CN112516990B - A kind of synthesis method of layered perovskite type photocatalyst and its application - Google Patents

Abstract

The invention discloses a method for synthesizing a layered perovskite type photocatalyst. The steps are: (1) dissolving SrCl ₂ ·6H ₂ O, a bismuth source and tetrabutyl titanate in a nitric acid solution to obtain a raw material solution; ( 2) drop the obtained raw material into the sodium hydroxide solution, then carry out hydrothermal synthesis to obtain a white suspension; (3) cool the suspension, filter, take the filter residue, wash the filter residue and dry to obtain a layered liquid Perovskite Sr ₂ Bi ₄ Ti ₅ O ₁₈ . The application of the above-mentioned layered perovskite photocatalyst in photocatalytic reaction is also disclosed. The preparation process of the present application is simple, the reaction controllability is good, the formed layered perovskite type Sr ₂ Bi ₄ Ti ₅ O ₁₈ has strong light absorption capacity, wide light absorption range, high photogenerated carrier activity, and photocatalytic hydrogen production capacity. The strength is more than 3.2 times that of traditional TiO ₂ , more than 2.8 times that of solid-phase sintering synthesis, and more than 2 times that of Bi ₄ Ti ₃ O ₁₂ .

Description

A kind of synthesis method of layered perovskite type photocatalyst and its application

technical field

The invention relates to a synthesis method and application of a layered perovskite type photocatalyst, and belongs to the field of photocatalysts.

Background technique

With the continuous increase of the world's population and the rapid development of industrialization, energy consumption and energy demand remain high, and the resulting energy crisis and environmental pollution have attracted more and more attention. In recent years, photocatalytic technology has developed rapidly, and its pollutant decomposition efficiency and hydrogen production efficiency have been continuously improved. However, most of the current semiconductor materials have short photo-generated carrier lifetimes, short average diffusion lengths, low separation efficiency of photo-generated electron-hole pairs, and low photocatalytic activity. Their photocatalytic properties are far from meeting the needs of practical applications. .

Perovskite materials exhibit high light absorption rate and energy conversion efficiency in the visible light range, and show good application prospects in renewable energy production such as photovoltaics and photocatalysis. Sr ₂ Bi ₄ Ti ₅ O ₁₈ is located at the intersection of conventional ferroelectric, layered bismuth-based semiconductors and perovskite-structured crystals, which combines many advantages and shows great photocatalytic potential. However, the current research on Sr ₂ Bi ₄ Ti ₅ O ₁₈ mainly focuses on its application in ferroelectric ceramics and has not been applied to the field of photocatalysis.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention proposes a synthesis method of a layered perovskite type photocatalyst. The chemical formula of the layered perovskite type photocatalyst is: Sr ₂ Bi ₄ Ti ₅ O ₁₈ ; the synthesis method includes the following steps: step:

(1) dissolving SrCl ₂ ·6H ₂ O, bismuth source and tetrabutyl titanate in a nitric acid solution to obtain a raw material solution;

(2) the gained raw material is added dropwise in sodium hydroxide solution, then carry out hydrothermal synthesis to obtain white suspension;

(3) cooling the suspension, filtering, taking the filter residue, washing and drying the filter residue to obtain layered perovskite type Sr ₂ Bi ₄ Ti ₅ O ₁₈ .

In step (2), after completing the dropwise addition of the raw material liquid to the sodium hydroxide solution, continue stirring for 30-120 minutes, while making the reaction fully carried out, the heat of reaction can also be discharged in time to avoid acid-base neutralization. The heat released during the reaction is too large, which affects the smooth progress of the subsequent hydrothermal reaction. The strong alkalinity of concentrated sodium hydroxide solution hydrolyzes tetrabutyl titanate into dissolved titanate, and a uniform reaction solution is beneficial to the formation of nanostructures. A further hydrothermal reaction dissolves the reactants—recrystallizes to achieve atomic-level homogeneous mixing.

