CN101623644B - Preparation for compound hollow sphere CdS-TiO* and application in photocatalytic hydrogen production by water decomposition - Google Patents

Abstract

The invention discloses the preparation of a composite hollow sphere CdS-TiO ₂ and its application in photocatalytic decomposition of water to produce hydrogen. The preparation method utilizes cheap cadmium source and titanium source, adopts hydrothermal method, two-step impregnation method, and sol-gel method to prepare composite hollow sphere CdS-TiO ₂ nanometer material, the process is simple and easy, and large-scale production can be realized. Combining CdS with TiO ₂ broadens the spectral response range of TiO ₂ , and the prepared composite hollow sphere CdS-TiO ₂ is used as a photocatalyst for solar visible light catalytic water splitting to produce hydrogen. Compared with TiO ₂ photocatalyst, solar light The energy utilization rate is greatly increased, and the hydrogen production rate is significantly increased.

Description

Preparation of composite hollow sphere CdS-TiO2 and its application in photocatalytic water splitting for hydrogen production

technical field

The invention belongs to the preparation of nano composite material and its application in the field of new energy. It specifically relates to a preparation method of a composite hollow sphere CdS-TiO ₂ nanometer material and the application of the material as a photocatalyst in solar visible light splitting water to produce hydrogen.

Background technique

Due to the long-term unrestrained exploitation of fossil energy, the energy shortage has attracted the attention of various countries in recent years, thus accelerating the pace of human exploration of new renewable energy. Hydrogen energy has become the focus of attention of the international community because of its clean combustion, green environmental protection, renewable and pollution-free. Countries are actively exploring many ways to obtain hydrogen energy. Using solar photocatalysis to split water to produce hydrogen is one of the most effective ways for circular economy and green hydrogen production.

The key technology of using solar photocatalytic water splitting to produce hydrogen is photocatalyst. TiO ₂ is the most widely studied photocatalyst for solar UV photocatalytic splitting water to produce hydrogen in recent years. However, TiO ₂ has a wide band gap (Eg=3.2eV ) has limited its photocatalytic application range [1, 2]. In order to broaden the spectral response range of TiO ₂ , coupling it with CdS which has an ideal band gap (CdS, Eg=2.3eV) and conduction band edge is more negative than the electrode potential of H ⁺ /H ₂ is an effective way to improve the utilization rate of solar energy. one of the ways. There are many reports on the composite of CdS nanoparticles and TiO ₂ nanoparticles (or nanotubes) and their application in solar photocatalytic water splitting for hydrogen production [3-5]. However, there is only one literature report on the preparation of direct hollow sphere CdS-TiO ₂ nanocomposites. Hu et al. [6] used a solution reaction method to prepare CdS-TiO ₂ hollow spheres. The specific method: dihydrate cadmium acetate and Thiourea and thioglycerol were dissolved in a mixed solution of N, N-dimethylformamide and water to form solution 1, and then Ti(OBu) ₄ and acetylacetone were dissolved in butanol to form solution 2, and solution 1 Mix and stir with solution 2, reflux, and post-process to obtain a composite structure of TiO ₂ /CdS hollow spheres. Through the systematic novelty search of domestic and foreign patents, many patents related to the preparation of nano-hollow spheres [7-52] were retrieved, but there was only one patent for the direct preparation of nano-CdS-TiO ₂ hollow spheres [53]. The present invention The template method-dipping method-sol-gel method is used to prepare composite CdS- _TiO2 hollow spheres, while the literature [6] and patent [53] report the preparation method using two kinds of solution reactions. Therefore, the present invention focuses on nano-CdS -The preparation method of TiO ₂ hollow spheres is completely different from the method reported in literature [6] and patent [53]; the use of the nano-CdS-TiO ₂ hollow spheres for solar photocatalytic water splitting to produce hydrogen has not been reported in literature or patents.

