Red fluorescent carbon dots prepared by solvent-free method as well as method and application of red fluorescent carbon dots

Abstract

The invention discloses red fluorescent carbon dots prepared by a solvent-free method as well as a method and application thereof, and belongs to the technical field of polymer functional materials. According to the method disclosed by the invention, o-phenylenediamine, a polyphenol compound and inorganic metal salt react through a solvent-free method, and then a reaction product is purified to obtain the red fluorescent carbon dots. The red fluorescent carbon dots are simple in preparation process, low in cost, free of pollution, uniform in synthesized carbon dots and easy for large-scale batch preparation. The red fluorescent carbon dots provided by the invention have wide application prospects in the aspect of enhancing photosynthetic energy conversion of microalgae. Related experiments show that the red fluorescent carbon dots have strong absorption on yellow-green light (480-600 nm) with low utilization rate of microalgae, can be excited by light in the region, and emit red fluorescence which has a wavelength range of 600-700 nm and can be efficiently utilized by the microalgae, so that the light conversion effect is realized, and the utilization rate of light energy is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer functional materials, and in particular relates to a red fluorescent carbon dot prepared by a solvent-free method and a method and application thereof. Background Art

[0002] Photosynthesis is the most important chemical reaction on Earth. Photosynthetic organisms provide energy for all life activities on Earth through photosynthesis. Sunlight is the energy source for microalgae to carry out photosynthesis, but the range of visible light used by microalgae photosynthesis is limited. The blue-violet light with a wavelength of 400-480 nm in sunlight can be strongly absorbed by chlorophyll and carotenoids, and the red-orange light with a wavelength of 600-700 nm is absorbed by chlorophyll, which can promote microalgae photosynthetic carbon fixation; the yellow-green light with a wavelength of 500-600 nm has almost no contribution to photosynthesis. Therefore, how to make full use of the solar radiation irradiating the earth's surface for photosynthesis is the key to enhancing the photosynthetic energy conversion of microalgae.

[0003] As a 0D carbon-based nanomaterial, carbon dots have the characteristics of nanosize, non-toxicity, good biocompatibility, rich functional groups, and the ability to generate photoinduced electrons. They have great potential in enhancing photosynthesis. Carbon dots can combine with chloroplasts to form a photoconversion system, promote electron transfer in the photosystem through photoconversion or energy transfer, improve photosynthetic activity and efficiency, and thus promote carbon reactions and accumulate more biomass. Carbon dots also have excellent luminescence properties, and the luminescence wavelength can be adjusted; so far, the reported luminescence range covers almost the entire visible light region. Theoretically, if the fluorescence emission spectrum of carbon dots is consistent with the absorption spectrum of microalgae, the excitation spectrum of carbon dots can be absorbed by chloroplasts and used for photosynthesis, thereby improving photosynthetic efficiency.

[0004] In addition, the current synthesis methods of carbon dots are mostly solvothermal synthesis. Since the reaction process is uncontrollable, the synthesized carbon dots are not uniform and usually require further separation and purification, which has many limitations. Summary of the invention

[0005] The purpose of the present invention is to provide a solvent-free preparation of red fluorescent carbon dots and a method and application thereof, so as to solve the technical problem that the existing solvent thermal synthesis method is difficult to meet large-scale production due to the limitation of the preparation process.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention discloses a method for preparing red fluorescent carbon dots by a solvent-free method, comprising the following steps: Add o-phenylenediamine, polyphenol compound and inorganic metal salt into a mortar and grind thoroughly to obtain a mixed powder; The mixed powder is transferred to a reactor and heated for reaction, and after the reaction is completed, a carbonized solid is obtained after cooling; The carbonized solid is dissolved and then purified to obtain red fluorescent carbon dot powder.

[0007] Furthermore, the molar ratio of the o-phenylenediamine, the polyphenol compound and the inorganic metal salt is 1:(0.08-1):(0.05-0.1).

