CN116078431A - Au-based catalytic material based on hollow TTI-COF and application of Au-based catalytic material in catalyzing reduction of 4-nitrophenol - Google Patents

Au-based catalytic material based on hollow TTI-COF and application of Au-based catalytic material in catalyzing reduction of 4-nitrophenol Download PDF

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CN116078431A
CN116078431A CN202211601598.0A CN202211601598A CN116078431A CN 116078431 A CN116078431 A CN 116078431A CN 202211601598 A CN202211601598 A CN 202211601598A CN 116078431 A CN116078431 A CN 116078431A
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nitrophenol
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sio
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陈春燕
陈小迪
杜畅
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Xiangtan University
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Abstract

According to the invention, hollow spherical TTI-COF (H-COF) is used as a main matrix to support the growth of AuNPs for the first time, and a novel Au@H-COF composite material is prepared and used for catalyzing a reduction reaction of 4-nitrophenol. The invention relates to a method for preparing a medicine by twoSilicon oxide is used as a template, a solvent thermal method is used for coating the TTI-COF, then silicon dioxide is etched through hydrofluoric acid to obtain a hollow spherical TTI-COF, and then gold nanoparticles are loaded on the hollow COF through a chemical reduction method to obtain the Au@H-COF catalytic material. The Au@H-COF catalyst of the ultra-fine AuNPs (1.5-4 nm) with uniform load is obtained by optimizing the polymerization temperature, the reducing agent, the shell thickness of the hollow structure, the metal load rate and the like, and the catalyst shows excellent reaction activity (TOF is 1134 h) in the reduction reaction of 4-nitrophenol ‑1 ) And high recoverability, and excellent catalytic performance in large-scale 4-NP catalysis, the utility of the stable crystalline carrier for improving catalytic activity is proved, a general strategy is provided for reasonably designing a COF carrier supported catalyst with high stability and controllable activity for wide application, and the catalyst has important application prospect in the field of industrially preparing catalysts.

Description

Au-based catalytic material based on hollow TTI-COF and application of Au-based catalytic material in catalyzing reduction of 4-nitrophenol
Technical Field
The invention belongs to the technical field of nano catalysts, and particularly relates to preparation of an Au-based catalytic material Au@H-COF based on a hollow TTI-COF and application of the Au-based catalytic material Au@H-COF in catalyzing a reduction reaction of 4-nitrophenol.
Background
Gold nanoparticles (AuNPs) have attracted considerable attention in the field of catalysis due to their unique physicochemical properties of large surface area, high active atom ratio, and adjustable size, however, due to the high surface energy of AuNPs, they are easily aggregated during the catalytic reaction, resulting in reduced activity. The selection of suitable supports, establishing strong metal-support interactions and host pore size imposed geometric constraints to support AuNPs, is a viable strategy to improve stability and catalytic performance [ Menegazzo F, singnoretto M, pinna F. Journal of Catalysis,2014,309 (6): 241-247 ].
It has been reported that AuNPs can be significantly improved in stability when supported on porous metal oxides, silica and metal organic frameworks. However, among these widely studied materials, siO 2 And metal oxides generally have a relatively low surface area, most MOFs are less stable in acidic environments and difficult to recover, limiting their further use. The covalent organic framework material is an attractive material in the catalysis field due to the excellent designability, has low density, high surface area, adjustable function and definite regular pore structure, is stable under water and severe conditions (strong alkalinity or acidity), and is expected to be an ideal host for anchoring the catalytic activity AuNPs [ Huang J, liu X, zhang W.chemical Engineering Journal,2021,404 (2012): 127136.]. The TTI-COF consists of monomers with two planar structures of TT-ald and TT-am, has abundant covalent triazine units, has high crystallinity stability, large surface area, abundant available active sites and highly delocalized pi system, wherein abundant triazine and N elements can provide sufficient metal binding sites, high porosity can allow substrate molecules to diffuse rapidly, pi electronic structure can help absorption of the substrate molecules, while the TTI-COF is designed into a hollow spherical structure, and the hollow spherical structure can not only load AuNPs and is effectiveAvoiding the problem of easy aggregation of AuNPs, providing a fast path for the transport of substances and accelerating the catalytic reaction, these special structures and properties make hollow TTI-COFs a promising platform for supporting AuNPs [ Vyas V S, vishwakarma M, moudrakovski I. Advanced Materials,2016,28 (39): 8749-8754 ].]。
Disclosure of Invention
The invention aims to provide an Au-based catalytic material Au@H-COF of a hollow TTI-COF, and the Au-based catalytic material Au@H-COF is applied to catalytic reduction of 4-nitrophenol. The method aims to improve the catalytic performance of the composite material by adopting a simple process and by means of the synergistic effect of small-size gold nanoparticles and specific carrier properties through design regulation and control, and solve the problems that the nanoparticles are easy to agglomerate, the stability is low, the catalyst is difficult to recycle and the like in the catalytic process.
