CN113600194B - Nanometer photocatalyst containing cobalt with different valence states, preparation method and application thereof - Google Patents
Nanometer photocatalyst containing cobalt with different valence states, preparation method and application thereof Download PDFInfo
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- 239000011941 photocatalyst Substances 0.000 title claims abstract description 191
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 title claims abstract description 69
- 229910017052 cobalt Inorganic materials 0.000 title claims abstract description 68
- 239000010941 cobalt Substances 0.000 title claims abstract description 68
- 238000002360 preparation method Methods 0.000 title claims abstract description 35
- 238000001354 calcination Methods 0.000 claims abstract description 74
- 239000012921 cobalt-based metal-organic framework Substances 0.000 claims abstract description 53
- 239000002077 nanosphere Substances 0.000 claims abstract description 51
- 229910020599 Co 3 O 4 Inorganic materials 0.000 claims abstract description 36
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 26
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- 238000000034 method Methods 0.000 claims abstract description 25
- 239000002243 precursor Substances 0.000 claims abstract description 24
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 13
- 239000012752 auxiliary agent Substances 0.000 claims abstract description 10
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- 239000000203 mixture Substances 0.000 claims description 22
- 238000010438 heat treatment Methods 0.000 claims description 19
- 238000006243 chemical reaction Methods 0.000 claims description 16
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- 229910002092 carbon dioxide Inorganic materials 0.000 abstract description 24
- 239000001569 carbon dioxide Substances 0.000 abstract description 24
- 238000007540 photo-reduction reaction Methods 0.000 abstract description 18
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- DFGKGUXTPFWHIX-UHFFFAOYSA-N 6-[2-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperazin-1-yl]acetyl]-3H-1,3-benzoxazol-2-one Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)N1CCN(CC1)CC(=O)C1=CC2=C(NC(O2)=O)C=C1 DFGKGUXTPFWHIX-UHFFFAOYSA-N 0.000 description 2
- AFCARXCZXQIEQB-UHFFFAOYSA-N N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CCNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 AFCARXCZXQIEQB-UHFFFAOYSA-N 0.000 description 2
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
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- 206010003591 Ataxia Diseases 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 206010010947 Coordination abnormal Diseases 0.000 description 1
- GSEJCLTVZPLZKY-UHFFFAOYSA-N Triethanolamine Chemical compound OCCN(CCO)CCO GSEJCLTVZPLZKY-UHFFFAOYSA-N 0.000 description 1
- 229910021536 Zeolite Inorganic materials 0.000 description 1
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- VSANUNLQSRKIQA-UHFFFAOYSA-K trichlororuthenium hexahydrate Chemical compound O.O.O.O.O.O.Cl[Ru](Cl)Cl VSANUNLQSRKIQA-UHFFFAOYSA-K 0.000 description 1
- 230000007306 turnover Effects 0.000 description 1
- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/74—Iron group metals
- B01J23/75—Cobalt
-
- B01J35/39—
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/40—Carbon monoxide
Abstract
The application provides a non-containing materialThe method takes Co-MOF nanospheres without nitrogen as precursors and dicyandiamide as an auxiliary agent; calcining the Co-MOF nanospheres in an inert atmosphere to obtain a Co-C nano photocatalyst; or calcining Co-MOF nanospheres in inert atmosphere to obtain Co-C nano-photocatalyst, calcining Co-C nano-photocatalyst in air, and preparing (CoO+Co) by controlling calcining temperature and calcining time 3 O 4 ) -C nano-photocatalyst or Co 3 O 4 -a C nano photocatalyst. The preparation method of the nano photocatalyst containing cobalt with different valence states widens the selection range of precursor MOF, shortens the preparation period of the cobalt-carbon-based nano photocatalyst, and ensures that cobalt species are uniformly distributed in the nano photocatalyst in the form of small particles. The nano photocatalyst containing cobalt with different valence states is a high-efficiency photo-reduction carbon dioxide reaction catalyst.
Description
Technical Field
The application belongs to the technical field of nano photocatalytic materials, relates to a metal-carbon-based nano photocatalyst, and in particular relates to a nano photocatalyst containing cobalt with different valence states, a preparation method and application thereof.
Background
The photo-reduction of carbon dioxide refers to the use of light as an energy source, by adding a suitable catalyst to make CO 2 Is reduced to CO and CH under mild conditions 4 、CH 3 The reaction of OH and the like is an effective means for relieving energy shortage and greenhouse effect. The role of the catalyst in the photo-reduction of carbon dioxide is critical. Cobalt species are diverse in valence states and are CO 2 Has strong adsorption capacity and becomes an ideal active species of the photo-reduction carbon dioxide catalyst; the carbon-based material has excellent conductivity and can play a good role in dispersing active species. Therefore, the active cobalt species and the carbon-based material are combined, so that the cobalt-carbon-based photocatalyst with good catalytic performance can be obtained.
