Metalloporphyrin-zinc oxide photocatalyst and preparation method thereof

Abstract

The invention discloses a metalloporphyrin-zinc oxide photocatalyst and a preparation method thereof. According to the preparation method, L-lysine diisocyanate is taken as an electron transport bridge, and metalloporphyrin is connected with zinc oxide, so that effective connection between zinc oxide and metalloporphyrin is realized, and the photocatalyst in which metalloporphyrin and zinc oxide are connected through LDI is prepared. According to the photocatalyst, the response range of the photocatalyst to visible light is widened, rapid transfer of electrons in photocatalytic reaction is achieved, compounding of photo-induced electrons and holes is inhibited, and then the photocatalytic efficiency of the photocatalyst is improved.

Description

Technical Field

[0001] The invention belongs to the field of photocatalysts, and specifically relates to a method for preparing a photocatalyst based on metalloporphyrin and zinc oxide bridged by L-lysine diisocyanate, which is used for visible light catalytic decomposition of water to produce hydrogen. Technical Background

[0002] As we all know, fossil energy is limited, but solar energy is inexhaustible and can be used by us in large quantities. Nowadays, by converting solar energy into a new type of energy that we can use - hydrogen energy, we can greatly alleviate the energy crisis. At the same time, by using hydrogen energy, a clean energy, we can eliminate the emission of pollutants caused by the combustion of fossil fuels from the source. The common method internationally to convert solar energy into hydrogen energy is to use solar energy to split water or methanol to produce hydrogen using photocatalytic technology. Therefore, photocatalytic technology came into being. Photocatalysis mainly uses photocatalysts to achieve a series of catalytic conversion processes under visible light / ultraviolet light. In the presence of the sacrificial agent methanol, the photocatalyst is excited under light to form excited state molecules, generate electrons and holes, and the electrons reduce the protons in the water (H + ) produces hydrogen, while holes oxidize water to produce OH and H + , methanol will be oxidized to CH2OH by hydroxyl radicals, and CH2OH will decompose into formaldehyde and H + , H + It is further reduced to hydrogen by electrons, while methanol is reduced to formic acid. Under sunlight / ultraviolet light, photocatalytic technology has become a hot field of contemporary scientific research due to its mild reaction conditions, relatively simple operating conditions, and high catalytic conversion efficiency.

[0003] Metalloporphyrin is a photosensitizer with a wide light response range, high visible light absorption efficiency, and stable photochemical properties. Nano transition metal oxides have a variety of morphologies, and the crystal morphology is easy to control and has good photoelectric conversion activity, but there are still some defects: (1) The band gap is generally wide, and it can only absorb ultraviolet light, and the visible light utilization rate is low. (2) The recombination rate of photogenerated carriers is high, and the photocatalytic activity is low. (3) The acid-base stability is low.

[0004] When the ultraviolet light in the sunlight shines on the surface of the metal oxide, the electrons in the metal oxide are excited and transitions occur, generating photogenerated electron-hole pairs with redox characteristics. The photogenerated electron-hole pairs of the metal oxide are very easy to recombine, resulting in low photocatalytic efficiency. The use of metal porphyrins to sensitize the semiconductor oxide-zinc oxide can improve the shortcomings of zinc oxide's wide band gap, low visible light utilization rate, and only ultraviolet light and low recombination rate of photogenerated carriers, thereby obtaining a photocatalyst with high visible light utilization rate. The current traditional way of connecting metal porphyrins to metal oxides is that the carboxyl group of the metal porphyrin is directly connected to the hydroxyl group on the surface of the metal oxide. However, since the hydroxyl group on the surface of the metal oxide is easy to fall off, the photocatalyst is easily affected by external forces and "disintegrates". Summary of the invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a photocatalyst in which metal porphyrin and zinc oxide are connected via LDI, namely ZnTCPP-LDI-ZnO and a preparation method thereof, which can realize the effective connection between zinc oxide and metal porphyrin, improve its response range to visible light, realize the rapid transfer of electrons in the photocatalytic reaction, inhibit the recombination of photogenerated electrons and holes, and improve the photocatalytic efficiency of the photocatalyst.

