A MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst and its preparation method

Abstract

This invention relates to the field of photocatalyst technology, specifically to a MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst and its preparation method. The MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst provided by this invention is obtained by combining MIL-101(Fe) and BiOBr, specifically including the following steps: using ferric chloride as raw material, reacting it with terephthalic acid in a first solvent, then keeping it at a first temperature for a certain time, filtering, washing the precipitate, and drying to obtain MIL-101(Fe); using bismuth nitrate as raw material, reacting it with KBr in a solvent, then adding a certain amount of MIL-101(Fe) prepared in step S1, keeping it at a second temperature for a certain time, cooling to separate the solid, washing impurities, and drying to obtain the MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst. This invention combines photocatalysis and Fenton, using photocatalysis to generate active oxygen, which can react with organic matter more quickly and shorten the degradation time of organic pollutants. This can solve the problem of poor quantum efficiency of MIL-101(Fe) material and its limited application in the field of photocatalysis.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst technology, specifically relating to a MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst and its preparation method. Background Technology

[0002] Phenolic wastewater is complex in composition, contains many impurities, and possesses a certain degree of biotoxicity, exerting a toxic effect on microorganisms involved in the treatment process. The characteristics of phenolic wastewater increase the difficulty of treatment processes and also raise treatment costs, yet the importance of phenol control does not seem to be fully recognized. It poses serious harm to humans, water bodies, fish, and crops, and is difficult to treat using conventional methods, causing severe environmental pollution. Therefore, adopting appropriate technologies for its complete degradation is particularly important.

[0003] Environmental materials possess advantages such as being non-toxic, harmless, recyclable, easily recyclable, and highly efficient, holding immense potential for creating new production processes, new substances, and new products. Photocatalytic oxidation technology using semiconductor materials is attracting increasing attention, particularly for its promising application in the removal of recalcitrant pollutants, making it a research hotspot both domestically and internationally. In recent years, TiO2, as a highly efficient catalyst, has been applied in industrial production. Under ultraviolet light irradiation, TiO2 can oxidize recalcitrant organic matter into CO2, H2O, and inorganic salts. Experimental studies have found that TiO2, as a catalyst, is not sensitive to the pH value of wastewater, and in most cases, it is more effective in treating neutral wastewater. Due to its high treatment efficiency, especially its excellent performance in removing recalcitrant pollutants, this technology has consistently been a research focus.

[0004] Metal-organic frameworks (MOFs) have wide applications in catalysis, separation, chemical sensors, gas storage, drug delivery, and biomedicine due to their high specific surface area, tunable pore size, functionality, and designable framework structure. Among these MOFs, MIL-101(Fe) is a typical MOF material with advantages such as large specific surface area, open active sites inherent to the metal, and good adsorption properties. However, MIL-101(Fe) also suffers from drawbacks such as poor quantum efficiency, which limits its application in photocatalysis.

[0005] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0006] The purpose of this invention is to provide a MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst to solve the problem of poor quantum efficiency of MIL-101(Fe) material and its limited application in the field of photocatalysis.

[0007] Another objective of this invention is to provide a method for preparing the aforementioned MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst, wherein the photocatalyst is obtained by combining MIL-101(Fe) and BiOBr.

[0010] Preferably, the mass ratio of MIL-101(Fe) to BiOBr is (0.005~0.04):1.

[0011] The preparation method of any of the above-mentioned MIL-101(Fe) / BiOBr S-type heterojunction photocatalysts includes the following steps:

[0012] S1. Using ferric chloride as raw material, react with terephthalic acid in the first solvent, then keep warm at the first temperature for a certain time, filter, wash the precipitate, and dry to obtain MIL-101(Fe).

[0013] S2. Using bismuth nitrate as a raw material, react it with KBr in a solvent, then add a certain amount of MIL-101(Fe) prepared in step S1, keep it at a second temperature for a certain time, cool it to separate the solid, wash off impurities and dry it to obtain the MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst.

[0014] Preferably, in step S2, the mass ratio of MIL-101(Fe) to BiOBr is (0.005~0.04):1.

[0015] Preferably, in step S1, the ferric chloride is FeCl3·6H2O, and the first solvent is DMF.

[0016] Preferably, in step S1, the molar ratio of ferric chloride to terephthalic acid is not less than 1.5:1.

[0017] Preferably, in step S1, the first temperature is 110℃ and the heat preservation time is 20h.

[0018] Preferably, in step S2, bismuth nitrate is Bi(NO)3·5H2O, the molar ratio of Bi(NO)3·5H2O to KBr is 1:1, and the second solvent is water.

