A viologen polymer visible light catalyst, and a preparation method and application thereof

Abstract

The present application relates to the technical field of high polymer materials, and particularly relates to a viologen polymer visible light catalyst, a preparation method and application thereof, and specifically comprises the following steps: 4,4'-dipyridyl and poly (bromomethyl) substituted benzene are sequentially dissolved in a polar organic solvent to be fully dissolved, a potassium hydroxide solution is added, stirring and refluxing in an oil bath for 3-12 hours, after the reaction is completed, the mixture is cooled to room temperature, washed with acetonitrile three times in sequence, and then washed with deionized water until neutral, and finally, the product is treated by freeze-drying to obtain a brown-red solid; the polar organic solvent comprises at least one of acetonitrile, N,N-dimethylformamide and tetrahydrofuran. The present application shows excellent responsiveness to light, and can further improve the adsorption and removal effect on HCrO 4‑ under the promotion of visible light, effectively solves the problem of chromium adsorption recovery and removal in a solution with a high concentration, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a viologen polymer visible light catalyst, its preparation method, and its application. Background Technology

[0002] Rapid industrial development has led to an increasing number of heavy metal-containing wastewater leaks, posing a serious threat to water sources and human health. Cr(VI) has high solubility and mobility, easily penetrating cells and inducing the generation of reactive oxygen species, causing oxidative damage to cell tissues. It is a known carcinogen, teratogen, and mutagen. In contrast, Cr(III) is only one-thousandth as toxic as Cr(VI) and is an essential trace element for the human body. The World Health Organization stipulates that the maximum permissible concentration of Cr(VI) in domestic wastewater is 0.05 mg / L. Therefore, in complex aquatic environments containing competing ions, the efficient reduction of toxic Cr(VI) to the less toxic and less mobile Cr(III) remains a challenging problem to be solved.

[0003] Among various treatment technologies such as chemical precipitation, membrane separation, ion exchange, adsorption, and photocatalytic reduction, adsorption is favored due to its cost-effectiveness, high efficiency, and ease of operation. However, traditional adsorbents often suffer from limited adsorption capacity, slow kinetics, poor selectivity, and insufficient stability under strongly acidic conditions, severely restricting their practical application. Photocatalysis, with its advantages of low energy consumption, environmental friendliness, and sustainability, has been widely used and achieved significant results in environmental purification, energy conversion, and resource recycling. However, developing adsorbents that possess both high adsorption capacity and rapid adsorption capability, and can reduce hexavalent chromium to trivalent chromium under visible light irradiation, still faces significant challenges. Summary of the Invention

[0004] The features and advantages of the present invention are set forth in part in the description which follows, or may be apparent from the description, or may be learned by practicing the invention.

[0005] To overcome the problems of the prior art, the present invention provides a method for preparing a viologen polymer visible light catalyst, specifically including the following steps: 4,4'-bipyridine and poly(bromomethyl) substituted benzene are dissolved sequentially in a polar organic solvent until fully dissolved, potassium hydroxide solution is added, and the mixture is stirred and refluxed in an oil bath for 3-12 hours. After the reaction is completed, the mixture is cooled to room temperature and washed three times with acetonitrile, then washed with deionized water until neutral. The final product is freeze-dried to obtain a brownish-red solid. The polar organic solvent includes at least one of acetonitrile, N,N-dimethylformamide, and tetrahydrofuran.

[0006] Preferably, the poly(bromomethyl)substituted benzene comprises at least one of α,α'-dibromo-p-xylene, 1,3,5-tris(bromomethyl)benzene, 1,2,4,5-tetra(bromomethyl)benzene, 1,2,3,4,5-penta(bromomethyl)benzene, and 1,2,3,4,5,6-hexa(bromomethyl)benzene.

[0007] Preferably, the molar ratio of the 4,4'-bipyridine to the poly(bromomethyl) substituted benzene is 1-4:4-1.

[0008] Preferably, the temperature of the oil bath is 25~80 °C.

[0009] Preferably, the freeze-drying temperature is -50 °C and the drying time is 24 hours.

