CN118594526A - Method for preparing monoatomic photocatalyst - Google Patents
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Abstract
The invention discloses a preparation method of a single-atom photocatalyst, which comprises the steps of mixing a compound containing M n+, a T complex photocatalyst and water, performing ball milling reaction, and performing acid washing, calcining and acid washing treatment to obtain the single-atom photocatalyst, wherein the single-atom photocatalyst is an M/T photocatalyst, M is one of Pd, bi, cu Ni, zn and Y, and T is TiO 2 or g-C 3N4. The photocatalyst prepared by the invention has single atoms on the surface, has no other metal clusters or particles, can excite more photo-generated electrons under visible light, greatly reduces the electron-hole recombination rate, has obviously improved photocatalytic activity, particularly has very high catalytic activity in CO 2 RR, has simple preparation method and mild conditions, achieves the purposes of reducing cost, simplifying production flow and realizing kilogram-level mass production, and can be applied to the field of catalytic reduction of CO 2.
Description
Technical Field
The invention relates to the field of photocatalysts, in particular to a preparation method of a single-atom photocatalyst.
Background
In recent years, there have been many reports of the corner angles of single atoms and clusters of several atoms. Monoatomic catalysis is a new concept in the field of heterogeneous catalysis, and the atom utilization rate can be theoretically raised to 100%, and is widely focused due to the excellent catalytic activity and good selectivity.
The institute Zhang Tao of advanced single-atom catalysis is a research of the institute of advanced chemical and physical, and the team of the institute of advanced chemical and physical, which firstly and definitely puts forward the concept of single-atom catalysis, and the single-atom catalysis is demonstrated in experiments and theory, and the subject group takes ferric oxide as a carrier, so that the first single-atom platinum catalyst with practical significance is successfully prepared. The single-atom catalyst has higher catalytic activity and stability, and the catalytic activity is 2-3 times that of the traditional nano catalyst, thus providing a new choice for developing low-cost high-efficiency noble metal industrial catalysts.
The professor Tang Xingfu of the double denier university brings the subject group to successfully develop the single-atom silver catalyst in 2012, and the ultra-high catalytic activity, the catalytic rate close to 100 percent and the green circular economy concept make the catalyst realize a new breakthrough in formaldehyde removal. The single-atom silver catalyst consists of single-atom silver active center and can decompose formaldehyde into CO 2 and water at low temperature. Research results show that the single-atom silver catalyst has higher catalytic activity and stability, and the catalytic activity is 7-8 times that of the traditional supported nano metal catalyst and 30 times that of the traditional formaldehyde removal method.
The problems of Xiamen universities Zheng Nafeng, fu Gang and the like are combined, an ultrathin titanium dioxide nanosheet protected by glycol is used as a carrier, a photochemical method is applied, a monoatomic dispersed palladium catalyst with the mass fraction of 1.5% is successfully prepared, and research shows that efficient removal of chloride ions on a precursor chloropalladate is a key for successful preparation under mild conditions. In order to avoid agglomeration, the metal loading is generally difficult to increase (mostly below 0.5%).
The professor topic group of Beijing university of science and technology Wang Ge makes new progress in the research of supported noble metal catalysts, the research builds a novel superparamagnetism double-layer sea urchin-shaped cavity structure catalyst, high catalytic activity and magnetic separation recovery of the catalyst are realized, and the catalytic activity is not reduced after repeated cyclic use, so that the catalyst has important scientific significance and potential application value.
The single-atom catalyst brings the catalytic reaction from the macroscopic field to the microscopic world, and people can know the catalytic reaction from the atomic scale by means of advanced characterization means such as HAADF-STEM and XAFS. The metal is dispersed on the surface of the carrier in a form of single atom, so that the free energy of the surface of the catalyst is obviously increased, and the catalytic activity of the catalyst is greatly improved. The single-atom catalyst has the advantages of uniform and single active center of the homogeneous catalyst and stable and easily separated structure of the heterogeneous catalyst, and becomes a bridge for connecting homogeneous catalysis and heterogeneous catalysis.
