A Ba monatomic / TiO2-O v Photocatalyst, method for preparing the same, and use thereof

Abstract

This invention discloses a Ba single-atom / TiO2-O v Photocatalyst, its preparation method, and its application in the photocatalytic oxidative coupling of glycerol with inorganic nitrogen source reduction to synthesize glycine, wherein the Ba single atom / TiO2-O v The photocatalyst is composed of Ba single atoms dispersed in TiO2 nanosheets with oxygen vacancies. The Ba single atom / TiO2-O catalyst of this invention... v Photocatalysts possess both oxidation and reduction active sites. Under light irradiation, they can couple the glycerol oxidation reaction with nitrogen reduction or nitrate reduction reactions, and promote C–N bond construction through the oxidation-reduction dual active sites on the catalyst surface, thereby achieving the green synthesis of glycine.

Description

Technical Field

[0001] This invention belongs to the field of inorganic nitrogen resource conversion and green synthesis technology of amino acids, specifically relating to a Ba single atom / TiO2-O v Photocatalysts, their preparation methods, and their application in the photocatalytic oxidative coupling of glycerol with inorganic nitrogen source reduction to synthesize glycine. Background Technology

[0002] Glycine, the simplest amino acid in structure, is widely used in pharmaceuticals, food, pesticides, feed additives, and fine chemicals. With the development of the pharmaceutical industry, the nutrition and health industry, and green agriculture, the demand for glycine continues to increase. Existing industrial production routes for glycine mainly include the chloroacetic acid ammonolysis method and the Strecker process. The chloroacetic acid ammonolysis method typically uses chloroacetic acid and ammonia as raw materials, easily generating large amounts of inorganic salt byproducts during the reaction, resulting in complex post-processing and high energy consumption for product separation and purification. The Strecker process usually involves aldehydes, ammonia sources, and cyanide intermediates, posing problems such as high raw material toxicity, high safety risks, and heavy environmental burden. Therefore, developing new glycine synthesis methods with widely available raw materials, mild reaction conditions, and environmental friendliness is of great significance.

[0003] Glycerol is an important byproduct in the processing of biodiesel, bioethanol, and oils. It is widely available, inexpensive, and has a high functional group density. Upgrading glycerol into high-value-added oxygen-containing or nitrogen-containing chemicals through catalytic conversion is a crucial direction for realizing the high-value utilization of biomass resources. The glycerol molecule contains three carbon atoms and multiple hydroxyl groups. Theoretically, it can generate C1 or C2 oxygen-containing intermediates through selective oxidation and C–C bond cleavage, which can then further participate in C–N bond formation reactions. However, due to the similar bond energies of the C–C, C–H, and O–H bonds in the glycerol molecule, and the limited difference in reactivity between terminal and intermediate hydroxyl groups, multiple competing reaction pathways often accompany glycerol oxidation, easily generating various byproducts such as glyceraldehyde, dihydroxyacetone, glycolaldehyde, formic acid, and glycolic acid, making selective control of the target C2 intermediate difficult.

[0004] On the other hand, inorganic nitrogen sources such as nitrogen gas and nitrates have the advantages of wide availability, low cost, and strong environmental relevance. Nitrogen gas is a major component of air. If nitrogen gas can be activated under mild conditions and coupled with biomass carbon sources to prepare nitrogen-containing organic matter, it will provide a new pathway for artificial nitrogen fixation and green synthesis of amino acids. Nitrates are widely found in industrial wastewater, agricultural runoff, and groundwater pollution systems. If the nitrate reduction and conversion process can be coupled with the biomass oxidation process, not only can nitrogen-containing pollutants be utilized as resources, but the dependence of the reaction system on external sacrificial agents and high-energy-consuming reduction conditions can also be reduced.