However, for cobalt-based photocatalysts, the different valence states of cobalt may have an impact on the performance of the photo-reduction carbon dioxide reaction. The preparation of photocatalysts containing cobalt of different valence states by controlling reaction conditions is an important precondition for studying the above effects. By calcining the cobalt-based metal-organic framework material (Co-MOF), the cobalt-carbon-based photocatalyst containing cobalt in different valence states and having excellent catalytic performance can be conveniently obtained. Currently, in the field of electrocatalysis, research has been conducted on preparing cobalt-carbon-based nanocatalysts containing cobalt in different valence states by calcining using nitrogen-containing MOF precursors, mainly zeolite imidazole ester framework materials (ZIFs). Specifically, there is literature on the preparation of Co-loaded nanoparticles, co@Co, using ZIF-67 as a precursor 3 O 4 Core-shell structured nanoparticles and Co 3 O 4 Three cobalt-carbon based nanocatalysts containing cobalt of different valence states of the hollow nanoparticle, but wherein cobalt exists in the form of Co and Co only 3 O 4 Two kinds; there is also literature on the use of ZIFs as precursors for the preparation of Co, coO and Co containing materials 3 O 4 Cobalt-carbon based nanocatalysts of nanoparticles. However, in the prior literature, on one hand, because the synthesis of the used precursor ZIF takes a long time, generally takes tens of hours, and the synthesis yield is low, the preparation period of the cobalt-carbon-based nano catalyst is greatly prolonged; on the other hand, the physical and chemical properties of MOF, such as morphology, crystallinity, porosity and the like, are greatly influenced by the organic ligand, and the unchanged use of ZIF as a precursor for preparing the cobalt-carbon-based nano-catalyst can lead to excessively single morphology, structure and other properties of the cobalt-carbon-based nano-catalyst. Therefore, the development of a novel precursor for preparing cobalt-carbon-based nano-photocatalyst is beneficial to preparing various cobalt-carbon-based nano-photocatalysts.
However, if the more widely existing nitrogen-free MOFs are used as precursors, the constituent particles of the high temperature calcined product tend to be large and heterogeneous in size due to the lack of nitrogen complexation. It follows that when using a nitrogen-free Co-MOF as a preparation precursor, it is difficult to ensure that the cobalt species are uniformly distributed in the form of small particles, although the preparation period can be shortened.
Disclosure of Invention
Aiming at the defects and shortcomings in the prior art, the application aims to provide a nano photocatalyst containing cobalt with different valence states, a preparation method and application thereof, and solves the technical problems that the MOF of a cobalt-carbon-based nano photocatalyst precursor is limited in selection and long in preparation period in the prior art.
In order to solve the technical problems, the application adopts the following technical scheme:
the preparation method of the nano photocatalyst containing cobalt in different valence states is characterized in that Co-MOF nanospheres without nitrogen are used as precursors, and dicyan diamine is used as an auxiliary agent;
calcining the Co-MOF nanospheres in an inert atmosphere to obtain a Co-C nano photocatalyst;
or calcining the Co-MOF nanospheres in an inert atmosphere to obtain Co-C nano-photocatalyst, and then calcining the Co-C nano-photocatalyst in air to obtain (CoO+Co) by controlling the calcining temperature and the calcining time 3 O 4 ) -C nano-photocatalyst or Co 3 O 4 -a C nano photocatalyst.
The application also has the following technical characteristics:
specifically, the Co-C nano photocatalyst is calcined in air, the calcination temperature is controlled to be 190-210 ℃, and the calcination time is controlled to be 10-25 min, so that (CoO+Co) is obtained 3 O 4 ) -a C nano photocatalyst;
or calcining the Co-C nano photocatalyst in air, controlling the calcining temperature to be 190-210 ℃ and the calcining time to be 45-150 min to obtain Co 3 O 4 -a C nano photocatalyst.
Specifically, the preparation process of the nitrogen-free Co-MOF nanospheres comprises the following steps: equimolar amount of Co (Ac). 4H 2 Adding O and isophthalic acid into a clean reaction container, pouring N, N-dimethylformamide, stirring and mixing, reacting in a constant-temperature oil bath at 120 ℃ for 120min to obtain a mixture, cooling the mixture to room temperature, centrifugally collecting a precipitate of the mixture, washing the precipitate with N, N-dimethylformamide and absolute ethyl alcohol for several times, and vacuum dryingObtaining Co-MOF nanospheres.
Specifically, the method comprises a first step and a second step; or the method comprises a first step, a second step and a third step; or the method comprises a first step, a second step and a fourth step;
step one, preparing a Co-MOF nanosphere containing no nitrogen:
equimolar amount of Co (Ac) 2 ·4H 2 Adding O and isophthalic acid into a clean reaction container, pouring N, N-dimethylformamide, stirring and mixing, reacting in a constant-temperature oil bath at 120 ℃ for 120min to obtain a mixture, centrifuging and collecting a precipitate of the mixture after the mixture is cooled to room temperature, washing the precipitate with N, N-dimethylformamide and absolute ethyl alcohol for a plurality of times, and then carrying out vacuum drying to obtain Co-MOF nanospheres;
step two, preparing a Co-C nano photocatalyst:
grinding the Co-MOF nanospheres in the first step, placing the ground Co-MOF nanospheres at one end of a quartz boat in the downwind direction, and placing auxiliary dicyandiamide at one end of the quartz boat in the upwind direction, wherein the mass of the dicyandiamide is 0.5-2.5 times that of the Co-MOF nanospheres; calcining at the calcining temperature of 450-800 ℃ and the heating rate of 1-10 ℃/min for 30-240 min under the protection of argon atmosphere to obtain the Co-C nano photocatalyst;
step three, preparing (CoO+Co 3 O 4 ) -C nano-photocatalyst:
calcining the Co-C nano photocatalyst in the second step in air, controlling the calcining temperature at 190-210 ℃, the heating rate at 1-5 ℃/min and the calcining time at 10-25 min to obtain (CoO+Co) 3 O 4 ) -a C nano photocatalyst;
step four, preparing Co 3 O 4 -C nano-photocatalyst:
calcining the Co-C nano photocatalyst in the second step in air, controlling the calcining temperature at 190-210 ℃, the heating rate at 1-5 ℃/min and the calcining time at 45-150 min to obtain Co 3 O 4 -a C nano photocatalyst.
