oxide.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic nanopowder synthesis, and more particularly to a high-efficiency antibacterial magnesium oxide nanopowder and a preparation method thereof. BACKGROUND

[0003] As an important inorganic functional material, magnesium oxide exhibits unique physical and chemical properties when its particle size reaches the nanoscale due to the significant increase in specific surface area, surface atom number and defect density. It has great application potential in antibacterial materials, catalytic systems, aerospace, electronic information and food industry, and plays an important role in promoting high-quality development of national economy.

[0004] Currently, the mainstream preparation methods of magnesium oxide nanoparticles include mineral calcination and chemical precipitation. Although the mineral calcination method has the advantages of low raw material cost and wide source, it is limited by the process and has low product purity and difficulty in accurately controlling particle size and morphology. Although the chemical precipitation method can prepare high-purity products, it needs to rely on high-priced magnesium salt reagents, resulting in high production cost. Moreover, this technology produces a large amount of salt-containing wastewater, which will cause soil salinization if directly discharged, and is not suitable for large-scale industrial application.

[0005] As a large-tonnage and widely-sourced bulk chemical raw material, industrial magnesium sulfate heptahydrate can be converted into high-purity magnesium oxide nanoparticles by hydrothermal precipitation-calcination technology, which can not only break through the dual bottleneck of purity and cost of existing processes, but also significantly improve the comprehensive utilization efficiency of magnesium resources, and has significant economic and social benefits.

[0006] However, through the existing technology research, it is found that there is no related technology report on preparing magnesium oxide nanoparticles from industrial magnesium sulfate heptahydrate. Based on this, the present application proposes a preparation process of magnesium oxide nanoparticles from industrial magnesium sulfate heptahydrate combined with hydrothermal precipitation-calcination method, which provides a new technical path for the industrial production of magnesium oxide nanoparticles. SUMMARY

[0007] Therefore, the present application aims to develop a low-cost, high-purity, morphology-controllable and environment-friendly preparation process based on industrial magnesium sulfate heptahydrate, which can overcome the problems of high raw material cost, low purity, uncontrollable morphology and low process green degree in the existing preparation technology of magnesium oxide nanoparticles. Through the hydrothermal precipitation-calcination technology route, combined with precise process parameter control and surfactant synergistic effect, high-purity magnesium oxide nanoparticles with controllable morphology can be prepared, and the production cost can be greatly reduced. This process can promote the leap from laboratory preparation to large-scale industrial production of magnesium oxide nanoparticles, and meet the urgent needs of high-performance nanomaterials in antibacterial, electronic, catalytic, environmental protection and other high-end fields.

[0008] In order to achieve the above object, the present application adopts the following technical solutions:

[0009] A preparation method of high-efficiency antibacterial nano magnesium oxide, characterized in that the method comprises the following steps:

[0010] Step (1): preparation of raw material solution

[0011] Under the condition of magnetic stirring, first, urea (CO(NH2)2) is added to deionized water, and continuous stirring is carried out at room temperature until complete dissolution; then, industrial magnesium sulfate heptahydrate (MgSO4·7H2O) is slowly added, the feeding speed is controlled, and then magnetic stirring is continued, the stirring time is not less than 30 min, so as to ensure that the solute is fully dissolved and uniformly mixed, forming a mixed solution A;

[0012] Step (2): addition of surfactant

[0013] The surfactant is added to the mixed solution A, after the addition is completed, the stirring is continued, the magnetic stirring speed is adjusted, so that the surfactant is fully dispersed and complexed with the solute, forming a uniform mixed solution B;

[0014] Step (3): hydrothermal reaction

[0015] The mixed solution A in step (1) or the mixed solution B obtained in step (2) is transferred to a polytetrafluoroethylene-lined hydrothermal reaction kettle, the filling degree is controlled at 60%~80%, after the hydrothermal reaction kettle is sealed, it is placed in a constant temperature oven, the temperature is increased to 120~220℃ at a rate of 4~8℃ / min, and then the temperature is kept constant for 2~10h, the pressure generated during the reaction is 0.2~1.5MPa, and after the reaction is completed, the reaction kettle is naturally cooled to room temperature;

[0016] Step (4): product separation and washing

[0017] The white precipitate generated by the hydrothermal reaction is collected by centrifugal separation, first, the precipitate is transferred to a beaker, deionized water is added, and ultrasonic dispersion is used for auxiliary washing until the pH value of the washing liquid reaches 6.5~7.5, then the washed precipitate is dried to obtain magnesium carbonate powder;

[0018] Step (5): calcination treatment

[0019] The dried intermediate magnesium carbonate powder is ground to ensure uniform particle size, the ground powder is placed in an alumina crucible, and after calcination, it is cooled to room temperature, the calcined product is taken out, and then ground again to obtain the final nano magnesium oxide powder.

