Visible light response photocatalyst DTIDT-NC / g-C3N4 as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of photocatalyst preparation, and particularly relates to a visible light response photocatalyst DTIDT-NC / g-C3N4 as well as a preparation method and application thereof. The photocatalyst is of a heterostructure formed by an organic semiconductor DTIDT-NC and g-C3N4, and the structural formula of the organic semiconductor DTIDT-NC is as shown in the formula 5. Indenodithienothiophene (DTIDT) is used as a core D unit, cyano naphthyl indanone is used as an A unit, an acceptor (A)-donor (D)-acceptor (A) type organic semiconductor DTIDT-NC is designed and synthesized, the acceptor (A)-donor (D)-acceptor (A) type organic semiconductor DTIDT-NC is compounded with g-C3N4 to construct the DTIDT-NC / g-C3N4 heterojunction photocatalyst, the absorption spectrum of g-C3N4 is widened, compounding of photo-induced electrons and holes is inhibited, the photocatalyst is used for hydrogen production through water photolysis, and the photocatalytic activity of the photocatalyst is improved. More excellent water photolysis hydrogen evolution performance is shown. # imgabs0 #

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalyst preparation, and specifically relates to a visible light responsive photocatalyst DTIDT-NC / g-C3N4 and a preparation method and application thereof. Background Art

[0002] Photocatalytic hydrogen production is a promising strategy for hydrogen production. The principle is that the photogenerated electrons and holes generated by photocatalysts driven by sunlight undergo reduction and oxidation reactions with water molecules to generate hydrogen and oxygen, respectively. Designing high-performance photocatalysts is one of the key scientific issues facing this field. Graphitic carbon nitride (g-C3N4) is a polymer semiconductor photocatalyst with the advantages of simple synthesis, environmental friendliness, and stable physical and chemical properties. In 2009, Wang Xinchen et al. (Nature materials, 2009, 8(1):76-80) first reported the application of g-C3N4 in the field of photocatalytic hydrogen production, which then rapidly developed into a research hotspot. However, g-C3N4 has limited absorption of visible light, with a maximum absorption wavelength of only 450nm, and the electrons and holes generated by it under light are easy to recombine, resulting in poor photocatalytic hydrogen production performance of g-C3N4. At present, researchers have modified g-C3N4 in various ways in order to obtain excellent photocatalytic performance. Among them, constructing a heterojunction is one of the most effective means.

[0003] At present, most semiconductors used to construct heterojunctions with g-C3N4 are inorganic semiconductors, mainly including metal oxides (such as TiO2, WO3, ZnO, etc.), metal sulfides (CdS and ZnS, etc.) and metal halide oxides. However, inorganic semiconductors have small extinction coefficients, difficult to control molecular structures and band gap positions, and contain metal or heavy metal elements. Long-term use will cause certain harm to the environment. Compared with inorganic semiconductors, organic semiconductors have larger extinction coefficients, flexible and adjustable molecular structures, and do not contain toxic metal elements. Constructing heterojunction photocatalysts with organic semiconductors and g-C3N4 can not only improve the photocatalytic hydrogen evolution performance of g-C3N4, but also avoid the disadvantages of using inorganic semiconductors. Summary of the invention

[0004] The purpose of the present invention is to provide a visible light responsive photocatalyst DTIDT-NC / g-C3N4 and its preparation method and application. The photocatalyst uses indenodithienothiophene (DTIDT) as the core D unit and cyanonaphthylindenone as the A unit, and designs and synthesizes an acceptor (A)-donor (D)-acceptor (A) type organic semiconductor DTIDT-NC, and combines it with g-C3N4 to construct a DTIDT-NC / g-C3N4 heterojunction photocatalyst, which broadens the absorption spectrum of g-C3N4, inhibits the recombination of photogenerated electrons and holes, and is used in photolysis of water to produce hydrogen, showing a more excellent photolysis of water to produce hydrogen performance.

