CN108057452B - A kind of self-assembled high-efficiency electron transfer solar photocatalyst and its preparation method and application - Google Patents

Abstract

The present invention relates to the sunlight photocatalysis agent and its preparation method and application that electronics is efficiently shifted in a kind of self assembly.By colloidal sol hydro-thermal and method for calcinating, in Er³⁺: Y₃Al₅O₁₂@NiGa₂O₄And Bi₂Sn₂O₇Between be inserted into MoS₂As conductive channel, a novel Z-type photocatalytic system is formd.Prepared Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄/MoS₂/Bi₂Sn₂O₇Composite material shows the photocatalytic activity of efficient stable in nitrite and sulphite conversion process, has broad application prospects in nitrite and sulphite wastewater treatment.

Description

A kind of self-assembled solar photocatalyst with efficient electron transfer and preparation method thereof application

technical field

The invention belongs to the field of photocatalysis, and in particular relates to a self-assembled solar photocatalyst Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ capable of efficiently transferring electrons and the same Preparation method and application in photocatalytic conversion of nitrite and sulfite.

Background technique

Recently, the global water pollution problem has seriously endangered human life, especially nitrite and sulfite pollution. Nitrite is a strong oxidant. After entering the blood, it combines with hemoglobin to convert oxyhemoglobin into methemoglobin, thereby losing its oxygen-carrying ability, leading to tissue hypoxia, cyanosis and poisoning, and dilation of surrounding blood vessels. Sulfites are food preservatives that can cause allergies and other health problems. The most common symptoms of ingestion of sulfite-containing foods or beverages include difficulty breathing, shortness of breath, wheezing, and coughing. In healthy people who are sensitive to these substances, sulfites may cause adverse reactions such as rashes, nausea and chest pain. Some people also develop a distinctive red face from drinking wine that contains sulfites. Therefore, it is necessary to try to reduce the content of nitrite and sulfite in the water body as much as possible. Photocatalytic technology is one of the effective ways to remove nitrite and sulfite, and has broad application prospects.

Recently, Z-type photocatalytic systems have attracted extensive attention. The Z-type photocatalytic material system is a two-photon system composed of an electron transport medium, a photoreductant and a photooxidant. It has great advantages in photocatalytic reactions. With the help of the two-photon excitation process, the oxidation reactions are completed on different photocatalysts respectively. and reduction reaction, which effectively promotes the separation and migration of photogenerated charges. The photocatalysts in the Z-type reaction system only need to satisfy their respective photoexcitation processes and corresponding half-reactions, which provides a great space for the selection and design of photocatalytic materials. The photocatalytic reduction site and oxidation site are respectively on two photocatalytic semiconductors, and the reduction and oxidation processes are separated from each other, which can effectively suppress the occurrence of the reverse reaction. At the same time, the photogenerated holes in the photoreductant of the catalytic material are recombined by the photogenerated electrons from the photooxidant, and the stability of the photocatalytic system is enhanced accordingly. The Z-type photocatalytic material system exhibits broad spectral response, high stability, high separation efficiency of photogenerated carriers, and strong redox ability, and has broad application prospects. Among many photocatalysts, NiGa ₂ O ₄ has become one of the most attractive sonocatalysts due to its corrosion resistance, non-toxicity and low price. But for NiGa ₂ O ₄ as a photocatalyst itself, it also has its insurmountable shortcomings and deficiencies. Because of its wide forbidden band width (Eg=3.54eV), it can only absorb ultraviolet light (λ<387nm) and be excited. Unfortunately, the UV content of sunlight is quite low. Bi ₂ Sn ₂ O ₇ is another excellent semiconductor photocatalyst after NiGa ₂ O ₄ , which is used in photocatalytic reactions because of its nontoxicity, stability, and small forbidden band width. But for pure NiGa ₂ O ₄ and Bi ₂ Sn ₂ O ₇ , the photocatalytic conversion efficiency is also very low due to their easy recombination of photogenerated electron and hole pairs.

SUMMARY OF THE INVENTION

The purpose of the present invention is to design and synthesize a novel composite photocatalyst Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O that uses MoS ₂ as a conductive channel to effectively accelerate the electron transfer rate ₇ . The compound of the invention belongs to a novel Z-type semiconductor photocatalyst, which is applied to simultaneously convert nitrite and sulfite to generate ammonium sulfate fertilizer, and has the advantages of simple operation, no pollution, good catalyst stability and easy separation.

