Monoclinic-phase molybdenum-doped bismuth vanadate photoelectrode and preparation method and application thereof

Abstract

The invention discloses a monoclinic-phase molybdenum-doped bismuth vanadate photoelectrode and a preparation method and application thereof, and belongs to the technical field of photoelectrochemical degradation of pollutants and hydrogen production. The monoclinic-phase molybdenum-doped bismuth vanadate photoelectrode is synthesized through a hydrothermal-annealing method, the monoclinic-phase molybdenum-doped bismuth vanadate photoelectrode stands in a sodium hydroxide solution before a tetragonal phase is converted into a monoclinic phase, then the monoclinic-phase molybdenum-doped bismuth vanadate photoelectrode is coated with a molybdenum salt solution, finally phase transformation is achieved through annealing, and the monoclinic-phase molybdenum-doped bismuth vanadate photoelectrode is obtained. The photoelectrode has a columnar structure composed of nanoparticles, has a large specific surface area, is beneficial to carrier separation, and has better performance of photoelectrochemically degrading amino acid and producing hydrogen. And the photoelectrochemical hydrogen production performance of the photoelectrode can be greatly improved and the degradation of the amino acid can be completed by dissolving the amino acid with a certain concentration in water.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoelectrochemical degradation of pollutants and hydrogen production, and specifically relates to a monoclinic molybdenum-doped bismuth vanadate photoelectrode and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Photoelectrochemical degradation of pollutants and hydrogen production is a relatively ideal method, mainly because: (1) the external energy source of photoelectrochemical technology is only solar energy, which is a pollution-free renewable energy; (2) the photoelectrochemical degradation of pollutants and hydrogen production technology is relatively simple and can be produced on both small and large scales.

[0004] Existing technologies use molybdenum-doped bismuth vanadate as a photoelectrode for pollutant degradation and hydrogen production. However, the inventors discovered that this photoelectrode is only suitable for degrading rhodamine B and does not degrade amino acid pollutants. Furthermore, this photoelectrode has low energy conversion efficiency for rhodamine B degradation and requires use with g-C₃N₄. This significantly limits its pollutant degradation and hydrogen production efficiency, as well as its practical application. Summary of the Invention

[0005] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a monoclinic molybdenum-doped bismuth vanadate photoelectrode and its preparation method and application. The preparation method provided by the present invention can improve the photoelectrochemical performance of the monoclinic molybdenum-doped bismuth vanadate photoelectrode, further improve its efficiency in degrading amino acid pollutants and producing hydrogen, and reduce the required energy loss.

[0006] In order to achieve the above object, the technical solution of the present invention is: The first aspect of the present invention provides a method for preparing a monoclinic molybdenum-doped bismuth vanadate photoelectrode, comprising: Mixing bismuth salt, disodium ethylenediaminetetraacetic acid, vanadium salt, nitric acid, sodium hydroxide and water to obtain a precursor solution; placing the conductive glass in the precursor solution and performing a hydrothermal reaction to obtain a tetragonal bismuth vanadate photoelectrode; The tetragonal bismuth vanadate photoelectrode is placed in a sodium hydroxide solution, taken out, and then coated with a molybdenum salt solution on the surface. After coating, the photoelectrode is annealed to obtain a monoclinic molybdenum-doped bismuth vanadate photoelectrode.

[0007] In some embodiments of the present invention, in the precursor solution, the concentration of bismuth salt is 0.04-0.06 M, the concentration of disodium EDTA is 0.04-0.06 M, the concentration of vanadium salt is 0.04-0.06 M, the concentration of nitric acid is 1.9-2.1 M, and the concentration of sodium hydroxide is 0.9-1.1 M.

[0008] Preferably, in the precursor solution, the concentration of bismuth salt is 0.05 M, the concentration of disodium ethylenediaminetetraacetic acid is 0.05 M, the concentration of vanadium salt is 0.05 M, the concentration of nitric acid is 2 M, and the concentration of sodium hydroxide is 1 M.

[0009] Preferably, the bismuth salt includes any one of bismuth nitrate or its hydrate, bismuth chloride or its hydrate, preferably bismuth nitrate pentahydrate.

[0010] Preferably, the vanadium salt includes any one of sodium metavanadate, potassium metavanadate and ammonium metavanadate, preferably sodium metavanadate.

[0011] In some embodiments of the present invention, the hydrothermal reaction is carried out at a temperature of 170-190° C. and for a time of 15-21 h.

[0012] Preferably, the hydrothermal reaction temperature is 180° C. and the time is 18 h.

[0013] In some embodiments of the present invention, the concentration of the sodium hydroxide solution is 0.1-1 M, and the tetragonal bismuth vanadate photoelectrode is placed in the sodium hydroxide solution for 1-9 hours.

[0014] Preferably, the concentration of the sodium hydroxide solution is 0.3 M, and the tetragonal bismuth vanadate photoelectrode is placed in the sodium hydroxide solution for 3 h.

