Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects and shortcomings in the background technology, and provide a carbon-based-multi-metal composite nano catalytic material capable of catalytically degrading high-concentration organic wastewater difficult to degrade, and a preparation method and application thereof.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a carbon-based-multi-metal composite nano catalytic material is prepared by taking microorganisms as an adsorbent, adsorbing multi-metal ions, carbonizing, and activating, wherein the multi-metal ions are loaded on the surface and in micropores of the carbon-based-multi-metal composite nano catalytic material in the form of nano particles of multi-metal simple substances and/or multi-metal oxides.
The invention relates to a nano catalytic material formed by carbonizing after adsorbing metal by living microorganisms, in particular to a carbon-based-multi-metal composite nano catalytic material which is prepared by taking the microorganisms as an adsorbent, adsorbing multi-metal ions, transporting the multi-metal ions to the inside of a body to generate an oxidation reduction reaction, insulating air for high-temperature carbonization, and activating after carbonization so that nano particles of multi-metal simple substances or multi-metal oxides are precipitated on the surface and in micropores of a carbonized microbial carbon-based material. Compared with the use of microorganism living bodies, the carbonized microorganism is not easy to lose and rot in the use process, is easy to store, and is easy to recycle after use.
Preferably, the multi-metal simple substance comprises one or more simple substances of copper, iron, manganese, aluminum, titanium, platinum, palladium and tungsten; the multi-metal oxide comprises CuO and Cu2O、FeO、Fe2O3、Fe3O4、MnO、MnO2、Mn2O3、Mn3O4、Al2O3、TiO、TiO2、Ti3O5、WO2、WO3、PtO2And oxides of one or more metals of PdO. The selected metal is a transition metal, inThe catalyst has wide application in the fields of ozone catalysis, photocatalysis and catalytic hydrogenation. The transition metal ions are calcined under the condition of oxygen deficiency, and the transition metal ions form metal oxides coexisting in a plurality of valence states due to the oxygen deficiency. Taking copper as an example, after the microorganism adsorbs copper ions, CuO and Cu are formed by calcining under the condition of oxygen isolation2O。
Preferably, the carbon-based-multi-metal composite nano catalytic material is irregular flaky nano carbon, and the size of the irregular flaky nano carbon is 20-500 nm; the particle size of the nano-particles of the multi-metal simple substance or the multi-metal oxide is 3-60 nm.
Preferably, the microorganism is Escherichia coli (Escherichia coli BL21) or Shewanella oneidensis MR-1. When the microorganisms adsorb metal ions, the surface groups of the microorganisms play a main role, so that the microorganisms containing groups such as hydroxyl, carboxyl, amino, sulfydryl, phosphoric acid and the like outside cells need to be selected, and in the microorganisms containing the groups, escherichia coli has larger adsorption capacity, while shiva can be reduced in vivo to form a metal simple substance.
The microorganism can adsorb various metal ions from the solution due to the characteristics of large specific surface area, abundant surface groups and the like, and after the microorganism adsorbs the metal ions, the surface of the microorganism is subjected to redox reaction to form micro-precipitates of metal simple substances or compounds; or metal ions are transported into cells through transmembrane transport, and a metal simple substance or compound precipitate is formed in the cells through a series of complex oxidation-reduction reactions, so that the multi-metal nano catalytic material formed by microorganisms has the properties of a common single-metal nano catalytic material, and also has a synergistic effect, an interface effect and a strain effect, and can be widely applied to the fields of electro-catalysis, photocatalysis and other catalysis.