[0019] Preferably, in step S2, the second temperature is 100-130℃, the holding time is 6-10h, and the drying temperature is 0-80℃.

[0020] Beneficial effects:

[0021] This invention combines photocatalysis and Fenton, using photocatalysis to generate active oxygen, which can react with organic matter more quickly and shorten the degradation time of organic pollutants. This can solve the problem of poor quantum efficiency of MIL-101(Fe) material and its limited application in the field of photocatalysis. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0023] Figure 1 The adsorption and degradation rates of the MIL-101(Fe) / BiOBr S-type heterojunction photocatalysts provided in Examples 3-6 of this invention when degrading phenol without the addition of formic acid.

[0024] Figure 2 The adsorption and degradation rates of the MIL-101(Fe) / BiOBr S-type heterojunction photocatalysts provided in Examples 3-6 of this invention during the degradation of phenol with the addition of formic acid are shown.

[0025] Figure 3 The performance of the MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst prepared in Example 5 of this invention in degrading phenol under different conditions.

[0026] Figure 4 XRD and DRS spectra of MIL-101(Fe), BiOBr, and MIL-101(Fe) / BiOBr.

[0027] Figure 5 SEM and TEM images of MIL-101(Fe), BiOBr, and MIL-101(Fe) / BiOBr.

[0028] Figure 6 XPS full spectra of the prepared MIL-101(Fe), BiOBr, and MIL-101(Fe) / BiOBr. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0030] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0031] This invention addresses the problem that the poor quantum efficiency of current MIL-101(Fe) materials limits their application in the field of photocatalysis by providing a MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst, which is obtained by compositing MIL-101(Fe) and BiOBr.

[0032] Preferably, the mass ratio of MIL-101(Fe) to BiOBr is (0.005~0.04):1, for example 0.006:1, 0.008:1, 0.01:1, 0.02:1, 0.03:1.

[0033] This invention also proposes a method for preparing any of the above-mentioned MIL-101(Fe) / BiOBr S-type heterojunction photocatalysts, comprising the following steps:

[0034] S1. Using ferric chloride as raw material, react with terephthalic acid in the first solvent, then keep warm at the first temperature for a certain time, filter, wash the precipitate, and dry to obtain MIL-101(Fe).

[0035] S2. Using bismuth nitrate as a raw material, react it with KBr in a solvent, then add a certain amount of MIL-101(Fe) prepared in step S1, keep it at a second temperature for a certain time, cool it to separate the solid, wash off impurities and dry it to obtain the MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst.

[0036] In a preferred embodiment of the present invention, in step S2, the mass ratio of MIL-101(Fe) to BiOBr is (0.005~0.04):1, for example 0.005:1, 0.01:1, 0.02:1, 0.03:1, or 0.04:1.

[0037] In a preferred embodiment of the present invention, in step S1, the ferric chloride is FeCl3·6H2O, and the first solvent is DMF.

[0038] In a preferred embodiment of the present invention, in step S1, the molar ratio of ferric chloride to terephthalic acid is not less than 1.5:1.

[0039] In a preferred embodiment of the present invention, in step S1, the first temperature is 110°C and the heat preservation time is 20h.

[0040] In a preferred embodiment of the present invention, in step S2, bismuth nitrate is Bi(NO)3·5H2O, the molar ratio of Bi(NO)3·5H2O to KBr is 1:1, and the second solvent is water.

[0041] In a preferred embodiment of the present invention, in step S2, the second temperature is 100-130℃ (e.g., 101℃, 103℃, 105℃, 107℃, 109℃, 110℃, 115℃, 120℃, 125℃, 129℃), the heat preservation time is 6-10h (e.g., 6.5h, 7.0h, 7.5h, 8.0h, 8.5h, 9.0h, 9.5h), and the drying temperature is 40-80℃ (e.g., 41℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 79℃).

[0042] The following detailed description of a MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst and its preparation method is provided through specific embodiments.

[0043] Example 1

[0044] Preparation of MIL-101(Fe):

[0045] 2.7 g of FeCl3·6H2O (9.8 mmol) and 0.824 g of terephthalic acid (4.96 mmol) were weighed and dissolved in 60 mL of LDMF (N,N-dimethylformamide). After stirring and dissolving, the solution was placed in an oven and kept at 110 °C for 20 hours. After naturally cooling to room temperature, a brick-red precipitate was obtained. The precipitate was washed three times alternately with anhydrous ethanol and dried in a vacuum drying oven at 60 °C to constant weight to obtain MIL-101 (Fe).