[0010] Preferably, the present invention also provides a viologen polymer visible light catalyst, which is prepared by the above-described method for preparing a viologen polymer visible light catalyst.

[0011] Preferably, the present invention also provides an application of a viologen polymer visible light photocatalyst, wherein the prepared viologen polymer visible light photocatalyst is used as an adsorption catalytic material in Cr 6+ In selective adsorption and reduction.

[0012] The beneficial effects of this invention are as follows: This application successfully designed and constructed a viologen-based ionic liquid polymer and discovered its highly efficient adsorption-catalytic reduction behavior of Cr(VI) in water under both dark and visible light conditions. By adjusting the monomer ratio, a multifunctional material with a mesoporous structure and visible light response was obtained, exhibiting excellent adsorption capacity and photocatalytic activity. Regarding adsorption performance, the maximum adsorption capacity of the product for Cr(VI) obtained in this application reached 449.461 mg / g and 667.495 mg / g under dark and visible light conditions, respectively. The adsorption behavior conforms to the Langmuir model and the pseudo-second-order kinetic model, indicating that it is a spontaneous monolayer chemisorption process. Thermodynamic parameters further confirm that this process is endothermic and driven by entropy increase. In actual metallurgical wastewater with strong acidity (pH = 1) and the coexistence of multiple ions, the catalyst still maintains excellent selective removal capacity of Cr(VI), demonstrating good potential for practical application. In summary, this application not only develops a class of high-performance adsorption-photocatalytic materials suitable for the removal of Cr(VI) in highly acidic and complex water bodies, but also reveals its structure-activity relationship and multi-mechanism synergistic effect at the molecular level.

[0013] The viologen polymer visible light catalyst prepared in this invention can also be used as an adsorbent for Cr. 3+This invention enables selective adsorption and degradation of chromium, such as in the removal of chromium from strongly acidic industrial wastewater. Furthermore, the viologen polymer visible light adsorption-catalyst prepared in this invention exhibits excellent photoresponse performance. By systematically controlling the monomer geometry and crosslinking strategy, the specific surface area, surface charge distribution, and optical properties of the material were optimized. The adsorption behavior of Cr(VI), including its kinetics, adsorption isotherm, and thermodynamic properties, was comprehensively studied under both dark and visible light conditions. This material demonstrates excellent Cr(VI) adsorption capacity under dark conditions and exhibits enhanced removal rate and photoreduction efficiency under visible light irradiation.

[0014] The viologen polymer visible light catalyst prepared in this invention is prepared by ionic liquid modification, which enriches its surface with positive charges, enabling it to react with HCrO, which exhibits a negative charge in aqueous solution. 4- Selective enrichment and adsorption are achieved; its interaction with HCrO 4- The adsorption process involves multiple reaction mechanisms, including electrostatic interactions, coordination interactions, and redox reactions, resulting in high adsorption capacity and good adsorption effect. Furthermore, due to its excellent light responsiveness, its adsorption of HCrO can be further enhanced under visible light. 4- Its adsorption and removal effect can effectively solve the problem of chromium adsorption, recovery and removal in high concentration solutions, and has broad application prospects. Attached Figure Description

[0015] The present invention will be described in detail below with reference to the accompanying drawings and examples. The advantages and implementation methods of the present invention will become more apparent from this description. The accompanying drawings are for illustrative purposes only and do not constitute any limitation on the present invention. In the accompanying drawings: Figure 1 This is a flowchart illustrating the preparation method of a viologen polymer visible light catalyst in a specific embodiment of the present invention. Figure 2 This is a scanning electron microscope image of an adsorption-promoting adsorbent of a viologen polymer visible light catalyst in a specific embodiment of the present invention. Figure 3 This is a graph showing the effect of pH on the adsorption process of viologen polymer visible light catalyst in a specific embodiment of the present invention. Figure 4 HCrO under both illuminated and unilluminated conditions is described in specific embodiments of the present invention. 4- Graph illustrating the effect of adsorption time on adsorption capacity; Figure 5 This is a graph showing the effect of initial concentration on adsorption capacity under both light and no light conditions in a specific embodiment of the present invention; Figure 6This invention provides a specific embodiment of a viologen polymer visible light photocatalyst for HCrO in a complex mixed solution. 4- Selective influence analysis diagram; Figure 7 This is a graph showing the effect of temperature on the adsorption process of viologen polymer visible light catalyst in a specific embodiment of the present invention. Figure 8 This is a radical diagram of a viologen polymer visible light catalyst in a specific embodiment of the present invention. Detailed Implementation