[0005] Photocatalysis technology can drive redox reactions using sunlight or simulated sunlight, achieving the oxidation of organic substrates and the reduction of small molecules under ambient temperature and pressure conditions. It offers advantages such as low energy consumption, mild conditions, and environmental friendliness. Coupled with glycerol oxidation and nitrogen or nitrate reduction, it holds promise for simultaneously realizing the high-value utilization of biomass carbon sources and the resource recovery of inorganic nitrogen sources, and further synthesizing amino acid compounds such as glycine through C–N coupling reactions. However, this reaction system involves multi-electron and multi-proton transfer processes and complex interfacial coupling steps, still facing significant challenges.

[0006] First, the N≡N bonds in nitrogen molecules have high bond energies and low molecular polarity, making adsorption and activation difficult at room temperature and pressure, resulting in low nitrogen reduction efficiency. Second, the nitrate reduction process involves NO3. ‒ NO2 ‒ The reaction involves multiple possible intermediates such as NO, NHOH, NH2OH, and NH2, resulting in a complex reaction pathway, numerous side reactions, and difficulties in controlling the formation and stability of active nitrogen intermediates. Furthermore, the oxidation of glycerol requires the selective conversion of C3 molecules to C2 carbon-containing intermediates; however, the close energy levels of various chemical bonds in the glycerol molecule easily lead to over-oxidation or non-selective breakage. Finally, the C–N coupling reaction requires spatiotemporal matching between the carbon-containing intermediate produced by glycerol oxidation and the active nitrogen intermediate produced by the reduction of the inorganic nitrogen source on the catalyst surface; if the oxidation and reduction sites are too far apart, the electron transfer efficiency is low, or the intermediate lifetimes are mismatched, it is difficult to effectively form C–N bonds, resulting in low efficiency in the formation of the target glycine. Summary of the Invention

[0007] To address the above problems, the present invention aims to provide a Ba single-atom / TiO2-O v Photocatalyst, its preparation method, and its application in the photocatalytic oxidation-coupling of glycerol with inorganic nitrogen source reduction to synthesize glycine. The catalyst has both oxidative and reductive active sites. Under light irradiation, it can couple the glycerol oxidation reaction with nitrogen reduction or nitrate reduction reaction, and promote the construction of C–N bonds through the redox dual active sites on the catalyst surface, thus realizing the green synthesis of glycine.

[0008] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: A Ba single atom / TiO2-O v The photocatalyst is composed of Ba single atoms dispersed in TiO2 nanosheets with oxygen vacancies.

[0009] Furthermore, the Ba single atom / TiO2-O v The photocatalyst has a Ba single-atom loading of 0.2~0.6 wt%.

[0010] The present invention also provides the above-mentioned Ba single atom / TiO2-O v The photocatalyst is prepared by dispersing TiO2 nanosheets in an aqueous solution containing potassium nitrate and barium chloride, then adding ethylene glycol, and subjecting the solution to phototreatment under an inert atmosphere to obtain Ba single atoms / TiO2-O. v Photocatalyst.

[0011] In this invention, TiO2 nanosheets can be prepared using existing conventional methods, such as mixing tetrabutyl titanate, hydrofluoric acid and ethanol and then carrying out a hydrothermal reaction, which will not be elaborated here.

[0012] Furthermore, the mass ratio of TiO2 nanosheets to potassium nitrate is 1:1.2~1.6; the mass ratio of TiO2 nanosheets to barium chloride is 1:0.8~1.2; and the amount of TiO2 nanosheets to ethylene glycol is 100mg:5~15mL.

[0013] Furthermore, the inert atmosphere is an argon or helium atmosphere.

[0014] Furthermore, the light treatment process is as follows: irradiate with a 300 W xenon lamp for 2-8 hours.

[0015] The present invention also provides the above-mentioned Ba single atom / TiO2-O v The photocatalyst was used to catalyze the oxidative coupling of glycerol with an inorganic nitrogen source to synthesize glycine.

[0016] Furthermore, the inorganic nitrogen source is nitrogen gas and / or nitrate.

