Preparation method and application of highly crystallized cadmium sulfide photocatalyst

Abstract

The invention belongs to the technical field of photocatalysis, and particularly relates to a preparation method and application of a highly-crystallized cadmium sulfide photocatalyst. The preparation method comprises the following steps: respectively adding a cadmium source and a sulfur source into an alkaline aqueous solution, stirring to obtain a precursor solution, carrying out heat preservation, centrifugation and drying on the precursor solution to obtain a cadmium sulfide precursor, mixing the cadmium sulfide precursor with molten salt, calcining, and finally washing, centrifuging and drying to obtain the cadmium sulfide photocatalyst. The preparation process is simple to operate, high in controllability and cheap in raw materials, and can solve the problems of complex preparation process, high cost, difficulty in batch production and the like in the preparation of the CdS-based photocatalyst in the prior art; the cadmium sulfide photocatalyst prepared by the method is extremely high in crystallinity and excellent in photocatalytic performance, and can be widely applied to the fields of hydrogen production by photocatalytic decomposition of water, artificial photosynthesis, organic matter degradation and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysis, and particularly relates to a preparation method and application of a highly crystalline cadmium sulfide photocatalyst. Background Art

[0002] The photocatalytic overall water splitting technology based on the Honda-Fujishima effect has many advantages such as "zero-carbon" emissions throughout the process, mild reaction conditions, low cost, and easy scale-up, and is considered one of the ideal "green hydrogen" preparation technologies; limited by the slow kinetic process of water oxidation to produce oxygen, low economic value, and high separation cost, there is still a large gap between the photocatalytic overall water splitting technology and industrial application. Therefore, researchers have proposed to replace the traditional water oxidation process for oxygen production with the preparation of high-value chemicals, and construct a new system for photocatalytic hydrogen production coupled with the production of high-value chemicals, aiming to achieve the dual goals of "green hydrogen" supply and green preparation of high-value chemicals, and open up a new path for the industrial application of photocatalytic technology.

[0003] Cadmium sulfide (CdS) photocatalyst exhibits broad application prospects in the research directions of photocatalytic water splitting for hydrogen production, organic synthesis, and pollutant degradation due to its excellent visible light response characteristics, simple preparation process, and low raw material cost; however, limited by severe bulk photogenerated carrier recombination, slow surface reaction kinetics, and poor photochemical stability, its photocatalytic performance still needs to be improved; therefore, developing a CdS photocatalyst preparation technology with simple process, low cost, batch preparation, and excellent photocatalytic performance, and exploring its application potential in the production of high-value-added chemicals not only has important scientific research value, but also will provide a practical solution for promoting the industrial application of photocatalytic technology.

[0004] In the prior art, the patent publication number is CN 119368210A, and the name is "A preparation method and application of a polycrystalline molybdenum carbide / cadmium sulfide composite catalyst", which discloses a method for preparing a molybdenum carbide / cadmium sulfide composite catalyst by combining solid-phase sintering-wet chemistry-electrostatic adsorption. By introducing a molybdenum carbide cocatalyst, efficient water splitting for hydrogen production by a cadmium sulfide photocatalyst is achieved, with a hydrogen generation rate of 66.51 mmol g -1 h -1 However, it has problems such as complex preparation process, poor catalytic performance of the cadmium sulfide bulk, and neglect of the photophysical properties of cadmium sulfide itself.

[0005] In the prior art, the patent publication number is CN 119140148A, and the name is "A Nickel Sulfide / Cadmium Sulfide / Sulfur-Doped Graphitic Carbon Nitride Double Heterojunction Composite Photocatalyst and Its Preparation Method", which discloses a method for preparing a nickel sulfide / cadmium sulfide / sulfur-doped graphitic carbon nitride double heterojunction composite photocatalyst by a one-pot wet chemical method. By constructing a multi-heterojunction interface to introduce an internal electric field, efficient separation of photo-generated electrons and holes is achieved, and it has a hydrogen generation rate of 602 μmol g -1 h -1 , but it has problems such as low photocatalytic reaction rate, complex composition, and poor reproducibility. SUMMARY OF THE INVENTION

[0006] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to propose a preparation method and application of a highly crystalline cadmium sulfide photocatalyst. By adding a cadmium source and a sulfur source to an alkaline aqueous solution and stirring to obtain a precursor solution, then keeping the precursor solution warm, centrifuging, and drying to obtain a cadmium sulfide precursor, and then calcining the cadmium sulfide precursor after mixing it with a molten salt, and finally washing, centrifuging, and drying to obtain a cadmium sulfide photocatalyst. This preparation process is simple to operate, has strong controllability, and uses cheap raw materials, and can solve the problems existing in the preparation of CdS-based photocatalysts in the prior art, such as complex preparation process, high cost, and difficulty in mass production. The cadmium sulfide photocatalyst prepared by this method has extremely high crystallinity and excellent photocatalytic performance, and can be widely applied in the fields of photocatalytic water splitting for hydrogen production, artificial photosynthesis, and organic matter degradation.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] In the first aspect, a preparation method of a highly crystalline cadmium sulfide photocatalyst includes the following steps:

[0009] S1: Add a cadmium source to an alkaline aqueous solution and stir for at least 10 min to obtain a turbid solution of cadmium hydroxide. Add a sulfur source to the turbid solution of cadmium hydroxide and stir for at least 10 min to obtain a precursor solution;

