A metal sulfide@silica composite photocatalyst, its preparation method and application
By preparing metal sulfide@silica composite photocatalysts, the problems of low efficiency and poor stability of metal sulfide photocatalysts are solved, and efficient visible photocatalytic reaction and multiple cycles are achieved, simplifying the preparation process.
Patent Information
- Application Number
- CN202311058320.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-08-22
- Publication Date
- 2025-07-25
- Estimated Expiration
- 2043-08-22
AI Technical Summary
The existing metal sulfide photocatalysts have low photocatalytic efficiency, poor stability and difficult to recycle, and the traditional synthesis methods are complex and lead to loss or aggregation of metal sulfides.
The metal complex is used as the template agent, and mixed with the silicon source under hydrothermal conditions to form a metal complex silica composite material. The metal sulfide silica composite photocatalyst is prepared by high-temperature calcination and sulfur ion exchange. The metal sulfide is bound in the silicon dioxide pore in situ to avoid aggregation and loss.
The photogenerated charge separation efficiency is improved, the stability and activity of the catalyst are enhanced, and the benzyl sp3 carbon-hydrogen bond oxidation reaction of ether compounds can be catalyzed under visible light. The reaction conversion and selectivity are maintained above 93%, and can be recycled multiple times.
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Figure CN117085702B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of photocatalysis technology, relates to photocatalysts, and particularly relates to a metal sulfide semiconductor@silica composite photocatalyst, a preparation method thereof, and an application thereof. Background Art
[0002] The oxidation of benzyl groups is one of the most useful chemical transformations in organic synthesis, and through this transformation, a structural unit with high synthetic value can be directly obtained from easily available alkyl aromatic precursors. However, the sp 3 C-H bond is relatively stable and difficult to break. Traditional benzyl oxidation reactions usually require stoichiometric amounts of toxic or corrosive oxidants such as Br2, CrO3, and KMnO4 and are carried out under harsh conditions. The solar power irradiating the earth's surface is approximately 1000 W·m -2 , and the solar radiation spectrum consists of 4% ultraviolet light, 43% visible light, and 53% infrared light. Driving organic synthesis using clean and renewable solar energy at room temperature is a green and promising alternative. In the 1970s, Fujishima and Honda discovered that TiO2 decomposes water under ultraviolet light, thus opening the door to photocatalysis technology.
[0003] Metal sulfides have unique optical and electrical properties such as a high specific surface area to volume ratio, a narrow bandgap, fast electron migration rate and charge generation rate, as well as high sensitivity, large specific capacity, and low redox potential. They are considered to be a promising photocatalytic material and have received extensive attention from people in the past few decades. However, the fast recombination rate of photo-generated charges in metal sulfides leads to low photocatalytic efficiency, which limits the possibility of their practical use. By changing the morphology of metal sulfides and reducing their size, the charge separation efficiency of metal sulfides can be improved, thereby affecting the photocatalytic efficiency. The currently commonly used method is to use the structural characteristics of the host material to direct the size of the target material metal sulfide. By pre-synthesizing a porous material and then impregnating the precursor of the metal sulfide into the pores of the host material, it is converted into metal sulfide under certain conditions. This synthesis method is not only complex, but also due to the adsorption effect, part of the metal sulfide is inevitably dispersed on the surface of the porous material, causing problems such as the loss or aggregation of metal sulfide during the catalytic process, and ultimately resulting in the loss and inactivation of metal sulfide. Summary of the Invention
[0004] The object of the present invention is to solve the problems in the prior art that metal sulfides have low efficiency, poor stability and are difficult to recycle in photocatalytic organic transformation, and to provide a metal sulfide@silica composite photocatalyst, its preparation method and application. The metal sulfide in the metal sulfide@silica composite photocatalyst is highly dispersed inside the silica, with a size less than 10 nm, and the photogenerated charge separation efficiency is significantly improved. At the same time, due to the spatial confinement effect of silica on the metal sulfide, the aggregation and loss of the metal sulfide during the reaction process are avoided, greatly improving its stability during the photocatalytic reaction process.
[0005] Another object of the present invention is to provide an application of the metal sulfide composite photocatalyst.
[0006] The technical solution adopted by the present invention is as follows:
[0007] A preparation method of a metal sulfide@silica composite photocatalyst, using a metal complex as a template agent and a silicon source as a raw material, hydrolyzing and condensing under hydrothermal conditions in a mixed solvent system of methanol and water, and wrapping the metal complex in the silica network to form a metal complex@silica composite material; the molar ratio of the metal to silicon is 1:10 - 50.