[0015] In some embodiments of the present invention, the concentration of the molybdenum salt solution is 0.04-0.06 M, and the molybdenum salt solution is coated on the surface of the tetragonal bismuth vanadate photoelectrode by spin coating at a spin coating rate of 700-900 rpm for 10-14 s.

[0016] Preferably, the concentration of the molybdenum salt solution is 0.05 M; the spin coating rate is 800 rpm, and the time is 13 s.

[0017] Preferably, the molybdenum salt includes any one of ammonium molybdate or its hydrate, sodium molybdate or its hydrate, potassium molybdate or its hydrate, preferably ammonium molybdate tetrahydrate.

[0018] In some embodiments of the present invention, the annealing temperature is 440-460° C. and the time is 110-130 min.

[0019] Preferably, the annealing temperature is 450° C. and the annealing time is 120 min.

[0020] The second aspect of the present invention provides a monoclinic molybdenum-doped bismuth vanadate photoelectrode, which is prepared by the above-mentioned preparation method.

[0021] In some embodiments of the present invention, the monoclinic molybdenum-doped bismuth vanadate photoelectrode includes conductive glass and molybdenum-doped bismuth vanadate nanorods grown in situ on the surface of the conductive glass.

[0022] Preferably, the thickness of the molybdenum-doped bismuth vanadate on the surface of the conductive glass is 1-1.5 μm.

[0023] Preferably, the molybdenum-doped bismuth vanadate nanorods have a length of 700-900 nm and a diameter of 350-400 nm.

[0024] The third aspect of the present invention provides a use of the above-mentioned monoclinic molybdenum-doped bismuth vanadate photoelectrode in the degradation of amino acids in water and / or hydrogen production.

[0025] Preferably, the amino acids include any one or more of natural amino acids and artificial amino polycarboxylic acids.

[0026] Preferably, the natural amino acids include any one or more of arginine, threonine and lysine.

[0027] Preferably, the artificial aminopolycarboxylic acid includes any one or more of ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid and N-β-hydroxyethylethylenediaminetriacetic acid.

[0028] A fourth aspect of the present invention provides a method for degrading amino acids and producing hydrogen using the above-mentioned monoclinic molybdenum-doped bismuth vanadate photoelectrode, comprising: The monoclinic molybdenum-doped bismuth vanadate photoelectrode is used as the working electrode, potassium borate buffer containing amino acids is used as the electrolyte, and a three-electrode system is adopted to degrade amino acids and produce hydrogen under the conditions of light and external bias.

[0029] In some embodiments of the present invention, the concentration of amino acids in the electrolyte is 0.01-4 M.

[0030] In some embodiments of the present invention, the bias voltage is ≥0.2 V, preferably 0.2-2 V.

[0031] In some embodiments of the present invention, the illumination includes illumination by sunlight.

[0032] The beneficial effects of the present invention are: The present invention synthesizes a monoclinic molybdenum-doped bismuth vanadate photoelectrode via a hydrothermal-annealing method. The photoelectrode is then placed in a sodium hydroxide solution before the tetragonal phase transforms to the monoclinic phase. A molybdenum salt solution is then applied, and the phase transition is finally achieved through annealing. This photoelectrode has a columnar structure composed of nanoparticles and a large specific surface area, which facilitates carrier separation, increases photocurrent density, and improves the efficiency of amino acid pollutant degradation and hydrogen production.

