Preparation of biomass carbon quantum dots and application of biomass carbon quantum dots in microalgae culture

Abstract

The invention discloses preparation of biomass carbon quantum dots with pine sawdust as a raw material and an application method of the biomass carbon quantum dots in microalgae culture. According to the method, high-yield biomass carbon quantum dots are synthesized through an alkali-assisted oxidation process, and the blue light emission characteristic of the biomass carbon quantum dots is matched with the absorption spectrum of a microalgae photosynthetic system II (PSII). The method comprises the following specific steps: pretreating pine sawdust, then carrying out hydrothermal reaction to prepare pine derived hydrothermal carbon, and then carrying out alkaline oxidation stripping on the hydrothermal carbon through NaOH and H2O2 to extract the carbon quantum dots. The prepared biomass carbon quantum dots have the advantages of high yield, excellent optical performance, good water solubility and biocompatibility. In microalgae culture, the biomass concentration of microalgae and the synthesis efficiency of protein and lipid can be remarkably improved by adding a proper amount of the carbon quantum dots, and an efficient and environment-friendly solution is provided for waste recycling and microalgae high-value culture.

Description

Technical Field

[0001] The present invention belongs to the fields of nanomaterial preparation and biotechnology, and particularly relates to a green synthesis method of biomass carbon quantum dots using pine sawdust as a raw material, and the application of the biomass carbon quantum dots in promoting microalgae growth and biomass production. Background Art

[0002] Population growth and industrialization have exacerbated the shortage of fresh water resources and environmental pollution. Microalgae cultivation technology has become a potential solution to resource and environmental problems because it can efficiently utilize light energy and fix CO 2 and synthesize high-value biomass such as carotenoids, proteins, and lipids. Microalgae photosynthesis has a high demand for light energy, but light attenuation leads to low light utilization efficiency, which limits biomass production and affects the economic benefits and application potential of microalgae cultivation.

[0003] As a light conversion material, carbon quantum dots can improve the light energy utilization of microalgae to a certain extent. However, there are many deficiencies in the currently widely used carbon quantum dot preparation technologies. On the one hand, their raw materials mostly rely on non-renewable resources such as petrochemical products or special chemical reagents, which not only increases production costs but also causes greater pressure on the environment. On the other hand, traditional preparation processes often need to be carried out under harsh conditions such as high temperature and strong acid, which not only requires high equipment requirements, increases energy consumption, but also results in a low quantum yield, making it difficult to meet the needs of large-scale applications. In addition, carbon quantum dots prepared by traditional methods also have certain limitations in optical properties and biocompatibility, which restricts their wide application in the field of biotechnology. Summary of the Invention

[0004] Aiming at the deficiencies of traditional carbon quantum dot preparation methods and light energy utilization in microalgae cultivation, the present invention provides a method for preparing biomass carbon quantum dots and their application in microalgae cultivation. This method uses cheap pine sawdust as a raw material, and through pretreatment, hydrothermal reaction, and alkaline oxidation exfoliation, it efficiently prepares biomass carbon quantum dots with high yield and excellent optical properties. Its characteristic of absorbing ultraviolet light and emitting blue light (430 - 480 nm) matches the absorption spectrum (450 - 475 nm) of the microalgae photosystem II (PSII), significantly improving microalgae biomass and the synthesis efficiency of proteins and lipids, and realizing the resource utilization of waste and the high-value cultivation of microalgae.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] Using pine sawdust as a precursor material and performing pretreatment on it;

[0007] Preparing pine-derived hydrochar by subjecting the pretreated precursor material to a hydrothermal reaction;

[0008] Through NaOH and H2 O 2 Perform alkaline oxidation exfoliation on the pine-derived hydrochar to extract carbon quantum dots.

[0009] The pretreatment method is as follows: further pulverize the precursor material pine sawdust and pass through a 200-mesh sieve, wash it 3 times with deionized water and then dry it.

[0010] The preparation method of the pine-derived hydrochar is as follows: mix the pretreated pine powder with deionized water to obtain a pine powder solution with a mass-volume fraction of 10%, place it under a temperature condition of 200 °C for hydrothermal reaction for 6 h, and the heating rate is 5 °C / min. After cooling and filtration, wash it 3 times with deionized water and anhydrous ethanol respectively to remove soluble impurities and then dry it to obtain the pine-derived hydrochar.