[0006] According to the first object of the present invention, the present invention provides a method for preparing a metalloporphyrin-zinc oxide photocatalyst.

[0007] Specifically, the preparation method of the metalloporphyrin-zinc oxide photocatalyst comprises the following steps: (1) Preparation of ZnTCPP; (2) Synthesis of LDI-ZnO: ZnO powder is dispersed in acetone to form a suspension, and then L-lysine diisocyanate is slowly added and heated under reflux for reaction; the mixture after the reaction is washed with acetone and vacuum dried to obtain LDI-ZnO bridged oxide; (3) Synthesis of ZnTCPP-LDI-ZnO: Add the ZnTCPP obtained in step (1) and the LDI-ZnO obtained in step (2) into acetone, slowly stir and continuously introduce an inert atmosphere for reflux reaction; (4) The product obtained in step (3) is washed with acetone and dried to obtain a ZnTCPP-LDI-ZnO photocatalyst.

[0008] Furthermore, in step (1), the preparation of ZnTCPP is a conventional technique in the art. A typical preparation method of ZnTCPP comprises: adding HTCPP, zinc nitrate hexahydrate, N,N-dimethylformamide and ethanol into a reactor; then adding nitric acid, mixing the mixture evenly by water bath ultrasound, and maintaining the mixture at a constant temperature of 70-85°C for 20-26h; cooling, performing solid-liquid separation on the reaction mixture, and vacuum drying the obtained solid to obtain a purple crystalline product.

[0009] Furthermore, in step (1), the molar ratio of HTCPP to zinc nitrate hexahydrate is 1:3-1:5, the volume ratio of N,N-dimethylformamide to ethanol is 3:1-5:1, and the volume ratio of DMF, nitric acid, and ethanol is 150:1:50-150:1:100. The solid-liquid separation can be performed by suction filtration or centrifugation, and the drying is a conventional operation in the art, such as vacuum drying at 25-35°C.

[0010] Furthermore, in step (2), the concentration of the suspension is 1.0-1.2 g / 100 mL; the molar ratio of the added L-lysine diisocyanate to the zinc oxide powder is 1:1-1:3. The temperature of the reflux reaction is 50-60°C, and the time of the reflux reaction is 0.5h-0.6h. The temperature of the drying is 25-35°C, and the drying time is 4-5h.

[0011] Furthermore, in step (3), the mass ratio of ZnTCPP to LDI-ZnO is 1:5-1:2. The temperature of the reflux reaction in step (3) is 50-60°C, and the reflux reaction time is 2-3h.

[0012] Furthermore, the drying in step (4) is a conventional operation in the art, preferably vacuum drying. The drying temperature is 25-35° C., and the drying time is 4-5 h.

[0013] According to the second object of the present invention, the present invention also provides a metalloporphyrin-zinc oxide photocatalyst, which is prepared by the method described above.

[0014] According to the third object of the present invention, the present invention also provides an application of a metalloporphyrin-zinc oxide photocatalyst.

[0015] Furthermore, the metalloporphyrin-zinc oxide photocatalyst prepared by the present invention can be widely used in photocatalytic hydrogen production reactions.

[0016] Furthermore, the metalloporphyrin-zinc oxide photocatalyst of the present invention can be applied to the fields of photocatalytic degradation of organic matter and dyes.

