CN113667698A

CN113667698A - Microbial self-synthesis cadmium sulfide semiconductor, preparation method thereof and method for enhancing and fixing carbon dioxide

Info

Publication number: CN113667698A
Application number: CN202111043701.XA
Authority: CN
Inventors: 熊宇杰; 高超; 刘光宇; 高峰; 张宏玮
Original assignee: University of Science and Technology of China USTC
Current assignee: University of Science and Technology of China USTC
Priority date: 2021-09-07
Filing date: 2021-09-07
Publication date: 2021-11-19
Anticipated expiration: 2041-09-07
Also published as: CN113667698B

Abstract

The invention provides a microbial self-synthesis cadmium sulfide semiconductor, a preparation method thereof and a method for enhancing fixed carbon dioxide, wherein the preparation method of the semiconductor comprises the following steps: inoculating thiobacillus thioparus into a sulfur-containing culture medium for amplification culture, and centrifuging to obtain wet thalli; adding a mixed solution of cadmium nitrate and cysteine into the wet thalli, and performing adsorption culture to obtain a mixture; and introducing mixed atmosphere of carbon dioxide and oxygen into the mixture, culturing at constant temperature, and performing vacuum freeze drying to obtain the microbial self-synthesized cadmium sulfide semiconductor. The method is simple, low in cost and environment-friendly, and the prepared nano particles are small in size and uniform in distribution and have various advantages of high photoelectron excitation capability, good reusability, good stability and the like; under the irradiation of visible light, photoproduction electrons enter the interior of the bacteria to participate in carbon fixation circulation, so that the efficiency of carbon dioxide sealing and fixation is effectively improved.

Description

Microbial self-synthesis cadmium sulfide semiconductor, preparation method thereof and method for enhancing and fixing carbon dioxide

Technical Field

The invention belongs to the technical field of non-noble metal semiconductor nano materials, and particularly relates to a microbial self-synthesis cadmium sulfide semiconductor, a preparation method thereof and a method for enhancing and fixing carbon dioxide.

Background

Photocatalysis can convert solar energy into chemical substances by photochemical redox reactions under ambient conditions using electron/hole pairs generated by a photocatalyst, depicting the beautiful blueprint for achieving artificial carbon cycling. Due to the interest in photocatalytic materials, a large number of chemical photocatalysts have been developed. And chemical photocatalysts can be classified into two different categories-homogeneous photocatalysts and heterogeneous photocatalysts, according to well-defined reaction center sites. The former is usually a well-defined monoatomic metal center containing molecular complexes, while the latter is a surface science and solid state chemistry dependent design. Photocatalysis, and in particular photocatalytic carbon dioxide conversion, has entered a period of rapid development. However, due to the current state of the art, solar photocatalytic carbon dioxide conversion remains costly, long-term photo-instability, and low reactivity, and low activity and selectivity to multi-carbon products in addition to carbon-one products remains challenging. These challenges directly lead to inefficient catalytic processes and lack of product selectivity, especially for high value-added chemicals.

Natural biological organisms can specifically and efficiently catalyze the fixation of carbon dioxide to multi-carbon products by using a large number of enzymes. In this regard, semiconductor-based biological hybrids have been initiated, combining light-capturing semiconductors with catalytic organisms to achieve the conversion of carbon dioxide into higher value liquid fuels and chemicals beyond carbon-one products. Such a biological hybrid can combine the high light absorption capabilities of inorganic semiconductors with the high specific catalytic capabilities of biological catalysts, thereby surpassing the performance of a single chemical or biological pathway. In addition, the microorganism has wide distribution in nature, rapid growth and reproduction and easy separation and culture. However, successful cultivation of these bacteria and maintenance of their stability in semiconductor-based biosystems requires essentially uneconomical organic nutrients and anaerobic conditions, which severely limit their economic viability and applicability for practical use. Therefore, it is very important to the art to study a semi-artificial photosynthesis system based on inorganic salts for carbon dioxide fixation.