[0020] Preferably, the industrial magnesium sulfate heptahydrate in step (1) is a magnesium sulfate product produced by treating low-grade magnesite with sulfuric acid method, and the molar ratio of the industrial magnesium sulfate heptahydrate to urea is 1:1-1:8; the feeding speed is 0.5 g / min; the concentration of the magnesium sulfate heptahydrate solution is 1.5-2.5 mol / L; and the stirring speed of the magnetic stirring is 200-500 rpm.

[0021] More preferably, the molar ratio of the industrial magnesium sulfate heptahydrate to urea is 1:6; and the concentration of the magnesium sulfate heptahydrate in the mixed solution A is 2 mol / L.

[0022] Preferably, in step (2), the surfactant is weighed according to the molar ratio of the industrial magnesium sulfate heptahydrate to the surfactant of 1:0.01-1:0.1.

[0023] More preferably, the molar ratio of the industrial magnesium sulfate heptahydrate to the surfactant is 1:0.03.

[0024] Preferably, in step (2), the surfactant is ethylenediaminetetraacetic acid disodium or cetyltrimethylammonium bromide; the stirring speed of the magnetic stirring is 300-600 rpm, and the stirring time is 1-2 h.

[0025] In the present application, no surfactant is added, and the prepared nano-magnesium oxide is in a spherical morphology; after adding the surfactant ethylenediaminetetraacetic acid disodium (EDTA-2Na), first, the nucleation is delayed through complexation, then the flake growth is induced through selective adsorption, and finally the flower-like structure is formed by driving the nanosheet; after adding the surfactant cetyltrimethylammonium bromide (CTAB), the magnesium oxide is induced to directional growth through the mechanisms of selective adsorption of quaternary ammonium salt (N + (CH3)3) and steric hindrance of cetyl chain (C 16 H 33 ), and the prepared magnesium oxide is in a flaky morphology.

[0026] Specifically, EDTA-2Na: by chelating metal ions, the nucleation rate and free ion concentration are controlled from the source, which is conducive to forming smaller and more uniform crystal nuclei, and is conducive to adjusting the uniformity, inhibiting growth and preventing agglomeration to obtain fine and uniform nanoparticles, and its influence on morphology is relatively indirect.

[0027] CTAB: by the micellar template formed by the self-assembly of the surfactant and the adsorption on the particle surface, the specific morphology is directly guided, the formation of high specific surface area mesoporous structure is obtained, and the agglomeration is prevented by steric hindrance. At the same time, the adsorption produces steric hindrance, which has a relatively indirect influence on inhibiting grain growth and agglomeration, obtaining smaller and more narrowly distributed nanoparticles.

[0028] Preferably, the hydrothermal reaction temperature in step (3) is controlled at 180℃, and the hydrothermal time is controlled at 4h.

[0029] Preferably, the centrifugal separation parameters in step (4) are as follows: the centrifugal speed is 2000-5000rpm, and the centrifugal time is 5-15min.

[0030] Preferably, the ultrasonic dispersion assisted washing in step (4) is as follows: the ultrasonic power is 100-300W, and the ultrasonic time is 10-30min; the washing process is repeated for 3-5 times, and centrifugal separation is performed after each washing.

[0031] Preferably, the drying treatment in step (4) is as follows: the washed precipitate is placed in a blast drying oven at 80℃ for drying for 12-24h, and the sample is turned over every 2h during the drying process to ensure uniform drying.

[0032] Preferably, the calcination in step (5) is heated to 500-1000℃ at a heating rate of 2-10℃ / min, and kept at constant temperature for 1-2h.

[0033] More preferably, the calcination temperature is controlled at 600℃, and the calcination time is controlled at 1.5h.

[0034] Preferably, the grinding in step (5) is all ground to pass through a 100-250 mesh screen.

[0035] According to the above technical solution, compared with the prior art, the present application has the following beneficial effects:

[0036] The present application significantly improves the preparation efficiency and product performance of nano magnesium oxide through raw material innovation, process optimization and green design, and has economic value and environmental benefits, and the specific advantages are as follows:

[0037] Raw material innovation and cost advantage: industrial magnesium sulfate heptahydrate is used to replace traditional high-priced magnesium salt reagent, which has the characteristics of abundant reserves, good chemical stability and easy storage, solves the problems of high production cost and poor process stability caused by high price or easy moisture absorption of traditional magnesium salt reagent, and provides stable and low-cost raw material basis for large-scale industrial production.

