Preparation method of carbon quantum dot reinforced subcritical artificial humic acid and use method of carbon quantum dot reinforced subcritical artificial humic acid in rice field

Abstract

The invention provides a method for preparing carbon quantum dot reinforced subcritical artificial humic acid and applying the carbon quantum dot reinforced subcritical artificial humic acid to a rice field, which comprises the following steps: collecting organic wastes, and drying, grinding and sieving the organic wastes to obtain pretreated raw materials; the preparation method comprises the following steps: mixing pretreated raw materials with water, reacting in a hydrothermal carbonization system at 200-280 DEG C for 1-3 hours, modifying through acid-base pretreatment, adjusting a reaction medium or an additive, and naturally cooling to obtain a natural substance subjected to hydrothermal carbonization; carrying out solid-liquid separation on the natural substance subjected to hydrothermal carbonization by using a 100-mesh coarse filter screen to obtain solid-phase hydrothermal carbon and liquid-phase artificial humic acid; carrying out purification treatment on the liquid-phase artificial humic acid for 48 hours by using a dialysis bag to obtain carbon quantum dots and characterizing the carbon quantum dots; the carbon quantum dot reinforced subcritical artificial humic acid is applied to a rice field, and is additionally applied in a fertilization period. Compared with a traditional composting technology, the scheme has the advantages that the carbon conversion rate is increased by 2-3 times, the soil fertility can be improved, and the rice yield is increased.

Description

Technical Field

[0001] The present invention relates to the field of soil fertilizer, and in particular to a method for preparing carbon quantum dot-enhanced subcritical artificial humic acid and using the same in a paddy field. Background Art

[0002] While excessive application of traditional chemical fertilizers can boost crop yields in the short term, long-term use can lead to soil compaction and a decrease in organic matter content. This can also cause the loss of nutrients like nitrogen and phosphorus, exacerbating non-point source pollution such as eutrophication. Furthermore, the massive generation and inefficient utilization of urban organic waste (such as vegetable waste, cow dung, sludge, and kitchen waste) not only wastes resources but also creates an environmental burden. There is an urgent need to develop technologies that combine waste resource utilization with soil improvement.

[0003] Traditional humic acid production technologies mostly use lignite and weathered coal as raw materials, which have problems such as limited raw material sources, long preparation cycles (usually requiring several months of composting), and high costs. In addition, the product has a low content of carbon quantum dots, making it difficult to achieve efficient regulation of soil microbial activity and nutrient cycling. Although the simple application of organic waste (such as straw and manure) can replenish soil organic matter, the imbalance in the carbon-nitrogen ratio and the low content of water-soluble organic carbon can easily lead to nutrient release being out of sync with crop demand, and the short-term fertilization effect is not significant. In addition, although existing farmland drainage management measures (such as intermittent irrigation) can reduce nitrogen and phosphorus losses, they lack coordinated design with soil fertilization, making it difficult to simultaneously achieve the dual goals of increasing productivity and reducing pollution. Summary of the Invention

[0004] The purpose of the invention is to provide a method for preparing carbon quantum dot-enhanced subcritical artificial humic acid and its use in rice fields, in order to solve at least one technical problem existing in the prior art.

[0005] Technical solution: a method for preparing carbon quantum dot-enhanced subcritical artificial humic acid, comprising: Raw material collection and pretreatment, collecting organic waste, the organic waste is at least one selected from leafy vegetables; drying and grinding and screening the organic waste to obtain pretreated raw materials; Hydrothermal carbonization reaction treatment: the pretreated raw materials are mixed with water in a certain mass ratio, placed in a hydrothermal carbonization system, reacted at 200°C-280°C in the hydrothermal carbonization system for 1-3 hours, and then cooled to obtain a hydrothermal carbonized natural product; Solid-liquid separation: use a 100-mesh coarse filter to separate the natural product after hydrothermal carbonization to obtain solid-phase hydrothermal carbon and liquid-phase artificial humic acid; Characterization and purification: Liquid artificial humic acid was purified using a dialysis bag for 48 hours to obtain carbon quantum dot components.

[0006] Furthermore, the organic waste in the raw material collection and pretreatment is leafy vegetables, and the leafy vegetable waste includes one or more of cabbage leaves, lettuce leaves, green vegetable leaves, spinach leaves, and lettuce leaves; the collected organic waste is placed in a constant temperature drying oven at 60°C and dried to constant weight, and then ground using a grinder and passed through a 60-mesh sieve to obtain the pretreated raw material.

[0007] Furthermore, when the pretreated raw materials are mixed with water, 10%-30% by volume of ethanol or acetone is added to the water to reduce the surface tension of the medium, promote the dispersion of the carbon precursor, reduce agglomeration, and improve the dispersibility and yield of the carbon quantum dots; 0.5%-1% of H2SO4 or 1%-2% of NaOH is added to adjust the pH of the reaction system to acidic or weakly alkaline; and small molecules of ethylenediamine and citric acid are added as templates or surface passivators for the growth of carbon quantum dots to control the particle size distribution and avoid the formation of large carbon particles.

