A kind of eight hydrated hexanitrodibismuth crystal adsorbent and its preparation method and application

Abstract

The application relates to the technical field of inorganic functional materials, in particular to a hexanitrodibismuthate crystal adsorbent, a preparation method and application thereof, the chemical formula of the hexanitrodibismuthate crystal adsorbent is Bi2(NO2)6*8H2O, the hexanitrodibismuthate crystal adsorbent belongs to a triclinic crystal system, and the space group is P ‑1 ; the hexanitrodibismuthate crystal adsorbent has a three-dimensional open skeleton structure constructed by nitrite bridged bismuth ions and a crystallization water hydrogen bond network; the preparation method is prepared by adopting solvent hydrothermal synthesis of bismuth nitrate pentahydrate and 4-amino pyridine quaternary ammonium salt in an ethyl alcohol hydrobromide system and combining with a room-temperature crystallization method; the preparation process is simple, the conditions are mild, the cost is controllable, and the hexanitrodibismuthate crystal adsorbent has significant industrial application potential in the field of industrial printing and dyeing wastewater deep decolorization treatment.

Description

Technical Field

[0001] This invention relates to the field of inorganic functional materials technology, specifically to a bismuth octahydrate nitrite crystal adsorbent, its preparation method, and its application. Background Technology

[0002] Dye wastewater from industries such as dyeing and textiles is characterized by its complex composition, high color intensity, high toxicity, and difficulty in biodegradation, making it one of the most challenging aspects of industrial wastewater treatment. Adsorption methods, due to their ease of operation, high treatment efficiency, and lack of secondary pollution, have become one of the mainstream technologies for the deep treatment of dye wastewater. Among these, activated carbon is the most commonly used commercial adsorbent, but it suffers from drawbacks such as limited adsorption capacity (typically <200 mg / g for methylene blue), difficult regeneration, high cost, and easy saturation, which limit its large-scale application.

[0003] However, existing research mainly focuses on a few forms such as bismuth oxide and bismuth halide, and the exploration of their application as adsorbents is relatively limited, with performance needing improvement. Bismuth nitrate pentahydrate (Bi(NO3)3·5H2O), as a common bismuth salt precursor, is widely used in materials synthesis, but its performance as an adsorbent material itself is rarely studied or reported. In existing technologies, although there are various adsorbent materials for dye wastewater, such as modified clay, polymers, and metal-organic frameworks (MOFs), they often suffer from complex synthesis processes, high costs, poor stability, or unsatisfactory adsorption effects. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, the present invention aims to provide a bismuth octahydrate crystal adsorbent, its preparation method, and its application. The adsorbent forms a rich network of active sites and pores through a unique coordination polymer structure and hydrogen bond network. The method employs a solvothermal synthesis combined with room temperature crystallization, using readily available raw materials, with mild reaction conditions, requiring no complex equipment, and suitable for large-scale production.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A bismuth octahydrate crystalline adsorbent with the chemical formula Bi₂(NO₂)₆·8H₂O, has a triclinic crystal system and space group P. -1 The unit cell parameters are: a = 9.1076(3) Å, b = 9.5113(2) Å, c = 11.0313(3) Å, α = 101.438(2)°, β = 101.214(2)°, γ = 105.963(2)°, and the unit cell volume V = 868.49(5) ų.

[0007] The structure of the bismuth octahydrate hexanitrite crystal adsorbent contains two different nine-coordinate bismuth centers. The nitrite ions bridge adjacent bismuth ions through oxygen atoms, and the water molecules of crystallization jointly construct a three-dimensional supramolecular framework through coordination bonds and hydrogen bonds.

[0008] In a preferred embodiment of the present invention, the preparation method of the bismuth octahydrate hexahydrate crystal adsorbent includes the following steps:

[0009] Bismuth nitrate pentahydrate and 4-aminopyridine quaternary ammonium salt were dissolved in anhydrous ethanol to form a homogeneous solution of bismuth nitrate pentahydrate and an ethanol solution of 4-aminopyridine quaternary ammonium salt.

[0010] Add hydrobromic acid aqueous solution to a homogeneous solution of bismuth nitrate pentahydrate and carry out the first reflux reaction to form a reaction system.

