Preparation method of an anionic covalent organic framework material and application thereof in dye adsorption

Abstract

The present application relates to a kind of anionic covalent organic framework material and its application in dye adsorption, the covalent organic framework material is prepared by one-pot through solvothermal method, with hexachloro-cyclotriphosphazene and 4,4'-diamino stilbene-2,2'-disulfonic acid as comonomer, dimethyl sulfoxide and pyridine mixed solvent as reaction medium to carry out polymerization reaction and obtain.The anionic covalent organic framework material obtained in the application can exert good adsorption effect on cationic dye in wide pH range wastewater, and show high adsorption capacity, fast adsorption rate, good adsorption selectivity, easy recycling and other advantages.The method of the present application prepares a new anionic covalent organic framework material connected by dynamic covalent bond nitrogen-phosphorus bond;Preparation process is simple and easy to operate, convenient, conducive to industrial production;The comprehensive adsorption performance of dye in wastewater is excellent, and has good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental adsorption of new functional materials, and particularly relates to a preparation method of an anionic covalent organic framework material and application thereof in dye adsorption. BACKGROUND

[0002] With the rapid development of global economy and modern industry, water pollution problems are increasingly prominent, especially the discharge of a large amount of harmful industrial wastewater, which has become a major problem in need of urgent solution in the world today. Dye wastewater is one of the main members of harmful industrial wastewater, which is derived from textile, printing, leather manufacturing, food and dye processing industries. Due to its non-biodegradable, toxic, potential carcinogenic and mutagenic properties, it will cause great harm to human health and the ecological environment. Therefore, effectively treating these dye wastewaters is of great strategic significance to the protection of human beings and the ecological environment and to the realization of sustainable development.

[0003] In order to purify these dye wastewaters, some physical, chemical, biological methods (such as adsorption method, ion exchange method, flocculation precipitation method, chemical catalytic oxidation method, photocatalytic method, electrochemical method, biological degradation method, etc.) have been widely studied. Among them, the adsorption method is considered to be the most common and effective method for treating dye wastewater, and the adsorbent is the core of the adsorption method. At present, the commonly used adsorbents for treating wastewater such as activated carbon, slag, diatomite, cellulose, resin, humic acid, biomass, etc. have been studied a lot. These adsorbents have the advantages of low cost, high adsorption efficiency and environmental friendliness, but still have the disadvantages of poor adsorption selectivity, slow adsorption process, and difficult regeneration. Therefore, it is still desirable to find a new type of high-efficiency adsorbent with strong adsorption capacity, good adsorption selectivity, easy regeneration, low cost and fast adsorption speed.

[0004] A feasible measure to improve the adsorption capacity and adsorption rate of the adsorbent is to increase the specific surface area by reducing the structural size of the adsorbent, thereby forming more adsorption sites on the unit mass of the adsorbent. Generally, improving the selective adsorption of the adsorbent to the adsorbate requires the adsorbent to carry specific functional groups or specific pore structures. Based on this, in recent years, researchers in the adsorption field have paid great attention to covalent organic framework materials (COF). This kind of material can easily carry various functional groups through chemical modification, and shows the advantages of strong adsorption capacity, fast adsorption speed and high adsorption efficiency for dye molecules. At the same time, the functional groups on the surface of the COF material such as -OH, -COOH, -NH2, etc. can selectively adsorb dyes through electrostatic interaction, coordination interaction or hydrogen bond interaction, etc. and show good selective adsorption behavior. However, the building units of the existing covalent organic framework materials are often connected by borate ester bond, triazine bond, imine bond, amide bond and hydrazone bond, etc. The structural stability is poor, the preparation process is complicated, and the post-modification will also lead to the complexity of the preparation process, which is not conducive to its application in the field of environmental adsorption.