[0008] Furthermore, the specific process of the hydrothermal carbonization reaction treatment is as follows: The reaction temperature is adjusted using a staged control process. The pretreated raw materials are mixed with water in a mass ratio of 1:5-1:10 and placed in a hydrothermal carbonization system. The reaction is first carried out at 220°C for 1 hour, then the temperature is raised to 260°C and the reaction is continued for 1 hour. After natural cooling, the hydrothermal carbonized natural product is obtained. The heating rate is controlled at 3-7°C / min and is fine-tuned according to the volume and heat transfer efficiency of the hydrothermal carbonization system. The temperature is 3-5°C / min for reactors below 100L, and is optimized to 5-7°C / min for large-scale industrial equipment. The reaction pressure is controlled at 1.5-8MPa and the reaction is maintained for 1-3 hours. The hydrothermal carbonization system uses an autoclave reactor equipped with a stirring device with a rotation speed of 300-500 rpm to ensure uniform mixing of the raw materials and the medium and avoid local overheating that causes carbon particle agglomeration; After the reaction is completed, the temperature and pressure are quickly lowered within 10 minutes through a water cooling system to inhibit further carbonization of the carbon quantum dots; the reaction liquid is filtered while hot to remove unreacted solid residues, and the filtrate is purified by centrifugation at 10,000 rpm for 15 minutes or dialysis with a molecular weight cutoff of 500-3,000 Da to obtain a carbon quantum dot solution with a mass ratio greater than 30%.

[0009] In addition, the present invention also provides a method for using carbon quantum dot enhanced subcritical artificial humic acid in rice fields. The application method of carbon quantum dot enhanced subcritical artificial humic acid is foliar spraying, root irrigation, drip irrigation, or a combination thereof. Among them, the foliar spraying method is to dilute the carbon quantum dot enhanced subcritical artificial humic acid to a mass concentration of 0.5%-1%, spray it once during the tillering stage and the booting stage of rice, with a dosage of 50-100L per mu each time. The spraying time is in the early morning or evening to avoid strong light exposure that may cause the solution to evaporate too quickly; The root irrigation method is to dilute the carbon quantum dot enhanced subcritical artificial humic acid to a mass concentration of 1%-2%. The root irrigation treatment is carried out 10-15 days after the rice is transplanted, and 100-200 mL is applied to each plant to allow the solution to evenly penetrate around the root system. The drip irrigation method involves mixing carbon quantum dot-enhanced subcritical artificial humic acid with irrigation water at a ratio of 1:500-1:1000. The solution is then applied in batches throughout the rice's growth period through a drip irrigation system, with a dosage of 3-5 L per mu each time. The drip irrigation rate is controlled at 1-2 L / min. The solution is filtered through a 100-200 mesh filter at three stages, with a concentration of 0.1%-0.2% and a drip irrigation flow rate of 1-2 L / min. The solution is rinsed with clean water before and after application and chemically cleaned every 20-30 days. The system uses a DN32-DN50 main line, a 12-16 mm inner diameter drip tape, and 0.5 mm pore emitters. The system also takes measures to adjust the pipe diameter, water quality, and concentration, supplemented by real-time monitoring of flow and pressure to effectively prevent clogging. The mixing method can be selected according to needs, but the total application amount of carbon quantum dot-enhanced subcritical artificial humic acid during the entire growth period of the rice field shall not exceed 10L per mu to prevent and control the risks of soil salt accumulation and root osmotic pressure imbalance damage caused by excessive application, as well as the risk of ecotoxicity caused by excessive enrichment of carbon quantum dots in the soil or crops, to ensure the stability of the rice field ecosystem and the safety of rice growth.

[0010] Furthermore, this method is suitable for rice fields with medium to low soil fertility, acidic to neutral pH between 5.5-7.5, conventional irrigation conditions, and problems of continuous cropping or degradation. These rice fields can use carbon quantum dots to enhance subcritical artificial humic acid to supplement organic carbon sources and improve soil structure and microbial environment; while rice fields with high salinity, waterlogging or poor drainage with pH>8.5, excessive heavy metals in the soil, and the use of strong oxidizing pesticides or fertilizers are not suitable for use. The high salinity and alkalinity environment can easily lead to the agglomeration and failure of carbon quantum dots, and waterlogging can easily cause soil hypoxia and the generation of harmful substances. Excessive heavy metals may increase the enrichment risk due to the chelation of carbon quantum dots, and strong oxidizing substances will destroy the carbon quantum dots and humic acid structure, affecting the application effect and ecological safety.

