Microbial supported palladium-gold bimetallic nano-catalyst and preparation method and application thereof
Technical Field
The invention belongs to the technical field of precious metal nano-catalysts, and particularly relates to a microorganism supported palladium-gold bimetallic nano-catalyst, and a preparation method and application thereof.
Background
Compared with the traditional metal material, the nano-scale metal particles have quantum size effect, small size effect, surface effect and macroscopic quantum tunneling effect, and simultaneously show new effects caused by combination of nano-structures such as quantum coupling effect, synergistic effect and the like. The noble metal nanoparticles have unique optical, electrical and photo-thermal properties and are widely applied to the fields of catalysis, electronics, sensing, medicine, biological marking and the like. At present, the synthesis of noble metal nanoparticles mainly comprises a physical synthesis method, a chemical synthesis method and a microbiological synthesis method, wherein the physical synthesis method requires complex instruments and high-energy-consumption experimental conditions (such as vacuum, laser ablation and the like), and chemical reagents used in the chemical synthesis method have strong toxicity and can cause negative effects on the environment. The microbial synthesis method can be used for synthesis under relatively mild conditions, and has the advantages of environmental friendliness, greenness, low toxicity and the like. In addition, the microorganism has wide distribution in nature, rapid growth and reproduction and easy separation and culture.
Palladium (Pd) is one of the noble metals, and the nano-catalyst has very good hydrogenation reduction activity, however, the slow reaction kinetics, the inactivation of the active sites of the catalyst caused by CO and sulfide poisoning, and the instability of the catalytic performance are the main obstacles preventing the palladium nano-catalyst from achieving environmental improvement through hydrogenation reaction.
On the other hand, the microorganisms have variety, metabolic diversity and uncontrollable metabolic conditions, and the bimetallic ligand effect makes the electrocatalytic performance of the bimetallic nano-catalyst synthesized by the microorganisms unstable, so that the subsequent catalytic application has limitations, and the application of the bimetallic nano-catalyst in the electrocatalytic field is limited. At present, most reports about the microbial synthesis of the bimetallic nano-catalyst are focused on the application aspect, and no clear strategy is provided on the controllability of the electrical conductivity. In addition, because the biomass has low conductivity and cannot be directly used as an electrocatalyst, a carbonization reaction is usually required to improve the conductivity of microbial cells, but the method has high energy consumption and complex operation.
Disclosure of Invention
Aiming at the technical problems, the invention provides a microorganism supported palladium-gold bimetallic nano-catalyst and a preparation method and application thereof. The preparation method of the microbial supported palladium-gold bimetallic nano-catalyst can realize the preparation of the microbial supported palladium-gold bimetallic nano-catalyst with controllable morphology and particle size, obtains different products showing different activities in an electro-catalysis system, can be used for different electro-catalysis systems, and has the advantages of simple process, low cost and environmental protection.
In order to solve the technical problem, the embodiment of the invention adopts the following technical scheme:
in a first aspect, an embodiment of the present invention provides a preparation method of a microbial supported palladium-gold bimetallic nano-catalyst, specifically including the following steps:
s1, preparing dissimilatory metal reducing bacteria liquid;
s2, dissolving sodium tetrachloropalladate and sodium tetrachloroaurate in deionized water to obtain a palladium-gold mixed solution, adding the palladium-gold mixed solution into the bacterial solution, exposing nitrogen or inert gas to form an anaerobic environment, adding an electron donor to perform a reduction reaction for more than 3 hours, performing solid-liquid separation, and drying the obtained solid to obtain the microorganism supported palladium-gold bimetallic nano-catalyst, wherein the mass ratio of palladium ions to gold ions in the palladium-gold mixed solution is (1-9) to (9-1), and the mass ratio of the total mass of the palladium ions and the gold ions to the dissimilatory metal reducing bacteria is (1) (0.8-1.2).
