CN112777634A

CN112777634A - Preparation method of bismuth vanadate with high (010) crystal face exposure ratio

Info

Publication number: CN112777634A
Application number: CN202110141863.0A
Authority: CN
Inventors: 陆源; 曾海波; 张侃
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2021-02-02
Filing date: 2021-02-02
Publication date: 2021-05-11
Anticipated expiration: 2041-02-02
Also published as: CN112777634B

Abstract

The invention discloses a preparation method of bismuth vanadate with high (010) crystal face exposure ratio. Dissolving bismuth nitrate pentahydrate, ammonium metavanadate and citric acid in a nitric acid solution, adding ethanol and polyvinyl alcohol, coating the formed mixed solution on the surface of FTO in a spinning mode, and calcining at 450 ℃ to obtain a seed layer; dissolving bismuth nitrate pentahydrate and ammonium metavanadate in concentrated nitric acid, adding a titanium chloride solution, and adjusting the pH to 0.9 by using ammonia water to obtain a precursor solution; then immersing the seed layer in the precursor solution, and carrying out hydrothermal reaction at 180 ℃; finally, heating the product of the hydrothermal reaction to 450 ℃ for annealing to obtain the bismuth vanadate with the high (010) crystal face exposure ratio. According to the invention, the morphology regulator titanium chloride is added into the precursor solution, and the pH value of the precursor solution is regulated, so that the porous bismuth vanadate with high (010) crystal face exposure ratio is synthesized, the selectivity of the porous bismuth vanadate in photoelectrocatalysis hydrogen peroxide production is improved, and the selectivity can reach 66.5%.

Description

Preparation method of bismuth vanadate with high (010) crystal face exposure ratio

Technical Field

The invention belongs to the field of preparation of photoelectric catalytic materials, and relates to a preparation method of bismuth vanadate with a high (010) crystal face exposure ratio.

Background

Hydrogen peroxide (H)₂O₂) Are widely used in industrial manufacture and as disinfectants and bleaches. Currently, about 95% of H₂O₂The production uses an anthraquinone process, which is a multi-step process, requiring high plant investment and large energy input. Therefore, there is a need to find alternative anthracenesH of quinone method₂O₂Production processes, in particular processes which allow small-scale production under safe production conditions. Although O is reduced by hydrogenation or electrochemical processes₂In H₂O₂A rapid development in synthesis has been achieved, but it is generally accepted that water is directly decomposed to H₂And H₂O₂Two high value-added chemicals are production H₂O₂A more desirable and economically viable route. To date, researchers have discovered several metal oxides, including BiVO₄、WO₃、SnO₂、TiO₂And ZnO, optionally in the presence of HCO₃ ^-Or CO₃ ^2-Selectively producing H by water oxidation in the electrolyte of₂O₂. BiVO considering the influence of factors such as light collection efficiency and band edge energy₄Due to the narrow band gap (2.4-2.5eV), the light absorption coefficient is higher (104-105 cm in the intrinsic absorption region)^-1) And a deeper Valence Band (VB) edge, which is expected to convert solar energy to H by Water Oxidation Reaction (WOR)₂O₂Is desirable for the photo-anode of (1). However, H is compared to oxygen generated by 4e-WOR (1.23V vs. RHE)₂O₂The resulting two electron water oxidation (2e-WOR) pathway (1.76V vs. RHE) is thermodynamically unfavorable. Thus, the current solar-driven WOR is relative to particle-based BiVO₄Photo-electric anode pair H₂O₂The selectivity of (a) is not ideal and is usually less than 40%.

From a thermodynamic perspective, modulating the thermodynamic process of an intermediate is an effective way to modulate the selectivity to the desired product in an electrocatalytic multiple electron transfer reaction. BiVO₄OH on the surface^*Free energy of adsorption (. DELTA.G)_OH*) Is considered to competitively produce O₂And H₂O₂The critical bifurcation point of (a). Several successful strategies have been developed to date to modulate BiVO₄Δ G on the surface_OH*. Furthermore, BiVO₄The surface state of (a) also plays a key role in controlling the kinetics, and the passivation method affects the rate constant of charge transfer. For O₂The 4e-WOR requirement ratio of precipitation is used for H₂O₂Higher surface hole concentration of the generated 2 e-WOR. The transport rate of light-induced holes can thus be delayed by using a surface passivation coating, resulting in H₂O₂The production activity is obviously improved. BiVO (BiVO) is caused by slow hole migration due to hole transfer to other surfaces caused by space charge separation behavior and high density of surface states₄The (010) surface of (D) is not suitable for O ₂4 e-WOR. In contrast, BiVO₄The (010) face of (a) should promote 2e-WOR by a kinetically favorable process in a kinetically-thermally favorable region.