[0011] An ethanol solution of 4-aminopyridine quaternary ammonium salt was added to the reaction system, and an aqueous solution of hydrobromic acid was added to maintain the acidic environment of the reaction system. A second reflux reaction was carried out to obtain the filtrate.

[0012] After the filtrate was allowed to stand and crystallize, bismuth nitrite octahydrate crystal adsorbent was obtained.

[0013] In a preferred embodiment of the present invention, the molar ratio of bismuth nitrate pentahydrate to 4-aminopyridine quaternary ammonium salt is 1:1 to 1.2.

[0014] In a preferred embodiment of the present invention, the mass concentration of the hydrobromic acid aqueous solution is 33%~48%, and the molar ratio of bismuth nitrate pentahydrate to hydrobromic acid is 1:3.0~3.2.

[0015] In a preferred embodiment of the present invention, the static crystallization adopts a staged temperature control strategy: the concentrated filtrate is first placed at 15°C~20°C for 2~3 weeks to induce crystal nuclei formation, and then transferred to a 25°C environment to continue static for 6~8 weeks to promote crystal growth. This method can obtain products with larger average particle size and better crystal integrity, and the yield is increased to more than 55%.

[0016] In a preferred embodiment of the present invention, the temperature in the first reflux reaction is 40°C to 50°C and the time is 16h to 24h; the temperature in the second reflux reaction is 60°C to 70°C and the time is 16h to 24h.

[0017] In a preferred embodiment of the present invention, the post-treatment of the second reflux reaction is to concentrate the reaction solution to 1 / 5 to 2 / 5 of its original volume by rotary evaporation under conditions of 45°C to 65°C water bath and vacuum degree ≥0.09 MPa, and then filter it.

[0018] The application of the bismuth octahydrate hexanitrite crystal adsorbent described in this invention in the treatment of dye wastewater.

[0019] The application of the bismuth octahydrate crystal adsorbent in dye wastewater treatment is characterized by its adsorption and removal of the cationic dye methylene blue by the bismuth octahydrate crystal adsorbent.

[0020] The application of the bismuth octahydrate nitrite crystal adsorbent of the present invention in the treatment of dye wastewater is characterized in that, in dye wastewater with an initial methylene blue concentration of 200 mg / L-300 mg / L, the adsorbent dosage is 0.5 g / L-1.0 g / L, the adsorption equilibrium time is 2 h-4 h, and the equilibrium adsorption capacity is not less than 600 mg / g.

[0021] The adsorption of methylene blue exhibits significant concentration-responsive characteristics: in the low concentration range of 0 mg / L-100 mg / L, the adsorption rate is low; when the concentration increases to 200 mg / L-300 mg / L, the adsorption rate steadily increases and reaches an equilibrium level of approximately 27%; at an initial concentration of 300 mg / L, the equilibrium adsorption capacity is as high as 639.79 mg / g, far exceeding the adsorption capacity of commercial activated carbon and the raw material bismuth nitrate pentahydrate, which have adsorption capacities of 170.56 mg / g for commercial activated carbon and 474.38 mg / g for the raw material bismuth nitrate pentahydrate.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. The novelty of the structure of the bismuth octahydrate crystal adsorbent of the present invention: The present invention is the first to synthesize and resolve the crystal structure of Bi2(NO2)6·8H2O, a compound that has never been reported before, filling the gap in bismuth nitrite hydrate crystal materials. The bismuth octahydrate crystal adsorbent has a large adsorption capacity and exhibits superior performance at high dye concentrations, making it particularly suitable for the pretreatment or deep decolorization of high-concentration dyeing and printing wastewater, and has clear industrial application value and market potential.

[0024] 2. The preparation method described in this invention employs a combination of solvothermal synthesis and room temperature crystallization. The reaction conditions are mild, requiring no complex equipment such as high-pressure reactors. The raw material conversion rate is >55%, making it easy to scale up production. Example 3 has been successfully scaled up 10 times, with controllable costs. The bismuth octahydrate crystal adsorbent prepared by the method exhibits good stability. Thermogravimetric-differential thermal analysis shows that the material is structurally stable below 100°C, fully meeting the requirements of conventional water treatment applications. The stable crystal structure allows for long-term storage under light-protected and dry conditions, demonstrating potential for industrial application. It shows significant efficiency in treating high-concentration dye wastewater, and the bismuth-based material itself is low in toxicity and environmentally friendly, possessing clear market value and industrialization prospects in the field of deep treatment of recalcitrant dye wastewater.

