Plasma silver nanocluster coated mesoporous molecular sieve TS-1 photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalysts, in particular to a plasma silver nanocluster coated mesoporous molecular sieve TS-1 photocatalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: 1, synthesizing mesoporous molecular sieve TS-1 powder; and 2, mixing the mesoporous molecular sieve TS-1 and CH3OH to prepare a suspension, injecting an AgNO3 aqueous solution into the suspension, and carrying out ultraviolet irradiation, filtration, washing and freeze drying to obtain the plasma silver nanocluster coated mesoporous molecular sieve TS-1 photocatalyst. The obtained electron-rich Ag cluster / mTS-1 shows an Ag-Ag coordination number (CN = 2.0 + / -0.1) lower than that of a mesoporous molecular sieve TS-1 (CN = 2.9 + / -0.2) loaded with Ag nanoparticles, so that the electron-rich Ag cluster / mTS-1 has higher CO2 adsorption and activation performance. In addition, the silver nanoclusters are firmly anchored on the surface of the mesoporous molecular sieve TS-1, so that the mesoporous molecular sieve TS-1 has high stability, and therefore, the mesoporous molecular sieve TS-1 shows high-stability CO2-to-CO photocatalytic conversion activity under simulated sunlight irradiation, and the yield of CO within 4 hours is 350 [mu] mol g <-1 >.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst and a preparation method and application thereof. Background Art

[0002] The excessive consumption of fossil fuels has led to a series of serious environmental problems, such as the greenhouse effect produced by carbon dioxide. Therefore, using renewable solar energy to convert carbon dioxide into carbon monoxide fuel can solve environmental problems while proposing a new energy development strategy. From a thermodynamic point of view, photocatalysis converts CO 2 Reduction to CO is an endothermic reaction that requires the supply of more electrons and protons to break the C=O bond. 2 The high bond energy, low utilization rate of solar energy and rapid recombination of photogenerated charges are still the limitations of CO 2 Therefore, it is urgent to develop an efficient photocatalyst to achieve carbon dioxide emission reduction.

[0003] Porous materials can absorb CO 2 And achieve CO 2 The enrichment of CO 2 can be achieved by using porous materials, such as activated carbon, porous metal oxides, metal organic frameworks, etc., which is attributed to the sealing effect of the porous structure and is an effective CO 2 For example, Wang et al. prepared coated hollow TiO 2 The microporous palladium porphyrin-based polymer exhibits excellent CH 4 and CO production, 48.0 and 34.0 μmol g -1 h -1 , which can be seen from CO 2 In addition, molecular sieves are excellent catalysts due to their unique cage structure, high specific surface area and super hydrothermal stability. In particular, constructing three-dimensional mesoporous channels in molecular sieves can not only promote the diffusion and mass transfer of substances, but also enrich CO 2 More importantly, the interpenetrating micropores and mesopores as microreaction cages can increase the contact time between intermediates and active sites, which will provide the possibility for efficient reduction of carbon dioxide. 2 In the reduction reaction, the electron transfer from CO to the carbon monoxide radical anion requires a potential as high as -1.9 V (vs RHE), which makes CO activation a limiting step in the thermodynamic process. Fortunately, electron-rich catalysts will promote the efficient activation of CO. For example, Huang et al. prepared an electron-rich Cu-Bi bimetallic nanosheet through an electronic structure regulation strategy, in which Cu acts as an electron donor to provide electrons to the Bi electron acceptor, effectively promoting CO2 In addition, the introduction of oxygen vacancy defects can also adjust the electronic structure of the catalyst and promote the activation of CO 2 For example, Xie et al. designed an oxygen-rich Co 3 O 4 Ultra-thin sheets, they found that the presence of oxygen vacancies can reduce CO 2 activation energy to achieve CO 2 Designing electron-rich catalysts with oxygen vacancies is an important way to promote CO 2 Effective strategies for activation.