[0033] The synthesis method of the monoclinic molybdenum-doped bismuth vanadate electrode provided by the present invention is simple. By hydrothermal annealing, a monoclinic molybdenum-doped bismuth vanadate photoelectrode grown in situ on conductive glass can be obtained. The photoelectrode has a columnar structure composed of nanoparticles and has good photoelectrochemical degradation of amino acids and hydrogen production performance. And by dissolving a certain concentration of amino acids in water, the photoelectrochemical hydrogen production performance of the photoelectrode can be greatly improved and the degradation of amino acids can be completed. For example, at a potential of 1.00 V vs. RHE, 9 mA cm -2 current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0035] Figure 1 1 is a graph showing the relevant characterization tests of the monoclinic molybdenum-doped bismuth vanadate photoelectrodes obtained in Example 1 of the present invention and Comparative Example 1; wherein, a is a schematic diagram of the preparation process of the monoclinic molybdenum-doped bismuth vanadate photoelectrode, b is an SEM image of the M-BVO photoelectrode obtained in Comparative Example 1, c is an SEM image of the etched-M-BVO photoelectrode obtained in Example 1, d is a TEM image of the M-BVO photoelectrode obtained in Comparative Example 1, e is a TEM image of the etched-M-BVO photoelectrode obtained in Example 1, f is an HRTEM image of the etched-M-BVO photoelectrode obtained in Example 1, g is an HRTEM image of the etched-M-BVO photoelectrode obtained in Example 1, and h is a mapping image of the etched-M-BVO photoelectrode obtained in Example 1; Figure 2 SEM images of the tetragonal bismuth vanadate photoelectrode in Example 1 of the present invention before (a) and after (b) corrosion in a sodium hydroxide solution; Figure 3 1 is a graph showing the characterization of the monoclinic molybdenum-doped bismuth vanadate photoelectrodes obtained in Example 1 of the present invention and Comparative Example 1; wherein a is an XRD graph, b is a texture coefficient graph, c is a RAMAN graph, d is a DRS graph, e is a Tauc-plot graph, and f is a BET graph; Figure 4Related test spectra of the amino acid degradation and hydrogen production performance of the monoclinic molybdenum-doped bismuth vanadate photoelectrode obtained in Example 1 of the present invention and Comparative Example 1; wherein, a is an LSV diagram in a potassium borate buffer and a potassium borate buffer containing an amino acid, b is an LSV diagram in a potassium borate buffer and a potassium borate buffer containing arginine, threonine and lysine, c is an LSV diagram in a potassium borate buffer and a potassium borate buffer containing ethylenediaminetetraacetic acid, nitrilotriacetic acid, N-β-hydroxyethylethylenediaminetriacetic acid and diethylenetriaminepentaacetic acid, d is an ESCA diagram in a potassium borate buffer and a potassium borate buffer containing an amino acid, e is an IT diagram in a potassium borate buffer and a potassium borate buffer containing an amino acid, and f is a Faraday efficiency diagram when the IT test is performed in a potassium borate buffer containing an amino acid; Figure 5 These are LSV diagrams of the etched-M-BVO photoelectrode obtained in Example 1 of the present invention in potassium borate buffer solutions containing different concentrations of EDTA. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described 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 are within the scope of protection of the present invention. The present invention provides a method for preparing a monoclinic molybdenum-doped bismuth vanadate photoelectrode, comprising: Mixing bismuth salt, disodium ethylenediaminetetraacetic acid, vanadium salt, nitric acid, sodium hydroxide and water to obtain a precursor solution; placing the conductive glass in the precursor solution and performing a hydrothermal reaction to obtain a tetragonal bismuth vanadate photoelectrode; The tetragonal bismuth vanadate photoelectrode is placed in a sodium hydroxide solution, taken out, and then coated with a molybdenum salt solution on the surface. After coating, the photoelectrode is annealed to obtain a monoclinic molybdenum-doped bismuth vanadate photoelectrode.

[0037] It can be understood that during the hydrothermal reaction, tetragonal bismuth vanadate grows in situ on the surface of the conductive glass to obtain a tetragonal bismuth vanadate photoelectrode.

[0038] The present invention synthesizes a monoclinic molybdenum-doped bismuth vanadate photoelectrode via a hydrothermal-annealing method. The photoelectrode is then placed in a sodium hydroxide solution before the tetragonal phase transforms to the monoclinic phase. A molybdenum salt solution is then applied, and the phase transition is finally achieved through annealing. This photoelectrode has a columnar structure composed of nanoparticles and a large specific surface area, which facilitates carrier separation, increases photocurrent density, and improves the efficiency of amino acid pollutant degradation and hydrogen production.

[0039] The synthesis method of the monoclinic molybdenum-doped bismuth vanadate photoelectrode provided by the present invention is simple. A monoclinic molybdenum-doped bismuth vanadate photoelectrode grown in situ on conductive glass can be obtained by a hydrothermal-annealing method. The photoelectrode has a columnar structure composed of nanoparticles and has good photoelectrochemical degradation of amino acids and hydrogen production performance. By dissolving a certain concentration of amino acids in water, the photoelectrochemical hydrogen production performance of the photoelectrode can be greatly improved and the degradation of amino acids can be completed. For example, at a potential of 1.00V vs. RHE, 9 mA cm-1 can be achieved. -2 current density.

[0040] In certain embodiments of the present invention, the precursor solution comprises a bismuth salt concentration of 0.04-0.06 M, a disodium EDTA concentration of 0.04-0.06 M, a vanadium salt concentration of 0.04-0.06 M, a nitric acid concentration of 1.9-2.1 M, and a sodium hydroxide concentration of 0.9-1.1 M. In the precursor solution, excessively low or high concentrations of the bismuth salt, disodium EDTA, vanadium salt, nitric acid, and sodium hydroxide may result in uneven or incomplete growth of bismuth vanadate on the conductive glass. Within this concentration range, bismuth vanadate can be uniformly grown on the surface of the conductive glass through a hydrothermal reaction.

[0041] In certain embodiments of the present invention, the precursor solution comprises a bismuth salt concentration of 0.05 M, a disodium ethylenediaminetetraacetic acid concentration of 0.05 M, a vanadium salt concentration of 0.05 M, a nitric acid concentration of 2 M, and a sodium hydroxide concentration of 1 M. At these concentrations, the in-situ growth of tetragonal bismuth vanadate on the conductive glass surface is more uniform.

[0042] In certain embodiments of the present invention, the bismuth salt includes any one of bismuth nitrate or its hydrate, bismuth chloride or its hydrate, preferably bismuth nitrate pentahydrate.

