Honeycomb porous nano zinc oxide photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalytic degradation of pollutants, in particular to a honeycomb porous nano zinc oxide photocatalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: preparation of a polystyrene microsphere photonic crystal template, and preparation and construction of doped porous nano zinc oxide. According to the invention, the highly ordered polystyrene photonic crystal formed by self-assembly is used as a template, and the zinc oxide material with a regular, through and honeycomb porous structure is successfully copied through electro-deposition and template removal, and has the characteristics of high mass transfer efficiency and full exposure of active sites; by introducing an Mg element with an accurate control proportion into a three-electrode electrodeposition system, accurate regulation and optimization of an energy band structure of a zinc oxide electronic structure are realized, light response is expanded, charge separation is promoted, and the solar energy utilization rate is improved; through a dual modification strategy of a porous structure and Mg doping synergistic interaction, a leap of photocatalytic performance is realized, and the product has remarkable energy conservation and emission reduction and sustainable benefits.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic degradation of pollutants, and in particular to a honeycomb porous nano zinc oxide photocatalyst, its preparation method, and its application. Background Technology

[0002] Solar energy is an inexhaustible, clean, and renewable energy source, and photocatalysis is one of the effective ways to utilize it. As a new technology that uses clean and renewable energy to address environmental pollution, photocatalysis has received widespread attention since its inception. Photocatalysts can fully utilize clean energy while effectively protecting the ecological environment, and are widely used in the field of environmental pollution control. Among them, zinc oxide (ZnO) has become one of the most promising photocatalysts due to its low price, ease of preparation, and non-toxicity.

[0003] However, as research has progressed, it has been found that there is still considerable room for improvement in the light energy utilization efficiency and photogenerated carrier recombination rate of ordinary bulk zinc oxide materials, and the photocatalytic efficiency urgently needs to be improved.

[0004] With the development of nanoscience, different types of nano zinc oxide have been reported. The advantages of nano zinc oxide preparation materials are easy to obtain, preparation methods are diverse, and the material has a large specific surface area, which makes it show great potential in the field of photocatalysis. With the deepening of research, it has been found that the photocatalytic properties of single nanomaterials have certain limitations. By preparing doped nanomaterials in different ways, the shortcomings of the catalytic performance of single nanomaterials can be made up for, the balance between light utilization and photogenerated carrier recombination rate can be achieved, and the catalytic efficiency of photocatalytic materials can be improved. Sa-nguanprang et al. (Reference [1] Sa-Nguanprang S, Phuruangrat A, Thongtem T, et al. Visible-Light-Driven Photocatalysis of Gd-Doped ZnO Nanoparticles Prepared by Tartaric Acid Precipitation Method[J].Russian Journal of Inorganic Chemistry, 2019, 64(12):1600-1608.) prepared Gd-doped zinc oxide nanoparticles by tartaric acid-assisted precipitation method and used them for the degradation of the dye molecule methylene blue under visible light conditions. The nano zinc oxide prepared under optimal conditions can achieve 100% degradation of methylene blue within 45 min; Franco et al. (Reference [2] Franco P, Sacco O, Marco ID, et al. Photocatalytic Degradation of Eriochrome Black-T Azo Dye Using Eu-Doped ZnO Prepared by Supercritical Antisolvent Precipitation Route: A Preliminary Investigation[J]. Topics in Catalysis, 2020, 63(11):1193-1205.) prepared Eu-doped zinc oxide by supercritical reverse fluid technology and studied its degradation and removal of dye Eriochrome Black T. The results showed that 240 min of ultraviolet irradiation basically achieved complete removal of Eriochrome Black T.Li Benzheng et al. (Reference [3] Li Benzheng, Hao Jialiang, Feng Wei. Preparation of hierarchical porous NiO / ZnO composite material and its formaldehyde gas-sensing properties [J]. Journal of Jilin University (Science Edition), 2023, 61(01):162-171.) synthesized a porous nickel oxide-doped zinc oxide nanocomposite material using a biological template. By constructing a porous structure, its specific surface area was increased, and the sensitivity of the doped zinc oxide to formaldehyde was significantly improved compared with that of the undoped zinc oxide; Zhang Huabing et al. (Reference [4] Zhang Huabing, Du Yan, Sun Houxiang. Preparation of Flower-shaped Cadmium-Doped ZnO and its Photocatalytic Degradation of Tetracycline Hydrochloride [J]. Industrial Water Treatment, 2023, 43(07):120-127. Using zinc acetate, cadmium acetate, and trisodium citrate as raw materials, flower-shaped Cd-ZnO composite photocatalytic materials with different Cd doping amounts were prepared by precipitation method and used for the degradation of tetracycline hydrochloride. The highest removal rate of tetracycline hydrochloride, 85.3%, was achieved within 120 min, and the catalytic efficiency was significantly improved compared with the undoped material. The above research shows that introducing doping elements to regulate the band gap of nano-zinc oxide or constructing a porous structure to increase the specific surface area of ​​nano-zinc oxide can effectively improve its photocatalytic performance. In addition, increasing the specific surface area or porosity of nano zinc oxide is also one of the important ways to improve its photocatalytic efficiency (Reference [5] Babajani N, Jamshidi S. Investigation of photocatalyticmalachite green degradation by iridium doped zinc oxide nanoparticles: Application of response surface methodology [J]. Journal of Alloys and Compounds, 2018, 782: 533-544.).