Disclosure of Invention

In view of the above, the present invention provides a microbial self-synthesized cadmium sulfide semiconductor, a preparation method thereof, and a method for enhancing carbon dioxide fixation, wherein the semiconductor uses a microorganism as a carrier, nano-scale cadmium sulfide nanoparticles are loaded outside cells of the microorganism, the cadmium sulfide generates photo-generated electrons by light irradiation, and the photo-generated electrons enter the cells through electron conduction to enhance carbon fixation circulation, thereby achieving the effect of enhancing carbon dioxide fixation.

The invention provides a preparation method of a microbial self-synthesis cadmium sulfide semiconductor, which comprises the following steps:

inoculating thiobacillus thioparus into a sulfur-containing culture medium for amplification culture, and centrifuging to obtain wet thalli;

adding a mixed solution of cadmium nitrate and cysteine into the wet thalli, and performing adsorption culture to obtain a mixture; the mass ratio of thiobacillus thioparus to cadmium nitrate to cysteine is (10-100) to (5-10);

and introducing mixed atmosphere of carbon dioxide and oxygen into the mixture, culturing at constant temperature, and carrying out vacuum freeze drying to obtain the microbial self-synthesized cadmium sulfide semiconductor.

In the invention, the microbial thiobacillus thioparus has short growth cycle and high yield, is suitable for industrial culture production, is a typical chemoautotrophic bacterium, has strong electron release capacity, sulfur metabolism capacity, high tolerance to toxicity and tolerance to pH change, can realize the reduction of exogenous carbon dioxide by transferring reductive substances such as protein, polysaccharide and the like inside and outside cells through a series of electrons participated by cytochrome C through classical Karlvin circulation in the growth and propagation processes, has a self-protection mechanism, can desulfurize and combine with sulfydryl in cysteine under the stimulation of exogenous cadmium to generate cadmium sulfide nano-particles with similar size and dense distribution on the surface of the bacterium, avoids the agglomeration of a traditional light absorption unit, simultaneously, the cadmium sulfide is used as a light absorption unit and can capture photogenerated electrons to enter the bacterium as extra reduction equivalent, plays a role in promoting the carbon dioxide fixation and growth of bacteria.

In the invention, the time of the amplification culture is 24-48 h; the rotating speed of the centrifugation is 6000-12000 rpm, and the time of the centrifugation is 5-20 min.

In the invention, the mass ratio of thiobacillus thioparus, cadmium nitrate and cysteine is (10-100) to 1 (5-10); more preferably 50:1: 10.

The pH value of the mixed solution is 6-8. The growth of bacteria in the pH range is proper, the self-protection mechanism can be fully excited under the influence of potential cadmium toxicity, cysteine is subjected to sulfydryl removal and is combined with cadmium ions to generate cadmium sulfide light absorption units with similar size and compact distribution, the cadmium sulfide light absorption units can be adsorbed on the surface of cells more easily, and the growth of the bacteria is greatly influenced when the pH is lower than 4 or higher than 8, so that the preparation of the nano cadmium sulfide light absorption units is hindered.

In the invention, the concentration of the wet thallus in the mixed solution is 1-10 g/L; within this concentration range, bacteria can be well dispersed in the culture medium, providing sufficient nucleation sites for nanoparticle formation, and further affecting the size, shape, etc. of the nanoparticles.

In the invention, the temperature of the adsorption culture is 26-30 ℃, and the time of the adsorption culture is 24-72 h.

In the invention, the volume ratio of the carbon dioxide to the oxygen is 4.5-5.5: 3, preferably 5: 3.

In the invention, the time for introducing the mixed atmosphere of carbon dioxide and oxygen is 5-20 min;

the vacuum freeze drying time is 5-20 h.

The invention provides a microbial self-synthesis cadmium sulfide semiconductor, which is prepared by the preparation method of the technical scheme;

the microorganism self-synthesis cadmium sulfide semiconductor comprises thiobacillus thioparus and cadmium sulfide nano-particles uniformly distributed on the surface of the thiobacillus thioparus;

the particle size of the cadmium sulfide nano-particles is 20-40 nm.

