A preparation method of iron-doped carbon quantum dots and its application in photosynthetic hydrogen production

Abstract

The invention provides a preparation method of iron-doped carbon quantum dots and application thereof in photosynthetic hydrogen production, belonging to the technical field of crossover between materials and environmental energy. 3+ The material is prepared by a one-step hydrothermal method to obtain iron-doped metal carbon quantum dots; the iron-doped metal carbon quantum dots are added to a photosynthetic fermentation system using dark fermentation liquid of organic waste as a fermentation substrate. The present invention has the following advantages: (1) Environmental friendliness: reducing the pollution of organic waste to the environment; (2) High conversion efficiency: using iron-doped metal carbon quanta to broaden the available spectral properties of photosynthetic bacteria, and improving substrate conversion and light energy conversion rates; (3) Low time cost: using iron-doped metal carbon quanta to promote electron transfer and accelerate the hydrogen production rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of material and environmental energy intersection, and in particular relates to a method for preparing iron-doped carbon quantum dots and an application thereof in photosynthetic hydrogen production. Background Art

[0002] As the cleanest energy source in the 21st century, hydrogen energy can be produced through photosynthetic fermentation of organic waste, which has many advantages such as alleviating environmental pollution, low energy input and efficient energy output.

[0003] The existing types of hydrogen-increasing additives added to photosynthetic hydrogen production systems to promote the photosynthetic hydrogen production rate mainly include metal additives, amino acid additives, vitamin additives and chemical additives. Metal additives include metal monomers and metal oxides. The mechanism of promoting photosynthetic hydrogen production is mainly to promote nitrogenase activity and improve electron transfer efficiency. Different metal elements have different effects, and a combination of multiple elements is required to achieve complementary effects. Excessive concentrations of metal elements can cause cell poisoning, resulting in poor growth of photosynthetic bacteria. Amino acids and vitamin additives are essential substances for bacterial growth. By adding different types and concentrations of amino acids and vitamin additives, the optimal amount of addition is finally obtained. Chemical additives achieve different promotion effects by changing the external environment, such as defoamers, surfactants, degradation enzymes, pH buffers, etc. Chemical substances are precursors of all substances, and the composition of any substance will be affected by chemical substances. Therefore, chemical additives lack specificity.

[0004] Carbon quantum dots (CDs, <10 nm) are a new type of carbon nanomaterial that has attracted much attention due to its excellent photoelectric properties, water solubility, biocompatibility, non-toxicity, low cost, etc. It has significant photoluminescence (fluorescence) properties. Although carbon quantum dots can be used to promote hydrogen production, the efficiency of promoting hydrogen production is low. Summary of the invention

[0005] In order to solve the problem of low hydrogen production efficiency of photosynthetic system, the present invention proposes a preparation method of iron-doped carbon quantum dots (Fe-CDs) and its application in photosynthetic hydrogen production. Fe-CDs can increase photosynthetic fermentation hydrogen production by 20%.

[0006] To achieve the above object, the present invention provides a method for preparing Fe-CDs, comprising the following steps:

[0007] Step 1: Add the carbon source and the soluble trivalent iron source into water, and perform ultrasonication until uniform to obtain a mixed solution;

[0008] Step 2: subjecting the mixed solution to a hydrothermal reaction, and after the reaction is completed, cooling the mixed solution to room temperature;

[0009] Step 3: Centrifuge the reaction product of step 2, dialyze overnight and collect the filtrate;

[0010] Step 4: freeze-dry the filtrate from step 3 to obtain Fe-CDs.

[0011] Further, in the preparation method of Fe-CDs, in step 1, the molar ratio of the carbon source to the soluble trivalent iron source is 1:1.6. The carbon source is disodium ethylenediaminetetraacetate (EDTA-2Na), diethyltriaminepentaethylene (DTPA) or triethylenetetraaminehexaacetic acid (TTHA). EDTA-2Na, DTPA and TTHA are all carbon-containing metal chelators with good effects, which can form doping by better combining metal ions on the basis of providing carbon. Further, in the preparation method of Fe-CDs, in step 2, the reaction temperature is 180-210°C and the reaction time is 10-12h. Temperature and time will affect the yield, fluorescence intensity, carbonization degree and nanoparticle size of carbon quantum dots. Further, in the preparation method of Fe-CDs, in step 3, the centrifugal speed is 15000r / min and the centrifugal time is 20min; the purpose of centrifugation is to separate impurities and allow the carbon quantum dots to dialyze and retain substances with a molecular weight of 500-1000Da in the supernatant. The supernatant also contains small molecules such as tar and organic soluble substances. Dialysis is used to remove the small molecules while retaining the carbon quantum dots. The purpose of retaining the molecular weight of 500-1000Da is to retain the carbon quantum dots. The Fe-CDs obtained by the preparation method are used in photosynthetic hydrogen production. In the process of photosynthetic hydrogen production, Fe-CDs are used as hydrogenation additives.

