CN115475647A - Method for in-situ construction of monoatomic Ti-grafted carbon nitride photocatalyst and catalytic reduction of nitroarene - Google Patents

Method for in-situ construction of monoatomic Ti-grafted carbon nitride photocatalyst and catalytic reduction of nitroarene Download PDF

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CN115475647A
CN115475647A CN202211224693.3A CN202211224693A CN115475647A CN 115475647 A CN115475647 A CN 115475647A CN 202211224693 A CN202211224693 A CN 202211224693A CN 115475647 A CN115475647 A CN 115475647A
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carbon nitride
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CN115475647B (en
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顾泉
张薇
高子伟
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Shaanxi Normal University
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    • C07C209/36—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of nitrogen-to-oxygen or nitrogen-to-nitrogen bonds by reduction of nitro groups by reduction of nitro groups bound to carbon atoms of six-membered aromatic rings in presence of hydrogen-containing gases and a catalyst
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Abstract

The invention discloses a method for constructing a monatomic Ti-grafted carbon nitride photocatalyst in situ and catalytically reducing nitroaromatic hydrocarbon, which is characterized in that melamine is pretreated by concentrated hydrochloric acid, carbon nitride (HCN) rich in-OH is obtained through heat treatment and a high-temperature molten salt method, titanocene dichloride and the carbon nitride rich in-OH are used as pre-catalysts, the monatomic Ti-grafted carbon nitride photocatalyst is prepared in a one-pot photocatalytic reduction reaction of the nitroaromatic hydrocarbon, and aromatic amine is obtained. The method is simple to operate, can be suitable for preparing the Ti monatomic photocatalyst with a definite structure, and has the advantages of realizing the efficient chemo-selective reduction of nitroarene containing various substituents, especially sensitive substituents (C = C, C ≡ C, C = O, C = N, C ≡ N, -OH, -SMe, -CF) 3 C-X, X is halogen).

Description

Method for constructing monatomic Ti grafted carbon nitride photocatalyst in situ and catalytically reducing nitroarene
Technical Field
The invention relates to a method for constructing a monatomic Ti grafted carbon nitride photocatalyst in situ and catalytically reducing nitroarene.
Background
The selective reduction of nitroarenes is an important organic conversion reaction. The reduction product aromatic amines are important industrial organic chemicals for the synthesis of imines, amides and azo compounds, which are the basic units for nitrogen-containing biologically active compounds, pesticides, dyes, polymers, etc. In addition, nitro-aromatic hydrocarbon is used as a raw material, other compounds (such as aldehyde) and the in-situ reduction product aromatic amine are further reacted through a one-pot reaction in a domino reaction, so that the direct synthesis of the nitrogen-containing compound has important significance, and the problems of instability and high price of the amine can be solved. In recent years, much research has been devoted to the development of efficient, highly selective, green catalytic systems for selective reduction of nitroarenes. In particular, heterogeneous photocatalysis has the advantages of recoverability, sunlight utilization, low energy consumption, mild reaction conditions and the like, and has attracted extensive attention of people. Many photocatalytic materials have been widely reported for direct reduction of nitro compounds. The single-atom catalyst has the advantages of low synthesis cost, clear structure, easy explanation of reaction mechanism, acceleration of charge separation and transfer efficiency, and enhancement of molecular adsorption and activation. Therefore, the synthesis of the efficient and stable monatomic catalyst has important research significance in the photocatalytic chemoselective reduction.
The conversion pathways of nitro groups and substituents are difficult to control, which requires that the photocatalyst not only has efficient charge separation characteristics, but also has controllable selective adsorption and activation sites on the surface. Construction of heterojunction to promote photo-generated electron migration and metal active site pair-NO 2 Selective adsorption and activation of (a) is an effective way to solve the problems of efficiency and chemoselectivity. The adsorption mode of nitroaromatics on the surface of materials (taking 4-nitrostyrene as an example) can be divided into-NO 2 Adsorption at the end position of the surface, adsorption of alkenyl at the end position of the surface and adsorption of nitroarene on the side position of the whole surface. For the commonly used semiconductor composite photocatalyst and metal supported catalyst, all adsorption modes can occur simultaneously due to the large surface area and the uneven surface adsorption active sites. Thanks to the properties of the monatomic/single-site catalysts, the adsorption of nitroaromatic molecules on the atom separation sites presents a more defined, more uniform adsorption configuration. For noble metals, such as Pd, pt and Au, although they are effective metal active centers for hydrogenation, they are expensive and these metals are p-NO 2 And sensitive substituent groups have higher adsorption and activation performances, and the practical application is limited. Thus, the selection can be preferentially linked to-NO 2 The construction of single-site catalytic active centers from interacting non-noble metals is a better approach to solve the efficiency and selectivity problems. According to the theory of soft and hard acids and bases, non-noble metal Ti 4+ Is an oxophilic metal (stearic acid) which preferentially reacts with oxygen (stearic acid) -NO in nitroarenes 2 Coordinately and singly electron reduced Ti 3+ Is a good oneThe reducing agent of (1). This indicates that single-site titanium grafted photocatalyst is an ideal choice for photocatalytic chemoselective reduction of functionalized nitroarenes.
