Preparation method, product and application of boron-doped hollow carbon spheres

Abstract

The invention relates to the technical field of electrochemical catalysis, in particular to a preparation method of boron-doped hollow carbon spheres, a product and application of the boron-doped hollow carbon spheres. The preparation method of the boron-doped hollow carbon spheres comprises the following steps: uniformly mixing boron, ethanol, water, ammonia water and formaldehyde to obtain a mixed solution; adding resorcinol and tetrapropoxysilane into the mixed solution at the same time, and carrying out a stirring reaction to obtain a precipitate; and after cleaning the precipitate, sequentially calcining and etching to obtain the boron-doped hollow carbon spheres. The boron-doped hollow carbon sphere disclosed by the invention shows excellent performance of electro-catalyzing O2 reduction to produce. OH in degradation of organic pollutants in an electro-Fenton system, and the performance is stable.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical catalysis, in particular to a preparation method of boron-doped hollow carbon spheres, products and applications thereof. BACKGROUND

[0002] With the rapid development of global economy and the rapid growth of population, environmental pollution has become a global problem that needs to be solved. Among the many environmental pollutants, the degradation of organic pollutants is difficult due to its stable chemical properties, high toxicity, persistence and difficult to handle characteristics, which has caused serious pollution to the water environment, and then through the food chain to the potential threat to human health. In recent years, electrochemical advanced oxidation technology (Electrochemical Advanced Oxidation Processes, EAOPs) has become a powerful means for treating refractory organic pollutants due to its high efficiency and environmental protection. Among them, the heterogeneous electro-Fenton (Heterogeneous Electro-Fenton, EF) technology has attracted widespread attention due to its fast reaction speed, low toxicity, and good environmental compatibility. In the process of heterogeneous electro-Fenton, hydrogen peroxide (H2O2) is generated in situ by electrochemical method, and reacts with the added ferrous ion (Fe 2+ ) to generate hydroxyl radicals (·OH) with high oxidation reduction potential, thereby realizing the effective degradation and mineralization of organic pollutants. However, the traditional heterogeneous electro-Fenton technology still faces some challenges in practical application. For example, iron-based catalysts are easy to form iron sludge under acidic conditions, resulting in catalyst deactivation, and in neutral and alkaline conditions, the regeneration rate of iron is slow, which limits its application in a wider pH range. In addition, the generation efficiency and selectivity of hydrogen peroxide still need to be improved to reduce the processing cost and improve the processing efficiency.

[0003] In order to overcome the above problems, researchers have devoted to developing new heterogeneous catalysts. Therefore, it is crucial to prepare a carbon-based non-metallic doped heterogeneous catalyst material with enhanced H2O2 synthesis and in-situ activation of ·OH performance, efficient ·OH production and independent of transition state metal, and apply it to the electro-Fenton system. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of boron-doped hollow carbon spheres, products and electro-Fenton applications thereof, to solve the technical problem of heterogeneous electro-Fenton cathode material dependent on transition state metal.

[0005] To achieve the above purpose, the present application provides the following solutions:

[0006] One of the technical solutions of the present application is a preparation method of boron-doped hollow carbon spheres, comprising the following steps:

[0007] Mixing boron, ethanol, water, ammonia and formaldehyde to obtain a mixed solution;

[0008] The ammonia concentration is 25%-28%;

[0009] Resorcinol and tetrapropoxysilane are added into the mixed solution to perform stirring reaction to obtain a precipitate;

[0010] After the precipitate is cleaned, calcination and etching are sequentially performed to obtain the boron-doped hollow carbon sphere.

[0011] The boron-doped hollow carbon sphere prepared by the preparation method described above.

[0012] The boron-doped hollow carbon sphere described above is applied to synthesis of H2O2 or degradation of pollutants in an electro-Fenton system.

[0013] The electro-Fenton system comprises a cathode electrode, an anode electrode, a reference electrode and an electrolyte.