[0005] Based on the above research background, this invention attempts to prepare a doped honeycomb nano-zinc oxide material. On the one hand, by constructing a honeycomb porous structure, the specific surface area of ​​zinc oxide is effectively increased; on the other hand, Mg element is doped into zinc oxide during the preparation and growth process by electrodeposition to control the band gap of zinc oxide. Through the above dual approaches, the photocatalytic performance of nano-zinc oxide is improved. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a honeycomb porous nano zinc oxide photocatalyst, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a honeycomb porous nano-zinc oxide photocatalyst includes the following steps: (1) Preparation of polystyrene microsphere photonic crystal template A vertical deposition method was used, with polystyrene (PS) microsphere suspension as the deposition liquid, and surface tension and capillary forces at the gas-liquid-solid three-phase interface were utilized under isothermal conditions to deposit a tightly ordered photonic crystal template (PC) on indium tin oxide (ITO) conductive glass. (2) Preparation and construction of doped porous nano zinc oxide Using a photonic crystal (PC) as a template, zinc oxide material was filled into the gaps between polystyrene microspheres by a three-electrode cathode electrodeposition method with zinc nitrate aqueous solution as the electrolyte. Different proportions of Mg dopant were added to the electrolyte to obtain a doped zinc oxide-PC template composite material. Then, the PC template was removed to obtain a honeycomb porous nano zinc oxide photocatalyst.

[0008] The three-electrode electrodeposition system used, such as Figure 2 As shown, the mechanism of cathodic electrodeposition of zinc oxide is as follows: This design utilizes cathodic electrodeposition to prepare nano-zinc oxide on a photonic crystal template. The electrochemical reaction mechanism is as follows: Zn 2+ NO3 is adsorbed onto the cathode, forming an electrical double layer on the cathode surface. - The electrostatic repulsion between the cathode and the cathode decreases, and NO3 near the cathode... - Electrons are gained at the electrode surface and reduced to NO2. - At the same time, a large amount of OH is generated. - (As shown in Equations 1 and 2), OH - With Zn adsorbed on the cathode 2+ Zn(OH)2 is formed, and Zn(OH)2 dehydrates to form ZnO on the cathode surface (as shown in Formula 3).

[0009] Zn(NO3)2→Zn 2+ +2NO3 - (Equation 1); NO3 - +H₂O + 2e - →NO2 - +2OH - (Equation 2); Zn 2+ +2OH-→Zn(OH)2→ZnO+H2O(Equation 3; The overall reaction equation is: Zn 2+ +NO3 - +2e - →ZnO + NO2 - (Equation 4).

[0010] Preferably, in step (1), the concentration of polystyrene microspheres in the polystyrene microsphere suspension is 0.5-2.0 wt%, and the particle size of the polystyrene microspheres is 200-400 nm. Smaller microsphere particle size and suitable suspension concentration are conducive to the formation of an ordered photonic crystal template. Excessive particle size or excessive concentration will lead to an excessively fast deposition rate, affecting the ordered arrangement.

[0011] Preferably, the deposition temperature of the three-electrode cathode electrodeposition method in (1) is 45-55℃ and the deposition time is 24-48h.

[0012] Preferably, in step (2), the molar concentration of zinc nitrate in the electrolyte is 0.05-0.2 mol / L, and the amount of Mg doping in the electrolyte is 1-7 at the molar amount of Zn.

[0013] Preferably, in step (2), the deposition voltage is -1 to -1.5V, the deposition temperature is 65-75℃, and the deposition time is 20-45min.

[0014] This invention also proposes a honeycomb porous zinc oxide nano-photocatalyst prepared by the aforementioned method, with a specific surface area of ​​35-46 m². 2 / g, pore size distribution: 180-300nm, band gap: 3.20-3.30eV.

[0015] This invention also applies the honeycomb porous nano zinc oxide photocatalyst to the photocatalytic degradation of organic pollution, including the following steps: Using Rhodamine B dye as the target degradation product, the aforementioned honeycomb porous nano zinc oxide photocatalyst was placed in a beaker, and Rhodamine B solution was added to the beaker. The beaker was then irradiated under visible light, and samples were taken every hour. The changes in the absorption spectrum of the samples over time were recorded using a UV-Vis absorption spectrometer. The degradation rate was calculated using the absorbance value A at the maximum absorption wavelength of Rhodamine B (λ=554nm).

[0016] Preferably, the concentration of Rhodamine B in the Rhodamine B solution is 5-20 mg / L, and the weight ratio of Rhodamine B solute to honeycomb porous nano zinc oxide photocatalyst in the beaker is 5-20:1.

[0017] Using Rhodamine B dye as the target degradation product, four types of zinc oxide—non-porous and undoped, porous and undoped, non-porous and doped, and porous and doped—were placed in different beakers. Equal amounts of Rhodamine B solution of the same concentration were added to each beaker. The beakers were then irradiated with visible light, and samples were taken every hour. The changes in the absorption spectrum of the samples over time were recorded using a UV-Vis absorption spectrometer. The degradation rate was calculated using the absorbance value A at the maximum absorption wavelength of Rhodamine B (λ=554nm).

