Oxygen release material based on alkali-activated silicon-rich biochar as well as preparation method and application of oxygen release material

Abstract

The invention belongs to the technical field of oxygen-releasing biochar, and particularly relates to an oxygen-releasing material based on alkali-activated silicon-rich biochar as well as a preparation method and application of the oxygen-releasing material. The alkali-activated modified silicon-rich biochar and calcium peroxide are compounded to form a synergistic oxygen release system. On one hand, alkali activation treatment enables the silicon-rich biochar to form a developed porous structure and a high specific surface area, so that the loading capacity of calcium peroxide is remarkably improved, calcium peroxide particles can be uniformly dispersed through a surface adsorption effect, agglomeration and inactivation are avoided, and the utilization efficiency of calcium peroxide is greatly improved; on the other hand, the surface of the silicon-rich biochar subjected to alkali activation treatment is rich in conductive groups and active sites, a micro-electric field effect is formed at a solid-liquid interface, the electron transfer rate of calcium peroxide and a water body is effectively increased, and calcium peroxide is promoted to be rapidly decomposed to generate oxygen. The oxygen release rate is improved through the synergistic effect of the dual optimization organic carrier-active component, and breakthrough improvement is achieved in the aspects of oxygen release material utilization efficiency and reaction kinetics performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of oxygen-releasing biochar, and particularly relates to an oxygen-releasing material based on alkali-activated silicon-rich biochar, its preparation method and application. Background Art

[0002] In the field of environmental governance materials, the dynamic oxygen-releasing efficiency is the core index for evaluating the performance of oxidants. As a multi-scenario environmental remediation material, calcium peroxide (CaO2) has a theoretical oxygen release amount of up to 0.47 g O2 / g. However, its slow oxygen-releasing rate (the release period is 5 - 15 days under conventional conditions) forms a significant contradiction with its excellent oxygen-releasing characteristics. This kinetic bottleneck leads to performance limitations in multiple application scenarios: 1) In sewage treatment, the oxygen transfer rate cannot meet the immediate needs of microbial metabolism; 2) In sudden hypoxia situations in aquaculture, minute-level emergency oxygenation cannot be achieved; 3) During soil remediation, the burst concentration of reactive oxygen species (ROS) is insufficient; 4) The surface passivation effect (caused by the Ca(OH)2 coating) leads to reduced material utilization efficiency. This contradiction system has spurred the exploration of new composite carriers, aiming to achieve an accurate match between the oxygen transfer rate and governance requirements by constructing a dynamic oxygen-releasing system.

[0003] Biochar, as a carbonaceous material formed by pyrolyzing biomass (such as wood, agricultural waste, or specific plant materials) under anoxic or anaerobic conditions at high temperature, is known for its high specific surface area, rich pore structure, and good electrical conductivity. In recent years, the research on modified biochar has become a hot topic. Through modification methods such as alkali activation, the surface chemical properties, pore size distribution, and pore structure of biochar can be significantly changed, thereby increasing its specific surface area and electrical conductivity. Modified biochar, as a carrier for calcium peroxide, has significant advantages: increasing the contact area with calcium peroxide, carrying more active ingredients, and the enhanced electrical conductivity provides a favorable electron transfer path for the rapid oxygen release of calcium peroxide, effectively overcoming the problem of slow oxygen release; the porous structure is conducive to improving the dispersion of calcium peroxide, promoting the generation of reactive oxygen species, and enhancing its utilization efficiency. Therefore, modified biochar is regarded as an ideal carrier for loading calcium peroxide and is expected to further improve the performance and application effect of calcium peroxide in environmental governance. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to provide an oxygen-releasing material based on alkali-activated silicon-rich biochar, its preparation method and application.

