CN111167499B - A kind of NiM-LDH/g-C3N4 composite photocatalytic material and preparation method thereof - Google Patents

Abstract

The invention discloses a NiM-LDH/g-C ₃ N ₄ composite photocatalytic material and a preparation method thereof. By using a mixed solvent of alcohol and water, g-C ₃ N ₄ , nickel salt and transition metal are added in the solvent heat treatment process Salt, surfactant and precipitating agent, so that g-C ₃ N ₄ can be stripped to obtain ultra-thin porous g-C ₃ N ₄ , and at the same time, ultra-thin two-dimensional NiM can be generated in situ on the surface of g-C ₃ N ₄ Hydrated hydroxide. The preparation method of the present invention is simple and easy, has good repeatability, is safe and reliable, and the NiM‑LDH/g‑C ₃ N ₄ composite photocatalytic material prepared by the present invention is an ultrathin two-dimensional composite photocatalytic material, and the cost is relatively low. Low, high specific surface area, and greatly enhanced photogenerated electron-hole separation efficiency and light absorption performance, has high catalytic activity and stability for visible light catalytic photolysis of water to produce hydrogen, and can realize visible light catalytic efficient hydrogen production.

Description

A kind of NiM-LDH/g-C3N4 composite photocatalytic material and preparation method thereof

technical field

The invention belongs to the technical field of composite photocatalytic materials, and in particular relates to a NiM-LDH/gC ₃ N ₄ composite photocatalytic material and a preparation method thereof.

Background technique

Hydrogen energy has a high combustion calorific value, and the combustion process is clean and pollution-free. It is the most promising secondary energy in the future. In recent years, fuel cell vehicles and distributed power stations based on hydrogen energy have flourished. Photolysis of water to produce hydrogen with the help of semiconductor photocatalysts converts solar energy into hydrogen energy, which is the ultimate way to achieve low-carbon, clean and sustainable energy in the entire process.

The design and development of photocatalytic materials is the key to realizing efficient hydrogen production by photolysis of water. The semiconductors used to catalyze photolysis of water to produce hydrogen mainly include TiO ₂ , ZnO, CdS and gC ₃ N ₄ , etc. Among them, the graphitized gC ₃ N ₄ sheet material has the advantages of simple preparation process, low cost, good chemical stability, visible light Response and other advantages, it is an ideal catalytic material. In the gC ₃ N ₄ plane, the "Melem" unit is connected by N atoms, and the interlayers are combined by van der Waals force, and the interlayer distance is 0.33nm. The band gap of gC ₃ N ₄ is about 2.7eV, and its conduction band and valence band positions are -1.3V and 1.4V respectively. Oxygenation of water. In 2009, Wang et al. reported for the first time that gC ₃ N ₄ prepared by thermal polymerization of cyanamide was used as a visible light catalyst for photolysis of water. Under visible light, the H ₂ generation rate was 106 μmol g ^{- 1} h ^-1 . Although the quantum yield reported at that time was low, gC ₃ N ₄ was non-toxic, easy to prepare, and good stability, showing its excellent characteristics as a photocatalytic material. Once reported, it attracted great attention in the field of photocatalysis. However, at present, gC ₃ N ₄ is mainly prepared by high-temperature heat treatment, which has the disadvantages of thicker sheets, weaker absorption of visible light, and faster recombination of photogenerated electrons and holes. Its performance for photocatalytic hydrogen production is still low, and it is far from practicality. .

In order to improve the photocatalytic hydrogen production performance of gC ₃ N ₄ , on the one hand, thin-layer two-dimensional materials can be prepared by exfoliating the bulk phase gC ₃ N ₄ to increase the specific surface area and active sites of gC ₃ N ₄ , as well as the electron-hole separation efficiency, thereby Improving the catalytic hydrogen production performance of gC ₃ N ₄ under visible light. On the other hand, constructing a heterojunction by compounding the second component semiconductor can not only increase its visible light absorption performance, but also the built-in electric field of the heterojunction can greatly improve the separation efficiency of photogenerated carriers. Hydrotalcite-like layered double hydroxides (LDH)[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^z+ (A ^n- ) _z/n ·yH ₂ O as a new class of two-dimensional materials , has the advantages of adjustable composition and structure, high specific surface area, good chemical stability, abundant surface hydroxyl groups, and visible light response. It has become a research hotspot as a heterojunction semiconductor in composite photocatalytic materials.