[0005] Specifically, the present invention provides the following technical solutions:

[0006] A visible light responsive photocatalyst DTIDT-NC / g-C3N4, wherein the photocatalyst is a heterostructure formed by an organic semiconductor DTIDT-NC and g-C3N4;

[0007] The structural formula of the organic semiconductor DTIDT-NC is shown in Formula 5:

[0008]

[0009] Preferably, the mass ratio of DTIDT-NC to g-C3N4 is 0.5-1.5: 100. Studies have found that if the dosage is too high, the photocatalyst has the disadvantage of strong hydrophobicity; if the dosage is too low, the light response ability of g-C3N4 cannot be significantly improved and the recombination of photogenerated electrons and holes cannot be suppressed.

[0010] The present invention also provides a method for preparing the above-mentioned photocatalyst DTIDT-NC / g-C3N4, comprising the following steps:

[0011] DTIDT-NC and g-C3N4 are added to an organic solvent and stirred for a period of time, and the organic solvent is removed to obtain the product.

[0012] Preferably, the mass volume ratio of the g-C3N4 and the organic solvent is 2.5-7.5 mg / mL.

[0013] Preferably, the organic solvent is selected from one or more of dichloromethane, chloroform and chlorobenzene.

[0014] Preferably, the preparation method of the DTIDT-NC is as follows, comprising steps 1 to 3:

[0015]

[0016] Step 1: reacting the compound of formula 1 with tert-butyl acetoacetate to obtain a compound of formula 2;

[0017] Step 2: reacting the compound of formula 2 with malononitrile to obtain a compound of formula 3;

[0018] Step 3: The compound of formula 3 reacts with the compound of formula 4 to obtain the organic semiconductor DTIDT-NC shown in formula 5.

[0019] Preferably, the g-C3N4 is prepared by the following method: adding urea to a crucible with a lid, placing the crucible in a muffle furnace and calcining at 520°C for 3 hours, cooling to room temperature, and calcining at 520°C for 4 hours in a nitrogen atmosphere to obtain g-C3N4. Studies have found that the g-C3N4 prepared by the above method, and the heterostructure formed with DTIDT-NC, has better hydrogen evolution performance.

[0020] Preferably, the method for removing the organic solvent is as follows: firstly, rotary evaporation is performed until no solvent is discharged, and then vacuum drying is performed for a period of time.

[0021] The present invention also provides application of the above-mentioned photocatalyst DTIDT-NC / g-C3N4 in the field of photolysis of water to produce hydrogen.

[0022] The beneficial effects of the present invention are at least:

[0023] 1) The visible light responsive photocatalyst DTIDT-NC / g-C3N4 provided by the present invention has indenodithienothiophene (DTIDT) as the core D unit and cyanonaphthylindanone as the A unit, and an acceptor (A)-donor (D)-acceptor (A) type organic semiconductor DTIDT-NC is designed and synthesized, and the DTIDT-NC / g-C3N4 heterojunction photocatalyst is constructed by combining the DTIDT-NC / g-C3N4 with g-C3N4, thereby broadening the absorption spectrum of g-C3N4 and inhibiting the recombination of photogenerated electrons and holes;

[0024] 2) The visible light responsive photocatalyst DTIDT-NC / g-C3N4 provided by the present invention is particularly suitable for photocatalytic hydrogen production from water, and exhibits better photocatalytic hydrogen evolution performance from water;

[0025] 3) The visible light responsive photocatalyst DTIDT-NC / g-C3N4 provided by the present invention preferably has a mass ratio of DTIDT-NC to g-C3N4 of 0.5-1.5:100. Studies have found that if the dosage is too high, the photocatalyst has the disadvantage of strong hydrophobicity; if the dosage is too low, the light responsiveness of g-C3N4 cannot be significantly improved and the recombination of photogenerated electrons and holes cannot be suppressed;

[0026] 4) The visible light responsive photocatalyst DTIDT-NC / g-C3N4 provided by the present invention further improves the hydrogen evolution performance of the photocatalyst by further optimizing the preparation method of g-C3N4. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 For DTIDT-NC 1 H NMR spectrum.

