Thin-layer nanosheet carbon material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of soil improvement materials, and relates to a thin-layer nanosheet carbon material as well as a preparation method and application thereof. The invention provides a preparation method of a thin-layer nanosheet carbon material, which comprises the following steps: preparing a straw main stem part into powder, carrying out dipping treatment by adopting dilute nitric acid, carrying out pyrolysis, and then carrying out dipping oxidation treatment by adopting concentrated nitric acid to obtain biochar. After the thin-layer nanosheet carbon material provided by the invention is mixed with the saline-alkali soil, the leaching of sodium ions in the saline-alkali soil can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of soil improvement materials and relates to a thin-layer nanosheet carbon material and a preparation method and application thereof. Background Art

[0002] Soil salinization is a widespread soil degradation problem worldwide, posing a serious threat to agricultural production. Saline-alkali soil, because of its high salinity, not only destroys the natural structure of the soil, but also seriously affects the normal growth of plants and crop yields. This phenomenon is mainly caused by two factors: primary salinization caused by natural causes and secondary salinization caused by human activities. According to statistics, about 1 billion hectares of arid and semi-arid areas in the world remain barren due to excessive salt content or lack of water resources. At the same time, about 20% of the irrigated area has suffered from secondary salinization. Long-term saline irrigation practices have exacerbated this trend, leading to the gradual salinization of the land and a significant decrease in crop yields. The problem of salinization is prevalent worldwide. According to statistics, about 15% of the land has degraded due to salinization, resulting in soil barrenness and widespread impact. Specifically, about 11 million hectares of soil are eroded by salinization worldwide, and the total area of ​​soil affected by salt exceeds 3.0×10 6 Hectares. The formation and evolution of saline-alkali land are affected by many factors, including topography, climate and human activities. Especially in salinized areas, there are a large number of salt lakes and wetlands, where the groundwater depth is low and the mineral content in the water is high, among which NaHCO3 is one of the main mineral compounds. These factors together restrict the improvement and utilization of saline-alkali soil, resulting in a large amount of saline-alkali land being abandoned and unable to be used for agricultural production.

[0003] The mechanism of the impact of salinized soil on crop growth is complex and diverse. First, excessive soil salt content will destroy the salt balance between crops and soil. + Ions will increase the sol effect, interfere with the metabolism of crops, destroy the protoplasm in the crops, and thus inhibit the normal growth of crops. + Excessive ion content will also destroy the nutrient balance of the soil, reduce the nitrogen metabolism performance of crops, and may cause ammonia poisoning and induce plant diseases. + Ions also increase the alkalinity of the soil. When the pH value reaches a certain level, it will cause the root cells of crops to rot, further affecting the growth and yield of crops. Given that saline-alkali land is a potential food production resource, improving its utilization efficiency is of great significance to ensuring national food security in the context of the global food crisis. Therefore, it is necessary to develop effective methods to increase the Na content in saline-alkali soil. +Improving the leaching efficiency of Na ions, reducing soil salinity and restoring soil fertility have become important topics in current agricultural research and production. + The leaching of ions can effectively alleviate the adverse effects of salinization on soil and crops, and provide more solutions for the improvement and utilization of saline-alkali land. Summary of the invention

[0004] The purpose of the present invention is to improve the Na + The leaching of ions improves the saline-alkali soil. To this end, the present invention provides a thin-layer nano-sheet carbon material and a preparation method and application thereof to solve this need in the art.

[0005] On the one hand, the present invention relates to a method for preparing a thin-layer nanosheet carbon material, which comprises: powdering the main stem part of the straw, impregnating it with dilute nitric acid, pyrolyzing it, and then impregnating and oxidizing it with concentrated nitric acid to obtain biochar.

[0006] Furthermore, in the method for preparing the thin-layer nanosheet carbon material provided by the present invention, the particle size of the powder is not higher than 2 mm.

