A tunable hierarchical ZnO microsphere with sea urchin-like structure based on Chlorella, its preparation method and application

Abstract

This invention provides a method for preparing and applying tunable multi-level ZnO microspheres with a sea urchin-like structure based on Chlorella, belonging to the field of bioprocessing and photoelectrocatalytic degradation of pollutants. In this invention, Chlorella serves as a biological template, a micrometer-sized spherical template coated with a layer of Fe3O4 nanoparticles, further growing a layer of ZnO nanorods. This results in two scale levels, namely micrometer and nanometer sizes, hence the name micrometer-nano composite multi-level structured microspheres. Through rational structural design, tunable three-dimensional multi-level ZnO microspheres are prepared, yielding Chlorella-based ZnO microspheres with excellent light absorption performance and high-efficiency photoelectrocatalytic activity, which can be used in the field of photoelectrocatalytic degradation of organic pollutants.

Description

Technical Field

[0001] This invention relates to the fields of bioprocessing and photoelectrocatalytic degradation of pollutants, and particularly to a tunable multi-level ZnO microsphere with a sea urchin-like structure based on Chlorella, its preparation method, and its application. Background Technology

[0002] Compared to simple monolayer particles, micro- and nanoparticles with complex hierarchical structures possess unique properties in mechanics, chemistry, optics, and electronics. These complex hierarchical structures endow micro- and nanoparticles with enhanced functionality, showing great promise in fields such as energy, catalysis, and biomedicine. In nature, microorganisms exhibit diverse morphologies, uniform size, environmental friendliness, and ease of modification and expansion. The design and fabrication of micro- and nanoparticles with complex hierarchical structures based on microbial templates has become a research frontier.

[0003] Currently, micro- and nanoparticles prepared based on microbial templates are typically core-shell microparticles coated with metals or metal oxides. However, they are mostly simple surface depositions or disordered assemblies, lacking complex hierarchical structures, which greatly limits their functions and applications. Furthermore, ZnO nanomaterials are a typical inorganic photocatalytic functional material with advantages such as structural diversity and stable performance. Significant progress has been made in preparing core-shell ZnO nanomaterials and constructing complex structures. However, due to the simple stacking or disordered assembly of ZnO nanostructures on the surface, ZnO nanostructures suffer from poor photoelectrocatalytic efficiency. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a tunable multi-level ZnO microsphere with a sea urchin-like structure based on Chlorella, its preparation method, and its applications. The tunable multi-level ZnO microsphere with a sea urchin-like structure based on Chlorella provided by this invention possesses excellent light absorption and photoelectrocatalytic properties.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a urchin-shaped, tunable multi-level ZnO microsphere based on Chlorella. The microsphere is formed by a Chlorella cell as the core. From the inside out, the surface of the Chlorella cell is sequentially coated with a magnetic coating and a nanorod array shell. The magnetic coating is composed of iron oxide nanoparticles, and the nanorod array shell is composed of ZnO nanorods.

[0007] Preferably, the ZnO nanorods have a diameter of 0–403 nm and are not zero, and a length of 0–1381 nm and are not zero.

[0008] Preferably, the particle size of the iron oxide nanoparticles is 40–60 nm.

[0009] This invention also provides a method for preparing urchin-like tunable multi-level ZnO microspheres based on Chlorella as described in the above technical solution, comprising the following steps:

[0010] Chlorella was pretreated by soaking it in a glutaraldehyde solution to obtain pretreated Chlorella.

[0011] The pretreated Chlorella was dispersed in Fe3O4 suspension to obtain magnetic Chlorella;

[0012] A ZnO seed layer was deposited on the surface of the magnetic Chlorella by magnetron sputtering, followed by hydrothermal growth of ZnO to form a nanorod array shell, thus obtaining the urchin-like tunable multi-level structured ZnO microspheres based on Chlorella.

[0013] Preferably, the magnetron sputtering power is 50-150W and the time is 5-20min.

[0014] Preferably, the hydrothermal growth temperature of ZnO is 80-85℃, and the time is 0-16h, not 0.

[0015] Preferably, the hydrothermal growth temperature of ZnO is 80℃ and the time is 12-14h.

[0016] Preferably, the raw materials for the hydrothermal growth of ZnO include zinc nitrate and hexamethylenetetramine.

