CdS-TiO2-Ag ternary composite photocatalyst and method for preparing ethyl acetate from polylactic acid driven by visible light of CdS-TiO2-Ag ternary composite photocatalyst

Abstract

The invention belongs to the technical field of photocatalysis, waste recycling and green chemistry, and particularly relates to a CdS-TiO2-Ag ternary composite photocatalyst and a method for preparing ethyl acetate from polylactic acid driven by visible light of the CdS-TiO2-Ag ternary composite photocatalyst. The preparation method comprises the following steps: dissolving chromic nitrate and thiourea in ethylenediamine, carrying out a hydrothermal reaction to prepare CdS nanorods, dispersing the CdS nanorods in deionized water, adding silver nitrate and TiO2 nanoparticles, and finally adding sodium borohydride, and carrying out in-situ reduction deposition to prepare the CdS-TiO2-Ag ternary composite photocatalyst with a heterojunction structure and an efficient charge separation interface. According to the present invention, the method has characteristics of simple process, easy operation, and combination of the high quality reaction conditions, provides significant advantages and beneficial effects in the preparation of ethyl acetate through the solid PLA light reforming, realizes the green and environmentally-friendly waste recycling, and the catalyst maintains the high stability and the reusability in the multiple cycle experiments, and has good industrial application potential.

Description

Technical Field

[0001] This invention belongs to the fields of photocatalysis, waste resource utilization and green chemistry, specifically relating to a CdS-TiO2-Ag ternary composite photocatalyst and a visible light-driven method for preparing ethyl acetate from polylactic acid. Background Technology

[0002] Global plastic production has surged, particularly of biodegradable polylactic acid (PLA), whose waste accumulation has posed a serious environmental challenge. While PLA is biodegradable, its degradation rate is very slow in major polluting environments such as aquatic systems, often leading to the formation and accumulation of microplastics, posing a severe threat to ecosystems. Therefore, a sustainable waste recycling strategy is urgently needed. Current PLA waste management methods, such as landfill and incineration, incur significant environmental costs. Chemical recycling methods (such as hydrolysis and pyrolysis) typically rely on high temperatures or corrosive chemicals and are costly and uneconomical.

[0003] Existing PLA waste treatment methods suffer from severe environmental pollution (landfill / incineration) or excessive costs (traditional chemical methods), and are difficult to directly and efficiently convert solid PLA into high-value chemicals under mild conditions. There is an urgent need to develop a green, efficient, and low-energy-consumption solution: a visible light-driven photo-reforming method to directly convert solid PLA waste into the high-value chemical solvent ethyl acetate, thereby achieving waste resource recovery and solving the microplastic pollution problem. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a CdS-TiO2-Ag ternary composite photocatalyst and a visible light-driven method for preparing ethyl acetate from polylactic acid. In this invention, CdS nanorods are prepared by hydrothermal reaction of chromium nitrate and thiourea dissolved in ethylenediamine. These nanorods are then dispersed in deionized water, followed by the addition of silver nitrate and TiO2 nanoparticles. Finally, sodium borohydride is added for in-situ reduction deposition to obtain a CdS-TiO2-Ag ternary composite photocatalyst with a heterojunction structure possessing a highly efficient charge separation interface. Combined with optimal reaction conditions, this photocatalyst exhibits significant advantages and beneficial effects in the photoreforming of solid polylactic acid (PLA) to prepare ethyl acetate, achieving green and environmentally friendly waste resource utilization. The catalyst maintains high stability and reusability in multiple cycle experiments, demonstrating good potential for industrial application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for preparing a CdS-TiO2-Ag ternary composite photocatalyst, the method comprising the following steps: (1) Dissolve cadmium nitrate and thiourea in ethylenediamine, stir at room temperature and heat to react, take the precipitate, wash and dry to obtain CdS nanorods; (2) CdS nanorods were dispersed in deionized water, AgNO3 solution and TiO2 nanoparticle dispersion were added, and the mixture was stirred. Under ice-water bath conditions (the reduction process was carried out in an ice-water bath to precisely control the size and dispersion of Ag nanoparticles), sodium borohydride solution was added dropwise to the mixture, and the mixture was stirred continuously to complete the in-situ reduction and deposition of Ag nanoparticles. The deposit was collected, washed, and dried to obtain the CdS-TiO2-Ag ternary composite photocatalyst.

[0006] Further, in step (1), the molar ratio of cadmium nitrate and thiourea is 1:0.1-1:10.

[0007] Furthermore, in step (1), the stirring time is 30 min.

