Hierarchical porous biochar loaded with nanosized calcium carbonate, and preparation method and application thereof

Abstract

This invention discloses a method for preparing hierarchical porous biochar loaded with nano-calcium carbonate, comprising the following steps: mixing biomass powder with hydrated potassium oxalate, grinding evenly, adding nano-calcium carbonate, continuing grinding evenly, heating under a nitrogen atmosphere, and allowing the mixture to cool naturally after the reaction is complete to obtain the pyrolysis product; washing the pyrolysis product with deionized water, then separating the solid and liquid phases using a high-speed centrifuge to obtain a solid product; washing the solid product again with deionized water until the pH of the washing solution is constant; drying the washed solid product to obtain hierarchical porous biochar loaded with nano-calcium carbonate. This invention also discloses a hierarchical porous biochar loaded with nano-calcium carbonate and its applications. This invention uses deionized water washing instead of traditional acid washing, which increases both the specific surface area of ​​the carbon material and the adsorption sites for calcium ions, overturning the notion that the template agent needs to be completely removed to improve the adsorption performance of carbon materials.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials technology, and specifically relates to a hierarchical porous biochar supported on nano-calcium carbonate, its preparation method and application. Background Technology

[0002] Soil is the foundation of human daily life. With rapid industrial and economic development, soil pollution has intensified, causing significant harm to human health. The types of pollutants are numerous, mainly including heavy metals (Pb, Cd, Cr, Ni, etc.), metalloids (Se, As, etc.), and organic pollutants (dyes, antibiotics, etc.). Among these, heavy metals are non-biodegradable and can accumulate in organisms through the food chain. Therefore, soil heavy metal pollution has become a pressing environmental problem that my country urgently needs to address.

[0003] Biochar is a high-carbon material, typically obtained by thermally treating biomass (wood, manure, leaves, etc.) in an anaerobic environment. Its unique properties enable it to play a significant role in mitigating climate change, agriculture, environmental remediation, and energy production. Biochar is often used as a low-cost alternative to activated carbon for water and soil treatment to remove various pollutants, such as heavy metal ions, volatile organic compounds, pesticides, pharmaceuticals, dyes, and polycyclic aromatic hydrocarbons. Unlike activated carbon, raw biochar has a relatively low specific surface area, thus not showing great potential for pollutant adsorption. Therefore, researchers have focused on modifying raw biochar to improve its specific surface area and mechanical properties. Modification methods mainly include acid treatment, alkali treatment, organic modification, and composite material modification. Many biochar-based materials have been used as environmentally friendly adsorbents in recent years.

[0004] Porous materials have always been a hot topic in adsorption materials, attracting widespread attention in the field due to their high specific surface area and porosity, as well as fast mass transfer rates. Calcium carbonate exhibits high adsorption capacity and mild reaction conditions in the passivation of heavy metals, and its superior biological properties have garnered significant interest in its application as a novel material. Calcium carbonate is a very inexpensive material, widely found in nature, harmless to humans, and environmentally friendly. Currently, calcium carbonate can be used to remove various metal ions, including Hg. 2+ Pb 2+ Cd 2+Besides its ability to adsorb heavy metals, calcium carbonate can also improve the pore structure of carbon materials and enhance the stability of biochar. However, directly loading calcium carbonate onto carbon materials reduces the specific surface area of ​​the carbon materials, resulting in the loss of a large number of heavy metal adsorption sites. In recent years, porous carbon materials have been prepared using a template method. When calcium carbonate is used as a template agent on carbon materials, it can provide a large number of macroporous structures and improve the adsorption performance of carbon materials from the perspective of mass transfer. However, using it as a template agent leads to a large waste of calcium ions, reducing the added value of calcium carbonate. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention aims to provide a method for preparing hierarchical porous biochar loaded with nano-calcium carbonate, which solves the problem of calcium ion waste, increases the specific surface area of ​​carbon materials, and increases the adsorption sites of calcium ions.

[0006] Another object of the present invention is to provide a hierarchical porous biochar supported on nano-calcium carbonate.

[0007] Another object of the present invention is to provide an application of hierarchical porous biochar loaded with nano-calcium carbonate.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing hierarchical porous biochar loaded with nano-calcium carbonate includes the following steps:

[0010] (1) Mix biomass powder with hydrated potassium oxalate, grind evenly, add nano calcium carbonate, continue grinding evenly, heat under nitrogen atmosphere, and cool naturally after the reaction is complete to obtain the pyrolysis product.

