A zeolite-biomass carbon adsorbent, its preparation method and application

Abstract

This invention belongs to the field of adsorption materials technology, specifically disclosing a zeolite-biomass carbon adsorbent, its preparation method, and its application. The preparation method of the zeolite-biomass carbon adsorbent includes the following steps: mixing biomass carbon with an alkali and calcining it; adding an aluminum source, water, and a template agent to the calcined product, heating for the first time, and mixing; then heating for the second time to carry out the reaction; removing the template agent to obtain the adsorbent. This invention fully utilizes the abundant carbon and silicon sources in biomass carbon, employing a one-step synthesis method to prepare the zeolite-biomass carbon adsorbent. On one hand, the alkali is used to fully dissolve the silicon in the biomass carbon, forming silicates, which combine with the aluminum source to form aluminate zeolite products; on the other hand, the alkali is used to modify the biomass carbon, obtaining modified biomass carbon with a richer content of oxygen-containing functional groups on its surface, thereby improving the adsorption performance of the adsorbent and achieving a maximum adsorption capacity of 55 mg / g for cadmium.

Description

Technical Field

[0001] This invention belongs to the field of adsorption material technology, specifically relating to a zeolite-biomass carbon adsorbent, its preparation method, and its application. Background Technology

[0002] Cd pollution poses a serious threat to soil quality, plant growth, food safety, and human health; therefore, the remediation of Cd-contaminated soil is urgently needed. Currently, technologies for treating cadmium pollution in soil include bioremediation, chemical precipitation, electrolysis, ion exchange, and adsorption, all of which can effectively remove heavy metals from the environment. Among these, adsorption technology is one of the most widely used remediation techniques. Its effectiveness in remediating Cd-contaminated soil depends primarily on the properties of the adsorbent material; therefore, it is necessary to develop adsorbent materials with superior performance.

[0003] Biomass carbon is a solid material with a microporous structure and high carbon content (>65%), produced by high-temperature pyrolysis under limited or anaerobic conditions. It possesses abundant surface functional groups, a large specific surface area, and a well-developed pore structure. Generally, ordinary biomass carbon has limited effectiveness in fixing or removing heavy metals from the environment. However, by modifying the raw biomass carbon through various methods (acid-base modification, steam modification, mineral impregnation, surface oxidation, and surface sulfonation, etc.), its effectiveness in fixing or removing heavy metals can be improved. Inorganic minerals are adsorbent materials with fast adsorption rates and low costs. Zeolites, due to their large specific surface area and good exchange adsorption capacity for heavy metal ions, are a widely used inorganic adsorbent material. Modifying biomass carbon with zeolite offers several advantages. Firstly, zeolite crystals possess strong adsorption capacity, and modifying biomass carbon with zeolite can significantly improve its adsorption performance, thus enhancing its application in the remediation of cadmium pollution in soil. Secondly, it can increase the physical stability of particles, significantly reducing CO2 and N2O emissions from soil, which is crucial for enhancing its carbon sequestration and emission reduction potential in soil. The main adsorption mechanisms of zeolite-biomass carbon composites are surface adsorption, chelation, ion exchange, electrostatic adsorption, diffusion, and complexation. Utilizing zeolite-biomass carbon composites to remove heavy metal pollution from soil and improve soil physicochemical properties has high application value.

[0004] Currently, the common method for preparing zeolite-biomass carbon composites is a two-step process. This method first synthesizes zeolite and biomass carbon materials separately, and then combines the two materials. For example, Katsuki, Het. synthesized Na-A and Na-X type zeolite / porous carbon composites using rice husks as raw material in a two-step process. The results showed that the materials synthesized under these conditions had a large cation exchange capacity (506 meq / 100g) and a large specific surface area (676 m²).2 The zeolite / biomass carbon composite material has a certain adsorption capacity for heavy metals. However, the two-step preparation process of zeolite / biomass carbon composite material is complex, time-consuming, and the adsorbent prepared has a limited adsorption capacity for heavy metals. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a zeolite-biomass carbon adsorbent, its preparation method and application, which makes full use of the abundant carbon and silicon sources in biomass carbon and uses a one-step method to directly synthesize zeolite-biomass carbon composite adsorbent materials, which have the characteristics of being fast, efficient and having excellent adsorption performance for heavy metals.

