阅读说明：本技术 一种富介孔的六方氮化硼多孔材料的制备方法 (Preparation method of mesoporous-rich hexagonal boron nitride porous material ) 是由 王学斌 许晨阳 苗蒙 葛聪 于 2021-11-25 设计创作，主要内容包括：本发明公开了一种富介孔的六方氮化硼多孔材料的制备方法,其制备方法为：将硼砂溶于水中,同时加入氮源混合后形成悬浊液,加热搅拌,蒸干水分后得到前驱体。将前驱体压制成型或直接置于管式炉中,在保护气气氛下高温热解,反应一段时间后切换气氛刻蚀多余的碳后即可得到富介孔的六方氮化硼多孔材料。本发明方法具有原材料成本较低、易于操作、环境友好、原子利用率高、比表面积大、扩大化生产可行性高的特点。在水处理领域,该产品具有高吸附容量、吸附速率的特点,能够在高、低温或酸、碱等极端条件下稳定使用,并且可以通过简单的热处理等方式对使用后的产品进行循环再生。(The invention discloses a preparation method of a mesoporous-rich hexagonal boron nitride porous material, which comprises the following steps: dissolving borax in water, adding a nitrogen source, mixing to form a suspension, heating and stirring, and evaporating to remove water to obtain a precursor. And (3) pressing and molding the precursor or directly placing the precursor in a tubular furnace, carrying out high-temperature pyrolysis in a protective gas atmosphere, reacting for a period of time, and then switching the atmosphere to etch the redundant carbon to obtain the mesoporous-rich hexagonal boron nitride porous material. The method has the characteristics of low raw material cost, easy operation, environmental friendliness, high atom utilization rate, large specific surface area and high feasibility of expanded production. In the field of water treatment, the product has the characteristics of high adsorption capacity and adsorption rate, can be stably used under high and low temperatures or extreme conditions such as acid and alkali, and can be recycled and regenerated in a simple heat treatment mode and the like.)

1. The invention discloses a preparation method of a mesoporous-rich hexagonal boron nitride porous material and application of the mesoporous-rich hexagonal boron nitride porous material in the field of water treatment, and is characterized in that the hexagonal boron nitride porous material is a white light porous powder/block material, and has a high specific surface area (100-²The pore type is dominated by mesopores (the pore diameter is 2-50nm), and the preparation method comprises the following steps:

(1) dissolving borax in water, adding a nitrogen source, mixing to form a suspension, stirring, heating and evaporating to remove water to obtain a white precursor;

(2) after the precursor is formed or directly placed in a high-temperature heating furnace, introducing protective gas, heating to the reaction temperature A, and reacting for a certain time;

(3) and cooling to a certain temperature B, introducing an etching atmosphere for reaction for a period of time, and then cooling to room temperature to obtain the mesoporous-rich hexagonal boron nitride porous material.

2. The preparation method according to claim 1, wherein in the step (1), the borax can be any one or more of raw materials of borax such as sodium tetraborate decahydrate, sodium tetraborate pentahydrate, sodium tetraborate tetrahydrate, anhydrous sodium tetraborate and the like in any ratio.

3. The method according to claim 1, wherein in step (1), the nitrogen source is any one or more of melamine, cyanuric acid, dicyandiamide, urea, nitrogen carbide and ammonia.

4. The method according to claim 1, wherein in the step (1), the molar ratio of the boron atoms to the nitrogen atoms in the selected boron source and the nitrogen source is in the range of 1: 1-72.

5. The method according to claim 1, wherein the temperature for stirring and heating in step (1) is 60-95 ℃ for 2-36 hours.

6. The method as claimed in claim 1, wherein in the step (2), the temperature rise rate is 2-100 ℃/min, the reaction temperature A is 800-.

7. The method according to claim 1, wherein in the step (2), the shielding gas is any one or more of argon, nitrogen, hydrogen, helium, ammonia, and air.

8. The method according to claim 1, wherein in the step (2), when ammonia gas is used as the shielding gas, ammonia gas can be used as a nitrogen source for the reaction at the same time, no additional nitrogen source can be added during the reaction, and ammonia gas can be used as a gas for etching carbon.

9. The method according to claim 1, wherein in the step (3), the gas for etching carbon may be any one or more of oxygen, air, water vapor, and ammonia gas.

10. The method as claimed in claim 1, wherein the reaction temperature B in step (3) is 500-850 ℃, and the temperature is maintained at the reaction temperature B for 2-24h after the etching gas is replaced by the protective gas in claim 7.

11. The mesoporous-rich hexagonal boron nitride porous material of claim 1, comprising any one or a combination of more than one of a powder and a block.

