Use of thiocyanide-modified Ag / BiVO4 and photocatalytic oxidation of glyphosate to prepare aminomethylphosphonic acid

Abstract

The present invention provides thiocyanate-modified Ag / BiVO4 and its use in preparing aminomethylphosphonic acid by photocatalytic oxidation of glyphosate. The Ag / BiVO4 is mixed and stirred with an alcohol solution to obtain a suspension, and then a thiocyanate-containing solution is injected. After stirring for a certain period of time under an N2 atmosphere, the suspension is filtered, washed, and dried to obtain SCN-Ag / BiVO4. The technical solution of the present invention has a simple thiocyanate modification process, and S and Ag can be selectively adsorbed and coordinated in a stable manner. The product has good selectivity for aminomethylphosphonic acid (AMPA), can achieve photocatalytic oxidation of glyphosate, and recover aminomethylphosphonic acid, an important chemical intermediate, thereby transforming waste into treasure.

Description

Technical Field

[0001] The present invention mainly relates to the field of photocatalyst modification and glyphosate photocatalytic oxidation to prepare aminomethylphosphonic acid, and in particular to an SCN root-modified Ag / BiVO4, which is applied to the selective photocatalytic oxidation of glyphosate. Background Art

[0002] Aminomethylphosphonic acid (AMPA) is an expensive and important organic phosphate compound (90 yuan / g). It can be used as a metal corrosion inhibitor; it can be used as a chemical intermediate in the synthesis of flame retardants; it can also be used as an electroplating additive to improve the deposition properties of metals. The traditional preparation method of aminomethylphosphonic acid requires formaldehyde and ammonia under high temperature and high pressure, which consumes a lot of energy and resources and has a very high cost. Glyphosate is a low-cost, high-efficiency, and widely applicable organic phosphorus compound (1.4 yuan / g) that is widely used in the field of weed control. There are generally two pathways in the photocatalytic oxidation process of glyphosate: one is the CP cleavage pathway with glycine and phosphate as the final products; the other is the CN bond cleavage pathway with aminomethylphosphonic acid (AMPA) as the final product.

[0003] In the photocatalytic oxidation of glyphosate, two key concerns are improving glyphosate oxidation performance and achieving complete mineralization to oxidize glyphosate into small molecules. Current approaches to improving catalytic performance rely on adding an appropriate amount of metal or metal compound to the catalyst. However, the presence of metals and metal compounds often increases the possibility of amino groups coordinating with the catalyst, elongating the CN bond and making it more susceptible to cleavage during the protection process. Without the addition of metals and metal compounds, the photocatalytic oxidation efficiency of glyphosate is also limited. Therefore, an organic group capable of coordinating with the metal is needed to mask the exposed metal sites while maintaining glyphosate photocatalytic oxidation efficiency, preventing CN bond elongation and gradually enhancing selectivity for the product AMPA. Therefore, photocatalysts modified with thiocyanate (-SCN), which exhibits electron-donating properties, have shown promising results for the simultaneous selective production of AMPA from glyphosate oxidation. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides a preparation method and application of thiocyanate-modified Ag / BiVO4. The obtained SCN-Ag / BiVO4 is used for the photocatalytic oxidation of glyphosate, and the chemical intermediate aminomethyl phosphate AMPA is simultaneously and selectively generated.

[0005] The present invention is achieved through the following technical solutions:

[0006] On the one hand, the present invention provides a thiocyanate-modified Ag / BiVO4, wherein Ag / BiVO4 is mixed and stirred with an alcohol solution to obtain a suspension, and then a thiocyanate-containing solution is injected. After stirring for a certain period of time under a N2 atmosphere, the suspension is filtered, washed, and dried to obtain SCN-Ag / BiVO4.

[0007] The alcohol solution is a methanol solvent, and the volume fraction of the alcohol solution is 10-90 vol%.

[0008] The thiocyanate-containing solution includes any one of HSCN, NaSCN, and KSCN, with a concentration of 0.1-10 mmol / L. Because the amino group of glyphosate has a lone pair of electrons that easily coordinates with the metal, this breaks the C-N bond near the amino group, resulting in reduced selectivity for AMPA production. To avoid the coordination effect of the amino group, the electron-donating SCN group is used to repel the amino group, increasing the likelihood of AMPA production.

