Method for continuous hydrogen production by photosynthesis of organic / inorganic material hybrid green algae

Abstract

The application discloses a method for continuously photosynthetic hydrogen production of organic / inorganic material hybrid green algae, and the method can maintain the survival rate and growth rate of microalgae under high light intensity and the chlorophyll content by constructing a sunlight-driven hybrid microalgae light reaction system based on a photothermal material MXene and a heat-sensitive material PNIPAM, and can enable the microalgae to stably and rapidly photosynthetic hydrogen production under high light intensity of 1000 µmol photons ·m ‑2 ·s ‑1 The Chlorella vulgaris can continuously produce hydrogen for 1.47×10 5 ppm within 17 days. Mg(OH)2 is added to the ordinary culture medium containing glucose, and magnesium ions serve as the core component of chlorophyll molecules and play a key role in photosynthesis and life maintenance of the microalgae, and the hydroxyl ions can adjust the pH of the culture medium, so that the acid-alkali environment of the culture medium is suitable for the growth of the microalgae.

Description

Technical Field

[0001] This invention belongs to the field of bioenergy technology and relates to a hydrogen production method, specifically a method for continuous photosynthetic hydrogen production by organic / inorganic hybrid green algae. Background Technology

[0002] Hydrogen energy, as a clean energy source with zero carbon emissions, has great potential. However, its large-scale application is limited by the dependence on fossil fuels and high costs of traditional hydrogen production technologies. Traditional hydrogen production technologies mainly produce hydrogen through methods such as steam reforming of hydrocarbons, coal gasification, water electrolysis, and refining of chemical by-products, which are characterized by high energy consumption and high costs.

[0003] Research has found that some algae can directly generate hydrogen gas through solar energy decomposition of water using internal hydrogenases under anaerobic conditions, completing the photosynthetic hydrogen production process. The entire process requires no organic matter as a substrate or energy source, making it a truly clean and renewable energy production method with environmental friendliness and sustainable development potential. Currently, microalgae cannot continuously produce hydrogen under high light intensity conditions mainly due to two factors: 1. The oxygen production rate of microalgae increases with light intensity, but hydrogenases are extremely sensitive to oxygen and can only maintain photosynthetic hydrogen production activity under strictly anaerobic conditions. High light intensity will cause hydrogenase inactivation, stopping the hydrogen production process; 2. Excessive light will damage the photoreaction centers of microalgae, causing photoinhibition, further affecting hydrogenase activity, ultimately leading to hydrogenase inactivation and even algal cell apoptosis. Solving these two problems will enable key technological breakthroughs in the large-scale outdoor photosynthetic hydrogen production application of microalgae. Summary of the Invention

[0004] To address the problem in existing technologies where microalgae cannot sustain hydrogen production under high light intensity conditions, this invention provides a method for the continuous photosynthetic hydrogen production of organic / inorganic hybrid green algae. This method can maintain microalgae under high light intensity conditions (1000 µmol photons·m⁻¹). -2 · s -1 Chlorella continuously produces hydrogen through photosynthesis, with Chlorella being able to continuously produce up to 1.47 × 10⁻⁶ hydrogen over 17 days. 5 ppm.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for continuous photosynthetic hydrogen production by organic / inorganic hybrid green algae includes the following steps:

[0007] Step 1: Microalgae Cultivation: Transfer 100 mL of microalgae culture to 1.5 L of TAP medium and incubate under light at 20–30 °C. Harvest the microalgae when the cell number reaches the logarithmic growth phase. The microalgae is *Chlorella vulgaris*; the light source is continuous illumination at an intensity of 50–150 µmol photons·m⁻¹. -2 ·s -1 ;

[0008] Step 2: Synthesis of poly(N-isopropylacrylamide) copolymer: Dissolve 3-5 g of N-isopropylacrylamide (NIPAM) monomer and 20-40 mg of azobisisobutyronitrile solution in 30-50 mL of anhydrous acetonitrile. Under magnetic stirring, purge the solution with an inert gas for 20-60 min to remove oxygen. After deoxygenation, react the solution in an oil bath at 60-80 °C for 6-10 h, and then cool. Add the solution dropwise to a mixed solution of diethyl ether and petroleum ether to obtain PNIPAM precipitate. Filter the precipitate and freeze-dry it under vacuum for 10-15 h to obtain the dried PNIPAM product.

[0009] Step 3: Hydrogen production by microalgae under high light intensity: Take 50 mL of the microalgae solution obtained in Step 1, centrifuge for 5-10 minutes (3000-5000 rpm) to collect the microalgae, disperse the collected microalgae in 50 mL of glucose medium, and transfer it to 50 mL of the photoreaction system; then add 1-3 g of PNIPAM2 and 20-30 mg of MXene to the photoreaction system, shake well to obtain a hybrid photoreaction system; transfer the hybrid photoreaction system containing microalgae to a light intensity of 500-1500 µmol photons·m -2 ·s -1 The medium is continuously illuminated in a light incubator at a temperature of 20~30℃. Each liter of glucose medium contains the following components: 10g glucose, 100mL BG-11 medium, 1.17g Mg(OH)2, 2g PNIPAM, 25mg MXene, and finally deionized water is added to prepare a mixed medium.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] 1. This invention constructs a sunlight-driven hybrid microalgal photoreaction system based on the photothermal material MXene and the thermosensitive material PNIPAM. This system can maintain the survival rate, growth rate, and chlorophyll content of microalgae under high light intensity, endowing microalgae with the ability to grow at 1000 µmol photons·m -2 ·s -1 Under high light intensity, it can stably and rapidly produce hydrogen through photosynthesis.

