Method for producing hydrogen by utilizing photocatalysis of waste crab shells and method for producing hydrogen by utilizing photocatalysis of chitin

Abstract

The invention discloses a method for producing hydrogen through photocatalysis by using waste crab shells and a method for producing hydrogen through photocatalysis by using chitin, and belongs to the technical field of hydrogen production through photocatalysis. The method comprises the following steps: (1) carrying out ball milling on crab shell powder or chitin powder to obtain a to-be-leached substance; (2) placing the to-be-leached substance in 10-50 times of water, stirring and leaching, carrying out solid-liquid separation, and collecting filtrate to obtain a depolymerization solution; and (3) adding a TiO2 photocatalyst into the depolymerization solution to obtain a suspension, placing the suspension in a reaction system, carrying out vacuum pumping treatment, and carrying out photocatalysis for 1-6 hours under the irradiation of a xenon lamp or an ultraviolet lamp to obtain a reaction gas. According to the method, waste crab shells or chitin is used as a raw material, a depolymerization solution with high N-acetylglucosamine content is obtained through ball milling treatment, hydrogen is produced through catalysis of a TiO2 photocatalyst, and the method has the advantages of being convenient to operate, environmentally friendly, low in cost and high in hydrogen production efficiency.

Description

TECHNICAL FIELD

[0001] The application relates to a method for producing hydrogen by photocatalysis of waste crab shells and a method for producing hydrogen by photocatalysis of chitin, and belongs to the technical field of photocatalytic hydrogen production. BACKGROUND

[0002] In the seafood processing industry and daily life in coastal areas, a large amount of waste crab shells will be produced. These seemingly useless wastes actually contain valuable resources, the most eye-catching of which is the rich chitin. Scientific tests and analysis show that the content of chitin in waste crab shells is quite high, so that waste crab shells become one of the ideal raw materials for obtaining chitin.

[0003] As a new technology, photocatalytic biomass reforming has unique advantages in relieving environmental pressure and optimizing resource utilization. However, chitin is a high polymer, and the highly organized hydrogen bond network structure inside it leads to its stable chemical properties and extremely low solubility in water. At present, it is difficult to directly apply chitin in waste crab shells to photocatalytic reaction. Therefore, it is urgent to develop an environmentally friendly and efficient method for photocatalytic hydrogen production from waste crab shells or chitin. SUMMARY

[0004] In order to solve the above problems, a method for producing hydrogen by photocatalysis of waste crab shells and a method for producing hydrogen by photocatalysis of chitin are provided. The method uses waste crab shells or chitin as raw material, obtains a depolymerization solution with high N-acetylglucosamine content by processing, and then catalyzes hydrogen production by TiO2 photocatalyst. The method has the advantages of convenient operation, environmental protection, low cost and high hydrogen production efficiency.

[0005] According to one aspect of the application, a method for producing hydrogen by photocatalysis of waste crab shells is provided, comprising the following steps: (1) crushing waste crab shells to obtain crab shell powder, and ball milling the crab shell powder to obtain a leachable substance; (2) placing the leachable substance in 10-50 times water, stirring and leaching, and collecting the filtrate by solid-liquid separation to obtain a depolymerization solution; (3) adding TiO2 photocatalyst to the depolymerization solution to obtain a suspension, the mass / volume ratio of the TiO2 photocatalyst to the depolymerization solution is 0.5-2, and the suspension is placed in a reaction system for vacuum treatment under the irradiation of an ultraviolet lamp or a xenon lamp for 1-6 hours to obtain a reaction gas.

[0006] In the above preparation method, step (1) crushes the crab shells, which lays the foundation for the subsequent ball milling treatment and improves the ball milling effect. The ball milling in step (1) not only refines the crab shell powder, increases its specific surface area, and increases the contact area with water during stirring and leaching, thereby facilitating the dissolution of the effective ingredients; it can also effectively reduce the crystallinity of chitin in the crab shells, destroy its hydrogen bond network structure, and increase the solubility of chitin structural monomer N-acetylglucosamine (NAG) in water, so as to increase the content of N-acetylglucosamine in the depolymerization solution, thereby increasing the yield of formic acid, acetic acid, acetamide and hydrogen.