Specifically, the bismuth source is bismuth nitrate or bismuth sulfate.

The preparation process of the present application is simple, the reaction controllability is good, the formed layered perovskite type Sr ₂ Bi ₄ Ti ₅ O ₁₈ has strong light absorption capacity, wide light absorption range, high photogenerated carrier activity, and photocatalytic hydrogen production capacity. The strength is more than 3.2 times that of traditional TiO ₂ , more than 2.8 times that of solid-phase sintering synthesis, and more than 2 times that of Bi ₄ Ti ₃ O ₁₂ .

Sr ₂ Bi ₄ Ti ₅ O ₁₈ is a typical bismuth layered perovskite structure ferroelectric material, its basic structural feature is that a fluorite structure bismuth oxide layer (Bi ₂ O ₂ ) ²⁺ , due to the insertion of the bismuth oxygen layer, the material system exhibits obvious anisotropy, which makes the material system tend to form a nanosheet morphology with high surface area during the synthesis and preparation; its valence band The energy levels consist of highly discrete Bi 6s and O 2p hybrid orbitals, which are more favorable for the migration of photogenerated holes and the corresponding photocatalytic oxidation reactions. And due to the existence of the bismuth oxide layer, Sr ₂ Bi ₄ Ti ₅ O ₁₈ has very high structure and performance tunability. The rational use of doping and other means may be able to improve its ferroelectric properties to a certain extent, which is very beneficial to effectively separate photogenerated carriers and improve photocatalytic activity, but the existing Sr ₂ Bi ₄ Ti ₅ O ₁₈ products cannot be used as photocatalysts. catalyst used.

It has been found through experiments that the existing Sr ₂ Bi ₄ Ti ₅ O ₁₈ products are mainly used in ferroelectric ceramics, and the production of Sr ₂ Bi ₄ Ti ₅ O ₁₈ is synthesized by high-temperature solid-phase reaction, which results in a relatively small particle size of the product. large, the effective reaction sites are insufficient, and photons cannot be effectively absorbed, and photogenerated carriers are generated. The Sr ₂ Bi ₄ Ti ₅ O ₁₈ product produced by the hydrothermal synthesis method has a suitable forbidden band width and nanostructure, which can absorb photons effectively and generate photo-generated carriers to the maximum extent, so that it has the function of photocatalyst . Compared with the solid-phase sintered crystal, the hydrothermal synthesis has fewer growth defects and better orientation, and the appropriate size effectively reduces the recombination of photogenerated electrons and holes. The spontaneous ferroelectric polarization of Sr ₂ Bi ₄ Ti ₅ O ₁₈ further promotes the photogenerated The separation and migration of electrons and holes greatly increases its photocatalytic performance.

Specifically, the temperature of the hydrothermal synthesis is 180-240° C., and the time is 24-72 h. Under this condition, the as-synthesized Sr ₂ Bi ₄ Ti ₅ O ₁₈ exhibited flake-like morphology. Within this temperature and time range, the synthesis of Sr ₂ Bi ₄ Ti ₅ O ₁₈ is favorable and the generation of impurities is reduced, and the crystallinity is improved with the increase of temperature and time.

Specifically, the concentration of the nitric acid solution is 4-5 mol/L, and the concentration of the sodium hydroxide solution is 6-9 mol/L. The volume ratio of nitric acid solution and sodium hydroxide solution is 1:1-1:1.2.

Under the above concentration of nitric acid solution, metal ions can be quickly and fully dissolved, but layered perovskite type Sr ₂ Bi ₄ Ti ₅ O ₁₈ cannot be synthesized under acidic conditions. Sodium is used to provide the strong alkaline environment required for the reaction to obtain the desired product. The desired product can be obtained under the limitations of the concentration of the nitric acid solution, the concentration of the sodium hydroxide solution and the volume ratio of the nitric acid solution and the sodium hydroxide solution. When the alkali concentration is insufficient or too alkaline, the product impurities are too much, which is not conducive to the acquisition of pure-phase products.