According to the invention, a microbial thallus self-protection mechanism is utilized to synthesize a nanoscale cadmium sulfide light absorption unit on the surface of a microbial cell, the size of the nano-particles is 20-40nm, meanwhile, the bacterium has a self-protection mechanism, sulfydryl in cysteine can be desulfurized and combined with the sulfydryl under the stimulation of exogenous cadmium, the densely distributed cadmium sulfide nano-particles with similar sizes are generated on the surface of the bacterium, meanwhile, the cadmium sulfide is used as the light absorption unit, and under the condition that a photoproduction cavity is effectively filled, photoproduction electrons are captured to enter the bacterium to serve as extra reduction equivalent and are applied to the fixation of carbon dioxide. Compared with a single chemical catalyst, the invention utilizes the synergistic effect of the microorganism self-protection mechanism and cysteine containing sulfydryl and cadmium ions, the microorganism self-protection mechanism can promote the generation and the uniform distribution of cadmium sulfide nano particles, and meanwhile, electron transfer can be generated between the microorganism and the cadmium sulfide nano particles, so that the transfer and the absorption of bacteria to electrons are enhanced, and the performance of the catalyst is far better than that of the single chemical catalyst.

The invention provides a method for fixing carbon dioxide by using a microbial self-synthesis cadmium sulfide semiconductor prepared by the preparation method in the technical scheme or the microbial self-synthesis cadmium sulfide semiconductor in the technical scheme, which comprises the following steps:

mixing the microorganism self-synthesized cadmium sulfide semiconductor with a sulfur-free culture medium, introducing a mixed gas of carbon dioxide and oxygen, and carrying out light irradiation reaction by using sodium lactate as a sacrificial agent.

In the invention, the volume ratio of carbon dioxide to oxygen in the mixed gas of carbon dioxide and oxygen is 4.5-5.5: 3, preferably 5: 3. The sodium lactate accounts for 0.1 wt%.

The time of the light irradiation reaction is 60-80 h; in a specific embodiment, the reaction time for light irradiation is 72 hours.

The formula of the sulfur-free culture medium is as follows:

the invention uses the kit to detect the content of Glutamate synthase (Glutamate synthase) which is a bacterial carbon dioxide fixation end product to express the capability of fixing carbon dioxide. The brand of the kit is a glutamic acid synthetase activity detection kit (D799301) of Shanghai biological engineering company.

The principle of enhanced carbon dioxide fixation is as follows: under visible light conditions, cadmium sulfide nanoparticles from biosynthesis excite photoelectrons to be transferred to cells through membrane-bound electron acceptors and then to enzymes in the calvin cycle through a series of electron transfer chains. The intimate contact of the biosynthetic cadmium sulfide nanoparticles with the bacterial cells improves the electron transfer from the cadmium sulfide nanoparticles to the cells. The Photosynthetic Electron Transfer (PET) chain mediates the conversion of photocatalytic electrons to enhanced regeneration of reduced coenzyme. Thus, these photo-generated electrons may interact with NADP + (the final electron acceptor in bacteria) via PET chain conduction, raising the reduced coenzyme level of the bacteria, leading to carbon dioxide reduction and immobilization. Subsequently, some important intermediates of the calvin cycle become key substances or cytoskeletal components in cells through a series of complex biochemical reactions including transamination, enhancing the carbon dioxide fixation ability of bacteria.

Compared with the prior art, the invention has the beneficial effects that:

1. according to the method for fixing the carbon dioxide by enhancing the microorganisms through the self-synthesized photocatalytic semiconductor, the microorganisms are used as carriers and synthetic substrates, and the prepared nanoparticles are small in size and uniform in distribution and have various advantages of high photoelectron excitation capability, high reusability, high stability and the like.

2. According to the preparation method of the microbial self-synthesis cadmium sulfide semiconductor, provided by the invention, the self-synthesis photocatalytic semiconductor enhanced microbial carbon dioxide fixing method can be formed by simply adding the divalent cadmium salt and the cysteine and combining and culturing the divalent cadmium salt and the cysteine with the microbes, and a high-temperature high-pressure and additional toxic reducing agent and stabilizing agent are not needed, so that the preparation process of the semiconductor is simple, the cost is low and the semiconductor is environment-friendly.