[0010] S2: Keep the precursor solution obtained in step S1 at 60 - 105 °C for at least 2 h. After the precursor solution cools to room temperature, wash the cooled precursor solution with water and ethanol by centrifugation at least once to obtain a precursor. Vacuum dry the precursor at a temperature not lower than 40 °C for at least 2 h to obtain a cadmium sulfide precursor, namely CdS-precursor;

[0011] S3: Thoroughly grind the CdS-precursor obtained in step S2 and a molten salt in a mass ratio of (1:1) to (1:10) to form a CdS-molten salt mixture. Calcinate the CdS-molten salt mixture in an inert atmosphere at 450 - 650 °C for 2 - 20 h and then cool it;

[0012] S4: Centrifuge and wash the CdS-molten salt mixture after calcination and cooling in step S3 with water and ethanol respectively for at least once, and then vacuum dry the CdS-molten salt mixture after centrifugal washing at a temperature not lower than 40 °C for at least 2 h to obtain a CdS photocatalyst;

[0013] Among them, the cadmium source in step S1 is cadmium chloride or cadmium acetate, the sulfur source is sodium sulfide, thioacetamide or thiourea, the alkaline aqueous solution is 0.05-10 mol / L sodium hydroxide or potassium hydroxide aqueous solution, and the Cd in the precursor solution 2+ , S 2- and OH - The molar ratio is (1:1:1) to (1:10:100); the molten salt in step S3 is a mixture prepared from lithium chloride and potassium chloride in a mass ratio of (2:1) to (1:2).

[0014] Furthermore, the mass ratio of lithium chloride to potassium chloride in the molten salt in step S3 is 9:11.

[0015] Furthermore, the calcination time of the CdS-molten salt mixture in step S3 is 5-10 h.

[0016] Furthermore, the CdS-molten salt mixture after calcination and cooling in step S4 is centrifuged and washed 3 times with ultrapure water and ethanol respectively.

[0017] Furthermore, the CdS-molten salt mixture after centrifugal washing in step S4 is vacuum dried at 60 °C for 12 h.

[0018] Furthermore, the alkaline aqueous solution in step S1 is 0.5 mol / L sodium hydroxide or potassium hydroxide aqueous solution.

[0019] Furthermore, the stirring time in step S1 is at least 30 min, and the precursor solution cooled to room temperature in step S2 is centrifuged and washed 3 times with water and ethanol respectively to obtain a precursor.

[0020] Furthermore, the CdS-molten salt mixture in step S3 is calcined at 500 °C for 10 h under an inert atmosphere.

[0021] In a second aspect, a highly crystalline cadmium sulfide photocatalyst prepared based on the above preparation method, the full width at half maximum of the main peak in the X-ray diffraction spectrum of the cadmium sulfide photocatalyst is 2θ ≤ 0.14° (step 7° / min), and the scanning electron microscope image shows that the particle size of the cadmium sulfide photocatalyst is ≥ 100 nm.

[0022] In a third aspect, an application of a highly crystalline cadmium sulfide photocatalyst prepared based on the above preparation method in photocatalytic water splitting for hydrogen production, artificial photosynthesis, organic matter degradation or gas oxidation / reduction.

[0023] Compared with the existing technologies, the present invention has the following beneficial effects:

[0024] 1. Through a total of four steps of simple pretreatment, calcination, and washing and drying, the CdS photocatalyst with extremely high crystallinity can be obtained by this preparation method, which proves that the overall preparation process is simple in operation, strong in controllability, and good in repeatability. At the same time, the raw materials are cheap and widely available, which is conducive to large-scale preparation and practical application.

[0025] 2. For the highly crystalline CdS photocatalyst prepared by this preparation method, X-ray diffraction and ultraviolet-visible diffuse reflectance spectra show that CdS has extremely high crystallinity, its photocatalytic performance is excellent, it has good dispersibility in solvents such as water, acetonitrile, and toluene, and can be stored stably.

[0026] In summary, the preparation method of the cadmium sulfide photocatalyst in the present invention is simple in process and low in cost, suitable for large-scale preparation. The prepared cadmium sulfide photocatalyst has excellent optoelectronic properties and can be widely applied in fields such as photocatalytic water splitting for hydrogen production, artificial photosynthesis, and organic matter degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the X-ray diffraction pattern of the CdS series photocatalysts obtained in Examples 1 to 6 of the present invention.

[0028] Figure 2 It is the ultraviolet-visible diffuse reflectance spectra of the CdS series photocatalysts obtained in Examples 1 to 5 of the present invention. The inset is the Urbach energy of the CdS photocatalysts obtained by calculating Example 3 (CdS-10h) and Example 5 (CdS-Precursor) based on the Lambert-Beer law.

[0029] Figure 3 It is the thermogravimetric burnout curve of the CdS photocatalyst (CdS-10h) obtained in Example 3 of the present invention. The molten salt is a mixture of lithium chloride and potassium chloride with a mass ratio of 9:11.

[0030] Figure 4a It is the scanning electron microscope image of the CdS photocatalyst (CdS-Precursor) obtained in Example 5 of the present invention.