[0016] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0017] Example 1

[0018] like Figure 1 As shown, this invention provides a method for preparing a viologen polymer visible light catalyst, specifically including the following steps: In a 100 mL round-bottom flask, 1 mmol of 4,4'-bipyridine and 1 mmol of poly(bromomethyl)-substituted benzene are sequentially dissolved in a polar organic solvent until fully dissolved. After each addition, the mixture is sonicated for 5 minutes to ensure complete dissolution. Potassium hydroxide solution is added, and the mixture is stirred and refluxed in an 80 °C oil bath for 3 hours. After the reaction is complete, the mixture is cooled to room temperature and washed three times with acetonitrile to remove unreacted monomers. Then, it is washed with deionized water until neutral. The final product is freeze-dried at -50 °C for 24 hours to obtain a brownish-red solid, denoted as CPN-2. The polar organic solvent includes at least one of acetonitrile, N,N-dimethylformamide, and tetrahydrofuran. In this embodiment, the poly(bromomethyl)-substituted benzene is α,α'-dibromo-p-xylene, and the polar organic solvent is 40 mL of acetonitrile. The potassium hydroxide solution is prepared by dissolving 1.0 g of potassium hydroxide in 5 mL of deionized water.

[0019] In this embodiment, a viologen polymer with excellent adsorption and photocatalytic properties was successfully prepared via a one-pot method using 4,4-bipyridine and α,α'-dibromo-p-xylene as reactants. The prepared viologen polymer visible light photocatalyst reacts with HCrO. 4- The interaction between them, including electrostatic interactions, coordination interactions, and redox interactions, enables the control of HCrO. 4- Selective adsorption and degradation of HCrO in water. Furthermore, light irradiation is used to promote the adsorption process, achieving selective adsorption and degradation of HCrO in water. 4- Highly efficient removal.

[0020] Meanwhile, viologen polymer visible light catalysts were prepared using the same method described above, except that the molar ratios of 4,4'-bipyridine and α,α'-dibromo-p-xylene were 1:2.1:3, 1:4, 2:1, 3:1, and 4:1, respectively. Both methods yielded brownish-red solids, designated as CPN-2, for later use.

[0021] Example 2

[0022] This embodiment provides a method for preparing a viologen polymer visible light photocatalyst, specifically including the following steps: In a 100 mL round-bottom flask, 2 mmol of 4,4'-bipyridine and 1 mmol of 1,3,5-tris(bromomethyl)benzene were dissolved sequentially in 40 mL of acetonitrile, sonicated for 5 minutes after each addition to ensure complete dissolution. Then, 1.0 g of potassium hydroxide was dissolved in 5 mL of deionized water and added to the reaction mixture. The mixture was magnetically stirred and refluxed in an oil bath at 25 °C for 3 hours. After the reaction was complete, the mixture was cooled to room temperature and washed three times with acetonitrile to remove unreacted monomers, followed by washing with deionized water until neutral. The final product was freeze-dried at -50 °C for 24 h to obtain a brownish-red solid, designated CPN-3.

[0023] Meanwhile, viologen polymer visible light catalysts were prepared using the same method described above, except that the molar ratios of 4,4'-bipyridine and 1,3,5-tris(bromomethyl)benzene were 1:1, 1:2, 1:3, 1:4, 3:1, and 4:1, respectively. In all cases, a brownish-red solid was obtained and designated as CPN-3 for later use.

