Green adsorbent prepared based on rice straw as well as preparation method and application of green adsorbent

Abstract

The invention belongs to the technical field of adsorption materials, and particularly relates to a green adsorbent prepared on the basis of rice straw and a preparation method and application of the green adsorbent. The preparation method comprises the following steps: S1, mixing dried rice straw powder and a Fe < 3 + > solution according to a solid-to-liquid ratio of 1: 10, putting the mixture into a hydrothermal reaction kettle, reacting at 0.5 MPa and 250 DEG C for 4-10 hours, cooling, and sequentially performing suction filtration, cleaning and drying to obtain hydrothermal carbon; s2, mixing the hydrothermal carbon obtained by pretreatment with potassium hydroxide according to a mass ratio of 1: (1-2), then adding 40ml of deionized water to prepare an impregnation liquid, placing the impregnation liquid in a water bath at 45 DEG C to react for 4 hours, and then drying; and S3, calcining the hydrothermal carbon, and then treating to obtain the active hydrothermal carbon with high specific surface area. By optimizing the preparation and modification process of the rice straw-based hydrothermal carbon, the prepared adsorption material has excellent adsorption performance and high specific surface area, is suitable for removing heavy metal ions, and is high in removal efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of adsorption materials, and in particular relates to a green adsorbent prepared based on rice straw, and a preparation method and application thereof. Background Art

[0002] The emission of heavy metal ions (such as lead, cadmium, mercury, etc.) enters the ecosystem through the water enrichment effect and accumulates in the human body through the food chain, posing a serious threat to human health and ecological environmental safety.

[0003] Among many water treatment methods, adsorption has become one of the mainstream technologies for treating heavy metal wastewater due to its high efficiency, greenness and low cost. Hydrothermal carbon is one of the adsorption materials. With its unique surface chemical properties, rich oxygen-containing functional groups and excellent adsorption capacity, it has shown broad application prospects in the treatment of heavy metal wastewater.

[0004] In the prior art, the Chinese patent with publication number CN114917869A discloses "An adsorbent based on waste green tea biochar", which optimizes the adsorption performance of biochar through carbonization and nano-zero-valent iron composite, and can reach adsorption equilibrium within 30 to 120 minutes, which is suitable for a certain degree of heavy metal wastewater treatment. In addition, the Chinese patent with publication number CN116371362A discloses "A preparation method based on coffee shell activated carbon", which improves the pore structure and specific surface area of ​​the adsorbent by adding modified silica, and performs well in the adsorption capacity of heavy metal ions. However, in actual industrial wastewater treatment, the adsorption equilibrium time of these two adsorbents is relatively long, requiring 30-120 minutes and 120 minutes respectively, resulting in a slow adsorption rate, which is difficult to meet the needs of industrial applications that require rapid response, and there is still much room for improvement in rapid adsorption kinetics and overall efficiency.

[0005] Therefore, there is an urgent need for a green adsorbent prepared based on rice straw and its preparation method and application to solve the above problems. Summary of the invention

[0006] In order to overcome the defects in the prior art, the present invention provides a green adsorbent prepared based on rice straw and a preparation method and application thereof. The green adsorbent prepared by the present invention can efficiently remove heavy metal ions in wastewater in a short time.

[0007] To achieve one of the above purposes, the present invention adopts the following technical solution: A method for preparing a green adsorbent based on rice straw comprises the following steps: S1. Pretreatment of rice straw: dry rice straw powder and Fe 3+The solutions are mixed at a solid-liquid ratio of 1:10, and placed in a hydrothermal reactor to react at 0.5 MPa and 250° C. for 4-10 hours. After cooling, the solutions are filtered, washed and dried in sequence to obtain hydrothermal charcoal. S2. Alkaline activation of hydrothermal carbon: the hydrothermal carbon obtained by pretreatment was mixed with potassium hydroxide solid in a mass ratio of 1:(1-2), and then 40 ml of deionized water was added to prepare an impregnation solution, which was placed in a 45°C water bath for reaction for 4 hours and then dried; S3. Post-calcination treatment: calcine the dried hydrothermal carbon, wash the calcined product to neutrality, and then dry it to constant weight to obtain activated hydrothermal carbon with high specific surface area.

