A Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator with dual photothermal / photocatalytic properties, its preparation method and application

Abstract

This invention is mainly applied to seawater desalination technology and photocatalysis, providing an S-type heterojunction Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator with photothermal / photocatalytic performance, its preparation method, and applications. This invention prepares Bi2O3 nanofibers using electrospinning combined with a high-temperature calcination process. The obtained Bi2O3 nanofibers are uniformly dispersed in water, and after adjusting the pH value, zinc chloride, indium chloride, and thioacetamide are added sequentially to allow ZnIn2S4 nanosheets to grow in situ on the surface of the Bi2O3 nanofibers. After centrifugation, washing, and vacuum drying, an S-type heterojunction Bi2O3 / ZnIn2S4 catalyst with photocatalytic performance is obtained. The prepared Bi2O3 / ZnIn2S4 is uniformly dispersed in a 1% sodium alginate solution to form a homogeneous slurry. The slurry is uniformly coated onto the surface of a pretreated sugarcane substrate, dried at 60°C, and then reacted with Ca... 2+ Cross-linking allows sodium alginate to solidify and take shape. Finally, the sample is removed and rinsed with deionized water to remove residual Ca. 2+ After drying again, the Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator is obtained. The three-dimensional evaporator provided by this invention has a stable structure, low cost, and excellent dual performance of photocatalytic H2O2 production and photothermal evaporation, showing broad application prospects in the fields of seawater desalination and photocatalytic H2O2 production.

Description

Technical Field

[0001] This invention belongs to the fields of seawater desalination technology and photocatalysis, specifically relating to a Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator with dual photothermal / photocatalytic properties, its preparation method, and its application. Background Technology

[0002] In the study of photocatalytic hydrogen peroxide production, S-type heterojunctions have attracted widespread attention due to their ability to achieve spatial separation of photogenerated carriers while retaining the strong redox capabilities of each component. Bi₂O₃, as a wide-bandgap oxide semiconductor, possesses good stability and suitable band positions. When combined with ZnIn₂S₄, it forms a typical S-type charge-transfer structure, which is expected to suppress carrier recombination while retaining the strong reducing ability of ZnIn₂S₄'s conduction band electrons to drive the two-electron oxygen reduction reaction. To further expand the practical application scenarios of this material, considering the porous structure and good water transport capacity of natural sugarcane, it was used as a carrier to load the preferred composite material, constructing a Bi₂O₃ / ZnIn₂S₄@sugarcane three-dimensional evaporator. This integrated system was used to simultaneously investigate the interfacial water evaporation performance and the hydrogen peroxide production capacity in a 10% ethanol solution under one solar radiation intensity. Summary of the Invention

[0003] In view of this, the present invention provides a Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator, its preparation method and application.

[0004] One objective of this invention is to provide a method for preparing a Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator, comprising the following steps: Preparation of S1.Bi2O3 nanofibers S11. Preparation of precursor solution: Dissolve bismuth source in N,N-dimethylformamide solvent and stir until a clear solution is formed. Add polyvinylpyrrolidone to the clear solution and continue stirring to obtain a homogeneous and stable precursor solution for later use. S12. Electrospinning The electrospinning process was carried out at room temperature, and the key process parameters were set as follows: the precursor solution propulsion speed of the injection pump was 0.02-0.06 mm / min, the distance between the needle tip and the roller collector covered with aluminum foil was fixed at 12-18 cm, and a DC high voltage of 12-18 kV was applied between the two to deposit the composite nanofiber membrane. S13. Calcination and crystallization treatment The composite nanofiber membrane was placed in a muffle furnace and calcined under a programmed temperature rise in air atmosphere; after the calcination process was completed, it was naturally cooled to room temperature to obtain Bi2O3 nanofibers. Preparation of S2.ZnIn2S4 and Bi2O3 / ZnIn2S4 catalysts After uniformly dispersing the obtained Bi2O3 nanofibers in water and adjusting the pH value, zinc chloride, indium chloride and thioacetamide were added in sequence to allow ZnIn2S4 nanosheets to grow in situ on the surface of Bi2O3 nanofibers. After centrifugation, washing and vacuum drying, an S-type heterojunction Bi2O3 / ZnIn2S4 catalyst with photocatalytic performance was obtained. Preparation of S3.Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator The prepared Bi₂O₃ / ZnIn₂S₄ was uniformly dispersed in a 1% (w / w) sodium alginate solution to form a homogeneous slurry. The slurry was then uniformly coated onto the surface of a pretreated sugarcane substrate, dried at 60°C, and then mixed with Ca... 2+ Cross-linking, then rinse the surface with deionized water to remove residual Ca. 2+ The mixture was dried again to obtain Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator.

[0005] Preferably, the mass of bismuth nitrate pentahydrate is 1-3 g, the volume of N,N-dimethylformamide solvent is 5-15 mL, the mass of polyvinylpyrrolidone is 1-3 g, and the stirring time is 10-16 h.

