CN115215386A - Preparation of nickel cobaltate nanoparticles and method for promoting dark fermentation to produce hydrogen - Google Patents
Preparation of nickel cobaltate nanoparticles and method for promoting dark fermentation to produce hydrogen Download PDFInfo
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Abstract
The invention provides a nickel cobaltate nanoparticle (NiCo) 2 O 4 NPs) preparation method and application thereof in producing hydrogen (H) by medium-temperature dark fermentation 2 ) In the process. Adding appropriate amount of NiCo 2 O 4 NPs (dosage range is 50-400 mg/L) can optimize microbial community structure of fermentation system and increase H 2 The enrichment of the producing strain and the strengthening of the Ding Suanxing fermentation way (which is proved by the gene prediction result) can obviously increase the H of dark fermentation 2 And (4) yield. The invention provides a theoretical basis for the resource application of the glucose wastewater by using the simulated glucose wastewater as a substrate.
Description
Technical Field
The invention relates to the field of composite material synthesis and clean energy production, in particular to nickel cobaltate nanoparticles (NiCo) 2 O 4 NPs) and application thereof in the process of producing hydrogen by dark fermentation.
Background
With the increasing severity of the two problems of energy consumption and environmental pollution, new energy sources need to be developed to replace fossil energy. Hydrogen (H) 2 ) Is a new energy source which is concerned by the world. H 2 The combustion heat value is high, the combustion product is water, and pollutants and carbon emission generated by using traditional energy sources are avoided. Thus, H 2 Is the cleanest energy carrier. H 2 The fuel cell can be widely applied to the fields of transportation, industry, building and the like, can provide high-efficiency raw materials, reducing agents and high-quality heat sources for industries such as oil refining, steel, metallurgy and the like, can also be applied to automobiles, rail transit and ships through the fuel cell technology, and reduces the dependence of long-distance and high-load traffic on fossil energy such as petroleum, natural gas and the like. Further, H 2 The system can also be applied to distributed power generation, and guarantees are provided for residential power utilization and commercial power utilization. As a secondary energy source, H is currently produced 2 The technology mainly comprises the steps of fossil energy steam reforming, biomass cracking, water photolysis, electrochemical water decomposition and biological H preparation 2 And so on. However, the first four methods cause environmental pollution risks or have the defect of high energy consumption. Production of H with the above four 2 Process comparison, biological preparation of H 2 The above problem does not exist.
Biological hydrogen production can be divided into photolysis of water to produce H 2 Fermentation of light to produce H 2 Dark fermentation for preparing H 2 . Photolytic water preparation of H 2 Microalgae and cyanobacteria use solar energy as energy and water as raw material, and decompose water into H through photosynthesis and a special hydrogen-producing enzyme system 2 And O 2 But in the presence of H 2 Resulting in the disadvantages of slow efficiency and low substrate conversion efficiency. Dark fermentation for preparing H 2 The heterotrophic anaerobic bacteria utilize organic matters such as carbohydrate to generate H through dark fermentation 2 . If industrial and agricultural wastes are adoptedThe treated waste gas is directly discharged, and the environment is polluted. The waste water from paper-making industry, fermentation industry, agricultural waste (straw, animal dung, etc.), and waste liquid from food industry are used as raw materials to biologically produce hydrogen, so that clean H can be obtained 2 And no additional large energy consumption. Most industrial wastewater and agricultural waste contain a large amount of carbohydrates such as glucose, starch and cellulose, and high molecular compounds such as starch can be degraded into monosaccharides such as glucose. Preparation of H by light fermentation 2 Is restricted by illumination and is easy to produce light pollution. However, dark fermentation produces H 2 The speed and the substrate conversion rate are higher than those of the former two, and simultaneously, various industrial and agricultural wastes can be used for producing H 2 Raw materials are environment-friendly.
Production of H by dark fermentation 2 Typical microorganisms in the process are mainly Clostridium (Clostridium), clostridium butyricum (c.butyricum), enterobacter (Enterobacter), bacillus (Bacillus), and the like. Wherein Clostridium (Clostridium) is a predominant microorganism for butyric acid fermentation, and has the advantages of easy culture, multiple available substrate types, and easy acquisition of high yield H 2 Is a dark fermentation to produce H 2 Of interest are microorganisms. However, there is no currently available NiCo 2 O 4 NPs optimize the production of H by Clostridium (Clostridium) dark fermentation 2 The literature reports.
