A boron hydride / magnesium composite sheet, its preparation method and application

Abstract

This invention discloses a boron hydride / magnesium composite sheet, its preparation method, and its applications, relating to the fields of environmental functional materials and wastewater treatment technology. The preparation method includes the following steps: under an inert atmosphere, boron hydride nanosheets and magnesium powder are mixed and ground at a mass ratio of (98~99.8):(0.2~2), and then pressed into a boron hydride / magnesium composite sheet blank; the boron hydride / magnesium composite sheet blank is placed in a vacuum or inert atmosphere, heated to 250~600℃ at a rate of 0.5~10℃ / min, and sintered at this temperature for 0.5~10 hours to obtain the boron hydride / magnesium composite sheet. This method is simple, environmentally friendly, and low-cost. In the obtained boron hydride / magnesium composite sheet, magnesium exists in a highly dispersed state at the interface of the boron hydride amorphous network. This unique structure synergistically enhances the absorption and utilization of visible light, improves the photogenerated charge separation efficiency, and significantly enhances the paramagnetic responsiveness of the material.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials and wastewater treatment technology, and in particular to a boron hydride / magnesium composite sheet, its preparation method, and its application. Background Technology

[0002] With the acceleration of industrialization, the treatment of industrial wastewater containing recalcitrant organic pollutants such as azo dyes has become a severe challenge. Advanced oxidation technologies, especially photocatalysis, are considered a promising water treatment solution because they can utilize light energy to deeply mineralize pollutants under mild conditions. However, the large-scale application of this technology has long been constrained by two major bottlenecks: first, the lack of catalytic materials with both high activity and broad spectral (especially visible light) response; and second, the difficulty in efficiently separating and recovering nanoscale catalysts from the reaction system after use, leading to high operating costs and potential secondary pollution. Therefore, developing novel photocatalytic materials that are efficient, stable, and easily separable and recoverable is key to promoting the practical application of this technology.

[0003] Boron hydride (HB), a two-dimensional material, has attracted widespread attention in recent years due to its unique layered structure and tunable electronic properties. Existing technologies have disclosed various methods for preparing HB nanosheets from precursors such as magnesium diboride (MgB2), confirming its availability as a novel type of nanomaterial. Simultaneously, existing technologies have also explored the applications of HB nanosheets in fields such as biomedicine, primarily utilizing their specific chemical activities (such as hydrogen production and antioxidant properties).

[0004] However, when existing technologies directly apply HB nanosheets to environmental engineering scenarios such as water treatment, the following inherent and unresolved technical drawbacks exist:

[0005] First, the material morphology does not match engineering requirements. Known applications (such as biomedicine) typically require HB to exist in nanoparticle form to facilitate dispersion and functionality. However, environmental engineering applications require catalysts to have macroscopic forms (such as bulk, sheet, or large particles) that are easy to fix, load, and recycle. Directly using HB nanosheet powder for water treatment will face the inherent problem of difficulty in completely separating and recovering it from the liquid phase, which can easily lead to catalyst loss and secondary pollution.

[0006] Second, the functional design is singular, lacking integration for engineering applications. Existing research mostly focuses on developing or utilizing a single chemical or biological activity of HB, failing to address the core contradiction of "catalysis and separation" in environmental engineering by synergistically designing and controlling the physical properties (such as magnetic properties) of HB. Therefore, existing HB materials do not possess the physical characteristics designed for easy engineering separation and recycling.

[0007] Third, there is a lack of effective forming processes from nanopowders to engineered devices. Existing technologies mostly stop at the preparation of HB nanopowders, lacking simple and reliable methods to combine this nanomaterial with other functional components (such as components for imparting magnetic responsiveness) and process them into structurally robust, performance-integrated macroscopic devices. This hinders the transition of HB materials from the laboratory to practical water treatment engineering.

[0008] Therefore, although HB nanosheets are known as a material, there has long been a lack of HB-based products specifically designed for environmental remediation, particularly wastewater treatment. Such a product should possess: 1) a macroscopic morphology suitable for engineering applications; 2) integrated functions of efficient photocatalysis and convenient magnetic separation; and 3) be prepared using simple and scalable processes. This constitutes a clear technological gap that has not yet been addressed by existing technologies. Summary of the Invention

[0009] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a boron hydride / magnesium composite sheet, its preparation method and application. The boron hydride / magnesium composite sheet has both visible light catalysis and magnetically assisted separation functions, aiming to overcome the limitations of the prior art in which boron hydride (HB) is only used as an active nanoparticle, which is difficult to directly meet the needs of environmental engineering, especially the problems of unsuitable form, difficulty in recycling and single function in wastewater treatment.

[0010] The technical solution of the present invention is as follows:

[0011] In a first aspect, a method for preparing a boron hydride / magnesium composite sheet is provided, comprising the following steps:

[0012] In an inert atmosphere, boron hydride nanosheets and magnesium powder were mixed and ground at a mass ratio of (98~99.8):(0.2~2), and then pressed into shape to obtain boron hydride / magnesium composite sheet blanks.

[0013] The boron / magnesium hydride composite sheet blank is placed in a vacuum or inert atmosphere and heated to 250-600°C at a rate of 0.5-10°C / min, and then sintered at that temperature for 0.5-10 hours to obtain the boron / magnesium hydride composite sheet.

