Method for the preparation of hexagonal boron-nitride from ammonium borate precursors

Abstract

A method for preparing hexagonal boron-nitride includes processing a boron-containing aqueous solution, including introducing a water-soluble ammonium salt to the boron-containing aqueous solution, to obtain a processed solution, evaporating the processed solution to obtain a powder mixture, the powder mixture comprising ammonium borate and non-boron residues, and heat treating the powder mixture to obtain hexagonal boron nitride at a temperature in a range of 600 to 1000°C. A system includes a boron-containing aqueous solution source, at least one tank for boron-containing aqueous solutions, a first nitrogen source configured to introduce a water-soluble ammonium salt, a second nitrogen source that is different from the first nitrogen source configured to introduce ammonia gas, a solution evaporation system configured to hold at a temperature in a range of 50 to 300°C, and a powder heating system configured to hold at a temperature in a range of 600 to 1000°C.

Description

METHOD FOR THE PREPARATION OF HEXAGONAL BORONNITRIDE FROM AMMONIUM BORATE PRECURSORSBACKGROUND

[0001] The solution to the problems of hydrogen energy is based on the tasks associated with the production of hydrogen, its transportation, and its storage. Interest in technological applications of hexagonal boron nitride (h-BN) appeared in the second half of the twentieth century. Contribution to the development of techniques for its production began with using boric acid and urea as precursors materials where its final treatment at 1650 °C would produce boron nitride. This carbothermal reduction of boron oxide is now the predominant industrial method for producing h-BN. However, this process produces carbon dioxide, which is particularly undesirable in terms of environmental preservation. Further investigations have been dedicated to a wide range of boron and nitrogen precursors for h- BN synthesis have been studied, including syntheses that yield h-BN with high specific surface areas. However, many of these methods require extensive amounts of time and treatment processes including, microwave heating, chemical vapor deposition, physical vapor deposition, exfoliation, pyrolysis, etc.

[0002] Hydrogen storage methods can be divided into physical methods related to hydrogen liquefaction and chemical methods based on the strong interaction of molecular or atomic hydrogen with the storing materials. Nanostructures of hexagonal boron nitride are currently considered one of the most effective materials for ensuring effective physical sorption of hydrogen. The unique properties of this material, along with the capacity of its structure with respect to hydrogen and the methods of its optimization, are widely presented in the literature. However, the above-described methods of synthesizing h-BN do not extend to a method of simple mass production of hexagonal boron nitride nanostructures. Accordingly, there exists a need for systems and methods for the large- scale production of h-BN nanostructures that can be used for hydrogen storage.SUMMARY

[0003] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0004] In one aspect, embodiments disclosed herein relate to a system for preparing hexagonal boron-nitride from ammonium borate precursors. The system is used to select or create compounds of certain compositions, including intermediate phases as precursors. The system includes a boron-containing aqueous solution source, at least one tank for boron-containing aqueous solutions and brines of natural or artificial origin, a first nitrogen source fluidly connected to the at least one tank and configured to introduce a water-soluble ammonium salt, a second nitrogen source that is different from the first nitrogen source, fluidly connected to the at least one tank and configured to introduce ammonia gas, a solution evaporation system configured to hold at a temperature in a range of 50 to 300°C, and a powder heating system configured to hold at a temperature in a range of 600 to 1000°C.

[0005] Another embodiment described herein relates to a method for preparing hexagonal boron-nitride from ammonium borate precursors. The method is a sequence of steps to ensure the production of intermediate phases as precursors and their subsequent transformation into the final product, hexagonal boron nitride. The method includes processing a boron-containing aqueous solution, comprising introducing a water-soluble ammonium salt to the boron-containing aqueous solution, to obtain a processed solution, evaporating the processed solution to obtain a powder mixture, the powder mixture comprising ammonium borate and non-boron residues, and heat treating the powder mixture to obtain hexagonal boron nitride at a temperature in a range of 600 to 1000°C.

[0006] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.BRIEF DESCRIPTION OF DRAWINGS

[0007] FIG. 1 shows a schematic diagram representing a system in accordance with one or more embodiments.

[0008] FIG. 2 shows a schematic diagram representing a system including an ammonia gas source in accordance with one or more embodiments.

[0009] FIG. 3 shows another schematic diagram representing a system including an ammonia gas source in accordance with one or more embodiments.

[0010] FIG. 4 shows a schematic diagram representing a system including a dilution source in accordance with one or more embodiments.

