Water evaporation-photocatalysis bifunctional wood-based composite material and preparation method and application thereof

Abstract

The present application relates to a kind of water evaporation-photo catalysis bifunctional wood-based composite material and its preparation method and application, three-dimensional solar interface evaporator is prepared by combining catalytic mass transfer path with evaporation water transfer path, uses the wood of widely available and low cost as base, carbon nanotube coating is prepared by dipping coating, and water evaporation-photo catalysis bifunctional wood-based composite material is prepared by the controlled growth of manganese dioxide particles on the surface of material, can be used for water evaporation and simultaneously degrading pollutants in water.The wood-based composite material is used in water purification field, and the purification effect is good.

Description

Technical Field

[0001] This invention belongs to the field of water purification technology, specifically relating to a water evaporation-photocatalysis bifunctional wood-based composite material, its preparation method, and its application. Background Technology

[0002] Freshwater scarcity is posing a threat to the sustainable development of human society. Solar-powered water evaporation, which can produce clean water at a low cost without consuming fossil fuels, is considered a promising solution to global water pollution and shortage problems. Solar-powered interfacial evaporation, due to its excellent photothermal management, can convert solar energy into heat energy for water evaporation at the air / water interface. Solar-driven interfacial evaporation processes can efficiently produce clean water from various water sources, including rivers, lakes, oceans, and even industrial wastewater. Interfacial evaporation systems can exclude various ions, organic matter, and bacteria because the liquid-to-gas phase transformation of water can effectively extract water from other pollutants, resulting in high-quality clean water. However, if the water source is contaminated with non-biodegradable and toxic organic compounds, such as pharmaceuticals, the residual pollutants after water evaporation will cause secondary harm to the environment, requiring further treatment.

[0003] Semiconductor-based advanced oxidation processes (AOPs) are catalytic technologies with advantages such as low cost, clean energy, and minimal secondary pollution. Combining interfacial solar steam generation with AOPs can enable simultaneous freshwater production and pollution remediation. However, developing bifunctional evaporators with well-integrated synergistic photothermal-AOP catalytic performance remains challenging.

[0004] To address the aforementioned issues, this invention proposes a three-dimensional evaporator based on a bifunctional wood-based composite material that combines catalytic mass transfer with evaporative water transfer. The three-dimensional structural design expands the total evaporation surface area, harvesting additional energy from the environment to increase the evaporation rate. A carbon nanotube coating on the top surface of the wood enhances light absorption, while MnO2 particles degrade pollutants. The carbon nanotube and MnO2 composite material serves as the photothermal conversion material for interfacial water evaporation. The MnO2 on the sidewalls is used for catalytic degradation mass transfer and evaporative water supply, while the air-filled wood channels provide insulation, directing the generated heat to the evaporation interface. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a water evaporation-photocatalysis bifunctional wood-based composite material, its preparation method, and its application. By combining the catalytic mass transfer pathway with the evaporation water transfer pathway, it solves the problem of the difficulty in combining interfacial water evaporation and photocatalysis in three-dimensional evaporators. The water evaporation-photocatalysis bifunctional wood-based composite material of this invention has wide applications in water evaporation and pollutant degradation, and also provides technical support for the treatment of large-scale water bodies.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a water evaporation-photocatalysis bifunctional wood-based composite material, with wood as the substrate and MnO2 nanoparticles uniformly loaded on the material surface.

[0007] In a preferred embodiment of the present invention, the MnO2 particles in the wood-based composite material have a nanoflower structure, and the size of the MnO2 nanoflowers is preferably 100-200 nm. The nanoflower structure has a large specific surface area, which can provide more active sites and efficient pollutant transport, resulting in high catalytic activity.

[0008] This invention also protects a method for preparing the aforementioned water evaporation-photocatalytic bifunctional wood-based composite material, comprising the following steps:

[0009] (1) Pretreatment of the wood base: Cut the wood into strips along the growth direction, then cut the strips into blocks, clean the surface of the blocks, and let them dry for later use.