Disclosure of Invention
The invention aims to provide a method for preparing nickel cobaltate nanoparticles (NiCo) 2 O 4 NPs) and applied to medium temperatures (35-40 ℃, most preferably 37 ℃). Fastest growth temperature of mesophilic microorganisms at 37 ℃) to produce H by dark fermentation 2 A process for increasing H by promoting the growth and reproduction of Clostridium (Clostridium) and Clostridium butyricum (C.butyricum) and the expression of related genes 2 Yield and production rate objectives; meanwhile, the process has the advantages of convenience in operation and easiness in large-scale implementation. NPs, abbreviation for nanoparticles.
In order to achieve the purpose, the invention adopts the technical scheme that:
the invention provides NiCo 2 O 4 A process for the preparation of NPs comprising the steps of:
(1) Firstly, weighing a proper amount of deionized water, ni (NO) 3 ) 2 ·6H 2 O、Co(NO 3 ) 2 ·9H 2 Adding O into deionized water according to the molar ratio of 1: 2 and fully dissolving. The concentration ranges of both can be selected as desired by one skilled in the art.
(2) Adding total metal ions and citric acid monohydrate into the sample obtained in the step (1) and stirring the mixture into a stable liquid. Then ammonia is slowly added dropwise to adjust the pH. Total metal ion means Ni 2+ And Co 2+ Total moles of (a).
(3) Stirring the intermediate product obtained in the step (2) for 0.5-3 h to form gel.
(4) And (4) drying the sample obtained in the step (3) in an oven to obtain a purple precursor.
(5) And (5) calcining the precursor obtained in the step (4) in a muffle furnace to obtain black powder.
(6) And (5) grinding the calcined product, and then alternately washing with deionized water and absolute ethyl alcohol.
(7) Drying the purified product obtained in the step (6) in a vacuum drying oven and grinding to obtain NiCo 2 O 4 NPs。
Preferably, in the step (2), the molar ratio of n (total metal ions) to n (citric acid monohydrate) is n (total metal ions) = 1: 1-2. More preferably, n (total metal ions) = n (citric acid monohydrate) = 1: 1 to 1.5.
Preferably, the aqueous ammonia in step (2) is adjusted to pH =1.5 to 3. Slowly dripping ammonia water at the dripping speed of 1 drop in 3-5 seconds. More preferably, the aqueous ammonia in step (2) is adjusted to pH = 1.8-2.2.
Preferably, the stirring condition in the step (3) is 60-90 ℃ for 2-3 h. More preferably, the stirring condition in the step (3) is 60 to 85 ℃ for 2 to 3 hours.
Preferably, the oven condition in the step (4) is 100-120 ℃ and 12-24 h.
Preferably, the precursor in step (5) is calcined in a muffle furnace under the condition of 400-800 ℃ for 3-6 h. More preferably, the precursor in step (5) is calcined in a muffle furnace under the calcination condition of 550-700 ℃ for 3-6 h.
Preferably, the product obtained by incineration in the step (6) is washed with deionized water and absolute ethyl alcohol for 2 to 5 times alternately after being ground, that is, the deionized water and the absolute ethyl alcohol are washed for 2 to 5 times respectively.
Preferably, the vacuum drying oven in the step (7) is dried for 12 to 24 hours at the temperature of between 40 and 80 ℃, and the vacuum degree is-0.1 MPa. Then taking out, grinding, sealing and storing to obtain NiCo 2 O 4 And (4) NPs. Calcining to obtain nano particles (the particle size range is 20-100 nm), washing, purifying, and fully grinding to obtain powder without sieving.
The invention provides NiCo prepared by the method 2 O 4 And (4) NPs. The NiCo 2 O 4 NPs are nickel cobaltate nanoparticles.
The NiCo 2 O 4 The X-ray diffraction pattern of NPs showed that 2 θ =18.9 °,31.1 °, 36.6 °, 38.4 °, 44.6 °, 53.8 °, 59.0 °, and 64.9 °, respectively, correspond to the spinel-type nickel cobalt ore (NiCo) having a card number of 20-0781 in the JCPDS standard document 2 O 4 NPs) (111), (220), (311), (222), (400), (422), (511), and (440) characteristic peaks. The XRD pattern has almost no impurity peaks, which indicates that the crystallinity and purity of the material are high. The X-ray photoelectron spectrum shows O1s, co 2p3 and Ni 2p3 peaks at 529eV, 780eV and 855eV, respectively.
