A nanocrystalline superlattice catalyst and its preparation method and application

Abstract

The present invention discloses a nanocrystalline superlattice catalyst and a preparation method and application thereof. The catalyst has a molecular formula of FeSeS@C and a two-dimensional hollow structure. The preparation method comprises the following steps: calcining FeSe2@C NS and sulfur powder in an inert gas atmosphere to obtain the FeSeS@C NS superlattice catalyst. The catalyst introduces the element S into FeSe2@C to obtain FeSeS@C nanocrystals with a hollow structure and to increase the acidity of the catalyst surface, thereby improving the catalytic activity of the catalyst. The catalyst is highly efficient in activating peroxymonosulfate to degrade organic dyes.

Description

Technical Field

[0001] The present invention relates to a catalyst, in particular to a nanocrystalline superlattice catalyst and a preparation method and application thereof. Background Art

[0002] Self-assembled nanocrystal superlattices are an emerging class of materials with potential programmable functions that can meet different catalyst design requirements and show great potential in environmental remediation. However, previous superlattice materials are usually self-assembled from solid solid nanocrystals (such as Fe3O4 superlattice, CoFe2O4 superlattice, MnFe2O4 superlattice, Au superlattice, etc.), which inherently limits the exposure and reactivity of active sites in catalytic reactions. It is well known that the morphological structure of the catalyst has a significant impact on its catalytic performance. In fact, the exposure and mass transfer of active centers in the catalytic process largely depend on the structural characteristics of the catalyst. Therefore, the development of catalysts with high specific surface area and pore volume is crucial to improving the reaction activity of the catalyst. Summary of the Invention

[0003] Purpose of the invention: The first purpose of the present invention is to provide a catalyst with a two-dimensional hollow nanocrystalline superlattice structure, to increase the specific surface area of the catalyst, promote the exposure of active sites and reduce mass transfer resistance, thereby improving the catalytic activity of the catalyst; the second purpose of the present invention is to provide a method for preparing the nanocrystalline superlattice catalyst; the third purpose of the present invention is to provide an application of the nanocrystalline superlattice catalyst.

[0004] Technical solution: The nanocrystalline superlattice catalyst described in the present invention has a molecular formula of FeSeS@C and a two-dimensional hollow structure.

[0005] In catalytic reactions, the two-dimensional hollow nanocrystal superlattice structure has a higher specific surface area, which can promote the exposure of active sites and reduce mass transfer resistance.

[0006] The nanocrystal superlattice structure is formed by stacking single molecules or double molecules to present a lamellar structure.

[0007] Preferably, the mass ratio of the FeSe2@C precursor (FeSe2@C NS) to sulfur powder is 1:2-5. Solid FeSe2@C nanocrystals form hollow FeSeS@C nanocages, driven by the lower inward diffusion rate of sulfur atoms relative to the outward diffusion rates of Fe and Se atoms. The amount of sulfur doping affects the inward diffusion rate of sulfur, and thus the specific surface area and pore volume of the catalyst. A low degree of sulfurization makes it difficult to form a hollow structure. Excessive sulfurization can partially destroy the hollow structure.

[0008] The preparation method of the nanocrystalline superlattice catalyst of the present invention comprises the following steps: placing FeSe2@C NS and sulfur powder on both ends of corundum, and calcining the mixture in an inert gas atmosphere to obtain the FeSeS@C nanocrystalline superlattice catalyst.

[0009] Preferably, the calcination temperature is 340-360° C., the calcination time is 55-65 min, and the calcination heating rate is 4-6° C. / min.

[0010] Preferably, the preparation method of the FeSe2@C NS comprises the following steps:

[0011] (1) fully mixing ferric chloride, sodium oleate and water and aging;

[0012] (2) adding sodium sulfate to the liquid after aging in step (1), mixing, and then calcining in an inert gas to obtain Fe3O4@C NS;

[0013] (3) Fe3O4@C NS and selenium powder are selenized at high temperature to obtain FeSe2@C nanocrystalline superlattice powder.

