A Ho-MOF modified α-Fe2O3 photoanode catalyst and its preparation method and application

Abstract

The present invention discloses a Ho-MOF-modified α-Fe2O3 photoanode catalyst and its preparation method and application. The preparation method comprises: generating β-FeOOH on FTO conductive glass, annealing in air atmosphere to obtain an FTO / α-Fe2O3 photoanode; mixing formic acid, N,N-dimethylformamide, ethanol, a chiral H3L ligand, and a holmium salt to form a precursor solution; the chiral H3L ligand has the structural formula of #imgabs0# and the mass ratio of the holmium salt to the chiral H3L ligand is 0.95g:156-350mg; placing the FTO / α-Fe2O3 photoanode and the precursor solution in a hydrothermal reaction device to react to obtain a Ho-MOF-modified α-Fe2O3 photoanode catalyst. The method of the present invention is simple, low-cost, and reproducible. The product has uniform morphology and exhibits excellent catalytic performance as a catalyst in photoelectrocatalytic water oxidation reactions.

Description

Technical Field

[0001] The present invention relates to the technical field of photoelectrocatalytic materials, and in particular to a Ho-MOF-modified α-Fe2O3 photoanode catalyst, a preparation method thereof, and applications thereof. Background Art

[0002] Photoelectrochemical (PEC) water splitting to produce hydrogen is an economical and environmentally friendly approach to addressing global fossil energy depletion and environmental challenges. PEC cells, which mimic natural photosynthesis, can efficiently and cost-effectively convert sunlight into chemical fuels. However, due to the low efficiency of solar-to-hydrogen conversion, PEC cells remain far from practical application. Semiconductor photoelectrodes play a crucial role in PEC cells, harvesting solar energy and converting absorbed sunlight into photoexcited charge carriers to drive the PEC water splitting reaction. To date, significant efforts have been made and significant progress has been made in developing efficient and stable semiconductor photoelectrodes. Among the semiconductors studied, hematite (α-Fe2O3) is widely considered to be the best candidate for efficient PEC hydrogen production due to its suitable band gap and flat band potential. However, α-Fe2O3 photoanodes suffer from severe defects such as electron-hole recombination and photocorrosion in photoelectrochemical water splitting, hindering the efficient conversion of solar energy to hydrogen and hindering its industrialization. Therefore, improving the photoelectric conversion efficiency and stability of α-Fe2O3 photoanodes is a key research priority for anode catalysts in photoelectrochemical cells. Although some progress has been made in the modification of α-Fe2O3 photoanodes, their photocurrent density and photostability still do not meet the requirements of industrialization. Therefore, it is imperative to research and develop α-Fe2O3 composite photoanodes with higher photocurrent density and better stability.

[0003] Metal-organic frameworks (MOFs) are composed of metal nodes and organic linkers. Their porous structure and high specific surface area lend them to excellent adsorption and catalytic properties. Previous reports have shown that incorporating MOFs onto the surface of α-Fe₂O₃ photoanodes to form a passivation layer can effectively ameliorate the sluggish water oxidation kinetics and photocorrosion of α-Fe₂O₃ (DOI:10.1021 / acscatal.8b03233). Furthermore, studies have reported that doping catalysts with rare earth metal ions can provide more active sites, effectively enhancing catalytic activity (DOI:10.1002 / aenm.202203244). Among the many rare earth metals, holmium, as one of the most catalytically active, has attracted considerable research attention. Its stability in air and high-temperature oxidation susceptibility meet industrial standards; however, the catalytic performance of these materials remains suboptimal. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to improve the photocurrent density and photostability of α-Fe2O3 photoanode catalyst.

[0005] The present invention solves the above technical problems through the following technical means:

[0006] A method for preparing a Ho-MOF modified α-Fe2O3 photoanode catalyst comprises the following steps:

[0007] S1. Generate β-FeOOH on FTO conductive glass to obtain FTO / β-FeOOH photoelectrode; anneal the FTO / β-FeOOH photoelectrode in air atmosphere to obtain FTO / α-Fe2O3 photoanode;

[0008] S2, formic acid, N, N-dimethylformamide, ethanol, chiral H3L ligand and holmium salt are mixed uniformly to form a precursor solution; wherein the chiral H3L ligand has the structural formula: The mass ratio of the holmium salt to the chiral H3L ligand is 0.95g:156-350mg;

[0009] S3. Place the FTO / α-Fe2O3 photoanode and the precursor solution in a hydrothermal reaction device, seal it and react it, and cool it after the reaction to obtain the Ho-MOF modified α-Fe2O3 photoanode catalyst.

