A method for increasing phenolic hydroxyl groups of humic acid by catalytic oxidation of mesoporous alumina-supported copper oxide

Abstract

The present invention provides a method for directional increase of phenolic hydroxyl groups in humic acid by catalytic oxidation of mesoporous alumina-loaded copper oxide, and relates to the technical field of modified materials. The method for directional increase of phenolic hydroxyl groups in humic acid by catalytic oxidation of mesoporous alumina-loaded copper oxide provided by the present invention comprises the following steps: ball-milling and mixing aluminum isopropoxide, copper oxide and polyethylene glycol to obtain a mixture; calcining the mixture to obtain mesoporous alumina-loaded copper oxide; ball-milling humic acid and the mesoporous alumina-loaded copper oxide to obtain humic acid with increased phenolic hydroxyl content. The present invention utilizes mesoporous alumina-loaded copper oxide to perform solid-phase ball milling on humic acid, which can selectively break the C-O single bond in the humic acid without destroying other structures of the humic acid, thereby directionally increasing the phenolic hydroxyl content of the humic acid.

Description

Technical Field

[0001] The invention relates to the technical field of modified materials, and in particular to a method for directionally increasing phenolic hydroxyl groups of humic acid by catalytic oxidation of mesoporous alumina-loaded copper oxide. Background Art

[0002] Humic acid is a complex natural organic substance containing multiple functional groups, including carboxyl, carbonyl, quinone, phenolic hydroxyl, alcoholic hydroxyl, amino, amide, and methoxy groups. It is widely found in resources such as weathered coal, lignite, and peat. The phenolic hydroxyl content of humic acid is a key indicator of its biological activity. Phenolic hydroxyl groups not only inhibit soil urease activity, retard urea hydrolysis, and reduce urea-ammonia volatilization losses, but also enhance crop resistance, promote root growth and nutrient absorption, and thus increase crop yields. Humic acid plays an important role and significance in agricultural production.

[0003] Oxidative modification of humic acid is an important approach to increasing its phenolic hydroxyl content. Using ultrasound and highly oxidizing chemicals (such as HNO3, H2SO4, and H2O2), humic acid undergoes oxidative modification, breaking down chemical groups and complex branched chains within the humic acid, forming small molecules that increase its oxygen content and biological activity. However, current ultrasound or chemical activation processes are characterized by disordered modification direction, which can damage other functional groups and the overall structure of the humic acid, making it difficult to achieve targeted structural modification to increase its phenolic hydroxyl content. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for directional catalytic oxidation of mesoporous alumina-loaded copper oxide to increase the phenolic hydroxyl group of humic acid. The present invention uses mesoporous alumina-loaded copper oxide rich in oxygen vacancies as a catalyst, combined with a ball milling process to directional catalytic oxidation to prepare phenolic hydroxyl-rich humic acid.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for increasing the phenolic hydroxyl groups of humic acid by catalytic oxidation using mesoporous alumina-supported copper oxide, comprising the following steps:

[0007] Aluminum isopropoxide, copper oxide, and polyethylene glycol are ball-milled to obtain a mixture;

[0008] calcining the mixture to obtain mesoporous alumina-supported copper oxide;

[0009] Humic acid and the mesoporous alumina-loaded copper oxide are ball-milled to obtain humic acid with increased phenolic hydroxyl content.

[0010] Preferably, the molar ratio of the aluminum isopropoxide to copper oxide is 1-3:2-3; the mass ratio of the aluminum isopropoxide to polyethylene glycol is 1-3:1-2; and the molecular weight of the polyethylene glycol is 2000-4000 Daltons.

[0011] Preferably, the vibration frequency of the ball milling is 20 to 30 Hz; and the time of the ball milling is 30 to 60 minutes.

[0012] Preferably, the calcination temperature is 400-700° C., and the holding time is 6-10 h; the heating rate from room temperature to the calcination temperature is 1-3° C. / min.

[0013] Preferably, the mesoporous alumina-supported copper oxide comprises mesoporous alumina and copper oxide particles distributed on the mesoporous alumina.

