Diatomic metal complex / CdS nanorod composite photocatalyst and its preparation method and use

Abstract

The present invention belongs to the field of photocatalysis technology, and specifically discloses a diatomic metal complex / CdS nanorod composite photocatalyst, its preparation method and use. The specific preparation method is: using EDA to assist solvent thermal reaction to synthesize pure CdS nanorods; then using Schiff base reaction, heating in an oil bath, condensing and reflux to synthesize the diatomic metal complex; putting the two into a beaker, adding ethanol, stirring evenly and drying to obtain a diatomic metal complex and CdS nanorod photocatalytic composite material, that is, to obtain the target product. CdS nanorods have a rod-shaped hexagonal crystal structure, and the diatomic metal complex is block-shaped. After being composited with CdS nanorods, it is loaded on the wall of the CdS nanorods without changing the main morphology of the CdS nanorods. The present invention can effectively separate photogenerated electrons and holes by composited with CdS nanorods, thereby improving the activity of photocatalytic formic acid decomposition to produce synthesis gas (H2+CO).

Description

Technical Field

[0001] The present invention specifically belongs to the technical field of powder photocatalytic materials, and in particular relates to a diatomic metal complex / CdS nanorod composite photocatalyst and a preparation method and application thereof. Background Art

[0002] Due to the increasing global energy consumption, the development of alternatives to fossil fuels is highly desirable. Synthesis gas (syngas) has proven to be a useful fuel of the future, as it can be used directly in internal combustion engines or converted into liquid fuels via the Fischer-Tropsch process. Furthermore, syngas is a feedstock for the chemical industry to produce synthetic products. Currently, most syngas production comes from fossil fuel sources, which requires high temperature and pressure conditions. Formic acid can serve as a reproducible source for syngas production due to its low toxicity and high weight content of hydrogen and carbon. Furthermore, formic acid is a liquid at ambient temperature and does not require special handling conditions for transportation and storage. During the decomposition of formic acid, H2, CO and some carbon dioxide can be produced. The released carbon dioxide can be recycled to produce formic acid under appropriate conditions, thus creating a sustainable and viable cycle for the storage and release of chemical energy.

[0003] Solar energy is environmentally friendly, inexhaustible, and emission-free. Therefore, photocatalytic fatty acid dehydrogenation at room temperature and under sunlight has attracted significant attention. Efficient photocatalytic reactions of formic acid have been investigated using a variety of catalysts, including semiconductors, organic polymers, single-atom catalysts, and molecular complexes. CdS nanorods are generally considered a promising semiconductor catalyst due to their low cost, moderate redox capacity, and high photocatalytic activity. However, their susceptibility to photocorrosion and poor electron-hole separation limit their photocatalytic formic acid decomposition. Co-catalysts can further address this issue by improving the activity and stability of CdS nanorods. Numerous noble metals, such as Ir-Ru complexes, Pd, Pt, AuPd, and AgPd, have been applied to photocatalytic formic acid decomposition due to their synergistic catalytic effects. However, the high cost and rarity of noble metals limit the cost and feasibility of experiments. The development of noble metal-free photocatalytic systems is more sustainable. Fe-salen, a noble metal-free homogeneous single-atom catalyst, could serve as a low-cost and efficient photocatalytic FA decomposition catalyst. Although such single-site catalysts show potential advantages, single-atom catalysts may suffer from the problem of insufficient neighboring sites.

[0004] Therefore, the above-mentioned existing technical solutions have the following defects: the existing CdS nanorod photocatalysts are susceptible to photocorrosion and have poor electron-hole separation ability, and have certain limitations in the photocatalytic decomposition of formic acid. The high cost and rarity of the noble metal catalyst system limit the cost and feasibility of the experiment, and the non-noble metal single-atom catalysts may have insufficient active sites. Summary of the Invention

[0005] Based on the above-mentioned shortcomings of the prior art, such as the susceptibility of CdS nanorods to photocorrosion and poor electron-hole separation ability, the high cost and rarity of precious metal catalyst systems, and the possible lack of active sites in non-precious metal single-atom catalysts, one of the objectives of the present invention is to provide a diatomic metal complex / CdS nanorod composite photocatalyst that can effectively prevent the rapid recombination of photogenerated electrons and holes, and can also effectively avoid CdS from being photocorroded.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for preparing a diatomic metal complex / CdS nanorod composite photocatalyst, comprising the following steps:

[0007] S1. FeCl2·4H2O and methanol are placed in a nitrogen reflux container, and a boiling methanol solution containing 1,3-propylenediamine is added thereto, and a boiling methanol solution containing 2,6-diformyl-4-methylphenol is added thereto to obtain a mixed solution;

[0008] S2. The mixed solution was heated in an oil bath by condensation reflux. After the reaction was completed, the crystalline solid was collected by filtration and washed with cold methanol to obtain the final product Fe2C 26 H 34 N4O4Cl2, referred to as Fe2LCl2;

[0009] S3. Mix CdS nanorods and Fe2LCl2, add ethanol, stir to react, and then dry to collect the composite product Fe2-CdS.