[0012] 2. This invention is a multifunctional biohybrid system composed of Chlorella, thermosensitive polymers and photothermal materials, which has environmental adaptability and provides the possibility for large-scale outdoor application of green algae photosynthetic hydrogen production.

[0013] 3. In this invention, Mg(OH)2 is added to the ordinary culture medium containing glucose. Magnesium ions, as the core component of chlorophyll molecules, play a key role in the photosynthesis of microalgae and the maintenance of microalgae life, while hydroxide ions can regulate the pH of the culture medium, making the acid-base environment of the culture medium suitable for microalgae growth. Attached Figure Description

[0014] Figure 1 The graph shows the hydrogen production of Chlorella in a hybrid photoreaction system (blue curve) and Chlorella alone (orange curve) under strong light.

[0015] Figures 2-4 The image shows the microstructure of a hybrid photoreaction system containing 20 mg PNIPAM after 17 days of culture.

[0016] Figure 5 The OD values ​​of Chlorella before and after culturing are shown in the hybrid photoreaction system containing 20 mg PNIPAM and the photoreaction system without PNIPAM and MXene. Detailed Implementation

[0017] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0018] PNIPAM, as a thermosensitive material, exhibits a state change characteristic with temperature. Below the lower critical phase transition temperature (LCT), intermolecular hydrogen bonds exist between the polymer chains and surrounding water molecules, resulting in a transparent state. Above the LCT, these intermolecular hydrogen bonds break, and intramolecular hydrogen bonds form between the carbonyl and amide groups within the polymer chains, leading to phase separation, scattering incident light, and an opaque state. The entire phase transition process is completely reversible, meaning that the light intensity received by Chlorella can be controlled by changing the temperature. MXene is a photothermal conversion material capable of efficiently converting light energy into heat energy. The hybrid photoreaction system composed of the thermosensitive polymer PNIPAM and the photothermal material MXene possesses a dual hybrid response mechanism based on temperature and light intensity. When the light intensity is relatively strong (1000 µmol photons·m⁻¹), the system exhibits a transparent state. -2 ·s -1When MXene absorbs light energy and converts it into heat energy, the heat energy drives the thermosensitive material PNIPAM to undergo a phase transition, making the hybrid system opaque, thereby scattering some of the light, reducing the oxygen production rate, effectively maintaining the activity of hydrogenase, and thus ensuring a stable and high hydrogen production rate.

[0019] Example 1

[0020] Step 1: Chlorella Cultivation: Transfer 100 mL of Chlorella inoculum to 1.5 L of TAP medium and incubate under light at 25 ℃ with a light intensity of 100 µmol photons·m⁻¹. -2 ·s -1 It should be taken when the number of Chlorella cells reaches the logarithmic growth phase;

[0021] Step 2: Synthesis of poly(N-isopropylacrylamide) copolymer: 4g of N-isopropylacrylamide (NIPAM) monomer and 30mg of azobisisobutyronitrile solution were dissolved in 40mL of anhydrous acetonitrile. Under magnetic stirring, an inert gas was introduced into the solution to remove oxygen for 30min. After deoxygenation, the mixture was reacted in an oil bath at 70℃ for 8h and then cooled. The solution was added dropwise to a mixed solution of diethyl ether and petroleum ether to obtain PNIPAM precipitate. The precipitate was filtered and freeze-dried under vacuum for 12h to obtain the dried PNIPAM product.

[0022] Step 3: Hydrogen production by Chlorella under high light intensity: Take 50 mL of the Chlorella solution obtained in Step 1, centrifuge for 5 minutes (4000 rpm) to collect the Chlorella, disperse the collected Chlorella in 50 mL of glucose medium, and transfer it to 50 mL of the photoreaction system; then add 2 g of PNIPAM and 25 mg of MXene to the photoreaction system, shake well to obtain a hybrid photoreaction system; transfer the hybrid photoreaction system containing Chlorella to a light intensity of 1000 µmol photons·m -2 ·s -1 It is continuously illuminated in a light incubator with a temperature of 25℃.

[0023] Step 4: Use a portable hydrogen detector to measure the amount of hydrogen produced in the photoreaction system at different times. The results are as follows: Figure 1 As shown in the blue curve, Chlorella continuously produced 1.47 × 10⁻⁶ hydrogen over 17 days. 5 ppm.