[0017] In the present invention, L-lysine diisocyanate is an organic substance with two isocyanate groups. Compared with other isocyanate organic substances such as diphenylmethane diisocyanate (MDI), 4-4'-methylenedianiline generated during degradation can cause hepatitis in the human body. The final degradation products of LDI are ethanol, lysine, etc., which has the advantages of being non-toxic and biocompatible. Therefore, in the present invention, the two isocyanate groups of LDI can be used as a "bridge" for metalloporphyrin-sensitized zinc oxide, wherein one isocyanate group is connected to the carboxyl group (-COOH) of the metalloporphyrin, and the other isocyanate group is connected to the hydroxyl group (-OH) on the surface of zinc oxide to form a stable metalloporphyrin-LDI-ZnO photocatalyst, which can transfer the photogenerated electrons generated by zinc oxide after being irradiated with light to the metalloporphyrin in time through LDI, inhibit the recombination of photogenerated electron-hole pairs, and improve the electron mobility, so that LDI can be used as a bridge for electron transmission between metal oxide and metalloporphyrin. The composite photocatalyst obtained by this method has the advantages of metal porphyrin, which has a wide light response range and a low recombination rate of photogenerated electron-hole pairs, and also has the dual advantages of oxide, which has stable photochemical properties and high photoelectric conversion activity.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The catalyst provided by the present invention uses L-lysine diisocyanate as a bridge for electron transfer to connect metal porphyrin with zinc oxide, thereby improving the structural stability and photochemical stability of the metal porphyrin-zinc oxide photocatalyst, increasing the photogenerated electron transfer rate, reducing the photogenerated electron-hole recombination rate, and improving the photocatalytic efficiency of the photocatalyst.

[0019] 2. Since LDI is an environmentally friendly organic matter, the overall utilization rate of visible light by the catalyst is significantly improved. The photocatalyst containing LDI as a bridge is significantly better than the photocatalyst without LDI in terms of photocatalytic hydrogen production efficiency. The method of the present invention also greatly improves the structural stability of the catalyst. The photocatalyst prepared by the method is used to produce hydrogen from water, which has the advantages of simple equipment and low investment, and the products are formic acid and water, without secondary pollution, and the treatment is complete, which has broad application prospects and important environmental significance. Implementation

[0020] The present invention is described in more detail below in conjunction with specific embodiments. Example 1

[0021] (1) Preparation of ZnTCPP: 0.01mmol HTCPP and 0.04mmol zinc nitrate hexahydrate were added to the reactor, and N,N-dimethylformamide (1.5mL) and ethanol (0.5mL) were added. Then 10μ0 nitric acid (1M in ethanol) was slowly dripped in. The mixture was mixed by water bath ultrasound and kept at a constant temperature of 80oC for 24h. Then, the temperature was cooled by programmed cooling method at a rate of 0.1 o C / min, the temperature was lowered to room temperature, and finally a purple crystalline product was obtained; (2) Synthesis of LDI-ZnO: 0.012 mol ZnO powder was dispersed in acetone to form a suspension, and then 0.006 mol L-lysine diisocyanate was slowly added and heated under reflux at 50°C for a period of time. The mixture after the reaction was washed with acetone and vacuum dried at 30°C to obtain LDI-ZnO bridged oxide. (3) Synthesis of ZnTCPP-LDI-ZnO: ZnTCPP (0.1 g) obtained in step (1) and LDI-ZnO (0.3 g) obtained in step (2) were added to acetone, slowly stirred and nitrogen was continuously introduced, and refluxed at 50°C for reaction; (4) The product obtained in step (3) was washed with 20 mL of acetone and dried under vacuum at 30 °C for 4 h to obtain a ZnTCPP-LDI-ZnO photocatalyst. Example 2

[0022] (1) Preparation of ZnTCPP: Add 0.01mmol HTCPP and 0.03mmol zinc nitrate hexahydrate into the reactor, add N,N-dimethylformamide (1.5mL) and ethanol (0.5mL). Then slowly drip 10% nitric acid (1M inethanol), mix the mixture evenly by water bath ultrasound, and keep the temperature at 80oC for 24h, then cool it down to room temperature by programmed cooling method at a cooling rate of 0.1oC / min, and finally obtain a purple crystalline product; (2) Synthesis of LDI-ZnO: 0.006 mol ZnO powder was dispersed in acetone to form a suspension, and then 0.006 mol L-lysine diisocyanate was slowly added and heated under reflux at 50°C for a period of time. The mixture after the reaction was washed with acetone and vacuum dried at 30°C to obtain LDI-ZnO bridged oxide. (3) Synthesis of ZnTCPP-LDI-ZnO: Add ZnTCPP (0.1 g) obtained in step (1) and LDI-ZnO (0.2 g) obtained in step (2) into acetone, slowly stir and continuously introduce nitrogen, and reflux at 50°C for reaction; (4) The product obtained in step (3) was washed with 20 mL of acetone and dried under vacuum at 30 °C for 4 h to obtain a ZnTCPP-LDI-ZnO photocatalyst. Example 3