The preparation method of the invention takes microorganism (dissimilatory metal reducing bacteria) as a carrier, and loads bimetal palladium and gold outside the bacterial cells under anaerobic conditions, wherein the palladium has excellent capacity of adsorbing and activating hydrogen molecules and can be used as a catalyst for hydrogenation reduction, and the gold nano-catalyst has excellent electron transfer function and anti-poisoning capacity, so that the poisoning phenomenon of the palladium in the chemical catalysis process can be well relieved, the catalysis efficiency is improved, and the catalytic activity of the palladium is improved. In addition, the surface palladium atom can generate an electronic effect on the gold atom, so that a bimetallic structure formed by the surface palladium atom and the gold atom has higher catalytic activity in a hydrogenation reaction.
The prior art does not describe the relationship between the particle size of the biological supported bimetallic nano-catalyst and the electrocatalytic activity, and researches show that the microbial supported palladium-gold nano-catalyst with different particle sizes can show different activities in an electrocatalytic system. The preparation method can realize the preparation of the microorganism load type palladium-gold bimetallic nano-catalyst with controllable particle size and realize the size control of the biological load type bimetallic nano-catalyst by simultaneously using the palladium and the gold and controlling the proportion of the palladium and the gold and the reduction reaction time, thereby ensuring that the electro-catalysis performance of the biological load type bimetallic nano-catalyst is stable and controllable and can be used for different electro-catalysis systems. The invention provides a thought and a way for further obtaining the bimetallic nano-catalyst with high catalytic activity, and widens the application range of the biological load type bimetallic nano-catalyst in the field of electrocatalysis.
The mass ratio of the total mass of the palladium ions and the gold ions to the mass of the dissimilatory metal reducing bacteria can ensure that the sodium tetrachloropalladate and the sodium tetrachloroaurate can be uniformly distributed on the bacteria, thereby ensuring the catalytic activity of the obtained catalyst. The bacteria solution can be subjected to quality control by OD value so as to satisfy the above-mentioned mass ratio, for example, when the total concentration of palladium ions and gold ions in the palladium-gold mixed solution is about 100mg/L, the OD value of the bacteria solution in S1 is selected to be about 0.2 so that the mass ratio of the total mass of palladium ions and gold ions to the mass of the dissimilatory metal reducing bacteria is in the range of 1 (0.8-1.2).
The preparation method has low requirement on equipment, mild preparation conditions, no need of toxic reagents, simple process, low cost and environmental friendliness, and has obvious advantages in the aspect of improving the environment through hydrogenation reaction.
Preferably, the dissimilatory metal-reducing bacterium is a bacterium belonging to the genus Shewanella (genus Shewanella), a bacterium belonging to the genus Terrabacter, a bacterium belonging to the genus Desulfovibrio (genus Desulfovibrio) or a bacterium belonging to the genus Escherichia (genus Escherichia), and further preferably a bacterium belonging to the genus Shewanella oneidensis (MR-1), a bacterium belonging to the genus Geobacter sulfuridus (PCA), a bacterium belonging to the genus Desulfovibrio (Desulfovibrio desulfurization) or a bacterium belonging to the genus Escherichia (Escherichia coli). For example, Shewanella onadatumis is a typical dissimilatory metal-reducing bacterium, has short growth cycle and high yield, and is suitable for industrial culture and production. Under the anaerobic condition, the bacteria can transfer reductive substances such as proteins, polysaccharides and the like inside and outside cells through electrons participated by a series of cytochromes C to realize the reduction of exogenous metal ions, and meanwhile, functional groups of biological macromolecules such as the proteins and the like can provide nucleation sites for the growth of nanoparticles and interact with the nucleation sites to prevent the aggregation of the nanoparticles, thereby playing roles in reduction and stabilization.
Preferably, the method for preparing the bacterial liquid in S1 comprises the following steps: the dissimilatory metal-reducing bacteria are inoculated in an amplification medium for amplification culture, then centrifuged, and resuspended in a buffer solution to fix the biomass.
Preferably, an anaerobic environment is formed by nitrogen aeration in S2.