Disclosure of Invention
The object of the invention is to provide Cp in a simple and easy-to-handle manner 2 TiCl 2 and-OH-rich carbon nitride is used as a pre-catalyst, the preparation of a single-site photocatalyst is realized in the one-pot photocatalytic reduction reaction of the nitroarene, and the functionalized arylamine is obtained.
Aiming at the above purpose, the method adopted by the invention comprises the following steps:
1. stirring melamine in concentrated hydrochloric acid for 20-40 minutes, centrifuging to collect white precipitate, drying, and keeping at 300-500 ℃ for 2-4 hours in air atmosphere to obtain carbon nitride;
2. grinding and mixing carbon nitride, potassium chloride and lithium chloride uniformly, keeping the mixture at 450-550 ℃ for 3-4 hours in air atmosphere, washing the mixture with hot water for multiple times and centrifuging the mixture to obtain carbon nitride rich in-OH;
3. adding a mixed solution of deionized water and isopropanol in a volume ratio of 1-1.
In the step 1, the melamine is preferably stirred in concentrated hydrochloric acid for 20 to 40 minutes, white precipitate is collected by centrifugation, the mixture is dried at 50 to 80 ℃ after being placed for 5 to 6 hours in a ventilating way, and is heated to 500 ℃ at the heating rate of 8 to 12 ℃/minute under the air atmosphere, and the temperature is kept for 4 hours at constant temperature, so that the carbon nitride is obtained.
In the step 1, the mass concentration of HCl in the concentrated hydrochloric acid is 36-38%.
In the step 2, the mass ratio of the carbon nitride to the potassium chloride to the lithium chloride is preferably 1:5 to 6:4 to 5.
In the step 2, it is more preferable to heat the mixture to 550 ℃ at a temperature rise rate of 4 to 6 ℃/min in an air atmosphere and hold the mixture for 4 hours.
In the step 3, the mass ratio of the titanocene dichloride to the carbon nitride rich in-OH is preferably 1: 2-8, preferably the ratio of the nitro aromatic hydrocarbon to the titanocene dichloride is 1mmol: 20-100 mg.
In the step 3, the structural formula of the nitroaromatic hydrocarbon is R-C 6 H 4 -NO 2 Wherein R may be a C = C, C ≡ C, C = O, C = N, C ≡ N, -OH, -SMe, -CF 3 A substituent of any one of the functional groups or halogen.
In the step 3, the obtained monatomic Ti grafted carbon nitride photocatalyst can be repeatedly used for catalytic reduction of nitroarene.
The invention has the following beneficial effects:
the catalyst of the invention is carbon nitride C 3 N 4 As a carrier, with an organic compound Cp 2 TiCl 2 As precursor, use is made of Cp 2 TiCl 2 Specificity of the reactivity, in the photocatalytic reaction, by Cp 2 TiCl 2 Grafting reaction with-OH group on carbon nitride, and in-situ constructing monoatomic Ti in one-pot photocatalytic chemoselective reduction reaction of nitroarene. O-Ti bridging between monatomic Ti and-OH-rich carbon nitride can promote the migration of photogenerated electrons, while the strong reducing one-electron reducing agent Ti 3+ Can effectively convert-NO into 2 Reduction to-NH 2 To achieve highly efficient chemoselective reduction of nitroarenes containing various substituents, in particular sensitive substituents (C = C, C ≡ C, C = O, C = N, C ≡ N, -OH, -SMe, -CF 3 C-X, X is halogen).
Drawings
FIG. 1 is an SEM image of Ti + HCN prepared in example 1.
