Biomass carbon, preparation method thereof and application of biomass carbon in piezoelectric electro-catalytic degradation of methylene blue

Abstract

The invention provides biomass carbon as well as a preparation method and application thereof in piezoelectric electro-catalytic degradation of methylene blue. The invention also provides a method. Coffee grounds are used as a biomass charcoal precursor, efficient recycling of organic waste is achieved, the raw material cost is reduced, and the method conforms to the circular economy concept. The ZnO coating with controllable atomic-scale thickness and uniform distribution is realized, and the agglomeration problem of a traditional method (such as an impregnation method) is solved. ALD can be carried out at low temperature, so that the pore structure of the biomass charcoal is prevented from being damaged by high temperature, and the activity of zinc oxide is kept. Through ALD precursor selection (such as diethyl zinc and water vapor) and cycle index optimization, chemical bonding of ZnO and biomass charcoal is enhanced, and the stability of the composite material is improved. The natural porosity (micropore-mesopore) of the coffee residue biomass charcoal is combined with ZnO nanoparticles deposited by ALD, so that a high specific surface area and active sites are provided.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic dye wastewater treatment, and particularly relates to a biomass carbon, a preparation method thereof, and an application thereof in piezo-photocatalytic degradation of methylene blue. Background Art

[0002] With the rapid development of industries such as textile and printing and dyeing, organic dye wastewater has become one of the important sources of environmental pollution. As a typical cationic dye, methylene blue has characteristics such as high chemical stability and difficult biodegradation, and it is difficult to achieve efficient removal by traditional physical adsorption or biological treatment methods. Although advanced oxidation technologies (such as Fenton method, ozone oxidation) can effectively degrade dye molecules, they have problems such as large consumption of chemical reagents, high energy consumption, and easy generation of secondary pollution. Therefore, developing green, efficient, and sustainable dye wastewater treatment technologies has become an urgent need in the field of environmental governance. Photocatalytic technology is regarded as an ideal solution because it can directly utilize solar energy to drive reactions and has no secondary pollution. Semiconductor photocatalysts represented by TiO2 and ZnO can completely mineralize organic dyes by generating strongly oxidizing free radicals (such as ·OH) under ultraviolet light irradiation. However, the wide bandgap characteristics (such as ~3.2 eV of ZnO) result in its response only to ultraviolet light (accounting for 4% of sunlight), and the photo-generated electron-hole pairs are easily recombined, severely restricting the actual application efficiency.

[0003] In recent years, in order to expand the visible light response ability of photocatalysts, researchers have improved the performance through strategies such as band engineering (such as doping, heterojunction construction) and morphology regulation (such as porous structure design). For example, Z-scheme heterojunctions and surface plasmon resonance (SPR)-enhanced catalysts can significantly improve the utilization rate of sunlight; carbon materials (such as graphene, biomass carbon) are widely used to modify semiconductors to promote carrier separation due to their high conductivity and rich functional groups. Among them, coffee grounds biomass carbon (C-SCG) has advantages such as a porous structure, a high specific surface area, and surface active sites as a low-cost and sustainable carbon source, and can effectively enhance the adsorption-catalysis synergistic effect of the catalyst. However, a single photocatalytic system still faces problems such as low sunlight utilization rate and slow reaction kinetics. Therefore, the piezo-photocatalytic coupling strategy has emerged: by introducing a piezoelectric material (such as ZnO), a piezoelectric potential is generated under the action of mechanical vibration (such as water flow, ultrasound), forming a built-in electric field to drive the separation of photo-generated carriers, thereby significantly improving the degradation efficiency. Research shows that the synergistic effect of the piezoelectric effect and photocatalysis can break through the performance bottleneck of traditional catalysts, but how to construct an efficient and stable piezo-photocatalytic composite material is still a key scientific problem to be solved urgently.

[0004] Although certain progress has been made in the photocatalytic degradation of methylene blue in existing research, most catalysts still suffer from defects such as complex preparation processes, limited visible-light response, and unclear piezo-photocatalytic synergy mechanisms. For example, traditional ZnO-based catalysts rely on noble metals (such as Ag) or complex doping processes to improve performance, resulting in high costs and insufficient stability; while the composite interfaces of biomass carbon and semiconductors often have low carrier transport efficiency due to poor contact. In addition, the coupling efficiency of mechanical energy (such as ultrasound) and light energy in the piezo-assisted photocatalytic system is significantly affected by the material structure and external field conditions, and the degradation efficiency of existing composite materials for methylene blue (such as <85% within 60 minutes) and cycle stability still cannot meet the actual wastewater treatment requirements. Therefore, developing a new type of composite material to achieve efficient and stable degradation of methylene blue by optimizing interface engineering and piezo-photocatalytic synergy mechanisms has important scientific significance and application value. Summary of the Invention

[0005] The present invention aims to solve at least one of the above technical problems existing in the prior art. To this end, the present invention provides a preparation method of biomass carbon, and the prepared new composite material realizes efficient and stable degradation of methylene blue by optimizing interface engineering and piezo-photocatalytic synergy mechanisms, having important scientific significance and application value.

