Carbon-based calcium peroxide material with oxygen slow-release function as well as preparation method and application of carbon-based calcium peroxide material

Abstract

The invention belongs to the technical field of biochar oxygen release materials, and particularly relates to a carbon-based calcium peroxide material with an oxygen slow release function as well as a preparation method and application of the carbon-based calcium peroxide material. Silicon-rich agricultural wastes are converted into biochar through controllable pyrolysis, mesoporous biochar is prepared by regulating and controlling the pore structure of the biochar, phosphorus-rich biochar is prepared by combining phosphate modification, and finally, the carbon-based calcium peroxide material with the slow-release oxygen function is obtained by compounding the phosphorus-rich biochar with calcium peroxide. Oxygen can be continuously and stably released into the soil, and meanwhile, the phosphorus-rich biochar can also provide phosphorus nutrients to promote the growth of the rice. The material can be widely applied to improvement of gleying rice fields, effectively solves the problem of soil anoxia, improves soil fertility and rice yield, and has the characteristics of environmental protection, economy and high efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of biochar oxygen-release materials, and particularly relates to a carbon-based calcium peroxide material with a slow-release oxygen function, a preparation method thereof, and an application thereof. Background Art

[0002] Gley paddy fields are widely distributed in southern China, accounting for about one-third of the total paddy field area, and are particularly common in provinces such as Hunan, Hubei, and Guangdong. Although the soil of these paddy fields is rich in organic matter and nutrients, due to long-term waterlogging, the oxygen content in the soil decreases, and the redox potential decreases, resulting in the accumulation of a large amount of harmful reducing substances. These substances not only destroy the biological activity of the soil, reduce the availability of nutrients, but also inhibit the growth of rice, seriously limiting the rice yield. Traditional improvement measures, such as water conservancy project construction and land use pattern adjustment, although they can solve the problem, are often costly and have short-lived effects. For emerging improvement methods, such as applying a slow-release oxygen material with calcium peroxide as the core to increase the dissolved oxygen content in gley paddy fields, although they can precisely control the oxygen supply in the soil, their preparation process is complex, the cost is high, and they may have an adverse impact on the soil environment. Therefore, it is necessary to find an economical and environmentally friendly improvement method to improve the soil quality and rice yield of gley paddy fields.

[0003] A large amount of agricultural waste is generated in China every year, and through pyrolysis technology, it can be converted into biochar with environmental benefits and economic value. Due to its large specific surface area, low density, high stability, strong adsorption capacity, excellent chemical stability, and anti-microbial degradation ability, etc., biochar has been widely used in the fields of agriculture and environmental protection. Recent studies have found that biochar can be used as a carrier for calcium peroxide, and its good chemical stability and large specific surface area help to solve the agglomeration problem of calcium peroxide, thereby increasing its oxygen release amount. At the same time, the hydrophobicity and porosity of biochar may also reduce the mass transfer efficiency of water and prolong the oxygen release time of calcium peroxide. Although mixing biochar with calcium peroxide or using biochar as a coating material can improve the oxygen release performance, this method may result in a large oxygen release amount of calcium peroxide, but its effective utilization rate is not high. In particular, calcium hydroxide generated by the reaction of calcium peroxide with water will form a covering layer on its surface, hindering the further reaction inside calcium peroxide, thereby reducing its utilization efficiency. Therefore, studying how to effectively combine biochar with calcium peroxide to enhance the oxygen release performance of calcium peroxide and improve its utilization efficiency has become an important topic.

[0004] In the prior art, Patent CN2016102291547 discloses a slow-release oxidant with calcium peroxide as the matrix and polyethylene as the coating and its preparation method, which can effectively solve the problem of oxygen release time of calcium peroxide in gley paddy fields and improve the growth environment of rice in gley paddy fields. However, in the production process of the slow-release oxidant, the granulation and coating steps will cause a loss of 8.3% of calcium peroxide, mainly due to its hydrolysis in water and high-temperature treatment. Large-scale industrial production may further increase the loss. In addition, the xylene solvent used in production is toxic and carcinogenic, and the non-degradability of polyethylene may lead to soil pollution and ecological problems. A paper "Controlled synthesis of innovative carbon-based CaO2 materials with boosted oxygen release performance in the aqueous environment" discloses a novel carbon-based calcium peroxide material as an oxygen-releasing agent in the process of groundwater bioremediation. However, although the modification of biochar significantly increases the mass fraction of calcium peroxide in the carbon-based calcium peroxide material, compared with the oxygen-releasing materials prepared from pure calcium peroxide and raw biochar, the oxygen release rate of the carbon-based calcium peroxide material prepared from modified biochar is too fast, which instead limits its ability to slowly release oxygen. Summary of the Invention

[0005] Aiming at the above problems, the purpose of the present invention is to provide a carbon-based calcium peroxide material with slow-release oxygen function, its preparation method and application.