The technical scheme adopted in the present invention is: a self-assembled solar photocatalyst for efficient electron transfer, wherein the self-assembled solar photocatalyst for efficient electron transfer is Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

A preparation method of a self-assembled high-efficiency electron-transfer solar photocatalyst, comprising the following steps: mixing an appropriate amount of Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ nano-powder and Bi ₂ Sn ₂ O ₇ The nano powder is added to absolute ethanol, ultrasonically dispersed, the obtained suspension is heated and boiled, kept at a constant temperature of 100°C for 30-40min, filtered and dried, the obtained powder is ground finely, and calcined in a muffle furnace at 200°C for 2.0-3.0h Then, it was taken out and ground to obtain Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

In the above preparation method, the preparation method of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ nano-powder is: Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ nanometer Add an appropriate amount of anhydrous ethanol to the powder, disperse by ultrasonic, and mix uniformly with a magnetic stirrer at 40-60 °C. After 30-40 minutes of reaction, add MoS ₂ powder, continue stirring for 30 minutes, then wash with anhydrous ethanol and distilled water, and centrifuge dry. Then, put it in a muffle furnace, calcined at 500° C. for 2-3 hours, take it out, and grind it to obtain Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ nano-powder.

In the above-mentioned preparation method, the preparation method of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ nano-powder is: adding Ga ₂ O ₃ solid into the nickel nitrate solution, and the resulting mixed solution is oxidized with hydrogen The pH was adjusted to 12 with sodium (stir for 30 min while adjusting), then Er ³⁺ : Y ₃ Al ₅ O ₁₂ was added to continue stirring for 20 min, the obtained suspension solution was transferred to the reactor, hydrothermally reacted at 180 ° C for 48-50 h, cooled to At room temperature, the obtained precipitate was washed with deionized water, and dried at 80°C to obtain Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ powder; calcination for 2-3h and grinding to obtain Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ nano-powder.

The above preparation method, the described MoS ₂ preparation method is as follows: dissolving an appropriate amount of Na ₂ MoO ₄ and thioacetamide (CH ₃ CSNH ₂ ) in deionized water, ultrasonicating for 30 minutes, and transferring the obtained suspension solution to the reaction In the kettle, react at 200°C for 16h, cool to room temperature, wash the obtained precipitate with deionized water, and dry at 60°C for 8 hours to obtain MoS ₂ nanopowder.

In the above preparation method, the Bi ₂ Sn ₂ O ₇ preparation method is as follows: mix an appropriate amount of Bi(NO ₃ ) ₃ .5H ₂ O and K ₂ SnO ₃ .3H ₂ O in deionized water, and adjust the pH while stirring. =11-13, ultrasonically dispersed for 30 minutes, the obtained suspension solution was transferred to the reaction kettle, reacted at 180°C for 24h, cooled to room temperature, the obtained precipitate was washed with deionized water, and dried at 60°C for 8 hours to obtain Bi ₂ Sn ₂ O ₇ powder.

Application of the above-mentioned self-assembled high-efficiency electron transfer solar photocatalyst in photocatalytic conversion of nitrite and sulfite. The method is as follows: adding the above-mentioned Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ into the aqueous solution containing nitrite and sulfite, irradiating with a 500W xenon lamp, The illumination time is 4.0h.

The above self-assembled solar photocatalyst Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ for efficient electron transfer under simulated sunlight irradiation converts nitrite and sulfite Process analysis: Since the valence band of NiGa ₂ O ₄ is close to the conduction band potential of Bi ₂ Sn ₂ O ₇ , the electrons in the conduction band of Bi ₂ Sn ₂ O ₇ are easily transferred to the holes in the valence band of NiGa ₂ O ₄ . But to further increase their transfer rate. _MoS2 was chosen as the conductive channel. The conduction band potential of MoS ₂ is close to that of Bi ₂ Sn ₂ O ₇ , and the valence band potential is close to that of NiGa ₂ O ₄ . In this way, since the electron energy difference is relatively small, electrons in the conduction band of Bi ₂ Sn ₂ O ₇ enter the valence band of NiGa ₂ O ₄ through MoS ₂ and recombine with holes in the valence band of NiGa ₂ O ₄ , thereby inhibiting Bi ₂ Sn ₂ O ₇ valence band holes and NiGa ₂ O ₄ conduction band electrons recombine. The electrons in the valence band of NiGa ₂ O ₄ have strong reducing ability, which can reduce NO ₂ ^- which has a certain oxidative property to form NH ₄ ⁺ . At the same time, SO ₃ ^2- on the valence band of Bi ₂ Sn ₂ O ₇ is oxidized to SO ₄ ^2- by the holes on the valence band, which can combine with the generated NH ₄ ⁺ to form ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) .

