A saline-alkali soil modifier based on biochar-humic acid and a preparation method thereof

Abstract

The application discloses a saline-alkali soil modifier based on biochar-humic acid and a preparation method thereof, and relates to the technical field of soil modifiers, which comprises boron acid anchored biochar and hierarchical enrichment polyphenol site humic acid; the boron acid anchored biochar is biochar particles, an aryl covalent grafting layer is formed on the surface of the biochar particles through aryl diazonium salt surface coupling, and the aryl covalent grafting layer carries aryl boronic acid groups; the hierarchical enrichment polyphenol site humic acid is a polyphenol site enrichment component obtained by hierarchical treatment of humic acid; and the inner tight and outer loose distribution comprises that the bonding density of boronic ester on the outer surface and the pore opening area is higher than the bonding density of boronic ester in the pore area. The application forms a high-density boronic ester bonding layer on the outer surface and the pore opening area and solidifies through two-stage programmed treatment, the pore area remains low density, an interface structure of inner tight and outer loose is formed, the stability and active site distribution of the composite are improved, and the mass transfer performance of the pore opening and the structure coupling are improved.

Description

Technical Field

[0001] This invention relates to the field of soil conditioner technology, and in particular to a biochar-humic acid-based saline-alkali land conditioner and its preparation method. Background Technology

[0002] In recent years, saline-alkali land improvement materials have gradually shifted from single mineral conditioners to multi-component synergistic approaches. Biochar, with its porous structure and surface functional groups, has been widely used in salt migration regulation, nutrient slow-release carriers, and microenvironment construction. Humic acid and its active components rich in phenolic hydroxyl groups have also formed relatively mature preparation and characterization systems in terms of complexation, buffering, and interfacial reaction regulation. The composite and interfacial bonding of porous carbon materials with natural organic macromolecules have become important research directions.

[0003] The common approach to existing composite modified materials is to combine biochar and humic acid through physical adsorption or weak interaction. However, the interfacial layer is prone to redistribution in high ionic strength and weakly alkaline saline-alkali environments, resulting in insufficient retention and fixation of humic acid active sites on the outer surface and pore area. It is difficult to form a stable and spatially selective bonding density gradient at the pore interface, making it difficult to achieve structural coordination between pore mass transfer, salt flux and exposure of organic active sites simultaneously. Summary of the Invention

[0004] In view of this, this application provides a biochar-humic acid-based saline-alkali land conditioner and its preparation method.

[0005] According to one aspect of this disclosure, a biochar-humic acid-based saline-alkali land conditioner is provided, comprising boric acid-anchored biochar and graded enriched polyphenolic site humic acid; the boric acid-anchored biochar is biochar particles, and the surface of the biochar particles is coupled with an aryl diazonium salt to form an aryl covalent graft layer, the aryl covalent graft layer carrying aryl boric acid groups; the graded enriched polyphenolic site humic acid is a polyphenolic site enriched component obtained by graded treatment of humic acid; the aryl boric acid groups are connected to the polyphenolic sites of the polyphenolic site enriched component through dynamic reversible covalent bonds of borate esters, and the polyphenolic site enriched component is distributed on the outer surface and pore area of ​​the boric acid-anchored biochar in a dynamic reversible covalent bond manner of borate esters; the saline-alkali land conditioner satisfies the distribution of tight inner and loose outer layers; the tight inner and loose outer layers distribution includes a higher borate ester bonding density on the outer surface and pore area than the borate ester bonding density in the pore area.