[0017] In this invention, TiO2-O v The oxygen vacancies in the TiO2 nanosheets can enhance the adsorption and oxidative activation of glycerol, promote the selective cleavage of the C–C bond of glycerol and form carbon-containing intermediates suitable for C–N coupling; the Ba single-atom sites can enhance the adsorption and activation of nitrogen or nitrate and promote the formation of active nitrogen intermediates; at the same time, the synergistic effect of Ba single-atom sites and oxygen vacancies on the surface of TiO2 nanosheets can improve the interfacial matching degree between carbon-containing intermediates and active nitrogen intermediates, thereby promoting C–N bond coupling and generating glycine.

[0018] The present invention has the following beneficial effects: (1) This invention uses glycerol as a carbon source and nitrogen or nitrate as an inorganic nitrogen source to achieve glycine synthesis under photocatalytic conditions, avoiding the dependence on high-risk raw materials such as chloroacetic acid and cyanide in the traditional glycine synthesis route, and has better green chemical characteristics.

[0019] (2) The present invention couples glycerol oxidation with nitrogen reduction or nitrate reduction in the same photocatalytic system, which can simultaneously realize the high-value utilization of biomass glycerol and the resource conversion of inorganic nitrogen source.

[0020] (3) The present invention utilizes Ba single atoms and oxygen vacancies to construct redox dual active sites, wherein oxygen vacancies mainly regulate glycerol adsorption, oxidation and selective C–C bond cleavage, while Ba single atoms mainly regulate inorganic nitrogen source adsorption, activation and reduction, and the two work together to promote C–N coupling reaction.

[0021] (4) The present invention can be carried out under normal temperature, pressure and light conditions. The reaction conditions are mild and have good environmental friendliness and application potential.

[0022] (5) The present invention has excellent glycine production efficiency. For example, when nitrogen is used as the nitrogen source, the glycine production rate can reach 236 μmol g. -1 h -1 When nitrate is used as the nitrogen source, the glycine production rate can reach 1104 μmol g. -1 h -1 . Attached Figure Description

[0023] Figure 1 Scanning electron microscope image and transmission electron microscope image of Ba-TNS-5h.

[0024] like Figure 1 As shown, the Ba-TNS-5h photocatalyst exhibits a distinct two-dimensional nanosheet structure. SEM images reveal that the catalyst is assembled from a large number of wrinkled nanosheets, with a relatively clear sheet structure. TEM images further demonstrate that the sample has a thin sheet morphology, indicating that the Ba-TNS-5h photocatalyst retains the basic structural characteristics of TiO2 nanosheets.

[0025] Figure 2 AC-HAADF-STEM plot and corresponding intensity analysis plot for Ba-TNS-5h.

[0026] like Figure 2 As shown, Ba species in the Ba-TNS-5h sample are distributed as isolated bright spots, and the corresponding intensity analysis shows a characteristic peak of a single Ba atom, indicating that Ba forms highly dispersed Ba single-atom sites on the surface of TiO2 nanosheets.

[0027] Figure 3 The image shows the X-ray absorption spectrum of Ba-TNS-5h.

[0028] like Figure 3As shown, the valence state and local coordination environment of Ba species were analyzed by Ba K-edge X-ray absorption spectroscopy. XANES results showed that the absorption edge position of the Ba-TNS-5h sample differed from that of the BaO and BaCl2 reference samples, indicating that Ba does not exist as a simple BaO or BaCl2 phase, but interacts with the surface of TiO2 nanosheets to form a new local coordination structure.

[0029] EXAFS results showed that the Ba-TNS-5h sample mainly exhibited Ba–O coordination characteristics, with no obvious Ba–Cl or Ba–Ba coordination peaks, indicating that Ba species are mainly anchored to the TiO2 nanosheet surface through Ba–O bonds. The Ba–O coordination signal in the Ba-TNS-5h sample was clear, and no obvious Ba–Ba coordination characteristics were observed in the wavelet transform graph, suggesting that Ba species exist stably on the TiO2 nanosheet surface in single-atom form.