[0005] The application adopts a relatively simple method to realize the rapid preparation of a new anionic covalent organic framework material, the building units of which are connected by dynamic covalent nitrogen-phosphorus bond, and the structural stability is good. At the same time, the building units are rich in high-density anionic substituents (-SO3 - ), which shows the advantages of high adsorption capacity, fast adsorption rate, good selectivity and easy regeneration for cationic dyes. The application reports a new anionic covalent organic framework material connected by dynamic covalent nitrogen-phosphorus bond; the preparation process is simple and easy to operate, which is beneficial to industrial production; the comprehensive adsorption performance for dyes in wastewater is excellent, and has good application prospect. SUMMARY

[0006] In order to overcome the technical defects existing in the prior art, the application aims at providing an anionic covalent organic framework material, the building units of which are connected by dynamic covalent nitrogen-phosphorus bond, and the structural stability is good. At the same time, the building units are rich in high-density anionic substituents (-SO3 - ), which shows the advantages of high adsorption capacity, fast adsorption rate, good selectivity and easy regeneration for cationic dyes.

[0007] The application also provides a preparation method of the above-mentioned anionic covalent organic framework material and its application in dye adsorption.

[0008] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0009] A preparation method of an anionic covalent organic framework material, which uniformly mixes hexachlorocyclotriphosphazene and 4,4'-diaminostilbene-2,2'-disulfonic acid with a solvent, then performs a polycondensation reaction under a sealed condition by heating, and then performs post-treatment to obtain the anionic covalent organic framework material COF-ZZU.

[0010] Further, the preparation method of the anionic covalent organic framework material specifically comprises the following steps:

[0011] 1) hexachlorocyclotriphosphazene and 4,4'-diaminostilbene-2,2'-disulfonic acid are added to a reactor, then a solvent composed of dimethyl sulfoxide and pyridine is added, and ultrasonic oscillation is performed for 20-45 minutes to uniformly mix the reactants;

[0012] 2) the reactor is sealed, heated to 100-200 DEG C and kept for 10-16 hours to perform a polycondensation reaction;

[0013] 3) after the reaction is completed, natural cooling to room temperature is performed, the reaction product is subjected to centrifugal separation, fractional washing and ionization treatment, and vacuum drying, thereby obtaining the anionic covalent organic framework material COF-ZZU with dynamic covalent nitrogen-phosphorus bond connection.

[0014] Specifically, in step 1), the molar ratio of hexachlorocyclotriphosphazene and 4,4'-diaminostilbene-2,2'-disulfonic acid can be 1:2-4. Further preferably, the molar ratio of the two is 1:3, for example, the molar amount of the hexachlorocyclotriphosphazene can be 1.1 mmol, and the molar amount of 4,4'-diaminostilbene-2,2'-disulfonic acid can be 3.3 mmol.

[0015] Further, in step 1), the volume ratio of dimethyl sulfoxide and pyridine is 4-6:1. Preferably, the volume ratio of the two can be 5:1, when the molar amount of 4,4'-diaminostilbene-2,2'-disulfonic acid is 3.3 mmol, the total amount of the solvent can be 20-40 mL, preferably 30 mL. The volume of the reactor can be about 40 mL.

[0016] Further, in step 3), the fractional washing and ionization treatment specifically comprises: sequentially washing with dimethyl sulfoxide, 0.5 M sodium hydroxide or 0.5 M potassium hydroxide until the supernatant is colorless, washing with deionized water, and washing with ethanol.

[0017] Specifically, the vacuum drying is: drying in a vacuum oven at 60-70 DEG C for 10-14 hours.

[0018] The application provides an anionic covalent organic framework material prepared by the preparation method. Figure 1 + may be replaced by K + ).

[0019] The application further provides application of the anionic covalent organic framework material in dye adsorption.

[0020] In the application of the anionic covalent organic framework material in dye adsorption, the anionic covalent organic framework material COF-ZZU can be dispersed in dye-containing wastewater to be treated, and oscillation is performed at room temperature until adsorption and desorption balance, and the adsorption process is completed; then, the COF-ZZU adsorbed with dyes can be subjected to regeneration treatment, and enters the next adsorption / desorption cycle.

