Method for preparing nanoscale porous vanadium-doped bismuth oxide and photoanode

Abstract

The present disclosure relates to a preparation method of a nano-porous doped bismuth vanadate and a photoactive electrode, and relates to the technical field of doped bismuth vanadate preparation. The method comprises: 1. obtaining a first solution: obtaining a first citric acid solution, adding a bismuth source, a lanthanum source and a molybdenum source to obtain the first solution; the amount of substance of citric acid is N, and the amounts of substance of bismuth element, lanthanum element and molybdenum element are x, y and z respectively, so that N:(x+y+z)=(1.5-4):1; obtaining a second solution: obtaining a second citric acid solution and adding a vanadium source to obtain the second solution; the amount of substance of vanadium element is A, so that x:y:z:A=(6-9):(0.5-2):(0.5-2):10, and x+y+z=A; 2. adding the second solution to the first solution in batches to obtain a third solution; 3. adjusting the pH value of the third solution to 4-8 and drying; calcining the dried product to obtain the nano-porous doped bismuth vanadate.

Description

Technical Field

[0001] This disclosure relates to the field of bismuth vanadate semiconductor material preparation technology, and more specifically, to a method for preparing nanoscale porous doped bismuth vanadate and a photosensitive electrode. Background Technology

[0002] A biosensor is a special type of sensor that uses bioactive substances as sensitive units to capture analytes and converts changes in analyte concentration into changes in signal, thereby achieving quantitative detection of the target substance. Biosensors are high-performance detection products that integrate modern biotechnology and advanced electronic technology. After more than 50 years of development, biosensors are now a product of the integration and permeation of multiple disciplines such as chemistry, physics, biology, and electronics. Biosensors have advantages such as miniaturization, ease of operation, high sensitivity, and fast response speed, and are widely used in many fields such as chemical engineering, pharmaceuticals, food, clinical medicine, and environmental monitoring.

[0003] BiVO4 (bismuth vanadate) is a commonly used photoelectric anode semiconductor material. Due to its advantages such as small band gap, favorable band edge position, low initial potential, high theoretical catalytic efficiency, and good chemical stability, it is widely used in photocatalysis, photoelectric biosensing, and other fields. However, its low photogenerated carrier migration rate and short hole transport distance can lead to severe hole-electron recombination, which seriously affects the practical application performance of BiVO4 semiconductors.

[0004] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a method for preparing nanoporous doped bismuth vanadate and a photosensitive electrode. The method prepares nanoporous doped bismuth vanadate, increases the specific surface area of ​​the doped bismuth vanadate photosensitive material, and improves the testing efficiency of the electrode prepared by the photosensitive material.

[0006] According to the first aspect of this disclosure, a method for preparing nanoscale porous doped bismuth vanadate is provided, comprising the following steps:

[0007] S1. Obtain the first solution and the second solution;

[0008] Obtaining the first solution includes:

[0009] A first citric acid solution is obtained, wherein the first citric acid solution is a nitric acid solution containing citric acid; a bismuth source, a lanthanum source, and a molybdenum source are added to the first citric acid solution to obtain a first solution;

[0010] Wherein, the amount of citric acid in the first citric acid solution is N, the amount of bismuth in the bismuth source is x, the amount of lanthanum in the lanthanum source is y, and the amount of molybdenum in the molybdenum source is z, then N:(x+y+z)=(1.5~4):1;

[0011] Obtaining the second solution includes:

[0012] A second citric acid solution is obtained, which is a nitric acid solution containing dissolved citric acid; a vanadium source is added to the second citric acid solution to obtain a second solution.

[0013] Wherein, the amount of vanadium in the vanadium source is A, then x:y:z:A=(6~9):(0.5~2):(0.5~2):10, and x+y+z=A;

[0014] S2. Add the second solution to the first solution in batches to obtain the third solution;

[0015] S3. Adjust the pH value of the third solution to 4-8 and dry it; calcine the dried product to obtain lanthanum and molybdenum co-doped nanoporous bismuth vanadate.

[0016] In one exemplary embodiment of this disclosure, in step S1, the molar ratio of bismuth, lanthanum, and molybdenum is 8:1:1.

[0017] In an exemplary embodiment of this disclosure, in step S1, the bismuth source is Bi(NO3)3·5H2O, the lanthanum source is La(NO3)3·6H2O, the molybdenum source is (NH4)2MoO4·4H2O, and the vanadium source is NH4VO3.