[0011] (2) The pyrolysis product obtained in step (1) is washed with deionized water and then separated into solid and liquid by high-speed centrifuge to obtain solid product; the solid product is then washed with deionized water until the pH of the washing liquid is constant; the washed solid product is dried to prepare hierarchical porous biochar loaded with nano-calcium carbonate.

[0012] Preferably, the mass ratio of the biomass powder, the hydrated potassium oxalate, and the nano-calcium carbonate is 1 to 5:1:1.

[0013] Preferably, the specific steps of washing in step (2) are as follows:

[0014] The pyrolysis product is placed in a centrifuge tube and ultrasonically washed with deionized water for 5-10 minutes; the mass ratio of the pyrolysis product to the deionized water is 1:80-100.

[0015] More preferably, the washing time is 10 minutes.

[0016] Preferably, the particle size of the nano-calcium carbonate is 40-80 nm.

[0017] Preferably, in step (1), the specific steps of heating are as follows:

[0018] The temperature is increased at a rate of 3–5 °C / min until the reaction temperature of 600–800 °C is reached, and then maintained at the reaction temperature for 60–90 min.

[0019] More preferably, the heating rate is 3°C / min, the reaction temperature is 700°C, and the temperature is maintained at the reaction temperature for 60 min.

[0020] Preferably, during the heating process, the nitrogen flow rate is 40 mL / min.

[0021] Preferably, the preparation steps of the biomass powder are as follows:

[0022] The biomass is washed, air-dried, and then pulverized using a universal pulverizer. The pulverized biomass powder is obtained by sieving through a 60-mesh stainless steel sieve.

[0023] More preferably, the biomass is ginkgo yellow leaves.

[0024] Preferably, the speed of the high-speed centrifuge in step (2) is 5600 rpm.

[0025] Preferably, the freeze-drying time in step (2) is 24h to 48h.

[0026] More preferably, the freeze-drying time in step (2) is 48 hours.

[0027] A hierarchical porous biochar loaded with nano-calcium carbonate is prepared by the above-described method for preparing hierarchical porous biochar loaded with nano-calcium carbonate.

[0028] An application of a hierarchical porous biochar loaded with nano-calcium carbonate for the treatment of wastewater containing heavy metals.

[0029] Preferably, the heavy metal is Cd(II).

[0030] The present invention has the following advantages and beneficial effects compared with the prior art:

[0031] (1) This invention discloses a method for preparing hierarchical porous biochar loaded with nano-calcium carbonate. The method uses deionized water washing instead of traditional acid washing, which increases both the specific surface area of ​​the carbon material and the adsorption sites for calcium ions, resulting in biochar with a rich pore structure and loaded with calcium carbonate. This breaks the misconception that thoroughly removing the template agent is necessary to improve the adsorption performance of carbon materials. Using deionized water washing reduces the loss of calcium ions with the washing solution. Calcium ions not only increase the specific surface area but also remain on the carbon as adsorption sites, significantly improving the adsorption performance of the carbon material.

[0032] (2) The hierarchical porous biochar prepared by this invention has a rich pore structure, including micropores, mesopores, and macropores, with a high specific surface area and pore volume, providing more physical adsorption space and chemical adsorption active sites. First, this invention uses nano-calcium carbonate and potassium oxalate as activators and biomass as carbon precursors. After high-temperature pyrolysis, potassium carbonate and calcium oxide are generated. After washing with water, calcium oxide reacts with potassium carbonate dissolved in water to generate calcium carbonate, which is loaded onto the biochar to form mesopores. Second, due to the presence of dual activators in the pyrolysis process, carbon monoxide and carbon dioxide generated by pyrolysis generate micropores on the carbon. Excess calcium oxide is washed and dissolved in water to form macropores, thus forming a hierarchical porous structure. The structure of mesopores and macropores is beneficial to improving the mass transfer rate of the adsorption process, achieving efficient and rapid removal of pollutants, and improving the adsorption performance of hierarchical porous biochar for heavy metals.

[0033] (3) The nano-calcium carbonate supported on the surface of the hierarchical porous biochar disclosed in this invention has higher heavy metal adsorption performance compared with ordinary calcium carbonate particles, further improving the adsorption capacity of the hierarchical porous biochar. In the preparation process, the nano-calcium carbonate not only improves the pore structure but also acts as a reactant of the active component, greatly improving the utilization rate of calcium carbonate in the preparation process. As an adsorbent material, its maximum adsorption capacity for the heavy metal cadmium can reach 293.73 mg / g, with the characteristics of fast adsorption rate and high removal rate, and can be widely used in the field of environmental remediation.