[0043] In certain embodiments of the present invention, the vanadium salt includes any one of sodium metavanadate, potassium metavanadate and ammonium metavanadate, preferably sodium metavanadate.

[0044] In certain embodiments of the present invention, the conductive glass is placed in purified water containing detergent, deionized water, acetone, ethanol, and isopropyl alcohol for ultrasonic cleaning before use to fully remove impurities on the surface of the conductive glass.

[0045] In certain embodiments of the present invention, the hydrothermal reaction is carried out at a temperature of 170-190° C. and for a time of 15-21 hours, which is conducive to the in-situ growth of tetragonal bismuth vanadate on the surface of the conductive glass.

[0046] In certain embodiments of the present invention, the hydrothermal reaction is carried out at a temperature of 180° C. for 18 hours. At this temperature, the in-situ growth of tetragonal bismuth vanadate on the surface of the conductive glass is more complete.

[0047] In certain embodiments of the present invention, the concentration of the sodium hydroxide solution is 0.1-1 M, and the tetragonal bismuth vanadate photoelectrode is allowed to stand in the sodium hydroxide solution for 1-9 h.

[0048] In certain embodiments of the present invention, the concentration of the sodium hydroxide solution is 0.3 M, and the tetragonal bismuth vanadate photoelectrode is placed in the sodium hydroxide solution for 3 h.

[0049] The present invention significantly increases the electrode specific surface area and high-index surface exposure through alkaline corrosion, thereby enhancing the electrode active sites and the ability to adsorb amino acids, and ultimately enhancing the ability of the photoelectrode to degrade amino acids.

[0050] In certain embodiments of the present invention, the concentration of the molybdenum salt solution is 0.04-0.06 M, and the molybdenum salt solution is coated on the surface of the tetragonal bismuth vanadate photoelectrode by spin coating at a spin coating rate of 700-900 rpm for 10-14 s.

[0051] In certain embodiments of the present invention, the concentration of the molybdenum salt solution is 0.05 M; the spin coating rate is 800 rpm, and the time is 13 s.

[0052] In certain embodiments of the present invention, the molybdenum salt includes any one of ammonium molybdate or its hydrate, sodium molybdate or its hydrate, potassium molybdate or its hydrate, preferably ammonium molybdate tetrahydrate.

[0053] In certain embodiments of the present invention, the annealing temperature is 440-460°C and the duration is 110-130 minutes. This temperature can provide the driving force for the phase transition and ensure controllability, while the duration can ensure the completeness and uniformity of the phase transition. This annealing condition can achieve efficient and complete transformation from the tetragonal phase to the monoclinic phase, while suppressing grain growth to maintain specific surface area, without damaging the conductive glass substrate, and obtaining a highly photoelectrically active monoclinic molybdenum-doped bismuth vanadate photoelectrode.

[0054] In certain embodiments of the present invention, the annealing temperature is 450° C. and the annealing time is 120 min. Under such annealing conditions, the performance of the obtained monoclinic molybdenum-doped bismuth vanadate photoelectrode is optimal.

[0055] The present invention also provides a monoclinic molybdenum-doped bismuth vanadate photoelectrode, which is prepared by the above-mentioned preparation method. The monoclinic molybdenum-doped bismuth vanadate photoelectrode provided by the present invention has high activity and can efficiently degrade amino acids and produce hydrogen.

[0056] In certain embodiments of the present invention, the monoclinic molybdenum-doped bismuth vanadate photoelectrode comprises conductive glass and molybdenum-doped bismuth vanadate nanorods in-situ grown on the surface of the conductive glass.

[0057] It can be understood that the molybdenum-doped bismuth vanadate nanorods are monoclinic molybdenum-doped bismuth vanadate.

[0058] In certain embodiments of the present invention, the thickness of the molybdenum-doped bismuth vanadate on the surface of the conductive glass is 1-1.5 μm. In the monoclinic molybdenum-doped bismuth vanadate photoelectrode provided by the present invention, the monoclinic molybdenum-doped bismuth vanadate is uniformly distributed on the surface of the conductive glass, preferably with a thickness of 1.2-1.4 μm.

[0059] In certain embodiments of the present invention, the molybdenum-doped bismuth vanadate nanopillars have a length of 700-900 nm and a diameter of 350-400 nm. Preferably, the molybdenum-doped bismuth vanadate nanopillars have a length of 750-850 nm and a diameter of 350-400 nm. In the monoclinic molybdenum-doped bismuth vanadate photoelectrode provided by the present invention, the molybdenum-doped bismuth vanadate nanopillars have small and uniform size and a large specific surface area, which facilitates carrier separation.

[0060] The present invention also provides a use of the above-mentioned monoclinic molybdenum-doped bismuth vanadate photoelectrode in degrading amino acids in water and / or producing hydrogen.

[0061] In certain embodiments of the present invention, the application may be in photocatalytic degradation of amino acids and / or hydrogen production, electrocatalytic degradation of amino acids and / or hydrogen production, or photoelectrocatalytic degradation of amino acids and / or hydrogen production.

