CN114588925A

CN114588925A - Noble-metal-free supported nickel phosphide/carbon nitride visible-light-driven photocatalyst and preparation method thereof

Info

Publication number: CN114588925A
Application number: CN202210277463.7A
Authority: CN
Inventors: 赖跃坤; 许珅; 黄剑莹
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2022-03-21
Filing date: 2022-03-21
Publication date: 2022-06-07

Abstract

The invention discloses nickel phosphide (Ni) without noble metal load₂P)/carbon nitride (g-C)₃N₄) The simple preparation method of the visible light catalyst comprises the following specific steps: (1) g to C₃N₄Mixing with Ni salt solution, and reducing to obtain Ni/g-C₃N₄A low-temperature phosphating method using NaH₂PO₂Decomposed PH₃Gas phosphating to obtain Ni₂P/g‑C₃N₄. The method adopts an in-situ growth method to prepare Ni₂P/g‑C₃N₄The catalyst shows excellent water decomposition hydrogen production performance under visible light, and is even superior to Pt/g-C prepared by the conventional chloroplatinic acid light deposition method under the same load₃N₄. Simple process, easy operation and reverse reactionControllable reaction conditions, wide raw material sources, low cost and easy realization of industrial industrialization.

Description

Noble-metal-free supported nickel phosphide/carbon nitride visible-light-driven photocatalyst and preparation method thereof

Technical Field

The invention belongs to the technical field of photocatalytic hydrogen production materials, and relates to a noble metal-free supported nickel phosphide/carbon nitride visible-light-driven photocatalyst and a preparation method thereof.

Background

Photocatalytic water splitting has been widely studied as a green hydrogen production technology. Although technically feasible, the industrial production of hydrogen by decomposing water using solar energy on a large scale is still a great challenge. Furthermore, solar radiation is concentrated mainly in the visible part, which represents about 50% of the total energy of solar radiation. Therefore, the development of the visible light response catalyst is the key for improving the solar energy utilization rate and finally realizing the industrial application of the photocatalysis technology.

g-C of current visible light response₃N₄Showing great potential. 2009, g-C₃N₄The method is used for water decomposition hydrogen production under visible light irradiation for the first time. Structurally, the composite material only consists of carbon elements and nitrogen elements which are abundant in the earth, is simple to prepare, has cheap and easily-obtained raw materials, and shows outstanding economic advantages. It has excellent photocatalytic activity, thermal stability and chemical stability. But increasing g-C₃N₄There are some key bottlenecks to the photocatalytic activity of: (1) the band gap is large, and the light absorption is limited; (2) a higher density of defect sites acting as recombination centers for the photo-generated electron holes; (3) lack of active sites and high reaction activation energy; (4) high overpotentials are required to decompose water, with slow kinetics. To overcome these disadvantages, several modification methods are currently adopted, including ion doping, heterojunction structure, co-catalyst coupling, and dye sensitization. The coupling of the cocatalyst is one of the most common and simple methods, but the search for a suitable and cheap cocatalyst is a key problem.

Ni₂P is commonly used for electrocatalytic hydrogen production. By means of the special metal compound characteristic and good conductivity, high-efficiency hydrogen production can be achieved in the electrochemical process. Having such unique electrochemical properties, Ni₂P can also be used as a promoter in photocatalysis. After recombination with semiconductor material, Ni₂P not only can be used as an active site, but also can be used as an electron transmission channel to accelerate hydrogen productionThe process should be carried out.

In the invention, Ni is adopted without adding any noble metal₂P acts as a promoter, it exhibits synergistic catalytic properties comparable to noble metals. The use of this cheap and readily available promoter favors Ni₂P/g-C₃N₄Catalysts are widely used. The invention adopts a simple two-step method and utilizes a chemical reduction method to convert Ni into Ni₂The precursor Ni of P grows uniformly in g-C₃N₄Phosphating gave Ni with a tight bonding interface₂P/g-C₃N₄A catalyst. The problems of incompact combination and poor stability between the catalyst and the cocatalyst after simple physical mixing in the traditional method are solved to a great extent, and extra steps such as calcination and the like for improving the binding force are omitted. Meanwhile, Ni prepared in the invention₂P is nano-scale, enriches g-C₃N₄The catalytic active sites on the surface improve the catalytic hydrogen production performance of the composite catalyst under visible light.