Beneficial effects of the present invention:

The Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ nanometer photocatalyst prepared by the invention has stable properties, high temperature resistance, and is comparable to pure Er ³⁺ : Y ₃ Al ₅ O Compared with Bi ₂ Sn ₂ O _{7 12} @NiGa ₂ O ₄ , the efficiency of this catalyst to convert nitrite and sulfite under sunlight irradiation is greatly improved. In the present invention, the composite photocatalyst Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ not only has the advantages of traditional photocatalysts, but also has the most noteworthy effect on NiGa ₂ O ₄ and Bi ₂ Sn ₂ O ₇ bandwidth characteristics and the unique position of conduction and valence bands, a novel photocatalyst with MoS ₂ as the conductive channel was designed. The method solves the problem of recombination of photogenerated electrons and holes, and greatly improves the efficiency of photocatalytic conversion of nitrite and sulfite.

Description of drawings

Figure 1a-1 is a UV-Vis diffuse reflectance spectrum (DRS) image of NiGa ₂ O ₄ .

Figure 1b-1 is a UV-Vis diffuse reflectance spectrum (DRS) image of Bi ₂ Sn ₂ O ₇ .

Figure 1c- ₁ is a UV-Vis diffuse reflectance spectrum (DRS) map of MoS2.

Figure 1d is a UV-Vis diffuse reflectance spectrum (DRS) image of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 1a- ₂ is the bandwidth calculation diagram of _NiGa2O4 .

Figure 1b-2 is a bandwidth calculation diagram for Bi ₂ Sn ₂ O ₇ .

Figure 1c- ₂ is the bandwidth calculation diagram of MoS2.

Figure 2a is an X-ray photoelectron spectroscopy (XPS) image of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 2b is an XPS image of Er element of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 2c is an XPS diagram of the Y element of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 2d is an XPS image of the Al element of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 2e is an XPS image of Ni element of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 2f is an XPS image of Ga element of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 2g is an XPS image of Bi element of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 2h is an XPS image of Sn element of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 2i is an XPS image of the S element of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 2j is an XPS diagram of O element of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 2k is an XPS image of Mo element of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

3 is a transmission electron microscope (TEM) image of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

FIG. 4 is an infrared spectrum (IR) image of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Figure 5a-1 is a graph showing the effect of simulated sunlight irradiation time on the photocatalytic conversion of nitrite and sulfite.

Figure 5a-2 is a graph showing the effect of the corresponding reaction kinetics on the photocatalytic conversion of nitrite and sulfite.

Figure 6a is a graph showing the effect of the photocatalytic activity of the prepared samples on the photocatalytic conversion of nitrite and sulfite.

Figure 6b is a graph showing the effect of the number of applications on the photocatalytic conversion of nitrite and sulfite.

Figure 7 is a schematic diagram of the mechanism of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ under simulated sunlight irradiation to convert nitrite and sulfite.

Detailed ways

Example 1 Preparation and detection of a novel self-assembled solar photocatalyst capable of efficiently transferring electrons

(1) Preparation of NiGa ₂ O ₄ nanopowder

0.376g Ga ₂ O ₃ powder was added to 50mL of 1mol/L nickel nitrate solution, the resulting mixture was adjusted to pH 12 with sodium hydroxide (stir for 30min while adjusting), and the obtained suspension solution was transferred to the reactor at 180°C The reaction was carried out for 48 h, cooled to room temperature, and a light blue precipitate was obtained, which was washed several times with deionized water, and then dried at 60° C. for 8 h to obtain NiGa ₂ O ₄ powder. The powder is ground finely, calcined in a muffle furnace at 500° C. for 2 hours, taken out, and ground again to obtain NiGa ₂ O ₄ nano-powder.