3. The method for fixing the carbon dioxide by enhancing the microorganisms through the self-synthesized photocatalytic semiconductor has the effects of enhancing the absorption and fixation of the microorganisms on the carbon dioxide, and is low in modification cost, good in enhancement effect and high in system stability.

Drawings

FIG. 1 is a diagram of the UV-VIS-IR absorption spectrum of the microbial self-synthesized nanoscale cadmium sulfide light-absorbing unit prepared in example 1 of the present invention;

FIG. 2 is a scanning electron microscope image of a microorganism self-synthesized nano-scale cadmium sulfide light absorption unit prepared in example 1 of the present invention;

FIG. 3 is a high-angle round dark-field scanning transmission electron microscope photograph of a microbial self-synthesized nanoscale cadmium sulfide light-absorbing unit prepared in example 1 of the present invention;

FIG. 4 is a target-rotating X-ray powder diffraction pattern of the microorganism self-synthesized nano-scale cadmium sulfide light absorption unit prepared in example 1 of the present invention;

FIG. 5 is a graph showing the real-time variation of reduced coenzyme in the carbon dioxide fixation experiment of the microorganism optically-driven and loaded with nanoscale cadmium sulfide light-absorbing units in example 2 of the present invention;

FIG. 6 is a graph showing the real-time change of glyceraldehyde-3-phosphate in the carbon dioxide fixation experiment of the microorganism optically-driven and loaded with the nanoscale cadmium sulfide light absorption unit in example 2 of the present invention;

FIG. 7 is a graph showing the values of dry weight of biomass in a carbon dioxide fixation experiment of a microorganism optically-driven to load a nanoscale cadmium sulfide light-absorbing unit in example 2 of the present invention;

FIG. 8 is a graph showing the real-time variation values of glutamate synthetase in the carbon dioxide fixation experiment of the microorganism optically-driven with nano-scale cadmium sulfide light-absorbing unit in example 2 of the present invention;

FIG. 9 is a graph showing the value of the real-time change of glutamate synthase in the carbon dioxide fixation experiment of the microorganism optically-driven to load the nano-scale cadmium sulfide light-absorbing unit in comparative example 1 according to the present invention;

FIG. 10 is an average of cell densities of different final states achieved by using different concentrations of cadmium nitrate as initial concentrations of light-absorbing units for synthesizing cadmium sulfide in comparative example 2;

FIG. 11 is a graph showing the effect of different initial cadmium nitrate concentrations on deposition rates in comparative example 2.

Detailed Description

To further illustrate the present invention, the following examples are provided to describe the microbial self-synthesis cadmium sulfide semiconductor, the preparation method thereof and the method for enhancing the fixation of carbon dioxide, which are provided by the present invention, but should not be construed as limiting the scope of the present invention.

Example 1

The preparation method of the microbial self-synthesis cadmium sulfide semiconductor comprises the following steps:

(1) inoculating Thiobacillus Thioparus (Thiobacillus Thioparus) bacterial liquid into a sterilized 40mL culture medium 1 under an aseptic condition, carrying out amplification culture at 26 ℃ and 160rpm for 48h, centrifuging at 10000rpm for 10min, collecting wet bacteria subjected to activation culture, and transferring to a new culture medium 1;

the composition of medium 1 is shown in the following table:

(2) preparing a storage solution of cadmium ions and cysteine, preparing a mixed solution with the concentration of 100mg/L, and adjusting the pH value to 7.0;

(3) adding a mixed solution of cadmium ions and cysteine into the culture medium 1 after the transfer described in the step (1) so that the final concentration of the cadmium ions in the mixed solution is 0.1mM and the concentration of the cysteine is 1 mM;

(4) and (3) introducing mixed gas of carbon dioxide and oxygen into a thiobacillus thioparus and cadmium ion and cysteine mixed sample for 10min, finally placing the sample at 27 ℃, reacting for 48h, and finally carrying out vacuum freeze drying for 10h to obtain the microbial self-synthesized cadmium sulfide semiconductor.

