Method for preparing biochar-metal organic framework adsorbent by utilizing waste coffee grounds as well as product and application of biochar-metal organic framework adsorbent

Abstract

The invention belongs to the technical field of adsorbents, and particularly relates to a method for preparing a biochar-metal organic framework adsorbent by using waste coffee grounds as well as a product and application of the biochar-metal organic framework adsorbent. The preparation method comprises the following steps: washing coffee grounds with water, drying, sieving and pyrolyzing to obtain coffee grounds-based biochar; uniformly mixing an iron source, a ligand and a solvent to obtain a mixed solution; and adding the coffee residue-based biochar into the mixed solution, uniformly dispersing, carrying out heat treatment, washing, and drying to obtain the biochar-metal organic framework. The steps for preparing the adsorbent have the advantages of being simple, efficient, green, environmentally friendly, capable of saving energy, reducing emission and low in cost, the adsorbent can be effectively and repeatedly recycled, and the adsorbent shows excellent adsorption performance on toxic heavy metal Cr (VI).

Description

Technical Field

[0001] The present invention relates to the technical field of adsorbents, and in particular to a method for preparing a biochar-metal organic framework adsorbent by utilizing waste coffee grounds, and a product and application thereof. Background Art

[0002] Heavy metals are highly toxic compounds that are widely present in industrial emissions, certain electroplating processes, leather production, dye manufacturing and certain chemical syntheses, causing heavy metal pollution in water resources. Since heavy metals are easily enriched by organisms, there are potential environmental hazards and impacts on human health, making the hazards of heavy metal pollution in water bodies increasingly concerned. At present, the adsorbent method is mainly used on the market to treat heavy metals in water. Biochar is the main heavy metal adsorbent because of its easy availability of raw materials, simple manufacturing process, low cost and no pollution to the environment. At the same time, biochar is also widely used in environmental protection and soil remediation. As a soil conditioner, biochar can significantly improve the basic properties of soil nutrients, moisture, air permeability, acidity and alkalinity, thereby affecting the living environment and metabolic characteristics of soil microorganisms and helping the environment to repair itself. Another commonly used heavy metal adsorption material is the organic metal framework, which has a very high specific surface area, which provides a large number of active sites for adsorption. Synthesis may involve expensive raw materials and complex synthesis processes, which increases costs. However, when biochar or organic metal frameworks are used alone to adsorb heavy metals, there are problems such as high cost, low adsorption efficiency, and low saturated adsorption capacity. How to further improve the heavy metal treatment capacity of biochar or organic metal framework is a technical problem that needs to be urgently solved by technicians in this field. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing a biochar-metal organic framework (MOFs) adsorbent using waste coffee grounds, and its products and applications, so as to solve the problems existing in the above-mentioned prior art and achieve excellent adsorption of toxic heavy metals.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention is to provide a method for preparing a biochar-metal organic framework using waste coffee grounds, the steps comprising:

[0006] The coffee grounds are washed, dried, sieved and pyrolyzed to obtain coffee grounds-based biochar;

[0007] The iron source, the ligand and the solvent are mixed uniformly to obtain a mixed solution;

[0008] The coffee residue-based biochar is added to the mixed solution and dispersed evenly, and after heat treatment, washed and dried, the biochar-metal organic framework is obtained.

[0009] Furthermore, the iron source includes at least one of ferric chloride, ferric nitrate and anhydrous ferric chloride.

[0010] Furthermore, the ligand includes one of 2-aminoterephthalic acid, 4-aminobenzoic acid and 5-aminoisophthalic acid.

[0011] Furthermore, the solvent includes at least one of DMF, DMSO and ethanol.

[0012] Furthermore, the pyrolysis is carried out in an inert atmosphere by heating the temperature to 300-800° C. at a heating rate of 3-15° C. / min and keeping the temperature for 2-8 hours.

[0013] Furthermore, the water washing is performed by eluting with water until the pH value of the elution is neutral.

[0014] Furthermore, the drying temperature is 50-120°C.

[0015] Furthermore, the screening is to pass the undersize material through a 100-200 mesh sieve.

[0016] Furthermore, the usage ratio of the iron source, the ligand and the solvent is 7.5mmol:3.75mmol:60mL.

[0017] Furthermore, the usage ratio of the coffee grounds-based biochar to the solvent is 20-50 g:60 mL.

[0018] Furthermore, the heat treatment temperature is 100-120° C. and the time is 18-24 hours.

[0019] Furthermore, the washing is performed by sequentially washing with N,N-dimethylformamide and ethanol three times respectively.

[0020] Furthermore, the drying temperature is 50-120°C.

[0021] The second technical solution of the present invention is to provide a biochar-metal organic framework prepared by the above method.

