A photo-thermal catalyst, a preparation method and application thereof

Abstract

The application discloses a kind of photo-thermal catalyst, the photo-thermal catalyst is Bi@Bi5O7Br Composite nanotube, Bi5O7Br nanotube has atomic level thickness, the wall thickness of Bi5O7Br nanotube is 0.8-2.0nm;Bi Nanodot is dispersed in Bi5O7Br nanotube inside, average diameter is 2-4nm.The preparation method of the photo-thermal catalyst, including: the mannitol solution of Bi (NO3) 3·5H2O and PVP is mixed with the mannitol solution of NaBr, and mixed liquor is obtained;The PH of mixed liquor is adjusted to 10-12, then by hydrothermal reaction is obtained;The hydrothermal reaction temperature is 120-160 DEG C, and the holding time is 30-60min.The photo-thermal catalyst can be applied in catalytic reduction CO2 in the application, the yield of CO reaches mmol·g ‑1 ·h ‑1 Horizontal, compared with the yield under the condition of separate light, more than one order of magnitude is increased.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalysis, and particularly relates to a photo-thermal catalyst and a preparation method and application thereof. BACKGROUND

[0002] Photocatalytic CO2 reduction is to imitate the mechanism of natural photosynthesis to produce synthetic fuels or chemicals by the reaction between CO2 and H2O. A batch of promising catalysts have been explored by doping, introducing defects, compounding with narrow-band-gap semiconductors or loading noble metals, and the conversion efficiency has been doubled. However, the current photocatalysts have poor carrier separation effect and serious recombination, and the performance is difficult to further improve. The amount of CO produced by photocatalytic reduction of CO2 per hour only stays in the order of micromole. Therefore, the industrialization of photocatalytic reduction of CO2 still has a long way to go.

[0003] Integrating different catalytic systems is a feasible way to improve reaction rate and efficiency and optimize energy cost. Photo-thermal catalysis with high-purity hydrogen as a reducing agent has been widely used in the conversion of carbon dioxide, and ultimately millimole-level products can be obtained. However, in the CO2 hydrogenation reaction, it is doubtful whether the expensive preparation process of high-purity hydrogen and the value of hydrogen itself can be compensated. Perhaps, combining traditional photocatalysis with emerging photo-thermal hydrogenation, i.e. obtaining hydrogen ions by only adding water (without using any sacrificial agent), and then assisting with low-energy irradiation and thermal assistance, to realize efficient carbon value-added conversion, may be the preferred ultimate way to seek the lowest energy consumption and the highest return rate.

[0004] Bi a O b X c (X = Cl, Br, I) (such as BiOBr, Bi3O4Br, Bi4O5Br2, Bi5O7Br and Bi 12 O 17 Br2)

[0005] High-efficiency photo-reduction of CO2 has great advantages and research prospects. The unique layered structure, i.e. [Bi2O2] 2+ layer is staggered with the double-halogen layer, which builds a strong built-in electric field, can improve the separation efficiency of electrons and holes, enhance the migration of carriers, and reduce the recombination rate, providing a new direction for research and development. SUMMARY

[0006] Based on the above technical problems, the application provides a photo-thermal catalyst and a preparation method thereof, and the photo-thermal catalyst can efficiently catalyze the reduction of CO2 to CO, and the yield of CO reaches mmol·g -1 ·h -1 .

[0007] The specific scheme of the application is as follows

[0008] One of the purposes of the present application is to provide a photo-thermal catalyst, which is Bi@Bi5O7Br composite nanotube, the Bi5O7Br nanotube has an atomic level thickness, and the wall thickness of the Bi5O7Br nanotube is 0.8-2.0 nm; Bi nanodots are dispersed in the interior of the Bi5O7Br nanotube, and the average diameter is 2-4 nm.