The aim of the invention is achieved by the following technical scheme.
Au-based catalytic material based on hollow TTI-COF and application thereof in catalyzing reduction of 4-nitrophenol are characterized in that the method comprises the following process steps:
(1) Preparation of Au@H-COF catalytic material:
preparation of homogeneous SiO with particle size of about 233nm 2 And (3) particles. To make the monomer at SiO 2 Uniformly growing on the surface, and adopting a silane coupling Agent (APTES) to carry out SiO 2 Amination modification is carried out to obtain a template (NH) 2 -f-SiO 2 ) The template with amino on the surface can be anchored with aldehyde monomer through Schiff base reaction, and then further reacts with amino monomer to generate SiO 2 @ COF. Then, siO is etched in a 1% HF solution 2 The core, the H-COF hollow sphere is obtained, finally, the reducing agent is used for in situ reduction of HAuCl 4 AuNPs are fixed in the framework of H-COF, and Au@H-COF material is obtained.
(2) Application of Au@H-COF to catalyzing reduction of 4-nitrophenol:
adding the Au@H-COF aqueous solution with good ultrasonic dispersion into the 4-nitrophenol and sodium borohydride aqueous solution, stirring at 25 ℃ for 1.5min at maximum, so that the 4-nitrophenol can be completely reduced into 4-aminophenol, and the catalyst can be centrifugally recycled after the reaction is finished.
Compared with the prior art, the invention has the following beneficial effects:
(1) Gold nanoparticles loaded on the hollow TTI-COF have small particle size (1.5-4 nm), are uniformly dispersed, are simple and green in loading mode, can be loaded, and provide a general strategy for reasonably designing a high-stability and controllable-activity supported metal catalyst for wide application;
(2) The Au@H-COF prepared by the method has better property and specific surface area of 1253.42m 2 The thermal stability temperature reaches 550 ℃, the material has important reference significance in the field of catalyst preparation and synthesis, and the material not only has excellent catalytic performance and cycle stability in the low-concentration 4-nitrophenol reduction reaction, but also has better catalytic effect in the high-concentration 4-nitrophenol reduction reaction, and has great application potential;
drawings
FIG. 1 shows a schematic diagram of the synthesis of Au@H-COF.
[ FIG. 2]]SiO obtained at different prepolymerization temperatures 2 (a) XRD pattern of @ COF; (b-d) SEM images: (b) 25 ℃, (b) 80 ℃, (d) 120 ℃.
FIG. 3 (a) FTIR spectra of TTI-COF and its ligands; (b) FTIR spectra of Au@H-COF and intermediates thereof.
Figure 4 XRD patterns of TTI-COF after 24h immersion under different conditions.
[ FIG. 5]](a)SiO 2 、TTI-COF、SiO 2 XRD patterns of @ COF and H-COF; (b) XRD patterns of Au@H-COF obtained with different reducing agents.
[ FIG. 6]](a)TTI-COF、(b)SiO 2 And (c) SiO 2 SEM image of @ COF; TEM images of (d) H-COF and (e) Au@H-COF; (f) HR-TEM image of AuNPs in Au@H-COF; (g) EDX element map of Au@H-COF.
FIG. 7 is a TEM image of H-COF with different shell thicknesses. Reactive monomer amounts (a) TT-ald (0.08 mmol) and TT-am (0.08 mmol); (b) TT-ald (0.06 mmol) and TT-am (0.06 mmol); (c) TT-ald (0.04 mmol) and TT-am (0.04 mmol)
FIG. 8 color chart of Au@H-COF catalysts with different Au loading rates
FIG. 9 (a) Nitrogen adsorption isotherm plot of Au@H-COF and intermediates thereof; (b) TGA graphs of TTI-COF and Au@H-COF.
