Continuous preparation method of micro-nano bubbles

Abstract

The invention discloses a continuous preparation method of micro-nano bubbles, which comprises the following steps: (1) loading magnetic nanoparticles on an inert carrier, fixing the inert carrier loaded with the magnetic nanoparticles in a reaction container, and simultaneously placing the reaction container in an induction coil of an alternating magnetic field; (2) starting a magnetic field, conveying a gas-containing aqueous solution into the reaction container, generating a magnetothermal effect by the magnetic nanoparticles under the action of an alternating magnetic field, and enabling the magnetothermal effect to cause the temperature rise of a magnetic nanoparticle area and the reduction of the solubility of gas in water, so as to form micro-nano bubbles on the surfaces of the magnetic nanoparticles, the micro-nano bubbles on the surfaces of the magnetic nanoparticles are separated from the surfaces of the magnetic nanoparticles under the action of shearing force of the gas-containing aqueous solution to form bulk-phase micro-nano bubbles, and the bulk-phase micro-nano bubbles are discharged out of the reaction container through a drainage pipe. According to the method disclosed by the invention, continuous preparation of the micro-nano bubbles is realized, and the prepared micro-nano bubbles are high in yield, uniform in particle size and high in gas utilization rate.

Description

Technical Field

[0001] The invention relates to a continuous preparation method of micro-nano bubbles. Background Art

[0002] Nanobubbles, defined as bubbles with diameters ranging from tens of nanometers to ten microns, offer the following unique advantages over conventional bubbles: high solubility: their high gas solubility prolongs the bubble's lifetime in solution; large surface area: their large surface area enhances reaction efficiency at the gas-liquid interface; free radical generation: their ability to generate free radicals enhances chemical reactivity; and efficient mass transfer: their high mass transfer efficiency makes them suitable for a wide range of applications. These properties hold great promise for nanobubbles in areas such as precision device cleaning, ultrasound imaging, drug delivery, pollutant degradation, mineral flotation, and agricultural irrigation.

[0003] Existing methods for preparing micro-nano bubbles include cavitation effect method, pressure change method, temperature change method, microfluidics technology, solution replacement method, chemical electrolysis method, etc., but they all have obvious defects. For example, the cavitation effect method has the problem of low yield due to rapid energy attenuation and short action distance; the bubble particle size uniformity of the temperature change method is still limited by the temperature control accuracy and random nucleation of bubbles; microfluidics technology leads to uneven size due to the synergistic effect of shear stress and pressure.

[0004] In summary, the current micro-nano bubble preparation methods have problems such as low bubble concentration, uneven particle size distribution, poor stability, and difficulty in achieving continuous production. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method for continuously preparing micro-nano bubbles with uniform particle size distribution and good stability.

[0006] Technical solution: The continuous preparation method of micro-nano bubbles of the present invention comprises the following steps:

[0007] (1) loading magnetic nanoparticles onto an inert carrier, fixing the inert carrier loaded with magnetic nanoparticles in a reaction vessel, and placing the reaction vessel in an induction coil of an alternating magnetic field. The inert carrier loaded with magnetic nanoparticles is vertically placed in the reaction vessel, and the plane of the inert carrier loaded with magnetic nanoparticles is parallel to the direction of water flow in the reaction vessel;

[0008] (2) Turn on the magnetic field and transport the gas-containing aqueous solution into the reaction vessel, and the inert carrier is immersed in the gas-containing aqueous solution; the alternating magnetic field excites the magnetic nanoparticles to produce a magnetocaloric effect, forming a local hot spot in the solution, and the solubility of the gas in this area in water is reduced, thereby inducing the generation of micro-nano bubbles on the surface of the magnetic nanoparticles. Under the shear force of the gas-containing aqueous solution, the micro-nano bubbles on the surface of the magnetic nanoparticles detach from the surface of the magnetic nanoparticles to form bulk micro-nano bubbles, and are discharged from the reaction vessel through the drain pipe.