Based on a general technical concept, the invention also correspondingly provides a preparation method of the carbon-based-multi-metal composite nano catalytic material, which comprises the following steps:
(1) inoculating the microorganisms to an LB culture medium for amplification culture, and centrifuging after a logarithmic phase is reached to obtain wet thalli;
(2) putting the wet thalli obtained in the step (1) into a multi-metal ion solution for adsorption, and centrifuging to obtain a microorganism-multi-metal ion mixture after adsorption is completed;
(3) centrifugally collecting the microorganism-polymetallic ion mixture obtained in the step (2), preparing dry powder through vacuum freeze drying, and then carrying out carbonization roasting in a protective atmosphere to obtain a carbon-based-polymetallic and/or polymetallic oxide compound;
(4) and (3) uniformly mixing the compound obtained in the step (3) with alkali metal hydroxide or soaking the compound in a zinc chloride solution, activating and roasting the mixture in a protective atmosphere, washing the mixture with distilled water until the pH value is unchanged, and drying the mixture to obtain the carbon-based-multi-metal composite nano catalytic material.
In the preparation process, the first roasting is used for carbonizing microorganisms adsorbed with metal ions in an oxygen-free state, and the second roasting is used for activating the carbonized metal-loaded charcoal by adding alkali metal hydroxide or soaking the carbonized metal-loaded charcoal by using a zinc chloride solution. After carbonization, the reactivation can obtain larger specific surface area and more pores than direct carbonization or direct activation, thereby influencing the performance of the ozone catalyst.
The preparation method of the invention avoids the problems of harsh conditions required by the existing hydrothermal synthesis method, sol-gel method, seed crystal method and the like, and the agglomeration of toxic reagents and metal nano particles added in the process. Therefore, the application potential of preparing the carbon-based-multi-metal composite nano catalytic material by adsorbing the multi-metal by the microorganisms is huge.
In the preparation method, preferably, in the step (1), the time for the expanded culture is 6-72 hours; the rotating speed of the centrifugation is 5000-16000 rpm, and the time of the centrifugation is more than 5 min.
Preferably, in the step (2), the adsorption temperature is 10-50 ℃, the adsorption time is more than 0.5h, and more preferably 0.5 h-6 h; the concentration of metal ions in the multi-metal ion solution is more than 50mg/L, and more preferably 50-300 mg/L; in the step (2) and/or the step (3), the rotation speed for centrifugation is more than 6000rpm, and the centrifugation time is more than 5min, more preferably more than 10 min. The above adsorption temperature range is suitable for the growth of microorganisms.
Preferably, in the step (3), the time for vacuum freeze drying is more than 0.5, and more preferably 0.5-10 h; in the step (4), the drying temperature is 105 ℃, and the drying time is more than 1 hour, and more preferably 1-24 hours.
Preferably, in the step (3) and/or the step (4), the protective atmosphere comprises argon or nitrogen, the roasting temperature is 300-1200 ℃, the roasting temperature rise rate is 5-20 ℃/min, and the roasting time is 0.5-3 h; in the step (4), the alkali metal hydroxide is KOH or NaOH.
In the invention, living microorganisms are used as an adsorption matrix, and after metal ions are adsorbed to the surface by the microorganisms, part of the metal ions are transferred into cells and reduced into metal simple substances through the action of oxidoreductase; after the cell surface is roasted at high temperature in the absence of oxygen, the metal ions combined with the biomacromolecules (oxygen-containing functional groups) on the cell surface generate a fracture reaction to form metal oxides. However, because of oxygen deficiency, the formed metal oxide has a large number of oxygen vacancies, so that the metal oxide can be regarded as different valence states; the reduced metal simple substance in the body is not oxidized due to the protection of nitrogen and the existence of the carbon simple substance. Therefore, the carbon-based-multi-metal nano catalytic material is a loose and porous structure and simultaneously contains a metal simple substance and a metal oxide with oxygen vacancy.
Based on a general technical concept, the invention also provides an application of the carbon-based-multi-metal composite nano catalytic material, and the carbon-based-multi-metal composite nano catalytic material is used for catalyzing and degrading organic matters in organic wastewater or promoting a nitrobenzene catalytic hydrogenation reaction.