Technical Field

The invention belongs to the field of preparation of porous ceramic materials, and particularly relates to synthesis of a mesoporous-rich hexagonal boron nitride porous adsorbent material and application thereof in the field of water treatment.

Background

Hexagonal boron nitride is a typical two-dimensional material, often referred to as "white graphite" because of its crystal structure similar to that of graphite. In practical use, in order to avoid troubles caused by stacking and agglomeration of the powders, the two-dimensional structure is often reassembled during synthesis to form a stably-communicated three-dimensional structure, which is called a three-dimensional hexagonal boron nitride porous material. The hexagonal boron nitride porous material has a theoretically ultrahigh specific surface area and can be applied to the field of pollutant adsorption in water treatment. Compared with the sewage adsorbent activated carbon commonly used in the industry, the hexagonal boron nitride has the same excellent performance. In addition, the hexagonal boron nitride has the characteristic of high temperature resistance, so that the hexagonal boron nitride can be simply regenerated at high temperature after being used, and the acid and alkali corrosion resistance of the hexagonal boron nitride allows the hexagonal boron nitride to be used under special extreme conditions. Therefore, the hexagonal boron nitride porous material is expected to become a novel advanced adsorbent in the field of water treatment.

Currently, the main dilemma of hexagonal boron nitride porous materials is the difficulty and high cost of their synthesis. Mainstream synthetic routes include hard template, soft template and no template approaches. The hexagonal boron nitride porous material synthesized by the hard template method has thicker pore wall and smaller specific surface area (less than 1000 m)²/g), and in addition, often requires tedious and dangerous de-templating operations (adv. func. mater.2018, 28, 1801205). The soft template method can synthesize a hexagonal boron nitride porous material with high specific surface area, but the cost is high, and the cost is mainly derived from a boron source such as a boron block copolymer (nat. nanotechnol.2007, 2, 43). The template-free method has lower cost in the methods, but the synthesized boron nitride has poor controllability generally and is difficult to prepare into a block. In the prior synthesis method, boron-containing compounds such as boric acid and dehydrate thereof including boron oxide and the like and nitrogen-containing compounds such as urea, melamine and ammonium chloride are used as raw materials, are directly mixed or are mixed and then shaped, and are roasted at high temperature in the atmosphere of ammonia gas or nitrogen gas and the like, and the ammonia gas can also serve as a nitrogen source in partial reaction.

Aiming at the problems of more synthesis procedures, higher cost of raw materials and certain danger in the prior art. The method adopts the borax with extremely low cost and the nitrogen source (such as melamine) with low cost in the boron source to prepare the precursor for high-temperature pyrolysis, and then the mesoporous-rich hexagonal boron nitride porous material can be prepared. The method has the characteristics of fewer synthesis steps, easiness in operation and the like, and provides a new idea for synthesis of the hexagonal boron nitride porous material. Compared with the flake hexagonal boron nitride synthesized by a borax-urea method (patent CN109650355A), the porous powder and the porous block synthesized by the method have three-dimensional through and loose porous structures and ultrahigh specific surface area, and are more suitable for the adsorption field. Compared with the high micropore specific surface area (micropore diameter is less than 2nm) and the low micropore specific surface area (mesopore diameter is less than 50nm) of a boric acid-melamine method (patent CN111377418A), the mesoporous-rich hexagonal boron nitride porous material has more excellent performance in the field of water treatment, particularly in the field of pollutant adsorption of molecules with larger sizes, and meanwhile, the characteristics of low cost of raw materials, excellent performance and the like provide feasibility for industrial production and commercial application of the boron nitride adsorbent.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a preparation method of a hexagonal boron nitride porous adsorbent material with low cost, easy operation, environmental friendliness and high performance. The invention provides a method for preparing a hexagonal boron nitride porous material with a complete macroscopic structure by directly pyrolyzing a precursor formed by borax and a certain nitrogen source at high temperature, which is easy to operate and low in cost, wherein the obtained product has extremely high specific surface area, has excellent performances in the field of water treatment adsorption, particularly macromolecular dye adsorption, oil adsorption and oil-water separation, and can achieve the effect of regeneration and recycling by simple heat treatment after adsorbing pollutants by combining the chemical inertia and high-temperature resistance of boron nitride. The technical scheme adopted by the invention is as follows: a preparation method of a hexagonal boron nitride porous material rich in mesopores comprises the following steps:

(1) dissolving borax in water, adding a nitrogen source, mixing to form a suspension, stirring, heating and evaporating to remove water to obtain a white precursor;

(2) after the precursor is formed or directly placed in a high-temperature heating furnace, introducing protective gas, heating to the reaction temperature A, and reacting for a certain time;

(3) and cooling to a certain temperature B, introducing an etching atmosphere for reaction for a period of time, and then cooling to room temperature to obtain the mesoporous-rich hexagonal boron nitride porous material.

