Core-shell composite material as well as preparation method and application thereof

Abstract

The invention discloses a core-shell composite material as well as a preparation method and application thereof. The composite material structurally comprises an inner core and an outer core, wherein the inner core is made of calcium carbonate microspheres doped with at least one of Mn < 2 + >, Al < 3 + > and Fe < 3 + >; and the shell layer is made of titanium dioxide. In the high-performance calcium-based core-shell composite material, through doping of transition metal and construction of a titanium dioxide shell layer, high cycle stability and energy storage density of the core-shell composite material are realized. Through the synergistic effect of doping and core-shell construction, the light utilization rate, the energy storage density and the cycling stability are improved, and high-efficiency solar thermal conversion becomes possible.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar thermal chemical energy storage. More particularly, it relates to a core-shell composite material and a preparation method and application thereof. BACKGROUND

[0002] Developing abundant solar energy resources is a key approach to achieving the "double carbon goal", and is also an important strategy to alleviate the global energy crisis. Solar energy utilization methods include solar thermal utilization and light utilization. High-temperature thermal chemical energy storage has high energy storage density, long energy storage time, and low energy loss, and is considered as a promising energy storage technology in the field of solar thermal conversion. The performance of calcium-based thermal energy storage system mainly depends on the performance of calcium-based materials. An ideal CaCO3-based heat storage material has high heat storage density, good heat storage stability, and is suitable for medium-high temperature and medium-low temperature reactions, and has wide applicability, and is expected to be widely used in the field of thermal chemical energy storage. However, in the process of high-temperature cycle heat storage, the insufficient utilization of CaCO3 and the problem of CaO clumping and sintering in the cycle heat storage process result in low heat storage stability. SUMMARY

[0003] To solve the above problems, the purpose of the present application is to provide a core-shell composite material and a preparation method and application thereof.

[0004] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0005] A core-shell composite material, the structure of the composite material comprises:

[0006] An inner core, which is made of calcium carbonate microspheres doped with at least one of Mn 2+ , Al 3+ and Fe 3+ ; and

[0007] A shell layer, which is made of titanium dioxide.

[0008] It can be understood that in the core-shell composite material, the shell layer wraps the inner core.

[0009] The titanium dioxide shell layer is used to wrap the core-shell composite material to improve the sintering resistance of calcium-based materials. The synergistic effect of metal doping and core-shell structure not only makes full use of sunlight, but also improves the stability of heat storage cycle, which is of great significance to promote the development of CaCO3 / CaO material energy storage system in the field of high-performance solar thermal conversion.

[0010] In the present application, the titanium dioxide shell layer has obviously more excellent coating performance than other shell layers such as zirconium dioxide, silicon dioxide and the like, so that the structure of the composite material is more stable, and the heat storage cycle stability is better.

[0011] Further, the material of the inner core is calcium carbonate microspheres doped with two of Mn 2+ , Al 3+ and Fe 3+ .

[0012] Further, the material of the inner core is calcium carbonate microspheres doped with Mn 2+ and Fe 3+ , and the molar ratio of Ca 2+ to Mn 2 + , Fe 3+ in the structure is 100:(10-15):(5-10), preferably 100:14:7.

[0013] Further, the material of the inner core is calcium carbonate microspheres doped with Mn 2+ and Al 3+ , and the molar ratio of Ca 2+ to Mn 2 + , Al 3+ in the structure is 100:(10-15):(5-10), preferably 100:14:7.

[0014] Al, Mn and Fe, as typical inexpensive transition metals, have good light absorption capacity and can improve the ability to absorb sunlight; TiO2 has high melting point and heat resistance and can be used as a shell layer, which can effectively inhibit the phenomenon of agglomeration and sintering during the cyclic conversion of calcium-based materials. It is worth noting that the type of doped metal needs to be reasonably controlled, and different metal doping has different effects on light absorption capacity; the thickness of the shell layer determines the energy storage density and cycle stability, and reasonable control of the doping ratio and the core-shell thickness can achieve the best performance.

[0015] Further, the calcium-titanium ratio in the composite material is (18-23):1, preferably 20:1. At this time, the obtained core-shell structure can prevent collapse and aggregation and play a protective role. The "calcium-titanium ratio" refers to the molar ratio of calcium to titanium.

[0016] Further, the particle size of the core-shell composite material is 2-3 μm, and the thickness of the shell layer is 80-120 nm.