[0014] Preferably, the mass percentage of the copper oxide particles in the mesoporous alumina-supported copper oxide is 20% to 50%.

[0015] Preferably, the humic acid is humic acid extracted from weathered coal using an alkali dissolution and acid precipitation method.

[0016] Preferably, the mass ratio of the humic acid to the mesoporous alumina-loaded copper oxide is 10:0.01-0.3.

[0017] Preferably, the vibration frequency of the ball milling treatment is 20 to 30 Hz; and the time of the ball milling treatment is 30 to 60 minutes.

[0018] Preferably, the percentage of the molar content of phenolic hydroxyl groups in the humic acid with increased phenolic hydroxyl group content to the molar content of the total acidic functional groups is 35% to 50%.

[0019] The present invention provides a method for increasing the phenolic hydroxyl group content of humic acid through catalytic oxidation using mesoporous alumina-supported copper oxide. The method comprises the following steps: ball-milling aluminum isopropoxide, copper oxide, and polyethylene glycol to obtain a mixture; calcining the mixture to obtain mesoporous alumina-supported copper oxide; and ball-milling humic acid and the mesoporous alumina-supported copper oxide to obtain humic acid with increased phenolic hydroxyl group content. The present invention utilizes mesoporous alumina-supported copper oxide to perform solid-phase ball milling on humic acid, selectively breaking the CO single bond in the humic acid without destroying other functional groups in the humic acid, thereby achieving a targeted increase in the phenolic hydroxyl group content of the humic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Flowchart for the directed oxidation of humic acid phenolic hydroxyl groups catalyzed by mesoporous alumina-supported copper oxide;

[0021] Figure 2The scanning electron microscope and element distribution spectrum of CuO@Al2O3;

[0022] Figure 3 The X-ray photoelectron spectrum of CuO@Al2O3 and its peak fitting diagram;

[0023] Figure 4 is the Fourier infrared spectrum of humic acid;

[0024] Figure 5 The X-ray photoelectron spectrum of humic acid and its peak fitting diagram;

[0025] Figure 6 is the urea conversion rate;

[0026] Figure 7 is the ammonia volatilization rate and the cumulative amount of ammonia volatilization;

[0027] Figure 8 The growth condition of corn at harvest time;

[0028] Figure 9 Effects of different treatments on maize dry weight, nitrogen absorption, plant height and chlorophyll. DETAILED DESCRIPTION

[0029] The present invention provides a method for increasing the phenolic hydroxyl groups of humic acid by catalytic oxidation using mesoporous alumina-supported copper oxide, comprising the following steps:

[0030] Aluminum isopropoxide, copper oxide, and polyethylene glycol are ball-milled to obtain a mixture;

[0031] calcining the mixture to obtain mesoporous alumina-supported copper oxide;

[0032] Humic acid and the mesoporous alumina-loaded copper oxide are ball-milled to obtain humic acid with increased phenolic hydroxyl content.

[0033] The present invention ball-mills aluminum isopropoxide, copper oxide, and polyethylene glycol (PEG) to obtain a mixture. In the present invention, the molar ratio of the aluminum isopropoxide to the copper oxide is preferably 1 to 3:2 to 3, more preferably 2.67:2. In the present invention, the mass ratio of the aluminum isopropoxide to the polyethylene glycol is preferably 1 to 3:1 to 2, more preferably 1.36 to 2:1. In the present invention, the molecular weight of the polyethylene glycol is preferably 2000 to 4000 Daltons, more preferably 4000 Daltons.

[0034] In the present invention, the ball milling is preferably performed in a high-speed vibrating ball mill. The vibration frequency of the ball milling is preferably 20 to 30 Hz, more preferably 25 to 30 Hz; the ball milling time is preferably 30 to 60 minutes, more preferably 50 to 60 minutes. The grinding media used in the ball milling are preferably steel balls, and the diameter of the steel balls is preferably 2.5 cm.

[0035] In the present invention, after the ball milling, the sample is preferably washed and dried in sequence. In the present invention, the washing is preferably ethanol washing. In the present invention, the drying temperature is preferably 40°C and the drying time is preferably 6 hours.

