A sulfur-linked covalent organic framework material, preparation method and application

Abstract

The application discloses a sulfur-connected covalent organic framework material, a preparation method and application, and belongs to the technical field of new material synthesis and noble metal recovery. The preparation method comprises the following steps: taking 2,3,5,6-tetra (4'-amino phenyl sulfide) terephthalonitrile and a C2 aldehyde compound as a building unit, mixing the building unit and a reaction medium in a reaction container, adding an acid catalyst into the reaction container, performing cyclic degassing in liquid nitrogen, sealing and performing a reaction under vacuum, cooling the obtained reaction product to room temperature after the reaction is completed, filtering and collecting a solid product, washing the solid product, and then vacuum drying, so that the covalent organic framework material is obtained. The covalent organic framework material prepared by the application has good crystallinity, regularly arranged pore structures and densely distributed sulfur and cyano active sites. The application of the covalent organic framework material to gold ion adsorption experiments in water bodies shows that the material has excellent adsorption performance and good selectivity for gold elements.

Description

Technical Field

[0001] This invention relates to the field of new material synthesis and precious metal recycling technology, specifically to a sulfur-linked covalent organic framework material, its preparation method, and its application. Background Technology

[0002] Covalent organic frameworks (COFs) are a class of crystalline porous polymers formed by the directional assembly of organic structural units through strong covalent bonds. These materials achieve the directional extension of two-dimensional or three-dimensional networks through stepwise polymerization. Their rigid framework is guided by topological design, thus possessing long-range order. The synthesis process integrates covalent and non-covalent interactions, ultimately forming a well-ordered and extended crystalline architecture. Because the overall structure of the material is entirely determined by the design of the precursor molecules, COFs are considered a novel class of polymers with precisely pre-defined structures and controllable synthetic pathways. This characteristic is rare in traditional polymers and other molecular framework materials. Compared to other porous crystalline materials, COFs not only possess precise chemical functions but also exhibit many significant advantages, such as flexible porosity control, low material density, large specific surface area, good chemical resistance, and easily modularized functional customization. These characteristics enable COFs to demonstrate unique performance and broad prospects in several cutting-edge fields, including gas storage and separation, catalysis, chemical delivery, electronic devices, and drug delivery.

[0003] Since Professor Yaghi's team successfully prepared the first two COF materials (COF-1 and COF-5) in 2005, this field has developed a variety of COFs with different structures. Based on the different chemical bonding modes of organic structural units, COFs can be mainly divided into three categories: boron ester bond type, triazine ring type, and imine bond type. Among them, boron-containing COFs generally possess low density, high specific surface area, and excellent thermal stability (withstanding temperatures up to 450~600℃), and have a wide range of applications. However, their boron ester bonds are prone to hydrolysis under humid conditions, affecting the long-term stability of the material. Triazine-linked covalent triazine frameworks (CTFs) have significant specific surface area and excellent thermochemical stability, especially excelling in catalytic applications, but their generally low crystallinity limits the development of some properties. For imine bond-linked COFs, they not only have better stability in aqueous environments than boron-containing types, but their crystallinity is also generally higher than that of CTFs. However, existing imine-based COF materials often exhibit limited adsorption capacity and poor selectivity when adsorbing gold(III) ions due to a lack of sufficient active sites. Therefore, the development of COFs with high-density active sites to achieve efficient capture of gold(III) is of great value to the precious metal recycling industry.

[0004] The structural units of COF materials can be flexibly designed, endowing them with many superior properties, such as customizable structures, predominantly mesoporous pores with adjustable sizes, highly regular pore arrangement, and precisely controllable physicochemical properties, making them widely used in numerous scientific and technological fields. Furthermore, compared to metal-organic frameworks (MOFs) that rely on coordination bonds, COFs exhibit higher structural integrity and stability under practical application conditions (especially in harsh environments). These characteristics give COFs significant advantages over other porous materials in multiple application dimensions. Therefore, developing novel two-dimensional imine-based covalent organic frameworks with the ability to recognize specific noble metals not only helps expand the COF material library but also has important scientific and practical significance for broadening their application boundaries. Summary of the Invention