[0006] The technical content of the present invention is as follows:

[0007] The present invention provides a preparation method of a carbon-based calcium peroxide material with slow-release oxygen function, including the following steps:

[0008] 1) Preparation of mesoporous biochar

[0009] Take silicon-rich biochar, mix it evenly with Na2CO3 and K2CO3, then carry out calcination, and take it out after natural cooling to room temperature;

[0010] The dosages of the silicon-rich biochar, Na2CO3 and K2CO3 are mixed in a molar ratio equal to the SiO2 content calculated according to the Si content in the silicon-rich biochar;

[0011] The temperature of the calcination is 800-1000 °C, the heating rate is 20-30 °C / min, and the time is 150-200 min;

[0012] The carbonized product is subjected to suction filtration and washing until the conductivity of the suction filtrate remains constant. Then, the solid obtained by suction filtration is immersed in a hydrochloric acid solution, and the solid is collected by suction filtration and washed until the conductivity of the suction filtrate remains constant. Finally, the solid is dried and sieved to obtain mesoporous biochar;

[0013] The concentration of the hydrochloric acid solution is 3 mol / L;

[0014] The preparation of the silicon-rich biochar is as follows: Select silicon-rich agricultural and forestry waste and calcine it to obtain;

[0015] The silicon-rich agricultural and forestry waste includes one or more of rice husks, rice leaves, rice straws, reeds, switchgrass, miscanthus, bamboo poles, and sugarcane bagasse;

[0016] The temperature of the calcination is 300 - 700 °C, and the heating rate is 10 - 30 °C / min;

[0017] 2) Preparation of phosphorus-rich biochar

[0018] The silicon-rich biochar, mesoporous biochar, and phosphate particles are respectively placed in deionized water, stirred at room temperature, and then dried;

[0019] The phosphate particles include one of KH2PO4 and K2HPO4;

[0020] The mass ratio of the silicon-rich biochar, mesoporous biochar, and phosphate particles is 1:0.2;

[0021] The dried solid is calcined, naturally cooled to room temperature, then taken out, collected by suction filtration, and washed until the conductivity of the suction filtrate remains constant. Finally, the solid is dried and sieved to obtain two kinds of phosphorus-rich biochar, denoted as PBC and PBC M ;

[0022] The temperature of the calcination is 200 - 300 °C, the heating rate is 20 - 30 °C / min, and the time is 100 - 150 min;

[0023] 3) Preparation of carbon-based calcium peroxide material

[0024] Add nano calcium peroxide CaO2 and anhydrous ethanol to the phosphorus-rich biochar, mix evenly, oscillate, and then dry to constant weight and perform calcination;

[0025] The product after calcination is cooled to room temperature, extracted with cold deionized water (4 °C) until the conductivity of the suction filtrate remains constant, and then suction filtered with anhydrous ethanol. The final solid is collected, dried to constant weight, and sieved to obtain the carbon-based calcium peroxide materials CaO2@PBC and CaO2@PBC M ;

[0026] The mass ratio of the activated biochar to CaO2 is 2:1;

[0027] The temperature of the calcination is 200 - 300 °C, the heating rate is 15 - 25 °C / min, and the time is 100 - 150 min;

[0028] Until the conductivity of the filtrate remains constant and the relative deviation of the last two measurement values is less than 1%;

[0029] The preparation of the nano calcium peroxide CaO2 includes the following:

[0030] Mix the calcium salt, ammonium salt and dispersant, drop in hydrogen peroxide, and stir simultaneously until the suspension changes from white to light yellow, and adjust the pH value;

[0031] Centrifuge and precipitate the product until the conductivity of the supernatant is basically unchanged, and wash to obtain nano calcium peroxide;

[0032] The calcium salt includes calcium chloride;

[0033] The ammonium salt includes ammonium chloride and ammonia water;

[0034] The dispersant includes polyethylene glycol.

[0035] The present invention also provides a carbon-based calcium peroxide material obtained by the above preparation method, and the application of the carbon-based calcium peroxide material in improving gleyed soil not only has the effect of slow oxygen release, but also can significantly improve the efficiency of the conversion of CaO2 into dissolved oxygen.

[0036] The beneficial effects of the present invention are as follows:

[0037] The present invention provides a preparation method of a carbon-based calcium peroxide material with a slow-release oxygen function. By controllably pyrolyzing silicon-rich agricultural waste into biochar, raw materials such as xylene and polyethylene that may cause soil pollution and ecological problems are avoided, realizing the resource utilization of agricultural waste. Subsequently, by regulating the pore structure of the biochar, mesoporous biochar is prepared. Combined with phosphate modification, phosphorus-rich biochar is prepared. Finally, it is compounded with calcium peroxide to obtain a carbon-based calcium peroxide material with a slow-release oxygen function. This method constructs mesoporous biochar with a high specific surface area through the synergistic optimization of pyrolysis temperature and activator. The phosphorus-rich biochar can not only be used as a slow-release phosphate fertilizer but also as a carrier for calcium peroxide, significantly increasing the mass fraction and dispersibility of calcium peroxide and avoiding its agglomeration problem. Phosphate modification endows the biochar surface with abundant phosphorus-containing functional groups to form a phosphorus-rich biochar carrier, which has both the slow-release function of phosphate fertilizer and the stable fixation effect of CaO2. The finally prepared carbon-based calcium peroxide material has excellent slow-release oxygen performance, can continuously and stably release oxygen into the soil, and at the same time, the phosphorus-rich biochar can also provide phosphorus nutrients to promote the growth of rice. This material can be widely used in the improvement of gley paddy fields, effectively solve the problem of soil hypoxia, improve soil fertility and rice yield, and has the characteristics of environmental protection, economy and high efficiency. Brief Description of the Drawings