[0014] Preferably, the calcination temperature in step (2) is 590-620° C., and the calcination time is 2.5-3.5 h.

[0015] Preferably, in step (3), the high-temperature selenization is: placing Fe3O4@C NS and selenium powder at opposite corners of a quartz boat, and then selenizing in a mixture of hydrogen and inert gas, the selenization temperature is 340-370°C, the time is 7.5-8.5h, and the calcination heating rate is 4-6°C / min.

[0016] Preferably, in step (3), the mass ratio of the Fe3O4@C NS to selenium powder is 1:2-4.

[0017] The invention discloses an application of the nanocrystalline superlattice catalyst in activating peroxymonosulfate (PMS) to degrade organic dyes.

[0018] The application method involves adding a FeSeS@C nanocrystalline superlattice catalyst to wastewater, stirring until adsorption-desorption equilibrium is reached, and then adding peroxymonosulfate to initiate a catalytic degradation reaction to degrade organic pollutants, such as diatrizoic acid (DTZ).

[0019] Invention Mechanism: The present invention sulfides FeSe2@C NS to obtain FeSeS@C nanocrystalline superlattice catalyst. Structurally, S doping can transform the solid nanocrystalline superlattice into a hollow nanocrystalline superlattice structure. In the catalytic reaction, the two-dimensional hollow nanocrystalline superlattice structure has a higher specific surface area, and the high specific surface area can promote the exposure of active sites and reduce mass transfer resistance. In terms of coordination environment, S doping can change the coordination environment and physicochemical properties of the catalyst surface, thereby increasing the surface acidity of FeSeS@C NS, thereby forming a local acidic microenvironment on the catalyst surface. The presence of the surface acidic microenvironment can achieve Fe 3+ / Fe 2+ In the stable cycle of the slip surface, the instantaneous concentration of active sites increases, SO4 ·- Efficient generation and efficient degradation of pollutants.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The catalyst introduces the S element into FeSe2@C, thereby obtaining FeSeS@C nanocrystals with a hollow structure on the one hand and increasing the acidity of the catalyst surface on the other hand, thereby improving the catalytic activity of the catalyst; (2) The preparation method is simple, the raw materials are easily available, the metal content of the catalyst is rarely lost before and after the reaction, and the regeneration is simple, which is conducive to promotion; (3) The catalyst is highly efficient in activating peroxymonosulfate to degrade organic dyes. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 X-ray diffraction (XRD) patterns of the catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2;

[0022] Figure 2 This is a scanning electron microscope (SEM) image of the catalyst prepared in Example 3;

[0023] Figure 3 This is a transmission electron microscope (TEM) image of the catalyst prepared in Example 3;

[0024] Figure 4 TEM image of the catalyst prepared in Comparative Example 1;

[0025] Figure 5 TEM image of the catalyst prepared in Comparative Example 2;

[0026] Figure 6 The Raman spectra of the catalysts prepared in Example 3 and Comparative Examples 1-2 are shown;

[0027] Figure 7 The nitrogen adsorption / desorption curves (N2 adsorption-desorption isotherms) of the catalysts prepared in Example 3 and Comparative Examples 1-2 are shown;

[0028] Figure 8 The effect diagram of DTZ degradation by activated PMS in Examples 1 to 4 and Comparative Examples 1 to 2;

[0029] Figure 9 This is a cyclic stability test chart of the catalyst prepared in Example 3.

[0030] Figure 10 This is a verification diagram of active species in the catalytic reaction system of the catalyst of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be further described below in conjunction with embodiments.

[0032] Example 1

[0033] The preparation method of the nanocrystalline superlattice catalyst of the present invention comprises the following steps:

[0034] (1) 0.72 g of ferric chloride hexahydrate was dissolved in 2 ml of deionized water, and then 2.44 g of sodium oleate was thoroughly mixed with the mixture. The resulting mixture was aged at 85 °C for 3 h and then uniformly mixed with 20 g of sodium sulfate powder. The mixture was then calcined at 600 °C in a nitrogen atmosphere for 3 h. After natural cooling, it was washed three times with deionized water and dried at 100 °C for 6 h to obtain Fe3O4@CNS powder.