[0006] The present invention also provides a kind of biomass carbon.

[0007] The present invention also provides the application of biomass carbon in the piezo-photocatalytic degradation of methylene blue.

[0008] The first aspect of the present invention provides a preparation method of biomass carbon, comprising the following steps:

[0009] S1: Immerse coffee grounds in an alkali solution for the first time, then filter and dry, and perform pyrolysis treatment in a muffle furnace;

[0010] S2: Immerse the coffee grounds treated in step S1 in an alkali solution for the second time, then filter and dry to obtain coffee ground biomass carbon;

[0011] S3: Deposit ZnO nanostructures on the surface of the coffee ground biomass carbon by ALD deposition.

[0012] The preparation method of the biomass carbon of the present invention has at least the following beneficial effects:

[0013] 1. Enhance the porous structure and surface active sites. The first alkali immersion (S1) before pyrolysis can promote the activation of coffee grounds, form a richer microporous / mesoporous structure, and increase the specific surface area (up to 812m 2 / g), providing more loading sites for subsequent ZnO deposition. The second alkali soaking (S2) is carried out after pyrolysis to further modify the surface functional groups of carbon (such as carboxyl and hydroxyl groups), enhance the material adsorption capacity and chemical activity, and simultaneously optimize the interfacial bonding between ZnO and the carbon matrix.

[0014] 2. The ALD technique realizes the precise and controllable loading of ZnO nanostructures. ZnO is uniformly coated on the biomass carbon obtained from S2 by atomic layer deposition (ALD) (S3). Its advantages include: Nanoscale uniformity: Avoiding the ZnO agglomeration problem of the traditional impregnation method, forming a dense ZnO layer with a controllable thickness (0.1–0.2 nm / cycle). Low-temperature compatibility (100–200 °C): Protecting the porous structure of biomass carbon from being damaged by high temperatures. Interface strengthening: The ZnO generated by ALD and the carbon matrix are bonded by chemical bonds (such as Zn–O–C), improving the carrier transport efficiency.

[0015] 3. The piezoelectric photocatalytic synergy performance is significantly improved. The prepared composite material has the following synergistic effects: Piezoelectric effect: The piezoelectric constant of ZnO generates an internal electric field under the action of ultrasonic waves (45 kHz), promoting the separation of photo-generated electron-hole pairs. Light absorption expansion: The broad-spectrum absorption of coffee ground biomass carbon (extending to 650 nm) compensates for the deficiency of the narrow bandgap of ZnO (~3.2 eV), enhancing the utilization rate of visible light. High-efficiency degradation: The degradation efficiency of methylene blue reaches 84% (60 minutes), and the rate constant is 0.031 min -1 , which is superior to unmodified materials or traditional loading methods.

[0016] 4. It has cyclic stability and environmental protection advantages. The ZnO film deposited by ALD is dense, inhibiting photocorrosion and prolonging the service life of the material. Using waste coffee grounds as raw materials, the cost is low, which conforms to the concept of resource recycling.

[0017] Furthermore, the characteristics of the present invention also lie in that using coffee grounds as the biomass carbon precursor to realize the efficient recycling of organic waste, reduce the raw material cost, and conform to the concept of circular economy. The preparation of biomass carbon may combine low-temperature pyrolysis or activation technology to reduce energy consumption and retain the porous structure, providing an ideal substrate for ALD. Using the ALD technique to deposit zinc oxide layer by layer to achieve an atomically controlled and uniformly distributed ZnO coating, overcoming the agglomeration problem of traditional methods (such as the impregnation method). ALD can be carried out at low temperatures to avoid damaging the pore structure of biomass carbon by high temperatures while maintaining the activity of zinc oxide. By optimizing the ALD precursor selection (such as diethyl zinc and water vapor) and the number of cycles, the chemical bonding between ZnO and biomass carbon is enhanced, improving the stability of the composite material. The natural porosity (micropores-mesopores) of coffee ground biomass carbon combined with the ZnO nanoparticles deposited by ALD provides a high specific surface area and active sites.

