AU2021105884A4

AU2021105884A4 - Visible light responsive nano-polyhedral ferric vanadate thin film photoelectrode and preparation method and use thereof

Info

Publication number: AU2021105884A4
Application number: AU2021105884A
Authority: AU
Inventors: Yuhan Cao; Xijun Fu; Beibei GAO; Yong Liu; Yumei Wang; Liu Yang; Qingyi Zeng
Original assignee: University of South China
Current assignee: University of South China
Priority date: 2021-05-28
Filing date: 2021-08-19
Publication date: 2021-10-21
Anticipated expiration: 2029-08-19
Also published as: CN113332991A; CN113332991B

Abstract

(FIG. 10) The present disclosure provides a visible light-responsive nano-polyhedral ferric vanadate thin film photoelectrode and a preparation method and use thereof, belonging to the technical field of photoelectric materials. The method includes: mixing an iron salt, an alkali metal nitrate, water and an acid and then subjecting the mixture and a substrate to a hydrothermal reaction, to obtain a FeOOH thin film electrode; and coating a vanadium source solution on the FeOOH thin film electrode for a heat treatment, to obtain the nano-polyhedral ferric vanadate thin film photoelectrode. The ferric vanadate thin film photoelectrode prepared in the present disclosure has an ordered polyhedron nanostructure with a relatively uniform dispersion and high purity, achieving excellent photoelectrocatalysis performance. The example results show that the nano-polyhedral ferric vanadate thin-film photoelectrode prepared in the present disclosure has a response to a light with a wavelength of 610 nm or less, has a photoelectric conversion efficiency of up to 12% under 400 nm wavelength light, and achieves a relatively high degradation rate for various organic substances, among which the degradation efficiency of methyl orange, Congo red and Rhodamine B is more than 95%. - 5/7 0,6 light-off 0.5 light-on 0 4O 0 2 FeVO 4 021 0 .0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 voltage (V vs. Ag/AgCl) FIG.9 20i 315 FeVOra 10 CFeVrC -S FeVO1-b 400 450 500 550 600 wavelength (mn) FIG.1O

Description

- 5/7

,6

0.5 light-off light-on 4O

0 2 FeVO 4 021

.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 voltage (V vs. Ag/AgCl)

FIG.9

20i

315 FeVOra

10

CFeVrC

-S FeVO 1-b 400 450 500 550 600 wavelength (mn)

FIG.1O

VISIBLE LIGHT RESPONSIVE NANO-POLYHEDRAL FERRIC VANADATE THIN FILM PHOTOELECTRODE AND PREPARATION METHOD AND USE THEREOF TECHNICAL FIELD

[01] The present disclosure relates to the technical field of photoelectric materials, and in

particular to a visible light responsive nano-polyhedral ferric vanadate thin film photoelectrode

and a preparation method and use thereof.

BACKGROUNDART

[02] The photoelectrocatalysis for decomposition of water to produce hydrogen and the

degradation of organic matters based on visible light excitation is a greatly promising

technology. As a core part of photoelectrocatalysis, the performance of photocatalytic electrode

directly affects the effect of photocatalytic system. Therefore, the preparation of photoelectrode

materials with high photoelectrocatalysis (PEC) performance is of great significance.

[03] At present, it is generally believed that a desirable semiconductor photocatalytic electrode

should mainly have characteristics as follows: good visible light absorption performance,

ordered nanocrystalline structure, stability in aqueous solution, non-toxic, easy preparation and

low cost. Among the existing photoelectrocatalysis materials, the n-type semiconductor of

triclinic ferric vanadate (FeVO4) has advantages such as good visible light absorption

performance (with a band gap of about 2.0-2.1 eV and capacity to absorb the visible light

having a wavelength of <600 nm and the ultraviolet light), sufficiently low valence band energy

to generate high-energy holes for the oxidation of water and the degradation of organic matters,

as well as good stability under neutral and alkaline conditions, non-toxic and low cost, and

therefore it is regarded as a greatly promising photoelectrocatalysis material. The existing

preparation methods of FeVO4 mainly include the drop coating method, the spray thermal

decomposition method and the sol-gel method. However, the FeVO 4 prepared by these methods

is in the form of dense, porous or stacked coarse nanoparticles. Such disordered nanostructures

are not beneficial to the separation of electron/hole pairs and the interfacial charge transport,

resulting in poor overall charge transport capability and small space charge density of FeVO 4 , which greatly limits the use of FeVO 4 in the field of photoelectrocatalysis.

[04] Therefore, it is of great significance to prepare FeVO 4 with ordered nanostructures and

further to improve its photoelectrocatalysis performance.

SUMMARY

[05] Embodiments of the present disclosure provide a visible light responsive nano-polyhedral ferric vanadate thin film photoelectrode and a preparation method and use thereof. The

nano-polyhedral ferric vanadate thin film photoelectrode prepared in the present disclosure has

an ordered nanostructure and excellent photoelectrocatalysis performance.

[06] In order to achieve the above, the embodiments of the present disclosure provide the following technical solutions:

[07] The present disclosure provides a method for preparing a visible light responsive

nano-polyhedral ferric vanadate thin film photoelectrode, comprising:

[08] (1) mixing an iron salt, an alkali metal nitrate, water and an acid, to obtain a mixed solution;

[09] (2) subjecting a substrate and the mixed solution obtained in step (1) to a hydrothermal

reaction, to obtain a FeOOH thin film electrode; and

[10] (3) coating a vanadium source solution on the FeOOH thin film electrode obtained in step

(2) for a heat treatment, to obtain the nano-polyhedral ferric vanadate thin film photoelectrode.