[0008] Then, the obtained metal complex@silica composite material is calcined at a high temperature in an air atmosphere to decompose the organic ligand. According to the solubility product constant of the metal sulfide, the calcined material is subjected to ion exchange with a sulfur source to finally obtain the metal sulfide@silica composite photocatalyst.
[0009] Specifically, it includes the following steps:
[0010] (1) Dissolve a metal salt and an organic ligand in a mixed solvent of methanol and water to obtain a metal complex solution;
[0011] (2) Add a silica precursor silicon source to a mixed solvent of methanol and water, and carry out a hydrolysis reaction to obtain silica sol;
[0012] (3) Add the metal complex solution to the silica sol for hydrothermal treatment to obtain a gel with silica-coated metal complex;
[0013] (4) Dry the gel with silica-coated metal complex, transfer it to a muffle furnace, calcine it in an air atmosphere, and then carry out an ion exchange reaction with a sulfur source to obtain the metal sulfide@silica composite photocatalyst.
[0014] Further, the metal salt in step (1) is one or more of cadmium, indium, zinc, nickel, iron, cobalt, silver, and copper ions; the organic ligand is a carboxylic acid ligand and a pyridine ligand. The carboxylic acid ligand is preferably benzoic acid, picolinic acid, citric acid, 1-naphthoic acid, and 2-naphthoic acid, and the pyridine ligand is preferably 1,10-phenanthroline, 2,2'-bipyridine, 4,4'-bipyridine, 2,3-bipyridine, and terpyridine; the molar ratio of the metal salt to the organic ligand is 1:1 to 3.
[0015] The silicon source in step (2) is preferably tetraethyl orthosilicate, tetrapropyl orthosilicate, tetramethyl orthosilicate, and tetraethyl orthosilicate; the concentration of the silicon source is 0.9 - 4.6 mmol / mL, the hydrolysis reaction temperature is 20 - 80 °C, and the reaction time is 1 - 8 h.
[0016] In the silica-coated metal complex in step (3), the molar ratio of metal to silicon is 1:5 to 50, and the concentration of the metal is 0.05 mmol / mL; the hydrothermal treatment temperature is 50 - 160 °C, and the treatment time is 8 - 48 h.
[0017] In step (4), the calcination temperature is 500 - 700 °C, the calcination time is 1 - 24 h, the sulfur source is a sulfur-containing compound, preferably sodium sulfide, thioacetamide, and thiourea, the molar ratio of the metal in the silica-coated metal complex to the sulfur source is 1:1, the ion exchange reaction temperature is 20 - 120 °C, and the ion exchange reaction time is 8 - 48 h.
[0018] Further, the specific surface area of the metal sulfide@silica composite photocatalyst is 10 - 400 m 2 / g, the pore size is 1 - 14 nm, and the size of the metal sulfide is 1 - 10 nm.
[0019] The present invention also provides a metal sulfide@silica composite photocatalyst prepared by the preparation method of the metal sulfide@silica composite photocatalyst.
[0020] The present invention also provides an application of the metal sulfide@silica composite photocatalyst in photocatalytic organic transformation.
[0021] In the said application, the photocatalytic reaction is the oxidative reaction of the benzylic sp 3 carbon-hydrogen bond of an ether compound under visible light (wavelength greater than 380 nm) irradiation, and the ether compound is isochroman (3,4-dihydro-1H-2-benzopyran).
[0022] Further, under visible light irradiation, the catalysis of the benzylic sp 3The specific operation of the C-H bond oxidation reaction is as follows: an ether compound, a cocatalyst, and a metal sulfide@silica composite photocatalyst are added in sequence. The molar ratio of the metal sulfide in the metal sulfide@silica composite photocatalyst to the ether compound is 1:50 - 200. Using acetonitrile as the solvent, the concentration of the ether compound is 0.1 - 1 mmol / mL. Under an atmosphere of 1 atm O2 and under visible light irradiation, the reaction proceeds for 1 - 20 h to catalyze the reaction of the ether compound.
[0023] In the preparation process of the present invention, a metal complex is used as a template agent and is in-situ encapsulated in silica during the dehydration and condensation of silica sol to form a gel. Through high-temperature calcination and sulfur ion exchange reaction, on the one hand, the metal complex is in-situ transformed into metal sulfide with nanoscale size as a metal source, and on the other hand, a porous silica material is prepared as a pore-forming agent, enabling the metal sulfide to be in-situ confined in the silica pores, avoiding the distribution of metal sulfide on the silica surface and the aggregation and loss during the reaction process, achieving the purpose of improving the photocatalytic efficiency and stability of the metal sulfide. The obtained metal sulfide@silica composite photocatalyst can be recycled at least 6 times in the visible-light catalytic oxidation reaction of isochroman, and the reaction conversion rate and selectivity are maintained above 93%.