[0010] Preferably, in S1, the annealing temperature is 500° C. and the time is 2 hours.

[0011] Preferably, in S2, the volume ratio of ethanol to N,N-dimethylformamide is 2.5:8-25.

[0012] Preferably, in S2, the mass volume ratio of the chiral H3L ligand to ethanol is 156-350 mg:2.5 ml.

[0013] Preferably, in S2, the ratio of the holmium salt to the chiral H3L ligand is 0.95 g:156-312 mg.

[0014] Preferably, in S2, the concentration of the chiral H3L ligand in the precursor solution is 5.5-39 mg / ml.

[0015] Preferably, in S3, the reaction temperature is 110-140°C and the reaction time is 12-16 hours.

[0016] Preferably, in S2, the ratio of formic acid to chiral H3L ligand is 0.05-0.1 ml: 156-350 mg; excessive formic acid will affect the growth of MOF.

[0017] Preferably, in S1, ferric chloride, sodium nitrate, concentrated hydrochloric acid and water are used as raw materials, mixed and then subjected to a hydrothermal reaction to generate β-FeOOH on the FTO conductive glass.

[0018] Preferably, the mass ratio of ferric chloride used in S1 to the mass ratio of chiral H3L ligand used in S2 is 0.6-0.7 g:156-350 mg.

[0019] Preferably, in S1, the following steps are specifically included: mixing ferric chloride, sodium nitrate, concentrated hydrochloric acid and water to form a mixed solution; transferring the mixed solution and FTO conductive glass to a hydrothermal reaction device, sealing and reacting; cooling to room temperature after the reaction is completed, and washing, drying and annealing the obtained product in an air atmosphere to obtain the FTO / α-Fe2O3 photoanode.

[0020] Preferably, in S1, after annealing, the process further includes using an ozone cleaner to obtain a FTO / α-Fe2O3 photoanode.

[0021] Preferably, in S2, the holmium salt is holmium chloride.

[0022] The present invention also provides a Ho-MOF modified α-Fe2O3 photoanode catalyst, which is prepared by adopting the preparation method of the Ho-MOF modified α-Fe2O3 photoanode catalyst.

[0023] The present invention also proposes an application of the Ho-MOF modified α-Fe2O3 photoanode catalyst as a photoelectrocatalyst for catalyzing water oxidation reaction.

[0024] The FTO conductive glass in the present invention is fluorine-doped SnO2 conductive glass (SnO2:F), referred to as FTO for short.

[0025] The advantages of the present invention are:

[0026] The method of the present invention is simple in process, low in cost, and has good repeatability. The product has uniform morphology and consistent size. The prepared Ho-MOF modified α-Fe2O3 photoanode, i.e., α-Fe2O3 / Ho-MOF composite photoanode, has a high photoelectric conductivity at 1.23V. RHE The photocurrent density under bias voltage reached 0.57 mA cm -2 , 3.56 times that of a pure α-Fe₂O₃ photoanode. Systematic testing and characterization studies have shown that the designed Ho-MOF co-catalyst not only functions as a hole extraction layer to facilitate the separation of photogenerated charge carriers but also accelerates hole injection into the electrolyte, accelerating reaction kinetics. As a catalyst, it exhibits excellent catalytic performance in the photoelectrocatalytic water oxidation reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1A high-resolution scanning electron microscopy (SEM) image of the Ho-MOF-modified α-Fe2O3 photoanode catalyst and the α-Fe2O3 photoanode obtained in Example 1 of the present invention;

[0028] Figure 2 Surface scanning element distribution map (Mapping) of the Ho-MOF modified α-Fe2O3 photoanode catalyst obtained in Example 1 of the present invention; wherein af corresponds to the surface scanning area map, the element distribution map of Fe, N, O, C, and Ho, respectively;

[0029] Figure 3 This is an element content analysis diagram of the surface scanning element distribution diagram of the Ho-MOF modified α-Fe2O3 photoanode catalyst obtained in Example 1 of the present invention;

[0030] Figure 4 This is the X-ray photoelectron spectroscopy (XPS) of the Ho-MOF modified α-Fe2O3 photoanode catalyst obtained in Example 1 of the present invention;

[0031] Figure 5 The X-ray diffraction patterns (XRD) of the Ho-MOF modified α-Fe2O3 photoanode catalyst and α-Fe2O3 photoanode obtained in Example 1 of the present invention are shown in FIG.