[0009] If the concentration of SCN is too low, it cannot completely cover the Ag nanoparticles on the catalyst. The amino groups in glyphosate will strongly coordinate with Ag, causing the CN bond to be activated and the selective production of AMPA to be inhibited. If the concentration of SCN is too high, it will easily form an overly dense shell structure on the surface of the catalyst, thereby blocking the active sites where the catalytic reaction occurs.

[0010] The SCN-Ag / BiVO4 was prepared by stirring for 1-5 h under N2 atmosphere. In some embodiments, the preferred condition is stirring for 5 h.

[0011] On the other hand, the present invention uses the thiocyanate-modified Ag / BiVO4 as a photocatalyst to perform photocatalytic oxidation on glyphosate solutions containing different concentrations.

[0012] In a preferred embodiment, the thiocyanate-modified Ag / BiVO4 is used to selectively produce aminomethylphosphonic acid during the photocatalytic oxidation of glyphosate.

[0013] The photocatalytic oxidation reaction is carried out under visible light irradiation for 5-40 minutes.

[0014] The visible light mentioned above can be understood as light conditions with a wavelength of 420 nm or more.

[0015] The minimum glyphosate concentration in the glyphosate solution is 10 μmol / L or higher, preferably 50 μmol / L or higher. In some embodiments, the glyphosate concentration in the solution is 50-200 μmol / L. Excessively high glyphosate concentrations, on the one hand, lead to excessive glyphosate adsorption on the photocatalyst, masking the active sites of the reaction; on the other hand, the accumulation of AMPA in the system limits the forward shift of the reaction equilibrium, reducing the reaction rate and prolonging the reaction time. On the other hand, excessively low glyphosate concentrations limit the selective production of AMPA to a certain extent. Furthermore, too low a glyphosate concentration makes it difficult for the photocatalyst to fully capture glyphosate, resulting in the inhibition of both glyphosate oxidation and AMPA production.

[0016] The method for oxidizing glyphosate using thiocyanate-modified Ag / BiVO4 comprises the following steps:

[0017] SCN-Ag / BiVO4 was used as a photocatalyst and placed in a solution containing a certain amount of glyphosate. After stirring in the dark to reach adsorption equilibrium, it was irradiated with visible light for a certain period of time to photocatalytically oxidize the glyphosate in the water.

[0018] The amount of SCN-Ag / BiVO4 used is 0.1-1.0 mg / mL, preferably 0.1-0.4 mg / mL.

[0019] The photocatalyst in the technical solution of the present invention can completely oxidize glyphosate and simultaneously has the greatest selectivity for producing aminomethylphosphonic acid AMPA.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] This invention uses thiocyanate-modified SCN-Ag / BiVO4 as a photocatalyst for the oxidation of glyphosate, selectively synthesizing the chemically valuable aminomethylphosphonic acid (AMPA). Unlike previous methods that focused on complete glyphosate mineralization, this method, modified with thiocyanate, achieves 100% oxidation efficiency for 50 μmol / L glyphosate in 40 minutes, with selectivity for the simultaneous production of AMPA exceeding 60%, preferably exceeding 70%, more preferably exceeding 80%, and even more preferably exceeding 85%. This invention has the following advantages: 1) The SCN modification process is simple, and S and Ag can be selectively adsorbed and coordinated, maintaining a stable existence; 2) It exhibits excellent selectivity for AMPA, enabling the recovery of this important chemical intermediate in glyphosate, effectively transforming waste into valuable resources.

[0022] The present invention provides an SCN-Ag / BiVO4 photocatalyst for glyphosate oxidation, which can simultaneously and selectively produce aminomethylphosphonic acid, and provides a good example for the photocatalytic oxidation and recycling of glyphosate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the TEM-Mapping image of SCN-Ag / BiVO4 in Example 1.

[0024] Figure 2 1 is the XRD pattern of Ag / BiVO4 and SCN-Ag / BiVO4 in Example 1.