[0022] The third technical solution of the present invention is to provide an application of the above-mentioned biochar-metal organic framework as an adsorbent in the adsorption and enrichment of toxic heavy metals.

[0023] Furthermore, the toxic heavy metal is Cr(VI).

[0024] The fourth technical solution of the present invention is to provide a method for improving the adsorption efficiency of biochar on Cr(VI), wherein biochar is modified by metal organic framework to prepare biochar-metal organic framework material, and the biochar-metal organic framework material is used to adsorb Cr(VI); the steps of preparing the biochar-metal organic framework material include:

[0025] The coffee grounds are pyrolyzed, washed, dried, and sieved to obtain coffee grounds-based biochar;

[0026] Mixing ferric chloride, 2-aminoterephthalic acid and N,N-dimethylformamide (DMF solution) uniformly to obtain a mixed solution;

[0027] The coffee grounds-based biochar is added to the mixed solution and dispersed evenly. After heat treatment, the biochar-metal organic framework material is obtained by washing and drying.

[0028] The fifth technical solution of the present invention is to provide a method for improving the adsorption efficiency of metal organic framework for Cr (VI), using biochar to modify metal organic framework material to prepare biochar-metal organic framework material, and using the biochar-metal organic framework material to adsorb Cr (VI); the preparation steps of the biochar-metal organic framework material include:

[0029] The coffee grounds are pyrolyzed, washed, dried, and sieved to obtain coffee grounds-based biochar;

[0030] Mixing ferric chloride, 2-aminoterephthalic acid and N,N-dimethylformamide (DMF solution) uniformly to obtain a mixed solution;

[0031] The coffee grounds-based biochar is added to the mixed solution and dispersed evenly. After heat treatment, the biochar-metal organic framework material is obtained by washing and drying.

[0032] In the preferred embodiment, by limiting the ratio of the two, 30 mg of adsorbent to 200 mg of L -1 The adsorption effect of Cr(VI) solution is the best.

[0033] The present invention discloses the following technical effects:

[0034] The present invention uses coffee grounds waste as raw materials, converts coffee grounds waste into biochar with high adsorption performance, and then prepares biochar-metal organic frameworks, and uses the high specific surface area and porosity of biochar to increase the stability and adsorption capacity of MOFs. At the same time, the high selectivity and adjustability of MOFs are used to improve the overall adsorption efficiency. The steps for preparing the adsorbent are simple and efficient, green and environmentally friendly, energy-saving and emission-reducing, and low-cost. The adsorbent exhibits excellent adsorption performance for the toxic heavy metal Cr (VI), making it an ideal choice for treating this pollutant. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 Schematic diagram of the process flow in an embodiment of the present invention;

[0037] Figure 2 SEM images of the biochar-metal organic frameworks prepared in Examples 1 to 4 and the coffee grounds-based biochar adsorbent in Comparative Example 1, wherein (a) is Example 1, (b) is Example 2, (c) is Example 3, (d) is Example 4, and (e) is Comparative Example 1;

[0038] Figure 3 XRD patterns of the biochar-metal organic frameworks prepared in Examples 1 to 4;

[0039] Figure 4 This is the adsorption effect diagram of Cr(VI) in water with different adsorbent dosages;

[0040] Figure 5 This is the adsorption effect diagram of Cr(VI) solution under different pH conditions;

[0041] Figure 6 Pseudo-first-order and second-order kinetic equation curves of Cr(VI) adsorption on NH2-MIL101(Fe)@CGB30;

[0042] Figure 7 This is the internal diffusion curve of Cr(VI) adsorbed on NH2-MIL101(Fe)@CGB30. DETAILED DESCRIPTION

[0043] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0044] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0045] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0046] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0047] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0048] The raw materials used in the specific implementation mode of the present invention are all commercially available products, wherein the coffee grounds are coffee grounds of small-grain coffee beans that are abundant in Yunnan, and are provided by a coffee shop in Yunnan.

[0049] Figure 1 Schematic diagram of the process flow in an embodiment of the present invention.

[0050] Example 1

[0051] A method for preparing a biochar-metal organic framework using waste coffee grounds, the steps are as follows:

[0052] S1. The coffee grounds were washed with ultrapure water (18.25 MΩ·cm) until the pH of the filtrate was 7, and then dried at 60°C. After passing through a 200-mesh sieve, the mixture was transferred to a tubular furnace and heated to 500°C at a heating rate of 5°C / min under argon atmosphere. The mixture was pyrolyzed for 3 h, and coffee grounds-based biochar was obtained after the pyrolysis.