[0007] Furthermore, in the method for preparing the thin-layer nanosheet carbon material provided by the present invention, the conditions for the dilute nitric acid impregnation treatment are: temperature 60-80° C., stirring rate 100-300 rpm, and stirring time 10-14 h.

[0008] Furthermore, in the method for preparing the thin-layer nanosheet carbon material provided by the present invention, the time of the concentrated nitric acid immersion oxidation treatment is 10 to 14 hours.

[0009] Furthermore, in the method for preparing the thin-layer nanosheet carbon material provided by the present invention, the pyrolysis temperature is 300-500° C. and the time is 3-5 hours.

[0010] Furthermore, in the method for preparing the thin-layer nanosheet carbon material provided by the present invention, it also includes: subjecting the biochar to multiple instantaneous heat treatments.

[0011] Instantaneous heat treatment can effectively thin the biochar after pretreatment with dilute nitric acid and pyrolysis followed by oxidation with concentrated nitric acid, further significantly enhancing its leaching effect on sodium ions in saline-alkali soil.

[0012] Optionally, the multiple instantaneous heat treatments are performed at least twice.

[0013] Preferably, the multiple instantaneous heat treatments are performed three times.

[0014] Furthermore, in the method for preparing the thin-layer nanosheet carbon material provided by the present invention, the instantaneous heat treatment is heating to 500-700° C. and maintaining it for 2-4 minutes.

[0015] On the other hand, the present invention relates to a thin-layer nanosheet carbon material, which is prepared by the method for preparing the thin-layer nanosheet carbon material.

[0016] On the other hand, the present invention relates to the use of the thin-layer nanosheet carbon material in improving saline-alkali soil.

[0017] Furthermore, in the application provided by the present invention, the thin layer of nanosheet carbon material increases the sodium ion leaching of saline-alkali soil.

[0018] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0019] (1) The present invention prepares a thin layer of nano-sheet carbon material and mixes it with saline-alkali soil, which can effectively increase the leaching of sodium ions in saline-alkali soil, thereby helping to reduce the salinity of the soil. The application of the thin layer of nano-sheet carbon material can improve the soil structure of saline-alkali land, promote the normal growth of crops, and improve the fertility of the soil.

[0020] (2) The present invention provides an innovative method for preparing a thin-layer nanosheet carbon material, comprising the steps of preparing a main stem portion of a straw into powder, treating the main stem portion with dilute nitric acid and concentrated nitric acid, and performing an instantaneous heat treatment. The preparation process is simple and controllable. The raw material for preparing the thin-layer nanosheet carbon material is straw, which is an agricultural waste with a wide source and is renewable, thus facilitating the recycling of resources.

[0021] (3) This technology can not only effectively improve saline-alkali soil, but also the chemical reagents and treatment methods used in the preparation process have little impact on the environment, which is in line with the concept of sustainable development. By improving saline-alkali soil, soil salinity can be reduced and soil fertility can be restored, which is expected to increase crop yield and quality, and provide more solutions for agricultural production. The proposal and implementation of the present invention have promoted the progress of agricultural science and technology, provided more ideas and methods for the improvement and utilization of saline-alkali land, and helped solve the problem of soil salinization. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is the SEM image of CK500 prepared in Example 1.

[0024] Figure 2This is the SEM image of CN500 prepared in Example 2. DETAILED DESCRIPTION

[0025] The technical scheme of the present invention is described below in conjunction with the embodiments, but the present invention is not limited to the following embodiments. The experimental methods and detection methods described in each embodiment are conventional methods unless otherwise specified; the reagents and materials described are available on the market unless otherwise specified. The % in the following embodiments are all mass percentages unless otherwise specified. The ratios in the following embodiments are all mass ratios unless otherwise specified.

[0026] Example 1

[0027] This embodiment provides the preparation of straw carbon material.

[0028] Pretreatment: The main stem of wheat straw was selected, washed with clean water, dried and crushed, and then passed through a 2 mm sieve. The crushed straw was dissolved in dilute nitric acid (3 mol / L) at 70°C and stirred at 70°C for 12 hours at a stirring speed of 150 rpm for pretreatment.