[0024] Example 3

[0025] In a 100 mL round-bottom flask, 2 mmol of 4,4'-bipyridine and 1 mmol of 1,2,4,5-tetra(bromomethyl)benzene were dissolved sequentially in 40 mL of acetonitrile, sonicated for 5 minutes after each addition to ensure complete dissolution. Subsequently, 1.0 g of potassium hydroxide was dissolved in 5 mL of deionized water and added to the reaction mixture. The mixture was then refluxed magnetically in an oil bath at 80 °C for 12 hours. After the reaction was complete, the mixture was cooled to room temperature and washed three times with acetonitrile to remove unreacted monomers, followed by washing with deionized water until neutral. The final product was freeze-dried at -50 °C for 24 h to obtain a brownish-red solid, designated CPN-4.

[0026] Meanwhile, viologen polymer visible light catalysts were prepared using the same method described above, except that the molar ratios of 4,4'-bipyridine and 1,2,4,5-tetra(bromomethyl)benzene were 1:1, 1:2, 1:3, 1:4, 3:1, and 4:1, respectively. In both cases, a brownish-red solid was obtained and designated as CPN-4 for later use.

[0027] Example 4

[0028] In a 100 mL round-bottom flask, 2 mmol of 4,4'-bipyridine and 1 mmol of 1,2,3,4,5-penta(bromomethyl)benzene were dissolved sequentially in 40 mL of acetonitrile, sonicated for 5 minutes after each addition to ensure complete dissolution. Subsequently, 1.0 g of potassium hydroxide was dissolved in 5 mL of deionized water and added to the reaction mixture. The mixture was then refluxed magnetically in an oil bath at 80 °C for 12 hours. After the reaction was complete, the mixture was cooled to room temperature and washed three times with acetonitrile to remove unreacted monomers, followed by washing with deionized water until neutral. The final product was freeze-dried at -50 °C for 24 h to obtain a brownish-red solid, designated CPN-5.

[0029] Meanwhile, viologen polymer visible light catalysts were prepared using the same method described above, except that the molar ratios of 4,4'-bipyridine and 1,2,3,4,5-penta(bromomethyl)benzene were 1:1, 1:2, 1:3, 1:4, 3:1, and 4:1, respectively. In both cases, a brownish-red solid was obtained and designated as CPN-5 for later use.

[0030] Example 5

[0031] In a 100 mL round-bottom flask, 2 mmol of 4,4'-bipyridine and 1 mmol of 1,2,3,4,5,6-hexa(bromomethyl)benzene were dissolved sequentially in 40 mL of acetonitrile, sonicated for 5 minutes after each addition to ensure complete dissolution. Subsequently, 1.0 g of potassium hydroxide was dissolved in 5 mL of deionized water and added to the reaction mixture. The mixture was then refluxed magnetically in an oil bath at 80 °C for 12 hours. After the reaction was complete, the mixture was cooled to room temperature and washed three times with acetonitrile to remove unreacted monomers, followed by washing with deionized water until neutral. The final product was freeze-dried at -50 °C for 24 h to obtain a brownish-red solid, designated CPN-6.

[0032] Meanwhile, viologen polymer visible light catalysts were prepared using the same method described above, except that the molar ratios of 4,4'-bipyridine and 1,2,3,4,5,6-hexa(bromomethyl)benzene were 1:1, 1:2, 1:3, 1:4, 3:1, and 4:1, respectively. In both cases, a brownish-red solid was obtained and designated as CPN-6 for later use.

[0033] Product characterization in Examples 1-5: A random sample of the brownish-red solids obtained in Examples 1-5 was taken and its microstructure was observed using a scanning electron microscope (SEM). Figure 2As shown, CPN-2, CPN-3, CPN-4, CPN-5, and CPN-6 are all composed of uniformly sized spherical particles. This allows Cr(VI) ions to diffuse from the solution to the surface of the nanospheres over a very short distance, enabling them to quickly reach and occupy the active sites on the surface, resulting in a very rapid adsorption process that reaches adsorption equilibrium in a short time. Furthermore, their surfaces exhibit varying degrees of roughness, primarily due to the irregular surface growth caused by the formation of long polymer chains.