[0008] Preferably, Fe 3+ The solution is one of ferric chloride solution or ferric nitrate nonaqueous solution with a concentration of 1-4 g / L. 3+ The solution is mixed with rice straw powder and can be 3+ Active sites were introduced by coordinating with the hydroxyl groups on the surface of straw fibers, and the primary carbon skeleton was constructed by catalytic dehydration and polycondensation under hydrothermal conditions at 250 °C. 3+ Fe(OH) generated by hydrolysis 3 / Fe 2 O 3 Nanoparticles act as "hard templates" to promote the formation of micropores and mesopores, and the "hard templates" are removed in the subsequent potassium hydroxide activation and calcination at 700 ° C, leaving rich interconnected pores, thereby significantly improving the specific surface area and heavy metal ion adsorption capacity of hydrothermal carbon; 2g / L Fe 3+ At the concentration, the active site density and pore openness reach the best balance, so that the hydrothermal carbon has the largest specific surface area (about 753m² / g), and Hg 2+ The adsorption capacity is the highest (302 mg / g).

[0009] Preferably, in step S1, before using the hydrothermal reactor, nitrogen is used to purge and exhaust 3 times to remove oxygen in the reactor, create an anaerobic environment, prevent the straw from undergoing oxidation during the hydrothermal process, retain more organic structures, and thus improve the quality of the hydrothermal charcoal, enhance the formation of pore structures during the subsequent activation process, and provide more active sites for the adsorption of heavy metals; the stirring speed in the hydrothermal reactor is 500 r / min to ensure the uniformity of the reaction system and promote the hydrothermal reaction of straw and Fe 3+ The full contact of the solution improves the reaction efficiency, facilitates the formation of a uniform hydrothermal carbon structure, enhances the overall performance of the adsorbent, and avoids incomplete local reactions.

[0010] Preferably, in step S1, the cooling time after the hydrothermal reaction is 4 hours. The cooling time is controlled to avoid the destruction of the hydrothermal carbon structure caused by rapid cooling and to maintain the initially formed pores and functional groups. The stable cooling process is conducive to the formation of an ordered carbon-based structure, providing a good foundation for subsequent activation and indirectly improving the adsorbent's absorption of Fe. 3+ adsorption capacity.

[0011] Preferably, in step S2, the mass ratio of potassium hydroxide (KOH) to hydrothermal carbon is 1:1. KOH, as an activator, reacts with hydrothermal carbon to generate microporous and mesoporous structures, and introduces surface functional groups. The mass ratio of 1:1 determines the amount of activator and the degree of activation. This mass ratio can significantly increase the specific surface area and porosity of the adsorbent, and improve the adsorption of Hg. 2+ The adsorption capacity of heavy metal ions such as iodine and iodine can be increased; too high or too low a ratio may lead to pore collapse or insufficient activation.

[0012] Preferably, in step S3, the temperature in the tube furnace is raised to 700°C at a heating rate of 10°C / min, and calcination is performed for 1 hour.

[0013] The temperature was raised slowly at a heating rate of 10°C / min to avoid thermal stress from damaging the carbon structure, ensure the uniformity of pore development, facilitate the formation of a stable porous structure, and enhance the mechanical strength and adsorption performance of the adsorbent.

[0014] Calcination at 700°C can promote the chemical reaction between KOH and carbon, further expand the pores and remove impurities; the calcination time of 1 hour ensures that the reaction is sufficient but not excessive; optimizes the specific surface area and pore distribution, and improves the chemical adsorption and physical adsorption capacity of heavy metal ions.

