CN111408413B - Modified carbon nitride/Fe-based MOF composite material and preparation method and application thereof - Google Patents

Abstract

The invention discloses a modified carbon nitride/Fe-based MOF composite material and its preparation method and application in the field of photocatalysis. The preparation method comprises the steps of: (1) mixing melamine and triaminopyrimidine in a molar ratio of 1 : 2-4, after mixing evenly, calcining at 450-550 ℃ in an inert atmosphere, grinding the obtained product and adding it to dimethyl sulfoxide, after ultrasonic peeling for 1-3 hours, centrifuging, washing and drying with distilled water to obtain modified nitrogen carbon powder; (2) dispersing the modified carbon nitride powder obtained in step (1) in N,N-dimethylformamide to form a dispersion liquid, adding the dispersion liquid to a mixture containing ferric chloride, terephthalic acid The N,N-dimethylformamide solution of formic acid and aminoterephthalic acid is mixed, and then solvothermally reacted at 140-160° C. for 14-16 h to obtain a modified carbon nitride/Fe-based MOF composite material.

Description

A modified carbon nitride/Fe-based MOF composite material and its preparation method and application

technical field

The invention relates to the technical field of visible light catalysis, in particular to a modified carbon nitride/Fe-based MOF composite material and a preparation method and application thereof.

Background technique

Taking the heavy metal chromium as an example, the tanning, electroplating and other industries generate a large amount of chromium-containing Cr(VI) organic wastewater every year, which is difficult to control and the toxicity is enhanced. Therefore, how to effectively remove Cr(VI) in water is an urgent problem to be solved.

Traditional chemical reduction methods require step-by-step treatment and produce large amounts of chromium-containing sludge. Photocatalysis, as a clean and environment-friendly technology, can process Cr(VI)-containing complexes in one step due to its ability to generate electron-hole pairs under illumination and has both redox properties. However, the currently studied semiconductor catalysts such as TiO ₂ still have some shortcomings, such as small specific surface area, high band gap, and poor photoresponse ability. It is urgent to develop new and efficient visible light catalysts.

Metal-organic frameworks (MOFs) are a class of crystalline porous materials with periodic network structures formed by the self-assembly of inorganic metal centers (metal ions or metal clusters) and bridged organic ligands. Material. The advantages of MOFs are their large specific surface area and extremely high porosity. They have great potential in sensing, adsorption, pharmaceuticals, and other fields, and have attracted widespread attention. At the same time, MOFs are also a kind of material with catalytic properties. Since MOF-5 was the first MOF material synthesized in the laboratory in 1999, it has developed rapidly, and thousands of MOF materials have been reported.

In recent years, MOFs have shown good application prospects in the field of photocatalysis, especially Fe-MOFs with iron ions as metal centers, such as MIL-53(Fe), MIL-101(Fe), MIL-88(Fe), etc. The common point of these MOFs catalysts is the introduction of organic carboxylic acid groups into the inorganic metal centers, forming MOFs materials with stable properties, large specific surface area, and hollow three-dimensional spatial structure. Due to the structural and compositional diversity of MOFs and their strong tunability, the structure of MOFs can be designed and modified according to actual needs.

SUMMARY OF THE INVENTION

In view of the deficiencies in this field, the present invention provides a preparation method of modified carbon nitride/Fe-based MOF composite material, which adopts the method of "pre-functionalization" to modify carbon nitride (denoted as gC _{3 )} . N ₄ -M) as a modified substance, a new modified carbon nitride/Fe-based MOF composite (denoted as gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe)-X%) was prepared, which can be used as Photocatalyst for visible light catalytic reduction of Cr(VI). Performance tests show that the reduction efficiency of NH ₂ -MIL-53(Fe)-X% with a very small amount of modified carbon nitride gC ₃ N ₄ -M for Cr(VI) under visible light is significantly better than that of traditional gC ₃ N ₄ Composites composed of _gC3N4 / _{NH2 -} MIL-53(Fe)-X% and single _NH2 -MIL _- 53(Fe)-X% and single _{gC3N4 -} M, indicating _gC3N4 There is a strong synergy between -M and _NH2 -MIL-53(Fe)-X%.