In the above application, preferably, the organic wastewater is coking wastewater, and the COD concentration of the organic wastewater is 2500-20000 mg/L; mixing the carbon-based-multi-metal composite nano catalytic material with organic wastewater to obtain a mixture, wherein the concentration of the carbon-based-multi-metal composite nano catalytic material in the mixture is 0.5-10 g/L; the flow rate of the ozone is 1-2L/min, and the concentration of the ozone is 20-150 mg/L; after the reaction is finished, recovering the carbon-based-multi-metal composite nano catalytic material by a centrifugal or membrane separation method, wherein the centrifugal rotating speed is 5000-10000 rpm, and the centrifugal time is 1-15 min; the aperture of the filter membrane adopted by the membrane separation method is 0.05-0.5 mu m.
The carbon-based-multi-metal composite nano catalytic material can efficiently catalyze and degrade high-concentration organic wastewater, and on one hand, the specific surface area of the carbon-based-multi-metal composite nano catalytic material is large, so that the catalytic performance of the catalytic material is improved; secondly, the carbon-based-multi-metal composite nano catalytic material contains multi-metal simple substances or multi-metal oxides of nano particles, so that the surface of the carbon-based-multi-metal composite nano catalytic material has different properties of macroscopic multi-metal simple substances or multi-metal oxides, such as small-size effect, quantum effect and the like; and thirdly, the carbon-based-multi-metal composite nano catalytic material contains multi-metal, so that a synergistic effect exists among different metals during catalysis, and the catalytic degradation of organic matters in the organic wastewater can be promoted.
Compared with the prior art, the invention has the beneficial effects that:
1. the carbon-based-multi-metal composite nano catalytic material disclosed by the invention is large in specific surface area, rich in micropores, uniform in metal particle distribution, environment-friendly, capable of serving as a catalyst, loading multi-metal ions according to actual needs and wide in market application prospect, and has a synergistic effect, an interface effect and a strain effect.
2. The preparation method of the invention takes the microorganism as the carbon-based material, and can adsorb a plurality of metal ions through electrostatic action, ion exchange and complexation because the surface of the microorganism contains abundant hydroxyl, carboxyl, amino, sulfydryl, phosphate group and reducing carbohydrate, even if the selected microorganism has relative selectivity on the adsorption of the metal, the microorganism can still adsorb a plurality of metal ions at the same time, the microorganism is reduced to prepare the carbon-based material through carbonization and roasting, and then the carbon-based material is activated through activation and roasting.
3. The carbon-based-multi-metal composite nano catalytic material has good catalytic degradation effect on organic matters in high-concentration organic wastewater, and is strong in stability and high in treatment efficiency.
Detailed Description
In order to facilitate understanding of the invention, the invention will be described more fully and in detail with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.
Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein 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 present invention are commercially available or can be prepared by existing methods.
Example 1:
the carbon-based-multi-metal nano catalytic material takes a carbon-based material containing micropores, which is obtained by carbonizing and activating living Escherichia coli (Escherichia coli BL21), as a matrix, and Cu, CuO and Cu are loaded on the surface of the carbon-based material and in the micropores2O、Fe、FeO、Fe2O3、Fe3O4、Mn、MnO、MnO2、Mn2O3、Mn3O4、Al、Al2O3The carbon-based-multi-metal composite nano catalytic material is irregular flaky nano carbon, and the average size of the irregular flaky nano carbon is 80 multiplied by 300 nm; the mean particle diameter of the nanoparticles of the multimetal oxide was 33.4 nm.