[11] In some embodiments, in step (1), the iron salt is selected from the group consisting of

ferric chloride, ferric nitrate and ferric sulfate.

[12] In some embodiments, in step (1), the alkali metal nitrate is selected from the group

consisting of sodium nitrate and potassium nitrate.

[13] In some embodiments, in step (1), a ratio of the amount of substance of the iron salt to the

alkali metal nitrate is in a range of (0.05-0.4) : 1.

[14] In some embodiments, in step (1), a pH value of the mixed solution is in a range of 1.2-2.0.

[15] In some embodiments, in step (1), a ratio of the amount of substance of the iron salt to the volume of water is in a range of (5-10) mmol: 7 mL.

[16] In some embodiments, in step (2), the hydrothermal reaction is performed at a temperature of 80-120 °C, and the hydrothermal reaction is performed for 1-12 h.

[17] In some embodiments, in step (3), the heat treatment is performed at a temperature of 450-650 °C, and the heat treatment is performed for 1-20 h.

[18] The present disclosure provides a nano-polyhedral ferric vanadate thin film photoelectrode prepared by the method disclosed in above technical solutions.

[19] The present disclosure also provides use of the nano-polyhedral ferric vanadate thin film photoelectrode disclosed in above technical solutions in the field of photoelectrocatalysis.

[20] The present disclosure provides a method for preparing a visible light responsive nano-polyhedral ferric vanadate thin film photoelectrode, which comprises: mixing an iron salt, an alkali metal nitrate, water and an acid, to obtain a mixed solution; subjecting a substrate and the mixed solution obtained to a hydrothermal reaction, to obtain a FeOOH thinfilm electrode; and coating a vanadium source solution on the FeOOH thin film electrode obtained for a heat treatment, to obtain the nano-polyhedral ferric vanadate thin film photoelectrode. The present disclosure uses the combination of hydrothermal method and in-situ solid phase reaction to prepare the nano-polyhedral ferric vanadate thin film photoelectrode. The ferric vanadate thin film photoelectrode prepared has an ordered polyhedral nanostructure with a relatively uniform dispersion, and has high purity and thus excellent photoelectrocatalysis performance. The results of the examples show that ferric vanadate in the nano-polyhedral ferric vanadate thin film photoelectrode prepared in the present disclosure has a nano-polyhedral structure with high purity, achieving a response to the light with a wavelength of 610 nm or less, a photoelectric conversion efficiency of up to 12% under the light of 400 nm wavelength, and a high degradation rate for various organic matters, among which the degradation efficiency of methyl orange, Congo red and Rhodamine B after reacting for 120 min is more than 95%.

BRIEF DESCRIPTION OF THE DRAWINGS

[21] FIG. 1 shows a schematic flow diagram of the preparation method of the present disclosure.

[22] FIG. 2 shows a scanning electron micrograph of the FeOOH thin film electrode and nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 1 of the present

disclosure.

[23] FIG. 3 shows a high-resolution transmission electron micrograph of the nano-polyhedral

ferric vanadate thin film photoelectrode prepared in Example 1 of the present disclosure.

[24] FIG. 4 shows an XRD spectrum of the nano-polyhedral ferric vanadate thin film

photoelectrode prepared in Example 1 of the present disclosure.

[25] FIG. 5 shows a Raman spectrum of the nano-polyhedral ferric vanadate thin film

photoelectrode prepared in Example 1 of the present disclosure.

[26] FIG. 6 shows an XPS energy spectrum of the nano-polyhedral ferric vanadate thin film

photoelectrode prepared in Example 1 of the present disclosure.

[27] FIG. 7 shows a core level spectrum of Fe 2p in the nano-polyhedral ferric vanadate thin

film photoelectrode prepared in Example 1 of the present disclosure.

[28] FIG. 8 shows an ultraviolet-visible absorption spectrum of the nano-polyhedral ferric

vanadate thin film photoelectrode prepared in Example 1 of the present disclosure.

[29] FIG. 9 is a graph showing a volt-ampere curve of the nano-polyhedral ferric vanadate thin

film photoelectrodes prepared in Examples 1-3 of the present disclosure under an intermittent

light source.

[30] FIG. 10 is a graph showing a photoelectric conversion efficiency curve of the

nano-polyhedral ferric vanadate thin film photoelectrodes prepared in Examples 1-3 of the present disclosure.

[31] FIG. 11 is a graph showing a modulated photocurrent spectrum of the nano-polyhedral ferric vanadate thin film photoelectrodes prepared in Examples 1-3 of the present disclosure.

[32] FIG. 12 is a graph showing a photocurrent-time curve of the CoPi-modified

nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 4 of the present

disclosure.

[33] FIG. 13 is a graph showing aH 2 /02 production-time curve of the CoPi-modified

disclosure.

[34] FIG. 14 shows the degradation rates of the nano-polyhedral ferric vanadate thin film

photoelectrode prepared in Example 5 of the present disclosure for different degradation

systems.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[35] The present disclosure provides a method for preparing a visible light responsive

nano-polyhedral ferric vanadate thin film photoelectrode, comprising:

[36] (1) mixing an iron salt, an alkali metal nitrate, water and an acid, to obtain a mixed

solution;

[37] (2) subjecting a substrate and the mixed solution obtained in step (1) to a hydrothermal

reaction, to obtain a FeOOH thin film electrode; and

[38] (3) coating a vanadium source solution on the FeOOH thin film electrode obtained in step

[39] As shown in FIG. 1, the method for preparing a visible light responsive nano-polyhedral

ferric vanadate thin film photoelectrode provided in the present disclosure is performed by a

process as follows: firstly, a FeOOH nanorod array thin film is prepared; then a vanadium source solution is coated on the FeOOH nanorod array thin film for a heat treatment, to obtain ferric vanadate and vanadium pentoxide; and after washing with sodium hydroxide and deionized water, the nano-polyhedral ferric vanadate thin film photoelectrode is obtained.