[0017] The present invention also provides the application of the urchin-shaped tunable multi-level structure ZnO microspheres based on Chlorella as described in the above technical solution, or the urchin-shaped tunable multi-level structure ZnO microspheres based on Chlorella prepared by the above technical solution, in the photoelectrocatalytic degradation of organic pollutants.

[0018] Preferably, the organic pollutant includes tetracycline.

[0019] This invention provides a tunable, multi-level ZnO microsphere based on Chlorella, resembling a sea urchin. Using a microspherical Chlorella cell as the core, the surface of the cell is sequentially coated with a magnetic coating and a nanorod array shell. The magnetic coating is composed of iron(III) oxide nanoparticles, and the nanorod array shell is composed of ZnO nanorods. In this invention, Chlorella serves as a biological template, a micrometer-sized spherical template coated with a layer of Fe3O4 nanoparticles, further growing a layer of ZnO nanorods. This exhibits two scale levels simultaneously, namely micrometer and nanometer sizes, hence the name micrometer-nano composite multi-level structured microsphere. Through rational structural design, the preparation of three-dimensional multi-level tunable ZnO microspheres is achieved, resulting in Chlorella-based ZnO microspheres with excellent light absorption performance and highly efficient photoelectrocatalytic activity. These microspheres demonstrate excellent performance in the photoelectrocatalytic degradation of organic pollutants, along with excellent chemical stability and mechanical durability, showing significant potential in environmental remediation.

[0020] This invention also provides a method for preparing the urchin-shaped, tunable, multi-level ZnO microspheres based on Chlorella, as described in the above-mentioned technical solution. This invention achieves the deposition of superparamagnetic Fe3O4 nanoparticles on the surface of Chlorella cells through a bioforming method, and further prepares urchin-shaped, controllable, and tunable multi-level microspheres based on Chlorella through magnetron sputtering and hydrothermal growth. Leveraging the advantage of Chlorella as a biological template containing abundant chlorophyll, combined with the heterojunction between the Fe3O4 nanoparticle layer and the ZnO nanorod shell layer, and the presence of a regular three-dimensional ZnO nanorod array, these urchin-shaped, multi-level microspheres based on Chlorella exhibit excellent light absorption performance and photocatalytic activity. Under xenon lamp irradiation, they demonstrate excellent photocatalytic performance, achieving efficient degradation of organic pollutants such as tetracycline. Even after long-term ultrasonic vibration and photocorrosion processes, they maintain good chemical stability and mechanical durability. The process of this invention is simple and controllable, with mild conditions, and is easy to mass-produce. The prepared Chlorella-based sea urchin-shaped multi-level microspheres have excellent light absorption performance, photoelectrocatalytic performance, and cycle stability, and are suitable for wastewater treatment and other related fields. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of the method for preparing urchin-shaped tunable multi-level ZnO microspheres based on Chlorella in an embodiment of the present invention.

[0022] Figure 2 These are scanning electron microscope images of the original Chlorella, the Chlorella coated with Fe3O4 nanoparticles, and the Chlorella-based sea urchin-like hierarchical ZnO microspheres, as described in this embodiment of the invention.

[0023] Figure 3The images are scanning electron microscope (SEM) images of urchin-like tunable hierarchical ZnO microspheres based on Chlorella vulgaris before and after 12 hours of hydrothermal reaction at different ZnO seed layer sputtering times (5, 10, 15, 20 min).

[0024] Figure 4 The image shows a scanning electron microscope (SEM) image of urchin-like tunable hierarchical ZnO microspheres based on Chlorella, produced under the same ZnO seed layer sputtering time (10 min) and hydrothermal reaction time of 3–12 h in an embodiment of the present invention.

[0025] Figure 5 Hysteresis loop diagrams of Chlorella microparticles coated with Fe3O4 nanoparticle layers and ZnO microspheres with sea urchin-like hierarchical structure based on Chlorella, as shown in the embodiments of the present invention.

[0026] Figure 6 The UV-Vis diffuse reflectance spectra of Chlorella microparticles coated with Fe3O4 nanoparticle layers, pure ZnO nanoparticles, and ZnO microspheres with a sea urchin-like hierarchical structure based on Chlorella microparticles are shown in the embodiments of the present invention.

[0027] Figure 7 Impedance diagrams of Chlorella microparticles coated with Fe3O4 nanoparticle layers and ZnO microspheres with sea urchin-like hierarchical structure based on Chlorella, as shown in the embodiments of the present invention; transient photocurrent-time diagrams of Chlorella microparticles coated with Fe3O4 nanoparticle layers, pure ZnO nanoparticles, and sea urchin-like hierarchical microspheres based on Chlorella.

