Organic polymer photocatalyst for photocatalytic synthesis of nitric acid

Abstract

The invention provides a preparation method of an organic polymer photocatalyst and application of the organic polymer photocatalyst in the aspect of photocatalytic synthesis of nitric acid (HNO3) by directly taking nitrogen (N2) and oxygen (O2) as raw materials in water, and additional reagents do not need to be added. It is worthy of notice that the organic polymer photocatalyst (PyOP) shows excellent photocatalytic performance. When O2 is subjected to photocatalytic reduction, the yield of hydrogen peroxide (H2O2) reaches 10147.5 [mu] mol g <-1 > cat, and meanwhile, 672.8 [mu] mol g <-1 > cat of HNO3 can be synthesized by directly utilizing N2 and O2. The preparation method of the photocatalyst provided by the invention is simple, the raw materials are easy to obtain, the preparation cost is low, a metal-free photocatalytic platform only using H2O, N2 and O2 is constructed, and the photocatalyst is used for green and sustainable nitric acid production.

Description

Technical Field

[0001] The invention relates to an organic polymer photocatalyst for synthesizing nitric acid in water using nitrogen and oxygen as raw materials through a photocatalytic reaction, and belongs to the technical field of polymer materials and photocatalysis. Background Art

[0002] Photocatalytic synthesis is a promising green synthetic strategy that can produce a variety of chemicals under ambient conditions while efficiently converting solar energy into chemical energy. However, the photocatalytic synthesis of inorganic acids such as nitric acid remains a major challenge. Globally, millions of tons of nitric acid are produced each year, mainly for the manufacture of fertilizers and other industrial uses. The traditional Ostwald process, widely used for industrial nitric acid production, involves catalytic oxidation of ammonia (NH2). Although this method is effective, it requires high temperature and pressure conditions, resulting in large amounts of nitrogen oxide pollutants. Developing an alternative route to synthesize nitric acid under ambient conditions would have significant advantages: reduced energy consumption, reduced pollutant generation, and direct utilization of nitrogen and oxygen - a transformative prospect for sustainable chemical production.

[0003] To directly convert nitrogen and oxygen into nitric acid under ambient conditions, the photocatalytic system should be capable of activating nitrogen and oxygen in water. Organic polymers, a novel class of materials with rich porosity, controllable redox activity, strong visible light absorption, and excellent gas adsorption properties, are emerging as highly efficient catalysts in various photocatalytic reactions, such as photocatalytic carbon dioxide reduction and light-driven hydrogen production. Notably, organic polymers exhibit a unique ability to activate oxygen to produce hydrogen peroxide. Of particular importance in this process is the simultaneous generation of hydroxyl radicals (·OH), strong oxidants with high redox potentials. Under photocatalytic conditions, the photolysis of hydrogen peroxide can trigger the in situ generation of hydroxyl radicals. Hydroxyl radicals have been reported to promote the oxidation of nitrogen to nitric acid. Therefore, organic polymers are potential candidates for the in situ photocatalytic conversion of oxygen and nitrogen to nitric acid via a multi-step cascade reaction.

[0004] Based on this background, an organic polymer photocatalyst was prepared to achieve photocatalytic synthesis of nitric acid. The pyridine groups not only facilitate the separation of photogenerated charge carriers but also serve as reaction sites for the O2 reduction reaction, thereby enhancing photocatalytic activity. The organic polymer photocatalyst prepared by this invention exhibits high H2O2 and HNO3 yields and high selectivity. Summary of the Invention

[0005] The present invention provides a method for preparing an environmentally friendly and low-cost organic polymer photocatalyst and application of the catalyst in photocatalytic synthesis of nitric acid in water directly using nitrogen and oxygen as raw materials.

[0006] The present invention discloses a method for preparing the organic polymer photocatalyst, comprising the following steps: dispersing thiobarbituric acid and p-phenylenediamine in water and stirring at 50-80°C for 30 minutes. Then, adding 2,2'-bipyridine-5,5'-dicarbaldehyde to the above solution causes a rapid reaction to generate a brownish-red precipitate. After stirring for 3-6 hours to ensure sufficient reaction, the precipitate is collected, washed three times with ethanol and water, and then vacuum-dried. The obtained product is named PyOM. The dried brownish-red solid is placed in a tube furnace, calcined under an N2 atmosphere, cooled to room temperature, washed 3-5 times with dichloromethane and methanol, and dried in a vacuum drying oven for 6-8 hours to obtain the organic polymer photocatalyst PyOP.

[0007] Through XPS ( Figure 1 )、FT-IR( Figure 2 ), 13 C NMR ( Figure 3 )、XRD( Figure 4 )、SEM( Figure 5 ) and BET nitrogen adsorption ( Figure 6 ) tested and studied the morphology, structure and chemical composition of organic polymer photocatalysts. The results showed that PyOM was successfully polymerized through Schiff base reaction to form organic polymer photocatalyst PyOP containing carbon-nitrogen double bonds. By mass spectrometry ( Figure 7 )The test verified that PyOM was successfully prepared.