A preparation method of modified carbon nitride/Fe-based MOF composite material, comprising the steps of:

(1) After uniformly mixing melamine and triaminopyrimidine in a molar ratio of 1:2 to 4, calcining at 450 to 550° C. in an inert atmosphere, grinding the resulting product, adding it to dimethyl sulfoxide (DMSO), and ultrasonically stripping it for 1 After ~3h, centrifuge, wash and dry with distilled water to obtain modified carbon nitride powder;

(2) Dispersing the modified carbon nitride powder obtained in step (1) in N,N-dimethylformamide (DMF) to form a dispersion liquid, adding the dispersion liquid to a mixture containing ferric chloride, p-benzene In the N,N-dimethylformamide solution of dicarboxylic acid and aminoterephthalic acid, the modified carbon nitride/Fe-based MOF composite is obtained by solvothermal reaction at 140～160℃ for 14～16h after mixing.

The preparation process of the invention is simple in process and mild in reaction conditions, and the obtained composite material is gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe)-X%, which can be used as a photocatalyst. The present invention firstly prepares heterojunction NH ₂ -MIL-53/MIL-53 (namely NH ₂ -MIL-53(Fe)-X%, X% represents Amination ratio), it was found that the amination of MIL-53 significantly affected the cycling stability of the material, and the ratio of amination also affected the change of photocatalytic activity. Then, on the basis of this optimization, the present invention prepares p-type semiconductor modified carbon nitride gC ₃ N ₄ -M (ordinary gC ₃ N ₄ is an n-type semiconductor), and further research finds that the conduction band and valence band of gC ₃ N ₄ -M are Matching the conduction band and valence band of Fe-based MOF _NH2 -MIL-53(Fe)-X% functionalized with amino moiety, a pn-type heterojunction can be formed, which can further exert the synergy between the two in photocatalysis. It can effectively improve the efficiency of photocatalytic reduction of Cr(VI). The composite material prepared by the invention has the advantages of high photocatalytic activity, convenient synthesis, low cost, easy recovery and the like.

The inert atmosphere is N ₂ , rare gas and the like.

Preferably, in step (1), the calcination time is 1-3h.

Preferably, in step (2), the molar ratio of the ferric chloride, terephthalic acid and amino terephthalic acid is 2:0.5-1.5:0.5-1.5, and the molar amount of the ferric chloride and p-benzene The ratio of the sum of the molar amounts of dicarboxylic acid and aminoterephthalic acid is 1:1.

Preferably, in step (2), the ratio of the modified carbon nitride powder in the dispersion to the ferric chloride is 0.5-2 mg:2 mmol. After NH ₂ -MIL-53(Fe)-X% is compounded with a very small amount of modified carbon nitride, the photocatalytic performance can be significantly improved.

The invention also provides the modified carbon nitride/Fe-based MOF composite material prepared by the preparation method, which can be used as a photocatalyst.

The invention also provides the application of the modified carbon nitride/Fe-based MOF composite material in the field of photocatalysis. For example, the modified carbon nitride/Fe-based MOF composite material can be used as a photocatalyst, or used to prepare a photocatalyst.

The present invention also provides a method for treating Cr(VI)-containing wastewater, comprising the steps of: adding the modified carbon nitride/Fe-based MOF composite material into the Cr(VI)-containing wastewater, dark reaction adsorption equilibrium Then, visible light irradiation was carried out to carry out photocatalytic degradation.

Preferably, before the dark reaction adsorption, ammonium oxalate is also added to the Cr(VI)-containing wastewater, and the added amount is 20-40 mg/L.