[0004] Among many reported photocatalysts, metal oxides have been widely used in the photocatalytic reduction of CO. 2 It shows unique advantages, such as CeO 2 、ZnO、Bi 2 O 3 , CuO x and TiO 2 However, most of these metal oxides are wide-bandgap semiconductors with low utilization of sunlight. It is reported that metallic Ag can be excited by visible light, leading to the localized surface plasmon resonance effect (LSPR), thereby improving the absorption efficiency of visible light. In addition, Ag catalysts are also a promising candidate for converting CO 2 Silver nanoclusters are the preferred catalysts for the conversion of CO into CO, mainly because of their excellent catalytic performance and relatively low cost. The CO yield over silver-based catalysts can be greatly improved to the tens of micromoles per gram range by adjusting the crystal structure, particle size, interface state, and coordination environment. In contrast, the CO yield is still low, and improving CO yield remains a huge challenge. In recent years, metal nanoclusters with unique atomic stacking patterns, quantum confinement effects, and abundant active centers have shown physical and chemical properties that are different from traditional metal nanocrystals. Due to their ultrasmall size (<2nm) and special electronic structure, metal nanoclusters exhibit semiconductor-like light absorption properties, showing the potential for photocatalytic reduction of carbon dioxide. Therefore, it is rational to construct a heterogeneous photocatalytic system based on silver nanoclusters to drive CO 2 The photocatalytic reduction of will provide an effective way to achieve efficient conversion of solar energy into chemical energy. Summary of the invention

[0005] In order to comprehensively solve the above problems, the present invention successfully prepared the oxygen vacancy-rich silver nanocluster encapsulated mesoporous molecular sieve TS-1 (Ag nanocluster / mTS-1) through a surfactant-assisted ultraviolet light reduction strategy. The obtained electron-rich Ag cluster / mTS-1 showed a lower Ag-Ag coordination number (CN=2.0±0.1) than the mesoporous molecular sieve TS-1 loaded with Ag nanoparticles (CN=2.9±0.2), which gave it a higher CO 2In addition, the silver nanoclusters were firmly anchored on the surface of the mesoporous molecular sieve TS-1, which made it highly stable and thus exhibited highly stable photocatalytic CO2 conversion under simulated sunlight irradiation. 2 The conversion activity to CO was 350 μmol g -1 This work provides new ideas for the optimal design of high-performance photocatalysts.

[0006] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst, comprising:

[0007] Step 1: Synthesize mesoporous molecular sieve TS-1 powder;

[0008] Step 2: Mix the mesoporous molecular sieve TS-1 and CH 3 OH was mixed to prepare a suspension, and AgNO 3 The aqueous solution is injected into the suspension, and after ultraviolet irradiation, filtration, washing and freeze-drying, a plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst is obtained.

[0009] Preferably, step 1 comprises:

[0010] Step 1.1: Mix tetrapropylammonium hydroxide and deionized water;

[0011] Step 1.2: Add KCl, Na 2 CO 3 , H 2 SiO 3 and Ti(SO 4 ) 2 Add to the mixed solution of step 1.1 and stir at room temperature to obtain a precursor solution;

[0012] Step 1.3: aging the precursor solution and then transferring it to the reactor for hydrothermal treatment;

[0013] Step 1.4: The product of the hydrothermal treatment is filtered, washed with deionized water, dried, and then heat-treated to remove the organic agent, and then the powdered mesoporous molecular sieve TS-1 is collected.

[0014] Preferably, in step 1.1, the amount of tetrapropylammonium hydroxide added is 10.4 g and the amount of deionized water added is 8 g.

[0015] Preferably, in step 1.2, KCl is 0.14 g, Na 2 CO 3 0.09g, H 2 SiO 3 50mmol and Ti(SO 4 ) 2is 2mmol.

[0016] Preferably, in step 1.3, the aging condition of the precursor solution is: aging at 40° C. for 12 hours; and the hydrothermal treatment condition is: hydrothermal treatment at 160° C. for 24 hours.

[0017] Preferably, in step 1.4, the heat treatment conditions are: calcination at 550° C. for 8 hours.

[0018] The second aspect of the present invention provides a plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst prepared by the method described above.

[0019] The second aspect of the present invention provides a plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst for preparing a photocatalytic CO 2 Use of catalytic materials to reduce CO.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention uses a surfactant-assisted ultraviolet light reduction method to carefully design silver nanoclusters encapsulating mesoporous molecular sieve TS-1 (Ag nanoclusters / mTS-1). The obtained electron-rich Ag nanoclusters / mTS-1 combined with oxygen-rich vacancies can promote CO 2 The adjacent spacing of Ag nanoclusters will adjust the electronic structure of the catalyst, so that the Ag nanoclusters have a suitable adsorption strength for CO. In addition, Ag nanoclusters can also induce localized surface plasmon resonance (LSPR), promote the adsorption of visible light and the separation of photogenerated charges, and improve the photocatalytic CO 2 Restored performance.

