CdS / HEPH MgCoNiCuZn photocatalyst, preparation method and application

Abstract

The invention belongs to the technical field of photocatalysis, and particularly relates to a CdS / HEPH MgCoNiCuZn photocatalyst as well as a preparation method and application thereof. And an S-type heterojunction constructed between the CdS and the HEPH MgCoNiCuZn high-entropy hydroxide improves the separation efficiency of photon-generated carriers, and also enables the composite material to retain the strongest oxidation-reduction capability. In addition, the HEPH MgCoNiCuZn high-entropy hydroxide provides more active sites for the reaction, so that adsorption and activation of PLA are facilitated, and the conversion efficiency of a substrate is improved. A result of a photocatalytic performance test proves that the CdS / HEPH MgCoNiCuZn composite material shows remarkable performance improvement in the aspect of photo-reforming PLA plastic.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to a CdS / HEPH MgCoNiCuZn photocatalyst, its preparation method, and its application. Background Technology

[0002] Metal sulfide-based semiconductors possess unique electronic structures and excellent optical properties, leading to their widespread application in photocatalysis. These materials typically have suitable band gaps, absorbing visible light and generating photogenerated electrons and holes under illumination, driving various redox reactions. For example, cadmium sulfide-based semiconductors have been widely used in photocatalytic water splitting for hydrogen production and photocatalytic degradation of organic pollutants. CdS, as a typical metal sulfide semiconductor, exhibits a suitable band gap and good photocatalytic activity. However, the high recombination rate of photogenerated carriers in CdS limits its photocatalytic hydrogen production efficiency. Furthermore, CdS suffers from poor stability and is prone to photocorrosion during photocatalysis, affecting its lifespan. Particularly in photoreforming reactions, the oxidation of small organic molecules requires semiconductors with high oxidation potentials. To address these issues, researchers are continuously exploring various methods to further promote the application of CdS in photocatalysis. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a CdS / HEPHMgCoNiCuZn photocatalyst, its preparation method, and its application.

[0004] The technical solution adopted in this invention is as follows: A CdS / HEPH MgCoNiCuZn photocatalyst, comprising HEPHMgCoNiCuZn high-entropy hydroxide crystals and CdS particles, wherein the CdS particles are loaded on the surface of the HEPH MgCoNiCuZn high-entropy hydroxide crystals.

[0005] The preparation method of the CdS / HEPH MgCoNiCuZn photocatalyst described above includes the following steps: preparing HEPHMgCoNiCuZn high-entropy hydroxide crystals, Cd²⁺... + Source and S² - The source is dispersed and mixed into a solvent to generate CdS particles loaded on the surface of HEPHMgCoNiCuZn high-entropy hydroxide crystals in a one-pot process.

[0006] Preferably, the method includes the following steps: dispersing HEPH MgCoNiCuZn high-entropy hydroxide crystals in ethanol, and adding Cd²⁺ dropwise. + Source solution and S² -The source solution was stirred and dispersed, and then heated at 60-100℃ to react, yielding the CdS / HEPHMgCoNiCuZn photocatalyst.

[0007] Preferably, the HEPH MgCoNiCuZn high-entropy hydroxide crystals are prepared by a co-precipitation method.

[0008] Preferably, the preparation process of the HEPH MgCoNiCuZn high-entropy hydroxide crystal includes the following steps: (1) Prepare a solution containing Mg² + Co² + Ni² + Cu² + Zn² + And solution A of C6H5Na3O7; (2) Configuration containing Sn 4+ The ethanol solution is denoted as solution B; (3) Mix solution A and solution B, add precipitant, and react to form a precipitate, which is HEPH MgCoNiCuZn high entropy hydroxide crystal.

[0009] Mg² + Co² + Ni² + Cu² + Zn² + Sn 4+ The molar ratio is 2:2:2:2:1:10.

[0010] Preferably, in step (3), solution A and solution B are mixed and stirred evenly, heated to 60-100℃, and a precipitant is added to carry out the reaction.

[0011] Preferably, the precipitant is a 2 M sodium hydroxide solution.