[40] In the present disclosure, unless otherwise specified, there is no special limitation on the source of respective component, and the commercially available products well known to those skilled in the art may be used.

[41] In the present disclosure, an iron salt, an alkali metal nitrate, water and an acid are mixed, to obtain a mixed solution.

[42] According to the present disclosure, the iron salt is preferably selected from the group consisting of ferric chloride, ferric nitrate and ferric sulfate, is more preferably ferric chloride, and is most preferably ferric chloride hexahydrate. In the present disclosure, the iron salt is used to provide iron ions.

[43] According to the present disclosure, the alkali metal nitrate is preferably selected from the group consisting of sodium nitrate and potassium nitrate, and is more preferably sodium nitrate. In the present disclosure, the alkali metal nitrate is used to adjust the morphology of the generated FeOOH.

[44] According to the present disclosure, a ratio of the amount of substance of the iron salt to the alkali metal nitrate is preferably in a range of (0.05-0.4) : 1, further preferably (0.1-0.35) : 1, more preferably (0.15-0.3) : 1, and most preferably (0.2-0.25) : 1. In the present disclosure, the molar ratio of the iron salt to the alkali metal nitrate is limited to the above range, which could better adjust the morphology of the generated FeOOH and form a dense and uniform nanorod array thin film.

[45] According to the present disclosure, the water is preferably deionized water. In the present disclosure, the deionized water could avoid the influence of the impurities in water on the product, and further improve the purity of the product.

[46] According to the present disclosure, a ratio of the amount of substance of the iron salt to the volume of water is preferably in a range of (5-10) mmol : 7 mL, further preferably (6-9) mmol : 7 mL, and more preferably (7-8) mmol : 7 mL. In the present disclosure, the ratio of the amount of substance of the iron salt to the volume of water is limited to the above range, which could make each component be fully dissolved.

[47] According to the present disclosure, the acid is preferably selected from the group consisting of hydrochloric acid, sulfuric acid and nitric acid, and is more preferably

hydrochloric acid. In the present disclosure, the acid is used to adjust the pH value of the mixed

solution. According to the present disclosure, a pH value of the mixed solution is preferably in a

range of 1.2-2.0, more preferably 1.4-1.8, and most preferably 1.5-1.6. In the present disclosure,

there is no special limitation on the concentration and the amount of the acid, as long as the pH

value of the mixed solution may be ensured within the above range. In the present disclosure,

the pH value of the mixed solution is limited within the above range, which could make the iron

salt react to obtain FeOOH.

[48] In the present disclosure, there is no special limitation on the mixing operation of the

iron salt, the alkali metal nitrate, water and the acid, and the technical solutions of mixing

materials well known to those skilled in the art may be used. According to the present

disclosure, in some embodiments, the mixing of the iron salt, the alkali metal nitrate, water and

the acid is performed as follows: mixing the iron salt and the alkali metal nitrate with water, and

then adding the acid thereto. In the present disclosure, the acid is added lastly to ensure that the

pH value of the mixed solution is within the above range, which is beneficial to the

hydrothermal reaction of the iron salt.

[49] In the present disclosure, after the mixed solution is obtained, a substrate and the mixed

solution are subjected to a hydrothermal reaction, to obtain a FeOOH thin film electrode.

[50] According to the present disclosure, in some embodiments, the substrate is a FTO

conductive glass. According to the present disclosure, in some embodiments, the substrate is

cleaned before use. In the present disclosure, the cleaning could remove the impurities on the

surface of the substrate and prevent them from entering the thin film to reduce the purity of the

thin film.

[51] In the present disclosure, there is no special limitation on the size of the substrate, and the sizes of the substrate for preparing the thin film electrode well known to those skilled in the art may be used.

[52] According to the present disclosure, in some embodiments, the conductive surface of the substrate is immersed downwards into the mixed solution for a hydrothermal reaction. According to the present disclosure, the hydrothermal reaction is performed at a temperature of preferably 80-120 °C, more preferably 90-110 °C, and most preferably 100 °C; the hydrothermal reaction is performed for preferably 1-12 h, further preferably 3-10 h, more preferably 5-8 h, and most preferably 7 h. In the present disclosure, the temperature and the time for the hydrothermal reaction are limited within the above ranges, which could allow the iron salts to react fully to form a FeOOH nanorod array thin film, and at the same time to make the thin film have an appropriate thickness, further improving the photoelectrocatalysis performance of the product.

[53] In the present disclosure, during the hydrothermal reaction, the iron salt reacts to generate FeOOH.

[54] In the present disclosure, there is no special limitation on the equipment for the hydrothermal reaction, and the equipments used for hydrothermal reaction well known to those skilled in the art may be used. According to the present disclosure, in some embodiments, the hydrothermal reaction is carried out in a reaction kettle.

[55] According to the present disclosure, in some embodiments, after the hydrothermal reaction, the product of the hydrothermal reaction is cooled, washed and dried in sequence, to obtain the FeOOH thin film electrode.

[56] According to the present disclosure, in some embodiments, the cooling is performed by natural cooling, and in some embodiments, the terminal temperature of the cooling is a temperature of room temperature.

