Application of hollow carbon nanoparticle material as adsorbent for adsorbing gold ions

Abstract

The present invention relates to the field of gold adsorption technology, and discloses the use of a hollow carbon nanoparticle material as an adsorbent for adsorbing gold ions. The present invention uses the adsorption and reduction effect of the graphene layer of the hollow carbon nanoparticle material on metal ions to adsorb and reduce gold ions, and uses metal organic framework nanoparticles with a hollow structure as the starting material. During the pyrolysis process, the carbon element is graphitized to form a hollow structure, and nitrogen and oxygen elements are doped at the same time, thereby significantly improving the selective adsorption performance for gold ions. The preparation process of the hollow carbon nanoparticle material of the present invention is simple, and the source of the preparation material is wide. The preparation of metal organic framework nanoparticles is a relatively mature technology in the prior art. Based on the present invention, a new application for metal organic framework nanoparticles can be provided, and a new idea for gold recovery can be provided.

Description

Technical Field

[0001] The present invention relates to the technical field of gold adsorption, in particular to an application of a hollow carbon nanoparticle material as an adsorbent for adsorbing gold ions. Background Art

[0002] Gold (Au), a precious metal, has a wide range of applications in science, industry, and commerce, particularly in catalysis, antimicrobial agents, and anticancer drugs. Furthermore, gold is a core material for electronics and jewelry. With the continued growth in demand for gold in industries such as electronics and new energy, relying solely on primary ore mining is no longer sufficient to meet the increasing demand. The value of gold continues to rise, primarily due to its scarcity, high consumption, and growing global demand. Notably, the manufacture of electronic devices consumes approximately 300 metric tons of gold annually. The gold content in products such as mobile phones and computer circuit boards can reach as high as 200-350 grams per metric ton, far exceeding the concentration found in currently recoverable deposits. Significant quantities of gold are also present in secondary reservoirs such as incineration ash, wastewater, freshwater bodies, and marine environments, offering new avenues for extracting gold from "electronic waste." However, efficiently extracting gold from these secondary sources remains an unmet challenge.

[0003] Currently, one of the main difficulties in extracting gold from "electronic waste" is the extremely low gold concentration in these sources. For example, the gold concentration in wastewater is usually less than 10 μg / L, and in seawater it is less than 10 ng / L. In addition, another difficulty is the presence of a large amount of metal impurities in these secondary sources, and their concentrations are much higher than gold. For example, the liquids from these sources usually contain a variety of organic compounds and competing metal ions, such as sodium, potassium, copper, nickel, iron and rare earth metals, whose concentrations are significantly higher than gold, thereby increasing the complexity of the extraction process. Therefore, developing a material that is low in cost, simple to prepare and can stably and efficiently extract trace amounts of gold in complex water quality has become an urgent and challenging task. Summary of the Invention

[0004] To address the challenge of efficiently extracting gold from complex environments with extremely low gold ion concentrations and high metal impurity concentrations, this invention provides the use of hollow carbon nanoparticles as an adsorbent for gold ion absorption. This invention not only effectively addresses the challenge of efficiently extracting gold from complex environments with low gold concentrations and high impurity concentrations, but also provides a new solution for the efficient recovery of gold from complex liquids.

[0005] The specific technical solutions of the present invention are:

[0006] The present invention provides an application of hollow carbon nanoparticles as an adsorbent for gold ion adsorption. The unique feature of this application is that the hollow carbon nanoparticles are obtained by calcining metal-organic framework nanoparticles with a hollow structure.

[0007] The calcination process transforms the structure of the metal organic framework nanoparticles into a graphene layer.

[0008] To address the technical difficulties in extracting gold in a complex environment with extremely low gold ion concentration, numerous metal impurities and relatively high impurity concentration, the present invention uses metal-organic framework nanoparticles with a hollow structure as raw material, and through calcination, converts the carbon in the structure of the metal-organic framework nanoparticles into graphene layers to prepare a hollow carbon nanoparticle material adsorbent with high selectivity for gold ions and high adsorption capacity.

[0009] The hollow carbon nanoparticle material of the present invention has excellent adsorption performance for gold ions. The principle is as follows:

[0010] Through the adsorption and reduction effect of the graphene layer of the hollow carbon nanoparticle material on metal ions, efficient adsorption of gold ions is achieved. In addition, since metal-organic framework nanoparticles with a hollow structure are used as the starting material, the carbon element is doped with nitrogen and oxygen elements in the process of converting into graphene layers, which plays a key role in improving the selective adsorption of gold ions in the hollow carbon nanoparticle material.