[0017] In another aspect, the present application provides a preparation method of the core-shell composite material as described above, which comprises the following steps:

[0018] dissolving a Ca source, at least one of a Mn source, a Fe source, and an Al source in water and ethylene glycol to obtain a mixed solution;

[0019] adding a carbonate solution to the mixed solution under stirring to form a precipitate;

[0020] dissolving a Ti source, ammonia, and a surfactant in ethanol with the precipitate to obtain the core-shell composite material.

[0021] Further, the carbonate solution is slowly added dropwise when being added, and the amount of the carbonate solution added is at least such that the mass of the generated precipitate no longer increases.

[0022] Further, the carbonate in the carbonate solution is selected from sodium carbonate.

[0023] Further, the surfactant is selected from hexadecylamine. The hexadecylamine molecules form hydrogen bonds with the hydrolysis products of the Ti source through their amino groups, thereby promoting the formation of inorganic-organic composite materials, which subsequently coat the surface of the calcium carbonate microspheres to form a titanium dioxide shell.

[0024] Further, the Ca source is selected from one or more of calcium chloride and calcium nitrate.

[0025] Further, in the mixed solution, the concentration of the Ca source is 0.09-0.15 mol·L -1 ; and the volume ratio of the water to the ethylene glycol is 1:(4-5).

[0026] Further, the Mn source is selected from one or more of manganese chloride and manganese nitrate.

[0027] Further, the Fe source is selected from one or more of iron chloride and iron nitrate.

[0028] Further, the Al source is selected from one or more of aluminum chloride and aluminum nitrate.

[0029] Further, the molar ratio of the Ti source to the Ca source is (5-25):1, preferably (18-23):1, and more preferably 20:1.

[0030] Further, the Ti source is selected from isopropyl titanate.

[0031] Further, the method of dissolving the Ti source, ammonia, and the surfactant in ethanol with the precipitate includes the following steps:

[0032] dispersing the precipitate in ethanol, sequentially adding the surfactant and ammonia, and then adding the Ti source after stirring at room temperature.

[0033] Further, the mass concentration (g / ml) ratio of the titanium source, ammonia water and surfactant is (2-6):2:1, preferably 2:2:1.

[0034] In another aspect, the application provides the use of the core-shell composite material as described above or prepared by the preparation method as described above in solar thermochemical energy storage.

[0035] In the application, the preparation method is a conventional method unless otherwise specified. The raw materials used are available from public commercial channels unless otherwise specified.

[0036] The beneficial effects of the application are as follows:

[0037] The high-performance calcium-based core-shell composite material provided by the application realizes high cycle stability and energy storage density of the core-shell composite material through transition metal doping and titanium dioxide shell construction. The synergistic effect of the doped metal ions and the core-shell structure construction improves the light utilization rate, energy storage density and cycle stability, which provides the possibility for efficient solar thermal conversion.

[0038] The high-performance calcium-based core-shell composite material provided by the application shows great application prospect in a thermal cycle integrated system. Compared with natural calcium-based materials, the composite material exhibits higher heat storage density and cycle stability, which promotes the research and development of efficient solar thermochemical conversion technology.

[0039] The preparation method of the calcium-based core-shell composite material provided by the application mainly adopts a simple sol-gel method. By adjusting the core-shell thickness and other conditions, the effective conversion rate and energy storage density are improved. The preparation method is simple in operation and suitable for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0040] The specific embodiments of the application will be further described in detail below with reference to the accompanying drawings.

[0041] Figure 1 The CaCO3 spectrum obtained in Example 1 of the application is shown, Figure 1 (a) is a scanning electron microscope (SEM) spectrum, Figure 1 (b) is a powder diffraction (XRD) spectrum.

[0042] Figure 2 The SEM spectrum of CaCO3(Mn,Fe) obtained in Example 1 of the application is shown.

[0043] Figure 3 The TEM spectrum of CaCO3(Mn,Fe)@TiO2 obtained in Example 2 of the application is shown.

[0044] Figure 4 The CaCO3(Mn,Fe)@TiO2 obtained in Example 2 of the application is shown.3( SEM-EDS spectrum of Mn,Fe)@TiO2.

[0045] Figure 5 The SEM spectrum of CaCO3(Mn,Al) obtained in Example 3 of the present invention is shown.

[0046] Figure 6 The TEM spectrum of CaCO3(Mn,Al)@TiO2 obtained in Example 4 of the present invention is shown.

[0047] Figure 7 This illustrates the CaCO3 obtained in Embodiment 4 of the present invention. 3( SEM-EDS spectrum of Mn,Al)@TiO2.

[0048] Figure 8 The diagram shows the cyclic stability of CaCO3(Mn,Fe)@TiO2 obtained in Example 2 of the present invention.