Preferably, in the second step, the mass of the dicyandiamide is 1 time of that of the Co-MOF nanospheres; the calcination temperature is 500 ℃, the heating rate is 2 ℃/min, and the calcination time is 120min.
Preferably, in the third step, the calcination temperature is 200 ℃, the heating rate is 2 ℃/min, and the calcination time is 15min.
Preferably, in the fourth step, the calcination temperature is 200 ℃, the heating rate is 2 ℃/min, and the calcination time is 120min.
The application also provides a nano photocatalyst containing cobalt with different valence states, which is prepared by adopting the preparation method of the nano photocatalyst containing cobalt with different valence states.
Specifically, the nano photocatalyst containing cobalt with different valence states is a Co-C nano photocatalyst, (CoO+Co) 3 O 4 ) -C nano-photocatalyst or Co 3 O 4 -a C nano photocatalyst.
The application of the nano-photocatalyst containing cobalt with different valence states as a photo-reduction carbon dioxide reaction catalyst.
Compared with the prior art, the application has the beneficial technical effects that:
according to the preparation method disclosed by the application, the Co-MOF nanospheres without nitrogen are used as precursors, and the preparation period of the whole nano photocatalyst is greatly shortened due to the short synthesis period of the Co-MOF nanospheres; by adopting dicyandiamide as an auxiliary agent, the phenomenon that the nano particles formed by the MOF high-temperature calcined product are large in size and nonuniform in distribution due to the lack of coordination of nitrogen is avoided, and under the action of the dicyandiamide, the nano particles can be uniformly distributed in the nano photocatalyst in the form of small-size particles, so that the nano photocatalyst with excellent catalytic performance is obtained.
The preparation method of the application ensures that the selection range of the precursor MOF for synthesizing the cobalt-carbon-based nano photocatalyst is not limited to the nitrogen-containing MOF, thereby further enriching the morphology and structural characteristics of the nano photocatalyst.
And (III) the preparation method can prepare the cobalt-carbon-based nano photocatalyst containing cobalt with different valence states only by regulating and controlling the calcining temperature and the calcining time in the reaction process of synthesizing the nano photocatalyst.
The preparation method of the application has simple reaction process, can prepare by using simple equipment, and has the prospect of popularization to mass production.
The nano photocatalyst containing cobalt with different valence states of the application shows catalytic activity far superior to that of commercial cobalt-based catalysts in the photo-reduction carbon dioxide reaction, and is a high-efficiency photo-reduction carbon dioxide reaction catalyst.
Drawings
FIG. 1 is a schematic diagram of a method for preparing a nano-photocatalyst containing cobalt in different valence states.
Fig. 2 is an SEM image and a TEM image of the Co-C nano-photocatalyst in example 1, wherein a is an SEM image and b is a TEM image.
FIG. 3 is a graph of (CoO+Co) in example 2 3 O 4 ) -SEM images and TEM images of C nano-photocatalysts, wherein a is the SEM image and b is the TEM image.
FIG. 4 is Co in example 3 3 O 4 -SEM images and TEM images of C nano-photocatalysts, wherein a is the SEM image and b is the TEM image.
FIG. 5 shows the Co-C nano-photocatalyst, (CoO+Co) in examples 1 to 3 3 O 4 ) -C nano-photocatalyst and Co 3 O 4 XRD spectra of the C nano-photocatalyst, wherein 1 is XRD spectra of the Co-C nano-photocatalyst in example 1, and 2 is (CoO+Co) in example 2 3 O 4 ) XRD spectrum of C nano-photocatalyst, 3 is Co in example 3 3 O 4 -XRD spectrum of the C nano-photocatalyst; co, coO and Co 3 O 4 Corresponding spectral lines are Co, coO and Co respectively 3 O 4 Standard XRD patterns of the three substances.
FIG. 6 shows the results of examples 2 and 3 (CoO+Co 3 O 4 ) -C nano-photocatalyst and Co 3 O 4 HRTEM image and selected area electron diffraction image of C nanocatalyst, where a is (CoO+Co) in example 2 3 O 4 ) -C sodiumHRTEM image of Mimi photocatalyst, b is (CoO+Co) in example 2 3 O 4 ) Selected area electron diffraction image of C nano-photocatalyst, C is Co in example 3 3 O 4 HRTEM image of C nano-photocatalyst, d is Co in example 3 3 O 4 -a selected area electron diffraction image of a C nano-photocatalyst.
