Method for preparing sulfur-doped chiral carbon nanotube in molten salt

Abstract

The invention discloses a method for preparing a sulfur-doped chiral carbon nanotube in molten salt, which comprises the following steps: introducing mixed gas of SO2 and CO2 into the molten salt of carbonate, electrolyzing, and collecting to obtain the sulfur-doped chiral carbon nanotube. According to the method, SO2 gas is adopted as a sulfur source, CO2 gas is adopted as a carbon source, the experiment conditions are mild, the process is simple, raw materials are wide in source and low in price, and good economic benefits and wide application prospects are achieved. According to the method, the liquid-phase molten salt is used as a reaction medium, the absorption efficiency of SO2 is improved, and the prepared sulfur-doped chiral carbon nanotubes are small in tube diameter, relatively long and uniform in tube diameter, have optical chirality and have good microwave absorption performance. According to the method, harmful gas SO2 and greenhouse gas CO2 can be converted into the sulfur-doped chiral carbon nanotubes with high added value, and the method is an important invention for the fields of environment and materials.

Description

Technical Field

[0001] The invention relates to the technical field of preparing carbon materials by electrolysis, and in particular to a method for preparing sulfur-doped chiral carbon nanotubes in molten salt. Background Art

[0002] With the global emphasis on environmental protection and sustainable development and the continuous progress of science and technology, carbon dioxide reduction reaction (CO2RR) will gradually become a research hotspot. Promoting the system integration and industrial application of CO2RR and realizing the large-scale production of high-value-added chemicals and fuels has become a future development trend. However, the current low-temperature CO2RR process is often limited by the competition of hydrogen evolution reaction and the problem of product selectivity diversification. Therefore, CO2RR technology with molten salt as the medium at high temperature has become a promising solution. Compared with the low-temperature conversion to organic chemicals, the high-temperature conversion of CO2 to carbon materials has the advantages of moderate energy consumption and particularly high product added value. In particular, carbon nanotubes (CNTs) are worth more than $5,500 per ton.

[0003] Industrial flue gas is an inevitable product of industrial production, but its impact on the environment and human health cannot be ignored. In addition to CO2, the coexistence of SO2 has also attracted attention to CO2 capture and conversion. At present, CO2RR technology at low temperature can only use pure CO2 gas to convert it into chemicals such as formic acid and ethylene. The presence of SO2 will poison the electrocatalyst and deactivate it during the reaction. Therefore, if the conversion of flue gas is achieved, it will face high CO2 purification costs and severe technical difficulties. In order to implement it more effectively, directly using flue gas to capture and convert high value-added products will have greater development prospects. The low-temperature wet desulfurization technology in industry uses lime slurry to convert SO2 in flue gas into gypsum. However, the product obtained by this method is liquid or sludge, which is difficult to handle. If it is discarded, a large amount of sulfur resources will be wasted to a certain extent.

[0004] Rationally utilizing SO2 and CO2 gases in industrial flue gas and using them as raw materials to prepare carbon nanotube materials has application prospects, but few related studies have been reported so far. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a method for preparing sulfur-doped chiral carbon nanotubes in molten salt, comprising: A mixed gas of SO2 and CO2 is introduced into the molten salt of carbonate, and electrolysis is performed to collect sulfur-doped chiral carbon nanotubes.

[0006] Further, the flow rate of the mixed gas of SO2 and CO2 is 50-300 mL / min; The concentration of SO2 in the mixed gas of SO2 and CO2 is 50-4000ppm, the concentration of CO2 is 0.04-50vol.%, and the remainder is carrier gas. The carrier gas does not need to be strictly limited, but should not introduce other impurities and consume the generated carbon material, and preferably, it can be N2.

[0007] Furthermore, the electrolysis is continued for 2-6 hours at a voltage of 2.0-3.0 V and a temperature of 700-1000° C.

[0008] Furthermore, the carbonate molten salt includes two alkali metal carbonates.

[0009] Furthermore, the two alkali metal carbonates are obtained by mixing Na2CO3 and K2CO3 in a molar ratio of 0.5-2:1.

[0010] Furthermore, alkaline earth metal carbonate is added to the carbonate molten salt, and the alkaline earth metal carbonate accounts for 5%-30% of the total mass of the carbonate molten salt. The alkaline earth metal carbonate can be at least one of CaCO3, SrCO3 or BaCO3.

[0011] Furthermore, the SO2 and CO2 are separated from industrial flue gas.