[0007] The stirring leaching step in step (2) is beneficial to the dissolution of N-acetylglucosamine in the extract and increases the content of N-acetylglucosamine in the depolymerization solution. However, the depolymerization solution also contains metal cations such as magnesium ions and calcium ions, which can inhibit the precipitation of H2.

[0008] Step (3) photocatalyzes the depolymerization solution. Under the above conditions, N-acetylglucosamine in the depolymerization solution can be efficiently catalyzed and converted into hydrogen, and value-added organic substances such as formic acid, acetic acid and acetamide can be produced, thereby improving the utilization rate of raw materials. The H2 precipitation rate in step (3) is as high as 89.7 μmol.g -1 .h -1 , which has extremely high application value.

[0009] Optionally, the stirred leachate of step (2) is passed through a reverse osmosis membrane for solid-liquid separation to intercept the calcium ions and magnesium ions therein, which is beneficial to enhancing the photocatalytic hydrogen evolution performance.

[0010] Optionally, the temperature of the photocatalysis in step (3) is 5-25°C, and the power of the lamp is 100-300 W.

[0011] The temperature of the above-mentioned photocatalysis is room temperature catalysis, which is conducive to H2 precipitation and ensures economic benefits. If the temperature is lower than this range, the H2 precipitation activity will decrease. If the temperature is higher than this range, energy consumption will increase and economic benefits will be reduced. The power of this lamp is conducive to the progress of the catalytic reaction. If the power is lower than this range, the catalytic reaction cannot occur. If the power is higher than this range, the catalyst stability will decrease and energy consumption will increase.

[0012] Optionally, the lamp in step (3) is a xenon lamp, whose illumination range covers the ultraviolet-visible-infrared region, simulating natural sunlight and can effectively excite the TiO2 photocatalyst.

[0013] Optionally, the crab shell powder obtained by crushing in step (1) has a particle size of less than 50 μm.

[0014] The crushed particle size is conducive to the subsequent ball milling. If the particle size is larger than this, the subsequent ball milling uniformity will deteriorate, resulting in a worse stirring and leaching effect in step (2), thereby reducing the overall photocatalytic hydrogen production.

[0015] Optionally, in step (1), the crab shell powder is ball-milled using kaolin and grinding balls, the ball-milling time is 1-12 h, and the ball-milling speed is 120-480 rpm.

[0016] The present application not only uses grinding balls in the ball milling of crab shell powder, but also adds kaolin for ball milling, which can improve the fluidity and dispersibility of the material, reduce the agglomeration and agglomeration phenomena during the ball milling process, thereby improving the ball milling efficiency and shortening the ball milling time.

[0017] Specifically, the ball milling time can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h and any time therebetween, preferably 12h; the ball milling speed can be 120 rpm, 240 rpm, 360 rpm, 480 rpm and any time therebetween, preferably 480 rpm.

[0018] Optionally, the weight ratio of kaolin to crab shell powder is (1-10):1, and the particle size of kaolin is 2-5 μm.

[0019] The weight of kaolin in the above ball milling is greater than the weight of crab shell powder because kaolin can improve the fluidity and dispersibility of the material. Under the above weight ratio, the agglomeration and aggregation during the ball milling process can be reduced, thereby improving the ball milling efficiency and shortening the ball milling time. The particle size of kaolin can reduce the particle size and further reduce the crystallinity. Specifically, the weight ratio of kaolin to crab shell powder can be 10:1, 5:1, 2:1, 1:1 and any ratio therebetween, preferably 2:1.

[0020] Optionally, the grinding balls include large-diameter grinding balls and small-diameter grinding balls, the particle size of the large-diameter grinding balls is 10-20 mm, and the particle size of the small-diameter grinding balls is 3-10 mm.

[0021] The grinding balls used in the ball mill of this application are divided into two diameters. This setting can crush large balls and refine small balls, which can synergistically improve the ball milling efficiency.

[0022] Optionally, the quantity ratio of the large-diameter grinding balls to the small-diameter grinding balls is 1:(1-10), and the mass ratio of the crab shell powder to the grinding balls is 1:(100-300).

[0023] The above-mentioned large-diameter grinding balls and small-diameter grinding balls can significantly shorten the ball milling time, improve the ball milling efficiency, and ensure uniform particle size distribution after ball milling.