[0018] Photocatalytic degradation principle: In the band structure of zinc oxide, there is a valence band filled with electrons and an empty conduction band. The area between the top of the valence band and the bottom of the conduction band is called the band gap (Reference [6] Li D, Sun J, Ma R, et al. High-efficient solar-driven hydrogen production by full-spectrum synergistic photo-thermo-catalytic methanol steamreforming with in-situ photoreduced Pt-CuOx catalyst[J]. Journal of Energy Chemistry, 2022, 71:460-469.). When a beam of light with energy higher than the band gap shines on a semiconductor material, the semiconductor will be excited, and electrons in the valence band will transfer to the conduction band, leaving positively charged holes in the valence band, thereby generating conduction band electron carriers (e - ) and valence band hole carriers (h + (Reference [7] Guo Ziyang. Controllable preparation of ZnO-based heterostructures and study on the reaction mechanism of photocatalytic NOx oxidation [D]. Chongqing: Chongqing University, 2021: 4-11.). Among them, e - Its restoration ability is very strong, h + Its oxidizing power is very strong, so e - and h + It will undergo a redox reaction with the compounds adsorbed on the catalyst surface, ultimately photocatalytically degrading the organic matter into CO2 and H2O. The photocatalytic principle is as follows: Figure 3 As shown.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses a highly ordered polystyrene photonic crystal formed by self-assembly as a template, and through electrodeposition and template removal, successfully replicates a zinc oxide material with a regular, interconnected, honeycomb (inverse opal) porous structure. Its ordered porous structure and large specific surface area offer the following advantages: 1) High mass transfer efficiency: The regularly arranged channels provide an unobstructed "highway" for the diffusion of reactants and products, avoiding mass transfer bottlenecks and "dead pores" in disordered channels. Comparative experiments (Comparative Example 1) demonstrate that template quality directly determines the final performance, and disordered templates cause the degradation rate to plummet to 55%.

[0020] 2) Full exposure of active sites: The huge specific surface area greatly increases the number of surface active sites, providing ample space for catalytic reactions.

[0021] 2. This invention achieves precise control and optimization of the band structure of zinc oxide's electronic structure by introducing precisely controlled proportions of Mg into a three-electrode electrodeposition system, thereby expanding photoresponse and promoting charge separation. 2+ The successful incorporation of ZnO caused a red shift in the absorption edge, effectively broadening the light response range and improving the utilization rate of solar energy. Furthermore, this invention has clarified the optimal concentration window (1-7 at%) for Mg doping through systematic experiments, with 3 at% being particularly optimal. Within this window, doping can effectively regulate the band structure and promote charge separation without introducing too many fatal defects that become recombination centers. Excessive doping (10 at%) leads to decreased crystallinity, a sharp reduction in specific surface area, and defects becoming the main recombination centers, ultimately causing a drastic drop in photocatalytic performance.

[0022] 3. This invention employs a dual modification strategy of synergistic enhancement through porous structure and Mg doping, and through the ingenious integration of structural engineering and bandgap engineering, generates a synergistic effect of "1+1>2," achieving a leap in photocatalytic performance. The synergistic mechanism is as follows: 1) Adsorption-catalysis synergy: The highly ordered honeycomb porous structure provides a huge specific surface area, which acts like a "molecular enrichment device" to efficiently adsorb and concentrate target pollutant molecules, greatly increasing the probability of contact between pollutants and active sites.

[0023] 2) Light-matter synergy: The inverse opal structure of the photonic crystal facilitates multiple reflections and scatterings of light within the channels, enhancing the light capture efficiency; at the same time, appropriate Mg doping optimizes the band gap of zinc oxide from 3.37 eV to 3.25 eV, broadening the absorption range of visible light and generating more photogenerated electron-hole pairs.

[0024] 3) Charge separation-transport synergy: appropriate amount of Mg 2+ The incorporation of ZnO lattice introduces micro-strain and controllable defects that can effectively trap electrons or holes, suppress their recombination, and extend carrier lifetime. These separated, highly active carriers can then rapidly migrate along the continuous framework formed by the ordered porous structure to surface reaction sites, thereby efficiently participating in degradation reactions.

[0025] 4. The photocatalyst of the present invention has significant energy-saving, emission-reduction, and sustainability benefits, which are reflected in the following aspects: 1) Energy saving: The preparation process adopts the electrodeposition method, and the reaction conditions are mild (medium and low temperature). Compared with the traditional high temperature solid phase method, the energy consumption is significantly reduced, and the carbon emissions of ZnO material preparation process are effectively reduced, and no environmentally harmful by-products are generated.

[0026] 2) High efficiency and recyclability of raw materials: The material is firmly attached to the conductive glass substrate in the form of a thin film. It does not fall off during use, is easy to recycle and can be directly reused. Its performance is stable after 5 consecutive cycles, which greatly reduces the consumption of catalyst and secondary pollution, and conforms to the principles of green chemistry.

[0027] 3) High efficiency in utilizing solar energy: The final product has high efficiency in utilizing sunlight (especially visible light). When applied in the field of environmental purification, it can reduce dependence on traditional electrical energy or chemical reagents and has direct carbon emission reduction potential.