[0014] In a preferred embodiment, the method for preparing the boron hydride nanosheets includes:

[0015] Precursor intercalation expansion: Magnesium diboride powder is reacted with a reaction solvent at 120~300℃ for 5~48 hours. After the reaction, the magnesium diboride precursor is obtained by solid-liquid separation, washing and drying.

[0016] Ion exchange and boron hydride stripping: The intercalated magnesium diboride precursor was dispersed in an acidic ion exchange system and stirred at 40~90℃ for 24~72 hours. Subsequently, the boron hydride nanosheets were obtained by ultrasonic treatment and gradient centrifugation.

[0017] The reaction solvent includes acetonitrile and ammonia; the volume ratio of acetonitrile to ammonia is (3~8):1.

[0018] The acidic ion exchange system comprises: a proton-type ionic liquid and water; the volume ratio of the proton-type ionic liquid to water is (0.5~2):1.

[0019] In a further preferred embodiment, the proton-type ionic liquid is selected from one or more of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methylimidazolium nitrate.

[0020] A further preferred technical solution is that the specific steps of the ultrasonic treatment include: ultrasonic treatment for 10 to 120 minutes under the conditions of power of 100 to 800W and frequency of 20 to 40kHz.

[0021] In a further preferred embodiment, the gradient centrifugation process includes: first, centrifuging at 1000-5000 rpm to collect the supernatant, and then centrifuging the supernatant at 8000-15000 rpm to collect the precipitate, thereby obtaining the boron hydride nanosheets.

[0022] In a preferred embodiment, the sintering process includes: heating to 300-500°C at a rate of 1-5°C / min and holding at that temperature for 1-5 hours.

[0023] In a second aspect, a boron hydride / magnesium composite sheet is provided, which is prepared by the preparation method described in the first aspect.

[0024] Thirdly, the application of boron hydride / magnesium composite sheet as described in the second aspect as a photocatalyst in the degradation of organic pollutants in water bodies under visible light irradiation is provided.

[0025] In a preferred embodiment, the organic pollutant in the water is an azo dye.

[0026] Fourthly, a wastewater treatment method is provided, which uses boron hydride / magnesium composite sheets as described in the second aspect as a photocatalyst in wastewater treatment, and performs assisted separation with the aid of a magnetic field after use.

[0027] Compared with the prior art, the advantages of the present invention are as follows:

[0028] (1) A material form and function system for engineering applications was created for the first time: HB nanosheets were combined with inexpensive magnesium through solid-phase composite sintering process to create a macroscopic self-supporting sheet with both photocatalytic activity and magnetically assisted separation function, which solved the core problem of HB material in environmental engineering that "has good performance but cannot be used".

[0029] (2) Achieving a leap from nanomaterials to practical devices: This invention not only focuses on the properties of the material itself, but also provides a simple method for processing it into devices that can be directly used in water treatment systems. The sheet form facilitates integration in fixed-bed or suspended-bed reactors, and its enhanced paramagnetism makes separation and recovery operations simple and efficient.

[0030] (3) It has outstanding industrialization potential: the entire preparation process (composite, tableting, sintering) has low raw material costs, simple steps, environmental friendliness, and is easy to scale up production. The resulting products have good stability and are very suitable for practical water treatment applications. Attached Figure Description

[0031] Figure 1 The X-ray diffraction (XRD) pattern of the boron hydride sheet prepared in Example 1 of this invention.

[0032] Figure 2 This is a scanning electron microscope (SEM) image of the boron hydride sheet prepared in Example 1 of the present invention.

[0033] Figure 3 The Fourier transform infrared (FT-IR) spectrum of the boron hydride sheet prepared in Example 1 of this invention is shown.

[0034] Figure 4 The image shows the X-ray diffraction (XRD) pattern of the boron hydride / magnesium composite sheet prepared in Example 2 of this invention.

[0035] Figure 5 The magnetization intensity-temperature (MT) curves of the boron hydride / magnesium composite sheets prepared in Examples 2 and 3 of this invention are shown.

[0036] Figure 6 This is a scanning electron microscope (SEM) image of the boron hydride / magnesium composite sheet prepared in Example 3 of the present invention.

[0037] Figure 7 Visible light catalytic degradation kinetic curves of the boron hydride sheet prepared in Example 1, the boron hydride / magnesium composite sheet prepared in Examples 3 and 4, and the unsintered boron hydride / magnesium composite sheet blank (physically mixed control sample) prepared in Example 3.

[0038] Figure 8This is a scanning electron microscope (SEM) image of the boron hydride / magnesium composite sheet prepared in Example 5 of the present invention. Detailed Implementation

[0039] This invention provides a boron hydride / magnesium composite sheet, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below.

[0040] This invention provides a method for preparing boron hydride / magnesium composite sheets, comprising the following steps:

[0041] In an inert atmosphere, boron hydride nanosheets and magnesium powder were mixed and ground at a mass ratio of (98~99.8):(0.2~2), and then pressed into shape to obtain boron hydride / magnesium composite sheet blanks.

[0042] The boron / magnesium hydride composite sheet blank is placed in a vacuum or inert atmosphere and heated to 250-600°C at a rate of 0.5-10°C / min, and then sintered at that temperature for 0.5-10 hours to obtain the boron / magnesium hydride composite sheet.