[0015] Preferably, in step S3, the calcined product is washed with deionized water and acetone in sequence until it is neutral and has a pH value of 7. Acetone is an organic solvent that can wash away residual bio-oil and accelerate the drying process. A pH value of 7 can remove residual potassium hydroxide (KOH) and other alkaline substances, preventing the adsorbent surface from being strongly alkaline, which affects its applicability in actual wastewater treatment. Neutral pH ensures that the adsorbent is resistant to Hg 2+ The adsorption process of heavy metal ions will not be limited by the surface acidity and alkalinity, and the environmental friendliness of the adsorbent will be improved.

[0016] To achieve the second objective above, the present invention provides a green adsorbent prepared by a method for preparing a green adsorbent based on rice straw.

[0017] To achieve the third objective above, the present invention provides an application of a green adsorbent prepared based on rice straw, wherein the adsorbent is applied to remove heavy metal ions in water.

[0018] Preferably, the heavy metal ions are one or more of lead, cadmium, copper and mercury.

[0019] The advantages of the present invention are: (1) The present invention optimizes the preparation and modification process of rice straw-based hydrothermal carbon, so that the obtained material has excellent adsorption performance and high specific surface area, which significantly improves the rapid adsorption performance of rice straw-based adsorption materials, especially the efficient removal of heavy metal ions in a short time, greatly shortening the wastewater treatment time. In addition, the preparation method uses cheap and easily available rice straw, which reduces the cost of industrial wastewater treatment and has the advantages of green, environmentally friendly, efficient and economical wastewater treatment.

[0020] (2) The present invention uses waste biomass rice straw as the main raw material, combines green and environmentally friendly hydrothermal treatment and chemical modification processes, and successfully prepares a high-efficiency hydrothermal carbon adsorbent. Specifically, the prepared hydrothermal carbon green adsorbent has a specific surface area greater than 500m² / g, an adsorption capacity for heavy metal ions greater than 100mg / g, and can reach Hg within 5 minutes. 2+ and Pb 2 + More than 85% of the maximum adsorption capacity, the maximum adsorption capacity can reach 302.36 mg / g, which is significantly better than the existing technology and has excellent adsorption rate and capacity. The preparation method is green and environmentally friendly, the process is simple, and rice straw is abundant, cheap and easy to obtain as a raw material, and has wide potential for industrial application. By optimizing the hydrothermal reaction and chemical modification process, the hydrothermal carbon of the present invention exhibits an excellent microporous structure, which not only provides a large number of active adsorption sites, but also improves the mass transfer rate of solute molecules and the diffusion efficiency of solute molecules, thereby significantly reducing the adsorption time and meeting the rapid response of industrial wastewater treatment needs. Compared with the prior art, the hydrothermal carbon of the present invention has significant advantages in adsorption rate and capacity, can quickly remove heavy metal ions, and provides a more efficient solution to solve heavy metal pollution in industrial wastewater.

[0021] (3) The present invention introduces Fe on the pore surface of hydrothermal carbon 3+ , achieving efficient adsorption of heavy metal ions. Positively charged Fe 3+ Can react with negatively charged heavy metal ions in water (such as Hg 2+ and Pb 2+ ) undergo electrostatic interaction, firmly fixing it on the surface of the hydrothermal carbon. At the same time, the present invention optimizes the pore structure design and constructs a three-dimensional porous structure with abundant micropores, mesopores and macropores. The micropores provide a large number of active adsorption sites, significantly increasing the adsorption capacity; the mesopores and macropores form efficient mass transfer channels, promoting the rapid transmission and diffusion of solute molecules, thereby greatly improving the adsorption rate. And Fe 3+The introduction of Fe does not hinder the flow space of the pores, and the fluidity of the liquid is still good, ensuring the rapid contact and transmission of ions in the solution. 3+ Evenly grafted onto the surface of hydrothermal carbon and calcined at high temperature to ensure Fe 3+ The stable fixation avoids the residue of chemical reagents, thereby preventing secondary pollution. This optimized pore structure not only enhances the overall adsorption performance of the material, but also ensures its excellent adaptability and high efficiency in actual industrial wastewater treatment. In summary, the rice straw-based activated carbon of the present invention significantly improves its performance in the rapid removal of heavy metal ions by rationally designing the pore structure and surface chemical properties, showing broad application prospects and significant environmental and economic benefits.