[0009] In step (1), the inert carrier loaded with magnetic nanoparticles is prepared by the following method: specifically, the magnetic nanoparticles are prepared by a conventional coprecipitation method, and then dispersed in water to form a 3-5 mg / mL aqueous dispersion of magnetic nanoparticles. The inert carrier is placed in the aqueous dispersion of magnetic nanoparticles and stirred at 60-70° C. and 100-150 rpm for 6-8 hours.

[0010] The loading amount of the magnetic nanoparticles on the inert carrier is 0.28 to 0.53% of the total mass of the inert carrier loaded with the magnetic nanoparticles. In the present invention, the magnetic nanoparticles loaded on the inert carrier have uniform particle size, so the heat generation efficiency is uniform under the same frequency and current, and the micro-nano bubbles formed on the surface of the magnetic nanoparticles have uniform particle size.

[0011] The magnetic nanoparticles are iron oxide (γ-Fe2O3, Fe3O4) nanoparticles or the iron oxide compound MFe2O4; where M is one of Mn, Mg, Zn, Co, Fe, Ni, or Cu. The surface of the magnetic nanoparticles is modified with citric acid, sodium citrate, polyethylene glycol, or polylysine. The inert carrier is one of wood, polyurethane sponge, or graphene aerogel; the wood is delignified wood.

[0012] The particle size of the magnetic nanoparticles is 100 to 1000 nm. Magnetic nanoparticles of different particle sizes can generate micro-nano bubbles of different sizes.

[0013] In step (2), the gas-containing aqueous solution is obtained by adding gas to deionized water, wherein the gas is at least one of carbon dioxide, oxygen, nitrogen, or hydrogen. At the same temperature, different gases have different solubility in water. Generally speaking, under the same conditions, gases with higher solubility produce larger micro-nano bubbles.

[0014] In step (2), the oscillation frequency of the alternating magnetic field is 7 to 500 kHz, the current is 5 to 45 A, and the power is 50 to 1500 W. The magnetic field is always on during the entire reaction process.

[0015] In step (2), the flow rate of the gas-containing aqueous solution is 2.5 to 100 mL / min.

[0016] The present invention introduces a gas-containing aqueous solution into a reaction vessel containing an inert carrier loaded with magnetic nanoparticles, utilizes an alternating magnetic field to excite the magnetic nanoparticles on the inert carrier to produce a magnetocaloric effect, and forms a local "hot spot". The gas solubility at the hot spot decreases significantly, and bubbles precipitate on the surface of the magnetic field nanoparticles to produce surface micro-nano bubbles. When the surface micro-nano bubbles grow to a certain size, they desorb under the shear force of the gas-containing water fluid to form free micro-nano bubbles.

[0017] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: the method of the present invention quickly generates hot spots by applying an alternating magnetic field to magnetic nanoparticles of uniform size loaded on an inert carrier, thereby reducing the solubility of the gas dissolved in water under the action of the hot spots, forming bubbles with uniform particle size distribution, and desorbing from the inert carrier under the action of the shear force of the water flow; the method of the present invention realizes the continuous preparation of micro-nano bubbles, and the prepared micro-nano bubbles have a high yield, uniform particle size, and high gas utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a system diagram corresponding to the method of the present invention. DETAILED DESCRIPTION

[0019] Example 1

[0020] The continuous preparation method of nitrogen micro-nano bubbles of the present invention comprises the following steps:

[0021] (1) Sodium citrate-modified iron oxide (Fe3O4) nanoparticles with a particle size of 101.13 nm were loaded onto delignified wood. The specific preparation method was as follows: sodium citrate-modified Fe3O4 nanoparticles were prepared by a conventional coprecipitation method, and then dispersed in water to form a 5 mg / mL aqueous dispersion of magnetic nanoparticles. The delignified wood was placed in the aqueous dispersion of magnetic nanoparticles and stirred at 60°C and 150 rpm for 6 h to obtain wood loaded with magnetic nanoparticles. The loading amount of sodium citrate-modified iron oxide (Fe3O4) nanoparticles on the wood was 0.28% of the total mass of the wood loaded with magnetic nanoparticles.