[0012] In the present invention, the anode used in electrolysis is made of an inert anode material that can be stable in carbonates, can convert absorbed carbon dioxide into oxygen, and precipitate oxygen at the anode. For example, the material used in the anode can be Ni10Cu11Fe alloy, SnO2, and graphite, amorphous carbon, carbon obtained by pyrolysis of biomass, carbon nanotubes, graphene, graphite oxide or reduced oxidized graphene. The material of the cathode used in electrolysis is at least one of stainless steel, Ni, Mo, W, Fe, Cu, and carbon paper.

[0013] Specifically, after the electrolysis is completed, the deposited product on the cathode electrode is collected, centrifuged, cleaned, and dried to obtain sulfur-doped chiral carbon nanotubes. The centrifugal cleaning uses acid washing, and the acid solution used for the acid washing does not need to be strictly limited, and is exemplarily selected from an aqueous solution of at least one of hydrochloric acid, sulfuric acid, and acetic acid. At the same time, the concentration of the acid solution does not need to be strictly limited, and it can be prepared in accordance with the requirements. The centrifugal cleaning lasts for 4-12 minutes at 5000-8000 rpm. Drying is kept warm at a temperature of 60-120°C for 2-24 hours.

[0014] The present invention also provides a sulfur-doped chiral carbon nanotube, which is obtained by the above method for preparing sulfur-doped chiral carbon nanotube.

[0015] The present invention also provides application of the sulfur-doped chiral carbon nanotubes in microwave absorbing materials.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses SO2 gas as a sulfur source and CO2 gas as a carbon source, has mild experimental conditions, simple process, wide raw material sources, low prices, good economic benefits and broad application prospects.

[0017] The present invention utilizes liquid molten salt as a reaction medium, thereby improving the absorption efficiency of SO2. The prepared sulfur-doped chiral carbon nanotubes have a small diameter, a long tube length, a uniform tube diameter, optical chirality, and good microwave absorption performance.

[0018] The present invention can convert harmful gas SO2 and greenhouse gas CO2 into high value-added sulfur-doped chiral carbon nanotubes, and is an invention that is extremely important to both the environment and the material fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] 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 or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are 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.

[0020] Figure 1 shows the XRD pattern of the sulfur-doped chiral carbon nanotubes prepared in Example 1; FIG2(a), FIG2(b) and FIG2(c) respectively show the fitting results of C 1s, O 1s and S 2p of the sulfur-doped chiral carbon nanotubes prepared in Example 1 by XPS test; Figure 3a The scanning electron microscope image of the sulfur-doped chiral carbon nanotubes prepared in Example 1 is shown. Figure 3b The scanning electron microscope image of the carbon nanotubes prepared in Comparative Example 1 is shown; Figure 4a The transmission electron microscope image of the sulfur-doped chiral carbon nanotubes prepared in Example 1 is shown. Figure 4b The transmission electron microscope image of the sulfur-doped chiral carbon nanotubes prepared in Example 2 is shown; Figure 5 The single particle circular differential scattering spectrum of the sulfur-doped chiral carbon nanotubes prepared in Example 1 is shown; Figure 6 A comparison graph of electromagnetic wave reflection losses of sulfur-doped chiral carbon nanotubes prepared in Example 1 and carbon nanotubes prepared in Comparative Example 1 is shown. DETAILED DESCRIPTION

[0021] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0022] The following will be combined with the specific embodiments of the present invention and the drawings of the specification to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example 1 A method for preparing sulfur-doped chiral carbon nanotubes in molten salt, comprising the following steps: S1, Na2CO3 and K2CO3 were mixed in a molar ratio of 59:41, heated to 750°C in an argon atmosphere to melt, and then CaCO3 was added and mixed to obtain molten salt. The amount of CaCO3 added was 10% of the total mass of the molten salt. S2, a mixed gas of SO2 and CO2 is introduced at a flow rate of 200 mL / min, the concentration of SO2 in the mixed gas of SO2 and CO2 is 100 ppm, the concentration of CO2 is 14 vol.%, and the remainder is carrier gas N2, and SO2 and CO2 are separated from industrial flue gas; a carbon paper with a length of 20 mm, a width of 10 mm, and a thickness of 1 mm is used as a cathode electrode, and a columnar Ni10Cu11Fe with a length of 20 mm and a diameter of 10 mm is used as an anode electrode, and the molten salt is electrolyzed at a temperature of 750°C and a voltage of 2.2 V for 2.2 h; S3. After the electrolysis is completed, the deposited products on the cathode electrode are collected, washed with 7 mol / L hydrochloric acid for 6 min, centrifuged at 7000 rpm for 2 min, and then dried at 60 °C for 10 h to obtain sulfur-doped chiral carbon nanotubes.

