A two-dimensional copper coordination polymer, its preparation method and application

Abstract

The present invention discloses a two-dimensional copper coordination polymer, its preparation method and application, and claims a two-dimensional copper coordination polymer with the chemical formula [Cu(Hcpota)(4,4'-bpy)(H2O)] n , where Hcpota in the chemical formula refers to Hcpota 2‑ , which is the deprotonated form of o-(p-carboxyphenyl)oxy terephthalic acid H3cpota, 4,4'-bpy is 4,4'-bipyridine, and n represents polymerization; the structural formula of the polymer is as follows. This copper coordination polymer can not only stably exist in water but also be used as a photocatalyst to degrade methylene blue in water. In addition, this copper coordination polymer is obtained under hydrothermal synthesis conditions, and the preparation process is simple, with high yield and purity. #imgabs0#

Description

Technical Field

[0001] The present invention belongs to the field of chemistry, relates to coordination polymers, and particularly relates to a two-dimensional copper coordination polymer, a preparation method thereof, and a catalytic application thereof. Background Art

[0002] Due to the continuous and rapid development of industry, water pollution worldwide is becoming increasingly serious. One of the most abundant and commonly observed pollutants in water is dye molecules. Most dyes are toxic. For example, methylene blue was classified as a Group 3 carcinogen by the International Agency for Research on Cancer of the World Health Organization in 2017, which damages human health. In addition, this dye can consume a large amount of oxygen in water, leading to hypoxia in the water body and affecting the growth of aquatic organisms and microorganisms. Therefore, from the aspects of environmental protection and human safety, it is very important to find an effective method for treating organic dyes. Currently, the treatment methods for waste - aqueous organic dyes mainly rely on microbial degradation, adsorption, photocatalysis, and advanced oxidation methods. Among them, catalytic degradation is an effective method for treating sewage. However, these catalytic methods have the following disadvantages: expensive, limited application scope, etc. More efficient and economical water purification catalytic systems are still a key research direction. Recently, the application of metal - organic coordination polymers as efficient heterogeneous photocatalysts has developed rapidly because they can provide simple, fast, highly selective, and cost - effective photocatalytic methods. However, among these coordination polymer catalysts, some materials cannot exist stably in aqueous solutions, and their applications are greatly limited. Therefore, designing and synthesizing coordination polymers with selectivity and efficient catalytic degradation function for dyes in sewage in aqueous solutions is an urgent problem to be solved currently and also a key research direction in this type of research. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a two - dimensional copper coordination polymer, a preparation method thereof, and the application of this coordination polymer as an efficient heterogeneous photocatalyst for catalytic degradation of methylene blue in aqueous solutions.

[0004] The above - mentioned purpose of the present invention is achieved through the following technical solutions:

[0005] A two - dimensional copper coordination polymer with the chemical formula [Cu(Hcpota)(4,4'-bpy)(H2O)] n , where Hcpota in this chemical formula refers to Hcpota 2- , which is the deprotonated form of o-(p - carboxyphenyl)oxyterephthalic acid H3cpota, 4,4'-bpy is 4,4'-bipyridine, and n represents polymerization; the structural formula of this polymer is as follows:

[0006]

[0007] The crystal of the copper coordination polymer belongs to the monoclinic system, and the space group is The unit cell parameters are: α = 90°, β = 95.41(3)°, γ = 90°. The copper atom is pentacoordinated in a square pyramidal shape, and the atom coordinates with two O atoms of two different carboxyl groups, one coordinated water molecule, and two N atoms from 4,4'-bipyridine respectively; the range of the Cu-O bond length is The range of the Cu-N bond length is Hcpota 2– Two carboxyl groups of the ligand connect two Cu ions in a single-link mode. At the same time, each copper ion connects two Hcpota 2– The ligand and two 4,4'-bipyridines form a square structure with a length of . This structure expands continuously as a unit to form a two-dimensional copper metal-organic coordination polymer. X-ray powder diffraction confirms that the crystal sample is homogeneous and stable.