Ni according to the photocatalytic hydrogen production reaction mechanism₂P roughly promotes g-C from these three aspects₃N₄Hydrogen production: black Ni₂P is increased by g-C₃N₄Light absorption of (2); the conductive material has good conductivity, accelerates electron transfer, and greatly inhibits electron hole recombination; in g-C₃N₄The nano-scale is closely grown on the ground, catalytic active sites are increased, and the rapid hydrogen production reaction is added. Ni₂P/g-C₃N₄The hydrogen production rate can reach 645.7 mu mol.h^-1·g^-1The performance of the catalyst is even better than that of Pt/g-C prepared by the conventional chloroplatinic acid light deposition method under the same loading₃N₄. In addition, the material used in the invention has wide sources, low price and easy obtaining, and the preparation process is simple, thus having wide application prospect in practical application.

Disclosure of Invention

The invention aims to solve the problems and develop a nickel phosphide/carbon nitride (Ni) capable of producing hydrogen under visible light₂P/g-C₃N₄) Materials and methods for their preparation. The invention is achieved by₃N₄In situ growthNi₂P particles, which make them tightly bound, exhibit good stability. Uniformly dispersed Ni₂The P particles are used as catalytic active sites, so that the electron transfer rate is improved, and the g-C is inhibited₃N₄The electron hole of (2) is heavily recombined, and finally Ni₂P/g-C₃N₄The excellent photocatalytic hydrogen evolution capability is shown.

The purpose of the present invention is to realize Ni having excellent photocatalytic hydrogen evolution capability₂P/g-C₃N₄The material is prepared by the following specific steps:

(1) a certain amount of g-C₃N₄Dispersing in water, adding NiCl of different volumes₂In the solution, a uniformly dispersed suspension is formed through stirring and ultrasonic treatment.

(2) Heating the suspension obtained in the step (1) in water bath, and then adding NaBH₄And (3) solution. Centrifuging after the reaction is finished, filtering and washing the mixture for multiple times by using ethanol and water, drying the mixture in vacuum, and grinding the mixture into uniform Ni/g-C by using a mortar₃N₄Powder;

(3) reacting NaH with₂PO₂And Ni/g-C obtained in step (2)₃N₄The powder is placed in a porcelain boat, the temperature is programmed to rise in a tubular furnace under the nitrogen atmosphere, and the temperature is naturally reduced to the room temperature after the reaction is finished.

Further, the NiCl in the step (1)₂The concentration of the solution is 0.02-0.06 mol.l^-1The volume is 0.1-10 ml.

Further, g to C described in step (1)₃N₄The mass of (A) is 100-300 mg.

Further, NaBH described in step (2)₄And NiCl₂The molar ratio of (1) is (0.002-0.02).

Further, the water bath heating in the step (2) is carried out at the temperature of 50-70 ℃, the reaction time is 30 min, and the stirring is kept ceaselessly.

Further, Ni/g-C described in step (3)₃N₄With NaH₂PO₂The mass ratio of (1): (5-10).

Further, step (ii)Ni/g-C described in step (3)₃N₄With NaH₂PO₂Respectively placing the two ends of the same porcelain boat with nitrogen gas from NaH₂PO₂Side blow to Ni/g-C₃N₄Laterally keeping the temperature at 250-350 ℃ for 1-3 h, wherein the heating rate is 0.5-3 ℃ per minute^-1And naturally cooling to room temperature.