[0022] (4) The reason why the present invention uses rice straw is that: ①. High ratio of cellulose to hemicellulose Rice straw contains high levels of cellulose (30%-35%) and hemicellulose (25%-35%), but low levels of lignin (5%-10%). This composition has a dual effect during the activation process: Basis of pore development: Cellulose and hemicellulose are more easily decomposed to form micropores and mesopores during pyrolysis, while the low lignin content reduces its hindrance to the pore structure.

[0023] Activator permeability: The loose structure of the lignin-carbohydrate complex (compared to raw materials with high lignin content) makes it easier for the KOH activator to penetrate and promote pore expansion.

[0024] ②. Resources are abundant and cheap Due to the huge annual rice production, the by-product straw is extremely abundant and is usually burned or discarded, resulting in low resource utilization. Using it as a hydrothermal charcoal raw material is low-cost and highly sustainable.

[0025] ③. Environmentally friendly, solving the problem of straw burning Rice straw burning is an important source of air pollution. Using it to prepare hydrothermal carbon adsorption materials can effectively reduce atmospheric pollutant emissions and achieve resource recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a curve chart showing the variation of the adsorption amount of heavy metals by the activated hydrothermal carbon prepared in Example 1 of the present invention over time within 5 minutes.

[0027] Figure 2 This is a particle size distribution diagram of the micropores of the activated hydrothermal carbon prepared in Example 1 of the present invention before and after adsorbing heavy metals.

[0028] Figure 3This is a graph showing the change in adsorption capacity of the activated hydrothermal carbon prepared in Example 1 of the present invention for a mixed heavy metal solution under different pH conditions. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0030] Example 1 S1. Pretreatment of rice straw Weigh 10g of dried rice straw powder and mix it with 100mL of 2g / L iron nitrate nine aqueous solution; then transfer the mixture to the glass lining of the hydrothermal reactor, pass nitrogen gas to purge it three times and then pressurize it to 0.5MPa, use mechanical stirring to ensure that the straw powder and iron nitrate nine aqueous solution are evenly mixed, set the stirring speed to 500r / min, and react at 250℃ for 10 hours. After the reaction is completed, cool it naturally to room temperature (about 4 hours), collect the solid phase product by suction filtration, and wash it with deionized water and acetone in turn until it is clear; the washed product is placed in a 105℃ oven and dried to constant weight to obtain hydrothermal carbon F2.

[0031] S2. Alkaline activation of hydrothermal carbon The hydrothermal carbon F2 obtained by pretreatment was mixed with potassium hydroxide (KOH) in a mass ratio of 1:1, and then 40 ml of deionized water was added to prepare the impregnation solution, and the mixture was reacted in a 45°C water bath for 4 hours. After the reaction, the sample was poured into a beaker and then placed in an oven at 105°C for 12 hours to complete the impregnation and drying process.

[0032] S3. High temperature calcination treatment The dried hydrothermal carbon was placed in a tube furnace for calcination. The calcination conditions were: heating to 700°C at a rate of 10°C / min and maintaining for 1 hour. After calcination, it was washed with deionized water and acetone in sequence until neutral, and then the washed sample was placed in a 105°C oven to dry to constant weight, and finally ground and collected to obtain activated hydrothermal carbon F2-K1, which is a green adsorbent.

[0033] Example 2 S1. Pretreatment of rice straw Weigh 10g of dried rice straw powder and mix it with 100mL of 2g / L iron nitrate nine aqueous solution. Transfer the mixture to the glass lining of the hydrothermal reactor, pass nitrogen gas to purge it three times, and then pressurize it to 0.5MPa. Use mechanical stirring to ensure that the straw powder and the iron nitrate nine aqueous solution are evenly mixed. The stirring speed is set to 500r / min, and the reaction is carried out at 250℃ for 10 hours. After the reaction is completed, it is naturally cooled to room temperature (about 4 hours), and the solid phase product is collected by suction filtration, and washed with deionized water and acetone in turn until it is clear. The washed product is placed in a 105℃ oven and dried to constant weight to obtain hydrothermal carbon F2.