[0006] According to another aspect of this disclosure, a method for preparing a saline-alkali land conditioner based on biochar-humic acid is provided, comprising: Step 1: performing surface cleaning and activation treatment on biochar to obtain an activated biochar dispersion; performing a diazotization reaction on an aromatic amine with boric acid groups to obtain an aryl diazonium salt solution containing boric acid groups; Step 2: conducting a contact reaction between the aryl diazonium salt solution containing boric acid groups and the activated biochar dispersion in a reaction medium with water as the continuous phase to obtain a boric acid-anchored biochar dispersion; Step 3: performing a diazotization reaction on an aromatic amine with boric acid groups to obtain a aryl diazonium salt solution containing boric acid groups; Acid fractionation was performed to obtain a humic acid solution with fractionated enriched polyphenol sites; the boric acid-anchored biochar dispersion and the humic acid solution with fractionated enriched polyphenol sites were reacted under weak alkaline conditions with low ionic strength to obtain a first-stage boric ester bonded complex; Step 4: the first-stage boric ester bonded complex was subjected to salt-alkali aging treatment in a simulated salt-alkali extract to complete the exchange of boric ester bonds and obtain an interfacial network complex with a tight inner and loose outer distribution; the interfacial network complex was then washed, dried and granulated to obtain a saline-alkali soil conditioner.

[0007] The beneficial effects of this invention are as follows: The two-stage programmed processing preferentially promotes the formation of a borate ester bonded layer between the outer surface and the pore area under low ionic strength and weak alkaline conditions. Then, in a high ionic strength saline-alkali medium, it triggers borate ester bond exchange and interfacial segment conformational rearrangement, continuously increasing the bond density between the outer surface and the pore area and solidifying the spatial distribution of the interfacial network. Through this controlled bond exchange and rearrangement pathway, the composite forms a rearrangeable interfacial network in the outer layer of the particles and the pore area while maintaining a higher bond density, while the internal pore area maintains a lower bond density. This results in an interfacial structure that is tight inside and loose outside, allowing for manageable structural coupling between the distribution of active sites and the pore mass transfer boundary. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 A schematic diagram of the interface structure between boric acid-anchored biochar and humic acid.

[0010] Figure 2 This is a schematic diagram of a two-stage procedural processing procedure. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0012] This invention aims to construct a biochar-humic acid-based saline-alkali land conditioner. In this embodiment, the biochar-humic acid-based saline-alkali land conditioner comprises: boric acid-anchored biochar and graded enriched polyphenolic site humic acid; the boric acid-anchored biochar is biochar particles, with an aryl covalently grafted layer formed on the surface of the biochar particles through surface coupling with aryl diazonium salts, the aryl covalently grafted layer carrying aryl boric acid groups; the graded enriched polyphenolic site humic acid is a polyphenolic site enriched component obtained by graded treatment of humic acid; the aryl boric acid groups are connected to the polyphenolic sites of the enriched polyphenolic site component through dynamic reversible covalent bonds of borate esters, and the enriched polyphenolic site component is distributed on the outer surface and pore area of ​​the boric acid-anchored biochar in a dynamic reversible covalent bond manner of borate esters; the saline-alkali land conditioner satisfies the distribution of a tight inner and loose outer structure; the tight inner and loose outer structure includes a higher borate ester bonding density on the outer surface and pore area than the borate ester bonding density in the pore area.

[0013] In some embodiments of this application, the boric acid-anchored biochar accounts for 70% to 98% of the total mass of the modifier, and the graded enrichment of polyphenol sites humic acid accounts for 2% to 30% of the total mass of the modifier.

[0014] In some embodiments of this application, the arylboronic acid group is derived from the aryl diazonium salt generated by diazotization of aromatic amines with borate groups. The aryl diazonium salt undergoes a covalent grafting reaction with the surface of biochar to form an aryl covalent graft layer.

[0015] In some embodiments of this application, the aromatic amine with a borate group includes any one or any combination of 4-aminophenylboronic acid and 3-aminophenylboronic acid.

[0016] In some embodiments of this application, the graded enrichment of polyphenolic humic acid sites is obtained by molecular weight graded, polarity graded, or pH graded, and the titration volume of phenolic hydroxyl groups is used as the graded criterion for polyphenolic site enrichment.

[0017] In some embodiments of this application, the network structure formed by the dynamic reversible covalent bonds of borate esters in the outer surface and orifice region is a rearrangeable interface network.

[0018] The rearrangeable interface network undergoes boronic acid ester bond exchange and is accompanied by interface segment conformational rearrangement in a saline-alkali environment.