JCPDS (Joint Committee on Powder Diffraction Standards): joint committee on powder diffraction standards, a term of art in X-ray diffraction analysis. In 1969, the Joint Committee on Powder Diffraction Standards (JCPDS) was established, which is specially responsible for collecting and collating Diffraction data of various substances, and uniformly classifying and numbering The data, and compiling The data into card publication, namely called PDF card (The Powder Diffraction is called PDF card File), and sometimes called JCPDS card.
Preferably, niCo prepared as described above 2 O 4 The atomic weight percentages of Co, ni, and O of the NPs were 62.8%, 12.9%, and 19.0%, respectively.
Preferably, niCo prepared as described above 2 O 4 NPs have a polyhedral structure with smooth surfaces, and the distribution of Co, ni and O is uniform.
NiCo of the invention 2 O 4 NPs can selectively improve H production under the condition of medium temperature 2 Activity of microorganism Clostridium (Clostridium) and Clostridium butyricum (C.butyricum), and optimization of H 2 The sludge microbial community structure of a dark fermentation system enhances the production of H by Ding Suanxing fermentation 2 Approach, promoting the related production of H 2 And (4) expressing the gene. In addition, niCo 2 O 4 NPs can release Co and Ni ions in a trace amount in weakly acidic fermentation liquor, and the ions supplement trace elements required by microorganisms.
The larger the specific surface area and the smaller the particle size, the more favorable the NiCo 2 O 4 The NPs promote electron transfer and thus accelerate hydrogen production. See Table 1 for example 1NiCo 2 O 4 NPs specific surface area data. Preferably, the BET specific surface area is 12.4249m 2 /g。
The invention also provides NiCo 2 O 4 Use of NPs in production of hydrogen by dark fermentation, niCo 2 O 4 NPs (neutral nitrogen plus phosphate) dark fermentation system H for increasing medium temperature (35-40 ℃, preferably 37 ℃), and 2 yield and rate.
The invention also provides NiCo 2 O 4 NPs promote dark fermentation to produce hydrogen (H) 2 ) The method is characterized by using NiCo 2 O 4 NPs (neutral-temperature neutral fermentation) system H for improving medium temperature 2 Yield and rate. The medium temperature is 35-40 ℃, preferably 37 ℃.
The invention also provides nickel cobaltate nanoparticles (NiCo) 2 O 4 NPs) to promote dark fermentation to produce hydrogen (H) 2 ) The method is characterized by comprising the following steps: culturing and domesticating sludge from citric acid wastewater plant at 35-40 deg.c in anaerobic condition, heating the domesticated inoculated sludge in water bath to enrich hydrogen producing bacteria, cooling to 35-40 deg.c, adding glucose and culturing under anaerobic condition to realize H 2 Mass propagation of producing bacteria.
The invention also provides NiCo 2 O 4 Production of H by NPs increased dark fermentation 2 A method of performance, comprising the steps of:
(1) Domesticating inoculated sludge: sludge (with water content of 90%) of a citric acid wastewater plant is cultured in an anaerobic environment for a period of time under the condition of 35-40 ℃ (preferably 37 ℃).
(2) The inoculated sludge domesticated in the step (1) is heated in water bath for a period of time at the temperature of 85-90 ℃ to realize H 2 Enrichment of producing bacteria while inhibiting the activity of methanogen.
(3) Cooling the sludge in the step (2) to 35-40 ℃ (preferably 37 ℃), adding glucose, and continuing culturing under anaerobic condition to realize mass propagation of hydrogen-producing bacteria.
(4) Batch dark fermentation experiment: three sets of parallel experiments were designed, and NiCo was performed 2 O 4 NPs are added into a dark fermentation reactor at different concentration levels, glucose and peptone are added as substrates, and 100-200 mL of domesticated and enriched H-producing substances are respectively inoculated 2 Sludge was inoculated and the reactor headspace was rapidly flushed with nitrogen to ensure an anaerobic environment. Preferably, niCo 2 O 4 The addition amount of NPs is 0-800 mg/L.
(5) In the step (4), the dark fermentation reactor is placed in a water bath kettle at 37 ℃ for fermentation to produce H 2 Performance evaluation, collection and measurement of H 2 And (4) yield.
Preferably, the sludge culture time in the step (1) is optimized to be 15-25 d.
Preferably, the water bath heating time in the step (2) is 30-45 min.
Preferably, the glucose adding amount in the step (3) is 0.1-0.2 g/L, and the culture is continued for 36-48 h under the anaerobic condition.
Preferably, the substrate is added in the step (4) in an amount of 10-15 g/L glucose and 0.1-0.2 g/L peptone.