[0012] The CdS / HEPH MgCoNiCuZn photocatalyst described above is used in the photo-reforming of polylactic acid.

[0013] A method for photo-reforming polylactic acid includes the following steps: (1) Pretreatment of PLA in an alkaline solution, stirring at 25-100℃ for 1-24h; (2) The pretreated solution was mixed with the CdS / HEPH MgCoNiCuZn photocatalyst as described above, and the reaction was carried out under light irradiation with a wavelength greater than 420 nm.

[0014] The beneficial effects of this invention are as follows: This invention prepares a five-membered high-entropy hydroxide HEPH MgCoNiCuZn (MgCoNiCuZnSn(OH)6) via a simple co-precipitation method, and synthesizes a CdS / HEPH MgCoNiCuZn composite material in a one-pot process, thereby solving the photocorrosion problem of CdS and improving its stability for photocatalytic reactions. The S-shaped heterojunction constructed between CdS and HEPH MgCoNiCuZn high-entropy hydroxide improves the separation efficiency of photogenerated carriers and also increases the redox potential of the material. In addition, HEPH MgCoNiCuZn high-entropy hydroxide provides more active sites for the reaction, which is beneficial to the adsorption and activation of PLA and improves the conversion efficiency of the substrate. The results of photocatalytic performance testing confirm that the CdS / HEPH MgCoNiCuZn composite material exhibits significant performance improvement in photo-reforming PLA plastics. Among them, the hydrogen production rate of 10% CdS / HEPH MgCoNiCuZn reaches 4.08 mmol g. -1 h -1 It is a pure CdS sample (0.54 mmol g). - 1 h -1 It is 7 times the rate of hydrogen production. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0016] Figure 1 (a) XRD pattern of sample and (b) FT-IR pattern of sample; Figure 2 In the middle, (a) and (b) SEM images of HEPH MgCoNiCuZn high-entropy hydroxide; (c) and (d) SEM images of pure CdS sample; (e) and (f) SEM images of 10% CdS / HEPH MgCoNiCuZn; Figure 3 In the image, (a) and (b) TEM images of 10% CdS / HEPH MgCoNiCuZn; (c) HR-TEM image of 10% CdS / HEPH MgCoNiCuZn; (d) TEM-EDX image of 10% CdS / HEPH MgCoNiCuZn; Figure 4XPS spectra of (a) Mg 1s, (b) Co 2p, (c) Ni 2p, (d) Cu 2p, (e) Zn 2p, (f) Sn 2p, (g) Cd3d, (h) S 2p, and (i) O 1s for pure HEPH MgCoNiCuZn hydroxide and 10% CdS / HEPH MgCoNiCuZn sample before and after reaction, respectively. Figure 5 Adsorption isotherms of CdS and CdS / HEPH MgCoNiCuZn high-entropy hydroxide samples; Figure 6 In the above, (a) hydrogen production of the sample after 4 hours of photo-reforming; (b) hydrogen production of the 10% CdS / HEPH MgCoNiCuZn photo-reforming reaction after 12 hours; and (c) hydrogen production of the liquid products. 1 H NMR and (d) liquid products 13 C NMR; Figure 7 In the image, (a) Mott-Schottky plots of HEPH MgCoNiCuZn high-entropy hydroxide and (b) CdS, (c) UV-vis DRS spectra, (d) αhν ) 2 With photon energy ( hν Tauc plot of (e) αhν ) 1 / 2 With photon energy ( hν Tauc plot of CdS / HEPH MgCoNiCuZn, (f) S-type heterojunction mechanism; Figure 8 In the figure, (a) electrochemical impedance (EIS) Nyquist plot, (b) transient photocurrent plot, (c) steady-state photoluminescence (PL) spectrum (excited at 365 nm) and (d) time-resolved PL decay spectrum (TRPL). Figure 9 Schematic diagram of the heterostructure of CdS / HEPH MgCoNiCuZn composite material: reaction mechanism in S-mode before contact, after contact. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0018] Example 1 (1) Preparation of HEPH MgCoNiCuZn high-entropy hydroxide: Solution A: 0.8 mmol Mg(NO3)2·6H2O, 0.8 mmol CoCl2·6H2O, 0.8 mmol NiCl2·6H2O, 0.8 mmol CuSO4·5H2O, 0.4 mmol Zn(NO3)2·6H2O, and 2 mmol C6H5Na3O7 were added to 140 mL of deionized water. Solution B: 4 mmol SnCl4·5H2O was dissolved in 20 mL of ethanol. Then, Solution B was mixed with Solution A and stirred for 30 min. Next, 20 mL of 2 M sodium hydroxide solution was rapidly added to the mixed solution at 80 °C. After reacting for 1 hour, the mixture was cooled to room temperature, and the centrifuged precipitate was washed with ethanol and deionized water, respectively. Finally, the mixture was dried at 60 °C for 12 hours.