[0062] In certain embodiments of the present invention, the amino acids include any one or more of natural amino acids and artificial aminopolycarboxylic acids.

[0063] The natural amino acids include, but are not limited to, any one or more of arginine, threonine, and lysine. The artificial amino polycarboxylic acids include, but are not limited to, any one or more of ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA, also known as nitrilotriacetic acid), diethylenetriaminepentaacetic acid (DTPA), and N-β-hydroxyethylethylenediaminetriacetic acid (HEDTA).

[0064] The present invention also provides a method for degrading amino acids and producing hydrogen using the above-mentioned monoclinic molybdenum-doped bismuth vanadate photoelectrode, comprising: The monoclinic molybdenum-doped bismuth vanadate photoelectrode is used as the working electrode, potassium borate buffer containing amino acids is used as the electrolyte, and a three-electrode system is adopted to degrade amino acids and produce hydrogen under the conditions of light and external bias.

[0065] In certain embodiments of the present invention, the three-electrode system comprises the monoclinic molybdenum-doped bismuth vanadate photoelectrode as the working electrode, a platinum sheet as the counter electrode, and a calomel electrode as the reference electrode.

[0066] In certain embodiments of the present invention, the concentration of amino acids in the electrolyte is 0.01-4 M. Too low or too high an amino acid concentration may affect the performance of the photoelectrode in degrading amino acids and producing hydrogen.

[0067] In certain embodiments of the present invention, the concentration of amino acids in the electrolyte is 0.1 M.

[0068] In certain embodiments of the present invention, the concentration of the potassium borate buffer is 0.1-2.0 M, and the pH is 9-11.

[0069] In certain embodiments of the present invention, the concentration of the potassium borate buffer is 1 M and the pH is 9.5.

[0070] In some embodiments of the present invention, the bias voltage is ≥0.2 V, that is, the lower limit of the applied bias voltage is 0.2 V, preferably 0.2-2 V.

[0071] In some embodiments of the present invention, the illumination includes illumination by sunlight.

[0072] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0073] The present invention has no particular limitation on the sources of the raw materials used in the following examples, and they can be generally commercially available.

[0074] The test methods in the following examples without specific conditions are usually carried out under conventional conditions.

[0075] Photoelectrochemical degradation of pollutants and hydrogen production tests were carried out using the following methods: Photoelectrochemical degradation of pollutants and hydrogen production tests were conducted using electrochemical linear sweep voltammetry (LSV). The LSV test was carried out under a three-electrode structure with an electrolyte of potassium borate buffer containing amino acids. The pollutant degradation and hydrogen production performance were compared by comparing the current density at the same bias value.

[0076] Example 1 A monoclinic molybdenum-doped bismuth vanadate photoelectrode, the preparation method of which comprises the following steps: The area is 3×4 cm 2 The conductive glass was ultrasonically cleaned in purified water containing detergent, deionized water, acetone, ethanol and isopropanol for 1 hour respectively and set aside.

[0077] Add 1.0 mmol of bismuth nitrate pentahydrate, 1.0 mmol of disodium ethylenediaminetetraacetate, 1.0 mmol of sodium metavanadate, 20 mL of nitric acid, and 40 mmol of sodium hydroxide to 40 mL of deionized water. After ultrasonication and stirring for 1 hour, a precursor solution was obtained for standby use.

[0078] A piece of 3×4 cm 2 The conductive glass was placed in a 100 mL hydrothermal kettle, the precursor solution was poured into the hydrothermal kettle, and hydrothermaled at 180 ° C for 18 hours to obtain a tetragonal phase bismuth vanadate photoelectrode. After cooling to room temperature naturally, the precursor solution was poured into the hydrothermal kettle at a concentration of 0.3 molL -1 After standing for 3 hours, take it out and add 0.05 mol L -1 An aqueous solution of ammonium molybdate tetrahydrate was spin-coated onto the surface of a tetragonal bismuth vanadate photoelectrode at 800 rpm for 12 seconds. The resulting film was then annealed at 450°C in a muffle furnace for 120 minutes to yield a monoclinic molybdenum-doped bismuth vanadate photoelectrode, named etched-M-BVO.

[0079] Comparative Example 1 A monoclinic molybdenum-doped bismuth vanadate photoelectrode. Compared with Example 1, the preparation method is as follows: after the tetragonal bismuth vanadate photoelectrode prepared by hydrothermal reaction is cooled to room temperature, an aqueous ammonium molybdate tetrahydrate solution is directly spin-coated on the surface without the step of standing in a sodium hydroxide solution. The remaining steps are exactly the same as those in Example 1.

[0080] The monoclinic molybdenum-doped bismuth vanadate photoelectrode obtained in this comparative example 1 is named M-BVO.