[0011] FIG. 5 shows a schematic diagram representing a system including an alkaline source in accordance with one or more embodiments.

[0012] FIG. 6 shows a flowchart in accordance with one or more embodiments.

[0013] FIG. 7 shows a flowchart in accordance with one or more embodiments.

[0014] FIG. 8 shows a workflow process in accordance with one or more embodiments.

[0015] FIG. 9 shows a flowchart in accordance with one or more embodiments.

[0016] FIG. 10 shows a flowchart in accordance with one or more embodiments.DETAILED DESCRIPTION

[0017] In one aspect, embodiments disclosed herein relate to a system for preparing hexagonal boron nitride.

[0018] FIG. 1 shows a schematic diagram in accordance with one or more embodiments. As shown in FIG. 1, a system for preparing hexagonal boron nitride 100 may include at least one tank 105, a boron-containing aqueous solution source 102, a first nitrogen source 101, a second nitrogen source 103, a powder heating system 113, and a solution evaporation system 109. Each of these components are described in detail below.

[0019] The system for preparing hexagonal boron nitride 100 is configured to synthesize hexagonal boron-nitride nanostructures through the formation of ammonium borate precursors. In reference to FIG. 1, the at least one tank 105 may contain and process boron- containing aqueous solutions and brines of natural or artificial origin from a boron- containing aqueous solution source 102. As shown in FIG. 1, the at least one tank 105 may be a single tank that is connected to a first nitrogen source 101, a second nitrogen source 103, a powder heating system 113, and a solution evaporation system 109. However, it is also envisioned that the at least one tank 105 may include a sequential solution tank system where any of the sequential tanks may be connected to a first nitrogen source 101 , a second nitrogen source 103, a powder heating system 113, and a solution evaporation system 109. For example, a first tank may be connected to a first nitrogen source, while a second tank, downstream of the first tank may be connected to a second nitrogen source.

[0020] In keeping with FIG. 1, the at least one tank 105 is fluidly connected to a first nitrogen source 101 and a second nitrogen source 103. The first nitrogen source 101 is configured to introduce a water-soluble ammonium salt to the at least one tank 105. The second nitrogen source 103 is different from the first nitrogen source 101 and is configured to introduce ammonia gas to the at least one tank 105 as well as to the solution evaporation system 109 and the powder heating system 113.

[0021] The solution evaporation system 109 is configured to evaporate a mixture generated from the combination of a boron-containing aqueous solution and a water-soluble ammonium salt. The solution evaporation system 109 may be configured to evaporate the mixture at a temperature in the range of 50°C to 300°C. The solution evaporation system may include at least a temperature controller, a heating element to increase the temperature of the mixture to be evaporated, a stage that is either fixed or removable for holding the substance to be evaporatively heated, a vacuum pump, a temperature gauge, a pressure gauge, an gas inlet configured to introduce a gas or a mixture of gases and a plurality of valves configured to control the flow of an inlet and outlet. A suitable system known in the art may be used to evaporate the boron-containing aqueous solution so long as the evaporation takes place. For example, the solution evaporation system 109 may be an independent system that includes an inlet configured to receive a solution to be evaporated,an outlet for the which the non-evaporated residues may be removed, as well as the above- mentioned components. The solution evaporation may take place at atmospheric pressure, or the evaporation stage can also be adapted to vacuum conditions where the evaporation takes place under reduced pressure. Furthermore, the heating element used to heat the substance to drive evaporation may provide direct or indirect heating. However, it is also envisioned that vaporization of the solutions may take place in a settling tank. Thus, the solution evaporation system may also be used for evaporating and concentrating the boron- containing aqueous solutions.

[0022] The at least one tank 105 may also be connected to a powder heating system 113. The powder heating system may be configured to hold a temperature in the range of 600 to 1000°C. The powder heating system may include at least a timer and a controller which includes functionality to perform at least temperature ramping and temperature monitoring with the use of a thermocouple. For example, the powder heating system may include a controller that ramps the temperature to a set point temperature of 750°C, then maintains the set point temperature for 1 hour before cooling. The powder heating system 113 may further include an inlet to introduce ammonia gas 103.