[0018] In one exemplary embodiment of this disclosure, in step S3, the pH value of the third solution is adjusted to pH=7 using ammonia water.

[0019] In one exemplary embodiment of this disclosure, in step S3, the drying temperature is 90–120°C.

[0020] In one exemplary embodiment of this disclosure, in step S3, the calcination is carried out in a muffle furnace, air is introduced into the muffle furnace, the calcination temperature is 400-800°C, and the calcination time is 3-6 hours.

[0021] In one exemplary embodiment of this disclosure, in step S1, the volume fraction of the nitric acid solution is 10-30%.

[0022] According to a second aspect of this disclosure, a method for preparing nanoscale porous doped bismuth vanadate is provided, comprising the following steps:

[0023] S1. Obtain the fourth and fifth solutions;

[0024] Obtaining the fourth solution includes:

[0025] A third citric acid solution is obtained, wherein the third citric acid solution is a nitric acid solution containing citric acid; a bismuth source and a lanthanum source are added to the third citric acid solution to obtain a fourth solution;

[0026] Wherein, the amount of citric acid in the third citric acid solution is N, the amount of bismuth in the bismuth source is x, and the amount of lanthanum in the lanthanum source is y, then N:(x+y)=(1.5~4):1;

[0027] Obtaining the fifth solution includes:

[0028] A fourth citric acid solution is obtained, wherein the fourth citric acid solution is a nitric acid solution containing dissolved citric acid; a vanadium source is added to the fourth citric acid solution to obtain a fifth solution;

[0029] Wherein, the amount of vanadium in the vanadium source is A, then x:y = (6~9):(0.5~2), and x+y = A;

[0030] S2. Add the fifth solution to the fourth solution in batches to obtain the sixth solution;

[0031] S3. Adjust the pH value of the sixth solution to 4-8 and dry it; calcine the dried product to obtain lanthanum-doped nanoporous bismuth vanadate.

[0032] According to a third aspect of this disclosure, a method for preparing nanoscale porous doped bismuth vanadate is provided, comprising the following steps:

[0033] S1. Obtain the seventh and eighth solutions;

[0034] Obtaining the seventh solution includes:

[0035] A fifth citric acid solution is obtained, wherein the fifth citric acid solution is a nitric acid solution containing citric acid; a bismuth source and a molybdenum source are added to the fifth citric acid solution to obtain a seventh solution;

[0036] Wherein, the amount of citric acid in the fifth citric acid solution is N, the amount of bismuth in the bismuth source is x, and the amount of molybdenum in the molybdenum source is z, then N:(x+z)=(1.5~4):1;

[0037] Obtaining the eighth solution includes:

[0038] A sixth citric acid solution is obtained, wherein the sixth citric acid solution is a nitric acid solution containing citric acid; a vanadium source is added to the sixth citric acid solution to obtain an eighth solution;

[0039] Wherein, the amount of vanadium in the vanadium source is A, then x:z = (6~9):(0.5~2), and x+z = A;

[0040] S2. Add the eighth solution to the seventh solution in batches to obtain the ninth solution;

[0041] S3. Adjust the pH value of the ninth solution to 4-8 and dry it; calcine the dried product to obtain molybdenum-doped nanoporous bismuth vanadate.

[0042] According to a fourth aspect of this disclosure, a photosensitive electrode is provided, comprising bismuth vanadate doped with nanoscale pores prepared by the above-described preparation method.

[0043] This disclosure discloses a method for preparing nanoscale porous doped bismuth vanadate using a citric acid-sol-gel method. The preparation process does not use harmful organic reagents and has a short preparation cycle. Electrodes prepared using this La and / or Mo-doped BiVO4 composite material, based on its multi-nanoporous structure, increase the effective contact area with the analyte. Simultaneously, it reduces the recombination of photogenerated carriers and lowers the recombination rate of electrons and holes, thus improving testing performance. Therefore, this preparation method is simple, convenient, environmentally friendly, and suitable for large-scale production.

[0044] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0045] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0046] Figure 1 This is a scanning electron microscope (SEM) image of an LM-BVO composite semiconductor material in one embodiment of the present disclosure; wherein (a) and (b) are SEM images at two different resolutions.

[0047] Figure 2 X-ray diffraction patterns of LM-BVO composite semiconductor materials and BVO semiconductor materials are shown in some embodiments of this disclosure.