[0019] (2) Preparation of CdS / HEPH MgCoNiCuZn photocatalyst: 0.2 g of HEPH MgCoNiCuZn high-entropy hydroxide was dispersed in 70 mL of ethanol and sonicated for 30 minutes. Certain amounts of 0.1 M cadmium acetate solution and 0.1 M sodium sulfide solution were added dropwise to the above solution, and the mixture was stirred rapidly for 10 minutes. The solution was then heated in an oil bath at 80 °C for 1 hour. By adjusting the amount of cadmium acetate used, composite samples with different theoretical CdS contents were synthesized. These composite samples were labeled as 5%, 10%, and 15% CdS / HEPH, respectively.

[0020] Figure 1a is the powder X-ray diffraction (XRD) pattern of HEPH MgCoNiCuZn high-entropy hydroxide, CdS, and CdS / HEPH MgCoNiCuZn composite material. The sharp diffraction peaks of HEPH MgCoNiCuZn high-entropy hydroxide indicate that the sample has a high degree of crystallinity. The diffraction peaks at 19.92°, 22.93°, 32.74°, 46.88°, 52.84°, and 58.33° correspond to the (111), (200), (220), (400), (420), and (422) crystal planes of the HEPH MgCoNiCuZn high-entropy hydroxide sample, respectively. Pure CdS has a low degree of crystallinity due to its lower synthesis temperature, resulting in weaker diffraction peaks. In CdS, the diffraction peaks at 26.8°, 44.2°, and 52.3° correspond to the (002), (110), and (112) crystal planes of hexagonal CdS (JCPDS No. 41-1049), respectively. When different amounts of CdS were loaded, the diffraction peaks of CdS / HEPH MgCoNiCuZn did not change, indicating that the effect of CdS loading on the HEPH crystal structure is negligible. However, the intensity of the diffraction peaks decreased, possibly due to the CdS loading. No CdS-related diffraction peaks were observed in the XRD pattern of the composite material CdS / HEPH MgCoNiCuZn. This is because the CdS content in the composite material is low, and the diffraction peak intensity of pure CdS is low and difficult to distinguish. Furthermore, the chemical structure of the HEPH MgCoNiCuZn high-entropy hydroxide and the composite sample was studied using FT-IR spectroscopy. In the FT-IR spectra ( Figure 1 b), 3096 cm -1 The peak at 520 cm⁻¹ corresponds to the stretching vibration of the OH bond. The stretching vibration of the Sn-O bond and the bending vibration of the Sn-OH bond are located at 520 cm⁻¹, respectively. -1 and 1173 cm -1 Nearby. 766 cm -1 The peak at that point represents hydrogen bonds between H2O and H2O. The crystal structure of the sample can be determined from the XRD and FT-IR spectra.

[0021] Figure 2 The scanning electron microscope images revealed the microstructure of the sample. Figure 2 In both a and b, the HEPH MgCoNiCuZn high-entropy hydroxide exhibits a regular cubic morphology and uniform size, indicating that the crystals of HEPH MgCoNiCuZn high-entropy hydroxide grew well during the preparation process. In contrast, Figure 2 The CdS particles in c and d are small in size and exhibit irregular morphology due to aggregation. However, when CdS is combined with HEPH MgCoNiCuZn high-entropy hydroxide, as... Figure 2As shown in e and f, CdS particles are uniformly dispersed on the surface of the HEPH MgCoNiCuZn high-entropy hydroxide cubes. This indicates that the HEPH MgCoNiCuZn high-entropy hydroxide acts as a support, effectively suppressing CdS aggregation and improving CdS dispersibility. Furthermore, scanning electron microscopy images reveal that the CdS particles in the composite material do not alter the overall morphology of the HEPH MgCoNiCuZn high-entropy hydroxide cubes, maintaining their regular cubic structure.