[0034] (4) The hierarchical porous biochar of this invention provides a new approach to the preparation of carbon materials using nano-calcium carbonate, achieving an increase in the specific surface area of ​​biochar while loading nano-calcium carbonate particles. The specific surface area, pore size, and pore volume of the biochar can be controlled by adjusting the preparation reaction conditions. Compared to commonly used calcium carbonate passivating agents, it features high adsorption activity and a fast adsorption rate. It has a wide range of applications and suitable objects in the field of environmental remediation, such as being applicable to different degrees of heavy metal pollution in water or soil. Furthermore, the preparation method provided by this invention is simple, convenient to operate, and easy to scale up and industrialize for production and application. No toxic reagents are required during the preparation process, and no toxic byproducts are generated. Attached Figure Description

[0035] Figure 1 The image shows the infrared spectrum of the product obtained in Example 1.

[0036] Figure 2 The thermogravimetric curve of the product obtained in Example 1 under dry air atmosphere.

[0037] Figure 3 The thermogravimetric curve of the product obtained in Example 1 under a nitrogen atmosphere is shown.

[0038] Figure 4 The image shows the XRD pattern of the product obtained in Example 1.

[0039] Figure 5 The image shown is a SEM-EDS image of the product obtained in Example 1.

[0040] Figure 6 This is the adsorption-desorption curve of the product obtained in Example 1.

[0041] Figure 7 This is a pore size distribution diagram of the product obtained in Example 1.

[0042] Figure 8 This is an SEM image of the product obtained in Example 2.

[0043] Figure 9 This is a SEM image of the product obtained in Example 3.

[0044] Figure 10 This is an SEM image of the product obtained in Example 4.

[0045] Figure 11 The adsorption capacity diagram of the product obtained in Example 1 for Cd(II) adsorption at different contact times is shown.

[0046] Figure 12 The adsorption isotherm of Cd(II) by the product obtained in Example 1 at the same contact time is shown. Detailed Implementation

[0047] The invention's objective will be further described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described in detail here, but the implementation of the invention is not limited to the following embodiments.

[0048] Example 1

[0049] This embodiment provides a method for preparing hierarchical porous biochar loaded with nano-calcium carbonate.

[0050] (1) Wash and air-dry the yellow ginkgo leaves, then grind them into powder using a universal grinder. Use a 60-mesh stainless steel sieve to sieve the powder. The material that passes through the sieve is the obtained dried ginkgo leaf powder.

[0051] (2) Place 500 mg of dried ginkgo leaf powder and 200 mg of hydrated potassium oxalate in an agate mortar and grind for 5 min until the powder is evenly mixed. Add 200 mg of nano calcium carbonate to the ginkgo leaf and potassium oxalate mixed powder and grind for 5 min until the powder is evenly mixed to obtain a mixed powder. Under a nitrogen atmosphere, the nitrogen flow rate is 40 mL / min, and the mixed powder is carbonized at 700℃ for 1 h with a heating rate of 3℃ / min. After carbonization, it is naturally cooled to room temperature to obtain the pyrolysis product.

[0052] (3) Place the pyrolysis product obtained above into a centrifuge tube, add deionized water at a solid-liquid mass ratio of 1:100, shake well and place it in an ultrasonic cleaner for 10 minutes. Use a high-speed centrifuge to separate the solid and liquid products, and repeatedly ultrasonically wash the solid products with deionized water until the pH of the washing liquid is constant.

[0053] (4) After the solid product obtained above was washed, it was dried in a vacuum freeze dryer for 48 hours to prepare a hierarchical porous biochar loaded with nano-calcium carbonate.

[0054] The chemical functional group composition and stability of the hierarchical porous biochar prepared in this example were analyzed using infrared spectroscopy and thermogravimetric analysis, such as... Figure 1 , 2 As shown.

[0055] The adsorption steps are as follows: The graded porous biochar prepared in this embodiment is added to a heavy metal Cd(II) solution at a concentration of 100-500 mg / L, an adsorbent dosage of 0.25-1.25 g / L, a pH of 5.5, a contact time of 2-1440 min, a temperature of 298 K, and an oscillation speed of 180 rpm. Then, the mixture is centrifuged and filtered.

[0056] Example 2

[0057] Except for the following technical features, the technical features in this embodiment are the same as those in Embodiment 1:

[0058] The difference between this embodiment and embodiment 1 is that in step (2), the mixed powder is carbonized at 800°C for 90 minutes.