[0023] According to one or more embodiments, the ammonia gas introduced to one or both of the powder heating system and the solution evaporation system may be the same or different from the second source of nitrogen 103. For example, the ammonia gas introduced to one or both of the powder heating system and the solution evaporation system may be different from the second source of nitrogen, if a sequential tank system is used. When the ammonia gas introduced to the powder heating system is different from the second nitrogen source, the powder heating system 113 may include an inlet to introduce ammonia gas 211 as shown for system 200 in FIG. 2. However, if the ammonia gas introduced to the solution evaporation system is different from the second source of nitrogen, the solution evaporation system may include an inlet to introduce ammonia gas 311 as shown for system 300 in FIG. 3.

[0024] As shown in FIG. 4, for system 400, the at least one tank 105 may also be connected to a dilution source 402. The dilution source 402 is configured to introduce diluents tobring the target borate concentration of a supersaturated boron-containing aqueous solution to an unsaturated state.

[0025] As shown in FIG. 5, for system 500, the at least one tank 105 may also include a connection to an alkaline source 515. The alkaline source may be configured to introduce a pH adjuster such that the reaction between the boron-containing aqueous solution and that of the water-soluble ammonium salt may be maintained at a pH of at least 8.

[0026] While the above-described powder heating and evaporative systems are introduced independently, it is envisioned that the system for preparing hexagonal boron nitride may include the powder heating system and evaporative systems as a combined system that may perform a plurality of functions. For example, the powder heating system and evaporative systems may be combined such that a single system may perform heating to cover both ranges of temperatures, 50°C to 300°C, for evaporating the boron-containing aqueous solutions, and 600°C to 1000°C for heat treating the powder mixtures.

[0027] Another aspect of the present disclosure relates to a method of preparing hexagonal boron-nitride. The above-described systems may be used to perform a method of preparing hexagonal boron-nitride. FIG. 6 shows a flowchart in accordance with one or more embodiments. Specifically, FIG. 6 describes a method 600 for preparing hexagonal boron- nitride. In block 604, boron-containing aqueous solution is processed to obtain a processed solution. As described above, the at least one tank 605 may be used to process the boron- containing aqueous solution using a dilution, alkaline or concentration source. Thus, processing the boron-containing aqueous solution may include diluting, adjusting the pH or concentrating the boron-containing aqueous solution depending on the borate concentration of the boron-containing aqueous solution.

[0028] In reference to FIG.7, the processing at block 604 includes diluting or concentrating the boron-containing aqueous solution depending on the borate concentration of the boron- containing aqueous solution. As shown in block 702, if the boron-containing aqueous solution is less than 1.0 wt% B2O3, then the boron-containing aqueous solution is concentrated, as shown in block 705, at the preparation stage to increase the subsequent yield of dry residue (BN precursor) after evaporation. In one or more embodiments, theconcentration of boron-containing aqueous solution may be increased by evaporating the solution or by mixing the solution with a similar solution of higher wt% B2O3 concentration. Thus, the solution evaporation system 109 may be used as a concentration source for the boron-containing aqueous solutions. If, however, the boron-containing aqueous solution is supersaturated, greater than 30.0 wt% B2O3, as shown in block 704, such as in the range of from 30 to 40 wt% B2O3, the boron-containing aqueous solution may be diluted as shown in block 710. According to one or more embodiments, the dilution source may be water or a low concentration water-salt solution of lower concentration than the boron-containing aqueous solution. However, if the boron-containing aqueous solution comprises a borate concentration in the range of 1.0 to 30.0 wt% B2O3, neither dilution nor concentration is required and the water-soluble ammonium salt may be introduced to the processed solution as-is according to block 711.

[0029] Referring again to FIGs. 6-7, given the ability to dilute or concentrate the boron- containing aqueous solution during processing at block 604, the boron-containing aqueous solution may be derived from natural or artificial sources. Solutions available for processing to form a precursor for the synthesis of h-BN can be complex multicomponent salt systems of different concentrations. The main requirement for the treatment of solutions is the presence of all salts in a dissolved state and the absence of residue. According to one or more embodiments, the boron-containing aqueous solution may be a boron-containing waste solution, natural boron solutions, borate solutions, brines, boron- containing solutions after drilling, drilling mud and mixtures thereof. Suitable boron- containing waste solutions may include but are not limited to byproducts of one or more of production of boric acid, production of boron compounds, production of dyes, the production of ceramics, metalworking, byproduct streams from paper industries, byproduct streams from pharmaceutical industries and byproduct streams from technological processes. Typical byproducts may include but are not limited to minerals such as datholite CaBSiOiOH and danburite CaB2Si20s, as well as their decomposition products of datholite concentrate, borogypsum, the main components of which are calcium sulfate dihydrate and amorphous silica. The average composition of borogypsum includes wt. %: SiO2 - 26-28, CaO - 26-28, SO ’ - 38-40, Fe2O3- 1.8-2, AI2O3 - 0.6-0.8, B2O3 - 0.7-1.2, MnO - 0.2,MgO - 0.1-0.2. However, it is envisioned that a boron-containing aqueous solution source may include a stream comprising a borate concentration of at least 0.1 wt% B2O3 in the range of 0.1 to 40 wt% B2O3, that has a presence of all salts in a dissolved state and an absence of residues, may be used in the method of the present disclosure.