[0035] (2) Weigh 50 mg of Fe3O4@C NS powder and 100 mg of selenium powder, mix them evenly and place them in a quartz boat. The quartz boat is transferred to a tube furnace and calcined at 340°C in an argon-hydrogen mixture (5 vol% H2) atmosphere at a heating rate of 4°C / min for 7.5 h. After cooling, the FeSe2@C NS catalyst is obtained.

[0036] (3) Weigh 0.1 g of FeSe2@C NS and 0.2 g of sulfur powder and place them at both ends of a porcelain boat (sulfur powder is placed upstream and FeSe2@CNS is located downstream). Heat to 340 °C at 4 °C / min in an argon atmosphere, keep warm for 55 min, and cool naturally to room temperature to obtain the FeSeS@C NS catalyst.

[0037] Example 2

[0038] The preparation method of the nanocrystalline superlattice catalyst of the present invention comprises the following steps:

[0039] (1) Fe3O4@C NS powder was prepared in the same manner as in step (1) of Example 1;

[0040] (2) Weigh 50 mg of Fe3O4@C NS powder and 150 mg of selenium powder, mix them evenly and place them in a quartz boat. The quartz boat is transferred to a tube furnace and calcined at 350°C in an argon-hydrogen mixture (5 vol% H2) atmosphere at a heating rate of 4.5°C / min for 7.8 h. After cooling, the FeSe2@C NS catalyst is obtained.

[0041] (3) Weigh 0.1 g of FeSe2@C NS and 0.3 g of sulfur powder and place them at both ends of a porcelain boat (sulfur powder is placed upstream and FeSe2@CNS is located downstream). Heat to 350°C at 4°C / min in an argon atmosphere, keep warm for 58 min, and cool naturally to room temperature to obtain the FeSeS@C NS catalyst.

[0042] Example 3

[0043] The preparation method of the nanocrystalline superlattice catalyst of the present invention comprises the following steps:

[0044] (1) Fe3O4@C NS powder was prepared in the same manner as in step (1) of Example 1;

[0045] (2) Weigh 50 mg of Fe3O4@C NS powder and 200 mg of selenium powder, mix them evenly and place them in a quartz boat. The quartz boat is transferred to a tube furnace and calcined at 360°C in an argon-hydrogen mixture (5 vol% H2) atmosphere at a heating rate of 5°C / min for 8 h. After cooling, the FeSe2@C NS catalyst is obtained.

[0046] (3) Weigh 0.1 g of FeSe2@C NS and 0.4 g of sulfur powder and place them at both ends of a porcelain boat (sulfur powder is placed upstream and FeSe2@CNS is located downstream). Heat to 350°C at 5°C / min in an argon atmosphere, keep warm for 60 min, and cool naturally to room temperature to obtain the FeSeS@C NS catalyst.

[0047] Example 4

[0048] The preparation method of the nanocrystalline superlattice catalyst of the present invention comprises the following steps:

[0049] (1) Fe3O4@C NS powder was prepared in the same manner as in step (1) of Example 1;

[0050] (2) Weigh 50 mg of Fe3O4@C NS powder and 180 mg of selenium powder, mix them evenly, and place them in a quartz boat. The quartz boat is transferred to a tube furnace and calcined at 370°C in an argon-hydrogen mixture (5 vol% H2) atmosphere at a heating rate of 6°C / min for 8.5 h. After cooling, the FeSe2@C NS catalyst is obtained.

[0051] (3) Weigh 0.1 g of FeSe2@C NS and 0.5 g of sulfur powder and place them at both ends of a porcelain boat (sulfur powder is placed upstream and FeSe2@CNS is located downstream). Heat to 360°C at 6°C / min in an argon atmosphere, keep warm for 65 min, and cool naturally to room temperature to obtain the FeSeS@CNS catalyst.