[0005] The technical content of the present invention is as follows:

[0006] The present invention also provides a preparation method for an oxygen-releasing material based on alkali-activated silicon-rich biochar, including the following steps:

[0007] 1) Preparation of silicon-rich biochar

[0008] Select silicon-rich agricultural and forestry waste and calcine it to prepare silicon-rich biochar;

[0009] 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;

[0010] The temperature of the calcination is 300-700 °C, and the heating rate is 10-30 °C / min;

[0011] 2) Preparation of alkali-activated silicon-rich biochar

[0012] Mix the silicon-rich biochar and KOH at a solid-liquid ratio of 1:10 g / mL, let it stand, and then filter to collect the solid, wash it until the conductivity of the filtrate remains constant, and finally dry the solid;

[0013] The concentration of the KOH is 5%;

[0014] Mix the dried solid with KOH powder at a mass ratio of 1:(3-5), put it into a nickel crucible, and then transfer it to a muffle furnace for calcination. Take it out after natural cooling to room temperature;

[0015] The KOH powder is ground KOH and passed through a 200-300 mesh sieve;

[0016] The temperature of the calcination is 700-900 °C, the heating rate is 20-30 °C / min, and the time is 20-50 min;

[0017] Mix the obtained sample with deionized water at a solid-liquid ratio of 1:10 g / mL, cool it to room temperature, filter to collect the solid, wash it until the conductivity of the filtrate remains constant, and finally dry and sieve the solid to obtain alkali-activated silicon-rich biochar;

[0018] 3) Preparation of CaO2@alkali-activated silicon-rich biochar

[0019] Mix the alkali-activated silicon-rich biochar, CaO2, and absolute ethanol evenly, shake it, and then dry it to constant weight and perform calcination;

[0020] Cool the calcined product to room temperature, extract it with cold deionized water (4 °C) until the conductivity of the filtrate remains constant, then filter it with absolute ethanol, collect the final solid, dry it to constant weight, and sieve it to obtain CaO2@alkali-activated silicon-rich biochar;

[0021] The mass ratio of the alkali-activated silicon-rich biochar to CaO2 is 2:1;

[0022] The temperature of the calcination is 200-300 °C, the heating rate is 15-25 °C / min, and the time is 100-150 min;

[0023] Until the conductivity of the filtrate remains constant, with the relative deviation of the last two measured values being less than 1%.

[0024] The beneficial effects of the present invention are as follows:

[0025] The preparation method of the oxygen-releasing material based on alkali-activated silicon-rich biochar of the present invention forms a synergistic oxygen-releasing system by compounding alkali-activated modified silicon-rich biochar with calcium peroxide. Its innovative mechanism lies in: on the one hand, the alkali activation treatment makes the silicon-rich biochar form a developed porous structure and a high specific surface area, which not only significantly improves the loading capacity of calcium peroxide, but also can evenly disperse calcium peroxide particles through surface adsorption, avoiding agglomeration and inactivation, thus greatly improving the utilization efficiency of calcium peroxide; on the other hand, the surface of the alkali-activated silicon-rich biochar is rich in conductive groups and active sites, forming a microelectric field effect at the solid-liquid interface, effectively accelerating the electron transfer rate between calcium peroxide and water, and promoting the rapid decomposition of calcium peroxide to produce oxygen. This dual optimization mechanism not only breaks through the technical bottleneck that the release of oxygen is blocked due to the calcium hydroxide passivation layer wrapping calcium peroxide in traditional applications, but also improves the oxygen release rate through the synergistic effect of the carrier-active component, achieving a breakthrough improvement in the utilization efficiency of the oxygen-releasing material and the reaction kinetic performance. Description of the Drawings

[0026] Figure 1 For the adsorption-desorption isotherms (A) of alkali-activated rice husk charcoal and rice husk charcoal, and the cumulative pore volume and pore volume increment diagrams (B and C);

[0027] Figure 2 For the mass fraction of CaO2 in CaO2@biochar;

[0028] Figure 3 For the FTIR (A) of biochar and the XRD (B) image of CaO2@biochar (the height of the green columns does not represent the content level of the compound);

[0029] Figure 4 For the oxygen release kinetic curve diagram of CaO2@biochar, and the solid line represents the fitted value of the data;

[0030] Figure 5 For the first-order kinetic curve diagram of the dissolved oxygen concentration changing with time, and the solid line represents the fitted value of the data;

[0031] Figure 4 and 5 In, A represents a strongly acidic low-oxygen environment (pH 4.5, DO = 0.5 mg / L); B represents a weakly acidic low-oxygen environment (pH 6.0, DO = 0.5 mg / L); C represents a strongly acidic high-oxygen environment (pH 4.5, DO = 3.0 mg / L). Detailed Embodiments

[0032] The present invention will be further described in detail below through specific embodiments and with reference to the accompanying 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 made by those skilled in the art fall within the scope defined by the appended claims of this application.