The preparation method of the carbon-based multi-metal nano catalytic material in the embodiment comprises the following steps:
1) inoculating Escherichia coli (Escherichia coli BL21) under aseptic condition, performing amplification culture to 1L LB culture medium, performing shake culture at 20 deg.C for 48h to logarithmic phase, and centrifuging at 10000rpm for 15min to obtain wet thallus;
the formulation of LB medium was as follows: tryptone 10g/L, yeast extract 5g/L, sodium chloride 10g/L, and NaOH to adjust the pH of the medium to 7.4;
2) preparing a multi-metal ion solution with the total concentration of copper, iron, manganese and aluminum ions being 200mg/L, adding wet thalli into the prepared multi-metal ion solution, and stirring and adsorbing for 5 hours at 25 ℃; centrifuging for 15min at 10000rpm to obtain a mixture of Escherichia coli loaded with copper, iron, manganese and aluminum;
3) centrifuging a mixture of escherichia coli loaded with copper, iron, manganese and aluminum at 10000rpm for 15min, collecting, performing vacuum freeze drying for 10h to prepare dry powder, then performing roasting carbonization at 700 ℃ under the condition of nitrogen protection atmosphere, wherein the heating rate is 10 ℃/min, the roasting time is 1h, and cooling to obtain a carbon-based compound of copper, iron, manganese and aluminum simple substances and oxides thereof;
4) uniformly mixing the compound with KOH, roasting and activating at the temperature of 900 ℃ under the condition of nitrogen protection atmosphere, wherein the heating rate is 10 ℃/min, the roasting time is 1h, and cooling to obtain the carbon-based-polymetallic simple substance and polymetallic oxide nano catalytic material;
5) washing the carbon-based-polymetallic simple substance and polymetallic oxide nano catalytic material with distilled water until the pH value is unchanged, and drying at 105 ℃ for 8h to obtain a carbon-based-polymetallic nano catalytic material finished product (shown in figures 1 and 2).
As can be seen from FIG. 1, Escherichia coli can load uniformly dispersed nanoparticles of simple multi-metal substance and multi-metal oxide on the cell surface.
As can be seen from fig. 2, in the carbon-based multi-metal nano catalytic material obtained in this example, the multi-metal simple substance and the multi-metal oxide nanoparticles are uniformly distributed, and the carbon-based material is loose and porous.
Example 2:
the invention relates to a carbon-based-multi-metal nano catalytic material, which takes a carbon-based material containing micropores, which is obtained by carbonizing and activating living Shewanella oneidensis MR-1, as a matrix, and Pt and PtO are loaded on the surface and in the micropores of the carbon-based material2Multi-metal simple substances such as PtO, Pd, PdO and the like and multi-metal oxides, wherein the carbon-based-multi-metal composite nano catalytic material is irregular flaky nano carbon, and the average size of the nano catalytic material is 80 multiplied by 300 nm; the mean particle diameter of the nanoparticles of the multimetal oxide was 32.6 nm.
The preparation method of the carbon-based multi-metal nano catalytic material in the embodiment comprises the following steps:
1) inoculating Shewanella oneidensis MR-1 under aseptic condition, performing amplification culture to 1L LB culture medium, performing shake culture at 30 deg.C for 36h to logarithmic phase, and centrifuging at 8000rpm for 20min to obtain wet thallus;
the formulation of LB medium was as follows: tryptone 10g/L, yeast extract 5g/L, sodium chloride 10g/L, and NaOH to adjust the pH of the medium to 7.4;
2) preparing a multi-metal ion solution with the total concentration of platinum and palladium ions being 300mg/L, adding wet thalli into the prepared multi-metal ion solution, and stirring and adsorbing for 3 hours at the temperature of 30 ℃; then centrifuging for 15min under the condition of 10000rpm to obtain a mixture of Shewanella loaded platinum and palladium;
3) centrifuging a mixture of Shewanella-loaded platinum and palladium for 15min at 10000rpm, collecting, performing vacuum freeze drying for 10h to prepare dry powder, roasting at 800 ℃ under the condition of nitrogen protection atmosphere, wherein the heating rate is 10 ℃/min, the roasting time is 2h, and cooling to obtain a carbon-based compound of platinum, palladium and oxides thereof;
4) uniformly mixing the compound with KOH, roasting at the temperature of 900 ℃ under the condition of nitrogen protection atmosphere, wherein the heating rate is 10 ℃/min, the roasting time is 1h, and cooling to obtain the carbon-based nano catalytic material of the platinum, palladium elementary substance and oxide thereof;
5) washing the carbon-based-platinum, palladium elementary substance and the nano catalytic material of the oxide thereof with distilled water until the pH value is unchanged, and drying at 105 ℃ for 24h to obtain a carbon-based-multi-metal nano catalytic material finished product (as shown in fig. 3 and 4).