The following are the references given by the inventor:

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Contents of the invention

In order to improve the utilization efficiency of solar energy and the production rate of hydrogen produced by photocatalytic decomposition of water, one of the purposes of the present invention is to provide a method for preparing composite hollow sphere CdS- _TiO2 nanomaterials, which uses template method-impregnation method- Composite hollow sphere CdS-TiO ₂ nanomaterials prepared by sol-gel method. Another object of the present invention is to use the prepared composite hollow sphere CdS- _TiO2 nanomaterial as a photocatalyst for exploratory application research in the new energy field of solar visible light catalytic decomposition of water to produce hydrogen.

In order to achieve the above tasks, the preparation method of the CdS- _TiO of the composite hollow sphere of the present invention takes the following technical solutions:

A method for preparing composite hollow spheres CdS-TiO ₂ is characterized in that the method sequentially adopts a hydrothermal method, a two-step impregnation method, and a sol-gel method to prepare composite hollow spheres CdS-TiO ₂ , specifically comprising the following steps:

1) Weighing an appropriate amount of sucrose to prepare an aqueous sucrose solution, putting it into a high-pressure reactor, and hydrothermally synthesizing nano-carbon spheres at a suitable temperature as a hard template;

2) Weigh an appropriate amount of Cd(NO ₃ ) ₂ ·4H ₂ O to prepare an aqueous solution;

3) Weigh an appropriate amount of Na ₂ S·9H ₂ O to prepare an aqueous solution;

4) At room temperature, disperse the carbon nanospheres in step 1) in absolute ethanol, perform ultrasonic dispersion, and dry; soak the aqueous solution of Cd(NO ₃ ) ₂ ·4H ₂ O in step 2) in step 1 ) in the carbon nanospheres prepared by drying at room temperature to obtain carbon nanospheres C-Cd ²⁺ wrapped with cadmium ions, wherein the amount of carbon nanospheres is 5 mol, and the amount of Cd(NO ₃ ) ₂ ·4H ₂ O is between Between 0.079mol～0.14mol;

5) At room temperature, slowly drop the Na ₂ S·9H ₂ O aqueous solution in step 3) to the carbon nanosphere C-Cd ²⁺ prepared in step 4), the Na ₂ S·9H ₂ O The dosage is between 0.0936mol and 0.168mol, impregnated overnight, and dried to obtain carbon nanospheres C-CdS wrapped with cadmium sulfide;

6) Weigh an appropriate amount of TiCl ₄ to be mixed with an ethanol solution;

7) Put the carbon nanosphere C-CdS prepared in step 5) into a three-necked flask with stirring, then add the TiCl ₄ ethanol solution in step 6), and stir, the amount of TiCl ₄ is 0.06mol;

8) Under continuous stirring, slowly drop an appropriate amount of ammonia solution into the three-necked flask solution in step 7), adjust the pH value to 7-8, filter and wash, and the carbon core is coated with cadmium sulfide and TiO _in turn. The core-shell structure C-CdS-TiO ₂ composite material;

9) Calcining the core-shell structure C-CdS-TiO ₂ composite material prepared in step 8) in a muffle furnace at 400° C. for 2 hours to obtain a composite hollow sphere CdS-TiO ₂ nanomaterial.

The composite hollow sphere CdS-TiO _nanometer material prepared by the present invention is used as a photocatalyst for the application research of solar visible light catalytic decomposition of water for hydrogen production. A xenon lamp was used as a simulated solar light source, and an optical filter was used to filter out ultraviolet light, and the yield of hydrogen production by solar visible light catalytic water splitting was evaluated. Specifically include the following steps:

1) Quantitatively weigh the hole sacrificial agents Na ₂ S and Na ₂ SO ₃ into 100 mL of Prex glass flat-bottomed reaction flask with 50 mL of distilled water, and weigh an appropriate amount of composite hollow spheres CdS-TiO ₂ Nano powder is added into the reaction flask;

2) Put the reaction bottle on the magnetic stirrer, insert the three-way sampling glass stopper into the reaction bottle, turn on the xenon lamp constant current power supply, filter out the ultraviolet light of λ<420nm with a filter, and the light source passes through the filter Then irradiate to the side of the reaction bottle;

3) The TCD detector equipped with the gas chromatograph and the TDX-01 packed column were used to detect the generated gas phase products, and the yield of hydrogen production from solar visible light catalytic water splitting was evaluated.