[0006] Preferably, the solution propulsion speed of the injection pump in the electrospinning process is 0.04~0.1 mm / min, and the applied DC high voltage is 12~17 kV, to obtain a nanofiber membrane composed of PVP and bismuth nitrate.

[0007] Preferably, the composite nanofiber membrane is annealed for 1-3 h; the annealing temperature is 300-500°C, and the heating rate is 2-5 °C / min, to obtain Bi2O3 nanofibers.

[0008] Preferably, the molar ratio of the Bi2O3 sample, zinc chloride, indium chloride, and thioacetamide is (0.02~0.08):(1~4):(2~6):(4~8).

[0009] Preferably, the reaction temperature for in-situ growth is 60~110°C, and the reaction time is 1~6 h.

[0010] Preferably, after the in-situ growth reaction, the product liquid is further subjected to centrifugation, washing and vacuum drying in sequence to obtain Bi2O3 / ZnIn2S4 catalyst; the centrifugation speed is 8000~10000 rpm and the centrifugation time is 5~10 min; the vacuum drying temperature is 50~80°C and the vacuum time is 10~20 h.

[0011] Preferably, the mass of the S-type heterojunction Bi2O3 / ZnIn2S4 catalyst is 0.2~1 g; the concentration of the sodium alginate aqueous solution is 2~5% and the volume is 15~20 mL; and the concentration of the CaCl2 solution is 1~5% and the volume is 10~15 mL.

[0012] Preferably, the reaction time after mixing the Bi2O3 / ZnIn2S4 catalyst with the sodium alginate aqueous solution is 12-20 h; the reaction is carried out under stirring conditions.

[0013] Preferably, the sugarcane soaking treatment time is 24~48 h; the refrigerator temperature is -50~-20°C, the freezing time is 1~5 h; and the freeze-drying time is 24~48 h, to obtain a porous sugarcane substrate material.

[0014] Preferably, the drying temperature is 60~80°C; the crosslinking time is 12~16 h; and a Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator is obtained.

[0015] The present invention also provides a Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator prepared by the preparation method described above, wherein the diameter of the Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator is 700~900 nm.

[0016] This invention also provides the application of the Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator described in the above technical solution in seawater desalination and photocatalytic H2O2 production.

[0017] As can be seen from the above technical solution, compared with the prior art, the beneficial effects achieved by the present invention are as follows: The preparation method of the present invention is simple and low in cost. In the prepared S-type heterojunction Bi2O3 / ZnIn2S4, ZnIn2S4 grows tightly on the surface of Bi2O3 nanofibers, which makes the photocatalytic production of H2O2 by the S-type heterojunction Bi2O3 / ZnIn2S4 catalyst highly stable. Attached Figure Description

[0018] 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1(ac) SEM images of ZnIn2S4, Bi2O3 and Bi2O3 / ZnIn2S4 catalysts; (d) HRTEM of BZ-25; (ej) TEM and EDS spectra; (k) SEM image of a cross section of sugarcane; (l) SEM image of a cross section of BZ-25@sugarcane; (m) Magnified view.

[0020] Figure 2 (a) Comparison of XRD patterns of synthesized ZnIn2S4, Bi2O3 and BZ-25 with standard samples; (b) FT-IR spectra; (c) pore characteristics; (d) nitrogen adsorption capacity.

[0021] Figure 3 (a) UV-Vis diffuse reflectance spectra of Bi2O3, ZnIn2S4, and BZ-25; (b) Tauc plots of Bi2O3 and ZnIn2S4 derived from absorption spectra. (c) and (d) Mott-Schottky curves of Bi2O3 at different frequencies. (d) ZnIn2S4.

[0022] Figure 4 (a) Steady-state photoluminescence (PL) spectra, and (b) time-resolved PL decay curves of Bi2O3, ZnIn2S4 and BZ-25 under 350 nm excitation. (c) Electrochemical impedance spectroscopy and photocurrent response of Bi2O3, ZnIn2S4 and BZ-25.

[0023] Figure 5 (a) Photocatalytic hydrogen peroxide production rate graphs of ZnIn2S4, Bi2O3, and BZ-X series composite materials. Recovery test (b) Accumulation test (c) Photocatalytic hydrogen peroxide production rate graphs of ZnIn2S4, Bi2O3, and BZ-25 three-dimensional evaporator. Recovery test (d) Accumulation test.

[0024] Figure 6 (a) Photothermal conversion; (b) Mass loss from photocatalytic water evaporation; (c) Rate diagram; (d) Mass loss of two-dimensional and three-dimensional evaporators under one sun. Figure 7(a) In-situ Fourier transform infrared (FT-IR) spectra acquired under O2 light irradiation. (b) RRDE polarization curves of different catalysts in O2-saturated 0.1 M sodium sulfate buffer solution at 1600 rpm (top: circulation; bottom: disk flow). (c) H2O2 selectivity as a function of applied potential (top) and the calculated average number of transferred electrons (n) as a function of applied potential (bottom). (d) RRDE polarization curves of O2 detected in a nitrogen atmosphere (rotation speed: 1600 rpm) using a platinum ring electrode (potential: -0.23 V compared to Ag / AgCl); the potential of the platinum ring electrode was set to 0.6 V (compared to Ag / AgCl) to detect H2O2.

