Solid-phase synthesis strontium carbonate / strontium titanate heterojunction friction catalyst and application thereof

Abstract

The invention belongs to the technical field of strontium carbonate / strontium titanate heterojunction materials, and particularly relates to a solid-phase synthesis strontium carbonate / strontium titanate heterojunction friction catalyst and application thereof. Raw materials of the material comprise strontium carbonate and titanium dioxide, the strontium carbonate and the titanium dioxide are prepared according to the molar ratio of 1: 1, deionized water is added after mixing, grinding and drying are performed, sintering is performed for 10 hours at the temperature of 1000-1150 DEG C, and the material is obtained, and the strontium carbonate generates lattice strain in the sintering process. The solid-phase synthesized strontium carbonate / strontium titanate heterojunction friction catalyst is used for degrading organic pollutants in water. According to the technical scheme provided by the invention, strontium carbonate which is induced by sintering and generates lattice strain is introduced into strontium titanate, defect sites are generated, the strontium carbonate / strontium titanate composite material is formed, and the composite material can enhance charge separation and create an additional electron transfer pathway under low-frequency stirring, namely, the composite material has a friction catalysis effect.

Description

Technical Field

[0001] The invention belongs to the technical field of strontium carbonate / strontium titanate heterojunction materials, and particularly relates to a solid-phase synthesized strontium carbonate / strontium titanate heterojunction friction catalyst and application thereof in water treatment. Background Art

[0002] Organic pollutants, such as dyes, drugs, and pesticides, seriously pollute water resources and threaten environmental safety and human health. Therefore, it is crucial to develop efficient and sustainable technologies for the degradation of organic pollutants. Photocatalysis is considered a promising method for the degradation of organic pollutants, but the photocatalytic activity of catalysts is limited by sunlight alone as an energy source. This is because only electrons excited from the valence band (VB) to the conduction band (CB) contribute to the degradation process. In addition, photocatalysis faces challenges when dealing with high-concentration or turbid dye pollutants, which block the transmission of light and inhibit the activation of catalysts.

[0003] As a new method of combining mechanical energy, electronic energy and chemical energy, tribocatalysis has attracted widespread attention due to its potential in environmental remediation. The process uses triboelectrons generated by mechanical actions such as vibration friction to react with oxygen dissolved in water to generate active oxygen with the ability to degrade organic pollutants. A major advantage of tribocatalysis is that it can work under ambient conditions without the need for an external light source.

[0004] A heterojunction refers to an interface region formed by the contact of two different semiconductor materials. By constructing a heterojunction, the efficiency of photogenerated carrier separation can be improved, thereby enhancing the photocatalytic efficiency. In the prior art, strontium carbonate / strontium titanate heterojunction (SrCO3 / SrTiO3, SCO@STO for short) has made significant progress in the field of photocatalysis. Studies have shown that strontium carbonate / strontium titanate heterojunctions have a synergistic effect, especially in reactions such as carbon dioxide reduction, methane oxidation, and removal of nitric oxide. For example, patent CN112058289A provides a strontium carbonate / strontium titanate heterojunction photocatalyst, which is synthesized in situ by a one-step hydrothermal method. Photoluminescence spectrum analysis shows that its spectral intensity is the lowest, indicating that the transmission and separation efficiency of photogenerated carriers has been significantly improved, thereby promoting the photocatalytic water decomposition hydrogen production reaction.

[0005] However, there has been no literature reporting that strontium carbonate / strontium titanate heterojunctions have tribocatalytic effects. This study found that strontium carbonate / strontium titanate heterojunctions were unexpectedly obtained during the solid phase synthesis of strontium titanate, and that the material unexpectedly had a special tribocatalytic effect, which has not been reflected in existing literature.

[0006] As is known to all, when strontium carbonate and titanium dioxide are used as raw materials for solid phase synthesis of strontium titanate, the decomposition temperature of strontium carbonate is relatively high, and it begins to decompose into SrO and CO2 at about 900°C. Under high temperature conditions, TiO2 and SrO react to synthesize SrTiO3. Therefore, the traditional solid phase synthesis method usually requires sintering for several hours to tens of hours above 1200°C to complete the reaction. In order to reduce the reaction temperature, a liquid phase (such as a glass phase) is often added or a ball milling process is used as an auxiliary, as described in CN103918088A. These methods are mainly used to improve the purity of strontium titanate, but no one has yet attempted to prepare a strontium carbonate / strontium titanate heterojunction by solid phase synthesis. Different from this, the present invention successfully prepared a strontium carbonate / strontium titanate heterojunction by rationally designing a solid phase synthesis process, and found that it has a friction catalytic effect. Summary of the invention

[0007] The invention provides a solid-phase synthesized strontium carbonate / strontium titanate heterojunction friction catalyst and its water treatment and purification application, so as to fill the current research gap.