[0011] As a preferred embodiment of the above application, the metal organic framework nanoparticles are ZIF-8 nanoparticles.

[0012] As a preferred embodiment of the above application, the temperature of the calcination treatment is 700-1000°C.

[0013] As a preference for the above application, the calcination treatment is carried out under an inert gas atmosphere.

[0014] Specifically, the present invention describes the preparation of the hollow carbon nanoparticle material by taking the following preparation method as an example. The preparation method of the hollow carbon nanoparticle material comprises the following steps:

[0015] Step S1: adding zinc nitrate hexahydrate and 2-methylimidazole to a solvent respectively, stirring to form nuclei, and obtaining metal organic framework nanoparticles;

[0016] Step S2: dispersing the metal organic framework nanoparticles obtained in step S1 in a solvent, adding tannic acid, and stirring to react to obtain metal organic framework nanoparticles with a hollow structure;

[0017] Step S3: taking the metal organic framework nanoparticles with a hollow structure obtained in step S2 and performing a calcination treatment to transform and form a graphene layer in the structure of the nanoparticles.

[0018] The principle of gold ion adsorption by the hollow carbon nanoparticle material of the present invention is that the gold ions are adsorbed and reduced by the adsorption-reduction effect of the graphene layer of the hollow carbon nanoparticle material on metal ions. Using hollow metal-organic framework nanoparticles as the starting material, nitrogen and oxygen are doped during the conversion of carbon into graphene, thereby enhancing the selective adsorption of gold ions by the finished hollow carbon nanoparticle material. Therefore, the preparation of the hollow metal-organic framework nanoparticles and the preparation of the graphene layer are of great importance. Through the above-mentioned steps S1 to S3, a specific method for preparing a hollow carbon nanoparticle material adsorbent with high selectivity and high adsorption capacity for gold ions can be provided.

[0019] Based on the principle of gold ion adsorption by hollow carbon nanoparticles, the present invention can use the above-mentioned preparation method as an example to adjust the specific preparation process to obtain an adsorbent with better gold ion adsorption performance. For example, the molar ratio of zinc nitrate hexahydrate and 2-methylimidazole can be adjusted, as can the mass ratio of metal-organic framework nanoparticles to tannic acid, the stirring reaction time, and the calcination temperature and gas atmosphere.

[0020] As a preferred embodiment of the above method, in step S1, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:6-10.

[0021] As a preferred embodiment of the above method, in step S2, the mass ratio of the metal organic framework nanoparticles to tannic acid is 1:4-6.

[0022] As a preferred embodiment of the above method, in step S2, the stirring reaction is carried out at a rotation speed of 200 rpm to 600 rpm and for a time of 5 minutes to 10 minutes.

[0023] As a preferred embodiment of the above method, in step S3, the calcination treatment is performed at a temperature of 700° C. to 1000° C. and for a time of 0.5 to 4 hours.

[0024] As a preferred embodiment of the above method, in step S3, the calcination treatment is performed under an inert gas atmosphere.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] (1) The present invention uses metal organic framework nanoparticles with a hollow structure as raw materials, and converts the carbon in the structure of the metal organic framework nanoparticles into graphene layers through calcination. The hollow carbon nanoparticle material prepared has a high selectivity and high adsorption capacity for gold ions.

[0027] (2) The present invention utilizes the adsorption and reduction effect of the graphene layer of the hollow carbon nanoparticle material on metal ions to adsorb and reduce gold ions. Using hollow metal organic framework nanoparticles as the starting material, nitrogen and oxygen are doped into the hollow carbon nanoparticles during the conversion of carbon elements into graphite, thereby enhancing the selective adsorption of gold ions by the hollow carbon nanoparticles. The preparation process is simple and the source of the materials is wide. The preparation of metal organic framework nanoparticles is a relatively mature technology in the prior art. Based on the present invention, a new application of metal organic framework nanoparticles can be provided, providing a new approach to gold recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 SEM / TEM structural characterization of hollow carbon nanoparticles;

[0029] Figure 2 XRD comparison diagram of metal organic framework nanoparticles, hollow modified metal organic framework nanoparticles and hollow carbon nanoparticles;

[0030] Figure 3 is the Raman spectrum of hollow carbon nanoparticles;