Compared with the prior art, the present invention has the following main advantages: the synthesis method provided by the present invention is simple and easy to implement, with mild conditions, and is suitable for large-scale production. The resulting composite gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe) can be used as a photocatalyst. Different from ordinary gC ₃ N ₄ , the gC ₃ N ₄ -M prepared by the present invention is a p-type semiconductor, because its conduction band and valence band are partially functionalized with the amino group of Fe-based MOF NH ₂ -MIL-53(Fe)- The conduction band and valence band of X% are matched, which can form a pn-type heterojunction, and give full play to the synergistic effect of the two in photocatalysis, thereby effectively improving the efficiency of photocatalytic reduction of Cr(VI). The composite material prepared by the invention has the advantages of high photocatalytic activity, convenient synthesis, low cost, easy recovery and the like.

Description of drawings

Fig. 1 is the photocatalytic reduction Cr(VI) performance comparison diagram of NH ₂ -MIL-53(Fe)-X% prepared with different ratios of starting aminoterephthalic acid and terephthalic acid in Example 1;

2 is a graph showing the effect of the initial gC ₃ N ₄ -M stripping solution addition volume on the photocatalytic performance of gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe)-50% in Example 3;

Figure 3 shows the performance comparison of photocatalytic reduction of Cr(VI) with different types of catalysts in Example 4, wherein (1) gC ₃ N ₄ , (2) gC ₃ N ₄ -M, (3) MIL-53(Fe), (4) NH ₂ -MIL-53(Fe), (5) NH ₂ -MIL-53(Fe)-50%, (6) gC ₃ N ₄ /NH ₂ -MIL-53(Fe)-50%- 1.5mL, (7) _{gC3N4 -} M/ _NH2 -MIL-53(Fe)-50%-1.5mL;

4 is a cycle stability diagram of gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe)-50%-1.5mL prepared in Example 5 for treating chromium-containing wastewater.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. The operation method without specifying the specific conditions in the following examples is usually in accordance with the conventional conditions, or in accordance with the conditions suggested by the manufacturer.

Example 1

Preparation of NH ₂ -MIL-53(Fe)-X% with Different Proportions of Aminoterephthalic Acid Ligands

1) Preparation of NH ₂ -MIL-53(Fe)-100% (ie NH ₂ -MIL-53(Fe))

First, 2mmol FeCl ₃ ·6H ₂ O and 2mmol aminoterephthalic acid were dissolved in 40mL of N,N-dimethylformamide, magnetically stirred for 60min, then transferred to a hydrothermal kettle, heated at 150°C for 15h, Naturally cooled to room temperature, centrifuged at 8000 rpm for 5 min, washed twice with DMF and methanol respectively, and finally vacuum-dried at 100° C. for 12 h to obtain the NH ₂ -MIL-53(Fe)-100%.

2) Preparation of NH ₂ -MIL-53(Fe)-75%

First, 2mmol FeCl ₃ ·6H ₂ O, 1.5mmol amino terephthalic acid and 0.5mmol terephthalic acid were dissolved in 40mL of N,N-dimethylformamide, magnetically stirred for 60min, and then transferred to a hydrothermal kettle , heated at 150°C for 15h, cooled to room temperature naturally, centrifuged at 8000rpm for 5min, washed twice with DMF and methanol respectively, and finally vacuum-dried at 100°C for 12h to obtain the NH ₂ -MIL- 53(Fe)-75%.

3) Preparation of NH ₂ -MIL-53(Fe)-50%

First, 2mmol FeCl ₃ 6H ₂ O and 1mmol aminoterephthalic acid, 1mmol terephthalic acid were dissolved in 40mL of N,N-dimethylformamide, magnetic stirring for 60min, then transferred to a hydrothermal kettle, in Heated at 150°C for 15h, cooled to room temperature naturally, centrifuged at 8000rpm for 5min, then washed twice with DMF and methanol respectively, and finally vacuum-dried at 100°C for 12h to obtain the NH ₂ -MIL-53 ( Fe) - 50%.

4) Preparation of NH ₂ -MIL-53(Fe)-25%

First, 2mmol FeCl ₃ .6H ₂ O, 0.5mmol amino terephthalic acid and 1.5mmol terephthalic acid were dissolved in 40mL of N,N-dimethylformamide, magnetically stirred for 60min, and then transferred to a hydrothermal kettle , heated at 150°C for 15h, cooled to room temperature naturally, centrifuged at 8000rpm for 5min, washed twice with DMF and methanol respectively, and finally vacuum-dried at 100°C for 12h to obtain the NH ₂ -MIL- 53(Fe)-25%.