[0032] Figure 6 The infrared spectrum of the Ho-MOF modified α-Fe2O3 photoanode catalyst obtained in Example 1 of the present invention and the Fourier transform infrared spectrum (FTIR) of the α-Fe2O3 photoanode catalyst;

[0033] Figure 7 The LSV curves of the Ho-MOF modified α-Fe2O3 photoanode catalyst and the α-Fe2O3 photoanode obtained in Example 1 of the present invention in 1M NaOH solution; wherein the α-Fe2O3 photoanode is a standard catalyst;

[0034] Figure 8 The IT curves of the Ho-MOF modified α-Fe2O3 photoanode catalyst and the α-Fe2O3 photoanode obtained in Example 1 of the present invention in 1M NaOH solution, wherein the α-Fe2O3 photoanode is a standard catalyst;

[0035] Figure 9 This is a comparison chart of the LSV curves of the La-MOF-modified α-Fe2O3 photoanode catalyst obtained in Comparative Example 3 of the present invention and the Ho-MOF-modified α-Fe2O3 photoanode catalyst obtained in Example 1;

[0036] Figure 10 This is a schematic diagram of the preparation method of Example 1 of the present invention;

[0037] Figure 11This is a high-resolution scanning electron microscope (SEM) image of the La-MOF-modified α-Fe2O3 photoanode catalyst obtained in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with 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 making creative efforts shall fall within the scope of protection of the present invention.

[0039] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0040] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0041] The chiral H3L ligand in the following examples and comparative examples is the chiral ligand H3L disclosed in the Chinese patent application publication number CN113354556A, and its structural formula is The synthesis method of H3L ligand is described in Chinese patent application publication number CN113354556A.

[0042] In the following examples and comparative examples, the pretreated FTO glass was prepared according to the following process: the FTO glass was placed in an ultrasonic cleaner, cleaned with acetone, ethanol and ultrapure water for a total of 30 minutes, repeatedly washed with deionized water and blown dry with nitrogen, and then placed in a clean oven for drying.

[0043] Example 1

[0044] Reference Figure 10 A method for preparing a Ho-MOF modified α-Fe2O3 photoanode catalyst comprises the following steps:

[0045] 3.5 g of FeCl3·6H2O and 3 g of NaNO3 were dissolved in 50 ml of deionized water to form a mixed aqueous solution, and 0.15 ml of concentrated hydrochloric acid was added to the obtained mixed aqueous solution and stirred for 15 minutes to obtain a precursor solution; the pretreated FTO glass conductive surface was placed face down in a polytetrafluoroethylene reactor, and 10 ml of the precursor solution was added along the inner wall of the polytetrafluoroethylene reactor. After sealing with a stainless steel hydrothermal reactor, the reactor was reacted at 100°C for 24 hours. After the reaction was completed, the reactor was cooled to room temperature. The obtained product was washed and dried with a mixed solution of N,N-dimethylformamide and ethanol, and then air annealed at 500°C for 2 hours in a tube furnace, and then treated with an ozone cleaner for 10 minutes to obtain an α-Fe2O3 photoanode.

[0046] Modification of Ho-MOF:

[0047] (1) Dissolve 0.95 g of HoCl3·6H2O in 15 ml of DMF solvent to form a metal salt solution;

[0048] (2) 7.5 mL of N,N-dimethylformamide solution (DMF) was mixed with 2.5 mL of anhydrous ethanol solution, and then 156 mg of chiral H3L ligand was added, and the mixture was stirred and ultrasonically mixed to obtain a mixed solution;

[0049] (3) adding the metal salt solution obtained in step (1) to the mixed solution obtained in step (2), and then adding 0.1 ml of formic acid;

[0050] (4) The conductive surface of the α-Fe2O3 photoanode is placed downward in a polytetrafluoroethylene reactor, and the solution obtained in step (3) is injected along the non-conductive surface of the α-Fe2O3 photoanode. After sealing with a stainless steel hydrothermal reactor, the reaction is carried out at 125°C for 14 hours. After cooling, Ho-MOF can be obtained. The obtained product is washed three times with a mixed solution of N,N-dimethylformamide and ethanol and dried at 60°C to obtain a Ho-MOF-modified α-Fe2O3 photoanode catalyst.