In the step (1), the borax may be any one or a combination of more of the raw materials of borax such as sodium tetraborate decahydrate, sodium tetraborate pentahydrate, sodium tetraborate tetrahydrate, anhydrous sodium tetraborate, etc. in any proportion. Preferably, borax is selected from sodium tetraborate decahydrate.

In the step (1), the nitrogen source may be any one or more of melamine, cyanuric acid, dicyandiamide, urea, nitrogen carbide and ammonia. Preferably, melamine and urea are selected. More preferably, melamine is selected.

In the step (1), the molar ratio of boron atoms to nitrogen atoms in the selected boron source and nitrogen source is 1: (1-72). Preferably, the boron atom is selected: the molar ratio of nitrogen atoms is 1: 16.

In the step (1), the temperature for stirring and heating is 60-95 ℃ and the time is 2-36 h. Preferably, the temperature is selected to be 85 ℃ and the time is selected to be 12 h.

In the step (2), the heating rate is 2-100 ℃/min, the reaction temperature A is 800-. Preferably, the heating rate is set to 10 ℃/min, the reaction temperature is 1000 ℃, and the holding time is 6 h.

In the step (2), the protective gas may be any one or more of argon, nitrogen, hydrogen, helium, ammonia, and air. Preferably, nitrogen is chosen as the shielding gas.

In the step (2), when ammonia gas is used as the protective gas, ammonia gas can be used as a nitrogen source for reaction at the same time, no additional nitrogen source is added in the reaction process, and ammonia gas can be used as a gas for etching carbon.

In the step (3), the carbon etching gas may be any one or more of oxygen, air, water vapor, and ammonia. It is preferable in terms of cost to select air as the atmosphere for etching carbon.

In the step (3), the reaction temperature B is 500-850 ℃, and the temperature is kept for 2-24h at the reaction temperature B after the protective gas described in the claim 7 is switched to the etching gas. Preferably, the reaction temperature B is 600 ℃.

Further, the specific surface area of the hexagonal boron nitride porous material rich in mesopores is usually more than 100m²Per g, the sample prepared at present can reach 1420m at most²The pore size of the mesoporous silica gel is mainly distributed in 2-20 nm.

The prepared hexagonal boron nitride block or powder can be directly used for water pollution treatment.

Compared with the prior art, the preparation method of the invention has the following outstanding advantages:

1) the method has the advantages of simple and convenient operation and low equipment requirement, and the borax is used as a boron source with extremely low cost, so that the cost of raw materials for synthesizing the hexagonal boron nitride porous material is greatly reduced, the source is wide and easy to obtain, and the method is applicable to various different nitrogen sources.

2) The hexagonal boron nitride porous material obtained by the invention has a complete and uniform block structure, and the change of the process parameters within the range specified in the claims of the application has little influence on the higher crystallinity and purity of the developed product, and has excellent stability.

3) The invention adopts a simple template-free method for direct pyrolysis, can realize controllable macro preparation of high-quality hexagonal boron nitride powder and hexagonal boron nitride porous material, and the final product has ultra-thin pore walls and ultra-high specific surface area.

4) The hexagonal boron nitride porous material provided by the invention has excellent performance in the application aspect of adsorbing dyes and organic matters, wherein the maximum adsorption capacity to Congo red can reach 1096mg/g, and the hexagonal boron nitride porous material is the highest level in the field of the existing boron nitride adsorbent. The product can also adsorb pump oil with the weight 5.7 times of the pump oil, and the performance of the product is far superior to that of a plurality of common adsorbents in the market. The ultra-low cost is combined, and the great application and development potential of the product in the fields of water treatment adsorption and the like is shown.

Drawings

Fig. 1 is a picture of a hexagonal boron nitride porous material prepared in example 1 of the present invention.

Fig. 2 is an X-ray diffraction spectrum of the hexagonal boron nitride porous material prepared in example 1 of the present invention.

Fig. 3 is a scanning electron microscope photograph of the hexagonal boron nitride porous material prepared in example 1 of the present invention.

FIG. 4 is a TEM photograph of the hexagonal boron nitride porous material prepared in example 1 of the present invention.

Fig. 5 is a nitrogen adsorption and desorption curve of the hexagonal boron nitride porous material prepared in example 1 of the present invention.

Fig. 6 is a pore size distribution curve of the hexagonal boron nitride porous material prepared in example 1 of the present invention.

Fig. 7 is an adsorption isotherm of the hexagonal boron nitride porous material prepared in example 1 of the present invention on congo red dye.