[0008] Furthermore, the polyphenol compound is one of dopamine hydrochloride, tea polyphenols, tannic acid, gallic acid and 3,4-dihydroxybenzoic acid.

[0009] Further, the inorganic metal salt is AlCl3 or AlCl3·6 H2O; The mixed powder is transferred to a reactor for heating reaction at a temperature of 180-200° C. for a heating time of 10-12 h.

[0010] Furthermore, the carbonized solid is dissolved, and the mass ratio of the carbonized solid to the solvent is 1:(1-100); the solvent is methanol or ethanol.

[0011] Furthermore, the purification process includes sequentially performing membrane filtration, dialysis, centrifugation and freeze-drying processes; The pore size of the filter membrane is 0.22 μm; the dialysis is performed using a dialysis bag with a molecular weight cutoff of 1000 Da; the centrifugal speed is 8000-10000 rpm, and the centrifugal time is 5-10 min.

[0012] The invention also discloses red fluorescent carbon dots prepared by the preparation method. The ultraviolet absorption wavelength and excitation wavelength of the red fluorescent carbon dots are 480-600 nm, and the emission peak wavelength range is 600-700 nm.

[0013] The invention also discloses the application of the red fluorescent carbon dots in enhancing the photosynthetic energy conversion of microalgae.

[0014] Further, the following steps are included: First, microalgae in the logarithmic growth phase were inoculated into a liquid culture medium, and then a red fluorescent carbon dot solution was added to the liquid culture medium, which was then placed in a constant temperature shaker for culture.

[0015] Furthermore, the red fluorescent carbon dot solution is obtained by mixing red fluorescent carbon dot powder and dimethyl sulfoxide; the concentration of the red fluorescent carbon dot solution is (0-10) μg / mL; The temperature for culturing in the constant temperature shaker is 25±1°C, the photoperiod is 12 / 12 h, and the light source is LED; The liquid culture medium is BG-11 culture medium, and is sterilized at 121°C for 20 min; the microalgae is Chlorella pyrenoidosa.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The invention discloses a method for preparing red fluorescent carbon dots by a solvent-free method. The method adopts o-phenylenediamine, a polyphenol compound and an inorganic metal salt aluminum chloride to synthesize the red fluorescent carbon dots by a solvent-free method. During the preparation process, the reaction pressure of the reaction process is reduced, the safety of the experiment is greatly improved, the material synthesis cost is reduced, and the preparation process is simple and easy to operate. The reaction process is controllable and industrialized production can be realized.

[0017] Furthermore, the raw materials and preparation process used in the method all follow the concept of green environmental protection, and the entire process has almost no pollution to the environment.

[0018] The present invention also discloses red fluorescent carbon dots prepared by the method. The red fluorescent carbon dots in the present invention are synthesized by a solvent-free method, have small particle size, stable properties, simple preparation process, and good biocompatibility. According to relevant experimental results, the red fluorescent carbon dots in the present invention have strong absorption of yellow-green light (480-600 nm) with low utilization rate of microalgae, and can be excited by light in this area to emit red fluorescence with a wavelength range of 600-700 nm that can be efficiently utilized by microalgae, thereby realizing light conversion and improving light energy utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is an emission spectrum of the red fluorescent carbon dots prepared by the present invention; Figure 2 The ultraviolet-visible absorption spectrum of the red fluorescent carbon dots prepared by the present invention; Figure 3 This is a transmission electron microscope image of the red fluorescent carbon dots prepared by the present invention; Figure 4 This is a confocal image of Chlorella pyrenoidosa / red fluorescent carbon dots of the present invention; Where: a-bright field image; b-Chlorella pyrenoidosa (λ ex =488 nm); c-red fluorescent carbon dots (λ ex =561 nm); d-confocal image of Chlorella vulgaris / red fluorescent carbon dots; Figure 5 is the growth curve of Chlorella pyrenoidosa cultured without red fluorescent carbon dots or with different concentrations of red fluorescent carbon dots in the present invention; Figure 6 In the present invention, the light intensity is 600 W / m 2Dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots under the same conditions; Figure 7 The dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots within 30 min under different light intensities in the present invention; Figure 8 It is the ATP content of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots in the present invention. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0021] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0022] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0023] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0024] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0025] The present invention provides a method for preparing red fluorescent carbon dots by a solvent-free method, comprising the following steps: O-phenylenediamine, polyphenol compounds and inorganic metal salts were mixed evenly in proportion and ground into powder in an agate mortar; the mixed powder was then transferred to a stainless steel reactor, heated at 200 °C for 12 h, and after the reaction was completed, it was naturally cooled to room temperature; the obtained carbonized solid was dissolved in anhydrous ethanol and filtered with a filter membrane, and red fluorescent carbon dot powder was obtained after dialysis, centrifugation and freeze-drying.