[0051] Figure 1 High-resolution scanning electron microscopy (SEM) images of the Ho-MOF-modified α-Fe2O3 photoanode catalyst (right) and the α-Fe2O3 photoanode catalyst (i.e., α-Fe2O3 photoanode, left) obtained in Example 1 of the present invention; Figure 1 It can be seen that the product obtained in this example has a heterogeneous structure and uniform morphology;

[0052] Figure 2 This is the surface scanning element distribution map (Mapping) of the Ho-MOF modified α-Fe2O3 photoanode catalyst obtained in Example 1. Figure 3The element content analysis diagram of the surface scanning element distribution diagram of the Ho-MOF modified α-Fe2O3 photoanode catalyst obtained in Example 1 (the SEM image of the surface scanning area is as follows Figure 2 a); Figures 2-3 It can be seen that the product obtained in this example successfully loaded Ho-MOF.

[0053] Figure 4 This is the X-ray photoelectron spectrum (XPS) of the Ho-MOF modified α-Fe2O3 photoanode catalyst obtained in Example 1 of the present invention, which reflects the elemental composition and element valence state of the sample surface; a is the full spectrum, indicating the presence and content of Fe, C, N, O, and Ho elements, where the peak intensity indicates their relative content. b, c, d, e, and f are the spectra of Fe, N, C, O, and Ho, respectively, revealing the valence state of these elements and their bonding types. The three peaks in Figure d represent the peaks of C=O (288.43eV), CO (285.98eV), and CC (284.78eV) bonds, respectively, indicating the presence of MOFs. The peak in Figure f also shows that Ho 3+ Successful doping.

[0054] Figure 5 The X-ray diffraction pattern (XRD) of the Ho-MOF-modified α-Fe2O3 photoanode catalyst (α-Fe2O3 / Ho-MOF) and the α-Fe2O3 photoanode obtained in Example 1 of the present invention is shown; peaks of Ho-MOF and α-Fe2O3 can be seen, indicating that the Ho-MOF-modified α-Fe2O3 photoanode catalyst was successfully prepared;

[0055] Figure 6 The infrared spectra of the Ho-MOF modified α-Fe2O3 photoanode catalyst (α-Fe2O3 / Ho-MOF) and the α-Fe2O3 photoanode obtained in Example 1 of the present invention are shown; Figure 6 The wavelengths of 1500-1740 cm-1 were detected on the composite photoanode. -1 The -COOH peak at 3050 cm -1 The -OH peak at 37° proved that Ho-MOF was successfully loaded onto the α-Fe2O3 photoanode catalyst.

[0056] Figure 7 and Figure 8The LSV curves and it curves of the Ho-MOF modified α-Fe2O3 photoanode catalyst and the α-Fe2O3 photoanode catalyst obtained in Example 1 in 1M NaOH solution are shown in the following table. The specific test method is: using an electrochemical workstation with a xenon lamp as the light source, 1M NaOH as the electrolyte, an Ag / AgCl electrode as the reference electrode, a platinum sheet as the counter electrode, and the catalyst as the working electrode, the LSV and it photoelectrochemical tests are performed using CHI66E software. The α-Fe2O3 photoanode is the standard catalyst (α-Fe2O3 shown in the figure). Figure 7 It can be seen that the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in Example 1 has a high photocatalytic activity at 1.23V. RHE The photocurrent density under bias voltage reached 0.57 mA cm -2 Compared with pure α-Fe2O3 (photocurrent density of 0.16mAcm -2 )’s photocurrent density is significantly improved. Figure 8 It can be seen that the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in Example 1 has a high photocatalytic activity at 1.23V. RHE The photocurrent density did not decay significantly within 10 minutes under bias. The photocurrent density of α-Fe2O3 photoanode catalyst was significantly lower than that of Ho-MOF modified α-Fe2O3 photoanode catalyst, and the photocurrent density did not decay significantly within 10 minutes.

[0057] Example 2

[0058] The preparation method of the Ho-MOF-modified α-Fe2O3 photoanode catalyst is different from that of Example 1 only in that: in (2), 10 mL of N,N-dimethylformamide solution (DMF) and 2.5 mL of anhydrous ethanol solution are mixed evenly; the remaining steps are the same as those of Example 1.

