A lutetium-based carbon nitride composite photocatalyst for reducing carbon dioxide

Abstract

The application provides a preparation method of a lutetium-based carbon nitride composite photocatalyst and application of the lutetium-based carbon nitride composite photocatalyst in photocatalytic reduction of CO2. The lutetium-based carbon nitride composite photocatalyst is a molecular-semiconductor type composite photocatalyst, and together with a photosensitizer 4CzIPN, an electron sacrificial agent TEA and a mixed solvent of N,N-dimethylacetamide and H2O, forms a photocatalytic system. The system can photocatalytically reduce CO2 into CO under irradiation of a white LED lamp with a wavelength of 420-780 nm, and the efficiency can reach 1377.5 micromoles / g, and the selectivity can reach 94.9%. The reduction efficiency and selectivity of the lutetium-based carbon nitride composite photocatalyst are 176 and 3.6 times of those of original carbon nitride under the same conditions. The photocatalyst preparation method is simple, raw materials are cheap and easy to obtain, and the preparation cost is low. The lutetium-based carbon nitride composite photocatalyst has good photo-generated carrier separation capacity, and shows high activity and selectivity in the photocatalytic reduction of CO2 into CO system.

Description

Technical Field

[0001] This invention relates to a lutetium-based carbon nitride composite photocatalyst for the photocatalytic reduction of CO2 to CO, belonging to the fields of semiconductor materials and photocatalysis technology. Background Technology

[0002] Excessive CO2 emissions severely impact climate change, leading to global warming and the greenhouse effect. Catalytically reducing CO2 with solar energy to obtain high-value-added chemicals is a common approach to CO2 utilization. This reaction typically occurs at room temperature and pressure, under mild conditions, and requires only solar energy as the external energy source. CO2 is a natural and abundant carbon source, while solar energy is a green and sustainable new energy source. This method not only effectively reduces CO2 emissions but also produces fuels such as CO and CH4, possessing considerable economic value.

[0003] In recent years, novel hybrid catalysts combining metal molecular complexes and semiconductors have been found to exhibit high photocatalytic CO2 reduction performance. The metal center of the metal molecular complex can serve as the active site for the CO2 reduction reaction, and ligands can be modified to adjust the redox potential of the complex for CO2 reduction; however, these ligands are difficult to recover from the catalytic system. Semiconductor materials, such as carbon nitride, possess good conductivity and a suitable band gap structure, but their rapid recombination of photogenerated carriers leads to low catalytic efficiency. Recent studies have reported that combining metal molecular complexes and semiconductors to form novel hybrid catalysts can solve these two problems. In these novel hybrid catalysts, the molecular complex can provide electron storage sites for the photogenerated carriers in the semiconductor, promoting the separation of these carriers. Furthermore, the poor solubility of these catalysts in the catalytic system facilitates their recovery.

[0004] Transition metals typically possess unfilled d orbitals, exhibiting strong redox properties. Therefore, transition metals such as Fe, Co, and Ru are commonly chosen as metal centers in the aforementioned composite catalysts. Besides transition metals, rare earth metals also possess unfilled electron orbitals (4f orbitals), which can capture excited-state electrons. Based on this characteristic of rare earth metals, rare earth metal single atoms, rare earth metal ions, and rare earth metal oxides are often used to modify semiconductor catalysts to achieve higher catalytic efficiency. Furthermore, the unfilled 4f orbitals of rare earth metals also result in rare earth metal ions typically possessing high coordination numbers and multiple coordination states, leading to a wide variety of complex rare earth metal molecular complexes, which have been reported in many fields. For example, complexes formed by lanthanide metal ions coordinated with terpyridyl ligands are widely used in gas storage, magnetism, and luminescence.

[0005] Based on the above background, considering the effective separation of photogenerated carriers from carbon nitride, this invention covalently links a terpyridine-lutetium complex molecular catalyst with a carbon nitride semiconductor catalyst to prepare a lutetium-based carbon nitride composite photocatalyst. The modified composite photocatalyst was then systematically compared with unmodified pure carbon nitride. On one hand, the terpyridine-lutetium complex can act as an electron storage site, promoting the separation of photogenerated carriers from carbon nitride; on the other hand, the terpyridine-lutetium complex catalyst can also serve as a reaction site for CO2 reduction, thereby improving photocatalytic activity. The lutetium-based carbon nitride photocatalyst prepared by this invention exhibits high CO yield, high selectivity, and easy recovery. Summary of the Invention

[0006] This invention provides an environmentally friendly and low-cost method for preparing a lutetium-based carbon nitride composite photocatalyst and its application in the photocatalytic reduction of CO2.