[0031] Figure 4 is the relationship between the adsorption rate of hollow carbon nanoparticles to gold ions and the pH value of the solution;

[0032] Figure 5 is the adsorption isotherm of hollow carbon nanoparticles at different initial gold ion concentrations;

[0033] Figure 6 The effect of adsorption time on the gold ion adsorption performance of hollow carbon nanoparticles;

[0034] Figure 7 This is a test diagram of the adsorption selectivity of hollow carbon nanoparticles for gold ions;

[0035] Figure 8 This is a test diagram of the adsorption cycle performance of hollow carbon nanoparticles. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the following embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only a portion of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0037] Example 1

[0038] This embodiment provides a hollow carbon nanoparticle material, which is prepared according to the following steps:

[0039] (1) Preparation of metal-organic framework nanoparticles

[0040] First, weigh 1.968 g of 2-methylimidazole (0.0239 mol) and 0.891 mol of zinc nitrate hexahydrate (0.003 mol), i.e., a molar ratio of 1:8 between zinc nitrate hexahydrate and 2-methylimidazole. Dissolve each of these ingredients in 50 mL of methanol. Once fully dissolved, mix the mixture at room temperature and react under magnetic stirring for 8 hours. After the reaction, centrifuge the resulting solution at 8000 rpm for 5 minutes to collect the solid precipitate. The precipitate is then washed with 30 mL of methanol and centrifuged at 8000 rpm for 5 minutes. The upper methanol layer is discarded and the washing and centrifugation steps are repeated three times. The resulting solid powder is placed in a vacuum oven and dried at 60°C for 24 hours to obtain metal-organic framework nanoparticles (ZIF-8), which are retained for the next step.

[0041] (2) Hollow modified ZIF-8 material

[0042] Weigh 200 mg of the ZIF-8 material prepared in step (1) and 1 g of tannic acid, that is, the ZIF-8 material and tannic acid are weighed in a mass ratio of 1:5. Ultrasonic dispersion of the weighed ZIF-8 material in 100 mL of methanol, dissolve the weighed tannic acid in 100 mL of deionized water, mix the dispersed methanol suspension and the dissolved tannic acid aqueous solution, and react with magnetic stirring at room temperature for 10 minutes at a stirring rate of 400 rpm. After the stirring reaction is completed, the resulting suspension is centrifuged at 8000 rpm for 5 minutes to obtain a solid precipitate. Then, the precipitate is washed with 30 mL of methanol. After washing, it is centrifuged at 8000 rpm for 5 minutes, the upper methanol is discarded, and the above washing and centrifugation steps are repeated 5 times. Finally, the solid powder obtained by washing and centrifugation is placed in a vacuum oven and vacuum-dried at 60°C for 24 hours to obtain hollow modified metal organic framework nanoparticles, namely HZIF-8 material, which is retained for the next step.

[0043] (3) Preparation of hollow carbon nanoparticle materials

[0044] 200 mg of the HZIF-8 material obtained in step (2) was weighed and placed in a porcelain boat in a tube furnace. Nitrogen was introduced for 30 minutes before heating to ensure that all air in the tube was expelled. The temperature was then raised to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcined at 900°C for 2 hours. After the temperature in the furnace cooled to room temperature, the calcined solid powder was removed to obtain hollow carbon nanoparticle material, which was recorded as HNPC material.

[0045] Example 2

[0046] In this example, the materials prepared in step (1), step (2) and step (3) in Example 1 were subjected to structural characterization analysis. The results are shown in Figure 1 、 Figure 2 and Figure 3 .in, Figure 1 The SEM / TEM structural characterization images of the hollow carbon nanoparticles (HNPC) prepared in step (3) of Example 1 are shown on the left as the SEM structural characterization image and on the right as the TEM structural characterization image; Figure 2 XRD comparison diagrams of metal organic framework nanoparticles (ZIF-8), hollow modified metal organic framework nanoparticles (HZIF-8) and hollow carbon nanoparticles (HNPC); Figure 3 This is the Raman spectrum of the hollow carbon nanoparticles (HNPC) prepared in step (3) of Example 1, where the G peak is the graphene peak and the D peak is the amorphous peak.

[0047] From the characterization results of this embodiment, it can be seen that:

[0048] Figure 1 The SEM and TEM images of the HNPC prepared in Example 1 are shown, and the surface morphology and internal hollow structure of the hollow nanocarbon particles of the HNPC are characterized. It can be seen from the TEM image that the HNPC successfully prepared a hollow structure. At the same time, the SEM and TEM characterizations show that the particle size of the HNPC is about 100 nm.

