Humic acid rich in aromatic oxygen and preparation method thereof

Abstract

The invention discloses humic acid rich in aromatic oxygen and a preparation method thereof, and belongs to the technical field of general methods of organic chemistry. The silicon dioxide loaded cobalt oxide-manganese oxide-magnesium oxide catalyst and the hydrogen peroxide solution are matched for use, a carboxyl structure generated in the humic acid oxidation process can be selectively fractured and damaged, meanwhile, an aromatic ring structure of humic acid is reserved to the maximum extent, and oxygen atoms exposed after carboxyl fracture are connected to an undamaged benzene ring, so that the corrosion resistance of the humic acid is improved, and the corrosion resistance of the humic acid is improved. Therefore, the aromatic oxygen content of humic acid is increased in a targeted manner. When the humic acid treated by the oxidizing agent is mixed with urea, the ammonia volatilization loss of the urea can be effectively reduced, and the adsorption of soil ammonium nitrogen is improved, so that more nitrogen is retained in the soil, the nitrogen supply intensity of the soil is improved, and the urea loss is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of general methods of organic chemistry, and specifically relates to humic acid rich in aromatic oxygen and a preparation method thereof. Background Art

[0002] Urea is the most important type of nitrogen fertilizer in my country, accounting for about 65% of the total nitrogen fertilizer consumption. After urea is applied to the soil, it will be rapidly hydrolyzed and transformed under the action of urease. In addition to being absorbed by crops and fixed in the soil, some nitrogen is lost through ammonia volatilization, nitrification, denitrification, runoff and leaching, thereby reducing fertilizer utilization.

[0003] Humic acid is a natural organic macromolecular substance containing multiple functional groups such as aromatic rings, carboxyl groups, phenolic hydroxyl groups and methoxy groups. It has a macromolecular network structure, high cation exchange capacity and strong physical adsorption capacity. Studies have shown that humic acid rich in aromatic oxygen can further absorb nutrients and water in the soil, stabilize soil urease activity, promote crop root growth and nutrient absorption, and improve nutrient utilization, which plays an important role and significance for the sustainable development of agriculture. At the same time, the presence of aromatic oxygen functional groups can inhibit the activity of microorganisms, slow down the decomposition of humic acid by microorganisms, and make the degradation rate of humic acid in the soil relatively slow, thereby maximizing the synergistic ability of humic acid.

[0004] In order to increase the aromatic oxygen content of humic acid, humic acid is usually oxidized by oxidation. Traditional oxidation methods (such as HNO3, H2SO4, H2O2, etc.) mainly increase the oxygen content and carboxyl content of humic acid after oxidation, but there is disorder in the modification direction. During the oxidation process, the oxidant will damage the aromatic ring structure of humic acid, resulting in a significant decrease in its aromaticity and a small increase in the aromatic oxygen content, making it difficult to increase the aromatic oxygen content of humic acid in a targeted manner. The difficulty in increasing the aromatic oxygen of humic acid in a targeted manner is to destroy the carboxyl structure generated during the oxidation of humic acid while retaining the aromatic ring structure of humic acid to the maximum extent. Adding a catalyst with selective catalytic ability during the oxidation process is expected to connect a large number of oxygen atoms exposed after the carboxyl group breaks to the intact benzene ring, thereby increasing the aromatic oxygen content of humic acid in a targeted manner. Summary of the invention

[0005] In view of the above-mentioned prior art, the present invention provides a humic acid rich in aromatic oxygen and a preparation method thereof, so as to solve the technical problem that it is difficult to carry out targeted modification of the carboxyl structure of humic acid to increase its aromatic oxygen content.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is to provide a method for preparing humic acid rich in aromatic oxygen, comprising the following steps: (1) dissolving humic acid in a sodium hydroxide solution having a concentration of 2 wt % to prepare a sodium humate solution having a concentration of 0.1-0.2 g / mL; (2) The humic acid-modified oxidant is added to the sodium humate solution under stirring conditions, and the reaction is carried out at 45-55 °C for 90-150 min; then the solution is cooled to room temperature in an ice-water bath; the humic acid-modified oxidant comprises a solid catalyst and a hydrogen peroxide solution; the solid catalyst is a silica-supported cobalt oxide-manganese oxide-magnesium oxide catalyst, and its chemical composition is Co3O4-Mn3O4-MgO@SiO2.

[0007] (3) Separate the liquid and freeze-dry it to obtain the product.

[0008] Based on the above technical solution, the present invention can also be improved as follows.