[0006] To address the aforementioned technical problems, a first aspect of the present invention provides a method for preparing a zeolite-biomass carbon adsorbent, comprising the following steps:

[0007] (1) After mixing biomass with alkali, calcination is carried out;

[0008] (2) Add aluminum source material, water and template agent to the calcined product obtained in step (1), heat for the first time and mix; then heat for the second time and react; remove the template agent to obtain the zeolite-biomass carbon adsorbent.

[0009] This invention employs a one-step direct synthesis method, fully utilizing the abundant carbon and silicon sources in biomass carbon to prepare a zeolite-biomass carbon adsorbent with excellent adsorption performance. Specifically, biomass is first mixed with alkali and then calcined. On the one hand, the alkali fully dissolves the silicon in the biomass carbon to form silicates (chemical reaction formula: This facilitates the later combination with aluminum to form aluminosilicate zeolite products. On the other hand, alkali can also modify biomass carbon to obtain alkali-modified biomass carbon, which, compared to the original biomass carbon, contains more oxygen-containing functional groups on its surface, thus greatly improving its adsorption performance. Then, the calcined product is mixed with the aluminum source material, and water and a template agent are added simultaneously. The reaction is carried out at a certain temperature to obtain aluminosilicate zeolite (taking sodium hydroxide as an example, its chemical reaction formula is:). ).

[0010] Preferably, in step (1), the biomass is at least one of rice husks, straw, and peanut shells; more preferably, the biomass is rice husks.

[0011] Specifically, the main components of biomass are carbon and silicon. When used as raw materials for zeolite-biomass carbon adsorption materials, carbon forms a porous structure after calcination, while silicon reacts with the aluminum source to form aluminosilicate zeolite products. The combined effect of the two increases the specific surface area, porous structure, and cation exchange capacity of the adsorption material, thereby improving the material's adsorption capacity for cationic heavy metals.

[0012] Preferably, the alkali is sodium hydroxide and / or potassium hydroxide.

[0013] Preferably, the mass ratio of the biomass to the alkali is 1:(0.1-1).

[0014] Preferably, in step (1), the calcination temperature is 400-600℃.

[0015] Preferably, in step (1), the calcination time is 0.5-4 hours.

[0016] As a further improvement to the above scheme, in step (1), the biomass is further acid-washed before being mixed with the alkali to remove impurities from the biomass.

[0017] Preferably, the acid washing process is as follows: adding an acid solution to biomass, followed by mixing, filtering, washing, drying, and grinding to obtain the final product.

[0018] Preferably, the acid solution is a hydrochloric acid solution with a concentration of 3-4 mol / L.

[0019] Preferably, the mixing is performed by magnetic stirring at room temperature for 20-28 hours.

[0020] Preferably, the washing process involves repeatedly washing the filtered cake with ultrapure water until the pH of the filtrate is neutral.

[0021] Preferably, the grinding is performed until it passes through a 200-mesh sieve.

[0022] Preferably, in step (2), the aluminum source material is sodium aluminate and / or aluminum hydroxide.

[0023] Preferably, in step (2), the template agent is tetrapropylammonium hydroxide or tetrapropylsodium hydroxide. Studies have found that the template agent can act as a carrier during the reaction process, promoting the formation of zeolite and thus improving the adsorption performance of the adsorbent.

[0024] Preferably, the mass ratio of the biomass, aluminum source material and water is 100:(0.1-0.5):(10-30).

[0025] Preferably, the mass-to-volume ratio of the biomass to the template agent is 100g:(1-10)mL.

[0026] Preferably, in step (2), the first temperature rise is to 70-90°C.

[0027] Preferably, in step (2), the mixing time is 1-3 hours.

[0028] Preferably, in step (2), the second temperature increase is to 140-160°C.

[0029] Preferably, in step (2), the reaction time is 6-48 hours; more preferably, the reaction time is 10-14 hours.

[0030] Preferably, in step (2), there are two ways to remove the template agent: one is to cool and filter after the reaction is completed, then wash with water or ethanol-sulfuric acid solution, and finally dry the product at 60-105℃ for 6-24 hours; the other is to cool and filter after the reaction is completed, wash with water, and then calcine in a nitrogen atmosphere at 500-700℃ for 0.5-4 hours.

[0031] A second aspect of the present invention provides a zeolite-biomass carbon adsorbent, which is prepared by the above-described method for preparing zeolite-biomass carbon adsorbent.

[0032] A third aspect of the present invention provides the application of the above-mentioned zeolite-biomass carbon adsorbent in the adsorption of heavy metals.