[0022] TEM images show the effect of 10% CdS / HEPH MgCoNiCuZn composite material ( Figure 3 As shown in a and b), CdS nanoparticles are dispersed on the surface of HEPH MgCoNiCuZn high-entropy hydroxide. High-resolution TEM (HR-TEM) images show clear lattice fringes of CdS (as shown in a and b). Figure 3 c), the interplanar spacing is 0.336 nm, corresponding to the (002) crystal plane of CdS. The crystal structure of the CdS sample revealed by TEM testing is consistent with the XRD characterization results. Furthermore, TEM-EDX images of 10% CdS / HEPH confirm the chemical composition and uniform elemental distribution of the composite material, such as... Figure 3 As shown in d. EDX elemental surface scanning results also confirmed the uniform dispersion of CdS on the surface of HEPHMgCoNiCuZn high-entropy hydroxide. Table 1 summarizes the ratios of metal elements in HEPHMgCoNiCuZn high-entropy hydroxide obtained from ICP-OES measurements.

[0023] Table 1. Molar ratios of each element in HEPH based on ICP-OES. To investigate the surface chemical states of various elements in the CdS / HEPH MgCoNiCuZn sample, XPS characterization was performed. Figure 4 As shown, the presence of Mg, Co, Ni, Cu, Zn, Sn, Cd, S, and O elements in the 10% CdS / HEPH MgCoNiCuZn composite sample was confirmed. For the HEPH MgCoNiCuZn high-entropy hydroxide sample, the presence of Mg, Co, Ni, Cu, Zn, Sn, Cd, S, and O elements in the Co 2p (…) was also confirmed. Figure 4 In the spectrum of b), the peak at 781.18 eV corresponds to Co. 3+ 2p 3 / 2 The peak at 784.59 eV corresponds to Co. 2+ 2p 3 / 2 , 786.49 eV and 803.36 eV correspond to the satellite peaks at the two locations, respectively. Figure 4In c, 855.78 eV and 858.16 eV correspond to Ni in HEPH MgCoNiCuZn high-entropy hydroxide, respectively. 2+ 3 / 2 and Ni 3+ 3 / 2 The peaks at 862.10 eV and 880.01 eV are satellite peaks. Compared with the pure HEPHMgCoNiCuZn high-entropy hydroxide, after loading 10 wt% CdS, the Mg 1s, Co 2p, Ni 2p, Cu 2p, Zn 2p and Sn 2p ( Figure 4 The binding energy of (af) shows a negative shift, indicating an increase in electron density on the HEPH MgCoNiCuZn high-entropy hydroxide after CdS loading. In the Cd 3d and S 2p spectra of pure CdS, the binding energies at 405.16 eV and 161.56 eV correspond to Cd 3d and S 2p, respectively. 5 / 2 and S 2p 3 / 2 In contrast, the peak positions of Cd 3d and S 2p in 10% CdS / HEPH MgCoNiCuZn showed a positive shift ( Figure 4 The g,h diagram indicates that electron transfer occurred between the two, with electrons transferring from CdS to the HEPH MgCoNiCuZn high-entropy hydroxide, making CdS an electron-rich center. Therefore, when the HEPH MgCoNiCuZn high-entropy hydroxide comes into contact with CdS, the flow of electrons generates a built-in electric field at the interface. In the O 1s spectrum of the HEPH MgCoNiCuZn high-entropy hydroxide ( Figure 4 (i) The binding energies at 530.46 eV, 531.21 eV, and 532.46 eV are attributed to lattice oxygen, surface hydroxyl oxygen, and oxygen from physically adsorbed water molecules, respectively. Compared to the 10% CdS / HEPH MgCoNiCuZn sample before the reaction, the binding energies of the Mg 1s, Co 2p, Ni 2p, Cu 2p, Zn 2p, and Sn 2p orbitals in the 10% CdS / HEPH MgCoNiCuZn composite sample after the reaction showed a positive shift in binding energies, while the peaks of Cd 3d and S 2p in CdS showed a negative shift. This indicates that the charge transfer direction is the transfer of electrons from the HEPH MgCoNiCuZn high-entropy hydroxide to CdS. This result provides strong evidence for the diffusion of photogenerated electrons on the CB orbitals in the HEPH MgCoNiCuZn high-entropy hydroxide to the CdS surface under the influence of the built-in electric field, corresponding to the S-type charge transfer mechanism.

