Method for enhancing microalgae carbon sequestration through cooperation of seaweed-based carbon quantum dots and plant hormones

Abstract

The invention relates to a method for enhancing microalgae carbon sequestration through cooperation of seaweed-based carbon quantum dots and plant hormones, and belongs to the technical field of biological carbon sequestration. According to the method, chlorella is used as a carbon sequestration carrier and is cultured in a vertical tubular photobioreactor, indole-3-acetic acid (IAA) and seaweed-based carbon quantum dots (U-CQDs) are added in an initial stage, and culture conditions (25-30 DEG C, 3000 Lux illumination and 15% CO2 supply) are optimized. The seaweed-based carbon quantum dots (U-CQDs) are prepared by taking enteromorpha prolifera as a raw material through a hydrothermal method, and have excellent light conversion characteristics. Through the synergistic effect of the U-CQDs and the IAA, the light energy utilization efficiency, the CO2 fixation rate and the biomass accumulation of the microalgae are remarkably improved, and meanwhile, the culture energy consumption is reduced. The method is easy and convenient to operate, low in cost and suitable for efficient capture and resource utilization of industrial flue gas CO2.

Description

Technical Field

[0001] The present invention relates to the field of biological carbon fixation technology, and more specifically, to a method for enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones, which is particularly suitable for the efficient capture and resource utilization of CO2 in industrial flue gas. Background Art

[0002] High concentrations of CO₂ in industrial flue gas exacerbate the greenhouse effect. Microalgae carbon sequestration technology has become a research hotspot due to its efficient photosynthetic capacity. However, high CO₂ concentrations and light attenuation limit microalgae's carbon sequestration efficiency. Exogenous plant hormones play a key role in microalgae cell cycle regulation and carbon sequestration metabolism by modulating photosynthetic electron transport chain activity, enhancing antioxidant defenses, and alleviating environmental stress. Carbon-based fluorescent materials (CQDs) are a type of nanoparticle that have attracted widespread attention due to their photochemical stability, low cytotoxicity, and environmental friendliness. These nanomaterials, with particle sizes less than 10 nm, possess unique photoluminescence properties, converting invisible wavelengths, such as ultraviolet light, into visible light. Adding CQDs to algae broth can increase the light absorption band of microalgae, thereby enhancing their growth rate and photosynthetic activity.

[0003] Although plant hormones have the function of regulating the internal metabolism of microalgae cells, their ability to enhance light energy capture is relatively weak, and it is difficult to cope with the regulation of the entire growth cycle of microalgae under industrial flue gas conditions alone. On the other hand, CQDs increase the light absorption band of microalgae, but the dimension of action is limited to the optimization of photophysical processes. If the carbon fixation capacity of microalgae is to be further improved, it is necessary to synchronize the regulation of light energy conversion and carbon flow metabolism. Therefore, the present invention aims to propose a method for improving the carbon fixation performance of microalgae by synergizing carbon quantum dots with plant hormones, promoting the accumulation of microalgae lipids and reducing cellular damage through plant hormones, and taking advantage of the unique advantages of carbon quantum dots in optimizing photophysical processes and improving light energy capture efficiency, as an internal light source to increase the light energy utilization rate of microalgae, thereby enhancing the photosynthetic carbon fixation efficiency of microalgae. Summary of the Invention

[0004] To address the problems of light attenuation in photobioreactors and unstable microalgae cultivation environment caused by high CO2 concentrations, the present invention provides a method for preparing seaweed-based carbon quantum dots (U-CQDs) and synergizing them with plant hormones (IAA) to enhance the carbon fixation performance of microalgae. Through the dual mechanisms of light conversion effect and metabolic regulation, the CO2 fixation rate and biomass energy production are improved.

[0005] The present invention provides a method for enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones, comprising: S1: Chlorella vulgaris was used as a carbon fixation carrier and cultured in a vertical tubular photobioreactor using BG-11 medium; S2: Plant hormone indole-3-acetic acid (IAA) and algae-based carbon quantum dots (U-CQDs) were added at the initial stage of culture. The culture conditions were: temperature 25-30°C, light intensity 3000 Lux, light-dark cycle 12 h light / 12 h dark, gas supply 15% CO2 mixed gas, flow rate 0.18L·min - ¹, culture until the biomass enters the stable growth phase; S3: Preparation of U-CQDs, specifically comprising: mixing Enteromorpha striata powder with deionized water in a weight-to-volume ratio of 1:10, reacting in a high-pressure hydrothermal autoclave under a nitrogen atmosphere, separating the aqueous phase product after cooling, and obtaining U-CQDs powder through hydrothermal synthesis, filtration, dialysis, and freeze-drying.

[0006] In this scheme, the vertical tubular photobioreactor is a multi-tube design, with a single tube working volume of 500 mL and a total capacity of 0.6 L×12.