[0024] Compared with the existing technologies, the present invention has the following technical effects:
[0025] 1. Using a metal complex as a bifunctional template agent, in-situ encapsulating the metal complex in the silica network. After high-temperature calcination and sulfur ion exchange, on the one hand, by utilizing the pore-forming effect of the metal complex, the specific surface area and porosity of the composite photocatalyst are increased, and on the other hand, the metal sulfide is in-situ confined in the silica pores. By using the spatial confinement effect of silica on the metal sulfide, the growth of the metal sulfide is restricted, and at the same time, the aggregation and loss of the metal sulfide during the reaction process are avoided.
[0026] 2. The preparation process of the metal sulfide@silica composite photocatalyst of the present invention is simple, with low cost and environmental friendliness.
[0027] 3. The components, structure, and particle size of the metal sulfide@silica composite photocatalyst of the present invention are easy to regulate, thereby regulating the photocatalytic activity of the material.
[0028] 4. As a photocatalyst, when the metal sulfide@silica composite photocatalyst of the present invention is used for the catalytic oxidation reaction of isochroman under visible light irradiation, the reaction conditions are mild, the catalytic activity is high, the energy consumption is low, meeting the requirements of green chemistry and sustainable development, and having important industrial application prospects. Description of the Drawings
[0029] Figure 1High-resolution transmission electron microscopy image of the metal sulfide@silica composite photocatalyst obtained in Example 1;
[0030] Figure 2 Particle size distribution diagram of the metal sulfide in the metal sulfide@silica composite photocatalyst obtained in Example 1;
[0031] Figure 3 Nitrogen adsorption isotherm of the metal sulfide@silica composite photocatalyst obtained in Example 1;
[0032] Figure 4 Nitrogen adsorption isotherm of the metal sulfide@silica composite photocatalyst obtained in Comparative Example 2;
[0033] Figure 5 High-resolution transmission electron microscopy image of the metal sulfide@silica composite photocatalyst obtained in Comparative Example 4;
[0034] Figure 6 Transmission electron microscopy image of the metal sulfide obtained in Comparative Example 1;
[0035] Figure 7 Size distribution diagram of the metal sulfide obtained in Comparative Example 1;
[0036] Figure 8 Transient photocurrent response diagrams of the metal sulfide@silica composite photocatalyst obtained in Example 1 and cadmium sulfide obtained in Comparative Example 1;
[0037] Figure 9 Photocatalytic recycling results of the composite photocatalyst prepared in Example 1. Detailed implementation manners
[0038] The following examples will help to understand the present invention, but the protection scope of the present invention is not limited to this content:
[0039] Example 1:
[0040] Benzoic acid (2mmol), 1,10-phenanthroline (1mmol) and Cd(NO3)2·4H2O (1.0mmol) were dissolved in a mixed solvent of anhydrous methanol (5mL) and water (5mL), and stirred at 20℃ for 60min to obtain a cadmium complex solution. Tetraethyl silicate (20mmol) was added dropwise to a mixed solvent of anhydrous methanol and water (11.0mL, V / V=4.5), and stirred and hydrolyzed at 20℃ for 5h to obtain a silica sol. The cadmium complex solution prepared above was added dropwise to the silica sol, transferred to a 50mL hydrothermal reactor, and heated at 160℃ for 24h to form a gel. After the gel was dried, it was placed in a muffle furnace and heated to 600°C at 5°C / min, maintained for 3 hours, cooled to room temperature, deionized water (20 mL) was added, ultrasonic dispersion was performed, 200 mL of Na2S solution (0.05 M) was added dropwise, stirred at 20°C for 12 hours, centrifuged, washed with deionized water until the supernatant was neutral, and vacuum dried overnight to obtain a yellow powder named CdS@SiO2-1. The corresponding high-resolution transmission electron microscopy image is shown in Figure 1 , it can be seen that CdS is evenly distributed inside the silica. Figure 2 This is the size distribution diagram of CdS in the composite photocatalyst. The average size of CdS is 3.7nm. Figure 3 is the nitrogen adsorption isotherm of the composite photocatalyst. The specific surface area of CdS@SiO2-1 is calculated to be 365 m 2 / g, pore distribution is 1-14nm, pore volume is 0.95cm 3 / g.