Monoatomic catalysts have great potential for use. In the reactions of preparing H 2 by photolysis water, removing NO x and VOCs in the chemical industry field by photocatalysis, reducing CO 2 and the like, the single-atom catalyst has the advantages of high efficiency, high selectivity and high stability. On the one hand, the application of the single-atom catalyst in the traditional field, such as purification of pollutants, preparation of energy fuels and the like, is expanded in the future; on the other hand, the catalyst is combined with the emerging fields, such as photoelectric conversion, fuel cells and the like, and the advantage of monoatomic catalysis is fully exerted.
The research of the single-atom catalyst is started soon, and the single-atom catalyst is predicted to replace the traditional catalyst too early. It is believed that, whether the nature of the catalytic reaction is understood theoretically or the potential for industrial use, single-atom catalysts are an important direction of future catalytic research, with the full potential of replacing traditional catalysts in certain particular areas. For example, a single-atom catalyst successfully enters the field of fine chemicals, and in 2011, zhang Tao research groups prepare a Pt/FeO x single-atom catalyst for the first time, wherein the Pt/FeO x single-atom catalyst and a quasi-single-atom catalyst are used for the selective hydrogenation reaction of aromatic nitro compounds, and higher activity and selectivity are obtained under mild reaction conditions (40 ℃ and hydrogen pressure of 0.3 MPa). The preparation method of the single-atom catalyst mainly comprises a coprecipitation method, a leaching method, a vapor deposition method and the like, and the key point is that the single-atom catalyst should find a proper single-atom carrier, such as iron oxide, titanium oxide, silicon oxide, aluminum oxide, certain molecular sieves and the like. If monoatomic catalysis can be finally realized, great economic benefits are generated in the industrial catalysis field.
The single-atom catalyst is generally complex in synthesis method, and single atoms are easy to agglomerate on the surface of a carrier.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a preparation method of a single-atom photocatalyst, which is simple to operate, mild in conditions and general in a single-atom catalyst synthesis method, the obtained single-atom photocatalyst can be widely applied to CO 2 reduction reaction and has better CO 2 reduction performance, the preparation method of the catalyst reduces the production cost, simplifies the production process and solves the problems that the single-atom catalyst is easy to agglomerate in the catalytic process.
The invention is realized by the following technical scheme:
The preparation method of the single-atom photocatalyst comprises the steps of mixing a compound containing M n+, a T complex photocatalyst and water, performing ball milling reaction, and performing acid washing, calcination and acid washing treatment to obtain the single-atom photocatalyst, wherein the single-atom photocatalyst is M/T photocatalyst, M is one of Pd, bi, cu, ni, zn and Y, and T is TiO 2 or g-C 3N4. The M of the present invention may be other metal elements which can be used as a raw material of the monoatomic photocatalyst, and is not limited to the description of the present invention. In practice, the present invention has found that some clusters and particles remain in the synthesized sample when treated in either the acid wash-calcine or calcine-acid wash mode. In the prior art, the phenomenon that single atoms are agglomerated on the surface of the carrier is caused by calcination, and the method is different from the prior art, and the three-stage acid washing-calcination-acid washing combination is adopted in the preparation process, so that metal particles are not generated on the surface of the carrier, namely, the agglomeration phenomenon is not generated in the catalysis process, clusters are not generated on the surface of the carrier, and the catalysis efficiency of the catalyst is excellent in 4 or 5 hours.
The molar ratio of M element to T substance is M: t=0.005: 1, wherein the amount of the substance of T ranges from 0.1 to 1.0mol.
Further, the molar ratio of M element to T substance is M: t=0.005: 1, wherein the amount of the substance of T ranges from 0.1 to 1.0mol.
During ball milling, the mass ratio of the raw materials to ball milling beads is 1:10. the raw materials are a mixture of M n+ -containing compound, T complex photocatalyst and water.
The first acid washing is carried out for 1 time, the calcination time is 4 hours, and the second acid washing is carried out for 3 times.
The pH value of the first acid washing is 1.0-4.0, the calcining temperature is 300-500 ℃, and the pH value of the second acid washing is 1.0-4.0.