[0010] Further improvement of diatomic metal complex / CdS nanorod composite photocatalyst:

[0011] Preferably, the preparation method of CdS nanorods in step S3 is as follows: cadmium nitrate tetrahydrate and thiourea are added to a Teflon-lined high-pressure reactor filled with ethylenediamine as a solvent, stirred, and then the high-pressure reactor is sealed and reacted in an oven. After the reaction is completed, the reaction is cooled to room temperature, washed with water and ethanol to obtain a precipitate, and dried to obtain CdS nanorods.

[0012] Preferably, the added concentration of cadmium nitrate tetrahydrate in ethylenediamine is 0.0385-0.1155 g / ml, the added concentration of thiourea in ethylenediamine is 0.0385-0.1155 g / ml, and the mass ratio of cadmium nitrate tetrahydrate to thiourea is (0.5-3):1.

[0013] Preferably, during the preparation of CdS nanorods, the stirring temperature is 20-50° C. and the time is 20-60 min; the reaction temperature is 140-160° C. and the time is 24-72 h.

[0014] Preferably, the amount of FeCl2·4H2O added to methanol in step S1 is 0.008-0.064 g / ml.

[0015] Preferably, in the boiling methanol solution containing 1,3-propylenediamine, the added amount of 1,3-propylenediamine is 0.0368-0.292 ml / ml; in the boiling methanol solution containing 2,6-diformyl-4-methylphenol, the concentration of 2,6-diformyl-4-methylphenol is 0.0068-0.0526 g / ml; when preparing the mixed solution, the quantitative relationship between FeCl2·4H2O, 1,3-propylenediamine, and 2,6-diformyl-4-methylphenol is 1:1:1.

[0016] Preferably, the oil bath heating temperature in step S2 is 50-80°C for 2-6 hours; the stirring reaction time in step S3 is 6-10 hours, and the drying temperature is 60-80°C.

[0017] Preferably, in step S3, CdS nanorods and Fe2LCl2 are mixed in a mass ratio of 1:1-4:1, and ethanol is added until the concentration of CdS nanorods in ethanol is 3-5 mg / ml.

[0018] A second object of the present invention is to provide a diatomic metal complex / CdS nanorod composite photocatalyst prepared by any of the preparation methods described above, wherein the composite photocatalyst consists of CdS nanorods and diatomic metal complexes loaded on the surface of the CdS nanorods; the CdS nanorods have a length of 1-3 μm and a hexagonal crystal structure; the diatomic metal complex is in block form, specifically a diiron atom complex; the mass ratio of the CdS nanorods to the diatomic metal complex is 2:1, and the two are physically composited with interfacial interaction.

[0019] The third object of the present invention is to provide a use of the above-mentioned diatomic metal complex / CdS nanorod composite photocatalyst for photocatalytic decomposition of formic acid to produce hydrogen and carbon monoxide.

[0020] The beneficial effects of the present invention compared to the prior art are:

[0021] 1) The present invention provides a diatomic metal complex / CdS nanorod composite photocatalyst. The main structure of the composite material is CdS nanorods, and the surface is coated with a diatomic metal complex. The CdS nanorods are 1-3 μm in length and have a hexagonal crystal structure. In this composite configuration, during the photocatalytic decomposition of formic acid, the CdS nanorods and the complex interact on the surface. An inherent electric field exists between the CdS nanorods and the diatomic metal complex, and the electrons in the central CdS nanorods are excited, promoting the transfer of outer-shell electrons toward the diatomic metal complex, resulting in the rapid transmission of photogenerated carriers, ensuring the effective separation and utilization of photogenerated electrons and holes, and thus further enhancing the photocatalytic activity. This can effectively prevent the rapid recombination of photogenerated electrons and holes, and can also effectively protect CdS from light corrosion.