[0038] Figure 1 is the mass fraction of CaO2 in the biochar-based oxygen-releasing material;

[0039] Figure 2 is the oxygen-releasing kinetic curve of CaO2 and the biochar-based oxygen-releasing material;

[0040] Figure 3 is the first-order kinetic curve of the dissolved oxygen concentration changing with time, and the solid line represents the fitting value of the data. Detailed Embodiments

[0041] The present invention will be further described in detail below through specific implementation cases and drawings. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art all fall within the scope defined by the appended claims of this application.

[0042] Unless otherwise specified, all raw materials and reagents of the present invention are raw materials and reagents on the conventional market.

[0043] Example 1

[0044] A preparation method of a carbon-based calcium peroxide material with a slow-release oxygen function

[0045] 1) Preparation of nano calcium peroxide

[0046] Dissolve 20 g of CaCl2 in 200 mL of deionized water, add 75 mL of 1 mol / L NH3·H2O and 75 mL of polyethylene glycol 200, and stir magnetically for 10 min (500 rpm). Slowly add 65 mL of 30% H2O2 dropwise at a rate of 1 mL / min using a peristaltic pump while stirring until the suspension changes from white to light yellow. Then add 1 mol / L NH3·H2O to adjust the pH to 10.

[0047] Centrifuge at 4000 rpm for 5 min, carefully decant the supernatant, add 40 mL of deionized water at about 4 °C to the sediment, stir evenly, and centrifuge as above. Repeat the operation 3 - 5 times until the conductivity of the supernatant remains basically unchanged (the relative deviation between two measurement values is less than 1%). Continue to add 40 mL of absolute ethanol, stir and centrifuge as above, and repeat the operation 3 times to remove the residual H2O. Collect the residue and dry it overnight at 60 °C to obtain CaO2.

[0048] 2) Preparation of silicon-rich biochar

[0049] Pass the washed, dried and pulverized rice husks through a 50-mesh sieve for standby. Put the rice husks into a 300 mL ceramic crucible and transfer it to a muffle furnace. Heat it to 500 °C at a rate of 20 °C / min, hold for 120 min, take it out after natural cooling to room temperature, and pass it through a 60-mesh sieve to obtain silicon-rich biochar, denoted as BC;

[0050] 3) Preparation of mesoporous biochar

[0051] Mix the silicon-rich biochar, Na2CO3 and K2CO3 evenly according to a mass ratio of 1:0.56:0.74, put them into a nickel crucible, cover the lid and transfer it to a muffle furnace. Heat it to 900 °C at a rate of 20 °C / min and hold for 180 min, then take it out after natural cooling to room temperature;

[0052] Filter and wash the carbonized product with deionized water until the conductivity of the filtrate remains constant. Then soak the solid obtained by filtration in 3 mol / L hydrochloric acid solution, filter and collect the solid with deionized water and wash it until the conductivity of the filtrate remains constant. Finally, dry the solid at 60 °C and pass it through a 60-mesh sieve to obtain mesoporous biochar, denoted as BC M ;

[0053] 4) Preparation of phosphorus-rich biochar

[0054] Respectively, put 10 g of BC and BC M and KH2PO4 phosphate particles into 250 mL of deionized water, stir magnetically at room temperature for 24 h, and dry in an oven at 60 °C;

[0055] The BC and BC METhe mass ratio to the phosphate particles is 1:0.2;

[0056] The dried solid was placed in a ceramic crucible and transferred to a muffle furnace. It was heated to 250 °C at a rate of 20 °C / min, held for 120 min, naturally cooled to room temperature, then taken out for suction filtration to collect the solid and washed until the conductivity of the suction filtrate remained constant. Finally, the solid was dried at 60 °C, passed through a 60-mesh sieve, and the phosphorus-rich biochar was obtained, denoted as PBC and PBC respectively. M .