[0007] In this protocol, the concentration of IAA in the culture medium in step S2 is 1-5 mg·L - ¹, the concentration of U-CQDs is 1-10 mg·L - ¹.

[0008] In this solution, the chlorella is Chlorella vulgaris FACHB-2723.

[0009] In this scheme, the preparation process of U-CQDs in step S3 is as follows: Enteromorpha striata powder and deionized water are mixed at a ratio of 1:10, placed in a stainless steel high-pressure hydrothermal autoclave, filled with nitrogen, and subjected to hydrothermal reaction in a nitrogen atmosphere at a nitrogen pressure of 4 MPa and a reaction temperature of 300°C for 1 h. After the stainless steel high-pressure hydrothermal autoclave was cooled, the aqueous phase and oil phase products after the hydrothermal reaction were collected by vacuum filtration, and then the aqueous phase product was separated by a separatory funnel, and the aqueous phase product was transferred to a hydrothermal synthesis autoclave and reacted in an oven at 180°C for 8 hours; after the hydrothermal synthesis autoclave was cooled to room temperature, the obtained product was filtered through a 0.22 μm microporous membrane, and after filtration, it was dialyzed using a dialysis bag with a molecular weight cutoff of 1000 Da for 24 to 36 hours, and finally freeze-dried using a freeze dryer to obtain U-CQDs powder.

[0010] In this solution, the U-CQDs are spherical particles with a diameter of 2-5 nm, a main UV absorption peak at 230 nm, a fluorescence emission peak at 580 nm, and a surface rich in amino, hydroxyl and carboxyl functional groups.

[0011] In this solution, the U-CQDs and IAA are used synergistically to improve the biomass accumulation, light energy utilization efficiency, and CO2 fixation rate of Chlorella.

[0012] Another aspect of the present invention provides an application of U-CQDs prepared according to the above method in synergistically combining IAA in microalgae carbon fixation.

[0013] The present invention solves the defects existing in the background technology and has the following beneficial effects: The present invention breaks through the limitations of single regulation and improves the carbon fixation performance of microalgae. In the existing technology, the use of plant hormones or carbon quantum dots alone can only improve the carbon fixation efficiency of microalgae to a limited extent. Through the synergistic effect of the two, the microalgae biomass accumulation, CO2 fixation rate, light energy utilization rate, etc. are significantly higher than the effect of single regulation methods. The U-CQDs prepared by the present invention realize the resource utilization of waste. Compared with carbon quantum dots made from graphene, blue honeysuckle, etc., the present invention uses hydrothermal waste liquid from Enteromorpha fascicularis as a carbon source to prepare U-CQDs, which not only reduces the cost of raw materials but also avoids the toxic solvent pollution of traditional synthesis processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the biomass accumulation of Chlorella under the regulation of U-CQDs and IAA in the embodiment of the present invention.

[0015] Figure 2 It is the biomass accumulation of Chlorella under the regulation of IAA in the embodiment of the present invention.

[0016] Figure 3 The chlorophyll and carotenoid content of Chlorella under the regulation of U-CQDs and IAA in the embodiment of the present invention.

[0017] Figure 4 The biomass energy, CO2 utilization rate and light energy utilization efficiency of Chlorella under the regulation of U-CQDs and IAA in the embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0019] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0020] The experimental methods in the following examples are all conventional methods unless otherwise specified; the instruments and equipment used in the following examples are all conventional laboratory instruments and equipment unless otherwise specified; the experimental materials used in the following examples are all purchased from conventional biochemical reagent stores unless otherwise specified. Chlorella vulgaris FACHB-2723) was purchased from the Freshwater Algae Seed Bank of Wuhan Institute of Hydrobiology, Chinese Academy of Sciences, and the plant hormone indole-3-acetic acid (IAA) was purchased from Sinopharm Reagent Co., Ltd. with high purity.

[0021] Example 1

[0022] A method for enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones, specifically comprising: Prepare algae solution: Spread the Chlorella vulgaris in BG11 culture medium and cultivate it in a constant temperature incubator with a light intensity of 3000 lux and 25°C until it reaches the logarithmic growth phase, which will be used as the algae seed solution for subsequent experiments.

[0023] Microalgae culture: Chlorella vulgaris was used as a carbon fixation carrier and cultured in a vertical tubular photobioreactor using BG-11 medium. In the initial stage of culture (2-3 days), 1 ppm of plant hormone indole-3-acetic acid (IAA) and 5 mg·L - ¹Algae-based carbon quantum dots (U-CQDs); culture conditions were controlled as follows: temperature: 25-30°C, light intensity 3000 Lux, light-dark cycle 12 h light / 12 h dark; gas supply 5% CO2 mixed gas, flow rate 0.18L·min - ¹; Cultivate until the Chlorella enters the stable growth phase (culture period is approximately 12-14 days). Measure optical density daily and determine the growth trend of the Chlorella by measuring dry weight. Measure cell dry weight at the end of the experiment.