[0008] The preparation method of the above two-dimensional copper coordination polymer includes the following steps:

[0009] (1) Add Cu(NO3)2·3H2O, 4,4'-bipyridine, and o-(p-carboxyphenoxy)terephthalic acid to a polytetrafluoroethylene tube in a molar ratio of 2:2:1;

[0010] (2) Add an appropriate amount of water and an appropriate amount of N,N-dimethylformamide solvent to the above polytetrafluoroethylene tube, with a total filling degree of 47% and a volume ratio of 6:1;

[0011] (3) Adjust the pH to 5 with 2 mol / L HCl;

[0012] (4) Place the polytetrafluoroethylene tube in a stainless steel reaction kettle, react at 393 K for 48 h, cool naturally to room temperature, then blue block crystals will precipitate. Collect the crystals, wash them with water, and dry them under vacuum to obtain the product.

[0013] The application of the above two-dimensional copper coordination polymer as an efficient heterogeneous photocatalyst in the degradation of methylene blue in water.

[0014] Beneficial effects:

[0015] The two-dimensional copper coordination polymer provided by the present invention is constructed by a partially deprotonated 2-(4-carboxyphenoxy)terephthalic acid (H3cpota) ligand. The partially deprotonated Hcpota 2– ligand and 4,4'-bipyridine connect the square pyramidal copper ions to form a two-dimensional structure. This copper coordination polymer can not only exist stably in water but also be used as a photocatalyst to degrade methylene blue in water. This copper coordination polymer is obtained under hydrothermal synthesis conditions, and the preparation process is simple, with high yield and purity. Description of the Drawings

[0016] Figure 1 It is the crystal structure diagram of the copper coordination polymer of the present invention;

[0017] Figure 2 It is the X-ray powder diffraction pattern of the copper coordination polymer of the present invention at 298K;

[0018] Figure 3 It is the change of the concentration of methylene blue with time under different conditions ([MB]=10mg L -1 ,[H2O2]=50mM, complex 1=5mg, T=25°C, pH=9);

[0019] Figure 4 It is the ultraviolet absorption spectrum of methylene blue catalytically degraded by complex 1 (5mg) under the conditions of pH=9 and H2O2=50mM;

[0020] Figure 5 It is for MB (10mg L -1 ) The graph of the relationship between the pseudo-first-order kinetic curve -ln(C / C0) and time of photocatalytic degradation. Detailed Embodiments

[0021] The following specifically introduces the substantial content of the present invention in combination with embodiments, but does not limit the protection scope of the present invention thereto.

[0022] Example 1: Preparation, determination and analysis of copper coordination polymer

[0023] Weigh 0.2 mmol of H3cpota, 0.2 mmol of 4,4'-bpy and 0.1 mmol of Cu(NO3)2·3H2O and add them to a 15 mL polytetrafluoroethylene tube containing 6 mL of H2O. Add 1 mL of DMF, slowly drop 2 mol / L HCl into the stirred mixture to adjust the pH to 5, and continue stirring for 30 minutes. Put this polytetrafluoroethylene tube into a stainless steel reaction kettle, heat it at 393K for 48h, then naturally cool it to room temperature, and blue block crystals can be precipitated. After washing with water and drying in vacuum, the yield is 83%. Elemental analysis: C 25 H 18 CuN2O8, calculated as: C 55.56, H 3.33, N 5.19%; experimental value: C 55.84, H 3.21, N 5.78%.

[0024] Crystal structure determination: The X-ray diffraction data of the crystal were collected at the 3W1A beamline of the Beijing Synchrotron Radiation. The detector for data collection was MARCCD-165, the wavelength was 0.7200, the working voltage was 2.5 GeV, and the diffraction data were collected under liquid nitrogen protection at 100(2) K. The data were processed after being reduced by the HKL2000 program. The crystal structure was solved by the direct method of SHELXL-2014 and refined by the full matrix least squares method using SHELXL-2014. The detailed crystal determination data are shown in Table 1, and the crystal structure is shown in Figure 1 the two-dimensional structure shown.

[0025] Table 1 Crystallographic data of the copper coordination polymer material

[0026]

[0027]

[0028] Analysis of the phase by powder diffraction method: The X-ray powder diffraction experimental pattern is consistent with the simulated pattern, indicating that the phase of the copper coordination polymer crystal sample of the present invention is homogeneous, as shown in Figure 2 .