FIG. 10 reaction equation for catalyzing 4-nitrophenol to 4-aminophenol by Au@H-COF, UV-vis spectra and color change pattern during catalysis
FIG. 11](a) UV-vis spectrum of the reaction system in the absence of catalyst; (b) A UV-vis spectrum of a TTI-COF catalyzed 4-nitrophenol reaction; (c) HAuCl 4 UV-vis spectra of catalytic 4-nitrophenol reactions.
FIG. 12 UV-vis spectra of Au@H-COF catalyzed reactions of 4-nitrophenol prepared with different reducing agents: (a) sodium citrate; (b) glutathione.
FIG. 13](a) Solid structure SiO 2 UV-vis spectrum of 4-nitrophenol catalyzed by COF@Au; (b) UV-vis spectrum of the hollow structure Au@H-COF catalyzed 4-nitrophenol reaction.
FIG. 14 is a graph of UV-vis spectra of Au@H-COF catalyzed 4-nitrophenol reactions with different shell thicknesses; (b) shell thickness 35mm; (c) the thickness of the shell layer is 45mm.
FIG. 15 is a graph of the UV-vis spectrum of a 4-nitrophenol reaction catalyzed by Au@H-COF of varying metal loading (a) 1.18wt% Au; (b) 2.11wt% au; (c) 2.78wt% au; (d) 7.30wt% au; (e) 15.30wt% Au.
FIG. 16 shows a graph of the cycling stability of Au@H-COF catalyzed 4-nitrophenol reaction.
FIG. 17 shows (a) FT-IR spectra and (b) TEM images of Au@H-COF catalyst after five cycles of catalyzing the reduction of 4-nitrophenol.
FIG. 18 color change chart of Au@H-COF catalyzed reaction of large concentration of 4-nitrophenol
Detailed description of the preferred embodiments
Specific embodiments of the present invention will now be described in further detail with reference to the drawings and examples. The following examples are illustrative of the present invention, but are not intended to limit the scope and extension of the present invention.
Example 1: a preparation method of Au-based catalytic material based on hollow TTI-COF.
(1)SiO 2 Is prepared from the following steps: 3.40mL of aqueous ammonia was added to a mixture of deionized water (20 mL) and ethanol (120 mL), followed by stirring at 25 ℃30min. 12mL of Tetraethoxysilane (TEOS) was added rapidly to the above solution and stirred for an additional 1h to yield monodisperse SiO 2 A ball. After the centrifugal and ultrasonic dispersion are fully washed by ethanol, the product is dried for 24 hours under the vacuum 50 ℃ to obtain SiO 2 White powder.
(2)SiO 2 -f-NH 2 Is prepared from the following steps: 1g of SiO was treated by ultrasound 2 Evenly dispersed in ethanol (180 mL). Then, a mixture of APTES (0.3 mL) and ethanol (20 mL) was slowly added with vigorous stirring at 25℃and stirred for 6 hours, and thoroughly washed with ethanol to give surface-aminated silica spheres (expressed as NH) 2 -f-SiO 2 ) Drying at 50deg.C under vacuum for 24 hr.
(3) TT-ald (0.06 mmol,23.60 mg) was added to 2.5mL NH in a 25mL Schlenk tube 2 -f-SiO 2 To 1, 4-dioxane/mesitylene (1, 1=v/v) dispersion (15 mg/mL), sonicated for 5min, prepolymerized and stirred at 80℃for 2h, TT-am (0.06 mmol,22.26 mg) dispersed in 2.5mL 1, 4-dioxane/mesitylene and 0.135mL 6M HAc were added sequentially with vigorous stirring, stirred for 1h, and heated in an oil bath at 120℃for 3 days under sealing. After cooling, the reaction mixture was washed with absolute ethanol, water, acetone, chloroform, THF, and dried under vacuum at 50 ℃ to give a yellow powder (yield: 93%). Fixing the amount of the template and adjusting the amount of the monomer to obtain SiO with different shell thicknesses 2 The specific amounts used are given in the following table:
table 1: siO with different shell thickness 2 Preparation ratio of @ COF
Figure SMS_1
(4) Preparation of H-COF: in the lining of the reaction kettle, 20mg of SiO 2 Dispersing @ COF in 15mL 1% (volume fraction) HF aqueous solution, stirring at room temperature for 12h, centrifuging to collect the solid, washing with ethanol, and vacuum drying at 50deg.C to give yellow powder.