(2) Preparation of MoS ₂ nanopowder

Dissolve _{2.42g Na2MoO4} and 1.94g thioacetamide in 30mL deionized water, ultrasonicate for 30 minutes, transfer the obtained suspension solution to the reaction kettle, react at 200°C for 16h, cool to room temperature, and obtain a precipitate for use Ionized water was washed several times, and then dried at 60 °C for 8 hours to obtain MoS ₂ powder.

(3) Preparation of Bi ₂ Sn ₂ O ₇ nanopowder

8.76 g Bi(NO ₃ ) ₃ ·5H ₂ O and 5.40 g K ₂ SnO ₃ ·3H ₂ O were mixed in 150 ml of deionized water, and adjusted to pH=12 with ammonia or potassium hydroxide while stirring. Ultrasonic dispersion was performed for 30 minutes to promote the completion of the reaction. The obtained suspension solution was transferred to the reaction kettle, reacted at 180 °C for 24 h, cooled to room temperature, and the obtained precipitate was washed several times with deionized water, and then dried at 60 °C for 8 hours to obtain Bi ₂ Sn ₂ O ₇ powder .

(4) Preparation of Er ³⁺ : Y ₃ Al ₅ O ₁₂ nano-powder

0.032 g Er ₂ O ₃ (99.99%), 5.679 g Y ₂ O ₃ (99.99%) powder were dissolved in 100 mL concentrated nitric acid (65.00%) and stirred with magnetic heating until colorless and transparent. Then, Al(NO ₃ ) ₃ ·9H ₂ O (99.99%) was weighed in proportion, dissolved in distilled water, stirred with a glass rod at room temperature and slowly added to the rare earth ion solution. Using citric acid as chelating agent and cosolvent, according to n citric acid: n rare earth ion = 3:1, weigh citric acid, dissolve in distilled water, heat and stir at 50-60 ℃, stop when the solution becomes viscous. No precipitate was formed during this process, and a foamed viscose solution was finally obtained. The viscous solution was heated in an oven at a constant temperature of 80°C for 36h. During the drying process, the solvent is evaporated to dryness and no precipitate is formed, and a foamed sol is finally obtained. The obtained sols were heated at 500 °C for 50 min, and then calcined at 1100 °C for 2 h respectively. Finally, the sintered mass was removed from the high temperature furnace and cooled to room temperature in air to obtain Er ³⁺ :Y ₃ Al ₅ O ₁₂ powder.

(5) Preparation of Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ nano-powder

0.376g Ga ₂ O ₃ solid was added in 50mL 1mol/L nickel nitrate solution, the resulting mixed solution was adjusted to pH 12 with 1mol/L sodium hydroxide (stir 30min while adjusting), then 2.1g Er ³⁺ was added: Y ₃ Al ₅ O ₁₂ continued stirring for 20 min. The obtained suspension solution was transferred to the reaction kettle for 48 hours at 180 °C, cooled to room temperature, and the obtained precipitate was washed with deionized water several times, and then dried at 80 °C for 8 hours to obtain Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ powder. The powder was ground finely, calcined in a muffle furnace at 500°C for 2 hours, taken out and then ground to obtain Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ nanoparticles.

(6) Preparation of Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ nano-powder

Put 6g of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ powder into a beaker, add 200mL of absolute ethanol, ultrasonically disperse for 30min, stir well with a magnetic stirrer at 40～60℃, stir for 30min , add 0.06g MoS ₂ powder, continue stirring for 30min, then wash with absolute ethanol and distilled water for several times, after centrifugal drying, put it in a muffle furnace, roast it at 500 ℃ for 2h, take it out, grind it, and obtain Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ nanopowder.

(VII) Preparation of Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ nano-powder

6g Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ and 6g Bi ₂ Sn ₂ O ₇ nanopowder were added to 200mL of absolute ethanol, ultrasonically dispersed for 30min, the suspension was heated and boiled at 100℃ The temperature was kept at a constant temperature for 30 min, after filtration, dried at 60 °C for 8.0 h, the obtained powder was ground finely, calcined in a muffle furnace at 200 °C for 2.0 h, taken out, and ground to obtain Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

(8) Detection

(1) Figures 1a-1 to 1c-2 are NiGa ₂ O ₄ , Bi ₂ Sn ₂ O ₇ , MoS ₂ and Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn UV _- Vis diffuse reflectance spectroscopy (DRS) image analysis of _2O7 .