[0041] The activity of the photocatalyst was evaluated by photocatalytic selective oxidation of isochroman. Isochroman (0.1mmol), NHPI (0.01mmol), acetonitrile (1.0mL) and CdS@SiO2-1 composite photocatalyst were added to a quartz test tube in sequence. The molar ratio of Cd to isochroman in the CdS@SiO2 composite photocatalyst was 1:160. The reaction was carried out under 1atm O2 atmosphere and blue light irradiation for 15h. After centrifugation of the reaction mixture, the supernatant was taken and the conversion rate of isochroman was calculated by GC-MS test to be 97.4%, and the selectivity of 1-isochromanone was 97.4%.
[0042] Embodiment 2:
[0043] Dissolve benzoic acid (2 mmol), 1,10-phenanthroline (1 mmol), Cd(NO3)2·4H2O (0.8 mmol) and InCl3 (0.2 mmol) in a mixed solvent of anhydrous methanol (5 mL) and water (5 mL), and stir at 20 °C for 60 min to obtain a cadmium complex solution. Dropwise add tetramethyl orthosilicate (10.0 mmol) to a mixed solvent of anhydrous methanol and water (11.0 mL, V / V = 4.5), and stir and hydrolyze at 20 °C for 5 h to obtain silica sol. Dropwise add the above-prepared cadmium complex solution to the silica sol, transfer it to a 50 mL hydrothermal reaction kettle, and heat at 120 °C for 48 h to form a gel. After drying the gel, place it in a muffle furnace, heat it to 600 °C at a rate of 5 °C / min, hold for 3 h, cool to room temperature, add deionized water (20 mL), disperse it by ultrasonic wave, dropwise add 200 mL of thioacetamide solution (0.05 M), stir at 80 °C for 24 h, centrifuge, wash with deionized water until the supernatant is neutral, and dry in vacuum overnight to obtain a yellow powder, named Cd / InS x @SiO2. The specific surface area of this composite photocatalyst is 267 m 2 / g, the pore size distribution is in the range of 1 - 14 nm, and the pore volume is 0.74 cm 3 / g.
[0044] Example 3:
[0045] Dissolve benzoic acid (2 mmol), 2,2'-bipyridine (1 mmol), Cd(NO3)2·4H2O (0.9 mmol) and NiCl2 (0.1 mmol) in a mixed solvent of anhydrous methanol (5 mL) and water (5 mL), and stir at room temperature for 60 min to obtain a cadmium complex solution. Dropwise add tetraethyl orthosilicate (50 mmol) to a mixed solvent of anhydrous methanol and water (11.0 mL, V / V = 4.5), and stir and hydrolyze at 80 °C for 1 h to obtain silica sol. Dropwise add the above-prepared cadmium complex solution to the silica sol, transfer it to a 50 mL hydrothermal reaction kettle, and heat at 80 °C for 48 h to form a gel. After drying the gel, place it in a muffle furnace, heat it to 600 °C at a rate of 5 °C / min, hold for 12 h, cool to room temperature, add deionized water (20 mL), disperse it by ultrasonic wave, dropwise add 200 mL of Na2S solution (0.05 M), stir at 20 °C for 12 h, centrifuge, wash with deionized water until the supernatant is neutral, and dry in vacuum overnight to obtain a yellow powder, named Cd / NiS x @SiO2. The specific surface area of this composite photocatalyst is 315 m 2 / g, the pore size distribution is in the range of 1 - 14 nm, and the pore volume is 0.93 cm 3 / g.
[0046] Example 4:
[0047] Dissolve citric acid (2 mmol) and Cd(NO3)2·4H2O (1.0 mmol) in anhydrous methanol (5 mL) and water (5 mL). Dropwise add tetrapropyl orthosilicate (20 mmol) into the mixed solvent of anhydrous methanol and water (11.0 mL, V / V = 4.5), stir and hydrolyze at 20 °C for 8 h to obtain silica sol. Dropwise add the prepared cadmium complex solution into the silica sol, stir at room temperature for 2 h, transfer it to a 50 mL hydrothermal reactor, heat at 50 °C for 48 h to form a gel. After drying the gel, place it in a muffle furnace, heat it to 600 °C at a rate of 5 °C / min, hold for 6 h, cool to room temperature, add deionized water (20 mL), disperse it by ultrasonic wave, then dropwise add 200 mL of Na2S solution (0.05 M), stir at 20 °C for 24 h, centrifuge, wash with deionized water until the supernatant is neutral, and dry overnight in vacuum to obtain a yellow powder, named CdS@SiO2-2.