Preferably, the nitrogen purge reactor headspace time in step (4) is between 10 and 30s.
Preferably, the gas generated in step (4) is collected by saturated NaOH solution, and the volume of alkali liquor removed is calculated by H 2 And (4) yield.
Production of H in dark fermentation 2 In-process NiCo 2 O 4 NPs not only increase the electron adsorption capacity by virtue of the quantum size effect and high specific surface area of the NPs, promote the electron transfer between the NPs and hydrogenase, but also release Co and Ni elements into H in a trace manner in fermentation liquor 2 The produced bacteria can supplement trace inorganic nutrient salt. These positive factors significantly increase H 2 Increasing activity and abundance of producing bacteria and promoting expression of related genes, thereby increasing H 2 And (4) yield.
Drawings
FIG. 1 is a NiCo of example 1 2 O 4 NPs X-ray diffraction patterns.
FIG. 2 is a NiCo of example 1 2 O 4 NPs elemental analysis profiles.
FIG. 3 is a NiCo of example 1 2 O 4 NPsX-ray photoelectron spectrum. Wherein a) is a full spectrum, b) O1s, c) Ni 2p, d) Co 2p.
FIG. 4 is NiCo of example 1 2 O 4 Electron scanning electron microscopy of NPs.
FIG. 5 is a NiCo of example 1 2 O 4 Accumulation of H in dark fermentation by the addition of NPs 2 Influence of the yield.
FIG. 6 is NiCo of example 1 2 O 4 Production of H by NPs addition in dark fermentation 2 The effect of the rate.
FIG. 7 is a NiCo of example 1 2 O 4 Production of H by NPs addition in dark fermentation 2 Soluble Metabolites (SMPs).
FIG. 8 is a NiCo of example 1 2 O 4 Production of H by NPs addition in dark fermentation 2 Profile of the effect of microorganisms at phylum (a) and genus (b) levels.
FIG. 9 is NiCo of example 1 2 O 4 Production of H by NPs addition in dark fermentation 2 The profile of the effect of microorganisms at the seed level.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The following examples are carried out on the premise of the technical scheme of the invention, and detailed embodiments and specific operation procedures are given, but the scope of the invention is not limited to the following examples.
Example 1
NiCo 2 O 4 Preparation of NPs
(1) 80mL of deionized water was first weighed and 2.91g of Ni (NO) was added 3 ) 2 ·6H 2 O (10 mmol) and 5.83g Co (NO) 3 ) 2 ·6H 2 O (20 mmol) was added to deionized water and dissolved well.
(2) 7.57g (42 mmol) of citric acid monohydrate was added to the solution obtained in step (1) and sufficiently dissolved with stirring. Slowly dropwise adding ammonia water to adjust the pH value to 2.
(3) And (3) reacting the solution obtained in the step (2) for 2 hours under the condition of water bath at the temperature of 80 ℃ by magnetic stirring.
(4) And (4) drying the sample obtained in the step (3) in a drying oven for 15h at the temperature of 110 ℃ to obtain a purple precursor.
(5) And (4) grinding the precursor obtained in the step (4), and calcining at 700 ℃ for 4h.
(6) Grinding the calcined product obtained in the step (5) into powder, and then alternately washing with deionized water and absolute ethyl alcohol for 3 times.
(7) And (4) drying the sample obtained in the step (6) in a vacuum drying oven at 60 ℃ for 24h. Taking out and grinding to obtain NiCo 2 O 4 NPs and sealed storage.
For the NiCo prepared 2 O 4 NPs were characterized as follows:
FIG. 1 is an X-ray diffraction pattern of NiCo 2 O 4 The diffraction peaks of NPs at 2 theta =18.9 degrees, 31.1 degrees, 36.6 degrees, 38.4 degrees, 44.6 degrees, 53.8 degrees, 59.0 degrees and 64.9 degrees respectively correspond to spinel NiCo with the number of 20-0781 in JCPDS standard document 2 O 4 The (111), (220), (311), (222), (400), (422), (511) and (440) diffraction peaks of the NPs correspond to each other. Also, there is no impurity peak in fig. 1 as a whole, which indicates that the purity of the prepared material is high.
FIG. 2 shows NiCo 2 O 4 Elemental Analysis (ANP) of NPs. The results showed that the atomic mass percentages of Ni, co and O were 12.9%, 62.8% and 19.0%, respectively.