[0019] In some embodiments of this application, the inner tight and outer loose distribution is formed by a two-stage programmed process, including a first stage and a second stage;

[0020] The first stage is carried out under low ionic strength and weak alkaline conditions, with the pH adjusted to 8-10. The borate ester bonding layer is preferentially formed on the outer surface and the pore opening area, and the formation density of the borate ester bonding layer is higher than that in the pore interior area.

[0021] The second stage is carried out in a high ionic strength saline-alkali environment, using a simulated saline-alkali extract as a medium to maintain a weak alkaline pH and allow borate ester bond exchange to occur, forming a high-density borate ester bond layer on the outer surface and the pore area.

[0022] In some embodiments of this application, the saline-alkali land conditioner further includes a granulating binder phase, which is any one or any combination of water-soluble polysaccharides, lignin sulfonates, and sodium carboxymethyl cellulose, and the granulating binder phase accounts for 0.1% to 5% of the total mass of the conditioner.

[0023] This application also provides a method for preparing a saline-alkali land conditioner based on biochar-humic acid, comprising: Step 1: performing surface cleaning and activation treatment on biochar to obtain an activated biochar dispersion; performing a diazotization reaction on an aromatic amine with borate groups to obtain an aryl diazonium salt solution containing borate groups; Step 2: conducting a contact reaction between the aryl diazonium salt solution containing borate groups and the activated biochar dispersion in a reaction medium with water as the continuous phase to obtain a borate-anchored biochar dispersion; Step 3: performing a fractionation treatment on humic acid to obtain a fractionally enriched humic acid solution with polyphenol sites; conducting a contact reaction between the borate-anchored biochar dispersion and the fractionally enriched humic acid solution with polyphenol sites under weak alkaline conditions with low ionic strength to obtain a first-stage borate ester bonded complex; Step 4: subjecting the first-stage borate ester bonded complex to saline-alkali aging treatment in a simulated saline-alkali extract to complete the exchange of borate ester bonds and obtain an interfacial network complex with a tight inner and loose outer distribution; and sequentially washing, drying, and granulating the interfacial network complex to obtain a saline-alkali land conditioner.

[0024] Example 1: 910g of biochar particles were washed with deionized water until the conductivity of the washing solution stabilized, then dried at 60℃ to constant weight and sieved to 0.5mm-1.5mm. 6.0g of 4-aminophenylboronic acid was dissolved in 120mL of 1mol / L hydrochloric acid, and 20mL of an aqueous solution prepared with 2.1g of sodium nitrite was added dropwise at 0℃-5℃. The mixture was kept at this temperature for 15min to obtain an aryl diazonium salt solution containing boric acid groups. The biochar obtained in the previous step was dispersed in 3L of deionized water and the pH was adjusted to 9.0. The aryl diazonium salt solution was slowly added and stirred for 2h, allowing the aryl diazonium salt to couple onto the surface of the biochar to form a graft layer carrying aryl boric acid groups. The mixture was filtered and washed with deionized water until the filtrate was colorless to obtain boric acid-anchored biochar. Humic acid was dissolved in 0.05mol / L sodium hydroxide solution and molecular weight fractionated. The phenolic hydroxyl groups were then added dropwise. A 4.2 mmol / g polyphenol site enrichment fraction was selected and converted to 80 g dry weight. Boric acid-anchored biochar and the polyphenol site enrichment fraction were added to a carbonate buffer system with an ionic strength controlled at 0.02 mol / L. The pH was adjusted to 9.0 and stirred for 4 h to obtain a low-ionic-strength, weakly alkaline forming stage product. This product was placed in a simulated saline-alkali extraction solution containing 0.50 mol / L NaCl and 0.05 mol / L NaHCO3 and maintained at a weakly alkaline pH. It was aged at 25 °C for 24 h to trigger borate ester bond exchange and solidify the high bonding density of the outer surface and pore area. After filtration and washing, it was dried at 60 °C for 12 h. A 2% aqueous solution prepared with 10 g of sodium carboxymethyl cellulose was added, mixed, granulated into 2 mm to 4 mm particles, and dried again to obtain the finished saline-alkali soil conditioner based on biochar-humic acid.