[0033] Unless otherwise specified, all raw materials and reagents of the present invention are raw materials and reagents available in the conventional market.

[0034] Example 1

[0035] A preparation method of an oxygen-releasing material based on alkali-activated silicon-rich biochar

[0036] 1) Preparation of silicon-rich biochar

[0037] The washed, dried and pulverized rice husks were sieved through a 50-mesh sieve and reserved. The rice husks were placed in a 300 mL ceramic crucible and transferred to a muffle furnace. The temperature was raised to 500 °C at a rate of 20 °C / min, held for 120 min, naturally cooled to room temperature and then taken out, and sieved through a 60-mesh sieve for reserve, denoted as rice husk charcoal.

[0038] 2) Preparation of alkali-activated silicon-rich biochar

[0039] The rice husk charcoal was mixed with 5% KOH at a ratio of 1:10 (mg / mL). The mixture was allowed to stand at 25 °C for 150 min, then the solid was collected by suction filtration and rinsed with deionized water until the conductivity value of the suction filtrate remained constant. Finally, the washed solid was dried at 60 °C.

[0040] The biochar dried in the previous step and KOH powder were mixed evenly at a ratio of 1:4 (w / w), put into a nickel crucible, and then the nickel crucible with the lid was transferred to a muffle furnace. The temperature was raised to 900 °C at a rate of 20 °C / min and held for 30 min, and then taken out after natural cooling to room temperature.

[0041] The prepared sample was mixed with deionized water at a solid-liquid ratio of 1:10 (mg / mL). After mixing evenly, it was cooled to room temperature. Then, the solid was collected by suction filtration and rinsed with deionized water until the conductivity of the suction filtrate remained constant (the relative deviation of the two measured values < 1%). Finally, the washed solid was dried at 60 °C, sieved through a 60-mesh sieve, and stored in the dark, denoted as alkali-activated rice husk charcoal.

[0042] 3) Preparation of CaO2@alkali-activated silicon-rich biochar material

[0043] Weigh 2 g of alkali-activated rice husk carbon into a 100 mL beaker, add 1 g of CaO2, add an appropriate amount of absolute ethanol to the mixture to form a homogeneous slurry, place it on a shaker and shake for 300 min (200 rpm), then dry at 60 °C to constant weight. Transfer the above mixture into a 25 mL ceramic crucible, transfer it to a muffle furnace, heat it to 250 °C at a rate of 20 °C / min, keep it for 120 min for calcination, take it out after cooling to room temperature, filter it with about 4 °C deionized water (100 mL / time) until the conductivity of the filtrate remains constant (the relative deviation of two measured values < 1%), then filter it with 50 mL of absolute 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 record it as CaO2@alkali-activated rice husk carbon.

[0044] Example 2

[0045] Preparation method of an oxygen-releasing material based on alkali-activated silicon-rich biochar

[0046] 1) Preparation of silicon-rich biochar

[0047] Pass the washed, dried and crushed bagasse through a 50-mesh sieve for standby. Put the bagasse into a 300 mL ceramic crucible, and transfer it to a muffle furnace. Heat it to 400 °C at a rate of 20 °C / min, keep it for 100 min, take it out after natural cooling to room temperature, and pass it through a 60-mesh sieve for standby, and record it as bagasse carbon;

[0048] 2) Preparation of alkali-activated silicon-rich biochar

[0049] Mix the bagasse carbon with 5% KOH in a ratio of 1:10 (mg / mL), let the mixture stand at 25 °C for 150 min, then filter to collect the solid, and rinse it with deionized water until the conductivity value of the filtrate remains constant. Finally, dry the washed solid at 60 °C;

[0050] Mix the biochar dried in the previous step and KOH powder evenly in a ratio of 1:3 (w / w), put it into a nickel crucible, then transfer the nickel crucible with the lid on to a muffle furnace, heat it to 800 °C at a rate of 20 °C / min, and keep it for 30 min, take it out after natural cooling to room temperature;

[0051] Mix the prepared sample with deionized water at a solid-liquid ratio of 1:10 (mg / mL), mix it evenly, then cool it to room temperature. After that, filter to collect the solid, and rinse it with deionized water until the conductivity of the filtrate remains constant (the relative deviation of two measured values < 1%). Finally, dry the washed solid at 60 °C, pass it through a 60-mesh sieve, and store it in the dark, and record it as alkali-activated bagasse carbon;