[0036] After obtaining the mixture, the present invention preferably calcines the mixture to obtain mesoporous alumina-supported copper oxide. In the present invention, the calcination temperature is preferably 400-700°C, more preferably 500-600°C; the holding time is preferably 6-10 hours, more preferably 7-8 hours; and the heating rate from room temperature to the calcination temperature is preferably 1-3°C / min, more preferably 2°C / min. In the present invention, the calcination atmosphere is preferably air. In the present invention, the polyethylene glycol is removed through the calcination to form a mesoporous structure.

[0037] In the present invention, water washing is preferably performed after the calcination to obtain mesoporous alumina-supported copper oxide. In the present invention, the water washing is preferably performed three times. In the present invention, surface impurities of the mesoporous alumina-supported copper oxide are removed by water washing.

[0038] In the present invention, the mesoporous alumina-supported copper oxide preferably comprises mesoporous alumina and copper oxide particles distributed on the mesoporous alumina. In the present invention, the specific surface area of ​​the mesoporous alumina is preferably 200 to 300 m 2 / g, more preferably 258m 2 / g; the average particle size of the copper oxide particles is preferably 0.1 to 10 microns, more preferably 0.8 to 5 microns. In the present invention, the mass percentage of the copper oxide particles in the mesoporous alumina-supported copper oxide is preferably 20% to 50%, more preferably 34% to 40%.

[0039] In the present invention, the mesoporous alumina-loaded copper oxide is rich in oxygen vacancies.

[0040] In the present invention, aluminum isopropoxide, copper oxide and polyethylene glycol are fully mixed to form a mixture of polyethylene glycol-loaded copper oxide and aluminum isopropoxide during ball milling; then, by high-temperature calcination, the polyethylene glycol is carbonized into carbon dioxide, and the aluminum isopropoxide is decomposed into aluminum oxide, forming a structure of mesoporous alumina-loaded copper oxide. The mesoporous alumina-loaded copper oxide provided by the present invention includes mesoporous alumina and copper oxide particles distributed on the mesoporous alumina. The mesoporous alumina has a large specific surface area. On the one hand, it can adsorb humic acid, and on the other hand, it can disperse copper oxide particles and improve catalytic activity. The mesoporous alumina-loaded copper oxide rich in oxygen vacancies prepared by the present invention can selectively break the CO single bond in the humic acid molecule, and directional catalytic oxidation can be used to prepare humic acid rich in phenolic hydroxyl groups.

[0041] After obtaining the mesoporous alumina-loaded copper oxide, the present invention ball-mills the humic acid and the mesoporous alumina-loaded copper oxide to obtain the humic acid with increased phenolic hydroxyl content.

[0042] In the present invention, the humic acid is preferably extracted from weathered coal by alkali dissolution and acid precipitation. In the present invention, the mass ratio of the humic acid to the mesoporous alumina-supported copper oxide is preferably 10:0.01-0.3, more preferably 10:0.1-0.2.

[0043] In the present invention, the vibration frequency of the ball milling process is preferably 20-30 Hz, more preferably 25-30 Hz; the ball milling time is preferably 30-60 minutes, more preferably 50-60 minutes. In the present invention, the grinding media used in the ball milling process are preferably steel balls; the diameter of the steel balls is preferably 2.5 cm. In the present invention, the ball milling process is preferably performed in air.

[0044] In the ball milling process of the present invention, mesoporous alumina loaded with copper oxide is used as a catalyst to catalyze the conversion of the phenyl benzoate structure in the humic acid into a phenolic hydroxyl structure, thereby directionally increasing the phenolic hydroxyl content of the humic acid.

[0045] In the present invention, the percentage of the molar content of phenolic hydroxyl groups in the humic acid with increased phenolic hydroxyl group content to the molar content of the total acidic functional groups is 35% to 50%, more preferably 40% to 50%.

[0046] In the present invention, the humic acid with increased phenolic hydroxyl content is preferably used to increase crop yields.