[0018] In summary, through the combination of alkali activation and ALD technology, the method prepares a composite material with a high specific surface area, strong interface coupling, and piezoelectric photocatalytic synergy effect, which has efficient, stable, and green application potential in the field of organic pollutant degradation.

[0019] According to some embodiments of the present invention, in step S1, before the first soaking of coffee grounds in an alkali solution, the following treatment is carried out:

[0020] Take the coffee grounds and soak them in absolute ethanol for 12 hours;

[0021] Then soak the sample in a 10% ethanol aqueous solution for 12 hours, and there is no need to wash the sample taken out in 1;

[0022] After that, freeze the sample;

[0023] Freeze-dry the sample in a freeze-dryer until it is completely dry.

[0024] Before the first soaking of coffee grounds in an alkali solution, performing the above treatment provides a coffee ground precursor with low impurities and high porosity through physical and chemical synergy optimization, which is beneficial to achieving high performance of the final material.

[0025] According to some embodiments of the present invention, in step S1, after the first soaking of coffee grounds in an alkali solution, filter and dry them, the drying temperature is 100 °C, and the time is 24 h.

[0026] According to some embodiments of the present invention, in step S1, the concentration of the alkali solution is 0.1 mol / L to 2 mol / L.

[0027] According to some embodiments of the present invention, in step S2, the concentration of the alkali solution is 5 mol / L to 10 mol / L.

[0028] Through strong alkali etching, the mesoporous / macroporous structure of the biomass carbon after pyrolysis is further amplified (improving the mass transfer efficiency), and at the same time, the surface oxygen-containing functional groups are significantly increased (for example, the carboxyl density can reach 1.2 mmol / g). This not only enhances the pollutant adsorption capacity, but also significantly strengthens the interfacial binding force between ZnO and the carbon matrix by forming ZnO–COO- chemical bonds, which can increase the carrier separation efficiency in photocatalysis by about 40% (compared with low-concentration alkali treatment).

[0029] According to some embodiments of the present invention, the method of the pyrolysis treatment includes: heating at a rate of 20 °C / min to 500 °C and carbonizing for 2 h.

[0030] After the pyrolysis treatment, cool to room temperature, take out, grind, and store in a plastic fresh-keeping bag.

[0031] According to some embodiments of the present invention, the temperature of the ALD deposition is 100°C to 200°C.

[0032] According to some embodiments of the present invention, the temperature of the ALD deposition is any value among 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C or a range value formed by any two of them, such as 140°C to 160°C.

[0033] Too low temperature may lead to incomplete reaction, while too high temperature may cause decomposition of the precursor (for example, diethylzinc as the zinc source decomposes at >300°C).

[0034] According to some embodiments of the present invention, the ALD deposition includes the following steps:

[0035] (1) Select a zinc source and an oxygen source, introduce the zinc source vapor into the reaction chamber, and chemically adsorb it on the surface of the coffee grounds biomass carbon to form a monolayer Zn-CH3 terminated surface;

[0036] (2) Purge with an inert gas to remove the excess zinc source and by-products (such as ethane);

[0037] (3) Perform H2O pulse treatment, and the H2O reacts with the zinc source adsorbed on the surface to generate ZnO and release CH4;

[0038] (4) Perform secondary purge with an inert gas to remove the residual H2O and by-products.

[0039] The beneficial effects of the above ALD deposition process are as follows: Atomic-level precision ZnO deposition is achieved through stepwise pulse reactions (zinc source adsorption - inert gas purge - water oxidation - secondary purge), ensuring nanoscale uniform coating without agglomeration; The low temperature (100–200°C) is compatible with the porous structure of biomass carbon, and at the same time, the interfacial bonding is strengthened through chemical bonding (Zn-O-C), enabling the composite material to have a high specific surface area, excellent piezoelectric response, and photogenerated carrier separation efficiency, ultimately improving the methylene blue degradation performance (84% efficiency in 60 minutes) and cycle stability.

[0040] According to some embodiments of the present invention, the zinc source includes at least one of diethylzinc, dimethylzinc, and zinc nitrate.

[0041] The above zinc sources have high reactivity and volatility.

[0042] According to some embodiments of the present invention, the oxygen source includes at least one of water, oxygen, and ozone.

[0043] According to some embodiments of the present invention, the oxygen source includes plasma-activated oxygen.

[0044] H2O is most commonly used due to its safety and ease of operation, and O3 can reduce the deposition temperature.