FIGS. 1 to 3 are respectively an ultraviolet-visible-infrared absorption spectrum, a scanning electron microscope picture and a high-angle annular dark field scanning transmission electron microscope picture of a microorganism self-synthesized cadmium sulfide semiconductor.

As can be seen from FIG. 1, thiobacillus thioparus is capable of extracellularly synthesizing cadmium sulfide light-absorbing units with smaller size;

as can be seen from FIG. 2, thiobacillus thioparus is capable of extracellularly synthesizing spherical cadmium sulfide light-absorbing units of 20-40 nm;

as can be seen from FIG. 3, thiobacillus thioparus can synthesize a spherical cadmium sulfide light absorption unit uniformly dispersed at 20-40nm outside cells;

as can be seen from FIG. 4, the light absorption unit of the nano-scale cadmium sulfide synthesized by the microorganism is of a face-centered cubic structure;

as can be seen from fig. 5, the nano-scale cadmium sulfide light absorption unit synthesized by the microorganism has 110 planes and 002 planes in the lattice.

Example 2Light-driven microorganism containing cadmium sulfide light absorption unit for enhancing carbon dioxide fixation efficiencyThe composition of the medium 2 described below corresponds to the composition of the above-described sulfur-free medium.

The obtained microorganism containing the self-synthesized nano-scale cadmium sulfide light absorption unit is evenly dispersed in the culture medium 2 after centrifugation. Injecting 25mL of carbon dioxide and 15mL of oxygen into all serum bottles under atmospheric pressure, and adding 0.1 wt% of sodium lactate as a sacrificial agent;

the 100W LED lamp with the AM1.5 optical filter is used for simulating sunlight, and the system is subjected to simulated sunlight photocatalysis for 12h/12h in a switching cycle;

setting up a sample comprising bacteria containing a cadmium sulfide light absorbing unit (light/dark) and bacteria containing no cadmium sulfide light absorbing unit (light/dark) to compare the photocatalytic effect;

at fixed time intervals (12h), 1mL aliquots of the photocatalytic reactions in Medium 1 and Medium 2 were extracted from the four groups and the amount of carbon dioxide-fixed end product Glutamate synthase (Glutamate synthase) was measured using the kit to indicate the carbon dioxide-fixing capacity.

FIG. 5 is a graph showing the real-time variation of glutamate synthetase in the carbon dioxide fixation experiment of the microorganism optically-driven and loaded with nanoscale cadmium sulfide light-absorbing units in example 2 of the present invention. As can be seen from fig. 5: under the illumination condition, the thiobacillus thioparus containing cadmium sulfide light absorption units achieves the average activity of 2.372 units of glutamic acid synthetase/10⁸The maximum amount of cells.

FIG. 6 is a graph showing the real-time variation values of reduced coenzyme in the carbon dioxide fixation experiment of the microorganism optically-driven and loaded with nanoscale cadmium sulfide light-absorbing units in example 2 of the present invention. As can be seen from fig. 6: under the illumination condition, the reduced coenzyme content in thiobacillus thioparus containing cadmium sulfide light absorption units reaches average 11.747pmol/10⁹The maximum amount of cells.

FIG. 7 is a graph showing the real-time change of glyceraldehyde-3-phosphate in the carbon dioxide fixation experiment of the microorganism optically-driven and loaded with the nanoscale cadmium sulfide light-absorbing unit in example 2 of the present invention. As can be seen from fig. 7: under the illumination condition, the content of 3-glyceraldehyde phosphate in thiobacillus thioparus containing cadmium sulfide light absorption units is reduced most slowly, and 1.84nmol/10 of the glyceraldehyde phosphate still exists after 72 hours of reaction⁸Maximum end value of cells.

FIG. 8 is a graph showing the values of dry weight of biomass in a carbon dioxide fixation experiment of a microorganism light-driven to load a nano-scale cadmium sulfide light-absorbing unit in example 2 of the present invention. As can be seen from fig. 8: under light conditions, thiobacillus thioparus containing cadmium sulfide light absorbing units reached a maximum biomass dry weight of 4.367g/L on average.