[0022] 2) The present invention provides a method for preparing a diatomic metal complex / CdS nanorod composite photocatalyst. First, CdS nanorods are synthesized by hydrothermal reaction. Then, a diatomic metal complex is synthesized by Schiff base reaction under oil bath heating and condensation reflux. The two are placed in a beaker and ethanol is added. The mixture is stirred evenly and dried to obtain a diatomic metal complex and CdS nanorod photocatalytic composite material. The advantages of this product are mainly divided into two aspects:

[0023] First, the co-catalysts commonly used for formic acid decomposition are essentially precious metal catalysts, such as Ir-Ru complexes, Pd, Pt, AuPd, and AgPd. However, the high cost and rarity of precious metals limit the cost and feasibility of experiments. Fe-salen, a homogeneous single-atom configuration in a precious metal-free photocatalytic system, can be used as a low-cost, highly efficient photocatalytic FA decomposition catalyst. However, single-atom catalysts may suffer from a lack of adjacent sites. The diatomic catalyst Fe2LCl2, as a co-catalyst, has two metal active sites, which can provide effective surface reaction sites, making surface catalytic reactions more likely to occur and improving reaction activity.

[0024] Finally, photocatalytic formic acid decomposition performance testing of conventional photocatalytic materials composited with CdS nanorods produces only hydrogen, with no carbon monoxide. However, the photocatalytic system composited with Fe2LCl2 as a co-catalyst and CdS nanorods produces synthesis gas (hydrogen and carbon monoxide). Furthermore, Fe2LCl2 acts as a co-catalyst, further suppressing the recombination of photogenerated electrons and holes by migrating photogenerated charges to the co-catalyst. This accelerates the photocatalytic formic acid decomposition reaction, prevents photocorrosion and oxidation of the photocatalytic system, improves the stability of the photocatalytic system, reduces the activation energy of the catalytic reaction, and enhances the reactivity of the photocatalytic formic acid decomposition. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1These are the scanning electron microscope images of the CdS nanorods obtained in Preparation Example 1 of the present invention and the lattice fringe pattern of the CdS nanorods; wherein, Figure (a) is a scanning electron microscope image, and Figure (b) is a lattice fringe pattern of the CdS nanorods.

[0026] Figure 2 This is a scanning electron microscope image of Fe2LCl2 prepared in Preparation Example 2 characterized using a scanning electron microscope.

[0027] Figure 3 This is a scanning electron microscope image of the Fe2-CdS composite photocatalyst prepared in Example 1 characterized using a scanning electron microscope.

[0028] Figure 4 This is a transmission electron microscope image of the Fe2-CdS composite photocatalyst prepared in Example 1 characterized using a transmission electron microscope.

[0029] Figure 5 These are electron microscope images of the Fe2-CdS composite photocatalyst prepared in Example 1 characterized by transmission electron microscopy, wherein (a) is a transmission electron microscope image of a single Fe2-CdS composite photocatalyst, and (b) is a mapping image of a single Fe2-CdS composite photocatalyst.

[0030] Figure 6 The X-ray diffraction patterns of Preparation Examples 1 and 2 and Example 1 were characterized using an X-ray diffractometer.

[0031] Figure 7 The X-ray diffraction patterns of Preparation Examples 2, 3, and 4 were characterized using an X-ray diffractometer.

[0032] Figure 8 These are the results of characterization of Preparation Example 2 and Example 1 using a Fourier transform infrared spectrometer.

[0033] Figure 9 The X-ray photoelectron spectroscopy spectrum of Example 1 is characterized by using an X-ray photoelectron spectrometer and includes Fe 2p, Cd 3d, S 2p, and Cl 2p spectra.

[0034] Figure 10 This is a total X-ray photoelectron spectrum diagram of Example 1 characterized by using X-ray photoelectron spectroscopy.

[0035] Figure 11 The UV-visible spectra of Preparation Examples 1 and 2 and Example 1 were characterized using a UV-visible spectrophotometer.

[0036] Figure 12These are performance diagrams for optimizing the experimental conditions of Examples 2-5; (a) is a diagram for optimizing the photocatalytic performance of Fe2LCl2 concentration, (b) is a diagram for optimizing the photocatalytic performance of pH, and (c) is a diagram for optimizing the photocatalytic performance of formic acid concentration.

[0037] Figure 13 This is a performance comparison chart of Example 2 and Comparative Examples 1-4 in photocatalytic decomposition of formic acid to produce synthesis gas (H2+CO).

[0038] Figure 14 This is a performance cycle diagram of photocatalytic formic acid decomposition to produce synthesis gas (H2+CO) in Example 2. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] First, buy from the market or make it yourself:

[0041] Anhydrous formic acid; acetonitrile; methanol; sodium hydroxide; ferrous chloride tetrahydrate; cobalt nitrate hexahydrate; nickel chloride hexahydrate; 1,3-propylenediamine; 2,6-diformyl-4-methylphenol; 5-methylsalicylaldehyde; cadmium nitrate tetrahydrate; thiourea; ethylenediamine; isopropyl alcohol; deionized water.