[0009] The photo-thermal catalyst provided by the present application is an atomic level thickness Bi@Bi5O7Br composite nanotube, and this unique composite material can efficiently catalyze CO2 to be reduced to CO under the synergistic action of light and economic auxiliary heat (<200℃) in the presence of water vapor, and the yield of CO reaches mmol·g -1 ·h -1 , which is more than one order of magnitude higher than the yield under the condition of light alone, breaks through the bottleneck of μmol·g -1 ·h -1 of CO under the condition of light, and after deducting the part of heat energy, the quantum efficiency is as high as 23.65%, which is 45 times of that at room temperature; the injection of heat field can heat the photoexcited electrons to high energy state, and these 'hot' electrons can overcome the Schottky barrier through quantum tunneling effect, and the 'hot' electrons can be effectively transferred from the Bi5O7Br NTs to the BiNDs as electron traps, so as to improve the separation ability of the electron-hole pairs; the atomic level thickness of the Bi5O7Br NTs makes the photoexcited carriers easy to transfer from the interior to the surface, so as to shorten the charge transfer distance and improve the utilization rate of the photo-generated carriers.

[0010] The second purpose of the present application is to provide a preparation method of the photo-thermal catalyst, which comprises: mixing a mannitol solution of Bi(NO3)3·5H2O and PVP and a mannitol solution of NaBr in a volume ratio of 3-5:1 to obtain a mixed solution; adjusting the PH of the mixed solution to 10-12, and then obtaining through a hydrothermal reaction; the hydrothermal reaction temperature is 120-160℃, and the holding time is 30-60 min.

[0011] The present application respectively prepares a mannitol solution of Bi(NO3)3·5H2O and PVP and a mannitol solution of NaBr, in order to ensure the generation of nanotube structure; Bi(NO3)3·5H2O, PVP and NaBr cannot generate hollow tubular structure together in mannitol. Further, by adjusting the hydrothermal reaction temperature and time, Bi5O7Br with different curling degrees can be obtained. If the hydrothermal temperature is too low or the holding time is too short, complete Bi5O7Br nanotube will not be formed. If the hydrothermal temperature is too high or the holding time is too long, the Bi5O7Br nanotube will be damaged, and holes will be formed on the surface of the Bi5O7Br nanotube or the nanotube will be directly cracked.

[0012] Preferably, in the mannitol solution of Bi(NO3)3·5H2O and PVP, the mass-volume ratio of Bi(NO3)3·5H2O is 0.1-1:5-30 mmol / mL, and the mass-volume ratio of PVP is 0.05-0.5:5-30 g / mL.

[0013] Preferably, in the mannitol solution of NaBr, the mass-volume ratio of NaBr is 0.1-1:1-10 mmol / mL.

[0014] Preferably, the pH of the mixed solution is adjusted to 11.5; the pH adjusting agent is NaOH, and the molar concentration of NaOH is 1-4 M.

[0015] Preferably, Bi(NO3)3·5H2O and PVP are dissolved in mannitol, and stirred to obtain a mannitol solution of Bi(NO3)3·5H2O and PVP. More preferably, the stirring time is 0.5-1 h.

[0016] Preferably, NaBr is dissolved in mannitol, and stirred to a transparent solution to obtain a mannitol solution of NaBr.

[0017] Preferably, the concentration of mannitol is 0.05-0.3 M.

[0018] The third object of the present application is to provide the application of the photo-thermal catalyst in catalytic reduction of CO2.

[0019] The present application has the following advantages:

[0020] The photo-thermal catalyst provided by the present application is an atomic-level-thickness Bi@Bi5O7Br composite nanotube, which can effectively improve the separation ability of electron-hole pairs, shorten the charge transfer distance, and improve the utilization rate of photo-generated carriers, and can efficiently catalyze the reduction of CO2 to CO, and the yield of CO reaches mmol·g -1 ·h -1 .