[0021] The dye can be one or two or more of methylene blue, crystal violet, malachite green, rhodamine B, aniline violet, cationic yellow X-6G, cationic red GTL and other cationic dyes.

[0022] Further, in application, the dye concentration in the dye-containing wastewater to be treated can be 150-300 mg / L, and the feeding concentration of the anionic covalent organic framework material COF-ZZU can be 200-300 mg / L.

[0023] In addition, the anionic covalent organic framework material COF-ZZU is easy to regenerate and has good cyclic adsorption performance. The regeneration treatment of the anionic covalent organic framework material COF-ZZU adsorbed with dyes is specifically as follows: the anionic covalent organic framework material COF-ZZU adsorbed with dyes is washed with deionized water, and then is transferred into a 0.4-0.6M sodium hydroxide or potassium hydroxide solution, is subjected to ultrasonic oscillation for 20-40 minutes to perform desorption and anionization of the framework structure, and is then washed with deionized water and is subjected to centrifugal separation, so that the regeneration of the COF-ZZU is completed.

[0024] ​In the application applied to dye adsorption, the anionic covalent organic framework material COF-ZZU has a fast adsorption rate for dyes, and the adsorption equilibrium time is 20 minutes. COF-ZZU can exert good adsorption effect on cationic dyes in wastewater in a wide pH range (pH=3-12). The adsorption capacity of COF-ZZU for cationic dyes is as high as 600-1000 mg / g; in a cationic dye / anionic dye binary blended system solution, the adsorption selectivity for cationic dyes is good, and the relative separation coefficient of cationic dyes to anionic dyes is as high as 100-200.

[0025] The anionic covalent organic framework material obtained in the application can exert good adsorption effect on cationic dyes in wastewater in a wide pH range, and has the advantages of high adsorption capacity, fast adsorption rate, good adsorption selectivity, easy recycling and the like. The method of the application prepares a new anionic covalent organic framework material connected by dynamic covalent nitrogen-phosphorus bond; the preparation process is simple and easy to operate, and is convenient for operation and industrial production; the comprehensive adsorption performance of the material for dyes in wastewater is excellent, and the material has good application prospect. Compared with the prior art, the beneficial results of the application are as follows:

[0026] 1) The anionic covalent organic framework material (COF-ZZU) prepared in the application has the following structural characteristics: the molecular skeleton of COF-ZZU is connected by dynamic covalent nitrogen-phosphorus bond between inorganic phosphine ring and organic aromatic ring (rich in sulfonic acid group anion), and is a new covalent organic framework material with a novel structure;

[0027] 2) The process for preparing the anionic covalent organic framework material (COF-ZZU) in the application is simple, has strong operability, has a large sample yield, is easy to meet the reaction conditions, has low requirements on equipment, and greatly reduces the production cost;

[0028] 3) The dye adsorbent (COF-ZZU) prepared by the preparation method of the application has a simple method for treating dye wastewater, and does not need to adjust the reaction temperature, but can be carried out at room temperature. The pH value of the wastewater does not need to be strictly adjusted, and good adsorption and decolorization effect can be obtained in a wide pH range (pH=3-12) from acidic to alkaline;

[0029] 4) The dye adsorbent (COF-ZZU) prepared by the preparation method of the application has a dye adsorption capacity of 600-1000 mg / g in dye wastewater, and the adsorption reaches equilibrium in only 20 minutes, and in a binary mixed adsorption system of anionic dyes / cationic dyes, the relative separation coefficient of the cationic dyes is as high as 100-200, and after adsorption, the solute can be simultaneously regenerated and the framework structure is anionized by washing with 0.5 M sodium hydroxide (or potassium hydroxide), which shows that the COF-ZZU as an adsorbent has the comprehensive performance advantages of high adsorption capacity, fast adsorption rate, good adsorption selectivity and easy recycling. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a periodic structural unit (counterion Na + may be replaced by K + ) of the anionic covalent organic framework material (COF-ZZU) prepared in Example 1;