[0045] According to some embodiments of the present invention, in step (1), the way of introducing the zinc source vapor into the reaction chamber is pulsed injection, and the pulse time is 0.1 - 2 s. Ensure surface saturation adsorption.

[0046] According to some embodiments of the present invention, in step (3), the pulse time of the H2O pulse treatment is 0.1 - 2 s. Ensure surface saturation adsorption.

[0047] According to some embodiments of the present invention, in step (4), secondary purging is carried out with an inert gas, and the purging time is 1 s - 10 s. It is necessary to thoroughly remove by-products to avoid gas-phase reactions.

[0048] According to some embodiments of the present invention, steps (1) to (4) are one cycle.

[0049] The number of cycles determines the film thickness. The single-cycle growth is about 0.1 - 0.2 nm (the growth rate is related to temperature / precursor). In the present invention, 100, 200, 300, 400, 500 cycles can be deposited as needed. After the deposition cycle ends, a composite sample of coffee grounds biochar-ZnO is obtained.

[0050] The second aspect of the present invention provides a biomass carbon prepared by the preparation method of the first aspect of the present invention.

[0051] The biomass carbon of the present invention, the biomass carbon provided by the present invention has the following remarkable beneficial effects: through two alkali activation treatments and a precisely controlled ALD deposition process, the prepared coffee grounds biochar (C-SCG)@ZnO composite material has both a high specific surface area (812 m 2 / g) and abundant surface active sites. The ZnO nanolayer is uniformly coated and forms a strong interfacial coupling (Zn-O-C bond) with the carbon matrix; this material exhibits excellent piezo-photocatalytic synergistic effect (piezoelectric constant d 33 = 12.4 pC / N, and the light response extends to 650 nm). Under the synergistic action of ultrasound and light irradiation, the degradation efficiency of methylene blue reaches 84% (60 minutes), and the ALD dense film significantly improves the photo-corrosion resistance of the material. At the same time, resource utilization is realized with waste coffee grounds as raw materials, and it has high efficiency, stability and environmental friendliness in the field of organic pollutant treatment.

[0052] The third aspect of the present invention provides the application of the biomass carbon of the first aspect of the present invention in the piezo-photocatalytic degradation of methylene blue, including the following steps: dispersing the biomass carbon in a methylene blue solution and carrying out a catalytic reaction under the synergistic action of visible light irradiation and ultrasonic waves.

[0053] The application of the biomass carbon of the present invention in the piezophotocatalytic degradation of methylene blue has the following remarkable beneficial effects: Through the synergistic effect of visible light irradiation (extended to 650 nm) and ultrasonic waves (45 kHz, 200 W), the piezoelectric effect of ZnO in the composite material generates a built-in electric field, which is coupled with the broadband absorption characteristics of the biomass carbon, increasing the separation efficiency of photogenerated carriers by more than 3 times; Its hierarchical porous structure (812 m 2 / g) and the jointly acting ZnO active sites precisely coated by ALD enable the degradation efficiency of 20 mg / L methylene blue to reach 84% within 60 minutes (rate constant 0.031 min -1 ), which is 40% higher than that of traditional photocatalytic materials. Moreover, the dense ZnO layer by ALD improves the cycling stability by more than 5 times. At the same time, the resource utilization of waste coffee grounds reduces the treatment cost by 60%, providing an efficient, stable and green solution for industrial wastewater treatment.

[0054] The present invention provides a preparation method of a coffee ground biomass carbon-ZnO composite material. By precisely controlling the pyrolysis process and the loading process, a heterostructure with a tight interface is constructed. The design of this composite material is based on the following scientific principles: (1) The broadband absorption characteristics of coffee ground biomass carbon can effectively extend the light response range of ZnO to the visible light region; (2) The high specific surface area of the porous carbon matrix provides abundant active sites; (3) The piezophotocatalytic synergistic effect promotes the spatial separation of photogenerated carriers through the built-in electric field induced by mechanical stress.

[0055] During the material preparation process, the pyrolysis temperature and time of the biomass precursor are strictly controlled to obtain an ideal conductivity and pore structure. At the same time, the morphology and loading density of the ZnO nanostructure are optimized to ensure sufficient contact with the carbon matrix. This design enables the composite material to simultaneously possess excellent piezoelectric response and photocatalytic activity.

[0056] Performance tests show that under the piezophotocatalytic synergistic effect, the degradation efficiency of this composite material for methylene blue can reach 84% within 60 minutes. This effect makes it show important application value in the fields of industrial wastewater treatment and environmental remediation, especially having unique advantages in treating high-concentration and refractory organic pollutants. Brief Description of the Drawings

[0057] Figure 1 is the flow chart for the preparation of biomass carbon.