[0057] 5) Preparation of carbon-based calcium peroxide material

[0058] Put 2 g of BC (PBC or PBC M ) in a 100 mL beaker, and add 1 g of CaO2. An appropriate amount of absolute ethanol was added to the mixture to form a homogeneous slurry. After shaking on a shaker for 30 min (200 rpm), it was dried at 60 °C to constant weight. The above mixture was placed in a 25 mL ceramic crucible, transferred to a muffle furnace, heated to 250 °C at a rate of 20 °C / min, and calcined for 120 min. After cooling to room temperature, it was taken out. Suction filtration was carried out with cold (about 4 °C) deionized water (100 mL / time) until the conductivity of the filtrate was basically unchanged (the relative deviation between two measured values was less than 1%). Then, suction filtration was carried out 3 times with 50 mL of absolute ethanol in the same way to remove the residual H2O. The solid was collected and dried at 60 °C to constant weight. It was pulverized and passed through a 60-mesh sieve, denoted as CaO2@BC (CaO2@PBC or CaO2@PBC M ).

[0059] Example 2

[0060] A preparation method of a carbon-based calcium peroxide material with slow-release oxygen function

[0061] 1) Preparation of nano calcium peroxide

[0062] Dissolve 25 g of CaCl2 in 200 mL of deionized water, add 85 mL of 1 mol / L NH3·H2O and 80 mL of polyethylene glycol 200, and stir magnetically for 10 min (500 rpm). Use a peristaltic pump to slowly add 70 mL of 30% H2O2 at a rate of 1 mL / min while stirring until the suspension changes from white to light yellow. Then add 1 mol / L NH3·H2O to adjust the pH to 10.

[0063] Centrifuge at 4000 rpm for 5 min, carefully pour off the supernatant, add 40 mL of deionized water at about 4 °C to the sediment, stir evenly, centrifuge as above, and continue the operation 3 - 5 times until the conductivity of the supernatant remains basically unchanged (the relative deviation between two measurement values is less than 1%). Continue to add 50 mL of absolute ethanol, stir and centrifuge as above, and repeat the operation 3 times to remove H2O from the residue. Collect the residue and dry it overnight at 60 °C to obtain CaO2.

[0064] 2) Preparation of silicon-rich biochar

[0065] Pass the washed, dried and crushed bamboo poles through a 50-mesh sieve for standby. Put the bamboo poles into a 300 mL ceramic crucible, transfer it to a muffle furnace, heat it to 700 °C at a rate of 15 °C / min, keep it for 100 min, take it out after natural cooling to room temperature, and pass it through a 60-mesh sieve to obtain silicon-rich biochar, denoted as BC;

[0066] 3) Preparation of mesoporous biochar

[0067] Mix the silicon-rich biochar, Na2CO3 and K2CO3 evenly according to the mass ratio of 1:0.46:0.61, put them into a nickel crucible, cover the lid and transfer it to a muffle furnace, heat it to 800 °C at a rate of 25 °C / min, and keep it for 200 min, take it out after natural cooling to room temperature;

[0068] Filter and wash the carbonized product with deionized water until the conductivity of the filtrate remains constant. Then soak the solid obtained by filtration in 3 mol / L hydrochloric acid solution, filter and collect the solid with deionized water and wash it until the conductivity of the filtrate remains constant. Finally, dry the solid at 60 °C, pass it through a 60-mesh sieve to obtain mesoporous biochar, denoted as BC M ;

[0069] 4) Preparation of phosphorus-rich biochar

[0070] Respectively put 10 g of BC and BC M and KH2PO4 phosphate particles into 250 mL of deionized water, stir magnetically at room temperature for 24 h, and dry in an oven at 60 °C;

[0071] The mass ratio of the said BC and BC ME to the phosphate particles is both 1:0.2;

[0072] Put the dried solid into a ceramic crucible, transfer it to a muffle furnace, heat it to 280 °C at a rate of 20 °C / min, keep it for 100 min, take it out after natural cooling to room temperature, filter and collect the solid and wash it until the conductivity of the filtrate remains constant. Finally, dry the solid at 60 °C, pass it through a 60-mesh sieve to obtain phosphorus-rich biochar, denoted as PBC and PBC respectively M .

[0073] 5) Preparation of carbon-based calcium peroxide material

[0074] Put 2 g of BC (PBC or PBC M ) in a 100 mL beaker, and add 1 g of CaO2. Add an appropriate amount of absolute ethanol to the mixture to form a homogeneous slurry. After shaking on a shaker for 30 min (200 rpm), dry at 60 °C to constant weight. Put the above mixture into a 25 mL ceramic crucible, transfer it to a muffle furnace, heat it to 300 °C at a rate of 15 °C / min, and keep it calcined for 100 min. Take it out after cooling to room temperature. Filter it with cold (about 4 °C) deionized water (100 mL / time) until the conductivity of the filtrate is basically unchanged (the relative deviation of two measured values is less than 1%). Then filter it 3 times with 50 mL of absolute ethanol in the same way to remove the residual H2O. Collect the solid, dry it at 60 °C to constant weight. Crush it through a 60-mesh sieve, and record it as CaO2@BC (CaO2@PBC or CaO2@PBC M ).