[0042] Preparation Example 1

[0043] This embodiment provides a method for preparing CdS nanorods, and the specific steps are as follows:

[0044] S1. Weigh 4.62 g of cadmium nitrate tetrahydrate and 4.62 g of thiourea (mass ratio of 1:1), add them sequentially into a Teflon-lined autoclave filled with 60 mL of ethylenediamine (EDA) as solvent, and stir at 40°C for 30 min.

[0045] S2, sealing the autoclave and maintaining the temperature at 150° C. for 48 hours. After the reaction is completed, cooling the autoclave to room temperature to obtain a reaction product;

[0046] S3. The reaction product is washed three times with water and ethanol and then dried to obtain CdS nanorods.

[0047] Preparation Example 2

[0048] This embodiment provides a method for preparing Fe2LCl2, and the specific steps are as follows:

[0049] S1. Place 0.56 g of FeCl2·4H2O and 17.5 mL of deoxygenated methanol into a 50 mL three-necked flask under nitrogen reflux.

[0050] S2. 2.5 mL of a boiling methanol solution containing 0.356 mL of 1,3-propylenediamine and 17.5 mL of a boiling methanol solution containing 0.46 g of 2,6-diformyl-4-methylphenol were added in sequence to obtain a mixed solution;

[0051] S3, the mixed solution was refluxed in an oil bath at 65 ° C for 2 hours by condensation reflux, the crystalline solid was collected by filtration, and washed with cold methanol to obtain the final product Fe2C 26 H 34 N4O4Cl2, abbreviated as Fe2LCl2.

[0052] Preparation Example 3

[0053] This embodiment provides a method for preparing Co2L(NO3)2, and the specific steps are as follows:

[0054] S1. Place 0.233 g of Co(NO3)2·6H2O, 0.46 g of 2,6-diformyl-4-methylphenol, and 10 mL of deoxygenated methanol into a 50 ml three-necked flask under nitrogen reflux.

[0055] S2, adding 2 ml of boiling methanol solution containing 0.0665 mL of 1,3-propylenediamine in turn to obtain a mixed solution;

[0056] S3, the mixed solution was heated to reflux in an oil bath at 65°C for 3 hours by condensation reflux, the crystalline solid was collected by filtration, and washed with cold methanol to obtain the final product Co2C 25 H 32 N6O 10 , referred to as Co2L(NO3)2.

[0057] Preparation Example 4

[0058] This embodiment provides a method for preparing Ni2LCl2, and the specific steps are as follows:

[0059] S1. Place 0.42 g of NiCl2·6H2O, 0.195 g of 2,6-diformyl-4-methylphenol, 0.0665 mL of 1,3-propylenediamine, and 25 mL of isopropyl alcohol (deoxygenated) into a 50 mL three-necked flask under nitrogen reflux.

[0060] S2, by condensation reflux, heating in an oil bath at 82.5 ° C for 18 hours, collecting the crystalline solid by filtration, and washing with boiling methanol to obtain the final product Ni2C 24 H 30 N4O4Cl2, abbreviated as Ni2LCl2.

[0061] Preparation Example 5

[0062] This embodiment provides a method for preparing FeMCl, and the specific steps are as follows:

[0063] S1. Place 0.3 g of FeCl2·4H2O and 25 mL of deoxygenated methanol into a 50 mL three-necked flask under nitrogen reflux.

[0064] S2. 1 ml of a boiling methanol solution containing 0.125 ml of 1,3-propylenediamine and 8 ml of a boiling methanol solution containing 0.41 g of 5-methylsalicylaldehyde were added in sequence to obtain a mixed solution;

[0065] S2, by condensation reflux, reflux at 65 ° C for 2 hours, filter and collect the crystalline solid, and wash it with boiling methanol to obtain the final product FeC 19 H 20 N2O2Cl, abbreviated as FeMCl.

[0066] Example 1

[0067] This embodiment provides a method for preparing a diatomic metal complex / CdS nanorod composite photocatalyst, and the specific steps are as follows:

[0068] S1. Place 80 mg of the CdS nanorods prepared in Preparation Example 1 and 20 mg of the Fe2LCl2 prepared in Preparation Example 2 in a 50 ml beaker, add 20 ml of ethanol, and stir for 8 h until the reaction is fully completed.

[0069] S2. The reaction product is placed in an oven at 80° C. to dry, and the composite product Fe2-CdS is collected, which is a diatomic metal complex / CdS nanorod composite photocatalyst.