[0038] Controllable morphology: Through the hydrothermal precipitation-calcination process and the synergistic regulation of surfactants, the morphology of nano magnesium oxide is precisely controlled: without surfactant, spherical powder with a particle size of 20-80 nm can be prepared, and the specific surface area can reach 138.74 m² / g, and the oxygen vacancy concentration is 31.32%; adding surfactant disodium ethylenediaminetetraacetate can form flower-like morphology, which is composed of nanosheets with a thickness of 5-10 nm, and the specific surface area can reach 147.35 m² / g, and the oxygen vacancy concentration is 39.47%; adding surfactant cetyltrimethylammonium bromide forms a sheet-like morphology, and the sheet thickness is 60-70 nm, and the specific surface area can reach 178.25 m² / g, and the oxygen vacancy concentration is 57.30%. Different morphologies of nano magnesium oxide can meet the special needs of high-end fields such as antibacterial materials, electronic packaging, efficient catalysis, and environmental purification.

[0039] High purity: The prepared nano magnesium oxide powder has a purity of >99%.

[0040] Green production: Environmentally friendly urea is selected as a green precipitant to replace traditional strong irritant ammonia or sodium hydroxide; and through a closed-loop production process, the ammonium-containing waste liquid generated after the reaction is directly converted into an economically valuable ammonium sulfate fertilizer product, thereby realizing resource utilization and near-zero emission of waste liquid, eliminating environmental pollution from the source, and conforming to the principles of green chemistry and the strategic direction of national green manufacturing.

[0041] Excellent performance: The prepared nano magnesium oxide exhibits excellent antibacterial activity, and at a concentration of 600 μg / mL, the antibacterial rate of Staphylococcus aureus (10 5 CFU / ml) within 24 hours is as high as 99.11%, which has a broad application prospect in the fields of medical treatment, coating and food packaging.

[0042] Industrial value: The present application breaks through the technical bottlenecks of high raw material cost, low purity, uncontrollable morphology and particle size, and low green degree of process in the existing preparation technology of nano magnesium oxide, provides a new path for the industrial production of nano magnesium oxide, promotes the upgrading of magnesium resource deep processing industry chain, and has significant economic and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0044] Figure 1 The process flow chart for preparing nano magnesium oxide powder of the present application;

[0045] Figure 2 XRD pattern of Example 1 of the present application.

[0046] Figure 3 and Figure 4 SEM and TEM pictures of Example 1 of the present application.

[0047] Figure 5 SEM picture of Example 2 of the present application.

[0048] Figure 6 SEM picture of Example 3 of the present application.

[0049] Figure 7 SEM picture of Example 4 of the present application.

[0050] Figure 8 SEM picture of Comparative Example 1 of the present application.

[0051] Figure 9 XRD pattern of Comparative Example 2 of the present application. Figure 10 SEM picture of Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present application will be apparently and completely described below with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0053] The present application discloses a kind of high-efficiency antibacterial nano magnesium oxide and its preparation method, by hydrothermal precipitation-calcination two-step method realizes from raw material to product high-efficiency conversion.The method takes industrial magnesium sulfate heptahydrate, urea as core raw material, in combination with surfactant control technology, realizes the controllable morphology synthesis of nano magnesium oxide, and its core chemical reaction is as follows:

[0054] (1) hydrothermal precipitation reaction: CO (NH2) 2+ 2H2O = (NH4) 2CO3

[0055] MgSO4·7H2O + (NH4) 2CO3 = MgCO3↓ + (NH4) 2SO4 + 7H2O

[0056] Through the alkaline environment produced by urea hydrolysis, it promotes Mg 2+ Reaction with CO3 2- To generate magnesium carbonate intermediate.

[0057] (2) high-temperature calcination decomposition: MgCO3 = MgO + CO2↑

[0058] The magnesium carbonate is converted into nano magnesium oxide by thermal decomposition, and the crystal type reconstruction and morphology control are simultaneously realized.

[0059] To further illustrate the implementation process and technical effects of the present application, the following detailed description is made in combination with specific examples and characterization data:

[0060] Example 1 (preferred conditions)

[0061] (1) 0.14 mol of industrial magnesium sulfate heptahydrate and 0.84 mol of urea were accurately weighed according to a molar ratio of 1:6. The urea was first slowly added to deionized water, and after complete dissolution under magnetic stirring at 300 rpm, the magnesium sulfate heptahydrate was gradually added at a speed of 0.5 g / min, and stirring was continued for 40 min to prepare a mixed solution with a (magnesium ion) concentration of 2 mol / L.

[0062] (2) The mixed solution was transferred to a 100 ml hydrothermal reactor with a polytetrafluoroethylene lining, with a filling degree of 70%. After sealing the hydrothermal reactor, it was placed in a thermostat for heating, with a heating rate of 6 ℃ / min. When the temperature reached 180 ℃, it was kept for 4 h, and then naturally cooled to room temperature.

[0063] (3) The reaction product was separated by centrifugation at 4000 rpm, and the white precipitate was washed with deionized water for 5 times (each time for 20 min with ultrasonic assistance, ultrasonic power 200 W), until the pH value of the washing liquid was stable at 7.0. Then the precipitate was placed in a 80 ℃ air drying oven for drying for 16 h to obtain the intermediate magnesium carbonate.