[0043] Specifically, this embodiment uses boron hydride (HB) nanosheets as the base material. Through solid-phase mixing, pressing, and controlled sintering with magnesium powder (Mg), a boron hydride / magnesium composite sheet was successfully prepared. The core innovation of this design lies in:

[0044] (1) Innovation in morphology and engineering adaptability: Through solid-state sintering process, nanoscale HB is transformed into macroscopic and robust self-supporting sheet material, which fundamentally solves the inherent problems of easy loss and difficult recycling of nanopowder catalysts in engineering applications.

[0045] (2) Functional integration innovation: The introduced magnesium element forms a unique interface structure with HB during the sintering process, and synergistically achieves dual functions: on the one hand, it regulates the electronic structure of HB and enhances its visible light photocatalytic activity; on the other hand, it significantly enhances the intrinsic paramagnetic response intensity of the material, so that it can be effectively captured by a high gradient magnetic field and achieve convenient separation after the reaction.

[0046] (3) Innovation in process path: The solid-state composite molding process of "mixing-pressing-sintering" is simple in steps and does not require complex equipment, providing a new and easily scalable technical path for transforming high-performance nanomaterials into practical engineering devices.

[0047] In some embodiments, the method for preparing the boron hydride nanosheets includes:

[0048] Precursor intercalation expansion: Magnesium diboride powder is reacted with a reaction solvent at 120~300℃ for 5~48 hours. After the reaction, the magnesium diboride precursor is obtained by solid-liquid separation, washing and drying.

[0049] Ion exchange and boron hydride stripping: The intercalated magnesium diboride precursor was dispersed in an acidic ion exchange system and stirred at 40~90℃ for 24~72 hours. Subsequently, the boron hydride nanosheets were obtained by ultrasonic treatment and gradient centrifugation.

[0050] The reaction solvent includes acetonitrile and ammonia; the volume ratio of acetonitrile to ammonia is (3~8):1.

[0051] The acidic ion exchange system comprises: a proton-type ionic liquid and water; the volume ratio of the proton-type ionic liquid to water is (0.5~2):1.

[0052] In some more specific embodiments, the proton-type ionic liquid is selected from one or more of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][PF4]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][PF4]), and 1-butyl-3-methylimidazolium nitrate ([BMIM][NO3]).

[0053] In some more specific embodiments, the concentration of the ammonia water is 15wt% to 28wt%.

[0054] In some more specific embodiments, the ultrasonic treatment includes the following steps: ultrasonic treatment for 10 to 120 minutes at a power of 100 to 800 W and a frequency of 20 to 40 kHz. Further, the ultrasonic treatment is performed in an intermittent mode, with a working cycle of 2 to 10 seconds and an intermittent cycle of 2 to 10 seconds.

[0055] In some more specific embodiments, the gradient centrifugation process includes: first, centrifuging at 1000-5000 rpm to collect the supernatant, and then centrifuging the supernatant at 8000-15000 rpm to collect the precipitate, thereby obtaining the boron hydride nanosheets.

[0056] In some embodiments, the sintering process includes heating to 300-500°C at a rate of 1-5°C / min and holding at that temperature for 1-5 hours.

[0057] In one specific embodiment, the method for preparing the boron hydride / magnesium composite sheet includes the following steps:

[0058] Step 1: Precursor intercalation expansion

[0059] Take 0.1-5 g of MgB2 powder and place it in a high-pressure reactor lined with polytetrafluoroethylene. Then add 10-100 mL of a mixed solvent prepared by acetonitrile and concentrated ammonia in a volume ratio of (3-8):1, where the concentrated ammonia serves as the intercalating agent and reaction medium. Place the sealed reactor in a drying oven and react at 120-300°C for 5-48 hours to allow ammonium ions to intercalate and achieve sufficient expansion of the precursor. After the reaction, filter and wash with ethanol 2-6 times to obtain the intercalated MgB2 precursor, and dry it at 40-100°C for later use.

[0060] Step 2: Ion exchange and boron hydride stripping

[0061] Weigh 0.05–2 g of the above precursor and disperse it in 50–200 mL of an acidic ion exchange system. The system can be a mixture of a proton-type ionic liquid and water (volume ratio (0.5–2):1). Under inert gas protection, stir the reaction at 40–90 °C for 24–72 hours to complete the H2O reaction. + For Mg 2+ Ion exchange yielded crude boron hydride (HB). The crude HB suspension was then sonicated for 10–60 minutes to facilitate its exfoliation into nanosheets. Finally, gradient centrifugation was used for separation and purification: first, unreacted material and thick flakes were removed by centrifugation at 1000–5000 rpm; then, the HB nanosheets were collected by centrifugation at 8000–15000 rpm to obtain an HB nanosheet dispersion, which was then dried to obtain HB nanosheet powder.