[0059] The chemical functional group composition and stability of the hierarchical porous biochar prepared in this example were analyzed using infrared spectroscopy and thermogravimetric analysis. The phase composition of the material was determined by XRD, its morphology and structure were observed by SEM, and its specific surface area and pore size distribution were determined by nitrogen adsorption-desorption isotherms. The results were similar to those of Example 1. The SEM images of the hierarchical porous biochar are shown below. Figure 8 As shown, the specific surface area is 537.45 m². 2 / g.

[0060] Example 3

[0061] Except for the following technical features, the technical features in this embodiment are the same as those in Embodiment 1:

[0062] The difference between this embodiment and Example 1 is that the mass ratio of dried ginkgo leaf powder, hydrated potassium oxalate, and nano calcium carbonate is 5:1:1.

[0063] The chemical functional group composition and stability of the hierarchical porous biochar prepared in this example were analyzed using infrared spectroscopy and thermogravimetric analysis. The phase composition of the material was determined by XRD, its morphology and structure were observed by SEM, and its specific surface area and pore size distribution were determined by nitrogen adsorption-desorption isotherms. The results were similar to those of Example 1. The SEM images of the hierarchical porous biochar are shown below. Figure 9 As shown, the specific surface area is 436.54 m². 2 / g.

[0064] Example 4

[0065] Except for the following technical features, the technical features in this embodiment are the same as those in Embodiment 1:

[0066] The difference between this embodiment and Example 1 is that the mass ratio of dried ginkgo leaf powder, hydrated potassium oxalate, and nano calcium carbonate is 5:3:3.

[0067] The chemical functional group composition and stability of the hierarchical porous biochar prepared in this example were analyzed using infrared spectroscopy and thermogravimetric analysis. The phase composition of the material was determined by XRD, its morphology and structure were observed by SEM, and its specific surface area and pore size distribution were determined by nitrogen adsorption-desorption isotherms. The results were similar to those of Example 1. The SEM images of the hierarchical porous biochar are shown below. Figure 10 As shown, the specific surface area is 281.51 m². 2 / g.

[0068] Figure 1 The infrared spectrum of the product obtained in Example 1 is shown below. Figure 1 It can be seen that the graded porous biochar at 1792 cm⁻¹... -1 The distinct vibrational peak at 1462 cm⁻¹ is the C=O vibrational peak of calcite-type carbonate ions. -1 There is a strong absorption peak nearby, which is the characteristic v3 absorption peak of calcite-type calcium carbonate crystals, representing the asymmetric stretching vibration of the CO bond. 874 cm⁻¹ -1 and 719cm -1 The absorption peaks are v2 and v4 absorption peaks in calcite crystals, respectively. The v2 peak is strong and sharp, while the v4 peak is sharp but less intense than v2. They are related to the bending vibrations of the CO bond. (1054 cm⁻¹) -1 The point is PO stretchable, 571cm -1The P=O stretching vibration indicates that the biochar contains a small amount of phosphate. 3302cm -1 Absorption at -OH, 3692 cm⁻¹ -1 This is the stretching vibration of the OH group, an intermolecular hydrogen bond. 3061 cm⁻¹ -1 CH is located on the unsaturated carbon of an aromatic hydrocarbon.

[0069] Figure 2 The thermogravimetric curve of the product obtained in Example 1 under dry air atmosphere is shown below. Figure 2 It can be seen that the graphite carbon oxidation temperature of hierarchical porous biochar is 475℃;

[0070] Figure 3 The thermogravimetric curve of the product obtained in Example 1 under a nitrogen atmosphere is shown below. Figure 3 It can be seen that the pyrolysis temperature of calcium carbonate in graded porous biochar is 741℃.

[0071] Figure 4 The XRD pattern of the product obtained in Example 1 is shown below. Figure 4 It can be seen that the diffraction peak at 29.4° is the characteristic diffraction peak of calcite calcium carbonate (JCPDF 47-1743), corresponding to its 104 crystal plane, indicating that the crystal properties of calcium carbonate are well preserved in hierarchical porous biochar.

[0072] Figure 5 The image shown is a SEM-EDS image of the product obtained in Example 1. Figure 5 It can be seen that the pore structure on the surface of hierarchical porous biochar is distributed in a foam-like manner, with pore sizes ranging from tens of nanometers.

[0073] Figure 6 This is the adsorption-desorption curve of the product obtained in Example 1. Figure 7 The pore size distribution diagram of the product obtained in Example 1 is shown below. Figure 6 and 7 It can be seen that on the N2 adsorption isotherm, when the relative pressure is close to 1.0, the adsorption is significant, indicating that the hierarchical porous biochar has a macroporous structure. The addition of nano-calcium carbonate gives the biochar more macroporous structures, acting as a template agent. When the relative pressure is low, the nitrogen adsorption capacity increases rapidly, indicating that the hierarchical porous biochar has a large number of micropores. The H3-type hysteresis loop indicates that the hierarchical porous biochar has a mesoporous structure. Figure 7 This confirms that hierarchical porous biochar simultaneously contains micropores, mesopores, and macropores. BET theory calculates the surface area of ​​the hierarchical porous biochar to be 562.87 m². 2 / g.