[0010] (2) Impregnate one side of the wood block with carbon nanotube dispersion, perform adsorption treatment, and air dry; this step is used for solar steam generation, and then drying is used for in-situ growth of MnO2;

[0011] (3) The wood blocks treated in step (2) were sequentially immersed in potassium permanganate solution and manganese sulfate solution to grow MnO2 particles on the material surface. After the reaction, the wood was washed with water and dried to obtain a water evaporation-photocatalytic bifunctional wood-based composite material. At this time, KMnO4 was reduced by MnSO4, and MnO2 nanoparticles were uniformly loaded on the material surface. The amount of MnO2 was easily controlled by the KMnO4 impregnation time. As the impregnation time increased, the color of the wood gradually changed from white to dark brown or black, but the interior remained white.

[0012] In a preferred embodiment of the present invention, the wood is preferably balsa wood, the size of the wood strip is preferably 2*2cm, and the length of the wood strip cut into blocks is preferably 2-8cm; the adsorption treatment is to immerse the wood blocks in a carbon nanotube dispersion for 30-60s; preferably, the wood blocks are immersed in 5mL of carbon nanotube dispersion in a circular container with a bottom diameter of 5cm for 30-60s.

[0013] In a preferred embodiment of the present invention, the carbon nanotube dispersion is a carboxylated carbon nanotube aqueous dispersion with a mass concentration of <1 wt.%, preferably 0.15 wt.%; the molar ratio of the potassium permanganate solution to the manganese sulfate solution is 1:1; the molar concentration is 0.5–1.5 M, preferably 1 M; the adsorption reaction time in the potassium permanganate solution is 0–40 minutes, preferably 20 minutes; the reaction time in the manganese sulfate solution is 5–10 minutes; the reaction is a reaction in solution at room temperature; and the drying is natural drying at room temperature to remove moisture.

[0014] This invention also protects the application of the aforementioned water evaporation-photocatalysis bifunctional wood-based composite material, specifically a three-dimensional evaporator based on the water evaporation-photocatalysis bifunctional wood-based composite material with an "integrated" function of interfacial solar heating, efficient water transport, and high catalytic activity. The water evaporation-photocatalysis bifunctional wood-based composite material is placed in a square plastic heat insulation plate with a central through-hole. The internal dimensions of the through-hole are the same as the external dimensions of the material. This plate is then placed in a square container filled with liquid, with the wood-based composite material in direct contact with the liquid. The size of the square plastic heat insulation plate is the same as the internal dimensions of the square container. The volume of the liquid in the container is equal to the container volume minus the volume of the material inside the container. The evaporator is positioned 1-3 cm above the heat insulation plate and 1-5 cm below it. The heat insulation plate serves to prevent the evaporation of water outside the wood-based composite material from causing an excessively high evaporation rate. Simulated sunlight generated by a xenon lamp (AM 1.5G) is used as the light source to illuminate the material downwards, and a solar power meter is used to calibrate the sunlight intensity.

[0015] In a preferred embodiment of the present invention, the through-hole size of the square plastic heat insulation board is preferably 2*2cm, the size of the square plastic heat insulation board is preferably 4*4cm, the internal size of the square container is preferably 4*4*5cm, the liquid volume in the container is preferably 60-76mL, and the liquid is pure water, methylene blue solution or tetracycline solution.

[0016] In a preferred embodiment of the present invention, the evaporator is positioned 3 cm above the insulation plate and 5 cm below the plate.

[0017] The evaporator of the present invention has a carbon nanotube coating and MnO2 nanoparticles loaded in situ at room temperature to achieve interfacial evaporation and organic matter degradation, and has the advantage of using photothermal and photochemical energy to simultaneously carry out water evaporation and photocatalysis.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. This invention prepares a three-dimensional solar interface evaporator by combining a catalytic mass transfer pathway with an evaporative water transfer pathway. Using widely available and inexpensive wood as a substrate, a water evaporation-photocatalytic bifunctional wood-based composite material is prepared by impregnating and coating with carbon nanotubes to controllably grow manganese dioxide particles on the material surface. This composite material can be used for water evaporation and simultaneous degradation of pollutants in water. The wood-based composite material exhibits good purification effects in the field of water purification.

[0020] 2. This invention breaks through the limitations of two-dimensional evaporators in existing water evaporation photocatalytic systems and uses a three-dimensional evaporator to improve the water evaporation rate and photocatalytic rate.