[0031] Figure 4b It is the scanning electron microscope image of the CdS photocatalyst (CdS-10h-None Salt) obtained in Example 6 of the present invention.

[0032] Figure 4c It is the scanning electron microscope image of the CdS photocatalyst (CdS-10h) obtained in Example 3 of the present invention.

[0033] Figure 5aTEM image of the CdS photocatalyst (CdS-Precursor) obtained in Example 5 of the present invention.

[0034] Figure 5b TEM image of the CdS photocatalyst (CdS-10h-None Salt) obtained in Example 6 of the present invention.

[0035] Figure 5c TEM image of the CdS photocatalyst (CdS-10h) obtained in Example 3 of the present invention.

[0036] Figure 6a Photocatalytic performance of the CdS photocatalysts obtained in Examples 1 to 6 of the present invention for the dehydrogenative coupling of benzylamine to produce hydrogen and N-benzylidene butylamine (NBBA) in a 0.1 mol / L benzylamine acetonitrile solution at 25 °C.

[0037] Figure 6b Quantum utilization efficiency and solar energy-chemical energy conversion efficiency of the CdS photocatalyst obtained in Example 3 of the present invention for the dehydrogenative coupling of benzylamine to produce hydrogen and N-benzylidene butylamine (NBBA) in a 0.1 mol / L benzylamine acetonitrile solution at 25 °C. Detailed Description of the Invention

[0038] The following further describes the present invention in detail with reference to the attached Figure 1 to the attached Figure 6b :

[0039] First, a method for preparing a highly crystalline CdS photocatalyst includes the following steps:

[0040] Step S1: At room temperature, disperse a cadmium source in an alkaline aqueous solution and stir for at least 10 minutes to obtain a turbid solution of cadmium hydroxide. Then, add a sulfur source to the turbid solution of cadmium hydroxide and stir for at least 10 minutes to obtain a precursor solution.

[0041] Step S2: Transfer the precursor solution obtained in Step 1 to an oil bath, keep it at 60 - 105 °C for at least 2 hours. After the precursor solution is cooled to room temperature, centrifuge and wash the cooled precursor solution with water and ethanol respectively at least once, with a centrifuge speed not less than 4000 rpm, to obtain a precursor. Vacuum-dry the precursor at a temperature above 40 °C for not less than 2 hours to obtain a cadmium sulfide precursor, i.e., CdS-precursor.

[0042] Step S3: Thoroughly grind the CdS-precursor obtained in Step 2 with a molten salt in a mass ratio of 1:1 to 1:10 to form a CdS-molten salt mixture. Calcinate the CdS-molten salt mixture in an inert atmosphere (such as argon, nitrogen, or helium) at 450 - 650 °C for 2 - 20 hours and then cool it. Sintering can inhibit the volatilization of sulfur ions.

[0043] Step S4: Centrifugally wash the calcined and cooled CdS-molten salt mixture obtained in Step 3 with water and ethanol respectively for at least once. The purpose of washing is to remove the molten salt. Then, vacuum dry the centrifugally washed CdS-molten salt mixture at a temperature above 40 °C for no less than 2 h to obtain the CdS photocatalyst.

[0044] Among them, in Step S1, the cadmium source is cadmium chloride or cadmium acetate (i.e., cadmium acetate), the sulfur source is sodium sulfide, thioacetamide or thiourea, the alkaline aqueous solution is a 0.05-10 mol / L sodium hydroxide or potassium hydroxide aqueous solution, and the molar ratio of Cd 2+ , S 2- and OH - in the precursor solution is (1:1:1) to (1:10:100); in Step S3, the molten salt is a mixture prepared from lithium chloride and potassium chloride in a mass ratio of (2:1) to (1:2).

[0045] Among them, in Step S3, the flow rate of the inert atmosphere (such as argon, nitrogen or helium) is preferably 40 mL / min -1 ;

[0046] Among them, in Step S4, the purpose of centrifugally washing with water (such as ultrapure water) and ethanol respectively is to remove the molten salt, and the number of washing times is preferably 3 times.

[0047] Furthermore, in Step S3, the mass ratio of lithium chloride to potassium chloride in the molten salt is 9:11.

[0048] Furthermore, in Step S3, the calcination time of the CdS-molten salt mixture is 5-10 h.

[0049] Furthermore, in Step S4, the calcined and cooled CdS-molten salt mixture is centrifugally washed 3 times with ultrapure water and ethanol respectively.

[0050] Furthermore, in Step S4, the centrifugally washed CdS-molten salt mixture is vacuum dried at 60 °C for 12 h.

[0051] Furthermore, in Step S1, the alkaline aqueous solution is a 0.5 mol / L sodium hydroxide or potassium hydroxide aqueous solution.

[0052] Furthermore, in Step S1, the stirring time is at least 30 min, and the precursor solution cooled to room temperature in Step S2 is centrifugally washed 3 times with water and ethanol respectively to obtain the precursor.

[0053] Furthermore, in Step S3, the CdS-molten salt mixture is calcined at 500 °C for 10 h in an inert atmosphere.

[0054] Second aspect: A highly crystalline cadmium sulfide photocatalyst prepared based on the above preparation method. In the X-ray diffraction spectrum of the cadmium sulfide photocatalyst, the full width at half maximum of the main peak 2θ ≤ 0.14°, where the step condition is 7° / min. The scanning electron microscope image shows that the particle size of the cadmium sulfide photocatalyst ≥ 100 nm. The CdS photocatalyst is in block shape, and the grain size is in the order of hundreds of nanometers.