FIG. 7 shows the results of the photo-reduction of carbon dioxide in examples 4 to 6, wherein 1 is the result of the test of Co-C nano-photocatalyst in example 4, and 2 is (CoO+Co) in example 5 3 O 4 ) Test results of-C nano-photocatalyst, 3 is Co in example 6 3 O 4 Test results of C nano photocatalyst, 4 is test result of commercial Co catalyst, 5 is test result of commercial CoO catalyst, 6 is commercial Co 3 O 4 Test results of the catalyst.
Fig. 8 is an SEM image and a TEM image of the co—c nano photocatalyst in comparative example 1, where a is an SEM image and b is a TEM image.
Fig. 9 is a TEM image and an XRD spectrum of the Co-C nano-photocatalyst in comparative example 2, where a is a TEM image and b is an XRD spectrum.
Fig. 10 is an SEM image and an XRD spectrum of the CoO-C nano-photocatalyst of comparative example 3, where a is an SEM image and b is an XRD spectrum.
FIG. 11 is an XPS spectrum of the Co-C nano-photocatalyst in example 1 and comparative example 1, wherein a is a Co 2p XPS spectrum and b is an O1s XPS spectrum.
FIG. 12 is a thermal gravimetric graph of Co-C nano-photocatalyst in air in example 1.
FIG. 13 is Co in comparative example 4 3 O 4 XRD spectrum of the C nano-photocatalyst.
The technical scheme of the application is further described below by referring to examples.
Detailed Description
The preparation method of the nano photocatalyst containing cobalt with different valence states is shown in the figure 1, and the method takes Co-MOF nanospheres without nitrogen as precursors and dicyan diamine as an auxiliary agent; calcining Co-MOF nanospheres in an inert atmosphereObtaining a Co-C nano photocatalyst; or calcining Co-MOF nanospheres in inert atmosphere to obtain Co-C nano-photocatalyst, calcining Co-C nano-photocatalyst in air, and preparing (CoO+Co) by controlling calcining temperature and calcining time 3 O 4 ) -C nano-photocatalyst or Co 3 O 4 -a C nano photocatalyst.
In the application, the following components are added:
the photocatalysis test system is specifically a Labsor III-AI full-automatic online photocatalysis analysis system, which is purchased from Beijing Porphy science and technology Co., ltd (China); and was also equipped with a GC-7806 gas chromatograph, available from Beijing as a spectral analysis instruments Co., ltd (China).
The inductively coupled plasma spectrometer is specifically a Prodigy7 inductively coupled plasma emission spectrometer available from Leeman-Leeman Labs, inc. of America.
Commercial Co catalyst with the product number and specification of C804615-25g and CAS number of 7440-48-4; commercial CoO catalyst product number and specification C804560-25g, CAS number 1307-96-6; commercial Co 3 O 4 Catalyst size and specification C805292-100g, CAS number 1308-06-1; all three commercial cobalt-based photocatalysts were purchased from Shanghai Meilin Biochemical technologies Co.
(CoO+Co 3 O 4 ) the-C nano-photocatalyst refers to CoO and Co 3 O 4 While the nano-photocatalyst is supported on a carbon substrate.
Co-C nano photocatalyst, (CoO+Co) 3 O 4 ) -C nano-photocatalyst and Co 3 O 4 The C nano-photocatalyst is in particular a nanosphere photocatalyst consisting of nanoparticles.
The following specific embodiments of the present application are given according to the above technical solutions, and it should be noted that the present application is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solutions of the present application fall within the protection scope of the present application.
Example 1:
the embodiment provides a preparation method of a nano photocatalyst containing zero-valent cobalt, which comprises the following steps:
step one, preparing a Co-MOF nanosphere containing no nitrogen:
1mmol (249 mg) Co (Ac) 2 ·4H 2 Adding O and 1mmol (166 mg) of isophthalic acid into a clean single-neck flask, adding 40mL of N, N-dimethylformamide, stirring and mixing for 30min, and reacting in a constant-temperature oil bath at 120 ℃ for 120min to obtain a mixture; after the mixture is cooled to room temperature, centrifugally collecting the precipitate of the mixture, washing the precipitate with N, N-dimethylformamide and absolute ethyl alcohol for a plurality of times, and then carrying out vacuum drying to obtain Co-MOF nanospheres;
step two, preparing a Co-C nano photocatalyst:
grinding 60mg of the Co-MOF nanospheres in the step one, placing the ground Co-MOF nanospheres at one end of a quartz boat in the downwind direction, placing 60mg of auxiliary dicyandiamide at one end of the quartz boat in the upwind direction, and calcining the ground Co-MOF nanospheres for 120min under the protection of argon atmosphere at the calcining temperature of 500 ℃ and the heating rate of 2 ℃/min to obtain the Co-C nano photocatalyst;
the nano photocatalyst containing zero-valent cobalt prepared by the embodiment is specifically a Co-C nano photocatalyst, and the morphology of the nano photocatalyst is shown in figure 2.