However, the existing NiM-LDH/gC ₃ N ₄ composite photocatalytic materials have relatively thick sheets and low photocatalytic hydrogen production performance, which is still far from practical application.

Contents of the invention

The present invention aims to solve at least one of the technical problems existing in the prior art. For this reason, the present invention proposes a NiM-LDH/gC ₃ N ₄ composite photocatalytic material and its preparation method, using alcohol water mixed solvent, adding gC ₃ N ₄ , nickel salt, transition metal salt, surface Activator and precipitant, the prepared NiM-LDH/gC ₃ N ₄ ultrathin two-dimensional composite photocatalytic material can greatly enhance the photogenerated electron-hole separation efficiency and light absorption performance, and then realize the efficient hydrogen production by visible light catalysis.

In order to overcome the problems of the technologies described above, the technical scheme adopted in the present invention is as follows:

A kind of NiM-LDH/gC ₃ N ₄ preparation method of composite photocatalytic material, comprises the steps:

a) isolate the air and pyrolyze the urea to obtain gC ₃ N ₄ powder;

b) Add gC ₃ N ₄ powder, Ni salt, transition metal salt, surfactant and precipitant to the mixed solvent of alcohol and water, ultrasonicate, seal, perform solvent heat treatment, filter after natural cooling, and wash with pure water for 3-5 times, the NiM-LDH/gC ₃ N ₄ composite photocatalytic material was obtained by drying.

In step a), the heating rate during pyrolysis to prepare gC ₃ N ₄ is 2-5°C/min, the pyrolysis temperature is 500-600°C, and the pyrolysis time is 1-5h.

As a further improvement of the above scheme, the alcohol in the alcohol-water mixed solvent is selected from one of methanol, ethanol, n-propanol, n-butanol and n-pentanol. Preference is given to n-butanol.

As a further improvement of the above scheme, the volume ratio of alcohol to water in the alcohol-water mixed solvent is (1-9):3. Preferably 1:1.

As a further improvement of the above scheme, the molar ratio of the Ni salt to the transition metal salt, surfactant, precipitant is 1:(1-9):(5-10):(10-20), the NiM- The mass ratio of LDH to gC ₃ N ₄ is 1:(9-20).

As a further improvement of the above solution, the Ni salt is selected from one of nickel nitrate, nickel sulfate, nickel chloride or nickel oxalate.

As a further improvement of the above solution, the transition metal salt is selected from one of iron salts, cobalt salts, chromium salts or aluminum salts. The iron salt is selected from one of ferric nitrate, ferric chloride and ferric sulfate, preferably ferric nitrate; the cobalt salt is selected from one of cobalt nitrate, cobalt chloride and cobalt sulfate, preferably cobalt nitrate; the chromium salt is selected from chromium nitrate , one in chromium chloride, chromium sulfate, preferably chromium nitrate; the aluminum salt is selected from one of aluminum nitrate, aluminum chloride, aluminum sulfate, preferably aluminum nitrate;

As a further improvement of the above solution, the surfactant is selected from one of polyvinylpyrrolidone, cetyl ammonium bromide, sodium citrate or ascorbic acid. Sodium citrate is preferred.

As a further improvement of the above scheme, the precipitation agent is selected from one of sodium hydroxide, sodium carbonate or urea. Urea is preferred.

As a further improvement of the above solution, the temperature of the solvent heat treatment is 100-150° C., and the duration of the solvent heat treatment is 12-24 hours.

A NiM-LDH/gC ₃ N ₄ composite photocatalytic material is prepared according to the above preparation method.