[0024] Specifically, the ratio of the large-diameter grinding balls to the small-diameter grinding balls can be 1:1, 1:2, 1:5, 1:10, or any ratio therebetween, preferably 1:5.

[0025] Optionally, the material of the grinding balls is selected from at least one of Al2O3, ZrO2, and ZrSiO4.

[0026] Optionally, the stirring leaching in step (2) is carried out at a rotation speed of 500-900 rpm, a temperature of 15-25° C., and a time of 0.3-2 h.

[0027] The above-mentioned setting of step (2) can increase the content of N-acetylglucosamine in the depolymerization solution, and at the same time can pass through the reverse osmosis membrane to intercept the calcium ions and magnesium ions therein, which is beneficial to enhance the photocatalytic hydrogen evolution performance.

[0028] Optionally, the content of N-acetylglucosamine in the depolymerization solution in step (2) is 1.5-6.8 g / L.

[0029] Optionally, the TiO2 photocatalyst is TiO2-001.

[0030] The catalyst refers to TiO2 with a {001} crystal face, which has excellent hydroxyl radical (•OH) generation ability. The H2 evolution rate of the catalyst in hydrogen production using the above method is as high as 89.7 μmol.g -1 .h -1 , 58.9 times and 6.3 times that of TiO2-101 and TiO2-100, respectively. The highly exposed {001} facets facilitate the separation of photogenerated carriers, enhance the adsorption and activation of H2O, and accelerate the generation of •OH, thus demonstrating excellent photoreforming performance and further improving hydrogen production efficiency.

[0031] According to another aspect of the present application, a method for producing hydrogen by photocatalysis using chitosan is provided, characterized in that it comprises the following steps: (1) Ball milling chitosan to obtain the extract; (2) placing the object to be leached in 10-50 times the volume of water, stirring to leach, performing solid-liquid separation, and collecting the filtrate to obtain a depolymerization solution; (3) Adding a TiO2 photocatalyst to the depolymerization solution to obtain a suspension, wherein the mass volume ratio of the TiO2 photocatalyst to the depolymerization solution is 0.5-2, expressed in mg / mL. The suspension is placed in a reaction system and vacuumed, and photocatalyzed under irradiation with a xenon lamp or an ultraviolet lamp for 1-6 hours to obtain a reaction gas.

[0032] The ball milling of step (1) in the above preparation method can effectively reduce the crystallinity of chitin, destroy the hydrogen bond network structure, increase the solubility of chitin structural monomer N-acetylglucosamine in water, thereby increasing the content of N-acetylglucosamine in the depolymerization solution, and further increasing the yield of formic acid, acetic acid, acetamide and hydrogen.

[0033] The stirring leaching step of step (2) is beneficial to the dissolution of N-acetylglucosamine in the leaching object, and increases the content of N-acetylglucosamine in the depolymerization solution.

[0034] Step (3) is a photocatalysis of the depolymerization solution, which can efficiently catalyze the conversion of N-acetylglucosamine in the depolymerization solution into hydrogen under the above conditions, and produce value-added organic matters such as formic acid, acetic acid and acetamide, thereby increasing the utilization rate of raw materials. The hydrogen release rate of step (3) is as high as 262.8 μmol.g -1 .h -1 , which has extremely high application value.

[0035] Optionally, the stirring leaching solution of step (2) is subjected to solid-liquid separation by a reverse osmosis membrane to retain calcium ions and magnesium ions therein, which is beneficial to enhancing the photocatalytic hydrogen evolution performance.

[0036] Optionally, the temperature of the photocatalysis of step (3) is 5-25℃, and the power of the lamp is 100-300W.

[0037] The temperature of the above photocatalysis is normal temperature catalysis, which is beneficial to the hydrogen evolution and ensures economic benefits. If the temperature is lower than the range, the hydrogen evolution activity is reduced. If the temperature is higher than the range, the energy consumption is increased, and the economic benefits are reduced. The power of the lamp is beneficial to the catalytic reaction. If the power is lower than the range, the catalytic reaction cannot occur. If the power is higher than the range, the stability of the catalyst is reduced.

[0038] Optionally, the lamp of step (3) is a xenon lamp, which has a light range covering ultraviolet-visible-infrared region, simulates natural sunlight, and can effectively excite the TiO2 photocatalyst.

