PtPd bimetallic modified defect type cadmium sulfide photocatalyst, and preparation method and application thereof

Abstract

The application discloses a PtPd bimetal modified defect type cadmium sulfide photocatalyst and a preparation method and application thereof. 1‑x S, step 2, introducing a Pt source by using an impregnation reduction method, and step 3, introducing a Pd source by using the impregnation reduction method. The cadmium vacancy and the PtPd bimetal are cooperatively modified, the side reaction of CO desorption is inhibited, the traditional CO desorption path of a single metal is broken, the high selective conversion of CO2 to CH4 is realized through deep hydrogenation, and the catalyst structure is stable and the catalytic life is long.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, and in particular to a PtPd bimetallic modified defective cadmium sulfide photocatalyst, its preparation method, and its application in the photocatalytic reduction of carbon dioxide to methane. Background Technology

[0002] With the continuous advancement of global industrialization, the concentration of carbon dioxide (CO2) in the atmosphere is constantly rising, and the resulting greenhouse effect and climate change are becoming major environmental challenges that human society urgently needs to address. Photocatalytic CO2 reduction technology can convert the greenhouse gas CO2 into high-value-added fuels and chemicals such as methane (CH4) and carbon monoxide (CO), which is an important pathway to achieve solar-to-chemical energy conversion and carbon cycle. Cadmium sulfide (CdS) has become a photocatalytic material with great application potential for CO2 reduction due to its suitable band gap, good visible light response, and simple preparation. However, pure CdS suffers from severe recombination of photogenerated carriers, weak CO2 adsorption and activation capacity, and insufficient surface hydrogenation sites, resulting in products mainly consisting of the two-electron reduction product CO, making it difficult to selectively generate the deeply hydrogenated product CH4, thus limiting its practical application.

[0003] Introducing lattice defects (such as cadmium vacancies) can modulate the electronic structure of the CdS surface, providing anchoring sites for metal sites and optimizing intermediate adsorption strength, which is an effective means to improve catalytic selectivity and activity. Furthermore, introducing noble metals (such as Pt or Pd) as co-catalysts can effectively promote the migration and separation of photogenerated electrons. However, conventional single-metal modification systems often suffer from limitations in their single-function approach, resulting in low conversion efficiency for CO2 to CH4 via the traditional CO desorption pathway.

[0004] Therefore, developing a PtPd / CdS photocatalyst that can be prepared under mild conditions and can efficiently and selectively reduce CO2 to CH4 via a new pathway using a bimetallic synergistic effect is of great significance for reducing catalyst preparation costs, carbon emission reduction, and clean energy conversion. Summary of the Invention

[0005] The purpose of this invention is to address the technical deficiencies in the prior art by providing a PtPd bimetallic modified defective cadmium sulfide photocatalyst, its preparation method, and its application in the photocatalytic reduction of carbon dioxide to methane.

[0006] The technical solution adopted to achieve the purpose of this invention is: A method for preparing a PtPd bimetallic modified defect-type cadmium sulfide photocatalyst includes the following steps: Step 1, Preparation of defect carrier: A solution A is prepared by dissolving a cadmium source and an oxidant in an acidic aqueous solution, and a solution B is prepared by dissolving a sulfur source in deionized water. Solutions A and B are stirred until homogeneous to obtain a mixed solution. The mixed solution is then transferred to a reaction vessel for a hydrothermal reaction. After the reaction is complete, the precipitate is collected, washed, and vacuum dried to obtain a cadmium sulfide carrier (Cd) rich in cadmium vacancy defects. 1-x S; Step 2, import the Pt source: The cadmium sulfide carrier Cd prepared in step 1 1-x S is dispersed in deionized water, and a platinum precursor solution is added. After mixing thoroughly, the mixture is heated and stirred to impregnate, adsorb, and reduce in situ, thus anchoring the adsorbed Pt stably to Cd. 1-x Pt-Cd was obtained by washing and vacuum drying on the cadmium vacancies on the S surface. 1-x S intermediate.

[0007] Step 3, introduce the Pd source: The Pt-Cd prepared in step 2 1-x The S intermediate was dispersed in a solvent, and a palladium precursor solution was added. After mixing thoroughly, the mixture was heated, stirred, impregnated, and reduced in situ. Following washing and vacuum drying, a defect-type cadmium sulfide-supported PtPd bimetallic photocatalyst was finally obtained. In the above technical solution, in step 1, the cadmium source is selected from one of cadmium chloride, cadmium nitrate, cadmium acetate or cadmium sulfate, the sulfur source is one of sodium sulfide, thioacetamide or thiourea, and the molar ratio of cadmium source to sulfur source is (0.2~1):1; the oxidant is 3~30wt.% hydrogen peroxide, and the pH of the acidic aqueous solution is 1.