[0025] Figure 8 The composites of ZnIn2S4, Bi2O3, and BZ-25 under light and dark conditions: (a) DMPO-·OH, (b) DMPO-·O2 - (c)TEMPO-·e - (d)TEMPO-·h + The ESR spectrum.

[0026] Figure 9 Schematic diagram of the S-type heterostructure mechanism of BZ composite material. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the 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. The specific implementation of this invention will be described in detail below with reference to specific embodiments.

[0028] This invention synthesizes and constructs a rational Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator. Bi2O3 nanofibers synthesized by electrospinning followed by controlled calcination serve as the ideal substrate for subsequent ZnIn2S4 growth. The prepared Bi2O3 / ZnIn2S4 is uniformly dispersed in a 1% (w / w) sodium alginate solution to form a homogeneous slurry. This slurry is then uniformly coated onto the surface of a pretreated sugarcane substrate to obtain the three-dimensional evaporator. The optimized Bi2O3 / ZnIn2S4 composite material exhibits significant photocatalytic performance in hydrogen peroxide production, with a production rate far exceeding that of the original ZnIn2S4, Bi2O3, and most reported S-scheme heterojunctions. Furthermore, this composite material achieves highly efficient water evaporation, demonstrating its potential for multifunctional applications. This invention establishes a comprehensive design paradigm that integrates heterojunction structures to achieve advanced photocatalytic applications. Example 1: Preparation of Bi2O3 nanofibers Bi2O3 nanofibers are prepared by electrospinning technology combined with high-temperature calcination. The main process can be divided into three steps: precursor solution preparation, electrospinning and calcination treatment.

[0029] S11. First, the spinning precursor solution was prepared. 1.2 g of bismuth nitrate pentahydrate (Bi(NO3)3 5H2O) was used as the bismuth source and dissolved in 10 mL of N,N-dimethylformamide (DMF) solvent. The solution was continuously stirred magnetically at room temperature until a completely clear solution was formed. Subsequently, 1.7 g of polyvinylpyrrolidone (PVP, molecular weight approximately 1,300,000) was slowly added to the solution, and the mixture was continuously stirred at room temperature for 12 h, ultimately obtaining a homogeneous, stable, and slightly viscous white precursor solution.

[0030] S12. Next, electrospinning is performed. The prepared precursor solution is transferred to a 10 mL syringe, and a 21 G stainless steel spinning needle is installed. The electrospinning process is carried out at room temperature, with the following key process parameters set: the solution advance speed of the syringe pump is controlled at 0.04 mm / min, the distance between the needle tip and the roller collector covered with aluminum foil is fixed at 16 cm, and a 15 kV DC high voltage is applied between them. Under the action of the high-voltage electrostatic field, the precursor solution forms a stable Taylor cone jet, and the solvent evaporates rapidly, thereby depositing a nanofiber membrane composed of PVP and bismuth nitrate on the collector.

[0031] S13. Finally, calcination crystallization treatment is performed. The composite fiber membrane obtained above is placed in a muffle furnace and calcined under a programmed temperature rise in air: heated from room temperature to 450℃ at a heating rate of 2℃ / min, and held at this target temperature for 2 h. This heat treatment process aims to completely decompose and remove the organic polymer PVP, while promoting the conversion of the inorganic bismuth salt precursor into a well-crystallized oxide. After the calcination process is completed, the sample is naturally cooled to room temperature in the furnace, thus finally preparing the nanofiber material composed of Bi2O3.

[0032] Example 2 Preparation of ZnIn2S4 and Bi2O3 / ZnIn2S4 composite materials ZnIn2S4 and its composite material with Bi2O3 nanofibers were synthesized by a simple oil bath method, wherein the mass ratio of Bi2O3 nanofibers in the Bi2O3 / ZnIn2S4 composite material was 2-8%.

[0033] S2. The typical preparation steps for this composite material are as follows: 10 mg of Bi₂O₃ nanofibers were dispersed in a mixed solvent and sonicated to form a homogeneous suspension. Then, 1 mmol of zinc chloride (ZnCl₂), 2 mmol of indium chloride (InCl₃), and 4 mmol of thioacetamide (TAA) were added sequentially, and the mixture was magnetically stirred at room temperature for 1 h to ensure thorough mixing. The mixture was then transferred to a round-bottom flask equipped with a condenser and placed in an 80°C oil bath, where it was refluxed with stirring for 2 h. During the reaction, the system gradually transformed into a dark brown suspension, indicating that ZnIn₂S₄ grew in situ on the surface of the Bi₂O₃ fibers and formed heterojunctions. After the reaction was completed, the mixture was allowed to cool naturally, and the product was collected by centrifugation (8000 rpm, 5 min). It was washed three times each with deionized water and anhydrous ethanol, and finally dried in a vacuum oven at 60°C for 12 h to obtain the composite material.