[0022] (2) fixing the wood carrier loaded with magnetic nanoparticles obtained in step (1) in a reaction container, and placing the reaction container in an induction coil of an alternating magnetic field;

[0023] (3) A nitrogen-containing aqueous solution was introduced into the reaction vessel at a flow rate of 2.5 mL / min under the action of a peristaltic pump, and the magnetic field was turned on. The frequency of the alternating magnetic field was 307 kHz and the current was 25 A. The magnetic field was always turned on during the preparation process. The alternating magnetic field was used to stimulate the magnetocaloric effect of the magnetic nanoparticles, inducing the formation of "hot spots" in the local micro-regions near the magnetic nanoparticles, inducing the solubility of the gas in the solution to decrease and precipitate on the surface of the magnetic nanoparticles to form surface micro-nano bubbles. After the surface micro-nano bubbles were formed, they detached from the surface of the magnetic nanoparticles under the shear force of the fluid flow to form free micro-nano bubbles.

[0024] In 2000mL deionized water, the initial nitrogen gas charged was 0.06g. After all the preparations were completed, the concentration of micro-nano bubbles was obtained by nanoparticle tracking analyzer and was 2.7×10 7 Particles / mL water. The average particle size and PDI (dispersity index) of the prepared micro-nano bubbles were measured by a laser particle size analyzer and were 182.97 nm and 0.237, respectively. The average particle size of MNBs at different time points (0 min, 60 min, 120 min, and 240 min) after preparation was analyzed at 25°C. The average particle size changed from the initial 182.97±13.49 nm to 178.25±12.58 nm at 240 min, and the particle size change was not significant. This shows that the micro-nano bubbles prepared by this method can maintain stability at 25°C for at least 4 hours, showing excellent stability.

[0025] Example 2

[0026] The continuous preparation method of carbon dioxide micro-nano bubbles of the present invention comprises the following steps:

[0027] (1) Citric acid-modified γ-Fe2O3 nanoparticles with a particle size of 149.34 nm were loaded onto a polyurethane sponge. The specific preparation method was as follows: citric acid-modified γ-Fe2O3 nanoparticles were prepared by a conventional coprecipitation method, and then dispersed in water to form a 5 mg / mL aqueous dispersion of magnetic nanoparticles. A polyurethane sponge was placed in the aqueous dispersion of magnetic nanoparticles and stirred at 60°C and 150 rpm for 6 h to obtain a polyurethane sponge loaded with magnetic nanoparticles. The loading amount of citric acid-modified γ-Fe2O3 nanoparticles on the polyurethane sponge was 0.41% of the total mass of the polyurethane sponge loaded with magnetic nanoparticles.

[0028] (2) fixing the polyurethane sponge carrier loaded with magnetic nanoparticles obtained in step (1) in a reaction container, and placing the reaction container in an induction coil of an alternating magnetic field;

[0029] (3) An aqueous solution containing carbon dioxide is introduced into the reaction vessel at a flow rate of 2.5 mL / min under the action of a peristaltic pump, and the magnetic field is turned on. The frequency of the alternating magnetic field is 7 kHz and the current is 5 A. The magnetic field is always turned on during the preparation process. The alternating magnetic field excites the magnetocaloric effect of the magnetic nanoparticles, inducing the formation of "hot spots" in the local micro-regions near the magnetic nanoparticles, inducing the solubility of the gas in the solution to decrease and precipitate on the surface of the magnetic nanoparticles to form surface micro-nano bubbles. After the surface micro-nano bubbles are formed, they detach from the surface of the magnetic nanoparticles under the shear force of the fluid flow to form free micro-nano bubbles.