[0008] In the above technical solution, in step 2, the platinum precursor is chloroplatinic acid solution (H2PtCl6). In the above technical solution, in step 3, the palladium precursor solution is an ethanol solution of palladium chloride (PdCl2), and the solvent is deionized water or ethanol.

[0009] In the above technical solution, in steps 2 and 3, the temperature for heating, stirring, and impregnation is 65~95℃, and the time is 0.5~3 hours.

[0010] In the above technical solution, in steps 2 and 3, the reducing agent for in-situ reduction is ascorbic acid, and the reduction time is 0.5 to 3 hours.

[0011] In the above technical solution, steps 2 and 3 involve drying under vacuum at 50-80°C overnight. This step aims to enhance the interaction between the metal and the support, thereby improving the structural stability of the catalyst.

[0012] Another aspect of the present invention includes a PtPd bimetallic modified defect-type cadmium sulfide photocatalyst obtained based on the preparation method described above.

[0013] In the above technical solution, in the PtPd bimetallic modified defect-type cadmium sulfide photocatalyst, the mass ratio of Pt to Pd elements is (1~5):(1~10).

[0014] Another aspect of the present invention includes the application of the PtPd bimetallic modified defective cadmium sulfide photocatalyst in the photocatalytic reduction of carbon dioxide to methane.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses a hydrothermal method combined with an impregnation reduction method to prepare PtPd bimetallic modified defect-type cadmium sulfide photocatalysts. The process is simple, the reaction conditions are mild, and it significantly improves the efficiency of photogenerated carrier separation and interfacial charge transport, thereby greatly enhancing the photocatalytic activity.

[0016] 2. By synergistic modification of cadmium vacancies and PtPd bimetals, the electronic structure and adsorption sites on the surface of cadmium sulfide can be effectively regulated, enhancing the stability of CO2 activation and key hydrogenation intermediates, suppressing CO desorption side reactions, breaking the traditional CO desorption pathway of single metals, and achieving highly selective conversion of CO2 to CH4 through deep hydrogenation.

[0017] 3. The PtPd bimetallic modified defective cadmium sulfide photocatalyst prepared by this invention has a stable structure and long catalytic lifetime. It can efficiently drive the reduction of CO2 to CH4 under visible light, and has excellent catalytic performance and application prospects. Attached Figure Description

[0018] Figure 1 The present invention is based on CdS and Cd. 1-x S,Pt-Cd 1-x S,Pd-Cd 1-x S, Pt / Pd-Cd 1-x X-ray powder diffraction pattern of S; Figure 2 For the present invention Cd 1-x S,Pt-Cd 1-x S,Pd-Cd 1-x S, Pt / Pd-Cd 1-x Electron paramagnetic resonance spectrum of S; Figure 3 The present invention is a Pt / Pd-Cd 1-x Scanning electron microscope image of S; Figure 4 The present invention is a Pt / Pd-Cd 1-x Transmission electron microscope image of S, and aberration-corrected scanning transmission electron microscope (AC-STEM) and elemental mapping (EDS) image; Figure 5 The present invention is based on CdS and Cd. 1-x S,Pt-Cd 1-x S,Pd-Cd 1-x S, Pt / Pd-Cd 1-x Comparison of CO and CH4 yields of S; Figure 6 The present invention is based on CdS and Cd. 1-x S,Pt-Cd 1-x S,Pd-Cd 1-x S, Pt / Pd-Cd 1-x CH4 generation rate plot of S; Figure 7 The present invention is a Pt / Pd-Cd 1-x Photocatalytic CO2 reduction stability test diagram of S; Figure 8 The present invention is Pt-Cd 1-x S,Pd-Cd 1-x S, Pt / Pd-Cd 1-x In-situ diffuse reflectance infrared Fourier transform spectrum of S. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0020] Example 1 A PtPd bimetallic modified defect-type cadmium sulfide photocatalyst is prepared by the following steps: Step 1: Dissolve 3.5 mmol CdCl2·2.5H2O and 0.135 mL 30% H2O2 in 20 mL of acidic aqueous solution with pH=1 to obtain solution A. Dissolve 8 mmol Na2S·9H2O in 20 mL of deionized water to obtain solution B. Slowly add solution A to solution B with rapid stirring to obtain a suspension. Transfer the suspension to a PTFE-lined stainless steel autoclave and heat at 160 °C for 1080 min. After cooling to room temperature, wash the suspension three times with deionized water and then transfer it to a vacuum drying oven. Vacuum dry overnight at 60 °C. The resulting sample is denoted as CdCl2·2.5H2O. 1-x S.