[0034] S2. Alkaline activation of hydrothermal carbon The hydrothermal carbon F2 obtained by pretreatment was mixed with potassium hydroxide (KOH) at a mass ratio of 1:2, and then 40 ml of deionized water was added to prepare the impregnation solution, and the mixture was reacted in a 45°C water bath for 4 hours. After the reaction, the sample was poured into a beaker and placed in an oven at 105°C for 12 hours to complete the impregnation and drying process.

[0035] S3. High temperature calcination treatment The dried hydrothermal carbon was placed in a tube furnace for calcination. The calcination conditions were: heating to 700°C at a rate of 10°C / min and maintaining for 1 hour. After calcination, it was washed with deionized water and acetone in sequence until neutral, and then the washed sample was placed in a 105°C oven to dry to constant weight, and finally ground and collected to obtain activated hydrothermal carbon F2-K2, which is a green adsorbent.

[0036] Comparative Example 1 S1. Pretreatment of rice straw Weigh 10g of dried rice straw powder and mix it with 100mL of 2g / L iron nitrate nine aqueous solution. Transfer the mixture to the glass lining of the hydrothermal reactor, pass nitrogen gas to purge it three times, and then pressurize it to 0.5MPa. Use mechanical stirring to ensure that the straw powder and the iron nitrate nine aqueous solution are evenly mixed. The stirring speed is set to 500r / min. React at 250℃ for 10 hours. After the reaction is completed, cool it naturally to room temperature (about 4 hours), collect the solid phase product by suction filtration, and wash it with deionized water and acetone in turn until it is clear. The washed product is placed in a 105℃ oven and dried to constant weight to obtain hydrothermal carbon F2.

[0037] S2. Alkaline activation of hydrothermal carbon The hydrothermal carbon F2 obtained by pretreatment was mixed with potassium carbonate (K 2 CO 3) were mixed in a mass ratio of 1:1, and then 40 ml of deionized water was added to prepare the impregnation solution, and the mixture was reacted in a 45°C water bath for 4 hours. After the reaction, the sample was poured into a beaker and placed in an oven at 105°C for 12 hours to complete the impregnation and drying process.

[0038] S3. High temperature calcination treatment The dried hydrothermal carbon was placed in a tube furnace for calcination. The calcination conditions were: heating to 700°C at a rate of 10°C / min and maintaining for 1 hour. After calcination, it was washed with deionized water and acetone in sequence until neutral, and then the washed sample was placed in a 105°C oven to dry to constant weight, and finally ground and collected to obtain potassium carbonate modified activated carbon.

[0039] Comparative Example 2 Weigh 10g of dried rice straw powder and 100mL of 2g / L iron nitrate nonaqueous solution in a hydrothermal reactor, and disperse the rice straw powder evenly in the solution by mechanical stirring. After nitrogen purge three times, pressurize to 0.5MPa, and set the speed of the mechanical stirring shaft to 500r / min. Heat from room temperature to 250℃ and maintain for 10h. After the reaction is completed, cool naturally to room temperature (about 4h), then collect the solid phase product by suction filtration, wash with deionized water and acetone in turn until clear, and dry in an oven at 105℃ for more than 5h to obtain F2.

[0040] The materials prepared in Examples 1-2 and Comparative Examples 1-2 were respectively tested for their adsorption performance on heavy metal ions. The experiment was intended to determine the maximum adsorption capacity and initial specific surface area of ​​0.1 g of hydrothermal charcoal prepared from rice straw for 250 ml of a single heavy metal solution with a concentration of 300 mg / L at room temperature.