Example 2:
the embodiment provides a preparation method of a nano photocatalyst containing cobalt in a divalent state and a trivalent state, which comprises the following steps:
step one is the same as step one of example 1;
step two is the same as step two of example 1;
step three, preparing (CoO+Co 3 O 4 ) -C nano-photocatalyst:
calcining 40mg of the Co-C nano photocatalyst in the second step in air, controlling the calcining temperature at 200 ℃, the heating rate at 2 ℃/min and the calcining time at 15min to obtain (CoO+Co) 3 O 4 ) -a C nano photocatalyst.
The nano-photocatalyst containing cobalt in the divalent state and the trivalent state prepared in the embodiment is specifically (CoO+Co) 3 O 4 ) The morphology of the C nano photocatalyst is shown in figure 3.
Example 3:
the embodiment provides a preparation method of a nano photocatalyst containing cobalt in a divalent state and a trivalent state, which comprises the following steps:
step one is the same as step one of example 1;
step two is the same as step two of example 1;
step four, preparing Co 3 O 4 -C nano-photocatalyst:
calcining 40mg of the Co-C nano photocatalyst in the second step in air, controlling the calcining temperature at 200 ℃, the heating rate at 2 ℃/min and the calcining time at 120min to obtain Co 3 O 4 -a C nano photocatalyst.
The nano photocatalyst containing cobalt in divalent and trivalent states prepared by the embodiment is specifically Co 3 O 4 The morphology of the C nano photocatalyst is shown in figure 4.
Example 4:
this example shows the use of the zero-valent cobalt-containing nano-photocatalyst prepared in example 1 as a photo-reduction carbon dioxide reaction catalyst, the specific steps of which are as follows:
step one, ultrasonically dispersing 10mg of nano photocatalyst and 20mg of terpyridyl ruthenium chloride hexahydrate in a mixed solvent consisting of 36mL of acetonitrile, 12mL of water and 12mL of triethanolamine to obtain a mixture A;
transferring the mixture A in the step one into a photo-reactor of a photo-catalytic testing system, controlling the temperature of the mixture A at 15 ℃ by using circulating condensate water, vacuumizing the photo-catalytic testing system, and filling high-purity carbon dioxide gas (with the purity of 99.999%) after vacuumizing operation is completed, so that the photo-catalytic testing system reaches a normal pressure state, and repeating the vacuumizing and carbon dioxide filling processes for three times;
step three, 100 mL/min- 1 Continuously introducing high-purity carbon dioxide gas into the photoreactor in the second step for 1h, and then sealing the photocatalysis test system to control the air pressure in the photocatalysis test system to be about 50 kPa;
step four, using a filter (lambda) with ultraviolet cut-off>400 nm) of a 300W xenon lamp as a light source at 400 mW.cm- 2 The mixture A is irradiated from the top of the photoreactor by the left and right light intensity to carry out photoreduction carbon dioxide reaction; the generated hydrogen was detected using a thermal conductivity detector, the generated carbon monoxide was detected using a hydrogen flame ionization detector, and the yield was calculated from the corresponding standard curve.
In this example, a commercial cobalt-based photocatalyst was used as a control group; commercial cobalt-based photocatalysts are specifically commercial Co catalysts, commercial CoO catalysts and commercial Co 3 O 4 A catalyst.
The calculation of the TOF (Turnover Frequency, conversion frequency) values is as follows:
the TOF value is obtained by dividing the molar quantity of the product by the molar quantity of cobalt element in the nano photocatalyst when the photo-reduction carbon dioxide is reacted for 2.5 hours and dividing the molar quantity by the reaction time of the photo-reduction carbon dioxide. The mass of cobalt element in the nano photocatalyst is obtained by testing an inductively coupled plasma emission spectrometer, and the molar quantity of cobalt element in the nano photocatalyst is obtained through calculation according to the mass of cobalt element. The test results of the photo-reduced carbon dioxide reaction are shown in fig. 7.
Example 5:
this example shows the use of the nano-photocatalyst containing cobalt in the divalent and trivalent states prepared in example 2 as a photo-reduction carbon dioxide reaction catalyst, the specific procedure of which is the same as that of example 4.
The control group in this example was the same as in example 4.
The calculation process of the TOF value in this embodiment is the same as that of embodiment 4. The test results of the photo-reduced carbon dioxide reaction are shown in fig. 7.
Example 6:
this example shows the use of the nano-photocatalyst containing cobalt in the divalent and trivalent states prepared in example 3 as a photo-reduction carbon dioxide reaction catalyst, the specific procedure of which is the same as that of example 4.
The control group in this example was the same as in example 4.
The calculation process of the TOF value in this embodiment is the same as that of embodiment 4. The test results of the photo-reduced carbon dioxide reaction are shown in fig. 7.
Comparative example 1:
this comparative example shows a method for preparing a nano-photocatalyst containing cobalt in zero valence state, which is substantially the same as example 1 except that no auxiliary agent is used.
The nano photocatalyst containing zero-valent cobalt prepared in this comparative example is specifically a Co-C nano photocatalyst, as shown in FIG. 8.
Comparative example 2:
the comparative example shows a process for the preparation of a nano-photocatalyst containing cobalt in the zero valence state, the specific procedure of which is substantially the same as that of example 1, except that urea is used as an auxiliary agent.
The nano photocatalyst containing zero-valent cobalt prepared in this comparative example is specifically a Co-C nano photocatalyst, as shown in FIG. 9.