[0039] Optionally, kaolin and grinding balls are used for ball milling of the chitin powder in step (1), the ball milling time is 1-12h, and the ball milling rotation speed is 120-480 rpm.

[0040] In the present application, not only grinding balls but also kaolin is added for ball milling of the chitin powder, which can improve the flowability and dispersibility of the material, reduce the caking and agglomeration phenomenon in the ball milling process, thereby improving the ball milling efficiency and shortening the ball milling time.

[0041] Specifically, the ball milling time can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h and any time therebetween, preferably 12h; the ball milling speed can be 120 rpm, 240 rpm, 360 rpm, 480 rpm and any time therebetween, preferably 480 rpm.

[0042] Optionally, the weight ratio of kaolin to chitin powder is (1-10):1, and the particle size of kaolin is 2-5 μm.

[0043] The weight of kaolin in the above ball milling is greater than the weight of chitosan powder because kaolin can improve the fluidity and dispersibility of the material. Under the above weight ratio, the agglomeration and aggregation during the ball milling process can be reduced, thereby improving the ball milling efficiency and shortening the ball milling time. The particle size of kaolin can be reduced, further reducing the crystallinity.

[0044] Specifically, the weight ratio of ridge clay to chitosan powder can be 10:1, 5:1, 2:1, 1:1, or any ratio therebetween, preferably 2:1.

[0045] Optionally, the grinding balls include large-diameter grinding balls and small-diameter grinding balls, the particle size of the large-diameter grinding balls is 10-20 mm, and the particle size of the small-diameter grinding balls is 3-10 mm.

[0046] The grinding balls used in the ball mill of this application are divided into two diameters. This setting can synergistically improve the ball milling efficiency by crushing large balls and refining small balls.

[0047] Optionally, the ratio of the large-diameter grinding balls to the small-diameter grinding balls is 1:(1-10).

[0048] The above-mentioned large-diameter grinding balls and small-diameter grinding balls can significantly shorten the ball milling time, improve the ball milling efficiency, and ensure uniform particle size distribution after ball milling.

[0049] Specifically, the ratio of the large-diameter grinding balls to the small-diameter grinding balls can be 1:1, 1:2, 1:5, 1:10, or any ratio therebetween, preferably 1:5.

[0050] Optionally, the material of the grinding balls is selected from at least one of Al2O3, ZrO2, and ZrSiO4.

[0051] Optionally, the stirring leaching in step (2) is performed at a rotation speed of 500-900 rpm, a temperature of 15-25° C., and a time of 0.3-2 h.

[0052] Optionally, the content of N-acetylglucosamine in the depolymerization solution in step (2) is 3.2-18.9 g / L.

[0053] Optionally, the TiO2 photocatalyst is TiO2-001.

[0054] The catalyst refers to TiO2 with a {001} crystal face, which has excellent hydroxyl radical (•OH) generation ability. The H2 evolution rate of the catalyst in hydrogen production using the above method is as high as 262.8 μmol.g -1 .h -1 , which are 67.4 times and 5.7 times those of TiO2-101 and TiO2-100, respectively. The highly exposed {001} facets facilitate the separation of photogenerated carriers, enhance the adsorption and activation of H2O, and accelerate the generation of •OH, thus exhibiting excellent photoreforming performance and further improving hydrogen production efficiency.

[0055] The beneficial effects of this application include but are not limited to: 1. According to the method for photocatalytic hydrogen production from discarded crab shells disclosed herein, discarded crab shells are processed to obtain a depolymerization solution. This depolymerization solution is then catalyzed using a TiO2 photocatalyst to convert N-acetylglucosamine, a chitin structural monomer, in the depolymerization solution into formic acid, acetic acid, acetamide, and hydrogen (H2). This provides an innovative solution for biomass resource utilization and green hydrogen energy development.

[0056] 2. According to the method of photocatalytic hydrogen production from discarded crab shells of this application, the discarded crab shells can be reused to not only produce hydrogen but also obtain usable chemicals, thereby promoting the recycling and sustainable development of waste resources.