[0055] Third aspect: Application of a highly crystalline cadmium sulfide photocatalyst prepared based on the above preparation method in photocatalytic water splitting for hydrogen production, artificial photosynthesis, organic matter degradation, or gas oxidation / reduction.

[0056] The present preparation method is further illustrated by the following examples. According to the following examples, the present method can be better understood. However, those skilled in the art can easily understand that the specific material ratios, process conditions, and their results described in the examples are only used to illustrate the present invention and should not and will not limit the present invention described in detail in the claims.

[0057] Example 1

[0058] Step S1: At room temperature, disperse 4 mmol of cadmium acetate in 80 mL of 0.1 mol / L NaOH aqueous solution and stir for 30 min to obtain a turbid solution of cadmium hydroxide. Then, add 12 mmol of thioacetamide to the turbid solution of cadmium hydroxide and stir for 30 min to obtain a precursor solution.

[0059] Step S2: Transfer the precursor solution obtained in Step 1 to an oil bath and keep it at 95 °C for 2 h. After the precursor solution is cooled to room temperature, successively centrifuge and wash the cooled precursor solution three times (6000 rpm) with water and ethanol respectively to obtain a precursor. Vacuum dry the precursor at 60 °C for 2 h to obtain a CdS-precursor.

[0060] Step S3: Thoroughly grind the CdS-precursor obtained in Step 2 with a molten salt (a mixture of lithium chloride and potassium chloride, mass ratio 9:11) at a mass ratio of 1:4 to form a CdS-molten salt mixture. Calcine the CdS-molten salt mixture in an argon atmosphere (flow rate 40 mL / min -1 ) at 500 °C for 2 h.

[0061] Step S4: Successively centrifuge and wash the CdS-molten salt mixture after calcination and cooling in Step 3 three times (to remove the molten salt) with ultrapure water and ethanol respectively. Then, vacuum dry the centrifuged and washed CdS-molten salt mixture at 60 °C for 12 h to obtain a CdS-2h photocatalyst. In CdS-2h, 2h represents the calcination time of 2 h in Step 4, and the same applies hereinafter.

[0062] Figure 1It includes the X-ray diffraction pattern corresponding to Example 1 (CdS-2h). The full width at half maximum of the main peak of the X-ray photoelectron diffraction spectrum of the CdS-2h photocatalyst is 2θ = 0.14°, indicating that the CdS-2h photocatalyst is highly crystalline.

[0063] Figure 2 It includes the ultraviolet-visible diffuse reflectance spectrum corresponding to Example 1 (CdS-2h). The CdS-2h photocatalyst has a steep absorption shoulder, indicating that the CdS-2h photocatalyst is highly crystalline.

[0064] Figure 6a It includes the performance of photocatalytic dehydrogenative coupling of benzylamine to produce hydrogen and N-benzylidene butylamine corresponding to Example 1 (CdS-2h). Photochemical deposition of 2 wt% Pt (the Pt source is K2PtCl6), and the production rates of hydrogen and N-benzylidene butylamine are 4.66 mmol h -1 g -1 and 4.92 mmol h -1 g -1 .

[0065] Example 2

[0066] Step S1, at room temperature, disperse 4 mmol of cadmium acetate in 80 mL of 0.1 mol / L NaOH aqueous solution and stir for 30 min to obtain a turbid solution of cadmium hydroxide. Then, add 12 mmol of thioacetamide to the turbid solution of cadmium hydroxide and stir for 30 min to obtain a precursor solution.

[0067] Step S2, transfer the precursor solution obtained in Step 1 to an oil bath, keep it at 95 °C for 2 h. After the precursor solution is cooled to room temperature, centrifuge and wash the cooled precursor solution with water and ethanol three times (6000 rpm) respectively to obtain a precursor. Vacuum-dry the precursor at 60 °C for 2 h to obtain a CdS-precursor.

[0068] Step S3, fully grind the CdS-precursor obtained in Step 2 with a molten salt (a mixture of lithium chloride and potassium chloride, mass ratio 9:11) according to a mass ratio of 1:4 to form a CdS-molten salt mixture. Calcinate the CdS-molten salt mixture in an argon atmosphere (flow rate 40 mL min -1 ) at 500 °C for 5 h;

[0069] Step S4, centrifuge and wash the calcined and cooled CdS-molten salt mixture obtained in Step 3 with ultrapure water and ethanol three times (to remove the molten salt) respectively, and then vacuum-dry the centrifuged and washed CdS-molten salt mixture at 60 °C for 12 h to obtain a CdS-5h photocatalyst.

[0070] Figure 1It includes the X-ray diffraction pattern corresponding to Example 2 (CdS-5h). The full width at half maximum of the main peak of the X-ray photoelectron diffraction spectrum of the CdS-5h photocatalyst is 2θ = 0.12°, indicating that extending the calcination time can improve the crystallinity of the CdS photocatalyst.