[0021] 3. In order to combine solar interface evaporation technology with advanced oxidation processes, this invention combines the water transfer path of the evaporation process with the mass transfer path of the catalytic process. In order to achieve high utilization of solar spectrum, black carbon materials are combined with metal oxide particles, achieving excellent comprehensive results.

[0022] 4. The preparation process of the water evaporation-photocatalysis bifunctional wood-based composite material in this invention does not involve high temperature and high pressure reactions. The reaction is mild, and the wood is directly reacted with the solution at room temperature, which simplifies the preparation process of solar thermal composite materials. The product is more readily available and suitable for wide application.

[0023] 5. This invention investigates the application effects of the prepared water evaporation-photocatalysis bifunctional wood-based composite material in water evaporation and photocatalysis. By monitoring the mass change of tetracycline aqueous solution and the concentration change of tetracycline in the solution at different times, the simultaneous degradation of tetracycline in the solution at a high evaporation rate is achieved, avoiding the environmental harm caused by residual pollutants after water evaporation. Attached Figure Description

[0024] The following explanation, in conjunction with the accompanying drawings, will provide further details.

[0025] Figure 1 These are schematic diagrams illustrating the preparation of Examples 1 and 2 in this invention;

[0026] Figure 2 The M0CW and M in Embodiment 1 of this invention 10 CW, M 20 CW, M 40 Scanning electron microscope image of CW;

[0027] Figure 3 These are TEM images of MnO2 particles from Examples 1 and 2 of this invention.

[0028] Figure 4 The M0CW and M in Embodiment 1 of this invention 10 CW, M 20 CW, M40 CW's evaporation curve for treating pure water under a certain solar intensity, along with the corresponding evaporation rate and evaporation efficiency;

[0029] Figure 5 The M0CW and M in Embodiment 1 of this invention 10 CW, M 20 CW, M 40 CW catalytic degradation curve of MB solution under one solar radiation intensity and corresponding degradation efficiency;

[0030] Figure 6 M in Embodiment 2 of the present invention 20 CW, M 20 CW 2-1 M 20 CW 3-1 M 20 CW 3-3 M 20 CW 3-5 The evaporation rate curve and the evaporation amount curve of pure water under a certain solar radiation intensity;

[0031] Figure 7 M in Embodiment 2 of the present invention 20 CW, M 20 CW 2-1 M 20 CW 3-1 M 20 CW 3-3 M 20 CW 3-5 Catalytic degradation curves and corresponding degradation rates of MB solution treated under a certain solar radiation intensity;

[0032] Figure 8 The figure shows the mass change curve and corresponding degradation efficiency of tetracycline in a tetracycline solution during water evaporation and degradation under a certain sunlight intensity in Example 3 of this invention. Detailed Implementation

[0033] To make the technical content of this invention more apparent and understandable, the embodiments of this invention are described in detail below. However, the embodiments below are only used to explain this invention, and this invention is not limited to the embodiments below.

[0034] Example 1

[0035] A method for preparing a water evaporation-photocatalysis bifunctional wood-based composite material includes the following steps:

[0036] (1) Pretreatment of the wood base: Cut the balsa wood into 2*2cm strips along the growth direction, then cut the strips into 2cm long blocks, clean the wood chips on the surface of the blocks with distilled water, and let them dry for later use.

[0037] (2) Impregnate one side of a clean wooden block with carbon nanotube dispersion, perform adsorption treatment, and then air dry;

[0038] (3) The wood blocks treated in step (2) were immersed in a 1M potassium permanganate solution for 0, 10, 20, and 40 minutes, respectively. Then, they were immersed in a 1M manganese sulfate solution for 5-10 minutes. After the reaction, they were washed with deionized water and dried to obtain a water evaporation-photocatalytic bifunctional wood-based composite material. The reaction times in the potassium permanganate solution were denoted as M0CW, M0CW, and M0CW, respectively. 10 CW, M 20 CW, M 40 CW.