[0026] Preferably, the polyphenol compound is one of dopamine hydrochloride, tea polyphenols, tannic acid, gallic acid, and 3,4-dihydroxybenzoic acid.

[0027] Preferably, the inorganic metal salt is AlCl3 or AlCl3·6 H2O.

[0028] Preferably, the molar ratio of the o-phenylenediamine, the polyphenol compound and the inorganic metal salt is 1:(0.08-1):(0.05-0.1).

[0029] Preferably, the pore size of the filter membrane is 0.22 μm; the dialysis is performed using a dialysis bag with a molecular weight cutoff of 1000 Da; the centrifugal speed is 8000-10000 rpm, and the centrifugal time is 5-10 min.

[0030] Preferably, the ultraviolet absorption wavelength and excitation wavelength of the red fluorescent carbon dots are 480-600 nm, and the emission peak wavelength range is 600-700 nm.

[0031] The invention also discloses red fluorescent carbon dots prepared by the method.

[0032] The invention also discloses the application of the red fluorescent carbon dots in enhancing the photosynthetic energy conversion of microalgae.

[0033] Preferably, the specific steps are: first, inoculate the microalgae in the logarithmic growth phase into a liquid culture medium, then add different concentrations of red fluorescent carbon dots (0, 1, 2.5, 5, 10 μg / mL) to the culture medium, and then place it in a digital constant temperature shaker for culture, the temperature is 25±1°C, the photoperiod is 12 / 12 h (bright / dark), the light source is LED, all culture media and conical flasks are sterilized at 121°C for 20 min, the device for culturing Chlorella is a 250 mL conical flask, and it is sealed with a biological breathable sealing film to prevent contamination by other microorganisms.

[0034] Preferably, the microalgae is Chlorella pyrenoidosa, and the liquid culture medium is a sterile BG-11 culture medium suitable for the growth of blue-green algae.

[0035] Preferably, the red fluorescent carbon dots of different concentrations are prepared by dissolving red fluorescent carbon dot powder in dimethyl sulfoxide solvent to form a red fluorescent carbon dot solution.

[0036] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0037] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0038] Example 1 A method for preparing red fluorescent carbon dots by a solvent-free method comprises the following steps: 5 mmol o-phenylenediamine, 5 mmol dopamine hydrochloride and 0.33 mmol AlCl3·6 H2O were mixed and ground evenly in an agate mortar for 10 min to obtain a powder with uniform particles. The mixed powder was then transferred to the inner liner of a 30 mL autoclave, and the autoclave was placed in an oven at 200 °C for reaction for 12 h. After the reaction was completed, the autoclave was taken out and naturally cooled to room temperature. The obtained 1.57 g carbonized solid was dissolved in anhydrous ethanol and filtered through a 0.22 μm polyethersulfone membrane to remove large particles, wherein the mass ratio of carbonized solid to solvent was 1:10. The filtered solution was placed in a dialysis bag with a molecular weight cutoff of 1000 Da and dialyzed with deionized water for 3 d, with the deionized water replaced every 12 h. The liquid obtained after dialysis was centrifuged at 10000 r / min for 5 min, the supernatant was removed, and the obtained solid was freeze-dried to finally obtain a dark purple powder, which was the red fluorescent carbon dot powder.