[0028] 5. In summary, this invention not only provides a high-performance photocatalytic material, but also, through in-depth mechanistic analysis, offers clear theoretical guidance and technical pathways for the design and development of next-generation efficient, stable, and sustainable photocatalysts. Attached Figure Description

[0029] Figure 1 This is a flowchart of the research process of the present invention; Figure 2 This is a schematic diagram of the electrode system structure of the three-electrode cathode electrodeposition method in this invention; Figure 3 This is a schematic diagram illustrating the photocatalytic principle of zinc oxide in this invention. Figure 4 This is a 5000x SEM image of the photonic crystal template prepared in this invention; Figure 5 This is a 50,000x SEM image of the photonic crystal template prepared in this invention. Figure 6 This is a 10,000x SEM image of the honeycomb porous zinc oxide prepared according to the present invention. Figure 7 This is a 50,000x SEM image of the honeycomb porous zinc oxide prepared according to the present invention. Figure 8 A photograph of the honeycomb porous zinc oxide material prepared according to the present invention; Figure 9 The XRD patterns of samples obtained using different Mg doping ratios in this invention are shown below. Figure 10 The UV-Vis absorption spectra of samples with different Mg doping ratios in this invention; Figure 11This is a schematic diagram showing the change in the efficiency of Mg-doped porous zinc oxide photocatalytic degradation of Rhodamine B as a function of degradation time. Figure 12 A comparison of the catalytic degradation rates of Mg-doped porous zinc oxide with self-degradation and non-porous undoped zinc oxide. Figure 13 The change in the 5-hour degradation rate of Rhodamine B over 5 consecutive days using Mg-doped porous zinc oxide. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] I. Experimental Design Ideas: This invention focuses on the preparation of honeycomb porous nano zinc oxide photocatalysts, and mainly conducts research in three aspects: (1) preparation of polystyrene microsphere photonic crystal templates; (2) preparation and construction of doped porous nano zinc oxide; (3) comparative study of the photocatalytic performance of materials. The overall research approach is as follows: Figure 1 As shown.

[0032] The preliminary design steps are as follows: (1) Preparation of polystyrene microsphere photonic crystal template A vertical deposition method was used, with polystyrene (PS) microsphere suspension as the deposition liquid. Under isothermal conditions, the surface tension and capillary force of the gas-liquid-solid three-phase interface were utilized to deposit a tightly ordered photonic crystal template (PC) on indium tin oxide (ITO) conductive glass.

[0033] (2) Preparation and construction of doped porous nano zinc oxide Using a photonic crystal (PC) as a template, zinc oxide was filled into the gaps between polystyrene microspheres via a three-electrode cathode electrodeposition method using an aqueous zinc nitrate solution as the electrolyte. Different proportions of Mg dopant were added to the electrolyte to obtain a doped zinc oxide-PC template composite material. The PC template was then removed to obtain a honeycomb-like porous nano-zinc oxide photocatalyst. The three-electrode electrodeposition system used is as follows: Figure 2 As shown.

[0034] (3) Comparative study on photocatalytic performance Using Rhodamine B dye as the target degradation product, four types of zinc oxide—non-porous and undoped, porous and undoped, non-porous and doped, and porous and doped—were placed in different beakers. Equal amounts of Rhodamine B solution of the same concentration were added to each beaker. The beakers were then irradiated with visible light, and samples were taken every hour. The changes in the absorption spectrum of the samples over time were recorded using a UV-Vis absorption spectrometer. The degradation rate was calculated using the absorbance value A at the maximum absorption wavelength of Rhodamine B (λ=554nm).

[0035] II. Fabrication of photonic crystal templates: Preparation Example 1: A vertical deposition method was used, with polystyrene (PS) microsphere suspension as the deposition liquid, and surface tension and capillary forces at the gas-liquid-solid three-phase interface were utilized under isothermal conditions to deposit a tightly ordered photonic crystal template (PC) on indium tin oxide (ITO) conductive glass. The specific conditions were: PS microsphere particle size: 200 nm; suspension concentration: 0.5 wt%; deposition temperature: 45 ℃; deposition time: 48 h. Results: Template orderliness score: 85%; Microsphere arrangement: dense and ordered with few defects; Number of layers: 5-6 layers.

[0036] Preparation Example 2: Based on the steps of Preparation Example 1, the conditions were changed as follows: PS microsphere particle size: 300 nm; suspension concentration: 1.0 wt%; deposition temperature: 50 °C; deposition time: 36 h. Result: Reference Figure 4-5 Template orderliness score: 92%; microsphere arrangement: highly ordered with very few defects; number of layers: 6-7.

[0037] Preparation Example 3: Based on the steps of Preparation Example 1, the conditions were changed as follows: PS microsphere particle size: 400 nm; suspension concentration: 2.0 wt%; deposition temperature: 55 °C; deposition time: 24 h. Results: Template orderliness score: 78%; Microsphere arrangement: some areas are ordered, but there are defects; Number of layers: 4-5 layers.

[0038] Comparative preparation example 1: Based on the steps of Preparation Example 1, the conditions were changed as follows: PS microsphere particle size: 600 nm; suspension concentration: 5.0 wt%; deposition temperature: 60 °C; deposition time: 12 h.

[0039] result: Template orderliness score: 45%; Microsphere arrangement: disordered, with numerous defects; Number of layers: 2-3 layers.