[0030] In keeping with FIG. 7, the processing at block 604 includes, at block 711, introducing water-soluble ammonium salt to the boron-containing aqueous solution to obtain a processed solution. At block 714, the processed solution may then be injected with ammonia gas and then, at block 716, proceed to the evaporating step 612. As mentioned in the systems above with regard to FIG. 1, the first nitrogen source 101 is configured to introduce the water-soluble ammonium salt to the at least one tank 105. The introduction of the water-soluble ammonium salt to the at least one tank 105 with the boron-containing aqueous solution generates a processed solution which aids in the formation of ammonium borate and its hydrates. In block 711, the water-soluble ammonium salt is introduced to the boron-containing aqueous solution to form the processed solution that includes precursor phases of ammonium borate hydrates, water-soluble halide salts and residues of unreacted compounds. The reaction rate is influenced by several parameters including but not limited to solution composition, concentration of the components involved in the reaction, the content of the nitrogen source to be added, solution volume, homogenization intensity and environmental conditions. However, the amount of excess of the added ammonium salt affects the completeness of the reaction and its rate, and, consequently, the degree of processing of the solution into the final product, the ammonium borate precursor. The main part of borate precursors is synthesized at the stage of solution treatment before the evaporation process. According to one or more embodiments, the reaction time may range from 1 to 8 hours, such as a from a lower limit of 1, 2, 3, or 4 hours to an upper limit of 5, 6, 7 or 8 hours, where any lower limit may be paired with any upper limit.

[0031] According to one or more embodiments, the water-soluble ammonium salt introduced at block 711 may be an ammonium salt including but not limited to ammonium fluoride, ammonium chloride and mixtures thereof. Furthermore, the water-soluble ammonium salt may be added to the boron-containing aqueous solution within the at least one tank 105 in an amount that is in the range of 10-30% excess of the precursor ammoniumborate hydrates. The value of ammonium salt content in the range of 10-30% excess of the precursor ammonium borate hydrate is empirically determined to be the most effective to ensure a more complete interaction with the formation of precursor phases of ammonium borate hydrates. If the ammonium salt content is below the 10% excess, the reaction rate decreases and the time for reaction completion increases. When the addition of ammonium salt exceeds an excess of 30%, the products of the experiments contain an increased amount of unreacted salt, which has no effect on the course of the reaction. This excess of the water-soluble ammonium salt may also act as a source of nitrogen during subsequent stages such as heat treating of the powder mixture.

[0032] As shown in FIGs. 6-7, the method disclosed herein includes block 612. As shown in block 612, the processed solution may be evaporated to obtain a powder mixture. The above-described solution evaporation system 109 may be used to heat the processed solution and drive off the liquid to leave a powder. According to one or more embodiments, the powder mixture may include ammonium borate precursors, water-soluble salts, incompletely reacted and / or unreacted starting components and non-boron residues. The non-boron residues include reacted water-soluble salts that may be formed from the reaction of the water-soluble ammonium salts with non-boron species, i.e., other ions present in the boron-containing aqueous solution. Water-soluble chlorides are natural products of the reactions and are formed at the stages of solution treatment and evaporation. Residues of unreacted ammonium salts may also accumulate at these stages. The non-boron residues therefore may include but are not limited to water-soluble chloride salts, ammonium salts and mixtures thereof. The evaporation of the processed solution may take place at a temperature in the range of 50°C to 300°C.

