Magnesium modified lignin-based carbon material as well as preparation method and application thereof

Abstract

The invention provides a magnesium modified lignin-based carbon material as well as a preparation method and application thereof, and belongs to the technical field of soil improvement. Lignin is subjected to hydrolytic depolymerization to release active functional groups, a soluble magnesium compound is doped at the same time, and then through high-temperature calcination, the magnesium compound is converted into magnesium oxide to be successfully embedded into the lignin carbon material, so that porous sites of lignin can be improved, and the lignin carbon material can be used for preparing a composite material. And magnesium oxide can be uniformly fixed in the recombinant lignin carbon matrix. When the magnesium-modified lignin-based carbon material is applied to the field, the pH value of soil can be increased, soil salt-based ions can be supplemented in time, and the negative effect on crop growth caused by soil acidification is reduced. The magnesium-modified lignin-based carbon material is applied to tests for relieving urea-driven red soil re-acidification and simulating growth of corn in southern field red soil, and is a feasible and effective strategy for relieving soil acidification and improving the growth environment of crops.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil improvement, and particularly relates to a magnesium-modified lignin-based carbon material and a preparation method and application thereof. BACKGROUND

[0002] The acidification of farmland soil is mainly caused by the acid deposition from the unreasonable nitrogen and sulfur emission and the seasonal rain leaching in the tropical and subtropical regions, and the large amount of chemical fertilizer input. For example, the excessive application of urea will be converted to nitrate nitrogen in the soil through the comprehensive action of urease, ammonia monooxygenase, hydroxylamine oxidase, nitrous acid oxidase, nitrous acid oxidoreductase, etc., and a large amount of hydrogen ions are released to reduce the soil pH. In addition, the soil data analysis report shows that the pH value of farmland will decrease and the farmland will suffer from the aluminum toxicity caused by soil acidification, in combination with the VSD+soil acidification model prediction. Therefore, the development of an environmentally friendly soil acidification improver is helpful to ensure the sustainable production of farmland soil, reduce the toxicity of heavy metals in soil and improve the yield of crops.

[0003] At present, the traditional soil remediation agent mainly includes calcium hydroxide, alkaline slag, gypsum and its derivatives. However, their effects are often short-lived because these improvers cannot enhance the acid-base buffering capacity of the soil, and thus cannot prevent the continuous acid rain and nitrogen fertilizer-driven red soil re-acidification in most cases. In contrast, organic improvers (such as kitchen waste, animal manure, sewage sludge) not only can increase the soil pH, but also can enhance the pH buffering capacity, which is mainly through the adsorption of H + by weakly acidic functional groups (such as -COOH, -OH) and the chelation of part of active aluminum. However, in practical application, many modern organic improvers are limited by heavy metal pollution and strict policies and regulations. Therefore, bio-based materials are considered to be a promising alternative to traditional organic improvers, and have a wide application prospect. Some studies have confirmed that these materials can be used as effective soil conditioners, pollutant adsorbents and microbial activity promoters after modification. Therefore, it is of great significance to provide a new bio-based soil improvement conditioner. SUMMARY

[0004] The present application aims to provide a magnesium-modified lignin-based carbon material and a preparation method and application thereof, which has a good effect on relieving soil acidification and improving the crop growth environment.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions: The present application provides a preparation method of a magnesium-modified lignin-based carbon material, which comprises the following steps: mixing lignin, a soluble magnesium compound and water to perform a hydrothermal reaction to obtain a hydrothermal product; The hydrothermal product is sequentially subjected to freeze-drying and calcination to obtain a magnesium modified lignin-based carbon material.

[0006] Preferably, the lignin comprises one or more of alkali lignin, kraft lignin and lignin sulfonate.

[0007] Preferably, the soluble magnesium compound comprises one or more of magnesium chloride, magnesium sulfate, magnesium citrate and magnesium glycinate.

[0008] Preferably, the mass ratio of the soluble magnesium compound to the lignin is 1:10-20.

[0009] Preferably, the mixing comprises: first mixing the soluble magnesium compound with water to obtain a magnesium-containing solution, and second mixing the lignin with the magnesium-containing solution. The first mixing conditions comprise: a temperature of 25-40 ℃, a stirring rate of 180-240 rpm, and a stirring time of 15-30 min. The second mixing conditions comprise: a temperature of 25-40 ℃, a stirring rate of 100-200 rpm, and a stirring time of 1-3 h.

[0010] Preferably, the hydrothermal reaction conditions comprise: a temperature of 160-200 ℃, a time of 3-8 h, and a stirring speed of 300-600 rpm.