[0033] Preferably, the heavy metal is cadmium.

[0034] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages:

[0035] (1) This invention uses biomass as raw material, making full use of the abundant carbon and silicon sources in biomass carbon, and uses a one-step synthesis method to prepare zeolite-biomass carbon adsorbent. On the one hand, alkali is used to fully dissolve the silicon in biomass carbon to form silicates, which combine with aluminum source materials to form aluminate zeolite products; on the other hand, alkali is used to modify biomass carbon to obtain modified biomass carbon, making its surface contain more oxygen-containing functional groups, so as to improve the adsorption performance of the adsorbent. The zeolite-biomass carbon adsorbent prepared by this invention includes multiple adsorption modes such as surface complexation, cation exchange and electrostatic adsorption, which gives it a high specific surface area, pore structure and strong cation exchange capacity, and good adsorption capacity for cationic heavy metals. The maximum adsorption capacity for cadmium can reach 55 mg / g.

[0036] (2) The preparation process of the zeolite-biomass carbon adsorbent of the present invention is simple and has the characteristics of being fast, efficient and low cost. Attached Figure Description

[0037] Figure 1 The XRD patterns of the adsorbent samples prepared in Examples 1-3 are shown below.

[0038] Figure 2 The XRD patterns of the adsorbent samples prepared in Example 4 and Comparative Examples 1-2 are shown.

[0039] Figure 3SEM images of rice husks and adsorbent samples prepared in Examples 1-3;

[0040] Figure 4 The adsorption isotherm curves are shown for the adsorbent samples prepared in Examples 1-3 and Comparative Example 1.

[0041] Figure 5 The attached isotherm curves are for the adsorbent samples prepared in Example 4 and Comparative Example 2. Detailed Implementation

[0042] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0043] Example 1

[0044] A method for preparing a zeolite-biomass carbon adsorbent includes the following steps:

[0045] (1) Weigh 40g of cleaned rice husks and place them in a beaker; then add 100mL of 4mol / L HCl solution and stir magnetically for 24 hours at room temperature; then filter and wash the filter cake with ultrapure water until the pH of the filtrate is neutral; finally dry the filter cake, grind it through a 200-mesh sieve to obtain acid-washed rice husks.

[0046] (2) The acid-washed rice husks obtained in step (1) are thoroughly mixed with 4.8g of NaOH solid, and then calcined at 600℃ for 1 hour to obtain alkali-modified rice husks;

[0047] (3) Pour the alkali-modified rice husks obtained in step (2) into a polytetrafluoroethylene liner, and then add 0.054g Na2Al2O4.

[0048] 8.89g of ultrapure water and 2g of tetrapropylammonium hydroxide template agent; then magnetically stirred in an 80℃ water bath for 2 hours; finally reacted at 150℃ for 12 hours.

[0049] (4) After cooling the reaction product obtained in step (3), filter it; then wash it with ethanol-sulfuric acid solution, and then calcine it in a nitrogen atmosphere at 600°C for 2 hours to obtain the zeolite-biomass carbon adsorbent sample of this embodiment, denoted as KTC150-12.

[0050] Example 2

[0051] The only difference between Example 2 and Example 1 is that the reaction time in step (3) of Example 2 is 6, and the zeolite-biomass carbon adsorbent sample obtained is denoted as KTC150-6.

[0052] Example 3

[0053] The only difference between Example 3 and Example 1 is that the reaction time in step (3) of Example 3 is 48, and the zeolite-biomass carbon adsorbent sample obtained is denoted as KTC150-48.

[0054] Example 4

[0055] A method for preparing a zeolite-biomass carbon adsorbent includes the following steps:

[0056] (1) Weigh 40g of cleaned rice husks and place them in a beaker; then add 100mL of 4mol / L HCl solution and stir magnetically for 24 hours at room temperature; then filter and wash the filter cake with ultrapure water until the pH of the filtrate is neutral; finally dry the filter cake, grind it through a 200-mesh sieve to obtain acid-washed rice husks.

[0057] (2) The acid-washed rice husks obtained in step (1) are thoroughly mixed with 20 g of 3.0 mol / L NaOH solution, and then stirred in a water bath at 80°C for 12 hours to obtain alkali-modified rice husks;

[0058] (3) Pour the alkali-modified rice husks obtained in step (2) into a polytetrafluoroethylene liner, and then add 0.054g Na2Al2O4.