[0034] Batch adsorption experiments were conducted on the brownish-red solids obtained in Examples 1-5 using a photochemical reactor. The effects of initial Cr(VI) concentration and adsorption temperature on adsorption capacity were investigated by adjusting the solution pH and varying the adsorption time. All experiments were performed under both dark and visible light irradiation conditions. The entire adsorption process was carried out in a temperature-controlled shaker. Au before and after adsorption was measured. 3+ The concentration was determined by ICP-OES, and the adsorption capacity was calculated according to Formula 1: Formula 1, In the formula: Q e (mg / g) is the adsorption capacity; C0 (mg / L) is the initial concentration of the solution; C e (mg / L) is the equilibrium concentration of the solution; V (mL) is the volume of the solution; W (g) is the mass of the adsorbent.

[0035] The adsorption capacities of visible light photocatalysts prepared with different molar ratios of 4,4'-bipyridine and poly(bromomethyl)-substituted benzene are shown in Table 1. Table 1. Adsorption capacity of visible light catalysts prepared from 4,4'-bipyridine and poly(bromomethyl)-substituted benzenes in different molar ratios. , As can be seen from the adsorption capacity data in Table 1, the viologen polymer visible light catalysts prepared in each molar ratio in Example 3 all showed good adsorption effects. Therefore, subsequent adsorption experiments were all conducted by randomly selecting one sample from CPN-4.

[0036] Solution pH is a key parameter in the adsorption process, directly affecting the electrostatic interaction between the adsorbent and the target ions by regulating the surface charge properties of the adsorbent. Figure 3 As shown, the adsorption capacity of CPN-4 for Cr(VI) gradually decreased as the pH increased from 1.0 to 7.0. At lower pH conditions, the adsorbent surface was positively charged, and Cr(VI) was primarily expressed as the anionic species HCrO. 4-The electrostatic attraction between the adsorbent and the chromium significantly promotes the adsorption process. Conversely, under alkaline conditions, the adsorbent surface becomes negatively charged, resulting in electrostatic repulsion with the similarly negatively charged oxygen anions, leading to a decrease in adsorption performance. These results indicate that CPN-4 exhibits excellent adsorption performance in strongly acidic environments, which is highly consistent with the characteristic that Cr(VI) in typical metallurgical wastewater is often in an acidic medium, demonstrating its application potential in treating such wastewater. Furthermore, the effect of solution pH on adsorption capacity under darkness and visible light was investigated. The results show that visible light can promote adsorption, indicating that viologen polymers have excellent photo-promoting effects.

[0037] Adsorption time is one of the key factors affecting the Cr(VI) adsorption process. For example... Figure 4 As shown, within the initial 60 minutes, the adsorption of Cr(VI) proceeded rapidly under both dark and visible light conditions, primarily due to the abundant available sites on the adsorbent surface and the promoting effect of its mesoporous structure on the mass transfer process. After 60 minutes, the adsorption gradually reached equilibrium. The maximum adsorption capacities of CPN-4 under dark and visible light conditions were 447.730 mg / g and 667.007 mg / g, respectively. This material reached adsorption equilibrium within 60 minutes, exhibiting adsorption kinetics significantly superior to most reported adsorbents, demonstrating excellent adsorption efficiency.

[0038] Figure 5 The adsorption capacity curves of CPN-4 for Cr(VI) under dark and visible light conditions are shown. As the initial concentration of Cr(VI) increases, the adsorption capacity (Q) increases. e The adsorption capacity gradually increases, reaching a maximum of 449.461 mg / g in the dark and 667.495 mg / g in the visible light. This excellent adsorption performance can be attributed to the effective interaction between the functional groups on the material surface and Cr(VI).

[0039] In treating real-world, strongly acidic metallurgical wastewater, developing adsorbents with high selectivity for specific ions is crucial. Therefore, we evaluated the adsorption selectivity of CPN-4 in a mixed simulated wastewater containing Cd(II), Co(II), Ni(II), Zn(II), and Cr(VI). Figure 6 As shown, CPN-4 exhibits the highest adsorption capacity for Cr(VI). This significant selectivity stems from the specific binding sites in CPN-4 that have a high affinity for Cr(VI), enabling it to effectively capture Cr(VI) in complex systems with multiple coexisting ions. Furthermore, the photoresponsive conjugated framework structure of CPN-4 further synergistically enhances its selective separation and photocatalytic reduction performance under visible light.