[0011] Preferably, the freeze-drying is performed at a temperature of -40--20 ℃ for 36-48 h. The calcination is performed at a temperature of 300-500 ℃ for 2-4 h.

[0012] The application provides the magnesium modified lignin-based carbon material prepared by the preparation method.

[0013] The application provides an application of the magnesium modified lignin-based carbon material in a soil conditioner.

[0014] Preferably, the application method comprises: incubating the magnesium modified lignin-based carbon material with an acidic soil for 5-10 d.

[0015] The application provides a preparation method of a magnesium modified lignin-based carbon material, which comprises the following steps: subjecting lignin to a hydrothermal depolymerization reaction with a soluble magnesium compound, and then calcining to obtain the magnesium modified lignin-based carbon material.

[0016] The raw material used in the application is lignin, which is a natural biomass containing aromatic ring structure and has abundant ether, methoxy, carbonyl, carboxyl and hydroxyl groups.

[0017] The main raw material used in the application is lignin, a byproduct of pulping and papermaking. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1Characterization data of different lignin-based materials, wherein a is the infrared spectrum of the material prepared in Examples 1-2 and Comparative Examples 1-2; b is the XPS graph of the material prepared in Examples 1-2 and Comparative Examples 1-2, b1, b2 and b3 are the sub-peak graphs of C1s, O1s and Mg 1s, respectively; c is the XRD graph of the material prepared in Examples 1-2 and Comparative Examples 1-2; f1-f4 are the scanning electron micrographs of AL and the EDS scanning element graphs of C, O and Mg, respectively; g1-g4 are the scanning electron micrographs of LCM and the EDS scanning element graphs of C, O and Mg, respectively; h1-h4 are the scanning electron micrographs of MLCM1 and the EDS scanning element graphs of C, O and Mg, respectively; i1-i4 are the scanning electron micrographs of MLCM1.5 and the EDS scanning element graphs of C, O and Mg, respectively; Figure 2 Effects of different treatments in Application Example 1 on soil pH in the process of acidification of acidic red soil driven by nitrogen; Figure 3 Effects of different treatments in Application Example 1 on soil salt base ion content in the process of acidification of acidic red soil driven by nitrogen; Figure 4 Effects of different treatments in Application Example 1 on ammonium nitrogen (a) and nitrate nitrogen (b) contents in red soil; Figure 5 Effects of red soil improved by different treatments in Application Example 2 on corn growth under simulated acid rain conditions. DETAILED DESCRIPTION

[0019] In the present application, the required raw materials or reagents are all commercially available goods well known to those skilled in the art, unless otherwise specified.

[0020] The present application provides a preparation method of magnesium-modified lignin-based carbon material, comprising the following steps: Mixing lignin, soluble magnesium compound and water to perform hydrothermal reaction to obtain a hydrothermal product; Performing freeze-drying and calcination on the hydrothermal product in sequence to obtain the magnesium-modified lignin-based carbon material.

[0021] In the present application, the lignin preferably comprises one or more of alkali lignin, sulfate lignin and lignin sulfonate; when the lignin is two or more of the above, the present application does not have special limitation on the ratio of different types of lignin, which can be adjusted according to requirements.

[0022] In the present application, the soluble magnesium compound preferably comprises one or more of magnesium chloride, magnesium sulfate, magnesium citrate and glycine magnesium; when the soluble magnesium compound is two or more of the above, the present application does not have special limitation on the ratio of different types of soluble magnesium compound, which can be adjusted according to requirements. The water is preferably secondary water or ultrapure water.

[0023] In the present application, the mass ratio of the soluble magnesium compound to the lignin is preferably 1:10-20, and more preferably 1:13-15.

[0024] In the present application, the lignin is preferably crushed and sieved before being mixed with the soluble magnesium compound and water. The present application does not limit the particle size of the crushed and sieved material, and the subsequent second mixing can completely disperse the lignin. More preferably, the crushed powder is sieved through a 50-mesh screen to remove large particles and then sieved through a 100-mesh screen.

[0025] In the present application, the mixing preferably includes: first mixing the soluble magnesium compound with water to obtain a magnesium-containing solution, and second mixing the lignin with the magnesium-containing solution.

[0026] In the present application, the conditions of the first mixing preferably include: a temperature of 25-40 ℃, more preferably 25-30 ℃, a stirring rate of 180-240 rpm, more preferably 200-220 rpm, and a stirring time of 15-30 min, more preferably 20-25 min.

[0027] In the present application, the concentration of magnesium ions in the magnesium-containing solution is preferably 1.0 g / L.