[0025] Figure 3 These are the XPS graphs of Ag / BiVO4 and SCN-Ag / BiVO4 in Example 1.

[0026] Figure 4 yes Figure 3 Detailed map of the S 2p position in the XPS pattern of SCN-Ag / BiVO4.

[0027] Figure 5 This is the in-situ infrared image of the SCN modification process on the Ag / BiVO4 surface in Example 1. DETAILED DESCRIPTION

[0028] In order to further understand the present invention, the present invention is described below in conjunction with embodiments. These descriptions are only for further explaining the features and advantages of the present invention and are not intended to limit the claims of the present invention.

[0029] Example 1

[0030] 160 μL of 0.1 mol / L KSCN (concentration 0.2 mmol / L) was quickly injected into a mixture of 20 mg of Ag / BiVO4 and 80 mL of 10 vol% methanol solution and stirred for 1 h to obtain SCN-Ag / BiVO4. The TEM element mapping of the synthesized SCN-Ag / BiVO4 is shown in Figure 1 In the figure, the S, N, and Ag elements are distributed in a spherical shape. The spherical structures of S and N have a significantly larger radius, indicating that SCN is modified on the surface of Ag in a shell-like structure. The process of SCN modification of Ag / BiVO4 is shown in Figure 5 In the in situ infrared, the SCN on the catalyst surface gradually increased and tended to be stable with the increase of reaction time.

[0031] Figure 2 The XRD patterns of Ag / BiVO4 and SCN-Ag / BiVO4 in Example 1 are shown. SCN-Ag / BiVO4 and Ag / BiVO4 exhibit consistent crystal structures, indicating that the thiocyanate modification does not change the crystal structure of the catalyst, but is modified on the surface of the Ag nanoparticles in a bonding manner.

[0032] Figure 3The XPS spectra before and after thiocyanate modification show that the S 2p, S 2s, and N 1s peaks associated with thiocyanate appear on the Ag / BiVO4 surface, indicating successful SCN modification of the catalyst. The Bi 4f and S 2p peaks partially overlap, which requires further analysis in the detailed spectrum.

[0033] Figure 4 This is a detailed map of the S 2p position in the XPS map of SCN-Ag / BiVO4, where the binding peak of Ag and S appears at 163.4 eV, indicating that the binding of Ag and SCN is formed through the coordination of Ag and S.

[0034] Figure 5 This is an in situ infrared image of the SCN modification process on the Ag / BiVO4 surface. As the reaction progresses, the amount of thiocyanate on the catalyst surface gradually increases and finally stabilizes. The formation of Ag-S indicates that thiocyanate forms a coordination effect on the Ag surface. -SCN is successfully modified on the catalyst surface.

[0035] The prepared SCN-Ag / BiVO4 photocatalyst was used for the photocatalytic oxidation of glyphosate. Specifically, 20 mg of SCN-Ag / BiVO4 was placed in a 50 mL solution containing a certain amount of glyphosate. The solution was stirred in the dark for 30 minutes to reach adsorption equilibrium. The solution was then irradiated with 420 nm visible light for a specified period of time to photocatalytically oxidize the glyphosate in the water.

[0036] The oxidation efficiency of 50 μmol / L glyphosate can reach 85% in 40 min, and the product is phosphate, without AMPA generation.

[0037] Example 2

[0038] The same method as in Example 1 was used, except that the stirring time was changed: 160 μL of 0.1 mol / L KSCN (concentration of 0.2 mmol / L) was rapidly injected and stirred for 3 h. After 40 min, the oxidation rate of glyphosate was 100%, the concentration of generated AMPA was 12.5 μmol / L, and the selectivity was 25.7%.

[0039] Example 3

[0040] The same method as in Example 1 was used, except that the stirring time was changed: 160 μL of 0.1 mol / L KSCN (concentration of 0.2 mmol / L) was rapidly injected and stirred for 5 h. The oxidation rate of glyphosate was 100% in 40 min, the concentration of generated AMPA was 16.4 μmol / L, and the selectivity was 32.8%.

[0041] It can be seen that with the increase of stirring time, the photocatalytic removal efficiency of SCN-Ag / BiVO4 for glyphosate increases, and the selectivity for AMPA gradually increases.