FIG. 3 is NiCo 2 O 4 X-ray photoelectron spectra of NPs. FIG. 3a shows NiCo 2 O 4 NPs full spectrum plot, O1s, co 2p3 and Ni 2p3 orbitals show peaks at 529eV, 780eV and 855eV, respectively. When the nano material is characterized by XPS, the existence of C element is caused by material test, which indicates that the NiCo prepared by the method 2 O 4 The NPs are very pure. FIG. 3b shows XPS images of O1s and their fitted curves in NiCo 2 O 4 Two different oxygen components, labeled O1 and O2, are present in NPs. The peak O1 corresponds to the typical metal-oxygen bond in the oxide, with a binding energy value of 529.6eV; and the O2 peak at 530.9 eV represents an oxygen vacancy. Oxygen vacancy with mitigation of H + Resistance to movement and acceleration of its shuttling at the surface. FIG. 3c shows NiCo 2 O 4 The Ni 2p profile of the NPs, two peaks for 2p2/3 and 2p1/3 were 855.2eV and 872.3eV, respectively, indicating that Ni 2+ Existence, 860.5eV Peak evidences the existence of Ni 3+ 879.8eV Peak Explanation of Ni 2+ And Ni 3+ Coexistence phenomena. FIG. 3d is an XPS image of Co 2p with two peaks at 780.1eV and 795.5eV of 2p3/2 and 2p1/2, respectively, indicating that the material contains Co 3+ (ii) a Satellite peaks at 783.2eV and 802.9eV indicate Co 2+ Is present.
TABLE 1NiCo 2 O 4 Surface area characterization data for NPs
| Item | Data of |
| BET specific surface area | 12.4249m 2 /g |
| Average pore diameter of adsorption | 13.2636nm |
| Desorption ofAverage pore diameter | 1.7022nm |
Surface area characterization methods references:
zhou Gugong, li Jiang, huang Aigong, liu Min. Discussion of BET method for testing ternary material specific surface area conditions and routine maintenance [ J ]. Jiangxi chemical engineering, 2019 (05): 29-31.DOI
FIG. 4 shows a Scanning Electron Microscope (SEM) magnification of 20000 NiCo 2 O 4 NPs images, showing that the appearance of the particles had the shape of a polyhedron.
Example 2
The other steps are the same as in example 1 except for the reaction conditions. The reaction conditions are shown in Table 2.
TABLE 2
The product obtained in example 2 was subjected to X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy analysis, and specific surface area analysis, and was substantially the same as the product of example 1.
Example 3
Inoculation sludge domestication
The sludge comes from a certain citric acid wastewater treatment plant in Shandong and needs to be enriched with H 2 The producing strain comprises the following specific steps: anaerobic culture at medium temperature (37 deg.C) for 25d, and heat treatment in water bath at 90 deg.C for 40min to enrich H 2 Producing bacteria and inhibiting methane bacteria. Then cooling the sludge to 37 ℃, adding 0.15g/L glucose, and then carrying out fermentation reaction at medium temperature (37 ℃) for 48 hours to obtain the H produced by dark fermentation 2 A sludge inoculum.
For H production 2 The properties of the inoculated sludge were characterized and the results are shown in Table 3.
TABLE 3
Example 4
The other steps are the same as those in example 3 except for the reaction conditions. The reaction conditions are shown in Table 4.
TABLE 4
The properties of the seeded sludge obtained in example 3 were characterized and the results are essentially the same as in table 3.
Example 5
Batch dark fermentation for producing H 2 Scheme design:
three groups of parallel experiments are designed, and the domestication culture is carried out to obtain H 2 Respectively taking 150mL of inoculated sludge in a dark fermentation reactor, and adding NiCo with different dosages 2 O 4 NPs (0, 25, 50, 100, 200, 300 and 400 mg) are respectively dissolved in 150mL of deionized water, 5g of glucose and 0.1g of peptone are added, then the mixture is inoculated into a dark fermentation reactor to be mixed with inoculated sludge, and the volume is adjusted to 500mL by using the deionized water. Thus, in addition to glucose and peptone concentrations of 10g/L and 0.2g/L, respectively, for each reactor, different concentrations of NiCo were also present 2 O 4 NPs(0～800mg/L)。
In order to maintain the anaerobic environment, the headspace of each reactor was flushed with nitrogen for 30s, and three experiments were performed in a 37 ℃ water bath for dark fermentation.
Collecting gas generated by dark fermentation with saturated NaOH solution, H 2 Calculated by excluding the NaOH solution.