FIG. 2 is a TEM image of Ti + HCN prepared in example 1.
FIG. 3 is a titanium element analysis chart of Ti + HCN prepared in example 1.
FIG. 4 is an oxygen analysis chart of Ti + HCN prepared in example 1.
FIG. 5 is a carbon analysis chart of Ti + HCN prepared in example 1.
FIG. 6 is a nitrogen elemental analysis chart of Ti + HCN prepared in example 1.
FIG. 7 is a chart showing the chlorine analysis of Ti + HCN prepared in example 1.
FIG. 8 is a HAAD-STEM map of Ti + HCN prepared in example 1.
FIG. 9 is an FTIR plot of g-HCN, HCN in example 1, and g-CN in comparative example 1, CN in comparative example 2.
FIG. 10 is Cp 2 TiCl 2 、Cp 2 TiCl 2 XRD patterns of + HCN, HCN in example 1, and Ti + HCN.
FIG. 11 shows a solvent and Cp 2 TiCl 2 、HCN、Cp 2 TiCl 2 + EPR profile of HCN in solvent respectively.
Detailed Description
The invention will be further described in detail with reference to the following figures and examples, but the scope of the invention is not limited to these examples.
Example 1
1. 10g of melamine is stirred in 250mL of HCl aqueous solution with the mass concentration of 36% -38% for 40 minutes to form white suspension, white precipitate is collected by centrifugation, and the white precipitate is placed in an oven for drying at 80 ℃ for 24 hours after being ventilated and placed for 6 hours. The obtained sample was ground and transferred to a crucible with a lid, and heated to 500 ℃ at a temperature rise rate of 10 ℃/min under an air atmosphere, and held for 4 hours to obtain carbon nitride (g-HCN).
2. 600mg of-HCN, 3.3g of potassium chloride and 2.7g of lithium chloride are ground and mixed for 10 minutes, then the mixture is heated to 550 ℃ in a muffle furnace at the heating rate of 5 ℃/minute and is kept for 4 hours, and the mixture is washed by hot water and centrifuged to obtain the-OH-rich carbon nitride (HCN).
3. 2.5mL of a mixed solution of deionized water and isopropanol at a volume ratio of 1 2 TiCl 2 ) Adding 10 mu L (0.1 mmol) of nitrobenzene under continuous stirring, degassing the obtained suspension for 15 minutes by using argon to remove air, continuously stirring and reacting for 5 hours under the illumination of a 300W xenon lamp with lambda being more than or equal to 420nm, centrifuging, washing with alcohol, and drying to obtain the monatomic Ti grafted carbon nitride photocatalyst (Ti + HCN). With 4-phenyl groupsToluene was used as an internal standard, and the yield of aniline was 87% by gas chromatography.
30mg of the monoatomic Ti-grafted carbon nitride photocatalyst obtained in the above is taken and added into a light reaction tube, 2.5mL of a mixed solution of deionized water and isopropanol in a volume ratio of 1.
Example 2
The nitrobenzene from example 1 was replaced with an equimolar amount of 4-fluoronitrobenzene and the other steps were the same as in example 1, giving a yield of 4-fluoroaniline of 85%.
The monoatomic Ti-grafted carbon nitride photocatalyst obtained was reused for the catalytic reduction of 4-fluoronitrobenzene according to the method of example 1, with a yield of 4-fluoroaniline of 99%.
Example 3
The nitrobenzene from example 1 was replaced with equimolar 4-bromonitrobenzene and the other steps were the same as in example 1, giving 93% yield of 4-bromoaniline.
The monatomic Ti-grafted carbon nitride photocatalyst obtained was reused for catalytic reduction of 4-bromonitrobenzene according to the method of example 1, with a yield of 99% of 4-bromoaniline.
Example 4
The nitrobenzene from example 1 was replaced with equimolar 2-bromo-5-nitrobenzonitrile and the other steps were the same as in example 1, giving 90% yield of 5-amino-2-bromobenzonitrile.
The monatomic Ti-grafted carbon nitride photocatalyst obtained was reused for the catalytic reduction of 2-bromo-5-nitrobenzonitrile according to the procedure of example 1, with a yield of 99% of 5-amino-2-bromobenzonitrile.
Example 5
The nitrobenzene from example 1 was replaced with an equimolar amount of 3-chloronitrobenzene and the other steps were the same as in example 1, giving a 83% yield of 3-chloroaniline.