[0040] In addition, it should be noted that the selective adsorption effect of CPN-4 provided by the present invention is not limited to the specific recognition of Cr(VI) in a mixed solution of Cd(II), Co(II), Ni(II), Zn(II) and Cr(VI).

[0041] The effect of temperature on the adsorption process was investigated through thermodynamic experiments (contact time 1080 min, pH=2) at different temperatures ranging from 25℃ to 45℃. The results are as follows. Figure 7 As shown, under both dark and visible light conditions, the adsorption capacity of the adsorbent for Cr(VI) increases with increasing temperature. This indicates that within a certain temperature range, the adsorption capacity of the adsorbent for Cr(VI) continuously expands as the temperature gradually increases, suggesting that high-temperature conditions favor the adsorption of Cr(VI). This result may be due to the accelerated diffusion rate of Cr(VI) under high-temperature conditions.

[0042] To clarify the reduction mechanism and composition of active species during photocatalysis, EPR technology was used to study DMPO-·O 2- And the TEMP-102 adduct was detected. Figure 8 As shown, no obvious free radical signal was observed under dark conditions; however, after 30 min of visible light irradiation, both showed characteristic EPR signals, indicating that ·O 2- 102 and 102 are the main active species in the photocatalytic reaction. These species originate from the reduction process of oxygen under the action of photogenerated electrons, in which electrons are provided by photoexcitation of CPN-4. The above results confirm that CPN-4 can effectively promote the transfer of photogenerated electrons to oxygen molecules under light irradiation, thereby enhancing the removal capacity of Cr(VI) through the reduction pathway.

[0043] The preferred embodiments of the present invention have been described above with reference to the accompanying drawings. Those skilled in the art can implement the present invention in various modifications without departing from its scope and spirit. For example, a feature shown or described in one embodiment can be used in another embodiment to obtain yet another embodiment. The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. All equivalent changes made based on the description and drawings of the present invention are included within the scope of the present invention.

Claims

1. A method for preparing a viologen polymer visible light photocatalyst, characterized in that, Specifically, the following steps are included: 4,4'-bipyridine and poly(bromomethyl)-substituted benzene were dissolved sequentially in a polar organic solvent until fully dissolved. Potassium hydroxide solution was added, and the mixture was stirred and refluxed in an oil bath for 3-12 hours. After the reaction was completed, the mixture was cooled to room temperature and washed three times with acetonitrile, followed by washing with deionized water until neutral. The final product was freeze-dried to obtain a brownish-red solid. The polar organic solvent included at least one of acetonitrile, N,N-dimethylformamide, and tetrahydrofuran.

2. The method for preparing a viologen polymer visible light photocatalyst according to claim 1, characterized in that, The poly(bromomethyl) substituted benzenes include at least one of α,α'-dibromo-p-xylene, 1,3,5-tris(bromomethyl)benzene, 1,2,4,5-tetra(bromomethyl)benzene, 1,2,3,4,5-penta(bromomethyl)benzene, and 1,2,3,4,5,6-hexa(bromomethyl)benzene.

3. The method for preparing a viologen polymer visible light photocatalyst according to claim 1, characterized in that, The molar ratio of the 4,4'-bipyridine to the poly(bromomethyl) substituted benzene is 1-4:4-1.

4. A method for preparing a viologen polymer visible light photocatalyst according to any one of claims 1-3, characterized in that, The temperature of the oil bath is 25~80 °C.

5. A method for preparing a viologen polymer visible light photocatalyst according to any one of claims 1-3, characterized in that, The freeze-drying temperature is -50 °C and the drying time is 24 hours.

6. A viologen polymer visible light catalyst, characterized in that, It was prepared using the method described in any one of claims 1-5 for preparing a viologen polymer visible light catalyst.

7. An application of a viologen polymer visible light photocatalyst, characterized in that, A viologen polymer visible light catalyst prepared according to any one of claims 1-5 is used as an adsorption catalytic material in Cr. 6+ In selective adsorption and reduction.

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