[0011] The method for extracting carbon quantum dots is as follows: disperse 0.1 g of pine-derived hydrochar in 50 mL of 0.1 - 0.2 mol / L NaOH alkaline solution, stir and heat it to 80 °C, slowly dropwise add H 2 O 2 solution to make the mass fraction of hydrogen peroxide in the final alkaline solution reach 1.2% - 2.4%, and extract for 1 h. Cool to room temperature, filter to obtain the extracted carbon quantum dot solution, adjust the pH of the alkaline solution to the applicable range of the dialysis bag with hydrochloric acid, dialyze with a dialysis bag with a molecular weight cut-off of 3500 Da for 24 h and then lyophilize to obtain the carbon quantum dot powder.

[0012] Preferably, when extracting carbon quantum dots, prepare 0.2 mol / L NaOH alkaline solution and dropwise add H 2 O 2 to make the mass fraction of H 2 O 2 in the final solution reach 2.4%.

[0013] Compared with the prior art, the present invention has the following advantages and technical effects:

[0014] (1) The present invention uses pine sawdust as the precursor material. As a common biomass resource, pine has the advantages of wide source and low cost. Compared with the expensive and dangerous chemical reagents used in the traditional preparation of carbon quantum dots, the preparation cost is greatly reduced.

[0015] (2) The reagents and reaction conditions used in the present invention for preparing biomass carbon quantum dots are environmentally friendly, do not produce a large amount of harmful waste gas, waste water and waste residue, and conform to the development direction of contemporary green chemistry. The biomass carbon quantum dots have an extremely high yield, up to 56.26% of the mass fraction of the precursor material at most. It is suitable for large-scale industrial production and provides the possibility for the wide application of carbon quantum dots.

[0016] (3) The biomass carbon quantum dots prepared by the present invention have high quantum yield, excellent optical properties, good water solubility and biocompatibility. Its ultraviolet absorption and blue light emission (430-480nm) characteristics are consistent with the absorption spectrum (450-475nm) of the photosynthetic system II (PSII) of microalgae, significantly improving the growth and metabolism of microalgae and enhancing the value-added potential of microalgae. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a simplified diagram of the preparation of biomass carbon quantum dots.

[0018] Figure 2 Transmission electron microscopy (TEM) characterization of the biomass carbon quantum dots prepared in Example 4.

[0019] Figure 3 This is the fluorescence spectrum of the biomass carbon quantum dots prepared in Example 4 at different excitation wavelengths.

[0020] Figure 4 The UV-visible absorption spectrum and the optimal absorption and emission wavelengths of the biomass carbon quantum dots prepared in Example 4.

[0021] Figure 5 The effect of adding traditional carbon quantum dots in Example 5, and biomass carbon quantum dots prepared by the methods described in Examples 1, 2, 3 and 4 on the biomass of Chlorella.

[0022] Figure 6 The effect of adding different concentrations of biomass carbon quantum dots prepared in Example 4 on the biomass of Chlorella in Example 6.

[0023] Figure 7 The effect of adding different concentrations of biomass carbon quantum dots prepared in Example 4 on the protein and lipid proportion (dry weight) and yield of Chlorella vulgaris in Example 6. DETAILED DESCRIPTION

[0024] To illustrate the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific examples. The present invention uses cheap biomass pine sawdust as a prerequisite material and prepares high-yield carbon quantum dots through a green and efficient alkali-assisted oxidation hydrothermal carbonization method. Its photoluminescence properties match the absorption spectrum of microalgae, and when added to the culture medium of microalgae in appropriate amounts, it significantly improves the growth and metabolism of microalgae. The preparation diagram of carbon quantum dots is as follows Figure 1 shown.

[0025] Example 1

[0026] This embodiment is an application example of the preparation of biomass carbon quantum dots, and the specific steps are as follows:

[0027] Using pine sawdust as the precursor material, it is pre-treated as follows: The pine sawdust is further pulverized and passed through a 200-mesh sieve, and then washed with deionized water 3 - 5 times and dried.

[0028] The pre-treated precursor material is subjected to a hydrothermal reaction to prepare pine-derived hydrochar: The pre-treated pine powder is fully mixed with deionized water to obtain a pine powder solution with a mass-volume fraction of 10%. It is placed under a temperature condition of 200 °C for a hydrothermal reaction for 6 h, and the heating rate is 5 °C / min. After cooling and filtration, it is washed 3 times each with deionized water and absolute ethanol to remove soluble impurities and dried to obtain pine-derived hydrochar, labeled as HW-CD.

