Thiocyanide-modified Ag / BiVO4 and application of thiocyanide-modified Ag / BiVO4 in preparation of aminomethyl phosphoric acid through photocatalytic oxidation of glyphosate

Abstract

The invention provides thiocyanide-modified Ag / BiVO4 and application of photocatalytic oxidation of glyphosate to preparation of aminomethyl phosphoric acid, Ag / BiVO4 and an alcoholic solution are mixed and stirred to obtain a suspension, a thiocyanide-containing solution is injected into the suspension, the suspension is stirred for a certain time in an N2 atmosphere, suction filtration, washing and drying are performed, and SCN-Ag / BiVO4 is obtained. According to the technical scheme, the modification process of thiocyanide is simple, and S and Ag can be selectively adsorbed and coordinated and exist stably; the method has good selectivity on aminomethylphosphonic acid AMPA, can realize photocatalytic oxidation of glyphosate and recovery of an important chemical intermediate aminomethylphosphonic acid, and has the characteristic of turning waste into wealth.

Description

Technical Field

[0001] The present invention mainly relates to the field of modification of photocatalysts and photocatalytic oxidation of glyphosate to prepare aminomethylphosphonic acid, and particularly relates to an SCN root-modified Ag / BiVO 4 , which is applied to the selective photocatalytic oxidation of glyphosate. Background Art

[0002] Aminomethylphosphonic acid (AMPA) is an important and expensive organic phosphate compound ($90 / g), which can be used as a metal corrosion inhibitor; it can be used as a chemical intermediate for synthesizing flame retardants; it can also be used as an electroplating additive to improve the deposition performance of metals. The traditional method for preparing aminomethylphosphonic acid involves formaldehyde and ammonia at high temperature and high pressure, which requires a large amount of energy and resources and has a relatively high cost. Glyphosate is an organic phosphorus compound with low cost, high efficiency, and wide application ($1.4 / g), which is widely used in the weeding field. There are usually two paths in the photocatalytic oxidation process of glyphosate. One is the C-P cleavage path with glycine and phosphate as end products; the other is the C-N bond cleavage path with aminomethylphosphonic acid (AMPA) as the end product.

[0003] In the photocatalytic oxidation process of glyphosate, the two main concerns are the improvement of the oxidation performance of glyphosate and the complete mineralization of glyphosate into small molecules. The current method for improving the catalytic performance is to add an appropriate amount of metal or metal compound to the catalyst. However, the presence of metals and metal compounds usually increases the possibility of coordination of amino groups with the catalyst, causing the C-N bond to be stretched and more easily broken during the protection process. Without the addition of metals and metal compounds, the photocatalytic oxidation efficiency of glyphosate will also be limited. Based on this, an organic group that can coordinate with metals is needed to mask the exposed metal sites while ensuring the photocatalytic oxidation efficiency of glyphosate, prevent the C-N bond from being stretched, and gradually enhance the selectivity of the product AMPA. Therefore, the use of a photocatalyst modified with an electron-donating thiocyanate (-SCN) has a good application effect on the synchronous selective generation of AMPA by oxidizing glyphosate. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a preparation method and application of a thiocyanate-modified Ag / BiVO 4 , and the obtained SCN-Ag / BiVO 4 is used for the photocatalytic oxidation of glyphosate to synchronously and selectively generate the chemical intermediate aminomethylphosphonic acid AMPA.

[0005] The present invention is achieved through the following technical solutions: On the one hand, the present invention provides a thiocyanate-modified Ag / BiVO 4 , and Ag / BiVO4 Mix it with an alcohol solution and stir to obtain a suspension, then inject a solution containing a thiocyanate, and stir for a certain time under a nitrogen 2 atmosphere, then filter, wash, and dry to obtain SCN-Ag / BiVO 4 .

[0006] The alcohol solution is a methanol solvent, and the volume fraction of the alcohol solution is 10-90 vol%.