[0048] Figure 3LSV curves of LM-BVO composite semiconductor materials and BVO semiconductor materials are shown in some embodiments of this disclosure.

[0049] Figure 4 The switching characteristic curves of LM-BVO composite semiconductor materials and BVO semiconductor materials are shown in some embodiments of this disclosure.

[0050] Figure 5 The AC impedance spectra of LM-BVO composite semiconductor materials and BVO semiconductor materials are shown in some embodiments of this disclosure. Detailed Implementation

[0051] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore their detailed description will be omitted.

[0052] The terms “a,” “the,” and “the” are used to indicate the existence of one or more elements / components / etc.; the terms “including” and “having” are used to indicate an open-ended inclusion and to mean that there may be other elements / components / etc. in addition to the listed elements / components / etc.; the terms “first,” “second,” and “third,” etc., are used only as markers and are not a limitation on the number of objects.

[0053] This disclosure provides a method for preparing nanoscale porous doped bismuth vanadate to prepare lanthanum and molybdenum co-doped bismuth vanadate (La / Mo-BiVO4). The preparation method includes the following steps: S1, obtaining a first solution and a second solution.

[0054] The process of obtaining the first solution includes: obtaining a first citric acid solution, wherein the first citric acid solution is a nitric acid solution in which citric acid is dissolved; adding a bismuth source, a lanthanum source, and a molybdenum source to the first citric acid solution, and stirring until the bismuth source, lanthanum source, and molybdenum source are completely dissolved to obtain the first solution.

[0055] In the first citric acid solution, the amount of citric acid is N; the amount of bismuth in the bismuth source is x; the amount of lanthanum in the lanthanum source is y; and the amount of molybdenum in the molybdenum source is z. Therefore, N:(x+y+z)=(1.5~4):1. In the citric acid-sol-gel method (Pechini method), citric acid complexes with metal ions to form a complex, resulting in uniform distribution and fixation of each metal ion at the molecular level, reducing the segregation phenomenon caused by uneven mixing of bismuth, lanthanum, and molybdenum ions. The amount of citric acid is greater than the sum of the amounts of bismuth, lanthanum, and molybdenum ions, so that in the subsequent calcination stage, the citric acid decomposes at high temperature, causing a large number of nanoscale pores to form in lanthanum and molybdenum co-doped bismuth vanadate. This increases the specific surface area of ​​the lanthanum and molybdenum co-doped bismuth vanadate, improving the contact sites and contact area between the lanthanum and molybdenum co-doped bismuth vanadate as an electrode and the analyte, thereby improving the testing performance and efficiency. For example, the molar ratio of each metal ion (bismuth ion, lanthanum ion, molybdenum ion) to citric acid in the first citric acid solution can be 1:1.5, or 1:2, or 1:2.5, or 1:2.8, or 1:3.1, or 1:3.5, or 1:4, etc.

[0056] The process of obtaining the second solution includes: obtaining a second citric acid solution, wherein the second citric acid solution is a nitric acid solution in which citric acid is dissolved; and adding a vanadium source to the second citric acid solution to obtain the second solution.

[0057] In this context, the amount of bismuth in the bismuth source is x, the amount of lanthanum in the lanthanum source is y, the amount of molybdenum in the molybdenum source is z, and the amount of vanadium in the vanadium source is A. Therefore, x:y:z:A = (6–9):(0.5–2):(0.5–2):10, and x + y + z = A. Further, the molar ratio of bismuth, lanthanum, molybdenum, and vanadium is x:y:z:A = 8:1:1:10. For example, the molar ratio of bismuth, lanthanum, molybdenum, and vanadium can also be 9:0.5:0.5:10, 8.5:0.5:1:10, 8:1.5:0.5:10, 7.5:1.5:1:10, 7:1.5:1.5:10, 7:2:1:10, 6.5:2:1.5:10, 6:2:2:10, etc.

[0058] In one example, the concentrations of citric acid in the first and second citric acid solutions are the same, as are the volume fractions of nitric acid solution. Thus, the total citric acid can be weighed and dissolved in nitric acid solution to prepare a total citric acid solution. When preparing the first and second solutions, the first and second citric acid solutions are measured out according to the required amounts. Alternatively, the first and second citric acid solutions can be prepared separately. The inclusion of nitric acid solution in the first and second citric acid solutions facilitates the dissolution of various metal ions during operation; furthermore, nitrate ions can generate gas during the calcination stage and be released, thus avoiding the introduction of other impurities and the addition of steps to the preparation process of bismuth vanadate doped vanadate.