[0023] (1) Preparation of ZnTCPP: 0.01mmol HTCPP and 0.05mmol zinc nitrate hexahydrate were added to the reactor, and N,N-dimethylformamide (1.5mL) and ethanol (0.5mL) were added. Then 10μL nitric acid (1M in ethanol) was slowly dripped into the mixture, and the mixture was mixed evenly by water bath ultrasound and heated at 80 o C for 24 h, and then the temperature was lowered by programmed cooling at a rate of 0.1 o C / min, the temperature was lowered to room temperature, and finally a purple crystalline product was obtained; (2) Synthesis of LDI-ZnO: 0.006 mol ZnO powder was dispersed in acetone to form a suspension, and then 0.006 mol L-lysine diisocyanate was slowly added and heated under reflux at 50°C for a period of time. The mixture after the reaction was washed with acetone and vacuum dried at 30°C to obtain LDI-ZnO bridged oxide. (3) Synthesis of ZnTCPP-LDI-ZnO: Add ZnTCPP (0.1 g) obtained in step (1) and LDI-ZnO (0.2 g) obtained in step (2) into acetone, slowly stir and continuously introduce nitrogen, and reflux at 50°C for reaction; (4) The product obtained in step (3) was washed with 20 mL of acetone and dried under vacuum at 30 °C for 4 h to obtain a ZnTCPP-LDI-ZnO photocatalyst.

[0024] Comparative Example 1 Preparation of photocatalyst ZnTCPP-ZnO without bridging LDI: Add 0.01g ZnTCPP to a flask and dissolve it in a mixed solution of 30mL anhydrous ethanol and 10mL DMF. Ultrasonicate for 2h to fully disperse it. Add 0.03g zinc oxide and heat to 60℃ and reflux for 24h. After the reaction is complete, centrifuge the mixed solution and wash the precipitate with 20mL DMF until the washing liquid is colorless and transparent. Add 20mL anhydrous ethanol to soak and centrifuge. Vacuum dry the bottom precipitate at 70℃ and 0.02MPa for 4h to obtain the product ZnTCPP-ZnO.

[0025] Comparative Example 2 Preparation of ZnTCPP: 0.01 mmol HTCPP and 0.04 mmol zinc nitrate hexahydrate were added to the reactor, and N,N-dimethylformamide (1.5 mL) and ethanol (0.5 mL) were added. Then 10 μl of nitric acid (1 M in ethanol) was slowly added dropwise, and the mixture was mixed evenly by water bath ultrasound and heated at 80 o C for 24 h, and then the temperature was lowered by programmed cooling at a rate of 0.1 o C / min, the temperature was lowered to room temperature, and finally a purple crystalline product ZnTCPP was obtained.

[0026] Laboratory evaluation method based on ZnTCPP-LDI-ZnO photocatalyst: The photocatalytic hydrogen production performance of the catalyst was evaluated by photocatalytic water splitting reaction using methanol as sacrificial agent. The photocatalytic hydrogen production experiment was carried out in a photocatalytic reactor, the reaction temperature was 25°C, the xenon light source power was 150W, the color was pure white, and the distance between the light source and the reactor was 15 cm.

[0027] The photocatalytic hydrogen production performance evaluation method is as follows: 5 mg of catalyst and 5 mL of methanol aqueous solution (V 甲醇 :V 水 =1:4) was used as a sacrificial agent. Nitrogen was introduced for 30 min in dark conditions to remove dissolved oxygen and other gases in the system. Magnetic stirring was maintained during the reaction. The reaction was terminated after 4 h of xenon lamp irradiation. The analysis was performed using a gas chromatograph with a thermal conductivity detector at a column temperature of 40°C and a detector temperature of 60°C. The hydrogen content in the sample bottle was analyzed according to the external standard method.