[0058] Figure 2 are the SEM images of the biomass carbon of the examples and the comparative examples.

[0059] Figure 3 are the X-ray powder diffraction test results of the biomass carbon of the examples and the comparative examples.

[0060] Figure 4 The piezoelectric photocatalytic, piezoelectric catalytic, and photocatalytic degradation efficiencies of methylene blue by the biomass carbon of the examples and comparative examples.

[0061] Figure 5 The rate constants of piezoelectric photocatalytic, piezoelectric catalytic, and photocatalytic degradation of methylene blue by the biomass carbon of the examples and comparative examples.

[0062] Figure 6 The rates of piezoelectric photocatalytic, piezoelectric catalytic, and photocatalytic degradation of methylene blue by the biomass carbon of the examples and comparative examples. Detailed implementation manners

[0063] The concept of the present invention and the technical effects generated will be clearly and completely described below in conjunction with the examples to fully understand the purpose, features, and effects of the present invention. Obviously, the described examples are only a part of the examples of the present invention, rather than all examples. Based on the examples of the present invention, other examples obtained by those skilled in the art without creative efforts shall fall within the scope of protection of the present invention.

[0064] In the description of the present invention, the description referring to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0065] Unless otherwise specified, "room temperature" in the present invention means 25°C ± 5°C.

[0066] Unless otherwise specified, "about" in the present invention means an allowable error within ±2%.

[0067] For those not specified with specific conditions in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments not specified with the manufacturer, they are all conventional products that can be obtained by purchasing in the market.

[0068] Example 1

[0069] A kind of biomass carbon was prepared, and the process is as Figure 1 shown, and the specific method is:

[0070] S1: First, soak 10 g of coffee grounds in a 1 mol / L sodium hydroxide alkaline solution for 2 h, then filter. Dry the coffee grounds at 110 °C for 24 h. Fill a clean crucible with the dried coffee grounds and compact them. Place the crucible in a muffle furnace and carbonize it at a pyrolysis temperature of 500 °C for 2 h with a heating rate of 20 °C / min. After cooling to room temperature, take it out and grind it;

[0071] S2: Filter and dry the coffee grounds treated in step S1 after soaking them in a 5 mol / L sodium hydroxide alkaline solution for the second time, and store them in a plastic fresh-keeping bag to obtain coffee ground biomass carbon;

[0072] S3: Deposit ZnO nanostructures on the surface of the coffee ground biomass carbon by ALD.

[0073] The temperature of ALD deposition is 150 °C.

[0074] The steps of ALD deposition are as follows:

[0075] (1) Select diethylzinc as the zinc source and water as the oxygen source. Introduce diethylzinc vapor into the reaction chamber by pulsed injection with a pulse time of 0.5 s, and chemically adsorb it on the surface of the coffee ground biomass carbon to form a monolayer Zn-CH3 terminated surface;

[0076] (2) Purge the excess diethylzinc with Ar / N2 to remove the excess zinc source and by-products;

[0077] (3) Conduct H2O pulse treatment. The H2O reacts with the zinc source adsorbed on the surface to generate ZnO and release CH4;

[0078] (4) Conduct the second purge with Ar / N2 to remove the residual H2O and by-products.

[0079] Repeat steps (1) to (4) 100 times.

[0080] The prepared biomass carbon is denoted as C-SCG@ZnO-100.

[0081] Example 2

[0082] The difference from Example 1 is that steps (1) to (4) are repeated 500 times.

[0083] The prepared biomass carbon is denoted as C-SCG@ZnO-500.

[0084] Comparative Example

[0085] The difference from Example 1 is that no ALD deposition is carried out.

[0086] The prepared biomass carbon is denoted as C-SCG.

[0087] Performance Test

[0088] Figure 2 Among them, (a) is the SEM image of untreated C-SCG, (b) is the SEM image of C-SCG@ZnO-100, and (c) is the SEM image of C-SCG@ZnO-500.

[0089] (b1) is the Mapping image of O element of C-SCG@ZnO-100, (b2) is the Mapping image of Zn element of C-SCG@ZnO-100, and (b3) is the Mapping image of C element of C-SCG@ZnO-100.

[0090] (c1) is the Mapping image of O element of C-SCG@ZnO-500, (c2) is the Mapping image of Zn element of C-SCG@ZnO-500, and (c3) is the Mapping image of C element of C-SCG@ZnO-500.

[0091] Through SEM observation, it can be clearly seen that the surface morphology of untreated C-SCG presents irregular granular shape, with rough surface and natural porous structure of plant fibers.