[0059] S2. Add the second solution to the first solution in batches, stir to dissolve, and obtain the third solution.

[0060] S3. Adjust the pH of the third solution to 4-8 and then dry it. Within the pH range of 4-8, the third solution will become a gel after drying. Since bismuth, lanthanum, and molybdenum are all complexed with citric acid, the dispersion of these metal ions is good, resulting in a product with high uniformity and small particle size. For example, the pH of the third solution can be pH=4, pH=4.5, pH=5, pH=5.5, pH=6, pH=6.5, pH=7, pH=7.5, or pH=8.

[0061] S4. Calcine the dried product from step S3 to obtain lanthanum and molybdenum co-doped nanoporous bismuth vanadate (La / Mo-BiVO4, abbreviated as LM-BVO).

[0062] This embodiment employs the citric acid-sol-gel method to prepare nanoscale porous La / Mo-BiVO4. Bismuth, lanthanum, molybdenum, and vanadium sources are used in the aforementioned molar ratio to prepare the La / Mo-BiVO4 composite semiconductor material. The preparation process does not use harmful organic reagents and has a short preparation cycle. The co-doping of lanthanum and molybdenum in bismuth vanadate results in high stability of the prepared composite semiconductor material. Electrodes prepared using the nanoscale porous La / Mo-BiVO4 composite semiconductor material, based on the multi-nanoporous structure, increase the effective contact area with the analyte. Simultaneously, it reduces the recombination of photogenerated carriers and the recombination rate of electrons and holes, improving testing performance and efficiency. Therefore, this method is simple, easy to operate, environmentally friendly, and suitable for large-scale production, showing promising application prospects.

[0063] In one embodiment of this disclosure, in step S4, the dried product is calcined, which can be carried out in a muffle furnace. For example, air is introduced into the muffle furnace, and the calcination temperature is 400–800°C for 3–6 hours. For example, it can be calcined at 400℃ for 4 hours; or at 400℃ for 5 hours; or at 450℃ for 3 hours; or at 500℃ for 6 hours; or at 600℃ for 4 hours; or at 700℃ for 5 hours; or at 800℃ for 3 hours; or at 800℃ for 5 hours; or first calcined at 400℃ for 2 hours, then calcined at 600℃ for 2 hours; or first calcined at 500℃ for 1 hour, then calcined at 700℃ for 2 hours; or first calcined at 600℃ for 2 hours, then calcined at 800℃ for 2 hours; or first calcined at 400℃ for 2 hours, then calcined at 700℃ for 3 hours, etc.

[0064] In one embodiment of this disclosure, the bismuth source is Bi(NO3)3·5H2O, the lanthanum source is La(NO3)3·6H2O, the molybdenum source is (NH4)2MoO4·4H2O, and the vanadium source is NH4VO3. In this embodiment, the bismuth and lanthanum sources are nitrates of bismuth and lanthanum ions, the molybdenum source uses ammonium molybdate, and the vanadium source uses ammonium metavanadate. Thus, during the subsequent calcination process, nitrogen ions can be generated as gas and discharged under high-temperature reaction conditions, ensuring that no other impurities are introduced into the final product, simplifying experimental operations, saving product preparation time, and consequently saving time and economic costs. It is understood that other bismuth, lanthanum, molybdenum, and vanadium sources can also be used, but an impurity removal process needs to be added during the preparation process.

[0065] In one example, ammonia is used to adjust the pH of the third solution. Using ammonia for pH adjustment has two advantages: firstly, ammonia is weakly alkaline and will not disrupt the entire reaction system; secondly, it will not introduce other impurities into the final product. Using other alkaline solutions to adjust the pH might introduce other components, increasing the impurity removal steps in the preparation of nanoscale porous lanthanum-molybdenum co-doped bismuth vanadate, thus increasing costs.

[0066] Furthermore, the pH of the third solution was adjusted to pH=7.

[0067] In one example, the drying described in step S3 can be oven drying, with the drying temperature being 90–120°C. For example, the drying temperature can be 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C.