[0062] Step 3: Preparation of boron hydride / magnesium composite sheet

[0063] Under an inert atmosphere, the boron hydride (HB) powder obtained in step two is mixed with magnesium powder at a mass ratio of (98~99.8):(0.2~2) and ground for 10~120 minutes to achieve high homogeneity. The mixed powder is then pressed into a blank under a pressure of 5~50 MPa to obtain a boron hydride / magnesium composite sheet. The boron hydride / magnesium composite sheet blank is placed in a quartz tube and sealed, with the vacuum level inside the tube controlled at 1.5×10⁻⁶. -3 ~2.5×10 -3 Pa. The sealed quartz tube is placed in a tube furnace and sintered according to the set program: the temperature is increased from room temperature to the target temperature at a heating rate of 0.5~10℃ / min, and sintered at 250~600℃ for 0.5~10 hours. After sintering, a black, self-supporting boron hydride / magnesium composite sheet is obtained.

[0064] Based on X-ray diffraction (XRD) analysis and performance testing results, it is inferred that the magnesium element in the boron hydride / magnesium composite sheet obtained by the above preparation method exists in atomic clusters or a highly dispersed state at the amorphous network interface of HB. This unique structure helps to synergistically improve the material's absorption capacity for visible light, the separation efficiency of photogenerated charges, and the overall paramagnetic response intensity. Specifically, the XRD pattern of the boron hydride / magnesium composite sheet obtained by the above preparation method (as in Example 2) (…) Figure 4 The sample only showed diffraction peaks of elemental magnesium, without any new phase peaks of magnesium compounds or alloys, indicating that magnesium did not form a long-range ordered crystalline compound with HB. Meanwhile, the boron hydride / magnesium composite sheet obtained by the above preparation method (as in Example 3) exhibited significantly higher visible light photocatalytic activity than the boron hydride sheet (as in Example 1) and the physically mixed control sample (HB and magnesium powder cold-pressed without sintering). Figure 7 The presence of strong interfacial electronic interactions between magnesium and the HB matrix after sintering suggests that this enhances photocatalytic performance, consistent with the structural characteristics of highly dispersed magnesium and the formation of numerous active interfaces. Experiments show that the boron hydride / magnesium composite sheet prepared using the method described in this embodiment exhibits good degradation rates of organic pollutants under visible light. Furthermore, magnetic testing (MT curve) demonstrates significantly enhanced paramagnetism, enabling the sheet to be effectively enriched and separated by a high-gradient, strong magnetic field (such as an electromagnet) after the reaction, providing a feasible technical approach to solving the problem of nanocatalyst recovery.

[0065] This invention provides a boron hydride / magnesium composite sheet, which is prepared by the preparation method described above.

[0066] This invention provides an application of the boron hydride / magnesium composite sheet described above as a photocatalyst in the degradation of organic pollutants in water under visible light irradiation.

[0067] In some embodiments, the organic pollutant in the water is an azo dye.

[0068] This invention provides a wastewater treatment method that uses the boron hydride / magnesium composite sheet as described above as a photocatalyst in wastewater treatment, and then uses a magnetic field to assist in separation after use.

[0069] The present invention will be further described below through specific embodiments.

[0070] Example 1: Preparation of boron hydride (HB) sheets (control material, no Mg doping)

[0071] The steps in this embodiment are as follows:

[0072] Step 1: Precursor intercalation expansion

[0073] 0.1 g of MgB2 powder (99.8% purity) was placed in a high-pressure reactor lined with polytetrafluoroethylene. Then, 10 mL of a mixed solvent prepared by mixing acetonitrile and concentrated ammonia (28 wt%) in a 3:1 volume ratio was added, with the concentrated ammonia serving as both the intercalating agent and the reaction medium. The sealed reactor was placed in a drying oven and reacted at 120°C for 5 hours to allow ammonium ions to intercalate and fully expand the precursor. After the reaction, the precursor was filtered and washed three times with ethanol to obtain the intercalated MgB2 precursor, which was then dried at 40°C for later use.

[0074] Step 2: Ion exchange and boron hydride stripping

[0075] Weigh 0.05 g of the above-mentioned intercalated MgB2 precursor and disperse it in 50 mL of an acidic ion exchange system. The system is a mixture of a proton-type ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) and water (volume ratio 0.5:1). Under inert gas protection, the reaction is stirred at 40 °C for 36 hours to complete the H2 exchange process. + For Mg 2+ Ion exchange yielded crude boron hydride (HB). Subsequently, the HB crude product suspension was ultrasonically treated in an ultrasonic cleaner with a power of 300W and a frequency of 40kHz, using an intermittent working mode (5 seconds on, 5 seconds off), for a total treatment time of 60 minutes, to assist in its exfoliation into nanosheets. Finally, gradient centrifugation was used for separation and purification: first, unreacted matter and thick flakes were removed by centrifugation at 5000rpm, followed by centrifugation at 10000rpm to collect the HB nanosheets, obtaining an HB nanosheet dispersion, which was then dried to obtain HB nanosheet powder.

[0076] Step 3: Preparation of boron hydride sheets

[0077] Under an inert atmosphere, the boron hydride (HB) nanosheets obtained in step two were ground for 120 minutes. The mixed powder was then pressed into a blank at 10 MPa to obtain a boron hydride sheet blank. The boron hydride sheet blank was placed in a quartz tube and sealed, with the vacuum level inside the tube controlled at 1.5 × 10⁻⁶. -3 Pa. The sealed quartz tube was placed in a tube furnace and sintered according to the set program: the temperature was increased from room temperature to the target temperature at a heating rate of 5℃ / min, and sintered at 600℃ for 2.5 hours. After sintering, a black, self-supporting boron hydride sheet was obtained.