[0034] Preparation of S3.Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator Fresh sugarcane was selected, peeled, and cut into uniformly sized columnar segments. To remove lignin components, the sugarcane segments were soaked in a mixed solution for 48 h. The treated sugarcane segments were repeatedly washed with deionized water until neutral, then frozen at -20°C for 2 h, and then freeze-dried in a freeze dryer for 48 h to obtain a porous sugarcane substrate material. 0.2 g of the prepared Bi2O3 / ZnIn2S4 composite material was weighed and dispersed in 20 mL of a 1% sodium alginate solution, and magnetically stirred until a uniform slurry was formed. The slurry was uniformly coated onto the surface of the pretreated sugarcane substrate, and after full absorption, the coating operation was repeated to ensure uniform loading. The coated sample was dried in a 60°C oven, and then immersed in a 1% CaCl2 solution for crosslinking for 12 h to allow the sodium alginate to solidify and form the substrate. Finally, the sample was removed and rinsed with deionized water to remove residual CaCl2 on the surface, and then dried again to obtain the Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator.

[0035] Comparative Example 1 In contrast, a pure-phase ZnIn2S4@sugarcane three-dimensional evaporator was prepared using the same method as in Examples 2 and 3, but without the addition of Bi2O3 nanofibers.

[0036] The following sections describe the characterization, photocatalytic activity, photocatalytic water evaporation, and photocatalytic mechanism of the composite materials obtained in the examples and comparative examples. Material characterization and analysis: 1. Structural and morphological characteristics The morphology and microstructure of the prepared samples were studied using scanning electron microscopy and transmission electron microscopy systems. For example... Figure 1As shown in figure a, the original Bi₂O₃ exhibits a continuous fibrous structure with a smooth surface and a diameter of approximately 200 nm, which is the result of electrospinning followed by calcination. In contrast, pure ZnIn₂S₄ exhibits aggregated nanosheets ( Figure 1 b). After hybridization, the BZ composite material retains the one-dimensional morphology of Bi2O3, while ZnIn2S4 is uniformly anchored on the nanofiber surface, forming an integrated heterostructure. Figure 1 c). The rod-like morphology of ZnIn2S4 in the composite material indicates that the presence of the Bi2O3 substrate guided the anisotropic growth of ZnIn2S4 during the oil bath process. High-resolution TEM (HRTEM) Figure 1 d) Further analysis revealed the tight contact at the interface. Lattice fringes with spacings of 0.327 nm and 0.315 nm were clearly observed, corresponding to the (311) plane of cubic ZnIn2S4 and the (120) plane of monoclinic Bi2O3, respectively. The clear interface connection between the two phases indicates coherent interfacial coupling, which is beneficial for charge transfer. The spatial elemental distribution was analyzed using STEM-EDS mapping (…). Figure 1 (ej). The bismuth signal was concentrated on the nanofiber framework, while indium, zinc, and sulfur were distributed in a shell-like structure around the fiber core, confirming the uniform growth of ZnIn2S4 on the Bi2O3 support without obvious aggregation or phase separation. Figure 1 As shown in Figure k, a highly ordered biological tissue structure was observed inside the sugarcane stem: vascular bundles, as functional units responsible for the directional transport of water, are evenly distributed within a honeycomb-like matrix composed of numerous thin-walled cells. The longitudinal vascular bundle network composed of sieve tubes was effectively preserved after treatment and transformed into vertically arranged microchannels, providing an efficient water supply path for the evaporator. The surrounding thin-walled cells are arranged in a continuous honeycomb-like porous structure, which helps enhance the material's capture and absorption of incident sunlight through multiple light scattering effects. Further magnified observation (…) Figure 1 The data (m) shows that BZ-25 nanoparticles exhibit significant aggregation on the porous framework of sugarcane. These structural features provide an ideal foundation for efficient interfacial charge separation and transport, which is crucial for the enhanced photocatalytic activity observed in hydrogen peroxide production and photocatalytic water evaporation.