[0068] In one embodiment of this disclosure, in step S1, the volume fraction of the nitric acid solution is 10% to 30%. Nitric acid within this concentration range can better dissolve bismuth, lanthanum, molybdenum, and vanadium sources. For example, the volume fraction of the nitric acid solution can be 10%, 15%, 20%, 25%, or 30%.

[0069] This disclosure also provides a method for preparing nanoscale porous doped bismuth vanadate to prepare lanthanum-doped bismuth vanadate (La-BiVO4), the preparation method comprising the following steps:

[0070] S1. Obtain the fourth and fifth solutions.

[0071] Obtaining the fourth solution includes: obtaining a third citric acid solution, wherein the third citric acid solution is a nitric acid solution in which citric acid is dissolved. A bismuth source and a lanthanum source are added to the third citric acid solution to obtain the fourth solution. Wherein, the amount of citric acid in the third citric acid solution is N, the amount of bismuth in the bismuth source is x, and the amount of lanthanum in the lanthanum source is y, then N:(x+y)=(1.5~4):1.

[0072] Obtaining the fifth solution includes: obtaining a fourth citric acid solution, wherein the fourth citric acid solution is a nitric acid solution in which citric acid is dissolved. A vanadium source is added to the fourth citric acid solution to obtain the fifth solution. Wherein, the amount of vanadium in the vanadium source is A, then x:y = (6-9):(0.5-2), and x + y = A.

[0073] S2. Add the fifth solution to the fourth solution in batches to obtain the sixth solution.

[0074] S3. Adjust the pH value of the sixth solution to 4-8 and dry it; calcine the dried product to obtain lanthanum-doped nanoporous bismuth vanadate.

[0075] In this embodiment, single-doped La-BiVO4 is prepared without adding a molybdenum source in step S1. The selection of other lanthanum sources, bismuth sources, and reagents is basically the same as that for the preparation of LM-BVO, and will not be repeated here.

[0076] This disclosure also provides a method for preparing nanoscale porous doped bismuth vanadate to prepare molybdenum-doped bismuth vanadate (Mo-BiVO4), the preparation method comprising the following steps:

[0077] S1. Obtain the seventh and eighth solutions.

[0078] Obtaining the seventh solution includes: obtaining a fifth citric acid solution, wherein the fifth citric acid solution is a nitric acid solution in which citric acid is dissolved. A bismuth source and a molybdenum source are added to the fifth citric acid solution to obtain the seventh solution. Wherein, the amount of citric acid in the fifth citric acid solution is N, the amount of bismuth in the bismuth source is x, and the amount of molybdenum in the molybdenum source is z, then N:(x+z)=(1.5~4):1.

[0079] Obtaining the eighth solution includes: obtaining a sixth citric acid solution, wherein the sixth citric acid solution is a nitric acid solution containing dissolved citric acid. A vanadium source is added to the sixth citric acid solution to obtain the eighth solution. Wherein, the amount of vanadium in the vanadium source is A, then x:z = (6~9):(0.5~2), and x+z = A;

[0080] S2. Add the eighth solution to the seventh solution in batches to obtain the ninth solution.

[0081] S3. Adjust the pH value of the ninth solution to 4-8 and dry it; calcine the dried product to obtain molybdenum-doped nanoporous bismuth vanadate.

[0082] In this embodiment, single-doped Mo-BiVO4 is prepared without the addition of a lanthanum source in step S1. The selection of other molybdenum sources, bismuth sources, and other reagents is basically the same as that for the preparation of LM-BVO, and will not be repeated here.

[0083] This disclosure also provides a photosensitive electrode comprising nanoscale porous doped bismuth vanadate prepared by any of the methods described in the above-described preparation method embodiments. This photosensitive electrode can be used as an electrode for a biosensor or other types of sensors. Because this photosensitive electrode possesses any of the nanoscale porous doped bismuth vanadate prepared according to the corresponding embodiments of the above-described preparation method, its porous nature increases the contact area of ​​the photosensitive electrode and improves testing performance. Simultaneously, the lanthanum and molybdenum co-doped bismuth vanadate electrode reduces the recombination of photogenerated carriers and is more effective in separating photogenerated electron-hole pairs, resulting in a faster charge migration rate on the electrode surface, a lower electron-hole recombination rate, and superior performance.

[0084] The following examples further illustrate the preparation method of nanoscale porous doped bismuth vanadate and verify the characteristics of nanoscale porous doped bismuth vanadate and the photosensitive electrode prepared therefrom.