[0064] (4) The intermediate magnesium carbonate was ground to pass through a 150 mesh screen and placed in an alumina crucible, which was heated to 800 ℃ at a rate of 5 ℃ / min in a muffle furnace, and kept at constant temperature for 1.5 h. After natural cooling in the furnace, the product was taken out and ground again (through a 250 mesh screen) to prepare the nano magnesium oxide powder.

[0065] (5) Phase analysis: as shown in Figure 2 , by X-ray diffraction (XRD) analysis (CuKα radiation, scanning range 20°-80°, step size 0.02°), the obtained powder showed sharp and high intensity diffraction peaks at 2θ=37.1°, 43.2°, 62.9°, etc., corresponding to the (111), (200), (220) crystal planes of MgO (JCPDS card No. 87-0653), without other impurity peaks, indicating that the product was high-purity cubic magnesium oxide with good crystallinity.

[0066] (6) Morphology observation: scanning electron microscope (SEM) image ( Figure 3 ) and transmission electron microscope (TEM) image ( Figure 4) The nano-magnesium oxide is in regular spherical structure, with an average particle size of about 20-80 nm, and no agglomeration between particles, and excellent dispersibility.

[0067] (7) X-ray fluorescence spectrum test: the prepared nano-magnesium oxide powder has a purity of 99.58%.

[0068] (8) Specific surface area test: the prepared nano-magnesium oxide has a specific surface area of 138.74 m² / g.

[0069] (9) X-ray photoelectron spectroscopy test: the prepared nano-magnesium oxide has an oxygen vacancy concentration of 31.32%.

[0070] (10) Antibacterial performance: 600 μg / mL of nano-magnesium oxide powder is added into a staphylococcus aureus (initial concentration 10 5 CFU / ml) bacterial solution, and after 24 h of oscillation culture, the colony counting shows that the antibacterial rate is 96.4%.

[0071] Example 2 (adding disodium ethylenediaminetetraacetate)

[0072] (1) 0.14 mol of industrial magnesium sulfate heptahydrate and 0.84 mol of urea are accurately weighed according to a molar ratio of 1:6, urea is first slowly added into deionized water, and after complete dissolution under 300 rpm magnetic stirring, magnesium sulfate heptahydrate is gradually added at a speed of 0.5 g / min, and stirring is continued for 40 min to prepare a mixed solution with a (magnesium ion) concentration of 2 mol / L.

[0073] (2) 5.6 mmol of disodium ethylenediaminetetraacetate is weighed according to a molar ratio of industrial magnesium sulfate heptahydrate to disodium ethylenediaminetetraacetate of 1:0.04, and is added to the mixed solution obtained in step (1); after the addition is completed, stirring is continued for 1.5 h, and the stirring speed is adjusted to 400 rpm, so that the disodium ethylenediaminetetraacetate is fully dispersed and complexed with the solute to form a uniform mixed solution.

[0074] (3) The mixed solution is transferred to a 100 ml hydrothermal reaction kettle with a polytetrafluoroethylene lining, and the filling degree is 70%; after the hydrothermal reaction kettle is sealed, it is placed in a constant temperature oven for heating, and the heating rate is 6 ℃ / min; when the temperature rises to 180 ℃, it is kept for 4 h, and naturally cooled to room temperature.

[0075] (4) The reaction product is separated by centrifugation at 4000 rpm, and the white precipitate is collected and washed with deionized water for 5 times (each time is ultrasonic assisted washing for 20 min, and the ultrasonic power is 200 W), until the pH value of the washing liquid is stable at 7.0. Subsequently, the precipitate is placed in a 80 ℃ air drying oven for drying for 16 h to obtain an intermediate magnesium carbonate.

[0076] (5) The intermediate magnesium carbonate was ground to pass through a 150 mesh screen, placed in an alumina crucible, and heated to 800°C at a rate of 5°C / min in a muffle furnace, and held at temperature for 1.5 h. After natural cooling in the furnace, the product was removed and ground a second time (through a 250 mesh screen) to produce a nano-magnesium oxide powder.

[0077] (6) Phase analysis: As shown in FIG. 1, by X-ray diffraction (XRD) analysis, the powder obtained had sharp and high intensity diffraction peaks at 2θ = 37.1°, 43.2°, 62.9°, etc., corresponding to the (111), (200), (220) crystal planes of MgO (JCPDS card No. 87-0653), without other impurity peaks, indicating that the product was high-purity cubic magnesium oxide with good crystallinity. Figure 2

[0078] (7) Morphology observation: The scanning electron microscope (SEM) image (FIG. 2) shows that the nano-magnesium oxide produced has a flower-like morphology, composed of nanosheets with a thickness of 5-10 nm. Figure 5

[0079] (8) X-ray fluorescence spectrum test: The purity of the nano-magnesium oxide powder produced was 99.46%.