[0052] 3) Preparation of CaO2@alkali-activated silicon-rich biochar material

[0053] Weigh 2 g of alkali-activated sugarcane charcoal into a 100 mL beaker, add 1 g of CaO2, add an appropriate amount of absolute ethanol to the mixture to form a homogeneous slurry, place it on a shaker and shake for 300 min (200 rpm), then dry it at 60 °C to constant weight. Transfer the above mixture into a 25 mL ceramic crucible, transfer it to a muffle furnace, heat it to 300 °C at a rate of 20 °C / min, keep it for 100 min for calcination, take it out after cooling to room temperature, filter it with about 4 °C deionized water (100 mL / time) until the conductivity of the filtrate remains constant (the relative deviation of two measured values < 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@alkali-activated sugarcane charcoal.

[0054] Example 3

[0055] A preparation method of an oxygen-releasing material based on alkali-activated silicon-rich biochar 1) Preparation of silicon-rich biochar

[0056] Pass the washed, dried and crushed Miscanthus through a 50-mesh sieve for standby. Put the Miscanthus into a 300 mL ceramic crucible, transfer it to a muffle furnace, heat it to 600 °C at a rate of 25 °C / min, keep it for 120 min, take it out after natural cooling to room temperature, and pass it through a 60-mesh sieve for standby, and record it as Miscanthus charcoal;

[0057] 2) Preparation of alkali-activated silicon-rich biochar

[0058] Mix Miscanthus charcoal with 5% KOH in a ratio of 1:10 (mg / mL), let the mixture stand at 25 °C for 150 min, then filter it to collect the solid, and rinse it with deionized water until the conductivity value of the filtrate remains constant. Finally, dry the washed solid at 60 °C;

[0059] Mix the biochar dried in the previous step and KOH powder evenly in a ratio of 1:5 (w / w), put it into a nickel crucible, then transfer the covered nickel crucible to a muffle furnace, heat it to 1000 °C at a rate of 25 °C / min, and keep it for 30 min, take it out after natural cooling to room temperature;

[0060] Mix the prepared sample with deionized water at a solid-liquid ratio of 1:10 (mg / mL), mix it evenly, then cool it to room temperature. After that, filter it to collect the solid, and rinse it with deionized water until the conductivity of the filtrate remains constant (the relative deviation of two measured values < 1%). Finally, dry the washed solid at 60 °C, pass it through a 60-mesh sieve, and store it in the dark, and record it as alkali-activated Miscanthus charcoal;

[0061] 3) Preparation of CaO2@alkali-activated silicon-rich biochar material

[0062] Weigh 2 g of alkali-activated Miscanthus carbon into a 100 mL beaker, add 1 g of CaO2, add an appropriate amount of absolute ethanol to the mixture to form a homogeneous slurry, place it on a shaker and shake for 300 min (200 rpm), then dry it at 60 °C to constant weight. Transfer the above mixture into a 25 mL ceramic crucible, then transfer it to a muffle furnace, heat it to 300 °C at a rate of 25 °C / min, keep it for 100 min for calcination, take it out after cooling to room temperature, filter it with about 4 °C deionized water (100 mL / time) until the conductivity of the filtrate remains constant (the relative deviation of two measurement values < 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 label it as CaO2@alkali-activated Miscanthus carbon.

[0063] Example 4

[0064] Preparation method of an oxygen-releasing material based on alkali-activated silicon-rich biochar

[0065] 1) Preparation of silicon-rich biochar

[0066] After cleaning, drying and crushing, the reed is sieved through a 50-mesh sieve for standby. Put the reed 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, keep it for 100 min, take it out after natural cooling to room temperature, and sieve it through a 60-mesh sieve for standby, and label it as reed carbon;

[0067] 2) Preparation of alkali-activated biochar

[0068] Mix the reed carbon with 5% KOH in a ratio of 1:10 (mg / mL), let the mixture stand at 25 °C for 150 min, then filter it to collect the solid, and rinse it with deionized water until the conductivity value of the filtrate remains constant. Finally, dry the washed solid at 60 °C;

[0069] Mix the biochar dried in the previous step and KOH powder evenly in a ratio of 1:4 (w / w), put it into a nickel crucible, then transfer the nickel crucible with the lid on to a muffle furnace, heat it to 700 °C at a rate of 30 °C / min, and keep it for 50 min, take it out after natural cooling to room temperature;

