Preparation method and application of rare earth metal ion-doped bismuth oxysulfide

Abstract

The invention discloses a preparation method and application of rare earth metal ion-doped bismuth oxysulfide, which specifically comprises the following steps: step 1: preparing a bismuth nitrate pentahydrate aqueous solution, adding thiourea to the solution, and stirring to fully react; step 2: slowly adding lithium hydroxide monohydrate to the solution obtained in step 1, and stirring until a reddish-brown precipitate is generated; step 3: adding a hydrated nitrate of a rare earth metal to the product obtained in step 2, and stirring to fully mix; step 4: subjecting the mixture in step 3 to a hydrothermal reaction; and step 5: washing and drying the precipitate after the reaction in step 4 for multiple times to obtain the rare earth metal ion-doped bismuth oxysulfide.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to a preparation method and application of rare earth metal ion-doped bismuth oxysulfide. Background Art

[0002] Bismuth-based oxychalcogenide materials (Bi2O2S), as an emerging two-dimensional material in the field of optoelectronics, have attracted much attention in the fields of photodetection, ferroelectricity, superconductivity and photocatalysis due to their advantages such as fast photoelectric response, ultra-high Hall mobility, narrow band gap, loose structure and layered structure. In the crystal structure of Bi2O2S, two [Bi2O2] 2+ Layer is a column [S] 2- Separate, the interlayers are formed by weak electrostatic interactions. [Bi2O2] 2+ The presence of interlayer sulfur atoms can reduce its band gap and improve the stability of its photocatalytic reaction. This reduced band gap allows for a broad range of light absorption across the solar spectrum, thereby increasing solar energy utilization. However, Bi2O2S suffers from poor photocatalytic activity due to its low separation efficiency of photogenerated electron and hole pairs, limiting its practical application. Because the unique structure of Bi2O2S is amenable to modification, the crystalline structure will be targeted to enhance its catalytic activity.

[0003] Doping with impurity elements is considered to be one of the most effective methods to adjust the electronic structure of semiconductors and improve the efficiency of separation of photogenerated electron-hole pairs. At present, the elements doped in bismuth-based oxychalcogenide materials mainly include cobalt ions and iron ions. However, there are problems with the doping of these two elements: 1. The doping of cobalt elements requires a long reaction time to achieve successful doping; 2. The doping of iron elements requires the preparation of pure phase Bi2O2S first, and then the use of ball milling to synthesize the iron-doped material. This shows that when doping different elements into Bi2O2S, completely different doping processes need to be adopted. Moreover, the catalysts prepared after successful doping of the above two elements are not ideal. They both require the synergistic degradation of pollutants by activating peroxymonosulfate (PMS) or by using light and activated peroxymonosulfate (PMS). This makes the application conditions of the catalyst more harsh, thereby affecting the application range of the catalyst. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a preparation method and application of rare earth metal ion-doped bismuth oxysulfide, so as to solve the problems in the prior art of long preparation reaction time, complicated preparation steps, harsh application conditions of the prepared catalyst, and poor catalytic effect.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for preparing rare earth metal ion-doped bismuth oxysulfide comprises the following steps:

[0007] Step 1: preparing an aqueous solution of bismuth nitrate pentahydrate, adding thiourea to the solution, and stirring to fully react; the molar ratio of bismuth nitrate pentahydrate to thiourea is (1.9-2.2):1;

[0008] Step 2: slowly adding lithium hydroxide monohydrate to the solution obtained in step 1 and stirring until a reddish-brown precipitate is formed; the concentration of lithium hydroxide monohydrate in the solution obtained in step 1 is 1.5 to 2.5 mol / L;

[0009] Step 3: adding a hydrated nitrate of a rare earth metal to the product obtained in step 2, and stirring to fully mix; wherein the molar ratio of the rare earth metal ion to the bismuth ion is (0.01-0.1):1;

[0010] Step 4: subjecting the mixture of step 3 to a hydrothermal reaction;

[0011] Step 5: After the reaction in step 4 is completed, the precipitate is washed and dried multiple times to obtain the rare earth metal ion-doped bismuth oxysulfide.