[0039] The red fluorescent carbon dot powder is dissolved in an organic solvent (an organic solvent that can dissolve carbon dots and has high volatility, such as methanol and ethanol) to produce a purple-red red fluorescent carbon dot solution with red fluorescence.

[0040] Example 2 A method for preparing red fluorescent carbon dots by a solvent-free method comprises the following steps: 5 mmol o-phenylenediamine, 1.25 mmol tea polyphenols and 0.33 mmol AlCl3·6 H2O were mixed and ground evenly in an agate mortar for 10 min to obtain a powder with uniform particles. The mixed powder was then transferred to the inner liner of a 30 mL autoclave, and the autoclave was placed in an oven at 200 °C for reaction for 12 h. After the reaction was completed, the autoclave was taken out and naturally cooled to room temperature. The obtained 0.97 g carbonized solid was dissolved in anhydrous ethanol and filtered through a 0.22 μm polyethersulfone membrane to remove large particles, wherein the mass ratio of carbonized solid to solvent was 1:10. The filtered solution was placed in a dialysis bag with a molecular weight cutoff of 1000 Da and dialyzed with deionized water for 3 d, with the deionized water replaced every 12 h. The liquid obtained after dialysis was centrifuged at 10000 r / min for 5 min, the supernatant was removed, and the obtained solid was freeze-dried to finally obtain a dark red powder, which was the red fluorescent carbon dots. The red fluorescent carbon dot powder is dissolved in an organic solvent (an organic solvent that can dissolve carbon dots and has high volatility, such as methanol and ethanol) to produce a purple-red red fluorescent carbon dot solution with red fluorescence.

[0041] Example 3 A method for preparing red fluorescent carbon dots by a solvent-free method comprises the following steps: 5 mmol o-phenylenediamine, 0.4 mmol tannic acid and 0.33 mmol AlCl3·6 H2O were mixed and ground evenly in an agate mortar for 10 min to obtain a powder with uniform particles. The mixed powder was then transferred to the inner liner of a 30 mL autoclave, and the autoclave was placed in an oven at 200 °C for reaction for 12 h. After the reaction was completed, the autoclave was taken out and naturally cooled to room temperature. The obtained 1.30 g carbonized solid was dissolved in anhydrous ethanol and filtered through a 0.22 μm polyethersulfone membrane to remove large particles, wherein the mass ratio of carbonized solid to solvent was 1:10. The filtered solution was placed in a dialysis bag with a molecular weight cutoff of 1000 Da and dialyzed with deionized water for 3 d, with the deionized water replaced every 12 h. The liquid obtained after dialysis was centrifuged at 10000 r / min for 5 min, the supernatant was removed, and the obtained solid was freeze-dried to finally obtain a dark gray powder, which was the red fluorescent carbon dots. The red fluorescent carbon dots are dissolved in an organic solvent (an organic solvent that can dissolve carbon dots and has high volatility, such as methanol and ethanol) to produce a purple-red red fluorescent carbon dot solution with red fluorescence.

[0042] Example 4 A method for preparing red fluorescent carbon dots by a solvent-free method comprises the following steps: 5 mmol o-phenylenediamine, 3.3 mmol gallic acid and 0.33 mmol AlCl3·6 H2O were mixed and ground evenly in an agate mortar for 10 min to obtain a powder with uniform particles. The mixed powder was then transferred to the inner liner of a 30 mL autoclave, and the autoclave was placed in an oven at 200 °C for reaction for 12 h. After the reaction was completed, the autoclave was taken out and naturally cooled to room temperature. The obtained 1.18 g carbonized solid was dissolved in anhydrous ethanol and filtered through a 0.22 μm polyethersulfone membrane to remove large particles, wherein the mass ratio of carbonized solid to solvent was 1:10. The filtered solution was placed in a dialysis bag with a molecular weight cutoff of 1000 Da and dialyzed with deionized water for 3 d, with the deionized water replaced every 12 h. The liquid obtained after dialysis was centrifuged at 10000 r / min for 5 min. The supernatant was removed and the obtained solid was freeze-dried to finally obtain a dark brown powder, which was the red fluorescent carbon dots. The red fluorescent carbon dots are dissolved in an organic solvent (an organic solvent that can dissolve carbon dots and has high volatility, such as methanol and ethanol) to produce a purple-red red fluorescent carbon dot solution with red fluorescence.