[0059] Characterization showed that the product obtained in this example had a heterogeneous structure and uniform morphology.

[0060] The same method as in Example 1 was used to test the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in this example at 1.23V. RHE The photocurrent density under bias voltage reached 0.54 mA cm -2 , the photocurrent density has no obvious decay within 10 min.

[0061] Example 3

[0062] The preparation method of the Ho-MOF-modified α-Fe2O3 photoanode catalyst is different from that of Example 1 only in that: in (2), 5 mL of N,N-dimethylformamide solution (DMF) and 2.5 mL of anhydrous ethanol solution are mixed evenly; the remaining steps are the same as those of Example 1.

[0063] Characterization showed that the product obtained in this example had a heterogeneous structure and uniform morphology.

[0064] The same method as in Example 1 was used to test the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in this example at 1.23V. RHE The photocurrent density under bias voltage reached 0.49 mA cm -2 , the photocurrent density has no obvious decay within 10 min.

[0065] Comparative Example 1

[0066] The preparation method of the Ho-MOF modified α-Fe2O3 photoanode catalyst comprises the following steps:

[0067] 3.5 g of FeCl3·6H2O and 3 g of NaNO3 were dissolved in 50 ml of deionized water to form a mixed aqueous solution, and 0.15 ml of concentrated hydrochloric acid was added to the obtained mixed aqueous solution and stirred for 15 minutes to obtain a precursor solution; the pretreated FTO glass conductive surface was placed face down in a polytetrafluoroethylene reactor, and 10 ml of the precursor solution was added along the inner wall of the polytetrafluoroethylene reactor. After sealing with a stainless steel hydrothermal reactor, the reactor was reacted at 100°C for 24 hours. After the reaction was completed, the reactor was cooled to room temperature. The obtained product was washed and dried with a mixed solution of N,N-dimethylformamide and ethanol, and then air annealed at 500°C for 2 hours in a tube furnace, and then treated with an ozone cleaner for 10 minutes to obtain an α-Fe2O3 photoanode.

[0068] Modification of Ho-MOF:

[0069] (1) Dissolve 0.95 g of HoCl3·6H2O in 15 ml of DMF solvent to form a metal salt solution;

[0070] (2) 7.5 mL of N,N-dimethylformamide solution (DMF) was mixed with 2.5 mL of anhydrous ethanol solution, and then 78 mg of chiral H3L ligand was added and stirred and ultrasonically mixed to obtain a mixed solution;

[0071] (3) adding the metal salt solution obtained in step (1) to the mixed solution obtained in step (2), and then adding 0.1 mL of formic acid;

[0072] (4) Place the conductive surface of the α-Fe2O3 photoanode facing downward in a polytetrafluoroethylene reactor, then slowly inject the solution obtained in step (3) along the non-conductive surface of the α-Fe2O3 photoanode. After sealing with a stainless steel hydrothermal reactor, react at 125°C for 14 hours to obtain Ho-MOF. The obtained product is washed three times with a mixed solution of N,N-dimethylformamide and ethanol and dried at 60°C to obtain a Ho-MOF-modified α-Fe2O3 photoanode catalyst.

[0073] Characterization showed that the product obtained in this comparative example had a heterogeneous structure and uniform morphology.

[0074] The same method as in Example 1 was used to test the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in this comparative example. RHE The photocurrent density under bias voltage reached 0.32 mA cm -2 , the photocurrent density has no obvious decay within 10 min.

[0075] Example 4

[0076] The preparation method of the Ho-MOF modified α-Fe2O3 photoanode catalyst comprises the following steps:

[0077] (1) 3.5 g of FeCl3·6H2O and 3 g of NaNO3 were dissolved in 50 ml of deionized water to form a mixed aqueous solution, and 0.15 ml of concentrated hydrochloric acid was added to the obtained mixed aqueous solution and stirred for 15 min to obtain a precursor solution; the pretreated FTO glass conductive surface was placed face down in a polytetrafluoroethylene reactor, and 10 ml of the precursor solution was added along the inner wall of the polytetrafluoroethylene reactor. After sealing with a stainless steel hydrothermal reactor, the reaction was carried out at 100 ° C for 24 h. After the reaction was completed, it was cooled to room temperature. The obtained product was washed and dried with a mixed solution of N, N-dimethylformamide and ethanol, and then air annealed at 500 ° C for 2 h in a tube furnace, and then treated with an ozone cleaner for 10 min to obtain an α-Fe2O3 photoanode;