[0007] This invention discloses a method for preparing the lutetium-based carbon nitride composite photocatalyst, comprising the following steps: 4'-(4-bromo)-2,2':6',2”-terpyridine is thoroughly mixed with carbon nitride and calcined in a tube furnace at 300°C for 4 hours under nitrogen protection. After cooling to room temperature, excess terpyridine ligand is washed away with dichloromethane, and the mixture is then vacuum dried to obtain a terpyridine-based carbon nitride composite material. Subsequently, the obtained terpyridine-based carbon nitride is added to an acetonitrile solution containing Lu(NO3)3·6H2O, and stirred at 80°C for 12 hours under nitrogen protection. Excess Lu(NO3)3·6H2O is washed away with acetonitrile, and the mixture is then vacuum dried to obtain the lutetium-based carbon nitride composite photocatalyst, denoted as LutpyCN.

[0008] Through XRD ( Figure 1 XPS Figure 2 ), FT-IR ( Figure 3 SEM Figure 4 ) and BET nitrogen adsorption-desorption ( Figure 5 The morphology, structure, and chemical composition of the lutetium-based carbon nitride composite photocatalyst were investigated. The results showed that the terpyridine-lutetium complex was successfully linked to carbon nitride. Furthermore, the lutetium-based carbon nitride composite photocatalyst retained the porous structure and phase structure of carbon nitride.

[0009] The lutetium-based carbon nitride composite photocatalyst prepared in this invention, while retaining the carbon nitride structure, exhibits significantly enhanced photocatalytic performance under the combined action of the photosensitizer 4CzIPN, the sacrificial agent TEA, and a mixed solvent of N,N-dimethylacetamide and H2O. On one hand, its CO yield is 1377.5 μmol / g, 176 times that of carbon nitride; on the other hand, compared to the reaction byproduct H2, the selectivity of the main product CO is 94.9%, 3.6 times that of carbon nitride. Its catalytic effect is shown in […]. Figure 6 .

[0010] By fluorescence spectroscopy ( Figure 7 ),impedance( Figure 8 ), photocurrent ( Figure 9 The tests verified that the lutetium-based carbon nitride composite photocatalyst has higher photogenerated carrier separation efficiency and photoelectric effect compared to carbon nitride. Attached Figure Description

[0011] Figure 1 The XRD patterns of the lutetium-based carbon nitride composite photocatalyst prepared in this invention and carbon nitride are shown.

[0012] Figure 2 XPS full spectrum of lutetium-based carbon nitride composite photocatalyst and carbon nitride prepared in this invention;

[0013] Figure 3 The FT-IR spectra of the lutetium-based carbon nitride composite photocatalyst prepared in this invention and carbon nitride are shown below.

[0014] Figure 4 SEM image of the lutetium-based carbon nitride composite photocatalyst prepared in this invention;

[0015] Figure 5 The image shows the BET nitrogen adsorption-desorption isotherm of the lutetium-based carbon nitride composite photocatalyst prepared in this invention.

[0016] Figure 6 The diagram shows the lutetium-based carbon nitride composite photocatalyst prepared in this invention and the photocatalytic reduction performance of carbon nitride for CO2.

[0017] Figure 7 The images show the fluorescence spectra of the lutetium-based carbon nitride composite photocatalyst and carbon nitride prepared in this invention.

[0018] Figure 8 Impedance images of the lutetium-based carbon nitride composite photocatalyst prepared in this invention and carbon nitride.

[0019] Figure 9 Images showing the lutetium-based carbon nitride composite photocatalyst prepared in this invention and the photocurrent of carbon nitride. Detailed Implementation

[0020] The present invention will be described more clearly below with reference to comparative examples and embodiments. The comparative examples mentioned below are only used to explain the present invention and are not restrictive.