[0012] Furthermore, the application of Fe-CDs in photosynthetic hydrogen production includes the following steps:

[0013] Step 1: Add hydrogen production culture medium and organic waste dark fermentation liquid into the photosynthetic fermentation tank;

[0014] Step 2: inoculating photosynthetic bacteria into a photosynthetic fermentation tank, wherein the amount of photosynthetic bacteria inoculated liquid is 20% to 30% of the total volume of the liquid in step 1;

[0015] Step 3: Adjust the pH, temperature and light intensity in the photosynthetic fermentation tank to the optimal conditions for photosynthetic bacteria to produce hydrogen;

[0016] Step 4: Add Fe-CDs into the photosynthetic fermentation tank and collect the fermentation gas.

[0017] Furthermore, in the application process of Fe-CDs in photosynthetic hydrogen production, in step 1, the components of the hydrogen production medium are: K2HPO4: 5.7 g / L, MgCl2: 0.2 g / L, NaCl: 2 g / L, yeast extract: 0.1 g / L, sodium glutamate: 2 g / L. K2HPO4 acts as a pH buffer, MgCl2 and NaCl provide metal ions and maintain physiological activity, yeast extract provides trace elements, and sodium glutamate provides a nitrogen source.

[0018] Furthermore, in the application process of Fe-CDs in photosynthetic hydrogen production, in step 1, the dark fermentation liquid of organic waste is diluted with water at a volume ratio of 1:2 and then added to the photosynthetic fermentation tank. As a carbon source for fermentation and hydrogen production, the dark fermentation liquid of organic waste has many organic acids remaining. During photofermentation, excessive organic acid content will inhibit the growth of photosynthetic bacteria, so it needs to be diluted to a suitable concentration. Furthermore, the dark fermentation liquid of organic waste is obtained by dark fermentation bacteria degrading macromolecular organic matter (such as starch, cellulose) in organic waste (kitchen waste, straw, etc.) into small molecular organic acids.

[0019] Furthermore, in the application process of Fe-CDs in photosynthetic hydrogen production, in step 2, the photosynthetic bacteria are inoculated in the logarithmic growth phase. Bacteria in the logarithmic growth phase are most active and metabolize quickly, and inoculation in the logarithmic growth phase is beneficial to hydrogen production.

[0020] Furthermore, in the application process of Fe-CDs in photosynthetic hydrogen production, in step 3, the pH is adjusted to 7.0±0.05, the temperature is adjusted to 30-35° C., and the light intensity is adjusted to 3000-5000 lux.

[0021] Furthermore, during the application of Fe-CDs in photosynthetic hydrogen production, in step 4, the concentration of Fe-CDs in the total liquid of the fermentation tank is 100-2000 mg / L.

[0022] The present invention adds the nutritional metal element Fe in the process of preparing carbon quantum dots. 2+ , which can promote the flow of substrate electrons to the hydrogen production pathway; and can act as a bioactivator to increase the activity of hydrogen-related enzymes, promote the transfer of electrons in enzymatic reactions, and accelerate hydrogen production. In the hydrogen production process, by adding iron-doped carbon quantum dots (Fe-CDs), the advantages of carbon quantum dots and metal elements are brought into play, greatly improving the rate of photosynthetic fermentation hydrogen production.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] (1) Environmental friendliness: Using dark fermentation liquid of organic waste as substrate for photosynthetic fermentation increases waste recovery rate and simultaneously treats dark fermentation liquid of organic waste to reduce secondary environmental pollution;

[0025] (2) Conversion efficiency: During the dark fermentation hydrogen production process, a large amount of small molecular organic acids will remain, which cannot be used by dark fermentation bacteria. Combining the characteristics of light fermentation bacteria using small molecular acids to produce hydrogen under anaerobic light conditions can maximize the hydrogen production rate. At the same time, due to the addition of Fe-CDs, the spectral band that can be used by photosynthetic bacteria is increased, which can effectively improve the light energy conversion rate.