[0005] One objective of this invention is to provide a method for preparing sulfur-linked covalent organic framework materials. A COFs material rich in sulfur and cyano groups is prepared via a Schiff base dehydration condensation reaction, which is effective for Au... 3+ It exhibits good adsorption selectivity and adsorption efficiency, providing an important reference for the application of COFs materials in the field of noble metal adsorption.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a sulfur-linked covalent organic framework material includes the following steps: a. Using 2,3,5,6-tetra(4'-aminophenyl sulfide) terephthalonitrile and C2 aldehyde compounds as building blocks, the building blocks and reaction medium are added to a reaction vessel and mixed evenly; the molar ratio of 2,3,5,6-tetra(4'-aminophenyl sulfide) terephthalonitrile and C2 aldehyde compounds is 1:2. b. Add the acid catalyst to the reaction vessel, circulate and degas it in liquid nitrogen, seal it under vacuum, and react it at 120°C for 72 hours. c. Following step b, after the reaction is complete, cool the resulting reaction product to room temperature, filter and collect the solid product. d. The solid product is washed sequentially with N,N-dimethylformamide, tetrahydrofuran, and methanol, and then dried under vacuum to obtain the final product.

[0007] In the above-mentioned method for preparing a sulfur-linked covalent organic framework material, in step a, the C2 aldehyde compound is terephthalaldehyde or 2,5-dimethyl sulfide terephthalaldehyde.

[0008] The above-mentioned method for preparing a sulfur-linked covalent organic framework material uses 2,5-dimethyl sulfide terephthalaldehyde as the C2 aldehyde compound.

[0009] In the above-mentioned method for preparing a sulfur-linked covalent organic framework material, in step a, the reaction medium is one or a mixture of solvents selected from mesitylene, 1,4-dioxane, o-dichlorobenzene, or n-butanol.

[0010] In the above-mentioned method for preparing a sulfur-linked covalent organic framework material, in step b, the acid catalyst is trifluoroacetic acid or p-benzenesulfonic acid.

[0011] The preparation method of the sulfur-linked covalent organic framework material described above uses a mixed solvent of mesitylene and 1,4-dioxane in a volume ratio of 3:7, a mixed solvent of o-dichlorobenzene and n-butanol in a volume ratio of 3:7, or a mixed solvent of o-dichlorobenzene and n-butanol in a volume ratio of 7:3.

[0012] In the preparation method of the sulfur-linked covalent organic framework material described above, the acid catalyst is a 0.3 mol / L, 100 μL aqueous solution of trifluoroacetic acid or a 6 mol / L, 100 μL aqueous solution of p-benzenesulfonic acid.

[0013] In the above-mentioned method for preparing a sulfur-linked covalent organic framework material, step d involves a vacuum drying temperature of 60°C and a drying time of 24 hours.

[0014] Compared with the prior art, the present invention brings the following beneficial technical effects: This invention proposes a method for preparing a sulfur-linked covalent organic framework material. In terms of raw material selection, 2,3,5,6-tetra(4'-aminophenyl sulfide) terephthalonitrile and C2 aldehyde compounds are chosen as building blocks. 2,3,5,6-tetra(4'-aminophenyl sulfide) terephthalonitrile contains sulfide and amino groups, resulting in an organic framework material rich in sulfur and cyano units. This not only significantly improves the structural flexibility of the adsorbent material but also enhances the selective recognition and adsorption process of gold ions through one-step synthesis of the target material from monomers containing sulfide and cyano structures, thus significantly improving the material's adsorption efficiency for gold ions.

[0015] In terms of preparation method, the present invention uses Schiff base dehydration condensation method to prepare COFs material rich in sulfur and cyano groups. The covalent organic framework material prepared by the method of the present invention has good crystallinity, regular pore structure and densely distributed sulfur and cyano active sites. When applied to the adsorption experiment of gold ions in water, the results show that the material exhibits excellent adsorption performance and adsorption efficiency for gold.