Preferably, the electron donor in S2 is an aqueous solution of sodium formate. In the preparation method provided by the invention, the sodium formate is used as an electron donor, so that the obtained catalyst has a better catalytic effect. The concentration of the sodium formate aqueous solution is adjusted according to the molar weight of palladium ions and gold ions in the palladium-gold mixed solution, so that the molar number of electrons provided by the electron donor is more than that required by reduction of the palladium ions and the gold ions.
Preferably, the temperature of the reduction reaction in S2 is 25-35 ℃.
In a second aspect, the embodiment of the invention also provides a microbial supported palladium-gold bimetallic nano-catalyst prepared by the preparation method.
Preferably, in the preparation method, the time of the reduction reaction is 24 hours. Tests show that the particle size of the product can be increased along with the prolonging of the reaction time and finally tends to be stable, and when the reaction time reaches 24 hours, the product with good electrocatalytic activity can be obtained.
Preferably, in the preparation method, the mass ratio of the palladium ions to the gold ions is 1 (1.5-4). According to the invention, tests show that when the mass ratio of palladium ions to gold ions is 1 (1.5-4), the obtained catalyst has higher activity.
The electrocatalytic activity of the microorganism supported palladium-gold bimetallic nano-catalyst prepared under the specific conditions is higher than that of a commercial Pd/C catalyst, and the performance of the catalyst in electrocatalytic application is excellent.
In a third aspect, the embodiment of the invention also provides an application of the microbial supported palladium-gold bimetallic nano-catalyst in a high-activity electro-catalysis system.
The microorganism supported palladium-gold bimetallic nano-catalyst has excellent electro-catalytic activity and can be used for preparing a high-activity electro-catalytic system.
Preferably, the high-activity electro-catalysis system is a three-electrode system, the working electrode can be selected from carbon cloth, carbon paper or glassy carbon electrode and the like, the counter electrode can be selected from platinum mesh electrode or platinum wire electrode, the reference electrode can be selected from Ag/AgCl or saturated calomel electrode, and the microorganism supported palladium-gold bimetallic nano-catalyst is supported on the working electrode.
Preferably, the method for loading the working electrode with the microorganism-supported palladium-gold bimetallic nano-catalyst comprises the following steps:
and polishing, cleaning and drying the surface of the working electrode, dripping the microorganism supported palladium-gold bimetallic nano-catalyst on the surface of the working electrode, and then drying at room temperature.
The load capacity of the microorganism supported palladium-gold bimetallic nano-catalyst on the working electrode directly influences the activity of the obtained electro-catalysis system, and the load capacity can be selected according to actual requirements.
In an electrocatalysis system, the microbial load type palladium-gold bimetallic nano-catalyst prepared in the early stage is directly dripped on a working electrode without complex operations such as carbonization and the like, so that the cost of the biological load type bimetallic in the electrocatalysis application is greatly reduced.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, the microorganism supported palladium-gold bimetallic nano-catalyst is adopted, microorganisms are used as a reducing agent and a stabilizing agent, the palladium-gold bimetallic nano-catalyst can be quickly synthesized only by two steps of simple microorganism culture and reduction reaction, and high-temperature and high-pressure reaction conditions and additional toxic reagents are not required, so that the preparation process of the catalyst is simple, the cost is low, and the environment is friendly.
2. Compared with the general physical and chemical synthesis methods, the microbial supported palladium-gold bimetallic nano-catalyst with different particle sizes and compositions can be prepared by changing the mass ratio of palladium to gold and the reduction time, and the controllable preparation of the microbial supported palladium-gold bimetallic nano-catalyst with adjustable particle sizes and components is realized.
3. Compared with the limitation of the existing bimetallic nano-catalyst in the aspect of hydrogenation reduction, the microbial supported palladium-gold bimetallic nano-catalyst with adjustable particle size and components prepared by the method has adjustable catalytic activity in the hydrogenation reduction process of different systems (electrocatalysis and suspension).