[0029] Pyrolysis and reoxidation: The acid-modified wheat straw powder was then pyrolyzed at 400 °C for 4 h. The biochar obtained after pyrolysis was oxidized in concentrated nitric acid (10 mol / L) for 12 h and filtered to obtain biochar (hereinafter named CH400).

[0030] Preparation of ordinary biochar: The main stem of wheat straw was selected, washed with clean water, dried and crushed, and then passed through a 2 mm sieve. The crushed straw was pyrolyzed at 500 °C for 4 h and filtered to obtain biochar (hereinafter named CK500).

[0031] Depend on Figure 1 It can be seen that CK500 made from raw wheat straw mainly presents a tubular structure, and the carbon material basically maintains the straw characteristics of the raw material wheat straw. The main stem of wheat straw contains vascular bundles, mainly including xylem and phloem, which are responsible for the transportation of water and nutrients. Cellulose fibers are arranged in a network in the cell wall, which enhances the mechanical strength.

[0032] Example 2

[0033] This embodiment provides the preparation of straw carbon material after instantaneous heat treatment.

[0034] Transient heat treatment: CH400 in Example 1 was placed in a corundum crucible, and after the muffle furnace reached the specified temperature (500°C, 700°C, 900°C), it was placed in a muffle furnace. After 3 minutes, the crucible was taken out and cooled at room temperature. This action was repeated 3 times, and the resulting products were thin-layer nanosheet carbon materials, which were named CN500, CN700 and CN900 respectively.

[0035] The elements of CN500 were analyzed, and the EDS analysis results are shown in Table 1.

[0036] Table 1: EDS analysis of CN500

[0037]

[0038] Straw biochar mainly contains O, Mg, Si, Mo, S, Cl, K, Ca, among which Au is introduced during the pre-testing of samples during SEM testing. O accounts for 27.57% and K accounts for 16.83%, which are two elements with relatively high proportions. K can enhance plant stress resistance and water regulation. The contents of other elements are relatively low. The element table of straw biochar is relatively simple and has no negative impact on saline-alkali land restoration. Considering its element composition, modified biochar is a safe improver that can be applied to saline-alkali land improvement.

[0039] Depend on Figure 2 It can be seen that after instantaneous heat treatment modification of CN500, the cellulose and hemicellulose in the wheat straw formed a rich multilayer structure, the vascular bundle lysis edges were relatively neat, and the thin layer of nanosheets was formed to form an efficient exfoliation biochar.

[0040] Test Case

[0041] The test selected a transparent plastic tube with a height of 30 cm and an inner diameter of 7.5 cm. There were 5 small infiltration holes at the bottom of the tube. Quartz sand, a layer of nylon mesh and a layer of filter paper were laid at the bottom of each plastic tube to prevent soil sample loss and facilitate infiltration. The column was thoroughly cleaned with deionized water and the saline-alkali soil (Na +Content 1g / kg) and 0.5% mass ratio of modified biochar CN500 are mixed and filled. In order to ensure the experimental period, sand is added to speed up the leaching time and shorten the test period. The sand ratio is 10%, the mass of the mixed soil sample of each soil column is 1000g, and the soil layer height is 20cm. Each soil column maintains the same height and mass, and the bulk density is consistent. A Buchner funnel is placed at the bottom of each soil column device, and a glass bottle is connected to collect the elution liquid. After filling, a 100-mesh stainless steel screen is placed on the upper part of the plexiglass column, and 1cm quartz sand is added to facilitate uniform distribution of the water head. Distilled water is added to the maximum field water holding capacity. The soil column is placed for one month of cultivation and then eluted. It is eluted 3 times, and 200mL of distilled water is added each time. The elution liquid is collected and the content of water-soluble sodium in the elution liquid is detected.