[0043] Example 5 A method for preparing red fluorescent carbon dots by a solvent-free method comprises the following steps: 5 mmol o-phenylenediamine, 5 mmol 3,4-dihydroxybenzoic acid and 0.33 mmol AlCl3·6 H2O were mixed and ground evenly in an agate mortar for 10 min to obtain a powder with uniform particles. The mixed powder was then transferred to the inner liner of a 30 mL autoclave, and the autoclave was placed in an oven at 200 °C for reaction for 12 h. After the reaction was completed, the autoclave was taken out and cooled to room temperature naturally. The obtained 1.39 g carbonized solid was dissolved in anhydrous ethanol and filtered through a 0.22 μm polyethersulfone membrane to remove large particles, wherein the mass ratio of carbonized solid to solvent was 1:10. The filtered solution was placed in a dialysis bag with a molecular weight cutoff of 1000 Da and dialyzed with deionized water for 3 d, with the deionized water replaced every 12 h. The liquid obtained after dialysis was centrifuged at 10000 r / min for 5 min, the supernatant was removed, and the obtained solid was freeze-dried to finally obtain a yellow-brown powder, which was the red fluorescent carbon dots. The red fluorescent carbon dots are dissolved in an organic solvent (an organic solvent that can dissolve carbon dots and has high volatility, such as methanol and ethanol) to produce a purple-red red fluorescent carbon dot solution with red fluorescence.

[0044] Application Example 1 Chlorella vulgaris in the logarithmic growth phase was inoculated into a sterile BG-11 liquid culture medium suitable for the growth of blue-green algae, and different concentrations of red fluorescent carbon dots (0, 1, 2.5, 5, 10 μg / mL) obtained in Example 1 were added thereto, and then placed in a digital constant temperature shaker for culture at a temperature of 25±1°C, a photoperiod of 12 / 12 h (bright / dark), and an LED light source. All culture media and conical flasks were sterilized at 121°C for 20 min. The device for culturing Chlorella vulgaris was a 250 mL conical flask, and it was sealed with a bio-permeable sealing film to prevent contamination by other microorganisms. The interaction between Chlorella vulgaris and red fluorescent carbon dots was confirmed using a confocal laser scanning microscope (CLSM); the absorbance of the culture solution at a wavelength of 680 nm (OD 680 ) was used to monitor the growth activity of Chlorella pyrenoidosa. Samples were taken daily and the absorbance at 680 nm was measured using UV-Vis-NIR to characterize its biomass and draw growth curves. A portable dissolved oxygen meter was used to detect the dissolved oxygen content. 2 Under the same conditions, the dissolved oxygen content of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured every 5 min. The dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured within 30 min under different light intensities. The ATP content in Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was determined using an ATP detection kit.

[0045] Application Example 2 Chlorella vulgaris in the logarithmic growth phase was inoculated into a sterile BG-11 liquid culture medium suitable for the growth of blue-green algae, and different concentrations of red fluorescent carbon dots obtained in Example 2 (0, 1, 2.5, 5, 10 μg / mL) were added thereto, and then placed in a digital constant temperature shaker for culture at a temperature of 25±1°C, a photoperiod of 12 / 12 h (bright / dark), and an LED light source. All culture media and conical flasks were sterilized at 121°C for 20 min. The device for culturing Chlorella vulgaris was a 250 mL conical flask, and it was sealed with a bio-permeable sealing film to prevent contamination by other microorganisms. The interaction between Chlorella vulgaris and red fluorescent carbon dots was confirmed using a confocal laser scanning microscope (CLSM); the absorbance of the culture solution at a wavelength of 680 nm (OD 680 ) was used to monitor the growth activity of Chlorella pyrenoidosa. Samples were taken daily and the absorbance at 680 nm was measured using UV-Vis-NIR to characterize its biomass and draw growth curves. A portable dissolved oxygen meter was used to detect the dissolved oxygen content. 2Under the same conditions, the dissolved oxygen content of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured every 5 min. The dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured within 30 min under different light intensities. The ATP content in Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was determined using an ATP detection kit.