[0028] Figure 8 The figures show the photoelectrocatalytic degradation curves of tetracycline under xenon lamps for Chlorella microparticles coated with Fe3O4 nanoparticle layers, pure ZnO nanoparticles, and ZnO microspheres with a sea urchin-like hierarchical structure based on Chlorella; and the photoelectrocatalytic degradation curves of tetracycline under xenon lamp, 365nm ultraviolet lamp, and visible light irradiation for ZnO microspheres with a sea urchin-like hierarchical structure based on Chlorella. Detailed Implementation

[0029] This invention provides a tunable multi-level structured ZnO microsphere (Ch.@Fe3O4.ZnO nanorods) based on Chlorella, with microspherical Chlorella cells as the core. From the inside out, the surface of the microspherical Chlorella cells is sequentially coated with a magnetic coating layer and a nanorod array shell. The magnetic coating layer is composed of iron(III) oxide nanoparticles, and the nanorod array shell layer is composed of ZnO nanorods.

[0030] In this invention, the diameter of the ZnO nanorod is preferably 0 to 403 nm and not 0, and the length is preferably 0 to 1381 nm and not 0.

[0031] In this invention, the particle size of the iron oxide nanoparticles is preferably 40-60 nm.

[0032] This invention also provides a method for preparing urchin-like tunable multi-level ZnO microspheres based on Chlorella as described in the above technical solution, comprising the following steps:

[0033] Chlorella (Ch.) was pretreated by soaking in glutaraldehyde solution to obtain pretreated Chlorella;

[0034] The pretreated Chlorella was dispersed in Fe3O4 suspension to obtain magnetic Chlorella (Ch@Fe3O4);

[0035] A ZnO seed layer was deposited on the surface of the magnetic Chlorella by magnetron sputtering, followed by hydrothermal growth of ZnO to form a nanorod array shell, thus obtaining the urchin-like tunable multi-level structured ZnO microspheres based on Chlorella.

[0036] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0037] This invention involves pretreating Chlorella by soaking it in a glutaraldehyde solution to obtain pretreated Chlorella.

[0038] In this invention, the Chlorella is preferably dispersed evenly in deionized water and ultrasonically cleaned for 5-10 minutes. Then, it is collected using a high-speed centrifuge (8000-10000 r / min) and repeatedly cleaned to obtain monodisperse Chlorella with a smooth surface and uniform morphology, which is then subjected to the pretreatment described above.

[0039] In this invention, the mass fraction of the glutaraldehyde solution is preferably 2-3%, more preferably 2.5%.

[0040] In this invention, the soaking temperature is preferably 2-4°C and the soaking time is preferably 12-16 hours, so as to fix the cell structure of Chlorella and maintain the integrity and stability of the spherical structure.

[0041] In this invention, the soaking process preferably includes sequential washing and centrifugal collection. This invention does not have any particular limitation on the specific methods of washing and centrifugal collection, and any method known to those skilled in the art can be used.

[0042] After obtaining the pretreated Chlorella, the present invention disperses the pretreated Chlorella in Fe3O4 suspension to obtain magnetic Chlorella.

[0043] In this invention, the preferred ratio of the pretreated Chlorella to Fe3O4 suspension is 200 mg: 50 mL, and the Fe3O4 nanoparticles in the Fe3O4 suspension are preferably prepared from 8 mmol of ferric chloride hexahydrate and 16 mmol of ferrous chloride tetrahydrate.

[0044] In this invention, the particle size of the Fe3O4 nanoparticles in the Fe3O4 suspension is preferably 40-60 nm.

[0045] In this invention, the Fe3O4 suspension is preferably prepared by a method comprising the following steps:

[0046] Ferric chloride hexahydrate (FeCl3·6H2O, 8 mmol) and ferrous chloride tetrahydrate (FeCl2·4H2O, 16 mmol) were added to deionized water (40 mL) and sonicated for 5–10 min to mix thoroughly. The mixture was then placed in an ultrasonic water bath to maintain the temperature at 45–50 °C. Sodium hydroxide (NaOH, 0.5 mmol) was weighed and prepared into a 10 mL aqueous solution, which was then added dropwise to the mixture under ultrasonication. The mixture gradually became a uniform black suspension. The suspension was sonicated at 50–55 °C for 55–60 min. The suspension was then washed 3–5 times with deionized water, and Fe3O4 nanoparticles with a particle size of 40–60 nm were obtained by magnetic separation. The Fe3O4 nanoparticles were dispersed in 50 mL of deionized water, and dilute hydrochloric acid (1 M) was added to adjust the pH of the solution to 3–4. The mixture was then sonicated for 30–35 min to obtain the Fe3O4 suspension.