Comparative example 3:
this comparative example shows a method for preparing a nano-photocatalyst containing cobalt in a divalent state, which is substantially the same as example 1, except that thiourea is used as an auxiliary agent.
The nano-photocatalyst containing cobalt in a divalent state prepared in this comparative example is specifically a CoO-C nano-photocatalyst, as shown in fig. 10.
Comparative example 4:
this comparative example shows a process for the preparation of a nano-photocatalyst comprising cobalt in the divalent and trivalent state, which is substantially identical to example 2, except that the calcination temperature in step three is 250 ℃.
The nano photocatalyst containing cobalt in divalent state and trivalent state prepared in the comparative example is specifically Co 3 O 4 -C nano-photocatalyst, as shown in fig. 13.
From fig. 2 to 13, the following can be concluded:
(A) As can be seen from FIGS. 2 to 4, co-C nano-photocatalyst, (CoO+Co) in examples 1 to 3 3 O 4 ) -C nano-photocatalyst and Co 3 O 4 -C nano-meterThe photocatalyst is a nanosphere with regular morphology, the monodispersity is good, the size and the position of the nano particles forming the nanosphere are uniformly distributed, and no obvious agglomeration large particles exist;
as can be seen from fig. 8, in comparative example 1, the size and position distribution of the nanoparticles constituting the co—c nano photocatalyst are extremely uneven, and agglomerated large particles exist locally;
as can be seen from fig. 9, in comparative example 2, the nanoparticles constituting the co—c nano photocatalyst were not uniform in size, although they were distributed uniformly in position, and large particles having a particle diameter of several tens of nanometers were present;
as can be seen from fig. 10, in comparative example 3, both the nanoparticle size and the position distribution of the constituent CoO-C nano-photocatalyst were extremely uneven.
From the comparison of examples 1 to 3 and comparative examples 1 to 3, it is understood that when the nano-photocatalyst is prepared using Co-MOF containing no nitrogen as a precursor, the size and position distribution of the constituent particles of the high temperature calcined product of the precursor tends to be non-uniform under an inert atmosphere. By adding dicyandiamide, the component particles can be uniformly distributed in the nano photocatalyst in the form of small-size nano particles, so that the dicyandiamide can effectively avoid migration, agglomeration and overgrowth of the nano particles, and plays a role in maintaining the uniformity of the small-size and position distribution of the nano particles. No auxiliary dicyandiamide was used, such as comparative example 1; or replacing dicyandiamide with other nitrogen-containing organic additives such as urea in comparative example 2 or thiourea in comparative example 3, a nano photocatalyst in which small-sized particles are uniformly distributed cannot be obtained. From the above analysis, dicyandiamide is indispensable in the preparation method of the present application, and has a unique effect, and not other nitrogen-containing organic matters can be optionally substituted.
(B) As can be seen from fig. 5, cobalt in the co—c nano photocatalyst in example 1 exists in an elemental form;
as can be seen from FIG. 11, the Co-C nano-photocatalyst of comparative example 1 has surface Co 2+ Is significantly higher than the Co-C nano-photocatalyst of example 1 in terms of surface Co 2+ Is a ratio of Co-C nano-photocatalyst in comparative example 1 2+ Is reduced to a degree lower than that of the actual oneSurface Co of Co-C nano-photocatalyst in example 1 2+ Is a degree of reduction of (2); the surface lattice oxygen ratio (18.65%) of the Co-C nano-photocatalyst in comparative example 1 was significantly higher than the surface lattice oxygen ratio (9.49%) of the Co-C nano-photocatalyst in example 1, indicating that more cobalt element exists in the form of oxygen bonding in the surface of the Co-C nano-photocatalyst in comparative example 1;
as can be seen from FIG. 10, in the CoO-C nano-photocatalyst of comparative example 3, cobalt exists not in the form of simple substance but in the form of CoO, which indicates that some nitrogen-containing organic matters (such as thiourea of comparative example 3) are instead responsible for Co during the high-temperature calcination of Co-MOF nanospheres 2+ Is adversely affected by the reduction of (c).
As can be seen from the comparison of example 1 and comparative examples 1 and 3, when the nano-photocatalyst is prepared by using the nitrogen-free Co-MOF as the precursor, the precursor is calcined at high temperature under an inert atmosphere to form Co in the particles 2+ Is not easy to perform and cobalt species are easily oxidized. Co can be produced by adding dicyan diamine 2+ Is easy to carry out and cobalt species are not easily oxidized. No auxiliary dicyandiamide was used, such as comparative example 1; or substitution of dicyandiamide with other nitrogen-containing organic additives such as thiourea in comparative example 3, all of which are detrimental to Co in the constituent particles of the high temperature calcination product of the precursor under an inert atmosphere 2+ Cobalt species are easily oxidized, which is disadvantageous to obtain a nano-photocatalyst with uniformly distributed small-sized particles.