[0046] Example 2

[0047] Preparation of BiOBr:

[0048] 2.328 g of FeCl3·6H2O and 0.5712 g of KBr were dissolved in a mixed solution of 12 mL of H2O and 28 mL of ethylene glycol, and then stirred for 30 min. The solution was then transferred to a high-pressure reactor with a polytetrafluoroethylene liner and maintained at 110 °C for 8 h. After natural cooling, the material was centrifuged and washed three times alternately with water and anhydrous ethanol to remove impurities. The sample was then dried at a constant temperature of 60 °C, and the resulting sample was BiOBr.

[0049] Example 3

[0050] MIL-101(Fe) / BiOBr

[0051] 2.328 g of Bi(NO)3·5H2O and 0.5712 g of KBr were dissolved in a mixed solution of 12 mL of H2O and 28 mL of ethylene glycol. The mixture was stirred for 30 min. Then, a certain amount of MIL-101(Fe) was weighed and added to the above solution. The mixture was then transferred to a high-pressure reactor with a polytetrafluoroethylene liner and kept at 110 °C for 8 h. After natural cooling, the mixture was centrifuged to obtain the material. The material was washed three times alternately with water and anhydrous ethanol to remove impurities. Then, it was dried at a constant temperature of 60 °C. The resulting sample was MIL-101(Fe) / BiOBr, with a mass ratio of MIL-101(Fe) to BiOBr of 0.005:1, and was labeled as MFB0.5.

[0052] Example 4

[0053] MIL-101(Fe) / BiOBr

[0054] 2.328 g of Bi(NO)3·5H2O and 0.5712 g of KBr were dissolved in a mixed solution of 12 mL of H2O and 28 mL of ethylene glycol, and then stirred for 30 min. A certain amount of MIL-101(Fe) was then weighed and added to the above solution, and the mixture was transferred to a high-pressure reactor with a polytetrafluoroethylene liner. The reactor was kept at 110 °C for 8 h, and after natural cooling, centrifuged to obtain the material. The material was washed three times alternately with water and anhydrous ethanol to remove impurities, and then dried at a constant temperature of 60 °C. The resulting sample was MIL-101(Fe) / BiOBr, with a mass ratio of MIL-101(Fe) to BiOBr of 0.01:1, and labeled as MFB1.

[0055] Example 5

[0056] MIL-101(Fe) / BiOBr

[0057] 2.328 g of Bi(NO)3·5H2O and 0.5712 g of KBr were dissolved in a mixed solution of 12 mL of H2O and 28 mL of ethylene glycol, and then stirred for 30 min. A certain amount of MIL-101(Fe) was then weighed and added to the above solution, and the mixture was transferred to a high-pressure reactor with a polytetrafluoroethylene liner. The reactor was kept at 110 °C for 8 h, and after natural cooling, centrifuged to obtain the material. The material was washed three times alternately with water and anhydrous ethanol to remove impurities, and then dried at a constant temperature of 60 °C. The resulting sample was MIL-101(Fe) / BiOBr, with a mass ratio of MIL-101(Fe) to BiOBr of 0.02:1, and labeled as MFB2.

[0058] Example 6

[0059] MIL-101(Fe) / BiOBr

[0060] 2.328 g of Bi(NO)3·5H2O and 0.5712 g of KBr were dissolved in a mixed solution of 12 mL of H2O and 28 mL of ethylene glycol, and then stirred for 30 min. A certain amount of MIL-101(Fe) was then weighed and added to the above solution, and the mixture was transferred to a high-pressure reactor with a polytetrafluoroethylene liner. The reactor was kept at 110 °C for 8 h, and after natural cooling, centrifuged to obtain the material. The material was washed three times alternately with water and anhydrous ethanol to remove impurities, and then dried at a constant temperature of 60 °C. The resulting sample was MIL-101(Fe) / BiOBr, with a mass ratio of MIL-101(Fe) to BiOBr of 0.03:1, labeled as MFB3.

[0061] Phenol degradation test:

[0062] Under visible light irradiation, an initial phenol concentration in the influent of 20 mg·L⁻¹, and a catalyst dosage of 0.5 g·L⁻¹, the adsorption + degradation rates of phenol by photocatalytic degradation of MFB0.5, MFB1, MFB2, MFB3, BiOBr, and MIL-101(Fe) were 14.74%, 18.27%, 26.93%, 20.51%, 34.62%, and 4.45%, respectively. Figure 1 As shown.

[0063] Under visible light irradiation, with a formic acid (HCOOH) mass fraction of 5% and an initial phenol concentration of 20 mg·L⁻¹ in the influent, -1 The catalyst dosage is 0.5 g·L. -1 Under the conditions described, the adsorption + degradation rates of phenol by photo-self-Fenton degradation of MFB-0.5, MFB-1, MFB-2, MFB-3, BiOBr, and MIL-101(Fe) were 9.74%, 60.61%, 85.57%, 22.01%, 45.89%, and 1.29%, respectively. Figure 2 As shown.