[0008] Further, in step (1), the heating reaction temperature is 100-200 °C, and the heating reaction time is 12-96 h. Ethylenediamine is used as a solvent to prepare CdS host materials with nanorod morphology.

[0009] Furthermore, in step (1), the drying temperature is 60 °C.

[0010] Furthermore, in step (2), the TiO2 nanoparticles are anatase TiO2 nanoparticles with a particle size of approximately 5–10 nm.

[0011] Further, in step (2), the concentration of the AgNO3 solution is 20 μM, and the concentration of the TiO2 nanoparticle dispersion is 20 μM.

[0012] Further, in step (2), the concentration of the sodium borohydride solution is 0.01 M.

[0013] A second aspect of the present invention provides a CdS-TiO2-Ag ternary composite photocatalyst prepared by the above-described preparation method.

[0014] A third aspect of this invention provides a method for preparing ethyl acetate from polylactic acid under visible light driven by the above-mentioned CdS-TiO2-Ag ternary composite photocatalyst, comprising the following steps: CdS-TiO2-Ag ternary composite photocatalyst was dispersed in an ammonia solution, polylactic acid was added, and ethyl acetate was prepared by visible light irradiation driven by the reaction under an inert gas atmosphere and constant temperature and pressure conditions.

[0015] Furthermore, the polylactic acid has a molecular weight of 10,000-100,000 and a particle size of 1-10 mm.

[0016] Furthermore, the inert gas is N2.

[0017] Furthermore, the isothermal and pressure control is maintained at a temperature of 25 °C and a pressure of 1.0 bar to achieve efficient and selective conversion of ethyl acetate.

[0018] Furthermore, the visible light has a wavelength > 420 nm and an intensity of 150 mW / cm². 2 .

[0019] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a CdS-TiO2-Ag ternary composite photocatalyst and a visible light-driven method for preparing ethyl acetate from polylactic acid (PLA). The invention involves a hydrothermal reaction of chromium nitrate and thiourea dissolved in ethylenediamine to obtain CdS nanorods, which are then dispersed in deionized water. Silver nitrate and TiO2 nanoparticles are added, followed by in-situ reduction deposition with sodium borohydride to obtain a CdS-TiO2-Ag ternary composite photocatalyst with a heterojunction structure possessing a highly efficient charge separation interface. Combined with optimal reaction conditions, this photocatalyst exhibits significant advantages and beneficial effects in the photoreforming of solid PLA to prepare ethyl acetate, achieving green and environmentally friendly waste resource utilization. The catalyst maintains high stability and reusability in multiple cycle experiments, demonstrating good potential for industrial application.

[0020] Specifically, the present invention has the following advantages: (1) The core advantage of this invention lies in its ultra-high conversion efficiency and product yield: under optimized nitrogen atmosphere and visible light irradiation conditions, the yield of the target product ethyl acetate is as high as 21.11 mmol g. cat . -1 (20 h) Compared to a single CdS catalyst, the yield increased by approximately 8 times. Simultaneously, this catalyst exhibits extremely rapid digestion of solid PLA, achieving a PLA digestion rate of up to 92.3% within 5 h.

[0021] (2) This superior performance stems from the excellent photoelectric properties brought about by the catalyst structure: the composite material integrates the visible light absorption capacity of CdS, the efficient charge transport characteristics of TiO2, and the localized surface plasmon resonance (LSPR) effect of Ag nanoparticles. Structural characterization shows that its visible light absorption capacity is significantly enhanced, the photoluminescence (PL) intensity is the lowest, and the transient photocurrent response is the highest (approximately ~3 µA / cm). 2The smallest semicircle radius in the electrochemical impedance spectroscopy (EIS) demonstrates that the CdS-TiO2-Ag composite catalyst has the highest visible light utilization and charge separation and transport efficiency.

[0022] (3) Furthermore, this invention achieves green and environmentally friendly waste resource utilization: in an aqueous medium, solid waste PLA is directly converted into high-value-added chemical ethyl acetate by visible light, meeting the requirements of sustainable chemistry. The catalyst maintains high stability and reusability in multiple cycle experiments and has good potential for industrial application. Attached Figure Description

[0023] Figure 1 The diagram shows the preparation process flow chart and SEM image of the CdS-TiO2-Ag ternary composite photocatalyst of this invention. In the diagram, A is the preparation process flow chart of the CdS-TiO2-Ag ternary composite photocatalyst, B is the SEM image of CdS nanotubes, C is the TEM image of CdS-TiO2-Ag nanotubes, D is the HR-TEM image of CdS-TiO2-Ag nanotubes, E is the HR-TEM image of CdS-TiO2-Ag nanotubes, F is the TEM image of CdS-TiO2-Ag nanotubes, and G is the elemental mapping diagram of the corresponding TEM image.