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

(1) the invention adopts a two-step method to prepare the tightly combined Ni₂P/g-C₃N₄A photocatalyst. As cocatalyst, black Ni₂P enhances Ni₂P/g-C₃N₄And the visible light is absorbed, so that more photogenerated electrons are obtained to participate in the hydrogen production reaction. Furthermore, uniformly dispersed Ni₂The P particles can also be used as active sites for catalytic reaction, greatly accelerating g-C₃N₄Separation and transfer of photogenerated electrons and holes. g-C₃N₄The problems of serious inherent electron-hole recombination, poor conductivity and the like are relieved, Ni₂P/g-C₃N₄Shows excellent photocatalytic performance under visible light.

(2) Conventional noble metal promoters such as Pt, Au, Ru, etc. are expensive because of their limited widespread use. As cocatalyst, Ni₂P is a very potential precious metal substitute. At the same loading amount, Ni₂P/g-C₃N₄Expression ratio Pt/g-C₃N₄More excellent photocatalytic performance.

(3) The preparation method disclosed by the invention is simple in preparation steps, does not relate to a complicated chemical synthesis method and complicated technical processing, and the prepared composite material has excellent stability and photocatalytic hydrogen production performance and has a wide application prospect in practical application.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed to be used in the description of the embodiments will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other similar drawings can be obtained by those skilled in the art according to the drawings, wherein,

FIG. 1 shows Ni of the present invention₂P/g-C₃N₄A preparation flow chart of the visible light photocatalyst;

FIG. 2 shows Ni of the present invention₂P/g-C₃N₄A TEM image of a visible photocatalyst;

FIG. 3 shows Ni of the present invention₂P/g-C₃N₄HRTEM of visible photocatalyst;

FIG. 4 shows Ni of the present invention₂P/g-C₃N₄A UV-visible light diffuse reflection spectrogram of the visible light catalyst;

FIG. 5 shows Ni of the present invention₂P/g-C₃N₄Current-time curve of visible photocatalyst;

FIG. 6 shows Ni of the present invention₂P/g-C₃N₄Electrochemical impedance spectroscopy of a visible light photocatalyst;

FIG. 7 shows Ni of the present invention₂P/g-C₃N₄A fluorescence spectrum of the visible light catalyst;

FIG. 8 shows Ni of the present invention₂P/g-C₃N₄A performance diagram of hydrogen production by photocatalytic decomposition of water of the visible light catalyst;

FIG. 9 shows Ni of the present invention₂P/g-C₃N₄The stability of hydrogen produced by photocatalytic decomposition of visible light catalyst can be shown.

Detailed Description

The invention provides Ni without noble metal load₂P/g-C₃N₄The visible light photocatalyst and the preparation method thereof comprise the following steps:

the first step is as follows: preparation of Ni/g-C by chemical reduction method₃N₄Material

In one embodiment, the process is implemented as follows: 100-250 mg of g-C₃N₄Dispersing in 100 ml water, adding 0.02-0.06 mol.l of 0.1-10 ml^-1NiCl₂In the solution, a uniformly dispersed suspension is formed through stirring and ultrasonic treatment. Placing the suspension in a water bath, keeping the temperature at 50-70 ℃, and then adding NaBH₄Solution, stirring was continued. After 30 min of reactionCentrifuging, filtering and washing with ethanol and water for several times, vacuum drying, and grinding into uniform Ni/g-C₃N₄A powder;

the second step: preparation of Ni by low-temperature phosphating method₂P/g-C₃N₄Material

In one embodiment, the process is implemented as follows: reacting NaH with₂PO₂And Ni/g-C in the first step₃N₄The powder is respectively placed at two ends of the same porcelain boat according to the mass ratio of 1 (5-10), and nitrogen is introduced into the porcelain boat from NaH in a tube furnace₂PO₂Side blow to Ni/g-C₃N₄Laterally keeping the temperature at 250-350 ℃ for 1-3 h, wherein the heating rate is 0.5-3 ℃ per minute^-1And naturally cooling to room temperature.