5) Preparation of NH ₂ -MIL-53(Fe)-0% (ie MIL-53(Fe))

First, 2 mmol FeCl ₃ ·6H ₂ O and 2 mmol terephthalic acid were dissolved in 40 mL of N,N-dimethylformamide, magnetically stirred for 60 min, then transferred to a hydrothermal kettle, heated at 150 ° C for 15 h, naturally Cooled to room temperature, centrifuged at 8000rpm for 5min, then washed twice with DMF and methanol respectively, and finally vacuum-dried at 100°C for 12h to obtain the NH ₂ -MIL-53(Fe)-0%

6) Performance test of photocatalytic reduction of Cr(VI)

Take 10 mg of the above-mentioned NH ₂ -MIL-53(Fe)-X% containing aminoterephthalic acid ligands in different proportions, add it to a potassium dichromate solution (100 mL) with a Cr(VI) concentration of 80 μmol/L, add 3 mg of ammonium oxalate was used as a coexisting organic compound and a hole trapping agent, and the pH was adjusted to 4.7. Under the condition of magnetic stirring, after dark reaction for 30 minutes, the xenon lamp light source was turned on, and the photocatalytic reaction was carried out under the action of visible light. After 20 minutes of visible light irradiation, sampling, centrifugation, taking the supernatant and measuring its absorbance at 540nm by color development, by comparing the absorbance before and after the reaction, the reduction rate of Cr(VI) can be calculated, and the result is shown in the figure 1 shown.

As can be seen from Figure 1, comparing the performance of NH ₂ -MIL-53(Fe)-X% with different amination ratios for photocatalytic reduction of Cr(VI), the molar ratio of starting aminoterephthalic acid and terephthalic acid is The 1:1 prepared NH ₂ -MIL-53(Fe)-50% exhibited the best photocatalytic performance. The photocatalytic performance of MIL-53(Fe) after full amination is not as good as that of partial amination. It can be seen that there is a synergistic effect between NH ₂ -MIL-53(Fe) and MIL-53(Fe) prepared in situ by the method of the present invention, which promotes The photocatalytic performance was improved.

In addition, during the experiment, it was found that in the case of adding ammonium oxalate, MIL-53(Fe) without amino groups had poor stability, was easy to dissolve, and could not be effectively separated and recovered, while NH ₂ -MIL-53(Fe) containing amino groups and The compound has good stability and can be used stably in cycles.

Example 2

Preparation of gC ₃ N ₄ -M dispersion (stripping solution)

1) Preparation of gC ₃ N ₄ -M

Weigh melamine and triaminopyrimidine in a molar ratio of 1:3 and mix them evenly, spread them out on a quartz boat, and heat them in a tube furnace under a nitrogen atmosphere. ℃ and maintained for 120 min, and finally cooled to room temperature under nitrogen purging to obtain powdered gC ₃ N ₄ -M. After grinding into powder, ultrasonically treated in pure DMSO for 120 min to peel off gC ₃ N ₄ -M particles. The samples were centrifuged five times with distilled water at 8000 rpm in a centrifuge, dried at 60° C. for 12 hours in a vacuum drying cabinet, and collected.

2) Preparation of gC ₃ N ₄ -M dispersion

Weigh 50 mg of the good gC ₃ N ₄ -M particles prepared in step 1), add them to DMF and sonicate for half an hour to obtain a gC ₃ N ₄ -M dispersion with a concentration of 1 mg/mL.