[0071] Figure 6a It includes the performance of photocatalytic dehydrogenative coupling of benzylamine to produce hydrogen and N-benzylidene butylamine corresponding to Example 2 (CdS-5h). 2 wt% Pt was photochemically deposited (the Pt source was K2PtCl6), and the generation rates of hydrogen and N-benzylidene butylamine were 7.97 mmol h -1 g -1 and 7.05 mmol h -1 g -1 , indicating that improving the crystallinity of the CdS photocatalyst is beneficial to improving the catalytic performance.

[0072] Example 3

[0073] Step S1, at room temperature, 4 mmol of cadmium acetate was dispersed in 80 mL of 0.1 mol / L NaOH aqueous solution and stirred for 30 min to obtain a turbid solution of cadmium hydroxide. Then, 12 mmol of thioacetamide was added to the turbid solution of cadmium hydroxide and stirred for 30 min to obtain a precursor solution;

[0074] Step S2, the precursor solution described in Step 1 was transferred to an oil bath and kept at 95 °C for 2 h. After the precursor solution was cooled to room temperature, the cooled precursor solution was centrifugally washed 3 times (6000 rpm) with water and ethanol respectively to obtain a precursor. The precursor was vacuum dried at 60 °C for 2 h to obtain CdS-precursor;

[0075] Step S3, the CdS-precursor described in Step 2 was thoroughly ground with a molten salt (a mixture of lithium chloride and potassium chloride, mass ratio 9:11) at a mass ratio of 1:4 to form a CdS-molten salt mixture. The CdS-molten salt mixture was calcined at 500 °C for 10 h in an argon atmosphere (flow rate 40 mL min -1 );

[0076] Step S4, the CdS-molten salt mixture after calcination and cooling described in Step 3 was centrifugally washed 3 times (to remove the molten salt) with ultrapure water and ethanol respectively, and then the centrifugally washed CdS-molten salt mixture was vacuum dried at 60 °C for 12 h to obtain a CdS-10h photocatalyst.

[0077] Figure 1 It includes the X-ray diffraction pattern corresponding to Example 3 (CdS-10h). The full width at half maximum of the main peak of the X-ray photoelectron diffraction spectrum of the CdS-10h photocatalyst is 2θ = 0.12°, indicating that further extending the calcination time has a relatively small contribution to the improvement of the crystallinity of the CdS photocatalyst.

[0078] Figure 2 It includes the UV-visible diffuse reflectance spectrum corresponding to Example 3 (CdS-10h). Based on the Beer-Lambert formula, the Urbach energy of the CdS-10h photocatalyst is 29.8 meV, indicating that the recrystallization process significantly reduces the bulk defect density of CdS.

[0079] Figure 4c and Figure 5c are the scanning electron microscope and transmission electron microscope images corresponding to Example 3 (CdS-10h), respectively.

[0080] Figure 6a It includes the performance of photocatalytic dehydrogenative coupling of benzylamine to produce hydrogen and N-benzylidene butylamine corresponding to Example 3 (CdS-10h). Photochemical deposition of 2 wt% Pt (Pt source is K2PtCl6), and the production rates of hydrogen and N-benzylidene butylamine are 19.47 mmol h -1 g -1 and 18.93 mmol h -1 g -1 , Figure 6b It includes that the solar-chemical energy conversion efficiency of Example 3 (CdS-10h) is 2.69%.

[0081] Example 4

[0082] Step S1: At room temperature, disperse 4 mmol of cadmium acetate in 80 mL of 0.1 mol / L NaOH aqueous solution and stir for 30 min to obtain a turbid solution of cadmium hydroxide. Then, add 12 mmol of thioacetamide to the turbid solution of cadmium hydroxide and stir for 30 min to obtain a precursor solution.

[0083] Step S2: Transfer the precursor solution obtained in Step 1 to an oil bath, keep it at 95 °C for 2 h. After the precursor solution is cooled to room temperature, the cooled precursor solution is centrifugally washed 3 times (6000 rpm) with water and ethanol in sequence to obtain a precursor. The precursor is vacuum dried at 60 °C for 2 h to obtain CdS-precursor.

[0084] Step S3: The CdS-precursor obtained in Step 2 and the molten salt (a mixture of lithium chloride and potassium chloride, mass ratio 9:11) are sufficiently ground according to a mass ratio of 1:4 to form a CdS-molten salt mixture. The CdS-molten salt mixture is calcined at 500 °C for 15 h in an argon atmosphere (flow rate 40 mL min -1 ).

[0085] Step S4: The CdS-molten salt mixture after calcination and cooling in Step 3 is centrifugally washed 3 times (to remove the molten salt) with ultrapure water and ethanol in sequence, and then the centrifugally washed CdS-molten salt mixture is vacuum dried at 60 °C for 12 h to obtain the CdS-15h photocatalyst.

[0086] Figure 1 、 Figure 2 respectively include the X-ray diffraction pattern and ultraviolet-visible diffuse reflectance spectrum corresponding to Example 4 (CdS-15h).

[0087] Figure 6a Include the performance of photocatalytic dehydrogenative coupling of benzylamine to produce hydrogen and N-benzylidene butylamine corresponding to Example 4 (CdS-15h). Photochemically deposit 2 wt% Pt (the Pt source is K2PtCl6). The production rates of hydrogen and N-benzylidene butylamine are 13.47 mmol h -1 g -1 and 13.55 mmol h -1 g -1 .