[0078] Modification of Ho-MOF:

[0079] (1) Dissolve 0.95 g of HoCl3·6H2O in 15 ml of DMF solvent to form a metal salt solution;

[0080] (2) 7.5 mL of N,N-dimethylformamide solution (DMF) was mixed with 2.5 mL of anhydrous ethanol solution, and then 312 mg of chiral H3L ligand was added, and the mixture was stirred and ultrasonically mixed to obtain a mixed solution;

[0081] (3) adding the metal salt solution obtained in step (1) to the mixed solution obtained in step (2), and then adding 0.1 mL of formic acid;

[0082] (4) Place the conductive surface of the α-Fe2O3 photoanode facing downward in a polytetrafluoroethylene reactor, then slowly inject the solution obtained in step (3) along the non-conductive surface of the α-Fe2O3 photoanode. After sealing with a stainless steel hydrothermal reactor, react at 125°C for 14 hours to obtain Ho-MOF. The obtained product is washed three times with a mixed solution of N,N-dimethylformamide and ethanol and dried at 60°C to obtain a Ho-MOF-modified α-Fe2O3 photoanode catalyst.

[0083] Characterization showed that the product obtained in this example had a heterogeneous structure and uniform morphology.

[0084] The same method as in Example 1 was used to test the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in this example at 1.23V. RHE The photocurrent density under bias voltage reaches 0.50 mA cm -2 , the photocurrent density has no obvious decay within 10 min.

[0085] Comparative Example 2

[0086] The preparation method of the Ho-MOF modified α-Fe2O3 photoanode catalyst comprises the following steps:

[0087] 3.5 g of FeCl3·6H2O and 3 g of NaNO3 were dissolved in 50 ml of deionized water to form a mixed aqueous solution, and 0.15 ml of concentrated hydrochloric acid was added to the obtained mixed aqueous solution and stirred for 15 min to obtain a precursor solution; the pretreated FTO glass conductive surface was placed face down in a polytetrafluoroethylene reactor, and 10 ml of the precursor solution was added along the inner wall of the polytetrafluoroethylene reactor. After sealing with a stainless steel hydrothermal reactor, the reaction was carried out at 100 ° C for 24 h. After the reaction was completed, it was cooled to room temperature. The obtained product was washed and dried with a mixed solution of N, N-dimethylformamide and ethanol, and then air annealed at 500 ° C for 2 h in a tube furnace, and then treated with an ozone cleaner for 10 min to obtain an α-Fe2O3 photoanode;

[0088] Modification of Ho-MOF:

[0089] (1) Dissolve 0.95g HoCl3·6H2O in 15ml DMF solvent to form a metal salt solution

[0090] (2) 7.5 mL of N,N-dimethylformamide solution (DMF) was mixed with 2.5 mL of anhydrous ethanol solution, and then 145 mg of chiral H3L ligand was added and stirred and ultrasonically mixed to obtain a mixed solution;

[0091] (3) adding the metal salt solution obtained in step (1) to the mixed solution obtained in step (2), and then adding 0.5 mL of formic acid;

[0092] (4) Place the conductive surface of the α-Fe2O3 photoanode facing downward in a polytetrafluoroethylene reactor, then slowly inject the solution obtained in step (3) along the non-conductive surface of the α-Fe2O3 photoanode. After sealing with a stainless steel hydrothermal reactor, react at 125°C for 14 hours to obtain Ho-MOF. The obtained product is washed three times with a mixed solution of N,N-dimethylformamide and ethanol and dried at 60°C to obtain a Ho-MOF-modified α-Fe2O3 photoanode catalyst.

[0093] Characterization showed that the product obtained in this comparative example had a heterogeneous structure and uniform morphology.

[0094] The same method as in Example 1 was used to test the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in this comparative example. RHE The photocurrent density under bias voltage reached 0.31 mA cm -2 , the photocurrent density has no obvious decay within 10 min.