[0037] X-ray diffraction (XRD) is used to analyze the crystal structure of prepared samples. According to XRD... Figure 2a) The diffraction peaks of sample BZ-25 can be clearly attributed to two phases, and no impurity peaks appear, verifying that it is successfully composed of ZnIn2S4 and Bi2O3. The diffraction peaks of pure ZnIn2S4 at 2θ=21.6, 27.6, 39.7, 47.3, 52.4 and 55.5 are completely consistent with the characteristic peak positions and relative intensities of the standard card of hexagonal ZnIn2S4 (JCPDS:65-2023), corresponding to its (006), (102), (108), (110), (116) and (022) crystal planes, respectively. The diffraction peaks of pure-phase Bi₂O₃ at 2θ values ​​of 27.4, 28.0, 33.0, and 46.3 precisely match the characteristic peaks of the monoclinic Bi₂O₃ standard card (JCPDS: 71-2274), mainly corresponding to its (120), (012), (200), and (041) crystal planes. Composite structure verification: Both sets of diffraction peaks appear simultaneously in the graph, and all peak positions show no significant shift, indicating that no solid solution was formed during the composite process, but rather a composite structure of ZnIn₂S₄ and Bi₂O₃ coexisting was successfully constructed. No other impurity phase peaks were detected in the spectrum, further proving the phase purity of the composite product. Figure 2 In section b, BZ series samples synthesized under different preparation conditions can be observed. All samples show diffraction patterns consistent with standard ZnIn2S4. This is because ZnIn2S4 is the main component in the composite material. As the amount of Bi2O3 gradually increases, the diffraction peaks belonging to ZnIn2S4 gradually decrease, directly proving the successful preparation of the BZ series composite materials.

[0038] according to Figure 2 Fourier transform infrared (FT-IR) spectroscopy was used in image c to analyze the surface functional groups of the sample. This FT-IR spectroscopy analysis revealed the presence of significant hydroxyl groups and adsorbed water characteristics in the material, as shown at 3425 cm⁻¹. -1 The OH stretching vibration peak at 1615 cm⁻¹ -1 The nearby HOH bending vibration peak. And at 1000-1200 cm⁻¹. -1 The Bi-O and SO bonds at the sites originate from the calcination of the Bi2O3 / PVP nanofiber membrane in a muffle furnace, and from the reaction of the calcined Bi2O3 with ZnIn2S4 in an oil bath. The infrared spectrum of the composite material BZ-25 shows the superposition of the characteristic peaks of both components, indicating that it successfully combines ZnIn2S4 and Bi2O3. Overall, the spectrum clearly reflects the chemical bond composition and structural differences in the sample. Figure 2As shown in d and e, Brunauer-Emmett-Teller (BET) measurements were performed to evaluate the specific surface area and pore structure of the synthesized material. Type IV isotherms with hysteresis loops (P / P0 = 0.4–1.0) indicate the presence of a mesoporous structure. The calculated BET specific surface area of ​​the BZ composite is 54.375 m². 2 / g, significantly higher than ZnIn2S4 nanosheets (24.502 m 2 / g) and Bi2O3 nanofibers (3.535 m 2 / g). The total pore volume also increased from 0.266 cm³ of ZnIn₂S₄ nanosheets. 3 / g and 0.016 cm of Bi2O3 nanofibers 3 / g, increased to 0.290 cm³ of BZ composite material. 3 / g. This increase is attributed to the uniform dispersion of ZnIn2S4 nanosheets on the surface of Bi2O3 nanofibers, which improves charge transfer efficiency, increases the number of active sites for water reduction, and enhances light utilization through multiple scattering and reflection. These properties collectively enhance the photocatalytic hydrogen peroxide production performance of the BZ composite material.

[0039] 2. Band Structure and Charge Transfer As shown in Figure 10a, the three materials exhibit strong light absorption in the 200-400 nm ultraviolet region, based on their absorption trends. Notably, significant differences arise in the visible light region (wavelengths greater than 400 nm): the absorption of Bi₂O₃ and ZnIn₂S₄ decreases sharply, approaching zero after 500 nm, indicating their photoresponse is primarily concentrated in the ultraviolet region. In contrast, BZ-25 maintains relatively stable absorption performance across the entire 200-800 nm wavelength range without significant attenuation, as shown in Figure 10b, where the band gaps for Bi₂O₃ and ZnIn₂S₄ are 2.9 eV and 2.86 eV, respectively. In summary, BZ-25 demonstrates balanced and sustained light absorption across a wide spectral range, exhibiting excellent light utilization potential, particularly suitable for photocatalytic systems requiring a full-spectrum photoresponse. While Bi₂O₃ and ZnIn₂S₄ possess high absorption peaks in the ultraviolet region, their weaker visible light response may limit their application scenarios.

[0040] Mott-Schottky measurements can elucidate semiconductor type and flat band potential, parameters that are crucial for understanding the band structure of catalysts. Figure 3Figures c and d show the UV-Vis diffuse reflectance spectra of the original Bi₂O₃, ZnIn₂S₄, and the composite material represented by BZ-25. Under the Ag / AgCl electrode, Bi₂O₃ exhibits a positive slope in its Mott-Schottky curve at different frequencies (500, 1000, 1500 Hz), indicating it is a typical p-type semiconductor, with a flat band potential of 2.76 V at the X-axis intersection. Conversely, ZnIn₂S₄ exhibits the opposite behavior at different frequencies (1000, 2000, 3000 Hz), indicating it is a typical n-type semiconductor with a flat band potential of -0.94 V. Since the conduction and valence bands of semiconductors are typically about 0.2 V further negative than the flat band potential, and considering their band gaps, the conduction band of Bi₂O₃ is approximately +0.06 V, and its valence band is approximately +2.96 V; the conduction band of ZnIn₂S₄ is approximately -1.14 V, and its valence band is approximately +1.72 V.