Disclosure of Invention

The invention aims to provide a preparation method of bismuth vanadate with high (010) crystal face exposure ratio, and a bismuth vanadate crystal face regulation method for improving hydrogen peroxide yield₄The efficiency of producing hydrogen peroxide by photoelectrochemistry can be effectively improved, and the selectivity of the hydrogen peroxide is improved.

The technical scheme for realizing the purpose of the invention is as follows:

the preparation method of the bismuth vanadate with high (010) crystal face exposure ratio comprises the following specific steps:

(1) dissolving bismuth nitrate pentahydrate, ammonium metavanadate and citric acid in a nitric acid solution, then adding ethanol and polyvinyl alcohol, stirring until the ethanol and the polyvinyl alcohol are completely dissolved, coating the obtained solution on the surface of a clean FTO (fluorine-doped tin oxide), then placing the FTO in a muffle furnace, and calcining at 450 ℃ to obtain a seed layer;

(2) dissolving bismuth nitrate pentahydrate and ammonium metavanadate in concentrated nitric acid, then adding a titanium chloride solution, and adjusting the pH to 0.9 by using ammonia water to obtain a precursor solution;

(3) immersing the seed layer in the precursor solution, enabling the seed layer to face downwards, and carrying out hydrothermal reaction at 180 ℃;

(4) after the reaction is finished, washing the product with water, placing the product in a muffle furnace, heating to 450 ℃, annealing, and cooling to room temperature to obtain the bismuth vanadate with high (010) crystal face exposure ratio ((010) P-BiVO)₄)。

Preferably, in step (1), the calcination time is 2 h.

Preferably, in the step (3), the hydrothermal reaction time is 12 h.

Preferably, in step (4), the annealing time is 2 h.

Preferably, in step (4), the temperature increase or decrease rate is 10 ℃/min.

Compared with the prior art, the invention has the following advantages:

according to the invention, the morphology regulator titanium chloride is added into the precursor solution, and the pH value of the precursor solution is regulated, so that the porous bismuth vanadate with high (010) crystal face exposure ratio is synthesized, the selectivity of the porous bismuth vanadate in photoelectrocatalysis hydrogen peroxide production is improved, and the selectivity is improved to 66.5% from the existing 40%.

Drawings

FIG. 1 shows (010) BiVO in comparative example 1 and comparative example 2₄-1 and (010) BiVO₄-XRD pattern of 2.

FIG. 2 shows (010) BiVO in comparative example 1 and comparative example 2₄-1 and (010) BiVO₄SEM picture of-2.

FIG. 3 shows (010) BiVO in comparative example 1 and comparative example 2₄-1 and (010) BiVO₄-2 in cross-section.

FIG. 4 shows MnO in comparative example 1 and comparative example 2₂After photoelectrochemical deposition of (a) (010) BiVO₄-1 and (b) (010) BiVO₄-2 SEM images and energy dispersive X-ray images of the photoanode.

FIG. 5 shows (010) BiVO in comparative example 1 and comparative example 2₄-1 and (010) BiVO₄-2 Raman spectrum.

FIG. 6 shows P-BiVO (010) in example 1₄SEM image of (d).

FIG. 7 shows P-BiVO (010) in example 1₄TEM and HR-TEM images of.

FIG. 8 shows P-BiVO in example 1₄SEM image of (d).

FIG. 9 shows P-BiVO (010) in example 1₄XRD pattern of (a).

FIG. 10 shows (010) BiVO in example 1₄-1、(010)P-BiVO₄、P-BiVO₄Current-voltage curve of (a).

FIG. 11 is a sample of 1M NaHCO as in example 1₃In the electrolyte(010)P-BiVO₄And P-BiVO₄Polarization curves of the photoanode, data were collected without illumination.

FIG. 12 is a sample of 1M NaHCO as in example 1₃(010) P-BiVO in electrolyte under AM 1.5G irradiation₄And P-BiVO₄PEC generation H of photoanode₂O₂The faraday efficiency of.

FIG. 13 is a diagram showing the synthesis of (010) P-BiVO in comparative example 3₄The appearance is formed when the pH value of the precursor solution is higher.

FIG. 14 shows the synthesis of (010) P-BiVO in comparative example 3₄The appearance formed when the pH of the precursor solution is low.

Detailed Description

The present invention will be described in further detail with reference to the following examples and accompanying drawings.

Comparative example 1

0.3234g of bismuth nitrate pentahydrate, 0.078g of ammonium metavanadate and 0.167g of polyvinyl alcohol are dissolved in a mixed solution of 1ml of concentrated nitric acid and 2ml of deionized water, the mixed solution is vigorously stirred until the mixed solution is clear and transparent, the obtained solution is coated on the surface of clean FTO at the speed of 1500rpm, the spin coating time is 20s, the spin-coated FTO is placed into a muffle furnace, annealing is carried out for 2h at the temperature of 450 ℃, and BiVO is obtained₄A seed layer.