[0025] 3. The bismuth nitrite octahydrate crystal adsorbent of this invention has excellent adsorption properties: the equilibrium adsorption capacity of the crystal adsorbent for methylene blue reaches 639.79 mg / g, which is 3.75 times that of commercial activated carbon. Compared with the raw material bismuth nitrate pentahydrate, it achieves a performance leap from "inferior to superior", proving that its excellent performance is due to the unique nitrite coordination and crystal structure, rather than the simple effect of bismuth element; it has concentration-responsive characteristics: the adsorbent exhibits excellent adsorption effect in high-concentration dye wastewater, and is particularly suitable for deep decolorization treatment of industrial printing and dyeing wastewater, solving the problem of the sharp decline in efficiency of traditional adsorbents under high concentration conditions. Attached Figure Description

[0026] Figure 1 This is a structural diagram of the bismuth octahydrate nitrite crystal adsorbent of the present invention.

[0027] Figure 2 The XRD patterns of the experimental and theoretical simulation of the bismuth octahydrate nitrite crystal adsorbent of this invention are shown.

[0028] Figure 3 The infrared spectrum of the bismuth octahydrate crystal adsorbent prepared in Example 1 of this invention is shown.

[0029] Figure 4 This is a thermal performance curve of the crystal of the present invention.

[0030] Figure 5 This is a comparison chart of the adsorption rates of the crystals of the present invention, bismuth nitrate pentahydrate, and commercial activated carbon on methylene blue solution.

[0031] Figure 6 This is a bar chart comparing the adsorption capacities of the crystals of this invention, bismuth nitrate pentahydrate, and commercial activated carbon for methylene blue solution. Detailed Implementation

[0032] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0034] The hydrobromic acid aqueous solution used in the embodiments of the present invention has the following density parameters: 33 wt% HBr solution with a density of 1.31 g / mL at 20°C; 40 wt% HBr solution with a density of 1.38 g / mL at 20°C; and 48 wt% HBr solution with a density of 1.48 g / mL at 20°C. The molar mass of HBr is 80.91 g / mol. The volumetric feed amounts in the following embodiments are all calculated precisely based on the above parameters.

[0035] Example 1

[0036] (1) Weigh 1.0 mmol of bismuth nitrate pentahydrate and 1.0 mmol of 4-aminopyridine quaternary ammonium salt (N-ethyl-4-aminopyridine bromide) respectively, dissolve them in 10 mL of anhydrous ethanol, and sonicate them for 5 minutes to form a homogeneous and clear solution system.

[0037] (2) Transfer the bismuth nitrate pentahydrate ethanol solution to a 50 mL round-bottom flask, and slowly add 0.30 mL of 48 wt% hydrobromic acid aqueous solution under continuous magnetic stirring. The mass of HBr is 0.213 g and the number of moles is 2.63 mmol. After the acid is added, place the reaction system under reflux at 40°C for 24 hours.

[0038] (3) Subsequently, the ethanol solution of 4-aminopyridine quaternary ammonium salt was slowly added dropwise to the above reaction system, controlling the molar ratio of bismuth nitrate pentahydrate to 4-aminopyridine quaternary ammonium salt to be 1:1, and 0.06 mL of 48 wt% hydrobromic acid was added, with HBr mass of 0.043 g and molar number of 0.53 mmol, to maintain the acidic environment of the reaction system; at this time, the total molar ratio of bismuth nitrate pentahydrate to hydrobromic acid was 1:3.0. The temperature was raised to 60°C, and the reaction was continued under reflux for 24 hours to obtain a yellow transparent reaction solution.