[0021] Compare with Example 1:

[0022] 3.0 g of cyanamide was added to 7.5 g of silica sol (Ludox HS-40, 40 wt%) and stirred at 60 °C for 12 h to obtain a white solid. This solid was placed in a tube furnace and calcined at 550 °C for 4 h under a N2 atmosphere. After cooling to room temperature, a yellow solid was obtained. The yellow solid and NH4HF2 were added sequentially to water and stirred at room temperature for 24 h. The solid product was collected by filtration, washed sequentially with water and ethanol, and then dried in a vacuum drying oven for 10 h to obtain carbon nitride solid, denoted as CN.

[0023] 10 mg of carbon nitride was placed in a 45 mL test tube, followed by the addition of 1 mL of 4CzIPN in N,N-dimethylacetamide solution (1 mg / mL), 6 mL of N,N-dimethylacetamide, 3 mL of H2O, and 100 μL of TEA. The reaction solution was degassed with high-purity CO2 for 15 min, and the test tube was immediately sealed with a rubber stopper. The test tube was irradiated with a white LED lamp (3STECH AL3, 420-780 nm, 1 W). The reduction products of CO2 were determined using a gas chromatograph (GC-2014). The CO yield was 7.8 μmol / g, with a selectivity of 26.2%.

[0024] Example 1:

[0025] The synthesis method of the lutetium-based carbon nitride composite photocatalyst prepared in this invention specifically includes the following steps:

[0026] S1. Add 1.0 g of carbon nitride to 100 mL of dichloromethane solution containing 100 mg of 4'-(4-bromo)-2,2':6',2”-terpyridine, stir at room temperature for 4 h, remove the dichloromethane solvent by rotary evaporator, and dry the resulting brown solid in a vacuum drying oven.

[0027] S2. The dried brown solid was placed in a tube furnace and calcined at 300°C for 4 hours under a N2 atmosphere. After cooling to room temperature, excess 4'-(4-bromo)-2,2':6',2”-terpyridine was washed away with dichloromethane to obtain a terpyridine-based carbon nitride composite material.

[0028] S3. 426.8 mg of the terpyridyl carbon nitride composite material was added to 100 mL of acetonitrile solution containing 1.5 mM Lu(NO3)3·6H2O. The mixture was stirred at 80 °C for 12 h under a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered. The brown solid obtained by filtration was thoroughly washed with acetonitrile. Subsequently, the solid was dried in a vacuum drying oven to obtain the lutetium-based carbon nitride composite photocatalyst, denoted as LutpyCN.

[0029] 10 mg of lutetium-based carbon nitride composite photocatalyst was placed in a 45 mL test tube, followed by the addition of 1 mL of 4CzIPN N,N-dimethylacetamide solution (1 mg / mL), 6 mL of N,N-dimethylacetamide, 3 mL of H2O, and 100 μL of TEA. The reaction solution was degassed with high-purity CO2 for 15 min, and the test tube was immediately sealed with a rubber stopper. The test tube was irradiated with a white LED lamp (3STECH AL3, 420-780 nm, 1 W). The reduction products of CO2 were determined using a gas chromatograph (GC-2014), showing a CO yield of 1377.5 μmol / g and a selectivity of 94.9%.

Claims

1. A lutetium-based carbon nitride composite photocatalyst for reducing carbon dioxide, characterized in that, Its structure is as follows: Abbreviated as LutpyCN.

2. A method for synthesizing the lutetium-based carbon nitride composite photocatalyst as described in claim 1, characterized in that, Includes the following steps: Step 1: Add carbon nitride to a dichloromethane solution containing 4'-(4-bromo)-2,2':6',2”-terpyridine, stir at room temperature, remove the dichloromethane solvent by rotary evaporator, and dry the resulting brown solid in a vacuum drying oven; Step 2: Place the dried brown solid in a tube furnace and calcine it under N2 atmosphere. After cooling to room temperature, wash away the excess 4'-(4-bromo)-2,2':6',2”-terpyridine with dichloromethane to obtain terpyridine-based carbon nitride composite material. Step 3: The terpyridine-based carbon nitride composite material was added to an acetonitrile solution containing Lu(NO3)3·6H2O, stirred under a nitrogen atmosphere, cooled to room temperature and filtered. The brown solid obtained by filtration was thoroughly washed with acetonitrile. Subsequently, the solid was placed in a vacuum drying oven to dry, and the lutetium-based carbon nitride composite photocatalyst LutpyCN was obtained.

3. The application of the lutetium-based carbon nitride composite photocatalyst according to claim 1 in the photocatalytic reduction of CO2.

Images