The technical effects brought by the composite hollow sphere CdS- _TiO2 nanomaterial prepared by the present invention and its application in solar photocatalytic water splitting to produce hydrogen are:

(1) Composite hollow sphere CdS-TiO ₂ nanomaterials can be prepared using cheap cadmium and titanium sources, the process is simple and easy, and large-scale preparation can be realized.

(2) Composite hollow sphere CdS-TiO ₂ is a new type of photocatalyst with excellent performance. The combination of CdS and TiO ₂ broadens the corresponding range of TiO ₂ spectrum, greatly improves the efficiency of solar light energy utilization and hydrogen production efficiency.

The innovation of the present invention is:

(1) A new method for the preparation of composite hollow sphere CdS- _TiO2 nanomaterials using cheap cadmium and titanium sources is proposed.

(2) The composite hollow sphere CdS-TiO ₂ was proposed as a photocatalyst for solar photocatalytic water splitting to produce hydrogen, which improved the hydrogen production rate.

(3) CdS is coated in TiO ₂ and the Na ₂ S-Na ₂ SO ₃ sacrificial agent system is used to avoid the occurrence of CdS photocorrosion phenomenon and improve the life and activity of the composite hollow sphere CdS-TiO ₂ photocatalyst .

Description of drawings

Figure 1. Block diagram for the preparation of C-CdS;

Figure 2. Block diagram of preparing composite hollow spheres CdS-TiO ₂ ;

Figure 3. SEM photo of the core-shell structure C-CdS- _TiO composite;

Figure 4. SEM photos of composite hollow sphere CdS- _TiO2 nanomaterials;

Figure 5. TEM photo of composite hollow sphere CdS- _TiO nanomaterials;

The present invention will be further described in detail below in conjunction with the accompanying drawings and the embodiments given by the inventor.

Detailed ways

The preparation method of the composite hollow sphere CdS- _TiO2 nanomaterial of the present invention adopts the nano-carbon sphere synthesized by the hydrothermal method as the hard template method, and adopts two-step impregnation method, sol-gel method and roasting and other technical routes to prepare the composite hollow sphere. Spherical CdS-TiO ₂ nanomaterials. During the synthesis process, the dosage of carbon nanospheres is 5 mol; the dosage of Cd(NO ₃ ) ₂ ·4H ₂ O is between 0.079mol and 0.14mol; the dosage of Na ₂ S·9H ₂ O is between 0.0936mol and 0.168mol ; TiCl ₄ consumption is 0.06mol.

The technical route for preparing C-CdS is shown in Figure 1, and the technical route for preparing composite hollow sphere CdS-TiO ₂ nanomaterials is shown in Figure 2.

The following are examples given by the inventors. It should be noted that these examples are only for better explaining the present invention, and the present invention is not limited to these examples. The chemical reagents involved in the examples are analytical reagents.

Example 1:

Weigh 15g of glucose solid powder, measure 150mL of deionized water, dissolve the glucose solid powder in deionized water, and stir evenly for 10min.

Pour the formed homogeneous solution into a polytetrafluoroethylene-lined autoclave (volume 200mL), put it in an electric heating box and heat it to 165°C, keep it warm for 5h, take it out and let it cool down to room temperature naturally. Filter, wash with deionized water and absolute ethanol three times respectively, and put the solid in a drying oven at 60° C. for 5 hours to obtain brown carbon nanospheres.

Weigh 60 g (5 mol) of the prepared brown carbon nanospheres, put them into a beaker of absolute ethanol, ultrasonicate for 30 min at a frequency of 31 Hz, and dry at 50° C. Weigh 42 g (0.14 mol) of Cd(NO ₃ ) ₂ ·4H ₂ O solid, add it into 80 mL of deionized water, and prepare an aqueous solution. The solution was immersed in 60 g of carbon nanospheres for 2 hours, and dried at room temperature to obtain a composite (C—Cd ²⁺ ) in which carbon nanospheres encapsulated cadmium ions.