[0021] Step 2, 80 mg Cd 1-xS was dispersed in 10 mL of deionized water, and 3% H₂PtCl₆ solution (10 mg / mL) was added. The mixture was then stirred in an oil bath at 85 °C for 1.5 h, followed by the addition of 160 mg of ascorbic acid and stirring for another 0.5 h. The product was filtered, washed several times with deionized water, and dried overnight under vacuum at 60 °C. The resulting sample was designated Pt-Cd. 1-x S.

[0022] Step 3, add 40 mg of Pt-Cd 1-x S was dispersed in 5 mL of deionized water, and 5% PdCl2 ethanol solution (1 mg / mL) was added. Then, the mixture was stirred in an oil bath at 85 °C for 1.5 h, 80 mg of ascorbic acid was added, and the mixture was stirred for another 0.5 h. The product was filtered and washed several times with deionized water and ethanol, and dried overnight under vacuum at 60 °C to obtain a PtPd bimetallic modified defect-type cadmium sulfide photocatalyst.

[0023] Comparative Example 1 Preparation of CdS: 3.5 mmol CdCl₂·2.5H₂O and 3.5 mmol Na₂S·9H₂O were dissolved separately in 20 mL of deionized water. The two solutions were mixed with rapid stirring to obtain a suspension. The suspension was transferred to a PTFE-lined stainless steel autoclave and heated at 160 °C for 1080 min. After cooling to room temperature, the suspension was washed three times with deionized water and then transferred to a vacuum drying oven. It was vacuum dried overnight at 60 °C. The resulting sample was designated CdS.

[0024] Comparative Example 2 Preparation of Pd-Cd 1-x S: 80 mg Cd 1-x S was dispersed in 10 mL of deionized water, and 5% PdCl2 ethanol solution (10 mg / mL) was added. The mixture was then stirred in an oil bath at 85 °C for 1.5 h, followed by the addition of 160 mg of ascorbic acid and stirring for another 0.5 h. The product was filtered, washed several times with deionized water, and dried overnight under vacuum at 60 °C. The resulting sample was designated Pd-Cd. 1-x S.

[0025] Comparative Example 3 Preparation of Pt-Cd 1-x S: 80 mg Cd 1-xS was dispersed in 10 mL of deionized water, and 3% H₂PtCl₆ solution was added. The mixture was then stirred in an oil bath at 85 °C for 1.5 h, followed by the addition of 160 mg of ascorbic acid and stirring for another 0.5 h. The product was filtered, washed several times with deionized water, and dried overnight under vacuum at 60 °C. The resulting sample was designated Pt-Cd. 1-x S.

[0026] Figure 1 The CdS and CdS prepared in the embodiments and comparative examples of this invention are shown. 1-x S,Pt-Cd 1-x S,Pd-Cd 1-x S, Pt / Pd-Cd 1- x The X-ray powder diffraction pattern of CdS shows that a mixed crystalline material of cubic CdS and hexagonal CdS was prepared. 1-x The S material exhibited typical diffraction peaks of cubic CdS (111), (200), (220), and (311) crystal planes and (100), (002), and (101) crystal planes of hexagonal CdS. After loading Pt and Pd, it showed similar characteristics to Cd. 1-x Compared to S, the X-ray powder diffraction pattern showed almost no significant change, which is attributed to the lower metal loading.

[0027] Figure 2 For Cd 1-x S,Pt-Cd 1-x S,Pd-Cd 1-x S, Pt / Pd-Cd 1-x Electron paramagnetic resonance (EPR) spectra of S. Signals with g-factors of 1.99 and 2.03 confirm the presence of Cd. 1-x The presence of Cd vacancies in S. The introduction of Pt and Pd metals resulted in a decrease in signal intensity allocated to Cd vacancies, indicating that individual Pt and Pd atoms occupied and partially covered the Cd vacancy sites. Simultaneous loading of Pt and Pd metals resulted in an even greater decrease in signal intensity, suggesting that the synergistic effect of the two metals formed a strong electron acceptor interface, further accelerating electron migration and reducing the number of unpaired electrons at the vacancies.

[0028] Figure 3 Pt / Pd-Cd at different scales 1-x Scanning electron microscopy images of S, characterization results show that Pt / Pd-Cd 1-x The S material possesses a highly wrinkled, porous microstructure with an irregular nanoparticle morphology, indicating a large specific surface area. This large specific surface area helps increase the number of surface active sites, enhancing CO2 adsorption capacity and light capture efficiency.