0.1164g of bismuth nitrate pentahydrate and 0.028g of ammonium metavanadate are dissolved in 1.6ml of concentrated nitric acid, deionized water is added to dilute the total volume of the nitric acid to 60ml, the obtained precursor solution is poured into a clean polytetrafluoroethylene lining, and BiVO is added₄The seed layer was immersed in the solution with the seed layer facing down. And (3) putting the polytetrafluoroethylene lining into a matched steel sleeve, screwing down, putting into a forced air drying oven, and reacting for 12h at 180 ℃. After the reaction is finished, (010) BiVO in the polytetrafluoroethylene lining is taken out₄And (1) putting the steel strip into a muffle furnace after being washed clean by deionized water, and annealing for 2 hours at the temperature of 450 ℃.

Comparative example 2

0.3234g of bismuth nitrate pentahydrate, 0.078g of ammonium metavanadate and 0.167g of polyvinyl alcohol are dissolved in a mixed solution of 1ml of concentrated nitric acid and 2ml of deionized water, the mixed solution is vigorously stirred until the mixed solution is clear and transparent, and the obtained solution isSpin-coating the liquid on the surface of clean FTO at 1500rpm for 20s, putting the spin-coated FTO into a muffle furnace, and annealing at 450 ℃ for 2h to obtain BiVO₄A seed layer.

0.1164g of bismuth nitrate pentahydrate and 0.028g of ammonium metavanadate are dissolved in 1.6ml of concentrated nitric acid, deionized water is added to dilute the total volume to 60ml, and then 0.5g of polyvinylpyrrolidone is added and stirred uniformly. Pouring the obtained precursor solution into a cleaned polytetrafluoroethylene lining, and adding BiVO₄The seed layer was immersed in the solution with the seed layer facing down. And (3) putting the polytetrafluoroethylene lining into a matched steel sleeve, screwing down, putting into a forced air drying oven, and reacting for 12h at 180 ℃. After the reaction is finished, (010) BiVO in the polytetrafluoroethylene lining is taken out₄And (2) putting the steel strip into a muffle furnace after being washed clean by deionized water, and annealing for 2 hours at the temperature of 450 ℃.

As shown in FIG. 1, (010) BiVO was determined by XRD₄-1 and (010) BiVO₄The crystal phases of the-2 crystals are all monoclinic BiVO₄. In addition, with polycrystalline BiVO₄Reference powder comparison, (010) BiVO₄-1 and (010) BiVO₄The-2 photoanode showed and had a strong (010) diffraction peak, while the (121) diffraction peak was much weaker, clearly indicating that (010) BiVO₄-1 and (010) BiVO₄-2 the photoanode is a preferential edge [010]Directionally oriented and dominated by the (010) face.

The morphology of the two photoanodes was characterized by field emission scanning electron microscopy (FE-SEM). As shown in FIG. 2, (010) BiVO₄-1 photo-anode presents densely packed cuboid crystallites comprising symmetric (011)/(110) facets on the sides and (010) facets on the top. For (010) BiVO₄-2 photo-anode, the crystal having a truncated rectangular pyramid morphology due to the use of PVP during the synthesis. Cross-sectional FE-SEM images show that both photoanodes are dense BiVO₄Film composition, thickness about 450nm (FIG. 3).

By photoelectrochemical deposition of MnO₂Deposited on (010) BiVO₄-1 and (010) BiVO₄-2 surfaces. As shown in FIG. 4, with (010) BiVO₄-2 lightMnO formed on the surface of the electric anode₂In sharp contrast, MnO formed by a hole oxidation process is distributed on (110) facets₂Uniformly distributed in (010) BiVO₄-1 on the surface of a photoanode. The results show that (010) BiVO was produced under PEC conditions₄-1 and (010) BiVO₄-2 photo-anodes have different hole transport paths, which also correspond to the water oxidation reaction surface that occurs in the water splitting of the PEC.

As can be seen from FIG. 5, (010) BiVO₄-1 and (010) BiVO₄The Raman spectra of the-2 photoanode were almost identical, which means that (010) BiVO₄-1 and (010) BiVO₄The structural defects in-2 are few or almost identical.