[0030] In 2000mL deionized water, the initial carbon dioxide charged was 6.73g, and the concentration of micro-nano bubbles obtained by nanoparticle tracking analyzer was 6.2×10 7 Particles / mL water. The average particle size and PDI (dispersity index) of the prepared micro-nano bubbles were measured by a laser particle size analyzer and were 58.21nm and 0.258, respectively. The average particle size of MNBs at different time points (0min, 60min, 120min, and 240min) after preparation was analyzed at 25°C. The average particle size changed from the initial 58.21±5.59nm to 59.25±6.86nm at 240min, and the particle size change was not significant. This shows that the micro-nano bubbles prepared by this method can maintain stability at 25°C for at least 4 hours, showing excellent stability.

[0031] Example 3

[0032] The continuous preparation method of oxygen micro-nano bubbles of the present invention comprises the following steps:

[0033] (1) Polyethylene glycol-modified MnFe2O4 nanoparticles with a particle size of 1000 nm were loaded onto graphene aerogels. The specific preparation method was as follows: polyethylene glycol-modified MnFe2O4 nanoparticles were prepared by a conventional coprecipitation method, and then dispersed in water to form a 5 mg / mL aqueous dispersion. The graphene aerogel was placed in the magnetic nanoparticle aqueous dispersion, and stirred at 60°C and 150 rpm for 6 h to obtain a graphene aerogel loaded with magnetic nanoparticles. The loading amount of polyethylene glycol-modified MnFe2O4 nanoparticles on the graphene aerogel was 0.53% of the total mass of the graphene aerogel loaded with magnetic nanoparticles.

[0034] (2) fixing the graphene aerogel carrier loaded with magnetic nanoparticles obtained in step (1) in a reaction container, and placing the reaction container in an induction coil of an alternating magnetic field;

[0035] (3) An aqueous solution containing oxygen is introduced into the reaction vessel at a flow rate of 100 mL / min under the action of a peristaltic pump, and the magnetic field is turned on. The frequency of the alternating magnetic field is 500 kHz and the current is 45 A. The magnetic field is always turned on during the preparation process. The alternating magnetic field excites the magnetocaloric effect of the magnetic nanoparticles, inducing the formation of "hot spots" in the local micro-regions near the magnetic nanoparticles, inducing the solubility of the gas in the solution to decrease and precipitate on the surface of the magnetic nanoparticles to form surface micro-nano bubbles. After the surface micro-nano bubbles are formed, they detach from the surface of the magnetic nanoparticles under the shear force of the fluid flow to form free micro-nano bubbles.

[0036] The initial oxygen gas charged into 2000 mL of deionized water was 0.14 g. After the preparation was completed, the concentration of micro-nano bubbles was 5.8 × 10 8 Particles / mL water. The average particle size and PDI (dispersity index) of the prepared micro-nano bubbles were measured by a laser particle size analyzer and were 808.36nm and 0.185, respectively. The average particle size of MNBs at different time points (0min, 60min, 120min, and 240min) after preparation was analyzed at 25°C. The average particle size changed from the initial 808.36±25.38nm to 778.25±31.95nm at 240min, and the particle size change was not significant. This shows that the micro-nano bubbles prepared by this method can maintain stability at 25°C for at least 4 hours, showing excellent stability.

[0037] As can be seen from Examples 1 to 3, the larger the magnetic nanoparticles, the greater the loading, and the greater the intensity of the alternating magnetic field, the more heat is generated, and thus the larger the bubble size. When the intensity of the alternating magnetic field is determined, the size of the magnetic nanoparticles loaded on the carrier and the loading amount are determined, the heat generated is determined, and therefore the bubble size is also determined. The method of the present invention can produce micro-nano bubbles with a uniform particle size distribution in a determined magnetic nanoparticle size and a determined magnetic field.

[0038] Comparative Example 1

[0039] The only difference between Comparative Example 1 and Example 1 is that in step (3), the current is 45A, so that the magnetic field intensity increases, the heat generation of the magnetic nanoparticles on the carrier per unit time increases, and the resulting micro-nano bubble particle size uniformity deteriorates (PDI = 0.289) and the stability deteriorates. The average particle size of MNBs at different time points (0 min, 60 min, 120 min, 240 min) after preparation was analyzed at 25°C. The average particle size changed from the initial 245.36 ± 25.98 nm to 158.25 ± 33.59 nm at 240 min, and the particle size change was significant; this indicates that the micro-nano bubbles prepared by this method are less stable than those in Example 1.