UV-Vis diffuse reflectance spectroscopy (DRS) can be used to study the optical properties of semiconductor photocatalysts. Therefore, the solid UV of NiGa ₂ O ₄ , Bi ₂ Sn ₂ O ₇ , MoS ₂ and Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ was determined, and the results are as follows Figures 1a-1 to 1c-2. Figures 1a- ₁ and 1b _{- 1} depict that the absorption edges of _NiGa2O4 and _Bi2Sn2O7 appear at approximately 350 nm and 450 nm, respectively. While in Figure 1c- ₁ , it can be found that the absorption band of MoS2 is relatively broad, covering almost the entire visible light range. This indicates that the as _- prepared MoS is a narrow-bandgap semiconducting sulfide. _{In Fig} . 1d, the absorption range is significantly enlarged compared with that of monomeric _NiGa2O4 or _{monomeric Bi2Sn2O7} . Moreover, the added _MoS can also expand the light absorption range. The optical band gap of the prepared sample can be estimated from the following equation:

αhν=A(hν-E _bg ) ^1/2

where α, h, ν, E _bg and A denote the absorption coefficient, Planck's constant, optical frequency, band gap and constant, respectively. As shown in Fig. 1a-2 and _Fig . 1b- ₂ , the band gaps of as _- prepared _NiGa2O4 and _Bi2Sn2O7 are 3.55 eV and 2.80 eV, respectively, which is almost consistent with the previously reported literature. Therefore, it is speculated that NiGa ₂ O ₄ and Bi ₂ Sn ₂ O ₇ , which are wide-bandgap and narrow-band semiconductor photocatalysts, can utilize long-wavelength light and short-wavelength light in sunlight, respectively. In addition, Fig. 1c- ₂ indicates that the calculated band gaps of MoS are 1.15 eV, respectively. Apparently, this narrow bandgap semiconducting sulfide is sufficient to form an electron channel (e-) and increase the electron (e-) transport rate.

(2) Figures 2a to 2k are X-ray photoelectron spectroscopy (XPS) image analysis of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

The chemical composition of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ was studied by X-ray photoelectron spectroscopy (XPS). As can be seen from Fig. 2a to Fig. 2k, peaks of Er, Y, Al, O, Ni, Ga, S, Bi, Mo and Sn elements can be found. The peaks appearing at 74.0 eV (Al 2p), 157.4 eV (Y 3d), 173.7 eV (Er 4d) and 530.5 (O 1s) are consistent with the composition of Er ³⁺ : Y ₃ Al ₅ O ₁₂ . The peaks presented at 530.5 eV (O 1s) and 20.5 eV (Ga 3d) are in close agreement with the composition of NiGa ₂ O ₄ . Bi(4f _7/2 ) and Bi(4f _5/2 ) peaks of Bi ₂ Sn ₂ O ₇ are 158.7 and 164.5 eV, respectively, indicating that Bi ^{3 +} exists in Bi ₂ Sn ₂ O ₇ . Sn(3d _5/2 ) and Sn(3d _3/2 ) appeared two peaks at 486.9 and 494.8 eV, indicating the existence of Sn ₄ ⁺ . These results indicate that the predicted Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ has been prepared.

(3) FIG. 3 is a transmission electron microscope (TEM) image analysis of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

Further in-depth observation was carried out by a transmission electron microscope (TEM) shown in FIG. 3 . From Fig. 3(a-1), it can be determined that the regular particles with larger size are Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ particles. The darker part in Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ is Er ³⁺ :Y ₃ Al ₅ O ₁₂ , which is wrapped in NiGa ₂ O ₄ . As can be seen, smaller particles with a size of _20-50 nm _were identified as _Bi2Sn2O7 particles. Also, between Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ and Bi ₂ Sn ₂ O ₇ , there are many smaller particles, which should be MoS ₂ nanoparticles. Further magnified TEM in Fig. 3(a-2) shows their exact relationship and composition. In Figure 3(a-2), the measurement points of 0.298nm, 0.281nm, 0.331nm and 0.610nm are respectively associated with Er ³⁺ : Y ₃ Al ₅ O ₁₂ d ₂₂₁ plane, NiGa ₂ O ₄ d ₂₂₀ plane, _{The d311} plane of _{Bi2Sn2O7 matches} the _d002 plane of _MoS2 . Through TEM study, not only its structure and composition can be determined, but also it can be proved that the predicted Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ has been prepared.