[0081] Figure 1 Figure (b) is a SEM image of the M-BVO photoelectrode obtained in Comparative Example 1, which is composed of uniform nanorods. Figure 1 Figure (c) is a SEM image of the etched-M-BVO photoelectrode obtained in Example 1, showing that the nanopillars of the photoelectrode are composed of multiple irregular nanoparticles. Figure 1 Figure (d) is a TEM image of the M-BVO photoelectrode obtained in Comparative Example 1, and the nanocolumn particles are about 800 nm long. Figure 1 Figure (e) is a TEM image of the etched-M-BVO photoelectrode obtained in Example 1, showing that the size of the nanopillars did not change significantly after standing in a sodium hydroxide solution and spin-coating with an aqueous ammonium molybdate tetrahydrate solution. Figure 1 Figure (f) in the middle is the HRTEM image of the etched-M-BVO photoelectrode obtained in Example 1, showing that the exposed crystal surface contains the (121) plane. Figure 1 Figure (g) in the middle is the HRTEM image of the etched-M-BVO photoelectrode obtained in Example 1, showing that the exposed crystal surface contains the (040) plane. Figure 1Figure (h) is a mapping diagram of the etched-M-BVO photoelectrode obtained in Example 1, showing that the elements (bismuth, vanadium, oxygen, and molybdenum) are evenly dispersed.

[0082] Figure 2 Figure (a) is the SEM image of tetragonal bismuth vanadate before standing in sodium hydroxide solution. Figure 2 Figure (b) shows an SEM image of tetragonal bismuth vanadate after standing in a sodium hydroxide solution. Comparing the two images shows that the alkaline corrosion does not change the nanocolumnar structure of the tetragonal bismuth vanadate, but the surface becomes rougher.

[0083] Figure 3 Figure (a) is the XRD pattern of the photoelectrodes obtained in Example 1 of the present invention and Comparative Example 1, showing that except for the peak from the conductive glass substrate, all diffraction peaks of the photoelectrode correspond to the standard card JCPDS No. 14-688, that is, they are all monoclinic bismuth vanadate. Figure 2 Figure (b) is a texture coefficient diagram of the photoelectrodes obtained in Example 1 of the present invention and Comparative Example 1, showing that the texture coefficient changed significantly after standing in a sodium hydroxide solution and spin-coating an aqueous solution of ammonium molybdate tetrahydrate. Figure 3 Figure (c) is a RAMAN diagram of the photoelectrodes obtained in Example 1 of the present invention and Comparative Example 1, showing that the Raman spectra did not change significantly after standing in a sodium hydroxide solution and spin-coating with an aqueous solution of ammonium molybdate tetrahydrate. Figure 3 Figure (d) is a DRS graph of the photoelectrodes obtained in Example 1 of the present invention and Comparative Example 1, showing that the light absorption of the photoelectrode is slightly enhanced after standing in a sodium hydroxide solution and spin-coating an aqueous solution of ammonium molybdate tetrahydrate. Figure 3 Figure (e) is a Tauc-plot of the photoelectrodes obtained in Example 1 of the present invention and Comparative Example 1, showing that the band gap is slightly increased after standing in a sodium hydroxide solution and spin-coating with an aqueous solution of ammonium molybdate tetrahydrate. Figure 3 Figure (f) is the BET diagram of the photoelectrode obtained in Example 1 of the present invention and Comparative Example 1, showing that after standing in sodium hydroxide solution and spin-coating with ammonium molybdate tetrahydrate aqueous solution, the specific surface area of ​​the photoelectrode is significantly increased from 5.8509 m 2 g -1 Raised to 23.3815 m 2 g -1 .

[0084] Example 2 A method for degrading amino acids and producing hydrogen comprises the following steps: Dissolve 0.05 mol potassium chloride, 0.05 mol boric acid, and 0.01 mol arginine in 100 mL of deionized water to obtain a potassium borate buffer solution with amino acids added, pH = 9.5, and set aside.

[0085] The etched-M-BVO photoelectrode obtained in Example 1 or the M-BVO photoelectrode obtained in Comparative Example 1 was used as the working electrode, a platinum sheet as the counter electrode, and a calomel electrode as the reference electrode. A potassium borate buffer containing amino acids was added as the electrolyte. Under the influence of an external light source and bias voltage, the amino acids were efficiently degraded and hydrogen was produced. The external light source was simulated sunlight, and the bias voltage was 0.4 V.

[0086] Example 3 A method for degrading amino acids and producing hydrogen, differing from Example 2 in that 0.05 mol of arginine is replaced with 0.01 mol of threonine, 0.01 mol of lysine, 0.01 mol of ethylenediaminetetraacetic acid, 0.01 mol of nitrilotriacetic acid, 0.01 mol of N-β-hydroxyethylethylenediaminetriacetic acid, or 0.01 mol of diethylenetriaminepentaacetic acid. The remaining steps are identical to those of Example 2.

[0087] Example 4 A method for degrading amino acids and producing hydrogen, which differs from Example 2 in that 0.05 mol of arginine is replaced with 0.0001, 0.0002, 0.0005, 0.001, 0.002, 0.005, 0.01, and 0.02 mol of EDTA. The remaining steps are identical to those of Example 2.