[0040] Preliminary comparisons between Preparation Examples 1-3 and Comparative Preparation Example 1 indicate that smaller microsphere sizes (200-400 nm) and suitable suspension concentrations (0.5-2.0 wt%) are beneficial for forming ordered photonic crystal templates. Excessively large particle sizes or excessively high concentrations can lead to excessively rapid deposition rates, affecting the ordered arrangement.

[0041] Preparation of photocatalysts:

[0042] Example 1:

[0043] Using the photonic crystal (PC) of Preparation Example 1 as a template, zinc oxide material was filled into the gaps between polystyrene microspheres by three-electrode cathode electrodeposition with zinc nitrate aqueous solution as electrolyte. Different proportions of Mg dopant were added to the electrolyte to obtain a doped zinc oxide-PC template composite material. Then the PC template was removed to obtain a honeycomb porous nano zinc oxide photocatalyst. The three-electrode electrodeposition system used, such as Figure 2 As shown, the specific conditions were: Zn(NO3)2 concentration: 0.1M; Mg doping ratio: 1at%; deposition voltage: -1.2V; deposition temperature: 70℃; deposition time: 30min. Result: Specific surface area: 42.5 m² 2 / g; pore size distribution: 200-250nm; band gap: 3.30eV.

[0044] Example 2: Based on the steps of Example 1, the conditions were changed as follows: using the photonic crystal (PC) of Example 2 as a template, the Zn(NO3)2 concentration was 0.1M; the Mg doping ratio was 3at%; the deposition voltage was -1.2V; the deposition temperature was 70℃; and the deposition time was 30min.

[0045] Result: Reference Figure 6-7 Specific surface area: 45.8 m² 2 / g; pore size distribution: 200-250nm; band gap: 3.25eV.

[0046] Example 3: Based on the steps of Example 1, the conditions were changed as follows: using the photonic crystal (PC) of Example 3 as a template, the Zn(NO3)2 concentration was 0.05M; the Mg doping ratio was 5at%; the deposition voltage was -1.0V; the deposition temperature was 65℃; and the deposition time was 45min. Result: Specific surface area: 38.2 m² 2 / g; pore size distribution: 180-220nm; band gap: 3.22eV.

[0047] Example 4: Based on the steps of Example 1, the conditions are changed as follows: Zn(NO3)2 concentration: 0.2M; Mg doping ratio: 7at%; deposition voltage: -1.5V; deposition temperature: 75℃; deposition time: 20min; Result: Specific surface area: 35.6 m² 2 / g; pore size distribution: 250-300nm; band gap: 3.20eV.

[0048] Comparative Example 1 (Template Replacement): The photonic crystal template of Example 2 was replaced with the photonic crystal template of Comparative Preparation Example 1.

[0049] Comparative Example 2 (no pores, no doping): Based on the steps of Example 2, the conditions were changed as follows: no photonic crystal template; no Mg doping; other conditions were the same as in Example 2.

[0050] Result: Specific surface area: 12.3 m² 2 / g; Band gap width: 3.37eV.

[0051] Comparative Example 3 (with pores, no doping): Based on the steps of Example 2, the conditions are changed as follows: A photonic crystal template was used, without Mg doping; other conditions were the same as in Example 2.

[0052] Result: Specific surface area: 40.2 m² 2 / g; Band gap width: 3.37eV.

[0053] Comparative Example 4 (without pores but with doping): Based on the steps of Example 2, the conditions are changed as follows: No photonic crystal template was used, and the Mg doping ratio and other conditions were the same as in Example 2.

[0054] Result: Specific surface area: 13.8 m² 2 / g; Band gap width: 3.25eV.

[0055] Comparative Example 5 (Mg doping excess): Based on the steps of Example 2, the conditions are changed as follows: Mg doping ratio: 10 at%; other conditions are the same as in Example 2.

[0056] Result: Specific surface area: 28.5 m² 2 / g; Band gap width: 3.15eV.

[0057] Taking Example 2 as an example, the SEM images of the prepared photonic crystal template and the honeycomb porous zinc oxide nanoparticles are as follows: Figure 4-7 As shown. From Figure 4 and5 It can be seen that the prepared photonic crystal template microspheres are densely and orderly arranged and have a multilayered structure, which is beneficial for constructing porous structures based on this. Figure 6 and 7 The honeycomb-like multi-layered porous structure of the prepared zinc oxide material can be clearly seen, which has a large specific surface area, providing very favorable conditions for photocatalytic degradation of organic dyes.

[0058] Based on this, different proportions of Mg were doped during the electrodeposition process to control the photonic bandgap of zinc oxide. Figure 9 The XRD patterns of doped porous zinc oxide nanoparticles prepared with different doping ratios are shown. From the positions of the diffraction peaks in the figure, it can be seen that the prepared zinc oxide conforms to the structural characteristics of wurtzite zinc oxide, but grows preferentially along the (002) crystal plane, and the preferential growth of the (002) crystal plane becomes more and more obvious as the doping ratio of Mg increases.