[0029] Through NaOH and H 2 O 2 The pine-derived hydrochar is exfoliated and oxidized to extract carbon quantum dots: 0.1 g of pine-derived hydrochar is dispersed in 50 mL of 0.1 mol / L NaOH alkaline solution, stirred and heated to 80 °C, and a solution of H 2 O 2 with a mass fraction of 30% is slowly added dropwise to make the mass fraction of hydrogen peroxide in the final alkaline solution reach 1.2%, and extraction is carried out for 1 h. After cooling to room temperature, the extracted carbon quantum dot solution is obtained by filtration. The pH of the alkaline solution is adjusted to the applicable range of the dialysis bag with hydrochloric acid, and dialysis is carried out for 24 hours using a dialysis bag with a molecular weight cut-off of 3500 Da and then freeze-dried to obtain carbon quantum dot powder, labeled as CQD-1.

[0030] Example 2

[0031] This example is another application example for the preparation of biomass carbon quantum dots. In this example, except that the final addition concentration of H 2 O 2 is different from that in Example 1, the remaining steps are the same as those in Example 1.

[0032] Through NaOH and H 2 O 2 The pine-derived hydrochar is exfoliated and oxidized to extract carbon quantum dots: 0.1 g of pine-derived hydrochar is dispersed in 50 mL of 0.1 mol / L NaOH alkaline solution, stirred and heated to 80 °C, and a solution of H 2 O 2 with a mass fraction of 30% is slowly added dropwise to make the mass fraction of hydrogen peroxide in the final alkaline solution reach 2.4%, and extraction is carried out for 1 h. After cooling to room temperature, the extracted carbon quantum dot solution is obtained by filtration. The pH of the alkaline solution is adjusted to the applicable range of the dialysis bag with hydrochloric acid, and dialysis is carried out for 24 hours using a dialysis bag with a molecular weight cut-off of 3500 Da and then freeze-dried to obtain carbon quantum dot powder, labeled as CQD-2.

[0033] Example 3

[0034] This example is another application example for the preparation of biomass carbon quantum dots. Except that the concentration of the NaOH alkaline solution configured during the extraction of carbon quantum dots is different from that in Example 1, the remaining steps are the same as those in Example 1.

[0035] Through NaOH and H 2 O 2 Exfoliate and oxidize the pine-derived hydrothermal carbon to extract carbon quantum dots: Disperse 0.1 g of pine-derived hydrothermal carbon in 50 mL of 0.2 mol / L NaOH alkaline solution, stir and heat to 80 °C, and slowly add a solution of H 2 O 2 such that the mass fraction of hydrogen peroxide in the final alkaline solution reaches 1.2%, and extract for 1 h. Cool to room temperature, filter to obtain the extracted carbon quantum dot solution, adjust the pH of the alkaline solution to the applicable range of the dialysis bag using hydrochloric acid, dialyze for 24 hours using a dialysis bag with a molecular weight cut-off of 3500 Da, and then lyophilize to obtain carbon quantum dot powder, labeled as CQD-3.

[0036] Example 4

[0037] This example is another application example for the preparation of biomass carbon quantum dots. Except that the concentration of the NaOH alkaline solution configured and the final addition concentration of H 2 O 2 during the extraction of carbon quantum dots are different from those in Example 1, the remaining steps are the same as those in Example 1.

[0038] Through NaOH and H 2 O 2 Exfoliate and oxidize the pine-derived hydrothermal carbon to extract carbon quantum dots: Disperse 0.1 g of pine-derived hydrothermal carbon in 50 mL of 0.2 mol / L NaOH alkaline solution, stir and heat to 80 °C, and slowly add a solution of H 2 O 2 such that the mass fraction of hydrogen peroxide in the final alkaline solution reaches 2.4%, and extract for 1 h. Cool to room temperature, filter to obtain the extracted carbon quantum dot solution, adjust the pH of the alkaline solution to the applicable range of the dialysis bag using hydrochloric acid, dialyze for 24 h using a dialysis bag with a molecular weight cut-off of 3500 Da, and then lyophilize to obtain carbon quantum dot powder, labeled as CQD-4.

[0039] Method for preparing traditional carbon quantum dots using biomass pine sawdust:

[0040] Using pine sawdust as the precursor material, perform pretreatment on it: Further crush the pine sawdust and pass it through a 200-mesh sieve, wash it 3 - 5 times with deionized water, and then dry it.