[0009] Furthermore, the solid-liquid ratio of the solid catalyst to the hydrogen peroxide solution in the humic acid modified oxidant is 1 g:75~85 mL.

[0010] Further, the solid catalyst is prepared by the following steps: S1: Dissolve hexadecyltrimethylammonium bromide in water to prepare a base solution with a concentration of 0.02-0.05 mol / L; S2: Add silicate, cobalt salt, manganese salt and magnesium salt to the base solution, stir for 0.5-1 h, then adjust the pH of the system to 8-10, and then age at 80-100 °C for 1-5 h, then filter and collect the solid to obtain the precursor; S3: Dry the precursor at 100-120 °C for 10-15 h, and then calcine at 280-320 °C for 3-8 h to obtain.

[0011] Furthermore, the molar ratio of silicate, cobalt salt, manganese salt and magnesium salt is 10:1~3:1~2:0.5~2; and the material-liquid ratio of silicate to substrate solution is 1 mol:10 mL.

[0012] Furthermore, the silicate is sodium silicate; the cobalt salt is cobalt chloride or cobalt nitrate; the manganese salt is manganese sulfate, manganese chloride or manganese nitrate; and the magnesium salt is magnesium sulfate, magnesium chloride or magnesium nitrate.

[0013] Furthermore, the aging temperature in S2 is 90 °C, and the aging time is 3 h; the drying temperature in S3 is 110 °C, and the drying time is 12 h; the calcination temperature is 300 °C, and the calcination time is 5 h.

[0014] Furthermore, the mass concentration of the hydrogen peroxide solution is 0.5%.

[0015] Furthermore, the mass ratio of the humic acid modified oxidant to the humic acid is 1:100 based on the mass of the solid catalyst.

[0016] Furthermore, in step (2), the reaction temperature is 50° C. and the reaction time is 120 min.

[0017] The invention also discloses humic acid rich in aromatic oxygen, which is prepared by adopting the preparation method.

[0018] The beneficial effects of the present invention are: 1. The present invention uses a silica-loaded cobalt oxide-manganese oxide-magnesium oxide catalyst in combination with a hydrogen peroxide solution to selectively break and destroy the carboxyl structure generated during the oxidation of humic acid, while retaining the aromatic ring structure of humic acid to the maximum extent. The oxygen atoms exposed after the carboxyl group is broken are connected to the intact benzene ring, thereby targetedly increasing the aromatic oxygen content of humic acid.

[0019] 2. When the humic acid treated with the oxidant of the present invention is mixed with urea, the ammonia volatilization loss of urea can be effectively reduced, and the adsorption of ammonium nitrogen in the soil can be improved, thereby retaining more nitrogen in the soil, improving the nitrogen supply intensity of the soil, and reducing urea loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the XPS C1s peak fitting diagram of HA, OHA and COHA; Figure 2 is the average double bond equivalent oxygen reduction value of COHA, OHA and HA; Figure 3 is the average aromaticity index of COHA, OHA, and HA; Figure 4 The effects of COHA, OHA and HA on the volatilization rate of urea ammonia; Figure 5 The effects of COHA, OHA and HA on the cumulative amount of ammonia volatilization; Figure 6 This is the effect of COHA, OHA and HA on the soil ammonium nitrogen content during urea conversion. DETAILED DESCRIPTION

[0021] The specific implementation modes of the present invention are described in detail below with reference to the embodiments.

[0022] Example 1 A humic acid modified oxidant comprises a solid catalyst and a hydrogen peroxide solution, wherein the solid catalyst and the hydrogen peroxide solution have a solid-liquid ratio of 1 g:80 mL; wherein the mass concentration of the hydrogen peroxide solution is 0.5%; the solid catalyst is a silicon dioxide-supported cobalt oxide-manganese oxide-magnesium oxide catalyst, and its chemical composition is Co3O4-Mn3O4-MgO@SiO2, and is prepared by the following steps: S1: Dissolve 6 mmol of hexadecyltrimethylammonium bromide (CTMAB) in 200 mL of distilled water and ultrasonicate for 15 min to prepare a base solution with a concentration of 0.03 mol / L; S2: 10 mmol sodium silicate, 2 mmol cobalt chloride, 1.5 mmol manganese sulfate and 1 mmol magnesium sulfate were added to the base solution, stirred for 0.5 h, then the pH of the system was adjusted to 9, and then aged at 90 °C for 3 h, then filtered, the solid was collected, and washed with hot water (90 °C) 3 times to obtain the precursor; S3: Place the precursor into an oven at 110 °C, dry for 12 h, and then calcine at 300 °C for 5 h to obtain the solid catalyst Co3O4-Mn3O4-MgO@SiO2.