[0008] The organic polymer photocatalyst PyOP prepared by the present invention has a significantly improved photocatalytic performance under the conditions of oxygen atmosphere and H2O as solvent. On the one hand, its H2O2 yield is 10147.5μmol g -1 cat Its catalytic effect is shown in Figure 8 On the other hand, in a mixed atmosphere of oxygen and nitrogen, the yield of nitric acid was 672.8 μmol g -1 cat Its catalytic effect is shown in Figure 9 .

[0009] By fluorescence spectroscopy ( Figure 10 ),impedance( Figure 11 ), photocurrent( Figure 12 ) The test verified that the organic polymer photocatalyst has a high efficiency of photogenerated carrier separation and a good photoelectric effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is the XPS spectrum of the organic polymer photocatalyst;

[0011] Figure 2 is the FT-IR spectrum of the organic polymer photocatalyst;

[0012] Figure 3 Organic polymer photocatalysts 13 C NMR spectrum;

[0013] Figure 4 is the XRD spectrum of the organic polymer photocatalyst;

[0014] Figure 5 is the SEM image of the organic polymer photocatalyst;

[0015] Figure 6 BET nitrogen adsorption-desorption isotherm of organic polymer photocatalyst;

[0016] Figure 7 is the mass spectrum of PyOM;

[0017] Figure 8 This is a time curve diagram of the photocatalytic reduction of O2 to H2O2 by an organic polymer photocatalyst;

[0018] Figure 9 This is a time curve of the organic polymer photocatalyst synthesizing HNO3 through photocatalytic reaction using N2 and O2 as raw materials in water.

[0019] Figure 10 This is the fluorescence spectrum of the organic polymer photocatalyst;

[0020] Figure 11 This is the impedance image of the organic polymer photocatalyst;

[0021] Figure 12 This is the photocurrent image of the organic polymer photocatalyst. DETAILED DESCRIPTION

[0022] The present invention will be more clearly described below with reference to the embodiments. The embodiments involved below are only used to explain the present invention and are not intended to limit the present invention.

[0023] Example 1:

[0024] The synthesis method of the organic polymer photocatalyst prepared by the present invention specifically comprises the following steps:

[0025] S1. Disperse thiobarbituric acid (0.24 mmol, 34.6 mg) and p-phenylenediamine (0.12 mmol, 13.0 mg) in 60 mL of water and stir at 50-80°C for 30 minutes. Then, add 2,2'-bipyridine-5,5'-dicarbaldehyde (0.12 mmol, 25.5 mg) to the above solution. A rapid reaction occurs, forming a brown-red precipitate. Stir for 3 hours to ensure sufficient reaction. Collect the precipitate, wash it three times with ethanol and water, and then vacuum dry it. The resulting product is named PyOM.

[0026] S2. Place the dried brown-red solid in a tube furnace and heat it in a nitrogen atmosphere at 3°C ​​min -1 The mixture was calcined at 300°C for 4 hours at a heating rate of 0.5 ℃. After cooling to room temperature, it was washed with dichloromethane and methanol three times and dried in a vacuum drying oven for 24 hours to obtain an organic polymer photocatalyst PyOP.

[0027] 10 mg of PyOP was placed in a 45 mL test tube, and 20 mL of water was added. The reaction solution was degassed with high-purity O₂ for 15 minutes, and the test tube was immediately sealed with a rubber stopper. A white LED light source was used to illuminate the test tube. The O₂ reduction products were measured using a UV-visible spectrophotometer. The results showed that the H₂O₂ yield was 10147.5 μmol g₄ after 4 hours of illumination. -1 cat .

[0028] A mixed solution of 10 mg PyOP and 20 mL water was added to the reaction tube in sequence. Subsequently, the photocatalytic system was saturated in a gas atmosphere of N2:O2 1:1 and immediately sealed. The reaction solution was continuously irradiated with a white LED light source for 36 hours at room temperature. After the reaction was completed, the solution was centrifuged to obtain the supernatant, and the concentration of HNO3 in the solution was quantitatively analyzed using an ion chromatograph. The yield of HNO3 was 672.8 μmol g -1 cat .

Claims

1. An organic polymer photocatalyst for photocatalytic synthesis of nitric acid, characterized in that: Its structure is: Abbreviated as PyOP.

2. A method for synthesizing an organic polymer photocatalyst according to claim 1, characterized in that: The following steps are involved: Step 1: Disperse thiobarbituric acid and p-phenylenediamine in water and stir at 50-80°C for 30 minutes. Then, add 2,2'-bipyridine-5,5'-dicarbaldehyde to the solution, causing a rapid reaction to form a brownish-red precipitate. Stir for 3 hours to ensure complete reaction. The precipitate is collected, washed three times with ethanol and water, and then dried under vacuum. The resulting product is named PyOM. Step 2: The dried brown-red solid was placed in a tube furnace and calcined under a N2 atmosphere. After cooling to room temperature, it was washed three times with dichloromethane and methanol and dried in a vacuum drying oven to obtain an organic polymer photocatalyst, which was recorded as PyOP.

3. Use of the organic polymer photocatalyst according to claim 1 in the photocatalytic synthesis of nitric acid (HNO3) directly in water using nitrogen (N2) and oxygen (O2) as raw materials.

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