[0028] In the present application, the conditions of the second mixing preferably include: a temperature of 25-40 ℃, more preferably 30-40 ℃, a stirring rate of 100-200 rpm, more preferably 150-180 rpm, and a stirring time of 1-3 h, more preferably 1.5-2 h.

[0029] In the present application, the concentration of the lignin in the magnesium-containing solution is preferably 100 g / L.

[0030] In the present application, the conditions of the hydrothermal reaction preferably include: a temperature of 160-200 ℃, more preferably 180-190 ℃, a time of 3-8 h, more preferably 5-7 h, and a stirring speed of 300-600 rpm, more preferably 400-500 rpm. The present application depolymerizes the lignin into small molecules through the hydrothermal reaction, and the magnesium ions can be fully chelated by the lignin.

[0031] After the hydrothermal reaction is completed, the present application preferably cools the obtained product to 20-30 ℃ by standing, filters the precipitate, freeze-dries the obtained liquid phase, places the obtained gray-black powder in a muffle furnace for calcination, and obtains a magnesium-modified lignin-based carbon material.

[0032] In the present application, the temperature of the freeze-drying is preferably -40--20 ℃, and the time is preferably 36-48 h, more preferably 36-42 h. The present application removes water by freeze-drying.

[0033] In the present application, the temperature of the calcination is preferably 300~500 ℃, more preferably 350~450 ℃, and further preferably 400 ℃, and the time is preferably 2~4 h, more preferably 2~3 h.

[0034] After the calcination is completed, the present application preferably dries the obtained product at 80 ℃ for 24 h (to prevent moisture absorption) to obtain a magnesium-modified lignin-based carbon material.

[0035] The present application provides a magnesium-modified lignin-based carbon material prepared by the preparation method described in the above technical solution.

[0036] The present application provides an application of the magnesium-modified lignin-based carbon material described in the above technical solution in a soil conditioner.

[0037] In the present application, the method of the application comprises: incubating the magnesium-modified lignin-based carbon material with an acidic soil for 5~10 d after mixing, and a crop can be planted; the acidic soil is preferably red soil.

[0038] The present application preferably uses the magnesium-modified lignin-based carbon material to alleviate red soil complex acidification.

[0039] The specific embodiments of the present application are described in detail below, but it should be understood that the protection scope of the present application is not limited by the specific embodiments. Based on the examples in the present application, all other examples obtained by a person of ordinary skill in the art without making creative efforts fall within the protection scope of the present application.

[0040] The experimental methods described in the embodiments of the present application are all conventional methods unless otherwise specified; the reagents and raw materials described below are all commercially available unless otherwise specified. The reagents or instruments not marked with a manufacturer are all conventional products that can be purchased on the market.

[0041] The kraft lignin used in the embodiments and comparative examples of the present application is purchased from Hubei Shuaiyan Liao Gao Biomedicine Co., Ltd., and the magnesium sulfate used is purchased from Guangxi Keyue Biotechnology Co., Ltd.

[0042] Example 1

[0043] 5 g of anhydrous magnesium sulfate was accurately weighed and dissolved in 1 L of laboratory secondary water, and stirred at 200 rpm and 25 ℃ for 20 min to obtain a magnesium sulfate solution with a magnesium ion concentration of 1.0 g / L; The kraft lignin was crushed by a powder machine, the powder was collected and passed through a 50-mesh sieve, the large particles were removed and then passed through a 100-mesh sieve, 100 g of lignin powder was collected and added to the magnesium sulfate solution, so that the lignin concentration was 100 g / L, and the mixture was stirred and dispersed at 180 rpm and 40 ℃ for 2 h to obtain a mixed solution; The mixed solution was placed in a reaction kettle and hydrothermally reacted at 400 rpm and 190 ℃ for 7 h, and then cooled to 25 ℃, the precipitate was filtered, the obtained liquid phase was freeze-dried at -40 ℃ for 36 h, the obtained gray-black powder was calcined in a muffle furnace, the calcination condition was 400 ℃ for 2 h, and the obtained black powder was dried at 80 ℃ for 24 h to obtain a magnesium-modified lignin-based carbon material, which was recorded as MLCM1.