[0048] Evaluate the activity of the photocatalyst by the photocatalytic selective oxidation reaction of isochroman. Sequentially add isochroman (0.1 mmol), NHPI (0.01 mmol), acetonitrile (1.5 mL) and the CdS@SiO2-2 composite photocatalyst into a quartz test tube. The molar ratio of Cd to isochroman in the CdS@SiO2-2 composite photocatalyst is 1:160. Under an atmosphere of 1 atm O2, react under visible light irradiation for 15 h. After centrifuging the reaction mixture, take the upper layer clear liquid, and calculate the conversion rate of isochroman to be 91.1% and the selectivity of 1-isochromanone to be 98.9% by GC-MS test.
[0049] Example 5:
[0050] Dissolve citric acid (1 mmol) and Cd(NO3)2·4H2O (1.0 mmol) in anhydrous methanol (5 mL) and water (5 mL). Dropwise add tetrapropyl orthosilicate (20 mmol) into the mixed solvent of anhydrous methanol and water (11.0 mL, V / V = 4.5), stir and hydrolyze at 20 °C for 8 h to obtain silica sol. Dropwise add the prepared cadmium complex solution into the silica sol, stir at room temperature for 2 h, transfer it to a 50 mL hydrothermal reactor, heat at 160 °C for 8 h to form a gel. After drying the gel, place it in a muffle furnace, heat it to 500 °C at a rate of 5 °C / min, hold for 24 h, cool to room temperature, add deionized water (20 mL), disperse it by ultrasonic wave, then dropwise add 200 mL of Na2S solution (0.05 M), stir at 20 °C for 48 h, centrifuge, wash with deionized water until the supernatant is neutral, and dry overnight in vacuum to obtain a yellow powder, named CdS@SiO2-3. This composite photocatalyst has excellent specific surface area and pore volume, avoids the aggregation and loss of metal sulfide on the surface of silica during the distribution and reaction process, and has excellent photocatalytic efficiency and stability.
[0051] Example 6:
[0052] Dissolve pyridinecarboxylic acid (3 mmol) and Cd(NO3)2·4H2O (1.0 mmol) in anhydrous methanol (5 mL) and water (5 mL). Dropwise add tetraethyl orthosilicate (20 mmol) to the mixed solvent of anhydrous methanol and water (11.0 mL, V / V = 4.5), and stir and hydrolyze at 50 °C for 8 h to obtain silica sol. Dropwise add the cadmium complex solution prepared above to the silica sol, stir at room temperature for 2 h, transfer it to a 50 mL hydrothermal reaction kettle, heat at 160 °C for 8 h to form a gel. After drying the gel, place it in a muffle furnace, heat it to 700 °C at a rate of 5 °C / min, hold for 1 h, cool to room temperature, add deionized water (20 mL), disperse it by ultrasonic, dropwise add 200 mL of Na2S solution (0.05 M), stir at 20 °C for 48 h, centrifuge, wash with deionized water until the supernatant is neutral, and dry it overnight in vacuum to obtain a yellow powder, named CdS@SiO2-4. This composite photocatalyst has excellent specific surface area and pore volume, avoids the aggregation and loss of metal sulfide on the surface of silica during the distribution and reaction process, and has excellent photocatalytic efficiency and stability.
[0053] Comparative Example 1:
[0054] Take Cd(OAc)2·2H2O (1.6 mmol) and thiourea (8.0 mmol) and dissolve them in deionized water (20 mL). Transfer the reaction mixture to a 25 mL hydrothermal reaction kettle and heat at 140 °C for 24 h. After the reaction is completed, cool to room temperature, filter under reduced pressure, wash the filter cake with deionized water, and dry to obtain a yellow solid CdS. Figure 6 and Figure 7 are the transmission electron microscope image and particle size distribution diagram of CdS respectively. It can be seen that the catalyst is spherical particles with an average size of 245 nm, which is much larger than the size of CdS in Example 1. It can be seen that the preparation method provided by the present invention can reduce the size of metal sulfide. Figure 8 is the transient photocurrent response diagram of CdS and CdS@SiO2-1 obtained in Example 1. Under the same test conditions, the photocurrent response value of CdS@SiO2-1 is higher than that of CdS. It can be seen that CdS@SiO2-1 provided by the present invention improves the photocurrent separation efficiency.