[0016] For the selection of C2 aldehyde compounds, this invention uses terephthalaldehyde or 2,5-dimethyl sulfide terephthalaldehyde, with a more preferred choice of 2,5-dimethyl sulfide terephthalaldehyde. The reason is that, according to the acid-base strength principle (HSAB), more easily dissociated soft gold ions tend to preferentially form stable complexes with groups that readily accept basic groups (especially sulfur), because favorable orbital overlap allows for effective chelation. In this case, designing building blocks containing CS single bonds provides a feasible strategy to increase the density of soft binding sites within the electron-rich channels of the sulfur-bridged COF, thereby improving gold absorption efficiency. The combination of 2,5-dimethyl sulfide terephthalaldehyde with 2,3,5,6-tetra(4'-aminophenyl sulfide) terephthalonitrile aims to give the material a high density of soft binding sites for efficient gold recovery. This framework design is achieved through a custom-designed four-arm monomer rich in CS bonds, which facilitates the formation of topological isomers under controlled Schiff base condensation conditions. By further adding S-terminated groups to the pore walls to enhance soft-soft interactions, the resulting electron-rich COF achieved a gold ion adsorption capacity of 6420 mg / g. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings: Figure 1 In the figures (a), (b), and (c), respectively, are the XRD patterns and structural simulation patterns of the sulfur-linked covalent organic framework materials prepared in Examples 1, 2, and 3 of this invention; Figure 2 (a), (b), and (c) are the FT-IR spectra of the sulfur-linked covalent organic framework materials prepared in Examples 1, 2, and 3 of this invention, respectively. Figure 3 (a), (b), (c), (d), (e), and (f) are nitrogen isothermal adsorption-desorption curves and pore size distribution diagrams of the sulfur-linked covalent organic framework materials prepared in Examples 1, 2, and 3 of this invention at 77 K. Figure 4 (a), (b), and (c) are thermogravimetric spectra of the sulfur-linked covalent organic framework materials prepared in Examples 1, 2, and 3 of this invention. Figure 5 The solid-state carbon NMR spectra of the sulfur-linked covalent organic framework materials prepared in Examples 1, 2, and 3 of this invention are shown. Figure 6 This is a graph showing the relationship between the adsorption capacity of the sulfur-linked covalent organic framework materials and the gold ion concentration in Application Examples 1, 2, and 3 of this invention. Figure 7Figures (a), (b), and (c) show the relationship between the adsorption equilibrium capacity and adsorption time of the sulfur-linked covalent organic framework materials in Application Examples 1, 2, and 3 of this invention. Figure 8 This is a schematic diagram of the reaction process of obtaining a sulfur-linked covalent organic framework material by polymerizing an amino compound containing a thioether group and an aldehyde compound, as described in Example 1 of this invention. Detailed Implementation

[0018] This invention proposes a sulfur-linked covalent organic framework material, its preparation method, and its application. To make the advantages and technical solutions of this invention clearer and more explicit, the invention will be further described below with reference to specific embodiments.

[0019] All the raw materials mentioned in this invention can be purchased through commercial channels.

[0020] In this invention, 2,3,5,6-tetra(4'-aminophenyl sulfide) terephthalonitrile is formed by attaching a 4'-aminophenyl sulfide group to the 2, 3, 5, and 6 positions of the benzene ring as the parent compound.

[0021] This invention discloses a method for preparing a sulfur-linked covalent organic framework material, specifically comprising the following steps: Step 1: Using 2,3,5,6-tetratetra(4'-aminophenyl sulfide) terephthalonitrile and C2 aldehyde compounds as building blocks, add the building blocks and reaction medium into the reaction vessel and mix thoroughly. Specifically, the molar ratio of 2,3,5,6-tetra(4'-aminophenyl sulfide) terephthalonitrile to C2 aldehyde compounds is 1:2; The C2 aldehyde compound is terephthalaldehyde or 2,5-dimethyl sulfide terephthalaldehyde; more preferably, the C2 aldehyde compound is 2,5-dimethyl sulfide terephthalaldehyde.

[0022] The reaction medium is one or a mixture of solvents selected from methylbenzene, 1,4-dioxane, o-dichlorobenzene, or n-butanol.

[0023] Furthermore, the solvent is a mixed solvent of mesitylene and 1,4-dioxane in a volume ratio of 3:7, a mixed solvent of o-dichlorobenzene and n-butanol in a volume ratio of 3:7, or a mixed solvent of o-dichlorobenzene and n-butanol in a volume ratio of 7:3.