[0007] The solution containing a thiocyanate includes any one of HSCN, NaSCN, and KSCN, and the concentration of the solution containing a thiocyanate is 0.1-10 mmol / L. Since the amino group of glyphosate has a lone pair of electrons and is prone to forming coordination with metals, the C-N bond near the amino group is broken, resulting in a decrease in the selectivity of AMPA production. To avoid the coordination of the amino group, the electron-donating SCN group is used to repel the amino group, increasing the possibility of AMPA production.

[0008] If the concentration of SCN is too low, it cannot completely cover the Ag nanoparticles on the catalyst, and the amino group in glyphosate will strongly coordinate with Ag, resulting in the activation of the C-N bond and the inhibition of the selectivity of AMPA production; while if the concentration of SCN is too high, it is easy to form an overly dense shell structure on the surface of the catalyst, thus blocking the active sites for the catalytic reaction to occur.

[0009] Stir under a nitrogen 2 atmosphere for 1-5 h to achieve the preparation of SCN-Ag / BiVO 4 . In some embodiments, the preferred condition is to stir for 5 h.

[0010] On the other hand, the present invention relates to the use of the thiocyanate-modified Ag / BiVO 4 as a photocatalyst for photocatalytic oxidation of glyphosate solutions with different concentrations.

[0011] In a preferred embodiment, the use of the thiocyanate-modified Ag / BiVO 4 in the selective production of aminomethylphosphonic acid during the photocatalytic oxidation of glyphosate.

[0012] The photocatalytic oxidation reaction is irradiated with visible light for 5-40 min.

[0013] The visible light can be understood as a light irradiation condition with a light wavelength of 420 nm or more.

[0014] The minimum concentration of glyphosate in the glyphosate solution is above 10 μmol / L, preferably above 50 μmol / L. In some embodiments, the concentration of glyphosate in the solution is 50 - 200 μmol / L. If the concentration of glyphosate is too high, on the one hand, the adsorption amount of glyphosate on the photocatalyst will be too high, masking the active sites of the reaction; on the other hand, the accumulated AMPA in the system limits the forward movement of the reaction equilibrium, reducing the reaction rate and prolonging the reaction time. If the concentration of glyphosate is too low, to a certain extent, the selective generation of AMPA is restricted. And if the concentration of glyphosate is too low, it is difficult for the photocatalyst to completely capture it, resulting in the co - inhibition of the oxidation of glyphosate and the generation of AMPA.

[0015] SCN - modified Ag / BiVO 4 The method for oxidizing glyphosate comprises the following steps: Put SCN - Ag / BiVO 4 As a photocatalyst, into a solution containing a certain amount of glyphosate, stir in the dark until adsorption equilibrium is reached, and then irradiate with visible light for a certain time to perform photocatalytic oxidation of glyphosate in water.

[0016] The dosage of SCN - Ag / BiVO 4 is 0.1 - 1.0 mg / mL, preferably 0.1 - 0.4 mg / mL.

[0017] In the technical solution of the present invention, the photocatalyst can completely oxidize glyphosate and at the same time has the maximum selectivity for generating aminomethylphosphonic acid (AMPA).

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention uses SCN - modified SCN - Ag / BiVO 4 as a photocatalyst for the oxidation of glyphosate to selectively synthesize aminomethylphosphonic acid (AMPA) with chemical industrial value. Different from the previous focus on the complete mineralization of glyphosate, under the modification of thiocyanate, the oxidation efficiency of 50 μmol / L glyphosate can reach 100% in 40 min, and the selectivity for simultaneously generating aminomethylphosphonic acid (AMPA) reaches more than 60%, and can be further preferably more than 70%, further preferably more than 80%, and further preferably more than 85%. The present invention has the following advantages: 1) The modification process of - SCN is simple, S and Ag can be selectively adsorbed and coordinated and exist stably; 2) It has good selectivity for aminomethylphosphonic acid (AMPA), can realize the recovery of important chemical intermediates in glyphosate, and has the characteristic of turning waste into treasure.