[0057] 3. According to the methods for photocatalytic hydrogen production using discarded crab shells and chitin, ball milling of crab shell powder or chitin can effectively reduce the crystallinity of chitin, disrupt its hydrogen bond network structure, and increase the solubility of N-acetylglucosamine, a chitin structural monomer, in water, thereby increasing the content of N-acetylglucosamine in the depolymerization solution and thereby improving the yield of the photocatalytic product.

[0058] 4. The method for photocatalytic hydrogen production using discarded crab shells and the method for photocatalytic hydrogen production using chitin according to this application have the advantages of convenient operation, environmental protection, low cost, efficient hydrogen production, and high raw material utilization. They have great guiding significance in practical applications and have great commercial value.

[0059] 5. This application and the method for photocatalytic hydrogen production using chitosan can catalyze the depolymerization solution of chitosan with a TiO2 photocatalyst to obtain hydrogen, broadening the application prospects of chitosan. At the same time, additional chemicals such as formic acid, acetic acid and acetamide are obtained, providing an innovative solution for the resource utilization of chitosan and the development of green hydrogen energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 This is a color comparison chart of the depolymerization solution obtained by different ball milling times of chitosan involved in Example 1 of the present application.

[0061] Figure 2 This is a comparison chart of the hydrogen production activity of the depolymerized solutions obtained with different ball milling times of chitin involved in Example 1 of the present application.

[0062] Figure 3 This is a comparison chart of the hydrogen production activity of the depolymerization solution of TiO2 photocatalysts with different crystal planes involved in Example 2 of the present application.

[0063] Figure 4 This is the ESR graph of •OH of TiO2 photocatalysts with different crystal planes involved in Example 2 of the present application.

[0064] Figure 5 This is a comparison chart of the appearance and hydrogen production activity of the water and discarded crab shell depolymerization solution involved in Example 3 of the present application.

[0065] Figure 6 Examples 3 and 4 of the present application relate to a preparation flow chart for photocatalytic hydrogen production using discarded crab shells. DETAILED DESCRIPTION

[0066] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0067] Unless otherwise specified, the raw materials in the examples and comparative examples of the present application were purchased through commercial channels.

[0068] Unless otherwise specified, the methods used in the examples and comparative examples of the present application are conventional methods in the prior art.

[0069] Example 1 This embodiment relates to a method for producing hydrogen using chitosan photocatalysis, comprising the following steps: (1) 2.0 g of chitosan powder and 4.0 g of kaolin with a particle size of 2 μm were mixed evenly and placed in a 50 mL corundum ball mill. Subsequently, 4 Al2O3 grinding balls with a diameter of 15 mm and 20 Al2O3 grinding balls with a diameter of 10 mm were added to the corundum ball mill. The resulting mixture was placed in a ball mill at a ball mill speed of 480 rpm and ball milled for a certain period of time to obtain the extract. (2) Place the extract in 50 times the volume of water, stir and leach at a speed of 600 rpm and a temperature of 25°C for 1 h, and collect the filtrate for solid-liquid separation to obtain a depolymerization solution; (3) 50 mg of TiO2-001 photocatalyst was added to 100 mL of the depolymerization solution to obtain a suspension. The suspension was then transferred to a test system equipped with a closed gas cycle. The reaction system was evacuated before testing to completely remove dissolved air. A 300 W xenon lamp was then used as the test light source, and the reaction temperature was controlled at 15 °C by cooling the circulating water. After 4 h of photocatalytic reaction, the reaction gas was obtained.

[0070] The ball milling times set in this example are 0 h (no ball milling), 1 h, 3 h, 6 h, and 12 h, respectively named 1-0#, 1-1#, 1-3#, 1-6#, and 1-12#. The colors of the depolymerization solutions obtained at different ball milling times are compared. The test results are shown in Table 1. Figure 1 At the same time, the hydrogen production activity was compared according to step (3), and the test results are shown in Figure 2 .

[0071] like Figure 1 As shown in the figure, the color of the depolymerization solution gradually changes from colorless to dark yellow with the continuous extension of ball milling time. This indicates that mechanical ball milling can reduce the crystallinity of chitin and increase its depolymerization degree and solubility in water, and this process is enhanced with the extension of ball milling time.