[0075] Example 3

[0076] Preparation method of a carbon-based calcium peroxide material with slow-release oxygen function

[0077] 1) Preparation of nano calcium peroxide

[0078] Take 30 g of CaCl2 and dissolve it in 250 mL of deionized water, add 90 mL of NH3·H2O with a concentration of 1 mol / L and 85 mL of polyethylene glycol 200, and stir magnetically for 10 min (500 rpm). Dropwise add 80 mL of H2O2 with a concentration of 30% at a speed of 1 mL / min with a peristaltic pump, and stir while adding until the suspension changes from white to light yellow. Then dropwise add 1 mol / L of NH3·H2O to adjust the pH to 10.

[0079] Centrifuge at 4000 rpm for 5 min, carefully pour off the supernatant, add 40 mL of deionized water at about 4 °C to the sediment, stir evenly, and centrifuge as above, and continue the operation 3 - 5 times until the conductivity of the supernatant is basically unchanged (the relative deviation of two measured values is less than 1%). Continue to add 55 mL of absolute ethanol, stir and centrifuge as above, and repeat the operation 3 times to remove the residual H2O. Collect the residue and dry it overnight at 60 °C to obtain CaO2.

[0080] 2) Preparation of silicon-rich biochar

[0081] The washed, dried and crushed switchgrass was sieved through a 50-mesh sieve for standby. The switchgrass was loaded into a 300 mL ceramic crucible and transferred to a muffle furnace. It was heated to 400 °C at a rate of 25 °C / min, held for 150 min, naturally cooled to room temperature and then taken out. It was sieved through a 60-mesh sieve to obtain silicon-rich biochar, denoted as BC;

[0082] 3) Preparation of mesoporous biochar

[0083] The silicon-rich biochar, Na2CO3 and K2CO3 were mixed evenly according to a mass ratio of 1:0.32:0.42 and then put into a nickel crucible. The lid was covered and transferred to a muffle furnace. It was heated to 1000 °C at a rate of 30 °C / min and held for 150 min, and then taken out after natural cooling to room temperature;

[0084] The carbonized product was filtered and washed with deionized water until the conductivity of the filtrate remained constant. Then the solid obtained by filtration was soaked in a 3 mol / L hydrochloric acid solution, and the solid was collected by filtration with deionized water and washed until the conductivity of the filtrate remained constant. Finally, the solid was dried at 60 °C and sieved through a 60-mesh sieve to obtain mesoporous biochar, denoted as BC M ;

[0085] 4) Preparation of phosphorus-rich biochar

[0086] 10 g of BC and BC M and KH2PO4 phosphate particles were placed in 250 mL of deionized water and magnetically stirred at room temperature for 24 h, and then dried in an oven at 60 °C;

[0087] The mass ratio of the BC and BC ME to the phosphate particles was 1:0.2;

[0088] The dried solid was loaded into a ceramic crucible and transferred to a muffle furnace. It was heated to 200 °C at a rate of 30 °C / min, held for 150 min, naturally cooled to room temperature and then taken out. The solid was collected by filtration and washed until the conductivity of the filtrate remained constant. Finally, the solid was dried at 60 °C and sieved through a 60-mesh sieve to obtain phosphorus-rich biochar, denoted as PBC and PBC respectively M .

[0089] 5) Preparation of carbon-based calcium peroxide material

[0090] 2 g of BC (PBC or PBC M) In a 100 mL beaker, add 1 g of CaO₂. Add an appropriate amount of anhydrous ethanol to the mixture to form a homogeneous slurry. After shaking on a shaker for 30 min (200 rpm), dry at 60 °C to constant weight. Transfer the above mixture into a 25 mL ceramic crucible, and transfer it to a muffle furnace. Heat it to 200 °C at a rate of 25 °C / min and keep it calcined for 150 min. Take it out after cooling to room temperature. Filter it with cold (about 4 °C) deionized water (100 mL / time) until the conductivity of the filtrate is basically unchanged (the relative deviation between two measured values is less than 1%). Then filter it with 50 mL of anhydrous ethanol three times in the same way to remove the residual H₂O. Collect the solid, dry it at 60 °C to constant weight. Crush it through a 60-mesh sieve, and denote it as CaO₂@BC (CaO₂@PBC or CaO₂@PBC M ).

[0091] Take Example 1 as a representative case for the following tests:

[0092] 1. Elemental analysis

[0093] Perform elemental analysis on the prepared biochar materials, and the results are shown in Table 1:

[0094] Table 1 Elemental content of biochar materials

[0095]

[0096]

[0097] As can be seen from Table 1, the phosphorus content of the PBC material after phosphate modification only slightly increases from 0.09% to 0.11%, indicating that the conventional impregnation method has limited phosphorus loading efficiency. However, the activated PBC M material exhibits significant elemental reconstruction characteristics: its oxygen content is greatly increased compared with BC and PBC, which is due to the deep oxidation reconstruction of rice husk charcoal during the carbonate activation process. Hydrocarbons and surface oxygen-containing functional groups (such as carboxyl groups and hydroxyl groups) undergo oxidative cleavage under the catalysis of K₂CO₃ / Na₂CO₃ to form a richer oxidized carbon skeleton. At the same time, the activation process causes the silicon element content to significantly decrease from 14.95% to 0.02%. The selective removal of siliceous minerals effectively reduces the physical barrier effect of non-carbon components on the pore structure of the material. It should be noted that the phosphorus element content of PBC M (4.72%) is significantly higher than that of BC (0.09%) and PBC (0.11%), confirming that the activation process realizes the stable enrichment of phosphorus elements through the synergistic effect of carbon matrix oxidation and phosphate anchoring.