[0088] Comparative Example 2 A method for degrading amino acids and producing hydrogen differs from Example 2 in that the electrolyte does not contain amino acids. The remaining steps are identical to those of Example 2.

[0089] Figure 4 Figure (a) is the LSV diagram of the photoelectrodes obtained in Example 1 of the present invention and Comparative Example 1 in potassium borate buffer (Comparative Example 2) and potassium borate buffer containing amino acids (Example 2), respectively, showing that after standing in sodium hydroxide solution and spin-coating with ammonium molybdate tetrahydrate aqueous solution, the efficiency of the photoelectrode in degrading amino acids and producing hydrogen is significantly improved.

[0090] Figure 4 Figure (b) shows the LSV plots of the etched-M-BVO photoelectrode obtained in Example 1 of the present invention in potassium borate buffer and potassium borate buffer containing different types of amino acids (arginine, threonine, and lysine, all at a concentration of 0.1 M), respectively, demonstrating that the etched-M-BVO photoelectrode can degrade a variety of natural amino acids.

[0091] Figure 4Figure (c) shows the LSV plots of the etched-M-BVO photoelectrode obtained in Example 1 of the present invention in potassium borate buffer and potassium borate buffer containing different types of amino polycarboxylic acids (EDTA, NTA, HEDTA, DTPA, all at a concentration of 0.1 M), respectively, showing that the etched-M-BVO photoelectrode can degrade a variety of artificial amino polycarboxylic acids.

[0092] Figure 4 Figure (d) in the middle is the ESCA graph of the photoelectrodes obtained in Example 1 of the present invention and Comparative Example 1 in potassium borate buffer and potassium borate buffer containing amino acids (0.1 M EDTA), respectively, showing that the ESCA of the photoelectrode is significantly improved after standing in sodium hydroxide solution and spin coating with ammonium molybdate tetrahydrate aqueous solution.

[0093] Figure 4 Figure (e) is the IT diagram of the photoelectrode obtained in Example 1 of the present invention in potassium borate buffer and potassium borate buffer containing amino acids (0.1 M EDTA), showing that the etched-M-BVO photoelectrode exhibits good stability.

[0094] Figure 4 Figure (f) is a Faradaic efficiency diagram of the photoelectrode obtained in Example 1 of the present invention when subjected to IT testing in potassium borate buffer (0.1 M EDTA) containing amino acids, showing that the etched-M-BVO photoelectrode exhibits a Faradaic efficiency close to 100%.

[0095] Figure 5 The LSV plots of the etched-M-BVO photoelectrode obtained in Example 1 of the present invention in potassium borate buffer solutions containing different EDTA concentrations show that the efficiency of the etched-M-BVO photoelectrode in degrading amino acids and producing hydrogen increases with increasing amino acid concentrations.

[0096] The above analysis and experimental test results comprehensively prove that the etched-M-BVO photoelectrode prepared in this example has excellent photoelectrochemical performance in amino acid degradation and hydrogen production, which has important guiding significance for actual production selection.

[0097] Comparative Example 3 A monoclinic molybdenum-doped bismuth vanadate photoelectrode, the preparation method of which comprises the following steps: The area is 4 × 5 cm 2 The conductive glass was ultrasonically cleaned in purified water containing detergent, deionized water, acetone, ethanol and isopropanol for 1 hour respectively and set aside.

[0098] Add 1.0 mmol of bismuth nitrate pentahydrate and 1.0 mmol of disodium ethylenediaminetetraacetate to 20 mL of nitric acid, and add 1.0 mmol of sodium metavanadate and 40 mmol of sodium hydroxide to 40 mL of deionized water. After ultrasonication and stirring for 1 hour, the mixture is mixed to obtain a precursor solution, which is set aside with continuous stirring.

[0099] A piece of 4×5 cm 2 The precursor solution was poured into a 100 mL hydrothermal kettle and hydrothermalized at 160°C for 12 hours to obtain a tetragonal bismuth vanadate photoelectrode. After cooling naturally to room temperature, the resulting product was transferred to a muffle furnace and annealed at 550°C for 240 minutes to obtain a monoclinic molybdenum-doped bismuth vanadate photoelectrode, named BVO.

[0100] Comparative Example 4 A method for degrading amino acids and producing hydrogen comprises the following steps: Dissolve 0.05 mol potassium chloride, 0.05 mol boric acid, and 0.5 mol ethylenediaminetetraacetic acid in 100 mL of deionized water to obtain a potassium borate buffer solution containing amino acids, which is ready for use.

[0101] The BVO photoelectrode obtained in Comparative Example 3 was used as the working electrode, a platinum sheet as the counter electrode, and a calomel electrode as the reference electrode. A potassium borate buffer containing amino acids was added as the electrolyte. Under the influence of an external light source and bias voltage, the amino acids were degraded and hydrogen was produced. The external light source was simulated sunlight, and the bias voltage was 1.0 V.