[0074] Figure 8 , 9 Images 10 and 10 are SEM images of the products prepared in Examples 2, 3, and 4, respectively. Figure 8 ,9 As can be seen from 10, the morphology of the products prepared in each embodiment is similar to that in Example 1, with a specific surface area of ​​537.45 m². 2 / g, 436.54m 2 / g and 281.51m 2 / g.

[0075] Figure 11 , 12 The figures show the adsorption capacity diagrams of Cd(II) for the product obtained in Example 1 at different contact times and the adsorption isotherm diagrams of Cd(II) for the same contact time, respectively. Figure 11 , 12 It can be seen that when the experimental conditions are set as follows: initial Cd(II) concentration of 200 mg / L, pH value of 5.5, and adsorbent dosage of 0.25 g / L, the adsorption equilibrium capacity of the hierarchical porous biochar is 246 mg / g, which exceeds the Cd(II) adsorption capacity of most calcite calcium carbonate, indicating its superior adsorption performance for Cd(II). The adsorption isotherm model conforms to the Langmuir model, indicating that its adsorption behavior is monolayer adsorption. The maximum adsorption capacity of the hierarchical porous biochar is calculated to be 293.73 mg / g.

[0076] The above-described specific embodiments are preferred embodiments of the present invention and are not intended to limit the present invention. Any other changes or equivalent substitutions made without departing from the technical solution of the present invention are included within the protection scope of the present invention.

Claims

1. A method for preparing hierarchical porous biochar loaded with nano-calcium carbonate, characterized in that, Includes the following steps: (1) Mix biomass powder with hydrated potassium oxalate, grind evenly, add nano calcium carbonate, continue grinding evenly, heat under nitrogen atmosphere to the reaction temperature of 600~800 ℃, keep constant temperature at the reaction temperature for 60~90 min, and cool naturally after the reaction is complete to obtain the pyrolysis product. (2) Add the pyrolysis product obtained in step (1) to deionized water for ultrasonic washing instead of acid washing, and then use a high-speed centrifuge for solid-liquid separation to obtain a solid product; then wash the solid product with deionized water until the pH of the washing liquid is constant; dry the washed solid product to prepare hierarchical porous biochar loaded with nano-calcium carbonate.

2. The method for preparing hierarchical porous biochar supported on nano-calcium carbonate according to claim 1, characterized in that, In step (1), the mass ratio of the biomass powder, the hydrated potassium oxalate and the nano calcium carbonate is 1~5:1:

1.

3. The method for preparing hierarchical porous biochar supported on nano-calcium carbonate according to claim 1, characterized in that, In step (2), the specific steps for adding deionized water and ultrasonic washing are as follows: The pyrolysis product is placed in a centrifuge tube and ultrasonically washed with deionized water for 5-10 minutes; the mass ratio of the pyrolysis product to the deionized water is 1:80~100.

4. The method for preparing hierarchical porous biochar supported on nano-calcium carbonate according to claim 1, characterized in that, In step (1), the particle size of the nano-calcium carbonate is 40~80 nm.

5. The method for preparing hierarchical porous biochar supported on nano-calcium carbonate according to claim 1, characterized in that, In step (1), The temperature is increased at a rate of 3~5 ℃ / min.

6. The method for preparing hierarchical porous biochar supported on nano-calcium carbonate according to claim 1, characterized in that, The preparation steps of the biomass powder are as follows: The biomass is washed, air-dried, and then pulverized using a universal pulverizer. The pulverized biomass powder is obtained by sieving through a 60-mesh stainless steel sieve.

7. The method for preparing hierarchical porous biochar supported on nano-calcium carbonate according to claim 6, characterized in that, The biomass is yellow ginkgo leaves.

8. A hierarchical porous biochar supported on nano-calcium carbonate, characterized in that, It is prepared by the method for preparing hierarchical porous biochar loaded with nano-calcium carbonate as described in any one of claims 1 to 7.

9. The application of the hierarchical porous biochar supported on nano-calcium carbonate as described in claim 8, characterized in that, It is used to treat wastewater containing heavy metals.

10. The application of the hierarchical porous biochar supported on nano-calcium carbonate according to claim 9, characterized in that, The heavy metal is Cd(II).

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