[0070] Example 2

[0071] This embodiment provides an application of a diatomic metal complex / CdS nanorod composite photocatalyst, and the specific steps are as follows:

[0072] S1. Measure 5 ml of acetonitrile, 15 ml of deionized water, and 1 ml of formic acid into a 50 ml reactor and adjust the pH of the solution to 3.5 with sodium hydroxide. Repeat the process to prepare 6 portions in total, place them in the reactors, and number them 1-6.

[0073] S2. Take 2 mg of the CdS nanorods obtained in Preparation Example 1 and add them to the above reactor respectively. To adjust the concentration of Fe2LCl2, take 0 mg, 0.5 mg, 0.75 mg, 1 mg, 1.25 mg, and 1.5 mg of Fe2LCl2 obtained in Preparation Example 2 and add them to the above reactor respectively. The reactor is sealed.

[0074] S3. Place the reaction flask on a stirring platform, flow Ar gas for 30 min, and irradiate under a 300W xenon lamp with a 420nm cutoff filter for 3 h to perform photocatalytic formic acid decomposition reaction. Take 500 μl of the gas in the reactor every hour and inject it into the gas chromatograph to calculate the yields of H2 and CO.

[0075] This example is to adjust the concentration of Fe2LCl2 to optimize the experimental conditions.

[0076] Example 3

[0077] This embodiment provides an application of a diatomic metal complex / CdS nanorod composite photocatalyst, and the specific steps are as follows:

[0078] S1. Measure 5 ml of acetonitrile, 15 ml of deionized water, and 1 ml of formic acid into a 50 ml reactor; repeat the process to prepare 5 portions in total, place them in the reactors and number them 1-5; to adjust the pH of the solution, use sodium hydroxide to adjust the pH of the solution to 2.5, 3, 3.5, 4, and 4.5, respectively;

[0079] S2. Place 2 mg of the CdS nanorods obtained in Preparation Example 1 and 1 mg of the Fe2LCl2 obtained in Preparation Example 2 in the above reactor, and seal the reactor.

[0080] S3. Place the reaction flask on a stirring platform, flow Ar gas for 30 min, and irradiate under a 300W xenon lamp with a 420nm cutoff filter for 3 h to perform photocatalytic formic acid decomposition reaction. Take 500 μl of the gas in the reactor every hour and inject it into the gas chromatograph to calculate the yields of H2 and CO.

[0081] This example is to adjust the pH of the solution to optimize the experimental conditions.

[0082] Example 4

[0083] This embodiment provides an application of a diatomic metal complex / CdS nanorod composite photocatalyst, and the specific steps are as follows:

[0084] S1. 5 ml of acetonitrile and 15 ml of deionized water were respectively added to a 50 ml reactor; the operation was repeated to prepare 5 portions in total, which were placed in reactors and numbered 1-5; to adjust the formic acid concentration, 1 ml, 2 ml, 3 ml, 4.5 ml, and 6 ml of formic acid were respectively added to the 50 ml reactor, and the pH of the solution was adjusted to 3.5 with sodium hydroxide;

[0085] S2. Place 2 mg of the CdS nanorods obtained in Preparation Example 1 and 1 mg of the Fe2LCl2 obtained in Preparation Example 2 in the above reactor, and seal the reactor.

[0086] S3. Place the reaction flask on a stirring platform, flow Ar gas for 30 min, and irradiate under a 300W xenon lamp with a 420nm cutoff filter for 3 h to perform photocatalytic formic acid decomposition reaction. Take 500 μl of the gas in the reactor every hour and inject it into the gas chromatograph to calculate the yields of H2 and CO.

[0087] This example optimizes the experimental conditions by adjusting the formic acid concentration.

[0088] Example 5

[0089] This embodiment provides an application of a diatomic metal complex / CdS nanorod composite photocatalyst, and the specific steps are as follows:

[0090] S1. 5 ml of acetonitrile, 15 ml of deionized water, and 4.5 ml of formic acid were respectively added to a 50 ml reactor, and the pH of the solution was adjusted to 3.5 with sodium hydroxide;

[0091] S2. Place 2 mg of the CdS nanorods obtained in Preparation Example 1 and 1 mg of the Fe2LCl2 obtained in Preparation Example 2 in the above reactor, and seal the reactor.

[0092] S3. Place the reaction flask on a stirring platform, flow Ar gas for 30 min, and irradiate under a 300W xenon lamp with a 420nm cutoff filter for 3 h to perform photocatalytic formic acid decomposition reaction. Take 500 μl of the gas in the reactor every hour and inject it into the gas chromatograph to calculate the yields of H2 and CO.