[0044] Example 2

[0045] 7.5 g of anhydrous magnesium sulfate was accurately weighed and dissolved in 1 L of laboratory secondary water, stirred at 200 rpm and 25 ℃ for 20 min to obtain a magnesium sulfate solution, and the magnesium ion concentration was 1.5 g / L; The kraft lignin was crushed by a powder machine, the powder was collected and passed through a 50-mesh sieve, the large particles were removed and then passed through a 100-mesh sieve, 100 g of lignin powder was collected and added to the magnesium sulfate solution, so that the lignin concentration was 100 g / L, and the mixture was stirred and dispersed at 180 rpm and 40 ℃ for 2 h to obtain a mixed solution; The mixed solution was placed in a reaction kettle and hydrothermally reacted at 400 rpm and 190 ℃ for 7 h, and then cooled to 25 ℃, the precipitate was filtered, the obtained liquid phase was freeze-dried at -40 ℃ for 36 h, the obtained gray-black powder was calcined in a muffle furnace, the calcination condition was 400 ℃ for 2 h, and the obtained black powder was dried at 80 ℃ for 24 h to obtain a magnesium-modified lignin-based carbon material, which was recorded as MLCM1.5.

[0046] Comparative Example 1

[0047] The kraft lignin was crushed by a powder machine, the powder was collected and passed through a 50-mesh sieve, the large particles were removed and then passed through a 100-mesh sieve, 100 g of lignin powder was collected and added to 1 L of secondary water, so that the lignin concentration was 100 g / L, and the mixture was stirred and dispersed at 180 rpm and 40 ℃ for 2 h to obtain a lignin dispersion solution; The lignin dispersion solution was placed in a reaction kettle and reacted at 400 rpm and 190 ℃ for 7 h, and then cooled to 25 ℃, the precipitate was filtered, the obtained liquid phase was freeze-dried at -40 ℃ for 36 h to obtain a gray-black powder, which was dried at 80 ℃ for 24 h to obtain a lignin-based material (AL).

[0048] Comparative Example 2

[0049] The sulfate lignin was pulverized using a powder sampler, the powder was collected and passed through a 50-mesh sieve to remove large particles, and then passed through a 100-mesh sieve. 100g of lignin powder was collected and added to 1 L of secondary water to make the lignin concentration 100 g / L. The mixture was stirred and dispersed at 180 rpm and 40 ℃ for 2 h to obtain a lignin dispersion. The lignin dispersion was placed in a reactor and reacted at 400 rpm and 190 °C for 7 h. After cooling to 25 °C and filtering off the precipitate, the resulting liquid phase was freeze-dried at -40 °C for 36 h. The resulting gray-black powder was calcined in a muffle furnace at 400 °C for 2 h. The resulting black powder was then dried at 80 °C for 24 h to obtain lignin-based carbon material (LCM).

[0050] Figure 1 Characterization data for different lignin-based materials are shown below. a) are the infrared spectra of the materials prepared in Examples 1-2 and Comparative Examples 1-2; b) are the XPS images of the materials prepared in Examples 1-2 and Comparative Examples 1-2, with b1, b2, and b3 being the peak profiles for C1s, O1s, and Mg1s, respectively; c) are the XRD patterns of the materials prepared in Examples 1-2 and Comparative Examples 1-2; f1-4 are the scanning electron microscope (SEM) and EDS (Electron Suppression) elemental maps of Al and C, O, and Mg, respectively; g1-4 are the SEM and EDS (Electron Suppression) elemental maps of LCM and LCM1, respectively; h1-4 are the SEM and EDS (Electron Suppression) elemental maps of MLCM1 and LCM1, respectively; i1-i4 are the SEM and EDS (Electron Suppression) elemental maps of MLCM1.5, respectively. from Figure 1 As can be seen from Figure a, the number of oxygen-containing functional groups in lignin decreases after modification and carbonization. From... Figure 1 XPS results for MLCM1.5 show successful magnesium incorporation. Peak separation of MLCM1.5, including C1s, O1s, and Mg1s peaks, further confirms the formation of magnesium oxide (b1~b3) within MLCM1.5. Scanning electron microscopy (SEM) and EDS also confirm the successful magnesium incorporation. Figure 1 (f1~4, g1~4, h1~4, i1~4). Further XRD analysis confirmed the formation of magnesium oxide in MLCM1.5. Figure 1 (c)

[0051] Application Example 1

[0052] Experiment of different cases of materials prepared to mitigate soil acidification driven by acid red soil nitrogen: South acid red soil as the test object, the test contains 5 treatments: Ca(OH)2, AL (comparative example 1), LCM (comparative example 2), MLCM1 (example 1) and MLCM1.5 (example 2), each treatment is set up three repetitions. Specifically, 200 grams of air-dried red soil is mixed with the corresponding modifier (different cases of materials prepared) and urea to achieve a nitrogen concentration of 250 mg N·kg of soil, cultivated for 70 days, and deionized water is added as needed to keep the soil moisture at 60% of the maximum water holding capacity. The container is covered with a perforated plastic film to allow gas exchange while minimizing water loss. The pH value is analyzed in the soil samples collected at 1, 3, 7, 14, 28, 42, 56 and 70 d. Subsequently, the remaining air-dried sieved (0.25 mm) is analyzed for cation exchange capacity (CEC), ammonium nitrogen (NH4 + ) and nitrate nitrogen (NO3 - ) content.