[0049] Figure 2 The results show that the diffraction peak positions of synthesized ZIF-8 and HZIF-8 are the same as those of the simulated crystal structure, proving the successful synthesis of the crystal structure. The XRD diffraction curve of HNPC shows that HNPC has obvious carbon material diffraction peaks. HNPC is amorphous and the crystal planes have all disappeared, proving the successful preparation of carbon materials. Figure 2It can be seen that the HNPC does not have a diffraction peak associated with zinc metal, indicating that zinc is no longer present in the HNPC structure after calcination. Furthermore, in this example, X-ray photoelectron spectroscopy was performed on the HNPC prepared in Example 1, confirming that the HNPC contains only C, N, and O elements, with a C content of 91%, a N content of 4%, and an O content of 5%.

[0050] Figure 3 The Raman spectrum of HNPC prepared in Example 1 is shown. Figure 3 It can be seen that the HNPC structure has a graphene layer, and the proportion of the graphene layer, that is, the degree of grapheneization is 0.88.

[0051] Example 3

[0052] In this example, the adsorption performance of the HNPC obtained in Example 1 was tested under the conditions of gold ion solutions with different pH values, and the effect of liquid states with different pH values ​​on the adsorption and recovery of gold ions was studied with a single variable.

[0053] Prepare Au with pH values ​​of 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, and 11.0 3+ Ionic sample solution, in which Au 3+ The ion concentration was 100 mg / L, and the pH was adjusted using HCl or NaOH solutions. 2 mg of HNPC was added to 5 mL of sample solution, and the mixture was stirred at room temperature for 60 minutes. The supernatant was centrifuged and filtered, and the gold ion concentration in the supernatant was measured using inductively coupled plasma mass spectrometry (ICP-MS). The adsorption rate was calculated using the following equation:

[0054]

[0055] Where R is the removal efficiency, C0 is the initial concentration, C t is the final concentration at a specific time. Figure 4 As shown in the figure, at different pH values ​​from 1 to 11, HNPC has an adsorption rate of more than 99%, which proves that HNPC has good anti-interference ability in gold adsorption. HNPC has significant gold recovery effects at different pH values.

[0056] Example 4

[0057] In this example, the adsorption saturation concentration of the HNPC prepared in Example 1 was determined to explore the adsorption behavior of HNPC.

[0058] The adsorption isotherm results of HNPC are as follows: Figure 5 As shown. Figure 5It shows that as the concentration of gold ions increases, the adsorption capacity of HNPC also increases rapidly. When the gold ion concentration reaches 4000ppm, the adsorption process reaches saturation, and the adsorption amount at this time is 2670mg / g.

[0059] The adsorption amount is calculated by the following equation:

[0060]

[0061] Where C0 is the initial concentration, Ce is the equilibrium concentration, V is the volume, and m is the mass of the composite material initially used.

[0062] Example 5

[0063] In this example, the HNPC prepared in Example 1 was subjected to an adsorption kinetics test to determine the adsorption rate of gold ions on the HNPC and to study the adsorption kinetics of the HNPC.

[0064] The operation of this example is as follows: 5 mg of HNPC was dispersed in 50 mL of a gold ion sample with an initial concentration of 100 ppm. The solution was stirred at room temperature at 25°C for 1 min, 3 min, 10 min, 30 min, 60 min, 2 h, 5 h, 10 h, 24 h and 48 h. The gold ion concentration of the solution was tested at each time point. The adsorption amount was analyzed by ICP-OES and ICP-MS. The results are shown in Figure 2. Figure 6 shown.

[0065] Depend on Figure 6 It can be seen that the maximum adsorption capacity of HNPC for gold ions is 2461 mg / g.

[0066] Example 6

[0067] In this example, the HNPC prepared in Example 1 was added to a mixture containing Cu 2+ 、Na + 、Zn 2+ 、Ni 2+ and Mg 2+ Au as a competing ion 3+ Selective adsorption experiments were carried out in mixed solutions to explore the selective adsorption performance of HNPC for gold ions.