[0095] Example 5

[0096] The preparation method of the Ho-MOF modified α-Fe2O3 photoanode catalyst comprises the following steps:

[0097] 3.5 g of FeCl3·6H2O and 3 g of NaNO3 were dissolved in 50 ml of deionized water to form a mixed aqueous solution, and 0.15 ml of concentrated hydrochloric acid was added to the obtained mixed aqueous solution and stirred for 15 minutes to obtain a precursor solution; the pretreated FTO glass conductive surface was placed face down in a polytetrafluoroethylene reactor, and 10 ml of the precursor solution was added along the inner wall of the polytetrafluoroethylene reactor. After sealing with a stainless steel hydrothermal reactor, the reactor was reacted at 100°C for 24 hours. After the reaction was completed, it was cooled to room temperature. The obtained product was washed and dried with a mixed solution of N,N-dimethylformamide and ethanol, and then air annealed at 500°C for 2 hours in a tube furnace, and then treated with an ozone cleaner for 10 minutes to obtain an α-Fe2O3 photoanode.

[0098] Modification of Ho-MOF:

[0099] (1) Dissolve 0.95 g of HoCl3·6H2O in 15 ml of DMF solvent to form a metal salt solution;

[0100] (2) 7.5 mL of N,N-dimethylformamide solution (DMF) was mixed with 2.5 mL of anhydrous ethanol solution, and then 156 mg of chiral H3L ligand was added, and the mixture was stirred and ultrasonically mixed to obtain a mixed solution;

[0101] (3) adding the metal salt solution obtained in step (1) to the mixed solution obtained in step (2), and then adding 0.05 mL of formic acid;

[0102] (4) Place the conductive surface of the α-Fe2O3 photoanode facing downward in a polytetrafluoroethylene reactor, then slowly inject the solution obtained in step (3) along the non-conductive surface of the α-Fe2O3 photoanode. After sealing with a stainless steel hydrothermal reactor, react at 125°C for 14 hours to obtain Ho-MOF. The obtained product is washed three times with a mixed solution of N,N-dimethylformamide and ethanol and dried at 60°C to obtain a Ho-MOF-modified α-Fe2O3 photoanode catalyst.

[0103] Characterization showed that the product obtained in this example had a heterogeneous structure and uniform morphology.

[0104] The same method as in Example 1 was used to test the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in this example at 1.23V. RHE The photocurrent density under bias voltage reached 0.51 mA cm -2 , the photocurrent density has no obvious decay within 10 min.

[0105] Example 6

[0106] A method for preparing a Ho-MOF-modified α-Fe2O3 photoanode catalyst, wherein the steps thereof are different from those in Example 1 only in that the reaction temperature of (4) in the Ho-MOF modification is 140° C. The remaining steps are the same as those in Example 1.

[0107] Characterization showed that the product obtained in this example had a heterogeneous structure and uniform morphology.

[0108] The same method as in Example 1 was used to test the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in this example at 1.23V. RHE The photocurrent density under bias voltage reached 0.53 mA cm -2 , the photocurrent density has no obvious decay within 10 min.

[0109] Example 7

[0110] A method for preparing a Ho-MOF modified α-Fe2O3 photoanode catalyst, wherein the steps thereof are different from those in Example 1 only in that the reaction temperature of (4) in the Ho-MOF modification is 110°C.

[0111] Characterization showed that the product obtained in this example had a heterogeneous structure and uniform morphology.

[0112] The same method as in Example 1 was used to test the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in this example at 1.23V.RHE The photocurrent density under bias voltage reached 0.52 mA cm -2 , the photocurrent density has no obvious decay within 10 min.

[0113] Example 8

[0114] A method for preparing a Ho-MOF modified α-Fe2O3 photoanode catalyst, wherein the steps thereof are different from those in Example 1 only in that the reaction time of (4) in the Ho-MOF modification is 16 h.

[0115] Characterization showed that the product obtained in this example had a heterogeneous structure and uniform morphology.

[0116] The same method as in Example 1 was used to test the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in this example at 1.23V. RHE The photocurrent density under bias voltage reached 0.54 mA cm -2 , there is no obvious decay of photocurrent density within 10 minutes.

[0117] Example 9

[0118] A method for preparing a Ho-MOF modified α-Fe2O3 photoanode catalyst, wherein the steps thereof are different from those in Example 1 only in that the reaction time of (4) in the Ho-MOF modification is 12 h.

[0119] Characterization showed that the product obtained in this example had a heterogeneous structure and uniform morphology.