[0047] In a specific embodiment of the present invention, the pretreated Chlorella is preferably added to the Fe3O4 suspension, transferred to a shaker and subjected to continuous gentle shaking (100-150 r / min). After 22-24 h, vacuum filtration is performed using a filter membrane with a pore size of 0.8-1.2 μm, and the mixture is repeatedly dispersed and washed with deionized water to collect the magnetic Chlorella.

[0048] After obtaining the magnetic Chlorella, the present invention performs magnetron sputtering deposition of a ZnO seed layer on the surface of the magnetic Chlorella, and then performs hydrothermal growth of ZnO to form a nanorod array shell, thereby obtaining the urchin-shaped tunable multi-level structured ZnO microspheres based on Chlorella.

[0049] In this invention, the magnetron sputtering power is preferably 50-150W, and the time is preferably 5-20min.

[0050] The present invention preferably involves uniformly dispersing the magnetic Chlorella particles in ethanol, and then spraying them onto a 10×10cm surface. 2 The glass plate was allowed to air dry naturally, and a ZnO seed layer was deposited on the glass plate, which was uniformly coated with magnetic Chlorella particles, by magnetron sputtering.

[0051] In this invention, different arrangements of zinc oxide nanorod shells are obtained by magnetron sputtering deposition of ZnO seed layers. The diameter, length, and density of the zinc oxide nanorods are controlled by the magnetron sputtering time of the ZnO seed layer. When the magnetron sputtering time increases from 5 to 20 minutes, under the condition that the hydrothermal growth conditions of ZnO remain unchanged, the shell of the ZnO nanorod array based on urchin-like hierarchical ZnO microspheres of Chlorella changes from a loose and disordered arrangement to a tight, ordered, and well-directional regular arrangement, and the diameter and length of the ZnO nanorods also change.

[0052] In this invention, the hydrothermal growth temperature of ZnO is preferably 80–85°C, more preferably 80°C, and the time is preferably 0–16 h, more preferably 12–14 h. In this invention, the diameter and length of the zinc oxide nanorods are controlled by adjusting the hydrothermal growth time of ZnO; when the reaction time increases from 0 to 12 h, the diameter and length of the ZnO nanorods increase while the solution concentration remains constant.

[0053] In this invention, the raw materials for the hydrothermal growth of ZnO include zinc nitrate and hexamethylenetetramine.

[0054] In this invention, the molar ratio of zinc nitrate to hexamethylenetetramine is preferably 1:1.

[0055] In this invention, zinc nitrate and hexamethylenetetramine are preferably added to deionized water and ultrasonically mixed for 5-10 minutes to obtain a mixture. The glass plate with the magnetron sputtered ZnO seed layer is ultrasonically treated in an ethanol solution to collect magnetic Chlorella particles from the magnetron sputtered ZnO seed layer and add them to the mixture for hydrothermal growth of ZnO. After the reaction is completed, the particles are separated by a permanent magnet and repeatedly dispersed and washed with deionized water 3-5 times to collect the urchin-shaped tunable multi-level structure ZnO microspheres based on Chlorella. These microspheres are then freeze-dried for 12-15 hours for later use.

[0056] The present invention also provides the application of the urchin-shaped tunable multi-level structure ZnO microspheres based on Chlorella as described in the above technical solution, or the urchin-shaped tunable multi-level structure ZnO microspheres based on Chlorella prepared by the above technical solution, in the photoelectrocatalytic degradation of organic pollutants.

[0057] In this invention, the organic pollutant preferably includes tetracycline.