[0039] (4) The obtained reaction solution was transferred to a rotary evaporator and concentrated to 4 mL under a vacuum of ≥0.09 MPa in a 45°C water bath. This volume was 1 / 5 of the original volume. After filtration, the filtrate was transferred to a 20 mL screw-top glass bottle and sealed. The bottle was then placed at 15°C for 2 weeks to induce crystal nuclei formation. Subsequently, it was transferred to a 25°C environment and placed for another 6 weeks to promote crystal growth. The total crystallization period was 8 weeks. During this period, yellow crystals and trace amounts of powder were slowly precipitated. After the crystals were fully precipitated, the solid product was collected by primary filtration. The filtrate was then sealed and placed for another 2 weeks. The second batch of crystals was collected by filtration again. The products obtained from the two filtrations were combined and dried under vacuum to obtain the target product, bismuth octahydrate crystals, with the chemical formula Bi2(NO2)6·8H2O and a yield of 57%.

[0040] Example 2

[0041] (0) Weigh 1.0 mmol of bismuth nitrate pentahydrate and 1.1 mmol of 4-aminopyridine quaternary ammonium salt (N-ethyl-4-aminopyridine bromide) respectively, dissolve them in 10 mL of anhydrous ethanol, and sonicate them for 5 minutes to form a homogeneous and clear solution system.

[0042] (1) Transfer the bismuth nitrate pentahydrate ethanol solution to a 50 mL round bottom flask. Under continuous magnetic stirring, slowly add 0.28 mL of 40 wt% hydrobromic acid aqueous solution. The mass of HBr is 0.155 g and the molar number is 1.91 mmol. After the acid is added, place the reaction system under reflux at 50°C for 20 hours.

[0043] (2) Subsequently, the ethanol solution of 4-aminopyridine quaternary ammonium salt was slowly added dropwise to the above reaction system, controlling the molar ratio of bismuth nitrate pentahydrate to 4-aminopyridine quaternary ammonium salt to be 1:1.1, and 0.14 mL of 48 wt% hydrobromic acid was added, with HBr mass of 0.100 g and molar number of 1.23 mmol, to maintain the acidic environment of the reaction system; at this time, the total molar ratio of bismuth nitrate pentahydrate to hydrobromic acid was 1:3.14. The temperature was raised to 65°C, and the reaction was continued under reflux for 20 hours to obtain a deep red transparent reaction solution.

[0044] (4) The obtained reaction solution was transferred to a rotary evaporator and concentrated to 5 mL under a vacuum of ≥0.09 MPa in a 50°C water bath. This volume was 1 / 4 of the original volume. After filtration, the filtrate was transferred to a 20 mL screw-top glass bottle and sealed. The bottle was then placed at 20°C for 2 weeks to induce crystal nuclei formation. Subsequently, it was transferred to a 25°C environment and placed for another 7 weeks to promote crystal growth. The total crystallization period was 9 weeks. During this period, yellow crystals and trace amounts of powder were slowly precipitated. After the crystals were fully precipitated, the solid product was collected by primary filtration. The filtrate was then sealed and placed for another 2 weeks. The second batch of crystals was collected by filtration again. The products obtained from the two filtrations were combined and dried under vacuum to obtain the target product, bismuth octahydrate crystals, with the chemical formula Bi2(NO2)6·8H2O and a yield of 56%.

[0045] Example 3

[0046] (3) Weigh 10.0 mmol of bismuth nitrate pentahydrate and 12.0 mmol of 4-aminopyridine quaternary ammonium salt (N-ethyl-4-aminopyridine bromide) respectively, dissolve them in 100 mL of anhydrous ethanol, and sonicate them for 5 minutes to form a homogeneous and clear solution system.

[0047] (4) Transfer the bismuth nitrate pentahydrate ethanol solution to a 250 mL three-necked flask, and slowly add 5.0 mL of 33 wt% hydrobromic acid aqueous solution under continuous magnetic stirring. The mass of HBr is 6.55 g and the molar number is 26.7 mmol. After the acid is added, place the reaction system under reflux at 50°C for 24 hours.

[0048] (5) Subsequently, the ethanol solution of 4-aminopyridine quaternary ammonium salt was slowly added dropwise to the above reaction system, controlling the molar ratio of bismuth nitrate pentahydrate to 4-aminopyridine quaternary ammonium salt to be 1:1.2, and 0.85 mL of 48 wt% hydrobromic acid was added, with HBr mass of 0.43 g and molar number of 5.27 mmol, to maintain the acidic environment of the reaction system; at this time, the total molar ratio of bismuth nitrate pentahydrate to hydrobromic acid was 1:3.2. The temperature was raised to 70°C, and the reaction was continued under reflux for 16 hours to obtain a yellow transparent reaction solution.