[0024] Figure 2 The image shows an XPS comparison of the CdS-TiO2-Ag ternary composite photocatalyst in Example 1 and pure CdS, where A represents Cd 3d, B represents S 2p, and C represents Ag 3d and Ti 2p.

[0025] Figure 3 The figures show a comparison of the photoluminescence (PL) spectra and transient photocurrents of different photocatalysts. In the figure, A is a comparison of the PL spectra of different photocatalysts in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3, and B is a comparison of the transient photocurrents of different photocatalysts in Example 1 and Comparative Example 3.

[0026] Figure 4 The images show the Mott-Schottky curve and Tauc plot of the CdS-TiO2-Ag ternary composite photocatalyst in Example 1, where A is the Mott-Schottky curve and B is the Tauc plot.

[0027] Figure 5 The ¹H NMR spectra of the reaction solution were measured at different time intervals.

[0028] Figure 6 Comparison of ethyl acetate yield and polylactic acid digestion rate for different samples under 5-hour light irradiation conditions. Detailed Implementation

[0029] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0031] Example 1: Preparation and characterization of CdS-TiO2-Ag ternary composite photocatalyst This embodiment describes the optimal preparation scheme for a CdS-TiO2-Ag composite catalyst with a CdS nanorod host structure and an Ag / TiO2 heterojunction interface. The preparation flowchart is shown below. Figure 1 As shown in A: (1) Synthesis of CdS nanorods (CdS NRs) (classical hydrothermal method) Cadmium nitrate (15 mmol) and thiourea (45 mmol) were dissolved in 50 mL of ethylenediamine at a molar ratio of 1:3. The solution was stirred at room temperature for 30 min to ensure thorough mixing. The solution was transferred to a polytetrafluoroethylene-lined reactor, heated to 160 °C, and maintained at this temperature for 48 h. After the reaction was completed, the mixture was allowed to cool naturally. The yellow precipitate was collected, washed repeatedly with deionized water and ethanol, and then centrifuged. The precipitate was dried at 60 °C to obtain CdS nanorods.

[0032] (2) Synthesis of CdS-TiO2-Ag ternary composite photocatalyst (sodium borohydride reduction deposition method) 100 mg of CdS NRs obtained in step (1) were dispersed in 100 mL of deionized water. Then, 10 mL of AgNO3 solution (20 μM) and 10 mL of TiO2 nanoparticle (NPs) dispersion (20 μM) (the TiO2 used was anatase phase NPs with a particle size of approximately 5–10 nm) were added, and the mixture was stirred for 30 min. Under ice-water bath conditions, 20 mL of freshly prepared sodium borohydride (0.01 M) solution was slowly added dropwise to the mixture. Stirring was continued for 30 min to complete the in-situ reduction deposition of Ag NPs. The product was collected and thoroughly washed with ethanol and deionized water, then dried at 60 °C to obtain the target CdS-TiO2-Ag ternary composite photocatalyst.

[0033] The SEM image of the CdS-TiO2-Ag ternary composite photocatalyst obtained in this embodiment is shown below. Figure 1 As shown in BG, it can be seen that, Figure 1 As shown in Figure A, a two-step synthesis strategy was employed: the first step involved preparing CdS nanorods via a hydrothermal method, followed by the synergistic assembly of Ag nanoparticles and TiO2 nanoparticles in the second step. This method ultimately resulted in a CdS-TiO2-Ag ternary composite material. The morphology of the synthesized sample was characterized by scanning electron microscopy / transmission electron microscopy (SEM / TEM). The original CdS nanotubes had smooth surfaces, an average diameter of approximately 50 nanometers, and lengths reaching several hundred nanometers. Figure 1 (B). For example Figure 1 As shown in the CE image, both Ag nanoparticles and TiO2 nanoparticles are anchored on the surface of CdS nanorods, forming a clear interfacial contact. The high-resolution transmission electron microscopy image of the CdS-TiO2-Ag composite material reveals three distinct lattice fringes with spacings of 0.311 nm, 0.240 nm, and 0.235 nm, corresponding to the (101) crystal plane of CdS, the (111) crystal plane of Ag nanoparticles, and the (001) crystal plane of TiO2, respectively. Figure 1 E). Furthermore, transmission scanning electron microscopy images and corresponding elemental mapping analysis (… Figure 1 The F and G of 1 clearly confirmed the successful integration of TiO2 and Ag nanoparticles on the CdS substrate, which was verified by the unique spatial distribution of Cd, S, Ag, and Ti elements. The energy dispersive spectroscopy (EDS) results revealed that these components have well-defined localizations in the heterostructure, which is crucial for elucidating potential synergistic effects in the photocatalytic process.