[0029] Example 2: Efficient catalytic degradation of methylene blue in water by the copper coordination polymer of the present invention

[0030] First, a methylene blue (MB) solution with a concentration of 10 mg / L was prepared. 5 mg of the coordination polymer, copper ions, and H3cpota ligand were respectively added to 10 mL of the methylene blue (MB) solution, and a blank sample was prepared. The pH was adjusted to 9 with KOH, then wrapped with tin foil paper and stirred in the dark until the adsorption-desorption equilibrium was reached (the concentration of MB no longer changed). The tin foil paper was removed, irradiated with light, and a certain amount of H2O2 was added, and ultraviolet tests were performed at the same time intervals. As Figure 3 shown, in the absence of an additional catalyst, the degradation rate of the H2O2 / MB system within 32 minutes was 25%, indicating that H2O2 could only slowly degrade MB. Under the same time and conditions, the H3cpota / H2O2 / MB system and the Cu 2+ / H2O2 / MB system could also only slowly degrade MB, while the degradation rate of the 1 / H2O2 / MB system could reach 97%. The degradation efficiency of this copper complex for methylene blue was significantly higher than that of a single ligand and a single metal respectively. The results show that: in the presence of H2O2, this complex 1 can be used as an effective photocatalyst to degrade the dye methylene blue.

[0031] Example 3: Degradation sensitivity of the copper coordination polymer of the present invention to methylene blue in water

[0032] Take 10 mL of methylene blue (MB) solution with a concentration of 10 mg / L, add 5 mg of this coordination polymer, adjust the pH to 9 with KOH, then wrap it with tin foil and stir in the dark until the adsorption-desorption equilibrium is reached (the MB concentration no longer changes). Remove the tin foil, perform light irradiation, and add a certain amount of H2O2, and conduct UV tests at the same time intervals. As Figure 4 shown, as time increases, the UV absorption of this solution decreases significantly with time. In addition, as Figure 5 shown, the degradation of most organic pollutants follows the pseudo-first-order reaction kinetic model and can be processed with the pseudo-first-order reaction equation: -ln(C / C0) = -ln(A / A0) = Kt, where C and C0 represent the concentration of the dye at time "t" and the initial concentration of the dye, respectively, and A and A0 represent the absorbance of the dye at time "t" and the initial absorbance of the dye, respectively; K is the rate constant, and a higher rate constant K indicates higher catalytic activity. The rate constant for the degradation of methylene blue by this coordination polymer is K = 0.074 min -1 , indicating that this coordination polymer has a high response sensitivity to the degradation of methylene blue in aqueous solution. The above experiments show that this coordination polymer can be used as a photocatalyst to catalytically degrade methylene blue in aqueous solution.

[0033] The role of the above embodiments is to specifically introduce the substantial content of the present invention. However, those skilled in the art should know that the protection scope of the present invention should not be limited to this specific embodiment.

Claims

1. A two-dimensional copper coordination polymer with the chemical formula [Cu(Hcpota)(4,4'-bpy)(H2O)] n , where Hcpota in the chemical formula refers to Hcpota 2- , which is the deprotonated form of o-(p-carboxyphenyl)oxyterephthalic acid H3cpota, 4,4'-bpy is 4,4'-bipyridine, and n represents polymerization; the structural formula of the polymer is as follows: The crystal of this copper coordination polymer belongs to the monoclinic system, and the space group is The unit cell parameters are: α = 90°, β = 95.41(3)°, γ = 90°.

2. The preparation method of the two-dimensional copper coordination polymer according to claim 1, characterized in that, It includes the following steps: (1) Add Cu(NO3)2·3H2O, 4,4'-bipyridine and o-(p-carboxyphenoxy)terephthalic acid into a polytetrafluoroethylene tube according to a molar ratio of 2:2:1; (2) Add an appropriate amount of water and an appropriate amount of N,N-dimethylformamide solvent into the above polytetrafluoroethylene tube, with a total filling degree of 47% and a volume ratio of 6:1; (3) Adjust the pH to 5 with 2 mol / L HCl; (4) Place the polytetrafluoroethylene tube in a stainless steel reactor, react at 393 K for 48 h, and naturally cool to room temperature. Then blue block crystals can be precipitated. Collect the crystals, wash them with water and dry them under vacuum to obtain the product.

3. The application of the two-dimensional copper coordination polymer according to claim 1 as an efficient heterogeneous photocatalyst in the degradation of methylene blue in water.

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