Drawings
FIG. 1 is an SEM image of the microbial supported Pd-Au bimetallic nano-catalyst obtained in examples 1-15 of the present invention;
FIG. 2 is a fitting graph of linear relationship between different Pd ratios and the particle diameters of the obtained microbial supported Pd-Au bimetallic nano-catalyst in examples 1-5 of the present invention;
FIG. 3 is an LSV diagram of a glassy carbon electrode loaded with the microbial supported palladium-gold bimetallic nano-catalyst obtained in examples 1 to 5 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Unless otherwise defined, all terms of art used in the following examples have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in the following examples is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the following examples are commercially available or can be prepared by an existing method.
Example 1
The embodiment provides a microorganism supported palladium-gold bimetallic nano-catalyst, and the preparation method comprises the following steps:
1. preparing a bacterial liquid:
1) preparing 1L of LB culture medium, which comprises tryptone 10g, yeast extract 5g and NaCl 10g as main components, and has a pH value of 7.00 +/-0.02, and sterilizing at high temperature for later use;
preparing 2L PBS buffer solution with Na as main component2HPO4·12H2O 23.1g,NaH2PO4·2H2O5.44g,KCl 0.26g,NH40.62g of Cl, and sterilizing at high temperature for later use;
2) the Shewanella oneidensis MR-1 strain was inoculated into sterilized LB medium at an inoculum size of 1% under aerobic conditions, incubated at 35 ℃ at 140rpm for 12 hours, centrifuged at 6000rpm for 10 minutes,resuspend and wash with PBS buffer solution, repeat centrifugation 3 times, collect the bacterial liquid after activation culture. Adjusting the absorbance value of the bacterial suspension at 600nm to 0.2 (i.e., OD)6000.2) to obtain a bacterial liquid for later use.
2. Palladium-gold loaded bimetal
Dissolving sodium tetrachloropalladate and sodium tetrachloroaurate in deionized water to obtain a palladium-gold mixed solution (the total amount of palladium and gold is 100mg/L, the mass ratio of palladium to gold is 9:1), adding the palladium-gold mixed solution into the resuspended bacterial solution, and exposing to N2And after 20 minutes, adding 25mM sodium formate solution, placing the mixture on a magnetic stirrer, magnetically stirring the mixture at 140rpm for 24 hours at room temperature (below 30 ℃) to perform reduction reaction, then centrifuging the reaction product (6000rpm for 10 minutes), and performing vacuum freeze drying on the solid product obtained by centrifuging to obtain the microorganism supported palladium-gold bimetallic nano-catalyst.
Examples 2 to 18
Examples 2 to 18 provide the microbial supported palladium-gold bimetallic nano-catalyst prepared under different conditions, in the preparation method, the preparation of the bacterial liquid is the same as that in example 1, the mass ratio of palladium to gold and the reduction reaction time are shown in table 1, and other parameters are the same as those in example 1.
TABLE 1 examples 2-18 mass ratio of palladium and gold and time of reduction reaction
And (4) checking:
in the above embodiments, the color of the solution changes during the process of loading the pd/au bimetallic, and the SEM images of the supported pd/au bimetallic nanocatalysts obtained in examples 1-15 are shown in fig. 1. The upper corner marks of Pd and Au in the figure are used for representing the mass ratio of palladium to gold, such as bio-Pd9Au1The mass ratio of palladium to gold is 9:1, and the other is similar.
In the figure1, obvious particles on the surface of the thallus can be seen in the SEM image, which indicates that the microorganism supported palladium-gold bimetallic nanoparticles (bio-Pd)xAuyNPs) have been synthesized on the surface of the thallus, and the larger the mass ratio of Pd/Au, the more nanoparticle "dendrites" are formed.
Particle size measurements of the microbial supported palladium-gold bimetallic nano-catalysts prepared in examples 1-6 and 16-18 show that the particle sizes of examples 16, 6, 17, 18 and 2 are 49.08 + -5.34, 80.94 + -5.58, 95.26 + -6.13, 103.65 + -6.78 and 112.34 + -6.77 nm respectively. Similar conclusions were drawn for the products from the other examples, i.e. the particle size of the product increased with longer reaction times and finally stabilized.