[0028] Figure 2 This is the scanning electron microscope image of 1%-DTIDT-NC / g-C3N4 prepared in Example 1.

[0029] Figure 3 UV-visible diffuse reflectance images of g-C3N4 and 1%-DTIDT-NC / g-C3N4.

[0030] Figure 4 Steady-state fluorescence spectra of g-C3N4 and 1%-DTIDT-NC / g-C3N4.

[0031] Figure 5 The average hydrogen evolution rate diagram of g-C3N4 and 1%-DTIDT-NC / g-C3N4. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in the field or the product manual shall be followed.

[0033] The method for testing the water decomposition and hydrogen evolution performance of the photocatalyst prepared in the following example is as follows:

[0034] The photocatalyst (50 mg) was dispersed in a solvent containing 1% Pt (90 mL H2O, 10 mL triethylamine), the dispersion was ultrasonically treated, and then added to a reaction vessel. After the reactor was evacuated, it was illuminated, and the generated hydrogen entered the gas chromatograph to obtain the H2 production. The light source used in the experiment was a 300W xenon lamp with a wavelength of 420 to 780 nm.

[0035] Example 1

[0036] Preparation of g-C3N4:

[0037] 1) Weigh 30 g of urea and add it into a crucible with a lid;

[0038] 2) The crucible was placed in a muffle furnace for calcination at a heating rate of 5°C / min, heated to 520°C and kept at that temperature for 3 hours. After cooling naturally to room temperature, the crucible was calcined in a tubular furnace at 520°C for 4 hours under a nitrogen atmosphere.

[0039] 3) After calcination, the mixture was cooled to room temperature to obtain solid g-C3N4;

[0040] 4) After grinding the obtained solid, wash it with deionized water three times, and then place it in a vacuum oven at 70°C for 12 h to obtain pure g-C3N4 powder.

[0041] Synthesis of DTIDT-NCs:

[0042]

[0043] 1) Under nitrogen atmosphere, add 2,3-naphthalene dicarboxylic anhydride (Formula 1, 2 g), acetic anhydride (16 mL) and triethylamine (8 mL) into a two-necked flask, stir for 10 min, then slowly add tert-butyl acetoacetate (5 g), stir for 30 min, then transfer to a 60°C oil bath and stir for 16 h.

[0044] 2) Prepare an ice-water mixture (about 250 mL) in a beaker, add hydrochloric acid (15 mL) and stir thoroughly, drop the black reaction solution obtained in step 1) into the ice-water mixture of hydrochloric acid, stir until the ice cubes melt, immediately transfer the beaker to a 55° C. oil bath and stir for 10 min, obtain a yellow precipitate aggregated into blocks on the upper layer, filter and wash the precipitate, then place it in a vacuum oven and dry it at 55° C. for 9 h to obtain a yellow solid (Formula 2).

[0045] 3) Add the yellow solid (1.0 g) and malononitrile (0.67 g) to a round-bottom flask, add ethanol (20 mL) and stir for 5 min. Add anhydrous sodium acetate (0.63 g) to the flask and stir for about 30 min. During the reaction, monitor the degree of reaction by thin layer chromatography silica gel plate. After the reaction is completed, add water (20 mL), and add 40% hydrochloric acid solution to adjust the pH of the solution to 1-2 to obtain a precipitate. Filter and wash the resulting precipitate, and purify the precipitate by flash column chromatography using dichloromethane as an eluent to obtain an orange-yellow solid (Formula 3).