The volume ratio of the above-mentioned nitric acid solution and the sodium hydroxide solution also plays the function of absorbing the reaction heat in time under the condition that the effective alkali concentration is guaranteed to be improved. , due to the sharp rise of the solution temperature, the volatilization of the solution and the pyrolysis of some precursors in the solution are caused.

Further, the drying temperature of the filter residue is 60-80° C., and the drying time is 7-10 h. After hydrothermal synthesis, it was naturally cooled to room temperature, and then filtered. At the above temperature, the product after the hydrothermal reaction can be rapidly dried without affecting the structure of the product.

The layered perovskite type Sr ₂ Bi ₄ Ti ₅ O ₁₈ described in any one of the above is used as a photocatalyst.

According to the preparation method of the layered perovskite-type Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst provided by the present invention, all preparations are pure phases, exhibiting regular sheet-like morphology, providing active sites for photocatalytic reaction, and The water splitting performance of the prepared photocatalyst materials is better than that of traditional photocatalysts, and the synthesis conditions are mild, the product purity is high, the crystal grains are well developed, the particle size is small and uniformly distributed, and the morphology is highly controllable. The synthesis route and device Simple and conducive to large-scale production.

Description of drawings

FIG. 1 is an X-ray diffraction (XRD) pattern of Sr ₂ Bi ₄ Ti ₅ O ₁₈ synthesized in Example 4. FIG.

FIG. 2 is a scanning electron microscope (SEM) image of Sr ₂ Bi ₄ Ti ₅ O ₁₈ synthesized in Example 4. FIG.

Detailed ways

Example 1

1. Measure 30mL of 4mol/L nitric acid solution and pour it into a beaker, and weigh 1.5mmol SrCl ₂ ·6H ₂ O, 1.5mmol Bi ₂ (SO ₄ ) ₃ , 3.75 mol according to the stoichiometric ratio of Sr ₂ Bi ₄ Ti ₅ O ₁₈ mmol tetrabutyl titanate was dissolved in the nitric acid solution and stirred for 10 min to obtain a raw material solution.

2. Dissolve 7.2 g of NaOH in 30 mL of deionized water, stir for 5 min, and let it cool to room temperature to obtain a sodium hydroxide solution.

3. While stirring, drop the raw material into the sodium hydroxide solution with a dropper. After the dropwise addition is completed, stir for 30 minutes to make it evenly mixed, and then transfer it to a 100 mL hydrothermal reaction kettle, and keep it at 180 °C for 72 hours. After the reaction was completed, the reaction solution was cooled to room temperature, and then the precipitate was collected by centrifugation, washed three times with ethanol and deionized water, dried in an oven at 60°C for 10 hours, and ground into powder to obtain Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 1 #.

Detection:

40mg Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 1#, 40mg traditional photocatalyst TiO ₂ , 40mg photocatalyst Bi ₄ Ti ₃ O ₁₂ and 40mg solid phase sintered Sr ₂ Bi ₄ Ti ₅ O ₁₈ were put into methanol solution respectively, Four test solutions were made, and then the four test solutions were irradiated with a 500W medium pressure mercury lamp for 5 hours, and it was measured that Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 1# catalyzed and generated 16μmol H ₂ , Bi ₄ Ti ₃ O ₁₂ photocatalyst The catalyst catalyzed the production of 7.9μmol H ₂ , while the Sr ₂ Bi ₄ Ti ₅ O ₁₈ synthesized by solid-phase sintering catalyzed 5.6μmol of H ₂ , and the TiO ₂ photocatalyst catalyzed only 5μmol of H ₂ . The methanol solution was prepared by mixing 3 ml methanol and 30 ml deionized water.

Example 2

1. Measure 28.4mL of 4.3mol/L nitric acid solution and pour it into a beaker, weigh 1.5mmol SrCl ₂ ·6H ₂ O, 3mmol Bi(NO ₃ ) ₃ ·5H according to the stoichiometric ratio of Sr ₂ Bi ₄ Ti ₅ O _{18 2} O and 3.75 mmol of tetrabutyl titanate were dissolved in the nitric acid solution and stirred for 10 min to obtain a raw material solution.