[0021] The preparation method of the photo-thermal catalyst provided by the present application has mild conditions and simple process, and the obtained atomic-level-thickness Bi@Bi5O7Br composite nanotube has uniform and controllable size; when applied, H2O is used as the H + source, without using any sacrificial agent, and the low energy consumption and high return rate can be applied to the reduction of CO2 industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The XRD pattern of the photo-thermal catalyst described in Example 1;

[0023] Figure 2 The TEM pattern of the photo-thermal catalyst described in Example 1;

[0024] Figure 3 CO production rate graph of the photo-thermal catalyst described in Example 1;

[0025] Figure 4 SEM graph of the photo-thermal catalyst described in Comparative Example 1;

[0026] Figure 5 SEM graphs of the photo-thermal catalysts described in Comparative Examples 2-5, respectively;

[0027] Figure 6 SEM graph of the photo-thermal catalyst described in Comparative Example 6;

[0028] Figure 7 CO production rate graph of the photo-thermal catalysts described in Comparative Examples 1-6; DETAILED DESCRIPTION

[0029] Hereinafter, the technical solutions of the present application will be described in detail through specific embodiments, but it should be made clear that these embodiments are used for illustration, but not to be interpreted as limiting the scope of the present application.

[0030] Example 1

[0031] A photo-thermal catalyst, which is a Bi@Bi5O7Br composite nanotube, the Bi5O7Br nanotube has an atomic level thickness, the wall thickness of the Bi5O7Br nanotube is 1 nm, and Bi nanodots are dispersed inside the Bi5O7Br nanotube with an average diameter of 2-4 nm. The preparation method of the photo-thermal catalyst comprises:

[0032] (1) 0.5 mmol of Bi(NO3)3·5H2O and 0.2 g of PVP were dissolved in 15 mL of mannitol (0.1 M), and stirred vigorously for 30 min to obtain a mannitol solution of Bi(NO3)3·5H2O and PVP;

[0033] (2) 0.5 mmol of NaBr was dissolved in 3 mL of mannitol (0.1 M) and stirred vigorously to a transparent solution to obtain a mannitol solution of NaBr;

[0034] (3) The mannitol solution of Bi(NO3)3·5H2O and PVP and the mannitol solution of NaBr were mixed and stirred at a volume ratio of 5:1 for 20 min to obtain a mixed solution, and 2M NaOH was slowly added to the mixed solution to adjust the pH to 11.5;

[0035] (4) After stirring for 60 min, the mixed solution was transferred to a Teflon-lined stainless steel autoclave with a capacity of 25 mL, and was kept at a temperature of 160℃ for 60 min; after the reaction was completed, the solution was naturally cooled to room temperature, and was washed several times with ethanol and water to remove residual ions, to obtain Bi@Bi5O7Br composite nanotubes.

[0036] Example 2

[0037] A preparation method of a photothermal catalyst, comprising:

[0038] (1) 0.5 mmol Bi(NO3)3·5H2O and 0.2 g PVP were dissolved in 15 mL of mannitol (0.1 M), and were stirred vigorously for 30 min to obtain a mannitol solution of Bi(NO3)3·5H2O and PVP;

[0039] (2) 0.5 mmol NaBr was dissolved in 3 mL of mannitol (0.1 M), and was stirred vigorously until a transparent solution was obtained, to obtain a mannitol solution of NaBr;

[0040] (3) The mannitol solution of Bi(NO3)3·5H2O and PVP was mixed with the mannitol solution of NaBr at a volume ratio of 5:1, and was stirred for 20 min to obtain a mixed solution, 2M NaOH was slowly added to the mixed solution, and the pH was adjusted to 11.5;

[0041] (4) After stirring for 60 min, the mixed solution was transferred to a Teflon-lined stainless steel autoclave with a capacity of 25 mL, and was kept at a temperature of 120℃ for 30 min; after the reaction was completed, the solution was naturally cooled to room temperature, and was washed several times with ethanol and water to remove residual ions, to obtain Bi@Bi5O7Br composite nanotubes.

[0042] Comparative Example 1

[0043] A preparation method of a photothermal catalyst, compared with Example 1, the only difference is that the solvent is changed from mannitol to water, and other steps and parameters are the same as those of Example 1.