[0064] Comparing the phenol degradation rate and H2O2 production in the optimal catalyst MFB-2 photo-Fenton reaction and photocatalytic reaction, the performance of MFB-2 in phenol degradation by photo-Fenton reaction far surpasses that of photocatalytic degradation. In the photocatalytic H2O2 production, MFB-2 can produce 12.59 mmol·L⁻¹ within 90 min. -1 ·g -1 The H2O2 production in the photo-Fenton degradation of phenol was much lower than in the photocatalytic system, and the H2O2 production in the photo-Fenton system did not increase in the first 75 minutes of phenol degradation. This indicates that the H2O2 produced was decomposed by Fe(II) to generate ·OH, which then degraded the phenol. Figure 3 As shown.

[0065] Figure 4 a, Figure 4 b is the XRD pattern of the prepared MIL-101(Fe), BiOBr, and MIL-101(Fe) / BiOBr. Figure 4 The peak shape and position of a are consistent with the model of simulated MIL-101(Fe), with its diffraction peaks mainly located between 5-30°. The diffraction peaks at 5.16°, 8.44°, and 9.08° correspond to the (111), (220), and (311) crystal planes [207,208]. The peaks of the prepared BiOBr are completely consistent with the peak shape and position of the international standard card library JCPDS No. 85-0862. The characteristic peaks at 10.95°, 25.26°, 31.80°, 32.311°, 39.432°, and 44.855° correspond to the (001), (011), (012), (110), (112), and (004) of BiOBr, respectively. The peak shape and position of the composite photocatalyst MFB-2 are completely consistent with those of BiOBr. No MIL-101(Fe) was found. This may be because the amount of MIL-101(Fe) composite is small and its peak intensity is much lower than that of BiOBr, which leads to its peak being masked. However, the peak intensity of the composite photocatalyst is significantly weaker because the crystallinity of BiOBr is reduced due to the composite MIL-101(Fe).

[0066] The light absorption performance of a photocatalyst is also crucial to its activity. Generally, better light absorption performance corresponds to better photocatalytic activity. The light absorption performance of the prepared MIL-101(Fe), BiOBr, and MIL-101(Fe) / BiOBr was determined using DRS spectra. Figure 4 As shown in Figure c, both the prepared BiOBr and MIL-101(Fe) / BiOBr exhibit strong absorption in the ultraviolet region, with MIL-101(Fe) showing a wider absorption range, possibly due to its inherent color. Compared to pure BiOBr, MFB-2 shows a slight redshift, indicating better visible light response. The Tauc diagram can be further calculated and plotted using its UV-Vis diffuse reflectance spectra to estimate the bandgap of the semiconductor catalyst. Figure 4 The band gap estimates for MIL-101(Fe) and BiOBr can be obtained from d as 2.53 eV and 2.8 eV, respectively.

[0067] The morphology and crystal size of the prepared MIL-101(Fe), BiOBr, and MFB-2 were studied by SEM and TEM, such as... Figure 5 As shown, BiOBr is a sphere composed of agglomerated sheet-like structures, with a single diameter of approximately 2 μm. Irregular sheet-like structures are also attached to the surface of the sphere. Figure 5b is a scanning electron microscope image of the prepared MIL-101(Fe) material, in which MIL-101(Fe) has a relatively uniform octahedral structure with an uneven surface and a size of approximately 1 μm.

[0068] Depend on Figure 6 As can be seen, the main elements and states present in MIL-101(Fe) are Fe2p, C1s, and O1s; while the main elements present in BiOBr are Bi4f, Br3d, C1s, O1s, and O2s. The MFB-2 spectrum shows the simultaneous presence of Fe2p, C1s, Bi4f, Br3d, and O1s, indicating that MIL-101(Fe) and BiOBr are well-combined and form an S-type heterojunction.

[0069] To further analyze the elemental chemical states, structures, and electronic interactions between surface elements in MIL-101(Fe), BiOBr, and especially MFB-2, we tested the XPS high-resolution spectra of Bi4f, Br3d, Fe2p, and O1s. The results are listed below. Figure 6 b~ Figure 6 f.

[0070] Depend on Figure 6 b indicates that BiOBr has two characteristic peaks, Bi4f, at 164.7 eV and 159.4 eV, which can be attributed to Bi. 3+ Bi 4f 5 / 2 and Bi 4f 7 / 2 Orbit. Compared with BiOBr, the peak of Bi 4f in MFB-2 showed a blue shift.