[0058] The present invention preferably tests and analyzes the photoelectrocatalytic degradation performance of the urchin-shaped tunable multi-level ZnO microspheres based on Chlorella through a xenon lamp photoelectrocatalytic degradation experiment with a full spectrum range, preferably including the following steps:

[0059] 100 mL of a mixed electrolyte of tetracycline (20 mg / L) and Na2SO4 (0.1 M) was added to the electrolytic cell. ITO glass coated with the urchin-shaped tunable multi-level ZnO microspheres based on Chlorella was used as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The xenon lamp was turned on, and 1 mL of the mixed solution was aspirated every 30 min under a bias voltage of 0.9 V vs RHE. The supernatant was separated by centrifugation, and its absorbance at 357 m was measured using a UV-Vis spectrophotometer. The change in tetracycline concentration was calculated based on the calibration results.

[0060] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0061] The units of measurement used in this article are explained as follows:

[0062]

[0063] Figure 1 This document outlines the process flow for preparing urchin-like, tunable multi-level ZnO microspheres based on Chlorella.

[0064] Example 1

[0065] Step S1: Chlorella pretreatment. Chlorella powder was dispersed in deionized water and thoroughly stirred before ultrasonic cleaning for 10 min. Then, it was centrifuged 5 times using a high-speed centrifuge (10000 r / min) to obtain monodisperse Chlorella with clean surfaces and uniform morphology. Finally, the cleaned Chlorella was immersed in a 2.5 wt% glutaraldehyde solution and kept at 4℃ for 12 h to fix the cell structure.

[0066] Step S2: Preparation of Fe3O4 nanoparticles. Ferric chloride hexahydrate (FeCl3·6H2O, 8 mmol) and ferrous chloride tetrahydrate (FeCl2·4H2O, 16 mmol) were added to deionized water (40 mL) and ultrasonically mixed for 5 min. The mixture was then placed in an ultrasonic water bath to maintain the temperature at 50 °C. Sodium hydroxide (NaOH, 0.5 mol) was weighed and prepared into a 10 mL solution, which was then added dropwise to the above mixed solution under ultrasonication. The mixed solution gradually became a uniform black suspension, which was ultrasonically maintained at 50 °C for 60 min. The solution was then washed 5 times with deionized water, and the Fe3O4 nanoparticles were finally separated using a magnet. The washed nanoparticles were further dispersed in 50 mL of deionized water, and an appropriate amount of dilute hydrochloric acid (1 M) was added to adjust the pH of the solution to approximately 4. Finally, the mixture was ultrasonically dispersed for 30 min.

[0067] Step S3: Coating Chlorella with Fe3O4 nanoparticles. Add 200 mg of pretreated Chlorella powder to the above Fe3O4 dispersion, and then perform a shaking process (150 r / min) for 24 h. After the process, wash three times with deionized water, and then perform vacuum filtration through a filter membrane with a pore size of 0.8–1.2 μm. Repeat this process five times, and finally collect the magnetic Chlorella.

[0068] Step S4: Sputtering of ZnO seed layer on the surface of magnetic Chlorella. First, 200 mg of magnetic Chlorella particles were uniformly dispersed in 100 mL of ethanol, and then sprayed to a depth of 10 × 10 cm. 2 The glass plate was allowed to air dry naturally; a ZnO seed layer was deposited on the glass plate by magnetron sputtering, with a power of 150W and a sputtering time of 10-20 minutes.

[0069] Step S5: Hydrothermal growth of ZnO nanorod arrays on the surface of magnetic Chlorella. Zinc nitrate (Zn(NO3)2, 25 mmol) and hexamethylenetetramine (C6H2O) were added. 12 N4 (25 mmol) was added to deionized water (150 mL) and sonicated for 5 min. The glass plate with the above magnetron sputtered seed layer ZnO was sonicated in ethanol solution to collect the magnetic Chlorella particles of the magnetron sputtered ZnO seed layer and added to the above mixture. The reaction was carried out at 80 °C with stirring for 3–12 h. After the reaction was completed, the particles were separated by a permanent magnet and repeatedly dispersed and washed with deionized water 3 times to collect the urchin-shaped tunable multi-level structure ZnO microspheres based on Chlorella. The microspheres were freeze-dried for 12 h for later use.

