Preparation method and application of iron-based metal organic framework composite photocatalyst for reducing carbon dioxide

Abstract

The invention belongs to the field of green low carbon, and particularly relates to a preparation method of an iron-based metal organic framework composite photocatalyst and application of the iron-based metal organic framework composite photocatalyst in photocatalytic reduction of CO2. In a photocatalytic system constructed by the invention, the iron-based metal organic framework composite photocatalyst is taken as a core catalyst, 4CzIPN is taken as a photosensitizer, TEA is taken as a sacrificial agent, and N, N-dimethylacetamide and water are taken as solvents together. The system shows excellent photocatalytic performance, CO2 can be efficiently subjected to photocatalytic reduction to CO, the yield is up to 731.7 mmol / g, the selectivity reaches 99%, and compared with MOF-808 (the yield of CO is only 0.5 mmol / g, and the selectivity is 47%), the system has remarkable advantages. The iron-based metal organic framework composite photocatalyst is excellent in photocatalytic performance, simple and convenient in preparation process and low in raw material cost. In addition, the catalyst also has a wide visible light absorption range and excellent photo-generated charge separation and transfer capability, and has great application potential and value.

Description

Technical Field

[0001] The present invention belongs to the field of green and low-carbon, and specifically relates to an iron-based metal organic framework composite photocatalyst for photocatalytic reduction of CO2 to generate CO. Background Art

[0002] CO2 emissions are the main factor causing global warming in recent years. Continuous global warming will cause irreparable harm to the natural ecological environment and human survival. Based on these factors, artificial use of CO2 is one of the effective measures to mitigate global warming. Using endless solar energy to convert CO2 into value-added chemicals is a feasible and low-energy approach, but in the research process of photocatalytic CO2 reduction, low selectivity and low catalytic efficiency limit the further application of this approach. A catalyst that efficiently photocatalytically reduces CO2 and ultimately converts it into value-added chemicals needs to be developed.

[0003] MOF (metal organic framework) is a type of crystalline porous material assembled by connecting metal or metal cluster nodes with organic ligands. Due to its adjustable structure, permanent porosity, large specific surface area and customizable properties, it has been widely used in gas adsorption, sensing, catalysis and other fields in recent decades. MOF-808 has attracted the attention of many researchers due to its stable framework, cage structure and acid resistance. MOF-808 and its derivatives are often used to study the adsorption of CO2, but a single MOF-808 structure is difficult to efficiently catalyze CO2 reactions. In the analysis of the MOF-808 structure, it was found that the formic acid ligands in the framework are easily replaced. Based on this feature, we explored the modification and modification of MOF-808 to seek a way to efficiently catalyze CO2 reduction.

[0004] Traditional molecular complexes, such as 4'-(4-carboxyphenyl)-2,2':6',2''-terpyridine (Tpy) and its derivatives, are usually used to study the photocatalytic reduction of CO2, showing good catalytic efficiency. However, the limitation of molecular catalysts is that they are difficult to separate from the catalytic system, difficult to recycle, and often involve precious metals in the catalytic system, which limits their wide-scale use. Here, we explored a post-synthesis ligand exchange and subsequent metallization process to replace the formic acid group with Tpy. After ligand exchange, the metal center Fe was introduced into the chelating site of Tpy for metallization modification to form Fetpy / MOF-808, and then its photocatalytic performance and catalytic mechanism were further studied. Summary of the invention

[0005] The present invention provides a method for preparing an easily obtainable iron-based metal organic framework composite photocatalyst with excellent catalytic performance and application of the catalyst in photocatalytic reduction of CO2.

[0006] The invention discloses a method for preparing the iron-based metal organic framework composite photocatalyst, comprising the following steps: 4'-(4-carboxyphenyl)-2,2':6',2''-terpyridine is dissolved in a mixed solvent of dimethyl sulfoxide and methanol, and then MOF-808 is added to the solution. The mixture is stirred at 80 °C for 72 hours under a nitrogen atmosphere. After the reaction is completed, it is washed with water and methanol for many times to remove unreacted raw materials. The washed sample is then soaked in methanol for 24 hours, and then dried in a vacuum oven at 60 °C for 6 hours to obtain a Tpy / MOF-808 composite material. FeCl2·4H2O is dissolved in methanol and ultrasonically treated. Thereafter, 0.1 g of Tpy / MOF-808 is added to the solution, and the mixture is heated to 70 °C and stirred for 24 hours. The collected solids were then washed with methanol to remove any residual impurities, and finally the samples were dried in a vacuum oven at 60 °C for 6 h to obtain the iron-based metal organic framework composite photocatalyst, denoted as Fetpy / MOF-808.