[0024] Example 2 A method for preparing sulfur-doped chiral carbon nanotubes in molten salt, comprising the following steps: S1, Na2CO3 and K2CO3 were mixed in a molar ratio of 59:41, heated to 700°C in an argon atmosphere to melt, and then CaCO3 was added and mixed to obtain molten salt. The amount of CaCO3 added was 30% of the total mass of the molten salt. S2, a mixed gas of SO2 and CO2 is introduced at a flow rate of 200mL / min, the concentration of SO2 in the mixed gas of SO2 and CO2 is 1000ppm, the concentration of CO2 is 40vol.%, the remainder is carrier gas N2, SO2 and CO2 are separated from industrial flue gas; an iron sheet with a length of 20mm, a width of 10mm and a thickness of 1mm is used as a cathode electrode, a columnar Ni10Cu11Fe with a length of 20mm and a diameter of 10mm is used as an anode electrode, and the molten salt is electrolyzed at a temperature of 700℃ and a voltage of 2.8V for 4h; S3. After the electrolysis is completed, the deposited products on the cathode electrode are collected, washed with 1 mol / L hydrochloric acid for 12 min, centrifuged at 8000 rpm for 3 min, and then dried at 60 °C for 10 h to obtain sulfur-doped chiral carbon nanotubes.

[0025] Example 3 A method for preparing sulfur-doped chiral carbon nanotubes in molten salt, comprising the following steps: S1, Na2CO3 and K2CO3 were mixed in a molar ratio of 59:41, heated to 900°C in an argon atmosphere to melt, and then CaCO3 was added and mixed to obtain molten salt. The amount of CaCO3 added was 25% of the total mass of the molten salt. S2, a mixed gas of SO2 and CO2 is introduced at a flow rate of 200mL / min, the concentration of SO2 in the mixed gas of SO2 and CO2 is 2000ppm, the concentration of CO2 is 40vol.%, the remainder is carrier gas N2, SO2 and CO2 are separated from industrial flue gas; a copper sheet with a length of 20mm, a width of 10mm and a thickness of 1mm is used as a cathode electrode, a columnar Ni10Cu11Fe with a length of 20mm and a diameter of 10mm is used as an anode electrode, and the molten salt is electrolyzed at a temperature of 900℃ and a voltage of 3.0V for 2h; S3. After the electrolysis is completed, the deposited products on the cathode electrode are collected, washed with 7 mol / L hydrochloric acid for 12 min, centrifuged at 8000 rpm for 4 min, and then dried at 60 °C for 10 h to obtain sulfur-doped chiral carbon nanotubes.

[0026] Comparative Example 1 A method for preparing carbon nanotubes in molten salt, comprising the following steps: S1, Na2CO3 and K2CO3 were mixed in a molar ratio of 59:41, heated to 750°C in an argon atmosphere to melt, and then CaCO3 was added and mixed to obtain molten salt. The amount of CaCO3 added was 10% of the total mass of the molten salt. S2, CO2 gas is introduced at a flow rate of 200mL / min, the concentration of CO2 in the CO2 gas is 14vol.%, and the remainder is carrier gas N2; a carbon paper with a length of 20mm, a width of 10mm, and a thickness of 1mm is used as a cathode electrode, and a columnar Ni10Cu11Fe with a length of 20mm and a diameter of 10mm is used as an anode electrode, and the molten salt is electrolyzed at a temperature of 800℃ and a voltage of 2.2V for 2.2h; S3. After the electrolysis is completed, the deposited product on the cathode electrode is collected, washed with 7 mol / L hydrochloric acid for 6 min, centrifuged at 7000 rpm for 2 min, and then dried at 60°C for 10 h to obtain carbon nanotubes.

[0027] Test Case The crystal structure of the sulfur-doped chiral carbon nanotubes prepared in Example 1 was observed by X-ray diffractometer. Figure 1 As shown, it can be seen that a diffraction peak of graphite phase carbon with higher diffraction intensity appears.

[0028] X-ray photoelectron spectroscopy was used to test the composition of the sulfur-doped chiral carbon nanotubes prepared in Example 1. Figures 2(a), 2(b), and 2(c) are the fitting results of C 1s, O 1s, and S 2p, respectively, indicating the successful preparation of sulfur-doped chiral carbon nanotubes.