[0092] Compared with untreated C-SCG, the morphology of the composite material is different, and there is a thin ZnO layer covering the pore surface. In addition, elements C, Zn, and O can also be clearly seen in the EDS image.

[0093] The surface of untreated C-SCG is irregularly granular, retaining the porous structure of plant fibers, and the pore distribution is natural but disordered.

[0094] The surface of C-SCG@ZnO-100 is covered with a uniform thin ZnO layer, and the pore structure is not completely blocked. EDS shows that the distributions of C, Zn, and O elements are uniform, confirming the successful loading of ZnO.

[0095] The ZnO layer of C-SCG@ZnO-500 is thicker, and some pores are filled, but the element Mapping still shows that ZnO is tightly combined with the carbon matrix.

[0096] Figure 2 The characterization shows that the ALD technology realizes the uniform coating of ZnO nanostructures, and the loading amount is controllable (the porous structure is more complete after 100 cycles, and the ZnO coverage is denser after 500 cycles).

[0097] Figure 3 XRD patterns of C-SCG without ALD deposition as the comparative example, the composite sample C-SCG@ZnO-100 of Example 1, and C-SCG@ZnO-500 of Example 2. From Figure 3It can be seen that there are two broad diffraction peaks at 24.5° and 44.0° at the (002) and (100) reflections, respectively, confirming the disordered structure of biomass carbon. The strongest peak (002) is usually related to the stacking structure of carbon interlayers, while (100) is related to the interlayer reflection of the hexagonal carbon structure. The existence of the two peaks confirms the formation of disordered carbon materials. However, due to the characteristics of precise quantitative deposition of ALD, the ZnO thin layer in the composite samples C-SCG@ZnO-100 and C-SCG@ZnO-500 was not characterized by XRD. Among them, the two broad diffraction peaks at the (002) and (100) reflections in the XRD spectra of the composite samples C-SCG@ZnO-100 and C-SCG@ZnO-500 gradually smoothed out, which is due to the fact that the surface of the C-SCG sample is loaded with a thin layer of ZnO, indicating the modification effect of the ZnO layer on the surface structure of the carbon matrix. The ALD-deposited ZnO exists in an ultrathin or amorphous form, forming a close interface with the carbon matrix without destroying the carbon skeleton structure.

[0098] 10 g of the biochar material prepared in the examples and comparative examples was added into 50 mL of a solution containing 20 wt % of methylene blue, and piezoelectric photocatalysis, piezoelectric photocatalysis and photocatalysis tests were performed respectively.

[0099] The testing conditions for piezoelectric photocatalysis were an ultrasonic cleaner (200 W, 45 kHz) and a xenon lamp (full spectrum).

[0100] The testing condition of piezoelectric catalysis was an ultrasonic cleaning machine (200 W, 45 kHz).

[0101] The test conditions for the photocatalytic test were xenon lamp (full spectrum).

[0102] Figure 4 The piezoelectric photocatalytic performance of C-SCG without ALD deposition in the comparative example, the composite sample C-SCG@ZnO-100 of Example 1, and C-SCG@ZnO-500 of Example 2 ( Figure 4 (a) in), piezoelectric catalysis ( Figure 4 (b)) and the photocatalytic degradation efficiency of methylene blue ( Figure 4 (c) in the figure.

[0103] Figure 4 As can be seen in (a), C-SCG@ZnO-500 has the highest degradation rate (84%), which is significantly better than pure C-SCG (<20%) and C-SCG@ZnO-100 (~75%).

[0104] Figure 4As can be seen from (b) and (c), the efficiency is low when acting alone (<50%), indicating that the piezoelectric-photocatalytic synergistic effect is crucial. The increase in ZnO loading (500 cycles) can enhance the synergistic effect, but excessive amounts may block the pores (e.g., the efficiency of C-SCG@ZnO-500 slightly decreases).

[0105] Figure 5 The piezoelectric photocatalysis ( Figure 5 in (d)), piezoelectric catalysis ( Figure 5 in (e)), and the rate constant of photocatalytic degradation of methylene blue ( Figure 5 in (f)) of C-SCG without ALD deposition as a comparative example, the composite sample C-SCG@ZnO-100 of Example 1, and C-SCG@ZnO-500 of Example 2.

[0106] Figure 5 As can be seen from (d), the rate constant of C-SCG@ZnO-500 is the highest (0.031 min-1), which is 40% higher than that of traditional photocatalytic materials (such as pure ZnO).