[0055] The activity of the photocatalyst was evaluated by photocatalytic selective oxidation of isochroman. In a quartz test tube, isochroman (0.1 mmol), NHPI (0.01 mmol), acetonitrile (1.0 mL) and CdS photocatalyst were added in sequence. The molar ratio of Cd to isochroman in the CdS photocatalyst was 1:160. Under 1 atm O2 atmosphere, the reaction was carried out under visible light irradiation for 15 h. After the reaction mixture was centrifuged, the supernatant was taken, and the conversion rate of isochroman was calculated to be 51.3% and the selectivity for 1-isochromanone was 97.7% by GC-MS test.
[0056] Comparative Example 2:
[0057] 1-Naphthoic acid (1 mmol) and Cd(NO3)2·4H2O (1.0 mmol) were dissolved in a mixed solvent of anhydrous methanol (5 mL) and water (5 mL), and stirred at 20 °C for 60 min to obtain a cadmium complex solution. Tetraethyl orthosilicate (20 mmol) was added dropwise to a mixed solvent of anhydrous methanol and water (11.0 mL, V / V = 4.5), and stirred and hydrolyzed at 20 °C for 5 h to obtain silica sol. The above-prepared cadmium complex solution was added dropwise to the silica sol, transferred to a 50 mL hydrothermal reaction kettle, and heated at 160 °C for 8 h to form a gel. After the gel was dried, it was placed in a muffle furnace, heated to 800 °C at 5 °C / min, held for 1 h, cooled to room temperature, deionized water (20 mL) was added, ultrasonically dispersed, 200 mL of thiourea solution (0.05 M) was added dropwise, stirred at 120 °C for 8 h, centrifuged, washed with deionized water until the supernatant was neutral, and vacuum dried overnight to obtain a yellow powder, named CdS@SiO2-5. Figure 4 This is the nitrogen adsorption isotherm of the composite photocatalyst. The specific surface area of the composite photocatalyst calculated from the nitrogen adsorption isotherm is 10 m 2 / g, and the pore volume is 0.06 cm 3 / g.
[0058] The activity of the photocatalyst was evaluated by photocatalytic selective oxidation of isochroman. In a quartz test tube, isochroman (0.1 mmol), NHPI (0.01 mmol), acetonitrile (5.0 mL) and CdS@SiO2-5 composite photocatalyst were added in sequence. The molar ratio of Cd to isochroman in the CdS@SiO2-5 composite photocatalyst was 1:100. Under 1 atm O2 atmosphere, the reaction was carried out under visible light irradiation for 15 h. After the reaction mixture was centrifuged, the supernatant was taken, and the conversion rate of isochroman was calculated to be 66.9% and the selectivity for 1-isochromanone was 97.3% by GC-MS test.
[0059] Comparative Example 3:
[0060] Dissolve benzoic acid (2 mmol), 1,10-phenanthroline (1 mmol) and Cd(NO3)2·4H2O (1.0 mmol) in a mixed solvent of anhydrous methanol (5 mL) and water (5 mL), and stir at 20 °C for 60 min to obtain a cadmium complex solution. Dropwise add tetraethyl orthosilicate (10 mmol) to a mixed solvent of anhydrous methanol and water (11.0 mL, V / V = 4.5), and stir and hydrolyze at 20 °C for 5 h to obtain a silica sol. Dropwise add the above-prepared cadmium complex solution to the silica sol, transfer it to a 50 mL hydrothermal reaction kettle, and heat at 160 °C for 24 h to form a gel. After drying the gel, place it in a muffle furnace, heat it to 400 °C at a rate of 5 °C / min, hold for 24 h, cool to room temperature, add deionized water (20 mL), disperse it by ultrasonic wave, dropwise add 200 mL of thioacetamide solution (0.05 M), stir at 20 °C for 48 h, centrifuge, wash with deionized water until the supernatant is neutral, and dry overnight in vacuo to obtain a yellow powder, named CdS@SiO2-6. The specific surface area of this composite photocatalyst is 146 m 2 / g, and the pore volume is 0.28 cm 3 / g.
[0061] Evaluate the activity of the photocatalyst by the photocatalytic selective oxidation reaction of isochroman. Add isochroman (0.1 mmol), NHPI (0.01 mmol), acetonitrile (1.0 mL) and CdS@SiO2-6 composite photocatalyst into a quartz test tube in sequence. The molar ratio of Cd to isochroman in the CdS@SiO2-6 composite photocatalyst is 1:160. Under 1 atm O2 atmosphere, react under visible light irradiation for 15 h. After centrifuging the reaction mixture, take the supernatant, and calculate the conversion rate of isochroman to be 60.5% and the selectivity of 1-isochromanone to be 98.2% by GC-MS test.