[0012] Preferably, the hydrated nitrate of the rare earth metal includes one of lanthanum nitrate hexahydrate and cerium nitrate hexahydrate.

[0013] Preferably, in step 4, the hydrothermal reaction is carried out at a constant temperature of 180-220° C. for 5-7 hours.

[0014] Preferably, the molar ratio of the rare earth metal ions to the bismuth ions is (0.0125-0.1):1.

[0015] The present invention also provides an application of rare earth metal ion-doped bismuth oxysulfide. The rare earth metal ion-doped bismuth oxysulfide prepared by the above preparation method is used as a photocatalyst.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention uses a simple hydrothermal method to prepare rare earth metal ion-doped bismuth oxysulfide catalyst in one step, and uses lanthanum ions (La 3+ ) or cerium ions (Ce 3+) doped Bi2O2S to improve the separation efficiency of its photogenerated electron and hole pairs and thus enhance its photocatalytic activity. By incorporating lanthanum or cerium metal ions, the band structure of Bi2O2S is changed, making its conduction band position more negative, which makes it easier for photogenerated electrons to react with oxygen molecules to form superoxide radicals. Superoxide radicals are further oxidized by photogenerated holes to generate singlet oxygen radicals, which in turn oxidize and degrade organic pollutants. In addition, due to the incorporation of lanthanum or cerium metal ions, their unique electronic configuration reduces the recombination rate of photogenerated electron-hole pairs, which is beneficial to increase the yield of singlet oxygen and thus enhance the photocatalytic performance of Bi2O2S. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 XRD patterns of prepared pure Bi2O2S, Bi2O2S doped with different lanthanum ion concentrations, and Bi2O2S doped with cerium ions.

[0019] Figure 2 Preparation of Ce for Comparative Example 3 3+ / Bi 3+ and La 3+ / Bi 3+ XRD pattern of the catalyst when the molar ratio of is 0.3.

[0020] Figure 3 This is the TEM-mapping image of La-Bi2O2S-2 prepared in Example 2.

[0021] Figure 4 UV-visible spectra of the prepared pure Bi2O2S and Bi2O2S doped with different lanthanum ion concentrations.

[0022] Figure 5 The photodegradation efficiency curves of tetracycline by pure Bi2O2S and Bi2O2S doped with different lanthanum ion concentrations are shown.

[0023] Figure 6 This is a curve of the photodegradation efficiency of tetracycline by Bi2O2S doped with cerium ion concentration. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] 1. A method for preparing rare earth metal ion-doped bismuth oxysulfide

[0026] The preparation method of the present invention specifically comprises the following steps:

[0027] Step 1: Prepare a bismuth nitrate pentahydrate aqueous solution, add thiourea to the solution, and stir to fully react; the molar ratio of bismuth nitrate pentahydrate to thiourea is (1.9-2.2):1.

[0028] Step 2: slowly add lithium hydroxide monohydrate to the solution obtained in step 1, and stir until a reddish-brown precipitate is formed; in the solution obtained in step 1, the concentration of lithium hydroxide monohydrate is 1.5 to 2.5 mol / L.

[0029] Step 3: adding a hydrated nitrate of a rare earth metal to the product obtained in step 2, and stirring to fully mix; wherein the molar ratio of the rare earth metal ion to the bismuth ion is (0.01-0.1):1;

[0030] Step 4: subjecting the mixture of step 3 to a hydrothermal reaction;

[0031] Step 5: After the reaction in step 4 is completed, the precipitate is washed and dried multiple times to obtain the rare earth metal ion-doped bismuth oxysulfide.