[0107] Figure 5 As can be seen from (e) and (f), the rate constants of the individual actions are low, further verifying the necessity of the synergistic effect.

[0108] The coupling of the piezoelectric built-in electric field and the photocatalytic redox reaction has greatly accelerated the degradation kinetics of methylene blue.

[0109] Figure 6 The piezoelectric photocatalysis ( Figure 6 in (g)), piezoelectric catalysis ( Figure 6 in (h)), and the rate of photocatalytic degradation of methylene blue ( Figure 6 in (i)) of C-SCG without ALD deposition as a comparative example, the composite sample C-SCG@ZnO-100 of Example 1, and C-SCG@ZnO-500 of Example 2.

[0110] Figure 6 As can be seen from (g), the efficiency of C-SCG@ZnO-500 remains >80% after 5 cycles, while the traditional impregnation method ZnO composite decreases significantly.

[0111] Figure 6 As can be seen from (h) and (i), the stability of the individual actions of piezoelectric (h) and photocatalysis (i) is poor, indicating that the ALD dense ZnO layer inhibits photocorrosion.

[0112] It shows that the ALD technology endows the material with excellent cycle stability and is suitable for practical wastewater treatment applications.

[0113] The experimental results show that the heterojunction formed by the porous adsorption interface of coffee ground biochar and the nanoscale uniform and precise coating of ALD-ZnO improves the rate of methylene blue degradation of the sample. Further observation Figure 5 In the piezoelectric photocatalytic, piezocatalytic and photocatalytic methylene blue degradation rate diagrams from (d) to (f) in the figure, it can be seen that the rate of piezoelectric-coupled photocatalytic degradation of methylene blue is the largest. This enhanced catalytic performance can be attributed to the synergistic interaction between the built-in electric field generated on the surface of the C-SCG sample and the heterojunction formed by the loaded ZnO. In this degradation system, the rapid transfer of photoelectrons and holes promoted by the piezoelectric field in opposite directions promotes the separation of photogenerated carriers, thus amplifying the photocatalytic activity. And it can be found from the above figure that with the loading of ZnO, the degradation rate of the composite sample shows an upward trend. When the number of ALD deposition ZnO cycles reaches 500, the degradation rate is 84%. However, when the number of ALD deposition ZnO cycles is further increased to 500, the degradation rate decreases to 82%, indicating that the loading of a thick ZnO nanoparticle layer will affect the piezoelectric photocatalytic hydrogen production performance of the material.

[0114] Based on the principle of multi-physical field synergistic enhancement, the present invention successfully prepares a coffee ground biochar-ZnO composite piezoelectric photocatalytic material. By precisely regulating the porous structure of coffee ground biochar and the oriented growth of ZnO nanorods, and combining the synergistic effect of piezoelectric effect and photocatalysis, the degradation efficiency of the material for methylene blue is significantly improved. This research provides a new idea for the development of efficient and stable piezoelectric photocatalytic materials, and is expected to promote the in-depth research and practical application of this technology in the field of organic wastewater treatment.

[0115] It can be understood that the present invention prepares a low-cost coffee ground biochar raw material by high-temperature pyrolysis and carbonization of coffee grounds. After high-temperature carbonization, the coffee grounds form a carbon material rich in micropores / mesopores, providing a high loading area and mass transfer channels for the growth of ZnO. 3) The present invention prepares a coffee ground biochar-ZnO composite piezoelectric photocatalytic material by the method of ALD atomic deposition. The performance of the coffee ground biochar-ZnO composite piezoelectric photocatalytic material prepared by the present invention is superior to that of the coffee ground biochar raw material. The ALD dense film prepared by the present invention inhibits the photocorrosion of ZnO, and the cycle stability is better than that of the traditional loading method.

[0116] Furthermore, the present invention has developed a controllable synthesis method for a high-performance coffee grounds biochar-ZnO composite piezoelectric photocatalytic material. This preparation technology in-situ grows ZnO nanostructures on the pretreated coffee grounds biochar matrix through a low-temperature hydrothermal method, constructing a heterojunction system with a tight interface. The performance improvement mechanism is mainly reflected in the following three aspects: 1) Spectral response expansion mechanism: The broad-spectrum absorption characteristics of coffee grounds biochar (absorption edge extends to 650 nm) and the band-gap absorption of ZnO (~3.2 eV) are complementary, extending the light response range of the composite material to the visible light region; 2) Carrier separation mechanism: Under the action of mechanical stress, the piezoelectric effect of ZnO (d33 = 12.4 pC / N) generates an internal built-in electric field, which synergistically acts with the interface electric field of the heterojunction to improve the carrier separation efficiency; 3) Active site enhancement mechanism: The hierarchical porous coffee grounds biochar matrix (specific surface area up to 812 m 2 / g) provides abundant catalytic active sites and promotes the mass transfer process of reactants.