[0062] It can be seen from Comparative Examples 2-3 that the structural properties of the metal sulfide@silica composite photocatalyst can be regulated by changing the calcination temperature in the synthesis conditions. Among them, when the calcination temperature is too low, the organic ligand is not completely decomposed, resulting in a smaller specific surface area. When the calcination temperature is too high, the silica structure collapses and transforms into a non-porous structure, leading to a sharp decrease in the specific surface area. Generally, the composite photocatalyst prepared at a calcination temperature of 500-700 °C has good specific surface area and pore volume, which is beneficial to improving the catalytic performance.
[0063] Comparative Example 4:
[0064] Benzoic acid (2 mmol), 4,4'-bipyridine (1 mmol), and Cd(NO3)2·4H2O (1.0 mmol) were dissolved in a mixed solvent of anhydrous methanol (5 mL) and water (5 mL). The mixture was stirred at 20 °C for 60 min to obtain a cadmium complex solution. Tetrapropyl orthosilicate (5 mmol) was added dropwise to a mixed solvent of anhydrous methanol and water (11.0 mL, V / V = 4.5), and the mixture was stirred and hydrolyzed at 50 °C for 5 h to obtain a silica sol. The prepared cadmium complex solution was added dropwise to the silica sol, and the mixture was transferred to a 50 mL hydrothermal reaction kettle and heated at 150 °C for 36 h to form a gel. After drying the gel, it was placed in a muffle furnace and heated to 600 °C at a rate of 5 °C / min and maintained for 6 h. After cooling to room temperature, deionized water (20 mL) was added, and the mixture was ultrasonically dispersed. Then, 200 mL of a thiourea solution (0.05 M) was added dropwise, and the mixture was stirred at 120 °C for 8 h. After centrifugation, the mixture was washed with deionized water until the supernatant was neutral, and then dried under vacuum overnight to obtain a yellow powder, named CdS@SiO2-7. Figure 5 This is the high-resolution transmission electron microscopy image of the composite photocatalyst. In the figure, the CdS particles are aggregated together, and the interfaces between the particles cannot be distinguished. It can be seen that by changing the molar ratio of metal to silicon, the aggregation and dispersion degree of metal sulfide can be adjusted. Among them, in the range of the molar ratio of metal to silicon from 1:10 to 50, the aggregation and loss of metal sulfide during the reaction can be avoided.
[0065] The activity of the photocatalyst was evaluated by the photocatalytic selective oxidation reaction of isochroman. In a quartz test tube, isochroman (0.1 mmol), NHPI (0.01 mmol), acetonitrile (1.0 mL), and the CdS@SiO2-7 composite photocatalyst were added in sequence. The molar ratio of Cd to isochroman in the CdS@SiO2-7 composite photocatalyst was 1:160. Under an atmosphere of 1 atm O2 and visible light irradiation, the reaction was carried out for 15 h. After the reaction mixture was centrifuged, the supernatant was taken, and the conversion rate of isochroman was calculated to be 75.4% and the selectivity for 1-isochromanone was 96.8% by GC-MS testing.
[0066] Stability experiment:
[0067] The CdS@SiO2-1 prepared in Example 1 was used as the photocatalyst for the photocatalytic oxidation reaction of isochroman. In a quartz test tube, isochroman (0.1 mmol), NHPI (0.01 mmol), acetonitrile (1.0 mL), and the CdS@SiO2-1 composite photocatalyst were added in sequence. The molar ratio of Cd to isochroman in the CdS@SiO2-1 composite photocatalyst was 1:160. Under an atmosphere of 1 atm O2 and visible light irradiation, the reaction was carried out for 15 h. After the reaction mixture was centrifuged, the supernatant was used for gas chromatography analysis, and the solid catalyst was washed 3 times with acetonitrile and then dried overnight in a vacuum drying oven at 80 °C and reused. The conversion rate of isochroman and the selectivity for 1-isochromanone in six cycles of photocatalytic reactions are asFigure 9 As shown. The results show that the composite photocatalyst obtained in Example 1 not only has high photocatalytic activity, but also has high stability, can be recycled multiple times and maintain high catalytic activity.