[0078] Figure 1 This is the X-ray diffraction (XRD) pattern of the boron hydride sheet prepared in this embodiment. Figure 1As shown, identifiable diffraction peaks exist at 2θ = 1.14° and 1.48° in the spectrum, corresponding to the (100) and (110) crystal planes of the boron hydride (HB) phase, respectively. This indicates that the synthesized boron hydride sheet has a short-range ordered structure. Furthermore, as shown in the inset, the XRD pattern of the boron hydride sheet in this embodiment exhibits a very broad diffuse peak in the range of 10° to 30°, which further confirms that the boron hydride sheet does not possess long-range ordered characteristics and belongs to a typical amorphous / nanocrystalline structure.

[0079] Figure 2 This is a scanning electron microscope (SEM) image of the boron hydride sheet prepared in this embodiment. From... Figure 2 As can be observed, the boron hydride sheet exhibits a non-uniformly stacked nanosheet dispersion morphology, with its aggregates resembling flowers. This morphology indicates that the boron hydride sheet is composed of highly stacked two-dimensional layers and exhibits good flexibility and ductility.

[0080] Figure 3 This is the Fourier transform infrared (FT-IR) spectrum of the boron hydride sheet prepared in this embodiment. By analyzing the position, intensity, and shape of the absorption bands in the mid-infrared region, the functional groups and molecular structure on the material surface can be identified. Figure 3 As shown, the FT-IR spectroscopy results confirm the successful synthesis of boron hydride sheets: located at 621 cm⁻¹ -1 1194cm -1 and 2921cm -1 The absorption peak at 1703 cm⁻¹ belongs to the vibrational mode of the BH group; while the absorption peak at 1703 cm⁻¹ belongs to the vibrational mode of the BH group. -1 The absorption peak at that point corresponds to the bending and stretching vibrations of the BHB bridge bond.

[0081] Figure 7 The catalytic degradation curves of the boron hydride sheets prepared in this embodiment on methylene blue (MB) solution under visible light irradiation are shown. The results show that within 70 minutes of simulated visible light irradiation, the degradation rate of the boron hydride sheets prepared in this embodiment is only about 20%, indicating that its visible light catalytic activity is weak.

[0082] Example 2: Preparation of boron hydride / magnesium composite sheets under low magnesium content, low temperature and short time conditions

[0083] This embodiment demonstrates the feasibility of preparing boron hydride / magnesium composite sheets under conditions of lower magnesium content, lower temperature, and shorter time.

[0084] Step 1: Precursor intercalation expansion

[0085] 1.0 g of MgB2 powder (99.8% purity) was placed in a high-pressure reactor lined with polytetrafluoroethylene. Then, 40 mL of a mixed solvent prepared by mixing acetonitrile and concentrated ammonia (28 wt%) in a 5:1 volume ratio was added, with the concentrated ammonia serving as both the intercalating agent and the reaction medium. The sealed reactor was placed in a drying oven and reacted continuously at 180°C for 12 hours to allow ammonium ions to intercalate and achieve sufficient expansion of the precursor. After the reaction, the precursor was filtered and washed four times with ethanol to obtain the intercalated MgB2 precursor, which was then dried at 60°C for later use.

[0086] Step 2: Ion exchange and boron hydride stripping

[0087] Weigh 0.5 g of the above-mentioned intercalated MgB2 precursor and disperse it in 80 mL of an acidic ion exchange system. The system is a mixture of a proton-type ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) and water (volume ratio 1:1). Under inert gas protection, the reaction is stirred at 60 °C for 48 hours to complete the H2 exchange process. + For Mg 2+ Ion exchange yielded crude boron hydride (HB). Subsequently, the HB crude product suspension was ultrasonically treated in an ultrasonic cleaner with a power of 300W and a frequency of 40kHz, using an intermittent working mode (5 seconds on, 5 seconds off), for a total treatment time of 30 minutes, to assist in its exfoliation into nanosheets. Finally, gradient centrifugation was used for separation and purification: first, unreacted matter and thick flakes were removed by centrifugation at 2500 rpm, followed by centrifugation at 12000 rpm to collect the HB nanosheets, obtaining an HB nanosheet dispersion, which was then dried to obtain HB nanosheet powder.

[0088] Step 3: Preparation of boron hydride / magnesium composite sheet

[0089] Under an inert atmosphere, the boron hydride (HB) nanosheets obtained in step two were mixed with magnesium powder at a mass ratio of 99.8:0.2 and ground for 40 minutes to achieve high homogeneity. The mixed powder was then pressed into a blank under a pressure of 20 MPa to obtain a boron hydride / magnesium composite sheet blank. The boron hydride / magnesium composite sheet blank was placed in a quartz tube and sealed, with the vacuum level inside the tube controlled at 2.0 × 10⁻⁶. -3 Pa. The sealed quartz tube was placed in a tube furnace and sintered according to the set program: the temperature was increased from room temperature to the target temperature at a heating rate of 8.5℃ / min, and sintered at 350℃ for 7.5 hours. After sintering, a black, self-supporting boron hydride / magnesium composite sheet was obtained.