[0023] Example 2 A humic acid modified oxidant comprises a solid catalyst and a hydrogen peroxide solution, wherein the solid catalyst and the hydrogen peroxide solution have a solid-liquid ratio of 1 g:75 mL; wherein the mass concentration of the hydrogen peroxide solution is 0.5%; the solid catalyst is a silicon dioxide-supported cobalt oxide-manganese oxide-magnesium oxide catalyst, and its chemical composition is Co3O4-Mn3O4-MgO@SiO2, and is prepared by the following steps: S1: Dissolve 4 mmol of hexadecyltrimethylammonium bromide (CTMAB) in 200 mL of distilled water and ultrasonicate for 15 min to prepare a base solution with a concentration of 0.02 mol / L; S2: 10 mmol sodium silicate, 1 mmol cobalt nitrate, 2 mmol manganese chloride and 0.5 mmol magnesium chloride were added to the base solution, stirred for 0.5 h, then the pH of the system was adjusted to 8, and then aged at 80 °C for 5 h, then filtered, the solid was collected, and washed with hot water (80 °C) 3 times to obtain the precursor; S3: Place the precursor into an oven at 100 °C, dry for 15 h, and then calcine at 280 °C for 8 h to obtain the solid catalyst Co3O4-Mn3O4-MgO@SiO2.

[0024] Example 3 A humic acid modified oxidant comprises a solid catalyst and a hydrogen peroxide solution, wherein the solid catalyst and the hydrogen peroxide solution have a solid-liquid ratio of 1 g:85 mL; wherein the mass concentration of the hydrogen peroxide solution is 0.5%; the solid catalyst is a silicon dioxide-supported cobalt oxide-manganese oxide-magnesium oxide catalyst, and its chemical composition is Co3O4-Mn3O4-MgO@SiO2, and is prepared by the following steps: S1: Dissolve 10 mmol of hexadecyltrimethylammonium bromide (CTMAB) in 200 mL of distilled water and ultrasonicate for 15 min to prepare a base solution with a concentration of 0.05 mol / L; S2: 10 mmol sodium silicate, 3 mmol cobalt chloride, 1 mmol manganese nitrate and 2 mmol magnesium nitrate were added to the base solution, stirred for 0.5 h, then the pH of the system was adjusted to 10, and then aged at 100 °C for 1 h, then filtered, the solid was collected, and washed with hot water (100 °C) 3 times to obtain the precursor; S3: Place the precursor into an oven at 120 °C, dry for 10 h, and then calcine at 320 °C for 3 h to obtain the solid catalyst Co3O4-Mn3O4-MgO@SiO2.

[0025] Experimental example The humic acid modified oxidants prepared in the three embodiments of the present invention have similar performances. Taking the humic acid modified oxidant prepared in Embodiment 1 as an example, the performance of the humic acid modified oxidant is described.

[0026] The humic acid is subjected to a directional catalytic oxidation modification using a humic acid modified oxidant to prepare humic acid rich in aromatic oxygen. The specific steps are as follows: 10 g of humic acid sample was dissolved in 92 mL of 2wt% sodium hydroxide solution. The solid catalyst Co3O4-Mn3O4-MgO@SiO2 (0.1 g) in the humic acid modified oxidant was first added to the sodium humate solution under continuous stirring, and then the hydrogen peroxide solution (mass concentration of 0.5%, 8 mL) in the humic acid modified oxidant was added, mixed well and reacted at 50°C for 2 h. After the reaction was completed, the reaction system was immediately placed in ice water for rapid cooling to prevent the reaction from continuing; when it was cooled to room temperature, solid-liquid separation was performed, the solution after the reaction was collected, and the collected solution was freeze-dried to obtain humic acid rich in aromatic oxygen, recorded as COHA.

[0027] At the same time, humic acid is oxidized using H2O2 solution as an oxidant. The specific steps are as follows: 10 g of humic acid sample was dissolved in 92 mL of 2wt% sodium hydroxide solution, and 8 mL of 5% H2O2 solution was added to the humic acid solution under continuous stirring, mixed well, and reacted at 50 °C for 2 h. After the reaction, the reaction system was immediately placed in ice water for rapid cooling to prevent the reaction from continuing; when it was cooled to room temperature, solid-liquid separation was performed, the solution after the reaction was collected, and the collected solution was freeze-dried to obtain oxidized humic acid, which was recorded as OHA.