[0026] (3) Low time cost: The addition of Fe-CDs promotes the flow of substrate electrons to the hydrogen production pathway, promotes the transfer of light-induced charges to the photosynthetic electron transport chain, accelerates the synthesis of bacterial photosynthetic pigments, and effectively reduces the fermentation time. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 The present invention is a flow chart of the preparation method of Fe-CDs and its application in photosynthetic hydrogen production;

[0029] Figure 2 Comparison of hydrogen production without adding Fe-CDs and adding 800 mg / L Fe-CDs;

[0030] Figure 3 The effect of different Fe-CDs concentrations on hydrogen production;

[0031] Figure 4 The effect of Fe-CDs prepared for different carbon sources on hydrogen production;

[0032] Figure 5 The effect of Fe-CDs prepared from different metal ion sources on hydrogen production;

[0033] Figure 6 Effect of Fe-CDs prepared under different reaction conditions on hydrogen production. DETAILED DESCRIPTION

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0036] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0037] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0038] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0039] The raw materials in the embodiments of the present invention can all be purchased.

[0040] The present invention does not limit the source of the photosynthetic bacteria, which can be obtained by purchasing a bacterial agent and then compounding it, or by sampling and enrichment. As long as the finally obtained bacterial community contains Rhodopseudomonas, Macellibacteroides, Acetoanaerobium, Enterococcus, Paraclostridium and Trichococcus, the proportion of each genus is not limited.

[0041] As an example, the photosynthetic bacteria in the following embodiments are enriched by the Environment and Energy +X Innovation Laboratory of Tianjin Commercial University, including 42wt% of Rhodopseudomonas, 20wt% of Macellibacteroides, 2wt% of Acetoanaerobium, 1wt% of Enterococcus, 5wt% of Paraclostridium, 9wt% of Trichococcus, and 21wt% of others.

[0042] The room temperature in the embodiments of the present invention refers to 25±2°C.

[0043] The preparation method of Fe-CDs of the present invention and its application in photosynthetic hydrogen production are shown in the flow chart Figure 1 .

[0044] The method for preparing dark fermentation liquid of organic waste in the embodiment of the present invention is as follows: the anaerobic fermentation liquid is removed from the anaerobic fermentation methanogenic system, and treated at 100° C. for 30 min (methanogens are inactivated) to obtain a dark fermentation hydrogen-producing mixed bacterial community. Organic waste food waste is used as a raw material, and a dark fermentation stage experiment is carried out under the conditions of 20 g VS / L organic load and 37° C. After the system reaction is nearing the end of 3-5 days, the fermentation tail liquid is collected and sieved (100 mesh) to obtain a dark fermentation liquid.

[0045] Example 1

[0046] (1) Dissolve 1 mmol EDTA-2Na and 1.6 mmol Fe(NO3)3·9H2O in 100 mL ultrapure water, sonicate until the solution is homogeneous, then transfer to a 100 mL polytetrafluoroethylene-lined autoclave and heat at 180°C for 10 h;

[0047] (2) After the reaction mixture was cooled to room temperature, it was centrifuged at 15000 r / min for 20 min to remove impurities;

[0048] (3) the supernatant was further dialyzed overnight using a dialysis bag with a molecular weight retention of 500 to 1000 Da, purified, and freeze-dried to obtain Fe-CDs powder, which was then redispersed in 100 mg / mL ultrapure water and stored at 4°C;

[0049] (4) Add 100 mL of hydrogen production medium to a 500 mL fermenter. Dilute the dark fermentation liquid of organic waste with water at a volume ratio of 1:2. Take 100 mL of the dilution and inoculate photosynthetic bacteria in the logarithmic growth phase at an inoculation ratio of 20 wt%. Adjust the pH to 7.0±0.05, the temperature to 30°C, the light intensity to 3000 lux, and add Fe-CDs at a concentration of 800 mg / L. The composition of the hydrogen production medium is: K2HPO4: 5.7 g / L, MgCl2: 0.2 g / L, NaCl: 2 g / L, yeast extract: 0.1 g / L, sodium glutamate: 2 g / L. Compared with the fermenter without Fe-CDs, the hydrogen production of the fermenter with Fe-CDs increased by 20% (see Figure 2 ).

[0050] Example 2

[0051] By changing the Fe-CDs concentration, the effect of different Fe-CDs concentrations on hydrogen production was investigated:

[0052] (1) Dissolve 1 mmol EDTA-2Na and 1.6 mmol Fe(NO3)3·9H2O in 100 mL ultrapure water, sonicate until the solution is homogeneous, then transfer to a 100 mL polytetrafluoroethylene-lined autoclave and heat at 180°C for 10 h;

[0053] (2) After the reaction is cooled to room temperature, centrifuge at 15000 r / min for 20 min to directly remove the product with large particle size from the resulting solution;