[0024] Step 2: Add the acid catalyst to the reaction vessel, circulate and degas it in liquid nitrogen, seal it under vacuum, and react at 120°C for 72 hours. Furthermore, the acid catalyst is trifluoroacetic acid or p-benzenesulfonic acid; the acid catalyst is a 0.3 mol / L, 100 μL aqueous solution of trifluoroacetic acid or a 6 mol / L, 100 μL aqueous solution of p-benzenesulfonic acid.

[0025] Step 3: After the reaction is complete, cool the resulting reaction product to room temperature, filter and collect the solid product; Step 4: Wash the solid product sequentially with N,N-dimethylformamide, tetrahydrofuran, and methanol, and then dry it under vacuum to obtain the final product.

[0026] The present invention will be further described below with reference to specific embodiments.

[0027] Example 1: This invention discloses a method for preparing a sulfur-linked covalent organic framework material, specifically comprising the following steps: Step 1: Add 12.4 mg of 2,3,5,6-tetratetra(4'-aminophenyl sulfide) terephthalonitrile and 5.4 mg of terephthalaldehyde to a Pyrex tube and mix thoroughly.

[0028] Step 2: Add 0.3 mL of mesitylene, 0.7 mL of 1,4-dioxane and 0.1 mL of 0.3 mol / L trifluoroacetic acid sequentially to a Pyrex tube. Degas the tube by performing three freeze cycles, then seal it with a flame and heat it at 120 °C for 72 h.

[0029] Step 3: After the reaction was complete, the product was washed sequentially with N,N-dimethylformamide, tetrahydrofuran, and methanol. Finally, it was vacuum dried at 60°C for 24 h to obtain the sulfur-linked covalent organic framework material (S-COF-). SQL ).

[0030] Figure 1 Image (a) shows the X-ray powder diffraction (XRD) characterization pattern of the covalent organic framework material. The results indicate that the covalent organic framework material has diffraction peaks at 4.22° and 8.56°. The optimal S-COF- was obtained using Materials Studio 2019 software. SQL The structure was simulated, and the geometry of the molecule and the model were optimized sequentially. The Reflex Plus module generated the calculated PXRD pattern, and the refined PXRD pattern was obtained after fitting. The final S-COF- SQL The Pawley optimization parameters are R. wp = 2.53%, R p = 1.78%.

[0031] Example 1 of this invention illustrates the reaction process of polymerizing amino compounds containing sulfide groups with aldehyde compounds to obtain sulfur-linked covalent organic framework materials. Figure 8 As shown.

[0032] Example 2: This invention discloses a method for preparing a sulfur-linked covalent organic framework material, specifically comprising the following steps: Step 1: Add 12.4 mg of 2,3,5,6-tetratetra(4'-aminophenyl sulfide) terephthalonitrile and 5.4 mg of terephthalaldehyde to a Pyrex tube and mix thoroughly. Step 2: Add 0.3 mL of o-dichlorobenzene, 0.7 mL of n-butanol and 0.1 mL of 4 mol / L p-toluenesulfonic acid sequentially to a Pyrex tube. Degas the tube after three freeze cycles, then seal it with a flame and heat it at 120°C for 72 h.

[0033] Step 3: After the reaction was complete, the product was washed sequentially with N,N-dimethylformamide, tetrahydrofuran, and methanol. Finally, it was vacuum dried at 60°C for 24 h to obtain the sulfur-linked covalent organic framework material (S-COF-). kgm ).

[0034] Figure 1 (b) shows the X-ray powder diffraction pattern of the covalent organic framework material. The results indicate that the covalent organic framework material has diffraction peaks at 2.83° and 5.64°. The optimal S-COF- was obtained using Materials Studio 2019 software. kgm The structure was simulated, and the geometry of the molecule and the model were optimized sequentially. The Reflex Plus module generated the calculated PXRD pattern, and the refined PXRD pattern was obtained after fitting. The final S-COF- kgm The Pawley optimization parameters are Rwp = 2.49% and Rp = 2.19%.

[0035] Example 3: This invention discloses a method for preparing a sulfur-linked covalent organic framework material, specifically comprising the following steps: Step 1: Add 12.4 mg of 2,3,5,6-tetratetra(4'-aminophenyl sulfide) terephthalonitrile and 9.1 mg of 2,5-dimethyl sulfide terephthalaldehyde to a Pyrex tube and mix thoroughly. Step 2: Add 0.7 mL of o-dichlorobenzene, 0.3 mL of n-butanol and 0.1 mL of 6 mol / L p-toluenesulfonic acid sequentially to a Pyrex tube. Degas the tube by performing three freeze cycles, then seal it with a flame and heat it at 120°C for 72 h.