[0024] Preparation of U-CQDs: Using Enteromorpha striata as the starting material, 1 g of Enteromorpha striata powder was mixed with 10 mL of deionized water. The mixture was placed in a 25 mL stainless steel autoclave, filled with nitrogen to a pressure of 4 MPa, and heated to 300°C under a nitrogen atmosphere for 1 hour. After the autoclave cooled, the aqueous and oily phases of the hydrothermal reaction were collected by vacuum filtration, and the aqueous phase was separated using a separatory funnel. The aqueous phase was transferred to a 25 mL hydrothermal synthesis reactor and reacted in an oven at 180°C for 8 hours. After the autoclave cooled to room temperature, the resulting product was filtered through a 0.22 μm microporous membrane to remove larger aggregated particles. After filtration, the product was dialyzed using a 1000 Da molecular weight cutoff dialysis bag for 24–36 hours. Finally, the product was freeze-dried using a freeze dryer to obtain U-CQD powder.

[0025] Figure 1 The blank control group and the group supplemented with 1ppm IAA and 5mg·L - Comparison of the biomass accumulation of Chlorella vulgaris with U-CQDs. The experimental results show that under the condition of 1ppm IAA, the addition of 5mg·L -The U-CQDs promoted the biomass accumulation of Chlorella: the biomass of Chlorella accumulated rapidly from the 6th to the 10th day. After the completion of the culture on the 13th day, the biomass accumulation of Chlorella reached 1.62 mg·L - ¹. Figure 2 The following is a comparison of the biomass accumulation of Chlorella in the blank control group and the group with 1ppm IAA added. The experimental results show that under the condition of adding only 1ppm IAA, the final biomass accumulation of Chlorella is significantly higher than that of the blank control group (1.42mg·L - ¹) increased by 5.92%. Figure 1 The addition of U-CQDs significantly increased the biomass accumulation of Chlorella.

[0026] Example 2

[0027] A method for enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones, specifically comprising: Prepare algae solution: Spread the Chlorella vulgaris in BG11 culture medium and cultivate it in a constant temperature incubator with a light intensity of 3000 lux and 25°C until it reaches the logarithmic growth phase, which will be used as the algae seed solution for subsequent experiments.

[0028] Microalgae culture: Chlorella vulgaris was used as a carbon fixation carrier and cultured in a vertical tubular photobioreactor using BG-11 medium. In the initial stage of culture (2-3 days), 5 ppm of plant hormone indole-3-acetic acid (IAA) and 5 mg·L - ¹Algae-based carbon quantum dots (U-CQDs); culture conditions were controlled as follows: temperature: 25-30°C, light intensity 3000 Lux, light-dark cycle 12h light / 12h dark; gas supply: 15% CO2 mixed gas, flow rate 0.18L·min - ¹; Cultivate the Chlorella until it enters the stable growth phase (cultivation period is approximately 12-14 days). After the experiment, measure the chlorophyll and carotenoid content of the Chlorella, as well as its biomass energy, CO2 utilization, and light energy utilization efficiency.

[0029] Preparation of U-CQDs: Using Enteromorpha striata as the starting material, 1 g of Enteromorpha striata powder was mixed with 10 mL of deionized water. The mixture was placed in a 25 mL stainless steel autoclave, filled with nitrogen to a pressure of 4 MPa, and heated to 300°C under a nitrogen atmosphere for 1 hour. After the autoclave cooled, the aqueous and oily phases of the hydrothermal reaction were collected by vacuum filtration, and the aqueous phase was separated using a separatory funnel. The aqueous phase was transferred to a 25 mL hydrothermal synthesis reactor and reacted in an oven at 180°C for 8 hours. After the autoclave cooled to room temperature, the resulting product was filtered through a 0.22 μm microporous membrane to remove larger aggregated particles. After filtration, the product was dialyzed using a 1000 Da molecular weight cutoff dialysis bag for 24–36 hours. Finally, the product was freeze-dried using a freeze dryer to obtain U-CQD powder.

[0030] like Figure 3 As shown, when 5 ppm IAA was added, the U-CQDs dosage was 5 mg·L - Under the synergistic effect of IAA and U-CQDs, the total chlorophyll accumulation of Chlorella reached 17.51 mg·L - Chlorophyll accumulation in Chlorella increased by 15.61% compared to the control group, while the addition of 5 ppm IAA reduced carotenoid accumulation. This suggests that U-CQDs and IAA synergistically enhance the efficiency of the antioxidant system, reduce reactive oxygen species (ROS), and mitigate the accumulation of carotenoids as stress-sensitive antioxidants in Chlorella.