(5) Preparation of Au@H-COF: two methods (different reducing agents) are used to prepare Au@H-COF, the process is as follows:
H-COF (7.5 mg) was ultrasonically dispersed in 1mL of ultrapure water, and HAuCl was added thereto 4 The solution (3.3 mL,3 mM) was stirred at 25℃for 5min. Then, sodium citrate (C 6 H 5 Na 3 O 7 *3H 2 O,11.76mg,100 nM) was added to the mixture. After 30min of reaction, the precipitate was centrifuged, washed thoroughly with ultrapure water for 5 times and dried at 50℃under vacuum.
H-COF (10 mg) was ultrasonically dispersed in ultra pure water (5 mL), and 1% HAuCl was added 4 0.63mL of the solution was stirred for 2 hours, 7.43mg of glutathione reduced was added, stirred for 2 hours, heated to 80℃and reacted for 48 hours, washed with water, ethanol and dried at 50℃under vacuum.
Using the second method, HAuCl was examined 4 Is the variable, controls the added 1% HAuCl 4 The volume of the solution, thereby obtaining the catalyst with highest catalytic activity.
Example 2: the Au-based catalytic material Au@H-COF based on the hollow TTI-COF and the structural characterization of an intermediate product thereof.
By using Fourier transform infrared spectrometer, scanning electron microscope, X-ray diffractometer, thermogravimetric analyzer and N 2 Adsorption-desorption and the like are used for carrying out structural characterization on all the prepared materials.
FIG. 2 shows SiO obtained at different prepolymerization temperatures 2 XRD pattern and SEM pattern of @ COF. Polymerization at 80 ℃ with optimal crystal structure and smooth SiO 2 Most of the surface becomes rough, and the coating of the TTI-COF is more complete, showing good dispersibility. The pre-polymerization temperature of 80 ℃ was chosen as the final synthesis experimental temperature, analyzed by XRD and SEM images.
FIG. 3 is an infrared spectrum of Au@H-COF and an intermediate thereof. As can be seen from FIG. 3a, at 1613cm -1 There is an imine (C=N) stretching vibration band, while the TT-ald monomer aldehyde group C-H (2825 cm) -1 ) And c=o (1710 cm) -1 ) And N-H (3500-3200 cm) in TT-am monomer -1 ) The characteristic stretch zone disappeared, meaning that the condensation reaction was successful. SiO (SiO) 2 NPs at 1100cm -1 Has strong absorption peak of Si-O-Si vibration, and SiO 2 Besides Si-O-Si absorption, the @ COF also showed a characteristic absorption of TTI-COF, indicating successful growth of TTI-COF on the nanospheres. SiO removal 2 After the template, HFTIR spectra of-COF showed Si-O-Si characteristic peaks (1096 cm -1 ) Vanishing but retaining the characteristic peak of TTI-COF, indicating that the shell structure is composed of TTI-COF backbone. After incorporation of AuNPs in the H-COF support, the retention of TTI-COF characteristic peaks confirmed that the metal was loaded without interfering with the basic H-COF architecture, and the chemical composition in the COF framework remained unchanged by treatment with the reducing agent (fig. 3 b).
Figure 4 is an XRD pattern for TTI-COF after 24h of immersion under different conditions. TTI-COF is demonstrated to be stable in 12M HCl, 3M NaOH solution and various organic solvents (e.g., THF, DMSO, DMF, acetone, chloroform, methanol, boiling water, etc.).