[0046] Application Example 3 The pyrenoid Chlorella in the logarithmic growth phase was inoculated into a sterile BG-11 liquid culture medium suitable for the growth of blue-green algae, and different concentrations of the red fluorescent carbon dots obtained in Example 3 (0, 1, 2.5, 5, 10 μg / mL) were added thereto, and then placed in a digital constant temperature shaker for culture at a temperature of 25±1°C, a photoperiod of 12 / 12 h (bright / dark), and an LED light source. All culture media and conical flasks were sterilized at 121°C for 20 min. The device for culturing Chlorella was a 250 mL conical flask, and it was sealed with a bio-permeable sealing film to prevent contamination by other microorganisms. The interaction between pyrenoid Chlorella and the red fluorescent carbon dots was confirmed using a confocal laser scanning microscope (CLSM); the absorbance of the culture solution at a wavelength of 680 nm (OD 680 ) was used to monitor the growth activity of Chlorella pyrenoidosa. Samples were taken daily and the absorbance at 680 nm was measured using UV-Vis-NIR to characterize its biomass and draw growth curves. A portable dissolved oxygen meter was used to detect the dissolved oxygen content. 2 Under the same conditions, the dissolved oxygen content of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured every 5 min. The dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured within 30 min under different light intensities. The ATP content in Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was determined using an ATP detection kit.

[0047] Application Example 4 Chlorella vulgaris in the logarithmic growth phase was inoculated into a sterile BG-11 liquid culture medium suitable for the growth of blue-green algae, and different concentrations of red fluorescent carbon dots obtained in Example 4 (0, 1, 2.5, 5, 10 μg / mL) were added thereto, and then placed in a digital constant temperature shaker for culture at a temperature of 25±1°C, a photoperiod of 12 / 12 h (bright / dark), and an LED light source. All culture media and conical flasks were sterilized at 121°C for 20 min. The device for culturing Chlorella vulgaris was a 250 mL conical flask, and it was sealed with a bio-permeable sealing film to prevent contamination by other microorganisms. The interaction between Chlorella vulgaris and red fluorescent carbon dots was confirmed using a confocal laser scanning microscope (CLSM); the absorbance of the culture solution at a wavelength of 680 nm (OD 680 ) was used to monitor the growth activity of Chlorella pyrenoidosa. Samples were taken daily and the absorbance at 680 nm was measured using UV-Vis-NIR to characterize its biomass and draw growth curves. A portable dissolved oxygen meter was used to detect the dissolved oxygen content. 2 Under the same conditions, the dissolved oxygen content of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured every 5 min. The dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured within 30 min under different light intensities. The ATP content in Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was determined using an ATP detection kit.