[0080] (9) Specific surface area test: The specific surface area of the nano-magnesium oxide produced was 147.35 m² / g.

[0081] (10) X-ray photoelectron spectroscopy test: The oxygen vacancy concentration of the nano-magnesium oxide produced was 39.47%.

[0082] (11) Antibacterial performance: 600 μg / mL of the nano-magnesium oxide powder was added to a Staphylococcus aureus (initial concentration 10 5 CFU / ml) bacterial solution, and after 24 h of shaking culture, colony counting showed an antibacterial rate of 97.39%.

[0083] Example 3 (with addition of cetyltrimethylammonium bromide)

[0084] (1) 0.14 mol of industrial magnesium sulfate heptahydrate and 0.84 mol of urea were accurately weighed in a molar ratio of 1:6, the urea was first slowly added to deionized water, and after complete dissolution under 300 rpm magnetic stirring, the magnesium sulfate heptahydrate was gradually added at a rate of 0.5 g / min, and stirring was continued for 40 min to produce a mixed solution with a (magnesium ion) concentration of 2 mol / L.

[0085] ​​(2) 5.6 mmol of cetyltrimethylammonium bromide was weighed according to the molar ratio of industrial magnesium sulfate heptahydrate to cetyltrimethylammonium bromide of 1:0.04, and was added to the mixed solution obtained in step one; after the addition was completed, stirring was continued for 1.5 h, and the stirring speed was adjusted to 400 rpm, so that the cetyltrimethylammonium bromide was fully dispersed and complexed with the solute to form a uniform mixed solution.

[0086] (3) The mixed solution was transferred to a 100 ml hydrothermal reactor with a polytetrafluoroethylene lining, and the filling degree was 70%; after the hydrothermal reactor was sealed, it was placed in a thermostat for heating, and the heating rate was 6 ℃ / min; when the temperature rose to 180 ℃, it was kept for 4 h, and then naturally cooled to room temperature.

[0087] (4) The reaction product was separated by centrifugation at 4000 rpm, and the white precipitate was collected and washed with deionized water for 5 times (each time was ultrasonically assisted for 20 min, and the ultrasonic power was 200 W), until the pH value of the washing liquid was stable at 7.0. Subsequently, the precipitate was placed in a 80 ℃ air drying oven and dried for 16 h to obtain the intermediate magnesium carbonate.

[0088] (5) The intermediate magnesium carbonate was ground to pass through a 150 mesh screen and was placed in an alumina crucible, which was heated to 600 ℃ at a rate of 5 ℃ / min in a muffle furnace, and was kept at constant temperature for 1.5 h. After the furnace was naturally cooled, the product was taken out and was ground again (through a 250 mesh screen) to prepare the nano magnesium oxide powder.

[0089] (6) The phase analysis was performed by X-ray diffraction (XRD) analysis (CuKα radiation, scanning range 20°-80°, step size 0.02°), as shown in Figure 2 , the obtained powder had sharp and high intensity diffraction peaks at 2θ=37.1°, 43.2°, 62.9°, etc., corresponding to the (111), (200), (220) crystal planes of MgO (JCPDS card No. 87-0653), and no other impurity peaks, indicating that the product was high-purity cubic magnesium oxide with good crystallinity.

[0090] (7) The morphology observation was performed by scanning electron microscopy (SEM) image ( Figure 6 ) showed that the magnesium oxide had a sheet-like morphology, and the sheet thickness was 60-70 nm.

[0091] (8) The purity of the prepared nano magnesium oxide powder was 99.67% by X-ray fluorescence spectrum test.

[0092] (9) The specific surface area of the prepared nano magnesium oxide was 178.25 m² / g by specific surface area test.

[0093] (10) The oxygen vacancy concentration of the prepared nano magnesium oxide was 57.30% by X-ray photoelectron spectroscopy test.

[0094] (11) Antibacterial performance: 600 μg / mL of nano-magnesium oxide powder was added to the staphylococcus aureus (initial concentration 10 5 CFU / ml) bacteria solution, and after 24 h of shaking culture, the colony counting showed that the antibacterial rate was as high as 99.11%.

[0095] Example 4 (limit parameter verification)

[0096] (1) 0.105 mol of industrial magnesium sulfate heptahydrate and 0.105 mol of urea were accurately weighed according to a molar ratio of 1:1. The urea was first slowly added to deionized water, and after complete dissolution under 300 rpm magnetic stirring, the magnesium sulfate heptahydrate was gradually added at a speed of 0.5 g / min, and the stirring was continued for 40 h to prepare a clear precursor solution with a (magnesium ion) concentration of 1.5 mol / L.