[0088] Example 5 (preparation of CdS-precursor, i.e., CdS-Precursor)

[0089] Step S1: At room temperature, disperse 4 mmol of cadmium acetate in 80 mL of 0.1 mol / L aqueous NaOH solution and stir for 30 min to obtain a turbid solution of cadmium hydroxide. Then, add 12 mmol of thioacetamide to the turbid solution of cadmium hydroxide and stir for 30 min to obtain a precursor solution;

[0090] Step S2: Transfer the precursor solution obtained in Step 1 to an oil bath and keep it at 95 °C for 2 h. After the precursor solution is cooled to room temperature, successively centrifuge and wash the cooled precursor solution 3 times (6000 rpm) with water and ethanol respectively to obtain a precursor. Vacuum-dry the precursor at 60 °C for 2 h to obtain CdS-precursor. The sample prepared only in this example is named CdS-Precursor;

[0091] Figure 1 and Figure 2 respectively include the X-ray diffraction pattern and ultraviolet-visible diffuse reflectance spectrum corresponding to Example 5 (CdS-Precursor). The Urbach energy of Example 5 (CdS-Precursor) is 93.7 meV.

[0092] Figure 4a and Figure 5a are the scanning electron microscope image and transmission electron microscope image corresponding to Example 5 (CdS-Precursor) respectively.

[0093] Figure 6a Include the performance of photocatalytic dehydrogenative coupling of benzylamine to produce hydrogen and N-benzylidene butylamine corresponding to Example 5 (CdS-Precursor). Photochemically deposit 2 wt% Pt (the Pt source is K2PtCl6). No hydrogen and N-benzylidene butylamine production is detected.

[0094] Example 6

[0095] Step S1, at room temperature, disperse 4 mmol of cadmium acetate in 80 mL of 0.1 mol / L aqueous NaOH solution and stir for 30 min to obtain a turbid solution of cadmium hydroxide. Then, add 12 mmol of thioacetamide to the turbid solution of cadmium hydroxide and stir for 30 min to obtain a precursor solution.

[0096] Step S2, transfer the precursor solution obtained in Step 1 to an oil bath and keep it at 95 °C for 2 h. After the precursor solution is cooled to room temperature, successively centrifuge and wash the cooled precursor solution three times (6000 rpm) with water and ethanol respectively to obtain a precursor. Vacuum-dry the precursor at 60 °C for 2 h to obtain a CdS-precursor.

[0097] Step S3, calcine the CdS-precursor obtained in Step 2 in an argon atmosphere (flow rate 40 mL / min -1 ) at 500 °C for 10 h;

[0098] Step S4, successively centrifuge and wash the CdS-precursor after calcination and cooling in Step 3 three times with ultrapure water and ethanol respectively. Then, vacuum-dry the CdS-precursor after centrifugation and washing at 60 °C for 12 h to obtain a CdS-10h-None Salt photocatalyst.

[0099] Figure 1 Included is the X-ray diffraction pattern corresponding to Example 6 (CdS-10h-None Salt), indicating that molten salt solid-phase sintering is more effective than solid-phase sintering in improving crystallinity.

[0100] Figure 3 Included is the thermogravimetric loss spectrum corresponding to Example 6 (CdS-10h-None Salt), indicating that the molten salt can inhibit the volatilization process of the CdS-precursor, thereby promoting the crystallization of the CdS-precursor and improving crystallinity. Under the condition that the mass ratio of lithium chloride to potassium chloride is 9:11, the maximum heat treatment temperature is 650 °C.

[0101] Figure 4b and Figure 5b are the scanning electron microscope and transmission electron microscope images corresponding to Example 6 (CdS-10h-None Salt) respectively.

[0102] Figure 6a Included is the performance of the photocatalytic dehydrogenative coupling of benzylamine to produce hydrogen and N-benzylidene butylamine corresponding to Example 6 (CdS-10h-None Salt). Photochemically deposit 2 wt% Pt (the Pt source is K2PtCl6), and the hydrogen and N-benzylidene butylamine production rates are 1.96 mmol h -1 g -1and 2.42 mmol h -1 g -1 。

[0103] Example 7

[0104] Step S1: At room temperature, disperse 4 mmol of cadmium acetate in 80 mL of 0.05 mol / L aqueous NaOH solution and stir for 10 min to obtain a turbid solution of cadmium hydroxide. Then, add 4 mmol of thioacetamide to the turbid solution of cadmium hydroxide and stir for 10 min to obtain a precursor solution.

[0105] Step S2: Transfer the precursor solution obtained in Step 1 to an oil bath and keep it at 60 °C for 2 h. After the precursor solution is cooled to room temperature, centrifuge and wash the cooled precursor solution with water and ethanol once each (4000 rpm) to obtain a precursor. Vacuum-dry the precursor at 40 °C for 2 h to obtain a CdS-precursor.

[0106] Step S3: Thoroughly grind the CdS-precursor obtained in Step 2 with a molten salt (a mixture of lithium chloride and potassium chloride, mass ratio 2:1) at a mass ratio of 1:1 to form a CdS-molten salt mixture. Calcinate the CdS-molten salt mixture in an argon atmosphere (flow rate 40 mL min -1 ) at 450 °C for 10 h.