[0032] In some embodiments, the molar ratio of bismuth nitrate pentahydrate to thiourea is (1.9-2.2):1. Bismuth nitrate and thiourea react as follows:

[0033] Bi(NO3)3+H2O—BiONO3+2H + +2NO3 -

[0034] 2BiONO3+CH4N2S+2OH - —Bi2O2S+OC(NH2)2+2NO3 - +H2O

[0035] The amount of bismuth nitrate used will affect the type of product. If the amount is too high, the product will contain bismuth oxide as an impurity, while if the amount is too low, the target product cannot be obtained. Therefore, the molar ratio of bismuth nitrate pentahydrate to thiourea can be 1.9:1, 2:1, 2.1:1, 2.2:1, etc., as well as all ranges and sub-ranges between the above values. It should be understood that in embodiments, any of the above ranges can be combined with any other ranges.

[0036] In some embodiments, the hydrated nitrate of the rare earth metal comprises one of lanthanum nitrate hexahydrate and cerium nitrate hexahydrate. In principle, the nitrate corresponding to the rare earth metal element to be doped into the bismuth oxysulfide is selected.

[0037] In some embodiments, in step 4, the hydrothermal reaction is carried out at a constant temperature of 180 to 220°C for 5 to 7 hours. The hydrothermal reaction temperature will affect the doping effect. If the reaction temperature is too low, it will be difficult to dope the rare earth elements; if the reaction temperature is too high, it may lead to the generation of new substances, and the newly generated substances are not the products desired to be obtained by the present invention. Therefore, the hydrothermal reaction temperature can be 180°C, 190°C, 200°C, 210°C, 220°C, etc., and all ranges and sub-ranges between the above values. It should be understood that in the embodiment, any of the above ranges can be combined with any other ranges. The constant temperature reaction time can be 5h, 6h, 7h, etc., and all ranges and sub-ranges between the above values. It should be understood that in the embodiment, any of the above ranges can be combined with any other ranges.

[0038] In some embodiments, the molar ratio of the rare earth metal ions to the bismuth ions is (0.0125-0.1):1. The molar ratio of the rare earth metal ions to the bismuth ions also affects the doping effect. If the molar ratio of the rare earth metal ions to the bismuth ions is too low, the rare earth metal ions will not be able to be doped, while if it is too high, other substances that do not have catalytic properties will be generated. Therefore, the molar ratio of the rare earth metal ions to the bismuth ions is 0.0125, 0.025, 0.05, 0.075, 0.1, etc., as well as all ranges and sub-ranges between the above values. It should be understood that in the embodiment, any of the above ranges can be combined with any other ranges.

[0039] 2. Examples and Comparative Examples

[0040] 1. Lanthanum ion (La 3+ ) Preparation of doped Bi2O2S:

[0041] Step 1: Place 1.4553 g of bismuth nitrate pentahydrate in a 100 mL beaker, add 30 mL of deionized water, and stir magnetically until completely dissolved.

[0042] Step 2: Weigh 0.114 g of thiourea and add it to the solution obtained in the first step, and stir for 30 minutes to allow it to react fully;

[0043] Step 3: Weigh 2.5 g of lithium hydroxide monohydrate and slowly add it to the solution obtained in step 2, while continuing to stir until a reddish-brown precipitate is formed;

[0044] Step 4: Weigh a certain amount of lanthanum nitrate hexahydrate and add it to the solution obtained in step 3, and stir for 30 minutes to make it fully mixed. 3+ / Bi 3+ The molar ratio of La 3+ / Bi 3+The molar ratios are 0.0125, 0.025, 0.05, 0.075, and 0.1 respectively.

[0045] Step 5: The mixed solution obtained in step 4 was transferred to a reaction kettle with a polytetrafluoroethylene liner, and the reaction was carried out at a constant temperature of 200°C for 6 hours;

[0046] Step 6: Wash the reddish brown precipitate obtained after the reaction with deionized water and anhydrous ethanol three times respectively, and finally dry the product in a drying oven at 65°C; collect it for later use after drying. 3+ / Bi 3+ The samples with molar ratios of 0.0125, 0.025, 0.05, 0.075, and 0.1 were marked as Example 1 (La-BOS-1), Example 2 (La-BOS-2), Example 3 (La-BOS-3), Example 4 (La-BOS-4), and Example 5 (La-BOS-5), respectively.