Example 3

Preparation of multiple composite catalysts

1) Preparation of gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe)-50%

First, 2 mmol FeCl ₃ ·6H ₂ O, 1 mmol aminoterephthalic acid, 1 mmol terephthalic acid were dissolved in 40 mL of NN-dimethylformamide, and different volumes (0.5 mL, 1.0 mL, 1.5 mL, 2 mL) were added. ) The gC ₃ N ₄ -M dispersion prepared in Example 2 was magnetically stirred for 60 min, then transferred to a hydrothermal kettle, heated at 150° C. for 15 h, cooled to room temperature naturally, centrifuged at 8000 rpm for 5 min, and then used DMF respectively. Wash twice with methanol each, and finally vacuum dry at 100 °C for 12 h to obtain gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe)-50% with different loading ratios of gC ₃ N ₄ -M.

2) Performance test of photocatalytic reduction of Cr(VI)

10 mg of gC ₃ N ₄ -M with different loading ratios of gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe)-50% were added to potassium dichromate solution with a Cr(VI) concentration of 80 μmol/L ( 100 mL), add 3 mg of ammonium oxalate as a coexisting organic compound and a hole trapping agent, adjust the pH to 4.7, and under the condition of magnetic stirring, after 30 minutes of dark reaction, turn on the xenon lamp light source, and carry out the photocatalytic reaction under the action of visible light. After 20 minutes of visible light irradiation, sampling, centrifugation, taking the supernatant and measuring its absorbance at 540nm by color development, by comparing the absorbance before and after the reaction, the reduction rate of Cr(VI) can be calculated, and the result is shown in the figure 2 shown.

As can be seen from Figure ₂ , comparing the performance of the addition amount of gC ₃ N ₄ -M dispersion for photocatalytic reduction of Cr(VI _{), the gC 3 N 4} -M/ NH ₂ -MIL-53(Fe)-50%-1.5mL exhibited the best photocatalytic performance.

Example 4

Preparation of other control catalysts

₁ ) Preparation of _gC3N4 / _NH2 -MIL-53(Fe)-50%-1.5mL

First, 2 mmol FeCl ₃ ·6H ₂ O, 1 mmol of aminoterephthalic acid, and 1 mmol of terephthalic acid were dissolved in 40 mL of NN-dimethylformamide, and 1.5 mL of gC ₃ N ₄ stripping solution was added (except for the addition of three Except aminopyrimidine, the rest of the preparation process is the same as the gC ₃ N ₄ -M stripping solution in Example 2), magnetically stirred for 60 min, then transferred to a hydrothermal kettle, heated at 150 ° C for 15 h, naturally cooled to room temperature, and centrifuged at 8000 rpm. 5min, then washed twice with DMF and methanol respectively, and finally vacuum dried at 100°C for 12h to obtain gC ₃ N ₄ /NH ₂ -MIL-53(Fe)-50%.

2) Preparation of gC ₃ N ₄

Weigh the melamine and spread it on a quartz boat, heat it in a tube furnace under a nitrogen atmosphere, heat it up to 500 °C at a heating rate of 5 °C min ^-1 , maintain it for 120 min, and finally cool it to room temperature under nitrogen purging , get powdered gC ₃ N ₄ , grind it into powder, treat it in pure DMSO in ultrasonic bath for 120min to peel off gC ₃ N ₄ particles, centrifuge five times with distilled water at 8000rpm in a centrifuge, and put it in a vacuum drying box Collect after drying at 60°C for 12 hours.

3) Performance test of various types of catalysts for photocatalytic reduction of Cr(VI)

Take 10 mg of different catalysts, add them to a potassium dichromate solution (100 mL) with a Cr(VI) concentration of 80 μmol/L, add 3 mg of ammonium oxalate as a coexisting organic compound and a hole trapping agent, adjust the pH to 4.7, and under the condition of magnetic stirring After 30 minutes of dark reaction, the xenon light source was turned on, and the photocatalytic reaction was carried out under the action of visible light. After 20 minutes of visible light irradiation, sampling, centrifugation, taking the supernatant and measuring its absorbance at 540nm by color development, by comparing the absorbance before and after the reaction, the reduction rate of Cr(VI) can be calculated, and the result is shown in the figure 3 shown.