In order to make the preparation scheme of the invention more clear, the technical scheme of the invention is further explained by combining the attached drawings and the examples. It should be noted that the following examples are given by way of illustration only and are not to be construed as limiting the scope of the invention, which is intended to be exemplary of the invention and that numerous insubstantial modifications and variations can be made by those skilled in the art in light of the above teachings.

In addition, the acronyms used in the invention are all fixed acronyms in the field, and some acronyms are explained as follows: TEM: a projection electron microscope; HRTEM: high resolution projection microscopy.

Example one

This embodiment prepares Ni as follows₂P/g-C₃N₄Visible light catalyst material:

200 mg of g-C₃N₄Dispersed in 100 ml of water, and 0.5 ml of 0.05 mol/l was added^-1 NiCl₂In the solution, a uniformly dispersed suspension is formed through stirring and ultrasonic treatment. The suspension was placed in a water bath and maintained at 60 ℃ and then 30 ml of 30 mg/ml was added^-1NaBH₄Solution, stirring was continued. After 30 min of reaction, centrifugation, multiple filtration washing with ethanol and water, vacuum drying, grinding into uniform powder with mortarNi/g-C₃N₄Powder;

the second step is that: preparation of Ni by low-temperature phosphating method₂P/g-C₃N₄Material

450 mg of NaH₂PO₂And 50 mg of Ni/g-C₃N₄The powder is respectively placed at two ends of the same porcelain boat, and nitrogen is introduced into the porcelain boat from NaH in a tube furnace₂PO₂Side blow to Ni/g-C₃N₄Laterally keeping at 350 deg.C for 2 h, and heating at 1 deg.C/min^-1And naturally cooling to room temperature.

Example two

200 mg of g-C₃N₄Dispersed in 100 ml of water, and 2.5 ml of 0.05 mol/l was added^-1 NiCl₂In the solution, a uniformly dispersed suspension is formed through stirring and ultrasonic treatment. The suspension was placed in a water bath and maintained at 60 ℃ and then 30 ml of 30 mg/ml was added^-1NaBH₄Solution, stirring was continued. After 30 min of reaction, centrifugation, multiple filtration washing with ethanol and water, vacuum drying, grinding into uniform Ni/g-C with mortar₃N₄Powder;

450 mg of NaH₂PO₂And 50 mg Ni/g-C₃N₄The powder is respectively placed at two ends of the same porcelain boat, and nitrogen is introduced into the porcelain boat from NaH in a tube furnace₂PO₂Side blow to Ni/g-C₃N₄Laterally keeping at 350 deg.C for 2 h, and heating at 1 deg.C/min^-1And naturally cooling to room temperature.

EXAMPLE III

This embodiment produces Ni in the following manner₂P/g-C₃N₄Visible light catalyst material:

200 mg of g-C₃N₄Dispersed in 100 ml of water, and 8 ml of 0.05 mol.l was added^-1 NiCl₂In the solution, a uniformly dispersed suspension is formed through stirring and ultrasonic treatment. The suspension was placed in a water bath and maintained at 60 ℃ and then 30 ml of 30 mg/ml was added^-1NaBH₄Solution, stirring was continued. After 30 min of reaction, centrifuging, filtering and washing with ethanol and water for many times, drying in vacuum, grinding into uniform Ni/g-C with mortar₃N₄Powder;

Example four

200 mg of g-C₃N₄Dispersed in 100 ml of water, and 18 ml of 0.05 mol.l was added^-1 NiCl₂In the solution, a uniformly dispersed suspension is formed through stirring and ultrasonic treatment. The suspension was placed in a water bath and maintained at 60 ℃ and then 30 ml of 30 mg/ml was added^-1NaBH₄Solution, stirring was continued. After 30 min of reaction, centrifugation, multiple filtration washing with ethanol and water, vacuum drying, grinding into uniform Ni/g-C with mortar₃N₄Powder;

450 mg of NaH₂PO₂And 50 mg of Ni/g-C₃N₄The powder is respectively placed at two ends of the same porcelain boat and is put in a tube furnace with nitrogenFrom NaH₂PO₂Side blow to Ni/g-C₃N₄Laterally keeping the temperature at 350 ℃ for 2 h, and increasing the temperature rate at 1 ℃ min^-1And naturally cooling to room temperature.