[0014] The cathode electrode is prepared by coating a slurry of the boron-doped hollow carbon sphere described above, water, isopropyl alcohol and a Nafion film solution on a conductive solid carrier.

[0015] The following technical effects are disclosed in the present application:

[0016] (1) The boron-doped hollow carbon sphere with a hollow structure provided by the present application has significant advantages in activity, structural stability and practical application potential compared with traditional carbon-based materials, and the introduction of boron elements makes it have low overpotential, high H2O2 selectivity and the ability to continuously produce H2O2 and ·OH.

[0017] (2) The electro-Fenton system constructed by the boron-doped hollow carbon sphere of the present application has high selectivity, high activity and good stability; the boron-doped hollow carbon sphere of the present application exhibits excellent performance of electrocatalytic O2 reduction to produce ·OH in the degradation of organic pollutants in the electro-Fenton system, and the performance is stable. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 XRD pattern of the boron-doped hollow carbon sphere prepared for Example 1;

[0020] Figure 2 The Raman spectrum of the boron-doped hollow carbon spheres prepared in Example 1;

[0021] Figure 3 Fourier transform infrared spectrum of boron-doped hollow carbon spheres prepared in Example 1;

[0022] Figure 4 SEM image of the boron-doped hollow carbon spheres prepared in Example 1;

[0023] Figure 5 XPS images and elemental contents of boron-doped hollow carbon spheres prepared in Example 1;

[0024] Figure 6 The graph shows the yield of H2O2 synthesized from boron-doped hollow carbon spheres prepared in Example 1 in an electro-Fenton system.

[0025] Figure 7 The graph shows the degradation effect of boron-doped hollow carbon spheres prepared in Example 1 on different pollutants in an electro-Fenton system.

[0026] Figure 8 The results show the cyclic stability test of the boron-doped hollow carbon spheres prepared in Example 1 in the electro-Fenton system for degrading pollutants. Detailed Implementation

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0030] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0031] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0032] Boron-doped hollow carbon spheres, due to their unique structure and properties, have shown great potential for application in heterogeneous electro-Fenton technology.

[0033] The first aspect of this invention provides a method for preparing boron-doped hollow carbon spheres, comprising the following steps:

[0034] Boron, ethanol, water, ammonia and formaldehyde are mixed to obtain a mixture;

[0035] Resorcinol and tetrapropoxysilane were added to the mixture simultaneously and stirred to produce a precipitate.

[0036] After the precipitate is cleaned, it is calcined and etched in sequence to obtain the boron-doped hollow carbon spheres.

[0037] In a preferred embodiment of the present invention, the mass-to-volume ratio of boron, ethanol, water, ammonia, and formaldehyde is 50-500 mg: 65 mL: 15 mL: 2.5 mL: 0.8 mL.

[0038] In some specific embodiments of the present invention, the concentration of ammonia water used is 25%-28%.

[0039] In this invention, ethanol is mainly used as a solvent to disperse reactants and control the viscosity of the reaction system; formaldehyde is a crosslinking agent in the synthesis of phenolic resin, used to polymerize with phenolic compounds (such as resorcinol) to form phenolic resin; ammonia water is used as a catalyst to promote the polymerization reaction of phenolic resin, thereby affecting the pore structure and specific surface area of ​​the final carbon spheres; deionized water provides a uniform reaction environment, allowing the reactants to mix and react fully.

[0040] When preparing the mixture, the mixing method shall adopt the technical means commonly used by those skilled in the art, such as stirring, and the stirring speed shall adopt the stirring speed commonly used by those skilled in the art when mixing.

[0041] In a preferred embodiment of the present invention, the mass-to-volume ratio of boron to resorcinol and tetrapropoxysilane is 50-500 mg: 0.6 g: 6 mL.

[0042] In a preferred embodiment of the present invention, the stirring reaction time is 12-36 hours.