[0029] The microstructure of the carbon nanotube materials prepared in Example 1 and Comparative Example 1 was observed using a scanning electron microscope. Figure 3a It can be seen that the carbon nanotubes prepared in Example 1 present a spiral shape similar to a spring, and the carbon nanotubes have a small diameter, a long tube length, and a uniform tube diameter. Figure 3b It can be seen that the comparative example 1 without adding SO2 at the same CO2 gas flow rate is a conventional tube.

[0030] Transmission electron microscopy was also used to further characterize the morphology of the carbon nanotubes prepared in Example 1 and Example 2, respectively. Figure 4a and Figure 4b As shown, the carbon nanotubes of Example 1 are nano-helical tubes with a tube length of 1-10 μm and a tube diameter of about 80 nm; the carbon nanotubes of Example 2 are similar in shape and length to those of Example 1, but the tube diameter is reduced to about 50 nm.

[0031] The single-particle circular differential scattering spectrum was used to detect the sulfur-doped chiral carbon nanotubes prepared in Example 1. The results are as follows: Figure 5 As shown, the g-factor value of the CDS signal was observed to be 0.31, confirming that the material has obvious geometric chirality.

[0032] Reflection loss is an important indicator for evaluating the reflection performance of microwave absorbing materials. It is generally used to describe the reflection of incident waves by the material. The reflection loss of the carbon nanotube materials prepared in Example 1 and Comparative Example 1 was tested. The thickness of the coating on the tested samples was 4.6 mm. The results are as follows: Figure 6 As shown, it can be seen that the sulfur-doped chiral carbon nanotubes prepared in Example 1 have stronger microwave absorption than the carbon nanotube samples in Comparative Example 1, and the best microwave reflection loss is -31.5 dB.

[0033] In summary, the present invention uses SO2 gas as a sulfur source and CO2 gas as a carbon source. The experimental conditions are mild, the process is simple, the raw materials are widely available, and the price is low. It has good economic benefits and broad application prospects. The present invention uses liquid molten salt as a reaction medium to improve the absorption efficiency of SO2. The prepared sulfur-doped chiral carbon nanotubes have a small diameter and a long tube length, uniform diameter, optical chirality, and good microwave absorption performance. The present invention can convert harmful gas SO2 and greenhouse gas CO2 into high-value-added sulfur-doped chiral carbon nanotubes, which is an invention that is extremely important to both the environment and the materials field.

[0034] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing sulfur-doped chiral carbon nanotubes in molten salt, characterized in that: include, A mixed gas of SO2 and CO2 is introduced into the molten salt of carbonate, and electrolysis is performed to collect sulfur-doped chiral carbon nanotubes.

2. The method for preparing sulfur-doped chiral carbon nanotubes in molten salt according to claim 1, characterized in that: The flow rate of the mixed gas of SO2 and CO2 is 50-300 mL / min; The concentration of SO2 in the mixed gas of SO2 and CO2 is 50-4000ppm, the concentration of CO2 is 0.04-50vol.%, and the remainder is carrier gas.

3. The method for preparing sulfur-doped chiral carbon nanotubes in molten salt according to claim 1, characterized in that: The electrolysis is continued for 2-6 hours at a voltage of 2.0-3.0 V and a temperature of 700-1000° C.

4. The method for preparing sulfur-doped chiral carbon nanotubes in molten salt according to claim 1, characterized in that: The carbonate molten salt includes two alkali metal carbonates.

5. The method for preparing sulfur-doped chiral carbon nanotubes in molten salt according to claim 4, characterized in that: The two alkali metal carbonates are obtained by mixing Na2CO3 and K2CO3 in a molar ratio of 0.5-2:

1.

6. The method for preparing sulfur-doped chiral carbon nanotubes in molten salt according to claim 4, characterized in that: Alkaline earth metal carbonate is also added to the carbonate molten salt, and the alkaline earth metal carbonate accounts for 5%-30% of the total mass of the carbonate molten salt.

7. The method for preparing sulfur-doped chiral carbon nanotubes in molten salt according to any one of claims 1 to 6, characterized in that: The SO2 and CO2 are separated from industrial flue gas.

8. A sulfur-doped chiral carbon nanotube, characterized in that: The method for preparing sulfur-doped chiral carbon nanotubes according to any one of claims 1 to 7 is used to obtain the carbon nanotubes.

9. Use of the sulfur-doped chiral carbon nanotubes as claimed in claim 8 in microwave absorbing materials.

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