[0022] The results showed that under simulated sunlight irradiation for 4 h, Ag nanoclusters / mTS-1 (350 μmol g -1 ) has a CO production that is 1.6 times that of the mesoporous molecular sieve TS-1 loaded with Ag nanoparticles (AgNP / mTS-1). BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0024] In the attached picture:

[0025] Figure 1 Preparation and characterization of Ag nanoclusters / mTS-1: a) Schematic diagram of the synthesis of Ag nanoclusters / mTS-1, b) XRD patterns of samples mTS-1, AgNP / mTS-1, and Ag nanoclusters / mTS-1 and c) zeta potential;

[0026] Figure 2 Middle, a) TEM and HRTEM images, and ei) elemental analysis results of sample Ag nanoclusters / mTS-1;

[0027] Figure 3 In, ac)N 2 Adsorption / desorption isotherms and df) corresponding pore size distributions of samples mTS-1, AgNP / mTS-1, and Ag nanoclusters / mTS-1;

[0028] Figure 4 a) XPS fine spectra of samples mTS-1, AgNP / mTS-1 and Ag nanoclusters / mTS-1, and XPS energy spectra of b) Ti2p, c) O1s and d) Ag3d;

[0029] Figure 5 Structural characterization of AgNP / mTS-1 and Ag nanocluster / mTS-1 samples: a) Ag K-edge XANES, b) Ag K-edge EXAFS and c) Ag 2 O, Ag foil, AgNP / WT of mTS-1 and Ag cluster / mTS-1;

[0030] Figure 6 a) H of samples mTS-1, AgNP / mTS-1 and Ag nanoclusters / mTS-1 2 -TPR and b)CO 2 -TPD curve;

[0031] Figure 7 Photoelectrochemical characterization of electrodes mTS-1, AgNP / mTS-1, and Ag nanoclusters / mTS-1: a) UV-visible absorption spectra, b) band gap, c) Mott-Schottky plot at a constant frequency of 500 Hz, d) PL spectra, e) electrochemical impedance spectroscopy, f) transient photocurrent density at -1.4 V vs. Ag / AgCl;

[0032] Figure 8 a) CO of samples mTS-1, AgNP / mTS-1, and Ag nanoclusters / mTS-1 under 300WXe light and AM1.5G filter 2 The variation of CO production in photocatalytic reduction with reaction time, b) cycle test of Ag nanocluster / mTS-1, c) CO production on samples Ag nanocluster / mTS-1 with different silver contents, d) energy level diagram of samples mTS-1, AgNP / mTS-1 and Ag nanocluster / mTS-1;

[0033] Fig. 9 a) AgNP / mTS-1 and b) Ag 簇In situ FT-IR spectrum of Ag nanoclusters / mTS-1, c) Photocatalytic CO generation on Ag nanoclusters / mTS-1 2 Schematic diagram of the reduction mechanism;

[0034] Fig.10 Middle, ab) TEM images of mesoporous molecular sieve TS-1 (AgNP / mTS-1) samples loaded with Ag nanoparticles;

[0035] Fig.11 is the XRD pattern of the Ag nanocluster / mTS-1 sample after five cycles;

[0036] Fig.12 In the middle, ab) are TEM images of the sample Ag nanocluster / mTS-1 after five cycles;

[0037] Fig.13 It is a flow chart of the preparation method of the present invention. DETAILED DESCRIPTION

[0038] The following combination Figure 1-Figure 13 The preferred embodiments of the present invention are described. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0039] Embodiment 1:

[0040] The preparation method of plasma silver nanocluster coated mesoporous molecular sieve TS-1 photocatalyst comprises:

[0041] Step 1: Synthesize mesoporous molecular sieve TS-1 powder; including:

[0042] Step 1.1: Mix 10.4 g of tetrapropylammonium hydroxide (TPAOH, 25 wt%) with 8 g of deionized water;

[0043] Step 1.2: Add 0.14 g of KCl and 0.09 g of Na 2 CO 3 , 50mmol H 2 SiO 3 and 2 mmol Ti(SO 4 ) 2 Add to the mixed solution of step 1.1 and stir continuously at room temperature for 5 h to obtain a precursor solution;

[0044] Step 1.3: The precursor solution was aged at 40 °C for 12 h and then transferred to a 100 mL reactor for hydrothermal treatment at 160 °C for 24 h;

[0045] Step 1.4: The product of the hydrothermal treatment was filtered, washed with deionized water, dried at 80° C., and then calcined at 550° C. for 8 hours to remove the organic agent, and the powdered mesoporous molecular sieve TS-1 (mTS-1) was collected.