[0039] Image scanned by SEM ( Figure 2 As can be seen, with the extension of reaction time in potassium permanganate solution, the number of MnO2 particles loaded on the material surface also increases. As shown in the figure, M... 10 A small amount of MnO2 particles are distributed on the surface of the CW material. 40 The surface of the CW material is covered with a large number of MnO2 particles. This embodiment illustrates that by controlling the reaction time of the wood block in potassium permanganate solution, the number of MnO2 particles growing on the material surface can be controlled. The preparation method of this invention can obtain a wood-based composite material loaded with a specific number of particles. TEM transmission electron microscopy images (…) Figure 3 The specific morphology of the generated MnO2 particles can be seen. The MnO2 particles have a nanoflower structure with a size of about 100-200 nm. The nanoflower structure has a large specific surface area, which can provide more active sites and efficient pollutant transport, and has high catalytic activity.

[0040] To evaluate the water evaporation performance of the water evaporation-photocatalytic bifunctional wood-based composite material obtained in step (3), MOCW and M 10 CW, M 20 CW, M 40 CW is placed inside a square plastic insulation board with a 2*2cm through hole in the center, and then placed in a square container filled with water. The wood-based composite material is in direct contact with the water. The square plastic insulation board is 4*4cm in size, the internal dimensions of the square container are 4*4*5cm, and the volume of water in the container is 76mL. (M0CW, M) 10 CW, M 20 CW, M 40The position of CW relative to the insulation board is 1cm above the board and 1cm below the board. The purpose of the insulation board is to prevent the evaporation of water other than the wood-based composite material from causing an excessively high evaporation rate. Simulated sunlight generated by a xenon lamp (AM 1.5G) is used as the light source to shine downwards. A light intensity of sunlight is calibrated using a light power meter. The mass loss of water in the evaporation device over time under sunlight is recorded using an electronic balance. Figure 4 The graph shows the mass change and the corresponding evaporation rate and evaporation efficiency.

[0041] M 20 CW has the highest evaporation rate and evaporation efficiency, specifically because M... 20 The CW evaporator incorporates a carbon nanotube coating that absorbs sunlight and converts it into localized heat at the evaporation interface. This heat causes water to undergo a phase change from liquid water to water vapor. Furthermore, MnO2 particles loaded on the coating cause the heated water to separate into small clusters of water molecules, thereby promoting the release of water vapor.

[0042] To evaluate the photocatalytic performance of the water evaporation-photocatalysis bifunctional wood-based composite material obtained in step (3), methylene blue (MB) was selected as the model pollutant. Before each photocatalytic experiment, MOCW and M 10 CW, M 20 CW, M 40 CW was placed in 30 mL of a 20 mg / mL MB solution and treated in the dark for 30 min to reach adsorption-desorption equilibrium. Then, the material surface was irradiated with simulated sunlight, and the concentration of MB in the solution was measured by UV-Vis absorption spectroscopy every 10 min. The photocatalytic experimental setup was the same as the water evaporation experimental setup described above. Figure 5 The graph shows the catalytic degradation curve and the corresponding degradation efficiency.

[0043] M0CW, M 10 CW, M 20 CW, M 40 The CW evaporator's activity order for MB degradation is M. 40 CW=M 20 CW>M 10 CW>M0CW. When the immersion time in KMnO4 solution increased from 0 to 20 min, the degradation effect on MB increased. However, the degradation effect did not continue to improve with immersion time increasing to 40 min, because the excess catalyst competed with the reactants. The MnO2 loading plays a decisive role in photocatalytic performance.

[0044] Example 2

[0045] A method for preparing a water evaporation-photocatalysis bifunctional wood-based composite material includes the following steps:

[0046] (1) Pretreatment of the wood base: Cut the balsa wood into strips of 2*2cm along the growth direction, then cut the strips into blocks of 2, 3, 4, 6 and 8 cm in length, clean the wood chips off the surface of the blocks with distilled water, and let them dry for later use.

[0047] (2) Impregnate one side of a clean wooden block with carbon nanotube dispersion, perform adsorption treatment, and then air dry;

[0048] (3) The wood blocks treated in step (2) are soaked in a 1M potassium permanganate solution for 20 minutes, and then soaked in a 1M manganese sulfate solution for 5 to 10 minutes. After the reaction, the wood blocks are washed with deionized water and dried to obtain a water evaporation-photocatalysis bifunctional wood-based composite material.