[0008] In order to solve the above technical problems, the technical solution of the present invention is as follows: the raw materials of the solid-phase synthesized strontium carbonate / strontium titanate heterojunction friction catalyst are composed of strontium carbonate and titanium dioxide, and the molar ratio of strontium carbonate to titanium dioxide is 1:1. After the two raw materials are mixed, deionized water is added for grinding, followed by drying and sintering at a temperature of 1000-1150°C for 10 hours. During the sintering process, lattice strain occurs in strontium carbonate.

[0009] The ratio of raw materials and their composition directly affect the structure of the final product, and any deviation may lead to the formation of new substances. In addition, the sintering temperature has an important influence on the content of strontium carbonate in the catalyst. The experimental results show that with the increase of sintering temperature, the conversion of strontium carbonate is more complete, resulting in a decrease in its content. If the sintering time is too short, the decomposition of strontium carbonate is incomplete; if the sintering time is too long, the content of strontium carbonate will be too low and other by-products may be generated.

[0010] Optionally, the purity of strontium titanate is above 99%, and the purity of titanium dioxide is above 99%.

[0011] Optionally, the strontium carbonate in the friction catalyst accounts for 10-20% of the total weight of strontium titanate and strontium carbonate.

[0012] By strictly controlling the raw material ratio and sintering temperature, a strontium carbonate / strontium titanate heterojunction friction catalyst with corresponding composition can be obtained.

[0013] Optionally, the sintering temperature is 1100-1150°C.

[0014] Optionally, the titanium dioxide is rutile or anatase.

[0015] Optionally, the titanium dioxide is anatase type.

[0016] The samples synthesized from different crystalline starting materials showed similar XRD behaviors, indicating that the synthesis process had certain regularity and repeatability to a certain extent.

[0017] Optionally, the lattice volume of strontium carbonate in the solid-phase synthesized strontium carbonate / strontium titanate heterojunction friction catalyst is larger than the standard lattice volume.

[0018] The changes in the content and peak intensity of the strontium carbonate phase indicate that the sintering temperature has a significant effect on the structure of the impurity phase. Compared with pure commercial strontium carbonate, the shift in its peak position and the change in intensity are important signs of lattice strain. Lattice strain affects the physical and chemical properties of the material by changing its electronic structure, and has an important impact on its performance in the catalytic process.

[0019] The present invention also provides the application of the solid-phase synthesized strontium carbonate / strontium titanate heterojunction friction catalyst in the degradation of organic pollutants in water.

[0020] Optionally, the organic pollutant is rhodamine B, methylene blue, methyl orange and / or acid orange 7, preferably rhodamine B.

[0021] Optionally, during the catalytic degradation, a cylindrical (8 mm×20 mm) polytetrafluoroethylene magnetic stirrer is used, and the stirring rate is 1000-1200 rpm (lower than 20 Hz).

[0022] The technical solution of the present invention introduces strontium carbonate that generates lattice strain during sintering into strontium titanate to generate defect sites, thereby promoting the formation of a strontium carbonate / strontium titanate composite material. Under low-frequency stirring conditions, the composite material can significantly enhance charge separation and provide additional electron transfer pathways, thereby exhibiting an excellent friction catalytic effect. This invention provides a new and effective catalytic material for water pollution control and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the XRD pattern of STO(A)-1000 to 1150 synthesized in Example;

[0024] Figure 2 TEM image and local HRTEM magnified image of the STO(A)-1000 sample synthesized in Example;

[0025] Figure 3It is a schematic diagram of the tribo-catalytic degradation efficiency of STO(A)-1000, STO(A)-1050, STO(A)-1100, STO(A)–1150, STO(R)-1000, STO(R)-1050, STO(R)-1100, and STO(R)–1150 synthesized in the examples on RhB;

[0026] Figure 4 are the corresponding electronic band structures of C-SCO, C-STO, and STO(A)-1000, STO(A)-1150, STO(R)–1000, and STO(R)-1150 synthesized in the examples;

[0027] Figure 5 By using EDTA-2Na, BQ and tert-butyl alcohol TBA as + 、O2 - and ·OH active ion quencher, C-SCO, C-STO, and STO(A)-1000 and STO(R)-1000 catalysts synthesized in the examples were tested, and the degradation rate constant comparison chart was obtained;