[0053] S2. Dissolve 2.73 g of ferric chloride and 0.68 g of 2-aminoterephthalic acid in 30 mL of DMF respectively, disperse them evenly by ultrasonication for 10 min, then mix the two solutions, add 20 mg of coffee grounds-based biochar and stir evenly for 30 min. After stirring, transfer to a 100 mL polytetrafluoroethylene bottle, place it in a vacuum drying oven and heat it at 110 °C for 20 h. After natural cooling, wash the product with N,N-dimethylformamide and ethanol three times respectively, and dry it at 60 °C to obtain a biochar-metal organic framework, recorded as NH2-MIL101(Fe)@CGB20.

[0054] Example 2

[0055] Compared with Example 1, the only difference is that the amount of coffee grounds-based biochar used in step S2 is 30 mg, and the final product biochar-metal organic framework is recorded as NH2-MIL101(Fe)@CGB30.

[0056] Example 3

[0057] Compared with Example 1, the only difference is that the amount of coffee grounds-based biochar used in step S2 is 40 mg, and the final product biochar-metal organic framework is recorded as NH2-MIL101(Fe)@CGB40.

[0058] Example 4

[0059] Compared with Example 1, the only difference is that the amount of coffee grounds-based biochar used in step S2 is 50 mg, and the final product biochar-metal organic framework is recorded as NH2-MIL101(Fe)@CGB50.

[0060] Comparative Example 1

[0061] The preparation steps of coffee grounds-based biochar adsorbent are:

[0062] The coffee grounds were placed in a tubular furnace and heated to 500 °C at a heating rate of 5 °C / min under argon atmosphere. The mixture was kept for 3 h for pyrolysis. Ultrapure water (18.25 MΩ·cm) was used for leaching until the pH of the filtrate reached 7. The mixture was then dried at 60 °C to obtain coffee grounds-based biochar, which was recorded as CGB.

[0063] Comparative Example 2

[0064] The preparation steps of metal organic framework adsorbent are as follows:

[0065] 2.73 g of ferric chloride and 0.68 g of 2-aminoterephthalic acid were dissolved in 30 mL of DMF, respectively, and dispersed evenly by ultrasonication for 10 min. Then, they were transferred to a 100 mL polytetrafluoroethylene bottle and placed in a vacuum air drying oven and heated at 110 ° C for 20 h. After natural cooling, the obtained product was washed three times with N, N-dimethylformamide and ethanol respectively, and dried at 60 ° C to obtain a metal organic framework, which was recorded as NH2-MIL101(Fe).

[0066] Test example

[0067] Figure 2 The SEM images of the biochar-metal organic frameworks prepared in Examples 1 to 4 and the coffee grounds-based biochar adsorbent in Comparative Example 1 are shown in Figures 1 to 4, (a) is Example 1, (b) is Example 2, (c) is Example 3, (d) is Example 4, and (e) is Comparative Example 1. It can be seen from the figure that MOFs grow in situ on the biochar and are evenly distributed.

[0068] Figure 3 The XRD diagrams of the biochar-metal organic frameworks prepared in Examples 1 to 4 are shown in Figure 1. As can be seen from the figure, the biochar did not destroy the original structure of MOFs, all characteristic peaks pointed to the synthesized materials, and there were no obvious impurity peaks, which shows that the materials have been successfully prepared and the crystallinity of MOFs has not been changed.

[0069] The products obtained in Examples 1 to 4 and Comparative Examples 1 to 2 were used as adsorbents and 200 mg L -1 Cr(VI) solution was adsorbed.

[0070] The products prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were used as adsorbents to test the effect of different adsorbents on 200 mg L -1 The adsorption effect of Cr(VI) solution was measured at 25°C, 200 rpm and 24 h. Figure 4 shown.

[0071] Figure 4 The figure is a graph showing the adsorption effect of different adsorbent dosages on Cr(VI) in water. As can be seen from the figure, when the adsorbent content increases from 10 mg to 30 mg, the content of Cr(VI) in the residual solution continues to decrease. When the adsorbent content increases from 30 mg to 50 mg, the content of Cr(VI) in the residual solution remains basically unchanged. Therefore, the optimal dosage of the adsorbent selected in the present invention is 30 mg.

[0072] Figure 5 The products prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were used as adsorbents to absorb 200 mg L -1The adsorption effect diagram of Cr(VI) solution. It can be seen from the figure that when the pH is 3-4, the residual amount of Cr(VI) in water increases with the increase of pH; when the pH is 5-6, the residual amount of Cr(VI) in water is basically stable and maintains the lowest level; when the pH is 6-7, the residual amount of Cr(VI) in water increases slightly with the increase of pH, but is generally lower than the residual amount of pH 3-4. Therefore, the adsorbent shows the best adsorption effect under weak acid conditions.