Measuring the volume of discharged alkali liquor every 3H in the dark fermentation process and converting the volume into H under standard condition 2 Volume, the fermentation broth was sampled every 6h and tested for Soluble Metabolite (SMPs) concentration and composition.
Production of H by dark fermentation 2 The results are shown in FIG. 5, and the relevant data are shown in Table 5. As can be seen from Table 5 and FIG. 5, when NiCo is used 2 O 4 Amount of NPs addedAt 50-600 mg/L, H can be obviously increased 2 The yield is improved by more than 20 percent; and maximum H was obtained at a dose of 400mg/L 2 Yield (259.7 mg/L glucose), vs control group H 2 The yield (193.8 mL/g glucose) increased by 34.0%. NiCo 2 O 4 H when the addition amount of NPs is 100-400 mg/L 2 The yield is obviously improved.
TABLE 5 NiCo 2 O 4 Amount of NPs added to H 2 Effect of yield
FIG. 6 and Table 6 are NiCo 2 O 4 Amount of NPs added to H 2 Producing a rate effect which indicates when NiCo is present 2 O 4 H when the addition amount of NPs is 50-600 mg/L 2 The production rate is obviously higher than that of a control group and is all higher than that of the control group by more than 20 percent; wherein the dosage is 400mg/L NiCo 2 O 4 The NPs fermentation group obtained the highest H at the 15 th hour of the experiment 2 Production rate, H vs. control 2 The production rate increased by 59.8%. However, niCo 2 O 4 When the addition amount of NPs exceeds 400mg/L, H 2 The production rate begins to decrease. NiCo 2 O 4 H when the addition amount of NPs is 400mg/L 2 The production speed is highest.
TABLE 6 NiCo 2 O 4 Amount of NPs added to H 2 Influence of production rate
FIG. 7 is the composition of SMPs in the fermentation broth after the reaction is completed. With NiCo 2 O 4 The NPs dose increased and the SMPs showed an increasing trend to some extent. When NiCo is added 2 O 4 When NPs increased to 400mg/L, SMPs reached a maximum (5.86 g/L) and increased 28.34% over control SMPs (4.57 g/L). NiCo 2 O 4 NPs can promote the conversion rate of the substrate within a certain range (50-400 mg/L), and the conversion rate isPhenomenon and H 2 The results of the yields were consistent. Acetic acid and butyric acid of SMPs in each experimental group accounted for 26% -31% and 58% -62% of SMPs, respectively, and were much larger than the sum of propionic acid and ethanol (the sum of propionic acid and ethanol was 10% -16% of SMPs). This shows that the dark fermentation path of the microorganism is mainly butyric acid type fermentation, the butyric acid type fermentation product contains butyric acid and acetic acid, and the conversion process is shown in formulas (1) to (2).
C 6 H 12 O 6 →C 3 H 7 COOH+2CO 2 +2H 2 (1)
C 6 H 12 O 6 +2H 2 O→2CH 3 COOH+2CO 2 +4H 2 (2)
The results of microbial analysis of the sludge after the completion of the dark fermentation are shown in FIG. 8 a. At the door level, firmicute predominates, and NiCo 2 O 4 At an NPs dose of 400mg/L, the Firmicute abundance is 84.04%, which is 6.61% greater than that of the control group (0 mg/L, 77.43%). This indicates that the appropriate amount of NiCo 2 O 4 NPs increase Firmicute abundance. The microorganisms are distributed in a structure at genus level as shown in FIG. 8b, and Clostridium sensisteroto 1 is the absolute predominance, with the highest H 2 The yield group (400 mg/L, 71.48%) had a 123.07% abundance of Clostridium sensistricto 1 that of the control group (0 mg/L, 58.08%). Since Clostridium sensisteroto 1 can decompose glucose and produce H 2 Therefore H is 2 The yield was positively correlated with the abundance of Clostridium sensustricto 1. Furthermore, clostridium sensisterio 1 belongs to Firmicute, which corresponds to the results of the detection of microorganisms at the gate level.
FIG. 9 shows NiCo 2 O 4 The effect of the NPs dose on the species level of the microorganism during dark fermentation. Clostridium butyricum (c. Butyricum) is the absolute dominance, and the relative abundance of clostridium butyricum is in NiCo 2 O 4 The amounts of NPs added were 49.88% and 62.51% when the amounts of NPs added were 0mg/L and 400mg/L, respectively. 400mg/L NiCo 2 O 4 NPs were increased 25.32% over blank (0 mg/L). Clostridium butyricum is a typical dominant microorganism in butyric acid fermentation, belonging to Clostridium sensistucto 1, which indicates a proper amount of NiCo 2 O 4 NPs (400 mg/L) promote the growth and the propagation of Clostridium sensustricto 1 mainly comprising Clostridium butyricum and strengthen the production of H by a butyric acid type fermentation way 2 And (4) capability.