[0028] Figure 6 The present invention provides a schematic diagram of the mechanism of friction catalysis degradation of organic matter in water by solid phase synthesis of strontium carbonate / strontium titanate heterojunction friction catalyst. DETAILED DESCRIPTION

[0029] For ease of understanding, the solid phase synthesis of strontium carbonate / strontium titanate heterojunction friction catalyst is described below in conjunction with examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0030] Examples 1-8

[0031] Submicron strontium carbonate / strontium titanate composite particles were synthesized using traditional ceramic technology. The raw materials consisted of strontium carbonate (SrCO3, purity 99.5%, referred to as C-SCO) and two crystal forms of titanium dioxide (TiO2): anatase (referred to as A, purity 99.8%) and rutile (referred to as R, purity 99.8%), all of which were purchased from Aladdin Reagent Company. Strontium carbonate and titanium dioxide were mixed in a molar ratio of 1:1, mixed with deionized water, ground and dried, and the mixed powder was sintered at 1000℃, 1050℃, 1100℃ and 1150℃ for 10 hours to obtain a solid-phase synthesized strontium carbonate / strontium titanate heterojunction (SCO@STO) friction catalyst.

[0032] The difference between Examples 1-8 lies in the titanium dioxide crystal form and sintering temperature used in the raw materials. The samples obtained by different combinations are marked as STO(A)-1000 (anatase titanium dioxide, sintering temperature 1000°C), STO(A)-1050 (anatase titanium dioxide, sintering temperature 1050°C), STO(A)-1100 (anatase titanium dioxide, sintering temperature 1100°C), STO(A)-11 STO(R)-50 (anatase titanium dioxide, sintering temperature 1150℃), STO(R)-1000 (rutile titanium dioxide, sintering temperature 1000℃), STO(R)-1050 (rutile titanium dioxide, sintering temperature 1050℃), STO(R)-1100 (rutile titanium dioxide, sintering temperature 1100℃) and STO(R)-1150 (rutile titanium dioxide, sintering temperature 1150℃).

[0033] The microstructure and surface morphology of the composite particles were observed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The X-ray diffractometer was a MiniFlex / 600 from Rigaku Corporation of Japan, and the high-resolution transmission electron microscope was a Tecnai G2 F20 S-Twin from the United States.

[0034] like Figure 1 As shown in Figure 3, from the XRD patterns of four samples sintered at different temperatures for anatase titanium dioxide, distinct diffraction peaks corresponding to the (100), (110), (111), (200), (210), and (211) crystal planes of cubic perovskite SrTiO3 (space group Pm3m) can be observed, confirming the formation of well-crystalline SrTiO3 (PDF#35-0734). However, additional peaks appearing at 2θ angles of approximately 29.5°, 36.3°, 41.9°, 52.2°, and 60.8° do not match the standard diffraction peaks of SrTiO3. These additional peaks are attributed to SrCO3 impurities (space group Pmcn), corresponding to specific crystal planes of SrCO3 (PDF#05-0418), indicating the presence of SrCO3.

[0035] These observations are further supported by the Rietveld refinement parameters for four samples of anatase titanium dioxide sintered at different temperatures, as shown in Table 1. By fitting the positions of the non-SrTiO3 peaks, they all correspond to the crystal face markers of SrCO3, which confirms that the second phase is indeed SrCO3.

[0036] Table 1

[0037]

[0038] With the increase of sintering temperature, the content of SrCO3 phase has a downward trend, and the corresponding peak intensity is significantly weakened. Correspondingly, the unit cell volume of SrCO3 also shows an expansion trend with the sintering temperature, indicating that there is lattice strain in the SrCO3 phase, especially the unit cell volume of samples sintered at 1100℃ and 1150℃ expands significantly.

[0039] like Figure 2 Transmission electron microscopy (TEM) analysis shown, as well as a high-resolution transmission electron microscopy (HRTEM) magnified image of the highlighted area in the inset, shows that strontium carbonate (SrCO3) is located at the interface of strontium titanate (SrTiO3) grains. The observed lattice fringes correspond to the (002) crystal plane of SrCO3, and its interplanar spacing (d-spacing) value is consistent with literature data (PDF#05-0418). This observation is consistent with the findings of X-ray diffraction (XRD), indicating that residual SrCO3 may act as a grain boundary phase and affect the properties of the material.

[0040] Organic pollutant degradation experiment

[0041] Rhodamine B (RhB) and methylene blue (MB) dyes (each dye concentration of 5 mg / L at room temperature) were used to evaluate the degradation performance of the solid-phase synthesized strontium carbonate / strontium titanate heterojunction tribocatalysts. All dyes were purchased from Aladdin Reagents.