[0011] Furthermore, paddy field drainage needs to be optimized in conjunction with the application characteristics of carbon quantum dot enhanced subcritical artificial humic acid. Specifically, before application, ensure that the paddy field has a complete field drainage system. Drainage ditches 30 to 50 cm deep and 20 to 30 cm wide are dug around the field and connected to the main drainage channel to ensure smooth drainage. After application, if there is rainfall or irrigation, drainage must be carried out in time to keep the field water level no more than 5 cm to avoid water accumulation that may dilute the concentration of carbon quantum dot enhanced subcritical artificial humic acid solution or cause soil hypoxia. For paddy fields with heavy clay soil, a concealed pipe drainage system can be laid during tillage, with a pipe diameter of 5 to 8 cm, a buried depth of 40 to 60 cm, and a spacing of 8 to 12 m to accelerate the infiltration and drainage of excess water and prevent excessive enrichment of carbon quantum dots in the root zone due to poor drainage. When applied after the rice tillering period, drainage must be synchronized with the field drying operation. During the field drying period, the field surface should be kept moist without water accumulation, to promote the adsorption and fixation of carbon quantum dots and artificial humic acid by soil colloids, improve utilization efficiency and avoid loss with water, so as to reduce the risk of non-point source pollution.

[0012] Beneficial effects: achieving efficient conversion of waste into resources: through a hydrothermal reaction at 200-280°C (pressure 1.5-8MPa), 30%-40% of the carbon in organic waste is converted into a water-soluble carbon quantum dot and humic acid complex, increasing the carbon conversion rate by 2-3 times compared to traditional composting technology; synergistic strengthening effect of carbon quantum dots: the prepared carbon quantum dots (particle size <5nm) have fluorescent properties and strong antioxidant capacity, which can promote the decomposition of organic matter and nutrient activation by regulating soil microbial communities (such as increasing the abundance of Proteobacteria and Acidobacteria), and increase the effective phosphorus and potassium content in the soil by 15%-30% compared to single humic acid treatment; systematic prevention and control of non-point source pollution: through the application model of "three fertilization periods and root irrigation + 7 days of no drainage", the utilization rate of nitrogen and phosphorus nutrients is increased from 30%-40% in traditional fertilization to 50%-60%, while reducing the loss of total nitrogen in farmland drainage by 40%-60%, achieving integrated control of "fertilization-yield increase-pollution control". BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 1 is a transmission electron micrograph of carbon dots in artificial humic acid of each treatment group in the examples of the present invention.

[0014] Figure 2 is the weight of the fertility quality index in the embodiment of the present invention, and the soil quality index score chart from 2021 to 2024.

[0015] Figure 3 is the weight of the yield quality index in the embodiment of the present invention, and the rice yield quality index score chart from 2021 to 2024.

[0016] Figure 4 It is a three-dimensional fluorescence spectrum diagram of the products of the electrodialysis desalination chamber and the concentration chamber under different treatment degrees in the embodiment of the present invention.

[0017] Figure 5 3 is a diagram showing changes in DOM during electrodialysis treatment in an embodiment of the present invention.

[0018] Figure 6 3 is a graph of the electrical conductivity of the rhizosphere soil in an embodiment of the present invention.

[0019] Figure 7 Graph showing urease activity in rhizosphere soil according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] A method for preparing carbon quantum dot-enhanced subcritical artificial humic acid, comprising: Raw material collection and pretreatment: collecting organic waste, wherein the organic waste is at least one selected from the group consisting of waste vegetables, cow dung, pig dung, sludge, and kitchen waste; drying, grinding, and screening the organic waste to obtain pretreated raw materials; Hydrothermal carbonization reaction treatment: the pretreated raw materials are mixed with water in a certain mass ratio, placed in a hydrothermal carbonization system, reacted at 200°C-280°C in the hydrothermal carbonization system for 1-3 hours, and then cooled to obtain a hydrothermal carbonized natural product; Solid-liquid separation: use a 100-mesh coarse filter to separate the natural product after hydrothermal carbonization to obtain solid-phase hydrothermal carbon and liquid-phase artificial humic acid; Characterization and purification: Liquid artificial humic acid was purified using a dialysis bag for 48 hours to obtain carbon quantum dot components.

[0021] Furthermore, the organic waste in the raw material collection and pretreatment is leafy vegetables, and the leafy vegetable waste includes one or more of cabbage leaves, lettuce leaves, green vegetable leaves, spinach leaves, and lettuce leaves; the collected organic waste is placed in a constant temperature drying oven at 60°C and dried to constant weight, then ground using a grinder and passed through a 60-mesh sieve to obtain the pretreated raw material.

[0022] Furthermore, when the pretreated raw materials are mixed with water, 10%-30% by volume of ethanol or acetone is added to the water to reduce the surface tension of the medium, promote the dispersion of the carbon precursor, reduce agglomeration, and improve the dispersibility and yield of the carbon quantum dots; 0.5%-1% of H2SO4 or 1%-2% of NaOH is added to adjust the pH of the reaction system to acidic or weakly alkaline; and small molecules of ethylenediamine and citric acid are added as templates or surface passivators for the growth of carbon quantum dots to control the particle size distribution and avoid the formation of large carbon particles.