[0043] The cleaning process specifically involves washing with water and ethanol at least three times in sequence to remove excess phenolic resin and unreacted raw materials from the precipitate.

[0044] The precipitate is washed and then dried at a temperature of 50-80°C.

[0045] In a preferred embodiment of the present invention, the calcination specifically involves heating to 800-1200°C at a heating rate of 2°C / min and holding for 2 hours under an inert atmosphere.

[0046] The purpose of calcining in an inert atmosphere is to remove reactive gases, prevent carbon spheres from oxidizing and damaging their structure, improve the purity of the product in a stable environment, and prevent impurities from being mixed in.

[0047] In a preferred embodiment of the present invention, the etching specifically involves etching the calcined product in 10mM-1M hydrofluoric acid for 6-36 hours.

[0048] The purpose of etching is to remove silicon dioxide from the carbon spheres.

[0049] After etching, the process also includes rinsing with deionized water until neutral (the purpose of rinsing is to remove excess hydrofluoric acid) and drying at a temperature of 50-80°C.

[0050] A second aspect of the present invention provides a boron-doped hollow carbon sphere prepared according to the above-described preparation method.

[0051] The third aspect of this invention provides the application of the above-mentioned boron-doped hollow carbon spheres in the synthesis of H2O2 in an electro-Fenton system and in in-situ activation to produce ·OH or in the degradation of pollutants.

[0052] A fourth aspect of the present invention provides an electro-Fenton system, comprising a cathode electrode, an anode electrode, a reference electrode, and an electrolyte;

[0053] The cathode electrode is prepared by coating a conductive solid carrier with a slurry made of boron-doped hollow carbon spheres, water, isopropanol, and Nafion film solution.

[0054] In a preferred embodiment of the present invention, the anode electrode is an inert electrode;

[0055] In a preferred embodiment of the present invention, the anode electrode is an inert anode made of carbon-based, silicon-based, alloy-based, or titanium-based materials.

[0056] When the electro-Fenton system of this invention is used for the synthesis of H2O2 or for the degradation of pollutants, it is connected to a power source and a constant current or constant voltage is used. During the reaction, continuous aeration and stirring are carried out to keep the reaction solution in an oxygen-saturated and uniform state.

[0057] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0058] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0059] Example 1

[0060] A method for preparing boron-doped hollow carbon spheres, comprising the following steps:

[0061] A mixture was prepared by adding 50 mg of elemental boron, 65 mL of ethanol, 15 mL of deionized water, 2.5 mL of ammonia, and 0.8 mL of formaldehyde. Then, 0.6 g of resorcinol and 6 mL of tetrapropoxysilane (TPOS, CAS No.: 682-01-9) were simultaneously added to the mixture. After stirring continuously for 24 h, the precipitate was centrifuged and washed (three times each with water and ethanol to remove impurities), and then vacuum dried at 60 °C to constant weight. The calcined product was then calcined at 800 °C for 2 h at a heating rate of 2 °C / min under a N2 atmosphere. The calcined product was etched with 1 / 20 volume of hydrofluoric acid (0.5 M concentration) for 24 h to remove SiO2 from the porous carbon spheres. After etching, the product was rinsed with deionized water until neutral, and then vacuum dried again at 60 °C to constant weight to obtain the boron-doped hollow carbon sphere material.

[0062] The boron-doped hollow carbon spheres prepared in Example 1 were characterized and tested as follows:

[0063] 1. Material characterization of the boron-doped hollow carbon spheres prepared in Example 1:

[0064] The boron-doped hollow carbon spheres prepared in Example 1 were characterized by XRD, Raman spectroscopy, FI-RT, SEM, and XPS. Their XRD patterns are shown below. Figure 1 As shown, there is a broadened peak at a 2θ angle of approximately 20° to 30°, without any obvious sharp diffraction peaks. The intensity and shape of this broadened peak can reflect that it is an amorphous carbon material. Figure 2 The Raman spectral results for boron-doped hollow carbon spheres show that the ratio of the carbon defect peak D to the graphitization peak G is 0.863, and the width of the G peak is 137 cm⁻¹, indicating typical characteristics of amorphous carbon with similar defects. Figure 3 The Fourier transform infrared (FTIR) spectra of boron-doped hollow carbon spheres are shown at 3444.9 cm⁻¹.-1 The absorption peak at 2922.2 cm⁻¹ belongs to the -OH bond. -1 The absorption peak at [location] belongs to the -CH bond, and the absorption peak of the C=C bond shown in the spectrum is at 1635.6 cm⁻¹. -1 Absorption peak at 1543.1 cm⁻¹ -1 It belongs to the COC bond. 887.3cm -1 The absorption peak at that point is mainly due to fluctuations in the BOC bond. (The last sentence appears to be incomplete and possibly refers to a technical detail.) Figure 4 The SEM images show the morphology of the boron-doped hollow carbon spheres as nanoscale spherical carbon materials. The broken carbon spheres reveal their hollow structure, with a particle size of 278.87 ± 113.93 nm. XPS measurements of the boron-doped hollow carbon spheres are shown below. Figure 5 As shown, its boron content is 2.17%. The above material characterization tests prove the successful synthesis of boron-doped hollow carbon spheres.

[0065] 2. An electro-Fenton cathode electrode was prepared using the boron-doped hollow carbon spheres prepared in Example 1, and an electro-Fenton system was constructed for performance testing:

[0066] (1) Preparation of the electro-Fenton cathode electrode: Boron-doped hollow carbon spheres were ground in an agate mortar to form a powder. 8 mg of the powdered boron-doped hollow carbon spheres were weighed into a disposable centrifuge tube, and 1.52 mL of deionized water, 80 μL of isopropanol, and 0.4 mL of 5% Nafion membrane solution were added to form a slurry. The slurry was then sonicated for 30 min to ensure uniform dispersion, and then further dispersed at a concentration of 0.5 mg / cm³. 2 The loading amount is applied to a hydrophobic conductive carbon cloth, and after the liquid evaporates, it forms a cathode electrode. The role of isopropanol is to change the hydrophobicity of the slurry, and the role of Nafion film solution is to make it have good adhesion after the water evaporates.

[0067] (2) Construction of the electric Fenton system:

[0068] The aforementioned electro-Fenton cathode electrode and a titanium-based ruthenium-iridium anode electrode were fixed onto an electrochemical reactor made of acrylic sheet. A calomel reference electrode was then fixed in the reaction cell between the two electrodes, ensuring that the end of the reference electrode did not contact the reaction cell or the electrodes but was close to the cathode electrode. Finally, the electrolyte, magnetic rotor, and aeration needle were added to the reaction cell, with continuous stirring and aeration occurring simultaneously with the start of the reaction. The reactor was connected to an electrochemical workstation capable of performing it curve testing, with the cathode connected to the working electrode, the anode connected to the counter electrode, and the calomel electrode connected to the reference electrode. The addition of the electrolyte (50 mM NaSO4 solution) ensured that the entire electro-Fenton system formed a complete closed circuit, guaranteeing the normal transfer of electrons provided by the electrochemical workstation within the system.

[0069] The ability of the above-described electro-Fenton system to synthesize H₂O₂ was tested. Ultraviolet-visible (UV-vis) spectrophotometry was used, and the generated H₂O₂ was quantified by cerium sulfate titration. An aeration rate of 100 mL / min was continuously applied at a potential of -0.7 V, with constant stirring. 50 mL of 50 mM NaSO₄ solution (deionized water) was added to the reaction vessel, and an electro-Fenton experiment was conducted for 90 min. Figure 6 As shown, the yield of H2O2 steadily increased over time, with the cumulative yield of H2O2 reaching 7.626 mM in 50 mM NaSO4 after 90 min.