[0059] 8.98g of ultrapure water and 2g of tetrapropylammonium hydroxide template agent; then magnetically stirred in an 80℃ water bath for 2 hours; finally reacted at 150℃ for 12 hours.

[0060] (4) After cooling the reaction product obtained in step (3), filter it; then wash it with ethanol-sulfuric acid solution, and then calcine it in a nitrogen atmosphere at 600°C for 2 hours to obtain the zeolite-biomass carbon adsorbent sample of this embodiment, which is denoted as KSC150-12.

[0061] Comparative Example 1

[0062] The alkali-modified rice husk sample prepared in step (2) of Example 1 is denoted as KRH.

[0063] Comparative Example 2

[0064] The difference between Comparative Example 2 and Example 4 is that Comparative Example 2 did not add tetrapropylammonium hydroxide template agent in step (3), which is denoted as KC150-12.

[0065] Performance testing

[0066] XRD analysis Figure 1 The images show the XRD patterns of the adsorbent samples prepared in Examples 1-3 and Comparative Example 1. Figure 1 The horizontal axis 2θ represents the angle, and the vertical axis Intensity represents the intensity of the diffraction peak. Figure 1 The relevant parameters of the XRD pattern are shown in Table 1.

[0067] Table 1: Relevant Parameters of XRD Pattern

[0068]

[0069] Depend on Figure 1 As shown in Table 1, when the reaction time is 6 hours, the reaction product is mainly SiO2 with a broad peak shape, indicating that the product crystallization is incomplete and the relative crystallinity is low within a short reaction time. With increasing reaction time, characteristic peaks of cancrinite-type zeolite gradually appear. When the reaction time reaches 12 hours, the peak shape and intensity do not change significantly, and the relative crystallinity changes gradually, indicating that cancrinite-type zeolite can form a relatively complete crystal structure with a hydrothermal time of about 12 hours. When the hydrothermal time reaches 48 hours, the average particle size of the product increases, indicating that the reaction time is too long and the crystals continuously agglomerate. Therefore, a reaction time of about 12 hours is more suitable.

[0070] Meanwhile, the average particle size of the sample powder was calculated using the Scherrer formula. The crystal size of the zeolite significantly contributes to the intracrystalline diffusion rate of molecules, while the external surface area significantly contributes to the adsorption and reaction rates. Scherrer calculations show that the average particle size of the adsorbent decreases after washing with sulfuric acid-ethanol solution, indicating that most of the template agent is removed.

[0071] Figure 2 The XRD patterns of the adsorbent samples prepared in Example 4 and Comparative Examples 1-2 are shown below. Figure 2 It can be seen that when biomass carbon is activated with alkaline solution or without the addition of template agent and aluminum source, the peak shape of the reaction product is relatively broad, indicating that the product crystallization is incomplete and the relative crystallinity is low. The characteristic peak of cancrinite-type zeolite is not obvious, which makes the adsorbent's adsorption performance for heavy metal cadmium weak.

[0072] microstructure Figure 3 SEM images of rice husks and samples prepared in Examples 1-3, wherein... Figure 3 A, 3B, 3C, and 3D are SEM images of rice husks, KTC150-6, KTC150-12, and KTC150-48, respectively. Figure 3It can be seen that as the reaction time increases, the cubic structure of the sample becomes more regular, with a more three-dimensional morphology and crystallinity, while the content of amorphous substances decreases.

[0073] Adsorption isotherms reflect the adsorption performance of the adsorbent on the adsorbate and the equilibrium distribution of the adsorbate in the solid and liquid phases at adsorption equilibrium. Common isothermal adsorption equilibrium equations are used to obtain the surface properties of the adsorbent and its maximum adsorption capacity. To investigate the adsorption mechanism of Cd(II) by zeolite-biomass carbon materials, the commonly used Langmuir and Freundlich models were used to fit the adsorption curves. OriginPro 2018 was used to perform nonlinear fitting on the adsorption data. The fitting results and related parameters are as follows: Figure 4 As shown in Table 2.

[0074] The experimental procedure was as follows: 0.001-0.1 g of the samples prepared in Examples 1-3 and Comparative Example 1 were added to 10 mL of solutions with different Cd(II) concentrations, respectively. The mixtures were then inverted and shaken for 24 hours, and the solid material was separated from the solution by membrane filtration. The Cd(II) concentration in the solution before and after adsorption was determined using ICP-OES.