[0041] The charge transfer and utilization kinetics within the Bi₂O₃ / ZnIn₂S₄ heterostructure were investigated using photophysical characterization. Figure 4 As shown in Figure a, it can be clearly observed that the PL luminescence spectrum of the BZ-25 material measured at an excitation wavelength of 350 nm is smaller than that of the two individual materials. This indicates that the formed BZ heterojunction material can effectively improve the separation efficiency and suppress useless photogenerated electrons and holes; furthermore, Figure 4 b shows the time-varying TRPL spectra of the three materials. It's evident that the average carrier lifetime of pure-phase ZnIn2S4 is only 3.09 ns, and that of Bi2O3 is only 4.15 ns. However, the average carrier lifetime of the composite BZ-25 material is significantly increased to 9.10 ns, three times that of pure-phase ZnIn2S4. This indicates that the formation of the heterojunction significantly modulates the carrier transport path at the interface. The built-in electric field and band bending established at the heterojunction interface guide the spatially directional separation of photogenerated electrons and holes. Therefore, the substantial increase in carrier lifetime in the BZ-25 composite material directly confirms the successful construction and efficient operation of the S-type heterojunction structure, laying a crucial kinetic foundation for improving the material's photocatalytic activity (photocatalytic H2O2 production).

[0042] To systematically analyze the charge transfer kinetics and interfacial behavior of photocatalysts, this invention conducted photocurrent response and electrochemical impedance spectroscopy (EIS) tests. Figure 4 As shown in Figure c, the transient photocurrent response of the composite material exhibits significantly enhanced characteristics, rapidly and stably generating photocurrent under illumination. The consistently high photocurrent density and the almost non-decaying characteristic during multiple switching cycles confirm that the composite material possesses excellent photoinduced charge separation performance and suppressed recombination kinetics. Furthermore, the Nyquist plot ( Figure 4d) shows that the semicircular diameter of the heterostructure is significantly smaller than that of the original material, indicating that its charge transfer resistance is reduced and the interface charge separation efficiency is improved.

[0043] (II) Photocatalytic activity testing and analysis: 1. Photocatalytic hydrogen peroxide production testing and analysis The hydrogen peroxide generation rate of the prepared photocatalyst is as follows: Figure 5 As shown in Figure a, Bi₂O₃ itself does not possess the ability to photocatalytically produce hydrogen peroxide. However, after introducing different masses of Bi₂O₃ into ZnIn₂S₄, the rate of photocatalytic hydrogen peroxide production showed a trend of first increasing and then decreasing from BZ-10 to BZ-40, with the rate decreasing from 1.01 mmol·g⁻¹ in ZnIn₂S₄. -1 ·h -1 Gradually increased to 6.3 mmol·g for BZ-25. -1 ·h -1 The rate is five times that of pure-phase ZnIn2S4. Based on this, the ability of the BZ-25@sugarcane three-dimensional evaporator to produce hydrogen peroxide in a sacrificial agent was tested. The final production rate obtained is slightly different from the rate calculated for the powdered form. After six cycles, the BZ composite material maintained good efficiency in hydrogen peroxide production, and the catalyst structure did not show significant damage, indicating good photochemical stability. Regarding recyclability, the catalyst recovery rate was higher than 95% after each cycle, indicating that the material is easy to separate and reuse, possessing good potential for practical application. For the three-dimensional evaporator, recovery is even more convenient, and there is almost no catalyst loss, so performance is not reduced. In summary, the B composite material and the three-dimensional evaporator exhibit good cycle stability and recyclability in the photocatalytic hydrogen peroxide production reaction, providing experimental evidence for its practical application in sustainable energy conversion systems.

[0044] 2. Photocatalytic water evaporation test and analysis like Figure 6 The three-dimensional evaporator shown in figure a reaches 47°C in 180 s under dry conditions. Figure 8 Figures b and c demonstrate the mass loss and water evaporation rate of the BZ-25@sugarcane three-dimensional evaporator under three different light intensities, achieving an evaporation efficiency of 3.39 kg·m³ under one sun. -2 ·h -1 , Figure 8 d. A comparison of mass loss and water evaporation rate between two-dimensional and three-dimensional evaporators shows that the water evaporation rate of the three-dimensional evaporator is much higher than that of the two-dimensional structure, while the two-dimensional structure still suffers from downward heat loss. In contrast, the three-dimensional evaporator achieves a higher evaporation rate through increased surface area and environmental energy harvesting technology.