[0024] Comparative Example 1

[0025] Step 1: Chlorella Cultivation: Transfer 100 mL of Chlorella inoculum to 1.5 L of TAP medium and incubate under light at 25 ℃ with a light intensity of 100 µmol photons·m⁻¹. -2 ·s -1 It should be taken when the number of Chlorella cells reaches the logarithmic growth phase;

[0026] Step 2: Hydrogen production by Chlorella under high light intensity: Take 50 mL of the Chlorella solution obtained in Step 1, centrifuge for 5 minutes (4000 rpm) to collect the Chlorella, disperse the collected microalgae in 50 mL of glucose medium, and transfer it to 50 mL of the reaction system, mixing thoroughly; transfer the reaction system containing Chlorella (without PNIPAM and MXene) to a light intensity of 1000 µmol photons·m -2 ·s -1 It is continuously illuminated in a light incubator with a temperature of 25℃.

[0027] Step 3: Use a portable hydrogen detector to measure the amount of hydrogen produced in the photoreaction system at different times. The results are as follows: Figure 1 As shown in the orange curve, Chlorella's hydrogen production efficiency is significantly reduced due to environmental stress from strong light.

[0028] The microscopic images of the hybrid photoreaction system containing 20 mg PNIPAM after 17 days of cultivation show that *Chlorella vulgaris*, under the protection of PNIPAM and strong light conditions, still exhibited a proliferative state after 17 days of cultivation. Comparing the OD values ​​of *Chlorella vulgaris* before and after cultivation in the hybrid photoreaction system containing 20 mg PNIPAM and the photoreaction system without PNIPAM and MXene, it is evident that *Chlorella vulgaris* without PNIPAM and MXene showed significantly lower hydrogen production efficiency due to the environmental stress of strong light.

Claims

1. A method for continuous photosynthetic hydrogen production from organic / inorganic hybrid green algae, characterized in that... The method includes the following steps: Step 1, Microalgae Culture: Transfer 100 mL of microalgae culture to 1.5 L of TAP medium and incubate under light in a light incubator. When the number of microalgae cells reaches the logarithmic growth phase, take them out. Step 2, Synthesis of poly(N-isopropylacrylamide) copolymer: Dissolve 3-5g of N-isopropylacrylamide monomer and 20-40mg of azobisisobutyronitrile solution in 30-50mL of anhydrous acetonitrile. Under magnetic stirring, inert gas is introduced into the solution to remove oxygen. After deoxygenation, the reaction is carried out in an oil bath and then cooled. The solution was added dropwise to a mixed solution of diethyl ether and petroleum ether to obtain the precipitate PNIPAM; the precipitate was filtered and freeze-dried under vacuum to obtain the dried PNIPAM product; Step 3: Hydrogen production by microalgae under high light intensity: Take 50 mL of the microalgae solution obtained in Step 1, centrifuge to collect the microalgae, disperse the collected microalgae in 50 mL of glucose medium, and transfer it to 50 mL of the photoreaction system; then add 1-3 g of PNIPAM2 and 20-30 mg of MXene to the photoreaction system, shake well to obtain a hybrid photoreaction system; transfer the hybrid photoreaction system containing microalgae to a light incubator for continuous light irradiation.

2. The method for continuous photosynthetic hydrogen production by organic / inorganic hybrid green algae according to claim 1, characterized in that... In step one, the microalgae is Chlorella vulgaris.

3. The method for continuous photosynthetic hydrogen production by organic / inorganic hybrid green algae according to claim 1, characterized in that... In step one, the illumination is continuous, with an intensity of 50–150 µmol photons·m. -2 ·s -1 The temperature is 20~30℃.

4. The method for continuous photosynthetic hydrogen production by organic / inorganic hybrid green algae according to claim 1, characterized in that... In step two, the deoxygenation time is 20-60 minutes.

5. The method for continuous photosynthetic hydrogen production by organic / inorganic hybrid green algae according to claim 1, characterized in that... In step two, the vacuum freeze-drying time is 10-15 hours.

6. The method for continuous photosynthetic hydrogen production by organic / inorganic hybrid green algae according to claim 1, characterized in that... In step two, the oil bath reaction temperature is 60~80℃ and the time is 6~10h.

7. The method for continuous photosynthetic hydrogen production by organic / inorganic hybrid green algae according to claim 1, characterized in that... In step three, the centrifugation time is 5-10 minutes and the rotation speed is 3000-5000 rpm.

8. The method for continuous photosynthetic hydrogen production by organic / inorganic hybrid green algae according to claim 1, characterized in that... In step three, the light intensity is 500~1500 µmol photons·m -2 ·s -1 The temperature is 20~30℃.

9. The method for continuous photosynthetic hydrogen production by organic / inorganic hybrid green algae according to claim 1, characterized in that... In step three, each liter of glucose culture medium contains the following components: 10g glucose, 100mL BG-11 medium, 1.17g Mg(OH)2, 2g PNIPAM, 25mg MXene, and finally deionized water is added to prepare a mixed culture medium.

Images