[0075] Langmuir isothermal adsorption model:

[0076] Freundlich isothermal adsorption model:

[0077] Among them, Q e (mg g) -1 This refers to the amount of Cd(II) adsorbed by the material. e (mg L) -1 ) refers to the equilibrium concentration of Cd(II) in the solution, q max (mg g) -1 (k) refers to the saturated adsorption capacity of biomass carbon. L (L mg) -1 The adsorption affinity parameter (k) refers to the adsorption affinity of a material for Cd(II). It can be expressed as the ratio of adsorption to desorption rates. The larger the value, the more stable the solid-liquid two-phase fixation during the adsorption process. f (mg·g) -1 · (mg· L) ‐1 ) n-1 The magnitude of the reaction is the strength of the bond between the solid and liquid components in the solution system. The larger the value, the more stable the bond between the two components. n is the Freundlich constant, whose value is related to the physical properties of the material and the temperature.

[0078] Table 2: Relevant Parameters of Adsorption Isotherm

[0079]

[0080] Depend on Figure 4 It can be seen that with the increase of reaction time, the maximum adsorption capacity of the material for Cd(II) first increases and then decreases, with a maximum value of 55 mg / g. This may be because when the reaction time increases to 12 hours, the zeolite structure gradually forms, which improves the adsorption capacity of alkali-modified rice husk charcoal (KRH). However, when the reaction time increases to 48 hours, the zeolite grains continue to agglomerate, the grain size increases, and the specific surface area of ​​the material decreases, thus reducing its adsorption capacity. Washing the template agent in the material with sulfuric acid-ethanol solution did not significantly increase the adsorption capacity, but its binding capacity for Cd(II) increased. This may be because the sites occupied by the template agent become visible during the washing process, thus enhancing the binding capacity of the material for Cd(II). At the same time, the pores collapse during this process, and some sites disappear, thus reducing the adsorption performance.

[0081] Table 2 shows that the Langmuir model better describes the equilibrium data, with correlation coefficients (R²) ranging from 0.798 to 0.997. Furthermore, the maximum adsorption capacity after model fitting is closer to the experimental value, indicating that the adsorbent material primarily performs monolayer adsorption on the Cd(II) solution. In the Freundlich model, the 1 / n values ​​of the adsorbent are all between 0 and 1, indicating that the adsorption process is preferential. The affinity parameter K, reflecting the adsorption free energy, is also relevant. L The increase with the removal of the template agent indicates that the presence of the template agent affects the adsorption reaction.

[0082] Figure 5 The adsorption isotherm curves of the adsorbent samples prepared in Example 4 and Comparative Example 2 are shown below. Figure 5 It can be seen that when there is no zeolite in the adsorbent material or the zeolite structure is not obvious, the adsorption effect of the adsorbent is significantly weaker, indicating that the zeolite structure plays a promoting role in the adsorption process.

[0083] For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of this invention, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A method for preparing a zeolite-biomass carbon adsorbent, characterized in that, Includes the following steps: (1) After mixing biomass with alkali, calcination is carried out; The mass ratio of biomass to alkali is 1:(0.1-1); the calcination temperature is 400-600℃, and the calcination time is 0.5-4 hours; (2) Add aluminum source material, water and template agent to the calcined product obtained in step (1), heat for the first time and mix; then heat for the second time and react; remove the template agent to obtain the zeolite-biomass carbon adsorbent; The aluminum source is sodium aluminate and / or aluminum hydroxide, the template agent is tetrapropylammonium hydroxide, the mass ratio of biomass, aluminum source and water is 100:(0.1-0.5):(10-30), and the mass-volume ratio of biomass to template agent is 100g:(1-10)mL; The first heating is to 70-90°C; and / or the mixing time is 1-3 hours; the second heating is to 140-160°C; and / or the reaction time is 10-14 hours.

2. The preparation method of the zeolite-biomass carbon adsorbent according to claim 1, characterized in that, In step (1), the biomass is at least one of rice husks, straw, and peanut shells; the alkali is sodium hydroxide and / or potassium hydroxide.

3. The preparation method of the zeolite-biomass carbon adsorbent according to claim 1, characterized in that, In step (1), the biomass is further acid-washed before being mixed with the alkali.

4. A zeolite-biomass carbon adsorbent, characterized in that, It is prepared by the method of any one of claims 1 to 3 for the preparation of zeolite-biomass carbon adsorbent.

5. The application of the zeolite-biomass carbon adsorbent according to claim 4 in the adsorption of heavy metals.

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