[0093] This embodiment is the optimal experimental condition obtained after optimizing the experimental conditions.

[0094] Comparative Example 1

[0095] This comparative example provides an application of a CdS photocatalyst, which specifically includes the following steps:

[0096] S1. 5 ml of acetonitrile, 15 ml of deionized water, and 4.5 ml of formic acid were respectively added to a 50 ml reactor, and the pH of the solution was adjusted to 3.5 with sodium hydroxide;

[0097] S2. Place 2 mg of CdS nanorods obtained in Preparation Example 1 in a reactor and seal the reactor.

[0098] S3. Place the reaction flask on a stirring platform, flow Ar gas for 30 min, and irradiate under a 300W xenon lamp with a 420nm cutoff filter for 3 h to perform photocatalytic formic acid decomposition reaction. Take 500 μl of the gas in the reactor every hour and inject it into the gas chromatograph to calculate the yields of H2 and CO.

[0099] Comparative Example 2

[0100] This comparative example provides an application of a Co2-CdS composite photocatalyst, which specifically includes the following steps:

[0101] S1. Separately weigh 5 ml of acetonitrile, 15 ml of deionized water, and 4.5 ml of formic acid into a 50 ml reactor, and adjust the pH of the solution to 3.5 with sodium hydroxide.

[0102] S2. Place 2 mg of CdS nanorods obtained in Preparation Example 1 and 1 mg of Co2L(NO3)2 obtained in Preparation Example 3 in a reactor, and seal the reactor.

[0103] S3. Place the reaction flask on a stirring platform, flow Ar gas for 30 min, and irradiate under a 300W xenon lamp with a 420nm cutoff filter for 3 h to perform photocatalytic formic acid decomposition reaction. Take 500 μl of the gas in the reactor every hour and inject it into the gas chromatograph to calculate the yields of H2 and CO.

[0104] Comparative Example 3

[0105] This comparative example provides an application of a Ni2-CdS composite photocatalyst, which specifically includes the following steps:

[0106] S1. Separately weigh 5 ml of acetonitrile, 15 ml of deionized water, and 4.5 ml of formic acid into a 50 ml reactor, and adjust the pH of the solution to 3.5 with sodium hydroxide.

[0107] S2. Place 2 mg of CdS nanorods obtained in Preparation Example 1 and 1 mg of Ni2LCl2 obtained in Preparation Example 4 in a reactor, and seal the reactor.

[0108] S3. Place the reaction flask on a stirring platform, flow Ar gas for 30 min, and irradiate under a 300W xenon lamp with a 420nm cutoff filter for 3 h to perform photocatalytic formic acid decomposition reaction. Take 500 μl of the gas in the reactor every hour and inject it into the gas chromatograph to calculate the yields of H2 and CO.

[0109] Comparative Example 4

[0110] This comparative example provides an application of a Fe-CdS composite photocatalyst, which specifically includes the following steps:

[0111] S1. Separately weigh 5 ml of acetonitrile, 15 ml of deionized water, and 4.5 ml of formic acid into a 50 ml reactor, and adjust the pH of the solution to 3.5 with sodium hydroxide.

[0112] S2. Place 2 mg of CdS nanorods obtained in Preparation Example 1 and 1 mg of FeMCl obtained in Preparation Example 5 in a reactor, and seal the reactor.

[0113] S3. Place the reaction flask on a stirring platform, flow Ar gas for 30 min, and irradiate under a 300W xenon lamp with a 420nm cutoff filter for 3 h to perform photocatalytic formic acid decomposition reaction. Take 500 μl of the gas in the reactor every hour and inject it into the gas chromatograph to calculate the yields of H2 and CO.

[0114] Performance Testing

[0115] The structure and performance of the photocatalysts of the diatomic complexes and CdS nanorods prepared in Preparation Examples 1-5, Examples 1-5 and Comparative Examples 1-4 were characterized. Figure 1-14 The CdS nanorods prepared in Preparation Example 1 were characterized using a scanning electron microscope. The results are shown in Figure 1 As shown, Figure 1 (a) is a scanning electron microscope image of CdS nanorods, and (b) is a lattice stripe of CdS nanorods. Figure 1 It can be seen that the length of the CdS nanorods is 1-3 μm, with a hexagonal crystal structure. The d value of the lattice fringes is 0.34 nm, confirming the (001) crystal plane.

[0116] The Fe2LCl2 prepared in Preparation Example 2 was characterized using a scanning electron microscope. Figure 2 As shown. Figure 2 It can be seen that the individual Fe2LCl2 is in large blocks.