[0102] After testing, the efficiency of the BVO photoelectrode obtained in Comparative Example 4 in degrading amino acids and producing hydrogen was much lower than that of the etched-M-BVO photoelectrode obtained in Example 1.

[0103] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a monoclinic molybdenum-doped bismuth vanadate photoelectrode, characterized in that: include: Mixing bismuth salt, disodium ethylenediaminetetraacetic acid, vanadium salt, nitric acid, sodium hydroxide and water to obtain a precursor solution; placing the conductive glass in the precursor solution and performing a hydrothermal reaction to obtain a tetragonal bismuth vanadate photoelectrode; The tetragonal bismuth vanadate photoelectrode is placed in a sodium hydroxide solution, taken out, and then coated with a molybdenum salt solution on the surface. After coating, the photoelectrode is annealed to obtain a monoclinic molybdenum-doped bismuth vanadate photoelectrode.

2. The preparation method according to claim 1, wherein In the precursor solution, the concentration of bismuth salt is 0.04-0.06 M, the concentration of disodium ethylenediaminetetraacetic acid is 0.04-0.06 M, the concentration of vanadium salt is 0.04-0.06 M, the concentration of nitric acid is 1.9-2.1 M, and the concentration of sodium hydroxide is 0.9-1.1 M; Preferably, in the precursor solution, the concentration of bismuth salt is 0.05 M, the concentration of disodium ethylenediaminetetraacetic acid is 0.05 M, the concentration of vanadium salt is 0.05 M, the concentration of nitric acid is 2 M, and the concentration of sodium hydroxide is 1 M; Preferably, the bismuth salt includes any one of bismuth nitrate or its hydrate, bismuth chloride or its hydrate, preferably bismuth nitrate pentahydrate; Preferably, the vanadium salt includes any one of sodium metavanadate, potassium metavanadate and ammonium metavanadate, preferably sodium metavanadate.

3. The preparation method according to claim 1, wherein The hydrothermal reaction temperature is 170-190°C and the time is 15-21 hours; Preferably, the hydrothermal reaction temperature is 180° C. and the time is 18 h.

4. The preparation method according to claim 1, wherein The concentration of the sodium hydroxide solution is 0.1-1 M, and the tetragonal bismuth vanadate photoelectrode is placed in the sodium hydroxide solution for 1-9 hours; Preferably, the concentration of the sodium hydroxide solution is 0.3 M, and the tetragonal bismuth vanadate photoelectrode is placed in the sodium hydroxide solution for 3 h.

5. The preparation method according to claim 1, wherein The concentration of the molybdenum salt solution is 0.04-0.06 M, and the molybdenum salt solution is coated on the surface of the tetragonal bismuth vanadate photoelectrode by spin coating at a spin coating rate of 700-900 rpm for 10-14 s. Preferably, the concentration of the molybdenum salt solution is 0.05 M; the spin coating rate is 800 rpm, and the time is 13 s; Preferably, the molybdenum salt includes any one of ammonium molybdate or its hydrate, sodium molybdate or its hydrate, potassium molybdate or its hydrate, preferably ammonium molybdate tetrahydrate.

6. The preparation method according to claim 1, wherein The annealing temperature is 440-460°C and the time is 110-130 min; Preferably, the annealing temperature is 450° C. and the annealing time is 120 min.

7. A monoclinic molybdenum-doped bismuth vanadate photoelectrode, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 6; Preferably, the monoclinic molybdenum-doped bismuth vanadate photoelectrode comprises conductive glass and molybdenum-doped bismuth vanadate nanorods in situ grown on the surface of the conductive glass; Preferably, the thickness of the molybdenum-doped bismuth vanadate on the surface of the conductive glass is 1-1.5 μm; Preferably, the molybdenum-doped bismuth vanadate nanorods have a length of 700-900 nm and a diameter of 350-400 nm.

8. Use of the monoclinic molybdenum-doped bismuth vanadate photoelectrode according to claim 7 in degrading amino acids in water and / or producing hydrogen; Preferably, the amino acids include any one or more of natural amino acids and artificial aminopolycarboxylic acids; Preferably, the natural amino acids include any one or more of arginine, threonine and lysine; Preferably, the artificial aminopolycarboxylic acid includes any one or more of ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid and N-β-hydroxyethylethylenediaminetriacetic acid.

9. A method for degrading amino acids and producing hydrogen using the monoclinic molybdenum-doped bismuth vanadate photoelectrode according to claim 7, characterized in that: include: The monoclinic molybdenum-doped bismuth vanadate photoelectrode according to claim 7 is used as a working electrode, a potassium borate buffer solution containing amino acids is used as an electrolyte, and a three-electrode system is adopted to degrade amino acids and produce hydrogen under conditions of light and external bias.

10. The method according to claim 9, wherein The concentration of amino acids in the electrolyte is 0.01-4 M; Preferably, the bias voltage is ≥ 0.2 V, preferably 0.2-2 V; Preferably, the illumination includes illumination by sunlight.

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