[0068] The operation of this example is as follows: a mixed solution of Au³⁺ containing Cu²⁺, Na⁺, Zn²⁺, Ni²⁺, and Mg²⁺ as competing ions is prepared, wherein the concentrations of Cu²⁺, Na⁺, Zn²⁺, Ni²⁺, and Mg²⁺ are approximately 100 mg / L, and the concentration of Au³⁺ is 10 mg / L. Then 2 mg of HNPC is added to 5 mL of the mixed solution, stirred for 1 hour, and the adsorption results are tested. The results are as follows: Figure 7 shown.

[0069] Depend on Figure 7 It can be seen that HNPC has a strong effect on Na + 、Zn 2+ 、Ni 2+ and Mg 2+ The adsorption rate of interfering ions is below 0.05%, Cu 2+ The adsorption rate of Au is the largest, which is 0.09%, and other ions are almost not adsorbed; 3+ It has been almost completely adsorbed, with an adsorption rate of 99.6%, proving that it has good selective adsorption performance for gold ions.

[0070] Example 7

[0071] In this example, the recyclability of the HNPC prepared in Example 1 was tested to determine the recyclability of the HNPC.

[0072] In this example, the recycling performance of HNPC was tested. The adsorbed material was reduced with 20 mL of ascorbic acid (0.002 M). The results of the HNPC adsorption-reduction cycle experiment are shown in Figure 2. Figure 8 shown.

[0073] Depend on Figure 8 It can be seen that after 5 cycles, HNPC 3+ The adsorption performance of the hollow carbon nanoparticles was almost unchanged, which indicated that the hollow carbon nanoparticles prepared in Example 1 had good recyclability.

[0074] Example 8

[0075] The HNPC prepared in Example 1 was used to recover gold from waste CPUs.

[0076] The specific procedure is as follows: Used CPUs are cut into small pieces. Used CPUs contain copper, nickel, magnesium, zinc, and gold, with the mass contents of copper, nickel, magnesium, zinc, and gold being 90%, 8.1%, 0.5%, 0.6%, and 0.8%, respectively. 119.034 mL of distilled water, 0.966 mL of pyridine (100 mM), and 0.750 g of N-bromosuccinimide (35 mM) are mixed and 0.3 g of the used CPU is immersed in the mixture for 24 hours to obtain a CPU leaching solution. The initial gold concentration in the CPU leaching solution is then measured. 4 mg of HNPC is then added to 10 mL of the CPU leaching solution and allowed to stand for 1 hour to extract the gold. After extraction, the system is centrifuged at 8000 rpm, and the supernatant is analyzed by ICPMS to determine the final gold concentration. The gold adsorption rate is then calculated using the equation in Example 3, representing the gold recovery efficiency from the used CPUs in this experiment.

[0077] This experiment shows that HNPC can adsorb and recover gold ions in waste CPU samples with a recovery efficiency of 99.1%.

[0078] Example 9

[0079] Taking Example 1 as a control, this example prepares hollow carbon nanoparticle materials using different preparation processes to explore the influence of the preparation process of the hollow carbon nanoparticle material itself on the gold ion adsorption performance of the product.

[0080] First, various parameters in the preparation of metal organic framework nanoparticles in step (1) were adjusted. It was found that when the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole was 1:6-10, the hollow carbon nanoparticle material finally prepared had better adsorption performance for gold ions. Specifically, when the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole was 1:6 (other preparation conditions were the same as in Example 1), the prepared HNPC had a better adsorption performance for gold ions when the experiment shown in Example 6 was performed. 3+ The adsorption rate was 99.4%. When the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole was 1:10, the adsorption rate was 99.3%. When the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole was 1:5 (other preparation conditions were the same as those in Example 1), the prepared HNPC was subjected to the experiment shown in Example 6. 3+ The adsorption rate was 88.1%. When the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole was 1:12, the adsorption rate was 88.4%. The role of 2-methylimidazole is to provide organic ligands for metal-organic framework nanoparticles. Its role in HNPC is to provide nitrogen and oxygen doping elements for hollow carbon nanoparticle materials. Therefore, it can be seen that the amount of nitrogen and oxygen doping in hollow carbon nanoparticle materials will have a significant impact on the selective adsorption of gold ions by hollow carbon nanoparticle materials. The research results show that when the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is between 1:6 and 1:10, the gold ion selective adsorption performance of HNPC is most significant. Therefore, the nitrogen and oxygen doping amount within this ratio range helps to improve the selective adsorption capacity of hollow carbon nanoparticle materials for gold ions.