[0025] like Figure 1 As shown, arylboronic acid groups form a graft layer with biochar particles through a surface covalent grafting reaction, and then connect with polyphenol sites enriched in humic acid through dynamic reversible covalent bonds of borate esters, forming an interface with a specific distribution structure.

[0026] like Figure 2 As shown in Example 1, a borate ester bonded layer is first formed under low ionic strength weak alkaline conditions. Subsequently, in a high ionic strength salt-alkali leaching solution, borate ester bond exchange occurs and solidifies the high bond density of the outer layer region, ultimately achieving the goal of different bond densities between the inner and outer regions.

[0027] Example 2: 900g of biochar particles were washed, dried, and sieved according to the method in Example 1; 6.5g of 3-aminophenylboronic acid was diazotized under the temperature range of Example 1 to prepare an aryl diazonium salt solution containing borate groups; the biochar was dispersed in 3L of deionized water and the pH was adjusted to 9.2, the aryl diazonium salt solution was added, stirred for 2 hours, and washed until colorless to obtain borate-anchored biochar; humic acid was dissolved in an alkaline solution and subjected to polarity fractionation; the 4.4 mmol / g polyphenol site enrichment fraction was selected according to the titration capacity of the phenolic hydroxyl group and the value was calculated. 90g dry basis; add boric acid-anchored biochar and polyphenol site enrichment components into a buffer system and control the ionic strength to 0.02mol / L, adjust the pH to 9.2 and stir for 4h to complete the low ionic strength weak base forming stage; place the obtained composite in a simulated salt-alkali extraction solution of NaCl 0.50mol / L and NaHCO3 0.05mol / L and age at 25℃ for 24h, then filter, wash and dry at 60℃ for 12h, add 10g of sodium carboxymethyl cellulose in a 2% aqueous solution to granulate and dry to obtain the finished product.

[0028] Example 3: 885g of biochar particles were pretreated according to the method in Example 1; 3.0g of 4-aminophenylboronic acid and 3.0g of 3-aminophenylboronic acid were diazotized separately at 0℃~5℃ and then combined to obtain a mixed aryl diazonium salt solution; the biochar was dispersed in 3L of deionized water and the pH was adjusted to 8.8, the mixed aryl diazonium salt solution was added and stirred for 2h, and washed until colorless to obtain boric acid-anchored biochar; humic acid was dissolved in an alkaline solution and pH fractionated, and a titration of 4.5mmol / g was selected according to the phenolic hydroxyl titration capacity. The phenol site enrichment component was calculated to be 105 g on a dry basis. Boric acid-anchored biochar and the enriched component were added to a buffer system with the ionic strength controlled at 0.015 mol / L. The pH was adjusted to 8.8 and stirred for 3.5 h to form the first-stage complex. The first-stage complex was placed in a simulated saline-alkali extraction solution of 0.45 mol / L NaCl and 0.045 mol / L NaHCO3 and aged at 25 °C for 18 h. After filtration and washing, it was dried at 60 °C for 12 h. 10 g of water-soluble polysaccharide solution was added, granulated, and dried to obtain the finished product.

[0029] Example 4: 860g of biochar particles were pretreated according to the method in Example 1; 7.0g of 4-aminophenylboronic acid was diazotized at 0℃~5℃ to obtain an aryl diazonium salt solution; the biochar was dispersed in 3L of deionized water and the pH was adjusted to 9.5, the aryl diazonium salt solution was added and stirred for 2h, and washed until colorless to obtain boric acid anchored biochar; humic acid was molecular weight fractionated and 130g of polyphenol site enrichment component with a phenolic hydroxyl titration capacity of 4.6mmol / g was selected and converted to dry basis; the boric acid anchored biochar and enrichment component were added to a buffer system and the ionic strength was controlled at 0.03mol / L, the pH was adjusted to 9.5 and stirred for 4h to complete the low ionic strength weak base forming stage; the composite was placed in a simulated salt-alkali extraction solution of NaCl 0.60mol / L and NaHCO3 0.06mol / L and aged at 25℃ for 24h, filtered and washed and dried at 60℃ for 12h, granulated with 10g of lignin sulfonate solution and dried to obtain the finished product.