The monoatomic Ti-grafted carbon nitride photocatalyst obtained was reused for the catalytic reduction of 3-chloronitrobenzene according to the method of example 1, with a yield of 3-chloroaniline of 99%.
Example 6
The nitrobenzene from example 1 was replaced with an equimolar amount of 4-nitrostyrene and the procedure was otherwise the same as in example 1, giving a 90% yield of 4-vinylaniline.
The monoatomic Ti-grafted carbon nitride photocatalyst obtained was reused for catalytic reduction of 4-nitrostyrene according to the method of example 1, with a yield of 4-vinylaniline of 99%.
Example 7
The nitrobenzene in example 1 was replaced with equimolar 4-nitrobenzaldehyde and the other steps were the same as in example 1, with a yield of 85% 4-aminobenzaldehyde.
The monoatomic Ti-grafted carbon nitride photocatalyst obtained was reused for catalytic reduction of 4-nitrobenzaldehyde according to the procedure of example 1, with a yield of 4-aminobenzaldehyde of 99%.
Example 8
The nitrobenzene from example 1 was replaced with equimolar methyl 4-nitrobenzoate and the other steps were the same as in example 1, with a yield of methyl 4-aminobenzoate of 85%.
The obtained monoatomic Ti-grafted carbon nitride photocatalyst was reused for the catalytic reduction of methyl 4-nitrobenzoate according to the procedure of example 1, with a yield of methyl 4-aminobenzoate of 99%.
Example 9
The nitrobenzene in example 1 was replaced with an equimolar amount of 4-nitrophenylacetylene and the procedure was otherwise the same as in example 1, giving a yield of 4-ethynylaniline of 89%.
The monoatomic Ti-grafted carbon nitride photocatalyst obtained was reused for catalytic reduction of 4-nitrophenylacetylene according to the procedure of example 1, with a yield of 4-ethynylaniline of 99%.
Example 10
The nitrobenzene from example 1 was replaced with equimolar 4-nitroacetophenone and the other steps were the same as in example 1, giving a yield of 87% of p-aminoacetophenone.
The monoatomic Ti-grafted carbon nitride photocatalyst obtained was reused for catalytic reduction of 4-nitroacetophenone according to the method of example 1, with a yield of 99% for p-aminoacetophenone.
Example 11
The nitrobenzene from example 1 was replaced with equimolar 2, 6-dimethylnitrobenzene and the other steps were the same as in example 1, giving a yield of 87% 2, 6-dimethylaniline.
The monoatomic Ti-grafted carbon nitride photocatalyst obtained was reused for catalytic reduction of 2, 6-dimethylnitrobenzene according to the method of example 1, with a yield of 99% of 2, 6-dimethylaniline.
Example 12
The nitrobenzene from example 1 was replaced with an equimolar amount of 4-nitrotrifluorotoluene and the other steps were the same as in example 1, giving a yield of 86% of p-trifluoromethylaniline.
The monoatomic Ti-grafted carbon nitride photocatalyst obtained was reused for catalytic reduction of 4-nitrotrifluorotoluene according to the method of example 1, and the yield of p-trifluoromethylaniline was 99%.
Example 13
The nitrobenzene from example 1 was replaced by equimolar amount of p-nitrophenol and the other steps were the same as in example 1, giving a yield of 82% p-aminophenol.
The obtained monoatomic Ti-grafted carbon nitride photocatalyst was reused for catalytic reduction of p-nitrophenol, 99% of p-aminophenol, according to the method of example 1.
Example 14
The nitrobenzene in example 1 was replaced with equimolar 2-nitrofluorene and the other steps were the same as in example 1, with a yield of 80% 2-aminofluorene.
The monoatomic Ti-grafted carbon nitride photocatalyst obtained was reused for catalytic reduction of 2-nitrofluorene according to the method of example 1, with a yield of 99% of 2-aminofluorene.
Example 15
The nitrobenzene from example 1 was replaced with an equimolar amount of 5-nitroindole, and the other steps were the same as in example 1, giving 82% yield of 5-aminoindole.
The monoatomic Ti-grafted carbon nitride photocatalyst obtained was reused for catalytic reduction of p-5-nitroindole, 5-aminoindole 99%, according to the method of example 1.
Comparative example 1
10g of melamine was put in a crucible, and heated to 500 ℃ at a heating rate of 10 ℃/min under an air atmosphere, and held for 4 hours to obtain carbon nitride (g-CN).