Ni prepared in example two₂P/g-C₃N₄The process flow of preparing the visible-light-driven photocatalyst is shown in fig. 1.

Ni prepared in example two₂P/g-C₃N₄TEM image of visible light catalyst please refer to FIG. 2, wherein g-C₃N₄The nano-sheet is in a fold shape, and Ni is obviously loaded on the nano-sheet₂P particles, which show that the result synthesizes Ni₂P/g-C₃N₄。

Ni prepared in example two₂P/g-C₃N₄HRTEM for visible photocatalyst please refer to figure 3,

ni in the figure₂P/g-C₃N₄The surface of the catalyst is obviously seen with Ni₂Lattice fringes of P with lattice spacing of 0.223 nm and pointing to Ni₂The (111) plane of P (PDF # 03-0953).

Ni prepared in example two₂P/g-C₃N₄Referring to fig. 4, the ultraviolet-visible diffuse reflectance spectrum of the visible-light-driven photocatalyst can be seen from pure Ni₂P has good light absorption. In being loaded with Ni₂P is then compared with pure g-C₃N₄，Ni₂P/g-C₃N₄The light absorption in the visible region is significantly enhanced, indicating that Ni₂P can broaden g-C₃N₄Light absorption range of (1).

Ni prepared in example two₂P/g-C₃N₄Current-time diagram of visible light photocatalyst please refer to FIG. 5, Ni after light-on₂P/g-C₃N₄Current density of (2) is compared with that of pure g-C₃N₄The current density of (2) is obviously increased, which indicates that Ni₂P/g-C₃N₄Has higher photoelectric conversion efficiency, Ni₂P contributes to g-C₃N₄Electron hole separation.

Ni prepared in example two₂P/g-C₃N₄Electrochemical impedance diagram of visible light catalyst please refer to fig. 6, Ni₂P/g-C₃N₄Impedance semi-circle diameter of less than g-C₃N₄(ii) description of Ni₂P/g-C₃N₄The resistance of (3) is smaller. This indicates that Ni₂P can improve g-C₃N₄Problem of poor conductivity, Ni₂P/g-C₃N₄Has the fastest electron transfer rate.

Ni prepared in example two₂P/g-C₃N₄FIG. 7 shows the fluorescence spectrum of the visible-light-driven photocatalyst, wherein the electron-hole recombination generates fluorescence, g-C₃N₄The fluorescence intensity of (A) is obviously higher, which indicates that the electron-hole recombination of the (A) is serious. Ni₂P/g-C₃N₄The lower fluorescence intensity is due to supported Ni₂P，Ni₂P inhibits g-C₃N₄The electron-hole recombination of (2) promotes the transfer of electrons.

Ni prepared in example two₂P/g-C₃N₄Referring to FIG. 8, the hydrogen production performance of visible light catalyst by photocatalytic water decomposition using triethanolamine as sacrificial agent is shown in FIG. 8, wherein the visible light catalyst is continuously illuminated (lambda is more than or equal to 400 nm) in a closed reactor for five hours, g-C₃N₄Without evolution of hydrogen, Ni₂P/g-C₃N₄Shows excellent photocatalytic hydrogen production performance, even superior to Pt/g-C loaded with 3 wt% of Pt by using the conventional chloroplatinic acid photo-deposition method₃N₄A catalyst. The hydrogen production rate per hour under visible light can reach 645.7 [ mu ] mol.g^-1·h^-1。

Ni prepared in example two₂P/g-C₃N₄Referring to fig. 9, the hydrogen production performance of the visible light catalyst after photocatalytic water decomposition was continuously measured for 12 hours (gas in the closed reactor was replaced with argon every 3 hours, and a new sacrificial reagent solution was not replaced in the middle), and Ni₂P/g-C₃N₄The catalyst also maintains good hydrogen production stability.