[0042] During the entire tribocatalytic process, a cylindrical polytetrafluoroethylene magnetic stirrer with a diameter of 8 mm and a length of 20 mm was used to stir at a constant speed of 1200 rpm (20 Hz). To ensure the adsorption equilibrium between the dye and the catalyst, the solution was pre-stirred for 1 hour using the same polytetrafluoroethylene stirrer before the test. 50 mg of the selected catalyst was dispersed in the dye solution. At intervals, 3 mL of the suspension was taken and centrifuged at 6000 rpm for 10 minutes. The supernatant was analyzed using a UV-visible spectrophotometer to determine the absorption peak of the dye.

[0043] As shown in Table 2 and Figure 3 As shown, the degradation efficiency of the eight samples after 48 hours was between about 55% and 98%, and the rate constant K increased from 0.08h-1 to 0.20h-1. These values ​​were calculated using the formula ln(C0 / C)=K·t, where C0 is the initial concentration and C is the concentration at time t. Except for the two samples with a sintering temperature of 1050°C, the degradation efficiency of rhodamine B (RhB) increased with the increase of the strontium carbonate (SrCO3) unit cell size. Under the same conditions, STO(A)-1150 synthesized in the example showed a high efficiency of about 97% in degrading methylene blue (MB), and the K value was 3.08h-1. -1 .

[0044] Table 2

[0045] sample Eg(eV) <![CDATA[Degradation efficiency (C / C0)]]> <![CDATA[Rate constant K (h -1 )]]> STO(A)-1000 3.16 97.7％ 0.08 STO(A)-1050 3.10 56.4％ 0.02 STO(A)-1100 3.09 99.6％ 0.12 STO(A)-1150 3.10 99.9％ 0.20 STO(R)-1000 3.08 79.4％ 0.03 STO(R)-1050 3.17 55.2％ 0.016 STO(R)-1100 3.23 93.4％ 0.06 STO(R)-1150 3.15 97.2％ 0.11

[0046] For comparison, commercial SrTiO3 (C-STO) as well as the above-mentioned commercial SrCO3 (C-SCO) were also tested for RhB degradation under the same conditions.

[0047] After 48 h of light irradiation, the degradation rate of rhodamine B (RhB) by C-SCO was 79%, and the rate constant (K) was 0.03 h -1 , while the degradation rate of C-STO is 55% and the K value is 0.02h -1 In contrast, the current composite catalysts, especially STO(A)-1100, STO(A)-1150, STO(R)-1100 and STO(R)-1150, showed excellent degradation performance under light-free conditions, with the degradation rates of STO(A)-1100 and STO(A)-1150 both exceeding 99.5%, which is basically complete decomposition. The performance improvement is attributed to the presence of the lattice-strained strontium carbonate (SrCO3) phase, which significantly improves the degradation efficiency.

[0048] Figure 4 The corresponding electronic band structures of C-SCO, C-STO, STO(A)-1000, STO(A)-1150, STO(R)–1000, and STO(R)-1150 are shown (relative to the standard hydrogen electrode, NHE). For reference, O2 / ·O2 - and OH - The redox potentials of SCO@STO and SCO@STO are -0.33V and +1.99eV relative to NHE, respectively. It is worth noting that the valence band (VB) of C-SCO is close to +4.034eV, the conduction band (CB) is close to -1.256eV, and the band gap (Eg) is about 5.29eV. In contrast, the valence band / conduction band of C-STO is about +1.844 / -1.306eV, and the band gap is about 3.15eV. The band gap value of SCO@STO friction catalyst is between 3.10 and 3.16eV, and the conduction band position is more negative than -0.33eV. During the friction process, electrons can react with dissolved oxygen in the solution to generate active free radicals, such as superoxide radicals (·O2 - ). The valence band position is lower than +1.99eV (except C-SCO), so even under light conditions, it is difficult for the catalyst to react with hydroxide ions in the solution to generate active free radicals (such as hydroxyl radicals ·OH). This results in the catalyst having an extremely low degradation effect only under light conditions, which can be almost ignored.