[0030] Example 5: 905g of biochar particles were pretreated according to the method in Example 1; 3.5g of 4-aminophenylboronic acid and 3.5g of 3-aminophenylboronic acid were diazotized and combined to obtain a mixed aryl diazonium salt solution; the biochar was dispersed in 3L of deionized water and the pH was adjusted to 9.1, the mixed aryl diazonium salt solution was added, stirred for 2 hours, and washed until colorless to obtain boric acid-anchored biochar; humic acid was fractionated by polarity, and the 4.7mmol / g polyphenol site enrichment fraction was selected according to the phenolic hydroxyl titration capacity. Calculate 85g dry basis; add boric acid anchored biochar and enriched components to a buffer system and control the ionic strength to 0.02mol / L, adjust the pH to 9.1 and stir for 4.5h to form the first stage composite; place the first stage composite in a simulated salt-alkali extraction solution of NaCl 0.50mol / L and NaHCO3 0.05mol / L and age at 25℃ for 30h, filter, wash and dry at 60℃ for 12h, add 10g sodium carboxymethyl cellulose solution to granulate and dry to obtain the finished product.

[0031] Example 6: 930g of biochar particles were pretreated according to the method in Example 1; 6.0g of 3-aminophenylboronic acid was diazotized to obtain an aryl diazonium salt solution; the biochar was dispersed in 3L of deionized water and the pH was adjusted to 9.0, the aryl diazonium salt solution was added and stirred for 2h, and washed until colorless to obtain boric acid-anchored biochar; humic acid was molecular weight fractionated and a 4.3mmol / g polyphenol site enrichment fraction was selected based on the phenolic hydroxyl titration capacity, and the dry basis was calculated to be 60g; the boric acid-anchored biochar and the enrichment fraction were added to a buffer system and the ionic strength was controlled at 0.02mol / L, the pH was adjusted to 9.0 and stirred for 4h to form the first-stage complex; the first-stage complex was placed in a simulated salt-alkali extraction solution of 0.50mol / L NaCl and 0.05mol / L NaHCO3 and aged at 25℃ for 24h, filtered and washed, and dried at 60℃ for 12h, granulated by adding 10g of water-soluble polysaccharide solution and dried to obtain the finished product.

[0032] Example 7: 830g of biochar particles were pretreated according to the method in Example 1; 7.5g of 4-aminophenylboronic acid was diazotized to obtain an aryl diazonium salt solution; the biochar was dispersed in 3L of deionized water and the pH was adjusted to 9.6, the aryl diazonium salt solution was added and stirred for 2h, and washed until colorless to obtain boric acid anchored biochar; humic acid was subjected to pH fractionation and 150g of polyphenol site enrichment fraction with a phenolic hydroxyl titration capacity of 4.1mmol / g was selected and converted to dry basis; the boric acid anchored biochar and enrichment fraction were added to a buffer system and the ionic strength was controlled at 0.03mol / L, the pH was adjusted to 9.6 and stirred for 4h to form the first-stage complex; the first-stage complex was placed in a simulated salt-alkali extraction solution of NaCl 0.60mol / L and NaHCO3 0.06mol / L and aged at 25℃ for 24h, filtered and washed, and dried at 60℃ for 12h, granulated with 20g of lignin sulfonate solution and dried to obtain the finished product.

[0033] Example 8: 950g of biochar particles were pretreated according to the method in Example 1; 5.5g of 4-aminophenylboronic acid was diazotized to obtain an aryl diazonium salt solution; the biochar was dispersed in 3L of deionized water and the pH was adjusted to 8.6, the aryl diazonium salt solution was added and stirred for 2h, and washed until colorless to obtain boric acid-anchored biochar; humic acid was molecular weight fractionated and a 4.0 mmol / g polyphenol site enrichment component was selected according to the phenolic hydroxyl titration capacity, and the dry basis was calculated to be 40g; the boric acid-anchored biochar and the enrichment component were added to a buffer system and the ionic strength was controlled at 0.015mol / L, the pH was adjusted to 8.6 and stirred for 3.5h to form the first-stage complex; the first-stage complex was placed in a simulated salt-alkali extraction solution of 0.40mol / L NaCl and 0.04mol / L NaHCO3 and aged at 25℃ for 18h, filtered and washed, and dried at 60℃ for 12h, granulated with 10g of sodium carboxymethyl cellulose solution and dried to obtain the finished product.