[0023] Furthermore, the specific process of the hydrothermal carbonization reaction treatment is as follows: The reaction temperature was adjusted using a staged control process. The pretreated raw materials were mixed with water in a mass ratio of 1:5-1:10 and placed in a hydrothermal carbonization system. The reaction was first carried out at 220°C for 1 hour, then the temperature was raised to 260°C for a further 1 hour, and the hydrothermal carbonized product was obtained after natural cooling. The heating rate was controlled at 3-7°C / min and fine-tuned according to the volume and heat transfer efficiency of the hydrothermal carbonization system. The heating rate was 3-5°C / min for reactors under 100 L and optimized to 5-7°C / min for large-scale industrial equipment. The reaction pressure was controlled at 1.5-8 MPa and the reaction was maintained for 1-3 hours. The hydrothermal carbonization system uses an autoclave reactor equipped with a stirring device with a rotation speed of 300-500 rpm to ensure uniform mixing of the raw materials and the medium and avoid local overheating that causes carbon particle agglomeration; After the reaction is completed, the temperature and pressure are quickly lowered within 10 minutes through a water cooling system to inhibit further carbonization of the carbon quantum dots; the reaction solution is filtered while hot to remove unreacted solid residues, and the filtrate is purified by centrifugation at 10,000 rpm for 15 minutes or dialysis with a molecular weight cutoff of 500-3000 Da to obtain a carbon quantum dot solution with a mass ratio greater than 30%.

[0024] In addition, the present invention also provides a method for using carbon quantum dot enhanced subcritical artificial humic acid in rice fields. The application method of carbon quantum dot enhanced subcritical artificial humic acid is foliar spraying, root irrigation, drip irrigation, or a combination thereof. Among them, the foliar spraying method is to dilute the carbon quantum dot enhanced subcritical artificial humic acid to a mass concentration of 0.5%-1%, spray it once during the tillering stage and the booting stage of rice, with a dosage of 50-100 L per mu each time. The spraying time is in the early morning or evening to avoid strong light exposure that may cause the solution to evaporate too quickly; The root irrigation method involves diluting carbon quantum dot-enhanced subcritical artificial humic acid to a mass concentration of 1%-2%. Root irrigation is performed 10-15 days after rice transplanting, with 100-200 mL applied to each plant to ensure that the solution evenly penetrates around the root system. The drip irrigation method involves mixing carbon quantum dot-enhanced subcritical artificial humic acid with irrigation water at a ratio of 1:500-1:1000. The solution is then applied in batches throughout the rice's growth period through a drip irrigation system, with a dosage of 3-5 L per mu each time. The drip irrigation rate is controlled at 1-2 L / min. The solution is filtered through a 100-200 mesh filter at three stages, with a concentration of 0.1%-0.2% and a drip irrigation flow rate of 1-2 L / min. The solution is rinsed with clean water before and after application and chemically cleaned every 20-30 days. The system uses a DN32-DN50 main line, a 12-16 mm inner diameter drip tape, and 0.5 mm pore emitters. The system also adjusts the pipe diameter, water quality, and concentration, along with real-time flow and pressure monitoring, to effectively prevent clogging. The mixing method can be selected according to needs, but the total application amount of carbon quantum dot-enhanced subcritical artificial humic acid during the entire growth period of the rice field shall not exceed 10 L per mu to prevent and control the risks of soil salt accumulation and root osmotic pressure imbalance damage caused by excessive application, as well as the risk of ecotoxicity caused by excessive enrichment of carbon quantum dots in the soil or crops, to ensure the stability of the rice field ecosystem and the safety of rice growth.

[0025] Furthermore, this method is suitable for rice fields with medium to low soil fertility, acidic to neutral pH between 5.5-7.5, conventional irrigation conditions, and problems of continuous cropping or degradation. These rice fields can use carbon quantum dots to enhance subcritical artificial humic acid to supplement organic carbon sources and improve soil structure and microbial environment; while rice fields with high salinity, waterlogging or poor drainage with pH>8.5, excessive heavy metals in the soil, and the use of strong oxidizing pesticides or fertilizers are not suitable for use. The high salinity and alkalinity environment can easily lead to the aggregation and failure of carbon quantum dots, and waterlogging can easily cause soil hypoxia and the generation of harmful substances. Excessive heavy metals may increase the enrichment risk due to the chelation of carbon quantum dots, and strong oxidizing substances will destroy the carbon quantum dots and humic acid structure, affecting the application effect and ecological safety.