[0070] Mix the prepared sample with deionized water at a solid-liquid ratio of 1:10 (mg / mL), after mixing evenly, cool it to room temperature, then filter it to collect the solid, and rinse it with deionized water until the conductivity of the filtrate remains constant (the relative deviation of two measurement values < 1%). Finally, dry the washed solid at 60 °C, sieve it through a 60-mesh sieve, and store it in the dark, and label it as alkali-activated reed carbon;

[0071] 3) Preparation of CaO2@alkali-activated silicon-rich biochar material

[0072] Weigh 2 g of alkali-activated reed charcoal into a 100 mL beaker, add 1 g of CaO₂, add an appropriate amount of absolute ethanol to the mixture to form a homogeneous slurry, place it on a shaker and shake for 300 min (200 rpm), then dry it at 60 °C until constant weight. Transfer the above mixture into a 25 mL ceramic crucible, transfer it to a muffle furnace, heat it to 200 °C at a rate of 15 °C / min, keep it calcined for 150 min, take it out after cooling to room temperature, filter it with about 4 °C deionized water (100 mL / time) until the conductivity of the filtrate remains constant (the relative deviation of two measured values < 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 until constant weight, crush it and pass it through a 60-mesh sieve, denoted as CaO₂@alkali-activated reed charcoal.

[0073] 1. Elemental composition and structure of biochar

[0074] Detect the elemental contents of the rice husk charcoal in step 1) and the alkali-activated rice husk charcoal in step 2) of Example 1, and the results are shown in Table 1:

[0075] Table 1 Elemental contents of rice husk charcoal and alkali-activated rice husk charcoal

[0076]

[0077] It can be seen that the carbon (C) and oxygen (O) contents of the alkali-activated rice husk charcoal are significantly higher than those of the rice husk charcoal. This phenomenon is due to the deep oxidation of the surface and internal functional groups of the rice husk charcoal during the alkali activation process: in the KOH alkali activation system, the hydrocarbons and oxygen-containing functional groups (such as carboxyl groups, hydroxyl groups, etc.) in the rice husk charcoal undergo oxidative reconstruction to generate more oxygen-containing functional groups. It should be noted that a large amount of silicon element in the rice husk is lost during the alkali activation process (the final content is only 0.02%). The removal of this siliceous mineral not only reduces the interference of non-carbon components on the carbon skeleton, but also significantly increases the relative content of carbon element through the mass conservation effect. From the perspective of structural characterization, the H / C ratio can be used as an important index to evaluate the aromatization degree of biochar. When H / C < 0.1, it indicates the existence of a large number of C-C bonding structures (i.e., a higher degree of graphitization). The data in Table 1 show that the H / C value of the alkali-activated rice husk charcoal is significantly lower than that of the rice husk charcoal, confirming that a denser graphitized carbon network structure is formed after high-temperature alkali activation.

[0078] As Figure 1 shown, the adsorption-desorption isotherms and pore size distributions of the rice husk charcoal and the alkali-activated rice husk charcoal show significant differences. The specific pore structure parameters are shown in Table 2. The rice husk charcoal treated by KOH alkali activation shows better adsorption performance: its BET specific surface area reaches 2629.49 m 2 / g, the micropore volume (1.2220 m 3 / g) and the mesopore volume (0.3951 m 3 / g) were significantly higher than those of the un-alkali-activated samples. Pore size distribution analysis showed that the pore structure of alkali-activated rice husk carbon mainly consisted of micropores (<2 nm) and mesopores (2 - 50 nm), with mesopores mainly concentrated in the range of 2 - 7 nm; while the pores of rice husk carbon showed a wide distribution (1 - 100 nm), and the average pore size was significantly higher than that of alkali-activated rice husk carbon.

[0079] Table 2 Specific surface area and pore properties of alkali-activated rice husk carbon and rice husk carbon

[0080]

[0081] 2. Composition and structure of CaO2@biochar

[0082] The ability of biochar to load CaO2 was evaluated by 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. 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 potassium permanganate solution consumed was recorded.

[0083] The calculation formula for the mass fraction of CaO2 is as follows:

[0084]

[0085] Among them, W is the mass fraction of CaO2 (%); and are the molar concentration (mol / L) and volume (L) of KMnO4 respectively; The molar mass of CaO2 is 72.08 g / mol; m is the mass (g) of CaO2@biochar.