[0034] Comparative Example 1: 900g of unmodified biochar and 90g of ungraded humic acid were added to a carbonate solution with pH 9.0 and ionic strength 0.06mol / L and stirred for 1h. Only a physical adsorption binding system was formed. No diazotization of aromatic amines with borate groups or surface coupling of aryl diazonium salts were carried out. No low ionic strength weak base forming stage or high ionic strength salt-alkali aging stage was carried out. The mixture was directly filtered and dried at 60℃ for 12h. 10g of sodium carboxymethyl cellulose solution was added to granulate the mixture and dried to obtain the control sample.

[0035] Comparative Example 2: 900g of boric acid-anchored biochar was prepared according to Example 1, and 90g of humic acid enriched at polar fractionated polyphenol sites was obtained according to Example 2. After mixing the two, the low ionic strength weak alkali forming stage was not performed, but the mixture was directly placed in a simulated salt-alkali extraction solution of 0.50mol / L NaCl and 0.05mol / L NaHCO3 and aged at 25°C for 24h. The mixture was filtered, washed, and dried at 60°C for 12h. 10g of sodium carboxymethyl cellulose solution was added, granulated, and dried to obtain the comparative sample.

[0036] Comparative Example 3: 900g of boric acid-anchored biochar was prepared according to Example 1. 90g of ungraded humic acid with a phenolic hydroxyl titration capacity of approximately 3.5 mmol / g was taken. The mixture was subjected to a low ionic strength weak alkali forming stage with an ionic strength of 0.02 mol / L and a pH of 9.0, and a high ionic strength salt-alkali aging stage with NaCl 0.50 mol / L and NaHCO3 0.05 mol / L. The mixture was filtered, washed, and dried at 60°C for 12 h. 10g of sodium carboxymethyl cellulose solution was added to granulate the mixture and then dried to obtain the comparative sample.

[0037] For the products of Examples 1 to 8 and the samples of Comparative Examples 1 to 3, the bonding density ratio of the outer surface and the orifice area relative to the inner pore area, the humic acid dissolution under salt-alkali leaching conditions, and the polyphenol site loss rate under salt-alkali leaching conditions were tested.

[0038] Table 1 Comparison of Three Test Data

[0039] sample The bonding density between the outer surface and the orifice region is higher than that between the inner surface and the orifice region. The amount of humic acid dissolved after 24 hours of salt-alkali extraction is mg / L. Percentage of polyphenol site loss after 24 hours of salt-alkali extraction Example 1 3.2 34 9.5 Example 2 3.4 31 8.8 Example 3 3.0 38 10.6 Example 4 2.7 44 12.4 Example 5 3.6 28 7.9 Example 6 3.3 33 9.2 Example 7 2.6 49 14.8 Example 8 2.8 46 13.6 Comparative Example 1 1.1 118 41.5 Comparative Example 2 1.7 74 24.2 Comparative Example 3 2.1 63 19.7

[0040] Table 2 Comparison of parameters between Examples 1-8 and Comparative Examples 1-3

[0041] sample Biochar types Biochar mass percentage Humic acid grading method Phenolic hydroxyl titration volume mM molar per gram Two-stage procedural process Example 1 Boric acid anchored biochar 91.0 Molecular weight classification 4.2 implement Example 2 Boric acid anchored biochar 90.0 Polarity classification 4.4 implement Example 3 Boric acid anchored biochar 88.5 pH classification 4.5 implement Example 4 Boric acid anchored biochar 86.0 Molecular weight classification 4.6 implement Example 5 Boric acid anchored biochar 90.5 Polarity classification 4.7 implement Example 6 Boric acid anchored biochar 93.0 Molecular weight classification 4.3 implement Example 7 Boric acid anchored biochar 83.0 pH classification 4.1 implement Example 8 Boric acid anchored biochar 95.0 Molecular weight classification 4.0 implement Comparative Example 1 Unmodified biochar 90.0 Do not execute Unlimited Do not execute Comparative Example 2 Boric acid anchored biochar 90.0 Polarity classification 4.4 Partial execution Comparative Example 3 Boric acid anchored biochar 90.0 Do not execute Approximately 3.5 implement