[0024] Table 2. Structural parameters for different materials.

[0025] Figure 5The nitrogen adsorption-desorption curves of HEPH MgCoNiCuZn high-entropy hydroxide, CdS, and the CdS / HEPH MgCoNiCuZn composite are shown. As can be seen from the figure, the adsorption-desorption curves of these materials all exhibit Type IV characteristics, accompanied by H3-type hysteresis loops, indicating a highly irregular pore structure. The specific surface areas of pure CdS and HEPH MgCoNiCuZn high-entropy hydroxide are 152.46 m², respectively. 2 / g and 5.18 m 2 The specific surface area of ​​the composite sample is between the two values. Furthermore, the specific surface area of ​​the composite sample increases with increasing CdS loading. Table 2 lists the specific surface area, pore size, and pore volume data of the relevant materials. The specific surface area of ​​the 10% CdS / HEPH MgCoNiCuZn composite is 22.25 m² / g. 2 The specific surface area (S / g) falls between that of HEPH MgCoNiCuZn high-entropy hydroxide and pure CdS material. This indicates that loading CdS onto HEPH MgCoNiCuZn high-entropy hydroxide increases the specific surface area of ​​the composite material. Increased specific surface area means a larger surface area, providing more reactive sites and thus improving the material's activity in catalytic reactions.

[0026] Example 2: CdS / HEPH MgCoNiCuZn photocatalyst for PLA photo-reforming: (1) PLA pretreatment: PLA plastic was placed in an alkaline solution with a concentration of 5 M and then heated at 80 °C for 12 hours. Under the combined action of the alkaline solution and heating, the long chain structure of PLA gradually hydrolyzed, and over time, the long chain broke into small molecule lactic acid monomers. To determine the hydrolysis rate of PLA, proton nuclear magnetic resonance spectroscopy (NMR) was used. 1 Quantitative analysis was performed using ¹H NMR. Using 5 mg of maleic acid standard as an internal standard, the hydrolysis rate of PLA was calculated to be 84.4%.

[0027] (2) PLA photoreforming reaction: 20 mg of photocatalyst was dispersed in 50 mL of PLA pretreatment solution, with a solution concentration of 100 mg / mL. After ultrasonic treatment for 30 minutes, the sample was loaded into the reactor. During the reaction, a circulating cooling water system was used to maintain the temperature of the reaction system at a constant 6 °C. Before illumination, the entire system was under vacuum. A 300 W xenon lamp was used as the light source, equipped with a 420 nm cutoff filter to simulate the spectral distribution of visible light, ensuring that only light with wavelengths greater than 420 nm irradiated the sample. After illumination began, the reaction system was kept under vigorous stirring to ensure uniform dispersion of the photocatalyst in the solution.