[0098] 2. Structural analysis

[0099] Perform specific surface area and pore tests on the prepared biochar materials, and the results are shown in Table 2:

[0100] Table 2 Specific surface area and pore properties of biochar materials

[0101]

[0102] As can be seen from Table 2, significant differences are presented in the pore parameters of BC, PBC, and PBCM. Compared with the original biochar (BC), the PBC material shows significant improvements in key pore parameters such as specific surface area (increasing from 7.92 m 2 / g to 79.6712 m 2 / g), total pore volume (increasing from 0.01322 cm 3 / g to 0.049377 cm 3 / g), and mesopore volume (increasing from 0.008123 cm 3 / g to 0.019294 cm 3 / g). This phenomenon can be attributed to the elution of surface soluble substances and weakly bound functional groups during the phosphate loading process, effectively exposing the internal pores of the biochar.

[0103] For the PBC activated by carbonate M , its specific surface area further jumps to 786.85 m 2 / g, and the mesopore volume reaches 0.259 cm 3 / g (accounting for 48.8%). Its pore evolution mechanism involves multi-step reactions: at high temperatures, SiO2 reacts with carbonate to form soluble silicates (K2SiO3, Na2SiO3) and release CO2 gas, and then CO2 reacts with the carbon matrix to form CO gas and escape, thus forming a rich mesopore network inside the material. This multi-step activation treatment not only regulates the pore size distribution but also significantly improves the specific surface area and adsorption performance of the material by selectively removing non-carbon components.

[0104] 3. The ability of biochar to load CaO2 was evaluated by the potassium permanganate titration method. That is, 0.10 g of CaO2@biochar was weighed and placed in a 100 mL Erlenmeyer flask, 20 mL of deionized water was added, and it was stirred well to disperse. 10 mL of 2 mol / L sulfuric acid and 1 mL of 0.05 mol / L manganese sulfate solution were added, and it was stirred at 100 rpm for 5 min. It was filtered through a 0.45 μm filter membrane. The filtrate was titrated with a 0.02 mol / L potassium permanganate standard solution, and the volume of the potassium permanganate solution consumed was recorded.

[0105] The formula for calculating the mass fraction of CaO2 is as follows:

[0106]

[0107] Among them, is the mass fraction of CaO2 (%); and are the molar concentration (mol / L) and volume (L) of KMnO4, respectively; is the molar mass of CaO2 (72.08 g / mol); m is the mass (g) of CaO2@biochar rich in phosphorus.

[0108] From Figure 1 It can be seen that there are significant gradient differences in the calcium peroxide loading mass fractions of CaO2@BC, CaO2@PBC, and CaO2@PBCM, and their values show an increasing trend with the deepening of the biochar modification degree. This gradient improvement in the loading capacity is closely related to the co-evolution of the elemental composition and structural characteristics of the carrier material. Mechanism analysis shows that on the one hand, after the biochar is modified step by step, the contents of oxygen-containing and phosphorus-containing functional groups gradually increase. Research shows that these functional groups can form stable chelation structures with Ca through Ca-O and Ca-P coordination bonds 2+ to enhance the chemical adsorption ability. On the other hand, the hierarchical pore structure of the modified biochar provides anchoring sites for the loading of CaO2, and its microporous-mesoporous hierarchical structure realizes the efficient physical adsorption of CaO2 nanoparticles through van der Waals forces and capillary effects. Under the synergistic action of the two, the loading amount of CaO2@PBC M is 5.3 times higher than that of CaO2@PBCM, showing a significant structure-property coupling effect.

[0109] 4. To determine the oxygen release kinetic characteristics of the oxygen release material in gleyed acid sulfate paddy soil, a simulation experiment method

[0110] Weigh 0.33 g of CaCl2 into an Erlenmeyer flask, add 300 mL of deionized water to dissolve it, and adjust the pH to 4.5 with 1% acetic acid. Pass N2 (0.75 L / min, 20 min) to reduce the dissolved oxygen concentration to 0.5 mg / L. Quickly add 10 mg of pure CaO2 or a biochar-based oxygen release material with an equal CaO2 content to the medium. Seal the bottle mouth, avoid the top space, and place it in a 25°C dark incubator for the oxygen release kinetic experiment. Within 12 h after the start of the experiment, measure the dissolved oxygen concentration every 4 h. From 12 to 36 h, measure the dissolved oxygen concentration every 8 h. When the relative deviation between two measurement values is less than 1%, the oxygen release process is considered to end. If the experiment exceeds 36 h, change to measure once every 12 h.