[0059] The effect of Mg doping amount on photocatalyst performance was summarized, and the products of Examples 1-4 and Comparative Example 5 were prepared as follows: Figure 8 The sheet-like catalyst shown has a sample size of 1.5cm × 2.5cm. The sample is uniform and has a large surface area, which is beneficial for further performance comparison studies. The experimental results are shown in Table 1. Table 1. Effect of Mg doping concentration on photocatalyst performance

[0060] Table 1 shows that while Mg doping improves the photocatalytic performance of zinc oxide, more is not always better. Exceeding an optimal doping value leads to a series of negative effects. In general, excessive Mg doping results in decreased photocatalytic performance and crystallinity: the relative crystallinity drops from 95% to 75%, indicating poorer lattice quality and increased defects. Specific surface area also decreases: from 45.8 μm... 2 / g decreased to 28.5m 2 / g indicates that the porous structure may have been damaged. Performance plummeted: the degradation rate dropped sharply from the optimal 95.2% to 45.0%, indicating that excessive Mg doping had a serious negative impact.

[0061] Its mechanism may stem from the following aspects: 1) Lattice distortion and structural damage: Mechanism: Mg 2+ The ionic radius (0.57 Å) is smaller than that of Zn. 2+ The ionic radius of Mg is 0.60 Å. When doped with small amounts, Mg... 2+ It can successfully replace Zn 2+ The position of the Mg only causes slight lattice contraction, and this moderate stress can even be beneficial for catalysis. However, when the doping concentration is too high, excessive Mg...2+ When it floods into the ZnO lattice, it generates enormous internal stress, leading to severe lattice distortion.

[0062] Influence: Defects will be generated: a large number of point defects (vacancies, interstitial atoms) and even dislocations will be formed.

[0063] Formation of a second phase: When the Mg content exceeds its solid solubility in ZnO, a separate MgO phase or other impurity phases will precipitate. This disrupts the single wurtzite structure of ZnO.

[0064] XRD evidence: See Figure 9 In the XRD pattern, broadening of the diffraction peaks of ZnO (due to decreased crystallinity) may be observed, or new diffraction peaks belonging to MgO may appear.

[0065] 2) It becomes the recombination center of electron-hole pairs: Mechanism: The lattice defects (such as vacancies, interstitial atoms, dislocations, etc.) generated by excessive doping introduce new energy levels into the band gap. These energy levels no longer act as "helpers" to promote charge separation, but rather become "traps." Photogenerated electrons (e - ) and holes (h + Before diffusing to the surface to react, the light carriers are captured by these defect energy levels and recombine. This means that although the material absorbs light and generates more charge carriers, they self-annihilate before they can participate in the reaction, resulting in a sharp reduction in the number of charge carriers actually participating in the photocatalytic reaction. This is the most direct cause of performance degradation.

[0066] 3) Deterioration of specific surface area and pore structure: Excessive dopant can affect crystal nucleation and growth kinetics during electrodeposition. It may destabilize the deposition process, leading to uneven zinc oxide filling within the template or resulting in fragile crystal structures. After removing the PS template, the honeycomb porous structure may collapse or become incomplete. A decrease in specific surface area reduces the number of active sites for reactant adsorption, thus negating the advantages of constructing a porous structure.

[0067] 4) Excessive alteration of band structure: While moderate doping can fine-tune the bandgap, excessive doping can lead to undesirable and drastic changes in the band structure. This could result in an excessively narrow bandgap, which, while providing stronger absorption of visible light, lowers the reduction potential at the conduction band bottom, leading to insufficient reduction capacity of photogenerated electrons and an inability to effectively reduce molecules such as O2. Alternatively, the introduced defect levels could become overly complex, thereby promoting recombination.

[0068] 5) Summary: Although the bandgap may be further reduced, which would be beneficial for light absorption, the huge defects generated by high-concentration doping become the main electron-hole recombination centers. This negative effect completely offsets and outweighs any benefits brought by the narrow bandgap. At the same time, structural collapse also reduces active sites.

[0069] There is an optimal window for Mg doping. Appropriate Mg doping (such as 1-5 at%) in this invention improves performance by fine-tuning the band structure and introducing moderate stress. However, once this window is exceeded, excessive Mg doping significantly reduces photocatalytic performance by introducing recombination centers and disrupting the microstructure. Therefore, precise control of the doping concentration is crucial in material preparation.

[0070] IV. Photodegradation Test The photocatalysts of Examples 1-4 and Comparative Examples 1-5 were applied to the photocatalytic degradation of organic pollution, including the following steps: Using Rhodamine B dye as the target degradation product, the photocatalyst products of Examples 1-4 and Comparative Examples 1-5 were placed in different beakers. Rhodamine B solution was added to the beakers, and then the beakers were irradiated under visible light. Samples were taken every hour, and the changes in the absorption spectrum of the samples over time were recorded using a UV-Vis absorption spectrometer. The degradation rate was calculated using the absorbance value A at the maximum absorption wavelength of Rhodamine B (λ=554nm). The concentration of Rhodamine B in the solution was 10 mg / L, and the weight ratio of Rhodamine B solute to photocatalyst was 10:1. The results are summarized in Table 2 below. Table 2. Effects of different process parameters on photocatalyst performance

[0071] Based on Table 2 and in conjunction with Table 1, the following conclusions can be drawn: 1. Synergistic effect of porous structure and Mg doping: Comparative Example 2, using a non-porous and doped scheme compared to the catalyst-free control group, showed an increase in degradation rate from 19.2% to 58.3%. This demonstrates that even ordinary bulk ZnO possesses certain photocatalytic activity, proving ZnO's fundamental ability as a photocatalyst.