Comparative example 1

On the basis of example 2, a carbon dioxide fixation experiment of a microorganism carrying a nanoscale cadmium sulfide light-absorbing unit under light driving was performed under the same condition of 0.1 wt% of initial sodium thiosulfate by using sodium thiosulfate as a sacrificial agent. The experimental result shows that under the condition of 72h simulated sunlight, the sulfur sulfideThe sodium group only reaches 1.59 units of glutamic acid synthetase activity/10⁸A cell.

Comparative example 2

Through setting a series of experiments on the mass ratio of thiobacillus thioparus, cadmium nitrate and cysteine, the optimal group is screened so as to achieve the purposes of optimal deposition efficiency and maximum final state density of cells. At the same initial strain density (approximately equal to 3 multiplied by 10)⁶) And cadmium nitrate was added at different concentrations (0.1mM, 0.2mM, 0.3mM, 0.4mM, 0.5mM) at the same density cysteine concentration (1mM), and after the culture 48 was examined by an inductively coupled plasma mass spectrometer, the final concentration of cadmium nitrate in the supernatant was centrifuged. The results of the tests in FIG. 11 show that the initial cadmium nitrate concentration of 0.1mM reached a deposition rate of 98.76%. Meanwhile, the bacterial plate counting method is used for counting each group of bacterial colonies after culture, and the test result in FIG. 10 shows that: the final state of the group reached a mean value of 1.55X 10 bacteria density at an initial cadmium nitrate concentration of 0.1mM⁹cells/mL, therefore, 0.1mM cadmium nitrate was used as the initial concentration for synthesis of cadmium sulfide light absorbing units.

From the above embodiments, it can be seen that the method for preparing the microbial self-synthesis cadmium sulfide semiconductor provided by the invention uses the microbial thiobacillus thioparus as a carrier, and the nano-scale cadmium sulfide nanoparticles are loaded outside the cells of the microbes. In the nucleation process, a microorganism self-protection mechanism is excited, cysteine sulfydryl is desulfurized under the stimulation of cadmium ions, and the cysteine sulfydryl is combined with the cadmium ions to obtain a nano cadmium sulfide light absorption unit which is uniformly attached to cells; by controlling the proportion of cadmium ions and cysteine, the size of the nano particles can be controlled, the difficulty of size preparation is simplified, the conditions are mild, the process is simple, the cost is low, the yield is high, and the method is green and environment-friendly. Meanwhile, the cadmium sulfide light absorption unit with stable performance can be prepared under mild and convenient conditions, so that the cadmium sulfide light absorption unit has good photoresponse and the property of transferring electrons to microorganisms, and the carbon dioxide fixing efficiency is well enhanced. Therefore, the research has good research value and application prospect.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a microbial self-synthesis cadmium sulfide semiconductor comprises the following steps:

2. The method according to claim 1, wherein the time for the scale-up culture is 24 to 48 hours; the rotating speed of the centrifugation is 6000-12000 rpm, and the time of the centrifugation is 5-20 min.

3. The method according to claim 1, wherein the pH of the mixed solution is 6 to 8.

4. The method according to claim 1, wherein the concentration of the wet cells in the mixed solution is 1 to 10 g/L;

the temperature of the adsorption culture is 26-30 ℃, and the time of the adsorption culture is 24-72 h.

5. The method according to claim 1, wherein the volume ratio of the carbon dioxide to the oxygen is 4.5 to 5.5: 3.

6. The preparation method according to claim 1, wherein the time for introducing the mixed atmosphere of carbon dioxide and oxygen is 5-20 min;

the vacuum freeze drying time is 5-20 h.

7. A microbial self-synthesis cadmium sulfide semiconductor prepared by the preparation method of any one of claims 1 to 6;

the particle size of the cadmium sulfide nano-particles is 20-40 nm.

8. A method for fixing carbon dioxide by adopting the microbial self-synthesis cadmium sulfide semiconductor prepared by the preparation method of any one of claims 1 to 6 or the microbial self-synthesis cadmium sulfide semiconductor of claim 7, comprising the following steps:

9. The method according to claim 8, wherein the sacrificial agent accounts for 0.08-0.12% of the total mass of the reaction system.