It can be seen from Figure 3 that for the photocatalytic reduction of Cr(VI), when NH ₂ -MIL-53(Fe)-50% is used as the substrate (the molar ratio of starting aminoterephthalic acid and terephthalic acid is 1:1), The multi-component composite catalyst gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe)-50% prepared with gC ₃ N ₄ -M stripping solution as additive (addition amount of 1.5 mL) showed the best performance.

The photocatalytic activity of gC ₃ N ₄ -M of the present invention is lower than that of ordinary gC ₃ N ₄ , and both have almost no photocatalytic activity, but when a very small amount of gC ₃ N ₄ -M is combined with partially aminated MIL-53 (Fe ), the photocatalytic activity of the obtained composites can be significantly improved, which is significantly higher than that of ordinary gC ₃ N ₄ and partially aminated MIL-53(Fe) composites, indicating that gC ₃ N ₄ -M and some amino groups The synthesized MIL-53(Fe) formed a multivariate heterojunction with a strong synergistic effect.

Example 5

Cycling Stability Test

The optimally prepared gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe)-50% was used as a photocatalyst for photocatalytic reduction of Cr(VI) for 5 cycles, and the photocatalyst was centrifuged before each cycle. , washed with water and dried, put it into a new 80 μmol/L Cr(VI) (100 mL) solution, added 3 mg of ammonium oxalate as a coexisting organic compound and a hole trapping agent, adjusted the pH to 4.7, under the condition of magnetic stirring, darkened After 30 minutes of reaction, the xenon lamp light source was turned on, and the photocatalytic reaction was carried out under the action of visible light. After 20 minutes of visible light irradiation, sampling, centrifugation, taking the supernatant and measuring its absorbance at 540nm by color development, by comparing the absorbance before and after the reaction, the reduction rate of Cr(VI) can be calculated, and the result is shown in the figure As shown in 4, gC ₃ N ₄ -M/NH ₂ -MIL-53(Fe)-50% has good cycling stability, and its activity does not change significantly after 5 cycles, and is stable at 90% above.

In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims (8)

1. A preparation method of a modified carbon nitride/Fe-based MOF composite material is characterized by comprising the following steps:

(1) uniformly mixing melamine and triaminopyrimidine according to a molar ratio of 1: 2-4, roasting at 450-550 ℃ in an inert atmosphere, grinding the obtained product, adding the ground product into dimethyl sulfoxide, ultrasonically stripping for 1-3 hours, centrifuging with distilled water, washing, and drying to obtain modified carbon nitride powder;

(2) dispersing the modified carbon nitride powder obtained in the step (1) in N, N-dimethylformamide to form a dispersion liquid, adding the dispersion liquid into an N, N-dimethylformamide solution containing ferric chloride, terephthalic acid and amino terephthalic acid, uniformly mixing, and carrying out solvothermal reaction at 140-160 ℃ for 14-16 h to obtain a modified carbon nitride/Fe-based MOF composite material;

the molar ratio of the ferric chloride to the terephthalic acid to the amino terephthalic acid is 2: 0.5-1.5.

2. The preparation method according to claim 1, wherein in the step (1), the roasting time is 1-3 h.

3. The process according to claim 1, wherein in the step (2), the ratio of the molar amount of ferric chloride to the sum of the molar amounts of terephthalic acid and aminoterephthalic acid is 1: 1.

4. The method according to claim 1 or 3, wherein in the step (2), the ratio of the modified carbon nitride powder to the ferric chloride in the dispersion liquid is 0.5-2 mg:2 mmol.

5. The modified carbon nitride/Fe-based MOF composite material prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the modified carbon nitride/Fe-based MOF composite material according to claim 5 in the field of photocatalysis.

7. A method for treating wastewater containing Cr (VI) is characterized by comprising the following steps: adding the modified carbon nitride/Fe-based MOF composite material of claim 5 into the Cr (VI) -containing wastewater, and after dark reaction adsorption equilibrium, irradiating with visible light for photocatalytic degradation.

8. The treatment method according to claim 7, wherein before the adsorption of the dark reaction, ammonium oxalate is further added into the Cr (VI) -containing wastewater, and the addition amount is 20-40 mg/L.

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