[0049] Figure 9 The diagram shows the cyclic stability of CaCO3(Mn,Fe)@TiO2 obtained in Comparative Example 1 of the present invention.

[0050] Figure 10 The diagram shows the cyclic stability of CaCO3(Mn,Al)@TiO2 obtained in Example 4 of the present invention.

[0051] Figure 11 The diagram shows the cyclic stability of CaCO3(Mn,Al)@TiO2 obtained in Comparative Example 2 of this invention.

[0052] Figure 12 The diagram shows the cyclic stability of CaCO3(Mn,Fe) (left) of Example 1 of the present invention and CaCO3(Mn,Al) (right) of Comparative Example 1.

[0053] Figure 13 The SEM-EDS spectrum of CaCO3(Mn,Fe,Al)@TiO2 obtained in Comparative Example 3 of the present invention is shown.

[0054] Figure 14 The diagram shows the cyclic stability of CaCO3(Mn,Fe,Al)@TiO2 obtained in Comparative Example 3 of the present invention. Detailed Implementation

[0055] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1

[0057] A method for preparing calcium carbonate includes the following steps:

[0058] Weigh 0.666g of CaCl2 powder and 0.636g of Na2CO3 powder, and dissolve them separately in a mixed solution of 10ml H2O and 50ml ethylene glycol to prepare a 0.1mol / L salt solution. After stirring evenly, slowly add the Na2CO3 solution dropwise to the CaCl2 solution. After stirring the mixed salt solution continuously at room temperature for 1 hour, centrifuge the suspension at 3000rpm for 3 minutes to collect the product. Then wash the product three times in sequence with ethanol, methanol and acetone, and dry it to obtain calcium carbonate microspheres (named CaCO3).

[0059] A method for preparing a calcium carbonate composite material (CaCO3(Mn,Fe)) includes the following steps:

[0060] Two mixed solutions of 10 ml H2O and 50 ml ethylene glycol were prepared as solvents. 0.666 g CaCl2, 0.195 g FeCl3 and 0.072 g MnCl2 were weighed and dissolved in one of the solvents, and 0.636 g Na2CO3 powder was weighed and dissolved in the other solvent. The two solutions were prepared into 0.1 mol / L salt solutions. After stirring evenly, the Na2CO3 solution was slowly added dropwise to the Ca-containing solution. The mixed salt solution was stirred continuously at room temperature for 1 h. The suspension was then centrifuged at 3000 rpm for 3 min to collect the product. The product was then washed three times in sequence with ethanol, methanol and acetone and dried to obtain the calcium carbonate composite material, named CaCO3(Mn,Fe).

[0061] In this embodiment, the spectrum of the CaCO3 microspheres prepared above is as follows: Figure 1 As shown. The XRD pattern of the CaCO3 microspheres prepared above is shown below. Figure 1 As shown in Figure a, it can be seen that its XRD pattern only shows CaCO3 diffraction peaks.

[0062] The SEM images of the CaCO3 microspheres prepared above are as follows: Figure 1 As shown in b, the SEM spectrum shows CaCO3 microspheres.

[0063] In this embodiment, the SEM spectrum of the prepared calcium carbonate composite material (CaCO3(Mn,Fe)) is as follows: Figure 2 As shown. Figure 2 It can be seen that the CaCO3(Mn,Fe) obtained after Mn and Fe doping has an oval shape.

[0064] Example 2

[0065] A method for preparing a calcium-based core-shell composite material (CaCO3(Mn,Fe)@TiO2) includes the following steps:

[0066] Weigh 40 mg of CaCO3(Mn,Fe) prepared in Example 1 above, disperse it in 16 mL of ethanol solution by ultrasonication, then add 0.2 g of hexadecylamine and 0.4 mL of ammonium hydroxide in sequence, stir at room temperature for 15 min, and finally add 0.4 mL of isopropyl titanate, stir at room temperature for 15 min; after stirring, centrifuge, wash, and dry to obtain CaCO3(Mn,Fe)@TiO2 with a calcium-to-titanium molar ratio of 20:1.

[0067] To more clearly demonstrate the successful construction of the core-shell structure, the sample was calcined in an 800℃ furnace for 4 hours.

[0068] Figure 3 This is a TEM image of the core-shell composite material prepared in this embodiment. It can be seen that the successful construction of the titanium oxide shell can be more clearly observed using a transmission electron microscope.

[0069] Figure 4 The SEM-EDS spectrum of the core-shell composite material prepared in this embodiment is shown. Elemental analysis of CaCO3(Mn,Fe)@TiO2 reveals that Ti is densely distributed around CaCO3(Mn,Fe) in the energy spectrum, which was subsequently obtained through calcination.