The particle sizes of the products prepared in examples 1-5 are 120.91 + -7.09, 112.34 + -6.77, 88.94 + -6.06, 81.38 + -6.14 and 72.73 + -6.67 nm respectively, and it can be seen that the larger the mass ratio of Pd/Au, the larger the particle size of the obtained product. As can be seen from FIG. 2, the mass ratio of Pd/Au is remarkably adjusted in controlling the particle size of the prepared microbe-supported palladium-gold bimetallic nanoparticles, and the mass ratio of Pd/Au and the particle size show good linear relationship (R/Au mass ratio and particle size)2=0.958)。
The above results show that bio-Pd can be controlled by the Pd/Au mass ratio and the reduction reaction timexAuyParticle size of NPs.
Example 19
The embodiment provides an application of the microbial supported palladium-gold bimetallic nano-catalyst obtained in the embodiment 1-5 in preparing an electrocatalysis system:
and (3) respectively preparing a sodium tetrachloropalladate aqueous solution and a sodium tetrachloroaurate solution with gradient concentrations, and respectively drawing a palladium standard curve and a gold standard curve by flame Atomic Absorption Spectrometry (AAS) for measuring the total content of palladium and gold in the microbial supported palladium-gold bimetallic nano-catalyst prepared in the examples 1-5.
The microbial supported palladium-gold bimetallic nano-catalysts prepared in the above examples 1 to 5 were treated with aqua regia (concentrated HCl: concentrated HNO)3The volume ratio is 3:1), the total content of palladium and gold is measured after the palladium and gold are dissolved, and the palladium and gold are loaded on a glassy carbon electrode to prepare the palladium-gold alloy electrodeThe load capacity PdAu of palladium and gold is 50 mu g/cm2The glassy carbon electrode of (1). The method for loading the glassy carbon electrode with the microorganism supported palladium-gold bimetallic nano-catalyst comprises the following steps:
and respectively polishing the glassy carbon electrode by using alumina powder with the grain diameters of 1.00, 0.30 and 0.05 mu m, and then sequentially carrying out ultrasonic cleaning for 30s by using ethanol, deionized water and ethanol. And blowing nitrogen gas on the surface of the polished glassy carbon electrode for 1min to dry the glassy carbon electrode, dripping the microbial supported palladium-gold bimetallic nano catalyst obtained in the embodiment 1-5 on the surface of the glassy carbon electrode to load the corresponding catalyst on the surface of the glassy carbon electrode, and drying the glassy carbon electrode at room temperature for 12 hours.
The electrocatalysis system adopts a three-electrode system, wherein the working electrode is the glassy carbon electrode (the working area is 0.1256 cm)2) The counter electrode is a platinum mesh electrode (working area is 1 cm)2) And the reference electrode is Ag/AgCl. For comparison with commercial Pd/C catalysts, the loading capacity of the supported Pd-Au bimetallic nano-catalyst obtained in examples 1-5 on a glassy carbon electrode is selected as CPdAu=50μg/cm2。
And (4) checking:
50mM PBS (deoxidized) is prepared as a reaction system, and linear scanning voltammogram studies are carried out on glassy carbon electrodes respectively loading the microbial palladium-gold bimetallic nano-catalysts obtained in examples 1 to 5 in example 19 at a scanning speed of 10mV/s and a potential range of-1.0 to 0.1V (vs. Ag/AgCl), and the results are shown in FIG. 3.
As can be seen from FIG. 3, the catalyst obtained in example 4 has the highest electrocatalytic activity and is higher than that of the commercial Pd/C catalyst, while the catalysts obtained in other examples do not achieve the catalytic effect of the commercial Pd/C catalyst. This is mainly due to bio-Pd2Au8The NPs have proper and uniform particle size distribution on the surface of the microorganism, so that an effective conductive network is formed between microorganism cells and the surface of an electrode, and the transfer efficiency of electrons is improved. And from this, it can be inferred that the electrocatalytic system consisting of the glassy carbon electrode supporting the catalyst obtained in example 4 has the highest electrocatalytic activity.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.