[0086] As Figure 2 shown, is the mass fraction of CaO2 in CaO2@biochar. The mass fraction of calcium peroxide loaded in the CaO2@alkali-activated rice husk carbon composite was significantly higher than that of CaO2@rice husk carbon. This phenomenon may be closely related to the unique structural characteristics and surface chemical properties of alkali-activated biochar: Firstly, the rice husk carbon treated by KOH alkali activation has a higher specific surface area (2629.49 m 2 / g) and a well-developed hierarchical pore system (the ratio of micropores / mesopores is 1:0.32). Its multi-level pore structure can provide abundant active sites to effectively load CaO2 particles through physical adsorption and intermolecular forces; Secondly, the surface of alkali-activated rice husk carbon is rich in oxygen-containing functional groups such as carboxyl (-COOH) and hydroxyl (-OH). Studies have shown that these surface oxygen-containing functional groups can form coordination bonds with Ca 2+Combined to form stable Ca-O bonds, thus significantly enhancing the chemisorption ability of CaO2 on the carrier surface.

[0087] As Figure 3 shown in Figure A of -1 , the Fourier transform infrared spectroscopy (FTIR) characteristics of different biochar materials show significant differences. Although the spectra of rice husk char and alkali-activated rice husk char have similar functional group distributions, the intensities of the main absorption peaks of the latter are significantly enhanced. Specifically, a stretching vibration peak of phenolic hydroxyl (-OH) appears at 3419 cm -1 , 1617 cm -1 corresponds to the characteristic absorption band of aromatic carbon-carbon double bond (C=C), 1113 cm -1 is the stretching vibration peak of carbonyl oxygen (C-O) in the polysaccharide acetal structure, while the Si-O-Si symmetric stretching peak existing in rice husk char at 798 cm

[0088] As Figure 3 shown in Figure B of

[0089] 3. Oxygen release kinetic test of CaO2@biochar

[0090] A glass reactor with a capacity of 300 mL was combined with a dissolved oxygen (DO) concentration sensor system to systematically investigate the oxygen release kinetic characteristics of the CaO2@alkali-activated rice husk carbon composite material in different solution environments. By precisely controlling the dissolved oxygen concentration (0.5 mg / L and 3.0 mg / L) and the solution pH (pH 4.5 and pH 6.0), three different oxygen release environments were constructed to reveal the oxygen release performance of the material. The specific experimental procedures are as follows:

[0091] (1) Strongly acidic and low-oxygen environment (pH 4.5, DO = 0.5 mg / L)

[0092] Prepare 250 mL of deionized aqueous solution containing 0.33 g of CaCl2, adjust it to pH 4.5 with 1% acetic acid, and then introduce N2 (flow rate 0.75 L / min, aeration for 20 min) to achieve a low-oxygen environment. Add 10 mg of CaO2, an equal mass of CaO2@rice husk carbon, and the CaO2@alkali-activated rice husk carbon composite material respectively. After sealing the reactor, place it in a 25°C dark incubator. The oxygen release process was monitored using the interval sampling method: measure the DO concentration every 4 h in the first 12 h, detect it once every 8 h from 12 - 36 h, and terminate the experiment when the relative deviation of two consecutive measurement values ≤ 1%. If it exceeds 36 h, extend the sampling to every 12 h.

[0093] (2) Weakly acidic and low-oxygen environment (pH 6.0, DO = 0.5 mg / L)

[0094] Except for adjusting the solution pH to 6.0, all other experimental parameters (including reagent ratios, gas treatment, material addition, and monitoring procedures) were kept the same as those under strongly acidic conditions.

[0095] (3) Strongly acidic and high-oxygen environment (pH 4.5, DO = 3.0 mg / L)

[0096] Adjust the dissolved oxygen concentration to 3.0 mg / L by adjusting the N2 introduction time, and all other operation steps were exactly the same as those in the strongly acidic and low-oxygen group.

[0097] As Figure 4 shown, the oxygen release kinetic curves of different CaO2-based materials reveal the significant influence of the carrier structure on the oxygen release behavior and its rate characteristics. In the three different solution systems, these CaO2-based materials all show similar kinetic trends. Specifically, the oxygen release period of pure CaO2 is the longest, lasting 4 to 5.5 days. While the oxygen release period of CaO2@rice husk carbon is the shortest, and its duration is reduced compared to pure CaO2.