[0070] Example 3

[0071] A method for preparing a calcium carbonate composite material (CaCO3(Mn,Al)) includes the following steps:

[0072] Two mixed solutions of 10 ml H2O and 50 ml ethylene glycol were prepared as solvents. 0.666 g CaCl2, 0.15 g Al(NO3)3 and 0.072 g MnCl2 were weighed and dissolved in one of the solvents, and 0.636 g Na2CO3 powder was weighed and dissolved in the other solvent. The two solutions were prepared into 0.1 mol / L salt solutions. After stirring evenly, the Na2CO3 solution was slowly added dropwise to the Ca-containing solution. The mixed salt solution was stirred continuously at room temperature for 1 h. The suspension was then centrifuged at 3000 rpm for 3 min to collect the product. The product was then washed three times with ethanol, methanol and acetone in sequence and dried to obtain the calcium carbonate composite material, named CaCO3(Mn,Al).

[0073] The SEM image of the prepared calcium carbonate composite material (CaCO3(Mn,Al)) is shown below. Figure 5 As shown. Figure 5 It can be seen that the CaCO3(Mn,Al) obtained after Mn and Al doping exhibits a uniform spherical shape.

[0074] Example 4

[0075] A method for preparing a calcium-based core-shell composite material (CaCO3(Mn,Al)@TiO2) includes the following steps:

[0076] Weigh 40 mg of CaCO3(Mn,Al) from Comparative Example 1 above, disperse it in 16 mL of ethanol solution by ultrasonication, then add 0.2 g of hexadecylamine and 0.4 mL of ammonium hydroxide in sequence, stir at room temperature for 15 min, and finally add 0.4 mL of isopropyl titanate, stir at room temperature for 15 min; after stirring, centrifuge, wash, and dry to obtain CaCO3(Mn,Al)@TiO2.

[0077] To more clearly demonstrate the successful construction of the core-shell structure, the sample was calcined in an 800℃ furnace for 4 hours.

[0078] The TEM spectrum of the obtained core-shell composite material (CaCO3(Mn,Al)@TiO2) is shown below. Figure 6 As shown, the SEM-EDS spectrum is as follows: Figure 7 As shown. From Figure 6 and Figure 7 The successful construction of the titanium oxide shell is clearly visible. Elemental scanning also yielded a calcium-to-titanium ratio of 20:1.

[0079] Comparative Example 1

[0080] Example 2 was repeated, except that the calcium-to-titanium ratio was adjusted to 5:1.

[0081] Comparative Example 2

[0082] Example 4 was repeated, except that the calcium-to-titanium ratio was adjusted to 5:1.

[0083] Comparative Example 3

[0084] Example 2 was repeated, except that 0.195g FeCl3, 0.15g Al(NO3)3 and 0.072g MnCl2 were mixed simultaneously.

[0085] Experimental Example 1

[0086] The effects of core-shell structure on cycle stability and energy storage density were tested.

[0087] The CaCO3(Mn,Fe) of Example 1, CaCO3(Mn,Al) of Example 3, CaCO3(Mn,Fe)@TiO2 of Example 2, CaCO3(Mn,Fe)@TiO2 of Example 4, as well as the good samples of Comparative Examples 1 and 2 and CaCO3(Mn,Fe,Al)@TiO2 of Comparative Example 3, were first calcined in an 800℃ furnace for 4 hours. In the thermogravimetric cycle test, the samples were first placed in argon gas and heated from room temperature to 800℃. The calcination conditions were: temperature 800℃, atmosphere pure argon, scan rate about 50 sccm / min, lasting for 5 minutes. The carbonization conditions were: temperature 800℃, atmosphere CO2+Ar, scan rate about 50 sccm / min, lasting for 5 minutes. A total of 100 isothermal cycles at 800℃ were performed in the cycle experiment.

[0088] The experimental results are as follows:

[0089] Figure 8 The test results of the core-shell composite material of Sample Example 2 show that after 100 cycles, the energy storage density is about 1133 kJ / kg, and the cycle stability decreases by about 3%.

[0090] The cyclic stability of Comparative Example 1 is from Figure 9 A significant decrease can be observed, with cycle stability decreasing by approximately 13%, while the energy storage density is not significantly different from that of Example 2. However, the test results for the samples without core-shell protection in Examples 1 and 3 show a severe decrease in stability, such as... Figure 12 As shown, the cycling stability of CaCO3(Mn,Fe) decreased by approximately 47.32%, and that of CaCO3(Mn,Al) decreased by approximately 59.43%. This demonstrates the significant impact of the core-shell structure on stability, and that a large perovskite molar ratio also affects cycling stability. Comparative Example 3... Figure 13 It can be seen that there is no AI present, and the results of subsequent loop tests are as follows: Figure 14 After 100 cycles, the stability decreased by 37.2%, and neither the energy storage density nor the cycle stability was improved. In Comparative Example 3, the Al doping was affected by Mn and Fe and was not truly incorporated, thus having no effect on performance.