[0048] Application Example 5 Chlorella vulgaris in the logarithmic growth phase was inoculated into a sterile BG-11 liquid culture medium suitable for the growth of blue-green algae, and different concentrations of red fluorescent carbon dots (0, 1, 2.5, 5, 10 μg / mL) obtained in Example 5 were added thereto, and then placed in a digital constant temperature shaker for culture at a temperature of 25±1°C, a photoperiod of 12 / 12 h (bright / dark), and an LED light source. All culture media and conical flasks were sterilized at 121°C for 20 min. The device for culturing Chlorella vulgaris was a 250 mL conical flask, and it was sealed with a bio-permeable sealing film to prevent contamination by other microorganisms. The interaction between Chlorella vulgaris and red fluorescent carbon dots was confirmed using a confocal laser scanning microscope (CLSM); the absorbance of the culture solution at a wavelength of 680 nm (OD 680 ) was used to monitor the growth activity of Chlorella pyrenoidosa. Samples were taken daily and the absorbance at 680 nm was measured using UV-Vis-NIR to characterize its biomass and draw growth curves. A portable dissolved oxygen meter was used to detect the dissolved oxygen content. 2Under the same conditions, the dissolved oxygen content of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured every 5 min. The dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured within 30 min under different light intensities. The ATP content in Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was determined using an ATP detection kit.

[0049] Performance Test: The red fluorescent carbon dot powder prepared by the present invention was tested, and the results are shown in the attached figure. Figure 1 To Attachment Figure 3 Attached Figure 1 The emission spectrum of the red fluorescent carbon dot powder is in the range of 600-700 nm, indicating that the red fluorescent carbon dots of the present invention can convert the yellow-green light with low utilization rate of microalgae into red light that can be efficiently utilized by microalgae, and have a high matching performance with the photosynthesis spectrum of microalgae.

[0050] Figure 2 This is the UV-visible absorption spectrum of the red fluorescent carbon dot powder. From the figure, we can see that the red fluorescent carbon dots have strong absorption in the 480~600 nm region, which matches the excitation spectrum.

[0051] Figure 3 This is a transmission electron microscope image of the red fluorescent carbon dot powder. It can be seen that the average size of the red fluorescent carbon dots is less than 20 nm and they are well dispersed.

[0052] The red fluorescent carbon dots obtained in Example 1 at different concentrations (0, 1, 2.5, 5, 10 μg / mL) were co-cultured with Chlorella pyrenoidosa, and the interaction between Chlorella pyrenoidosa and the red fluorescent carbon dots was confirmed using confocal laser scanning microscopy (CLSM). The absorbance of the culture solution at a wavelength of 680 nm (OD 680 ) was used to monitor the growth activity of Chlorella pyrenoidosa, and the absorbance at 680 nm was measured by UV-Vis-NIR to characterize its biomass and draw a growth curve; a portable dissolved oxygen meter was used to detect the dissolved oxygen content. 2 Under the same conditions, the dissolved oxygen content of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured every 5 min. The dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was measured within 30 min under different light intensities. The ATP content in Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots was determined using an ATP detection kit. The results are shown in the attached figure. Figure 4 To Attachment Figure 8 shown.

[0053] Figure 4This is a confocal image of Chlorella pyrenoidosa / red fluorescent carbon dots. Under excitation at a wavelength of 488 nm, the spontaneous green fluorescence of chloroplasts can be clearly observed. Under excitation at a wavelength of 561 nm, the red fluorescent carbon dots emit red fluorescence, and the red fluorescence of the red fluorescent carbon dots highly overlaps with the green fluorescence of Chlorella pyrenoidosa, indicating that the red fluorescent carbon dots are bound to Chlorella pyrenoidosa.

[0054] Figure 5 Figure 2 shows the growth curves of Chlorella pyrenoidosa cultured without or with different concentrations of red fluorescent carbon dots. The growth of Chlorella pyrenoidosa reflects the increase in overall biomass content and cell number. As photoautotrophs, their biomass is converted from photosynthetic carbon fixation. In addition, the energy and substances required for cell division are also provided by photosynthesis. Therefore, the accelerated growth of Chlorella pyrenoidosa directly indicates that the red fluorescent carbon dots promote the photosynthesis of Chlorella pyrenoidosa.

[0055] Figure 6 For a light intensity of 600 W / m 2 Under the same conditions, the dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots showed that the oxygen production of the group with the addition of red fluorescent carbon dots increased significantly, indicating that the photosynthetic efficiency was significantly improved after the addition of red fluorescent carbon dots.