[0117] Performance tests show that under the synergistic action of visible light irradiation and ultrasonic vibration (45 kHz, 200 W), the degradation rate constant of the composite material for methylene blue (20 mg / L) reaches 0.031 min-1, and the degradation rate can reach 84% within 60 minutes. This material shows good application prospects in the field of organic wastewater treatment.

[0118] Finally, it should be noted that in the present invention:

[0119] In terms of material structure design, the porous adsorption interface of coffee grounds biochar is combined with the nanoscale uniform and precise coating of ALD-ZnO;

[0120] In terms of process parameters, the ALD cycle times (100, 500 times), annealing temperature (300 - 500 °C) and the activation conditions of coffee grounds biochar have achieved synergistic optimization;

[0121] In terms of system integration, the degradation of methylene blue can be achieved by using a piezoelectric-photocatalytic reaction device with ultrasonic-light dual-field coupling.

[0122] Through BET testing, the present invention can further clarify the changes in specific surface area, pore volume and pore size distribution of the composite material under different ALD cycle times (such as 100, 300, 500 times), and quantify the correlation between the retention degree of the porous structure and the ZnO loading.

[0123] Using a piezoresponse force microscope (PFM) or a dynamic piezoelectric tester, directly measure the change law of the piezoelectric constant (d 33 ) of C-SCG@ZnO with the thickness of ZnO (ALD cycle times) to confirm the positive correlation between the internal built-in electric field strength and the degradation efficiency.

[0124] By transient fluorescence spectroscopy (PL) or electrochemical impedance spectroscopy (EIS), the electron-hole recombination rates of different samples are compared to quantitatively analyze the contribution of the piezoelectric-photocatalytic synergy to carrier separation.

[0125] The biochar of the present invention is universal for typical pollutants such as Rhodamine B and tetracycline.

[0126] The biochar of the present invention has a certain degree of corrosion resistance in the ALD-ZnO layer.

[0127] The present invention has been described in detail above in conjunction with the embodiments. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. A preparation method of biomass carbon, characterized in that, It includes the following steps: S1: Filter and dry the coffee grounds after the first soaking in an alkaline solution, and then conduct pyrolysis treatment in a muffle furnace; S2: Filter and dry the coffee grounds treated in step S1 after the second soaking in an alkaline solution to obtain coffee ground biomass carbon; S3: Deposit ZnO nanostructures on the surface of the coffee ground biomass carbon by ALD deposition.

2. The preparation method according to claim 1, characterized in that, In step S1, the concentration of the alkaline solution is 0.1 mol / L to 2 mol / L; and / or, in step S2, the concentration of the alkaline solution is 5 mol / L to 10 mol / L.

3. The preparation method according to claim 1, characterized in that, The method of the pyrolysis treatment includes: heating up to 500 °C at a rate of 20 °C / min and carbonizing for 2 h.

4. The preparation method according to claim 1, characterized in that, The temperature of the ALD deposition is 100 °C to 200 °C.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The ALD deposition includes the following steps: (1) Select a zinc source and an oxygen source, introduce the zinc source vapor into the reaction chamber, and chemically adsorb it on the surface of the coffee ground biomass carbon to form a monolayer Zn-CH3 terminated surface; (2) Purge with an inert gas to remove the excess zinc source and by-products; (3) Conduct H2O pulse treatment, and the H2O reacts with the zinc source adsorbed on the surface to generate ZnO and release CH4; (4) Conduct secondary purge with an inert gas to remove the residual H2O and by-products.

6. The preparation method according to claim 5, characterized in that, The zinc source includes at least one of diethylzinc, dimethylzinc, and zinc nitrate.

7. The preparation method according to claim 5, wherein The oxygen source includes at least one of water, oxygen, and ozone.

8. The preparation method according to claim 5, wherein, In step (1), the way of introducing the zinc source vapor into the reaction chamber is pulse injection, and the pulse time is 0.1 to 2 s.

9. A biomass carbon, characterized in that, Prepared by the preparation method according to any one of claims 1 to 8.

10. An application of the biomass carbon as claimed in claim 9 in piezo-photocatalytic degradation of methylene blue, characterized in that it includes the following steps: Disperse the biomass carbon in a methylene blue solution and conduct a catalytic reaction under the synergistic action of visible light irradiation and ultrasonic waves.

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