[0054] (3) The centrifugal supernatant was further dialyzed overnight using a dialysis bag with a molecular weight retention of 500-1000 Da, purified and freeze-dried to obtain Fe-CDs powder, which was then redispersed in 100 mg / mL ultrapure water and stored at 4 °C;

[0055] (4) Add 100 mL of hydrogen production medium to a 500 mL fermentation tank, dilute the dark fermentation liquid of organic waste with water at a volume ratio of 1:2, take 100 mL of the dilution, and inoculate photosynthetic bacteria in the logarithmic growth phase at an inoculation ratio of 20 wt%. Adjust the pH to 7.0 ± 0.05, the temperature to 30 ° C, and the light intensity to 3000 lux. Add Fe-CDs to a concentration of 0 mg / L, 400 mg / L, 600 mg / L, 1000 mg / L, 1200 mg / L and 1400 mg / L, respectively. The composition of the hydrogen production medium is the same as in Example 1.

[0056] As the Fe-CDs concentration increases, the hydrogen production of the fermentation system increases. When the concentration exceeds 800 mg / L, the hydrogen production decreases, but compared with the fermentation group without Fe-CDs addition, it still promotes hydrogen production (see Figure 3 ).

[0057] Example 3

[0058] By changing the carbon source, the effect of Fe-CDs prepared with different carbon sources on hydrogen production was investigated:

[0059] (1) 1 mmol of diethyltriamine pentaethylene (DTPA), triethylenetetraaminehexaacetic acid (TTHA) and 1.6 mmol of Fe(NO3)3·9H2O were dissolved in 100 mL of ultrapure water, ultrasonicated until the solution was homogeneous, and then transferred to a 100 mL polytetrafluoroethylene-lined autoclave and heated at 180°C for 10 h;

[0060] (2) After the reaction is cooled to room temperature, centrifuge at 15000 r / min for 20 min to directly remove the product with large particle size from the resulting solution;

[0061] (3) the supernatant was further dialyzed overnight using a dialysis bag with a molecular weight retention of 500 to 1000 Da, purified, and freeze-dried to obtain Fe-CDs powder, which was then redispersed in 100 mg / mL ultrapure water and stored at 4°C;

[0062] (4) 100 mL of hydrogen production medium was added to a 500 mL fermentation tank, and the dark fermentation liquid of organic waste was diluted with water at a volume ratio of 1:2. 100 mL of the dilution was taken and inoculated with photosynthetic bacteria in the logarithmic growth phase at an inoculation ratio of 20 wt%. The pH was adjusted to 7.0 ± 0.05, the temperature was adjusted to 30 ° C, the light intensity was adjusted to 3000 lux, and Fe-CDs was added at a concentration of 800 mg / L. The components of the hydrogen production medium were the same as those in Example 1.

[0063] Fe-CDs prepared with different carbon sources all have a promoting effect on the fermentation system, but the difference in the increasing effect of different Fe-CDs on hydrogen production is about 10%. Therefore, Fe-CDs with different carbon sources have the same trend in promoting hydrogen production, but the promoting effect is different (see Figure 4 ).

[0064] Example 4

[0065] By changing the Fe 3+ The effects of Fe-CDs prepared from different metal ion sources on hydrogen production were investigated:

[0066] (1) Dissolve 1 mmol EDTA-2Na and 2 mmol Fe(NO3)3·9H2O, FeCl3, and Fe2(SO4)3 in 100 mL ultrapure water, sonicate until the solution is homogeneous, and then transfer to a 100 mL polytetrafluoroethylene-lined autoclave and heat at 180 °C for 10 h.

[0067] (2) After the reaction is cooled to room temperature, centrifuge at 15000 r / min for 20 min to directly remove the product with large particle size from the resulting solution;

[0068] (3) the supernatant was further dialyzed overnight using a dialysis bag with a molecular weight retention of 500 to 1000 Da, purified, and freeze-dried to obtain Fe-CDs powder, which was then redispersed in 100 mg / mL ultrapure water and stored at 4°C;

[0069] (4) Add 100 mL of hydrogen production medium to a 500 mL fermenter, dilute the dark fermentation liquid of organic waste with water at a volume ratio of 1:2, take 100 mL of the dilution, and inoculate photosynthetic bacteria in the logarithmic growth phase at an inoculation ratio of 20 wt%. Adjust the pH to 7.0 ± 0.05, the temperature to 30 ° C, and the light intensity to 3000 lux. Add Fe-CDs at a concentration of 800 mg / L. The composition of the hydrogen production medium is the same as in Example 1.

[0070] Use different Fe 3+ The prepared Fe-CDs all have a promoting effect on the fermentation system, but the difference in the increasing effect of different Fe-CDs on hydrogen production is about 5%. Therefore, the Fe-CDs with different metal sources have the same trend in promoting hydrogen production, but the promoting effect is different (see Figure 5 ).