[0042] As shown in Table 2, Examples 1-8 all used boric acid to anchor biochar and performed a two-stage programmed process. At the same time, the humic acid was graded and the phenolic hydroxyl titration capacity was in the range of 4.0-4.7 mmol / g. The structural premises were concentrated on the two main lines of "polyphenol site enrichment" and "staged treatment". Comparative Example 1 canceled the boric acid anchoring and two-stage programmed process, Comparative Example 2 only retained the salt and alkali aging but lacked the low ionic strength weak base forming stage, and Comparative Example 3 retained the two-stage programmed process but canceled the humic acid grading and reduced the degree of polyphenol site enrichment. The three groups formed clear boundary differences.

[0043] As shown in Table 1, the bonding density ratio between the outer surface and the pore area in Examples 1-8 remained in the range of 2.6-3.6 compared to the pore area. Meanwhile, the humic acid dissolution and polyphenol site loss rate remained in a low range after 24 hours of salt-alkali leaching, and the indicators showed a consistent coupling relationship. In Comparative Example 1, the bonding density ratio decreased to 1.1 and the dissolution and loss rates increased, reflecting that physical mixing was difficult to maintain interface fixation and site retention under salt-alkali leaching conditions. In Comparative Example 2, the bonding density ratio and stability index declined simultaneously when the first stage of forming was missing, indicating that salt-alkali aging alone was insufficient to establish a preferential bonding layer between the outer surface and the pore area.

[0044] Comparative Example 3 retained the two-stage programmed process but the humic acid was not graded and the phenolic hydroxyl titration capacity was about 3.5 mmol / g. In Table 1, the bond density ratio and extraction stability both fell between the Example and Comparative Example 2, indicating that the degree of polyphenol site enrichment directly affects the formation efficiency of the borate bond layer and the available site scale for subsequent bond exchange curing. The graded enrichment and the two-stage process form a mutually supportive combination of conditions.

[0045] Through the two-stage programmed processing of this invention, a high-density borate ester bonded layer was successfully formed on the outer surface and in the pore area, achieving borate ester bond exchange and interfacial segment conformational rearrangement in a saline-alkali environment. Under low ionic strength and weak alkaline conditions, the high-density bonded layer on the outer surface and in the pore area preferentially forms, while the internal region maintains a lower bond density, ultimately forming an interfacial structure that is tight inside and loose outside. This structure significantly improves the stability of the composite, optimizes the pore mass transfer performance and structural coupling, enhances the effect of the saline-alkali soil conditioner on water and nutrient transfer, and strengthens the distribution and utilization efficiency of active sites.

[0046] The above description is only a specific embodiment of this disclosure, but the protection scope of this disclosure is not limited thereto. The protection scope of this disclosure should be determined by the protection scope of the claims.