[0117] The Fe2-CdS composite material prepared in Example 1 was characterized by scanning electron microscopy and transmission electron microscopy. Figure 3-5 As shown, Figure 3 Scanning electron microscopy of Fe2-CdS composite material. Figure 4 、 5 Transmission electron microscopy of Fe2-CdS composite material, Figure 5 (b) is the mapping image of Fe2-CdS composite material. Figure 3 It can be seen that Fe2LCl2 still has a rod-like morphology after being composited with CdS nanorods, and the original morphology of CdS nanorods has not changed. Figure 4 It can be seen that Fe2-CdS has a rod-like morphology, which further proves that the Fe2-CdS composite material was successfully prepared. A single composite sample was selected for transmission electron microscopy characterization. Figure 5 It can be seen that Cd, S, Fe, and Cl in the Fe2-CdS composite material are evenly distributed on the CdS rod, which once again verifies the successful preparation of the Fe2-CdS composite material.

[0118] Figure 6 The X-ray diffraction patterns of Preparation Examples 1, 2 and Example 1 were characterized using an X-ray diffractometer. Figure 6It can be seen that the X-ray diffraction spectra of the target products described in Preparation Examples 1 and 2 are consistent with the standard cards, proving that Preparation Examples 1 and 2 are successfully synthesized; the X-ray diffraction spectrum in Example 1 only shows the peak of CdS because the content of Fe2LCl2 added is relatively small.

[0119] Figure 7 The X-ray diffraction patterns of Preparation Examples 2, 3, and 4 were characterized using an X-ray diffractometer. Figure 7 It can be seen that the spectra of Preparation Examples 2, 3, and 4 are consistent with the theoretical X-ray diffraction spectra. Figure 1 The results show that the synthesis of Preparation Examples 2, 3 and 4 was successful.

[0120] Figure 8 The results of characterization of Preparation Example 2 and Example 1 using Fourier infrared spectrometer are shown. Figure 8 It can be seen that the successful preparations of Preparation Example 1 and Example 1 both have CO bond peaks and no C=O bond peaks.

[0121] Figure 9 The X-ray photoelectron spectrum of Example 1 is characterized by X-ray photoelectron spectroscopy. Figure 9 (a) The XPS Fe 2p spectrum shows that the Fe peak shifts to the negative direction by 0.22 eV. Figure 9 In the Cd 3d and S2p spectra in (b) and (c), it can be observed that the Cd and S peaks shift in the positive direction by 0.39 eV, indicating that the CdS nanorods and Fe2LCl2 interact with each other on the surface. There is an inherent electric field between the CdS nanorods and Fe2LCl2, which promotes the transfer of outer-shell electrons toward the complex. It is confirmed that the increase in the production of synthesis gas (H2+CO) is caused by Fe2LCl2, which promotes the photocatalytic decomposition of formic acid into H2 and CO.

[0122] Figure 10 This is the total X-ray photoelectron spectrum of Example 1 characterized by X-ray photoelectron spectroscopy. Figure 10 It can be seen that Example 1 contains C, O, N, Cd, S, Fe, and Cl elements.

[0123] Figure 6-10 The successful synthesis of diatomic and single-atom metal complexes and CdS nanorods, as well as the successful preparation of Fe2-CdS composite materials, were confirmed.

[0124] Figure 11 The UV-visible absorption spectrum images of Preparation Examples 1, 2 and Example 1 show that Fe2-CdS and CdS have similar absorption edges. Figure 11 It can be seen that the light absorption capacity of Fe2-CdS is significantly increased compared with CdS, especially in the λ>520nm region, which can be attributed to the strong intrinsic background absorption capacity of Fe2LCl2.

[0125] Figure 12 The figure is an optimization diagram of the experimental conditions for photocatalytic formic acid decomposition of Examples 2-5, indicating that the optimal experimental conditions are those of Example 5. Figure 12 It can be seen that the optimal implementation conditions for this experiment are 0.08mM Fe2LCl2, pH 3.5, and formic acid concentration 6M.

[0126] Figure 13 The photocatalytic formic acid decomposition performance comparison chart of Examples 2 and 5 and Comparative Examples 1-4 shows that the Fe2-CdS composite material has the highest performance in photocatalytic formic acid decomposition to produce synthesis gas (H2+CO), with an H2 yield of 330 μmol -1 h -1 , CO yield was 141 μmol -1 h -1 .