[0049] (6) The obtained reaction solution was transferred to a rotary evaporator and concentrated to 40 mL under a vacuum of ≥0.09 MPa in a 60°C water bath. This volume was 2 / 5 of the original volume. After filtration, the filtrate was transferred to a 200 mL sealed bottle. After sealing, the bottle was first placed at 18°C ​​for 2 weeks to induce crystal nuclei formation. Then, it was transferred to a 25°C environment and placed for another 8 weeks to promote crystal growth. The total crystallization cycle was 10 weeks. During this period, yellow crystals and trace amounts of powder were slowly precipitated. After the crystals were fully precipitated, the solid product was collected by primary filtration. The filtrate was then sealed and placed for another 2 weeks. The second batch of crystals was collected by filtration again. The products obtained from the two filtrations were combined and dried under vacuum to obtain the target product, bismuth octahydrate crystals, with the chemical formula Bi2(NO2)6·8H2O and a yield of 55%.

[0050] Comparative Example 1

[0051] Bismuth nitrate pentahydrate was purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd.

[0052] Comparative Example 2

[0053] Commercial activated carbon was purchased from Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd.

[0054] Results Analysis

[0055] Figure 1The diagram shows the structure of the bismuth octahydrate hexanitrite crystal adsorbent of this invention. The central bismuth ions Bi1 and Bi2 exhibit different coordination environments: Bi1 is coordinated with nine oxygen atoms, including O1, O2, O1#1, O12#2, O13#2, O14#3, and O15#3 from nitrite, as well as water of crystallization molecules O9W and O10W, forming a distorted coordination polyhedron; Bi2 also adopts a nine-coordinate mode, with coordinating atoms including O3, O4, O5, O6, O6#4, O7, O8, and water of crystallization molecules O11W and O In the 16W structure, the nitrite ions are bridged to adjacent bismuth ion centers by oxygen atoms. The adjacent bismuth atom polyhedra are bridged by sharing the NN edges of the nitrite ions. Crystallization water molecules play a key role in the construction of the three-dimensional network: O9W, O10W, O11W, and O16W are coordinated water molecules that are directly coordinated with bismuth ions, while free water molecules such as O17W, O18W, O19W, and O20W are connected to the coordinated water molecules and the oxygen atoms of the nitrite ions through a rich hydrogen bond network, together constructing a stable three-dimensional supramolecular framework.

[0056] Table 1 shows that Bi2(NO2)6·8H2O crystal belongs to the triclinic crystal system and has space group P. -1 Its unit cell parameters were determined to be a = 9.1076(3) Å, b = 9.5113(2) Å, c = 11.0313(3) Å, α = 101.438(2)°, β = 101.214(2)°, γ = 105.963(2)°, and the unit cell volume V = 868.49(5) ų. Compared with the standard bismuth nitrate pentahydrate structure (JCPDS 00-044-0314, a = 8.6521 Å, b = 10.6828 Å, c = 6.5253 Å, V = 568.6 ų), the cell volume of the new structure is significantly increased by 53%, and the triaxial lengths show a non-proportional change. The β angle in the axial angles decreases from 104.719° to 101.214°, indicating that the crystal has undergone a fundamental change in its packing mode.

[0057] Table 1 shows the data and structure refinement table for crystals.

[0058]

[0059] This open structure, formed by bismuth ion polyhedra linked by nitrite ions and combined with a complex hydrogen bond network, endows the material with abundant surface active sites and a well-developed pore system, providing a structural basis for its excellent adsorption performance.

[0060] Figure 2The experimental and theoretical XRD patterns of the bismuth octahydrate nitrite crystal adsorbent of this invention are shown. The positions of the main peaks of the measured and simulated curves are basically consistent, indicating that the experimental sample has crystallographic features similar to the simulated structure and the sample has high purity.