[0085] Example 1

[0086] 9.6 g of citric acid was dissolved in 20% (v / v) dilute nitric acid to obtain a first citric acid solution. 4.85 g of Bi(NO3)3·5H2O, 0.433 g of La(NO3)3·6H2O, and 1.236 g of (NH4)2MoO4·4H2O were added to the first citric acid solution, and the mixture was stirred until Bi(NO3)3·5H2O, La(NO3)3·6H2O, and (NH4)2MoO4·4H2O were fully dissolved to obtain a first solution.

[0087] 9.6 g of citric acid was dissolved in 20% (v / v) dilute nitric acid to obtain a second citric acid solution. 1.404 g of NH₄VO₃ was added to the second citric acid solution and stirred until fully dissolved to obtain a second solution.

[0088] The second solution is added to the first solution in batches and stirred to obtain the third solution.

[0089] The pH of the third solution was adjusted to 7 using ammonia water, and then dried at 120℃. The dried product was transferred to a muffle furnace and calcined at 600℃ for 4 hours to obtain a lanthanum and molybdenum co-doped bismuth vanadate with nanoscale pores, namely La / Mo-BiVO4 (LM-BVO) composite semiconductor material.

[0090] Example 2

[0091] Add 4.85g of Bi(NO3)3·5H2O to 20% dilute nitric acid, and then stir to fully dissolve Bi(NO3)3·5H2O to obtain the tenth solution;

[0092] 1.404 g of NH4VO3 was added to 20% (v / v) dilute nitric acid, and then stirred until the NH4VO3 was completely dissolved to obtain solution 11. Solution 11 was added in portions to solution 10, and stirred to obtain solution 12.

[0093] The pH of the 12-dioxanone solution was adjusted to pH=7 with ammonia, and then dried at 120℃. The dried product was transferred to a muffle furnace and calcined at 600℃ for 4 hours to obtain BiVO4 (BVO) semiconductor material.

[0094] Example 3

[0095] 9.6 g of citric acid was dissolved in 20% (v / v) dilute nitric acid to obtain a third citric acid solution. 4.85 g of Bi(NO3)3·5H2O and 0.433 g of La(NO3)3·6H2O were added to the third citric acid solution, and the mixture was stirred until Bi(NO3)3·5H2O and La(NO3)3·6H2O were fully dissolved to obtain a fourth solution.

[0096] 9.6 g of citric acid was dissolved in 20% dilute nitric acid to obtain a fourth citric acid solution. 1.404 g of NH₄VO₃ was added to the fourth citric acid solution and stirred until fully dissolved to obtain a fifth solution.

[0097] The fifth solution was added to the fourth solution in batches and stirred to obtain the sixth solution.

[0098] The pH of the sixth solution was adjusted to 7 using ammonia water, and then dried at 120℃. The dried product was transferred to a muffle furnace and calcined at 600℃ for 4 hours to obtain lanthanum-doped nanoporous bismuth vanadate, i.e., La-BiVO4 composite semiconductor material.

[0099] Upon testing, the La-BiVO4 composite semiconductor material obtained in this embodiment has nanopores with a structure similar to that of the LM-BVO composite semiconductor material obtained in Example 1.

[0100] Example 4

[0101] 9.6 g of citric acid was dissolved in 20% (v / v) dilute nitric acid to obtain the fifth citric acid solution. 4.85 g of Bi(NO3)3·5H2O and 1.236 g of (NH4)2MoO4·4H2O were added to the fifth citric acid solution, and the mixture was stirred until Bi(NO3)3·5H2O and (NH4)2MoO4·4H2O were fully dissolved to obtain the seventh solution.

[0102] 9.6 g of citric acid was dissolved in 20% dilute nitric acid to obtain the sixth citric acid solution. 1.404 g of NH₄VO₃ was added to the sixth citric acid solution and stirred until fully dissolved to obtain the eighth solution.

[0103] The eighth solution was added to the seventh solution in batches and stirred to obtain the ninth solution.

[0104] The pH of the ninth solution was adjusted to 7 using ammonia water, and then dried at 120℃. The dried product was transferred to a muffle furnace and calcined at 600℃ for 4 hours to obtain molybdenum-doped nanoporous bismuth vanadate, i.e., Mo-BiVO4 composite semiconductor material.