[0029] Depend on Figure 4Transmission electron microscopy (TEM) images show that the defective cadmium sulfide support possesses a highly transparent nanosheet structure, and the lattice fringes correspond to the standard crystal planes of CdS. Aberration-corrected electron microscopy (AC-STEM) and elemental mapping analysis revealed that Pt and Pd elements coexist in a highly co-located manner at the edges and defect sites on the material surface, and are uniformly dispersed in the form of ultrafine sub-nano clusters without large particle aggregation. This indicates that the mild liquid-phase in-situ reduction method successfully anchored the Pt and Pd bimetals firmly at the defect sites, forming spatially adjacent bimetallic synergistic catalytic centers.

[0030] Application Example 1 Photocatalytic carbon dioxide reduction performance test Test conditions: The photocatalytic reduction performance of CO2 was tested under the conditions of a closed gas system, atmospheric pressure 80 kPa, and ambient temperature 278 K. The reactor was equipped with a quartz gas-solid phase reaction platform approximately 5 cm high. Two CO2 inlets / outlets were located at the top of the reactor for the introduction of high-purity CO2 and the collection of gaseous products, while two condensate inlets / outlets were located at the bottom to maintain a constant temperature. First, 10 mg of photocatalyst was uniformly dispersed on glass fiber filter paper and placed together with the gas-solid phase reaction platform in a closed quartz reactor (Perfectlight PQ256 50 mL) containing 5 mL of deionized water. The system was first evacuated to below 1 kPa, then purged with 80 kPa of high-purity CO2 gas. This process was repeated twice to remove impurities from the system. The reactor was placed under a 300 W xenon lamp light source, connected to the condensate system to maintain a constant temperature, and the automatic gas chromatography injection program of the trace gas analysis system (Perfectlight Labsola 6A) was started. The reaction was carried out for 4 hours, with reaction products collected every 1 hour.

[0031] Figure 5 The present invention is based on CdS and Cd. 1-x S,Pt-Cd 1-x S,Pd-Cd 1-x S, Pt / Pd-Cd 1-x A comparison chart of CO and CH4 yields of S. (See figure) Figure 5 As shown in the figure, experiments revealed that the CO and CH4 formation rates of CdS were low. Introducing Cd vacancies improved the CO formation rate, but the CH4 yield did not improve significantly. With the introduction of Pt and Pd single metals, the CO yield decreased significantly, while the CH4 yield increased, achieving efficient conversion of CO to CH4. Compared to Pt-Cd... 1-x S and Pd-Cd 1-x S single-metal system, the Pt / Pd-Cd constructed in this invention 1-xThe CH4 yield of the S bimetallic co-modified catalyst far exceeds the simple sum of the yields of the two monometallic systems mentioned above, while the CO yield is significantly suppressed to a lower level, proving that Pt and Pd have a significant synergistic catalytic effect, thereby efficiently guiding the CO2 reduction reaction pathway to CH4.

[0032] Figure 6 CdS, Cd 1-x S,Pt-Cd 1-x S,Pd-Cd 1-x S, Pt / Pd-Cd 1-x CH4 generation rate plot of S. (See diagram) Figure 6 As shown, during the 4-hour photoreaction process, Pt / Pd-Cd 1-x The total CH4 yield of S reached 23.9 μmol / g, which is 119.5 times that of CdS (0.2 μmol / g) and CdS (0.2 μmol / g). 1-x 14.9 times that of S (1.6 μmol / g), Pt-Cd 1-x 6.0 times that of S (4.0 μmol / g), Pd-Cd 1-x It is 2.7 times that of S (9.0 μmol / g).

[0033] Application Example 2 The visible light catalytic CO2 reduction activity experiment of Pt / Pd-Cd according to Application Example 1 1-x S underwent a three-cycle test: after each reaction, the catalyst was filtered, dried, and recovered before the next reaction was carried out. This process was repeated three times to test its photocatalytic CO2 reduction stability. The results are as follows: Figure 7 .

[0034] Figure 7 Pt / Pd-Cd 1-x The graph shows the photocatalytic CO2 reduction stability of the S material. As shown in the figure, after three recycling cycles, the material still maintains good photocatalytic performance, indicating that it has good catalytic stability.