[0007] By SEM ( Figure 1 ), XRD (Figure 2), FT-IR ( Figure 3 ), XPS (Figure 4) and BET nitrogen adsorption and desorption (Figure 5) tests characterized the morphology, structure and chemical composition of the iron-based metal organic framework composite photocatalyst. The results showed that the terpyridine iron complex was successfully connected to MOF-808, which also means that the structure of MOF-808 will not be changed after the connection of terpyridine and subsequent metallization.

[0008] The iron-based metal organic framework composite photocatalyst prepared by the present invention is used as a catalyst for photocatalytic reduction of CO2 to CO, 4CzIPN is used as a photosensitizer, TEA is used as a sacrificial agent, N,N-dimethylacetamide and water are used as solvents, and has good photocatalytic performance. In this system, the CO yield is 731.7mmol / g and the selectivity is 99%, which is much higher than the CO yield of 0.5mmol / g and the selectivity of 47% when the simple MOF-808 is used as a catalyst. The specific catalytic effect is shown in Figure 6 .

[0009] The introduction of terpyridine and Fe metal center successfully broadened the visible light absorption range of MOF-808 ( Figure 7 ), through fluorescence spectroscopy (Figure 8), impedance (Figure 9), and photocurrent (Figure 10) tests, it was proved that the iron-based metal-organic framework composite photocatalyst is more conducive to the separation and transfer of photogenerated charges. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is the SEM image of the iron-based metal-organic framework composite photocatalyst;

[0011] Figure 2 It is the XRD spectrum of the iron-based metal organic framework composite photocatalyst and MOF-808;

[0012] Figure 3 It is the FT-IR spectra of the iron-based metal organic framework composite photocatalyst and MOF-808;

[0013] Figure 4 This is the full XPS spectrum of the iron-based metal organic framework composite photocatalyst and MOF-808;

[0014] Figure 5 This is the BET nitrogen adsorption-desorption isotherm image of the iron-based metal-organic framework composite photocatalyst;

[0015] Figure 6 It is the performance image of photocatalytic reduction of CO2 of iron-based metal organic framework composite photocatalyst and MOF-808;

[0016] Figure 7 It is the visible light absorption range spectrum of iron-based metal organic framework composite photocatalyst and MOF-808;

[0017] Figure 8 It is the fluorescence spectrum of iron-based metal organic framework composite photocatalyst and MOF-808;

[0018] Fig. 9 It is the impedance spectrum of iron-based metal organic framework composite photocatalyst and MOF-808;

[0019] Fig.10 It is the photocurrent spectrum of the iron-based metal organic framework composite photocatalyst and MOF-808; DETAILED DESCRIPTION

[0020] The specific embodiments of the present invention are further described in detail below in conjunction with the embodiments and reference examples. The reference examples involved below are only used to explain the present invention and are not restrictive.

[0021] Comparative Example 1:

[0022] 0.42 g of 1,3,5-benzenetricarboxylic acid and 1.94 g of ZrOCl2·8H2O were dissolved in 90 mL of a mixed solvent of N,N-dimethylformamide and formic acid in a volume ratio of 1:1 and ultrasonically treated for 30 min. The mixed solution was transferred to a flask, heated at 130 °C in a nitrogen environment, and magnetically stirred for 48 h. The solid was collected, washed with N,N-dimethylformamide, and then soaked in N,N-dimethylformamide, water, and acetone for three days for solvent exchange. The sample after acetone exchange was then dried in a vacuum for 24 h to obtain a white solid, which was recorded as MOF-808.

[0023] 2 mg of MOF-808, 3 mg of 4CzIPN, and 0.28 mol / L of TEA were added to 15 mL of a mixed solution of N,N-dimethylacetamide solution and water with a volume ratio of 7:3 and added to a 45 mL reaction tube. The system was purged with Ar for 10 min to ensure an inert atmosphere, and then purged with high-purity CO2 for 15 min to saturate the system with CO2. The test tube was then immediately sealed with a rubber stopper to prevent gas escape. The reaction system was kept at room temperature and irradiated with a white LED light source (3STECH AL3, 420-780 nm, 1 W) for 4 h. The generated gas products were analyzed using a gas chromatograph Shimadzu GC-2014, with a CO yield of 0.5 mmol / g and a selectivity of 47%.