[0097] (2) 10.5 mmol of cetyltrimethylammonium bromide was weighed according to a molar ratio of industrial magnesium sulfate heptahydrate to cetyltrimethylammonium bromide of 1:0.1 and added to the mixed solution obtained in step one; after the addition was completed, the stirring was continued for 1.5 h, and the stirring speed was adjusted to 400 rpm to make the cetyltrimethylammonium bromide fully dispersed and complexed with the solute to form a uniform mixed solution.

[0098] (3) The mixed solution was transferred to a 100 ml hydrothermal reaction kettle with a polytetrafluoroethylene lining, and the filling degree was 70%; after the hydrothermal reaction kettle was sealed, it was placed in a constant temperature oven for heating, and the heating rate was 4 ℃ / min; when the temperature rose to 120 ℃, it was kept for 10 h, and naturally cooled to room temperature.

[0099] (4) The reaction product was separated by centrifugation at 4000 rpm, and the white precipitate was washed with deionized water for 5 times (each time was ultrasonically assisted for 20 min, and the ultrasonic power was 200 W) until the pH value of the washing liquid was stable at 7.0. Subsequently, the precipitate was placed in a 80 ℃ air drying oven and dried for 16 h to obtain the intermediate magnesium carbonate.

[0100] (5) The intermediate magnesium carbonate was ground to pass through a 150 mesh screen and placed in an alumina crucible, which was heated to 1000 ℃ at a rate of 10 ℃ / min in a muffle furnace, and calcined at constant temperature for 1 h. After natural cooling in the furnace, the product was taken out and ground again (through a 250 mesh screen) to prepare nano-magnesium oxide powder.

[0101] (6) Phase analysis: as Figure 2As shown, by X-ray diffraction (XRD) analysis (Cu Kα radiation, scanning range 20°-80°, step 0.02°), the obtained powder appears sharp and high-intensity diffraction peaks at 2θ = 37.1°, 43.2°, 62.9° and other positions, corresponding to the (111), (200), (220) crystal faces of MgO (JCPDS card No. 87-0653), without other impurity peaks, indicating that high-purity cubic phase magnesium oxide can still be prepared under the parameter limit, and the crystallinity is good.

[0102] (7) Morphology observation: scanning electron microscope (SEM) images show that the nano-magnesium oxide has a sheet-like morphology, wherein the sheet thickness is 60-70 nm. Figure 7

[0103] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the present application shall be covered within the protection scope of the present application.

[0104] Comparative Example 1 (traditional analytical pure raw material method)

[0105] Compared with Example 1, analytical pure magnesium chloride was used instead of industrial magnesium sulfate heptahydrate, and other raw materials and ratios, process conditions were exactly the same as Example 1, as follows:

[0106] (1) 0.14 mol of analytical pure magnesium chloride and 0.84 mol of urea were accurately weighed according to a molar ratio of 1:6, urea was first slowly added to deionized water, and after complete dissolution under 300 rpm magnetic stirring, magnesium chloride was gradually added at a speed of 0.5 g / min, and stirring was continued for 40 min, to prepare a mixed solution with a concentration of (magnesium ion) 2.0 mol / L.

[0107] (2) The mixed solution was transferred to a 100 ml hydrothermal reaction kettle with a polytetrafluoroethylene liner, and the filling degree was 70%; after sealing the hydrothermal reaction kettle, it was placed in a constant temperature oven for heating, and the heating rate was 6 ℃ / min; when the temperature rose to 180 ℃, it was kept for 4 h, and naturally cooled to room temperature.

[0108] (3) The reaction product was separated by centrifugation at 4000 rpm, and the white precipitate was washed with deionized water for 5 times (each time was ultrasonically assisted for 20 min, and the ultrasonic power was 200 W), until the pH value of the washing liquid was stable at 7.0. Subsequently, the precipitate was placed in a 80 ℃ air drying oven for drying for 16 h, to obtain the intermediate magnesium carbonate.

[0109] ​(4) The intermediate magnesium carbonate was ground to pass through a 150 mesh screen, placed in an alumina crucible, and heated to 800°C at a rate of 5°C / min in a muffle furnace, and calcined for 1.5 h. After natural cooling in the furnace, the product was removed and ground a second time (through a 250 mesh screen) to produce a nano-magnesium oxide powder.

[0110] (5) Morphology observation: scanning electron microscope (SEM) images (Fig. 2) show that the nano-magnesium oxide powder is severely agglomerated and has uneven particle size distribution. Figure 8

[0111] (6) Specific surface area test: the specific surface area of the prepared flaky nano-magnesium oxide is 16.85 m² / g.