[0047] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] Example 1

[0049] 2.67mmol aluminum isopropoxide, 2mmol CuO and 0.4g PEG4000 were added to a 50mL screw-capped reactor (containing a 2.5cm diameter steel ball). After sealing the reactor, it was placed in a high-speed vibration ball mill (Retsch mixing mill MM400) and ball-milled at a vibration frequency of 30Hz for 60min; the obtained sample was washed with ethanol, dried at 40℃ for 6h, then heated to 600℃ at a heating rate of 2℃ / min, calcined at 600℃ for 6h, and washed with water three times to obtain mesoporous alumina-loaded copper oxide, which was recorded as CuO@Al2O3. The CuO@Al2O3 prepared in this embodiment consists of mesoporous alumina and copper oxide particles distributed on the mesoporous alumina; the specific surface area of ​​the mesoporous alumina is 258m 2 / g; the average particle size of the copper oxide particles is 0.8 microns; the mass content of the copper oxide particles in the mesoporous alumina-supported copper oxide is 34%.

[0050] 400 g of weathered coal was added to 4000 ml of 0.5 mol / L NaOH solution, stirred at room temperature for 24 h, and then centrifuged for 10 min (8000 rpm) to remove insoluble ash and humin components. The solution was filtered twice using a Buchner funnel (connected to a water circulation vacuum pump) equipped with double-layer filter paper (medium-speed quantitative). The pH of the filtrate was adjusted to 1.0 with 6.0 mol / L HCl solution, and the filtrate was allowed to stand for 12 h to precipitate humic acid. The solution was then centrifuged at 8000 rpm for 10 min, and the supernatant was discarded. The lower precipitate was the crude extracted humic acid.

[0051] The crude humic acid was washed three times with a HCl (0.1 mol / L)-HF (0.3 mol / L) mixed solution at a ratio of 1:10 (w:v) to remove silicate; and then washed three times with deionized water at a ratio of 1:10 (w:v) to remove chloride ions. After freeze-drying, a purified humic acid sample was obtained and stored at room temperature for future use.

[0052] like Figure 1 As shown in FIG, 10 g of the purified humic acid sample (HA) and 0.1 g of the CuO@Al2O3 (catalyst) prepared above were added to a screw-capped reactor (containing a steel ball with a diameter of 2.5 cm). After sealing the reactor, the mixture was placed in a high-speed vibration ball mill (Retsch mixing mill MM400) and ball milled at a vibration frequency of 30 Hz for 60 min to obtain humic acid with increased phenolic hydroxyl content, which was recorded as CuO@Al2O3-HA.

[0053] Comparative Example

[0054] The preparation method is basically the same as that of Example 1, except that CuO@Al2O3 is not added, and the humic acid obtained by ball milling alone is denoted as GHA.

[0055] Test Example 1 Structural characteristics of CuO@Al2O3 and humic acid with increased phenolic hydroxyl content

[0056] (1) Structural characteristics of CuO@Al2O3

[0057] Figure 2 This is the scanning electron microscope and element distribution energy spectrum of CuO@Al2O3. Figure 2 Scanning electron microscopy results show that the CuO@Al2O3 has a rich mesoporous structure (magnification 20,000x), which provides adsorption sites and active centers for the directional catalytic oxidation of humic acid. CuO is evenly distributed and highly dispersed on the surface of the Al2O3, indicating that the CuO@Al2O3 was successfully prepared.

[0058] Figure 3 This is the X-ray photoelectron energy spectrum of CuO@Al2O3 and its peak fitting diagram. Figure 3 Analysis of X-ray photoelectron spectroscopy (XPS) reveals that the CuO@Al2O3 surface is rich in oxygen vacancies (48.35%) and adsorbed oxygen (38.06%), as seen in the O1s spectrum. These surfaces provide active centers for the catalytic reaction and accelerate oxygen adsorption and transfer. The Al 2p spectrum reveals that CuO and Al2O3 interact to form Cu-O-Al bonds, accelerating electron transfer in the catalytic reaction system and enhancing catalytic activity.