[57] According to the present disclosure, in some embodiments, the washing is performed with deionized water.

[58] In the present disclosure, there is no special limitation on the operation of the drying, and the technical solutions for the drying well known to those skilled in the art may be used.

[59] In the present disclosure, after the FeOOH thin film electrode is obtained, a vanadium source solution is coated on the FeOOH thin film electrode for a heat treatment, to obtain the nano-polyhedral ferric vanadate thin film photoelectrode.

[60] According to the present disclosure, the vanadium source in the vanadium source solution is preferably selected from the group consisting of vanadium acetylacetonate and metavanadate, and is more preferably vanadium acetylacetonate; the solvent in the vanadium source solution is preferably selected from the group consisting of dimethyl sulfoxide, toluene and amyl alcohol, and is more preferably dimethyl sulfoxide. In the present disclosure, the vanadium source solution is used to provide vanadium ions.

[61] According to the present disclosure, the concentration of the vanadium source solution is preferably in a range of 0.01-0.5 mol/L, further preferably 0.05-0.45 mol/L, more preferably 0.1-0.4 mol/L, and most preferably 0.2-0.3 mol/L. In the present disclosure, the concentration of the vanadium source solution is limited within the above range, which could make the vanadium source dissolve more fully and uniformly.

[62] According to the present disclosure, in some embodiments, a ratio of the volume of the vanadium source solution to the surface area of the substrate is in a range of (0.01-0.1) mL : 1 cm2.2 In the present disclosure, the ratio of the volume of the vanadium source solution to the surface area of the substrate is limited within the above range, which could make the FeOOH react fully, thereby further improving the performance of the product.

[63] According to the present disclosure, in some embodiments, the coating is performed by drop coating. In the present disclosure, the drop coating could make the vanadium source solution coated on the FeOOH thin film electrode more uniformly.

[64] According to the present disclosure, in some embodiments, after the coating, the FeOOH thin film electrode coated with the vanadium source solution is dried, and then subjected to the heat treatment.

[65] According to the present disclosure, in some embodiments, the drying is performed at a temperature of 50-80 °C, and the drying is performed for 2-3 h. In the present disclosure, the

drying could make the solvent in the vanadium source solution volatilize, so that the vanadium

source is contacted with FeOOH in a solid form for subsequent reaction. In the present

disclosure, the temperature and the time for the drying are limited within the above ranges,

which could make the vanadium source solution have an appropriate volatilization rate, and

make the vanadium source be contacted with FeOOH more uniformly.

[66] In the present disclosure, there is no special limitation on the equipment for the drying,

and the equipments for drying well known to those skilled in the art may be used. According to

the present disclosure, in some embodiments, the drying is carried out on a plate heater.

[67] According to the present disclosure, the heat treatment is performed preferably at a

temperature of 450-650 °C, further preferably 500-600 °C and more preferably 550 °C; the heat

treatment is performed for 1-20 h, further preferably 2-15 h, more preferably 3-10 h, and most

preferably 4-6 h. In the present disclosure, the temperature and the time for the heat treatment is

limited within the above ranges, which could not only make the vanadium source react with

FeOOH to form ferric vanadate, but also avoid the sintering of the product caused by excessive

temperature and adjust the morphology and size of the product, so as to obtain an

nano-polyhedral ferric vanadate with an ordered structure, thereby further improving the

performance of the product.

[68] In the present disclosure, during the heat treatment, the vanadium source and FeOOH

undergo an in-situ solid-phase reaction to form ferric vanadate.

[69] According to the present disclosure, in some embodiments, after the heat treatment, the

product of the heat treatment is cooled, washed and dried in sequence, to obtain the

nano-polyhedral ferric vanadate thin film photoelectrode.

[70] According to the present disclosure, in some embodiments, the cooling is performed by

natural cooling, and in some embodiments, the terminal temperature of the cooling is a

temperature of room temperature.

[71] According to the present disclosure, in some embodiments, the washing is performed with a sodium hydroxide solution and deionized water in sequence. In the present disclosure,

there is no special limitation on the concentration and the amount of the sodium hydroxide

solution, and the concentrations and the amounts of sodium hydroxide used during the washing

well known to those skilled in the art may be used.

[72] In the present disclosure, there is no special limitation on the operation of the drying, and the technical solutions for the drying well known to those skilled in the art may be used.

[73] In the present disclosure, the combination of hydrothermal method and in-situ solid-phase

reaction is used to prepare the nano-polyhedral ferric vanadate thin film photoelectrode. By

controlling the technological parameters such as the amount of component and the temperature

and the time for reaction, the prepared ferric vanadate thin film photoelectrode has an ordered

polyhedron nanostructure with a relatively uniform dispersion, and has high purity, thereby

having excellent photoelectrocatalysis performance.

[74] The present disclosure provides a nano-polyhedral ferric vanadate thin film

photoelectrode prepared by the preparation method described in the above technical solutions.

According to the present disclosure, in some embodiments, the thickness of ferric vanadate thin

film in the nano-polyhedral ferric vanadate thin film photoelectrode is in a range of 200-800 nm.

In some embodiments, the length of the nano-polyhedral ferric vanadate is in a range of 50-550

nm.

[75] In the nano-polyhedral ferric vanadate thin film photoelectrode prepared in the present

disclosure, ferric vanadate has a nano-polyhedral ordered structure and high purity, and thus

having excellent photoelectrocatalysis performance.

[76] The present disclosure also provides use of the nano-polyhedral ferric vanadate thin

film photoelectrode described in the above technical solutions in the field of

photoelectrocatalysis.