[0026] Furthermore, the drainage of rice fields needs to be optimized in conjunction with the application characteristics of carbon quantum dot enhanced subcritical artificial humic acid, including: ensuring that the rice fields have a complete field drainage system before application, digging drainage ditches with a depth of 30 to 50 cm and a width of 20 to 30 cm around the fields, and connecting them to the main drainage channel to ensure smooth drainage; after application, if there is rainfall or irrigation, drainage must be carried out in time to keep the field water level no more than 5 cm to avoid water accumulation leading to dilution of the concentration of carbon quantum dot enhanced subcritical artificial humic acid solution or soil hypoxia; for rice fields with heavy clay soil, a concealed pipe drainage system can be laid during cultivation, with a pipe diameter of 5 to 8 cm, a buried depth of 40 to 60 cm, and a spacing of 8 to 12 m, used to accelerate the infiltration and drainage of excess water, and prevent excessive enrichment of carbon quantum dots in the root zone due to poor drainage; when applied after the rice tillering period, it is necessary to combine it with the field drying operation and drain the water simultaneously. During the field drying period, the field surface should be kept moist without water accumulation, so as to promote the adsorption and fixation of carbon quantum dots and artificial humic acid by soil colloids, improve utilization efficiency and avoid loss with water, so as to reduce the risk of non-point source pollution.

[0027] In order to further elaborate on the detailed process and effects of this scheme, the preparation of artificial humic acid prepared with different raw materials was analyzed and experimentally demonstrated from all aspects. The artificial humic acid in Example 1 was prepared using cow dung and tail vegetables as raw materials, the artificial humic acid in Example 2 was prepared using urban organic waste (i.e., sludge and kitchen waste) as raw materials, and the artificial humic acid in Example 3 was prepared using pig manure as raw material.

[0028] Example 1 1. Preparation of subcritical artificial humic acid enhanced by carbon quantum dots: Cow dung and tail vegetables were used as raw materials, respectively, and reacted in a hydrothermal carbonization system at 220 ℃ and 260 ℃ for 1 hour; in the hydrothermal carbonization (HTC), the material ratio of cow dung or tail vegetables to water was 1kg:10L, and the pressure in the reactor was 1.5 MPa. Solid hydrothermal carbon and liquid artificial humic acid were obtained. The cow dung-derived artificial humic acid prepared at 220 ℃ and 260 ℃ were respectively recorded as CM220 and CM260; the tail vegetable-derived artificial humic acid prepared at 220 ℃ and 260 ℃ were respectively recorded as GV220 and GV260. Table 1 and Figure 1 The basic physicochemical properties of the artificial humic acid are described.

[0029] Table 1 Basic physical and chemical properties of artificial humic acid derived from feces and vegetable waste experimental group pH Ζ potential TN NH4+-N NO3--N DOC AP AK CDs ratio CM220 7.34 10.73 368.17 28.95 357.33 7263.88 0.57 1130.55 12.1 CM260 6.60 14.50 364.33 28.93 334.33 8670.72 0.11 951.44 13.0 GV220 7.83 13.63 292.93 114.03 100.33 10002.33 1.77 2037.71 36.8 GV260 8.39 17.80 305.57 95.20 205.67 9125.33 1.53 1920.72 35.7 2. Daejeon in-situ verification: An in situ field experiment was conducted at a rice-growing cooperative in Nanjing, Jiangsu Province, from 2021 to 2024. The rice variety planted was Nanjing 46, with the planting period lasting from June to October each year. Six treatments were employed: no fertilization (CK0), conventional fertilization (CKU), and conventional fertilization combined with four subcritical fertilizers (CM220, CM260, GV220, and GV260). Eighteen bottomless polyvinyl chloride (PVC) tubes (40 cm in diameter, 40 cm in height, inserted 20 cm into the soil) were arranged in a 6×3 grid, with 80 cm between pairs of tubes. The tubes were randomly placed to minimize interference between treatments. Initially, six rice plants were planted in each tube, and ultimately three plants with similar growth conditions were selected to record yield and other indicators. During the rice cultivation process, the conventional fertilization rates were: 270 kg / ha of nitrogen fertilizer, 90 kg / ha of phosphorus fertilizer, and 90 kg / ha of potassium fertilizer. The fertilizers used included urea, superphosphate, and potassium chloride. The nitrogen fertilizer was applied in a ratio of 3:3:4 at the base, tillering, and heading stages. Phosphorus and potassium fertilizers were applied once at the base fertilizer application, while nitrogen fertilizer was applied once at the tillering and heading stages. Therefore, 200 mL of subcritical fertilizer was added to the rice fields at the base, tillering, and heading stages. The fertilization method followed the traditional rice cultivation practices of Jiangsu Province, and the irrigation and drainage of the rice fields also referred to the traditional rice cultivation methods.

[0030] 3. Yield and soil fertility assessment: like Figure 2Each year, at rice maturity, three samples are collected from rice husks and rice panicles and allowed to dry naturally to record yield indicators: panicle weight, number of panicles, number of rice grains per panicle, and seed set rate. After grinding, the straw and rice samples are then measured for total nitrogen (TN), total phosphorus (TP), and total potassium (TK) content using sulfuric acid digestion-Kjeldahl method, sulfuric acid digestion-molybdenum antimony colorimetry, and sulfuric acid digestion-flame photometry, respectively. Based on these yield indicators, a comprehensive assessment of the rice yield quality index (YQI) from 2021 to 2024 was conducted, with scores categorized into four levels: medium-high (M-HQ, 0.6-0.7), medium (MQ, 0.4-0.6), medium-low (M-LQ, 0.3-0.4), and low (LQ, <0.3).