[0068] The results of the above examples show that by adjusting the metal type, the ratio of metal to silicon, and the calcination conditions, the composition, pore structure, particle size, and aggregation and dispersion degree of metal sulfide of the photocatalyst can be regulated, and then different metal sulfide@silica composite photocatalysts can be prepared and selected according to the actual needs of different photocatalytic reactions.
[0069] The metal sulfide@silica composite photocatalyst has high selectivity in the photocatalytic selective oxidation reaction of isochroman and has high stability, can be recycled multiple times and maintain high catalytic activity.
[0070] The above are only some embodiments of the present invention, rather than a limitation on the implementation manner, and the obvious changes or variations derived therefrom are still within the protection scope of the present invention.
Claims
1. A preparation method of a metal sulfide@silica composite photocatalyst, characterized in that It includes the following steps: (1) Dissolve a metal salt and an organic ligand in a mixed solvent of methanol and water to obtain a metal complex solution; (2) Add a silica precursor silicon source to a mixed solvent of methanol and water, and carry out a hydrolysis reaction to obtain silica sol; (3) Add the metal complex solution to the silica sol for hydrothermal treatment, wherein the molar ratio of metal to silicon is 1:10 to 50, the concentration of the metal is 0.05 mmol / mL, the hydrothermal treatment temperature is 50 to 160 °C, and the treatment time is 8 to 48 h to obtain a gel of silica-coated metal complex; (4) Dry the gel of silica-coated metal complex and transfer it to a muffle furnace, calcine it in an air atmosphere, the calcination temperature is 500 to 700 °C, the calcination time is 1 to 24 h, and then carry out an ion exchange reaction with a sulfur source. The molar ratio of the metal in the silica-coated metal complex to the sulfur source is 1:1, the ion exchange reaction temperature is 20 to 120 °C, and the ion exchange reaction time is 8 to 48 h to obtain a metal sulfide@silica composite photocatalyst.
2. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of the metal salt to the organic ligand is 1:1 to 3, and the concentration of the metal salt is 0.1 mmol / mL; in step (2), the concentration of the silicon source is 0.9 - 4.6 mmol / mL, the hydrolysis reaction temperature is 20 to 80 °C, and the reaction time is 1 to 8 h; in step (4), the sulfur source is a sulfur-containing compound, which is one or more of sodium sulfide, thioacetamide, and thiourea.
3. The preparation method according to claim 1, wherein The organic ligand is a carboxylic acid ligand and a pyridine ligand.
4. The preparation method according to claim 3, wherein The carboxylic acid ligand is one or more of benzoic acid, picolinic acid, citric acid, 1-naphthoic acid, and 2-naphthoic acid, and the pyridine ligand is one or more of 1,10-phenanthroline, 2,2'-bipyridine, 4,4'-bipyridine, 2,3-bipyridine, and terpyridine.
5. The preparation method according to claim 1, characterized in that, The silicon source is one or more of tetraethyl orthosilicate, tetrapropyl orthosilicate, tetramethyl orthosilicate, and tetraethyl orthosilicate.
6. A metal sulfide@silica composite photocatalyst prepared by the preparation method of the metal sulfide@silica composite photocatalyst according to any one of claims 1 to 5, wherein the metal ions in the metal sulfide are composed of one or more of cadmium, indium, zinc, nickel, iron, cobalt, silver, and copper ions mixed in any ratio.
7. The metal sulfide@silica composite photocatalyst according to claim 6, wherein The specific surface area of the metal sulfide@silica composite photocatalyst is 10-400 m 2 / g, the pore size distribution is in the range of 1-14 nm, and the size of the metal sulfide is 1-10 nm.
8. An application of the metal sulfide@silica composite photocatalyst according to any one of claims 1 to 7 in a photocatalytic reaction.
9. The application according to claim 8, wherein The photocatalytic reaction is the oxidative reaction of the benzylic sp 3 carbon-hydrogen bond of an ether compound under visible light irradiation, and the ether compound is isochroman.
10. The application according to claim 9, wherein Visible light catalyzed benzylic sp 3 The specific operation of the carbon-hydrogen bond oxidation reaction of the ether compound is as follows: an ether compound, a co-catalyst, and a metal sulfide@silica composite photocatalyst are added in sequence. The molar ratio of the metal sulfide in the metal sulfide@silica composite photocatalyst to the ether compound is 1:50 to 200. Using acetonitrile as the solvent, the concentration of the ether compound is 0.1 to 1 mmol / mL; under an atmosphere of 1 atm O2, the reaction is carried out under visible light irradiation for 1 to 20 h to catalyze the reaction of the ether compound.