2. Dissolve 8.4 g of NaOH in 30 mL of deionized water, stir for 5 min, and let it cool to room temperature to obtain a sodium hydroxide solution.

3. Use a dropper to drop the raw material into the sodium hydroxide solution while stirring. After the dropwise addition is completed, stir for 60 minutes to make it evenly mixed, and then transfer it to a 100 mL hydrothermal reaction kettle, and keep it at 200 °C for 56 hours. After the reaction was completed, the reaction solution was cooled to room temperature, then centrifuged to collect the precipitate, washed three times with ethanol and deionized water each, dried in an oven at 67°C for 9 hours, and ground into powder to obtain Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 2 #.

Detection:

Put 40mg Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 2#, 40mg traditional photocatalyst TiO ₂ , 40mg photocatalyst Bi ₄ Ti ₃ O ₁₂ and 40mg solid phase sintered Sr ₂ Bi ₄ Ti ₅ O ₁₈ into methanol solution respectively, Four test solutions were made, and then the four test solutions were irradiated with a 500W medium pressure mercury lamp for 5 hours, and it was measured that Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 2# catalyzed and generated 15.4μmol H ₂ , Bi ₄ Ti ₃ O ₁₂ The photocatalyst catalyzed the generation of 7.9μmol H ₂ , while the Sr ₂ Bi ₄ Ti ₅ O ₁₈ synthesized by solid-phase sintering catalyzed 5.6μmol H ₂ , and the TiO ₂ photocatalyst catalyzed only 5μmol H ₂ . The methanol solution was prepared by mixing 3 ml methanol and 30 ml deionized water.

Example 3

1. Measure 26.7mL of 4.6mol/L nitric acid solution and pour it into a beaker, weigh 1.5mmol SrCl ₂ ·6H ₂ O, 1.5mmol Bi ₂ (SO ₄ ) ₃ according to the stoichiometric ratio of Sr ₂ Bi ₄ Ti ₅ O ₁₈ , 3.75mmol of tetrabutyl titanate was dissolved in nitric acid solution, stirred for 10min, to obtain a raw material solution.

2. Dissolve 9.6 g of NaOH in 30 mL of deionized water, stir for 5 min, and let it cool to room temperature to obtain a sodium hydroxide solution.

3. While stirring, drop the raw material into the sodium hydroxide solution with a dropper. After the dropwise addition is completed, stir for 90 minutes to make it evenly mixed, and then transfer it to a 100 mL hydrothermal reaction kettle, and keep it at 220 °C for 40 hours. After the reaction was completed, the reaction solution was cooled to room temperature, then centrifuged to collect the precipitate, washed three times with ethanol and deionized water each, dried in an oven at 73°C for 8 hours, and ground into powder to obtain Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 3 #.

Detection:

40mg Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 3#, 40mg traditional photocatalyst TiO ₂ , 40mg photocatalyst Bi ₄ Ti ₃ O ₁₂ and 40mg solid phase sintered Sr ₂ Bi ₄ Ti ₅ O ₁₈ were put into methanol solution respectively, Four test solutions were made, and then the four test solutions were irradiated with a 500W medium pressure mercury lamp for 5 hours, and it was measured that Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 3# catalyzed and generated 15.7μmol H ₂ , Bi ₄ Ti ₃ O ₁₂ The photocatalyst catalyzed the generation of 7.9μmol H ₂ , while the Sr ₂ Bi ₄ Ti ₅ O ₁₈ synthesized by solid-phase sintering catalyzed 5.6μmol H ₂ , and the TiO ₂ photocatalyst catalyzed only 5μmol H ₂ . The methanol solution was prepared by mixing 3 ml methanol and 30 ml deionized water.