As can be seen from FIG. 3, Shewanella can load uniformly dispersed metal nanoparticles on the cell surface.
As can be seen from fig. 4, the carbon-based multi-metal nano-catalytic material obtained in this example can maintain the cell morphology.
Example 3:
the invention relates to a carbon-based-multi-metal nano catalytic material, which takes a carbon-based material containing micropores, which is obtained by carbonizing and activating living Shewanella oneidensis MR-1, as a matrix, and Ti, TiO and TiO are loaded on the surface of the carbon-based material and in the micropores2、Ti3O5、W、WO2、WO3The carbon-based-multi-metal composite nano catalytic material is irregular flaky nano carbon, and the average particle size of the carbon-based-multi-metal composite nano catalytic material is 80 multiplied by 300 nm; the mean particle diameter of the nanoparticles of the multimetal oxide is 33.5nm。
The preparation method of the carbon-based multi-metal nano catalytic material in the embodiment comprises the following steps:
1) inoculating Shewanella oneidensis MR-1 under aseptic condition, performing amplification culture to 1L LB culture medium, performing shake culture at 25 deg.C for 12h to logarithmic phase, and centrifuging at 10000rpm for 20min to obtain wet thallus;
the formulation of LB medium was as follows: tryptone 10g/L, yeast extract 5g/L, sodium chloride 10g/L, and NaOH to adjust the pH of the medium to 7.4;
2) preparing a multi-metal ion solution with the total concentration of titanium ions and tungsten ions being 200mg/L, adding wet thalli into the prepared multi-metal ion solution, and stirring and adsorbing for 1h at 40 ℃; then centrifuging for 15min under the condition of 10000rpm to obtain a mixture of Shewanella loaded titanium and tungsten;
3) centrifuging a mixture of Shewanella loaded titanium and tungsten for 15min at the rotation speed of 10000rpm, collecting, preparing dry powder by vacuum freeze drying for 12h, roasting at the temperature of 800 ℃ under the condition of nitrogen protection atmosphere, wherein the heating rate is 20 ℃/min, the roasting time is 2h, and cooling to obtain a carbon-based compound of titanium, tungsten simple substance and oxide thereof;
4) uniformly mixing the composite material with NaOH, roasting at the temperature of 1000 ℃ under the condition of nitrogen protection atmosphere, wherein the heating rate is 10 ℃/min, the roasting time is 1h, and cooling to obtain the carbon-based nano catalytic material of titanium, tungsten simple substance and oxide thereof;
5) washing the carbon-based-titanium and tungsten simple substance and the nano catalytic material of the oxide thereof with distilled water until the pH value is unchanged, and drying at 105 ℃ for 24h to obtain a carbon-based-multi-metal nano catalytic material finished product (as shown in figures 5 and 6).
As can be seen from FIG. 5, Shewanella can load uniformly dispersed metal nanoparticles on the cell surface.
As can be seen from fig. 6, the carbon-based multi-metal nano-catalytic material obtained in this example can be distributed in cells.
Example 4:
the application of the carbon-based-multi-metal composite nano catalytic material in the embodiment 1 in catalytic degradation of coking wastewater specifically comprises the following steps:
0.5g of the carbon-based-multi-metal composite nano catalytic material prepared in the example 1 is weighed and respectively put into 500mL of coking wastewater with a COD value of 2500-2800 mg/L, an aeration disc is used for carrying out ozone aeration on the coking wastewater, the ozone flow is 2L/min, the ozone concentration is 60mg/L, and after the ozone is catalyzed and oxidized for 60min, the COD removal rate reaches 75.49% (the removal amount reaches 2082.79 mg/L). Under the same conditions, the removal rate of COD by the commercial catalyst is 68.64 percent, 64.97 percent and 56.19 percent respectively (the effect of 1h treatment by ozone is shown in figure 7 and figure 8).