[0112] It is found by comparison with Example 1 that the magnesium oxide powder prepared using analytical pure magnesium chloride as a raw material is severely agglomerated, has uneven particle size distribution, and has a specific surface area of only 16.85 m² / g. This is because the trace Fe³⁺ and Al³⁺ ions contained in the industrial magnesium sulfate heptahydrate can be adsorbed on the surface of the intermediate magnesium carbonate during the hydrothermal reaction process, forming a "natural ion barrier" to inhibit the agglomeration of the powder. This comparative example verifies that the use of industrial magnesium sulfate heptahydrate as a raw material in the present application can reduce the cost of raw materials and has a better control effect on powder agglomeration.

[0113] Comparative Example 2 (hydrothermal conditions below the scope of the claims)

[0114] Compared with Example 1, the hydrothermal temperature is set to 100°C (lower than the claimed 120°C), the hydrothermal holding time, raw materials and ratio are exactly the same as in Example 1, and are as follows:

[0115] (1) 0.14 mol of analytical pure magnesium chloride and 0.84 mol of urea were accurately weighed according to a molar ratio of 1:6. The urea was first slowly added to deionized water, and after complete dissolution under 300 rpm magnetic stirring, the magnesium sulfate heptahydrate was gradually added at a rate of 0.5 g / min, and the stirring was continued for 40 min to prepare a mixed solution with a concentration of (magnesium ions) 2.0 mol / L.

[0116] (2) The mixed solution was transferred to a 100 ml hydrothermal reaction kettle with a polytetrafluoroethylene liner, and the filling degree was 70%. After sealing the hydrothermal reaction kettle, it was placed in a constant temperature oven for heating, and the heating rate was 6°C / min. When the temperature rose to 100°C, it was kept for 4 h, and naturally cooled to room temperature.

[0117] (3) The reaction product was separated by centrifugation at 4000 rpm, and the white precipitate was collected and washed with deionized water for 5 times (each time for 20 min of ultrasonic assisted washing, ultrasonic power 200 W) until the pH value of the washing liquid was stable at 7.0. Subsequently, the precipitate was placed in a 80°C air drying oven for drying for 16 h to obtain an intermediate powder. ​

[0118] (4) Phase analysis: X-ray diffraction (XRD) pattern of the intermediate powder Figure 9 ) did not appear characteristic diffraction peaks, and the prepared intermediate powder could crystallize.

[0119] By comparison with Example 1, it was found that when the hydrothermal temperature was lower than the claim condition of 120℃, the obtained intermediate powder was amorphous structure, and the magnesium carbonate intermediate crystalline structure could not be formed. This was because low temperature could not effectively form crystal nucleus and grow into crystals, so amorphous particles were formed. This comparative example confirmed the key role of the hydrothermal temperature parameter in the crystallization process.

[0120] Comparative Example 3 (surfactant dosage exceeding the claim range)

[0121] Compared with Example 3, the molar ratio of industrial magnesium sulfate heptahydrate to cetyltrimethylammonium bromide was 1:0.12, which exceeded the claim range (1:0.01~1:0.1), and other process conditions were exactly the same as Example 3, as follows:

[0122] (1) 0.14 mol of industrial magnesium sulfate heptahydrate and 0.84 mol of urea were accurately weighed according to a molar ratio of 1:6, and urea was first slowly added to deionized water. After complete dissolution under 300 rpm magnetic stirring, the magnesium sulfate heptahydrate was gradually added at a speed of 0.5 g / min, and the stirring was continued for 40 min to prepare a mixed solution A with a (magnesium ion) concentration of 2 mol / L.

[0123] (2) 16.8 mmol of cetyltrimethylammonium bromide was weighed according to a molar ratio of industrial magnesium sulfate heptahydrate to cetyltrimethylammonium bromide of 1:0.12, and was added to the mixed solution A. After the addition was completed, the stirring was continued for 1.5 h, and the stirring speed was adjusted to 400 rpm to make the cetyltrimethylammonium bromide fully dispersed and complexed with the solute, forming a uniform mixed solution.

[0124] (3) The mixed solution was transferred to a 100 ml hydrothermal reaction kettle with a polytetrafluoroethylene liner, and the filling degree was 70%. After the hydrothermal reaction kettle was sealed, it was placed in a constant temperature oven for heating, and the heating rate was 6℃ / min. When the temperature rose to 180℃, it was kept for 4 h, and then naturally cooled to room temperature.

[0125] (4) The reaction product was separated by centrifugation at 4000 rpm, and the white precipitate was collected and washed with deionized water for 5 times (each time was ultrasonically assisted for 20 min, and the ultrasonic power was 200 W), until the pH value of the washing liquid was stable at 7.0. Subsequently, the precipitate was placed in a 80℃ air drying oven for drying for 16 h, and the intermediate magnesium carbonate was obtained.

[0126] (5) The intermediate magnesium carbonate was ground to pass through a 150 mesh screen, placed in an alumina crucible, and heated in a muffle furnace at 5°C / min to 600°C, and held at temperature for 1.5 h. After the furnace was allowed to cool naturally, the product was removed and ground a second time (through a 250 mesh screen) to produce the nano-magnesium oxide powder.