[0034] XPS analysis was performed on the CdS-TiO2-Ag ternary composite photocatalyst of this embodiment, and the results are as follows: Figure 2 As shown, the binding energies of Cd3d and S2p are significantly shifted relative to pure CdS. This confirms the strong electronic interactions between CdS and TiO2 and Ag, which effectively promote charge transfer.

[0035] The Mott-Schottky curve and Tauc plot of the CdS-TiO2-Ag ternary composite photocatalyst in this embodiment are shown below. Figure 4 As shown, A is the Mott-Schottky curve and B is the Tauc plot. The band structure was determined using the Mott-Schottky curve and Tauc plot. The band gap energy (Eg) of CdS-TiO2-Ag was determined to be 2.41 eV, the conduction band (CB) potential to be -0.47 V vs. NHE, and the valence band (VB) potential to be 1.94 V vs. NHE. This band structure data supports the theoretical design of an efficient electron transport path from CdS to TiO2 and Ag after CdS excitation.

[0036] The core advantage of the CdS-TiO2-Ag composite photocatalyst in this embodiment lies in the synergistic effect among the three components: CdS, TiO2, and Ag. The following comparative examples aim to demonstrate that none of the three components can be omitted, and the crucial role of the heterojunction structure in the photoreforming reaction.

[0037] Comparative Example 1: Preparation of CdS-Ag binary composite photocatalyst without TiO2 This comparative example aims to demonstrate the critical role of the TiO2 composition in constructing efficient charge transport pathways and improving charge separation efficiency.

[0038] 100 mg of the CdS nanorods prepared in Example 1 were weighed and dispersed in 100 mL of deionized water. Then, only 10 mL of AgNO3 solution (20 μM) was added, omitting the addition of TiO2 nanoparticles. Following step (2) of Example 1, 20 mL of sodium borohydride solution (0.01 M) was added dropwise in an ice-water bath, and the mixture was stirred continuously for 30 min to achieve reduction deposition. The mixture was centrifuged, washed, and dried to obtain the CdS-Ag binary composite photocatalyst.

[0039] Comparative Example 2: Preparation of Ag-free CdS-TiO2 binary composite photocatalyst This comparative example aims to demonstrate the critical role of Ag nanoparticles in providing LSPR enhancement, trapping electrons, and promoting reaction kinetics.

[0040] 100 mg of CdS nanorods were weighed and dispersed in 100 mL of deionized water. Then, only 10 mL of TiO2 NPs dispersion (20 μM) was added, omitting the addition of AgNO3 solution. Following the post-treatment method in step (2) of Example 1, the mixture was centrifuged, washed, and dried to obtain the CdS-TiO2 binary composite photocatalyst.

[0041] Comparative Example 3: Preparation of a single CdS nanorod photocatalyst This comparative example aims to demonstrate that constructing heterojunction composite structures is essential for photocatalytic PLA reforming reactions.

[0042] The pure CdS NRs were prepared using the CdS nanorods obtained in step (1) of Example 1.

[0043] The PL spectra and transient photocurrent comparisons of different photocatalysts prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are shown in the figure below. Figure 3As shown, A is a comparison of the photoluminescence (PL) spectra of different photocatalysts in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, and B is a comparison of the transient photocurrents of different photocatalysts in Example 1 and Comparative Example 3. The results show that CdS-TiO2-Ag has the lowest PL intensity and the highest transient photocurrent, indicating that it has the lowest recombination rate and the highest separation efficiency of photogenerated carriers, which is the direct reason for its high activity.

[0044] Example 2: Method for preparing ethyl acetate by photoreforming of solid PLA This example describes the optimal reaction conditions for the photo-reforming of PLA to prepare ethyl acetate using a CdS-TiO2-Ag ternary composite photocatalyst.

[0045] In a stainless steel reactor equipped with a quartz glass window, 10 mg of CdS-TiO2-Ag catalyst was dispersed in 10 mL of ammonia solution. 100 mg of polylactic acid (PLA) particles (approximately 3 mm in size and approximately 80,000 molecular weight) were added. The reaction mixture was reacted at a constant room temperature of 25 °C. The system was first purged with N2 gas, then pressurized to a stable pressure of 1.0 bar. The reaction was then passed through a Xe lamp (150 mW / cm²). 2 The reaction was initiated by irradiation with light wavelength > 420 nm (visible light). After the reaction, the solution was evaporated at 40 °C to remove ammonia. The remaining solution was double-filtered through a 0.22 μm PES membrane. 600 μL of the filtrate was mixed with 100 μL of D₂O, and 2.0 μL of DMSO was added as an internal standard. Finally, the solution was filtered through... 1 Quantitative analysis was performed using H NMR spectra.