[0028] In investigating the hydrogen production performance of HEPH MgCoNiCuZn high-entropy hydroxide, CdS, and CdS / HEPH MgCoNiCuZn composites, the following results were obtained: Figure 6 As shown in Figure a, during the initial 4-hour hydrogen production test, the HEPH MgCoNiCuZn high-entropy hydroxide exhibited almost negligible hydrogen production performance; in contrast, the pure CdS material also showed a low hydrogen production level. However, after loading CdS, the hydrogen production performance of the CdS / HEPH MgCoNiCuZn composite material showed a significant changing trend. The hydrogen production performance of the composite material changed with the CdS loading. When the CdS loading reached 10 wt%, the hydrogen production performance of the CdS / HEPH MgCoNiCuZn composite material reached its optimal state, with a hydrogen production rate of 4.08 mmol g. - ¹ h - ¹, This performance is achieved by pure CdS (0.54 mmol g) - ¹ h - The hydrogen production rate was 7 times that of the composite material (¹), demonstrating the superior hydrogen production performance of the CdS-HEPH MgCoNiCuZn high-entropy hydroxide composite. To test the stability of this composite material under long-term reaction conditions, the reaction time was extended to 12 hours. Figure 6 As shown in b, the hydrogen production rate of the 10% CdS / HEPH MgCoNiCuZn composite material decreased slightly to 3.98 mmol g. - ¹ h - ¹, but still maintains a relatively high hydrogen production efficiency. The slight decrease in hydrogen production rate may be because the CdS loaded on the surface of the composite material has a relatively low crystallinity. During long-term photo-reformation, CdS with lower crystallinity is more susceptible to photo-corrosion. After 12 hours of photo-reforming reaction, pyruvate and acetate were observed in the liquid phase products of the 10% CdS / HEPH MgCoNiCuZn composite material. Figure 6 c). Liquid products of 10% CdS / HEPH MgCoNiCuZn composite material 13 C NMR spectrum ( Figure 6 In step d), the presence of carbonate ions indicates that a peroxidation reaction occurred, producing carbon dioxide. This phenomenon demonstrates that the CdS / HEPH MgCoNiCuZn composite material exhibits good photoreforming properties under light conditions. Although this photoreforming process, which generates carbon dioxide from lactic acid, sacrifices the yield of organic acids (pyruvic acid, acetic acid), it also illustrates the potential of this composite material in the degradation of organic pollutants.

[0029] The band structures of HEPH MgCoNiCuZn high-entropy hydroxides and CdS were determined by Mott-Schottky curves, such as... Figure 7 As shown in a and b, the Mott-Schottky curves of HEPH MgCoNiCuZn high-entropy hydroxide and CdS have positive slopes, indicating that they possess n-type semiconductor characteristics. Flat band potential ( E fb The high-entropy hydroxide HEPH MgCoNiCuZn was determined by the Mott-Schottky curve. E fb -0.56 V (vs Ag / AgCl, pH=7). The conduction band position of the n-type semiconductor ( E CB )Compare E fb The value is approximately negative 0.1-0.2 V; we take an empirical value of 0.2 V. According to the Nernst formula... E NHE = E Ag / AgCl + 0.059×PH + 0.197 V, yielding HEPH MgCoNiCuZn high-entropy hydroxide. E CB (vs NHE) is -0.15 V. Similarly, the value of CdS is obtained. E CB,CdS = -0.27 V. The UV-Vis diffuse reflectance (DRS) spectrum of the sample is as follows: Figure 7 As shown in Figure c, the HEPH MgCoNiCuZn high-entropy hydroxide exhibits strong absorption in the ultraviolet region but weak absorption in the visible light region, while CdS shows strong absorption in the visible light region. The composite of the two, with CdS exhibiting a wider spectral response range, results in the CdS / HEPH MgCoNiCuZn composite sample displaying better light absorption characteristics. The 10% CdS / HEPH MgCoNiCuZn composite material shows the highest absorption intensity in the visible light region, indicating its strongest light absorption capacity under visible light, enabling it to generate more photogenerated carriers and thus improve photocatalytic activity. This is consistent with its results in hydrogen production experiments. To further determine the band gap of the material, the Kubelka-Munk method was used to... αhν ) 2 With photon energy ( hν Plot the graph. For CdS (direct bandgap semiconductor), such as... Figure 7 As shown in d, the band gap of CdS is obtained ( E g The value is 2.19 eV. For HEPH MgCoNiCuZn high-entropy hydroxide (indirect bandgap semiconductor), such as Figure 7As shown in e, ( αhν ) 1 / 2 With photon energy ( hν Plotting the graph yields the E of the high-entropy hydroxide HEPH MgCoNiCuZn. g The value is 2.83 eV. According to... E VB = E CB + E g The high-entropy hydroxides HEPH MgCoNiCuZn and CdS were calculated. E VB The band gaps are 2.73 V and 1.92 V, respectively. The band gap structures and mechanisms of action of HEPH MgCoNiCuZn high-entropy hydroxides and CdS are as follows: Figure 7 f, When HEPHMgCoNiCuZn high-entropy hydroxide and CdS are contacted under dark conditions, due to the interaction between the two materials... E fb The difference in energy distribution creates a built-in electric field at the interface, pointing from CdS towards the HEPH MgCoNiCuZn high-entropy hydroxide. The staggered band structure of CdS and HEPH MgCoNiCuZn causes electrons and holes to separate along different paths, thus forming an S-shaped heterojunction. During photocatalysis, the CdS / HEPH MgCoNiCuZn catalyst absorbs photon energy, causing electrons to transition from the valence band to the conduction band, generating photogenerated carriers. At this point, under the combined effect of the built-in electric field and band bending, electrons photoexcitedly transitioning to the conduction band of HEPH MgCoNiCuZn recombine with holes in the valence band (VB) of CdS, effectively suppressing the recombination rate of photogenerated carriers. Furthermore, the S-shaped charge transfer process endows the CdS / HEPH MgCoNiCuZn catalyst with strong reducing and oxidizing properties.