[0035] Real-time monitoring of photocatalytic reaction intermediates using in-situ diffuse reflectance infrared spectroscopy, such as Figure 8 As shown. The results show that the single-metal control group Pt-Cd 1-x S and Pd-Cd 1-x In the reaction, only adsorbed CO2* and the activated product HCO3 can be detected by S. - HCOO - The presence of COOH* and CO* intermediates associated with two-electron reduction indicates that the reaction pathway on the single-metal surface remains at the CO generation stage due to insufficient hydrogenation capacity. In contrast, the Pt / Pd-Cd prepared in this invention... 1-xThe S bimetallic catalyst exhibited specific and strong characteristic signals of the key deep hydrogenation intermediates methoxy (*CH3O) and adsorbed methyl (*CH3) during the reaction. This comparative result strongly confirms that the Pt / Pd bimetallic synergistic site constructed in this invention breaks the traditional single-metal CO desorption pathway, successfully driving the reaction to switch to an electron-based deep hydrogenation pathway, achieving highly selective and high-yield conversion of CO2 to CH4.

[0036] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a PtPd bimetallic modified defect-type cadmium sulfide photocatalyst, characterized in that, Includes the following steps: Step 1, Preparation of defect carrier: The cadmium source and oxidant are dissolved in an acidic aqueous solution to obtain solution A, and the sulfur source is dissolved in deionized water to obtain solution B. Solutions A and B are stirred evenly to obtain a mixed solution. The mixed solution was transferred to a reaction vessel for hydrothermal reaction; after the reaction was completed, the precipitate was collected, washed, and vacuum dried to obtain cadmium sulfide carrier Cd rich in cadmium vacancy defects. 1-x S; Step 2, import the Pt source: The cadmium sulfide carrier Cd prepared in step 1 1-x S is dispersed in deionized water, and a platinum precursor solution is added. After mixing thoroughly, the mixture is heated and stirred to impregnate and adsorb the Pt, allowing for in-situ reduction, thus stably anchoring the adsorbed Pt to Cd. 1-x Pt-Cd was obtained by washing and vacuum drying on the cadmium vacancies on the S surface. 1-x S intermediate; Step 3, introduce the Pd source: The Pt-Cd prepared in step 2 1-x The S intermediate is dispersed in a solvent, and a palladium precursor solution is added. After mixing evenly, the mixture is heated, stirred, impregnated, and reduced in situ. After washing and vacuum drying, a defective cadmium sulfide-supported PtPd bimetallic photocatalyst is finally obtained.

2. The preparation method of the PtPd bimetallic modified defect-type cadmium sulfide photocatalyst as described in claim 1, characterized in that, In step 1, the cadmium source is selected from one of cadmium chloride, cadmium nitrate, cadmium acetate, or cadmium sulfate; the sulfur source is one of sodium sulfide, thioacetamide, or thiourea; the molar ratio of cadmium source to sulfur source is (0.2~1):1; the oxidant is 3~30 wt.% hydrogen peroxide; and the pH of the acidic aqueous solution is 1.

3. The preparation method of the PtPd bimetallic modified defect-type cadmium sulfide photocatalyst as described in claim 1, characterized in that, In step 2, the platinum precursor is a chloroplatinic acid solution.

4. The preparation method of the PtPd bimetallic modified defect-type cadmium sulfide photocatalyst as described in claim 1, characterized in that, In step 3, the palladium precursor solution is an ethanol solution of palladium chloride, and the solvent is deionized water or ethanol.

5. The preparation method of the PtPd bimetallic modified defect-type cadmium sulfide photocatalyst as described in claim 1, characterized in that, In steps 2 and 3, the heating and stirring impregnation temperature is 65~95℃, and the time is 0.5~3 hours.

6. The preparation method of the PtPd bimetallic modified defect-type cadmium sulfide photocatalyst as described in claim 1, characterized in that, In steps 2 and 3, the reducing agent for in-situ reduction is ascorbic acid, and the reduction time is 0.5 to 3 hours.

7. The preparation method of the PtPd bimetallic modified defect-type cadmium sulfide photocatalyst as described in claim 1, characterized in that, In steps 2 and 3, the drying conditions are vacuum drying at 50-80°C overnight. This step aims to enhance the interaction between the metal and the support, thereby improving the structural stability of the catalyst.

8. A PtPd bimetallic modified defect-type cadmium sulfide photocatalyst obtained by the preparation method according to any one of claims 1-7.

9. The PtPd bimetallic modified defect-type cadmium sulfide photocatalyst as described in claim 8, characterized in that, In the PtPd bimetallic modified defect-type cadmium sulfide photocatalyst, the mass ratio of Pt to Pd elements is (1~5):(1~10).

10. The application of the PtPd bimetallic modified defective cadmium sulfide photocatalyst as described in claim 8 in the photocatalytic reduction of carbon dioxide to methane.

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