In summary, the present invention discloses a Chinese herbal medicine bagNi supported by noble metal₂P/g-C₃N₄The visible light catalyst and its preparation process features that based on available technology, Ni is first mixed with water₂P grains grow in situ at g-C₃N₄On the nano-chip, the interface is tightly combined. Ni₂P is used as a catalytic reaction site and an electron migration channel, and g-C is greatly improved₃N₄The photocatalytic performance of (2). The preparation condition is mild, the process is simple and easy to operate, the raw material source is wide, and the prepared composite material has excellent photocatalytic hydrogen production performance and is convenient for large-scale production and application. Can be well applied in the field of hydrogen production by photocatalytic decomposition.

It should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and although the present invention is described in detail with reference to the preferred embodiments, a person skilled in the art can modify or adjust the technical solutions of the present invention without departing from the essential scope of the technical solutions of the present invention, which should be covered in the scope of the claims of the present invention.

Claims

1. Ni without noble metal load₂P/g-C₃N₄The preparation method of the visible light catalyst is characterized in that the g-C₃N₄In-situ growth of Ni on nano-sheet₂The P particles have good tight combination, are not added with any noble metal, and still show excellent photocatalytic hydrogen production performance under visible light.

2. Ni supported noble metal free according to claim 1₂P/g-C₃N₄The preparation method of the visible light photocatalyst is characterized by comprising the following steps:

(1) g to C₃N₄Dispersing the nano-sheets in water, adding a Ni salt solution, and stirring and ultrasonically treating to form a uniform suspension;

(2) heating the suspension in the step (1) in water bath, and adding NaBH₄The solution, after the reaction, is centrifuged, repeatedly washed with water and ethanol, filtered, dried in vacuum and ground in a mortarForming into uniform powder;

(3) mixing the powder obtained in the step (2) with NaH₂PO₂And (4) programming the temperature in a tube furnace, and naturally cooling to room temperature.

3. Ni supported noble metal free according to claim 2₂P/g-C₃N₄The preparation method of the visible light photocatalyst is characterized in that the Ni salt in the step (1) is NiCl₂，NiCl₂The concentration of the solution is 0.01-0.08 mol/L, and the volume of the solution is 0.1-10 ml.

4. Ni supported without noble metal according to claim 2₂P/g-C₃N₄The preparation method of the visible light catalyst is characterized in that g-C in the step (1)₃N₄The mass of (A) is 100-300 mg.

5. Ni supported noble metal free according to claim 2₂P/g-C₃N₄The preparation method of the visible light photocatalyst is characterized in that NaBH is adopted in the step (2)₄And NiCl₂The molar ratio of (1) is (0.002-0.02).

6. Ni supported noble metal free according to claim 2₂P/g-C₃N₄The preparation method of the visible light photocatalyst is characterized in that the temperature of water bath heating in the step (2) is 50-70 ℃, the reaction time is 30 min, and the stirring is kept ceaselessly.

7. Ni supported without noble metal according to claim 2₂P/g-C₃N₄The preparation method of the visible light catalyst is characterized in that Ni/g-C in the step (3)₃N₄With NaH₂PO₂The mass ratio of (A) to (B) is 1 (5-10).

8. Ni supported noble metal free according to claim 2₂P/g-C₃N₄Method for preparing visible light catalyst, and visible light catalystCharacterized in that in step (3) Ni/g-C is put into a tube furnace₃N₄With NaH₂PO₂Respectively placing the two ends of the same porcelain boat with nitrogen gas from NaH₂PO₂Side blow to Ni/g-C₃N₄Laterally keeping the temperature at 250-350 ℃ for 1-3 h, wherein the heating rate is 0.5-3 ℃ per minute^-1。

9. Ni supported on a noble metal free material obtained by the method according to any one of claims 1 to 8₂P/g-C₃N₄A visible light photocatalyst.