[0019] The present invention provides a kind of SCN - Ag / BiVO 4The photocatalyst is applied to the oxidation of glyphosate to synchronously and selectively produce aminomethylphosphonic acid, providing a good example for the photocatalytic oxidation and recycling of glyphosate. Description of the Drawings

[0020] Figure 1 is the TEM-Mapping diagram of SCN-Ag / BiVO in Example 1 4

[0021] Figure 2 is Ag / BiVO in Example 1 4 and the XRD diagrams of SCN-Ag / BiVO 4

[0022] Figure 3 is Ag / BiVO in Example 1 4 and the XPS diagrams of SCN-Ag / BiVO 4

[0023] Figure 4 is Figure 3 in the detailed XPS diagram of the S 2p position in the XPS diagram of SCN-Ag / BiVO 4

[0024] Figure 5 is the in-situ infrared diagram during the process of SCN modification on the surface of Ag / BiVO in Example 1 4 Detailed Embodiments

[0025] To further understand the present invention, the present invention will be 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.

[0026] Example 1 To a mixed solution of 20 mg Ag / BiVO 4 and 80 mL of 10 vol% methanol solution, 160 μL of 0.1 mol / L KSCN (concentration 0.2 mmol / L) was rapidly injected and stirred for 1 h to obtain SCN-Ag / BiVO 4 . The TEM elemental Mapping diagram of the synthesized SCN-Ag / BiVO 4 is shown in Figure 1 . In the figure, the S, N, and Ag elements show a spherical distribution. The spherical structures of S and N have significantly larger radii, indicating that SCN is modified on the surface of Ag in a shell-like structure. The process of SCN modification of Ag / BiVO 4 is shown in the in-situ infrared in Figure 5 . As the reaction time increases, the SCN on the surface of the catalyst gradually increases and stabilizes. ​​​​​

[0027] Figure 2 is the XRD pattern of Ag / BiVO in Example 1 4 and SCN-Ag / BiVO 4 The XRD patterns of SCN-Ag / BiVO 4 and Ag / BiVO 4 show a consistent crystal structure, indicating that the modification of thiocyanate does not change the crystal structure of the catalyst, and it is modified on the surface of Ag nanoparticles in a bonding manner.

[0028] Figure 3 are the XPS spectra before and after the modification of thiocyanate. The peaks of S 2p, S 2s and N 1s belonging to thiocyanate appear on the surface of Ag / BiVO 4 indicating that SCN is successfully modified on the catalyst. Among them, the peak positions of Bi 4f and S 2p partially overlap and need to be shown in the fine spectrum.

[0029] Figure 4 is the fine spectrum of the S 2p position in the XPS spectrum of SCN-Ag / BiVO 4 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.

[0030] Figure 5 is the in-situ infrared spectrum during the process of SCN modification on the surface of Ag / BiVO 4 As the reaction time progresses, thiocyanate gradually increases on the surface of the catalyst and finally stabilizes. Coupled with the formation of Ag-S, it indicates that thiocyanate forms a coordination effect on the surface of Ag. -SCN is successfully modified on the surface of the catalyst.

[0031] Prepare SCN-Ag / BiVO 4 photocatalyst for the photocatalytic oxidation of glyphosate. Specifically: Use 20 mg of SCN-Ag / BiVO 4 as the photocatalyst, place it in 50 mL of a solution containing a certain amount of glyphosate, stir for 30 min in the dark to reach the adsorption equilibrium, and irradiate with 420 nm visible light for a certain time to carry out the photocatalytic oxidation of glyphosate in water.

[0032] The oxidation efficiency of 50 μmol / L glyphosate can reach 85% in 40 min, and the product is phosphate, without the formation of AMPA.

[0033] Example 2 Same as Example 1, change the stirring time: quickly inject 160 μL of 0.1 mol / L KSCN (concentration is 0.2 mmol / L), stir for 3 h, the oxidation rate of glyphosate at 40 min is 100%, the concentration of AMPA generated is 12.5 μmol / L, and the selectivity is 25.7%.