[0091] Experimental Example 2

[0092] Testing the cycle stability and energy density of materials with different doped elements:

[0093] The CaCO3(Mn,Al)@TiO2 samples obtained in Example 4 and Comparative Example 2 were initially calcined in an 800℃ furnace for 4 hours. In the thermogravimetric cycle (TGR) test, the samples were first placed in an argon atmosphere and heated from room temperature to 800℃. Calcination conditions: temperature 800℃, pure argon atmosphere, scan rate approximately 80 sccm / min, duration 4.5 minutes; carbonization conditions: temperature 800℃, CO2+Ar atmosphere, scan rate approximately 60 sccm / min, duration 8 minutes. A total of 100 isothermal cycles at 800℃ were performed.

[0094] Figure 10 The results show that after 150 cycles, the energy storage density of the CaCO3(Mn,Al)@TiO2 sample in Example 4 remained at approximately 1420 kJ / kg, with no decrease in stability. In contrast, the energy storage density of the CaCO3(Mn,Fe)@TiO2 sample was improved, while its cycle stability was also maintained.

[0095] Figure 11 Comparative Example 2 shows that after 100 cycles, the energy density of the CaCO3(Mn,Al)@TiO2 sample with adjusted doping elements decreased from 1267.5 kJ / kg to 1182.2 kJ / kg, and the stability decreased by 10.6%. The significant decrease in cycle stability is likely due to the thin core-shell coating in the early synthesis, which caused instability and easy breakage during the cycle test. Therefore, a calcium-titanium ratio of 20:1 is better than that of 5:1.

[0096] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A core-shell composite material, characterized by, The structure of the composite material comprises: a core of calcium carbonate microspheres doped with at least one of Mn 2+ , Al 3+ , and Fe 3+ ; and a shell layer made of titanium dioxide.

2. The core-shell composite of claim 1, wherein, The material of the inner core is calcium carbonate microspheres doped with Mn 2+ and Fe 3+ , and the molar ratio of Ca 2+ to Mn 2+ , Fe 3+ in the structure is 100:(10-15):(5-10); or The material of the core is calcium carbonate microspheres doped with Mn 2+ and Al 3+ , and the molar ratio of Ca 2+ to Mn 2+ , Al 3+ in the structure is 100:(10-15):(5-10).

3. The core-shell composite of claim 1, wherein, The ratio of calcium to titanium in the composite material is (18-23):

1.

4. The core-shell composite of claim 1, wherein, The particle size of the core-shell composite material is 2-3 μm, and the thickness of the shell layer is 80-120 nm.

5. The method of producing core-shell composite materials according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: dissolving a Ca source and at least one of a Mn source, an Fe source and an Al source in water and ethylene glycol to obtain a mixed solution; adding a carbonate solution to the mixed solution under stirring to form a precipitate; dissolving a titanium source, ammonia, a surfactant and the precipitate in ethanol, mixing uniformly to obtain the core-shell composite material.

6. The production method according to claim 5, wherein The Ca source is selected from one or more of calcium chloride, calcium nitrate, preferably, the concentration of the Ca source in the mixed solution is 0.09-0.15 mol·L -1 ; the volume ratio of the water to ethylene glycol is 1:(4-5); The Mn source is selected from one or more of manganese chloride and manganese nitrate; The Fe source is selected from one or more of ferric chloride and ferric nitrate; The Al source is selected from one or more of aluminum chloride and aluminum nitrate.

7. The preparation method according to claim 5, characterized in that, The molar ratio of the titanium source to the Ca source is (5-25):1, preferably 20:1; Preferably, the titanium source is selected from isopropyl titanate.

8. The preparation method according to claim 5, characterized in that, The method of dissolving the titanium source, ammonia, a surfactant and the precipitate in ethanol comprises the following steps: dispersing the precipitate in ethanol, sequentially adding the surfactant and ammonia, and then adding the titanium source after stirring at room temperature.

9. The production method according to claim 5 or 8, characterized by, The mass concentration ratio of the titanium source, ammonia and surfactant is (2-6):2:

1.

10. Use of the core-shell composite material according to any one of claims 1-4 or the core-shell composite material prepared by the preparation method according to any one of claims 5-9 in solar thermal chemical energy storage.

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