[0030] The photoinduced electron-hole pair dynamics were investigated using electrochemical impedance spectroscopy (EIS) and transient photocurrent. Figure 8 As can be seen from this, the 10% CdS / HEPH MgCoNiCuZn composite material has the smallest radius of curvature, indicating that it has the smallest charge transfer resistance and the highest carrier separation efficiency. Figure 8 In the photocurrent curves, the 10% CdS / HEPH MgCoNiCuZn composite material exhibited the highest and most stable photocurrent intensity, confirming its excellent carrier separation efficiency. Furthermore, the migration and separation of electron-hole pairs were investigated using steady-state fluorescence spectroscopy (PL) and time-resolved fluorescence spectroscopy (TRPL). Figure 8As can be seen from c, both the HEPHMgCoNiCuZn high-entropy hydroxide and the pure CdS sample exhibited strong emission peaks at 468 nm and 586 nm, respectively, which are attributed to the recombination of photogenerated carriers. Among them, the 10% CdS / HEPH MgCoNiCuZn composite material exhibited the lowest PL peak intensity, indicating that it possesses the lowest electron-hole recombination rate. To further explore the lifetime of photogenerated carriers, TRPL experiments were conducted (…). Figure 8 d), the decay parameters of the samples are shown in Table 3. The average fluorescence lifetime of 10% CdS / HEPH MgCoNiCuZn is 0.735 ns, which is significantly longer than that of CdS (0.286 ns). This indicates that the construction of the S-type heterojunction of CdS / HEPH MgCoNiCuZn is conducive to carrier separation and migration.

[0031] Table 3. Attenuation parameters for different materials.

[0032] like Figure 9 As shown, after HEPH MgCoNiCuZn high-entropy hydroxide comes into contact with CdS, due to the diffusion of electrons from CdS to HEPH MgCoNiCuZn high-entropy hydroxide, an electron depletion layer and an electron accumulation layer can be formed at the interface between HEPH MgCoNiCuZn high-entropy hydroxide and CdS. This leads to the formation of an internal electric field pointing from CdS to HEPH MgCoNiCuZn high-entropy hydroxide, which effectively enhances the unidirectional migration of photogenerated electrons from HEPH MgCoNiCuZn high-entropy hydroxide to CdS. After close contact between HEPH MgCoNiCuZn high-entropy hydroxide and CdS, their... E fAlignment to the same level causes the energy bands of CdS and HEPH MgCoNiCuZn high-entropy hydroxide to bend upwards and downwards, respectively. This band bending promotes the recombination of photogenerated electrons in the conduction band of HEPH MgCoNiCuZn high-entropy hydroxide and photogenerated holes in the valence band of CdS at the interface. Due to the Coulomb force between holes and electrons at the interface, photogenerated electrons in the conduction band of HEPH MgCoNiCuZn high-entropy hydroxide and photogenerated holes in the valence band of CdS recombine. Under illumination, reducing electrons in the CdS conduction band and oxidizing holes in the valence band of HEPH MgCoNiCuZn high-entropy hydroxide are transferred to the semiconductor surface to participate in different reactions. Thanks to the electron-rich nature of the hydroxyl groups on the surface of HEPH MgCoNiCuZn high-entropy hydroxide and its abundant active sites, PLA molecules are easily captured and activated on the HEPH MgCoNiCuZn high-entropy hydroxide surface. Photogenerated holes undergo the oxidation reaction of the substrate PLA on the surface of HEPHMgCoNiCuZn high-entropy hydroxide, while electrons accumulate on the CdS surface to participate in the reduction reaction of protons, producing hydrogen gas.