[0107] Step S4: Centrifuge and wash the CdS-molten salt mixture after calcination and cooling obtained in Step 3 with ultrapure water and ethanol once each (to remove the molten salt), and then vacuum-dry the centrifuged and washed CdS-molten salt mixture at 40 °C for 2 h to obtain a CdS-10h photocatalyst. Photochemically deposit 2 wt% Pt (the Pt source is K2PtCl6), and the hydrogen generation rate is 38.2 mmol h -1 g -1 。

[0108] Example 8

[0109] Step S1: At room temperature, disperse 4 mmol of cadmium acetate in 80 mL of 1 mol / L aqueous KOH solution and stir for 60 min to obtain a turbid solution of cadmium hydroxide. Then, add 12 mmol of thioacetamide to the turbid solution of cadmium hydroxide and stir for 60 min to obtain a precursor solution.

[0110] Step S2: Transfer the precursor solution obtained in Step 1 to an oil bath and keep it at 80 °C for 2 h. After the precursor solution is cooled to room temperature, centrifuge and wash the cooled precursor solution with water and ethanol six times each (8000 rpm) to obtain a precursor. Vacuum-dry the precursor at 80 °C for 6 h to obtain a CdS-precursor.

[0111] Step S3: The CdS-precursor described in Step 2 and the molten salt (a mixture of lithium chloride and potassium chloride with a mass ratio of 1:2) are thoroughly ground at a mass ratio of 1:10 to form a CdS-molten salt mixture. The CdS-molten salt mixture is calcined at 650 °C for 10 h in a nitrogen atmosphere (flow rate 40 mL / min -1 ).

[0112] Step S4: The CdS-molten salt mixture after the calcination and cooling in Step 3 is centrifugally washed once with ultrapure water and ethanol respectively (to remove the molten salt), and then the centrifugally washed CdS-molten salt mixture is vacuum dried at 80 °C for 6 h to obtain a CdS-10h photocatalyst. Photochemically deposit 2 wt% Pt (the Pt source is K2PtCl6), and in a 1 mM rhodamine B aqueous solution, the degradation efficiency reaches 98% in 3 hours.

[0113] Example 9

[0114] Step S1: At room temperature, disperse 4 mmol of cadmium chloride in 80 mL of 5 mol / L KOH aqueous solution and stir for 120 min to obtain a turbid solution of cadmium hydroxide. Then add 40 mmol of sodium sulfide to the turbid solution of cadmium hydroxide and stir for 60 min to obtain a precursor solution.

[0115] Step S2: Transfer the precursor solution described in Step 1 to an oil bath and keep it at 105 °C for 2 h. After the precursor solution cools to room temperature, the cooled precursor solution is centrifugally washed 6 times (at 10000 rpm) with water and ethanol respectively to obtain a precursor. The precursor is vacuum dried at 80 °C for 6 h to obtain a CdS-precursor.

[0116] Step S3: The CdS-precursor described in Step 2 and the molten salt (a mixture of lithium chloride and potassium chloride with a mass ratio of 1:2) are thoroughly ground at a mass ratio of 1:10 to form a CdS-molten salt mixture. The CdS-molten salt mixture is calcined at 550 °C for 20 h in a helium atmosphere (flow rate 40 mL / min -1 ).

[0117] Step S4: The CdS-molten salt mixture after the calcination and cooling in Step 3 is centrifugally washed once with ultrapure water and ethanol respectively (to remove the molten salt), and then the centrifugally washed CdS-molten salt mixture is vacuum dried at 80 °C for 6 h to obtain a CdS-20h photocatalyst.

[0118] Example 10

[0119] Step S1: At room temperature, disperse 8 mmol of cadmium chloride in 80 mL of 10 mol / L KOH aqueous solution and stir for 120 min, and then add 40 mmol of thiourea and stir for 120 min to obtain a precursor solution.

[0120] Step S2: Transfer the precursor solution described in Step 1 to an oil bath, keep it at 105 °C for 2 h. After the precursor solution cools to room temperature, centrifuge and wash the cooled precursor solution successively with water and ethanol 6 times (12,000 rpm) to obtain a precursor. Vacuum-dry the precursor at 80 °C for 6 h to obtain a CdS-precursor.

[0121] Step S3: Thoroughly grind the CdS-precursor described in Step 2 and molten salt (a mixture of lithium chloride and potassium chloride, mass ratio 1:2) in a mass ratio of 1:8 to form a CdS-molten salt mixture. Calcinate the CdS-molten salt mixture in a helium atmosphere (flow rate 40 mL / min -1 ) at 500 °C for 10 h.

[0122] Step S4: Centrifuge and wash the calcined and cooled CdS-molten salt mixture described in Step 3 successively with ultrapure water and ethanol once (to remove the molten salt), and then vacuum-dry the centrifuged and washed CdS-molten salt mixture at 80 °C for 6 h to obtain a CdS-10h photocatalyst.

[0123] For the CdS-10h photocatalyst prepared in Example 3, in a 0.1 mol / L benzylamine acetonitrile solution, the generation rates of hydrogen and N-benzylidene butylamine are 19.47 mmol h -1 g -1 and 18.93 mmol h -1 g -1 , and the solar energy-chemical energy conversion efficiency is 2.69%; for the CdS-10h photocatalyst prepared in Example 7, when 2% Pt is deposited and at 25 °C, in a reaction system with 0.1 mol / L Na2S and 0.1 mol / L Na2SO3 as electron donors, the hydrogen generation rate reaches 38.2 mmol h -1 g -1 ; for the CdS-10h photocatalyst prepared in Example 8, in an organic matter degradation reaction system, for a 1 mmol / L rhodamine B aqueous solution, the degradation efficiency reaches 98% in 3 hours.