[0070] The above-described electro-Fenton system was used for the degradation of electro-Fenton pollutants. Under a voltage of -0.7V vs SCE, aeration was continuously carried out at a rate of 100 mL / min with continuous stirring. 50 mL of reaction solution was added to the reaction tank, and six sampling points were set up during a 60-minute reaction time to quantitatively detect changes in pollutant concentration. The reaction solution was a mixture of 20 mg / L pollutant and 50 mM NaSO4. The pollutants were phenol, p-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol. The effect of the cathode electrode on the degradation of different pollutants in the electro-Fenton system is as follows: Figure 7 As shown, the degradation rate of phenol reached 99.91% in 60 minutes.

[0071] The theoretical lifetime of boron-doped hollow carbon spheres in electro-Fenton degradation of pollutants was investigated using the above-described electro-Fenton system. The same cathode electrode prepared according to the above method was used to conduct multiple cyclic degradation experiments under the same reaction conditions as the electro-Fenton pollutant degradation experiments to test its theoretical lifetime. The pollutant being degraded was phenol at a concentration of 20 mg / L. The results after five electro-Fenton degradation cycles are as follows: Figure 8 As shown, the boron-doped hollow carbon spheres prepared in this invention still achieved a phenol degradation efficiency of 97.2% after five cycles, indicating that they have good stability.

[0072] Comparative Example 1

[0073] The only difference from Example 1 is that the addition of 50 mg of boron is omitted; all other steps and parameters are the same as in Example 1.

[0074] The material prepared in Comparative Example 1 was subjected to the same tests as in Example 1. The results showed that the cumulative yield of H2O2 in 50 mM NaSO4 was only 5.18 mM after 90 min; the degradation rate of phenol was 45% after 60 min.

[0075] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing boron-doped hollow carbon spheres, characterized in that, Includes the following steps: Boron, ethanol, water, ammonia and formaldehyde are mixed to obtain a mixture; Resorcinol and tetrapropoxysilane were added to the mixture simultaneously and stirred to produce a precipitate. After the precipitate is cleaned, it is calcined and etched in sequence to obtain the boron-doped hollow carbon spheres.

2. The method for preparing boron-doped hollow carbon spheres according to claim 1, characterized in that, The mass-to-volume ratio of boron, ethanol, water, ammonia, and formaldehyde is 50-500 mg: 65 mL: 15 mL: 2.5 mL: 0.8 mL; the concentration of the ammonia is 25%-28%.

3. The method for preparing boron-doped hollow carbon spheres according to claim 1, characterized in that, The mass-to-volume ratio of boron to resorcinol and tetrapropoxysilane is 50-500 mg: 0.6 g: 6 mL.

4. The method for preparing boron-doped hollow carbon spheres according to claim 1, characterized in that, The stirring reaction time is 12-36 hours.

5. The method for preparing boron-doped hollow carbon spheres according to claim 1, characterized in that, The calcination process specifically involves heating the temperature to 800-1200℃ at a heating rate of 2℃ / min and holding it at that temperature for 2 hours under an inert atmosphere.

6. The method for preparing boron-doped hollow carbon spheres according to claim 1, characterized in that, The etching process specifically involves placing the calcined product in 10mM-1M hydrofluoric acid for 6-36 hours.

7. A boron-doped hollow carbon sphere prepared by the preparation method according to any one of claims 1-6.

8. The application of the boron-doped hollow carbon spheres as described in claim 7 in the synthesis of H2O2 or the degradation of pollutants in an electro-Fenton system.

9. An electro-Fenton system, characterized in that, It includes a cathode electrode, an anode electrode, a reference electrode, and an electrolyte; The cathode electrode is prepared by coating a conductive solid carrier with a slurry made of boron-doped hollow carbon spheres as described in claim 7, water, isopropanol, and Nafion film solution.

10. The electro-Fenton system according to claim 9, characterized in that, The anode electrode is an inert electrode.

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