[0033] As shown in FIG. 8, at block 612, the stage of evaporating the processed solution to form the powder mixture may also include, at block 812, adjusting the alkalinity of the mixture to maintain a pH of at least 8, at block 814, continuously mixing the mixture, at block 816, injecting the mixture with ammonia gas and, at block 818, crystallizing ammonium borate. According to one or more embodiments, the alkalinity of the mixture to be evaporated may require adjustment to a pH of at least 8, such that the mixture of the boron-containing aqueous solution and the water-soluble ammonium salt has a pH valuein the range of 8 to 14. While an acid or base may be used to adjust the alkalinity of the mixture, the alkalinity may preferably be maintained by the addition of a pH adjuster such as an alkali (e.g. sodium hydroxide) in solid or aqueous form. The mixture of the water- soluble ammonium salt and the boron-containing aqueous solution allows for ammonium salt dissociation and salt interaction with alkali metals from the pH adjuster or from alkalis already present in the boron-containing aqueous solution, and subsequent water-soluble chloride formation.

[0034] As mentioned above with regards to FIG. 1, the second nitrogen source 103 is configured to introduce ammonia gas. Referring to FIG. 8, the injection of the ammonia gas bubbling through the mixture to be evaporated during evaporation at block 612 may allow for the crystallization of borate precursors when the borate concentration of the boron-containing aqueous solution is in the range of 1.0-30 wt% B2O3. According to one or more embodiments, the ammonia gas may be injected into the mixture to be evaporated at a flow rate in the range of 1-10 mL / 10 liters of mixture to be evaporated per minute.

[0035] Referring again to FIG. 6, as mentioned above, the method may include heat treating or annealing the powder mixture at block 616. After the mixture is evaporated, the powder mixture may be heat treated at a temperature in the range of from 600 to 1000°C. According to the treatment temperature, powder volume, borate precursor content in the powder, and ammonia flow, the heating treatment time ranges from 20 to 90 minutes. According to one or more embodiments, and as shown in FIG.9, the heat treating 616 may include providing an atmosphere of ammonia gas, as shown in block 912 and volatilizing non-boron residues as shown in block 914. An atmosphere of ammonia gas may be provided in addition to the additional nitrogen source generated from a volatilization and / or thermal decomposition of the non-boron residues. Furthermore, the ammonia gas used during the heat treating 616 may be the same or different as the second nitrogen source described above and serve as a reaction gas to promote the formation of hexagonal boron nitride. For example, in a system comprising a single tank, as shown in FIG. 1, the second source of nitrogen, that is ammonia gas, may also be used as the source of ammonia gas for the heat treatment stage. If a sequential tank system is used, the ammonia gas introduced to the powder heating system may be different from the second source of nitrogen.

[0036] At the elevated temperatures of heat treating at block 616, the non-boron residues of the powder mixture may be volatilized, and excess water-soluble ammonium salts may be decomposed. At this stage of temperature treatment of borate precursor powder with dispersing water-soluble salts, ammonia acts as a reaction gas to promote the formation of hexagonal boron nitride. During this step, water-soluble chlorides are a very convenient and effective medium for dispersion. When the non-boron residues include a water-soluble chloride concentration of at least 15 wt% based on the total weight of the non-boron residues, the volatilization and / or thermal decomposition of the non-boron residues generates a dispersion medium that allows for more efficient heat treating of the powder mixture, efficient transformation of borate precursors and prevents the agglomeration of the ammonium borate and the formed hexagonal boron-nitride. Furthermore, an amount of more than 15wt%, contributes to a acceleration of the formation of hexagonal boron nitride and increases the completeness of the reaction. While the described method may still proceed when the water-soluble chloride concentration is less than 15 wt% of the non- boron residues or in the absence of the non-boron residues, the process does not display effective dispersion. Furthermore, the contents of the starting powder for heat treatment and the water-soluble chlorides as a dispersion medium in an amount of more than 15wt%, contribute to a significant acceleration of the formation of hexagonal boron nitride and increases the completeness of the reaction. At temperatures of 600-1000°C, residues of the excess water-soluble ammonium salts remaining after evaporation decompose and the non- boron residues volatilize, both of which serve as an additional source of nitrogen for the reaction of hexagonal boron nitride nanostructure formation. The excess is volatilized, but it is significantly less than 50 wt% of the residue. Exceeding an excess of 10-30 wt% water-soluble ammonium salt does not prevent effective dispersion.

[0037] As shown in FIG. 10, method 1000 may also include removing non-boron residues at block 1020. If during the heat treating 616, there is a remaining portion of non-boron residues that were not volatilized, the method may include removing the remaining portion of non-boron residues from the hexagonal boron nitride with distilled water or dilute aqueous dissolved salt solutions. After the completion of the reaction, distilled water willbe required for the final washing of boron nitride to remove the remaining water-soluble chloride salts from the system, if necessary.