[0047] Example 6:

[0048] In the lanthanum ion (La 3+ ) was improved on the basis of doping Bi2O2S, La 3+ / Bi 3+ The molar ratio of is 0.0125. The difference from Example 1 is that the reaction temperature of step 5 is different. The reaction temperature of step 5 in this embodiment is 180°C.

[0049] Example 7:

[0050] In the lanthanum ion (La 3+ ) was improved on the basis of doping Bi2O2S, La 3+ / Bi 3+ The molar ratio of is 0.0125. The difference from Example 1 is that the reaction temperature of step 5 is different. The reaction temperature of step 5 in this embodiment is 220°C.

[0051] 2. Cerium ion (Ce 3+ ) Preparation of doped Bi2O2S:

[0052] Step 1: Place 1.4553 g of bismuth nitrate pentahydrate in a 100 mL beaker, add 30 mL of deionized water, and stir magnetically until completely dissolved.

[0053] Step 2: Weigh 0.114 g of thiourea and add it to the solution obtained in the first step, and stir for 30 minutes to allow it to react fully;

[0054] Step 3: Weigh 2.5 g of lithium hydroxide monohydrate and slowly add it to the solution obtained in step 2, while continuing to stir until a reddish-brown precipitate is formed;

[0055] Step 4: Weigh 0.033g of cerium nitrate hexahydrate (Ce 3+ / Bi 3+ The solution obtained in the third step was added with a molar ratio of 0.025 and stirred for 30 min to fully mix.

[0056] Step 5: The mixed solution obtained in step 4 was transferred to a reaction kettle with a polytetrafluoroethylene liner, and the reaction was carried out at a constant temperature of 200°C for 6 hours;

[0057] Step 6: The reddish-brown precipitate obtained after the reaction was washed three times with deionized water and anhydrous ethanol respectively. The final product was placed in a drying oven at 65° C. and dried. After drying, the product was collected for later use. The sample was labeled as Example 8 (Ce-BOS-2).

[0058] 3. Comparative example:

[0059] Comparative Example 1 Preparation of pure Bi2O2S:

[0060] Step 1: Place 1.4553 g of bismuth nitrate pentahydrate in a 100 mL beaker, add 30 mL of deionized water, and stir magnetically until completely dissolved.

[0061] Step 2: Weigh 0.114 g of thiourea and add it to the solution obtained in the first step, and stir for 30 minutes to allow it to react fully;

[0062] Step 3: Weigh 2.5 g of lithium hydroxide monohydrate and slowly add it to the solution obtained in step 2, while continuing to stir until a reddish-brown precipitate is formed;

[0063] Step 4: Transfer the mixed solution obtained in step 3 to a reactor with a polytetrafluoroethylene liner and carry out a constant temperature reaction at 200°C for 6 hours;

[0064] Step 5: The reddish-brown precipitate obtained after the reaction was washed three times with deionized water and anhydrous ethanol respectively, and the final product was dried in a drying oven at 65°C; after drying, it was collected for later use, and the sample was labeled as BOS.

[0065] Comparative Example 2:

[0066] In the cerium ion (Ce 3+ ) is improved on the basis of Bi2O2S doping, and the difference is that: Ce 3+ / Bi 3+ The molar ratio is 0.01.

[0067] Comparative Example 3:

[0068] In the cerium ion (Ce 3+ ) is improved on the basis of Bi2O2S doping, and the difference is that: Ce3+ / Bi 3+ The molar ratio is 0.3.

[0069] Comparative Example 4:

[0070] In the lanthanum ion (La 3+ ) was improved on the basis of doping Bi2O2S, La 3+ / Bi 3+ The molar ratio of is 0.025, and the difference therefrom is that the reaction temperature of step 5 is different, and the reaction temperature of comparative example 4 is 150°C.

[0071] 3. Application Analysis

[0072] 1. Characterization experiments of the prepared catalyst

[0073] X-ray powder diffraction (XRD) analysis of the catalyst: The test equipment is Rigaku D / Max III, and the K α Radiation is measured using a continuous scanning test.