[0045] (III) Photocatalytic mechanism analysis Test and analysis: 1 In-situ infrared and rotating ring-disk electrode (RRDE) test and analysis In-situ diffuse reflectance infrared Fourier transform spectroscopy (drift) collected over time under visible light irradiation was used to monitor the evolution of key intermediates during the oxygen reduction reaction (ORR). As Figure 6 shown in a, in the dark condition, there is no signal. After the light is turned on, the absorption peak intensities at 1635, 1560, 1083, 1043, and 800 cm -1 etc. all show an increasing trend with the light irradiation time (2 - 14 min). This indicates that photoexcitation induces the generation of a series of surface oxygen-containing intermediates, which accumulate continuously during the reaction. Among them, the peak at 880 cm -1 can be attributed to the O - O bond; the peak at 1043 cm -1 is attributed to ·O 2- ; the peak at 1083 cm-¹ can be attributed to *OOH; the peak at 1560 cm -1 is attributed to *HOOH; the peak at 1635 cm -1 can be attributed to H2O molecules. These phenomena further illustrate that the generation of H2O2 by the BZ composite material under light irradiation is generated through the 2e - (ORR) pathway.

[0046] To clarify the origin of photocatalytic hydrogen peroxide generation, the present invention conducted control experiments using BZ-25 under different atmospheres. As Figure 6 shown in b (the following figure), as the potential shifts from 0.2 V to more negative values (relative to Ag / AgCl), the reduction disk currents of ZnIn2S4, Bi2O3, and the BZ-25 composite material gradually increase. At the same time, the hydrogen peroxide generated on the disk diffuses to the ring electrode, where it undergoes oxidation to generate a positive oxidation current. As Figure 6 shown in b (the upper figure), the order of the ring currents is Bi2O3 < ZnIn2S4 < BZ-25 composite material, indicating that the BZ-25 composite material generates the largest amount of hydrogen peroxide among all the catalysts. The hydrogen peroxide selectivity ([[ID=​​​​​​​​​​ Figure 7 As shown in a and b, with DMPO as the scavenger, no characteristic signals of DMPO-·OH or DMPO-·O2 were detected in all samples (BZ-25, ZnIn2S4, Bi2O3) under dark conditions. - Under light illumination conditions, obvious characteristic peak signals of DMPO-·OH and DMPO-·O2 appeared in all three samples. - The signal intensity order was: BZ-25 > ZnIn2S4 > Bi2O3. This order was completely consistent with the photocatalytic H2O2 production activity order, indicating that ·O2 - (generated by the reduction of O2 by photogenerated electrons) was the key precursor for H2O2 production, and its generation efficiency directly determined the final yield. In addition Figure 7 Figures c and d showed completely different results. With TEMPO as the scavenger, for e - and h + were captured. Under dark conditions, there was no signal for TEMPO-e - , while there was a signal for TEMPO-h + . Under light illumination conditions, obvious signals appeared for TEMPO-e - , and the signal intensity order was: BZ-25 > ZnIn2S4 > Bi2O3; for TEMPO-h + the signal weakened during light illumination, and the signal intensity order was: BZ-25 < ZnIn2S4 < Bi2O3.

[0048] Based on the above phenomena, BZ-25 showed the strongest ·OH / ·O2 - radical signals and e - signals under light illumination, but its h + signal was the weakest; while the Bi2O3 material showed the opposite trend. This contradictory phenomenon can be unifiedly explained by the S-scheme heterojunction mechanism: in BZ-25, the internal electric field drives the holes of ZnIn2S4 and the electrons of Bi2O3 to selectively recombine at the interface, thereby effectively separating and retaining the highly reducing e - (for the efficient reduction of O2 to generate H2O2) on the Bi2O3 side and the highly oxidizing h + on the Bi2O3 side. This not only inhibits the overall recombination of carriers but also maintains the strong redox ability of the system, ultimately making the photocatalytic H2O2 production activity of the composite BZ-25 significantly better than its single components.

[0049] (IV) Analysis of the S-scheme heterojunction mechanism When Bi₂O₃ and ZnIn₂S₄ are used as single materials, they each suffer from problems such as easy recombination of photogenerated carriers and limited catalytic efficiency. However, when they recombine upon contact, the Fermi levels align, forming a built-in electric field at the interface, causing band bending and forming an S-shaped heterojunction structure. This structure provides a directional transfer path for photogenerated charges: under illumination, electrons in the Bi₂O₃ conduction band migrate to the ZnIn₂S₄ valence band and recombine with holes, while electrons in the ZnIn₂S₄ conduction band and holes in the Bi₂O₃ valence band are retained and spatially separated, thus preserving both strong reducing and strong oxidizing sites. This mechanism not only significantly suppresses carrier recombination but also allows the reducing electrons accumulated in the ZnIn₂S₄ conduction band to continuously and efficiently convert O₂ into H₂O₂ through a two-electron reduction pathway, while holes in the Bi₂O₃ valence band are consumed in time, preventing the decomposition of already generated H₂O₂. Therefore, the S-shaped heterojunction, through the synergistic effect of band modulation and charge separation, significantly improves the performance of photocatalytic H₂O₂ production.