[0059] (2) Structural characteristics of humic acid that increases phenolic hydroxyl content

[0060] Table 1 Elemental composition and atomic percentage of humic acid

[0061]

[0062] The elemental analysis results in Table 1 show that compared with HA, GHA did not significantly increase the oxygen content of humic acid and the O / C ratio did not increase; the oxygen content of CuO@Al2O3-HA increased by 6.5% and the O / C ratio increased by 8.11%.

[0063] Table 2 Content and distribution of acidic functional groups in humic acid

[0064]

[0065] Table 2 Analysis of acidic functional groups of humic acid shows that the molar content of phenolic hydroxyl groups in GHA only increases by 3% compared with HA, while the molar content of phenolic hydroxyl groups in CuO@Al2O3-HA increases by 40%, indicating that CuO@Al2O3 successfully achieves the directional modification of humic acid and generates humic acid rich in phenolic hydroxyl groups.

[0066] Figure 4 This is the Fourier infrared spectrum of humic acid. Figure 4 The results of Fourier transform infrared spectroscopy showed that the oxygen-containing vibration peak intensity of CuO@Al2O3-HA increased compared with that of HA, indicating that the oxygen content of humic acid increased. -1 The phenolic hydroxyl vibration peak intensity increased, indicating that CuO@Al2O3 successfully achieved directional modification of humic acid phenolic hydroxyl groups.

[0067] Figure 5 The X-ray photoelectron spectrum of humic acid and its peak fitting diagram. Figure 5 The O1s results of X-ray photoelectron spectroscopy showed that compared with HA, GHA did not significantly increase the CO content of humic acid, while the CO content of CuO@Al2O3-HA increased by 46.34%, which was consistent with the result that the phenolic hydroxyl content of humic acid increased by 40% in the acidic functional group analysis.

[0068] Test Example 2 Effects of Phenolic Hydroxyl Humic Acid on Urea Conversion, Ammonia Volatilization and Corn Growth

[0069] Three humic acids (HA, GHA, and CuO@Al2O3-HA) were added to molten urea at 130°C at a dosage of 0.5% (the mass of the humic acid divided by the total mass of the humic acid and urea). The mixture was stirred for 30 seconds, cooled, and then pulverized and passed through a 100-mesh sieve to obtain the humic acid urea products HAU (corresponding to HA), GHAU (corresponding to GHA), and CuO@Al2O3-HAU (corresponding to CuO@Al2O3-HA). Urea (U), melted without the addition of humic acid, was used as a control.

[0070] (1) Urea conversion rate

[0071] According to GB / T 35113-2017, 0.5 g of the prepared HAU, GHAU, CuO@Al2O3-HAU, and U were added to 100 mL of urease solution (activity of 1 U / mg), respectively, and incubated in a (25±2)°C incubator for 30 min. The colorimetry was performed on a spectrophotometer, and the urea decomposition rate was calculated.

[0072] Urea decomposition rate (%) = (initial urea nitrogen content - residual urea nitrogen content after conversion) / initial urea nitrogen content × 100.

[0073] Figure 6 Urea conversion results showed that U achieved a 25.51% urea conversion rate. Compared with U, all three humic acid ureas significantly reduced urea conversion and delayed urea hydrolysis. CuO@Al2O3-HAU achieved a 18.66% urea conversion rate, a 26.85% decrease. Compared with HAU, the urea conversion rate of CuO@Al2O3-HAU decreased by 17.58%, indicating that humic acid (CuO@Al2O3-HA), with an increased phenolic hydroxyl content, has a stronger delaying effect on urea hydrolysis than original humic acid (HA), further reducing urea losses.

[0074] (2) Ammonia volatilization rate and cumulative ammonia volatilization

[0075] 0.068g of each of U, HAU, GHAU, and CuO@Al2O3-HAU were mixed with 100g of soil and added to culture bottles. A control (CK) without fertilizer was also used. The soil moisture content was adjusted to 20% and the plants were incubated in a 25°C climate chamber in the dark. During the incubation period, the soil moisture content was maintained at 20% by weighing. Each treatment was replicated three times. NH3 was absorbed using a sponge absorption method on days 1, 2, 3, and 5 after incubation.