[0052] Comparative Example 1

[0053] Based on Example 3, only steps (1) and (2) were performed to obtain the FeSe2@C NS catalyst.

[0054] Comparative Example 2

[0055] On the basis of Example 3, in step (3), the mass of sulfur powder was changed to 0.8 g, and the other conditions remained unchanged.

[0056] Structural characterization

[0057] Figure 1 The XRD patterns of the catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2 verify the crystal structure and phase composition of the catalysts.

[0058] Depend on Figure 1 It can be seen that the diffraction peak of the FeSe2@C NS prepared in Comparative Example 1 shows high crystallinity and is consistent with the orthorhombic ferrous crystal FeSe2 (JCPDS No: 74-0247). The diffraction peak of the FeSeS@C NS catalyst obtained by performing different degrees of sulfurization treatment on FeSe2@C NS in Examples 1 to 4 is located between the diffraction peaks of Fe2SeS (JCPDS No: 75-0609) and FeS2 (JCPDS No: 71-2219), indicating that FeSeS@C NS is composed of two phases, Fe2SeS and a small amount of FeS2. In Comparative Example 2, when FeSe2@C NS is oversulfurized, the generation of higher purity FeS2 (JCPDS No: 71-2219) can be observed from the diffraction peak, and the diffraction peak is mainly dominated by FeS2.

[0059] Figure 2 and 3 These are the SEM and TEM images of the catalyst prepared in Example 3.

[0060] Depend on Figure 2 It can be seen that the FeSeS@C NS catalyst prepared in Example 3 presents a lamellar structure, and most of it is composed of single or double molecular layers of tightly packed FeSeS nanocrystals.

[0061] Depend on Figure 3 It can be seen that each nanocube in the FeSeS@C NS catalyst prepared in Example 3 presents a hollow structure.

[0062] Figure 4 This is the TEM image of the catalyst prepared in Comparative Example 1. It can be seen from the figure that the unsulfurized FeSe2@CNS presents a solid nanocrystalline superlattice structure.

[0063] Figure 5 This is the TEM image of the catalyst prepared in Comparative Example 2. It can be seen from the figure that the hollow structure of the FeS2@C NS obtained by oversulfurization is partially destroyed.

[0064] Figure 6 These are Raman spectra of the catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2.

[0065] Depend on Figure 6 It can be seen that the catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2 have a high conductivity at 1350 cm -1 and ~1580cm -1 The corresponding D bands of carbon materials (I D ) and G band (I G ), and the three catalysts I D / I G The values are similar, indicating that the high temperature sulfurization treatment has little effect on the graphitization degree of carbon in the catalyst. In addition, the FeSeS@C NS prepared in Example 3 has a high carbon content of 100 cm -1 to 400cm -1 Several weak peaks appeared in the range, indicating the existence of Fe-Se and Fe-S bonds.

[0066] Performance Characterization

[0067] 1. Catalyst nitrogen adsorption / desorption test

[0068] The catalysts prepared in Example 3, Comparative Example 1, and Comparative Example 2 were used to test their ability to adsorb / desorb nitrogen, thereby investigating their pore structure and specific surface area. Test Method: N2 adsorption-desorption isotherms were obtained at -196°C using a Micrometrics ASAP 2460 system. Specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method within a relative pressure range of 0.04 to 0.3. The test results are shown in Figure 2. Figure 7 shown.

[0069] from Figure 7 It can be seen that the catalysts prepared in Example 3, Comparative Example 1 and Comparative Example 2 all exhibit a typical IV-type H2-type hysteresis loop, indicating that the catalysts all have a hierarchical porous structure. The specific surface area and pore size of the FeSeS@CNS prepared in Example 3 are 50.3 m 2 / g and 26nm; the specific surface area and pore size of FeSe2@C NS prepared in Comparative Example 1 are 37.9m2 / g and 22nm; the specific surface area and pore size of FeSeS@C NS prepared in Comparative Example 2 were 34.3m 2 / g and 21nm. The specific surface area and pore size of the catalyst prepared in Example 3 are larger than those of the catalysts prepared in Comparative Examples 1 and 2, which is attributed to the hollow structure of the FeSeS@CNS. In addition, the nitrogen adsorption-desorption isotherm of the FeSeS@CNS in Example 3 increases significantly at P / P0 > 0.8, further demonstrating the presence of a hollow structure.