[0090] Figure 4 The image shows the X-ray diffraction (XRD) pattern of the boron hydride / magnesium composite sheet prepared in this embodiment. Figure 4As shown, all diffraction peaks perfectly match the standard PDF card for elemental magnesium (Mg), and no diffraction peaks of other impurity phases or new phases were detected. This result indicates that the boron hydride (HB) component retains its amorphous structure and does not react with magnesium to form a long-range ordered crystalline compound, in which magnesium exists in a highly dispersed crystalline form.

[0091] Figure 5 The magnetization-temperature (MT) curves of the boron hydride / magnesium composite sheet prepared in this embodiment are shown. Figure 5 As can be seen, the magnetization of the sample decreases monotonically with increasing temperature, exhibiting typical paramagnetic characteristics. Notably, the curve is smooth throughout the entire test temperature range and does not show any abrupt characteristic peaks indicating a transition to ferromagnetic or antiferromagnetic order, directly proving that under these low magnesium doping ratios and mild processing conditions, the material did not form long-range magnetic order.

[0092] Example 3: Preparation of boron hydride / magnesium composite sheets under moderate magnesium content and moderate conditions

[0093] This embodiment demonstrates the preparation of boron hydride / magnesium composite sheets under conditions of moderate magnesium content, moderate temperature, and moderate time. It represents a more preferred and balanced combination of parameters in the technical solution of this invention.

[0094] Step 1: Precursor intercalation expansion

[0095] Two grams of MgB2 powder (99.8% purity) were placed in a high-pressure reactor lined with polytetrafluoroethylene. Then, 60 mL of a mixed solvent prepared by mixing acetonitrile and concentrated ammonia (28 wt%) at a volume ratio of 6:1 was added, with the concentrated ammonia serving as both the intercalating agent and the reaction medium. The sealed reactor was placed in a drying oven and reacted continuously at 200°C for 15 hours to allow ammonium ions to intercalate and achieve sufficient expansion of the precursor. After the reaction, the precursor was filtered and washed twice with ethanol to obtain the intercalated MgB2 precursor, which was then dried at 70°C for later use.

[0096] Step 2: Ion exchange and boron hydride stripping

[0097] Weigh 1 gram of the above-mentioned intercalated MgB2 precursor and disperse it in 100 mL of an acidic ion exchange system. The system is a mixture of a proton-type ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) and water (volume ratio 1.5:1). Under inert gas protection, the reaction is stirred at 70°C for 60 hours to complete the H2 exchange process. + For Mg 2+Ion exchange yielded crude boron hydride (HB). Subsequently, the HB crude product suspension was ultrasonically treated in an ultrasonic cleaner with a power of 300W and a frequency of 40kHz, using an intermittent working mode (5 seconds on, 5 seconds off), for a total treatment time of 40 minutes, to assist in its exfoliation into nanosheets. Finally, gradient centrifugation was used for separation and purification: first, unreacted matter and thick flakes were removed by centrifugation at 3000rpm, followed by centrifugation at 15000rpm to collect the HB nanosheets, obtaining an HB nanosheet dispersion, which was then dried to obtain HB nanosheet powder.

[0098] Step 3: Preparation of boron hydride / magnesium composite sheet

[0099] Under an inert atmosphere, the boron hydride (HB) nanosheets obtained in step two were mixed with magnesium powder at a mass ratio of 99:1 and ground for 60 minutes to achieve high homogeneity. The mixed powder was then pressed into a blank under a pressure of 30 MPa to obtain a boron hydride / magnesium composite blank (physical mixing control sample). The boron hydride / magnesium composite blank was placed in a quartz tube and sealed, with the vacuum level inside the tube controlled at 2.2 × 10⁻⁶. -3 Pa. The sealed quartz tube was placed in a tube furnace and sintered according to the set program: the temperature was increased from room temperature to the target temperature at a heating rate of 5℃ / min, and sintered at 450℃ for 5 hours. After sintering, a black, self-supporting boron hydride / magnesium composite sheet was obtained.

[0100] Figure 5 The magnetization-temperature (MT) curves of the boron hydride / magnesium composite sheet prepared in this embodiment are shown. Figure 5 It can be seen that the material still exhibits paramagnetic behavior throughout the temperature range, and no magnetic order transition peak was observed. Compared with Example 2, at the same test temperature, the MT curve of the boron hydride / magnesium composite sheet in this example shifted significantly upward overall, indicating that its magnetization is higher. This comparison confirms that appropriately increasing the magnesium content is an effective strategy to enhance the overall magnetic responsiveness of the material. Although the material is still in a paramagnetic state, the increase in magnetization provides a more favorable physical basis for subsequent use of external magnetic fields (such as electromagnets) to achieve assisted separation and recycling of the material.

[0101] Figure 6 This is a scanning electron microscope (SEM) image of the boron hydride / magnesium composite sheet prepared in this embodiment. The image clearly shows a complete and independent two-dimensional sheet structure, exhibiting excellent flexibility and ductility (with some areas showing bending or wrinkling). Notably, after mixing with magnesium powder and high-temperature sintering, the morphology of the boron hydride (HB) main sheet was well maintained, without significant melting, agglomeration, or structural collapse. This indicates that the solid-state sintering process used in this invention can effectively maintain the two-dimensional structural integrity of the HB matrix while introducing magnesium.