[0046] Step 2: Mix 1 g of mesoporous molecular sieve TS-1 and 100 mL of CH 3 OH was mixed to prepare a suspension, and (0.1MAgNO 3 The aqueous solution was injected into the suspension and stirred for 20 minutes (wherein AgNO 3 The optimal mass ratio of Ag nanoclusters to mesoporous molecular sieve TS-1 is 1%-4%). ​​After irradiation with UV light for 5 minutes, the color of the solution turned gray, and then the precipitate was filtered, washed and freeze-dried to obtain plasma silver nanoclusters coated with mesoporous molecular sieve TS-1 photocatalyst (Ag nanoclusters / mTS-1).

[0047] Embodiment 2:

[0048] The method described in Example 1 was used to prepare a plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst.

[0049] Embodiment 3:

[0050] Plasmonic silver nanoclusters coated mesoporous molecular sieve TS-1 photocatalyst for the preparation of photocatalytic CO 2 Use of catalytic materials to reduce CO.

[0051] Comparison example:

[0052] Synthesis of mesoporous molecular sieve TS-1 loaded with silver nanoparticles (AgNP / mTS-1): a certain amount of AgNO 3 The aqueous solution (0.1 M) was injected into the suspension containing mTS-1, and NaBH 4 As a reducing agent, it was added to the suspension (wherein the optimal ratio of Ag to sodium borate was 4:1). The precipitate was filtered, washed with water, and freeze-dried to obtain the final sample AgNP / mTS-1.

[0053] Experimental test:

[0054] 1. Experimental Methods

[0055] 1.1 Feature Description

[0056] The crystallization of the samples was examined by XRD using Cu Kα radiation (40 kV, 30 mA). The nitrogen adsorption / desorption curves of the samples were tested on a Micromeritics ASAP 3020 at -196 °C. The microstructure and morphology of the samples were observed by field emission scanning electron microscopy (EOL-2010F, operated at 200 kV) and enhanced by a field emission scanning electron microscope (FEI, Magellan 400) with a HAADF detector. UV-visible spectra and photoluminescence spectra (PL) were recorded on a V-570 (JASCO) instrument and a Shimadzu RF-6000 spectrometer, respectively. The valence states of the elements were studied by X-ray photoelectron spectroscopy (XPS, Thermo). Programmed temperature desorption of CO2 (CO 2 -TPD) and temperature-programmed reduction of hydrogen (H 2 -TPR). X-ray absorption spectroscopy (XAS) was performed using synchrotron radiation luminescence spectroscopy (ESCAlab250, Thermo). The silver content was determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0057] 1.2 Photocurrent test

[0058] The photocurrent and electrochemical impedance spectroscopy (EIS) were evaluated using a three-electrode system on a CHI 660A electrochemical workstation, with Pt sheet and Ag / AgCl as the counter electrode and reference electrode, respectively. The working electrode was prepared as follows: 40 mg of the catalyst was dispersed in a solution of 0.2 mL of ethanol and 0.05 mL of Nafion solution (5%) by ultrasonic technology, and then 0.02 mL of the slurry was coated on an active area of ​​1 cm 2 on the p-Si surface and dried at 60 °C. In addition, 0.5 M Na 2 SO 4 as the electrolyte, and a 300 W xenon lamp with an AM 1.5G filter was used as the light source.

[0059] 1.3 Photocatalytic CO 2 Reduction reaction

[0060] Photocatalytic CO 2 Restore and make the area 1cm 2 The photocatalyst coated on the p-Si surface was placed in a reaction vessel. Before light irradiation, high-purity CO 2The photoreaction system was purged for 1 hour to remove air. At the same time, 2 mL of distilled water was injected into the reaction system, and the reaction temperature was controlled by cooling water. Then, a 300 W Xe lamp with an AM 1.5 G filter was turned on and the photocatalytic reaction was started. The final reduction product was collected and analyzed by gas chromatography (TRACE 1300, Thermo).

[0061] 2. Results and Discussion

[0062] 2.1 Structure and morphology of samples

[0063] Figure 1 Figure a shows a schematic diagram of the synthesis of mesoporous molecular sieve TS-1 coated with silver nanoclusters. First, a TS-1 molecular sieve (mTS-1) with a mesoporous structure was prepared with the help of organic surfactants TPAOH and carbonate. Next, under ultraviolet light irradiation, the resulting silver nanoclusters were uniformly solidified on the surface of mTS-1.