[0098] To quantitatively evaluate the rapid oxygen release ability of these materials, the increase in dissolved oxygen within the initial 20 hours of the experiment was used as the evaluation index. The experimental results showed that in the three solution systems, the rapid oxygen release ability of CaO2@alkali-activated rice husk carbon was superior to that of CaO2@rice husk carbon and pure CaO2, and the improvement amplitude of its oxygen release ability increased with the enhancement of solution acidity.

[0099] Compared with untreated rice husk carbon, alkali-activated rice husk carbon has a more heterogeneous pore structure (with micropores accounting for up to 75.57%), which limits the deep embedding of CaO2 particles, causing the particles to stay more in the pore entrance area. At the same time, oxygen-containing functional groups such as carboxyl groups and phenolic hydroxyl groups introduced during the KOH activation process can form stable chemical adsorption interfaces through coordination bonds with Ca 2+ binding, thereby further promoting the surface activation of CaO2. In addition, the increase in the graphitization degree of alkali-activated rice husk carbon (the H / C value decreased from 0.10 to 0.09) also enhanced the electron transfer efficiency and reduced the activation energy required for the decomposition of calcium peroxide.

[0100] According to Figure 4 the changing trend of dissolved oxygen concentration over time, it can be seen that the curve shows an exponential growth characteristic.

[0101]

[0102] In(A / A0)=-kt; 2;

[0103]

[0104] Therefore, an exponential growth model was selected to fit the data (Equation 1). Through derivation, Equation 1 was converted into Equation 2 that conforms to the first-order reaction kinetics form, 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 4 and Equation 3, Figure 5 was plotted,

[0105] such as Figure 5 shown, after the first-order model fitting, the oxygen release kinetic curves of the composite materials showed significant differences. The slopes of these curves represent the oxygen release rate constant (k) of the test materials during the oxygen release period, and this parameter directly reflects the speed of oxygen release. According to the experimental data, under the three simulation conditions, the k values of CaO2@rice husk carbon and CaO2@alkali-activated rice husk carbon were significantly higher than that of CaO2. This improvement in oxygen release performance can be attributed to the unique structure-functional synergy mechanism of the biochar carrier. The high specific surface area of biochar (for example, the specific surface area of alkali-activated rice husk carbon is as high as 2629.49m 2 / g) By physical adsorption, CaO2 is evenly dispersed on the surface of the multi-level pores. This dispersion not only significantly increases the effective exposure area of active sites but also shortens the diffusion path of oxygen, thus accelerating the contact reaction process between CaO2 and water molecules.

[0106] Table 3 pH of the medium and the efficiency of CaO2 conversion to dissolved oxygen after oxygen release ends

[0107]

[0108] Note: A represents a strongly acidic and low-oxygen environment (pH 4.5, DO = 0.5 mg / L); B represents a weakly acidic and low-oxygen environment (pH 6.0, DO = 0.5 mg / L); C represents a strongly acidic and high-oxygen environment (pH 4.5, DO = 3.0 mg / L).

[0109] Table 3 shows the pH of the medium and the efficiency of CaO2 conversion to dissolved oxygen after oxygen release ends:

[0110]

[0111] Among them, η is the efficiency of CaO2 conversion to dissolved oxygen (%); DO1 is the dissolved oxygen concentration of the medium (mg / L) after oxygen release ends; DO0 is the original dissolved oxygen concentration of the medium (mg / L); V is the volume of the medium (L); DO is the amount of O2 theoretically generated by the complete reaction of CaO2 with water (mg).