(4) Infrared spectrum (IR) image analysis of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ .

In order to provide chemical information about the structure of the prepared samples, the infrared spectra of the as-prepared Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ were measured, and the corresponding results are shown in Fig. 4 Show. In Figure 4, the peak at 3434 cm ^-1 is due to the ν(OH) stretching vibration. The metal-oxygen vibration at about 789 cm ⁻¹ is characteristic of the stretching frequency of YO, which may be Er ³⁺ :Y ₃ Al ₅ O ₁₂ . In Figure 4, the infrared spectrum clearly shows the presence of two strong absorption peaks. The absorption peak at 459 cm ^-1 is assigned to the stretching vibration model of metal oxygen in the tetrahedral site, and the peak at about 682 cm ^-1 belongs to the octahedral complex. From these two absorption peaks, it was confirmed that NiGa ₂ O ₄ having a single-phase spinel structure having a sublattice tetrahedral site and an octahedral site was formed. The peaks at 515 cm ^-1 and 634 cm ^-1 are attributed to the Bi _- O stretching vibrations in the _BiO8 dodecahedron and the Sn _- O stretching vibrations in the _SnO6 octahedra of _Bi2Sn2O7 , respectively. In Fig. 4, the peak appearing at 598.00 cm ^-1 is assigned to the Mo _- S bending vibration mode of MoS2.

Example 2 Application of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ in photocatalytic conversion of nitrite and sulfite

(1) Effects of simulated sunlight irradiation time and corresponding reaction kinetics on the photocatalytic conversion of nitrite and sulfite

The photocatalytic conversion of nitrite and sulfite by Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ photocatalyst was carried out under simulated sunlight irradiation. Before light irradiation, the solution containing NO ₂ ^- and SO ₃ ^2- was stirred in the dark for 30 min and reached adsorption-desorption equilibrium. Then, samples of the solution were taken every 1.0 hours, and the conversion of nitrite and sulfite was examined by ion chromatography. It can be seen from Figure 5a-1 that with the increase of the simulated sunlight irradiation time, the photocatalytic conversion rate shows an upward trend. Under the irradiation of sunlight for 4.00 hours, the photocatalytic conversion rates of NO ₂ ^- and SO ₃ ^2- can reach 73.35% and 87.87%, respectively, and the generation rates of NH ₄ ⁺ , NO ₃ ^- , N ₂ and SO ₄ ^2- , respectively were 63.23%, 8.80%, 1.32% and 85.34%. It can be seen from the experimental results that the formation rates of NO ₃ ^- and N ₂ are much lower than that of NH ₄ ⁺ , which indicates that in the designed Z-type Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ / In the Bi ₂ Sn ₂ O ₇ photocatalytic system, most of NO ₂ ^- was converted to NH ₄ ⁺ at pH=5.00. In addition, in Fig. 5a-1, the conversion rate of SO ₃ ^2- is slightly lower than that of SO ₄ ^2- , which may be due to the fact that SO ₃ ^2- can convert a small amount of other sulfur-containing compounds besides SO ₄ ^2- .

In order to speculate the simulated sunlight photocatalytic conversion reaction formula of nitrite and sulfite, as shown in Fig. 5a-1 and Fig. 5a-2, the reaction kinetics were studied. It can be seen that all -ln(C _t /C ₀ ) (C _t : instantaneous concentration at t irradiation time, C ₀ : initial concentration) data for the first-order reaction and irradiation time (t) can be considered to be roughly linear. The reaction kinetic equations corresponding to NO ₂ ^- and SO ₃ ^2- are -ln(C _t /C ₀ )=0.3426t+0.0303(R ² =0.9857) and -ln(C _t /C ₀ )=0.5321t, respectively -0.0215 (R ² =0.9976). The ratio constants are 0.3426 min ^-1 , 0.5321 min ^-1 for NO ₂ ^- and SO ₃ ^2- , respectively.