[0070] 2. Application of the nanocrystalline superlattice catalyst of the present invention in activating PMS to degrade organic dyes

[0071] (1) Catalyst activation of PMS to degrade DTZ

[0072] The specific operations are as follows:

[0073] ① Disperse 10 mg of catalyst evenly in 50 mL of 30 mg / L DTZ solution, stir in the dark for 20 min, and establish adsorption-desorption equilibrium;

[0074] ② Add 1.5 mM PMS to the system to initiate the catalytic degradation reaction;

[0075] ③ Take out 0.8 mL of reaction solution at 1, 3, 5, 7, 9, 15, and 20 min respectively;

[0076] ④ Filter the reaction solution with a 0.22 μm nylon filter membrane and quench with 0.2 mL of methanol to terminate the catalytic reaction;

[0077] ⑤ Undegraded diatrizoate was detected by HPLC at λ=254 nm.

[0078] The test results are as follows Figure 8 shown.

[0079] Depend on Figure 8 The DTZ removal rates for the diatrizoate prepared in Examples 1-4 were 71.0%, 77.3%, 100%, and 100%, respectively. The degree of sulfidation affects the catalytic activity of the catalyst, and as the degree of sulfidation increases, the DTZ removal rate exhibits a volcanic-like trend. The FeSeS@C NS prepared in Example 3 achieved the highest removal rate. This is because the sulfidation under these conditions not only effectively forms a hollow structure, promoting the exposure of active sites, but also optimizes the coordination environment of the active sites on the catalyst surface.

[0080] The FeSe2@C NS prepared in Comparative Example 1 and the oversulfurized FeSeS@C NS prepared in Comparative Example 2 achieved diatrizoate removal rates of 60.9% and 53.7%, respectively. The catalysts prepared in Examples 1-4 all achieved higher diatrizoate removal rates than the catalysts in Comparative Examples 1 and 2, with the catalyst prepared in Example 3 achieving 8.6 and 8.9 times the diatrizoate removal rates of the catalysts in Comparative Examples 1 and 2, respectively. This is because, on the one hand, the high specific surface area of the FeSeS@C NS prepared in Examples 1-4, due to their hollow structure, exposes more active sites; on the other hand, the incorporation of sulfur causes strong interactions between the active components, further improving the coordination environment of the active sites.

[0081] (2) Cyclic stability of FeSeS@C NS catalyst

[0082] The FeSeS@C NS catalyst prepared in Example 3 was recycled 5 times to test its degradation rate of DTZ. The test results are as follows: Figure 9 shown.

[0083] Depend on Figure 9 The cyclic stability of the FeSeS@C NS catalyst prepared in Example 3 was shown to be strong, with no significant decrease in degradation efficiency after the first cycle, and the degradation efficiency still exceeding 89% after the fifth cycle. This demonstrates the cyclic stability of the catalyst and its strong reusability.

[0084] (3) Catalytic mechanism of FeSeS@C NS catalyst

[0085] The FeSeS@C NS catalyst prepared in Example 3 was used to verify the activation mechanism of the reaction system and clarify the activation mechanism of the catalyst on PMS. Figure 10 shown.

[0086] In order to identify the active species (SO4 ·- , ·OH, ·O2 ·- , 1 O2), free radical quenching experiments were conducted. Tert-butyl alcohol (TBA) is a widely used quenching agent for ·OH and SO4 ·- The reactivity of MeOH is negligible. ·- An effective quencher. Figure 10 As shown in (a), diatrizoate showed significant inhibition in 600 mM MeOH, but had a weaker inhibitory effect in 600 mM TBA. 1 O2 and O2 ·-When 10 mM histidine and 4-hydroxy-2,2,6,6-tetramethylpiperidin-N-hydroxy were present, the degradation efficiency of DTZ was found to be inhibited to a certain extent, indicating that 1 O2 and O2 ·- Partially involved in the degradation of DTZ.