[0040] Comparative Example 2

[0041] The only difference between Comparative Example 2 and Example 1 is that the flow rate in step (3) is 10.0 mL / min, which shortens the residence time of the bubbles in the hot zone. As a result, the uniformity of the particle size of the obtained micro-nano bubbles deteriorates (PDI=0.257) and the stability deteriorates. The average particle size of the MNBs at different time points (0 min, 60 min, 120 min, and 240 min) after preparation is analyzed at 25°C. The average particle size changes from the initial 178.63±37.12 nm to 134.92±45.34 nm at 240 min, and the particle size changes significantly. This indicates that the micro-nano bubbles prepared by this method are less stable than those in Example 1, and the concentration of the obtained micro-nano bubbles is lower, with a concentration of 1.2×10 7 particles / mL of water.

Claims

1. A method for continuously preparing micro-nano bubbles, characterized in that: The steps include: (1) loading magnetic nanoparticles onto an inert carrier, fixing the inert carrier loaded with magnetic nanoparticles in a reaction vessel, and placing the reaction vessel in an induction coil of an alternating magnetic field; (2) Turn on the magnetic field and transport the gas-containing aqueous solution into the reaction vessel. The magnetic nanoparticles generate a magnetocaloric effect under the action of the alternating magnetic field. The magnetocaloric effect causes the temperature of the magnetic nanoparticle region to increase and the solubility of the gas in water to decrease, forming micro-nano bubbles on the surface of the magnetic nanoparticles. The micro-nano bubbles on the surface of the magnetic nanoparticles detach from the surface of the magnetic nanoparticles under the shear force of the gas-containing aqueous solution to form bulk micro-nano bubbles, which are then discharged from the reaction vessel through the drain pipe.

2. The preparation method according to claim 1, wherein: In step (1), the inert carrier loaded with magnetic nanoparticles is prepared by the following method: specifically, the magnetic nanoparticles are prepared by a conventional coprecipitation method, and then dispersed in water to form a 3-5 mg / mL aqueous dispersion of magnetic nanoparticles. The inert carrier is placed in the aqueous dispersion of magnetic nanoparticles and stirred at 60-70° C. and 100-150 rpm for 6-8 hours.

3. The preparation method according to claim 2, wherein: The loading amount of the magnetic nanoparticles on the inert carrier is 0.28-0.53% of the total mass of the inert carrier loaded with the magnetic nanoparticles.

4. The preparation method according to claim 2, wherein: The magnetic nanoparticles are iron oxide nanoparticles or iron oxide compound MFe2O4 nanoparticles; wherein M is one of Mn, Mg, Zn, Co, Fe, Ni or Cu.

5. The preparation method according to claim 4, characterized in that: The particle size of the magnetic nanoparticles is 100-1000 nm.

6. The preparation method according to claim 4, characterized in that: The surfaces of the magnetic nanoparticles are modified by citric acid, sodium citrate, polyethylene glycol or polylysine.

7. The preparation method according to claim 2, characterized in that: The inert carrier is one of wood, polyurethane sponge or graphene aerogel; and the wood is delignified wood.

8. The preparation method according to claim 1, wherein: In step (2), the gas-containing aqueous solution is obtained by adding gas to deionized water, and the type of gas added is at least one of carbon dioxide, oxygen, nitrogen or hydrogen.

9. The preparation method according to claim 1, wherein: In step (2), the oscillation frequency of the alternating magnetic field is 7 to 500 kHz, and the current is 5 to 45 A.

10. The preparation method according to claim 1, characterized in that: In step (2), the flow rate of the gas-containing aqueous solution is 2.5 to 100 mL / min.

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