[77] In the present disclosure, there is no special limitation on the use of the nano-polyhedral

ferric vanadate thin film photoelectrode in the field of photoelectrocatalysis, and the technical solutions for use of the nano-polyhedral ferric vanadate thin film photoelectrode in the field of photoelectrocatalysis well known to those skilled in the art may be used.

[78] The technical solutions of the present disclosure will be clearly and completely described below with reference to the examples. It is obvious that the described examples are only part of

the examples of the present disclosure, not all of them. Those skilled in the art could also obtain

other embodiments based on above embodiments without creativity. These embodiments all fall

within the protection scope of the present disclosure.

[79] Example 1

[80] (1) 75 mmol FeC13-6H20 and 0.5 mol sodium nitrate were dissolved in 70 mL of deionized water, and hydrochloric acid was dropwise added thereto to adjust the pH to 1.5,

obtaining a mixed solution (a ratio of the amount of substance of FeCl3-6H 20 to sodium nitrate

was 0.15 : 1, and a ratio of the amount of substance of FeC3-6H20 to the volume of deionized

water was 7.5 mmol : 7 mL).

[81] (2) A cleaned 3 cmx3 cm FTO conductive glass with the conductive surface facing

downwards was transferred to a reaction kettle with the mixed solution obtained in step (1). A

hydrothermal reaction was performed at 100 °C for 6 h. After being naturally cooled to room

temperature, the resultant was washed with water and dried, obtaining a FeOOH thin film

electrode.

[82] (3) 0.18 mL of a 0.1 mol/L dimethyl sulfoxide solution of vanadium acetylacetonate was drop coated uniformly on the FeOOH thin film electrode (a ratio of the volume of the dimethyl

sulfoxide solution of vanadium acetylacetonate to the surface area of FTO conductive glass was

0.02 mL : 1 cm 2 ). After being dried on a plate heater, the drop coated FeOOH thin film

electrode was subjected to a heat treatment at 550 °C for 4 h, naturally cooled to room

temperature, and then washed with sodium hydroxide and deionized water in sequence and

dried, obtaining a nano-polyhedral ferric vanadate thin film photoelectrode.

[83] The surface micromorphology and the thickness of the FeOOH thin film electrode and

the nano-polyhedral ferric vanadate thin film photoelectrode prepared were tested with a scanning electron microscopy. The results are shown in FIG. 2. In FIG. 2, A shows the surface micromorphology and thickness of the FeOOH thin film electrode, B and C show the surface micromorphology of the nano-polyhedral ferric vanadate thin film photoelectrode at different resolutions, and D shows the film thickness of the nano-polyhedral ferric vanadate thin film photoelectrode. It can be seen from FIG. 2 that the surface of the FeOOH thin film electrode prepared in Example 1 has a nanorod array with an average diameter of about 50 nm, and the film thickness is about 410 nm. The nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 1 has a smooth surface, which has a nano-polyhedron structure with a size of 100-450 nm and a film thickness of about 560 nm.

[84] The high-resolution transmission electron microscope image of the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 1 was tested, and the result is shown in FIG. 3. It can be seen from FIG. 3A that the ferric vanadate prepared in Example 1 has a (220) crystal plane of monocrystal. It can be seen from FIG. 3B that the ferric vanadate has continuous lattice fringes with an interplanar spacing of about 0.233 nm, corresponding to the (220) crystal plane of triclinic phase ferric vanadate.

[85] The XRD spectrum of the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 1 was tested, and the result is shown in FIG. 4. It can be seen from FIG. 4 that except for the diffraction peaks of SnO2 on the FTO substrate, the rest are all the characteristic peaks of the triclinic phase ferric vanadate, indicating that the prepared nano-polyhedral ferric vanadate thin film has a composition of pure ferric vanadate.

[86] The Raman spectrum of the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 1 was tested, and the result is shown in FIG. 5. It can be seen from FIG. 5 that it shows the characteristic peak positions of ferric vanadate: the symmetrical vibrations of V-0-Fe at 471 cm-1 and 497 cm-1, the asymmetrical vibrations of V-0-Fe at 631 cm-1 and 659 cm-1, the asymmetric vibrations of V-Oat 735 cm-1, 770 cm-1, 831 cm-1, 846 cm-1 and 909 cm-1 and the symmetric vibrations of V-Oat 893 cm-1, 932 cm-land 965 cm-1, further indicating that the prepared nano-polyhedral ferric vanadate thin film has a composition of pure ferric vanadate.

[87] The XPS spectrum of the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 1 was tested, and the result is shown in FIG. 6. It can be seen from FIG. 6

that in addition to Fe, V and0 elements, the ferric vanadate thin film contains no other impurity

elements (C element in the figure is derived from C02 adsorbed on the surface of the film, and

Sn element is derived from the FTO substrate of the electrode).

[88] The core level spectrum of Fe 2p in the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 1was tested, and the result is shown in FIG. 7. It can be

seen from FIG. 7 that the peaks at around 710.8 eV and 725.6 eV corresponding to Fe 2p in the

thin film are the typical binding energy of Fe in the ferric vanadate, and the accompanying peak

at 719.2 eV further indicates the existence of Fe , indicating that the thin film is composed of

pure ferric vanadate.

[89] The ultraviolet-visible absorption spectrum of the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 1was tested, and the result is shown in FIG. 8. It can

be seen from FIG. 8 that the prepared nano-polyhedral ferric vanadate thin film photoelectrode

has good absorption performance for both of the visible light with wavelengths of less than 610

nm and the ultraviolet light.