[0031] Figure 2 is a scanning electron microscope photo of the anionic covalent organic framework material (COF-ZZU) prepared in Example 1;

[0032] Figure 3 is an infrared spectrum of the anionic covalent organic framework material (COF-ZZU) prepared in Example 1;

[0033] Figure 4 is an XPS spectrum of the anionic covalent organic framework material (COF-ZZU, sodium hydroxide washing) prepared in Example 1;

[0034] Figure 5 is the adsorption kinetics of the anionic covalent organic framework material (COF-ZZU) prepared in Example 1 on methylene blue dye. DETAILED DESCRIPTION

[0035] The technical solutions of the application are further described in detail below in combination with examples, but the protection scope of the application is not limited thereto.

[0036] In the following examples, unless otherwise specified, the raw materials used are ordinary commercially available products or can be prepared by conventional methods in the art. Room temperature refers to 25±5℃.

[0037] The anionic covalent organic framework material COF-ZZU described in the application has a dye adsorption performance test method for wastewater: a series of dye standard solutions with different concentrations are prepared, the absorbance is measured by means of ultraviolet visible spectrophotometer, and the standard curve is drawn with the measured data, so as to measure the concentration of dye in water. The relative separation coefficient (α) is calculated by the following formula:

[0038]

[0039] Here, K D is the static partition coefficient of the dye; q e is the equilibrium adsorption capacity of COF-ZZU for dye (mg / g); C e is the residual concentration of dye in water at adsorption equilibrium (mg / L); K D1 With K D2 is the static partition coefficient of dyes 1 and 2 in the binary adsorption system.

[0040] Example 1

[0041] A method for preparing an anionic covalent organic framework material COF-ZZU specifically comprises the following steps:

[0042] 1) 1.1 mmol of hexachlorocyclotriphosphazene and 3.3 mmol of 4,4'-diaminostilbene-2,2'-disulfonic acid were added to a 40 mL high-temperature, high-pressure reactor (made of polytetrafluoroethylene). Then, 25 mL of dimethyl sulfoxide and 5 mL of pyridine were added as solvents. Ultrasonic vibration was applied for 30 minutes to uniformly dissolve the comonomers hexachlorocyclotriphosphazene and 4,4'-diaminostilbene-2,2'-disulfonic acid in the mixed solvent.

[0043] 2) The polytetrafluoroethylene liner is then placed in a high-temperature and high-pressure reactor, sealed, and placed in a constant temperature oven at 150°C for 12 hours for polycondensation reaction;

[0044] 3) After the reaction, the reactor was removed and naturally cooled to room temperature. The dark brown solid precipitate was centrifuged, graded washed, and ionized (wherein, the order of graded washing and ionization treatment was washing with dimethyl sulfoxide three times, washing with 0.5 M sodium hydroxide until the supernatant was colorless, washing with deionized water three times, and washing with ethanol three times). The dark brown powder was then dried in a vacuum oven at 65°C for 12 hours to obtain the anionic covalent organic framework material COF-ZZU with dynamic covalent nitrogen-phosphorus bond linkages.

[0045] Figure 2 A scanning electron microscope photograph of the anionic covalent organic framework material (COF-ZZU) prepared in Example 1 is given. It can be clearly seen in the photograph that the product is an aggregate of nanoparticles, and the typical particle size of the nanoparticles is 50-80 nm.

[0046] Figure 3The infrared spectrum of the anionic covalent organic framework material (COF-ZZU) prepared in Example 1 is given, which shows characteristic absorption peaks of the framework structure derived from two comonomers, such as P-N in phosphine oxide ring (869 cm -1 ), P=N (1197 cm -1 ), aromatic ring (1162 cm -1 , 1492 cm -1 ), sulfonate anion (1032 cm -1 ) and P-N-C bond (971 cm -1 ) proving the occurrence of polycondensation reaction.