[0038] Advantageously, one or more embodiments described herein may provide one or more of the following improvements: ability to process low-cost, low-concentration natural boron-containing solutions and industrial waste, increased reaction rates and efficiency, reduced environmental impact through recycling and lower carbon dioxide emissions. Furthermore, an increase in the efficiency of the transformation of borate precursors into hexagonal boron nitride during thermal treatment in the presence of a dispersing solid phase in the powder mixture provides a more complete reaction within a shorter time.

[0039] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

CLAIMSWhat is claimed is:

1. A method for preparing hexagonal boron-nitride comprising: processing a boron-containing aqueous solution, comprising introducing a water- soluble ammonium salt to the boron-containing aqueous solution, to obtain a processed solution, evaporating the processed solution to obtain a powder mixture, the powder mixture comprising ammonium borate and non-boron residues, and heat treating the powder mixture to obtain hexagonal boron nitride at a temperature in a range of 600 to 1000°C.

2. The method of claim 1, wherein the boron-containing aqueous solution has a borate concentration of greater than 30.0 wt% B2O3, and processing the boron-containing aqueous solution comprises diluting the boron-containing aqueous solution.

3. The method of claim 1, wherein the boron-containing aqueous solution has a borate concentration in a range of 1.0 to 30.0 wt% B2O3.

4. The method of claim 1, wherein the boron-containing aqueous solution has a borate concentration in a range of 0.1 to 1.0 wt% B2O3, and processing the boron-containing aqueous solution comprises concentrating the boron-containing aqueous solution.

5. The method of claim 1, wherein the water-soluble ammonium salt is introduced in an amount in a range of 10-30% of an excess based on the ammonium borate.

6. The method of claim 1, wherein processing the boron-containing aqueous solution further comprises: injecting the boron-containing aqueous solution with ammonia gas, and crystallizing ammonium borate.

7. The method of claim 1, wherein evaporating the processed solution further comprises: adjusting an alkalinity of the mixture to maintain a pH in a range of 8 to 14,continuously mixing the mixture, injecting the mixture with ammonia gas, and obtaining powder of a mixture of borate, water-soluble chlorides and unreacted ammonium salts.

8. The method of claim 6, wherein the ammonia gas is injected at a flow rate of 1-10 mL / 10 liters of solution per minute.

9. The method of claim 1, wherein the water-soluble ammonium salt is selected from the group consisting of ammonium chloride, ammonium fluoride and mixtures thereof.

10. The method of claim 1, wherein non-boron residues are reacted salts selected from the group consisting of chloride salts, non-reacted ammonium salts and mixtures thereof.

11. The method of claim 1, wherein the non-boron residues comprise a water-soluble chloride concentration of at least 15 wt%, and heat treating the powder mixture further comprises: providing an atmosphere of ammonia gas, and volatilizing at least a portion of the non-boron residues thereby forming a dispersion medium comprising an additional nitrogen source.

12. The method of claim 1, further comprising, after heat treating the powder mixture: removing a remaining portion of the non-boron residues from the hexagonal boron nitride with distilled water.

13. The method of claim 1 , wherein the boron-containing aqueous solution and selected from the group consisting of borate solutions, natural boron solutions and brines, boron- containing solutions after drilling, and boron-containing waste solutions, and mixtures thereof, wherein the boron-containing waste solutions are byproducts of one or more of production of boric acid, production of boron compounds, production of dyes, production of ceramics, metalworking, production of paper, and production in a pharmaceutical industry.

14. The method of claim 1, wherein evaporating the mixture is conducted at a temperature in a range of 50 to 300°C.1 . A system for preparing hexagonal boron nitride comprising: a boron-containing aqueous solution source, at least one tank for boron-containing aqueous solutions and brines of natural or artificial origin, a first nitrogen source fluidly connected to the at least one tank and configured to introduce a water-soluble ammonium salt, a second nitrogen source that is different from the first nitrogen source, fluidly connected to the at least one tank and configured to introduce ammonia gas, a solution evaporation system configured to hold at a temperature in a range of 50 to 300°C, and a powder heating system configured to hold at a temperature in a range of 600 to 1000°C.

16. The system of claim 15, further comprising a dilution source configured to dilute boron- containing aqeuous solutions and brines of natural or artificial origin within the at least one tank.

17. The system of claim 15, wherein the solution evaporation system is configured to evaporate and remove aqueous solutions.

18. The system of claim 15, wherein the powder heating system comprises an inlet configured to introduce ammonia gas.

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