Beneficial effects of the present invention: the present invention proposes a NiM-LDH/gC ₃ N ₄ composite photocatalytic material and its preparation method, using alcohol-water mixed solvent, adding gC ₃ N ₄ , nickel salt, transition metal in the solvent heat treatment process Salt, surfactant and precipitant, so that gC ₃ N ₄ can be stripped to obtain ultrathin porous gC ₃ N ₄ , and at the same time, ultrathin two-dimensional NiM hydrated hydroxide can be generated in situ on the surface of gC ₃ N ₄ . The preparation method of the present invention is simple and easy, has good repeatability, is safe and reliable, and the NiM-LDH/gC ₃ N ₄ composite photocatalytic material prepared by the present invention is an ultrathin two-dimensional composite photocatalytic material with low cost. The specific surface area is high, and the photogenerated electron-hole separation efficiency and light absorption performance are greatly enhanced. It has high catalytic activity and stability for visible light catalytic photolysis of water to produce hydrogen, and can realize efficient hydrogen production through visible light catalysis.

Description of drawings

Figure 1 shows the NiFe-LDH/gC ₃ N ₄ two-dimensional ultra-thin photoresist with different loadings (NiFe-LDH loadings were 2.5wt%, 5.0wt%, 7.5wt% and 10wt%) obtained in Examples 2-5. Visible light catalytic photolysis water hydrogen production activity curves of the finished catalytic material and the bulk NiFe-LDH/gC ₃ N ₄ (comparative sample) prepared in Comparative Example 1;

Fig. 2 is the cycle stability curve of the NiFe-LDH/gC ₃ N ₄ -5.0 two-dimensional ultra-thin composite photocatalytic material with a loading of 5.0 wt% in Example 3.

Detailed ways

The present invention will be specifically described below in conjunction with the embodiments, so that those skilled in the art can understand the present invention. It is necessary to point out here that the embodiments are only used to further illustrate the present invention, and cannot be interpreted as limiting the protection scope of the present invention. Those skilled in the art can make non-essential improvements to the present invention according to the above-mentioned content of the invention And adjustments should still belong to the protection scope of the present invention. Meanwhile, if the raw materials mentioned below are not specified in detail, they are all commercially available products; the process steps or extraction methods not mentioned in detail are all process steps or extraction methods known to those skilled in the art.

Example 1

Preparation of High Specific Surface Porous gC ₃ N ₄

Put 20 g of urea into a 50 mL crucible, cover it, put it into a muffle furnace, raise the temperature to 550 °C at a heating rate of 2 °C/min, keep the temperature for 4 h, and then cool it down to room temperature naturally. Take it out and grind it finely to obtain gC ₃ N ₄ beige powder with high specific surface porosity.

Example 2

Preparation of NiFe-LDH/gC ₃ N ₄ -2.5 Two-Dimensional Ultrathin Composite Catalytic Material

Weigh 0.488g of the gC ₃ N ₄ powder prepared in Example 1 in a polytetrafluoroethylene tank, add 25mL of n-butanol and 25mL of purified water, then add 100mg of urea, 34mg of nickel nitrate, 7.5mg of iron nitrate and 200mg of sodium citrate , ultrasonically dispersed for 20min, then capped and sealed, placed in a water-heated oven at 120°C for heat treatment for 12h, filtered after natural cooling, washed 3-5 times with pure water, and dried at 80°C for 10h to obtain a NiFe-LDH content of 2.5wt%. The NiFe-LDH/gC ₃ N ₄ two-dimensional ultrathin composite photocatalytic material is recorded as NiFe-LDH/gC ₃ N ₄ -2.5.