[0072] Compared to the non-porous, doped scheme in Comparative Example 2, the degradation rate of the porous, doped scheme in Comparative Example 3 increased from 58.3% to 75.4%; the specific surface area surged from 12.3 m² to 40.2 m². 2 / g. This indicates the contribution of the honeycomb porous structure. The huge specific surface area provides more adsorption sites and reaction sites for Rhodamine B molecules, while also facilitating multiple reflections of light within the pores, thus improving light capture efficiency. This is a purely physical structural advantage.

[0073] Compared to Comparative Example 2 (which used a non-porous, doped scheme), Comparative Example 4, employing a non-porous, doped scheme, showed an increase in degradation rate from 58.3% to 68.9%; the band gap decreased from 3.37 eV to 3.25 eV. This indicates the contribution of Mg doping. 2+ The successful incorporation of [a specific substance] modulates the band structure of ZnO, narrowing its band gap and enabling it to absorb more photons with higher energy (i.e., expanding the visible light range), thereby generating more photogenerated electron-hole pairs. This is an advantage of the electronic structure.

[0074] Compared with Example 2, Comparative Examples 3-4 showed that Example 2 had a degradation rate as high as 95.2%, which was much higher than the 75.4% of Comparative Example 3 and the 68.9% of Comparative Example 4. This fully demonstrates the synergistic effect of porous structure and Mg doping.

[0075] The mechanism may be as follows: Adsorption-catalysis synergy: Porous structure efficiently adsorbs and enriches Rhodamine B molecules on the catalyst surface, shortening the time required for active species (·OH, O2· - (etc.) the distance that diffuses to the target molecule.

[0076] Light-matter synergy: The porous structure enhances light absorption, while Mg doping increases the yield of photogenerated carriers.

[0077] Charge separation synergy: Mg doping may optimize the carrier migration path, while the huge specific surface area greatly increases the reaction sites, accelerating the process of carriers reacting with adsorbates before recombination.

[0078] 2. The Influence of Template Quality: Structure Determines Performance Compared with the high-quality template of Example 2, the inferior template of Comparative Example 1 had a degradation rate of 55%, which was much lower than the 95.2% of Example 2, and even lower than the 68.9% of the non-porous Comparative Example 4. Analysis: Although Mg doping was successful (the band gap should be similar), the disordered template resulted in an incomplete pore structure and a low specific surface area.

[0079] Disordered pores can hinder mass transfer and diffusion of reactants, and some pores may become dead ends, reducing the utilization rate of active sites. This indicates that the concept of "porous" alone is insufficient; a highly ordered honeycomb structure is crucial for achieving efficient mass transfer and maximizing specific surface area.

[0080] 3. Effect of Mg doping concentration: As shown in Tables 1 and 2, the Mg doping amounts of Examples 1, 2, 3, 4, and Comparative Example 5 were 1%, 3%, 5%, 7%, and 10%, respectively. Their photodegradation performance first increased and then decreased, reaching a peak of 95.2% at 3 at% and then sharply decreasing to 45.0% at 10 at%. The mechanism is summarized in the mechanism analysis following Table 1 as follows: Band engineering: With the addition of Mg, the band gap was optimized from 3.30 eV (1%) to 3.25 eV (3%), enhancing the visible light response.

[0081] Moderate lattice strain: Slight lattice distortion may help separate electron-hole pairs.

[0082] High doping leads to decreased crystallinity: XRD ( Figure 9 The results show that high doping reduces crystallinity and increases defects. These defects become recombination centers for electron-hole pairs, significantly reducing the effective carrier concentration.

[0083] Second phase formation: When the solid solubility exceeds the limit, the MgO impurity phase is formed, which disrupts the continuity of the ZnO lattice and is not conducive to charge transport.

[0084] Structural damage: As shown in Comparative Example 5, excessive doping reduced the specific surface area from 45.8 m² to 45.8 m². 2 / g dropped sharply to 28.5m 2 / g indicates that the electrodeposition process was disturbed, leading to the collapse of the porous structure and the loss of its physical advantages.

[0085] Conclusion: There is an optimal concentration window for Mg doping (3 at%) in this invention. Too low a concentration results in insignificant control, while too high a concentration does more harm than good.

[0086] 4. Summary: Through a detailed analysis of the above embodiments and comparative examples, the following conclusions can be drawn: The synergistic effect is the core: combining the honeycomb porous structure (which provides high specific surface area and efficient mass transfer) with an appropriate amount of Mg element doping (which regulates the band structure and enhances visible light absorption) produces a synergistic effect of "1+1>2", which is the key to achieving ultra-high photocatalytic performance (95.2% degradation rate).

[0087] Template quality is fundamental: a highly ordered photonic crystal template is a prerequisite for constructing high-quality, high-performance porous structures.

[0088] Doping concentration is key: there is an optimal value for Mg doping concentration (3 at%). Precise control of the doping amount is crucial for balancing bandgap modulation and suppressing undesirable defects.

[0089] The mechanism of performance degradation is clear: excessive doping mainly leads to a sharp decline in photocatalytic performance through two pathways: the introduction of recombination centers and the destruction of porous structures.

[0090] The technical solution of this invention systematically solves the shortcomings of single nano zinc oxide materials in terms of light energy utilization and charge separation through ingenious material design, providing a clear and feasible path for the development of efficient and stable photocatalysts.