[0044] Comparative Example 2

[0045] A preparation method of a photothermal catalyst, compared with Example 1, the only difference is that NaBr in step (2) is replaced by NaI, and other steps and parameters are the same as those of Example 1.

[0046] Comparative Example 3

[0047] A preparation method of a photothermal catalyst, compared with Example 1, the only difference is that NaBr in step (2) is replaced by NaCl, and other steps and parameters are the same as those of Example 1.

[0048] Comparative Example 4

[0049] A preparation method of a photothermal catalyst, compared with Example 1, the only difference is that the hydrothermal reaction time (i.e. the holding time in the autoclave) in step (4) is replaced from 60 min to 24 h, and other steps and parameters are the same as Example 1.

[0050] Comparative Example 5

[0051] A preparation method of a photothermal catalyst, comprising: (1) dissolving 0.5 mmol Bi(NO3)3·5H2O, 0.2 g PVP, 0.5 mmol NaBr together in 18 mL mannitol (0.1 M), stirring for 60 min, to obtain a mannitol solution containing Bi(NO3)3·5H2O, PVP, NaBr; (2) slowly adding 2M NaOH to adjust the pH to 11.5; (3) after stirring for 60 min, transferring the mixture to a Teflon-lined stainless steel autoclave with a capacity of 25 mL, and holding at a temperature of 160℃ for 60 min; after the reaction is completed, naturally cooling to room temperature, and washing with ethanol and water several times to remove residual ions, to obtain the photothermal catalyst.

[0052] Comparative Example 6

[0053] A preparation method of a photothermal catalyst, compared with Example 1, the only difference is that the hydrothermal reaction time (i.e. the holding time in the autoclave) in step (4) is replaced from 60 min to 120 min, and the hydrothermal reaction temperature is replaced from 160℃ to 180℃, and other steps and parameters are the same as Example 1.

[0054] The photothermal catalysts described in the examples and comparative examples were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and gas chromatograph (GC-2014), as follows

[0055] Figure 1 The XRD pattern of the photothermal catalyst described in Example 1 can be seen that the XRD pattern shows strong and relatively concentrated peaks, pointing to Bi5O7Br (JCPDS 38-0493). In particular, the peak intensity at 27.1°, 37.9°, 39.6° and 48.7° is significantly higher, corresponding to the characteristic peaks of metallic Bi (JCPDS 44-1246).

[0056] Figure 2The TEM image of the photo-thermal catalyst described in Example 1 can be seen that the image shows that the product is mainly one-dimensional (1D) structure (>98%), indicating the formation of high yield of one-dimensional structure. The enlarged TEM image shows that the one-dimensional nanostructure is a hollow tubular structure with an ultra-thin wall. These ultra-thin tubular structures have a uniform outer diameter, and the wall thickness is about 1 nm. Dispersed Bi NDs are observed inside the hollow tube, with an average diameter of about 2-4 nm.

[0057] Figure 3 The CO yield graph of the photo-thermal catalyst described in Example 1. The test method is: fill the container with high-purity CO2, and inject 0.4 ml of deionized water into the reaction system as a reducing agent. The sample is irradiated with a 300 W xenon lamp, and a heating platform is placed under the reactor to control the temperature, and an infrared temperature detector is used to monitor the surface temperature of the sample.

[0058] It can be seen that with the increase of heat, the photo-reduction process of CO2 is obviously accelerated, and the CO yield also increases exponentially with the increase of temperature. At room temperature, the photo-reduction operation of Bi@Bi5O7Br shows that the CO yield in the first hour is 95.1 μmol·g -1 ( Figure 3 , which is 13.5 times higher than that of Bi5O7Br.

[0059] At the same time, it is found that the synergistic promotion of light and heat to the reduction of CO2 Figure 3 b and 3c). Under the condition of light irradiation at 160℃, the CO yield in the first hour jumps to 1.3 mmol·g -1 ( Figure 3 , which is more than an order of magnitude higher than that under ambient light conditions.