FIG. 5 is an XRD pattern for Au@H-COF and intermediates thereof, vs. amorphous SiO 2 After template binding, siO is compared with TTI-COF 2 There was a slight decrease in the intensity of the peak in @ COF. And with SiO 2 The hollow sphere TTI-COF (H-COF) obtained after etching for 12H with 1% hf showed a stronger peak at 3.99 ° compared to @ COF, which suggests that the H-COF structure remains intact after prolonged treatment under severe etching conditions. Au@H-COF is obtained by adding a reducing agent to HAuCl 4 And H-COF, two commonly used reducing agents, glutathione and sodium citrate are selected, and after AuNPs are encapsulated, four characteristic peaks of 2θ=38.2 °, 44.5 °, 64.6 ° and 77.5 ° can be seen in the XRD pattern of Au@H-COF (figure 5 b), which confirms that AuNPs successfully incorporate COF despite stronger AuNPs peaks obtained by GSH reduction and more complete preservation of small-angle peaks of sodium citrate reduced carriers. Both the PXRD pattern and FT-IR spectra of Au@H-COF indicate that the H-COF remains intact in both structure and chemical composition after incorporation into the AuNPs.
FIG. 6 is SEM and TEM images of Au@H-COF and its intermediates, and the solvothermal synthesized TTI-COF is generally a rod-like fiber (FIG. 6 a), showing poorly controlled morphology and randomly distributed size. FIG. 6b shows well-dispersed NH having a diameter of 233.+ -.12 nm 2 -f-SiO 2 Smooth contours of the microspheres. With SiO 2 After coating the TTI-COF, the smooth sphere surface became rough (FIG. 6 c), successful etching of SiO with hydrofluoric acid 2 After the template, the COF shell remains intact as shown in fig. 6 d. As can be seen from FIG. 6e, auNPs (black dots) are uniformly distributed in the H-COF materialHR-TEM imaging of Au@H-COF on the surface and inside of the material (FIG. 6 f) showed that the interplanar spacing of those AuNPs at the surface was 0.154nm, corresponding to the spacing of the (222) lattice planes of the Au crystals, with AuNPs particle sizes as small as 1.5-4nm, and energy dispersive X-ray spectroscopy (EDX) mapping analysis (FIG. 6 g) also confirmed the successful loading of AuNPs on the H-COF carrier.
FIG. 7 is a TEM image of H-COF with different shell thicknesses. In a typical H-COF synthesis (0.06 mmol TT-ald and 0.06mmol TT-am) the H-COF shell layer average thickness is about 35nm (FIGS. 6d and 7 b), when the monomer amount is increased by 0.08mmol, the shell layer thickness is increased to 45nm on average (FIG. 7 a) and the monomer amount is reduced to 0.04mmol, the template is deleted and the shell collapses and a complete spherical structure is not obtained (FIG. 7 c), so that a complete hollow sphere can be obtained with a shell thickness of more than 35 nm.
FIG. 8 is a graph of the color change of Au@H-COF catalysts with different Au loading rates. By changing HAuCl 4 To obtain catalysts with different Au loading amounts (1 wt% -15 wt%) and with HAuCl 4 The added amount of (2) increases and the color of the catalyst powder changes from yellow to brown.
FIG. 9 is a nitrogen adsorption isotherm plot and TGA plot of Au@H-COF and its intermediate. All COF materials show type IV isotherms with a sharp increase in nitrogen uptake at low relative pressure (P/P 0 <0.01 Indicating the presence of micropores, a step in the relative pressure range of 0.10-0.20, corresponding to the mesoporous structure of TTI-COF. BET surface area of Au@H-COF is 1253.42m 2 g -1 (fig. 9 a), is superior to most supported metal catalysts. FIG. 9b thermogravimetric analysis (TGA) shows that the thermal stability of Au@H-COF is similar to that of pure TTI-COF, with high thermal stability, up to 550 ℃.
Example 3: the nano catalyst Au@H-COF is applied to catalyzing reduction reaction of 4-nitrophenol.
The experimental conditions of this example were: the mass of the catalyst was 3mg and the temperature was 25 ℃.
The specific embodiment of the reduction reaction of the low-concentration 4-nitrophenol is as follows: 15mL of 4-nitrophenol solution (0.18 mM) and 12mL of NaBH were added in a 50mL beaker at 25 ℃ 4 Solution (0.36M), magneticTo the mixture was added 1mL of an aqueous Au@H-COF solution (3 mg/mL) with stirring, sampled at 30s with a 0.22um needle filter, and the whole reaction was always monitored by an ultraviolet-visible spectrophotometer.