[0028] Humic acid (HA) and OHA were used as controls to evaluate the directional modification ability of the catalyst in the present invention.

[0029] 1. Structural characteristics of directional modified humic acid The elemental composition of different humic acids is shown in Table 1. Compared with HA, the carbon, hydrogen, and nitrogen contents of OHA and COHA decreased, and the oxygen content increased, indicating that the oxidation process would reduce the carbon content of humic acid and increase the oxygen content. Compared with HA, the oxygen content of OHA and COHA increased by 3.4% and 4.8%, respectively, among which the oxygen content of COHA was further increased than that of OHA, indicating that the introduction of Co3O4-Mn3O4-MgO@SiO2 in the oxidation system can further increase the oxygen content of humic acid. Compared with OHA, the carbon content of COHA increased, indicating that the introduction of Co3O4-Mn3O4-MgO@SiO2 protected the aromatic ring structure of humic acid and prevented the aromatic ring structure from being excessively oxidized to generate carbon dioxide and escape.

[0030] Table 1 Elemental composition of humic acid

[0031] The C1s peak fitting of COHA, OHA and HA was performed, and the results were as follows: Figure 1 As shown. Figure 1 It can be seen that compared with HA, the carboxyl content of OHA increased by 35.56%, while the carboxyl content of COHA decreased by 20.16%, indicating that the carboxyl content of COHA was directionally destroyed. At the same time, it was found that compared with HA, the CO (aromatic oxygen) content of OHA and COHA increased by 21.89% and 44.99%, respectively, further indicating that the combination of Co3O4-Mn3O4-MgO@SiO2 and H2O2 can directionally break and destroy the carboxyl structure of humic acid, oxidize the carboxyl structure while protecting the aromatic carbon structure of humic acid, and connect the oxygen atom to the benzene ring, thereby directionally increasing the aromatic oxygen content of humic acid.

[0032] The average double bond equivalent oxygen reduction value and average aromaticity index of COHA, OHA and HA are as follows: Figure 2 and Figure 3 The average double bond equivalent oxygen reduction value reflects the unsaturation of the humic acid carbon skeleton. The higher the value, the lower the carboxyl content in the molecule. Figure 2 It can be seen that COHA has the lowest carboxyl content, while OHA oxidized with hydrogen peroxide alone has the highest carboxyl content. The average aromaticity index reflects the number of aromatic ring structures in the humic acid molecular structure. The higher the value, the more aromatic rings are contained in the molecule. Figure 3It can be seen that the number of aromatic rings in COHA is similar to that in HA, while the aromatic ring structure in OHA is further destroyed and the number of aromatic rings is greatly reduced. The above results show that the combination of Co3O4-Mn3O4-MgO@SiO2 and H2O2 can directionally destroy the carboxyl structure and prevent the aromatic ring structure of humic acid from being greatly destroyed, thereby directionally increasing the aromatic oxygen content of humic acid.

[0033] 2. Effect of humic acid on soil ammonium nitrogen content during urea ammonia volatilization and urea conversion Three humic acids (HA, OHA and COHA) were added to molten urea at 130°C at an addition rate of 0.5% (the mass of humic acid divided by the total mass of humic acid and urea), stirred for 30 seconds, crushed after cooling, and passed through a 100-mesh sieve to obtain three humic acid ureas HAU (corresponding to HA), OHAU (corresponding to OHA) and COHAU (corresponding to COHA). Urea (U) that was only melted without adding humic acid was used as a control.

[0034] 0.068 g of U, HAU, OHAU and COHAU were mixed with 100 g of soil and added to the culture bottle. The treatment without fertilizer was used as the control (CK). The soil moisture content was adjusted to 20% and cultured in a 25 ℃ climate chamber in the dark. During the culture period, the soil moisture content was kept at 20% by weighing method, and each treatment was repeated 3 times. The sponge absorption method was used to absorb NH3 on the 1st, 2nd, 3rd, 5th and 7th day after culture, and the soil ammonium nitrogen content was measured on the 1st, 2nd, 3rd, 5th and 7th day, 14th and 28th day of culture.

[0035] The effects of humic acid on the urea ammonia volatilization rate and the ammonia volatilization accumulation are shown in Figure 4 and 5 As shown. Figure 4 and Figure 5 It can be seen that compared with U, humic acid urea can reduce the average ammonia volatilization rate (2.95%~12.94%) and the cumulative amount of ammonia volatilization (2.1%~16.26%). Compared with HAU, the average ammonia volatilization rate and cumulative amount of ammonia volatilization of OHAU increased by 2.46% and 1.33%, respectively, and COHAU decreased by 8.22% and 13.41%, respectively, indicating that COHA rich in aromatic oxygen can further reduce the ammonia volatilization loss of urea compared with HA.