[0087] Further comparison of the inhibition of DTZ degradation by the four quenchers revealed that SO4 ·- As the main active species to degrade DTZ, ·OH, ·O2 ·- , 1 O2 plays a minor role in the degradation of DTZ. To further confirm the ROS involved in the FeSeS@C NS / PMS reaction, EPR tests were performed. Figure 10 As shown in (b), when DMPO is used as a trapping agent, two obvious DMPO-OH (α N =α H =14.9G) and DMPO-SO4(α N =13.2G,α H =9.6G,α H =1.48G,α H =0.78G) characteristic peak, and the characteristic peak intensity of DMPO-SO4 is significantly stronger than that of DMPO-OH. When DTZ is added to the FeSeS@C-4NS / PMS system, it is found that both characteristic peaks are weakened to varying degrees.

[0088] In addition, when TEMP was used as a capture agent ( Figure 10 (c) TEMP- in FeSeS@C NS / PMS and FeSeS@CNS / PMS / DTZ systems 1 The O2 signal intensity did not change significantly (1:1:1 triplet signal), indicating that 1 The role of O2 in the degradation of DTZ can be ignored.

[0089] Similar conclusions can also be drawn from DMPO-O2 ·- The spectrum obtained ( Figure 10 (d)). The above EPR results once again prove that SO4 is produced in the FeSeS@C-4NS / PMS system. ·- , ·OH, 1 O2, O2 ·- , and SO4 ·- As the main active species involved in the degradation of DTZ.

Claims

1. A nanocrystalline superlattice catalyst, characterized in that: Its molecular formula is FeSeS@C, and its structure is a two-dimensional hollow structure. The FeSe2@C NS superlattice catalyst is obtained by calcining FeSe2@C NS and sulfur powder in an inert gas atmosphere, wherein the mass ratio of FeSe2@C NS to sulfur powder is 1:2~5.

2. The nanocrystalline superlattice catalyst according to claim 1, characterized in that The nanocrystal superlattice structure is formed by stacking single molecules or double molecules to present a lamellar structure.

3. A method for preparing the nanocrystalline superlattice catalyst according to claim 1, characterized in that: FeSe2@C NS and sulfur powder were calcined in an inert gas atmosphere to obtain FeSeS@C NS superlattice catalyst.

4. The method for preparing the nanocrystalline superlattice catalyst according to claim 3, wherein: The calcination temperature is 340-360°C.

5. The method for preparing the nanocrystalline superlattice catalyst according to claim 3, characterized in that: The preparation method of the FeSe2@CNS comprises the following steps: (1) Thoroughly mix ferric chloride, sodium oleate and water and age them; (2) adding sodium sulfate to the liquid after aging in step (1), mixing, and then calcining in an inert gas to obtain Fe3O4@CNS; (3) Fe3O4@C NS and selenium powder are selenized at high temperature to obtain FeSe2@C nanocrystalline superlattice powder.

6. The method for preparing the nanocrystalline superlattice catalyst according to claim 5, characterized in that: In step (2), the calcination temperature is 590-620°C.

7. The method for preparing the nanocrystalline superlattice catalyst according to claim 5, characterized in that: In step (3), the high-temperature selenization is as follows: Fe3O4@C NS and selenium powder are selenized in a mixture of hydrogen and inert gas at a selenization temperature of 340-370°C.

8. Use of the nanocrystalline superlattice catalyst according to claim 1 or 2 in activating peroxymonosulfate to degrade organic dyes.

9. The use according to claim 8, characterized in that The application method is: FeSeS@C nanocrystalline superlattice catalyst is added to sewage, stirred until adsorption-desorption equilibrium is reached, and then peroxymonosulfate is added to initiate a catalytic degradation reaction to degrade organic pollutants.

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