[0127] Figure 14 The performance cycle diagram of Fe2-CdS composite material photocatalytic decomposition of formic acid to produce synthesis gas (H2+CO) is shown in Figure 2. Figure 14 It can be seen that the production of H2 and CO has been increasing steadily, indicating that the performance of the composite material is stable.

[0128] The above describes in detail the preferred embodiments of the present invention, and describes the basic principles, main features and advantages of the present invention. However, those skilled in the art should understand that the embodiments of the present invention are not limited to the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Within the scope of knowledge possessed by ordinary technicians in this field, various changes can be made without departing from the purpose of the embodiments of the present invention. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived from this are still within the scope of protection of the embodiments of the present invention.

Claims

1. A method for preparing a diatomic metal complex / CdS nanorod composite photocatalyst, characterized in that: The steps include: S1. FeCl2·4H2O and methanol are placed in a nitrogen reflux container, a boiling methanol solution containing 1,3-propylenediamine is added, and then a boiling methanol solution containing 2,6-diformyl-4-methylphenol is added to obtain a mixed solution; S2. The mixed solution was heated in an oil bath by condensation reflux. After the reaction was completed, the crystalline solid was collected by filtration and washed with cold methanol to obtain the final product Fe2C 26 H 34 N4O4Cl2, referred to as Fe2LCl2; S3. Mix CdS nanorods and Fe2LCl2, add ethanol, stir to react, and then dry to collect the composite product Fe2-CdS.

2. The method for preparing the diatomic metal complex / CdS nanorod composite photocatalyst according to claim 1, characterized in that: The preparation method of CdS nanorods in step S3 is as follows: cadmium nitrate tetrahydrate and thiourea are added to a Teflon-lined autoclave filled with ethylenediamine as a solvent, stirred, sealed, and placed in an oven for reaction. After the reaction is completed, the reaction is cooled to room temperature, washed with water and ethanol to obtain a precipitate, and dried to obtain CdS nanorods.

3. The method for preparing the diatomic metal complex / CdS nanorod composite photocatalyst according to claim 2, characterized in that: The added concentration of cadmium nitrate tetrahydrate in ethylenediamine is 0.0385-0.1155 g / ml, the added concentration of thiourea in ethylenediamine is 0.0385-0.1155 g / ml, and the mass ratio of cadmium nitrate tetrahydrate to thiourea is (0.5-3):

1.

4. The method for preparing the diatomic metal complex / CdS nanorod composite photocatalyst according to claim 2, characterized in that: During the preparation of CdS nanorods, the stirring temperature is 20-50° C. and the time is 20-60 minutes; the reaction temperature is 140-160° C. and the time is 24-72 hours.

5. The method for preparing the diatomic metal complex / CdS nanorod composite photocatalyst according to claim 1, characterized in that: In step S1, the amount of FeCl2·4H2O added to methanol is 0.008-0.064 g / ml.

6. The method for preparing the diatomic metal complex / CdS nanorod composite photocatalyst according to claim 1, characterized in that: In the boiling methanol solution containing 1,3-propylenediamine, the added amount of 1,3-propylenediamine is 0.0368-0.292 ml / ml; in the boiling methanol solution containing 2,6-diformyl-4-methylphenol, the concentration of 2,6-diformyl-4-methylphenol is 0.0068-0.0526 g / ml.

7. The method for preparing the diatomic metal complex / CdS nanorod composite photocatalyst according to claim 1, characterized in that: The oil bath heating temperature in step S2 is 50-80°C for 2-6 hours; the stirring reaction time in step S3 is 6-10 hours, and the drying temperature is 60-80°C.

8. The method for preparing the diatomic metal complex / CdS nanorod composite photocatalyst according to claim 1, characterized in that: In step S3, CdS nanorods and Fe2LCl2 are mixed in a mass ratio of (1-4):1, and ethanol is added until the concentration of CdS nanorods in ethanol is 3-5 mg / ml.

9. A diatomic metal complex / CdS nanorod composite photocatalyst prepared by the method for preparing a diatomic metal complex / CdS nanorod composite photocatalyst according to any one of claims 1 to 8, characterized in that: The composite photocatalyst consists of CdS nanorods and diatomic metal complexes loaded on the surface of the CdS nanorods; the CdS nanorods are 1-3 μm long and have a hexagonal crystal structure; the diatomic metal complexes are blocky, specifically diiron atom complexes; the mass ratio of the CdS nanorods to the diatomic metal complexes is 2:1, and the two are physically composited with interfacial interaction.

10. Use of the diatomic metal complex / CdS nanorod composite photocatalyst according to claim 9 as a photocatalyst for photocatalytic decomposition of formic acid to produce hydrogen and carbon monoxide.

Images