Weigh 40.32 g (0.168 mol) of Na ₂ S·9H ₂ O solid, add it into 80 mL of deionized water, and prepare an aqueous solution. Take the solution with a dropper and slowly add it dropwise to the surface of the sample surface of the compound (C-Cd ²⁺ ) coated with cadmium ions in carbon spheres (direct light source should be avoided during the dropping process), soak for 2 hours, filter, wash, and put it in a drying box for 60 ℃ constant temperature drying to prepare the carbon sphere-wrapped cadmium sulfide composite sample (C-CdS).

Measure 6.6mL (0.06mol) TiCl ₄ with a dry graduated cylinder, and slowly drop it into a beaker containing 100mL of absolute ethanol with a dropper to prepare titanium sol;

Put the obtained carbon sphere-wrapped cadmium sulfide composite material sample (C-CdS) into a three-necked flask filled with 150mL of absolute ethanol; under rapid stirring, add the prepared titanium sol into the three-necked flask.

Under continuous stirring, the ammonia solution (NH ₃ ·H ₂ O: _{H 2} O=1:5) was slowly dropped into the three-necked flask, and the pH value of the solution was adjusted to 7-8, and a large amount of TiO ₂ gel appeared, React at room temperature for 2 hours; then filter and wash to obtain a C-CdS-TiO ₂ composite material with a core-shell structure in which C (core) wraps CdS (subshell) and then wraps TiO ₂ (shell). Scanning electron microscope (SEM ) photos as shown in Figure 3.

The prepared core-shell structure C-CdS-TiO ₂ composite material was calcined in a muffle furnace at 400°C for 2h to obtain a composite hollow sphere CdS-TiO ₂ nanomaterial with TiO ₂ wrapped CdS. The scanning electron microscope (SEM) photo of the composite hollow sphere CdS-TiO ₂ nanomaterial is shown in Figure 4; the transmission electron microscope (TEM) photo is shown in Figure 5.

Example 2:

Weigh 1.25g of Na ₂ S and 0.25g of Na ₂ SO ₃ as sacrificial agents and dissolve them into a 100mL Prex glass flat-bottom reaction bottle filled with 50mL of distilled water. Weigh 0.10 g of the composite hollow sphere CdS-TiO ₂ nanopowder prepared in Example 1 and add it into the reaction flask.

Put the reaction bottle on the magnetic stirrer to stir, insert the three-way sampling glass bottle stopper into the reaction bottle, use the xenon lamp as the simulated sun light source, turn on the xenon lamp constant current power supply, and filter out the ultraviolet light of λ<420nm, the light source After being filtered by a filter, it was irradiated to the side of the reaction bottle, and the photocatalytic hydrogen production activity of the composite hollow sphere CdS-TiO ₂ catalyst irradiated with visible light for 6 hours was detected. The detection of hydrogen adopts TCD detector equipped with gas chromatograph and TDX-01 packed column. Table 1 shows the results of solar visible light photocatalytic splitting of water to produce H ₂ .

Table 1: Results of composite hollow sphere CdS-TiO ₂ solar visible light photocatalytic decomposition of water to produce H ₂

Lighting time (h) 1 2 3 4 5 6 H ₂ (mL/g) 0.81 2.10 3.81 5.56 7.43 9.16

Example 3:

The entire implementation steps are the same as in Example 1, the difference is: (1) Weigh 24g (0.78mol) Cd(NO ₃ ) ₂ ·4H ₂ O solid, add it to 80mL deionized water, and prepare an aqueous solution; (2) Weigh 22.46 g (0.0936 mol) of Na ₂ S·9H ₂ O solid, add deionized water, and prepare an aqueous solution.

Example 4:

The entire implementation steps are the same as in Example 2, except that 0.10 g of the composite hollow sphere CdS-TiO ₂ nanopowder prepared in Example 3 is weighed and put into a reaction bottle. Table 2 shows the results of solar visible light photocatalytic splitting of water to produce H ₂ .