[0105] Upon testing, the Mo-BiVO4 composite semiconductor material obtained in this embodiment has nanopores with a structure similar to that of the LM-BVO composite semiconductor material obtained in Example 1.

[0106] Results analysis:

[0107] I. Comparison of properties between the LM-BVO material obtained in Example 1 and the BVO material obtained in Example 2

[0108] (1) Analysis of scanning electron microscopy results of LM-BVO materials

[0109] like Figure 1 The image shows a scanning electron microscope (SEM) image of the LM-BVO material prepared in Example 1. Images (a) and (b) are SEM images at two different resolutions. As can be seen from the low-resolution image (a), the LM-BVO material prepared in Example 1 is in bulk form. As can be seen from the high-resolution image (b), the bulk LM-BVO material has a loose, porous structure. This loose, porous structure can increase the specific surface area of ​​the material, thereby increasing the contact sites between the electrode prepared from this material and the analyte, and improving the material's testing performance.

[0110] (2) Analysis of X-ray diffraction patterns of LM-BVO and BVO materials

[0111] like Figure 2 The images show the X-ray diffraction (XRD) patterns of the LM-BVO material prepared in Example 1 and the BVO material prepared in Example 2. Figure 2 As can be seen from the X-ray diffraction patterns of LM-BVO and BVO materials, the peaks at 2θ = 18.6°, 28.6°, 30.9°, 34.5°, 39.7°, 45.5°, and 47.0° correspond to (101), (112), (004), (200), (114), (203), and (204) respectively. The positions of these peaks are consistent with the peak positions of monoclinic bismuth vanadate on the standard XRD card (JCPDS No. 48-0744).

[0112] II. Photoelectric performance testing of the LM-BVO electrode prepared from the LM-BVO composite semiconductor material obtained in Example 1 and the BVO electrode prepared from the BVO semiconductor material obtained in Example 2.

[0113] LM-BVO can be used as a photocatalytic semiconductor material to fabricate photosensitive electrodes. For example, these photosensitive electrodes can be used in biosensors. The mechanism of action of a biosensor is as follows: the non-equilibrium charge carriers generated after the photosensitive electrode film absorbs photons oxidize or reduce the target material specifically trapped on its surface, achieving a depolarization reaction and thus inducing a change in photocurrent density. Since there is a linear relationship between the photocurrent density and the target material concentration, quantitative analysis of the target material can be achieved. The photoelectric performance of LM-BVO and BVO electrodes is tested below using Laval curves, photocurrent response, and electrochemical impedance spectroscopy verification experiments.

[0114] (1) Analysis of LSV curve results of LM-BVO electrode and BVO electrode

[0115] like Figure 3 As shown, at 1.23V vs. Ag / AgCl, the photocurrent density of the electrode prepared using LM-BVO obtained in Example 1 can reach 4.05 mA cm⁻¹. -2 Compared to the electrode prepared using BVO obtained in Example 2, the increase was 0.38 mA cm⁻¹. -2 The above results indicate that the performance of the composite semiconductor material LM-BVO electrode is significantly improved compared with that of the pure BVO electrode after doping with La and Mo. This La and Mo doping coupling mode reduces the recombination of photogenerated carriers, and the porous nature of the composite semiconductor material increases the contact area of ​​the LM-BVO electrode.

[0116] (2) Analysis of the switching characteristic curves of LM-BVO electrode and BVO electrode

[0117] The switching characteristic curve is used to detect the sensitivity of the LM-BVO electrode to light. A traditional three-electrode system is used, with 0.5M Na2SO4 solution as the electrolyte, a time of 160s, backlighting, and an applied bias voltage of 0.62V vs. Ag / AgCl electrode.

[0118] like Figure 4 As shown, the current is very low in the dark, but rises sharply and responds very quickly when the light is switched on. This indicates that the LM-BVO electrode and the BVO electrode are highly sensitive to light, and repeated switching does not reduce their photosensitivity. Compared to the BVO electrode, the LM-BVO electrode has a larger photocurrent and higher carrier (photogenerated electrons and photogenerated holes) separation efficiency.