[0041] The specific experimental steps are as follows: First, use HNO 3 and NaOH to adjust the pH value of 250 ml of a heavy metal solution with a concentration of 300 mg / L to 7; then pour the adjusted heavy metal solution into a beaker, and then put 0.1 g of the hydrothermal carbon prepared in Example 1-2 and Comparative Example 1-2 into the beaker, place it in a constant temperature oscillator, and set the oscillator speed to 160 rpm; after oscillating for 12 hours, separate the solid and liquid phases by suction filtration, collect the liquid phase sample, and use ICP-OES to detect the concentration of residual heavy metal ions in the solution to calculate the maximum adsorption capacity of the adsorbent carbon. The heavy metal is Cu 2+ , Pb 2+ 、Cd 2+ and Hg 2+ The results are shown in Table 1 below: Table 1 ; As shown in Table 1, the adsorption performance of the activated hydrothermal carbon prepared in Example 1 is particularly outstanding, especially for Hg 2+ The adsorption capacity is as high as 302.36 mg / g, which is nearly 20 times higher than that of comparative example 2; at the same time, its specific surface area reaches 753.24 m 2 / g, much higher than 40.31m / g in Comparative Example 2 2 / g. The significant increase in specific surface area effectively enhances the rapid adsorption capacity of activated carbon for heavy metal ions.

[0042] In addition, after increasing the amount of KOH in Example 2, although the adsorption performance and specific surface area are still relatively high, the adsorption of Hg 2+ The adsorption amount reached 241.89 mg / g, but was slightly inferior to that in Example 1. This may be due to the fact that the increase in the amount of KOH resulted in a decrease in the number of micropores, while the proportion of mesopores and macropores increased, thereby reducing the number of active sites for the adsorption of heavy metal ions.

[0043] Further, by comparing Example 1 with Comparative Example 1 (using K 2 CO 3 The performance difference of KOH activation (see Table 1) can verify that the KOH activation process is significantly superior to KOH in terms of adsorption capacity and specific surface area. 2 CO 3 Specifically, KOH, due to its strong alkalinity (pH>14), undergoes a reaction (6KOH + 2C → 2K + 3H 2 ↑ +2K 2 CO 3 ) severely etches the carbon skeleton to form a high-density microporous structure, leaving abundant pores after calcination; while K 2 CO 3 Due to its weak alkalinity (pH ≈ 11), it can be decomposed only by thermal decomposition (K 2 CO 3 →700℃ K 2 O + CO 2 ↑) Gas pores are generated, mainly mesopores, and K 2 The template effect of O is weak and the micropore density is low. In addition, the surface of the material generated by KOH activation is rich in –OH and –COOH functional groups, which can efficiently adsorb Hg through complexation. 2+ and Pb 2+ , and K 2 CO 3 The oxygen-containing functional group density of the activated product is lower. The above mechanism difference leads to the specific surface area of ​​comparative example 1 (334.52m 2 / g) and Hg 2+The adsorption capacity (180.5 mg / g) is only 44.4% and 59.7% of that in Example 1, respectively, which fully demonstrates the significant advantages of KOH in pore structure optimization and surface chemical regulation.

[0044] Figure 1 The activated hydrothermal carbon prepared in Example 1 reacted with different heavy metal ions (Hg 2+ , Pb 2+ 、Cd 2+ , Cu 2+ The curve of the adsorption amount of ) changes with time. The experimental method is the same as the detection method in Table 1, except that the samples are taken and tested at different time points. Figure 1 It can be seen that the activated hydrothermal carbon prepared in Example 1 exhibits significant rapid adsorption characteristics, among which Hg 2+ The adsorption capacity can reach more than 60% of the maximum capacity within 1 minute, and reach 292.1 mg / g in 5 minutes, showing excellent adsorption rate and capacity. This feature is due to the optimized pore structure design and the good dispersion ability of hydrothermal carbon in heavy metal solutions. The micropores provide a large number of active sites for adsorption, while the mesopores and macropores accelerate the mass transfer process. 2+ The adsorption amount of Cd also increased rapidly in a short time, approaching adsorption equilibrium within 2 minutes, with a maximum adsorption amount of 178.46 mg / g, showing a good adsorption effect. 2+ and Cu 2+ The adsorption amount is slightly lower, but it increases gradually with time, which also shows the ability of adsorbent carbon to treat these metal ions.