[0030] Figure 4 Electron paramagnetic resonance spectra of TNS, Ba-TNS-2h, Ba-TNS-5h, and Ba-TNS-8h.

[0031] like Figure 4 As shown, each sample exhibits a significant EPR signal around g≈2.002, which can be attributed to oxygen vacancy-related defect signals on the TiO2 surface. Compared to TNS, the EPR signals of Ba-TNS-2h, Ba-TNS-5h, and Ba-TNS-8h show significant changes, indicating that the introduction of Ba and phototreatment can modulate the defect structure on the TiO2 nanosheet surface. This result demonstrates the abundance of oxygen vacancies in the Ba-TNS photocatalyst, providing active sites for glycerol adsorption, oxidation, and selective C–C bond cleavage.

[0032] Figure 5 The graph shows the glycine production rate performance of TNS, Ba-TNS-2h, Ba-TNS-5h and Ba-TNS-8h.

[0033] like Figure 5 As shown in Figure a, compared with unloaded Ba-TNS, the glycine production rate of the Ba-TNS series samples was significantly increased, with the highest glycine production rate of Ba-TNS-5h reaching 1104 μmol g. -1 h -1 This indicates that the construction of dual active sites of Ba single atoms and oxygen vacancies is beneficial to promoting the C–N coupling reaction between glycerol oxidation and nitrogen-containing species reduction.

[0034] like Figure 5As shown in b, when Ba-TNS-5h is used as a photocatalyst, the amount of glycine generated increases continuously with the extension of reaction time, indicating that the catalyst can stably drive the reduction reaction of nitrogen-containing species by glycerol oxidative coupling and continuously generate glycine. Detailed Implementation

[0035] The following embodiments further illustrate the content of the present invention in detail, but the scope of protection of the claims of the present invention is not limited by the embodiments.

[0036] This invention evaluates the performance of different Ba-TNS photocatalysts by using the photocatalytic oxidative coupling of glycerol with inorganic nitrogen source to reduce and synthesize glycine.

[0037] When nitrate was used as the nitrogen source, the reaction system consisted of 40 mM KNO3 and 20 mM glycerol aqueous solution, with a reaction volume of 10 mL and a catalyst dosage of 10 mg. The reaction was carried out in a reaction tube. Before the reaction, the atmosphere was Ar by repeatedly evacuating the tube using a double-row tube and a vacuum pump and introducing Ar gas. The light source was a 365 nm LED lamp, the reaction temperature was room temperature, and the reaction time was 10 h.

[0038] When nitrogen was used as the nitrogen source, the reaction system consisted of 10 mL of 20 mM glycerol aqueous solution, and the catalyst dosage was 10 mg. An open-circuit nitrogen bubbling system was used, with N2 continuously introduced at a flow rate of 20 mL / min during the reaction. The reaction was then irradiated at room temperature with a 365 nm LED lamp for 10 h.

[0039] After the reaction was complete, the product was filtered through a 0.22 μm filter and analyzed using an amino acid analyzer. 1 The concentration of glycine was determined by means of 1H NMR and ninhydrin colorimetric method, and the glycine production rate was calculated based on catalyst mass and reaction time.

[0040] In this invention, TNS represents TiO2 nanosheets; Ba-TNS-2h, Ba-TNS-5h, and Ba-TNS-8h represent Ba-TNS photocatalysts obtained after 2h, 5h, and 8h of light treatment during Ba loading and oxygen vacancy construction, respectively.

[0041] Example 1

[0042] (1) Mix 10 mL of tetrabutyl titanate with 4 mL of hydrofluoric acid and stir for 30 min until a solution is formed. Then add 10 mL of ethanol and transfer to a reaction vessel. The mixture is then subjected to hydrothermal reaction in an oven at 180 °C for 16 h. After the reaction is completed, the product is washed twice each with 0.1 M NaOH solution, deionized water and ethanol, and then dried overnight in a vacuum drying oven at 60 °C to obtain TiO2 nanosheets, denoted as TNS.