Example 3

Preparation of NiFe-LDH/gC ₃ N ₄ -5.0 Two-dimensional Ultrathin Composite Catalytic Material

Weigh 0.475g of the _gC3N4 powder prepared in Example 1 in a polytetrafluoroethylene tank, add 25mL of n-butanol and 25mL _of purified water, then add 200mg of urea, 67mg of nickel nitrate, 15mg of ferric nitrate and 400mg of sodium citrate, Ultrasonic dispersion for 20 minutes, then capped and sealed, placed in a water-heated oven at 120°C for heat treatment for 12 hours, filtered after natural cooling, washed 3-5 times with pure water, and dried at 80°C for 10 hours to obtain a NiFe-LDH content of 5.0wt%. The NiFe-LDH/gC ₃ N ₄ two-dimensional ultrathin composite photocatalytic material is denoted as NiFe-LDH/gC ₃ N ₄ -5.0.

Example 4

Preparation of NiFe-LDH/gC ₃ N ₄ -7.5 Two-Dimensional Ultrathin Composite Catalytic Material

Weigh 0.463g of the gC ₃ N ₄ powder prepared in Example 1 in a polytetrafluoroethylene tank, add 25mL of n-butanol and 25mL of purified water, then add 300mg of urea, 101mg of nickel nitrate, 22.5mg of iron nitrate and 600mg of sodium citrate , ultrasonically dispersed for 20 minutes, then sealed with a cover, placed in a water-heated oven at 120°C for heat treatment for 12 hours, filtered after natural cooling, washed 3-5 times with pure water, and dried at 80°C for 10 hours to obtain a NiFe-LDH content of 7.5wt%. The NiFe-LDH/gC ₃ N ₄ two-dimensional ultrathin composite photocatalytic material is recorded as NiFe-LDH/gC ₃ N ₄ -7.5.

Example 5

Preparation of NiFe-LDH/gC ₃ N ₄ -10 Two-Dimensional Ultrathin Composite Catalytic Material

Weigh 0.463g of the gC ₃ N ₄ powder prepared in Example 1 into a polytetrafluoroethylene tank, add 25mL of n-butanol and 25mL of purified water, then add 400mg of urea, 134mg of nickel nitrate, 30mg of ferric nitrate and 800mg of sodium citrate, and ultrasonically Disperse for 20 minutes, then cover and seal, place in a water-heated oven at 120°C for heat treatment for 12 hours, filter after natural cooling, wash with pure water for 3-5 times, and dry at 80°C for 10 hours to obtain NiFe with a NiFe-LDH content of 10.0wt%. -LDH/gC ₃ N ₄ two-dimensional ultrathin composite photocatalytic material, recorded as NiFe-LDH/gC ₃ N ₄ -10.0.

Comparative example 1

Preparation of Bulk NiFe LDH/gC ₃ N ₄ -R Comparative Samples

Weigh 0.475g of the _gC3N4 powder prepared in Example 1 into a beaker _, add 50mL of pure water, then add 67mg of nickel nitrate and 15mg of ferric nitrate, ultrasonically disperse for 20min, and then dropwise add 0.1mol/L NaOH solution until the pH is 9 After aging for 12 hours, filter, wash with pure water for 3-5 times, and dry at 80°C for 10 hours to obtain a NiFe LDH/gC ₃ N ₄ -R bulk composite photocatalytic material with a NiFe-LDH content of 5.0 wt%.

Example 6

Activity evaluation of catalytic materials for visible light catalytic hydrogen production

Weigh 100 mg of the NiFe-LDH/gC ₃ N ₄ two-dimensional ultra- Thin photocatalytic material and the comparative sample of bulk phase NiFe-LDH/gC ₃ N ₄ -R prepared in Comparative Example 1 were placed in the photocatalytic reactor, and 80mL high-purity water and 20mL triethanolamine were taken in the photocatalytic reactor, and condensed at a constant temperature of 8 ℃, vacuum degassing for 30min. Then use a 300W xenon lamp light source to illuminate, the light source is 15cm away from the liquid surface, and add a 400nm filter to filter out the ultraviolet part. Every 1 hour of the reaction interval, the chromatographic automatic online sampling was carried out for analysis. The amount of H ₂ produced was quantitatively calculated by the external standard method. The amount of hydrogen produced was expressed in μmol, and the rate of hydrogen production was expressed in μmol.g ^-1 .h ^-1 .