[0041] The pretreated precursor material is subjected to hydrothermal reaction to prepare traditional carbon quantum dots: The pretreated pine wood powder is fully mixed with deionized water to obtain a pine wood powder solution with a mass-volume fraction of 10%. It is placed under hydrothermal reaction at a temperature of 200 °C for 6 h, and the heating rate is 5 °C / min. After cooling and filtration, it is dialyzed for 24 h using a dialysis bag with a molecular weight cut-off of 3500 Da and then freeze-dried to obtain traditional carbon quantum dot powder, labeled as CQD-0.

[0042] The yields of the pine-derived hydrothermal carbon, traditional carbon quantum dots, the preparation conditions of the biomass carbon quantum dots in Example 1, Example 2, Example 3, and Example 4, as well as the corresponding yields, quantum yields, optimal excitation wavelengths, and optimal emission wavelengths are shown in Table 1.

[0043] Table 1

[0044]

[0045] By comparison, it is found that the highest yield of the carbon quantum dots prepared by Example 4 can reach 56.26%, which is 3.9 times that of the traditional carbon quantum dot synthesis method. The optimal absorption wavelengths of the carbon quantum dots are all in the ultraviolet region, and the optimal emission wavelengths are all in the blue light region, having the potential to convert ultraviolet light into blue light for culturing microalgae.

[0046] Example 5

[0047] This example is an evaluation example of culturing Chlorella vulgaris by adding traditional carbon quantum dots and the biomass carbon quantum dots prepared by the methods described in Example 1, Example 2, Example 3, and Example 4.

[0048] The Chlorella vulgaris is pre-cultured in a constant temperature incubator, and an LED lamp simulating sunlight is used to provide light. The Chlorella vulgaris is harvested in the logarithmic growth phase, washed, and then inoculated into a 250 ml gas washing bottle containing 100 mL of F / 2 medium at a concentration of about 0.1 g / L. The culture conditions are: the light intensity is set to 6000 lux, a 12-12 h light-dark cycle is adopted, and the temperature is maintained at 25 °C. The medium is bubbled through a mixed gas (Air / CO 2 mixed gas (Air / CO 2Aeration was carried out at (98 / 2), and the flow rate was controlled by a rotameter to be 0.6 vvm. When evaluating the effect of biomass carbon quantum dots prepared by the methods described in the traditional carbon quantum dots (control group), Example 1, Example 2, Example 3, and Example 4 on the biomass of Chlorella vulgaris, the prepared carbon quantum dots CQD-0 (control group), CQD-1, CQD-2, CQD-3, and CQD-4 were added to the culture medium at a concentration of 25 mg / L, respectively. The blank control group did not add carbon quantum dots, and the biomass of Chlorella vulgaris after 12 d was measured. The experimental results were expressed as the mean ± standard deviation. Analysis of variance (ANOVA) and least significant difference test (LSD) were performed using SPSS 22.0 (IBM Corp., Armonk, NY), and the data were considered significant when p < 0.05. * indicates that the significance P < 0.05 compared with the blank control. ** indicates that the significance P < 0.01 compared with the blank control. The biomass of Chlorella vulgaris after culturing for 12 d was as Figure 5 shown. The biomass yields of each test group were all improved compared with the control group. Among them, the biomass carbon quantum dots (CQD-4) prepared by the method described in Example 4 had the best effect, and the minimum biomass of Chlorella vulgaris could reach 0.66 g / L, which was increased by 22.2% (P < 0.01) compared with the control group (0.54 g / L).

[0049] Example 6

[0050] This example is an evaluation example of culturing Chlorella vulgaris by adding biomass carbon quantum dots prepared by the method described in Example 4 at different concentrations. Except for the different concentrations of the biomass carbon quantum dots (CQD-4) prepared by the method described in Example 4 added to the culture medium, the other steps were the same as those in Example 5.