As can be seen from fig. 7 and 8, the carbon-based-multi-metal composite nano catalytic material of the present invention has superior performance to the catalyst in the market, can effectively promote the ozone catalytic coking wastewater, and has a good removal effect on coking wastewater.
After the reaction is finished, the carbon-based-multi-metal composite nano material is recovered by a membrane separation method, the aperture of the adopted filter membrane is 0.5 mu m, and the effect of multiple recovery and use is shown in figure 9.
As can be seen from FIG. 9, the carbon-based-multi-metal composite nano catalytic material can be continuously used for 5 times of catalytic degradation of coking wastewater, the catalytic capability of the carbon-based-multi-metal composite nano catalytic material is only slightly reduced, and the six degradation rates are all higher than 71%, which indicates that the carbon-based-multi-metal composite nano catalytic material has strong catalytic stability.
After the reaction is finished, the carbon-based-multi-metal composite nano material can be recovered by a centrifugal method, wherein the centrifugal rotation speed is 10000rpm, and the centrifugal time is 15 min.
Example 5:
the application of the carbon-based multi-metal composite nano catalytic material in the embodiment 2 in the catalytic hydrogenation of nitrobenzene specifically comprises the following steps:
5mg of the carbon-based-multi-metal composite nano-catalytic material prepared in the above example 2 was weighed and put into a mixed solution of 1mL of nitrobenzene and 19mL of methanol (solvent), and H was introduced2(N is introduced first2After air replacement, use H2Substitution of N2) The hydrogen amount is read by a gas meter, and after 30min, the prepared carbon-based-polyThe catalytic activity of the metal composite nano catalytic material is 1.87 times that of the catalyst.
The effect is shown in figure 10, which shows that the carbon-based-multi-metal composite nano catalytic material has better performance than the catalyst in the market, and can effectively promote the catalytic hydrogenation of nitrobenzene.
Example 6:
the application of the carbon-based-multi-metal composite nano catalytic material in the embodiment 3 in catalytic degradation of coking wastewater specifically comprises the following steps:
weighing 0.5g of the carbon-based-multi-metal composite nanoparticle material prepared in the example 3, respectively putting the weighed material into coking wastewater with the volume of 100mL and the COD value of 500-700 mg/L after ozone is excellent, respectively irradiating the coking wastewater with ultraviolet lamp tubes with the wavelengths of 187, 256 and 365nm, and after carrying out photocatalytic oxidation for 120min, enabling ultraviolet with the wavelength of 365nm to have no catalytic effect; 187. after ultraviolet catalysis with the wavelength of 256nm, the COD removal rates respectively reach 25.49 percent and 14.04 percent, and TiO is removed2Under the same conditions, the COD removal rate is 16.4 percent and 11.9 percent respectively.
The effect is shown in FIG. 11 (A catalyst is prepared carbon-based-multi-metal composite nano-particles, B is TiO)2) The carbon-based-multi-metal composite material has photocatalytic performance, can effectively promote the photocatalytic oxidation of coking wastewater, and has good removal effect on coking wastewater.
After the reaction is finished, recovering the carbon-based-degree-element metal nano catalytic material by a centrifugal or membrane separation method, wherein if the carbon-based-degree-element metal nano catalytic material is recovered by the centrifugal method, the centrifugal rotating speed is 10000rpm, and the centrifugal time is 15 min; if membrane separation is adopted for recovery, the aperture of the adopted filter membrane is 0.5 mu m.
In conclusion, the invention provides a carbon-based-multi-metal composite nano catalytic material, which can effectively degrade high-concentration mixed organic wastewater and provides a novel method for preparing the carbon-based-multi-metal nano catalytic material by utilizing microorganism-loaded multi-metal.