[0111] The results are as Figure 2 shown, showing a significant effect of the carrier structure on the oxygen release behavior and its rate characteristics. Both CaO2 and the biochar-based oxygen release materials show similar kinetic trends. Specifically, the oxygen release period of CaO2@PBC M is the longest, followed by CaO2 and CaO2@PBC, and CaO2@BC is the shortest.

[0112] According to Figure 2The changing trend of dissolved oxygen concentration over time shows that the curve exhibits the characteristics of exponential growth. Therefore, an exponential growth model was selected to fit the data (Equation 1). Through derivation, Equation 1 was transformed into Equation 2 that conforms to the form of first-order reaction kinetics, where A0 is the initial concentration, A is the dissolved oxygen concentration at a specific time t, and k is the rate constant. Based on Figure 2 and Equation 3, plot Figure 3 , and perform linear fitting. Among them, A1 is the initial concentration, y - y0 is the dissolved oxygen concentration at a specific time x, and -1 / b1 is the negative value of the rate constant.

[0113]

[0114] ln(A / A0) = -kt; 2;

[0115]

[0116] Figure 3 The fitting curves of the oxygen release kinetic parameters (k value) in show that the oxygen release rate constants of CaO2@BC and CaO2@PBC are significantly higher than those of CaO2 and CaO2@PBCM (p < 0.05), and there is no statistical difference between the latter two. This difference stems from the coupling effect between the biochar carrier structure and the active components: BC realizes the uniform dispersion of CaO2 particles by virtue of its homogeneous pore structure, promotes the full exposure of CaO2 to the liquid phase environment, thereby accelerating its hydrolysis reaction, and increasing the k value of CaO2@BC by 4.8 times compared with pure CaO2. In contrast, although PBC has a higher specific surface area, the abundant oxygen-containing and phosphorus-containing functional groups on its surface form a stable chelating structure through Ca-O and Ca-P coordination, significantly delaying the hydrolysis kinetics of CaO2, resulting in a 63.9% decrease in the k value of CaO2@PBC compared with CaO2@BC.

[0117] Regarding the oxygen release inhibition phenomenon of CaO2@PBCM, its mechanism has dual regulatory characteristics: firstly, the ultra-high specific surface area (786.85 m 2 / g) generated by carbonate activation, accompanied by a sharp increase in the number of oxygen-containing and phosphorus-containing functional groups, restricts the exposure of CaO2 active sites through chemical bonding; secondly, its optimized mesoporous structure (mesopore volume 0.259 cm 3 / g; mesopore ratio 48.81%) forms an accurate match with the particle size of CaO2 nanoparticles, avoiding both the surface enrichment and rapid release caused by small pore diameters and the particle shedding and instability caused by large pore diameters. This multi-scale synergistic regulation enables CaO2@PBC M to achieve the slow oxygen release characteristics in the simulated gleyic acid sulfate soil environment, showing significant structural adaptability advantages.

[0118] Table 3 shows the pH of the medium and the efficiency of CaO2 converted into dissolved oxygen after oxygen release:

[0119]

[0120] Among them, η is the efficiency (%) of the conversion of CaO2 into dissolved oxygen; DO1 is the dissolved oxygen concentration (mg / L) of the medium after the oxygen release ends; DO0 is the original dissolved oxygen concentration (mg / L) of the medium; V is the volume (L) of the medium; DO is the amount (mg) of O2 theoretically generated by the complete reaction of CaO2 with water.

[0121] Table 3 pH of the medium and the efficiency of the conversion of CaO2 into dissolved oxygen after the oxygen release ends

[0122]

[0123] As can be seen from Table 3, after the oxygen release ends, there is no significant difference in the pH of each treatment medium. The experimental data in Table 3 show that after the oxygen release reaction ends, the pH values of each treatment system do not show significant differences, but the oxygen conversion rate of the CaO2@biochar composite material is significantly improved compared with the pure CaO2 system (the improvement range reaches 6.31%-126.35%). The mechanism of this performance transition stems from the dynamic regulation of the hydrolysis reaction of CaO2 by the biochar carrier: the Ca(OH)2 precipitate generated by pure CaO2 during the reaction will form a dense passivation layer, which hinders the exposure of active sites through the physical shielding effect, resulting in a low efficiency of the conversion of CaO2 into dissolved oxygen. On the contrary, the biochar carrier realizes the uniform dispersion of CaO2 by virtue of its high specific surface area, effectively maintaining the permeability of the reaction interface, thereby significantly improving the oxygen conversion efficiency.