[0081] To verify the effects of nitrogen and oxygen doping on the selective adsorption of gold ions, this example used commercial graphene and expanded graphite as comparative adsorbents, conducting the saturation adsorption capacity tests described in Example 4 and the selective adsorption experiments described in Example 6. The results showed that commercial graphene exhibited varying degrees of adsorption and reduction for metal ions such as Cu⁺, Na⁺, Zn⁺, Ni⁺, and Mg⁺, with adsorption rates of 6.6%, 2.9%, 3.2%, 2.4%, and 1.3%, respectively, while the adsorption rate for Au⁺ was only 51%. The tests also showed that the saturation adsorption capacity of commercial graphene was 85 mg / g, while that of expanded graphite was 92 mg / g. These results demonstrate that the key role of the hollow carbon nanoparticle material in gold ion adsorption lies not only in the formation of the graphene layer but also in the doping of nitrogen and oxygen. It is precisely due to the nitrogen and oxygen doping that the hollow carbon nanoparticle material exhibits higher selectivity and enhanced adsorption capacity for gold ions. Therefore, starting with metal-organic framework nanoparticles, the preparation of hollow carbon nanoparticle materials with graphene layer structure plays a significant role in improving the selective adsorption and adsorption capacity of gold ions.

[0082] Secondly, by adjusting the various parameters in the preparation of hollow metal organic framework nanoparticles in step (2), it was found that when the mass ratio of metal organic framework nanoparticles to tannic acid was 1:4 to 6, the hollow carbon nanoparticle material finally prepared had better adsorption performance for gold ions. Specifically, when the mass ratio of metal organic framework nanoparticles to tannic acid was 1:4 (other preparation conditions were the same as in Example 1), the prepared HNPC had a better adsorption performance for gold ions when the saturated adsorption capacity test experiment shown in Example 4 was performed. 3+ The saturated adsorption capacity is 2664 mg / g. When the mass ratio of metal organic framework nanoparticles to tannic acid is 1:6, Au 3+ The saturated adsorption capacity of the HNPC was slightly increased to 2669 mg / g; when the mass ratio of metal organic framework nanoparticles to tannic acid was 1:3 (other preparation conditions were the same as those in Example 1), the prepared HNPC was subjected to the adsorption capacity test experiment shown in Example 4. 3+ The saturated adsorption capacity is 2001 mg / g. When the mass ratio of metal organic framework nanoparticles to tannic acid is 1:7, Au 3+The saturated adsorption capacity is 1994 mg / g. The role of tannic acid is to etch the metal-organic framework nanoparticles to produce a hollow structure. Its role in HNPC is to give the hollow carbon nanoparticle material a hollow structure. Different concentrations of tannic acid will affect the hollow morphology, hollowness, and porosity of HNPC. Therefore, it can be seen that the morphology and pore structure of the hollow structure in the hollow carbon nanoparticle material will have a significant impact on the adsorption capacity of gold ions in the hollow carbon nanoparticle material. Studies have shown that when the mass ratio of metal-organic framework nanoparticles to tannic acid is between 1:4 and 1:6, the hollow structure and porosity formed are most conducive to the adsorption of gold ions. Therefore, the hollow carbon nanoparticle material exhibits the best adsorption effect within this range.

[0083] In order to further verify the important role of the hollow structure and porosity of hollow carbon nanoparticle materials in gold adsorption performance, this example compares the adsorption performance of non-hollow structure carbon nanomaterials. Specifically, we used the ZIF-8 material prepared in step (1) of Example 1 and treated it according to the calcination method of step (3) of Example 1 to obtain a carbon nanomaterial. The Raman spectrum test results showed that a graphene layer was successfully formed in the structure of the carbon nanomaterial. Subsequently, the carbon nanomaterial was subjected to the saturated adsorption capacity test experiment shown in Example 4. The results showed that its saturated adsorption capacity for Au³⁺ was only 1237 mg / g. Compared with the adsorption performance of hollow carbon nanoparticle materials, this result is significantly lower, indicating that the hollow structure and porosity play a key role in improving the adsorption capacity of hollow carbon nanoparticle materials for gold ions. This experiment further demonstrates the importance of hollow structure and graphene layer in optimizing gold adsorption performance.