[0046] 4) Under nitrogen atmosphere, add the indacen-dithiophene derivative (Formula 4, 220 mg) to a round-bottom flask, connect a condenser to close the reaction system, and protect with nitrogen. The orange-yellow solid (Formula 3, 480 mg) synthesized in step 3 is dissolved in a deoxygenated chloroform (30 mL) solution, then transferred to a flask and stirred for 10 min. Pyridine (1 mL) is added to the flask, and the flask is placed in an oil bath, stirred and refluxed at 65 ° C for 3 h. During the reaction, a thin layer chromatography silica gel plate is used to monitor the degree of reaction. After completion, the crude product is purified by column chromatography using dichloromethane as an eluent. The purified product is dropped into a methanol solution, the precipitate is collected by suction filtration, and a solid powder product DTIDT-NC (Formula 5) is obtained after washing. Figure 1 For DTIDT-NC1 H NMR, 1 H NMR (600MHz, CDCl3) δ9.19(s,1H),8.95(s,1H),8.39(s,1H),8.26(s,1H),8.06(d,J=27.1Hz,2H),7.71(dd,J=6.1,3.0Hz,2H),7.65(s,1H),7.19 (dd,J=46.2,8.4Hz,8H),2.61-2.53(m,4H),2.23(d,J=7.8Hz,1H),2.01( s, 1H), 1.59 (d, J = 7.7Hz, 4H), 1.35-1.28 (m, 12H), 0.86 (t, J = 6.8Hz, 8H).

[0047] Preparation of DTIDT-NC / g-C3N4:

[0048] 1) Add g-C3N4 (200 mg) and DTIDT-NC (2 mg) into a round-bottom flask, add dichloromethane solution (40 mL), and stir for 24 h.

[0049] 2) The dichloromethane was removed by rotary evaporation, and then placed in a vacuum drying oven and dried at 40° C. for 12 h to obtain a solid product 1%-DTIDT-NC / g-C3N4.

[0050] The SEM image of 1%-DTIDT-NC / g-C3N4 is shown in Figure 2 ,Depend on Figure 2 It can be seen that the prepared 1%-DTIDT-NC / g-C3N4 presents a stacking structure with a loose and porous surface.

[0051] The UV-visible diffuse reflectance test results of g-C3N4 and 1%-DTIDT-NC / g-C3N4 are shown in Figure 3 .Depend on Figure 3 It can be seen that the absorption band edge of g-C3N4 is located near 450nm, and the absorption spectrum of the constructed 1%-DTIDT-NC / g-C3N4 heterojunction photocatalyst is red-shifted to around 850nm, which significantly improves the utilization rate of sunlight.

[0052] The steady-state fluorescence spectra of g-C3N4 and 1%-DTIDT-NC / g-C3N4 are shown in Figure 4 .Depend on Figure 4It can be seen that when the photocatalyst was excited by light with a wavelength of 385nm, g-C3N4 produced an obvious fluorescence emission peak at 450nm; 1%-DTIDT-NC / g-C3N4 produced a fluorescence quenching phenomenon, and its fluorescence intensity was lower than that of g-C3N4, which indicated that there was intermolecular charge transfer between g-C3N4 and DTIDT-NC, which would inhibit the recombination of carriers in g-C3N4 and improve the photocatalytic performance of the material.

[0053] Figure 5 The figure shows the hydrogen evolution rate of the two catalysts under light. It can be seen from the figure that the average hydrogen evolution rate of g-C3N4 is 415.4 μmol·h -1 ·g -1 The average hydrogen evolution rate of 1%-DTIDT-NC / g-C3N4 is 803.1 μmol·h -1 ·g -1 Compared with g-C3N4, the hydrogen evolution performance of 1%-DTIDT-NC / g-C3N4 is improved, which is due to the improvement of the light absorption performance and charge separation and transfer performance of the photocatalyst after the heterojunction is constructed.

[0054] Comparative Example 1

[0055] The preparation of g-C3N4 in Comparative Example 1 is the same as that in Example 1.

[0056] According to the method reported in the literature (Solar Energy 195 (2020) 429–435), another ADA-type organic small molecule IT-2Br was synthesized. IT-2Br has the same D unit as DTIDT-NC, and the A unit is bromocyanoindanone.

[0057] Preparation of IT-2Br / g-C3N4:

[0058] 1) Add g-C3N4 (200 mg) and IT-2Br (2 mg) into a round-bottom flask, add dichloromethane solution (40 mL), and stir for 24 h.

[0059] 2) The dichloromethane was removed by rotary evaporation, and then placed in a vacuum drying oven and dried at 40° C. for 12 h to obtain a solid product 1%-IT-2Br / g-C3N4.