[0071] Depend on Figure 6-6 c indicates that the XPS peaks of Br3d in BiOBr are located at 69.45 eV and 68.45 eV, and the characteristic peaks of Br3d in MFB-2 also show a certain blue shift, indicating that there is an interaction and valence electron transfer between BiOBr and MIL-101(Fe).

[0072] Depend on Figure 6As shown in d, the high-resolution spectrum of Fe 2p in MIL-101(Fe) can be divided into six peaks. The peaks at 711.5 eV and 725.1 eV correspond to Fe(II), 712.5 and 726.5 eV correspond to Fe(III), and the peaks at 717.8 eV and 730.6 eV correspond to the satellites of Fe(II) and Fe(III). This indicates that there are two Fe valence states, Fe(II) and Fe(III), in MIL-101(Fe). The red shift of the Fe 2p peak in MFB-2 in the figure also indicates that there is electron transfer between BiOBr and MIL-101(Fe). By calculating the relative areas of Fe(II) and Fe(III) peaks in MIL-101(Fe) and MFB-2 through integration, it can be found that the relative area of ​​Fe(II) in MFB-2 is greater than that in MIL-101(Fe), indicating that the relative content of Fe(II) in the composite material is higher, which provides more active sites for the reaction and is conducive to the self-Fenton reaction.

[0073] Depend on Figure 6 As can be seen from the data, the O1s peaks in MIL-101(Fe) and BiOBr are divided into two peaks, which are located at Bi-O or Fe-O and the free oxygen on the sample surface, respectively.

[0074] Depend on Figure 6 As can be seen from f, the O1s peak in MFB-2 can be divided into three different peaks, among which the peak at 530.5 eV corresponds to O 2- The peak at 532.35 eV indicates the presence of Bi-O or Fe-O; the peak at 533.55 eV represents the presence of oxygen vacancies; the characteristic peak at 533.55 eV indicates adsorbed or free oxygen on the sample surface, such as C=O and CO.

[0075] In summary:

[0076] This invention successfully combines MIL-101(Fe) and BiOBr to obtain an S-type heterojunction photocatalyst with high catalytic efficiency that does not require the addition of Fe(II) or H2O2. The adsorption and degradation rate of phenol can reach 85.57%. The performance of photo-auto-Fenton degradation of phenol far exceeds that of photocatalytic degradation, and the H2O2 production during the degradation process is much lower than that of the photocatalytic system, resulting in high utilization efficiency.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst in the photo-induced Fenton reaction treatment of phenol, characterized in that, Phenol was photodegraded by Fenton under the conditions of visible light irradiation, formic acid (HCOOH) mass fraction of 5%, initial phenol influent concentration of 20 mg·L⁻¹, and catalyst dosage of 0.5 g·L⁻¹. The photocatalyst was obtained by combining MIL-101(Fe) and BiOBr, with the mass ratio of MIL-101(Fe) to BiOBr being (0.005~0.04):

1. The preparation method of the MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst includes the following steps: S1. Using ferric chloride as raw material, react with terephthalic acid in DMF, then keep warm at the first temperature for a certain time, filter, wash the precipitate, and dry to obtain MIL-101(Fe). S2. Using bismuth nitrate as a raw material, react it with KBr in a solvent, then add a certain amount of MIL-101(Fe) prepared in step S1, keep it at a second temperature for a certain time, cool it to separate the solid, wash off impurities and dry it to obtain the MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst. In step S1, the molar ratio of ferric chloride to terephthalic acid is not less than 1.5:1; In step S2, the mass ratio of MIL-101(Fe) to BiOBr is (0.005~0.04):

1.

2. The application of the MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst as described in claim 1 in the photo-induced Fenton reaction treatment of phenol, characterized in that, In step S1, the ferric chloride is FeCl3·6H2O.

3. The application of the MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst as described in claim 1 or 2 in the photo-induced Fenton reaction treatment of phenol, characterized in that, In step S1, the first temperature is 110℃ and the holding time is 20h.

4. The application of the MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst as described in claim 1 in the photo-induced Fenton reaction treatment of phenol, characterized in that, In step S2, bismuth nitrate is Bi(NO)3·5H2O, the molar ratio of Bi(NO)3·5H2O to KBr is 1:1, and the second solvent is water.

5. The application of the MIL-101(Fe) / BiOBr S-type heterojunction photocatalyst as described in claim 1 in the photo-induced Fenton reaction treatment of phenol, characterized in that, In step S2, the second temperature is 100-130℃, the holding time is 6-10h, and the drying temperature is 40-80℃.

Images