It can be seen from Figure 1 that the NiFe-LDH/gC ₃ N ₄ two-dimensional ultrathin heterojunction photocatalytic material has a higher activity than the bulk NiFe-LDH/gC ₃ N ₄ . The effect of NiFe-LDH loading on the photocatalytic activity of the composite catalyst was a volcano-shaped curve. The highest activity was 1770μmol.g ^-1 .h ^-1 when the loading of NiFe-LDH was 5.0wt%.

Example 7

Study on Stability of Catalytic Materials for Photocatalytic Hydrogen Production

Weigh NiFe-LDH/gC ₃ N ₄ two-dimensional ultra-thin heterojunction photocatalytic material in the photocatalytic reactor, measure 80mL high-purity water and 20mL triethanolamine in the photocatalytic reactor, condense at a constant temperature of 8°C, and vacuumize Air for 30 minutes. Then use a 300W xenon lamp light source to illuminate, the light source is 15cm away from the liquid surface, and add a 400nm filter to filter out the ultraviolet part. Every 1 hour of the reaction interval, the chromatographic automatic online sampling was carried out for analysis. The amount of H ₂ produced was quantitatively calculated by the external standard method. The amount of hydrogen produced was expressed in μmol, and the rate of hydrogen production was expressed in μmol.g ^-1 .h ^-1 . After one cycle test is completed, vacuumize and degas, repeat the above steps to evaluate its activity, and check its stability through multiple cycles.

It can be seen from Figure 2 that after 4 cycles, the activity of the catalytic material did not decrease significantly, and the stability was high.

For those of ordinary skill in the technical field to which the present invention belongs, some simple deductions or substitutions can be made without departing from the concept of the present invention without creative work. Therefore, simple improvements made to the present invention by those skilled in the art based on the disclosure of the present invention should all be within the protection scope of the present invention. The above-mentioned embodiments are preferred embodiments of the present invention, and all processes similar to those of the present invention and equivalent changes should all belong to the protection category of the present invention.

Claims (7)

1. NiFe-LDH/g-C ₃ N ₄ The preparation method of the composite photocatalytic material is characterized by comprising the following steps:

a) Pyrolyzing urea in the absence of air to obtain g-C ₃ N ₄ A powder;

b) Adding g-C into alcohol-water mixed solvent ₃ N ₄ Powder, ni salt, ferric nitrate, surfactant and precipitant, ultrasonic treating, sealing, performing solvent heat treatment, naturally cooling, filtering, washing with purified water for 3-5 times, and drying to obtain NiFe-LDH/g-C ₃ N ₄ A composite photocatalytic material;

the surfactant is selected from one of polyvinylpyrrolidone, cetyl ammonium bromide, sodium citrate or ascorbic acid;

the molar ratio of the Ni salt to the ferric nitrate, the surfactant and the precipitator is 1 (1-9) to (5-10) to (10-20), and the NiFe-LDH and g-C are ₃ N ₄ The mass ratio of (1) to (9-20).

2. The method according to claim 1, wherein the alcohol in the alcohol-water mixed solvent is one selected from methanol, ethanol, n-propanol, n-butanol, and n-pentanol.

3. The production method according to claim 1, wherein the volume ratio of alcohol to water in the alcohol-water mixed solvent is (1-9): 3.

4. The method according to claim 1, wherein the Ni salt is one selected from nickel nitrate, nickel sulfate, nickel chloride, and nickel oxalate.

5. The method of claim 1, wherein the precipitating agent is selected from one of sodium hydroxide, sodium carbonate, or urea.

6. The method of claim 1, wherein the solvothermal treatment temperature is 100-150 ℃ and the solvothermal treatment time is 12-24h.

7. NiFe-LDH/g-C ₃ N ₄ The composite photocatalytic material is characterized in that the NiFe-LDH/g-C ₃ N ₄ The composite photocatalytic material is prepared according to the preparation method of any one of claims 1 to 6.

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