[0036] Step 3: After the reaction is complete, the product is washed sequentially with N,N-dimethylformamide, tetrahydrofuran, and methanol. Finally, it is vacuum dried at 60°C for 24 h to obtain the sulfur-linked covalent organic framework material (S-COF-SMe).

[0037] Figure 1 Image (c) shows the X-ray powder diffraction (XRD) characterization pattern of the covalent organic framework material. The results indicate that the covalent organic framework material exhibits diffraction peaks at 2.90° and 5.76°. The optimal S-COF-SMe structure was simulated using Materials Studio 2019 software. The molecular geometry and model geometry were optimized sequentially. The Reflex Plus module generated the calculated PXRD pattern, and the refined PXRD pattern was obtained after fitting. The final optimized PXRD parameters for S-COF-SMe are R0, R1, and R2, R3, R4, R5, R6, R7, R8, R9, R1, R2 ... wp = 5.26%, R p = 3.91%.

[0038] Figure 2 (a), (b), and (c) are the FT-IR spectra of the sulfur-linked covalent organic framework materials prepared in Examples 1, 2, and 3 of this invention, respectively. As can be seen from the figures, after the reaction is completed, the -NH stretching vibration peak in the amino compounds and the -C=O stretching vibration peak in the aldehyde compounds disappear, while a new characteristic vibration peak of -C=N appears in the spectrum of the newly generated S-COFs, proving that a Schiff base dehydration condensation reaction occurred between the two building units.

[0039] Figure 3 Figures (a), (b), (c), (d), (e), and (f) show the nitrogen isothermal adsorption-desorption curves and pore size distribution diagrams of the sulfur-linked covalent organic framework materials prepared in Examples 1, 2, and 3 of this invention at 77 K. The figures show that their BET surface areas are 565 m² / s, respectively. 2 / g, 689 m 2 / g, 614 m 2 / g.

[0040] Figure 4(a), (b), and (c) are thermogravimetric spectra of the sulfur-linked covalent organic framework materials prepared in Examples 1, 2, and 3 of this invention; the final S-COFs remained stable below 410℃ and 320℃, respectively.

[0041] In addition, the S-COFs were characterized by solid-state carbon NMR spectroscopy. Figure 5 The peaks in the solid-state NMR spectrum were assigned, and the characteristic peak of -C=N appeared at 150 ppm, further confirming the existence of -C=N and indicating the successful synthesis of the material.

[0042] The adsorption performance of the sulfur-linked covalent organic framework materials S-COFs prepared in Examples 1, 2, and 3 on gold ions was tested below through Application Examples 1, 2, and 3, respectively.

[0043] Application Example 1: This application example uses the sulfur-linked covalent organic framework material (S-COF-) prepared in Example 1. SQL ).

[0044] The sulfur-linked covalent organic framework material S-COF- prepared in Example 1 was used. SQL The adsorbent was added to HAuCl4 solutions with initial concentrations ranging from 50 to 2000 mg / L (pH = 4), and the mixture was shaken for 12 h at 25℃ and 300 r / min. A graph showing the relationship between the adsorption capacity of the adsorbent and the concentration of gold ions was plotted. The gold ion adsorption capacity was 3962 mg / g (bound to...). Figure 6 and Figure 7 (as shown) Figure 7 In Figure (a), the relationship between the adsorption equilibrium capacity and adsorption time of the sulfur-linked covalent organic framework material in Application Example 1 of this invention is shown.

[0045] Application Example 2: This application example uses the sulfur-linked covalent organic framework material (S-COF-) prepared in Example 2. kgm ).

[0046] The sulfur-linked covalent organic framework material (S-COF-) prepared in Example 2 was used. kgm The adsorbent was added to HAuCl4 solutions with initial concentrations ranging from 50 to 2000 mg / L (pH = 4), and the mixture was shaken for 12 h at 25℃ and 300 r / min. A graph showing the relationship between the adsorption capacity of the adsorbent and the concentration of gold ions was plotted. The gold ion adsorption capacity was 4399 mg / g (combined with...). Figure 6 and Figure 7 (As shown). Figure 7(b) is a graph showing the relationship between the adsorption equilibrium capacity and adsorption time of the sulfur-linked covalent organic framework material in Application Example 2 of the present invention.