In addition, when SMPs and microorganisms are analyzed, H is extracted 2 Sludge of the lowest yield group (800 mg/L), blank group and H 2 Comparing the groups with the highest yield, and finding that the SMPs and the hydrogen-producing bacteria with the advantages are lower than those of the control group. This indicates that the appropriate amount of NiCo 2 O 4 NPs (400 mg/L) contribute to H such as Clostridium butyricum 2 The growth and reproduction of the producing bacteria are excessively inhibited.
For blank group (0 mg/L) and H after dark fermentation 2 The microorganisms of the highest yield group (400 mg/L) and the lowest yield group (800 mg/L) were subjected to genetic analysis (see Table 7). The dark fermentation process is rich in the expression of genes that convert glucose to pyruvate and pyruvate to acetyl CoA: pyruvate kinase [ EC:2.7.1.40]And pyruvate ferredoxin/flavodoxin oxidoreductase [ EC: 1.2.7.1.2.7. ] -Alfa]Play a role in the metabolic pathways of K00873 and K03737, respectively. K00532 functions to encode ferredoxin hydrogenase [ EC:1.12.7.2 ]]Catalyzing the conversion of pyruvate to H 2 Is the most important H 2 Enzyme production, highest H in control group 2 The predicted gene abundance of the yield group is improved by 7.23%. The detailed data are presented in table 7 for the absolute abundance of key enzyme predictor genes. This confirms that the appropriate amount of NiCo 2 O 4 NPs (400 mg/L) contribute to the expression of the relevant genes to some extent and achieve high H 2 And (4) yield.
TABLE 7
The foregoing is a preferred embodiment of the present invention and modifications and variations may be made in the practice of the invention without departing from the principles thereof, which are intended to be within the scope of the invention.
Claims (10)
1. NiCo 2 O 4 Of NPsThe preparation method comprises the following steps:
(1) Weighing appropriate amount of deionized water, ni (NO) 3 ) 2 ·6H 2 O、Co(NO 3 ) 2 ·9H 2 Adding O into deionized water according to the molar ratio of 1: 2 and fully dissolving;
(2) Adding total metal ions and citric acid monohydrate into the sample obtained in the step (1) and stirring the mixture into stable liquid; then slowly dropwise adding ammonia water to adjust the pH value; total metal ion means Ni 2+ And Co 2+ Total moles of (a);
(3) Stirring the intermediate product obtained in the step (2) for 0.5-3 h to form gel;
(4) Drying the sample obtained in the step (3) in an oven to obtain a purple precursor;
(5) Calcining the precursor obtained in the step (4) in a muffle furnace to obtain black powder;
(6) Grinding the calcined product in the step (5), and then alternately washing with deionized water and absolute ethyl alcohol;
(7) Drying the purified product obtained in the step (6) in a vacuum drying oven and grinding to obtain NiCo 2 O 4 NPs。
2. The NiCo of claim 1 2 O 4 A process for producing NPs, which comprises,
in the step (2), the molar ratio of n (total metal ions) to n (citric acid monohydrate) is n (total metal ions) to n (citric acid monohydrate) = 1: 1-2. More preferably, n (total metal ions) = n (citric acid monohydrate) = 1: 1 to 1.5;
adjusting the pH value of the ammonia water in the step (2) to be 1.5-3; slowly dripping ammonia water at the dripping speed of 1 drop in 3-5 seconds. More preferably, the aqueous ammonia in step (2) is adjusted to pH =1.8 to 2.2.
3. The NiCo of claim 1 2 O 4 The preparation method of the NPs is characterized in that the stirring condition in the step (3) is stirring for 2-3 h at the temperature of 60-90 ℃. More preferably, the stirring condition in step (3) is 60 to 85 ℃ for 2 to 3 hours.
Preferably, the oven condition in the step (4) is 100-120 ℃ and 12-24 h.
4. The NiCo of claim 1 2 O 4 The preparation method of the NPs is characterized in that the precursor in the step (5) is calcined in a muffle furnace under the condition of 400-800 ℃ for 3-6 h. More preferably, the precursor in step (5) is calcined in a muffle furnace under the calcination condition of 550-700 ℃ for 3-6 h.