[0031] The soil quality index (SQI) for 2021 to 2024 was a comprehensive assessment of soil properties based on the above-mentioned measurements, with scores categorized into four levels: high fertility (HF, >0.8), medium-high fertility (M-HQ, 0.6-0.8), medium fertility (MF, 0.4-0.6), and low fertility (LF, <0.4).

[0032] Example 2 1. Preparation of subcritical artificial humic acid enhanced by carbon quantum dots: The resulting carbon solution was desalted to produce low-desalination carbon solution and high-desalination carbon solution, respectively. Electrodialysis desalination treatment parameters included a DC voltage of 30 V, a peristaltic pump at 60 RPM, an electrodialysis module with five cathodes, five anodes, and nine 5 cm × 10 cm compartments. Desalination took 30 minutes to produce a low-desalination carbon solution, or 75 minutes to produce a high-desalination carbon solution. Desalination was performed on 1 L of carbon solution at a time. The low-desalination carbon solutions obtained from multiple desalination operations were mixed to produce the final low-desalination carbon solution, while the high-desalination carbon solutions obtained from multiple desalination operations were mixed to produce the final high-desalination carbon solution. The physical and chemical properties of the undesalted, low-desalination, and high-desalination carbon solutions were determined.

[0033] 2. Potted plant test verification: The nitrogen application rate was 180 kg / ha (i.e., the total N, P, and K application rates were the same as in the CKU group). In this part of the experiment, HAP (non-desalinated charcoal), LD-HAP (low-desalinated charcoal), and HD-HAP (high-desalinated charcoal) were used. Nitrogen replacement rates ranged from 24% to 40%. Daily water management used tap water irrigation. CKU served as a control group with conventional fertilization; HAP was a control group with non-desalinated charcoal; LV and HV were treated with low-desalinated charcoal and high-desalinated charcoal, respectively, with the same charcoal application rates for the LV and HV treatments as for the HAP treatment; LN and HN were treated with low-desalinated and high-desalinated charcoal, respectively, with the charcoal application rates for the IN and HN treatments controlled to achieve the same nitrogen replacement rates as in the HAP group.

[0034] like Figure 4 During the electrodialysis desalination process, as the desalination degree increased, the fluorescence peak of the carbon solution in the electrodialysis desalination chamber decreased from 3148 to 2344. In contrast, the fluorescence peak of the product in the concentrating chamber gradually increased. When the desalination degree reached 90%, the fluorescence peak in the desalination chamber reached 2419. This indicates that during the electrodialysis desalination process, not only are inorganic salt ions removed, but some dissolved organic matter also migrates across the membrane from the desalination chamber to the concentrating chamber.

[0035] like Figure 5 , through Figure 4 PARAFAC analysis of the three-dimensional fluorescence spectrum showed that the products of the electrodialysis desalination chamber and the concentration chamber under different treatment degrees mainly included three types of DOM components. C1 and C3 are humic acids, which are high molecular weight humic substances. The complex aromatic structure of organic matter has a high degree of humification and represents stable or long-term degradable organic matter; C2 is fulvic acid, a low molecular weight humic substance with a low degree of humification and a simpler structure. Figure 5 The results reflect that the relative amount of DOM components in pig manure hydrothermal charcoal liquid that migrate across the membrane from the desalination compartment to the concentration compartment at different desalination degrees is proportional to the desalination degree. It can also reflect the relative order of transfer of different DOM components. Combined with the PARAFAC analysis results, it is mainly related to the molecular weight, and low molecular weight will migrate across the membrane first.

[0036] After two consecutive lettuce cropping seasons, the main physical and chemical properties of the soil were as follows: HAP, due to its lack of desalination, contains a large amount of inorganic ions, which significantly increases EC; desalination treatment (especially high desalination) removes ions, which reduces EC. At the same desalination level, the EC of the LN / HN group was lower than that of the LV / HV group (at the same application rate) due to the controlled use of liquid carbon (maintaining the nitrogen replacement rate). Figure 6 The urease activity of the desalination treatment group (especially LV and HV) may be higher than that of the non-desalination group (HAP) and the control group (CKU). Urease can catalyze the decomposition of urea into ammonia. The increased activity indicates that the soil nitrogen metabolism is more active, which may be related to the organic nitrogen or DOM (such as humic acid substances) retained in the desalination charcoal liquid promoting microbial activity. Figure 7, the enzyme activity of the high desalination group (HV, HN) may be slightly higher than that of the low desalination group (LV, LN), suggesting that moderate desalination may be more conducive to maintaining soil enzyme activity.