[0074] The morphology of the prepared catalyst was observed by transmission electron microscopy (TEM, equipment model: Tecnai G2F-20), and the sample was subjected to energy spectrum analysis.

[0075] UV-visible light test of the catalyst: The test was carried out using a UV-3600 spectrophotometer produced by Shimadzu Corporation of Japan.

[0076] The XRD results show that the diffraction peaks of BOS are sharp, indicating that the pure phase Bi2O2S powder is well crystallized. Compared with BOS, the diffraction peaks of Bi2O2S doped with lanthanum ions do not show any new diffraction peaks, angle shifts, or obvious changes in peak intensity. Similarly, the diffraction peaks of Bi2O2S doped with cerium ions do not show any new diffraction peaks, angle shifts, or obvious changes in peak intensity. The XRD results show that the high temperature hydrothermal method can be used to 3+ ) or cerium metal ions (Ce 3+ ) is doped into Bi2O2S crystals. When the reaction temperature is 150°C, impurities appear in the prepared sample, indicating that the doping is unsuccessful. At a reaction temperature of 180°C, Bi2O2S doped with lanthanum ions can be obtained. It can be clearly seen from the TEM image that the morphology of the La-BOS-2 catalyst is nanosheet-like, and the elemental composition and spatial distribution of La-BOS-2 are further analyzed by energy dispersive spectrometer (EDS). The elemental energy spectrum clearly shows that Bi, O, and S elements are evenly distributed. In addition, the La element is also evenly distributed in the La-BOS-2 nanosheets, indicating that La 3+Ions have been successfully incorporated into Bi2O2S catalysts. Compared to the prior art, which requires a long reaction time to prepare cobalt-doped Bi2O2S and has complicated steps to dope iron-doped Bi2O2S, the present invention can not only greatly shorten the reaction time, but also prepare lanthanum ions (La) in one step using a simple hydrothermal method. 3+ ) or cerium metal ions (Ce 3+ ) doped Bi2O2S material. It should be noted that when Ce 3+ / Bi 3+ When the molar ratio of Ce is 0.01, 3+ The performance of the Bi2O2S catalyst after doping is not significantly different from that of the undoped Bi2O2S catalyst. Although this ratio is successfully doped, successful doping does not necessarily mean that the catalytic performance will be improved. From the perspective of catalytic performance comparison, a certain doping amount is required to improve the catalytic performance of the product. 3+ / Bi 3+ Or Ce 3+ / Bi 3+ When the molar ratio of La is 0.3, new impurities appear in the prepared catalyst. The mass of the new impurities is large and they are not the effective components required by the present invention. This shows that when the molar ratio is large, the impurities generated have exceeded the doping range and most of them are not the effective components required by the present invention. 3+ After the addition of lanthanum ions, the light absorption ability of the Bi2O2S catalyst doped with lanthanum ions is slightly weaker than that of BOS, but it still has strong light absorption ability in the range of 200-600nm. In addition, compared with BOS, the absorption edge of the Bi2O2S catalyst doped with lanthanum ions has a blue shift, indicating that La 3+ Ion doping affects the band structure of BOS.

[0077] 2. Performance test of the prepared catalyst

[0078] Photocatalytic reaction instrument: XPA-7, Nanjing Xujiang Mechanical and Electrical Factory. The light source was a 300W high-pressure mercury lamp.

[0079] The specific photocatalytic process is as follows: 0.050g of catalyst is added to a 50mL quartz stoppered test tube, followed by 50mL of a 20mg / L tetracycline solution. The photoreaction tube is placed in the dark and stirred for 30 minutes to allow the catalyst and tetracycline in the solution to reach a dynamic equilibrium of adsorption and desorption. The tube is then illuminated. 5mL of the solution is sampled at regular intervals and centrifuged to remove the catalyst, obtaining a supernatant. The photocatalytic activity of the catalyst is determined using a UV-visible spectrophotometer (752N) by analyzing the characteristic absorbance of tetracycline at a wavelength of 350nm.