[0033] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A CdS / HEPH MgCoNiCuZn photocatalyst, characterized in that: It includes HEPH MgCoNiCuZn high-entropy hydroxide crystals and CdS particles, wherein the CdS particles are loaded on the surface of HEPH MgCoNiCuZn high-entropy hydroxide crystals.

2. The preparation method of the CdS / HEPH MgCoNiCuZn photocatalyst as described in claim 1, characterized in that... Includes the following steps: HEPH MgCoNiCuZn high-entropy hydroxide crystals, Cd² + Source and S² - The source is dispersed and mixed into a solvent to generate CdS particles loaded on the surface of HEPH MgCoNiCuZn high-entropy hydroxide crystals in a one-pot process.

3. The preparation method of the CdS / HEPH MgCoNiCuZn photocatalyst according to claim 2, characterized in that: High-entropy hydroxide crystals of HEPH MgCoNiCuZn were dispersed in ethanol, and Cd²⁺ was added dropwise. + Source solution and S² - The source solution was stirred and dispersed, and then heated at 60-100℃ to obtain the CdS / HEPH MgCoNiCuZn photocatalyst.

4. The preparation method of the CdS / HEPH MgCoNiCuZn photocatalyst according to claim 2, characterized in that: The HEPH MgCoNiCuZn high-entropy hydroxide crystals were prepared by co-precipitation.

5. The preparation method of the CdS / HEPH MgCoNiCuZn photocatalyst according to claim 4, characterized in that: The preparation process of the HEPH MgCoNiCuZn high-entropy hydroxide crystal includes the following steps: (1) Prepare a solution containing Mg² + Co² + Ni² + Cu² + Zn² + And solution A of C6H5Na3O7; (2) Configuration containing Sn 4+ The ethanol solution is denoted as solution B; (3) Mix solution A and solution B, add precipitant, and react to form a precipitate, which is HEPH MgCoNiCuZn high entropy hydroxide crystal.

6. The preparation method of the CdS / HEPH MgCoNiCuZn photocatalyst according to claim 5, characterized in that: Mg² + Co² + Ni² + Cu² + Zn² + Sn 4+ The molar ratio is 2:2:2:2:1:

10.

7. The preparation method of the CdS / HEPH MgCoNiCuZn photocatalyst according to claim 5, characterized in that: In step (3), solution A and solution B are mixed and stirred evenly, heated to 60-100℃, and a precipitant is added to carry out the reaction.

8. The preparation method of the CdS / HEPH MgCoNiCuZn photocatalyst according to claim 5, characterized in that: The precipitant is a 2 M sodium hydroxide solution.

9. The CdS / HEPH MgCoNiCuZn photocatalyst as described in claim 1 is used for photo-reforming polylactic acid.

10. A method for photo-reforming polylactic acid, characterized in that... Includes the following steps: (1) Pretreatment of PLA in an alkaline solution, stirring at 25-100℃ for 1-24h; (2) The pretreated solution is mixed with the CdS / HEPH MgCoNiCuZn photocatalyst as described in claim 1, and the reaction is carried out under light irradiation with a wavelength greater than 420 nm.

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