[0049] To evaluate the water evaporation performance of the water-evaporation-photocatalytic bifunctional wood-based composite material obtained in step (3), it was placed in a square plastic heat insulation board with a 2*2cm through hole in the middle, and then placed in a square container filled with water. The wood-based composite material was in direct contact with the water. The square plastic heat insulation board was 4*4cm in size, and the inner dimensions of the square container were 4*4*5cm. The positions of the 2, 3, and 4 cm long wooden blocks relative to the heat insulation board were 1, 2, and 3 cm above the board, and 1 cm below the board, respectively. The positions of the 6 and 8 cm long wooden blocks relative to the heat insulation board were 3 cm above the board, and 3 and 5 cm below the board, respectively. The different heights of the wooden blocks above and below the board were denoted as M. 20 CW, M 20 CW 2-1 M 20 CW 3-1 M 20 CW 3-3 M 20 CW 3-5 The purpose of the heat insulation board is to prevent the evaporation of water other than that from the wood-based composite material from causing an excessively high evaporation rate. Simulated sunlight generated by a xenon lamp (AM 1.5G) is used as the light source to illuminate the water downwards. A light intensity is calibrated using a power meter. The mass loss of water in the evaporation device over time under sunlight is recorded using an electronic balance. Figure 6 This is a graph showing the mass change and the corresponding evaporation rate.

[0050] To evaluate the photocatalytic performance of the water evaporation-photocatalysis bifunctional wood-based composite material obtained in step (3), methylene blue (MB) was selected as the model pollutant. Before each photocatalytic experiment, the wood-based composite material was placed in 30 mL of 20 mg / mL MB solution and treated in the dark for 30 min to reach adsorption-desorption equilibrium. Then, the surface of the material was irradiated with simulated sunlight, and the concentration of MB in the solution was measured by UV-Vis absorption spectroscopy every 10 min. The photocatalytic experimental setup was the same as the water evaporation experimental setup described above. Figure 7 This shows the catalytic degradation curve and the corresponding degradation rate.

[0051] M 20 CW 3-5 Evaporators combine interfacial evaporation with the catalytic degradation of pollutants in bulk water through heat loss management, enabling them to exhibit good photocatalytic behavior and the highest water evaporation rate. Wood-based composite evaporators feature a hydrophilic surface evaporation layer and a porous internal insulation section. The porous structure formed by the accumulation of MnO2 nanoparticles and the cavities in the sidewalls of the wood channels together create a porous structure for water and mass transfer. The mixed photothermal layer of MnO2 and carbon nanotubes converts solar energy into heat for steam generation. The abundant internal pores of the wood-based composite material, filled with air, act as an insulation layer, promoting localized heat utilization and reducing heat loss to the bulk water.

[0052] Example 3

[0053] A method for preparing a water evaporation-photocatalytic bifunctional wood-based composite material and its application in the evaporation and catalytic degradation of tetracycline solution includes the following steps:

[0054] (1) Pretreatment of the wood base: Cut the balsa wood into 2*2cm strips along the growth direction, then cut the strips into 8cm long blocks, clean the wood chips on the surface of the blocks with distilled water, and let them dry for later use.

[0055] (2) Impregnate one side of a clean wooden block with carbon nanotube dispersion, perform adsorption treatment, and then air dry;

[0056] (3) The wood blocks treated in step (2) were soaked in a 1M potassium permanganate solution for 20 minutes, and then soaked in a 1M manganese sulfate solution for 5 to 10 minutes. After the reaction, the wood blocks were washed with deionized water and dried to obtain a water evaporation-photocatalysis bifunctional wood-based composite material.

[0057] (4) The wood-based composite material obtained in step (3) is placed in a square plastic heat insulation plate with a 2*2cm through hole in the middle, and then placed in a square container containing tetracycline solution as a water evaporation-photocatalysis dual-function evaporator. The evaporator is in direct contact with the tetracycline solution, and the concentration of the tetracycline solution is 100mg / mL.-1 The volume was 60 mL. The square plastic heat insulation plate was 4*4 cm in size, and the internal dimensions of the square container were 4*4*5 cm. The evaporator was positioned 3 cm above the heat insulation plate and 5 cm below it. The purpose of the heat insulation plate was to prevent the evaporation rate from being too high due to the evaporation of liquid outside the evaporator. Simulated sunlight generated by a xenon lamp (AM1.5G) was used as the light source to illuminate the liquid downwards. A light intensity was calibrated using a light power meter. The mass loss of the liquid in the evaporation device over time under sunlight irradiation was recorded using an electronic balance. The concentration of tetracycline in the solution before and after evaporation was determined using ultraviolet-visible absorption spectroscopy. Figure 8 M in Example 2 20 CW 3-5 Mass change curves and corresponding degradation efficiencies of tetracycline in water during multiple evaporations.