(C) From the above analysis, it is known that when a cobalt species is used as a precursor for preparing a nano photocatalyst, although cobalt species are liable to undergo phenomena such as thermal migration, oxidation and agglomeration or overgrowth of nanoparticles during high-temperature calcination, volatile nitrogen-containing substances generated during high-temperature calcination of dicyandiamide can be carried around the Co-MOF nanospheres by inert gas flow, which affects the thermal decomposition process of the Co-MOF nanospheres, and the phenomena of thermal migration, combination with oxygen and agglomeration or overgrowth of cobalt species are inhibited by coordination protection of nitrogen, thereby maintaining uniformity of size and position distribution of nanoparticles constituting the product.
(D) As can be seen from FIG. 5, co in example 1The cobalt in the C nano-photocatalyst was present as elemental Co (CoO+Co) in example 2 3 O 4 ) The cobalt in the C nano-photocatalyst exists in the form of (CoO+Co) 3 O 4 ) Co in example 3 3 O 4 The existence form of Co in the-C nano photocatalyst is Co 3 O 4 。
As can be seen from the interplanar spacing of the HRTEM image and the corresponding crystal planes of the diffraction ring in the selected electron diffraction image in FIG. 6, the (CoO+Co) in example 2 3 O 4 ) The cobalt in the C nano-photocatalyst exists in the form of (CoO+Co) 3 O 4 ) Co in example 3 3 O 4 The cobalt in the-C nano photocatalyst exists in the form of Co 3 O 4 。
The results of FIGS. 5 and 6 are fully comparable, demonstrating that the cobalt is indeed present in the form of Co, (CoO+Co) in the several nano-photocatalysts 3 O 4 ) And Co 3 O 4 。
(E) The TOF value of the Co-C nano-photocatalyst in example 4 for catalyzing the formation of carbon monoxide in the photo-reduction reaction of carbon dioxide was 1.46×10 -4 s -1 TOF value of catalytic hydrogen generation is 6.79×10 -5 s -1 The method comprises the steps of carrying out a first treatment on the surface of the (CoO+Co) in example 5 3 O 4 ) The TOF value of the catalyst for catalyzing the carbon monoxide generation in the photo-reduction of carbon dioxide by the C nano-photocatalyst is 1.10X10 -4 s -1 TOF value of catalytic hydrogen generation is 5.16X10 -5 s -1 The method comprises the steps of carrying out a first treatment on the surface of the Co in example 6 3 O 4 The TOF value of the catalyst for catalyzing the carbon monoxide generation in the photo-reduction of carbon dioxide by the C nano-photocatalyst is 9.56 multiplied by 10 -5 s -1 TOF value of catalytic hydrogen generation of 4.25X10 -5 s -1 。
Referring to fig. 7, the TOF values of the three nano-photocatalysts for catalyzing and generating carbon monoxide are higher than those of the commercial cobalt-based catalyst of the control group, so that the catalytic performance of the three nano-photocatalysts is better than that of the commercial cobalt-based catalyst of the control group.
(F) As can be seen from fig. 12, when the Co-C nano photocatalyst is calcined in air, when the temperature reaches 100℃ or more,the mass of the Co-C nano photocatalyst begins to increase, namely, the simple substance Co begins to be obviously oxidized at the moment, so that if the calcining temperature is lower than 100 ℃, part of simple substance Co can not be oxidized all the time; when the temperature reaches more than 210 ℃, the mass of the Co-C nano photocatalyst is not increased, but is reduced, which means that the oxidation of the simple substance Co is basically completed at the moment, and the existence form of Co is all Co 3 O 4 Therefore, if the calcination temperature is higher than 210 ℃, the oxidation rate of Co is too fast, and the CoO-containing nano-photocatalyst may not be obtained.
As can be seen from FIG. 13, co in comparative example 4 3 O 4 The existence form of Co in the-C nano photocatalyst is Co 3 O 4 With (CoO+Co) prepared in example 2 3 O 4 ) Form of Co in the C nano photocatalyst (CoO+Co 3 O 4 ) Different, it is shown that Co in the nano-photocatalyst is completely oxidized into Co at the moment 3 O 4 No CoO in the intermediate oxidation state is present.
From the above analysis, it can be seen that if the Co-C nano-photocatalyst is to be prepared by calcining in air (CoO+Co) 3 O 4 ) The calcination temperature of the C nano photocatalyst is required to be controlled between 100 ℃ and 210 ℃. Under the condition that the calcination time is 10 min-25 min, the calcination temperature is 190-210 ℃.
Claims (8)
1. The preparation method of the Co-C nano photocatalyst is characterized in that the method takes nitrogen-free Co-MOF nanospheres as precursors and dicyandiamide as an auxiliary agent;
the method specifically comprises the following steps:
step one, preparing a Co-MOF nanosphere containing no nitrogen:
equimolar amount of Co (Ac) 2 ·4H 2 Adding O and isophthalic acid into a clean reaction container, pouring N, N-dimethylformamide, stirring and mixing, reacting in a constant-temperature oil bath at 120 ℃ for 120min to obtain a mixture, centrifuging and collecting a precipitate of the mixture after the mixture is cooled to room temperature, washing the precipitate with N, N-dimethylformamide and absolute ethyl alcohol for several times, and then feedingVacuum drying is carried out to obtain Co-MOF nanospheres;
step two, preparing a Co-C nano photocatalyst:
grinding the Co-MOF nanospheres in the first step, placing the ground Co-MOF nanospheres at one end of a quartz boat in the downwind direction, and placing auxiliary dicyandiamide at one end of the quartz boat in the upwind direction, wherein the mass of the dicyandiamide is 0.5-2.5 times that of the Co-MOF nanospheres; calcining at 450-800 ℃ at a heating rate of 1-10 ℃/min for 30-240 min under the protection of argon atmosphere to obtain the Co-C nano photocatalyst.