[0071] Example 5

[0072] The hydrothermal temperature and time were changed to investigate the effect of Fe-CDs prepared under different reaction conditions on hydrogen production:

[0073] (1) Dissolve 1 mmol EDTA-2Na and 1.6 mmol Fe(NO3)3·9H2O in 100 mL ultrapure water, sonicate until the solution is homogeneous, then transfer to a 100 mL polytetrafluoroethylene-lined autoclave and heat at 180°C for 12 h, 210°C for 10 h, and 210°C for 12 h, respectively;

[0074] (2) After the reaction is cooled to room temperature, centrifuge at 15000 r / min for 20 min to directly remove the product with large particle size from the resulting solution;

[0075] (3) the supernatant was further dialyzed overnight using a dialysis bag with a molecular weight retention of 500 to 1000 Da, purified, and freeze-dried to obtain Fe-CDs powder, which was then redispersed in 100 mg / mL ultrapure water and stored at 4°C;

[0076] (4) 100 mL of hydrogen production medium was added to a 500 mL fermentation tank, and the dark fermentation liquid of organic waste was diluted with water at a volume ratio of 1:2. 100 mL of the dilution was taken and inoculated with photosynthetic bacteria in the logarithmic growth phase at an inoculation ratio of 20 wt%. The pH was adjusted to 7.0 ± 0.05, the temperature was adjusted to 30 ° C, the light intensity was adjusted to 3000 lux, and Fe-CDs was added at a concentration of 800 mg / L. The components of the hydrogen production medium were the same as those in Example 1.

[0077] The Fe-CDs prepared at different reaction temperatures and reaction times have different promoting effects on the fermentation hydrogen production system, and the difference is large. The quantum yields at different temperatures and times are also very different. The best effect is heating at 180℃ for 10h, and the promoting effect of hydrogen production can reach 20% (see Figure 6 ).

[0078] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An application of iron-doped carbon quantum dots in photosynthetic hydrogen production, characterized in that: The following steps are involved: Step 1: Add hydrogen production culture medium and organic waste dark fermentation liquid into the photosynthetic fermentation tank; Step 2: inoculating photosynthetic bacteria into a photosynthetic fermentation tank, wherein the amount of photosynthetic bacteria inoculated liquid is 20% to 30% of the total volume of the liquid in step 1; Step 3: Adjust the pH, temperature and light intensity in the photosynthetic fermentation tank to the optimal conditions for photosynthetic bacteria to produce hydrogen; Step 4: adding iron-doped carbon quantum dots into a photosynthetic fermentation tank, collecting fermentation gas, and the concentration of iron-doped carbon quantum dots in the total liquid of the fermentation tank is 100-2000 mg / L; The method for preparing iron-doped carbon quantum dots comprises the following steps: Step (1): adding a carbon source and a soluble trivalent iron source into water, and ultrasonicating until uniform to obtain a mixed solution, wherein the molar ratio of the carbon source to the soluble trivalent iron source is 1:1.6; Step (2): subjecting the mixed solution to a hydrothermal reaction at 180-210° C. for 10-12 h, and cooling to room temperature after the reaction is completed; Step (3): centrifuge the reactant of step (2), dialyze overnight and collect the filtrate, the centrifugal speed is 15000r / min, the centrifugal time is 20min, and the dialyzed retention molecular weight is 500-1000Da; Step (4): freeze-drying the filtrate of step (3) to obtain iron-doped carbon quantum dots; The carbon source is disodium ethylenediaminetetraacetate, diethyltriaminepentaethylene or triethylenetetraaminehexaacetic acid; the soluble trivalent iron source is Fe(NO3)3·9H2O, FeCl3 or Fe2(SO4)3.

2. The use according to claim 1, characterized in that: In step 1, the composition of the hydrogen production medium is: K2HPO4: 5.7 g / L, MgCl2: 0.2 g / L, NaCl: 2 g / L, yeast extract: 0.1 g / L, sodium glutamate: 2 g / L.

3. The use according to claim 1, characterized in that: In step 1, the organic waste dark fermentation liquid is diluted with water at a volume ratio of 1:2 and then added into the photosynthetic fermentation tank.

4. The use according to claim 1, characterized in that: In step 2, the photosynthetic bacteria are inoculated during the logarithmic growth phase.

5. The use according to claim 1, characterized in that: In step 3, the pH is adjusted to 7.0±0.05, the temperature is adjusted to 30-35° C., and the light intensity is adjusted to 3000-5000 lux.

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