An M/T Shan Yuanzi photocatalyst for photocatalytic reduction of CO 2 as described above and a process for its preparation, said process comprising the steps of:
(1) Weighing 0.5mmol of M n+ compound and 0.1mol of T by using an analytical balance, putting the mixture into a ball milling tank, adding ball milling beads which are 10 times of the raw materials in mass, adding 15ml of distilled water, and adjusting the pH to 1.0-4.0 by using a dilute hydrochloric acid solution;
(2) Fixing the ball milling tank in a ball mill, and selecting a certain rotating speed for ball milling for a certain time;
(3) Transferring the reactant into a beaker, washing with hydrochloric acid, centrifuging and drying to obtain a solid substance;
(4) Placing the solid substances into a tube furnace, and calcining for a certain time in an argon/hydrogen atmosphere;
(5) The solid material was transferred to a beaker, washed with hydrochloric acid, centrifuged, and dried to give M/T Shan Yuanzi photocatalyst.
The invention adopts a high-energy ball milling method to prepare the M/T photocatalyst, and the catalytic activity of the obtained catalyst is better than that of a T carrier. The prepared monoatomic catalyst has enhanced response to visible light, has higher catalytic activity, particularly has higher activity in CO 2 RR, has simple preparation method and mild condition, and can be widely applied to CO 2 RR.
The ball milling reaction time is 8-12 h, preferably 12h.
The ball milling speed is 300-500 r/min, preferably 400r/min.
The pH of the acid wash is 1.0 to 4.0, preferably ph=1.0.
The calcination temperature is 300 to 500 ℃, for example 300 ℃,350 ℃,400 ℃,450 ℃,500 ℃, preferably 300 ℃.
Compared with the prior art, the invention has the following advantages and beneficial effects:
the photocatalyst prepared by the invention has no other metal particles on the surface, can excite more photo-generated electrons under visible light, greatly reduces the electron-hole recombination rate, obviously improves the photocatalytic activity, particularly has high activity in CO 2 RR, has simple preparation method and mild conditions, achieves the purposes of reducing cost and simplifying production flow, and can be applied to the reaction of catalytic reduction of CO 2.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:
FIG. 1 is a HAADF-STEM diagram of a Pd/TiO 2 photocatalyst;
FIG. 2 is an XRD pattern of a synthetic sample;
FIG. 3 is (a) XANES (b) EXAFS of Cu/TiO 2 photocatalyst;
FIG. 4 is a HAADF-STEM diagram of Pd/TiO 2 photocatalyst after testing;
FIG. 5 is a HAADF-STEM diagram of an acid washed+calcined Pd/TiO 2 photocatalyst;
FIG. 6 is a HAADF-STEM diagram of a calcined + acid washed Pd/TiO 2 photocatalyst.
Detailed Description
For the purpose of making apparent the objects, technical solutions and advantages of the present invention, the present invention will be further described in detail with reference to the following examples and the accompanying drawings, wherein the exemplary embodiments of the present invention and the descriptions thereof are for illustrating the present invention only and are not to be construed as limiting the present invention.
Example 1
Weighing 0.5mmol of PdCl 2 by an analytical balance, dissolving 0.1: 0.1molTiO 2 in 15mL of distilled water, dripping hydrochloric acid into the solution by using a rubber head dropper to adjust the pH to 2.0, adding ball-milling beads with 10 times of the mass of the raw materials, fixing a ball-milling tank in a ball mill, ball-milling for 12 hours at the stirring rate of 400r/min at room temperature, cleaning by using hydrochloric acid with the pH of 1.0, centrifuging and collecting precipitate; drying the precipitate in an oven at 90 ℃ for 4 hours, and calcining the obtained solid powder in a tubular furnace at 300 ℃ for 4 hours in Ar/H 2 atmosphere; the product was washed with ph=1.0 hydrochloric acid, centrifuged, dried and ground to give the final product, i.e. the modified Pd/TiO 2 monoatomic photocatalyst.
And HAADF-STEM characterization is carried out on the modified Pd/TiO 2 monoatomic photocatalyst, as shown in figure 1, the catalyst has isolated bright spots, is Pd monoatomic and has no obvious clusters and nano particles as shown in figure 1.
XRD characterization is carried out on the Pd/TiO 2 single-atom photocatalyst, as shown in figure 2, the Pd/TiO 2 single-atom photocatalyst has the same diffraction peak of a TiO 2 carrier, no obvious metal peak appears, the loading of different kinds of metals does not change the crystal structure of the carrier, and no particles of metal Pd appear on the surface of the carrier.