[0080] After 240 minutes of UV irradiation, the photocatalytic efficiency of BOS for TC was approximately 44.6%. Compared to BOS, BOS photocatalysts doped with lanthanum ions at different molar ratios showed significantly improved TC degradation efficiencies. After 240 minutes of UV irradiation, the photocatalytic degradation efficiencies of La-BOS-1, La-BOS-2, La-BOS-3, La-BOS-4, and La-BOS-5 were 66.8%, 76.5%, 74.1%, 73.6%, and 81.7%, respectively. Similarly, the TC degradation efficiency of BOS photocatalysts doped with cerium ions was significantly enhanced, reaching 70.3% after 240 minutes of UV irradiation. In contrast, the catalytic performance of cobalt- and iron-doped Bi2O2S requires activation of peroxymonosulfate (PMS) or the synergistic use of light and PMS to generate active species such as sulfate and superoxide radicals to degrade pollutants. Compared with the prior art, the catalyst prepared by the present invention does not require the addition of peroxymonosulfate compounds. The Bi2O2S doped with lanthanum or cerium metal ions improves the photogenerated carrier separation efficiency of the material under light-only conditions by utilizing the unique electronic structure of lanthanum or cerium ions to generate more superoxide radicals and singlet oxygen active substances, thereby promoting the degradation of pollutants.

[0081] In summary, the present invention successfully prepared pure-phase Bi2O2S and lanthanum or cerium metal ion-doped Bi2O2S catalysts using a simple hydrothermal method. Bi2O2S doped with lanthanum or cerium metal ions exhibits better photocatalytic performance than pure-phase Bi2O2S, which can be attributed to: first, the defect energy levels formed by the doping of lanthanum or cerium ions change the positions of the valence band and conduction band, making it easier to excite the generation of photogenerated electron-hole pairs and then form superoxide radicals with dissolved oxygen molecules, further forming singlet oxygen; second, the doped lanthanum or cerium ions have a unique electronic structure that can effectively capture photogenerated electrons, thereby improving the separation efficiency of the photogenerated electron-hole pairs of Bi2O2S and increasing the yield of singlet oxygen. Therefore, doping with rare earth metal ions (lanthanum, cerium) is an effective measure to improve the photocatalytic performance of Bi2O2S.

[0082] 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 the technical solutions. Those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present invention that do not depart from the purpose and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing rare earth metal ion-doped bismuth oxysulfide, characterized in that: The specific steps include: Step 1: Prepare an aqueous solution of bismuth nitrate pentahydrate, add thiourea to the solution, and stir to fully react; the molar ratio of bismuth nitrate pentahydrate to thiourea is (1.9-2.2):1; Step 2: slowly adding lithium hydroxide monohydrate to the solution obtained in step 1 and stirring until a reddish-brown precipitate is formed; the concentration of lithium hydroxide monohydrate in the solution obtained in step 1 is 1.5 to 2.5 mol / L; Step 3: adding a hydrated nitrate of a rare earth metal to the product obtained in step 2, and stirring to fully mix; wherein the molar ratio of the rare earth metal ion to the bismuth ion is (0.0125-0.1):1; Step 4: subjecting the mixture of step 3 to a hydrothermal reaction; the hydrothermal reaction is carried out at a constant temperature of 180-220° C. for 5-7 hours; Step 5: After the reaction in step 4 is completed, the precipitate is washed and dried multiple times to obtain the rare earth metal ion-doped bismuth oxysulfide.

2. The method for preparing rare earth metal ion-doped bismuth oxysulfide according to claim 1, wherein: The hydrated nitrate of the rare earth metal includes one of lanthanum nitrate hexahydrate and cerium nitrate hexahydrate.

3. An application of rare earth metal ion-doped bismuth oxysulfide, characterized in that: The rare earth metal ion-doped bismuth oxysulfide prepared by the preparation method according to any one of claims 1 to 2 is used as a photocatalyst.

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