2. The method for preparing a Co-C nano-photocatalyst according to claim 1, wherein in the second step, the mass of dicyandiamide is 1 time of the mass of Co-MOF nanospheres; the calcination temperature is 500 ℃, the heating rate is 2 ℃/min, and the calcination time is 120min.
3. CoO-Co 3 O 4 -a preparation method of a C nano photocatalyst, which is characterized in that the method takes nitrogen-free Co-MOF nanospheres as precursors and dicyan diamine as an auxiliary agent;
the method specifically comprises the following steps:
step one, preparing a Co-MOF nanosphere containing no nitrogen:
equimolar amount of Co (Ac) 2 ·4H 2 Adding O and isophthalic acid into a clean reaction container, pouring N, N-dimethylformamide, stirring and mixing, reacting in a constant-temperature oil bath at 120 ℃ for 120min to obtain a mixture, centrifuging and collecting a precipitate of the mixture after the mixture is cooled to room temperature, washing the precipitate with N, N-dimethylformamide and absolute ethyl alcohol for a plurality of times, and then carrying out vacuum drying to obtain Co-MOF nanospheres;
step two, preparing a Co-C nano photocatalyst:
grinding the Co-MOF nanospheres in the first step, placing the ground Co-MOF nanospheres at one end of a quartz boat in the downwind direction, and placing auxiliary dicyandiamide at one end of the quartz boat in the upwind direction, wherein the mass of the dicyandiamide is 0.5-2.5 times that of the Co-MOF nanospheres; calcining at the calcining temperature of 450-800 ℃ and the heating rate of 1-10 ℃/min for 30-240 min under the protection of argon atmosphere to obtain the Co-C nano photocatalyst;
step three, preparing CoO-Co 3 O 4 -C nano-photocatalyst:
calcining the Co-C nano photocatalyst in the second step in air, controlling the calcining temperature at 190-210 ℃, the heating rate at 1-5 ℃/min and the calcining time at 10-25 min to obtain CoO-Co 3 O 4 -a C nano photocatalyst.
4. The CoO-Co as described in claim 3 3 O 4 The preparation method of the C nano photocatalyst is characterized in that in the second step, the mass of dicyandiamide is 1 time of that of Co-MOF nanospheres; the calcination temperature is 500 ℃, the heating rate is 2 ℃/min, and the calcination time is 120min.
5. The CoO-Co as described in claim 3 3 O 4 The preparation method of the C nano photocatalyst is characterized in that in the third step, the calcination temperature is 200 ℃, the heating rate is 2 ℃/min, and the calcination time is 15min.
6. Co (cobalt) 3 O 4 -a preparation method of a C nano photocatalyst, which is characterized in that the method takes nitrogen-free Co-MOF nanospheres as precursors and dicyan diamine as an auxiliary agent;
the method specifically comprises the following steps:
step one, preparing a Co-MOF nanosphere containing no nitrogen:
equimolar amount of Co (Ac) 2 ·4H 2 Adding O and isophthalic acid into a clean reaction vessel, pouring N, N-dimethylformamide, stirring and mixing, reacting in a constant-temperature oil bath at 120 ℃ for 120min to obtain a mixture, cooling the mixture to room temperature, centrifugally collecting a precipitate of the mixture, and concentrating the precipitateWashing with N, N-dimethylformamide and absolute ethyl alcohol for a plurality of times, and then carrying out vacuum drying to obtain Co-MOF nanospheres;
step two, preparing a Co-C nano photocatalyst:
grinding the Co-MOF nanospheres in the first step, placing the ground Co-MOF nanospheres at one end of a quartz boat in the downwind direction, and placing auxiliary dicyandiamide at one end of the quartz boat in the upwind direction, wherein the mass of the dicyandiamide is 0.5-2.5 times that of the Co-MOF nanospheres; calcining at the calcining temperature of 450-800 ℃ and the heating rate of 1-10 ℃/min for 30-240 min under the protection of argon atmosphere to obtain the Co-C nano photocatalyst;
step three, preparing Co 3 O 4 -C nano-photocatalyst:
calcining the Co-C nano photocatalyst in the second step in air, controlling the calcining temperature at 190-210 ℃, the heating rate at 1-5 ℃/min and the calcining time at 45-150 min to obtain Co 3 O 4 -a C nano photocatalyst.
7. Co according to claim 6 3 O 4 The preparation method of the C nano photocatalyst is characterized in that in the second step, the mass of dicyandiamide is 1 time of that of Co-MOF nanospheres; the calcination temperature is 500 ℃, the heating rate is 2 ℃/min, and the calcination time is 120min.
8. Co according to claim 6 3 O 4 The preparation method of the C nano photocatalyst is characterized in that in the third step, the calcination temperature is 200 ℃, the heating rate is 2 ℃/min, and the calcination time is 120min.
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