The specific implementation scheme of the high-concentration 4-nitrophenol reduction reaction is as follows: the amount of 4-nitrophenol was increased 1000-fold for catalytic reduction. 36mL of the prepared 4-nitrophenol solution (0.083M, water/ethanol=5/1, v/v) and freshly prepared NaBH were placed in a 100mL beaker at room temperature 4 (30 mL, 1.925M) was mixed, 1mL of the prepared Au@H-COF aqueous solution (3 mg/mL) was added to the mixture under stirring, and sampling was performed with a 0.22um needle filter at regular intervals, and a color change was observed from bright yellow to colorless, indicating completion of the reaction.
(1) Process phenomenon of catalyzing and reducing 4-nitrophenol by Au@H-COF material
According to the experimental steps, the Au@H-COF catalyst disclosed by the invention is used for processing and analyzing 4-nitrophenol pollutants, and the process phenomenon is shown in figure 10, wherein the 4-nitrophenol is mixed with newly prepared NaBH 4 After the aqueous solutions are mixed, the aqueous solution is deprotonated to generate 4-nitrophenol ions, the color is changed from yellowish to yellowish green, and the highest absorption peak position of an ultraviolet absorption spectrum is also changed from 317nm to 400nm. As the catalyst was added to the above solution, the characteristic absorbance of 4-nitrophenol at 400nm was gradually decreased, while the characteristic absorbance peak of the reduced product 4-AP was gradually increased at 300nm, and accordingly, the color of the 4-nitrophenol solution was gradually changed from yellow-green to colorless.
(2) Influence of reducing agent used for preparing Au@H-COF material on catalytic performance
And selecting two mild reducing agents, namely trisodium citrate and glutathione to prepare the composite material. Fixedly added HAuCl 4 As shown in FIG. 12b, the absorbance at 400nm in the UV-vis spectrum is rapidly reduced, the absorption peak intensity at 300nm is increased, the catalytic activity is remarkable, and the conversion of 4-nitrophenol to 4-aminophenol is completed within 2min. The catalytic activity of Au@H-COF obtained by reducing sodium citrate is relatively low (conversion time: 6.5 mi)n). In contrast, the reaction did not occur in the absence of the Au@H-COF catalyst (FIG. 11 a) or in the catalysis of 4-nitrophenol using only pure TTI-COF (FIG. 11 b). By HAuCl without TTI-COF carrier protection 4 (FIG. 11 c) unprotected AuNPs would decompose rapidly, rendering them unrecoverable, and because of their large size, require a long reaction time (conversion time: 5 min) to approach full conversion, highlighting the significance of H-COF as a substrate for supported catalysts. While the reason why GSH reduced Au@H-COF shows significant activity may be very fine distribution of nanoparticles (1.5-4 nm) on the H-COF substrate, an increase in the surface atomic ratio of Au@H-COF leads to a significant increase in the catalytic activity, so that the latter materials were all obtained with GSH as the reducing agent.
(3) Influence of hollow structure of Au@H-COF material on catalytic performance
For comparison, siO of core-shell structure was also synthesized 2 The reduction reaction of 4-nitrophenol was tested under the same conditions with the @ COF @ Au material, as shown in FIG. 13, siO2@ COF @ Au required 4.5 minutes to reduce completely, and the hollow Au @ H-COF under the same synthesis conditions required only 2 minutes.
(4) Influence of shell thickness on catalytic performance in Au@H-COF material
au@h-COF of different shell thicknesses and the same Au loading content were synthesized and tested for reduction of 4-nitrophenol under the same reaction conditions (fig. 14). The reaction rate is reduced along with the increase of the thickness of the shell, the catalytic activity is highest when the thickness of the shell reaches 45nm, the conversion is complete within 1.5min, and the catalytic dynamics is 0.04074s -1 TOF value is 1134h -1 The catalyst is superior to a plurality of Au-based catalysts reported before, and the catalytic performance of the catalyst with the medium shell thickness and the catalyst with the optimal shell thickness has little difference from the view point of the catalytic time and the kapp value, and the material with the medium shell thickness is selected for further research by comprehensively considering the operation cost and the catalytic efficiency.