[0061] Figure 3 The infrared spectrum of the bismuth octahydrate nitrite crystal adsorbent prepared in Example 1 of this invention is shown at 3182 cm⁻¹. -1 The broadened absorption peak at 1614 cm⁻¹ is attributed to the stretching vibration of the OH bonds in the water of crystallization, while the peak at 1614 cm⁻¹ is attributed to the stretching vibration of the OH bonds in the water of crystallization. -1 The characteristic absorption peak appearing at 1535 cm⁻¹ corresponds to the HOH bending vibration of water molecules, and both together confirm the presence of water of crystallization in the crystal. -1 and 1338cm -1 The strong absorption peaks at these locations correspond to the asymmetric and symmetric stretching vibrations of the N=O bond in the nitrite group, respectively, with a wavenumber difference of Δν = 197 cm⁻¹. -1 This indicates that the nitrite ion is bonded to the bismuth ion in a monodentate coordination mode. 844cm -1 The absorption peak at 540 cm⁻¹ can be attributed to the bending vibration of the NO bond, while the absorption peak at 540 cm⁻¹ can be attributed to the bending vibration of the NO bond. -1 The characteristic peak at this location originates from the stretching vibration of the Bi-O bond. The position, intensity, and shape of the aforementioned characteristic absorption peaks are highly consistent with the target molecule structure, fully demonstrating the structural integrity of the water of crystallization and nitrite groups in this compound.

[0062] Figure 4 The thermal performance curves of the crystal of this invention show a typical three-stage thermal decomposition process. In the initial stage, from room temperature to 200°C, the sample loses approximately 5.62% of its weight. This process corresponds to the removal of surface adsorbed water and some crystal water. The thermogravimetric (TG) curve shows a gradual decrease, and differential scanning calorimetry (DSC) indicates an endothermic effect, proving that the material is structurally stable below 100°C, providing important evidence for its application under conventional water treatment conditions. In the main decomposition stage, from 200-300°C, a rapid weight loss occurs, reaching 35.97%. The derivative quotient TG curve shows a sharp peak at approximately 300°C, while the DSC shows a significant exothermic peak, indicating that the nitrite groups undergo rapid oxidative decomposition and release a large amount of heat. This stage is accompanied by the complete disintegration of the crystal structure. In the subsequent stage, from 300-600°C, the sample continues to lose weight slowly, with the residual mass decreasing from 58.4% to 20%. The derivative quotient TG curve shows a broad and gentle negative peak, indicating further pyrolysis of intermediate products rather than the decomposition of Bi₂O₃. This thermal behavior clearly defines the thermal stability range of the material.

[0063] The novel bismuth octahydrate Bi2(NO2)6·8H2O crystal adsorbent prepared by this invention exhibits unique concentration-responsive adsorption characteristics when treating dye wastewater.

[0064] Figure 5 The graph shows a comparison of the adsorption rates of the crystals, bismuth nitrate pentahydrate, and commercial activated carbon for methylene blue solution. In the low concentration range of 0-100 mg / L, the adsorption rate of methylene blue (MB) remains at a low level, indicating that its surface active sites need to be fully activated under a high mass transfer driving force. When the initial concentration of MB is increased to 200-300 mg / L, the adsorption rate shows a stable upward trend, eventually reaching an equilibrium level of about 27%, indicating that high concentration conditions are more conducive to the advancement of the adsorption reaction. Figure 6 This is a bar chart comparing the adsorption capacities of the crystal, bismuth nitrate pentahydrate, and commercial activated carbon for methylene blue solution, illustrating the synergistic effect of concentration-efficiency enhancement. Figure 6 Further explanation was obtained: at an initial MB concentration of 300 mg / L, the adsorption capacity increased dramatically to 639.79 mg / g, significantly higher than that of bismuth nitrate pentahydrate and conventional activated carbon (474.38 mg / g and 170.56 mg / g, respectively). This high adsorption capacity is attributed to the multi-layered porous structure of the crystal, constructed by nitrite bridging and a hydrogen bond network in the water of crystallization, which provides numerous accessible active sites for the dye molecules.