[0043] (2) Take 100 mg of TNS obtained in step (1) and add it to 100 mL of a mixed aqueous solution containing 1.44 g / L KNO3 and 1 g / L BaCl2·2H2O. Then add 10 mL of ethylene glycol. Under stirring, purge with Ar gas for 30 min at a flow rate of 50 mL / min. Then irradiate with a 300 W xenon lamp for 5 h. After the reaction is complete, wash the obtained solid product three times with deionized water and ethanol, and dry it under vacuum at 60 °C to obtain the Ba-TNS-5h photocatalyst. The Ba loading was 0.46 wt% as determined by ICP test.

[0044] Test results: When KNO3 is used as the nitrogen source, the glycine production rate of the Ba-TNS-5h photocatalyst is 1104 μmol g. -1 h -1 .

[0045] When N2 is used as the nitrogen source, the glycine production rate of the Ba-TNS-5h photocatalyst is 236 μmol g. -1 h -1 .

[0046] Example 2

[0047] Same as Example 1, except that the Ba-TNS-5h photocatalyst was replaced with Ba-TNS-2h. ICP testing showed that the Ba loading was 0.42 wt%.

[0048] The results showed that, with KNO3 as the nitrogen source, the glycine production rate of the TNS photocatalyst was 781 μmol g after 10 h of reaction. -1 h -1 .

[0049] Example 3

[0050] Same as Example 1, except that the Ba-TNS-5h photocatalyst was replaced with Ba-TNS-8h. ICP testing showed that the Ba loading was 0.35 wt%.

[0051] The results showed that, with KNO3 as the nitrogen source, the glycine production rate of the TNS photocatalyst was 887.42 μmol g after 10 h of reaction. -1 h -1 .

[0052] Comparative Example 1 Same as Example 1, except that the Ba-TNS-5h photocatalyst is replaced with TNS.

[0053] The results showed that, with KNO3 as the nitrogen source, the glycine production rate of the TNS photocatalyst was 62.67 μmol g after 10 h of reaction. -1 h -1 .

Claims

1. A Ba single-atom / TiO2-O v Photocatalyst, characterized in that: The Ba single atom / TiO2-O v The photocatalyst is composed of Ba single atoms dispersed in TiO2 nanosheets with oxygen vacancies.

2. The Ba single atom / TiO2-O according to claim 1 v Photocatalyst, characterized in that: The Ba single atom / TiO2-O v In the photocatalyst, the loading of Ba single atoms is 0.2~0.6 wt%.

3. The Ba single atom / TiO2-O as described in claim 1 or 2 v A method for preparing a photocatalyst, characterized in that: TiO2 nanosheets were dispersed in an aqueous solution containing potassium nitrate and barium chloride, and then ethylene glycol was added. The mixture was then subjected to phototreatment under an inert atmosphere to obtain Ba single atoms / TiO2-O. v Photocatalyst.

4. The preparation method according to claim 3, characterized in that: The mass ratio of TiO2 nanosheets to potassium nitrate is 1:1.2~1.6; the mass ratio of TiO2 nanosheets to barium chloride is 1:0.8~1.2; and the ratio of TiO2 nanosheets to ethylene glycol is 100mg:5~15mL.

5. The preparation method according to claim 3, characterized in that: The inert atmosphere is an argon or helium atmosphere.

6. The preparation method according to claim 3, characterized in that: The light treatment process is as follows: irradiate with a 300 W xenon lamp for 2-8 hours.

7. The Ba single atom / TiO2-O according to any one of claims 1-2 v Photocatalyst or Ba single atom / TiO2-O prepared by the preparation method according to any one of claims 3-6 v The application of photocatalysts is characterized by: It was used for photocatalytic oxidative coupling of glycerol with inorganic nitrogen source to synthesize glycine.

8. The application according to claim 7, characterized in that: The inorganic nitrogen source is nitrogen gas and / or nitrate.

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