[0042] After three leachings, the sodium ion content in the eluent showed a downward trend each time. In the first leaching, the sodium ion content in the eluent of biochar CK500, CH400, CN500, CN700, and CN900 increased by 63.38%, 81.69%, 126.85%, 147.31%, and 9.29% compared with the control CK treatment. Among them, the differences between CK500, CH400, CN500, and CN700 and the control CK treatment all reached a significant level (p < 0.05). In the second leaching, the sodium ion content in the eluent of biochar CK500, CH400, CN500, CN700, and CN900 increased by 41.26%, 65.11%, 100.63%, 76.04%, and 7.68% compared with the control CK treatment. Among them, the differences between CK500, CH400, CN500, CN700 and the control CK treatment all reached a significant level (p < 0.05). In the third leaching, the sodium ion content in the leaching liquid of biochar CK500, CH400, CN500, CN700 and CN900 treatments increased by 137.89%, 93.98%, 236.67%, 198.60% and 23.58% compared with the control CK treatment. Among them, the differences between CK500, CH400, CN500, CN700 and the control CK treatment all reached a significant level (p < 0.05).

[0043] It can be seen that, on the one hand, the present invention produces biochar through dilute nitric acid impregnation treatment and concentrated nitric acid impregnation oxidation treatment, which can effectively increase the sodium ion leaching of saline-alkali soil and improve the improvement of saline-alkali soil, but the leaching effect is slightly reduced relative to ordinary biochar in the third leaching. On the other hand, the present invention increases the sodium ion leaching of saline-alkali soil by adding an instantaneous heat treatment step, so that the straw carbon material tends to a thin layer, which can more effectively increase the sodium ion leaching of saline-alkali soil, further improve the improvement of saline-alkali soil, and the leaching effect still maintains good performance in the third leaching. In addition, the instantaneous heat treatment should not exceed 700°C, which will make the thin layer structure too thin or even destroyed, and instead reduce the sodium ion leaching effect.

[0044] As described above, the basic principle, main features and advantages of the present invention are well described. The above embodiments and descriptions are only descriptions of the preferred implementation modes of the present invention, and the present invention is not limited by the above embodiments. Without departing from the spirit and scope of the present invention, various changes and improvements made by ordinary technicians in this field to the technical solution of the present invention should fall within the protection scope determined by the present invention.

Claims

1. A method for preparing a thin layer of nanosheet carbon material, characterized in that: include: The main stem of the straw is made into powder, impregnated with dilute nitric acid, pyrolyzed, and then impregnated and oxidized with concentrated nitric acid to produce biochar.

2. The method for preparing a thin layer of nanosheet carbon material according to claim 1, characterized in that: The particle size of the powder is not higher than 2 mm.

3. The method for preparing a thin layer of nanosheet carbon material according to claim 1, characterized in that: The conditions for the dilute nitric acid immersion treatment are: temperature 60-80° C., stirring speed 100-300 rpm, and stirring time 10-14 h.

4. The method for preparing a thin layer of nanosheet carbon material according to claim 1, characterized in that: The concentrated nitric acid immersion oxidation treatment time is 10 to 14 hours.

5. The method for preparing a thin layer of nanosheet carbon material according to claim 1, characterized in that: The pyrolysis temperature is 300-500° C. and the time is 3-5 hours.

6. The method for preparing a thin-layer nanosheet carbon material according to any one of claims 1 to 5, characterized in that: include: The biochar is subjected to multiple transient heat treatments.

7. The method for preparing a thin layer of nanosheet carbon material according to claim 6, characterized in that: The instantaneous heat treatment is heating to 500-700° C. and maintaining for 2-4 minutes.

8. A thin layer nanosheet carbon material, characterized in that: The carbon nanosheet is prepared by the method for preparing the thin-layer nanosheet carbon material according to any one of claims 1 to 7.

9. Use of the thin-layer nanosheet carbon material according to claim 8 in improving saline-alkali soil.

10. The use according to claim 9, characterized in that: The thin-layer nanosheet carbon material improves the sodium ion leaching of saline-alkali soil.

Images