[0070] Figure 2The images show scanning electron microscope (SEM) images of the original Chlorella, Chlorella coated with Fe3O4 nanoparticles, and Chlorella-based urchin-like hierarchical ZnO microspheres (sputtered by magnetron sputtering for 10 min). The urchin-like tunable hierarchical ZnO microspheres based on Chlorella prepared in this embodiment of the invention were mainly obtained through a chemical co-deposition process. Iron(III) oxide (Fe3O4) nanoparticles were deposited on the cell shell of a Chlorella biotemplate, followed by ZnO seed layer sputtering (150 W, 10 min) and hydrothermal growth for 12 h. Figure 2 As shown, the original Chlorella surface is clean and wrinkled. The surface of the Chlorella microparticles coated with Fe3O4 nanoparticles is uniformly deposited with a nanoparticle layer. The surface of the urchin-shaped tunable multi-level structure ZnO microspheres based on Chlorella exhibits a regular and well-directional three-dimensional nanorod structure. The ZnO nanorods in the urchin-shaped tunable multi-level structure ZnO microspheres based on Chlorella have a length of 1380.34 nm and a diameter of 387.93 nm.

[0071] Figure 3 The images shown are scanning electron microscope (SEM) images of the urchin-shaped, tunable multi-level ZnO microspheres based on *Chlorella vulgaris*, according to embodiments of the present invention. The water bath reaction time for both was 12 h. The urchin-shaped, tunable multi-level ZnO microspheres based on *Chlorella vulgaris* prepared in these embodiments of the present invention mainly achieve variations in the ZnO nanorod arrangement, diameter, and length by controlling the magnetron sputtering time and hydrothermal reaction time. Figure 3 As shown, at a sputtering time of 5 min, the rod-shaped zinc oxide distribution is relatively disordered and lacks density. Excessive sputtering time (15–20 min) results in an overly dense morphology, reducing the nanorod diameter and inter-rod spacing, which is detrimental to light absorption and refraction, further affecting the final photoelectrocatalytic degradation performance. By magnetron sputtering the surface of *Chlorella* microparticles coated with Fe3O4 nanoparticles, with increasing sputtering time (150 W, 5, 10, 15, 20 min), the rough surface of the *Chlorella* microparticles coated with Fe3O4 nanoparticles is gradually filled by the ZnO seed layer, becoming smoother. Through a hydrothermal reaction for 12 h, the surface morphology of the urchin-like hierarchical ZnO microspheres based on *Chlorella* gradually changes from a relatively sparse arrangement to a more regular and ordered one. With increasing sputtering time, the ZnO nanorods become increasingly densely packed, and the nanorod diameter initially increases and then decreases.

[0072] Figure 4 The images shown are scanning electron microscope (SEM) images of the urchin-shaped, tunable multi-level ZnO microspheres based on *Chlorella vulgaris*, according to embodiments of the present invention. The urchin-shaped, tunable multi-level ZnO microspheres prepared in these embodiments primarily achieve variations in the ZnO nanorod arrangement, diameter, and length by controlling the magnetron sputtering time and hydrothermal reaction time. Figure 4As shown, magnetron sputtering (150 W, 10 min) was performed on the surface of Chlorella microparticles coated with Fe3O4 nanoparticles. In the early stage of the reaction, rough nano-blocks appeared on the surface of the magnetic Chlorella as the hydrothermal reaction time increased (3, 6, 9, 12 h). As the hydrothermal reaction time increased to 6 h, well-arranged hexagonal ZnO nanorods appeared on the surface of the magnetic Chlorella. With further increase in reaction time, the surface morphology of the ZnO microspheres based on the urchin-like hierarchical structure of Chlorella gradually became more regular and ordered, and the length and diameter of the nanorods gradually increased.

[0073] Figures 5-8 The sea urchin-like tunable multi-level ZnO microspheres based on Chlorella described in the paper were prepared under the following conditions: sputtering time of 10 min and hydrothermal reaction time of 12 h.

[0074] Figure 5 This is a hysteresis loop diagram of urchin-like tunable multi-level ZnO microspheres based on Chlorella vulgaris, according to an embodiment of the present invention. Figure 5 As shown, both the microalgae particles coated with Fe3O4 nanoparticles and the urchin-shaped tunable multilevel ZnO microspheres based on microalgae exhibit superparamagnetic properties and high saturation magnetization. The magnetic strength of the urchin-shaped tunable multilevel ZnO microspheres based on microalgae is directly related to the outer shell of the actual ZnO nanorods. Due to the coating and dense structure of the outer shell, the magnetism is somewhat weakened.