[0053] The changes in soil pH of different treatments are shown in Figure 2 It can be seen from Figure 2 that the pH of the red soil treated with Ca(OH)2 increases temporarily and then gradually decreases to a lower value, while the pH of the soil treated with MLCM1.5 increases slowly at the beginning, but eventually the soil pH tends to be higher than the initial pH of 4.58. It is proved that the magnesium modified lignin-based carbon material alleviates the red soil re-acidification process.

[0054] The changes in soil base ion content of different treatments are shown in Figure 3 It can be seen from Figure 3 that compared with other treatments, the magnesium modified lignin-based carbon material increases the content of soil base ions, which further confirms the internal mechanism of its alleviating red soil re-acidification.

[0055] The trends of ammonium nitrogen (a) and nitrate nitrogen content (b) in the soil of different treatments are shown in Figure 4 It can be seen that compared with Ca(OH)2 treatment, the magnesium modified lignin-based carbon material inhibits the conversion of ammonium nitrogen to nitrate nitrogen, which also supports that the magnesium modified lignin-based carbon material can alleviate the red soil re-acidification.

[0056] Application Example 2

[0057] A pot experiment of corn with different treatments is carried out on the soil improved in application example 1, a total of 5 treatments of Ca(OH)2, AL, LCM, MLCM1 and MLCM1.5 are set. According to the characteristics of acid rain in Guangxi, adjust the pH 4.5 aqueous solution to simulate acid rain H2S and HN The concentration ratio of the solution was 4:1. 100 ml of the solution was sprayed every pot every 5 days. The amount of fertilizer was 0.20 mg / kg of nitrogen, 0.15 mg / kg, 0.20 mg / kg. The soil moisture was kept under normal conditions, and the pest control was performed as needed. After 30 days of potting, the plant height, stem diameter, and aboveground and underground biomass of the corn were measured, and the results are shown in Figure 5 Table 1. The specific growth index is shown in Table 1.

[0058] Table 1. Effect of different treatments on the growth of corn

[0059] Note: Different letters in the same group indicate significant differences between groups (P<0.05). p <0.05).

[0060] From Figure 5 and Table 1, it can be seen that the aboveground and underground biomass, plant height, and stem diameter of the corn treated by MLCM1.5 were significantly higher than those treated by Ca(OH)2.

[0061] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A method for preparing a magnesium-modified lignin-based carbon material, characterized in that, Includes the following steps: Lignin, soluble magnesium compounds and water are mixed and subjected to a hydrothermal reaction to obtain hydrothermal products; The hydrothermal products were sequentially freeze-dried and calcined to obtain magnesium-modified lignin-based carbon materials.

2. The preparation method according to claim 1, characterized in that, The lignin includes one or more of alkali lignin, sulfate lignin, and lignin sulfonate.

3. The preparation method according to claim 1, characterized in that, The soluble magnesium compound includes one or more of magnesium chloride, magnesium sulfate, magnesium citrate, and magnesium glycine.

4. The preparation method according to claim 1, 2, or 3, characterized in that, The mass ratio of the soluble magnesium compound to lignin is 1:10~20.

5. The preparation method according to claim 4, characterized in that, The mixing process includes: first mixing a soluble magnesium compound with water to obtain a magnesium-containing solution, and second mixing lignin with the magnesium-containing solution; The conditions for the first mixing include: a temperature of 25~40 ℃, a stirring speed of 180~240 rpm, and a stirring time of 15~30 min; The conditions for the second mixing include: a temperature of 25~40 ℃, a stirring speed of 100~200 rpm, and a stirring time of 1~3 h.

6. The preparation method according to claim 1 or 5, characterized in that, The conditions for the hydrothermal reaction include: a temperature of 160~200℃, a time of 3~8 h, and a stirring speed of 300~600 rpm.

7. The preparation method according to claim 6, characterized in that, The freeze-drying temperature is -40 ~ -20℃, and the time is 36 ~ 48 hours; The calcination temperature is 300~500 ℃, and the time is 2~4 h.

8. Magnesium-modified lignin-based carbon materials prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the magnesium-modified lignin-based carbon material according to claim 8 in soil conditioners.

10. The application according to claim 9, characterized in that, The method of application includes: mixing the magnesium-modified lignin-based carbon material with acidic soil and incubating for 5-10 days.

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