[0045] In general, the difference in adsorption performance is closely related to the characteristics of metal ions and their ability to bind to the functional groups on the surface of adsorbent carbon, which fully demonstrates the importance of adsorbent carbon in the rapid removal of Hg 2+ and Pb 2+ It has superior performance in many aspects and has the potential to treat multiple metal ions, providing an efficient solution for industrial wastewater treatment. 2+ It exhibits remarkable rapid adsorption characteristics.

[0046] Figure 2 This is a comparison of the pore size distribution of the activated hydrothermal carbon prepared in Example 1 before and after the adsorption of heavy metals, showing the change in the pore size distribution of the rice straw-based green adsorbent before and after adsorption. Figure 2It can be seen that before adsorption, the peak of the pore size distribution is concentrated in the range of 0.8 to 1.2 nm, indicating that the adsorbed carbon has a rich microporous structure, providing a large number of active sites for the adsorption of heavy metal ions. After adsorption, the proportion of micropores decreases significantly, reflecting that heavy metal ions are mainly stored in the micropores. This change shows that micropores play a key role in the adsorption process, and their high-density active sites can quickly bind to metal ions, thus achieving efficient adsorption performance. It intuitively demonstrates the importance of optimizing the microporous structure in enhancing the ability of adsorbed carbon to remove heavy metals, providing strong support for the rapid adsorption and efficient treatment of industrial wastewater.

[0047] Using the detection method shown in Table 1, 0.1 g of the activated hydrothermal carbon prepared in Example 1 was used to adsorb 50 ml of a mixed solution of four heavy metals (Hg 2+ , Pb 2+ , Cd 2+ and Cu 2+ with a mass ratio of 1:1:1:1), and the pH of the heavy metal mixed solution was adjusted to 3, 5, 7, 9, and 11 with HNO 3 and NaOH. The results are as Figure 3 shown. Figure 3 The adsorption capacity changes of Hg 2+ , Pb 2+ , Cd 2+ and Cu 2+ on the surface of the activated hydrothermal carbon prepared from rice straw under different pH conditions. It can be seen that the adsorption performance of the activated hydrothermal carbon shows obvious regularity with the change of pH value. At pH = 7, the adsorption amounts of Hg 2+ and Pb 2+ reach the peaks, which are 106.25 mg / g and 75.7 mg / g respectively, indicating that the negative charge on the surface of the activated hydrothermal carbon is enhanced at this time, and the electrostatic attraction between the positively charged metal ions is significant. At a lower pH (pH = 3), due to the competitive adsorption of H + on the adsorption sites, the adsorption capacity is low; while at a high pH (pH = 11), some metal ions may precipitate, resulting in a slight decrease in the adsorption amount. However, the overall adsorption performance does not fluctuate greatly. This shows that the activated hydrothermal carbon exhibits good adsorption stability under different pH conditions, and at the same time, it has the best adsorption effect on Hg 2+ and Pb 2+ under neutral conditions, demonstrating its excellent rapid adsorption ability and reliability, providing an important optimization reference for industrial wastewater treatment.

[0048] In addition, when the activated hydrothermal carbon prepared in Example 1 is placed in a heavy metal solution, it can be seen that the solution is uniformly black, which further illustrates that the distribution of the activated hydrothermal carbon in the solution is relatively uniform, which is crucial for improving the mass transfer efficiency and reaction rate of green adsorbents in actual industrial wastewater treatment. In addition, the uniformly dispersed activated hydrothermal carbon can not only effectively cover a larger treatment volume, but also avoid the problem of reduced active sites due to agglomeration, providing a guarantee for the rapid adsorption of heavy metal ions.