[0064] The XRD patterns of samples mTS-1, AgNP / mTS-1 and Ag nanocluster / mTS-1 are shown in Figure 2. Figure 1 As shown in (b), strong characteristic peaks (7.9, 8.8, 14.8, 23.1 and 24.0°) can be clearly observed and well attributed to the pure molecular sieve TS-1 (PDF:#43-0055). At the same time, it cannot detect the diffraction peaks corresponding to Ag species on the samples AgNP / mTS-1 and Ag nanoclusters / mTS-1, which may be related to the small amount of Ag species. It is worth noting that the XRD diffraction peaks of Ag nanoclusters / mTS-1 move in the low-angle region, and the ζ potential of Ag nanoclusters / mTS-1 is much more negative than that of mTS-1, which may be because some silver atoms are incorporated into the molecular sieve framework. In addition, the negative ζ potential also indicates the successful preparation of the electron-rich catalyst.

[0065] like Figure 2 As shown in Figure a, the sample Ag nanoclusters / mTS-1 shows a regular morphology with a particle size of 200-300 nm. The TEM image also shows that the surface of the TS-1 molecular sieve is obviously covered by Ag nanoclusters ( Figure 2 (middle ac). Figure 2 The HRTEM images in the middle cd also clearly show uniformly distributed Ag nanoclusters with a particle size of less than 5 nm. In addition, the edge spacing of 0.236 nm is well attributed to the (111) plane of Ag. Figure 2The elemental mapping images in the ei show the locations of the elements Si, Ti, O, and Ag in the Ag nanocluster / mTS-1 catalyst, which is consistent with the results of TEM and HRTEM images. For the reference sample of mesoporous molecular sieve TS-1 loaded with silver nanoparticles (AgNP / mTS-1), it was found that silver nanoparticles with a particle size greater than 20 nm were highly distributed on the surface of the molecular sieve ( Fig.10 ).

[0066] The above results indicate that methanol-assisted UV-light reduction is beneficial to the formation of silver nanoclusters with smaller particle size.

[0067] CO 2 The adsorption of molecules is CO 2 The first step of light conversion, the porous structure can achieve CO 2 of enrichment. Figure 3 Figure 5 a-f shows the N of samples mTS-1, AgNP / mTS-1, and Ag nanoclusters / mTS-1. 2 Adsorption / desorption isotherms and corresponding pore size distributions.

[0068] The typical type I and type IV isotherms indicate the coexistence of microporous and mesoporous structures, respectively. 2 g -1 ) and Ag nanoclusters / mTS-1(317m 2 g -1 Interestingly, compared with mTS-1 and AgNP / mTS-1, the sample Ag nanocluster / mTS-1 is more likely to form a large mesoporous structure of 20-50 nm ( Figure 3 This not only provides a fast channel for the diffusion of substances, but also helps CO 2 Enrichment of molecules.

[0069] XPS spectra of mTS-1, AgNP / mTS-1, and Ag nanocluster / mTS-1 catalysts were investigated to study the surface chemical states of the elements, e.g. Figure 4 As shown. O1s, Ti 2p, Si 2p and Ag 3d signals were clearly observed on samples AgNP / mTS-1 and Ag nanocluster / mTS-1 ( Figure 4 (a). Figure 4 As shown in (b), the Ti2p peak shifts to a higher binding energy after modification with Ag due to the charge transfer between Ti and Ag. The O 1s spectrum can be fitted with two typical peaks at 532.8-533.2 eV and 530.5-530.7 eV ( Figure 4 c), corresponding to chemically adsorbed oxygen (O C ) and lattice oxygen (O LThe samples AgNP / mTS-1 and Ag nanocluster / mTS-1 showed abundant OC species, which means there are more oxygen vacancies, which can regulate the electronic structure of the catalyst and promote CO 2 activation. Figure 4 Figure d shows the Ag 3d XPS spectra of AgNP / mTS-1 and Ag nanocluster / mTS-1. For sample AgNP / mTS-1, the binding energies of 368.1-368.3 and 374.1-374.3 eV are assigned to Ag, respectively. 0 and Ag + Ag 3d5 / 2 and Ag 3d3 / 2 between them, indicating that the metal (Ag 0 ) and ions (Ag + Interestingly, the Ag 3d peak shifts toward higher binding energy compared with that of AgNP / mTS-1, indicating that there is a strong electron-level interaction between the Ag nanoclusters and the molecular sieve support, and the molecular sieve TS-1 binds to the adjacent Ag nanoclusters as an electron donor bond, which is likely to facilitate the transfer of photogenerated electron-hole pairs.