[0102] Figure 7 The catalytic degradation curves of methylene blue (MB) solution under visible light irradiation are shown for the boron hydride / magnesium composite sheet prepared in this embodiment and the unsintered physical mixture control sample. The results show that within 70 minutes of simulated visible light irradiation, the degradation rate of the sample prepared in this embodiment exceeds 90%, indicating that the boron hydride / magnesium composite sheet prepared in this embodiment has excellent visible light photocatalytic activity. In contrast, the degradation rate of the unsintered physical mixture control sample is only about 20%, close to that of the boron hydride sheet in Example 1, indicating that the sintering process is crucial for activating the interfacial synergistic effect between magnesium and boron hydride, thereby significantly improving photocatalytic performance.

[0103] Example 4: Preparation of boron hydride / magnesium composite sheets under high magnesium content, high temperature and high pressure conditions

[0104] This embodiment demonstrates the implementation of preparing boron hydride / magnesium composite sheets under high magnesium content, high temperature and pressure.

[0105] Step 1: Precursor intercalation expansion

[0106] 3 g of MgB2 powder (99.8% purity) was placed in a high-pressure reactor lined with polytetrafluoroethylene. Then, 80 mL of a mixed solvent prepared by mixing acetonitrile and concentrated ammonia (28 wt%) at a volume ratio of 7:1 was added, with the concentrated ammonia serving as both the intercalating agent and the reaction medium. The sealed reactor was placed in a drying oven and reacted continuously at 250°C for 24 hours to allow ammonium ions to intercalate and achieve sufficient expansion of the precursor. After the reaction, the precursor was filtered and washed five times with ethanol to obtain the intercalated MgB2 precursor, which was then dried at 80°C for later use.

[0107] Step 2: Ion exchange and boron hydride stripping

[0108] Weigh 1.5 g of the intercalated MgB2 precursor and disperse it in 150 mL of an acidic ion exchange system. The system is a mixture of a proton-type ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) and water (volume ratio 1.2:1). Under inert gas protection, the reaction is stirred at 80 °C for 72 hours to complete the H2O reaction. + For Mg 2+Ion exchange yielded crude boron hydride (HB). Subsequently, the HB crude product suspension was ultrasonically treated in an ultrasonic cleaner with a power of 300W and a frequency of 40kHz, using an intermittent working mode (5 seconds on, 5 seconds off), for a total treatment time of 50 minutes, to assist in its exfoliation into nanosheets. Finally, gradient centrifugation was used for separation and purification: first, unreacted matter and thick flakes were removed by centrifugation at 4000rpm, followed by centrifugation at 14000rpm to collect the HB nanosheets, obtaining an HB nanosheet dispersion, which was then dried to obtain HB nanosheet powder.

[0109] Step 3: Preparation of boron hydride / magnesium composite sheet

[0110] Under an inert atmosphere, the boron hydride (HB) nanosheets obtained in step two were mixed with magnesium powder at a mass ratio of 98.5:1.5 and ground for 90 minutes to achieve high homogeneity. The mixed powder was then pressed into a blank under a pressure of 50 MPa to obtain a boron hydride / magnesium composite sheet blank. The boron hydride / magnesium composite sheet blank was placed in a quartz tube and sealed, with the vacuum level inside the tube controlled at 2.5 × 10⁻⁶. -3 Pa. The sealed quartz tube was placed in a tube furnace and sintered according to the set program: the temperature was increased from room temperature to the target temperature at a heating rate of 7.5℃ / min, and sintered at 550℃ for 8.5 hours. After sintering, a black, self-supporting boron hydride / magnesium composite sheet was obtained.

[0111] Figure 7 The catalytic degradation curves of methylene blue (MB) solution by the boron hydride / magnesium composite sheet prepared in this embodiment under visible light irradiation are shown. The results show that the degradation rate of MB is approximately 50% within 70 minutes of simulated visible light irradiation. Compared with the preferred embodiment (Example 3, degradation rate >90% after 70 minutes), the catalytic efficiency of the boron hydride / magnesium composite sheet in this embodiment is reduced. This comparison indicates that although the material still retains significant photocatalytic activity when process parameters such as magnesium content and sintering temperature are increased, its catalytic performance is not optimal. This result provides important boundary data for optimizing the process parameter range of this invention, demonstrating the importance of "moderate conditions" (Example 3) for maximizing catalytic performance.

[0112] Example 5: Preparation of boron hydride / magnesium composite sheets under low energy consumption and mild conditions

[0113] This embodiment focuses on demonstrating the feasibility of implementing the technical solution under lower energy consumption and milder process conditions (including a mild ion exchange system, shorter grinding and sintering time, and lower sintering temperature and heating rate).

[0114] Step 1: Precursor intercalation expansion

[0115] Five grams of MgB2 powder (99.8% purity) were placed in a high-pressure reactor lined with polytetrafluoroethylene. Then, 100 ml of a mixed solvent prepared by mixing acetonitrile and concentrated ammonia (28 wt%) at a volume ratio of 8:1 was added, with the concentrated ammonia serving as both the intercalating agent and the reaction medium. The sealed reactor was placed in a drying oven and reacted continuously at 300°C for 48 hours to allow ammonium ions to intercalate and achieve sufficient expansion of the precursor. After the reaction, the precursor was filtered and washed six times with ethanol to obtain the intercalated MgB2 precursor, which was then dried at 100°C for later use.