(2) Comparison of the photocatalytic activity of the prepared samples and the effect of the number of times of use on the photocatalytic conversion of nitrite and sulfite

Simulated sunlight irradiation was carried out on three prepared photocatalysts (Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ , Bi ₂ Sn ₂ O ₇ and Er ³⁺ : Y ₃ Al ₅ O ₁₂ @NiGa Photocatalytic conversion of nitrite and sulfite in the presence of ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ ). From Figure 6a, it can be seen that the three prepared photocatalysts have different nitrite and sulfite conversions in aqueous solution in the presence of different photocatalysts. For NiGa ₂ O ₄ , as a wide-bandgap semiconductor photocatalyst, it has a more negative conduction band (CB) and shows stronger reducibility. NO ₂ ^- can be converted into NH ₄ ⁺ and N ₂ . The conversion of NO ₂ ^- is higher and the productivity of NH ₄ ⁺ is higher at the conduction band (CB) of NiGa ₂ O ₄ under simulated sunlight irradiation. For Bi ₂ Sn ₂ O ₇ , as a narrow-bandgap semiconductor photocatalyst, it has a more efficient valence band (VB), shows stronger oxidation, SO ₃ ^2- can be converted into SO ₄ ^2- , and can be in the valence band Get a higher conversion rate. The Z-type photocatalyst Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ has both a more negative conduction band (CB) and a more positive valence band (VB). Obviously, the conversion of NO ₂ ^- and SO ₃ ^2- is higher than that of single photocatalyst Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ or Bi ₂ Sn ₂ O ₇ under simulated sunlight irradiation. Conversion rate. In addition, the electron transfer rate is further enhanced due to the use of _MoS as a conductive channel.

The stability of Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ was evaluated by repeating the photocatalytic conversion experiments of nitrite and sulfite under simulated sunlight , as shown in Figure 6b. Apparently, for Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ , the simulated sunlight photocatalytic conversion of nitrite and sulfite with increasing number of uses rate decreased slightly. The conversion rates of NO ₂ ^- and SO ₃ ^2- reached 67.78% and 81.35%, respectively, after five repeated uses under simulated sunlight. It is indicated that the Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ photocatalyst can maintain high performance for a long time under simulated sunlight irradiation.

Figure 7 shows the photocatalytic conversion mechanism of nitrite and sulfite by Er ³⁺ :Y ₃ Al ₅ O ₁₂ @NiGa ₂ O ₄ /MoS ₂ /Bi ₂ Sn ₂ O ₇ :

In order to effectively suppress the recombination of electrons (e ^- ) on the conduction band (CB) and holes (h ⁺ ) on the valence band (VB), NiGa ₂ O ₄ and Bi ₂ Sn ₂ O ₇ are combined to form a Z-type photocatalyst system is necessary. Since the valence band of NiGa ₂ O ₄ is close to the conduction band potential of Bi ₂ Sn ₂ O ₇ , the electrons in the conduction band of Bi ₂ Sn ₂ O ₇ are easily transferred to the holes of NiGa ₂ O ₄ . But to further increase their transfer rate. We chose to combine _MoS2 with a _{narrower bandwidth} with _Bi2Sn2O7 and _{NiGa2O4 . The} band gap of MoS2 is 1.17eV, the valence band is _0.23eV , and the conduction band is _1.40eV . _The conduction band potential of MoS2 is close to that of _Bi2Sn2O7 , and the valence band potential is close to that of _{NiGa2O4 .} valence band potential. In this way, since the electron energy difference is relatively small, electrons in the conduction band of Bi ₂ Sn ₂ O ₇ enter the valence band of NiGa ₂ O ₄ through MoS ₂ and recombine with holes in the valence band of NiGa ₂ O ₄ , thereby inhibiting Bi ₂ Sn ₂ O ₇ valence band holes and NiGa ₂ O ₄ conduction band electrons recombine. The electrons in the valence band of NiGa ₂ O ₄ have strong reducing ability, which can reduce NO ₂ ^- which has a certain oxidative property, and generate NH ₄ ⁺ and N ₂ respectively. The specific product depends on the pH. The acidic conditions with pH less than 7 tend to generate NH ₄ ⁺ ions, and the alkaline conditions with pH greater than 7 tend to generate N ₂ . At the same time, SO ₃ ^2- on the valence band of Bi ₂ Sn ₂ O ₇ is oxidized to SO ₄ ^2- by the holes on the valence band, which can combine with the generated NH ₄ ⁺ to form ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) . In fact, in the process of NO ₂ ^- and SO ₃ ^2- treatment, an aqueous solution containing ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) is finally produced, which can be directly used as fertilizer after proper treatment.