[0070] In addition, the valence state and coordination conditions of Ag species were studied by Ag-K edge XANES and Ag-K edge EXAFS. The normalized Ag K edge EXAFS showed that the Ag foil and Ag 2 The white line intensities of AgNP / mTS-1 and Ag nanocluster / mTS-1 are similar ( Figure 5 In a), it shows that Ag 0 and Ag + The species coexist in samples AgNP / mTS-1 and Ag nanocluster / mTS-1, which is consistent with the XPS results ( Figure 3 d). Fourier transformed Ag-KEXAFS has been used to study the coordination conditions of Ag species, such as Figure 5 As shown in (b). For the AgNP / mTS-1 and Ag nanocluster / mTS-1 samples, the characteristic peaks of Ag-Ag and Ag-O bonds are and and In addition, the Ag-Ag coordination number (CN = 2.0 ± 0.1) of Ag nanocluster / mTS-1 is lower than that of AgNP / mTS-1 (CN = 2.9 ± 0.2), and there are unsaturated dangling bonds, which makes it have a higher CO 2 Adsorption and activation properties. In addition, wavelet transform (WT) analysis was performed on the k2-weighted EXAFS signals, as shown in Figure 3 As shown in Figure c. Two strong WT signals can be observed on samples AgNP / mTS-1 and Ag nanocluster / mTS-1, one at is attributed to Ag-O coordination, while the other It was assigned as Ag-Ag coordination.

[0071] 2.2 Redox activity and CO 2 Adsorption performance

[0072] like Figure 6 As shown in (a), samples mTS-1, AgNP / mTS-1, and Ag nanocluster / mTS-1 were subjected to H 2 Programmed temperature reduction (H 2 -TPR) to study the redox activity. After Ag modification, both AgNP / mTS-1 and Ag nanocluster / mTS-1 showed obvious H 2 Especially for the sample Ag nanoclusters / mTS-1, a strong H 2 The reduction peak indicates that the presence of Ag nanoclusters makes the sample Ag nanoclusters / mTS-1 have higher redox performance. Figure 6 As shown in b, CO 2 (CO 2 -TPD). All samples showed strong CO 2 The desorption peak corresponds to CO 2 This may be related to the unique microporous and mesoporous structure of the molecular sieve. Ag nanocluster / mTS-1 has an obvious CO 2 The desorption peak indicates that due to the electron-rich structure, CO 2 will chemically bind to the catalyst surface, which helps CO 2 Activate and promote its participation in subsequent chemical reactions.

[0073] 2.3 Photoelectrochemical activity

[0074] like Figure 7 As shown in (a), all synthesized samples show good light absorption properties in the ultraviolet and visible light regions. Figure 7 There is a slight bulge in a, which is caused by the plasma effect. But their absorption edges are different. The absorption band edge of Ag nanocluster / mTS-1 is larger than that of mTS-1, AgNP / mTS-1, mTS-1, AgNP / mTS-1 and Ag nanocluster / mTS-1. The corresponding band gaps are 2.75, 2.62 and 2.57 eV respectively ( Figure 7 b). It can be concluded that the localized surface plasmon resonance induced by silver nanoclusters can improve the light absorption performance. Mott-Schottky plots were performed to determine the conduction band position, such as Figure 7As shown in c. These samples are n-type semiconductors, and the flat band potential is usually close to the conduction band. The flat band potentials of mTS-1, AgNP / mTS-1, and Ag nanocluster / mTS-1 are -0.52, -0.70, and -0.80 V (relative to NHE), respectively, so the conduction band is considered to be -0.62, -0.80, and -0.90 V (relative to NHE). The negative conductive position of Ag nanocluster / mTS-1 means that the sample Ag nanocluster / mTS-1 may have the ability to convert CO 2 Optimal activity for conversion to CO.