Example 2
Weighing 0.5mmol of BiCl 3 by an analytical balance, dissolving 0.1mol of TiO 2 in 15mL of distilled water, dripping hydrochloric acid into the solution by using a rubber head dropper to adjust the pH to be 2.0, adding ball-milling beads with the mass 10 times that of the raw materials, fixing a ball-milling tank in a ball mill, performing ball milling for 12 hours at the stirring rate of 400r/min at room temperature, cleaning by using hydrochloric acid with the pH to be 1.0, centrifuging and collecting precipitate; drying the precipitate in an oven at 90 ℃ for 4 hours, and calcining the obtained solid powder in a tubular furnace at 300 ℃ for 4 hours in Ar/H 2 atmosphere; washing the product with hydrochloric acid with pH=1.0, centrifuging, drying and grinding to obtain the final product, namely the modified Bi/TiO 2 monoatomic photocatalyst.
As shown in figure 2, the XRD spectrum of the Bi/TiO 2 single-atom photocatalyst can be seen, and the Bi/TiO 2 single-atom photocatalyst has the same diffraction peak of a TiO 2 carrier, which shows that the loading of different metals does not change the crystal structure of the carrier, and the surface of the carrier does not have particles of the metal Bi.
The Bi/TiO 2 photocatalyst was subjected to a specific CO 2 RR photocatalytic activity test, and the results are shown in table 1.
Example 3
Weighing 0.5mmol of CuCl 2 by an analytical balance, dissolving 0.1: 0.1molTiO 2 in 15mL of distilled water, dripping hydrochloric acid into the solution by using a rubber head dropper to adjust the pH to be 2.0, adding ball-milling beads with the mass 10 times that of the raw materials, fixing a ball-milling tank in a ball mill, ball-milling for 12 hours at the stirring rate of 400r/min at room temperature, cleaning by using pH to be 1.0 hydrochloric acid, centrifuging and collecting precipitate; drying the precipitate in an oven at 90 ℃ for 4 hours, and calcining the obtained solid powder in a tubular furnace at 300 ℃ for 4 hours in Ar/H 2 atmosphere; the product was washed with ph=1.0 hydrochloric acid, centrifuged, dried and ground to give the final product, i.e. the modified Cu/TiO 2 monoatomic photocatalyst.
The Cu/TiO 2 monoatomic photocatalyst was XAFS characterized as shown in fig. 3, which shows that no Cu-Cu bond was present in the sample, indicating that no Cu clusters were present on the sample surface. The presence of a Cu-O bond indicates that the O atom provides an anchor point to form a Cu-O coordination bond.
Comparative example 1
This comparative example is presented to illustrate the carrier TiO 2 and the application. In contrast to example 1, comparative example 1 is the support TiO 2, without any loading.
Comparative example 2
The comparative example has no acid washing process after calcination in the synthesis process, and aims to illustrate the influence of acid washing and calcination on sample surface agglomeration and nano particles, thereby further influencing the activity and stability of Pd/TiO 2 photocatalyst. Comparative example 2 is a process in which acid washing after calcination was reduced during the synthesis of example 1.
Comparative example 3
The comparative example has no acid washing process before calcination in the synthesis process, and aims to illustrate the influence of the combination of calcination and acid washing on sample surface agglomeration and nano particles, thereby further influencing the activity and stability of the Pd/TiO 2 photocatalyst. Comparative example 3 is a process in which acid washing before calcination was reduced during the synthesis of example 1.
From the above examples and comparative examples, the results of table 1 show that: the M/T (M=Pd, bi, cu, ni, zn, Y) single-atom photocatalyst prepared by the method can excite more photo-generated electrons under visible light, the electron-hole recombination rate is greatly reduced, the photocatalytic activity is obviously improved, particularly, the activity in CO 2 RR is very high, and the activity still maintains the trend after 5 hours of testing. As shown in fig. 4, the single atom active center is still present and the single atoms are not agglomerated. The catalytic activity is reduced after the agglomeration of the single atoms. Therefore, the M/TiO 2 (M=Pd, bi, cu, ni, zn, Y) single-atom photocatalyst can effectively reduce CO 2 to generate CH 4, CO and other fuels, and the preparation method reduces the production cost, simplifies the production process, ensures that the prepared single-atom catalyst is not easy to agglomerate in the reaction process, and has a durable catalytic effect (figure 4). As shown in fig. 5, the sample synthesized in comparative example 2 was subjected to acid washing + calcination, and there were some distinct clusters and particles, which could affect the catalytic performance and the reason for the performance stability (decrease from the 5 th performance) during the catalytic process. Likewise, the samples synthesized in comparative example 2 were calcined and acid washed to give a catalyst performance far lower than the sample of example 1 acid washed, calcined and acid washed, indicating that some clusters and particles were still present in the synthesized samples (FIG. 6), which had an effect on the catalytic performance and performance stability. The invention obtains remarkable technical effects through the technical scheme of acid washing, calcination and acid washing.