Comparative example 2
10g of melamine was put in a crucible, and heated to 500 ℃ at a heating rate of 10 ℃/min under an air atmosphere, and held for 4 hours to obtain carbon nitride (g-CN). 600mg of-CN, 3.3g of potassium chloride and 2.7g of lithium chloride were mixed by grinding for 10 minutes, and then heated to 550 ℃ at a temperature rise rate of 5 ℃/minute in a muffle furnace for 4 hours, followed by rinsing with hot water and centrifugation to obtain Carbon Nitride (CN).
Comparative example 3
150mg of-OH-rich carbon nitride powder (prepared as in example 1) was dispersed in 30mL of distilled water, and 0.407mL of 2.5mg/mL H was added while stirring 2 PdCl 4 The aqueous solution was vigorously stirred for 2 hours, and then 100mg of NaBH was added 4 Stirring for 12 hours for metal reduction, thoroughly washing with distilled water, and finally drying at 60 ℃ to obtain Pd nanoparticle supported HCN (Pd NPs/HCN).
Comparative example 4
100mg of-OH-rich carbon nitride powder (prepared as in example 1) was dispersed in 30mL of deionized water, and 4mL of PdCl was added with stirring 2 NaCl (containing PdCl) 2 1.65mg, naCl 8.25 mg) in an oil bath at 80 ℃ for 8 hours, centrifugally separating, washing with deionized water for 3 times, drying in a vacuum oven at 60 ℃, dispersing the obtained powder in 15mL of deionized water, irradiating with a 300W Xe lamp for 1 hour at room temperature in Ar atmosphere, centrifugally collecting the product, washing with deionized water for 3 times, and drying in a vacuum oven at 60 ℃ to obtain monatomic Pd-supported HCN (Pd) 1 /HCN)。
Comparative example 5
1g of dicyandiamide, 5.5g of potassium chloride and 4.6g of lithium chloride are mixed and ground in a glove box for 30 minutes, the obtained mixture is transferred into a muffle furnace, the temperature is raised to 400 ℃ at the heating rate of 2 ℃/minute and is kept for 2 hours, then the temperature is raised to 500 ℃ at the heating rate of 1 ℃/minute under the vacuum condition and is kept for 24 hours, and the product is centrifugally washed by boiling water and is dried in vacuum at 60 ℃ to obtain crystalline carbon nitride (PTI).
As can be seen from the results of the above examples, the process of the present invention is applicable to the chemoselective reduction of various nitroarenes, including those containing unsaturated substituents (C = C, C.ident.C, C = O, C = N, C.ident.N) or halogen substituents (C-X, X being halogen) and special substituents-OH, -SMe, -CF 3 The compound of (2) uniformly realizes high-efficiency selective hydrogenation. Halogen-substituted nitroarenes are challenging substrates in photoreactions, while the presence of the C-X moiety allows further functionalization by cross-coupling and related chemistry. Under the reaction system of the invention, even iodonitrobenzene (easy to be hydrodehalogenated) or fluoronitrobenzene has higher yield and selectivity.
The photocatalyst prepared in example 1 was characterized using a field emission transmission electron microscope and a spherical aberration correction transmission electron microscope, and the results are shown in fig. 1 to 8. As can be seen from the scan of fig. 1 and the transmission of fig. 2, the Ti + HCN photocatalyst prepared in example 1 did not observe the presence of Ti nanoparticles and clusters, demonstrating that Ti atoms are highly dispersed on the carbon nitride support. As can be seen from FIGS. 3 to 7, ti, O, C, N and Cl elements are uniformly distributed. From the HAAD-STEM results of fig. 8, it can be seen that atomic-size bright spots correspond to Ti single atoms, and that Ti is well dispersed on the carbon nitride support, demonstrating that Ti is supported on the support HCN in a single atom form.