[0047] Figure 4 The XPS spectrum of the anionic covalent organic framework material (COF-ZZU, washed with sodium hydroxide) prepared in Example 1 is given, which can be seen from the figure that C, N, P, S, O, Na elements exist, which is consistent with the elements in the COF-ZZU framework structure.

[0048] The following anionic covalent organic framework material (COF-ZZU) prepared in Example 1 is subjected to relevant adsorption test.

[0049] Adsorption test 1

[0050] 5 mg of COF-ZZU adsorbent is taken and added to 20 mL of methylene blue dye wastewater with a concentration of 250 mg / L, and shaken for 20 minutes at room temperature and pH = 7 to reach adsorption equilibrium, and the adsorption capacity is detected.

[0051] The COF-ZZU after adsorption is washed with deionized water, and then transferred to 30 mL of 0.5 M sodium hydroxide solution and ultrasonically shaken for 30 minutes to desorb and anionize the framework structure, and then washed with deionized water and centrifuged to complete the regeneration of COF-ZZU and carry out the next adsorption / desorption cycle.

[0052] The test results show that the adsorption capacity of COF-ZZU for methylene blue dye is as high as 770 mg / g, and the adsorption capacity after 5 cycles of adsorption is still as high as 720 mg / g, and the relative separation absorption in the methylene blue / acidic chrome blue K binary mixed dye system is as high as 147.

[0053] Figure 5 The adsorption kinetics of the anionic covalent organic framework material (COF-ZZU) prepared in Example 1 for methylene blue dye is given, which can be seen from the figure that the adsorption process is very rapid, and the adsorption equilibrium time is only 20 minutes, and the adsorption capacity is as high as 770 mg / g.

[0054] Adsorption test 2

[0055] Take 5 mg of COF-ZZU adsorbent, add to 20 mL of 300 mg / L concentration of crystal violet dye wastewater, under room temperature, pH = 7, oscillate for 20 minutes to reach adsorption equilibrium, detect the adsorption capacity.

[0056] After the adsorption of COF-ZZU is completed, it is washed with deionized water, and then it is transferred into 30 mL of 0.5 M sodium hydroxide solution and ultrasonically oscillated for 30 minutes to desorb and anionize the framework structure, and then it is washed with deionized water and centrifuged to complete the regeneration of COF-ZZU and carry out the next adsorption / desorption cycle.

[0057] The test results show that the adsorption capacity of COF-ZZU for crystal violet dye is as high as 882 mg / g, and the adsorption capacity after 5 cycles of adsorption is still as high as 810 mg / g, and the relative separation absorption in the crystal violet / acid chrome blue K binary mixed dye system is as high as 136.

[0058] Adsorption test 3

[0059] Take 4 mg of COF-ZZU adsorbent, add to 20 mL of 200 mg / L concentration of cationic yellow X-6G dye wastewater, under room temperature, pH = 7, oscillate for 20 minutes to reach adsorption equilibrium, detect the adsorption capacity.

[0060] After the adsorption of COF-ZZU is completed, it is washed with deionized water, and then it is transferred into 30 mL of 0.5 M sodium hydroxide solution and ultrasonically oscillated for 30 minutes to desorb and anionize the framework structure, and then it is washed with deionized water and centrifuged to complete the regeneration of COF-ZZU and carry out the next adsorption / desorption cycle.

[0061] The test results show that the adsorption capacity of COF-ZZU for cationic yellow X-6G dye is as high as 763 mg / g, and the adsorption capacity after 5 cycles of adsorption is still as high as 710 mg / g, and the relative separation absorption in the cationic yellow X-6G / acid chrome blue K binary mixed dye system is as high as 114.

[0062] Adsorption test 4

[0063] Take 5 mg of COF-ZZU adsorbent, add to 20 mL of 300 mg / L concentration of cationic red GTL wastewater, under room temperature, pH = 7, oscillate for 20 minutes to reach adsorption equilibrium, detect the adsorption capacity.