5. The NiCo of claim 1 2 O 4 The preparation method of the NPs is characterized in that the product obtained by burning in the step (6) is ground and then is washed by deionized water and absolute ethyl alcohol for 2-5 times alternately;
and (4) drying the mixture in the vacuum drying oven in the step (7) at the temperature of between 40 and 80 ℃ for 12 to 24 hours at the vacuum degree of-0.1 MPa.
6. NiCo produced by the method of any of claims 1 to 5 2 O 4 NPs。
7. The NiCo of claim 8 2 O 4 NPs, characterized in that said NiCo 2 O 4 The X-ray diffraction pattern of NPs showed that 2 θ =18.9 °,31.1 °, 36.6 °, 38.4 °, 44.6 °, 53.8 °, 59.0 °, 64.9 ° correspond to spinel-type nickel-cobalt ore (NiCo) with a card number of 20-0781 in the JCPDS standard document, respectively 2 O 4 NPs) (111), (220), (311), (222), (400), (422), (511), and (440) characteristic peaks; the X-ray photoelectron spectrum shows O1s, co 2p3 and Ni 2p3 peaks at 529eV, 780eV and 855eV respectively; the NiCo 2 O 4 The atomic weight percentages of Co, ni, and O of the NPs were 62.8%, 12.9%, and 19.0%, respectively.
8. The NiCo of claim 6 2 O 4 NPs, characterized in that said NiCo 2 O 4 The BET specific surface area of NP is 12.4249m 2 The adsorption aperture and the desorption aperture are 13.2636nm and 1.7022nm respectively.
9. The NiCo of any of claims 6 to 8 2 O 4 Use of NPs or NiCo prepared by the method of any of claims 1 to 5 2 O 4 Use of NPs in the production of hydrogen by dark fermentation, using NiCo 2 O 4 NPs (neutral fermentation System) for improving medium temperature dark fermentation system H 2 Yield and rate; preferably, niCo is used 2 O 4 NPs (neutral fermentation System) for improving medium temperature dark fermentation system H 2 The medium temperature is 35-40 deg.C, preferably 37 deg.C.
10. The nickel cobaltate nanoparticles (NiCo) of claim 9 2 O 4 NPs) a method for promoting dark fermentation to produce hydrogen comprising the steps of: culturing and domesticating sludge from citric acid waste water plant at 35-40 deg.c in anaerobic environment, heating the domesticated inoculated sludge in water bath to enrich hydrogen producing bacteria, cooling to 35-40 deg.c, adding glucose for further culture under anaerobic condition to realize H 2 Mass propagation of producing bacteria.
Preferably, the nickel cobaltate nanoparticles (NiCo) 2 O 4 NPs) a method for promoting dark fermentation to produce hydrogen comprising the steps of:
(1) Domesticating inoculated sludge: the sludge of the citric acid wastewater plant is cultured in an anaerobic environment at the temperature of 35-40 ℃;
(2) The inoculated sludge domesticated in the step (1) is heated in water bath at the temperature of 85-90 ℃ to realize H 2 Enrichment of producing bacteria and inhibition of methanogen activity;
(3) Cooling the sludge in the step (2) to 35-40 ℃, adding glucose, and continuing culturing under an anaerobic condition to realize mass propagation of hydrogen-producing bacteria;
(4) Batch dark fermentation experiment: niCo 2 O 4 NPs are added into a dark fermentation reactor at different concentration levels, glucose and peptone are added as substrates, and 100-200 mL of domesticated and enriched H-producing substances are respectively inoculated 2 Inoculating sludge and rapidly flushing the reactor headspace with nitrogen gas to ensureAn anaerobic environment;
(5) The dark fermentation reactor in the step (4) is placed in a water bath kettle at 37 ℃ for fermentation to produce H 2 Performance evaluation, collection and measurement of H 2 And (4) yield.
More preferably, the sludge culture time in the step (1) is optimized to be 15-25 d; the water bath heating time in the step (2) is 30-45 min; the addition amount of the glucose in the step (3) is 0.1-0.2 g/L, and the culture is continued for 36-48 h under the anaerobic condition; the adding amount of the substrate in the step (4) is 10-15 g/L of glucose and 0.1-0.2 g/L of peptone; niCo 2 O 4 The addition amount of the NPs is 0-800 mg/L; and (5) flushing the headspace time of the reactor by using nitrogen in the step (4) for 10-30 s.
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