The FTIR spectrum of FIG. 9 shows that the-OH in the FTIR spectrum of HCN is 3500cm, compared to g-HCN, g-CN, CN -1 The peak is obviously enhanced, which shows that HCN surface contains rich-OH groups and is Cp 2 TiCl 2 The Ti in (1) provides anchor sites, enabling grafting of Ti species. Cp 2 TiCl 2 Mixture with HCN (Cp) 2 TiCl 2 + HCN) the XRD pattern (see FIG. 10) shows Cp 2 TiCl 2 Characteristic peak of (1), after the photocatalytic reaction, cp in XRD spectrogram of sample (Ti + HCN) 2 TiCl 2 The characteristic peak of (2) disappears and TiO is not formed 2 Peak of (2). In a photocatalytic reactionHCN is excited by light, and the 'molecular junction' of HCN-O-Ti promotes the migration of photo-generated electrons to Ti to form Ti reduced by one electron 3+ Species of the species. We tested the solvent and Cp 2 TiCl 2 、HCN、Cp 2 TiCl 2 + EPR before and after irradiation with HCN in the solvent respectively (see FIG. 11), when Cp 2 TiCl 2 When irradiated with light, a small amount of Ti is generated due to the light irradiation 3+ Species, a weak signal appears in the EPR spectrum at g = 1.976. Irradiation with light in the presence of HCN alone produced a strong, delocalized, single-electron signal on EPR of g = 2.003. For the Ti + HCN reaction system we found that at g =1.976, ti 3+ The signal of (a) is obviously enhanced, and the signal of HCN is weakened when the delocalized single electron is in g =2.001, which directly proves that the photoproduction electron of the carbon nitride migrates to Ti species to form Ti 3+ 。
The construction of surface Ti species by HCN surface hydroxyl groups and the covalent linkage Ti species generated thereby to-NO is verified by adopting a control experiment 2 Influence of radical reduction. Cp is 2 TiCl 2 Mixing with carbon nitrides lacking surface-OH (including PTI, g-CN, or CN, labeled as Ti + PTI, ti + g-CN, and Ti + CN, respectively) achieves reduction with difficulty due to the lack of anchoring sites for Ti species. When CN with less-OH groups is used, although the catalytic performance is improved, the selectivity is still lower than Ti + HCN, and the final product aniline selectivity is also lower (64% and 75% yield and selectivity, respectively). To further demonstrate the one-electron reduced state of single-site Ti 3+ For the promotion of nitro reduction, we investigated Zn + Cp 2 TiCl 2 And Zn + Ti + HCN system (using Zn as a reducing agent to generate Ti 3+ ) Photocatalytic performance in the absence of light. Although the reaction efficiency and selectivity of these systems are significantly lower than those of photocatalytic systems, it is indeed evident that Ti 3+ Is reduced-NO 2 The critical species of (a). When using Ir (ppy) 2 (dtbbpy)PF 6 When the organic photosensitizer replaces HCN, ir + Cp 2 TiCl 2 The system can not generate single-site Ti species, photosensitizer and Cp 2 TiCl 2 The contact between them does not allow electron transfer, and thus the photocatalytic reaction does not proceed. Specific results are shown in table 1 below.
TABLE 1 photocatalytic hydrogenation reactivity of different photocatalysts on nitrobenzene under visible light irradiation a
Figure BDA0003879143580000091
Figure BDA0003879143580000092
Note: in the table a Reaction conditions are as follows: nitrobenzene (0.1 mmol), catalyst (30 mg), solvent water/2-propanol (2.5ml, v/v =1, 9), xenon lamp 1.0W cm -2 420nm cut-off filter, 5 hours at room temperature. b Conversion and yield were determined by gas chromatography using 4-phenyl toluene as internal standard. c No light is emitted.
The activity of catalytic reduction of 4-nitrostyrene by different catalysts was tested by a controlled variable method and the results are shown in table 2. The original HCN showed poor activity and selectivity (for the photoreduction of nitrobenzene, it produced 43% aniline and 37% hydroxylamine, see table 1); for 4-nitrostyrene, conversion to the desired product is difficult. While long-term irradiation leads to-NO 2 And C = C, resulting in a 5% yield of p-aminophenethane. When single-site Ti species are built on the HCN surface (Ti + HCN), -NO 2 Can be completely reduced into amino, and the C = C of the 4-nitrostyrene is not reduced in the reduction process, and under the irradiation condition of more than 5 hours, the yield of the only product 4-vinylaniline of the Ti + HCN catalytic reduction 4-nitrostyrene is 90%, and the selectivity is 95%. Therefore, we consider Cp 2 TiCl 2 The active substance for selectively reducing the nitroarene in the + HCN mixed system is a monoatomic Ti substance on HCN. To demonstrate the superiority of the monatomic species, we tested TiO 2 HCN (TiO) supported nanoparticles 2 HCN) which has no influence on the improvement of activity and chemoselectivity. Since Pd is a widely used-NO 2 Reduced effective active metal, we put Pd nanoparticles even in the form of monatomic PdPhotocatalysts obtained by supporting on HCN (Pd NPs/HCN and Pd 1 /HCN) was used for the catalytic reduction of 4-nitrostyrene, although Pd can effectively promote-NO 2 Reduction to-NH 2 It does not exhibit selective reduction of functional groups. Thus, the selective reduction of non-noble metal Ti to nitroarenes is more efficient than noble metal Pd.