[0076] Figure 7 The results of ammonia volatilization rate and ammonia volatilization accumulation showed that compared with U, the three humic acid ureas could reduce the ammonia volatilization rate and ammonia volatilization accumulation, among which there was no significant difference between HAU and GHAU. Compared with HAU, CuO@Al2O3-HAU reduced the ammonia volatilization cumulative rate and ammonia volatilization cumulative amount by 15.91% and 16.36% on average, respectively, indicating that CuO@Al2O3-HA could further reduce the ammonia volatilization loss of urea compared with HA.

[0077] (3) Impact on the growth of potted corn

[0078] U, HAU, GHAU, and CuO@Al2O3-HAU were mixed with soil. Nitrogen was applied at a rate of 0.15 g N / kg dry soil. Phosphate and potassium fertilizers were also applied to all treatments, with phosphorus and potassium fertilizers applied at a rate of 0.20 g P2O5 / kg dry soil and 0.20 g K2O / kg dry soil, respectively. A control (CK) was used without nitrogen fertilizer. After soil filling, the plants were evenly irrigated. After the water had fully penetrated the soil, maize seeds, which had been germinated for 3 days, were sown in the center of the pots at a depth of 5 cm and covered with soil. Two maize seeds were sown in each pot. After 10 days of emergence, the seedlings were thinned to retain only one seedling per pot. Each treatment was replicated six times. The pots were placed in a climate chamber, and their positions were randomly rotated weekly. Samples were harvested after 30 days of incubation.

[0079] Figure 8 and Figure 9The results showed that compared with CK, all fertilization treatments promoted the growth of corn; compared with U, the three humic acid urea treatments significantly increased the total dry weight of corn by 8.8% to 21%; compared with HAU, GHAU did not significantly increase the total dry weight of corn, and CuO@Al2O3-HAU significantly increased the total dry weight of corn and root nitrogen uptake by 11.2% and 21.22%, respectively, indicating that CuO@Al2O3-HA can further improve the absorption and utilization of nitrogen by crops and promote crop growth compared with HA.

[0080] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for increasing the phenolic hydroxyl groups of humic acid by catalytic oxidation using mesoporous alumina-supported copper oxide, comprising the following steps: Aluminum isopropoxide, copper oxide, and polyethylene glycol are ball-milled to obtain a mixture; calcining the mixture to obtain mesoporous alumina-supported copper oxide; ball-milling the humic acid and the mesoporous alumina-loaded copper oxide to obtain humic acid with increased phenolic hydroxyl content; The mass ratio of the humic acid to the mesoporous alumina-loaded copper oxide is 10:0.01-0.

3.

2. The method according to claim 1, characterized in that The molar ratio of the aluminum isopropoxide to copper oxide is 1-3:2-3; the mass ratio of the aluminum isopropoxide to polyethylene glycol is 1-3:1-2; and the molecular weight of the polyethylene glycol is 2000-4000 Daltons.

3. The method according to claim 1, characterized in that The vibration frequency of the ball milling mixing is 20-30 Hz; the time of the ball milling mixing is 30-60 min.

4. The method according to claim 1, wherein The calcination temperature is 400-700° C., and the holding time is 6-10 hours; the heating rate from room temperature to the calcination temperature is 1-3° C. / min.

5. The method according to claim 1, wherein The mesoporous alumina-supported copper oxide comprises mesoporous alumina and copper oxide particles distributed on the mesoporous alumina.

6. The method according to claim 5, characterized in that The mass percentage of the copper oxide particles in the mesoporous alumina-loaded copper oxide is 20% to 50%.

7. The method according to claim 1, characterized in that The humic acid is extracted from weathered coal by using an alkali dissolution and acid precipitation method.

8. The method according to claim 1, characterized in that The vibration frequency of the ball milling treatment is 20-30 Hz; the time of the ball milling treatment is 30-60 min.

9. The method according to claim 1, characterized in that The percentage of the molar content of phenolic hydroxyl groups in the humic acid with increased phenolic hydroxyl group content to the molar content of the total acidic functional groups is 35% to 50%.

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