[0112] As can be seen from Table 3, after the oxygen release ended, there were no significant differences in the pH of the media among the treatments, except that under the condition of low dissolved oxygen concentration (0.5 mg / L) combined with a strong acidic solution (pH 4.5), the pH of the media treated with CaO2@rice husk charcoal was significantly lower than that of other treatments. In terms of the efficiency of converting CaO2 into dissolved oxygen, under the conditions of low dissolved oxygen concentration (0.5 mg / L) combined with a strong acidic solution (pH 4.5) and a weak acidic solution (pH 6.0), the conversion efficiency differed significantly among the treatments, showing that CaO2@alkali-activated rice husk charcoal > CaO2@rice husk charcoal > CaO2; while under the condition of high dissolved oxygen concentration (3.0 mg / L) combined with a strong acidic solution (pH 4.5), the conversion efficiency of CaO2@alkali-activated rice husk charcoal was significantly higher than that of CaO2@rice husk charcoal and CaO2, and there was no significant difference between the latter two. The reason for the increase in the conversion efficiency of CaO2 by alkali-activated rice husk charcoal and rice husk charcoal may be their larger specific surface area, which enables CaO2 to come into full contact with water, thus overcoming the problem that the insoluble Ca(OH)2 covering the surface of CaO2 hinders the further reaction of internal CaO2. In addition, the higher conversion efficiency of alkali-activated rice husk charcoal compared to rice husk charcoal may be due to the fact that alkali-activated rice husk charcoal not only has a higher specific surface area, but also has a higher degree of graphitization and more surface functional groups generated during the activation process, making it more active and able to more effectively promote the reaction of CaO2 with water, thereby promoting the conversion of the generated products into dissolved oxygen.

Claims

1. A method for preparing oxygen-releasing materials based on alkali-activated silicon-rich biochar, characterized in that: The steps include: 1) Preparation of silicon-rich biochar Select silicon-rich agricultural and forestry wastes and calcine them to prepare silicon-rich biochar; 2) Preparation of alkaline activated silicon-rich biochar Silicon-rich biochar was mixed with KOH at a solid-liquid ratio of 1:10 (g / mL), and allowed to stand. The solid was then collected by filtration and washed until the conductivity of the filtrate remained constant. Finally, the solid was dried. The dried solid was mixed with KOH powder in a mass ratio of 1:(3-5), placed in a nickel crucible, and then moved to a muffle furnace for calcination, and then taken out after naturally cooling to room temperature; The obtained sample was mixed with deionized water at a solid-liquid ratio of 1:10 (g / mL), cooled to room temperature, filtered to collect the solid, and washed until the conductivity of the filtrate remained constant. Finally, the solid was dried and sieved to obtain alkali-activated silicon-rich biochar; 3) Preparation of CaO2@alkali-activated silicon-rich biochar The alkali-activated silicon-rich biochar is mixed with CaO2 and anhydrous ethanol, shaken, dried to constant weight, and calcined; The calcined product was cooled to room temperature and extracted with cold deionized water until the conductivity of the filtrate remained constant, then filtered with anhydrous ethanol, the final solid was collected, dried to constant weight, and sieved to obtain CaO2@alkali-activated silicon-rich biochar oxygen-releasing material.

2. The method for preparing the oxygen-releasing material according to claim 1, characterized in that: Step 1) The silicon-rich agricultural and forestry wastes include one or more of rice husks, rice leaves, rice straw, reeds, switchgrass, miscanthus, bamboo poles, and sugarcane bagasse.

3. The method for preparing the oxygen-releasing material according to claim 1, characterized in that: Step 1) The calcination temperature is 300-700°C, and the heating rate is 10-30°C / min.

4. The method for preparing the oxygen-releasing material according to claim 1, characterized in that: Step 2) The concentration of KOH is 5%; The KOH powder is obtained by grinding KOH and passing through a 200-300 mesh sieve.

5. The preparation method based on oxygen-releasing material according to claim 1, characterized in that: Step 2) The calcination temperature is 700-900°C, the heating rate is 20-30°C / min, and the time is 20-50min.

6. The method for preparing the oxygen-releasing material according to claim 1, characterized in that: Step 3) The mass ratio of the alkali-activated silicon-rich biochar to CaO2 is 2:

1.

7. The method for preparing the oxygen-releasing material according to claim 1, characterized in that: Step 3) The calcination temperature is 200-300°C, the heating rate is 15-25°C / min, and the time is 100-150min.

8. The method for preparing the oxygen-releasing material according to claim 1, characterized in that: The step of keeping the conductivity of the filtrate constant means that the relative deviation of two measured values ​​is less than 1%.

9. An oxygen-releasing material obtained by the preparation method according to any one of claims 1 to 8, characterized in that: It is an oxygen-releasing material formed by CaO2 loaded on alkali-activated silicon-rich biochar.

10. The use of the oxygen-releasing material according to claim 9 in environmental treatment, characterized in that: The environmental treatment includes water treatment and soil remediation.

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