[0049] By using disodium ethylenediaminetetraacetate (EDTA-2Na), benzoquinone (BQ) and tert-butyl alcohol (TBA) as h + 、O2 - and ·OH active ion quencher, and tested C-SCO, C-STO, and STO(A)-1000 and STO(R)-1000 catalysts synthesized in the examples (referred to as Catalyst in the figure). Figure 5 The results showed that under tribocatalytic conditions, when C–SCO, C–STO, STO(A)–1000 and STO(R)–1000 were used to degrade RhB, C–SCO produced hydroxyl radicals (·OH) as the main active radical, while C–STO, STO(A)–1000 and STO(R)–1000 mainly produced superoxide radicals (·O2 - ).

[0050] like Figure 6 As shown, the role of friction catalysis can be further explained by reaction formulas (1) to (4).

[0051]

[0052] H2O2+2e - → OH+OH - (4)

[0053] During the tribocatalytic process, the free electrons generated react with the dissolved oxygen in the solution to generate superoxide radicals (·O2 - ) is the main reaction pathway. There are two main ways to obtain free electrons: one is the transition from the valence band (VB) to the conduction band (CB) in the electronic structure of the catalyst, and the heterogeneous structure of SCO@SRO is easy for electrons and holes to move. The other is the electrons generated by the external low-frequency vibration friction. These electrons first react with the dissolved oxygen in the solution to generate superoxide radicals (·O2 - ), or with hydrogen peroxide ions (HO2 - ) reacts to generate hydroxyl radicals (·OH). It can be seen that the electrons generated by low-frequency vibration friction can effectively generate active ions, such as ·O2 - and ·OH, thereby improving the degradation efficiency and catalytic performance of organic dyes in water.

[0054] In summary, tribocatalysis is driven by friction-induced free electrons and the interaction of electrons and holes within the catalyst conduction band (CB) and valence band (VB). Low-frequency vibrations generate friction and play an important role in the degradation process. When the sintering temperature is higher, such as for STO(A)-1150 and STO(R)-1150, the degradation performance is greatly improved. We attribute this to the "strained" SrCO3 impurity phase in SrTiO3, which generates more electrons for the degradation process under stirring conditions.

[0055] The presence of strained strontium carbonate impurities is not only conducive to the generation of active triboelectrons through mechanical stirring, but also optimizes the electronic structure characterized by good band alignment and increased carrier concentration, reduces the recombination of electrons and holes, promotes the formation of active ions, and thus synergistically improves the overall catalytic activity. As a result, the SCO@STO tribocatalyst exhibits excellent tribocatalytic performance. Through controllable sintering process adjustment, the tribocatalytic ability of the composite material based on strontium titanate is greatly enhanced, thereby broadening the application range of tribocatalytic processes for environmental purification and improving efficiency.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents, and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A solid phase synthesis of strontium carbonate / strontium titanate heterojunction friction catalyst, characterized in that: The raw materials are composed of strontium carbonate and titanium dioxide, and the molar ratio of strontium carbonate to titanium dioxide is 1:

1. After the two raw materials are mixed, deionized water is added for grinding, and then dried and sintered at a temperature of 1000-1150°C for 10 hours. During the sintering process, strontium carbonate undergoes lattice strain.

2. The solid phase synthesis strontium carbonate / strontium titanate heterojunction friction catalyst according to claim 1, characterized in that: The purity of the strontium titanate is above 99%, and the purity of the titanium dioxide is above 99%.

3. The solid phase synthesis strontium carbonate / strontium titanate heterojunction friction catalyst according to claim 1, characterized in that: In the friction catalyst, strontium carbonate accounts for 10-20% of the total weight of strontium titanate and strontium carbonate.

4. The solid phase synthesis strontium carbonate / strontium titanate heterojunction friction catalyst according to claim 1, characterized in that: The sintering temperature is 1100-1150°C.

5. The solid phase synthesis strontium carbonate / strontium titanate heterojunction friction catalyst according to claim 1, characterized in that: The titanium dioxide is of rutile type or anatase type, preferably anatase type.

6. The solid phase synthesis strontium carbonate / strontium titanate heterojunction friction catalyst according to claim 1, characterized in that: The lattice volume of strontium carbonate in the solid-phase synthesized strontium carbonate / strontium titanate heterojunction friction catalyst is larger than the standard lattice volume.

7. Use of the solid phase synthesized strontium carbonate / strontium titanate heterojunction friction catalyst according to any one of claims 1 to 6 in the degradation of organic pollutants in water.

8. The use according to claim 7, characterized in that: The organic pollutants are rhodamine B, methylene blue, methyl orange and / or acid orange 7, preferably rhodamine B and / or methylene blue.

9. The use according to claim 7, characterized in that: During the catalytic degradation, a stirring device made of polytetrafluoroethylene is used, and the stirring rate is 1000-1200 rpm.

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