[0034] Example 3 Same as Example 1, change the stirring time: quickly inject 160 μL of 0.1 mol / L KSCN (concentration is 0.2 mmol / L), stir for 5 h, the oxidation rate of glyphosate at 40 min is 100%, the concentration of AMPA generated is 16.4 μmol / L, and the selectivity is 32.8%.

[0035] It can be seen that as the stirring time increases, the photocatalytic removal efficiency of SCN-Ag / BiVO 4 for glyphosate increases, and the selectivity for AMPA gradually increases.

[0036] Example 4 Same as Example 3, change the volume of injected KSCN to 400 μL (concentration is 0.5 mmol / L), the oxidation rate of glyphosate at 40 min is 100%, the concentration of AMPA generated is 33.1 μmol / L, and the selectivity is 66.3%.

[0037] Example 5 Same as Example 3, change the volume of injected KSCN to 800 μL (concentration is 1 mmol / L), the oxidation rate of glyphosate at 40 min is 100%, the concentration of AMPA generated is 33.3 μmol / L, and the selectivity is 67.5%.

[0038] Example 6 Same as Example 3, change the volume of injected KSCN to 4 mL (concentration is 5 mmol / L), the oxidation rate of glyphosate at 40 min is 100%, the concentration of AMPA generated is 44.5 μmol / L, and the selectivity is 89.7%.

[0039] Example 7 Same as Example 3, change the volume of injected KSCN to 8 mL (concentration is 10 mmol / L), the oxidation rate of glyphosate at 40 min is 100%, the concentration of AMPA generated is 38.6 μmol / L, and the selectivity is 77.2%.

[0040] It can be seen that as the volume of injected KSCN increases, the concentration of -SCN in the suspension also increases, and the photocatalytic removal efficiency of SCN-Ag / BiVO 4 for glyphosate increases, and the selectivity for AMPA gradually increases.

[0041] Example 8 Same as Example 6, changing the SCN source to HSCN, the oxidation rate of glyphosate is 75.4% in 40 min, the concentration of AMPA generated is 21.1 μmol / L, and the selectivity is 57.9%.

[0042] Example 9 Same as Example 6, changing the SCN source to NaSCN, the oxidation rate of glyphosate is 85.4% in 40 min, the concentration of AMPA generated is 29.0 μmol / L, and the selectivity is 69.1%.

[0043] It can be seen that different SCN sources provide environments with different acid-base properties and different conductivities, affecting the activity of the generated SCN-Ag / BiVO 4 in the photocatalytic reaction, and also affecting the selectivity of AMPA production.

[0044] Example 10 Same as Example 6, changing the volume fraction of C1 methanol used to 50 vol%, the oxidation rate of glyphosate is 97.5% in 40 min, the concentration of AMPA generated is 38.0 μmol / L, and the selectivity is 78.1%.

[0045] Example 11 Same as Example 10, changing the volume fraction of C1 methanol used to 90 vol%, the oxidation rate of glyphosate is 80.5% in 40 min, the concentration of AMPA generated is 26.3 μmol / L, and the selectivity is 65.7%.

[0046] It can be seen that the concentration of C1 methanol as a solvent in the synthesis process of SCN-Ag / BiVO 4 plays an important role in the activity of the catalyst. As the volume fraction of the methanol solution increases, the oxidation effect of the catalyst on glyphosate decreases slightly, and the selectivity for AMPA gradually decreases.

[0047] Example 12 Same as Example 6, changing the visible light irradiation time to 5 min, the oxidation rate of glyphosate is 19.3%, the concentration of AMPA generated is 5.4 μmol / L, and the selectivity is 10.9%.

[0048] Example 13 Same as Example 6, changing the visible light irradiation time to 10 min, the oxidation rate of glyphosate is 54.1%, the concentration of AMPA generated is 7.8 μmol / L, and the selectivity is 15.8%.

[0049] Example 14 Same as Example 6, change the visible light irradiation time to 20 min. The oxidation rate of glyphosate is 70.3%, the concentration of AMPA generated is 14.2 μmol / L, and the selectivity is 28.5%.