[0120] The same method as in Example 1 was used to test the Ho-MOF modified α-Fe2O3 photoanode catalyst prepared in this example at 1.23V. RHE The photocurrent density under bias voltage reached 0.47 mA cm -2 , the photocurrent density has no obvious decay within 10 min.

[0121] Comparative Example 3

[0122] A method for preparing a La-MOF-modified α-Fe2O3 photoanode catalyst, wherein the steps thereof differ from those of Example 1 only in that LaCl3·6H2O is used instead of HoCl3·6H2O for modification.

[0123] After characterization, the product obtained in this comparative example cannot present a heterogeneous structure, such as Figure 11 shown.

[0124] The test was carried out in the same manner as in Example 1. The La-MOF modified α-Fe2O3 photoanode catalyst prepared in this comparative example was RHEThe photocurrent density under bias voltage reached 0.26 mA cm -2 , there is no obvious decay of photocurrent density within 10 minutes.

[0125] Depend on Figure 9 It can be seen that the La-MOF modified α-Fe2O3 photoanode catalyst prepared in this comparative example 3 has a high photocatalytic activity at 1.23V. RHE The photocurrent density under bias voltage reached 0.26 mA cm -2 , the photocurrent density of the Ho-MOF modified α-Fe2O3 photoanode catalyst is lower than that in Example 1.

[0126] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a Ho-MOF modified α-Fe2O3 photoanode catalyst, characterized in that: The following steps are involved: S1. Generate β-FeOOH on FTO conductive glass to obtain FTO / β-FeOOH photoelectrode; anneal the FTO / β-FeOOH photoelectrode in air atmosphere to obtain FTO / α-Fe2O3 photoanode; S2, formic acid, N, N-dimethylformamide, ethanol, chiral H3L ligand and holmium salt are mixed uniformly to form a precursor solution; wherein the chiral H3L ligand has the structural formula: The mass ratio of the holmium salt to the chiral H3L ligand is 0.95g:156-350mg; S3. Place the FTO / α-Fe2O3 photoanode and the precursor solution in a hydrothermal reaction device, seal it and react it, and cool it after the reaction to obtain the Ho-MOF modified α-Fe2O3 photoanode catalyst.

2. The method for preparing the Ho-MOF-modified α-Fe2O3 photoanode catalyst according to claim 1, characterized in that: In S1, the annealing temperature is 500° C. and the time is 2 hours.

3. The method for preparing the Ho-MOF modified α-Fe2O3 photoanode catalyst according to claim 1, characterized in that: In S2, the volume ratio of ethanol to N,N-dimethylformamide is 2.5:8-25.

4. The method for preparing the Ho-MOF modified α-Fe2O3 photoanode catalyst according to claim 1, characterized in that: In S2, the mass volume ratio of the chiral H3L ligand to ethanol is 156-350 mg:2.5 ml.

5. The method for preparing the Ho-MOF modified α-Fe2O3 photoanode catalyst according to claim 1, characterized in that: In S2, the ratio of the holmium salt to the chiral H3L ligand is 0.95 g:156-312 mg.

6. The method for preparing the Ho-MOF modified α-Fe2O3 photoanode catalyst according to claim 1, characterized in that: In S2, the concentration of the chiral H3L ligand in the precursor solution is 5.5-39 mg / ml.

7. The method for preparing the Ho-MOF modified α-Fe2O3 photoanode catalyst according to claim 1, characterized in that: In S3, the reaction temperature is 110-140° C. and the reaction time is 12-16 h.

8. The method for preparing a Ho-MOF-modified α-Fe2O3 photoanode catalyst according to any one of claims 1 to 7, characterized in that: In S1, the following steps are specifically included: mixing ferric chloride, sodium nitrate, concentrated hydrochloric acid and water to form a mixed solution; transferring the mixed solution and FTO conductive glass to a hydrothermal reaction device, sealing and reacting; cooling to room temperature after the reaction is completed, and washing, drying and annealing the obtained product in an air atmosphere to obtain the FTO / α-Fe2O3 photoanode.

9. A Ho-MOF modified α-Fe2O3 photoanode catalyst, characterized by: The photoanode catalyst is prepared by the preparation method of the Ho-MOF modified α-Fe2O3 photoanode catalyst according to any one of claims 1 to 8.

10. Use of the Ho-MOF modified α-Fe2O3 photoanode catalyst as claimed in claim 9 as a photoelectrocatalyst for catalyzing water oxidation reaction.

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