[0075] Photoluminescence spectroscopy (PL) analysis was performed to investigate the separation efficiency of photogenerated electron-hole pairs, such as Figure 7 As shown in Figure d. It can be clearly found that all samples show similar emission peaks at about 545 nm, but the peak intensity of Ag cluster / mTS-1 is significantly lower than that of mTS-1 and AgNP / mTS-1, proving that Ag nanoclusters can promote the separation of photogenerated electron-hole pairs. The interfacial charge transfer dynamics on the photoelectrode were also studied by EIS, as shown in Figure d. Figure 7 Figure e shows the Ag nanocluster / mTS-1 Rct The value is the smallest among all samples, indicating that Ag nanocluster / mTS-1 has a higher charge transfer efficiency than other catalysts. The charge separation efficiency can be further reflected by the photocurrent test, such as Figure 7 As shown in Figure 5, pure mTS-1 only shows a weak photocurrent signal, while samples AgNP / mTS-1 and Ag nanocluster / mTS-1 show considerable photoresponse. In particular, sample Ag nanocluster / mTS-1 shows a greatly improved photocurrent response (0.47 mA cm -2 ), showing enhanced charge separation behavior. The above results indicate that the design of silver nanocluster catalysts is indeed an effective way to improve charge transfer at the electrode / electrolyte interface.

[0076] 2.4CO 2 Photocatalytic activity of reduction

[0077] The photocatalytic CO emission of samples mTS-1, AgNP / mTS-1, and Ag nanoclusters / mTS-1 was studied under 300 W Xe irradiation using an AM 1.5G filter. 2 Restore performance. Figure 8 As shown in (a), the CO yield gradually increased with the increase of reaction time. Compared with mTS-1, the CO 2 The reduction activity was significantly enhanced. In particular, the CO production of the Ag nanocluster / mTS-1 sample reached 349 μmol g-1 within 4 h, which was higher than that of the AgNP / mTS-1 (225 μmol g -l) and mTS-1 (76 μmol g -1 ) by 4.59 times. The significant enhancement of the photocatalytic activity of Ag nanoclusters / mTS-1 depends on its high CO 2 Adsorption capacity, strong light absorption ability and fast electron transfer efficiency. Figure 8 Figure b shows the five cycle performances of the sample Ag nanocluster / mTS-1, and it can be found that the CO production remains basically unchanged. In addition, after 5 cycles, the XRD pattern and TEM image of the sample Ag nanocluster / mTS-1 did not change significantly ( Fig.11 and Fig.12 ), indicating that it has high photochemical stability. Figure 8 As shown in c, the content of silver nanoclusters has an effect on the photocatalytic CO 2 As shown in Table 1, the sample Ag nanocluster / mTS-1 containing 2 wt% Ag has the highest CO yield (96 μmol h -1 g -1 ), which is also superior to the reported photocatalysts. In contrast, lower Ag content may provide fewer active sites, while higher Ag may block the pores, resulting in lower CO production.

[0078] According to the results of UV-visible spectrum and Mott-Schottky plot ( Figure 7 (b) and (c) in Figure 7, the valence band potential and conduction band potential of mTS-1, AgNP / mTS-1 and Ag nanocluster / mTS-1 are shown in Figure 8 Compared with mTS-1 and AgNP / mTS-1, Ag nanocluster / mTS-1 has a narrower band gap and a more negative conduction band potential, which is more suitable for photocatalytic reduction of CO 2 , thereby promoting CO 2 Converted into CO.

[0079] Table 1 CO of related catalysts 2 Comparison of photocatalytic reduction performance

[0080]

[0081]

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[0088] The photocatalytic CO 2 Restore route( Fig. 9 ab). At 1630cm -1 There is a significant reaction at the *CO species, which indicates that CO 2 The samples AgNP / mTS-1 and Ag nanocluster / mTS-1 have been converted into CO at 1249 and 1251 cm -1 Some broad peaks were observed at 3 - In addition, an additional peak at 1589 cm -1 The bidentate carbonate (b-CO 3 2- ) and 1231cm -1 This is related to the ability of the photocatalyst to adsorb water vapor. In addition, there is a difference in the *CO peak intensity between the samples AgNP / mTS-1 and Ag nanoclusters / mTS-1, and the intensity of the *CO peak is slightly higher than that of the sample Ag nanoclusters / mTS-1. This is because the smaller Ag nanoclusters have a suitable adsorption strength for CO, which facilitates the desorption of CO and thus increases the amount of *CO. It is worth noting that the presence of silver nanoclusters can be related to the CO 3 2- and HCO 3- Ionic interactions promote the binding between reactants and catalysts, increasing CO 2 photocatalytic reduction activity.