Table 2. Results of composite hollow spheres CdS-TiO ₂ solar visible light photocatalytic decomposition of water to produce H ₂

Lighting time (h) 1 2 3 4 5 6 H ₂ (mL/g) 0.46 1.27 2.16 3.24 3.87 4.82

Claims (4)

1. A composite hollow sphere CdS-TiO ₂ preparation method, characterized in that the method adopts hydrothermal method successively, two-step dipping method, sol-gel method to prepare composite hollow sphere CdS-TiO ₂ , specifically comprising the following steps: 1) Weighing an appropriate amount of sucrose to prepare an aqueous sucrose solution, putting it into a high-pressure reactor, and hydrothermally synthesizing carbon nanospheres at a suitable temperature as a hard template; 2) Weigh an appropriate amount of Cd(NO ₃ ) ₂ ·4H ₂ O to prepare an aqueous solution; 3) Weigh an appropriate amount of Na ₂ S·9H ₂ O to prepare an aqueous solution; 4) At room temperature, disperse the carbon nanospheres in step 1) in absolute ethanol, perform ultrasonic dispersion, and dry; impregnate the carbon nanospheres prepared in step 1) in the Cd(NO ₃ ) in step 2) ₂ ·4H ₂ O aqueous solution, drying at room temperature to prepare carbon nanospheres C-Cd ²⁺ wrapped with cadmium ions, wherein the amount of carbon nanospheres is 5 mol, and the amount of Cd(NO ₃ ) ₂ ·4H ₂ O is between Between 0.079mol～0.14mol; 5) At room temperature, slowly drop the Na ₂ S·9H ₂ O aqueous solution in step 3) to the carbon nanosphere C-Cd ²⁺ prepared in step 4), the Na ₂ S·9H ₂ O The amount is between 0.0936mol and 0.168mol, impregnated, washed, and dried to obtain carbon nanospheres C-CdS wrapped with cadmium sulfide; 6) Weigh an appropriate amount of TiCl ₄ to be mixed with an ethanol solution; 7) Put the carbon nanosphere C-CdS prepared in step 5) into a three-necked flask with stirring, then add the TiCl ₄ ethanol solution in step 6), and stir, the amount of TiCl ₄ is 0.06mol; 8) Under continuous stirring, slowly drop an appropriate amount of ammonia solution into the three-necked flask solution in step 7), adjust the pH value to 7-8, filter and wash, and the carbon core is coated with cadmium sulfide and TiO _in turn. The core-shell structure C-CdS-TiO ₂ composite material; 9) Calcining the core-shell structure C-CdS-TiO ₂ composite material prepared in step 8) in a muffle furnace at 400° C. for 2 hours to obtain a composite hollow sphere CdS-TiO ₂ nanomaterial. 2. The composite hollow sphere CdS-TiO _nanometer material that the method for claim 1 prepares is used as photocatalyst for the application of solar energy visible light catalytic splitting water to produce hydrogen. 3. The application according to claim 2, characterized in that a xenon lamp is used as a simulated solar light source, and an optical filter is used to filter out ultraviolet light to evaluate the hydrogen production rate of solar visible light catalytic decomposition of water. 4. the described application of claim 2, is characterized in that, comprises the following steps: 1) Quantitatively weigh the hole sacrificial agents Na ₂ S and Na ₂ SO ₃ into 100 mL of Prex glass flat-bottomed reaction flask with 50 mL of distilled water, and weigh an appropriate amount of composite hollow spheres CdS-TiO ₂ Nano powder is added into the reaction flask; 2) Put the reaction bottle on the magnetic stirrer, insert the three-way sampling glass bottle stopper into the reaction bottle, turn on the xenon lamp constant current power supply, filter out the ultraviolet light of λ<420nm with a filter, and the light source passes through the filter Then irradiate to the side of the reaction bottle; 3) The TCD detector equipped with the gas chromatograph and the TDX-01 packed column are used to detect the generated gas phase products, and the yield of hydrogen production from solar visible light catalytic water splitting is evaluated.

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