[0124] For carbon-based calcium peroxide materials, with the increase in the modification depth of the biochar carrier (such as carbonate activation - phosphate loading), the efficiency of the conversion of CaO2 into dissolved oxygen also increases. This may be because the increase in specific surface area provides more active sites for CaO2, thus avoiding the reduction in conversion efficiency caused by the coverage of insoluble Ca(OH)2. In addition, the confinement effect of the mesoporous structure will increase the molecular diffusion resistance during the transmission of oxygen and water, making it difficult for them to move in the pore channels, thereby reducing the transmission efficiency.

[0125] In summary, CaO2@PBC M not only has the effect of slow oxygen release, but also can significantly improve the efficiency of the conversion of CaO2 into dissolved oxygen in the solution. It can be seen that CaO2@PBC M can be used for the improvement of gleyed soil.

[0126] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a carbon-based calcium peroxide material with a slow-release oxygen function, characterized in that, It includes the following steps: 1) Preparation of mesoporous biochar Mix silicon-rich biochar with Na2CO3 and K2CO3 evenly, then calcine it, and take it out after natural cooling to room temperature; The dosages of the silicon-rich biochar, Na2CO3, and K2CO3 are mixed in a molar ratio equal to the SiO2 content calculated based on the Si content in the silicon-rich biochar; Filter and wash the carbonized product until the conductivity of the filtrate remains constant, then soak the solid obtained by filtration in hydrochloric acid solution, filter and collect the solid, wash it until the conductivity of the filtrate remains constant, and finally dry and sieve the solid to obtain mesoporous biochar; 2) Preparation of phosphorus-rich biochar Put silicon-rich biochar, mesoporous biochar, and phosphate particles into deionized water respectively, stir at room temperature, and then dry; The dried solid is calcined, naturally cooled to room temperature, taken out, filtered by suction to collect the solid, and washed until the conductivity of the filtrate by suction remains constant. Finally, the solid is dried and sieved to obtain two kinds of phosphorus-rich biochars, denoted as PBC and PBC M ; 3) Preparation of carbon-based calcium peroxide material Add nano calcium peroxide CaO2 and absolute ethanol to the phosphorus-rich biochar, mix evenly, oscillate, then dry to constant weight and calcine; The calcined product is cooled to room temperature and extracted with cold deionized water until the conductivity of the filtrate remains constant. Then, it is filtered with absolute ethanol, and the final solid is collected, dried to a constant weight, and sieved to obtain the carbon-based calcium peroxide materials CaO2@PBC and CaO2@PBC M .

2. The preparation method of the carbon-based calcium peroxide material with a slow-release oxygen function according to claim 1, characterized in that, The preparation of the silicon-rich biochar in step 1) is as follows: select silicon-rich agroforestry waste and calcine it to obtain; The silicon-rich agroforestry waste includes one or more of rice husk, rice leaf, rice straw, reed, switchgrass, miscanthus, bamboo pole, and bagasse; The temperature of the calcination is 300-700 °C, and the heating rate is 10-30 °C / min.

3. The preparation method of the carbon-based calcium peroxide material with slow-release oxygen function according to claim 1, characterized in that, The phosphate particles in step 2) include one of KH2PO4 and K2HPO4.

4. The preparation method of the carbon-based calcium peroxide material with slow-release oxygen function according to claim 1, characterized in that, The mass ratio of the silicon-rich biochar, mesoporous biochar to the phosphate particles in step 2) is 1:0.

2.

5. The preparation method of the carbon-based calcium peroxide material with slow-release oxygen function according to claim 1, characterized in that The temperature of the calcination in step 2) is 200-300 °C, the heating rate is 20-30 °C / min, and the time is 100-150 min.

6. The preparation method of the carbon-based calcium peroxide material with a slow-release oxygen function according to claim 1, characterized in that, The mass ratio of the activated biochar to CaO2 in step 3) is 2:

1.

7. The preparation method of the carbon-based calcium peroxide material with slow-release oxygen function according to claim 1, characterized in that, The temperature of the calcination in step 3) is 200-300 °C, the heating rate is 20-30 °C / min, and the time is 100-150 min.

8. The preparation method of the carbon-based calcium peroxide material with a slow-release oxygen function according to claim 1, characterized in that, The conductivity of the filtrate remains constant means that the relative deviation between the last two measured values is less than 1%.

9. The preparation method of the carbon-based calcium peroxide material with a slow-release oxygen function according to claim 1, characterized in that, The preparation of the nano calcium peroxide CaO2 includes the following: mix calcium salt, ammonium salt, and dispersant, drop in hydrogen peroxide, and stir simultaneously until the suspension changes from white to light yellow, and adjust the pH; Centrifuge and precipitate the product until the conductivity of the supernatant remains basically unchanged, and wash it to obtain nano calcium peroxide; The calcium salt includes calcium chloride; The ammonium salt includes ammonium chloride and ammonia water; The dispersant includes polyethylene glycol.

10. Calcium peroxide based on carbon prepared by the preparation method according to any one of claims 1-9, characterized in that, Application of the carbon-based calcium peroxide material in improving gleyed soil

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