[0037] Therefore, desalinated charcoal significantly promotes vegetable growth by reducing soil salt damage (EC), activating the nitrogen cycle (increasing urease activity), and optimizing DOM composition (retaining humus). High desalination combined with controlled fertilization (HN group) offers both environmental friendliness and yield-enhancing potential, making it the optimal resource for pig manure hydrothermal charcoal.

[0038] Test method (all the above examples adopt this test method) Nitrogen (N) was measured using a continuous flow analyzer from San++ (Skara, the Netherlands). Dissolved organic carbon (DOC) concentration was measured after dilution using a Multi N / C 2100 TOC analyzer from Germany. Available phosphorus (AP) and available potassium (AK) were measured using an Optima TM8000 ICP-OES from PerkinElmer (USA).

[0039] Carbon quantum dots were obtained by purifying subcritical fertilizer for 48 hours using dialysis tubing (molecular weight cutoff: 500 Da, Solarbio, China). Transmission electron microscopy (TEM) images were acquired using a JEM-2100 electron microscope (JEOL, Tokyo, Japan) at an accelerating voltage of 200 kV. Fluorescence spectra were measured using a fluorescence spectrometer (Model F-7000, Hitachi, Japan).

[0040] -N, DOC, AP, AK, calculate soil quality index SQI.

[0041] Rice yield assessment: measure the weight of rice ears, number of rice ears, number of rice grains per ear, seed setting rate, and calculate the yield quality index (YQI).

[0042] Instruments and equipment: pH meter, elemental analyzer, continuous flow analyzer, ICP-OES.

[0043] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the scope of protection of the present invention.

Claims

1. A method for preparing carbon quantum dot-enhanced subcritical artificial humic acid, characterized in that: The following steps are involved: Raw material collection and pretreatment, collecting organic waste, the organic waste is at least one selected from leafy vegetables; drying and grinding and screening the organic waste to obtain pretreated raw materials; Hydrothermal carbonization reaction treatment: the pretreated raw materials are mixed with water in a certain mass ratio, placed in a hydrothermal carbonization system, reacted at 200°C-280°C in the hydrothermal carbonization system for 1-3 hours, and then cooled to obtain a hydrothermal carbonized natural product; Solid-liquid separation: use a 60-100 mesh filter to separate the natural product after hydrothermal carbonization to obtain solid-liquid hydrothermal carbon and liquid-phase artificial humic acid; Characterization and purification: Liquid phase artificial humic acid was purified using a dialysis bag for 24-48 hours to obtain a carbon quantum dot component.

2. The method for preparing carbon quantum dot-enhanced subcritical artificial humic acid according to claim 1, characterized in that: The organic waste in the raw material collection and pretreatment is leafy vegetables, and the leafy vegetable waste includes one or more of cabbage leaves, lettuce leaves, green vegetable leaves, spinach leaves, and lettuce leaves; the collected organic waste is placed in a constant temperature drying oven at 60°C and dried to constant weight, and then ground using a grinder and passed through a 60-mesh sieve to obtain the pretreated raw material.

3. The method for preparing carbon quantum dot-enhanced subcritical artificial humic acid according to claim 1, characterized in that: When the pretreated raw materials are mixed with water, 10%-30% by volume of ethanol or acetone is added to the water to reduce the surface tension of the medium, promote the dispersion of the carbon precursor, reduce agglomeration, and improve the dispersion and yield of carbon quantum dots; 0.5%-1% H2SO4 or 1%-2% NaOH is added to adjust the pH of the reaction system to acidic or weakly alkaline; small molecules of ethylenediamine and citric acid are added as templates or surface passivators for the growth of carbon quantum dots to control the particle size distribution and avoid the formation of large carbon particles.

4. The method for preparing carbon quantum dot-enhanced subcritical artificial humic acid according to claim 1, characterized in that: The specific process of the hydrothermal carbonization reaction treatment is as follows: The reaction temperature was adjusted using a staged control process. The pretreated raw materials were mixed with water in a mass ratio of 1:5-1:10 and placed in a hydrothermal carbonization system. The reaction was first carried out at 220°C for 1 hour, then the temperature was raised to 260°C for another 1 hour, and the hydrothermal carbonized product was obtained after natural cooling. The heating rate was controlled at 3-7°C / min and fine-tuned according to the volume and heat transfer efficiency of the hydrothermal carbonization system. The heating rate was 3-5°C / min for reactors below 100 L and optimized to 5-7°C / min for large-scale industrial equipment. The reaction pressure was controlled at 1.5-8 MPa and the reaction was maintained for 1-3 hours. The hydrothermal carbonization system uses an autoclave reactor equipped with a stirring device with a rotation speed of 300-500 rpm to ensure uniform mixing of the raw materials and the medium and avoid local overheating that causes carbon particle agglomeration; After the reaction is completed, the temperature and pressure are quickly lowered within 10-30 minutes through a water cooling system to inhibit further carbonization of the carbon quantum dots; the reaction liquid is filtered while hot to remove unreacted solid residues, and the filtrate is purified by centrifugation at 10,000 rpm for 15 minutes or dialysis with a molecular weight cutoff of 500-3000 Da to obtain a carbon quantum dot suspension with a mass ratio greater than 30%.