[0091] This invention also provides a specific degradation trend research report, wherein the degradation rate is verified by changes in ultraviolet absorption, as follows: Using Rhodamine B dye as the target degradation product, four types of zinc oxide—non-porous and undoped (Comparative Example 2), porous and undoped (Comparative Example 2), non-porous and doped (Comparative Example 4), and porous and doped (Example 2)—were placed in different beakers. Equal amounts of Rhodamine B solution of the same concentration were added to each beaker. The beakers were then irradiated with visible light, and samples were taken every hour. The changes in the absorption spectrum of the samples over time were recorded using a UV-Vis absorption spectrometer. The degradation rate was calculated using the absorbance value A at the maximum absorption wavelength of Rhodamine B (λ=554nm).

[0092] Further characterization of the UV-Vis absorption properties of samples with different Mg doping ratios was performed, such as... Figure 10 As shown, the prepared doped zinc oxide exhibits a steep bandgap absorption at 371 nm, and the absorption intensity at this position increases with the increase of the Mg doping ratio in the electrolyte. Linear fitting of the bandgap absorption yields a bandgap of 3.22 eV, which is smaller than the bandgap of ordinary zinc oxide (3.37 eV), thus improving light energy utilization.

[0093] Figure 11 This is a schematic diagram illustrating the change in the efficiency of Mg-doped porous zinc oxide photocatalytic degradation of Rhodamine B over degradation time according to the present invention. Figure 12 This study compares the experimental results of photocatalytic degradation of Rhodamine B aqueous solution using Mg-doped porous zinc oxide and non-porous undoped zinc oxide as photocatalysts. Based on the absorbance at 554 nm, the self-degradation rate of Rhodamine B without any photocatalyst was significantly increased by 3.57 times and 4.95 times, respectively, for non-porous undoped zinc oxide and Mg-doped porous zinc oxide.

[0094] To further investigate the reusability of this material, the photocatalytic degradation experiment was repeated for five consecutive days using the same set of samples. The experimental results demonstrated that the material has good reusability, and the photocatalytic efficiency did not show a significant downward trend during the experimental period. Figure 13 As shown, it therefore has good reusability.

[0095] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a honeycomb porous nano-zinc oxide photocatalyst, characterized in that, Includes the following steps: (1) Preparation of polystyrene microsphere photonic crystal template A vertical deposition method was used, with polystyrene microsphere suspension as the deposition liquid. Under isothermal conditions, the surface tension and capillary force of the gas-liquid-solid three-phase interface were utilized to deposit a tightly ordered photonic crystal template on indium tin oxide conductive glass. (2) Preparation and construction of doped porous nano zinc oxide Using a photonic crystal as a template, zinc oxide material was filled into the gaps between polystyrene microspheres by a three-electrode cathode electrodeposition method with zinc nitrate aqueous solution as the electrolyte. Different proportions of Mg dopant were added to the electrolyte to obtain a doped zinc oxide-PC template composite material. Then, the PC template was removed to obtain a honeycomb porous nano zinc oxide photocatalyst.

2. The method for preparing a honeycomb porous nano-zinc oxide photocatalyst according to claim 1, characterized in that, In (1), the concentration of polystyrene microspheres in the polystyrene microsphere suspension is 0.5-2.0 wt%, and the particle size of the polystyrene microspheres is 200-400 nm.

3. The method for preparing a honeycomb porous nano-zinc oxide photocatalyst according to claim 1, characterized in that, The deposition temperature of the three-electrode cathode electrodeposition method in (2) is 45-55℃ and the deposition time is 24-48h.

4. The method for preparing a honeycomb porous nano-zinc oxide photocatalyst according to claim 1, characterized in that, In (2), the molar concentration of zinc nitrate in the electrolyte is 0.05-0.2 mol / L, and the amount of Mg doping in the electrolyte is 1-7 at the molar amount of Zn.

5. The method for preparing a honeycomb porous nano-zinc oxide photocatalyst according to claim 1, characterized in that, In step (2), the deposition voltage is -1 to -1.5V, the deposition temperature is 65-75℃, and the deposition time is 20-45min.

6. The honeycomb porous nano-zinc oxide photocatalyst prepared by any one of the preparation methods described in claims 1-4, characterized in that, Its specific surface area is 35-46 m². 2 / g, pore size distribution: 180-300nm, band gap: 3.20-3.30eV.

7. The application of the honeycomb porous nano-zinc oxide photocatalyst according to claim 6 in the photocatalytic degradation of organic pollution, characterized in that, Includes the following steps: Using Rhodamine B dye as the target degradation product, the honeycomb porous nano zinc oxide photocatalyst described in claim 6 was placed in a beaker, and a Rhodamine B solution was added to the beaker. The beaker was then irradiated under visible light, and samples were taken every hour. The changes in the absorption spectrum of the samples over time were recorded using a UV-Vis absorption spectrometer. The degradation rate was calculated using the absorbance value A at the maximum absorption wavelength of Rhodamine B: λ=554nm.

8. The application of the honeycomb porous nano-zinc oxide photocatalyst according to claim 7 in the photocatalytic degradation of organic pollution, characterized in that, The concentration of Rhodamine B in the Rhodamine B solution is 5-20 mg / L, and the weight ratio of Rhodamine B solute to honeycomb porous nano zinc oxide photocatalyst in the beaker is 5-20:1.

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