[0060] The test results show that the average hydrogen evolution rate of 1%-IT-2Br / g-C3N4 is 750.2μmol·h -1 ·g -1 .

[0061] Example 2

[0062] Preparation of g-C3N4:

[0063] 1) Weigh 30 g of urea and add it into a crucible with a lid;

[0064] 2) Place the crucible in a muffle furnace and calcine it at a heating rate of 15°C / min. Heat it to 550°C / min and keep it at that temperature for 3 hours. After cooling it naturally to room temperature, calcine it in a tube furnace at 500°C / min for 3 hours under nitrogen atmosphere.

[0065] 3) After calcination, the mixture was cooled to room temperature to obtain solid g-C3N4;

[0066] 4) After grinding the obtained solid, wash it with deionized water three times, and then place it in a vacuum oven at 70°C for 12 h to obtain pure g-C3N4 powder.

[0067] The synthesis of DTIDT-NC was the same as in Example 1.

[0068] Preparation of DTIDT-NC / g-C3N4:

[0069] 1) Add g-C3N4 (200 mg) and DTIDT-NC (1 mg) into a round-bottom flask, add dichloromethane solution (40 mL), and stir for 24 h.

[0070] 2) The dichloromethane was removed by rotary evaporation, and then placed in a vacuum drying oven and dried at 40° C. for 12 h to obtain a solid product 0.5%-DTIDT-NC / g-C3N4.

[0071] The hydrogen evolution performance of the photocatalyst was tested, and the average hydrogen evolution rate of g-C3N4 was calculated to be 327.4 μmol·h -1 ·g -1 The average hydrogen evolution rate of 0.5%-DTIDT-NC / g-C3N4 is 523.8 μmol·h -1 ·g -1 .

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A visible light responsive photocatalyst DTIDT-NC / g-C3N4, characterized in that: The photocatalyst is a heterostructure formed by organic semiconductor DTIDT-NC and g-C3N4; The structural formula of the organic semiconductor DTIDT-NC is shown in Formula 5:

2. The photocatalyst DTIDT-NC / g-C3N4 according to claim 1, characterized in that: The mass ratio of the DTIDT-NC to g-C3N4 is 0.5-1.5:

100.

3. The method for preparing the photocatalyst DTIDT-NC / g-C3N4 according to claim 1 or 2, characterized in that: The following steps are involved: DTIDT-NC and g-C3N4 are added to an organic solvent and stirred for a period of time, and the organic solvent is removed to obtain the product.

4. The preparation method according to claim 3, characterized in that: The mass volume ratio of the g-C3N4 and the organic solvent is 2.5-7.5 mg / mL.

5. The preparation method according to claim 3 or 4, characterized in that: The organic solvent is selected from one or more of dichloromethane, chloroform and chlorobenzene.

6. The preparation method according to claim 3 or 4, characterized in that: The preparation method of the DTIDT-NC is as follows, comprising steps 1 to 3: Step 1: reacting the compound of formula 1 with tert-butyl acetoacetate to obtain a compound of formula 2; Step 2: reacting the compound of formula 2 with malononitrile to obtain a compound of formula 3; Step 3: The compound of formula 3 reacts with the compound of formula 4 to obtain the organic semiconductor DTIDT-NC shown in formula 5.

7. The preparation method according to claim 3 or 4, characterized in that: The g-C3N4 is prepared by the following method: urea is added into a crucible with a lid, and then the crucible is placed in a muffle furnace and calcined at 520° C. for 3 h. After cooling to room temperature, the crucible is calcined at 520° C. for 4 h in a nitrogen atmosphere to obtain g-C3N4.

8. The preparation method according to claim 3 or 4, characterized in that: The method for removing the organic solvent is specifically: firstly, rotary evaporation is performed until no solvent is discharged, and then vacuum drying is performed for a period of time.

9. Application of the photocatalyst DTIDT-NC / g-C3N4 according to claim 1 or 2 in the field of photocatalytic water splitting to produce hydrogen.

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