[90] The volt-ampere curve of the nano-polyhedral ferric vanadate thin film photoelectrode

prepared in Example 1 under the intermittent light source was tested, and the result is shown as

FeVO4-a in FIG. 9. It can be seen from FIG. 9 that the nano-polyhedral ferric vanadate thin film

photoelectrode prepared in Example 1 has a good photoresponse under the condition that the

bias voltage is higher than 0.25 V (vs. Ag/AgCl), and the photocurrent value continuously

increases with the increase in the bias voltage.

[91] The photoelectric conversion efficiency curve of the nano-polyhedral ferric vanadate thin

film photoelectrode prepared in Example 1 was measured at a bias voltage of 1.0 V (vs.

Ag/AgCl), and the result is shown as FeVO4-a in FIG. 10. It can be seen from FIG. 10 that the

nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 1 has a response

to the light with a wavelength of 610 nm or less, and has a photoelectric conversion efficiency

of up to 12% under 400 nm wavelength light.

[92] The intensity modulated photocurrent spectroscopy (IMPS) of the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 1was tested at a bias voltage of 1.0 V

(vs. Ag/AgCl), and the result is shown as FeVO4-a in FIG. 11. It can be seen from FIG. 11 that

the lowest point of the FeVO4-a curve corresponds to a frequency of 69.4 Hz. According to the

formula Td = (2itfnin(IMPS))-' (wherein Td represents the average migration time for the

majority of carriers (electrons) in the tested photocatalytic electrode to reach the conductive

substrate, andfnin(IMPS) represents the frequency value corresponding to the lowest point in

the IMPS curve), the average migration time of the photogenerated electrons in the thin film is

calculated to be 2.29 ms, indicating that the photogenerated carriers in the nano-polyhedral

ferric vanadate thin film photoelectrode prepared in Example 1 have a fast migration rate.

[93] Example 2

[94] (1) 75 mmol FeC13-6H20 and 0.5 mol sodium nitrate were dissolved in 70 mL of deionized water, and hydrochloric acid was dropwise added thereto to adjust the pH to 1.5,

water was 7.5 mmol : 7 mL).

[95] (2) A cleaned 3 cmx3 cm FTO conductive glass with the conductive surface facing downwards was transferred to a reaction kettle with the mixed solution obtained in step (1). A

hydrothermal reaction was performed at 100 °C for 1 h. After being naturally cooled to room

electrode.

[96] (3) 0.09 mL of a 0.01 mol/L dimethyl sulfoxide solution of vanadium acetylacetonate was

drop coated uniformly on the FeOOH thin film electrode (a ratio of the volume of the dimethyl

0.01 mL : 1 cm 2 ). After being dried on a plate heater, the drop coated FeOOH thin film

dried, obtaining a nano-polyhedral ferric vanadate thin film photoelectrode. In the nano-polyhedral ferric vanadate thin film photoelectrode, the film thickness was about 290 nm, and the size of nano-polyhedral ferric vanadate was about 50-300 nm.

[97] The volt-ampere curve of the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 2 under the intermittent light source was tested, and the result is shown as FeVO4-b in FIG. 9. It can be seen from FIG. 9 that the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 2 has a good photoresponse under the condition that the bias voltage is higher than 0.25 V (vs. Ag/AgCl), and the photocurrent value continuously increases with the increase in the bias voltage.

[98] The photoelectric conversion efficiency curve of the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 2 was measured at a bias voltage of 1.0 V (vs. Ag/AgCl), and the result is shown as FeVO4-b in FIG. 10. It can be seen from FIG. 10 that the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 2 has a response to the light with a wavelength of 610 nm or less, and has a photoelectric conversion efficiency of 4.1% under 400 nm wavelength light.

[99]The intensity modulated photocurrent spectroscopy (IMPS) of the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 2 was tested at a bias voltage of 1.0 V (vs. Ag/AgCl), and the result is shown as FeVO 4-b in FIG. 11. It can be seen from FIG. 11 that the lowest point of the FeVO 4 -b curve corresponds to a frequency of 109.2 Hz. According to the formula Td = (2itfnin(IMPS))-, the average migration time of the photogenerated electrons in the thin film is calculated to be 1.46 ms, indicating that the photogenerated carriers in the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 2 have a fast migration rate.

[100] Example 3

[101](1) 75 mmol FeC3-6H20 and 0.5 mol sodium nitrate were dissolved in 70 mL of deionized water, and hydrochloric acid was dropwise added thereto to adjust the pH to 1.5, obtaining a mixed solution (a ratio of the amount of substance of FeCl3-6H 20 to sodium nitrate was 0.15 : 1, and a ratio of the amount of substance of FeC3-6H20 to the volume of deionized water was 7.5 mmol : 7 mL).

[102] (2) A cleaned 3 cmx3 cm FTO conductive glass with the conductive surface facing downwards was transferred to a reaction kettle with the mixed solution obtained in step (1). A

hydrothermal reaction was performed at 100 °C for 12 h. After being naturally cooled to room

electrode.

[103] (3) 0.45 mL of a 0.5 mol/L dimethyl sulfoxide solution of vanadium acetylacetonate was drop coated uniformly on the FeOOH thin film electrode (a ratio of the volume of the

dimethyl sulfoxide solution of vanadium acetylacetonate to the surface area of FTO conductive

glass was 0.05 mL : 1 cm2 ). After being dried on a plate heater, the drop coated FeOOH thin

film electrode was subjected to a heat treatment at 550 °C for 4 h, naturally cooled to room

dried, obtaining a nano-polyhedral ferric vanadate thin film photoelectrode. In the

nano-polyhedral ferric vanadate thin film photoelectrode, the film thickness was about 790 nm,

and the size of nano-polyhedral ferric vanadate was about 100-550 nm.