Claims

1. A saline-alkali land conditioner based on biochar-humic acid, characterized in that: This includes boric acid-anchored biochar and graded enrichment of humic acid at polyphenol sites; The graded enrichment of polyphenolic humic acid sites was obtained by molecular weight graded, polarity graded, or pH graded, and the titration volume of phenolic hydroxyl groups was used as the graded criterion for polyphenolic site enrichment. The boric acid anchored biochar is biochar particles, and the surface of the biochar particles is coupled with an aryl diazonium salt to form an aryl covalent graft layer, which carries aryl boric acid groups. The graded enriched polyphenol site humic acid is a polyphenol site enriched component obtained by graded treatment of humic acid. The arylboronic acid group is connected to the polyphenol sites of the polyphenol site enrichment component through a dynamic reversible covalent bond of borate ester. The polyphenol site enrichment component is distributed on the outer surface and pore area of ​​the borate anchored biochar in a dynamic reversible covalent bond manner of borate ester. The saline-alkali land conditioner has a compact internal and loose external distribution. The inner tight and outer loose distribution includes a higher borate ester bonding density on the outer surface and in the orifice region than the borate ester bonding density in the orifice region. The network structure formed by the dynamic reversible covalent bonds of borate esters in the outer surface and orifice region is a rearrangeable interface network. The rearrangeable interface network undergoes boronic acid ester bond exchange and is accompanied by interface segment conformational rearrangement in a saline-alkali environment. The internally tight and externally loose distribution is formed by a two-stage programmed process, including a first stage and a second stage; The first stage is carried out under low ionic strength and weak alkaline conditions, with the pH adjusted to 8-10. The borate ester bonding layer is preferentially formed on the outer surface and the pore opening area, and the formation density of the borate ester bonding layer is higher than that in the pore interior area. The second stage is carried out in a high ionic strength saline-alkali environment, using a simulated saline-alkali extract as a medium to maintain a weak alkaline pH and allow borate ester bond exchange to occur, forming a high-density borate ester bond layer on the outer surface and the pore area.

2. The biochar-humic acid-based saline-alkali land conditioner as described in claim 1, characterized in that: The boric acid-anchored biochar accounts for 70% to 98% of the total mass of the modifier, and the graded enrichment of polyphenol sites humic acid accounts for 2% to 30% of the total mass of the modifier.

3. The saline-alkali land conditioner based on biochar-humic acid as described in claim 1, characterized in that: The arylboronic acid group is derived from the aryl diazonium salt generated by the diazotization of aromatic amines with borate groups. The aryl diazonium salt undergoes a covalent grafting reaction with the surface of biochar to form an aryl covalent graft layer.

4. The biochar-humic acid-based saline-alkali land conditioner as described in claim 3, characterized in that: The aromatic amines with borate groups include any one or any combination of 4-aminophenylboronic acid and 3-aminophenylboronic acid.

5. The biochar-humic acid-based saline-alkali land conditioner as described in claim 1, characterized in that: The saline-alkali soil conditioner further includes a granulating binder phase, which is any one or any combination of water-soluble polysaccharides, lignin sulfonates, and sodium carboxymethyl cellulose, and the granulating binder phase accounts for 0.1% to 5% of the total mass of the conditioner.

6. A method for preparing a biochar-humic acid-based saline-alkali land conditioner as described in any one of claims 1 to 5, characterized in that, include: Step 1: Perform surface cleaning and activation treatment on the biochar to obtain activated biochar dispersion; Aromatic amines with borate groups are subjected to a diazotization reaction to obtain a solution of aryl diazonium salts containing borate groups; Step 2: In a reaction medium with water as the continuous phase, a solution of aryl diazonium salt containing borate groups is reacted with activated biochar dispersion to obtain borate-anchored biochar dispersion. Step 3: Perform a fractionation treatment on the humic acid to obtain a fractionated humic acid solution with polyphenol sites; under low ionic strength and weak alkaline conditions, conduct a contact reaction between the boric acid anchored biochar dispersion and the fractionated humic acid solution with polyphenol sites to obtain the first-stage boric ester bonded complex. Step 4: The first-stage borate ester bonded complex is subjected to salt-alkali aging treatment in a simulated salt-alkali extract to complete the exchange of borate ester bonds and obtain an interfacial network complex with a tight inner and loose outer distribution; the interfacial network complex is then washed, dried and granulated to obtain a saline-alkali soil conditioner.

7. The preparation method according to claim 6, characterized in that: The diazotization reaction was carried out at 0℃ to 10℃. The low ionic strength weak alkaline conditions include a pH of 8-10 and an ionic strength lower than that of the simulated salt-alkali extract; the simulated salt-alkali extract contains sodium chloride and sodium bicarbonate and maintains a weakly alkaline pH. The salt-alkali aging treatment is carried out in a simulated salt-alkali extract and is accompanied by borate ester bond exchange and interfacial conformation rearrangement.

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