Claims (5)

1. the sunlight photocatalysis agent that electronics is efficiently shifted in a kind of self assembly, it is characterised in that: the self assembly is efficiently shifted The sunlight photocatalysis agent of electronics is Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄/MoS₂/Bi₂Sn₂O₇；Preparation method includes the following steps:

1) Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄The preparation of nanometer powder: by Ga₂O₃Solid is added in nickel nitrate solution, and generation mixes It closes liquid and adjusts pH to 12 with sodium hydroxide, Er is then added³⁺:Y₃Al₅O₁₂Continue to stir 20 min, obtained aaerosol solution transfer Into reaction kettle, 180 °C of lower hydro-thermal reaction 48-50 h are cooled to room temperature, and obtained sediment is cleaned with deionized water, and 80 ° It is dried under C, obtains Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄Powder；Powder is finely ground, in 500 °C of Muffle furnace, 2-3 h is roasted, is ground Mill, obtains Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄Nanometer powder；

2) Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄/MoS₂The preparation of nanometer powder: in Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄Add in nanometer powder Enter appropriate dehydrated alcohol, ultrasonic disperse is uniformly mixed at 40-60 °C with magnetic stirring apparatus, after reacting 30-40min, is added MoS₂Powder continues to stir 30 min, is then cleaned with dehydrated alcohol and distilled water, after centrifugal drying, be put into Muffle furnace, It is taken out after 500 °C of roasting 2-3 h, grinds, obtain Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄/MoS₂Nanometer powder；

3) by suitable Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄/MoS₂Nanometer powder and Bi₂Sn₂O₇Nanometer powder is added to dehydrated alcohol In, ultrasonic disperse, gained suspension heating is boiled, and the constant temperature 30-40 min at 100 DEG C is filtered, and dry, gained powder is finely ground, In Muffle furnace, is taken out after 200 oC calcine 2.0-3.0 h, grind, obtain Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄/MoS₂/ Bi₂Sn₂O₇。

2. the sunlight photocatalysis agent that electronics is efficiently shifted in a kind of self assembly as described in claim 1, it is characterised in that: described MoS₂The preparation method comprises the following steps: taking suitable Na₂MoO₄In deionized water with thioacetamide dissolution, ultrasound 30 minutes will obtain Aaerosol solution be transferred in reaction kettle, react 16h at 200 DEG C, be cooled to room temperature, obtain sediment and cleaned with deionized water, It is dried 8 hours at 60 DEG C, obtains MoS₂Nanometer powder.

3. the sunlight photocatalysis agent that electronics is efficiently shifted in a kind of self assembly as described in claim 1, it is characterised in that: described Bi₂Sn₂O₇The preparation method comprises the following steps: by appropriate Bi (NO₃)₃•5H₂O and K₂SnO₃•3H₂O is mixed in deionized water, is adjusted while stirring PH=11-13 is saved, ultrasonic disperse 30 minutes, obtained aaerosol solution was transferred in reaction kettle, is reacted for 24 hours, is cooled under 180 °C Room temperature, obtained sediment are cleaned with deionized water, are dried 8 hours under 60 °C, are obtained Bi₂Sn₂O₇Powder.

4. self assembly described in claim 1 efficiently shift the sunlight photocatalysis agent of electronics in photocatalytic conversion nitrite and Application in sulphite.

5. application as claimed in claim 4, which is characterized in that method is as follows: by Er described in claim 1³⁺:Y₃Al₅O₁₂@ NiGa₂O₄/MoS₂/Bi₂Sn₂O₇It is added in the aqueous solution containing nitrite and sulphite, is irradiated with 500 W xenon lamps, light It is 4.0 h according to the time.