All photocatalysts were tested for CO 2 RR photocatalytic activity and the results are shown in table 1. Examples 1 and 2 produced CH 4 in amounts as high as 1357.81 and 1043.86. Mu. Mol g -1, respectively, at 5h of catalytic reaction. The effect of example 3 is not better than that of examples 1 and 2 because there is a difference in the catalytic effect of the different monoatomic photocatalysts, and the catalytic effect of the copper atom photocatalysts in the present invention is less excellent than that of the Pd atom photocatalysts and the Bi atom photocatalysts. The catalytic performance of example 1 at 5h is improved by approximately 11 times compared with that of comparative example 1, and the improvement effect is very obvious, which also shows that the existence of single atoms on the surface of the carrier has a remarkable effect of improving the performance in the catalytic process. comparative example 2, CH 4 increased 140.82. Mu. Mol g -1 at 3-4h, CH 4 increased 88.64. Mu. Mol g -1 at 4-5 h; comparative example 3, CH 4 increased 200.84. Mu. Mol g -1 at 3-4h, CH 4 increased 29.15. Mu. Mol g -1 at 4-5 h. In comparative examples 2 to 3, the increase of the catalytic performance after 4 hours showed a remarkable tendency to be retarded, indicating the deactivation of the catalyst after 4 hours of catalysis in the presence of clusters. While comparative examples 1-3 produced much lower amounts of CH 4 over time than examples 1 and 2, indicating that comparative examples 1-3 all had lower catalytic performance. The three-stage acid washing-calcining-acid washing combination is adopted in the preparation process, so that no metal particles appear on the surface of the carrier, namely no agglomeration phenomenon appears in the catalysis process, no clusters appear on the surface of the carrier, and the catalysis efficiency of the catalyst is excellent in 4 or 5 hours. Compared with the modes of 'pickling + calcining' or 'calcining + pickling' in comparative examples 2 and 3, the catalytic activity of the 'pickling-calcining-pickling' in the invention is always kept active for 5 hours, the catalytic efficiency is high without the trend of reduction, and the catalytic performance of comparative examples 2 and 3 is obviously deactivated when the catalytic activity reaches 5 hours, so that the preparation method has obvious effect.
TABLE 1
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (8)
1. The preparation method of the single-atom photocatalyst is characterized by mixing a compound containing M n+, a T complex photocatalyst and water, performing ball milling, and performing acid washing, calcination and acid washing treatment to obtain the single-atom photocatalyst, wherein the single-atom photocatalyst is an M/T photocatalyst, M is one of Pd, bi, cu, ni, zn and Y, and T is TiO 2 or g-C 3N4.
2. The method for preparing the monoatomic photocatalyst according to claim 1, wherein the molar ratio of M element to substance T is M: t=0.005: 1.
3. The method for preparing a monoatomic photocatalyst according to claim 2, wherein the amount of the substance of T ranges from 0.1 to 1.0mol.
4. The method for preparing the single-atom photocatalyst according to claim 1, wherein the mass ratio of raw materials to ball-milling beads is 1:10.
5. The method for preparing a single-atom photocatalyst according to claim 1, wherein the first acid washing is performed 1 time, the calcination time is 4 hours, and the second acid washing is performed 3 times.
6. The method for preparing a monoatomic photocatalyst according to claim 1, wherein the pH value of the first acid washing is 1.0-4.0, the calcination temperature is 300-500 ℃, and the pH value of the second acid washing is 1.0-4.0.
7. The method for preparing a single-atom photocatalyst according to claim 1, wherein the ball milling rotation speed is 300-500 r/min.
8. The method for preparing a single-atom photocatalyst according to claim 1, wherein the ball milling reaction time is 8-12 hours.
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