[0075] Figure 6 This is the UV-Vis diffuse reflectance spectrum of urchin-shaped, tunable multi-level ZnO microspheres based on Chlorella vulgaris, according to an embodiment of the present invention. Figure 6 As shown, pure ZnO nanoparticles exhibit strong absorption in the ultraviolet light range but poor absorption in the visible light range. However, due to the enhanced visible light absorption brought about by active substances such as chlorophyll contained in Chlorella cells and the full-spectrum absorption of Fe3O4 nanoparticles, Chlorella microparticles coated with Fe3O4 nanoparticles exhibit strong light absorption peaks over a wide wavelength range. Based on the above reasons, urchin-like tunable multi-level ZnO microspheres based on Chlorella also have excellent light absorption performance over a wide wavelength range.

[0076] Electrodes were fabricated using tunable hierarchical microspheres resembling sea urchins based on Chlorella, and their photoelectrocatalytic activity was tested using an electrochemical workstation. The photoelectrocatalytic activity experiment of the tunable hierarchical microspheres based on Chlorella included: a working electrode composed of ITO glass and the tunable hierarchical microspheres based on Chlorella. 5 mg of Chlorella-based tunable hierarchical microspheres were ultrasonically dispersed in a mixed solution of 5 wt% Nafion (10 μL) and ethanol (990 μL) for 50 min. 400 μL of the above mixture was then dropped onto a 2 × 2 cm... 2The particles were dried on ITO glass and then stored for later use. A three-electrode system was used, with the microparticle-coated ITO glass as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode, to perform transient photocurrent and cyclic voltammetry tests.

[0077] Figure 7 This document presents impedance diagrams and transient photocurrent-time diagrams for ZnO microspheres with a tunable multi-level structure based on *Chlorella vulgaris*, as described in an embodiment of the present invention. A three-electrode system was employed, using ITO glass coated with *Chlorella vulgaris*-based tunable multi-level ZnO microspheres as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. Impedance testing was performed under xenon lamp irradiation, and transient photocurrent testing was conducted using timed chopping. Figure 7 As shown in Figure a, under xenon lamp irradiation, the urchin-shaped tunable multi-level ZnO microspheres based on Chlorella exhibit lower impedance compared to Chlorella microparticles coated with Fe3O4 nanoparticles, demonstrating lower resistance to photogenerated electron-hole transfer at the interface and effectively improving electron-hole separation; Figure 7 As shown in Figure b, the urchin-shaped tunable multi-level ZnO microspheres based on Chlorella exhibit the best transient photocurrent density under xenon lamp irradiation, demonstrating their superior photoelectrocatalytic activity.

[0078] Tetracycline was selected as the pollutant, and the photoelectrocatalytic degradation performance of urchin-shaped tunable hierarchical structure microspheres based on Chlorella was tested and analyzed through a xenon lamp photoelectrocatalytic degradation experiment covering the full spectrum. The photoelectrocatalytic degradation experiment of tetracycline based on urchin-shaped tunable hierarchical structure microspheres of Chlorella included:

[0079] 100 mL of a mixed electrolyte of tetracycline (20 mg / L) and Na₂SO₄ (0.1 M) was added to the electrolytic cell. ITO glass coated with microparticles was used as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The xenon lamp light source (500 W / m²) was turned on. 2 Under a bias voltage of 0.9V vs RHE, 1 mL of the mixed solution was aspirated every 30 min, and the supernatant was obtained by centrifugation. The absorbance at 357 nm was measured using a UV-Vis spectrophotometer, and the change in tetracycline concentration was calculated based on the calibration results.

[0080] Figure 8 This image shows the photoelectrocatalytic degradation curves of tetracycline using tunable, multi-level ZnO microspheres with a sea urchin-like structure based on *Chlorella*, as an embodiment of the present invention. Tetracycline was selected as the target organic pollutant, and the photoelectrocatalytic degradation performance of the tunable, multi-level ZnO microspheres based on *Chlorella* was tested and analyzed through photoelectrocatalytic degradation experiments under different light sources. Figure 8As shown in Figure a, under xenon lamp irradiation, the ZnO nanoparticles, the Chlorella microparticles coated with Fe3O4 nanoparticles, and the urchin-shaped tunable multi-level ZnO microspheres based on Chlorella can all perform photoelectrocatalytic degradation of tetracycline in solution. Among them, the urchin-shaped tunable multi-level ZnO microspheres based on Chlorella exhibit the best photoelectrocatalytic degradation effect. Figure 8 As shown in Figure b, the photoelectrocatalytic degradation effects of the urchin-shaped tunable multi-level ZnO microspheres based on Chlorella varied under different light source irradiation. Among them, the photoelectrocatalytic degradation effect of the urchin-shaped tunable multi-level ZnO microspheres based on Chlorella was the best under xenon lamp irradiation. This further demonstrates that the synergistic effect of the Chlorella template, heterojunction, and unique ZnO nanorod array shell effectively improves light absorption and light conversion efficiency, ultimately exhibiting excellent photoelectrocatalytic performance.