[0065] The superior performance of the bismuth octahydrate hexanitrite crystal adsorbent in high-concentration dye wastewater, as well as the abundant non-covalent interaction sites contained in its structure, provide an important material basis for its application in the field of advanced treatment of industrial high-concentration dye wastewater.

[0066] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0067] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A bismuth octahydrate nitrite crystal adsorbent, characterized in that, Its chemical formula is Bi₂(NO₂)₆·8H₂O, and its crystal structure belongs to the triclinic crystal system with space group P. -1 The unit cell parameters are: a = 9.1076(3) Å, b = 9.5113(2) Å, c = 11.0313(3) Å, α = 101.438(2)°, β = 101.214(2)°, γ = 105.963(2)°, and the unit cell volume V = 868.49(5) Å. 3 ; The structure of the bismuth octahydrate hexanitrite crystal adsorbent contains two different nine-coordinate bismuth centers. The nitrite ions bridge adjacent bismuth ions through oxygen atoms, and the water molecules of crystallization jointly construct a three-dimensional supramolecular framework through coordination bonds and hydrogen bonds.

2. The method for preparing the bismuth octahydrate nitrite crystal adsorbent according to claim 1, characterized in that, Includes the following steps: Bismuth nitrate pentahydrate and 4-aminopyridine quaternary ammonium salt were dissolved in anhydrous ethanol to form a homogeneous solution of bismuth nitrate pentahydrate and an ethanol solution of 4-aminopyridine quaternary ammonium salt. Add hydrobromic acid aqueous solution to a homogeneous solution of bismuth nitrate pentahydrate and carry out the first reflux reaction to form a reaction system. An ethanol solution of 4-aminopyridine quaternary ammonium salt was added to the reaction system, and an aqueous solution of hydrobromic acid was added to maintain the acidic environment of the reaction system. A second reflux reaction was carried out to obtain the filtrate. After the filtrate was allowed to stand and crystallize, bismuth nitrite octahydrate crystal adsorbent was obtained.

3. The method for preparing the bismuth octahydrate nitrite crystal adsorbent according to claim 2, characterized in that, The molar ratio of bismuth nitrate pentahydrate to 4-aminopyridine quaternary ammonium salt is 1:1 to 1.

2.

4. The method for preparing the bismuth octahydrate nitrite crystal adsorbent according to claim 2, characterized in that, The mass concentration of the hydrobromic acid aqueous solution is 33%~48%, and the molar ratio of bismuth nitrate pentahydrate to hydrobromic acid is 1:3.0~3.

2.

5. The method for preparing the bismuth octahydrate nitrite crystal adsorbent according to claim 2, characterized in that, The static crystallization process employs a staged temperature control strategy: the concentrated filtrate is first allowed to stand at 15°C~20°C for 2~3 weeks to induce crystal nuclei formation, and then transferred to a 25°C environment to continue standing for 6~8 weeks to promote crystal growth.

6. The method for preparing the bismuth octahydrate nitrite crystal adsorbent according to claim 2, characterized in that, In the first reflux reaction, the temperature was 40°C~50°C and the time was 16h~24h; in the second reflux reaction, the temperature was 60°C~70°C and the time was 16h~24h.

7. The method for preparing the bismuth octahydrate nitrite crystal adsorbent according to claim 2, characterized in that, The post-treatment of the second reflux reaction involves rotary evaporation to concentrate the reaction solution to 1 / 5 to 2 / 5 of its original volume under a water bath at 45°C to 65°C and a vacuum of ≥0.09 MPa, followed by filtration.

8. The application of the bismuth octahydrate nitrite crystal adsorbent according to claim 1 in the treatment of dye wastewater.

9. The application of the bismuth octahydrate nitrite crystal adsorbent according to claim 8 in dye wastewater treatment, characterized in that, Adsorption and removal of the cationic dye methylene blue by bismuth octahydrate crystal adsorbent.

10. The application of the bismuth octahydrate nitrite crystal adsorbent according to claim 9 in dye wastewater treatment, characterized in that, In dye wastewater with an initial methylene blue concentration of 200 mg / L to 300 mg / L, the adsorbent dosage is 0.5 g / L to 1.0 g / L, the adsorption equilibrium time is 2 h to 4 h, and the equilibrium adsorption capacity is not less than 600 mg / g.

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