[104] The volt-ampere curve of the nano-polyhedral ferric vanadate thin film photoelectrode

prepared in Example 3 under the intermittent light source was tested, and the result is shown as

FeVO4-c in FIG. 9. It can be seen from FIG. 9 that the nano-polyhedral ferric vanadate thin film

photoelectrode prepared in Example 3 has a good photoresponse under the condition that the

increases with the increase in the bias voltage.

[105] The photoelectric conversion efficiency curve of the nano-polyhedral ferric vanadate

thin film photoelectrode prepared in Example 3 was measured at a bias voltage of 1.0 V (vs.

Ag/AgCl), and the result is shown as FeVO4-c in FIG. 10. It can be seen from FIG. 10 that the

nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 3 has a response

of 8.5% under 400 nm wavelength light.

[106] The intensity modulated photocurrent spectroscopy (IMPS) of the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 3 was tested at a bias voltage of 1.0 V (vs. Ag/AgCl), and the result is shown as FeVO4-c in FIG. 11. It can be seen from FIG.11 that the lowest point of the FeVO4-c curve corresponds to a frequency of 55.1 Hz. According to the formula Td = (2tfmni(IMPS))-, the average migration time of the photogenerated electrons

in the thin film is calculated to be 2.89 ms, indicating that the photogenerated carriers in the nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 3 have a fast migration rate.

[107] Example 4

[108] (1) 50 mmol FeC3-6H20 and 0.3 mol sodium nitrate were dissolved in 70 mL of deionized water, and hydrochloric acid was dropwise added thereto to adjust the pH to 1.2, obtaining a mixed solution (a ratio of the amount of substance of FeCl3-6H 20 to sodium nitrate was 0.17 : 1, and a ratio of the amount of substance of FeC3-6H20 to the volume of deionized water was 5 mmol: 7 mL).

[109] (2) A cleaned 3 cmx3 cm FTO conductive glass with the conductive surface facing downwards was transferred to a reaction kettle with the mixed solution obtained in step (1). A hydrothermal reaction was performed at 120 °C for 12 h. After being naturally cooled to room temperature, the resultant was washed with water and dried, obtaining a FeOOH thin film electrode.

[110] (3) 0.9 mL of a 0.01 mol/L dimethyl sulfoxide solution of vanadium acetylacetonate was drop coated uniformly on the FeOOH thin film electrode (a ratio of the volume of the dimethyl sulfoxide solution of vanadium acetylacetonate to the surface area of FTO conductive glass was 0.1 mL : 1 cm2 ). After being dried on a plate heater, the drop coated FeOOH thin film electrode was subjected to a heat treatment at 450 °C for 6 h, naturally cooled to room temperature, and then washed with sodium hydroxide and deionized water in sequence and dried, obtaining a nano-polyhedral ferric vanadate thin film photoelectrode. In the nano-polyhedral ferric vanadate thin film photoelectrode, the film thickness was about 390 nm, and the size of nano-polyhedral ferric vanadate was about 50-350 nm.

[111] A CoPi-modified nano-polyhedral ferric vanadate thin film photoelectrode was prepared as follows. The nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 4 was used as a working electrode, a platinum electrode was used as a counter electrode, Ag/AgC1 was used as a reference electrode, and 0.1 M KPi buffer solution (pH=7) containing 0.5 mM Co(NO 3 ) 2 was used as a electrolyte to prepare the CoPi-modified nano-polyhedral ferric vanadate thin film photoelectrode. Under AM 1.5 illumination, a deposition was performed at 0.1 V for 300 s. Then the resultant was washed with deionized water and dried at °C for 1 h, obtaining the CoPi-modified nano-polyhedral ferric vanadate thin film photoelectrode.

[112] The photocurrent-time curve of the prepared CoPi-modified nano-polyhedral ferric vanadate thin film photoelectrode at a bias voltage of 1.0 V (vs. Ag/AgCl) was tested, and the result is shown in FIG. 12. Photoelectrochemical test conditions were as follows: 0.1 M KPi buffer solution (pH=7) was used as an electrolyte solution, the light intensity was AM 1.5 (100 mW/cm 2 ), the bias voltage was 1.0 V (vs. Ag/AgCl), and the testing period was 5 h. It can be

seen from FIG. 12 that the current density of photolysis of water is about 0.46 mA/cm 2 , and shows no obvious decrease with the extension of time, indicating that the prepared CoPi-modified nano-polyhedral ferric vanadate thin film photoelectrode has good photoelectrocatalysisstability.

[113] The H 2 /02 production-time curve of the prepared CoPi-modified nano-polyhedral ferric vanadate thin film photoelectrode at a bias voltage of 1.0 V (vs. Ag/AgCl) was tested, and the results are shown in FIG. 13. Photoelectrochemical test conditions were as follows: 0.1 M KPi buffer solution (pH=7) was used as an electrolyte solution, the light intensity was AM 1.5 (100 mW/cm 2 ), the bias voltage was 1.0 V (vs. Ag/AgCl), and the testing period was 5 min. It can be

seen from FIG. 13 that a molar ratio of 02 to H 2 produced by photolysis of water is about 1/2, and the gas generation rate is as high as 3.87 and 7.95 mol cm-2h 1 , respectively, indicating that the prepared CoPi-modified nano-polyhedral ferric vanadate film photoelectrode has a good application effect on the photoelectrocatalysis for decomposition of water to produce hydrogen.