[0124] The working principle of the present invention is:

[0125] The present invention uses cadmium source and sulfur source as raw materials, combines wet chemical method and solid-phase sintering (molten salt sintering) method, and based on the principles of coprecipitation, ion exchange, recrystallization, and molten salt inhibition of sulfur ion volatilization, realizes the preparation of highly crystalline cadmium sulfide photocatalyst, and successfully prepares large-size (≥100nm), highly crystalline CdS photocatalyst (the full width at half maximum of the main peak of the X-ray diffraction spectrum 2θ≤0.14° (step 7° / min)). The sources of its excellent photocatalytic performance can be attributed to the following three points: First, the chemical reaction rate is proportional to the density of photo-generated carriers on the catalyst surface. Under the condition of the same mass, the large-size photocatalyst has a higher surface photovoltage, which is beneficial to improving the kinetic process of surface photoreaction; Second, the high crystallinity indicates that the density of bulk defects of the catalyst is low, reducing the bulk recombination probability of photo-generated carriers and improving the utilization rate of incident photons; Finally, the catalyst gradually changes from amorphous to regular polyhedron, and under the drive of the interplanar electric field, effectively improves the kinetic process of photo-generated carrier migration.

Claims

1. A preparation method of a highly crystalline cadmium sulfide photocatalyst, characterized in that, It includes the following steps: S1: Add a cadmium source to an alkaline aqueous solution and stir for at least 10 min to obtain a cadmium hydroxide turbid solution. Add a sulfur source to the cadmium hydroxide turbid solution and stir for at least 10 min to obtain a precursor solution; S2: Keep the precursor solution obtained in step S1 at 60 - 105 °C for at least 2 h. After the precursor solution is cooled to room temperature, centrifuge and wash the precursor solution cooled to room temperature with water and ethanol respectively for at least once to obtain a precursor. Vacuum-dry the precursor at no less than 40 °C for at least 2 h to obtain a cadmium sulfide precursor, i.e., CdS-precursor; S3: Thoroughly grind the CdS-precursor obtained in step S2 and a molten salt in a mass ratio of (1:1) to (1:10) to form a CdS-molten salt mixture. Calcinate the CdS-molten salt mixture in an inert atmosphere at 450 - 650 °C for 2 - 20 h and then cool it; S4: Centrifuge and wash the CdS-molten salt mixture after calcination and cooling obtained in step S3 with water and ethanol respectively for at least once. Then vacuum-dry the centrifuged and washed CdS-molten salt mixture at no less than 40 °C for at least 2 h to obtain a CdS photocatalyst; Among them, the cadmium source in step S1 is cadmium chloride or cadmium acetate, the sulfur source is sodium sulfide, thioacetamide or thiourea, the alkaline aqueous solution is 0.05 - 10 mol / L sodium hydroxide or potassium hydroxide aqueous solution, and the molar ratio of Cd 2+ , S 2- and OH - in the precursor solution is (1:1:1) to (1:10:100); the molten salt in step S3 is a mixture prepared from lithium chloride and potassium chloride in a mass ratio of (2:1) to (1:2).

2. A preparation method as described in claim 1, characterized in that, In the molten salt in step S3, the mass ratio of lithium chloride to potassium chloride is 9:

11.

3. A preparation method as described in claim 1, characterized in that, In step S3, the calcination time of the CdS-molten salt mixture is 5 - 10 h.

4. A preparation method as described in claim 1, characterized in that, In step S4, the CdS-molten salt mixture after calcination and cooling is centrifuged and washed 3 times with ultrapure water and ethanol respectively.

5. A preparation method as described in claim 1, characterized in that, In step S4, the centrifuged and washed CdS-molten salt mixture is vacuum-dried at 60 °C for 12 h.

6. A preparation method as described in claim 1, characterized in that, The alkaline aqueous solution in step S1 is a 0.5 mol / L sodium hydroxide or potassium hydroxide aqueous solution.

7. A preparation method as described in claim 1, characterized in that, In step S1, the stirring time is at least 30 min. In step S2, the precursor solution cooled to room temperature is centrifuged and washed 3 times with water and ethanol respectively to obtain a precursor.

8. A preparation method as described in claim 1, characterized in that, In step S3, the CdS-molten salt mixture is calcined at 500 °C for 10 h in an inert atmosphere.

9. A highly crystalline cadmium sulfide photocatalyst prepared by the preparation method according to claim 1, characterized in that, In the X-ray diffraction spectrum of the cadmium sulfide photocatalyst, the full width at half maximum of the main peak 2θ ≤ 0.14° (step size 7° / min). The scanning electron microscope image shows that the particle size of the cadmium sulfide photocatalyst ≥ 100 nm.

10. Application of a highly crystalline cadmium sulfide photocatalyst prepared by the preparation method according to claim 1 in photocatalytic water splitting for hydrogen production, artificial photosynthesis, organic matter degradation, or gas oxidation / reduction.

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