[0084] Secondly, by adjusting the stirring reaction time of the hollow metal organic framework nanoparticles in step (2), the preparation process of the hollow carbon nanoparticle material was further optimized. The experimental results show that when the stirring time is 5 minutes, the prepared hollow carbon nanoparticle material shows a saturated adsorption capacity of Au³⁺ of 2665 mg / g in the saturated adsorption capacity test in Example 4; when the stirring time is shortened to 4 minutes, the saturated adsorption capacity decreases to 2341 mg / g; and when the stirring time is extended to 12 minutes, the saturated adsorption capacity increases slightly to 2669 mg / g. These results show that too short a stirring time leads to incomplete acid etching, affecting the formation of the hollow structure, thereby reducing the adsorption performance of the material. When the stirring time is extended to 12 minutes, the adsorption capacity does not change much compared to 10 minutes, indicating that the acid etching is basically completed at 10 minutes, and further extending the stirring time has limited improvement on the adsorption performance. Therefore, combined with the stirring time in Example 1, the optimal stirring reaction time should be 5 to 10 minutes to ensure the full formation of the hollow structure and optimize the adsorption performance.

[0085] Furthermore, the temperature of the calcination treatment for preparing the hollow carbon nanoparticle material in step (3) was adjusted. It was found that when the calcination temperature was 700°C, the obtained hollow carbon nanoparticle material was subjected to the saturated adsorption capacity test experiment shown in Example 4. 3+ The saturated adsorption capacity of Au is 2660 mg / g. When the calcination temperature is 1000℃, 3+ The saturated adsorption capacity is 2662 mg / g; when the calcination temperature is 600 ° C, the graphene layer of the obtained hollow carbon nanoparticle material is less, and the Raman spectrum shows that the degree of graphene is 0.31. The hollow carbon nanoparticle material is subjected to the saturated adsorption capacity test experiment shown in Example 4, Au 3+ The saturated adsorption capacity of Au is 1786 mg / g; when the calcination temperature is 1100℃, 3 + The saturated adsorption capacity of the hollow carbon nanoparticles was 1279 mg / g. Analysis showed that the reason for the significant decrease in saturated adsorption capacity may be that the excessively high calcination temperature destroyed the nitrogen and oxygen doping structure, thereby affecting the adsorption capacity of the material. Therefore, a calcination temperature in the range of 700°C to 1000°C can better balance the formation of the graphene layer and the stability of nitrogen and oxygen doping, thereby optimizing the adsorption performance of the hollow carbon nanoparticle material. Too low a temperature leads to insufficient graphene layers, while too high a temperature will destroy the key doping structure, both of which are not conducive to maximizing adsorption performance.

[0086] Finally, this example adjusts the gas atmosphere during the calcination process in step (3) to further optimize the preparation process of the hollow carbon nanoparticle material. When the calcination process gas atmosphere in step (3) of Example 1 was changed from inert nitrogen to air, it was found that the carbon material reacted in the air, causing the solid in the porcelain boat to completely disappear, and no product was obtained.

[0087] The commercial graphene and expanded graphite used in the examples of the present invention were purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd. Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; and the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0088] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. An application of hollow carbon nanoparticles as an adsorbent for adsorbing gold ions, characterized in that: The hollow carbon nanoparticle material is obtained by calcining metal organic framework nanoparticles with a hollow structure; in: The calcination treatment transforms the structure of the metal organic framework nanoparticles into a graphene layer; The preparation method of the hollow carbon nanoparticle material comprises the following steps: Step S1: adding zinc nitrate hexahydrate and 2-methylimidazole to a solvent respectively, stirring to form nuclei, and obtaining metal organic framework nanoparticles; Step S2: dispersing the metal organic framework nanoparticles obtained in step S1 in a solvent, adding tannic acid, and stirring to react to obtain metal organic framework nanoparticles with a hollow structure; Step S3: calcining the metal organic framework nanoparticles with a hollow structure obtained in step S2 to transform and form a graphene layer in the structure of the nanoparticles; In step S3, the calcination treatment is performed in an inert gas atmosphere.

2. The use according to claim 1, characterized in that: The metal organic framework nanoparticles are ZIF-8 nanoparticles.

3. The use according to claim 1, characterized in that: In step S1, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:6-10.

4. The use according to claim 1, wherein: In step S2, the mass ratio of the metal organic framework nanoparticles to tannic acid is 1:4-6.

5. The use according to claim 1, wherein: In step S2, the stirring reaction is carried out at a rotation speed of 200 rpm to 600 rpm and for a time of 5 minutes to 10 minutes.

6. The use according to claim 1, characterized in that: In step S3, the calcination temperature is 700° C. to 1000° C. and the calcination time is 0.5 hour to 4 hours.

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