5. A method for using carbon quantum dot enhanced subcritical artificial humic acid in rice fields, characterized in that: The application method of carbon quantum dot enhanced subcritical artificial humic acid is foliar spraying, root irrigation, drip irrigation, or a combination thereof; Among them, the foliar spraying method is to dilute the carbon quantum dot enhanced subcritical artificial humic acid to a mass concentration of 0.5%-1%, spray it once during the tillering stage and the booting stage of rice, with a dosage of 50-100 L per mu each time. The spraying time is in the early morning or evening to avoid strong light exposure that may cause the solution to evaporate too quickly; The root irrigation method is to dilute the carbon quantum dot enhanced subcritical artificial humic acid to a mass concentration of 1%-2%. The root irrigation treatment is carried out 10-15 days after rice transplanting, with 20-40 L per mu of irrigation, so that the solution can evenly penetrate around the root system. The drip irrigation method involves mixing carbon quantum dot-enhanced subcritical artificial humic acid with irrigation water at a ratio of 1:500-1:1000. The solution is then applied in batches throughout the rice's growth period through a drip irrigation system, with a dosage of 3-5 L per mu each time. The drip irrigation rate is controlled at 1-2 L / min. The solution is filtered through a 100-200 mesh filter at a three-stage concentration of 0.1%-0.2%, with a drip irrigation flow rate of 1-2 L / min. The solution is rinsed with clean water before and after application and chemically cleaned every 20-30 days. The system uses a DN32-DN50 main line, a 12-16 mm inner diameter drip tape, and 0.5 mm pore emitters. The system also adjusts the pipe diameter, water quality, and concentration, along with real-time flow and pressure monitoring, to effectively prevent clogging. The mixing method can be selected according to needs, but the total application amount of carbon quantum dot-enhanced subcritical artificial humic acid during the entire growth period of the rice field shall not exceed 10 L per mu to prevent and control the risks of soil salt accumulation and root osmotic pressure imbalance damage caused by excessive application, as well as the risk of ecotoxicity caused by excessive enrichment of carbon quantum dots in the soil or crops, to ensure the stability of the rice field ecosystem and the safety of rice growth.

6. The method for using carbon quantum dot enhanced subcritical artificial humic acid in rice fields according to claim 5, characterized in that: This method is suitable for rice fields with medium to low soil fertility, acidic to neutral pH between 5.5-7.5, conventional irrigation conditions, and problems of continuous cropping or degradation. These rice fields can use carbon quantum dots to enhance subcritical artificial humic acid to supplement organic carbon sources and improve soil structure and microbial environment; however, rice fields with high salinity and alkalinity, waterlogging or poor drainage with pH>8.5, excessive heavy metals in the soil, and the use of strong oxidizing pesticides or fertilizers are not suitable for use. The high salinity and alkalinity environment can easily lead to the aggregation and failure of carbon quantum dots, and waterlogging can easily cause soil hypoxia and the generation of harmful substances. Excessive heavy metals may increase the enrichment risk due to the chelation of carbon quantum dots, and strong oxidizing substances will destroy the carbon quantum dots and humic acid structure, affecting the application effect and ecological safety.

7. The method for using carbon quantum dot enhanced subcritical artificial humic acid in rice fields according to claim 5, characterized in that: The drainage of rice fields needs to be optimized in conjunction with the application characteristics of carbon quantum dot enhanced subcritical artificial humic acid, including: before application, ensure that the rice fields have a complete field drainage system, dig drainage ditches with a depth of 30 to 50 cm and a width of 20 to 30 cm around the fields, and connect them to the main drainage channel to ensure smooth drainage; after application, if there is rainfall or irrigation, drainage must be carried out in time to keep the field water level no more than 5 cm to avoid water accumulation leading to dilution of the concentration of carbon quantum dot enhanced subcritical artificial humic acid solution or soil hypoxia; for rice fields with heavy clay soil, a concealed pipe drainage system can be laid during cultivation, with a pipe diameter of 5 to 8 cm, a buried depth of 40 to 60 cm, and a spacing of 8 to 12 m, used to accelerate the infiltration and drainage of excess water, and prevent excessive enrichment of carbon quantum dots in the root zone due to poor drainage; when applied after the rice tillering period, it is necessary to combine it with the field drying operation and drain the water simultaneously. During the field drying period, the field surface should be kept moist without water accumulation, so as to promote the adsorption and fixation of carbon quantum dots and artificial humic acid by soil colloids, improve utilization efficiency and avoid loss with water, so as to reduce the risk of non-point source pollution.

Images