Example 1

2.4254g of bismuth nitrate pentahydrate, 0.5849g of ammonium metavanadate and 1.92g of citric acid were dissolved in a mixture of 5.8ml of concentrated nitric acid and 9.2ml of deionized water and stirred vigorously. Next, 3.75ml of acetic acid and 1.2g of polyvinyl alcohol were dissolved in the mixed solution, and vigorously stirred until clear and transparent, the obtained solution was spin-coated on a clean FTO surface at 2000rpm for 20s, the spin-coated FTO was placed in a muffle furnace, and annealing was performed at 450 ℃ for 2h to obtain BiVO₄A seed layer.

0.1164g of bismuth nitrate pentahydrate and 0.028g of ammonium metavanadate were dissolved in 2.0M HNO₃(60mL) of the aqueous solution, then 0.12mL of a titanium chloride solution (TiCl)₃In 20-30 wt.% HCl solution, solution concentration 1mol/L) was added to the solution. The pH of the mixture was then adjusted to 0.9 with aqueous ammonia solution. Pouring the obtained precursor solution into a cleaned polytetrafluoroethylene lining, and adding BiVO₄The seed layer was immersed in the solution with the seed layer facing down. And (3) putting the polytetrafluoroethylene lining into a matched steel sleeve, screwing down, putting into a forced air drying oven, and reacting for 12h at 180 ℃. After the reaction is finished, (010) P-BiVO in the polytetrafluoroethylene lining is taken out₄And putting the mixture into a muffle furnace after the mixture is washed clean by deionized water, and annealing for 2 hours at the temperature of 450 ℃.

This example synthesizes (010) a faceless, porous BiVO₄((010)P-BiVO₄) Light (es)Electrical anode to increase active facet/electrolyte contact area and shorten hole diffusion length to further improve solar energy to H₂O₂The conversion efficiency of (a). Prepared (010) P-BiVO₄The photoanode comprised a 3.5 μm thick film of nearly vertically aligned nanoplatelets, with the average size of the individual nanoplatelets being about 4 μm and the thickness being about 250nm (fig. 6a and b).

The exposed (010) face of the nanoplatelets was investigated by high resolution transmission electron microscopy (HR-TEM) and the (010) orientation was confirmed by electron diffraction (fig. 7). P-BiVO₄The FE-SEM image of (a) is shown in fig. 8, which contains polycrystalline nanoparticles with a size of less than 100 nm. (010) P-BiVO₄The XRD pattern of (a) shows better orientation, and the (010) diffraction peak clearly disappears at 2 θ ═ 30.8 ° (fig. 9). This is due to the (010) plane being aligned perpendicular to the FTO substrate (commercially available FTOs are polycrystalline and dominated by the (110) plane).

Porous (010) P-BiVO₄The photocurrent density of the photoanode was (010) BiVO₄-1 photo-anode 3 times or more (FIG. 10), and under the condition of 1.76V vs. RHE, the photo-current density is 3.0mA/cm². Although (010) P-BiVO₄The photocurrent density of the porous bismuth vanadate (P-BiVO) is slightly lower than that of the porous bismuth vanadate (P-BiVO) with an unexposed (010) surface₄) But oxidation of water to H₂O₂Shows (010) P-BiVO₄The cathode overpotential of (2) is shifted by 138mV (FIG. 11). In (010) P-BiVO₄Production of H₂O₂Has a Faraday efficiency of about P-BiVO ₄3 times higher (fig. 12). (010) P-BiVO at an applied bias of 0.6 to 1.8V relative to RHE₄To produce H₂O₂The Faraday efficiency of the composite material reaches 66.5 percent on average.

Comparative example 3

This comparative example is essentially the same as example 1, except that the pH is adjusted to 1.5.

Comparative example 4

This comparative example is essentially the same as example 1, except that the pH is adjusted to 0.4.

When preparing precursor solution, the pH value of the solution is opposite to the finally grown BiVO₄The appearance is greatly influenced. When the pH is greater than 0.9, BiV is formed, as shown in FIG. 13O₄In contrast to fig. 5, the shape was too thick to accurately expose the (010) face. When the pH is less than 0.9, BiVO is formed as shown in FIG. 14₄The whole is thin, the shape is broken flake-shaped, the surface is incomplete, and the growth is not successful to the required shape.

Claims

1. The preparation method of the bismuth vanadate with high (010) crystal face exposure ratio is characterized by comprising the following specific steps:

(4) and after the reaction is finished, washing the product with water, placing the product in a muffle furnace, heating to 450 ℃, annealing, and cooling to room temperature to obtain the bismuth vanadate with the high (010) crystal face exposure ratio.

2. The method according to claim 1, wherein in the step (1), the calcination time is 2 hours.

3. The method according to claim 1, wherein in the step (3), the hydrothermal reaction time is 12 hours.

4. The method according to claim 1, wherein in the step (4), the annealing time is 2 hours.

5. The method according to claim 1, wherein in the step (4), the temperature increase or decrease rate is 10 ℃/min.