[0119] (3) Analysis of AC impedance characteristics of LM-BVO electrode and BVO electrode

[0120] The migration and separation properties of photogenerated carriers can be characterized by electrochemical impedance spectroscopy. The AC impedance (electrochemical impedance) characteristics were also tested using a three-electrode system, with the prepared LM-BVO electrode and BVO electrode serving as photoanodes, i.e., working electrodes. A saturated silver / silver chloride electrode served as the reference electrode, and a platinum sheet electrode served as the counter electrode. The parameters were set as follows: initial voltage was the open-circuit voltage, high frequency 100,000 Hz, low frequency 0.1 Hz, amplitude 20 mV, and 50 mL of 0.5 M Na₂SO₄ solution was added to the quartz electrolytic cell. The light source was a 300 W xenon lamp (model PLS-SXE300C) manufactured by Beijing Pofilai Co., Ltd.

[0121] In electrochemical impedance spectroscopy (EIS), the Nynquist plot is generally used for analysis to determine the impedance. The relative size of the arc radius in the Nyquist plot corresponds to the magnitude of the charge transfer resistance and the separation efficiency of photogenerated electron-hole pairs. That is, the smaller the arc radius, the smaller the impedance, and the faster the reaction rate at the electrode surface. In other words, the smaller the arc radius in the electrochemical impedance spectroscopy, the more efficient the separation of electrons and holes, and the faster the separation and transport of charges on the surface of the photocatalyst (LM-BVO), potentially resulting in better photoelectrocatalytic performance.

[0122] like Figure 5 After mathematical fitting of the electrochemical impedance spectroscopy (EIS) spectra shown, it can be seen that under visible light irradiation, the radius of the arc corresponding to the LM-BVO electrode in the Nynquist plot of the EIS is smaller than that corresponding to the BVO electrode (all comparisons of Nynquist radii below are based on data fitting). This indicates that the La- and Mo-doped bismuth vanadate electrodes are more effective in separating photogenerated electron-hole pairs and have better photocatalytic performance. In other words, the charge migration rate on the surface of the LM-BVO electrode is faster, and the recombination rate of electrons and holes is lower.

[0123] It should be noted that although the steps of the preparation method of nanoscale porous lanthanum-molybdenum co-doped bismuth vanadate in this disclosure are described in a specific order in the accompanying drawings, this does not require or imply that these steps must be performed in that specific order, or that all the steps shown must be performed to achieve the desired result. Additional or alternative steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0124] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

Claims

1. A method for preparing nanoscale porous doped bismuth vanadate, characterized in that, Includes the following steps: S1. Obtain the first solution and the second solution; Obtaining the first solution includes: A first citric acid solution is obtained, wherein the first citric acid solution is a nitric acid solution containing citric acid; a bismuth source, a lanthanum source, and a molybdenum source are added to the first citric acid solution to obtain a first solution; Wherein, the amount of citric acid in the first citric acid solution is N, the amount of bismuth in the bismuth source is x, the amount of lanthanum in the lanthanum source is y, and the amount of molybdenum in the molybdenum source is z, then N:(x+y+z)=(1.5~4):1, and the molar ratio of bismuth, lanthanum and molybdenum is 8:1:1; Obtaining the second solution includes: A second citric acid solution is obtained, which is a nitric acid solution containing dissolved citric acid; a vanadium source is added to the second citric acid solution to obtain a second solution. Wherein, the amount of vanadium in the vanadium source is A, then x:y:z:A = (6~9):(0.5~2):(0.5~2):10, and x+y+z=A; S2. Add the second solution to the first solution in batches to obtain the third solution; S3. Adjust the pH of the third solution to 7 using ammonia water and dry it; calcine the dried product to obtain lanthanum and molybdenum co-doped nanoporous bismuth vanadate; wherein the calcination is carried out in a muffle furnace, air is introduced into the muffle furnace, the calcination temperature is 400~800℃, and the calcination time is 3~6 h.

2. The method for preparing nanoscale porous doped bismuth vanadate according to claim 1, characterized in that, In step S1, the bismuth source is Bi(NO3)3. 5H2O, wherein the lanthanum source is La(NO3)3 6H2O, wherein the molybdenum source is (NH4)2MoO4 4H2O; the vanadium source is NH4VO3.

3. The method for preparing nanoscale porous doped bismuth vanadate according to claim 1, characterized in that, In step S3, the drying temperature is 90~120℃.

4. The method for preparing nanoscale porous doped bismuth vanadate according to claim 1, characterized in that, In step S1, the volume fraction of the nitric acid solution is 10-30%.

5. A photosensitive electrode, characterized in that, This includes bismuth vanadate doped with nanoscale pores prepared by any one of the preparation methods of claims 1-4.

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