[0049] The present invention significantly improves the rapid adsorption performance and pore structure of rice straw-based activated hydrothermal carbon through optimized activation and calcination processes, especially showing outstanding advantages in the efficient removal of heavy metal ions in industrial wastewater. By rationally designing the pore structure and optimizing the ratio of micropores, mesopores and macropores, the material can quickly reach adsorption equilibrium in a short time. For example, for Hg 2+ , Pb 2+ The adsorption of heavy metal ions such as chlorinated polyols can reach more than 85% of the maximum adsorption capacity within 5 minutes, significantly shortening the wastewater treatment time. This feature effectively meets the rapid response requirements in industrial wastewater treatment. The present invention adopts a green and environmentally friendly preparation process, uses cheap and readily available rice straw as raw material, and ensures the high efficiency and stability of the material through a combined process of hydrothermal reaction, alkaline activation and high-temperature calcination. Compared with the traditional high-temperature carbonization method, this method optimizes the porosity and specific surface area of ​​the material, and improves its adsorption performance and adsorption rate. At the same time, the preparation process does not involve complex high-temperature and high-pressure equipment, and has better prospects for industrial application.

[0050] In summary, the rice straw-based activated hydrothermal carbon of the present invention has significant advantages in terms of performance, raw material sources and cost. By rationally designing a specific pore structure and combining an efficient green preparation process, the present invention has shown unique advantages in rapidly adsorbing heavy metals and improving the efficiency of industrial wastewater treatment. This invention can provide an economical and efficient solution to heavy metal pollution in practical applications and has a wide range of application potential.

[0051] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a green adsorbent based on rice straw, characterized in that: The steps include: S1. Pretreatment of rice straw: dry rice straw powder and Fe 3+ The solutions are mixed at a solid-liquid ratio of 1:10, and placed in a hydrothermal reactor to react at 0.5 MPa and 250° C. for 4-10 hours. After cooling, the solutions are filtered, washed and dried in sequence to obtain hydrothermal charcoal. S2. Alkaline activation of hydrothermal carbon: the hydrothermal carbon obtained by pretreatment was mixed with potassium hydroxide in a mass ratio of 1:(1-2), and then 40 ml of deionized water was added to prepare an impregnation solution, which was placed in a 45°C water bath for reaction for 4 hours and then dried; S3. Post-calcination treatment: calcine the dried hydrothermal carbon, wash the calcined product to neutrality, and then dry it to constant weight to obtain activated hydrothermal carbon with high specific surface area.

2. The method for preparing a green adsorbent based on rice straw according to claim 1, characterized in that: The Fe 3+ The solution is one of a ferric chloride solution or a ferric nitrate nonaqueous solution with a concentration of 1-4 g / L.

3. The method for preparing a green adsorbent based on rice straw according to claim 1, characterized in that: In step S1, before using the hydrothermal reactor, nitrogen was used to purge and exhaust the reactor three times, and the stirring speed of the hydrothermal reactor was 500 r / min.

4. The method for preparing a green adsorbent based on rice straw according to claim 1, characterized in that: In step S1, the cooling time after the hydrothermal reactor reaction is 4 hours.

5. The method for preparing a green adsorbent based on rice straw according to claim 1, characterized in that: In step S2, the mass ratio of potassium hydroxide to hydrothermal carbon is 1:

1.

6. The method for preparing a green adsorbent based on rice straw according to claim 1, characterized in that: In step S3, the temperature in the tube furnace is raised to 700°C at a heating rate of 10°C / min, and calcination is performed for 1 hour.

7. The method for preparing a green adsorbent based on rice straw according to claim 1, characterized in that: In step S3, the calcined product is washed with deionized water and acetone in sequence until it becomes neutral and has a pH value of 7.

8. A green adsorbent prepared by the preparation method according to any one of claims 1 to 7.

9. A use of the green adsorbent as claimed in claim 8, characterized in that: The adsorbent is used to remove heavy metal ions from water.

10. The use of a green adsorbent prepared based on rice straw according to claim 9, characterized in that: The heavy metal ions are one or more of lead, cadmium, copper and mercury.

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