Example 4

1. Measure 25mL of 5mol/L nitric acid solution and pour it into a beaker, weigh 1.5mmol SrCl ₂ ·6H ₂ O, 3mmol Bi(NO ₃ ) ₃ ·5H ₂ O according to the stoichiometric ratio of Sr ₂ Bi ₄ Ti ₅ O ₁₈ , 3.75mmol of tetrabutyl titanate was dissolved in nitric acid solution, stirred for 10min, to obtain a raw material solution.

2. Dissolve 10.8 g of NaOH in 30 mL of deionized water, stir for 5 min, and let it cool to room temperature to obtain a sodium hydroxide solution.

3. Use a dropper to drop the raw materials into the sodium hydroxide solution while stirring. After the dropwise addition is completed, stir for 120 minutes to make it evenly mixed, and then transfer it to a 100 mL hydrothermal reactor, and keep it at 240 °C for 24 hours. After the reaction was completed, the reaction solution was cooled to room temperature, and then the precipitate was collected by centrifugation, washed three times with ethanol and deionized water, dried in an oven at 80°C for 7 hours, and ground into powder to obtain Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 4 #.

Detection:

40mg Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 4#, 40mg traditional photocatalyst TiO ₂ , 40mg photocatalyst Bi ₄ Ti ₃ O ₁₂ and 40mg solid phase sintered Sr ₂ Bi ₄ Ti ₅ O ₁₈ were put into methanol solution respectively, Four test solutions were made, and then the four test solutions were irradiated with a 500W medium pressure mercury lamp for 5 hours, and it was measured that Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst 4# catalyzed and generated 16.1μmol H ₂ , Bi ₄ Ti ₃ O ₁₂ The photocatalyst catalyzed the generation of 7.9μmol H ₂ , while the Sr ₂ Bi ₄ Ti ₅ O ₁₈ synthesized by solid-phase sintering catalyzed 5.6μmol H ₂ , and the TiO ₂ photocatalyst catalyzed only 5μmol H ₂ . The methanol solution was prepared by mixing 3 ml methanol and 30 ml deionized water.

The above examples show that the performance of the layered perovskite-type Sr ₂ Bi ₄ Ti ₅ O ₁₈ photocatalyst prepared in the present application for splitting water is much better than that of traditional photocatalysts TiO ₂ , Bi ₄ Ti ₃ O ₁₂ photocatalysts and solid-state photocatalysts. Sr ₂ Bi ₄ Ti ₅ O ₁₈ synthesized by phase sintering.

Claims (6)

1. a synthetic method of layered perovskite type photocatalyst, is characterized in that, The chemical formula of the layered perovskite photocatalyst is: Sr ₂ Bi ₄ Ti ₅ O ₁₈ ; The synthetic method comprises the steps: (1) Dissolving SrCl ₂ ·6H ₂ O, bismuth source and tetrabutyl titanate in a nitric acid solution to obtain a raw material solution; (2) adding the obtained raw material dropwise to the sodium hydroxide solution, and then performing hydrothermal synthesis to obtain a white suspension; (3) cooling and filtering the suspension, taking filter residues, washing and drying the filter residues to obtain layered perovskite type Sr ₂ Bi ₄ Ti ₅ O ₁₈ ; The temperature of hydrothermal synthesis is 180-240℃, the time is 24-72h; the concentration of sodium hydroxide solution is 6-9mol/L. 2. synthetic method according to claim 1 is characterized in that, the concentration of nitric acid solution is 4-5mol/L. 3. synthetic method according to claim 2 is characterized in that, the volume ratio of nitric acid solution and sodium hydroxide solution is 1:1-1:1.2. 4. synthetic method according to claim 1 is characterized in that, bismuth source is bismuth nitrate or bismuth sulfate. 5 . The synthesis method according to claim 1 , wherein the drying temperature of the filter residue is 60-80° C., and the drying time is 7-10 h. 6 . 6. Application of the layered perovskite type photocatalyst according to any one of claims 1-5 in photocatalytic reaction.

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