[0042] Example 4

[0043] The same as Example 3, except that the volume of KSCN injected was changed to 400 μL (concentration of 0.5 mmol / L), the glyphosate oxidation rate was 100% in 40 min, the concentration of generated AMPA was 33.1 μmol / L, and the selectivity was 66.3%.

[0044] Example 5

[0045] The same as Example 3 was used, except that the volume of KSCN injected was changed to 800 μL (concentration was 1 mmol / L). The glyphosate oxidation rate was 100% in 40 min, the concentration of generated AMPA was 33.3 μmol / L, and the selectivity was 67.5%.

[0046] Example 6

[0047] The same as Example 3, except that the volume of KSCN injected was changed to 4 mL (concentration of 5 mmol / L), the oxidation rate of glyphosate was 100% in 40 min, the concentration of generated AMPA was 44.5 μmol / L, and the selectivity was 89.7%.

[0048] Example 7

[0049] The same as Example 3, except that the volume of KSCN injected was changed to 8 mL (concentration was 10 mmol / L), the glyphosate oxidation rate was 100% in 40 min, the concentration of generated AMPA was 38.6 μmol / L, and the selectivity was 77.2%.

[0050] It can be seen that with the increase of the volume of injected KSCN, the concentration of -SCN in the suspension also increases, the photocatalytic removal efficiency of SCN-Ag / BiVO4 for glyphosate increases, and the selectivity for AMPA gradually increases.

[0051] Example 8

[0052] The same method as Example 6 was used, except that the SCN source was changed to HSCN. The glyphosate oxidation rate was 75.4% in 40 min, the concentration of generated AMPA was 21.1 μmol / L, and the selectivity was 57.9%.

[0053] Example 9

[0054] The same method as Example 6 was used, except that the SCN source was changed to NaSCN. The glyphosate oxidation rate was 85.4% in 40 min, the concentration of generated AMPA was 29.0 μmol / L, and the selectivity was 69.1%.

[0055] It can be seen that different SCN sources provide environments with different acidity and alkalinity and different electrical conductivities, which affect the activity of the generated SCN-Ag / BiVO4 in the photocatalytic reaction and also affect the selectivity of AMPA production.

[0056] Example 10

[0057] The same method as Example 6 was used, except that the volume fraction of C1 methanol was changed to 50 vol%. The glyphosate oxidation rate was 97.5% in 40 min, the concentration of generated AMPA was 38.0 μmol / L, and the selectivity was 78.1%.

[0058] Example 11

[0059] The same method as Example 10 was used, except that the volume fraction of C1 methanol was changed to 90 vol%. The glyphosate oxidation rate was 80.5% in 40 min, the concentration of generated AMPA was 26.3 μmol / L, and the selectivity was 65.7%.

[0060] It can be seen that the concentration of C1 methanol as a solvent in the synthesis process of SCN-Ag / BiVO4 plays an important role in the activity of the catalyst. With the increase of the volume fraction of the methanol solution, the oxidation effect of the catalyst on glyphosate decreases slightly, and the selectivity for AMPA gradually decreases.

[0061] Example 12

[0062] The same method as Example 6 was used, except that the visible light irradiation time was changed to 5 min. The glyphosate oxidation rate was 19.3%, the concentration of generated AMPA was 5.4 μmol / L, and the selectivity was 10.9%.

[0063] Example 13

[0064] The same method as Example 6 was used, except that the visible light irradiation time was changed to 10 min. The glyphosate oxidation rate was 54.1%, the concentration of generated AMPA was 7.8 μmol / L, and the selectivity was 15.8%.

[0065] Example 14

[0066] The same method as Example 6 was used, except that the visible light irradiation time was changed to 20 min. The glyphosate oxidation rate was 70.3%, the concentration of generated AMPA was 14.2 μmol / L, and the selectivity was 28.5%.

[0067] It can be seen that with the increase of illumination time, the degree of photocatalytic oxidation reaction gradually increases, the photocatalytic oxidation efficiency of SCN-Ag / BiVO4 for glyphosate increases, and the selectivity for AMPA gradually increases.