[0036] Effect of humic acid on soil ammonium nitrogen content during urea conversion Figure 6As shown in the figure, compared with U, the ammonium nitrogen content in the soil of humic acid urea decreased on the first day of incubation, and the ammonium nitrogen content in the soil of COHAU was further reduced compared with HAU. At the peak of ammonia volatilization on the second day of incubation, the ammonium nitrogen content of HAU was lower, which was consistent with the increase in ammonia volatilization of HAU on the second day. Compared with HAU, the ammonium nitrogen content in the soil of COHAU increased by 5.60%, indicating that COHA, which is rich in aromatic oxygen, can further improve the adsorption of soil ammonium nitrogen compared with HA, retain more nitrogen in the soil, increase the nitrogen supply intensity of the soil, and reduce urea loss.

[0037] Although the specific implementation of the present invention is described in detail in conjunction with the embodiments, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for preparing humic acid rich in aromatic oxygen, characterized in that: The following steps are involved: (1) dissolving humic acid in a sodium hydroxide solution having a concentration of 2 wt % to prepare a sodium humate solution having a concentration of 0.1-0.2 g / mL; (2) adding a humic acid modified oxidant to a sodium humate solution under stirring conditions, reacting at 45-55°C for 90-150 min; and then cooling to room temperature in an ice-water bath; the humic acid modified oxidant comprises a solid catalyst and a hydrogen peroxide solution; the solid catalyst is a silica-supported cobalt oxide-manganese oxide-magnesium oxide catalyst, and its chemical composition is Co3O4-Mn3O4-MgO@SiO2. (3) Separate the liquid and freeze-dry it to obtain the product.

2. The method for preparing humic acid rich in aromatic oxygen according to claim 1, characterized in that: The solid-liquid ratio of the solid catalyst to the hydrogen peroxide solution in the humic acid modified oxidant is 1 g: 75-85 mL.

3. The method for preparing humic acid rich in aromatic oxygen according to claim 1 or 2, characterized in that: The solid catalyst is prepared by the following steps: S1: Dissolve hexadecyltrimethylammonium bromide in water to prepare a base solution with a concentration of 0.02-0.05 mol / L; S2: Add silicate, cobalt salt, manganese salt and magnesium salt to the base solution, stir for 0.5-1 h, then adjust the pH of the system to 8-10, and then age at 80-100 °C for 1-5 h, then filter and collect the solid to obtain the precursor; S3: Dry the precursor at 100-120 °C for 10-15 h, and then calcine at 280-320 °C for 3-8 h to obtain.

4. The method for preparing humic acid rich in aromatic oxygen according to claim 3, characterized in that: The molar ratio of the silicate, cobalt salt, manganese salt and magnesium salt is 10:1-3:1-2:0.5-2; the material-liquid ratio of the silicate to the substrate solution is 1 mol:10 mL.

5. The method for preparing humic acid rich in aromatic oxygen according to claim 4, characterized in that: The silicate is sodium silicate; the cobalt salt is cobalt chloride or cobalt nitrate; the manganese salt is manganese sulfate, manganese chloride or manganese nitrate; and the magnesium salt is magnesium sulfate, magnesium chloride or magnesium nitrate.

6. The method for preparing humic acid rich in aromatic oxygen according to claim 3, characterized in that: In S2, the aging temperature is 90 °C and the aging time is 3 h; in S3, the drying temperature is 110 °C and the drying time is 12 h; the calcination temperature is 300 °C and the calcination time is 5 h.

7. The method for preparing humic acid rich in aromatic oxygen according to claim 1 or 2, characterized in that: The mass concentration of the hydrogen peroxide solution is 0.5%.

8. The method for preparing humic acid rich in aromatic oxygen according to claim 1, characterized in that: The mass ratio of the humic acid modified oxidant to the humic acid is 1:100 based on the solid catalyst.

9. The method for preparing humic acid rich in aromatic oxygen according to claim 1, characterized in that: In step (2), the reaction temperature is 50°C and the reaction time is 120 min.

10. A humic acid rich in aromatic oxygen, characterized in that: The humic acid is prepared by the method for preparing humic acid rich in aromatic oxygen according to any one of claims 1 to 9.

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