[0058] The above embodiments illustrate and describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention and are not intended to limit the scope of the invention in any way. Various changes and modifications can be made to the invention without departing from its scope, and all such changes and modifications fall within the scope of the claims.

Claims

1. A method for preparing a water evaporation-photocatalytic bifunctional wood-based composite material, characterized in that, Includes the following steps: (1) Pretreatment of the wood base: Cut the wood into strips along the growth direction, then cut the strips into blocks, clean the surface of the blocks, and let them dry for later use. (2) Impregnate one side of the wood block with carbon nanotube dispersion, perform adsorption treatment, and then air dry; (3) The wood blocks treated in step (2) are soaked in potassium permanganate solution and manganese sulfate solution in turn to grow MnO2 particles on the surface of the material. After the reaction is completed, the wood blocks are washed with water and dried to obtain water evaporation-photocatalysis dual-function wood-based composite material. The carbon nanotube dispersion is a carboxylated carbon nanotube aqueous dispersion with a mass concentration of <1 wt.%; the molar ratio of the potassium permanganate solution to the manganese sulfate solution is 1:1; the adsorption reaction time in the potassium permanganate solution is 20-40 minutes; the reaction time in the manganese sulfate solution is 5-10 minutes; the reaction is a reaction in solution at room temperature; and the drying is natural drying at room temperature to remove moisture.

2. The preparation method according to claim 1, characterized in that, The wood is balsa wood, the wood strip is 2*2cm in size, and the wood strip is cut into blocks with a length of 2-8cm. The adsorption treatment involves immersing the wood blocks in a carbon nanotube dispersion for 30-60s; or immersing the wood blocks in 5mL of carbon nanotube dispersion in a circular container with a bottom diameter of 5cm for 30-60s.

3. The preparation method according to claim 1, characterized in that, The carbon nanotube dispersion is a carboxylated carbon nanotube aqueous dispersion with a mass concentration of 0.15 wt.%.

4. The water evaporation-photocatalytic bifunctional wood-based composite material prepared by the method according to any one of claims 1-3, characterized in that, Using wood as a substrate, MnO2 nanoparticles are uniformly loaded onto the surface of the material.

5. The water evaporation-photocatalysis bifunctional wood-based composite material according to claim 4, characterized in that, The MnO2 particles in the wood-based composite material have a nanoflower structure with a size of 100-200 nm; or, the number of crystals growing in the MnO2 particles in the wood-based composite material is controlled by controlling the reaction time in the potassium permanganate solution, with a reaction time of 20 min.

6. A three-dimensional evaporator based on a water evaporation-photocatalysis bifunctional wood-based composite material, characterized in that, The water evaporation-photocatalysis bifunctional wood-based composite material as described in claim 4 or 5 is placed in a square plastic heat insulation board with a through hole in the middle. The inner size of the through hole is the same as the outer size of the material. The board is then placed in a square container filled with liquid. The wood-based composite material is in direct contact with the liquid. The outer size of the square plastic heat insulation board is the same as the inner size of the square container. The volume of the liquid in the container is equal to the container volume minus the volume of the material in the container. The position of the wood-based composite material relative to the heat insulation board is 1-3 cm above the board and 1-5 cm below the board.

7. The three-dimensional evaporator according to claim 6, characterized in that, The through-hole size of the square plastic heat insulation board is 2*2cm, the outer size of the square plastic heat insulation board is 4*4cm, the inner size of the square container is 4*4*5cm, the liquid volume in the container is 60-76mL, and the liquid is pure water, methylene blue solution or tetracycline solution.

8. The three-dimensional evaporator according to claim 6, characterized in that, The evaporator combines solar interface evaporation technology with advanced oxidation processes by combining catalytic mass transfer pathways with evaporative water transfer pathways. The wood-based composite material is positioned 3cm above the insulation board and 5cm below the board.

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