[114] Example 5

[115] (1) 100 mmol FeC3-6H20 and 0.7 mol sodium nitrate were dissolved in 70 mL of deionized water, and hydrochloric acid was dropwise added thereto to adjust the pH to 2.0,

was 0.14 : 1, and a ratio of the amount of substance of FeC3-6H20 to the volume of deionized

water was 10 mmol : 7 mL).

[116] (2) A cleaned 3 cmx3 cm FTO conductive glass with the conductive surface facing downwards was transferred to a reaction kettle with the mixed solution obtained in step (1). A

hydrothermal reaction was performed at 120 °C for 4 h. After being naturally cooled to room

electrode.

[117] (3) 0.09 mL of a 0.5 mol/L dimethyl sulfoxide solution of vanadium acetylacetonate

was drop coated uniformly on the FeOOH thin film electrode (a ratio of the volume of the

glass was 0.01 mL : 1 cm2 ). After being dried on a plate heater, the drop coated FeOOH thin

film electrode was subjected to a heat treatment at 650 °C for 1 h, naturally cooled to room

dried, obtaining a nano-polyhedral ferric vanadate thin film photoelectrode.

[118] An aqueous solution containing 0.1 M Na2SO 4 and 20 mg/L organic matters (methyl

orange, Congo red, Rhodamine B, tetracycline and bisphenol A, respectively) was used as a

simulated organic wastewater, the nano-polyhedral ferric vanadate thin film photoelectrode

prepared in Example 5 was used as a working electrode, and the platinum electrode was used as

a counter electrode. Under the conditions of simulated sunlight of AM 1.5 (100 mW/cm 2 )

illumination and 1 V bias voltage, the degradation efficiency of the organic matters was

measured after 120 min. The result is shown in FIG. 14. It can be seen from FIG. 14 that the

nano-polyhedral ferric vanadate thin film photoelectrode prepared in Example 5 exhibits good

degradation efficiency for various organic matters, among which the degradation efficiency of

methyl orange, Congo red and Rhodamine B is more than 95% after 120 min, indicating that the nano-polyhedral ferric vanadate thin film photoelectrode prepared in the present disclosure has extremely bright application prospects in the field of wastewater treatment.

[119] In conclusion, the nano-polyhedral ferric vanadate thin film photoelectrode prepared in the present disclosure has an ordered nano-polyhedron structure and high purity, achieving

excellent photoelectrocatalysis performance.

[120] The above are only the preferred embodiments of the present disclosure. It should be

understood that for those of ordinary skill in the art, several improvements and modifications

could be made without departing from the principle of the present disclosure, and these

improvements and modifications should also be regarded as the protection scope of the present

disclosure.

[121] The term "comprise" and variants of the term such as "comprises" or "comprising" are used herein to denote the inclusion of a stated integer or stated integers but not to exclude any

other integer or any other integers, unless in the context or usage an exclusive interpretation of

the term is required.

[122] Other specific embodiments of the invention of the present disclosure herein follow:

1. A method for preparing a visible light responsive nano-polyhedral ferric vanadate thin film

photoelectrode, comprising:

(1) mixing an iron salt, an alkali metal nitrate, water and an acid, to obtain a mixed

solution;

(2) subjecting a substrate and the mixed solution obtained in step (1) to a hydrothermal

reaction, to obtain a FeOOH thin film electrode; and

(3) coating a vanadium source solution on the FeOOH thin film electrode obtained in step

2. The method of embodiment 1, wherein in step (1), the iron salt is selected from the group

consisting of ferric chloride, ferric nitrate and ferric sulfate.

3. The method of embodiment 1, wherein in step (1), the alkali metal nitrate is selected from the group consisting of sodium nitrate and potassium nitrate.

4. The method of embodiment 1, wherein in step (1), a ratio of the amount of substance of the

iron salt to the alkali metal nitrate is in a range of (0.05-0.4) : 1.

5. The method of embodiment 1, wherein in step (1), a pH value of the mixed solution is in a

range of 1.2-2.0.

6. The method of embodiment 1, wherein in step (1), a ratio of the amount of substance of the

iron salt to the volume of water is in a range of (5-10) mmol : 7 mL.

7. The method of embodiment 1, wherein in step (2), the hydrothermal reaction is performed

at a temperature of 80-120 °C, and the hydrothermal reaction is performed for 1-12 h.

8. The method of embodiment 1, wherein in step (3), the heat treatment is performed at a

temperature of 450-650 °C, and the heat treatment is performed for 1-20 h.

9. A nano-polyhedral ferric vanadate thin film photoelectrode prepared by the method of any

one of embodiments 1-8.

10. Use of the nano-polyhedral ferric vanadate thin film photoelectrode of embodiment 9 in the

field of photoelectrocatalysis.

Claims

photoelectrode, comprising:

solution;

reaction, to obtain a FeOOH thin film electrode; and

2. The method of claim 1, wherein in step (1) a ratio of the amount of substance of the iron

salt to the alkali metal nitrate is in a range of (0.05-0.4) : 1.

3. The method of claim 1, wherein in step (2) the hydrothermal reaction is performed at a

temperature of 80-120 °C, and the hydrothermal reaction is performed for 1-12 h.

4. The method of claim 1, wherein in step (3) the heat treatment is performed at a temperature

of 450-650 °C, and the heat treatment is performed for 1-20 h.

5. A nano-polyhedral ferric vanadate thin film photoelectrode prepared by the method of any

one of claims 1-4.