[0047] Application Example 3: This application example uses the sulfur-linked covalent organic framework material (S-COF-SMe) prepared in Example 3.

[0048] The sulfur-linked covalent organic framework material (S-COF-SMe) prepared in Example 3 was added to HAuCl4 solutions with initial concentrations of 50-2000 mg / L (pH=4), and shaken for 12 h at 25℃ and 300 r / min. A graph showing the relationship between adsorption capacity and gold ion concentration was plotted. The gold ion adsorption capacity was 6420 mg / g (bound to...). Figure 6 and Figure 7 (As shown). Figure 7 (c) is a graph showing the relationship between the adsorption equilibrium capacity and adsorption time of the sulfur-linked covalent organic framework material in Application Example 3 of this invention.

[0049] Any parts not mentioned in this invention can be achieved by referring to existing technologies.

[0050] Those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application should fall within the scope of protection of the claims of this application.

Claims

1. A method for preparing a sulfur-linked covalent organic framework material, characterized in that, The steps are as follows: a. Using 2,3,5,6-tetra(4'-aminophenyl sulfide) terephthalonitrile and C2 aldehyde compounds as building blocks, the building blocks and reaction medium are added to a reaction vessel and mixed evenly; the molar ratio of 2,3,5,6-tetra(4'-aminophenyl sulfide) terephthalonitrile and C2 aldehyde compounds is 1:

2. b. Add the acid catalyst to the reaction vessel, circulate and degas it in liquid nitrogen, seal it under vacuum, and react it at 120°C for 72 hours. c. Following step b, after the reaction is complete, cool the resulting reaction product to room temperature, filter and collect the solid product. d. The solid product is washed sequentially with N,N-dimethylformamide, tetrahydrofuran, and methanol, and then dried under vacuum to obtain the final product.

2. The method for preparing a sulfur-linked covalent organic framework material according to claim 1, characterized in that: In step a, the C2 aldehyde compound is terephthalaldehyde or 2,5-dimethyl sulfide terephthalaldehyde.

3. The method for preparing a sulfur-linked covalent organic framework material according to claim 2, characterized in that: The C2 aldehyde compound is 2,5-dimethyl sulfide terephthalaldehyde.

4. The method for preparing a sulfur-linked covalent organic framework material according to claim 1, characterized in that: In step a, the reaction medium is one or a mixture of solvents selected from mesitylene, 1,4-dioxane, o-dichlorobenzene, or n-butanol.

5. The method for preparing a sulfur-linked covalent organic framework material according to claim 1, characterized in that: In step b, the acid catalyst is trifluoroacetic acid or p-benzenesulfonic acid.

6. The method for preparing a sulfur-linked covalent organic framework material according to claim 4, characterized in that: The solvent is a mixed solvent of mesitylene and 1,4-dioxane in a volume ratio of 3:7, a mixed solvent of o-dichlorobenzene and n-butanol in a volume ratio of 3:7, or a mixed solvent of o-dichlorobenzene and n-butanol in a volume ratio of 7:

3.

7. The method for preparing a sulfur-linked covalent organic framework material according to claim 5, characterized in that: The acid catalyst is a 0.3 mol / L, 100 μL aqueous solution of trifluoroacetic acid or a 6 mol / L, 100 μL aqueous solution of p-benzenesulfonic acid.

8. The method for preparing a sulfur-linked covalent organic framework material according to claim 1, characterized in that: In step d, the vacuum drying temperature is 60℃ and the drying time is 24h.

9. A sulfur-linked covalent organic framework material, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 8, and contains abundant sulfur atom units and cyano units.

10. The application of a sulfur-linked covalent organic framework material according to claim 9 as an adsorbent in gold ion adsorption, characterized in that: The application includes: placing sulfur-linked covalent organic framework materials in a HAuCl4 solution at 298 K, pH 4, and concentration of 1500 ppm for 12 hours to treat Au... 3+ The adsorption capacities were 3962 mg / g, 4399 mg / g, and 6420 mg / g, respectively.

Images