[0046] The photo-reformed products are subjected to 1 ¹H NMR spectroscopy analysis showed that the characteristic peaks of the product spectrum were in high agreement with those of the commercial ethyl acetate standard solution (see [link]). Figure 5 This conclusively proves that the target product is ethyl acetate. In addition to ethyl acetate, lactic acid was also detected in the product after 5 hours of reaction. This indicates that solid PLA first degrades into soluble lactic acid (hydrolysis / degradation) under ammonia and photocatalysis, and then lactic acid, as an intermediate, is photocatalytically oxidized or esterified to ethyl acetate, thus confirming the multi-stage photo-reforming pathway of the reaction.

[0047] The CdS-TiO2-Ag ternary composite photocatalyst in this example was replaced with the photocatalysts in Comparative Examples 1, 2, and 3, respectively. The yield and PLA digestion rate of PLA photoreforming to ethyl acetate were compared with those of different catalysts, as well as the transient photocurrent and PLA intensity of different photocatalysts. The results are shown in Table 1. The comparison of the yield of ethyl acetate and the PLA digestion rate of different samples is shown in the figure below. Figure 6 As shown.

[0048] Table 1 It can be seen that, under the same photocatalytic conditions, the ethyl acetate yield of the CdS-TiO2-Ag ternary composite photocatalyst is significantly higher than that of all control groups, and the PLA digestion rate is the highest. This demonstrates that the synergistic effect among CdS, TiO2, and Ag is crucial for improving catalytic activity.

[0049] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing a CdS-TiO2-Ag ternary composite photocatalyst, characterized in that, The preparation method includes the following steps: (1) Dissolve cadmium nitrate and thiourea in ethylenediamine, stir at room temperature and then heat to react, take the precipitate, wash and dry it to obtain CdS nanorods; (2) CdS nanorods were dispersed in deionized water, AgNO3 solution and TiO2 nanoparticle dispersion were added, and the mixture was stirred. Under ice-water bath conditions, sodium borohydride solution was added dropwise to the mixture and the mixture was stirred continuously to complete the in-situ reduction and deposition of Ag nanoparticles. The deposit was collected, washed and dried to obtain CdS-TiO2-Ag ternary composite photocatalyst.

2. The preparation method of a CdS-TiO2-Ag ternary composite photocatalyst according to claim 1, characterized in that, In step (1), the molar ratio of cadmium nitrate and thiourea is 1:0.1-1:

10.

3. The preparation method of a CdS-TiO2-Ag ternary composite photocatalyst according to claim 1, characterized in that, In step (1), the temperature of the heating reaction is 100-200 °C, and the heating reaction time is 12-96 h.

4. The preparation method of a CdS-TiO2-Ag ternary composite photocatalyst according to claim 1, characterized in that, In step (2), the TiO2 nanoparticles are anatase phase TiO2 nanoparticles.

5. A CdS-TiO2-Ag ternary composite photocatalyst prepared by the preparation method according to any one of claims 1-4.

6. A method for preparing ethyl acetate from polylactic acid under visible light driven by the CdS-TiO2-Ag ternary composite photocatalyst according to claim 5, characterized in that, Includes the following steps: CdS-TiO2-Ag ternary composite photocatalyst was dispersed in an ammonia solution, polylactic acid was added, and ethyl acetate was prepared by visible light irradiation driven by the reaction under an inert gas atmosphere and constant temperature and pressure conditions.

7. The method for preparing ethyl acetate from polylactic acid driven by visible light according to claim 6, characterized in that, The polylactic acid has a molecular weight of 10,000-100,000 and a particle size of 1-10 mm.

8. The method for preparing ethyl acetate from polylactic acid driven by visible light according to claim 6, characterized in that, The inert gas is N2.

9. The method for preparing ethyl acetate from polylactic acid driven by visible light according to claim 6, characterized in that, The constant temperature and pressure are 25 ℃ and 1.0 bar.

10. The method for preparing ethyl acetate from polylactic acid driven by visible light according to claim 6, characterized in that, The visible light has a wavelength > 420 nm and an intensity of 150 mW / cm². 2 .

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