[0028] The results of photocatalytic hydrogen production of the catalysts prepared in the examples and comparative examples are listed in Table 1.

[0029] Table 1 <![CDATA[Hydrogen production rate, unit umol·g -1 ·h -1 > Example 1 1386.2 Example 2 1108.6 Example 3 3963.2 Comparative Example 1 694.3 Comparative Example 2 268.8 According to the above scheme, the prepared photocatalyst was used to carry out a photocatalytic hydrogen production experiment on water containing a methanol solution. The ZnTCPP-LDI-ZnO photocatalyst prepared by the present invention has excellent photocatalytic hydrogen production performance. After the experiment was completed, the catalyst was reused, and it was found that the catalyst had good reusability, and the performance did not significantly decrease after multiple consecutive photocatalytic hydrogen production experiments. The synthesis route of the metal porphyrin MOFs-sensitized oxide photocatalyst with an organic bridge as a connecting bridge proposed in the present invention has a lower photogenerated electron-hole recombination rate and a higher hydrogen production rate than the metal porphyrin MOFs-sensitized oxide photocatalyst without a bridge, which opens up new ideas for the preparation method of metal porphyrin MOFs-sensitized metal oxides.

Claims

1. A method for preparing a metalloporphyrin-zinc oxide photocatalyst, characterized in that: The following steps are involved: (1) Preparation of ZnTCPP; (2) Synthesis of LDI-ZnO: ZnO powder is dispersed in acetone to form a suspension, and then L-lysine diisocyanate is slowly added and heated under reflux for reaction; the mixture after the reaction is washed with acetone and vacuum dried to obtain LDI-ZnO bridged oxide; (3) Synthesis of ZnTCPP-LDI-ZnO: Add the ZnTCPP obtained in step (1) and the LDI-ZnO obtained in step (2) into acetone, slowly stir and continuously introduce an inert atmosphere for reflux reaction; (4) The product obtained in step (3) is washed with acetone and dried to obtain a ZnTCPP-LDI-ZnO photocatalyst.

2. The preparation method according to claim 1, characterized in that: The preparation of ZnTCPP described in step (1) comprises: adding HTCPP, zinc nitrate hexahydrate, N,N-dimethylformamide and ethanol into a reactor; then adding nitric acid, mixing the mixture evenly, and maintaining the mixture at a constant temperature of 70-85° C. for 20-26 hours; cooling, performing solid-liquid separation on the reaction mixture, and vacuum drying the obtained solid to obtain a purple crystalline product.

3. The preparation method according to claim 2, characterized in that: In step (1), the molar ratio of HTCPP to zinc nitrate hexahydrate is 1:3-1:5, and the volume ratio of N,N-dimethylformamide to ethanol is 3:1-5:

1.

4. The preparation method according to claim 2, characterized in that: In the mixed solution prepared in step (1), the molar ratio of HTCPP to zinc nitrate hexahydrate is 1:3-1:5, and the volume ratio of DMF: nitric acid: ethanol is 150:1:50-150:1:

100.

5. The preparation method according to claim 1, characterized in that: The concentration of the suspension in step (2) is 1.0-1.2 g / 100 mL; the molar ratio of L-lysine diisocyanate to zinc oxide powder is 1:1-1:

3.

6. The preparation method according to claim 1, characterized in that: The temperature of the reflux reaction in step (2) is 50-60° C., and the time of the reflux reaction is 0.5 h-0.6 h.

7. The preparation method according to claim 1, characterized in that: The mass ratio of ZnTCPP to LDI-ZnO in step (3) is 1:5~1:

2.

8. The preparation method according to claim 1, characterized in that: The temperature of the reflux reaction in step (3) is 50-60°C, and the reflux reaction time is 2-3h.

9. The metalloporphyrin-zinc oxide photocatalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the metalloporphyrin-zinc oxide photocatalyst according to claim 9 in a photocatalytic hydrogen production reaction.

11. Use of the metalloporphyrin-zinc oxide photocatalyst according to claim 9 in photocatalytic degradation of organic matter and dyes.