[0051] When evaluating the effect of adding biomass carbon quantum dots (CQD-4) prepared by the method described in Example 4 at different concentrations on the culture of Chlorella vulgaris, the prepared carbon quantum dots CQD-4 were added to the culture medium at concentrations of 0 mg / L (blank control group), 50 mg / L, and 250 mg / L, respectively. The final biomass of Chlorella vulgaris and the contents (dry weight) and corresponding yields of carbohydrates, proteins, and lipids in the cells were measured after 12 d. The experimental results were expressed as the mean ± standard deviation. Analysis of variance (ANOVA) and least significant difference test (LSD) were performed using SPSS 22.0 (IBM Corp., Armonk, NY), and the data were considered significant when p < 0.05. * indicates that the significance P < 0.05 compared with the blank control. ** indicates that the significance P < 0.01 compared with the blank control. The biomass results of Chlorella vulgaris after culturing for 12 d were as Figure 6 shown, and the (dry weight) and corresponding yields of carbohydrates, proteins, and lipids in the cells of each group of Chlorella vulgaris were as Figure 7As shown. It can be found that the optimal addition concentration of the prepared carbon quantum dots CQD-4 is 50 mg / L, corresponding to a Chlorella biomass dry weight of 753.46 mg / L, which is 40.01% higher than the 537.95 mg / L of the control group (P<0.01). The productivity of Chlorella protein reached 18.16 mg / (L·d), an increase of 49.95% over the control group (P<0.01). The productivity of Chlorella lipids reached 17.80 mg / (L·d), a significant increase of 66.57% over the control group (P<0.01). In addition, the addition of high concentrations of carbon quantum dots will inhibit the growth of Chlorella. The concentration of the carbon quantum dots prepared by the method should be optimized when used in microalgae culture.

[0052] In summary, the present invention provides a method for preparing high-yield biomass carbon quantum dots and their application in microalgae cultivation. The method uses pine sawdust as raw material, and the biomass carbon quantum dots synthesized by alkali-assisted oxidation process have high yield, excellent optical properties, good water solubility and biocompatibility. Its blue light emission characteristics match the absorption spectrum of microalgae photosynthetic system II (PSII), which can significantly improve the growth and metabolism of microalgae and enhance the value-added potential of microalgae. The present invention not only provides an efficient and environmentally friendly route for the preparation of biomass carbon quantum dots, but also provides a new strategy for high-value cultivation of microalgae and resource utilization of waste, with significant economic and environmental benefits.

Claims

1. A method for preparing biomass carbon quantum dots, characterized in that: The following steps are involved: Pine sawdust is used as a precursor material and is pretreated; the pretreated precursor material is subjected to a hydrothermal reaction to prepare pine-derived hydrothermal charcoal; the pine-derived hydrothermal charcoal is subjected to alkaline oxidation exfoliation by NaOH and H2O2 to extract carbon quantum dots.

2. The method for preparing biomass carbon quantum dots according to claim 1, characterized in that: The pretreatment is as follows: the precursor material pine sawdust is further crushed and passed through a 200-mesh sieve, washed with deionized water and then dried.

3. The method for preparing biomass carbon quantum dots according to claim 1, characterized in that: The specific preparation process of the pinewood-derived hydrothermal charcoal is as follows: the pretreated pinewood powder is mixed with deionized water to obtain a pinewood powder solution with a mass volume fraction of 10%, and the solution is placed under certain temperature conditions for hydrothermal reaction; after cooling and filtering, the solution is washed with deionized water and anhydrous ethanol to remove soluble impurities and dried to obtain the pinewood-derived hydrothermal charcoal.

4. The method for preparing biomass carbon quantum dots according to claim 3, characterized in that: The hydrothermal reaction conditions are: 200° C., 6 h, and a heating rate of 5° C. / min.

5. The method for preparing biomass carbon quantum dots according to claim 1, characterized in that: The method for extracting carbon quantum dots is as follows: dispersing pinewood-derived hydrothermal carbon in NaOH alkaline solution, stirring and heating to 80° C., slowly dripping H2O2 solution so that the mass fraction of hydrogen peroxide in the final alkaline solution reaches 1.2%-2.4%, and extracting for 1 hour; cooling to room temperature, filtering to obtain the extracted carbon quantum dot solution, using hydrochloric acid to adjust the pH of the alkaline solution to the applicable range of the dialysis bag, dialysis for 24 hours and then freeze-drying to obtain carbon quantum dot powder.

6. The method for preparing biomass carbon quantum dots according to claim 5, characterized in that: The concentration of the NaOH solution is 0.1-0.2 mol / L, and the ratio of the pine wood derived hydrothermal carbon to the NaOH solution is 0.1 g:50 mL.

7. The method for preparing biomass carbon quantum dots according to claim 5, characterized in that: The mass fraction of H2O2 added to the NaOH alkali solution finally reaches 1.2%-2.4%.

8. The method for preparing biomass carbon quantum dots according to claim 5, characterized in that: The dialysis used a dialysis bag with a molecular weight cut-off of 3500 Da.

9. Biomass carbon quantum dots, characterized in that The biomass carbon quantum dots are prepared by the preparation method of any one of claims 1 to 8.

10. Use of the biomass carbon quantum dots according to claim 9 in microalgae cultivation.

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