[0127] (6) Morphology observation: Scanning Electron Microscope (SEM) images (Fig. 3) show that the magnesium oxide has an irregular blocky morphology with a particle size of about 5 microns. Figure 10

[0128] By comparison with Example 3, it is found that too much surfactant will significantly increase the viscosity of the solution, reduce the diffusion rate of ions, and cause uneven supply of ions required for crystal growth, easily forming a large number of crystal nuclei and rapidly aggregating and growing irregularly, ultimately generating irregular blocky morphology. Compared with the nano-thickness flaky powder, the specific surface area of the micron irregular blocky powder is significantly reduced, the number of active sites on the surface is sharply reduced, the contact efficiency of active sites with reactants is reduced in antibacterial, catalytic or adsorption applications, and the performance is reduced accordingly.

[0129] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method part.

[0130] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.​

Claims

1. A method for preparing high-efficiency antibacterial nano-magnesium oxide, characterized in that, Comprising the following steps: Step (1): raw material solution preparation Under the condition of magnetic stirring, first add urea into deionized water, continuously stir at room temperature until completely dissolved; then slowly add industrial magnesium sulfate heptahydrate, control the feeding speed, then continue to stir under magnetic stirring, ensure that the solute is fully dissolved and uniformly mixed, to form a mixed solution A; Step (2): surfactant addition Add surfactant to mixed solution A, after the addition is completed, continue to stir, adjust the magnetic stirring speed, so that the surfactant is fully dispersed and complexed with the solute, to form a uniform mixed solution B; Step (3): hydrothermal reaction Transfer the mixed solution A in step (1) or the mixed solution B obtained in step (2) to a hydrothermal reactor with a polytetrafluoroethylene liner, control the filling degree to 60%~80%, after sealing the hydrothermal reactor, place it in a constant temperature oven, increase the temperature to 120~220℃ at a rate of 4~8℃ / min, keep constant temperature for 2~10h, the pressure generated during the reaction is 0.2~1.5MPa, after the reaction is completed, let the reactor cool to room temperature naturally; Step (4): product separation and washing Collect the white precipitate generated by hydrothermal reaction by centrifugal separation, then transfer the precipitate to a beaker, add deionized water, and wash with ultrasonic dispersion assistance until the pH value of the washing liquid reaches 6.5~7.5, dry the washed precipitate to obtain magnesium carbonate powder; Step (5): calcination treatment Grind the dried intermediate magnesium carbonate powder to ensure uniform particle size, place the ground powder in an alumina crucible, cool to room temperature after calcination, take out the calcined product, grind again to obtain nano magnesium oxide powder.

2. The method for preparing highly efficient antibacterial nano-magnesium oxide according to claim 1, characterized in that, The industrial magnesium sulfate heptahydrate in step (1) is a magnesium sulfate product produced by treating low-grade magnesite with sulfuric acid method, the molar ratio of the industrial magnesium sulfate heptahydrate to urea is 1:1~1:8; the feeding speed is 0.5g / min; the concentration of magnesium sulfate heptahydrate in the mixed solution A is 1.5~2.5mol / L; the rotation speed of magnetic stirring is 200~500rpm.

3. The method according to claim 1, wherein the method is characterized by, In step (2), the surfactant is weighed according to the molar ratio of industrial magnesium sulfate heptahydrate to surfactant of 1:0.01~1:0.

1.

4. The method according to claim 1, wherein the method is characterized by, In step (2), the surfactant is ethylenediaminetetraacetic acid disodium or cetyltrimethylammonium bromide; the magnetic stirring speed is 300~600rpm, and the stirring time is 1-2h.

5. The method according to claim 1, wherein the method is characterized by, In step (4), the parameters of centrifugal separation are: centrifugal speed of 2000~5000rpm, centrifugal time of 5~15min.

6. The method according to claim 1, wherein the method is characterized by, In step (4), the ultrasonic dispersion assisted washing is: ultrasonic power of 100~300W, ultrasonic time of 10~30min; repeat the washing process 3~5 times, and centrifugal separation is carried out after each washing.

7. The method according to claim 1, wherein the method is characterized by, In step (4), the drying treatment is: place the washed precipitate in a 80℃ air drying oven for 12~24h, and turn the sample over every 2h during the drying process to ensure uniform drying.

8. The method according to claim 1, wherein the method is characterized by, The calcining in step (5) is heating to 500-1000℃ at a heating rate of 2-10℃ / min and keeping constant temperature for 1-2h.

9. The method according to claim 1, wherein the method is characterized by, The grinding in step (5) is all grinding to pass through 100-250 mesh screen.

10. A high efficiency antibacterial nano magnesium oxide, characterized in that, The high-efficiency antibacterial nano magnesium oxide is prepared by the method of any one of claims 1-9.

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