[0116] Step 2: Ion exchange and boron hydride stripping

[0117] Weigh 2 g of the above-mentioned intercalated MgB2 precursor and disperse it in 200 mL of an acidic ion exchange system. The system can be a mixture of a proton-type ionic liquid (such as 1-butyl-3-methylimidazolium tetrafluoroborate) and water (volume ratio 2:1). Under inert gas protection, stir the reaction at 90 °C for 24 hours to complete the H2O reaction. + For Mg 2+ Ion exchange yielded crude boron hydride (HB). Subsequently, the HB crude product suspension was ultrasonically treated in an ultrasonic cleaner with a power of 300W and a frequency of 40kHz, using an intermittent working mode (5 seconds on, 5 seconds off), for a total treatment time of 10 minutes, to assist in its exfoliation into nanosheets. Finally, gradient centrifugation was used for separation and purification: first, unreacted matter and thick flakes were removed by centrifugation at 1000rpm, followed by centrifugation at 8000rpm to collect the HB nanosheets, obtaining an HB nanosheet dispersion, which was then dried to obtain HB nanosheet powder.

[0118] Step 3: Preparation of boron hydride / magnesium composite sheet

[0119] Under an inert atmosphere, the boron hydride (HB) nanosheets obtained in step two were mixed with magnesium powder at a mass ratio of 98:2 and ground for 10 minutes to achieve high homogeneity. The mixed powder was then pressed into a blank under a pressure of 5 MPa to obtain a boron hydride / magnesium composite blank. The boron hydride / magnesium composite blank was placed in a quartz tube and sealed, with the vacuum level inside the tube controlled at 1.8 × 10⁻⁶. - 3 Pa. The sealed quartz tube was placed in a tube furnace and sintered according to the set program: the temperature was increased from room temperature to the target temperature at a heating rate of 0.5℃ / min, and sintered at 250℃ for 0.5 hours. After sintering, a black, self-supporting boron hydride / magnesium composite sheet was obtained.

[0120] Figure 8 This is a scanning electron microscope (SEM) image of the boron hydride / magnesium composite sheet prepared in this embodiment. Figure 8As shown, the prepared boron hydride / magnesium composite sheet still maintains a clear two-dimensional lamellar structure, with intact layers and no obvious signs of melting or collapse. This fully demonstrates that the solid-state sintering process used in this invention has a wide process window and good robustness, and can successfully prepare structurally intact boron hydride / magnesium composite sheets even under relatively mild and low-energy conditions.

[0121] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a boron hydride / magnesium composite sheet, characterized in that, Includes the following steps: In an inert atmosphere, boron hydride nanosheets and magnesium powder were mixed and ground at a mass ratio of (98~99.8):(0.2~2), and then pressed into shape to obtain boron hydride / magnesium composite sheet blanks. The boron / magnesium hydride composite sheet blank is placed in a vacuum or inert atmosphere and heated to 250-600°C at a rate of 0.5-10°C / min, and then sintered at that temperature for 0.5-10 hours to obtain the boron / magnesium hydride composite sheet.

2. The preparation method according to claim 1, characterized in that, The method for preparing the boron hydride nanosheets includes: Precursor intercalation expansion: Magnesium diboride powder is reacted with a reaction solvent at 120~300℃ for 5~48 hours. After the reaction, the magnesium diboride precursor is obtained by solid-liquid separation, washing and drying. Ion exchange and boron hydride stripping: The intercalated magnesium diboride precursor was dispersed in an acidic ion exchange system and stirred at 40~90℃ for 24~72 hours. Subsequently, the boron hydride nanosheets were obtained by ultrasonic treatment and gradient centrifugation. The reaction solvent includes acetonitrile and ammonia; the volume ratio of acetonitrile to ammonia is (3~8):

1. The acidic ion exchange system comprises: a proton-type ionic liquid and water; the volume ratio of the proton-type ionic liquid to water is (0.5~2):

1.

3. The preparation method according to claim 2, characterized in that, The proton-type ionic liquid is selected from one or more of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methylimidazolium nitrate.

4. The preparation method according to claim 2, characterized in that, The specific steps of the ultrasonic treatment include: ultrasonic treatment for 10 to 120 minutes under the conditions of power of 100 to 800W and frequency of 20 to 40kHz.

5. The preparation method according to claim 2, characterized in that, The specific steps of the gradient centrifugation include: first, centrifuging at 1000~5000 rpm to collect the supernatant, and then centrifuging the supernatant at 8000~15000 rpm to collect the precipitate, thereby obtaining the boron hydride nanosheets.

6. The preparation method according to claim 1, characterized in that, The specific steps of the sintering process include: heating to 300-500°C at a rate of 1-5°C / min and holding at that temperature for 1-5 hours.

7. A boron hydride / magnesium composite sheet, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the boron hydride / magnesium composite sheet as described in claim 7 as a photocatalyst in the degradation of organic pollutants in water under visible light irradiation.

9. The application according to claim 8, characterized in that, The organic pollutant in the water is an azo dye.

10. A wastewater treatment method, characterized in that, The boron hydride / magnesium composite sheet as described in claim 7 is used as a photocatalyst in wastewater treatment, and after use, it is separated with the aid of a magnetic field.

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