[0060] Figure 4 The SEM image of the photo-thermal catalyst described in Comparative Example 1. It can be seen that the presence of PVP alone will cause the two-dimensional nanosheet structure of Bi5O7Br, and will not cause curling or the formation of Bi NDs.

[0061] Figure 5 The SEM images of the photo-thermal catalysts described in Comparative Examples 2-5, respectively. Among them, 5(a)(b) are the SEM images of the photo-catalysts prepared in Comparative Examples 2 and 3, respectively, and it can be seen that the replacement of Br - with Cl - , I - cannot form a hollow tubular structure; 5(c) is the SEM image of the photo-catalyst prepared in Comparative Example 4, and it can be seen that with the increase of reaction time, the hollow tubular structure is destroyed; 5(d) is the SEM image of the photo-catalyst prepared in Comparative Example 5, and it can be seen that the hollow tubular structure cannot be generated.

[0062] Figure 6 The SEM image of the photo-thermal catalyst of Comparative Example 6 shows that the product mainly has a nano-particle structure and no tubular structure is observed.

[0063] Figure 7 The CO yield diagrams of the photo-thermal catalysts of Comparative Examples 1-6, respectively, and the test conditions and Figure 3 (c) are the same. The experimental results are compared with Figure 3 (c) and the photo-thermal catalytic CO2 reduction efficiency under each experimental condition is obviously decreased.

[0064] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and the inventive concept of the present application, makes equivalent replacements or changes within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A photo-thermal catalyst, characterized by, The photo-thermal catalyst is Bi@Bi5O7Br composite nanotube, the Bi5O7Br nanotube has an atomic level thickness, the wall thickness of the Bi5O7Br nanotube is 0.8-2.0 nm; the Bi nanodot is dispersed in the interior of the Bi5O7Br nanotube, and the average diameter is 2-4 nm.

2. A method of preparing the photo-thermal catalyst of claim 1, characterized by, Comprise: Bi(NO3)3.5H2O and PVP mannitol solution and NaBr mannitol solution are mixed in a volume ratio of 3-5:1 to obtain a mixed solution; the pH of the mixed solution is adjusted to 10-12, and then a hydrothermal reaction is performed to obtain the Bi@Bi5O7Br composite nanotube; the hydrothermal reaction temperature is 120-160 DEG C, and the holding time is 30-60 min.

3. The method of preparing a photocatalyst according to claim 2, wherein In the Bi(NO3)3.5H2O and PVP mannitol solution, the mass / volume ratio of Bi(NO3)3.5H2O is 0.1-1:5-30 mmol / mL, and the mass / volume ratio of PVP is 0.05-0.5:5-30 g / mL.

4. The method of preparing a photo-thermal catalyst according to claim 2 or 3, characterized in that, In the NaBr mannitol solution, the mass / volume ratio of NaBr is 0.1-1:1-10 mmol / mL.

5. The method of preparing a photo-thermal catalyst according to any one of claims 2-4, characterized in that, The pH of the mixed solution is adjusted to 11.5; the pH adjuster is NaOH, and the molar concentration of NaOH is 1-4 M.

6. The method of preparing a photo-thermal catalyst according to any one of claims 2-5, wherein, Bi(NO3)3.5H2O and PVP are dissolved in mannitol, and stirred to obtain a Bi(NO3)3.5H2O and PVP mannitol solution.

7. The method of preparing a photo-thermal catalyst according to any one of claims 2-6, wherein, NaBr is dissolved in mannitol, and stirred to obtain a transparent solution, to obtain a NaBr mannitol solution.

8. The method of preparing a photo-thermal catalyst according to claim 6 or 7, characterized in that, The concentration of mannitol is 0.05-0.3 M.

9. The application of the photo-thermal catalyst of claim 1 or the photo-thermal catalyst prepared by the method of any one of claims 2-8 in catalytic reduction of CO2.

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