[0024] Embodiment 1:

[0025] The synthesis method of the iron-based metal organic framework composite photocatalyst prepared by the present invention specifically comprises the following steps:

[0026] S1. Dissolve 0.42 g of 1,3,5-benzenetricarboxylic acid and 1.94 g of ZrOCl2·8H2O in 90 mL of a 1:1 volume ratio N,N-dimethylformamide and formic acid mixed solvent and ultrasonically treat for 30 min. Transfer the mixed solution to a flask, heat it under a nitrogen atmosphere at 130 °C, and stir it magnetically for 48 h. Collect the solid, wash it with N,N-dimethylformamide, and then soak it in N,N-dimethylformamide, water, and acetone for three days for solvent exchange. Then dry the sample after acetone exchange in a vacuum for 24 h to obtain a white solid, which is recorded as MOF-808.

[0027] S2. Dissolve 0.5 g of 4'-(4-carboxyphenyl)-2,2':6',2''-terpyridine in 30 mL of a mixed solvent of dimethyl sulfoxide and methanol in a volume ratio of 1:1, and then add 0.3 g of MOF-808. The mixture was stirred for 72 h under a nitrogen environment at 80 °C. After the reaction, the solid was collected by filtration and washed several times with water and methanol to remove unreacted substances. The washed sample was then soaked in methanol for 24 h and dried in a vacuum oven at 60 °C for 6 h to obtain a white solid, which was recorded as Tpy / MOF-808.

[0028] S3. Dissolve 0.04 g of FeCl2·4H2O in 20 mL of methanol and treat with ultrasound. Then add 0.1 g of Fe / MOF-808 to the solution and heat and stir at 70 °C for 24 h. Collect the solid by filtration, then wash the collected solid with methanol to remove the residual impurities, and finally dry the sample in a vacuum oven at 60 °C for 6 h to obtain a purple solid iron-based metal organic framework composite photocatalyst, which is recorded as Fetpy / MOF-808.

[0029] 2 mg of Fetpy / MOF-808, 3 mg of 4CzIPN, and 0.28 mol / L of TEA were added to 15 mL of a mixed solution of N,N-dimethylacetamide solution and water with a volume ratio of 7:3 and added to a 45 mL reaction tube. The system was purged with Ar for 10 min to ensure an inert atmosphere, and then purged with high-purity CO2 for 15 min to saturate the system with CO2. The test tube was then immediately sealed with a rubber stopper to prevent gas escape. The reaction system was kept at room temperature and irradiated with a white LED light source (3STECH AL3, 420-780 nm, 1 W) for 4 h. The generated gas products were analyzed using a gas chromatograph Shimadzu GC-2014, with a CO yield of 731.7 mmol / g and a selectivity of 99%.

Claims

1. An iron-based metal organic framework composite photocatalyst Fetpy / MOF-808 for reducing carbon dioxide, characterized in that: Its structure is:

2. Abbreviated as Fetpy / MOF-808.

3. The method for synthesizing the iron-based metal organic framework composite photocatalyst according to claim 1, characterized in that: The steps include: Step 1: Dissolve 1,3,5-benzenetricarboxylic acid and ZrOCl2·8H2O in a mixed solvent of N,N-dimethylformamide and formic acid and treat with ultrasound for 30 minutes. Transfer the mixed solution to a flask and heat and stir under nitrogen. Collect the solid, wash it with N,N-dimethylformamide, and then soak it in N,N-dimethylformamide, water, and acetone for three days to exchange the solvent. Then dry the sample after acetone exchange in a vacuum to obtain a white solid, which is recorded as MOF-808.

4. Step 2: Add MOF-808 to 4'-(4-carboxyphenyl)-2,2':6',2''-terpyridine in a mixed solvent of dimethyl sulfoxide and methanol. The mixture is heated and stirred under nitrogen protection. After the reaction is completed, the solid is collected by filtration, washed with water and methanol respectively, and then soaked in methanol. The white solid is collected and recorded as Ty / MOF-808.

5. Step 3: Add Fetpy / MOF-808 to a methanol solution of FeCl2·4H2O and perform ultrasonic treatment. Transfer the mixed solution to a flask and heat and stir under a nitrogen atmosphere. Filter and collect the solid, wash it thoroughly with methanol, and vacuum dry the solid to obtain an iron-based metal organic framework composite photocatalyst, which is recorded as Fetpy / MOF-808.

6. Use of the iron-based metal organic framework composite photocatalyst according to claim 1 in photocatalytic reduction of CO2.

7. The photocatalytic system of the iron-based metal organic framework composite photocatalyst for photocatalytic reduction of CO2 according to claim 1, characterized in that: With Fetpy / MOF-808 as catalyst, 4CzIPN as photosensitizer, TEA as sacrificial agent, N,N-dimethylacetamide and water as solvent, the system selectively photocatalytically reduces CO2 to CO at room temperature.

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