[0072] Figure 2 As shown in Figure 2, the H2 generation rate of TiO2-001 photocatalyst in the unmilled depolymerization solution was only 74.4 μmol.g -1 .h -1 This is due to the highly organized structure of chitin and its low solubility in water. Therefore, chitin that has not been ball-milled is difficult to be used for photocatalytic hydrogen production. As the ball-milling time increases, the H2 generation rate gradually increases. The H2 generation rate of TiO2-001 photocatalyst in the solution after ball-milling for 1 h, 3 h, and 6 h is 102.2 μmol.g -1 .h -1 , 145.7μmol.g -1 .h -1 and 255.7 μmol.g -1 .h -1 When the ball milling time was extended to 12 h, the H2 generation rate tended to be balanced and reached 262.8 μmol.g -1 .h -1 The results showed that ball milling of chitin can effectively depolymerize chitin and increase the concentration of monomer N-acetylglucosamine in water, thereby obtaining a higher photocatalytic hydrogen production rate and improving the utilization of raw materials.

[0073] Example 2 Compared with the example of Example 1 in which the ball milling time was 12 h, this example uses TiO2-101, TiO2-100 and TiO2-001 photocatalysts with different crystal faces to catalyze hydrogen production. The hydrogen production activity comparison diagram is shown in FIG. Figure 3 ,according to Figure 3 It can be seen that the H2 evolution rate shows obvious crystal surface-dependent activity. When TiO2-101 is used as the photocatalyst, the hydrogen generation rate is only 3.9 μmol.g -1 .h -1 The hydrogen generation rate of TiO2-100 is higher than that of TiO2-101, reaching 46.3μmol.g -1 .h -1 When TiO2-001 is used as the photocatalyst, the hydrogen generation rate is as high as 262.8μmol.g -1 .h -1 , which are 67.4 times and 5.7 times that of TiO2-101 and TiO2-100 respectively.

[0074] •OH ESR measurements were performed on TiO2 with different facet-dominant structures. The test method was to uniformly disperse 5 mg of the photocatalytic material in 1 mL of water containing 10 mM 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a hydroxyl radical scavenger. Using a 300 W xenon lamp as the test light source, after 10 minutes of full illumination, the intensity of the DMPO-•OH adduct was measured using an electron spin resonance spectrometer.

[0075] The ESR graphs of •OH in TiO2 dominated by different crystal planes are shown in the figure below. Figure 4 The ESR test was used to compare the •OH generation capabilities of TiO2-101, TiO2-100, and TiO2-001. Figure 4 In the photocatalytic reaction, •OH can bind to the spin-trapping agent DMPO to produce a characteristic signal peak. Under the same test conditions, the characteristic signal peak intensity of TiO2-001 was higher, indicating that TiO2-001 has a stronger •OH generation ability than TiO2-101 and TiO2-100. Therefore, TiO2-001 exhibits superior catalytic performance in the photocatalytic reforming of chitin.

[0076] Example 3 This embodiment relates to a method for photocatalytic hydrogen production using discarded crab shells. The preparation flow chart is shown in FIG. Figure 6 , comprising the following steps: (1) The discarded crab shells were crushed to obtain crab shell powder with a particle size of less than 50 μm. 2.0 g of crab shell powder was evenly mixed with 2.0 g of kaolin with a particle size of 5 μm, and placed in a 50 mL corundum ball mill. Subsequently, two Al2O3 grinding balls with a diameter of 20 mm and 20 Al2O3 grinding balls with a diameter of 10 mm were added to the corundum ball mill. The obtained mixture was placed in a ball mill and ball milled for 12 h to obtain the extract. (2) Place the material to be leached in 50 times the volume of water, stir and leach at a speed of 900 rpm and a temperature of 25 °C for 2 h, collect the filtrate for solid-liquid separation, and obtain a depolymerization solution; (3) 50 mg of TiO2-001 photocatalyst was added to 100 mL of the depolymerization solution to obtain a suspension. The suspension was then transferred to a test system equipped with a closed gas cycle. The reaction system was evacuated before testing to completely remove dissolved air. A 300 W xenon lamp was then used as the test light source, and the reaction temperature was controlled at 15 °C by cooling the circulating water. After 4 h of photocatalytic reaction, the reaction gas was obtained.

[0077] The ball mill speeds set in this embodiment are 120 rpm, 240 rpm, 360 rpm, and 480 rpm, respectively, and are named 3-1#, 3-2#, 3-3#, and 3-4#, respectively.