(5) Influence of Metal Loading Rate in Au@H-COF Material on catalytic Performance
We have further studied the pair catalysis of au@h-COF materials with different Au loadings under the same catalytic conditionsInfluence of chemical properties. As shown in fig. 15, all materials can catalyze the reduction of 4-nitrophenol, but exhibit different degrees of activity. As can be seen from the reaction completion time and kappa, as the Au loading in Au@H-COF increases from 1% to 15%, the catalytic performance increases and decreases, and when the Au loading is 2.78wt%, the catalytic 4-nitrophenol rate constant is highest and is 0.03051s -1 The catalytic performance is proved to be best.
(6) Reproducibility and stability investigation of Au@H-COF material
The stability and reusability of au@h-COF were evaluated by continuous cycling catalytic reaction, and after one run, the catalyst was centrifuged from the reaction solution and used directly in the next cycle, as shown in fig. 16, similar conversions (100% to 97%,2 min) and apparent rate constants (3.051 ×10) were observed in all five consecutive reaction cycles -2 -2.86×10 -2 s -1 ) And there is no significant change in the chemical structure of the material after recycling (fig. 17 a), while the gradual slight decrease in catalytic effect may be due to local aggregation of gold nanoparticles during catalysis (fig. 17 b) and slight weight loss of catalyst during recovery. The results show that the Au@H-COF catalyst provided by the invention is satisfactory in stability and reproducibility.
(7) Au@H-COF material catalytic reduction large-concentration 4-nitrophenol
The amount of 4-nitrophenol was increased by 1000 times, and the progress of the reaction was judged by observing the color change of the solution by catalytic reduction with 3mg of Au@H-COF of the same mass at room temperature, and as can be seen from FIG. 18, the solution was changed from bright yellow to colorless only for 26 minutes, meaning that the conversion of 4-nitrophenol to 4-AP was completed, which is advantageous for practical production and living applications.

Claims (5)

1. An Au-based catalytic material based on hollow TTI-COF and application thereof in catalyzing reduction of 4-nitrophenol are characterized in that: the method takes a hollow spherical TTI-COF as a carrier, carries AuNPs in situ, obtains the Au@H-COF catalyst with the AuNPs size of 1.5-4nm by optimizing the prepolymerization temperature, the reducing agent, the shell thickness of a hollow structure, the metal loading rate and the like, and examines the catalytic performance of the Au@H-COF material in the reduction reaction of 4-nitrophenol and the catalytic reduction utilization performance of high-concentration pollutants.
2. The preparation of the catalyst material according to claim 1, characterized by comprising the steps of:
1) Preparation of homogeneous SiO with particle size of 233nm 2 Particles;
2) Based on the material in 1), adding a silane coupling Agent (APTES) to SiO 2 Amination modification is carried out to obtain a template (NH) 2 -f-SiO 2 )；
3) Based on 2), adding aldehyde monomer (TT-ald) to react with NH by Schiff base 2 -f-SiO 2 Prepolymerizing, further adding amino monomer (TT-am) to obtain SiO 2 @COF。
4) Adding 1% HF solution into the product obtained in the step 3) to etch SiO 2 Obtaining H-COF hollow spheres;
5) In situ reduction of HAuCl with reducing agent (sodium citrate, glutathione) based on 4) 4 AuNPs were immobilized in the framework of H-COF to obtain Au@H-COF material.
3. The method of claim 1, wherein the hollow TTI-COF is used as a metal nanoparticle carrier, has large surface area and good stability, has abundant available active sites and a highly delocalized pi system, can provide sufficient metal binding sites, avoids the problem that AuNPs are easy to aggregate as much as possible, and is an ideal platform for loading the AuNPs.
4. The preparation of the Au@H-COF material with optimal catalytic performance according to claim 1, wherein the preparation conditions are as follows: the prepolymerization temperature is 80 ℃, the reducing agent is glutathione, the thickness of a shell layer of a hollow structure is 35nm, the metal loading rate is 2.78wt%, and the BET specific surface area of the obtained material is 1253.42m 2 The heat stability temperature reaches 550 ℃.
5. The use of the hollow TTI-COF-based au@h-COF material for catalyzing the reduction of 4-nitrophenol according to claim 1, wherein the reaction conditions for catalyzing the reduction of 4-nitrophenol are: 15mL of 4-nitrophenol solution (0.18 mM), 12mL of sodium borohydride solution (0.36M) were added sequentially to a 50mL beaker at 25℃under magnetic stirring, followed by 1mL of Au@H-COF material suspension at a concentration of 3 mg/mL.
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