[0068] Example 15

[0069] The same as Example 6, except that the glyphosate concentration was changed to 100 μmol / L and other conditions remained unchanged, the glyphosate oxidation rate was 84.9%, the concentration of generated AMPA was 77.1 μmol / L, and the selectivity was 91.2%.

[0070] Example 16

[0071] The same as Example 15, except that the glyphosate concentration was changed to 150 μmol / L and other conditions remained unchanged, the glyphosate oxidation rate was 43.9%, the concentration of generated AMPA was 48.4 μmol / L, and the selectivity was 80.6%.

[0072] Example 17

[0073] The same as Example 15, except that the glyphosate concentration was changed to 200 μmol / L and other conditions remained unchanged, the glyphosate oxidation rate was 20.2%, the concentration of generated AMPA was 24.7 μmol / L, and the selectivity was 63.8%.

[0074] It can be seen that with the increase of glyphosate concentration, the oxidation efficiency of glyphosate decreased, the removal amount of glyphosate within 40 min was limited, and the selectivity of AMPA was maintained at a high level.

[0075] Example 18

[0076] Similar to Example 6, the catalyst that had been used once was washed and put into use a second time. In 40 minutes, the glyphosate oxidation rate was 97.3%, the concentration of generated AMPA was 41.6 μmol / L, and the selectivity was 83.4%.

[0077] Example 19

[0078] Similar to Example 18, the catalyst that had been used twice was washed and put into use for the third time. In 40 minutes, the glyphosate oxidation rate was 87.1%, the concentration of generated AMPA was 38.8 μmol / L, and the selectivity was 78.0%.

[0079] It can be seen that with the progress of multiple cycle experiments, the oxidation rate of glyphosate and the selectivity of AMPA did not decrease significantly, indicating that the SCN-Ag / BiVO4 photocatalyst has good stability.

[0080] Comparative Example 1

[0081] The same as Example 6, without adding KSCN and without prolonged stirring, the solution was irradiated with light for 40 min, and the oxidation rate of glyphosate was 100%, and no AMPA was detected in the solution.

[0082] It can be seen that compared with Ag / BiVO4 without thiocyanate modification, SCN-Ag / BiVO4 has no obvious effect on the oxidation of glyphosate, but has a significant effect on the selective production of AMPA, playing an important role in the generation of AMPA.

Claims

1. A thiocyanate-modified Ag / BiVO4, characterized in that: Ag / BiVO4 is mixed and stirred with an alcohol solution to obtain a suspension, and then a solution containing SCN roots is injected. After stirring for 1-5 hours under a N2 atmosphere, the suspension is filtered, washed, and dried to obtain SCN-Ag / BiVO4. The solution containing SCN roots includes any one of HSCN, NaSCN, and KSCN. The concentration of the SCN root-containing solution is 0.1-5 mmol / L.

2. The thiocyanate-modified Ag / BiVO4 according to claim 1, characterized in that The alcohol solution is a methanol solvent, and the volume fraction of the alcohol solution is 10-90 vol%.

3. Use of the thiocyanate-modified Ag / BiVO4 according to claim 1 or 2 for preparing aminomethylphosphonic acid by photocatalytic oxidation of glyphosate.

4. The use according to claim 3, characterized in that The SCN root-modified Ag / BiVO4 is used to selectively produce aminomethylphosphonic acid during the photocatalytic oxidation of glyphosate.

5. The use according to claim 4, characterized in that The photocatalytic oxidation is carried out under visible light irradiation for 5-40 minutes.

6. The use according to claim 5, characterized in that The glyphosate concentration is above 10 μmol / L.

7. The use according to any one of claims 3 to 6, characterized in that The method for oxidizing a glyphosate solution using thiocyanate-modified Ag / BiVO4 comprises the following steps: SCN-Ag / BiVO4 was used as a photocatalyst and placed in a solution containing glyphosate. After stirring in the dark to reach adsorption equilibrium, visible light was used to irradiate the solution to photocatalytically oxidize the glyphosate in the water.

8. The use according to claim 7, characterized in that The dosage of SCN-Ag / BiVO4 is 0.1-1.0 mg / mL.

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