[0078] The hydrogen production performance was compared using water and Example 1 with a ball milling time of 12 h and a rotation speed of 480 rpm. The test results are shown in Figure 5 , Figure 5 a in the figure is a comparison of appearances, and it can be seen that the color of the depolymerization solution in this embodiment is light yellow. Figure 5 Figure b is a comparison of hydrogen production activity. It can be seen that the hydrogen evolution rate of TiO2-001 photocatalyst in pure water is only 9.6 μmol.g -1 .h -1 , and the hydrogen evolution rate in the depolymerization solution was as high as 89.7 μmol.g -1 .h -1 , which is 9.3 times the activity of pure water. This proves that the depolymerization solution obtained by the present invention has excellent hydrogen production effect and is worthy of industrial promotion and use.

[0079] Example 4 This embodiment relates to a method for photocatalytic hydrogen production using discarded crab shells. The preparation flow chart is shown in FIG. Figure 6 , comprising the following steps: (1) The discarded crab shells were crushed to obtain crab shell powder with a particle size of less than 50 μm. 2.0 g of crab shell powder was evenly mixed with 20.0 g of kaolin with a particle size of 2 μm, and placed in a 50 mL corundum ball mill. Subsequently, 20 Al2O3 grinding balls with a diameter of 10 mm and 20 Al2O3 grinding balls with a diameter of 3 mm were added to the corundum ball mill. The obtained mixture was placed in a ball mill at a ball mill speed of 480 rpm for 12 h to obtain the extract. (2) The extract was placed in 50 times the volume of water, stirred and leached at a speed of 500 rpm and a temperature of 15°C, and the filtrate was collected for solid-liquid separation to obtain a depolymerization solution; (3) 50 mg of TiO2-001 photocatalyst was added to 100 mL of the depolymerization solution to obtain a suspension. The suspension was then transferred to a test system equipped with a closed gas cycle. The reaction system was evacuated before testing to completely remove dissolved air. A 300 W xenon lamp was then used as the test light source, and the reaction temperature was controlled at 15°C by cooling the circulating water. After 4 h of photocatalytic reaction, the reaction gas was obtained.

[0080] The leaching times of step (2) set in this embodiment are 0.3, 0.6, and 1.0 h, respectively, and are named 4-1#, 4-2#, and 4-3#, respectively.

[0081] Example 5 Compared with the example 3-4# in Example 3, the photocatalytic temperatures of this example are 5 and 25°C, respectively, and they are named 5-1# and 5-2#, respectively.

[0082] Example 6 Compared with the examples 3-4# in Example 3, the power of the photocatalytic lamp in this embodiment is 100W, and it is named 6#.

[0083] Example 7 Compared with Example 3 in which the ball milling time was 12 h, this example was named 7#, in which no kaolin was added during the ball milling.

[0084] Example 8 Compared with the example of Example 3 in which the ball milling time was 12 h, this example only used Al2O3 grinding balls with a diameter of 10 mm for ball milling, and was named 8#.

[0085] Comparative Example 1 Compared with the example of Example 3 in which the ball milling time was 12 h, this example did not perform the ball milling step (1), and only performed the step (2) on the crab shell powder of step (1), which was named D1#.

[0086] Test Case The reaction gases prepared in the above examples and comparative examples were tested to obtain the total amount of hydrogen generated, and the formic acid, acetic acid, and acetamide contents in the depolymerization solution were tested to obtain the total amount of formic acid generated, the total amount of acetic acid generated, and the total amount of acetamide generated. The test results are shown in the table below.

[0087] Table 1

[0088] According to the above test results, the yields of hydrogen, formic acid, acetic acid and acetamide were the highest when the ball milling time was 12 h, the ball milling speed was 480 rpm, the depolymerization stirring time was 1 h, the photocatalytic test temperature was 15 ℃, the xenon lamp power was 300 W, and kaolin and grinding balls of different sizes were added during the ball milling process.

[0089] Based on the comparison of the above-mentioned Example 3 and Examples 4-8, it can be seen that when adjusting the photocatalytic temperature, the power of the photocatalytic lamp, whether kaolin is added in the ball milling, and the diameter of the corundum ball, different hydrogen production effects will be exhibited. This change is consistent regardless of whether it is for the crab shell photocatalytic hydrogen production method or the chitin hydrogen production method, so this application does not set a single comparison example for chitin.