[0064] After adsorption is completed, the COF-ZZU is cleaned with deionized water, and then is transferred into a 30 mL 0.5 M sodium hydroxide solution for ultrasonic oscillation for 30 minutes to perform desorption and frame structure anionization, and then is cleaned with deionized water, centrifugal separation is performed, regeneration of the COF-ZZU is completed, and the next adsorption / desorption cycle is carried out.

[0065] The detection result shows that the adsorption capacity of the COF-ZZU for the cationic red GTL dye is as high as 823 mg / g, and the adsorption capacity after 5 cycles of adsorption is still as high as 750 mg / g, and the relative separation absorption in the cationic red GTL / methyl orange binary mixed dye system is as high as 135. Meanwhile, under different acid-base conditions at room temperature and pH=3-11, the adsorption capacity of the COF-ZZU for the cationic red GTL is as high as 605 (pH=3)-973 (pH=11) mg / g.

[0066] In summary, the anionic covalent organic framework material COF-ZZU has high adsorption capacity for dyes in dye wastewater, and the adsorption equilibrium time is short, only 20 minutes, and the COF-ZZU as an adsorbent shows the comprehensive performance advantages of high adsorption capacity, fast adsorption rate, good adsorption selectivity and easy recycling.

Claims

1. A method for preparing anionic covalent organic framework materials, characterized in that: The steps include: 1) Hexachlorocyclotriphosphazene and 4,4'-diaminobenzylbenzene-2,2'-disulfonic acid are added to a reactor, followed by addition of a solvent consisting of dimethyl sulfoxide and pyridine, and ultrasonic vibration is used to mix the reactants uniformly; 2) Seal the reactor, heat to 100-200°C and maintain for 10-16 hours to carry out polycondensation reaction; 3) After the reaction is completed, the mixture is naturally cooled to room temperature, and the reaction product is centrifuged, graded and washed, ionized, and vacuum dried to obtain the product.

2. The method for preparing anionic covalent organic framework materials according to claim 1, characterized in that: In step 1), the molar ratio of hexachlorocyclotriphosphazene to 4,4'-diaminostilbene-2,2'-disulfonic acid is 1:2-4.

3. The method for preparing anionic covalent organic framework materials according to claim 1, characterized in that: In step 1), the volume ratio of dimethyl sulfoxide to pyridine is 4-6:

1.

4. The method for preparing anionic covalent organic framework materials according to claim 1, characterized in that: In step 3), the graded washing and ionization treatment specifically comprises: washing with dimethyl sulfoxide, washing with 0.5 M sodium hydroxide or 0.5 M potassium hydroxide until the supernatant is colorless, washing with deionized water, and washing with ethanol.

5. An anionic covalent organic framework material prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the anionic covalent organic framework material according to claim 5 in dye adsorption.

7. The use of the anionic covalent organic framework material in dye adsorption according to claim 6, characterized in that: The anionic covalent organic framework material is dispersed in the wastewater to be treated containing the dye, and is shaken at room temperature until the adsorption and desorption equilibrium is reached to complete the adsorption process; the anionic covalent organic framework material adsorbed with the dye is regenerated; The dye is one or more of methylene blue, crystal violet, malachite green, rhodamine B, aniline violet, cationic yellow X-6G and cationic red GTL.

8. The use of the anionic covalent organic framework material in dye adsorption according to claim 7, characterized in that: The dye concentration in the dye-containing wastewater to be treated is 150-300 mg / L, and the feeding concentration of the anionic covalent organic framework material is 200-300 mg / L.

9. The use of the anionic covalent organic framework material in dye adsorption according to claim 7, characterized in that: The regeneration treatment of the dye-adsorbing anionic covalent organic framework material is specifically as follows: the dye-adsorbing anionic covalent organic framework material is washed with deionized water, then transferred to a 0.4-0.6 M sodium hydroxide or potassium hydroxide solution for ultrasonic oscillation, and then washed with deionized water and centrifuged to complete the regeneration.

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