[0081] In summary, (1) the urchin-shaped tunable multi-level ZnO microspheres based on Chlorella described in this invention have a stable urchin-shaped multi-level core-shell structure, controllable and tunable ZnO nanorod array shell, superparamagnetic properties, and excellent light absorption and photoelectrocatalytic activity. They can achieve efficient photoelectrocatalytic degradation under the full spectrum of wavelengths and have the potential for wastewater treatment.

[0082] (2) The preparation method described in this invention uses natural spherical Chlorella cells as templates, which not only provide uniformly sized microsphere templates, but also contain a large amount of chlorophyll that effectively promotes light absorption. Further surface modification is achieved through chemical co-deposition to efficiently coat Fe3O4 nanoparticles, resulting in superparamagnetism and recycling capabilities. Finally, the magnetron sputtering time and hydrothermal reaction time of the ZnO seed layer can be controlled and adjusted to achieve different tightly packed ZnO nanorod array shells. The length and diameter of the ZnO nanorods are controllable and adjustable, exhibiting good chemical stability and mechanical durability. The process is simple, controllable, and adjustable, enabling the controllable and mass production of urchin-like, tunable multi-level ZnO microspheres based on Chlorella.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A type of urchin-shaped, tunable multi-level ZnO microspheres based on Chlorella, characterized in that, Using microspherical Chlorella cells as the core, from the inside out, the surface of the microspherical Chlorella cells is sequentially coated with a magnetic coating layer and a nanorod array shell. The magnetic coating layer is composed of iron oxide nanoparticles, and the nanorod array shell layer is composed of ZnO nanorods. The ZnO nanorods have a diameter of 0–403 nm and are not zero, and a length of 0–1381 nm and are not zero; the iron oxide nanoparticles have a particle size of 40–60 nm. The method for preparing urchin-shaped, tunable multi-level ZnO microspheres based on Chlorella includes the following steps: Chlorella was pretreated by soaking it in a glutaraldehyde solution to obtain pretreated Chlorella. The pretreated Chlorella was dispersed in Fe3O4 suspension to obtain magnetic Chlorella; A ZnO seed layer was deposited on the surface of the magnetic Chlorella by magnetron sputtering, and then ZnO was grown hydrothermally to form a nanorod array shell, thus obtaining the urchin-shaped tunable multi-level structured ZnO microspheres based on Chlorella. The magnetron sputtering power was 150W and the time was 10 minutes.

2. The method for preparing urchin-like tunable multi-level ZnO microspheres based on Chlorella as described in claim 1, characterized in that, Includes the following steps: Chlorella was pretreated by soaking it in a glutaraldehyde solution to obtain pretreated Chlorella. The pretreated Chlorella was dispersed in Fe3O4 suspension to obtain magnetic Chlorella; A ZnO seed layer was deposited on the surface of the magnetic Chlorella by magnetron sputtering, and then ZnO was grown hydrothermally to form a nanorod array shell, thus obtaining the urchin-shaped tunable multi-level structured ZnO microspheres based on Chlorella. The magnetron sputtering power was 150W and the time was 10 minutes.

3. The preparation method according to claim 2, characterized in that, The hydrothermal growth temperature of ZnO is 80-85℃, and the time is 0-16h, not 0.

4. The preparation method according to claim 3, characterized in that, The hydrothermal growth of ZnO was carried out at a temperature of 80℃ for 12–14 hours.

5. The preparation method according to claim 2, characterized in that, The raw materials for the hydrothermal growth of ZnO include zinc nitrate and hexamethylenetetramine.

6. The application of the urchin-shaped tunable multi-level structure ZnO microspheres based on Chlorella as described in claim 1, or the urchin-shaped tunable multi-level structure ZnO microspheres based on Chlorella prepared by any one of claims 2 to 5, in the photoelectrocatalytic degradation of organic pollutants.

7. The application according to claim 6, characterized in that, The organic pollutants include tetracycline.

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