[0090] The foregoing is merely an embodiment of the present application, and the scope of protection of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the technical ideas and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for photocatalytic hydrogen production using discarded crab shells, characterized in that: The steps include: (1) crushing discarded crab shells to obtain crab shell powder, and ball-milling the crab shell powder to obtain an extract; (2) placing the material to be leached in 10-50 times the volume of water, stirring for leaching, performing solid-liquid separation, and collecting the filtrate to obtain a depolymerization solution with a high N-acetylglucosamine content; (3) Adding a TiO2 photocatalyst to the depolymerization solution to obtain a suspension, wherein the mass volume ratio of the TiO2 photocatalyst to the depolymerization solution is 0.5-2, expressed in mg / mL. The suspension is placed in a reaction system, evacuated, and photocatalyzed under ultraviolet light or xenon lamp for 1-6 hours to obtain a reaction gas.

2. The method for photocatalytic hydrogen production using discarded crab shells according to claim 1, characterized in that: The temperature of the photocatalytic step (3) is 5-25°C and the power of the lamp is 100-300 W; and / or The TiO2 photocatalyst is a TiO2 nanosheet with mainly exposed {001} crystal planes, namely TiO2-001.

3. The method for photocatalytic hydrogen production using discarded crab shells according to claim 1, characterized in that: The crab shell powder obtained by crushing in step (1) has a particle size of less than 50 μm; In step (1), the crab shell powder is ball-milled using kaolin and grinding balls, the ball-milling time is 1-12 h, the ball-milling speed is 120-480 rpm, the weight ratio of kaolin to crab shell powder is (1-10):1, and the particle size of kaolin is 2-5 μm.

4. The method for photocatalytic hydrogen production using discarded crab shells according to claim 3, characterized in that: The grinding balls include large-diameter grinding balls and small-diameter grinding balls. The particle size of the large-diameter grinding balls is 10-20 mm, and the particle size of the small-diameter grinding balls is 3-10 mm.

5. The method for photocatalytic hydrogen production using discarded crab shells according to claim 4, characterized in that: The ratio of the large-diameter grinding balls to the small-diameter grinding balls is 1:(1-10).

6. The method for photocatalytic hydrogen production using discarded crab shells according to claim 1, characterized in that: Step (2) stirring and leaching at a speed of 500-900 rpm, a temperature of 15-25°C, and a time of 0.3-2 h; The content of N-acetylglucosamine in the depolymerization solution in step (2) is 1.5-6.8 g / L.

7. A method for producing hydrogen by photocatalysis using chitin, characterized in that: The steps include: (1) Ball milling chitosan to obtain the extract; (2) placing the object to be leached in 10-50 times the volume of water, stirring to leach, separating the solid and liquid, and collecting the filtrate to obtain a depolymerization solution; (3) Adding TiO2 photocatalyst to the depolymerization solution to obtain a suspension, wherein the mass volume ratio of the TiO2 photocatalyst to the depolymerization solution is 0.5-2, expressed in mg / mL. The suspension is placed in a reaction system, evacuated, and photocatalyzed under a xenon lamp or ultraviolet lamp for 1-6 hours to obtain a reaction gas.

8. The method for producing hydrogen using chitosan photocatalysis according to claim 7, characterized in that: The temperature of the photocatalytic step (3) is 5-25°C and the power of the lamp is 100-300W; and / or The TiO2 photocatalyst is TiO2-001.

9. The method for producing hydrogen using chitosan photocatalysis according to claim 7, characterized in that: In step (1), the chitosan is ball-milled using kaolin and grinding balls, the ball-milling time is 1-12 h, the ball-milling speed is 120-480 rpm, the weight ratio of kaolin to chitosan is (1-10):1, and the particle size of the kaolin is 2-5 μm.

10. The method for producing hydrogen using chitosan photocatalysis according to claim 7, characterized in that: Step (2) stirring and leaching at a speed of 500-900 rpm, a temperature of 15-25°C, and a time of 0.3-2 h; The content of N-acetylglucosamine in the depolymerization solution of step (2) is 3.2-18.9 g / L.

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