[0089] Based on the above experimental results and discussions, the photocatalytic CO 2 Possible mechanisms of reduction, such as Fig. 9 As shown in Figure c, due to the rich mesoporous structure and Ag nanoclusters, the sample Ag nanoclusters / mTS-1 has a high CO 2 Adsorption capacity, which is the reduction of CO 2 At the same time, the electron-rich Ag nanoclusters / mTS-1 can promote the adsorption of CO 2 Under the irradiation of UV-visible light, the photogenerated electrons are excited from the valence band of the photocatalyst to the conduction band, and then the electrons and holes are effectively separated by the built-in electric field formed at the interface between the silver nanoclusters and the molecular sieve.

[0090] In addition, the negative conduction band potential of the Ag nanocluster / mTS-1 sample is also favorable for CO 2 More importantly, the localized surface plasmon resonance induced by silver nanoclusters can not only improve the light absorption performance, but also excite the electrons on the surface of silver nanoclusters to participate in the photocatalytic reaction. In the photocatalytic process, on the one hand, silver nanoclusters can be used as electron donors to increase the number of photogenerated carriers. On the other hand, silver nanoclusters can also act as electron acceptors to promote the effective separation of photogenerated carriers, thereby improving the photocatalytic efficiency. In addition, Ag nanoclusters as active sites have a suitable adsorption strength for CO and increase the amount of *CO ( Fig. 9 b), thereby increasing CO 2 The photocatalytic conversion rate to CO.

[0091] Summarize:

[0092] The present invention designs a TS-1 molecular sieve encapsulated by silver nanoclusters for photocatalytic CO 2 Due to the unique mesoporous structure and the formation of Ag nanoclusters, the sample Ag nanoclusters / mTS-1 showed excellent CO 2 High adsorption capacity, especially remarkable chemical adsorption of CO 2 , which helps the subsequent activation. In addition, the design of electron-rich states and oxygen-rich vacancy defects can promote CO 2 The presence of silver nanoclusters gives the catalyst a narrower band gap and a more negative conduction band potential, showing its ability to absorb light and reduce CO 2 In addition, the interface between the molecular sieve and the silver nanoclusters also promotes the separation of the photogenerated carriers. More importantly, the Ag nanoclusters have a suitable adsorption strength for CO and increase the amount of *CO, especially the localized surface plasmon resonance induced by the Ag nanoclusters jointly enhances the CO 2 The photocatalytic conversion of CO to 96 μmol h-1 g -1 High and stable CO yield.

[0093] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing a plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst, characterized in that: include: Step 1: Synthesize mesoporous molecular sieve TS-1 powder; Step 2: The mesoporous molecular sieve TS-1 and CH3OH are mixed to prepare a suspension, and the AgNO3 aqueous solution is injected into the suspension. After ultraviolet irradiation, filtration, washing and freeze-drying, the plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst is obtained.

2. The method for preparing the plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst according to claim 1, characterized in that: Step 1 includes: Step 1.1: Mix tetrapropylammonium hydroxide and deionized water; Step 1.2: Add KCl, Na2CO3, H2SiO3 and Ti(SO4)2 to the mixed solution of step 1.1 and stir at room temperature to obtain a precursor solution; Step 1.3: aging the precursor solution and then transferring it to the reactor for hydrothermal treatment; Step 1.4: The product of the hydrothermal treatment is filtered, washed with deionized water, dried, and then heat-treated to remove the organic agent, and then the powdered mesoporous molecular sieve TS-1 is collected.

3. The method for preparing the plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst according to claim 2, characterized in that: In step 1.1, the amount of tetrapropylammonium hydroxide added is 10.4 g, and the amount of deionized water is 8 g.

4. The method for preparing the plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst according to claim 3, characterized in that: In step 1.2, KCl is 0.14 g, Na2CO3 is 0.09 g, H2SiO3 is 50 mmol and Ti(SO4)2 is 2 mmol.

5. The method for preparing the plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst according to claim 4, characterized in that: In step 1.3, the aging conditions of the precursor solution are: aging at 40°C for 12 hours; and the hydrothermal treatment conditions are: hydrothermal treatment at 160°C for 24 hours.

6. The method for preparing the plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst according to claim 5, characterized in that: In step 1.4, the heat treatment conditions are: calcination at 550°C for 8 hours.

7. The plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst prepared by the method according to any one of claims 1 to 6.

8. Use of the plasma silver nanocluster-coated mesoporous molecular sieve TS-1 photocatalyst as claimed in claim 7 for preparing a catalytic material for photocatalytic conversion of CO2 to CO.

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