TABLE 2 Effect of different catalysts on the transfer reduction of 4-nitrostyrene a
Figure BDA0003879143580000101
Figure BDA0003879143580000102
Note: reaction conditions in table a: 4-nitrostyrene (0.1 mmol), catalyst (30 mg), solvent water/2-propanol (2.5ml, v/v =1 -2 420nm cut-off filter, 5 hours at room temperature. b Conversion and yield were determined by gas chromatography using 4-phenyl toluene as internal standard.

Claims (9)

1. A method for constructing a monoatomic Ti-grafted carbon nitride photocatalyst in situ and catalytically reducing nitroarene is characterized by comprising the following steps of:
(1) Stirring melamine in concentrated hydrochloric acid for 20-40 minutes, centrifuging to collect white precipitate, drying, and keeping at 300-500 ℃ for 2-4 hours in air atmosphere to obtain carbon nitride;
(2) Grinding and mixing carbon nitride, potassium chloride and lithium chloride uniformly, keeping the mixture at 450-550 ℃ for 3-4 hours in air atmosphere, washing the mixture with hot water for multiple times and centrifuging the mixture to obtain carbon nitride rich in-OH;
(3) Adding a mixed solution of deionized water and isopropanol in a volume ratio of 1-1.
2. The method for in-situ construction of the monatomic Ti-grafted carbon nitride photocatalyst and catalytic reduction of nitroaromatic hydrocarbons according to claim 1, wherein in step (1), the melamine is stirred in concentrated hydrochloric acid for 20-40 minutes, white precipitate is collected by centrifugation, dried at 50-80 ℃ after being placed for 5-6 hours in a ventilating way, heated to 500 ℃ at a heating rate of 8-12 ℃/minute in an air atmosphere, and kept at a constant temperature for 4 hours to obtain the carbon nitride.
3. The method for constructing the monatomic Ti-grafted carbon nitride photocatalyst and catalytically reducing nitroarene according to claim 1 or 2, wherein in step (1), the mass concentration of HCl in the concentrated hydrochloric acid is 36 to 38 percent.
4. The method for in-situ construction of the monatomic Ti-grafted carbon nitride photocatalyst and catalytic reduction of nitroarenes according to claim 1, wherein in step (2), the mass ratio of the carbon nitride to the potassium chloride and the lithium chloride is 1:5 to 6:4 to 5.
5. The method for in-situ construction of the monatomic Ti-grafted carbon nitride photocatalyst and catalytic reduction of nitroarene according to claim 1 or 4, wherein in step (2), the material is heated to 550 ℃ at a heating rate of 4 to 6 ℃/min under an air atmosphere for 4 hours.
6. The method for in-situ construction of a monatomic Ti-grafted carbon nitride photocatalyst and catalytic reduction of nitroarenes according to claim 1, wherein in step (3), the mass ratio of titanocene dichloride to-OH-rich carbon nitride is 1:2 to 8.
7. The method for in-situ construction of the monatomic Ti-grafted carbon nitride photocatalyst and catalytic reduction of nitroarene according to claim 1, wherein in step (3), the ratio of nitroarene to titanocene dichloride is 1mmol: 20-100 mg.
8. The method for in-situ construction of the monatomic Ti-grafted carbon nitride photocatalyst and catalytic reduction of nitroaromatic according to claim 1, wherein in step (3), the nitroaromatic has a structural formula of R-C 6 H 4 -NO 2 Wherein R is a group comprising C = C, C ≡ C, C = O, C = N, C ≡ N, -OH, -SMe, -CF 3 A substituent of any one of the functional groups or halogen.
9. The method for in-situ construction of the monatomic Ti-grafted carbon nitride photocatalyst and catalytic reduction of nitroarenes according to claim 1, wherein in step (3), the monatomic Ti-grafted carbon nitride photocatalyst obtained is repeatedly used for catalytic reduction of nitroarenes.
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