[0050] It can be seen that as the irradiation time increases, the degree of the photocatalytic oxidation reaction gradually increases, and the photocatalytic oxidation efficiency of SCN-Ag / BiVO 4 for glyphosate increases, and the selectivity for AMPA gradually increases.

[0051] Example 15 Same as Example 6, change the concentration of glyphosate to 100 μmol / L, and keep other conditions unchanged. The oxidation rate of glyphosate is 84.9%, the concentration of AMPA generated is 77.1 μmol / L, and the selectivity is 91.2%.

[0052] Example 16 Same as Example 15, change the concentration of glyphosate to 150 μmol / L, and keep other conditions unchanged. The oxidation rate of glyphosate is 43.9%, the concentration of AMPA generated is 48.4 μmol / L, and the selectivity is 80.6%.

[0053] Example 17 Same as Example 15, change the concentration of glyphosate to 200 μmol / L, and keep other conditions unchanged. The oxidation rate of glyphosate is 20.2%, the concentration of AMPA generated is 24.7 μmol / L, and the selectivity is 63.8%.

[0054] It can be seen that as the concentration of glyphosate applied increases, the oxidation efficiency of glyphosate decreases, the removal amount of glyphosate within 40 min is limited, and the selectivity of AMPA remains at a relatively high level.

[0055] Example 18 Same as Example 6, wash the catalyst used once and then put it into use for the second time. The oxidation rate of glyphosate in 40 min is 97.3%, the concentration of AMPA generated is 41.6 μmol / L, and the selectivity is 83.4%.

[0056] Example 19 Same as Example 18, wash the catalyst used twice and then put it into use for the third time. The oxidation rate of glyphosate in 40 min is 87.1%, the concentration of AMPA generated is 38.8 μmol / L, and the selectivity is 78.0%.

[0057] It can be seen that as the multiple cycle experiments are carried out, the oxidation rate of glyphosate and the selectivity of AMPA do not decrease significantly, indicating that SCN-Ag / BiVO 4 photocatalyst has good stability.

[0058] Comparative Example 1 Same as Example 6, without adding KSCN, without long-term stirring, irradiated for 40 min, the oxidation rate of glyphosate was 100%, and AMPA was not detected in the solution.

[0059] It can be seen that compared with Ag / BiVO without thiocyanate modification 4 SCN-Ag / BiVO 4 has no obvious effect on the oxidation of glyphosate, has a significant effect on the selective production of AMPA, and plays an important role in the formation of AMPA.

Claims

1. A thiocyanate-modified Ag / BiVO4, characterized in that: Ag / BiVO4 and alcohol solution are mixed and stirred to obtain a suspension, and then a solution containing SCN roots is injected. After stirring under a N2 atmosphere, the suspension is filtered, washed, and dried to obtain SCN-Ag / BiVO4.

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. The thiocyanate-modified Ag / BiVO4 according to claim 1, characterized in that: The solution containing SCN roots includes any one of HSCN, NaSCN and KSCN, and the concentration of the solution containing SCN roots is 0.1-5 mmol / L.

4. The thiocyanate-modified Ag / BiVO4 according to claim 1, characterized in that: Stir for 1-5h under N2 atmosphere to achieve the preparation of SCN-Ag / BiVO4.

5. Use of the thiocyanate-modified Ag / BiVO4 according to any one of claims 1 to 4 for preparing aminomethylphosphoric acid by photocatalytic oxidation of glyphosate.

6. The use according to claim 5, characterized in that The SCN root-modified Ag / BiVO4 is used in the selective production of aminomethylphosphonic acid during the photocatalytic oxidation of glyphosate.

7. The use according to claim 6, characterized in that The photocatalytic oxidation is carried out under the irradiation of visible light for 5-40 minutes.

8. The use according to claim 7, characterized in that The glyphosate concentration was above 10 μmol / L.

9. The use according to any one of claims 5 to 8, characterized in that: The method of oxidizing glyphosate solution by 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.

10. The use according to claim 9, characterized in that The dosage of SCN-Ag / BiVO4 is 0.1-1.0 mg / mL.

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