[0073] 30 mg NH2-MIL101(Fe)@CGB30 was added to 25 mL of a 200 mg L Cr(VI) solution with a pH of 4. -1 The adsorption kinetics curve of Cr(VI) in the solution is as follows: Figure 6 and Figure 7 shown.

[0074] Figure 6 Pseudo-first-order and second-order kinetic equation curves of Cr(VI) adsorption on NH2-MIL101(Fe)@CGB30; Figure 7 This is the internal diffusion curve of Cr(VI) adsorbed on NH2-MIL101(Fe)@CGB30.

[0075] Depend on Figures 6-7 It can be seen that:

[0076] The relevant data were fitted for the quasi-first-order kinetics, quasi-second-order kinetics and intra-particle diffusion equations respectively. It can be seen that the correlation coefficients of the quasi-first-order kinetics and intra-particle diffusion models are R 2 The adsorption amount obtained by fitting the pseudo-first-order kinetic model is relatively low, and the difference between the adsorption amount obtained by fitting the pseudo-first-order kinetic model and the value measured by experiment under actual conditions is large, indicating that these two models are not applicable;

[0077] The pseudo-second-order kinetic model can well simulate the adsorption of Cr(VI) on NH2-MIL101(Fe)@CGB30, and the saturated adsorption amount calculated by the relevant model is most consistent with the measured data, indicating that the adsorption process of Cr(VI) on NH2-MIL101(Fe)@CGB30 is mainly controlled by chemical adsorption.

[0078] The K1 value of the intraparticle diffusion model is greater than K2 and K3, indicating that the external diffusion rate is faster in the initial stage, and then the internal diffusion and other reaction processes affect the overall adsorption rate.

[0079] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a biochar-metal organic framework using waste coffee grounds, characterized in that the steps include: The coffee grounds are washed, dried, sieved and pyrolyzed to obtain coffee grounds-based biochar; The iron source, the ligand and the solvent are mixed uniformly to obtain a mixed solution; The coffee residue-based biochar is added to the mixed solution and dispersed evenly, and after heat treatment, washed and dried, the biochar-metal organic framework is obtained.

2. The method according to claim 1, characterized in that The iron source includes at least one of ferric chloride, ferric nitrate and anhydrous ferric chloride; the ligand includes one of 2-aminoterephthalic acid, 4-aminobenzoic acid and 5-aminoisophthalic acid; and the solvent includes at least one of DMF, DMSO and ethanol.

3. The method according to claim 1, characterized in that The pyrolysis is to heat the material to 300-800° C. at a heating rate of 3-15° C. / min in an inert atmosphere and keep the temperature for 2-8 hours; the water washing is to wash the material with water until the pH value of the leaching liquid is neutral.

4. The method according to claim 1, characterized in that The drying temperature is 50-120°C; the screening is to pass the sieve of 100-200 mesh; the heat treatment temperature is 100-120°C, and the time is 18-24h; the washing is to use N,N-dimethylformamide and ethanol to wash three times respectively; the drying temperature is 50-120°C.

5. The method according to claim 1, characterized in that The usage ratio of the iron source, the ligand and the solvent is 7.5mmol:3.75mmol:60mL; the usage ratio of the coffee grounds-based biochar and the solvent is 20-50mg:60mL.

6. A biochar-metal organic framework obtained by the method according to any one of claims 1 to 5.

7. Use of the biochar-metal organic framework as claimed in claim 6 as an adsorbent in the adsorption and enrichment of toxic heavy metals.

8. A method for improving the adsorption efficiency of biochar for Cr(VI), characterized in that: Biochar is modified by using a metal organic framework to prepare a biochar-metal organic framework material, and the biochar-metal organic framework material is used to adsorb Cr(VI); the steps of preparing the biochar-metal organic framework material include: The coffee grounds are pyrolyzed, washed, dried, and sieved to obtain coffee grounds-based biochar; Mixing ferric chloride, 2-aminoterephthalic acid and N,N-dimethylformamide uniformly to obtain a mixed solution; The coffee grounds-based biochar is added to the mixed solution and dispersed evenly. After heat treatment, the biochar-metal organic framework material is obtained by washing and drying.

9. A method for improving the adsorption efficiency of Cr(VI) by a metal organic framework, characterized in that: The biochar-metal organic framework material is modified by biochar to prepare a biochar-metal organic framework material, and the biochar-metal organic framework material is used to adsorb Cr(VI); the steps of preparing the biochar-metal organic framework material include: The coffee grounds are pyrolyzed, washed, dried, and sieved to obtain coffee grounds-based biochar; Mixing ferric chloride, 2-aminoterephthalic acid and N,N-dimethylformamide uniformly to obtain a mixed solution; The coffee residue-based biochar is added into the mixed solution and dispersed evenly, and after heat treatment, washed and dried, the biochar-metal organic framework is obtained.

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