[0031] like Figure 4 As shown, at 5 ppm IAA, the U-CQDs dosage was 5 mg·L - Under the conditions of ¹, the biomass energy of Chlorella vulgaris was significantly improved, increasing by 19.51% compared to the control group. Higher biomass energy can improve the production efficiency of biofuels and promote the development of high-value-added products. 5mg·L - The synergistic effect of U-CQDs and 5ppm IAA increased the CO2 utilization efficiency of Chlorella by approximately 17.84%, further strengthening the carbon sequestration capacity of Chlorella. Light energy utilization is an important indicator for evaluating the photosynthetic performance of Chlorella during growth. In the control group, the light energy utilization rate of Chlorella was 13.09%. When 5ppm IAA and 5mg·L were added, the light energy utilization rate of Chlorella was 13.09%. - When treated with U-CQDs, Chlorella achieved 15.65% light energy utilization, a 19.56% increase compared to the control group. This improved light energy utilization can shorten the microalgae cultivation cycle and reduce light energy consumption, making it feasible for large-scale microalgae biofuel production.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones, characterized in that: The following steps are involved: S1: Chlorella vulgaris was used as a carbon fixation carrier and cultured in a vertical tubular photobioreactor using BG-11 medium; S2: In the initial stage of culture, the plant hormone indole-3-acetic acid (IAA) and algae-based carbon quantum dots (U-CQDs) were added. The culture conditions were: temperature 25-30°C, light intensity 3000 Lux, light-dark cycle 12 h light / 12 h dark, gas supply 15% CO2 mixed gas, flow rate 0.18 L min - ¹, culture until the biomass enters the stable growth phase; S3: Preparation of seaweed-based carbon quantum dots U-CQDs, specifically including: mixing Enteromorpha striata powder and deionized water in a ratio of 1:10, placing the mixture in a high-pressure hydrothermal autoclave under a nitrogen atmosphere for reaction, separating the aqueous phase product after cooling, and obtaining seaweed-based carbon quantum dots U-CQDs powder through hydrothermal synthesis, filtration, dialysis and freeze-drying.

2. The method of enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones according to claim 1, characterized in that: The vertical tubular photobioreactor is a multi-tube design, with a single tube working volume of 500 mL and a total capacity of 0.6 L×12.

3. The method of enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones according to claim 1, characterized in that: The concentration of the plant hormone indole-3-acetic acid (IAA) in the culture medium in step S2 is 1-5 mg·L - ¹, the concentration of seaweed-based carbon quantum dots U-CQDs is 1-10 mg·L - ¹.

4. The method of enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones according to claim 1, characterized in that: The chlorella is Chlorella vulgaris FACHB-2723.

5. The method of enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones according to claim 1, characterized in that: The preparation process of seaweed-based carbon quantum dots U-CQDs in step S3 is as follows: Enteromorpha fasciata powder and deionized water are mixed in a weight-to-volume ratio of 1:10, placed in a stainless steel high-pressure hydrothermal autoclave, filled with nitrogen, and subjected to hydrothermal reaction in a nitrogen atmosphere at a nitrogen pressure of 4 MPa and a reaction temperature of 300°C for 1 h; After the stainless steel high-pressure hydrothermal autoclave was cooled, the aqueous phase and oil phase products after the hydrothermal reaction were collected by vacuum filtration, and then the aqueous phase product was separated by a separatory funnel, and the aqueous phase product was transferred to a hydrothermal synthesis autoclave and reacted in an oven at 180°C for 8 hours; after the hydrothermal synthesis autoclave was cooled to room temperature, the obtained product was filtered through a 0.22 μm microporous membrane, and after filtration, it was dialyzed with a dialysis bag with a molecular weight cutoff of 1000 Da for 24 to 36 hours, and finally freeze-dried using a freeze dryer to obtain seaweed-based carbon quantum dots U-CQDs powder.

6. The method of enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones according to claim 1, characterized in that: The seaweed-based carbon quantum dots U-CQDs are spherical particles with a diameter of 2-5 nm, a main ultraviolet absorption peak at 230 nm, a fluorescence emission peak at 580 nm, and a surface rich in amino, hydroxyl and carboxyl functional groups.

7. The method of enhancing microalgae carbon fixation by using seaweed-based carbon quantum dots in collaboration with plant hormones according to claim 1, characterized in that: The seaweed-based carbon quantum dots U-CQDs are synergistically used with the plant hormone indole-3-acetic acid IAA to improve the biomass accumulation, light energy utilization efficiency, and CO2 fixation rate of Chlorella.

8. An application of seaweed-based carbon quantum dots (U-CQDs) prepared according to the method according to any one of claims 1 to 7 in synergistically combining the plant hormone indole-3-acetic acid (IAA) in carbon fixation in microalgae.

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