Claims

1. A method for preparing a Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator, characterized in that, Includes the following steps: Preparation of S1.Bi2O3 nanofibers S11. Preparation of precursor solution: Dissolve bismuth source in N,N-dimethylformamide solvent and stir until a clear solution is formed. Add polyvinylpyrrolidone to the clear solution and continue stirring to obtain a homogeneous and stable precursor solution for later use. S12. Electrospinning The electrospinning process was carried out at room temperature, and the key process parameters were set as follows: the precursor solution propulsion speed of the injection pump was 0.02-0.06 mm / min, the distance between the needle tip and the roller collector covered with aluminum foil was fixed at 12-18 cm, and a DC high voltage of 12-18 kV was applied between the two to deposit the composite nanofiber membrane. S13. Calcination and crystallization treatment The composite nanofiber membrane was placed in a muffle furnace and calcined under a programmed temperature rise in air atmosphere; after the calcination process was completed, it was naturally cooled to room temperature to obtain Bi2O3 nanofibers. Preparation of S2.ZnIn2S4 and Bi2O3 / ZnIn2S4 catalysts After uniformly dispersing the obtained Bi2O3 nanofibers in water and adjusting the pH value, zinc chloride, indium chloride and thioacetamide were added in sequence to allow ZnIn2S4 nanosheets to grow in situ on the surface of Bi2O3 nanofibers. After centrifugation, washing and vacuum drying, an S-type heterojunction Bi2O3 / ZnIn2S4 catalyst with photocatalytic performance was obtained. Preparation of S3.Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator The prepared Bi₂O₃ / ZnIn₂S₄ was uniformly dispersed in a 1% (w / w) sodium alginate solution to form a homogeneous slurry. The slurry was then uniformly coated onto the surface of a pretreated sugarcane substrate, dried at 60°C, and then mixed with Ca... 2+ Cross-linking, then rinse the surface with deionized water to remove residual Ca. 2+ The mixture was dried again to obtain Bi2O3 / ZnIn2S4@sugarcane three-dimensional evaporator.

2. The preparation method according to claim 1, characterized in that, The bismuth nitrate pentahydrate was 1-3 g in mass, the N,N-dimethylformamide (DMF) solvent volume was 5-15 mL, the polyvinylpyrrolidone (PVP) was 1-3 g in mass, and the stirring time was 10-16 h. During the electrospinning process, the solution propulsion speed of the injection pump was 0.04-0.1 mm / min, and the applied DC high voltage was 12-17 kV, resulting in a nanofiber membrane composed of PVP and bismuth nitrate.

3. The preparation method according to claim 2, characterized in that, The composite nanofiber membrane was annealed for 1–3 h at a temperature of 300–500 °C at a heating rate of 2–5 °C / min to obtain Bi₂O₃ nanofibers. The molar ratio of Bi₂O₃ sample, zinc chloride, indium chloride, and thioacetamide was (0.02–0.08):(1–4):(2–6):(4–8). The in-situ growth reaction was carried out at a temperature of 60–110 °C for 1–6 h.

4. The preparation method according to claim 1, characterized in that, After the in-situ growth reaction, the product liquid is further subjected to centrifugation, washing and vacuum drying in sequence to obtain Bi2O3@ZnIn2S4 catalyst; the centrifugation speed is 8000~10000 rpm and the centrifugation time is 5~10 min; the vacuum drying temperature is 50~80℃ and the vacuum time is 10~20 h.

5. The preparation method according to claim 1, characterized in that, The mass of the S-type heterojunction Bi2O3@ZnIn2S4 catalyst is 0.2~1 g; the concentration of the sodium alginate aqueous solution is 2~5% and the volume is 15~20 mL; the concentration of the CaCl2 solution is 1~5% and the volume is 10~15 mL.

6. The preparation method according to claim 5, characterized in that, The reaction time of the Bi2O3@ZnIn2S4 catalyst mixed with sodium alginate aqueous solution is 12-20 h; the reaction is carried out under stirring conditions.

7. The preparation method according to claim 1, characterized in that, The sugarcane was soaked for 24-48 hours; the refrigerator temperature was -50 to -20°C, and the freezing time was 1-5 hours; the freeze-drying time was 24-48 hours, resulting in a porous sugarcane substrate material.

8. The preparation method according to any one of claims 1 to 7, characterized in that, The drying temperature is 60~80℃; the crosslinking time is 12~16 h; and a Bi2O3@ZnIn2S4@sugarcane three-dimensional evaporator is obtained.

9. The Bi2O3@ZnIn2S4@sugarcane three-dimensional evaporator prepared according to any one of claims 1 to 8, characterized in that, The diameter of the Bi2O3@ZnIn2S4@sugarcane three-dimensional evaporator is 700~900 nm.

10. The application of the Bi2O3@ZnIn2S4@sugarcane three-dimensional evaporator according to claim 9 in seawater desalination and photocatalytic H2O2 production.

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