Fig. 8 is a schematic diagram of the performance of the hexagonal boron nitride porous material prepared in example 1 of the present invention for adsorbing organic substances.

Detailed Description

The present invention will now be further described by way of specific examples, which are given by way of illustration and not of limitation, with reference to the accompanying drawings.

Example 1:

(1) dissolving 1.9 g of borax in a polytetrafluoroethylene container filled with 100 ml of water, adding 10.08 g of melamine after dissolving, stirring to form white emulsion, keeping the temperature of the emulsion in the container at 75 ℃, and stirring until the water is evaporated to dryness to obtain a precursor; (2) placing the precursor block in a stainless steel mold, placing the mold under a tablet press, performing compression molding under the pressure of 5MPa, placing the compression molded precursor in a tubular furnace, performing pyrolysis in a nitrogen atmosphere, heating to the first reaction temperature of 1000 ℃ at the heating rate of 10 ℃/min, and performing pyrolysis for 100 min; (3) and then cooling to 600 ℃, switching nitrogen into air, keeping the flow of the air at 1000ml/min, maintaining the second reaction temperature of 600 ℃ for 3h, and then naturally cooling to room temperature to obtain a hexagonal boron nitride porous material sample.

The hexagonal boron nitride porous material obtained in the above example 1 is a white light porous block structure (fig. 1); two peaks of 26 degrees, 43 degrees and 76 degrees in an X-ray diffraction spectrum (figure 2) respectively correspond to (002), (100) and (110) crystal faces of boron nitride, and no other miscellaneous diffraction peaks appear, which indicates that the crystallinity and the purity of the hexagonal boron nitride are better; the thin-wall honeycomb-shaped porous structure of the hexagonal boron nitride porous material obtained in example 1 can be observed in a scanning electron micrograph (figure 3) and a transmission electron micrograph (figure 4), and the obtained hexagonal boron nitride porous material has rich mesoporous structure in the transmission electron micrograph; the specific surface area of the sample of example 1 was calculated to be 1420m using standard Brunauer-Emmett-Teller analysis from the nitrogen desorption curve (FIG. 5)²(ii)/g; the pore size distribution curve (figure 6) can be obtained by applying a Quenching Solid Density Functional Theory (QSDFT) method, and the pore size of the sample is mainly distributed in the range of 2-20nm, and meanwhile, the sample with larger mesoporous specific surface area can be calculated.

The hexagonal boron nitride porous material obtained in example 1 is used for Congo red dye adsorption, and the maximum adsorption amount of 1096mg/g (figure 7) can be reached, which is the highest level in the current boron nitride adsorbent. The block sample is used for adsorbing oily pollutants (figure 8), can adsorb pump oil with the self weight of 5.7 times, can be easily separated from water, and avoids secondary pollution. The hexagonal boron nitride porous material prepared in example 1 is superior to common adsorbents in adsorption of various oily pollutants.

Examples 2 and 3

The first reaction temperature in step (2) of example 1 was changed to 900 ℃ and 1100 ℃, respectively, and the other operations were the same as in example 1. All can obtain hexagonal boron nitride porous materials with specific surface areas of 525m respectively²G and 458m²In terms of/g, the pore diameters are predominantly distributed in the range from 3 to 4nm and from 2 to 4nm, respectively. At higher temperatures (example 1), the slope of the initial rising curve of the specific surface area from the nitrogen desorption curve of example 2 is increased, indicating thatA greater specific surface area of the product is obtained at a pyrolysis temperature of 1000 ℃ compared to a pyrolysis temperature of 900 ℃, but with a further increase in the pyrolysis temperature (example 3), the specific surface area is reduced, due to the higher crystallinity of the product at the higher pyrolysis temperature.

Examples 4 and 5

The mass of melamine fed in step (1) of example 1 was changed to 5.04g and 15.12g, respectively, and the other operations were the same as in example 1. All can obtain boron nitride with a three-dimensional porous structure, and the specific surface areas are respectively 320m²G and 316m²In terms of a/g, the pore diameters are predominantly distributed in the range from 2 to 4nm and from 3 to 4nm, respectively.

Examples 6 and 7

The pyrolysis holding time in the step (2) of the example 1 is changed to 1h and 3h respectively, and other operations are the same as those in the example 1. The specific surface areas of the obtained hexagonal boron nitride porous materials are 353m respectively²(iv)/g and 261m²The pore diameters are mainly distributed in the range of 3-4 nm.

Example 8

The nitrogen source in step (1) of example 1 was changed to urea, and the mass was 28.83g (the molar ratio of boron and nitrogen was maintained as in example 1), and the other steps were the same as in example 1. The specific surface area of the obtained hexagonal boron nitride porous material is 169m²/g。