[0056] Figure 7 Figure 3 The dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots within 30 min under different light intensities. Higher light intensity increased the dissolved oxygen production of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots; but with the increase of light intensity, the amount of oxygen evolved decreased. It may be that with the increase of light intensity, the light of Chlorella gradually became saturated, and its own photosynthetic rate gradually reached saturation.

[0057] Figure 8 is the ATP content of Chlorella pyrenoidosa and Chlorella pyrenoidosa / red fluorescent carbon dots. It can be seen that the ATP production of Chlorella pyrenoidosa with the addition of red fluorescent carbon dots group increased significantly, and the photosynthetic efficiency of Chlorella pyrenoidosa was successfully improved.

[0058] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing red fluorescent carbon dots by a solvent-free method, characterized in that: The following steps are involved: Grinding o-phenylenediamine, polyphenol compound and inorganic metal salt to obtain mixed powder; The mixed powder is transferred to a reactor for heating reaction, and after the reaction is completed, a carbonized solid is obtained after cooling; The carbonized solid is dissolved and then purified to obtain red fluorescent carbon dot powder.

2. The method for preparing red fluorescent carbon dots by a solvent-free method according to claim 1, characterized in that: The molar ratio of the o-phenylenediamine, the polyphenol compound and the inorganic metal salt is 1:(0.08-1):(0.05-0.1).

3. The method for preparing red fluorescent carbon dots by a solvent-free method according to claim 1, characterized in that: The polyphenol compound is one of dopamine hydrochloride, tea polyphenols, tannic acid, gallic acid and 3,4-dihydroxybenzoic acid.

4. The method for preparing red fluorescent carbon dots by a solvent-free method according to claim 1, characterized in that: The inorganic metal salt is AlCl3 or AlCl3·6 H2O; The mixed powder is transferred to a reactor for heating reaction, the heating temperature is 180-200°C, and the heating time is 10-12 h.

5. The method for preparing red fluorescent carbon dots by a solvent-free method according to claim 1, characterized in that: Dissolving the carbonized solid is to mix the carbonized solid with a solvent, wherein the mass ratio of the carbonized solid to the solvent is 1:(1-100); the solvent is methanol or ethanol.

6. The method for preparing red fluorescent carbon dots by a solvent-free method according to claim 1, characterized in that: The purification process includes sequentially performing membrane filtration, dialysis, centrifugation and freeze-drying processes; The pore size of the filter membrane is 0.22 μm; the dialysis is performed using a dialysis bag with a molecular weight cutoff of 1000 Da; the centrifugal speed is 8000-10000 rpm, and the centrifugal time is 5-10 min.

7. A red fluorescent carbon dot, characterized in that: The red fluorescent carbon dots are prepared by the preparation method according to any one of claims 1 to 6, wherein the ultraviolet absorption wavelength and excitation wavelength of the red fluorescent carbon dots are 480-600 nm, and the emission peak wavelength range is 600-700 nm.

8. Use of the red fluorescent carbon dots according to claim 7 in enhancing photosynthetic energy conversion of microalgae.

9. The use of red fluorescent carbon dots in enhancing photosynthetic energy conversion of microalgae according to claim 8, characterized in that: The following steps are involved: First, microalgae in the logarithmic growth phase were inoculated into a liquid culture medium, and then a red fluorescent carbon dot solution was added to the liquid culture medium, which was then placed in a constant temperature shaker for culture.

10. The use of red fluorescent carbon dots in enhancing photosynthetic energy conversion of microalgae according to claim 9, characterized in that: The red fluorescent carbon dot solution is obtained by mixing red fluorescent carbon dot powder and dimethyl sulfoxide; the concentration of the red fluorescent carbon dot solution is (0-10) μg / mL; The temperature for culturing in the constant temperature shaker is 25±1°C, the photoperiod is 12 / 12 h, and the light source is LED; The liquid culture medium is BG-11 culture medium, and is sterilized at 121°C for 20 min; the microalgae is Chlorella pyrenoidosa.

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