CN113731412B - Alternately deposited photocatalyst and preparation method and application thereof - Google Patents

Alternately deposited photocatalyst and preparation method and application thereof Download PDF

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CN113731412B
CN113731412B CN202110880517.4A CN202110880517A CN113731412B CN 113731412 B CN113731412 B CN 113731412B CN 202110880517 A CN202110880517 A CN 202110880517A CN 113731412 B CN113731412 B CN 113731412B
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copper
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titanium dioxide
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CN113731412A (en
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郑昭科
刘木
黄柏标
王泽岩
王朋
刘媛媛
程合锋
张倩倩
张晓阳
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Shandong University
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
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    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
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    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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Abstract

The invention discloses an alternate deposition photocatalyst and a preparation method and application thereof. The invention can simultaneously enhance the stability and catalytic activity of the photocatalyst through atomic layer deposition.

Description

Alternately deposited photocatalyst and preparation method and application thereof
Technical Field
The invention belongs to the technical field of clean energy and photocatalytic carbon dioxide reduction, and relates to an alternately deposited photocatalyst, and a preparation method and application thereof.
Background
The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.
In recent years, people enjoy industryThe modern and convenient life style brought by the development and the accompanying environmental problems such as global warming and the like are troubling people. So it is becoming more and more important to say how to eliminate the chief culprit of this crisis. In all reduction of CO in air 2 Among all solutions of concentration, photocatalysis has a wide prospect, since it enables the reduction of carbon dioxide to other valuable products, such as CO, CH, by direct use of solar energy 4 . Researchers have conducted extensive research in this area, hoping to improve the photocatalytic CO of photocatalysts 2 And (4) reduction performance. In addition to improving the performance of the photocatalyst, CO 2 Another equally critical problem in the field of reduction is the stability of the photocatalyst during the reaction. Despite the significant improvement in performance or selectivity, the stability of the photocatalyst has a long way away from meeting real-world needs. The catalyst is likely to be saturated with active sites, resulting in deactivation of the performance of various photocatalysts after only a few hours. This also exists in Cu-based photocatalysts, which have been extensively studied for their ability to enhance the separation of photogenerated carriers. However, the stability of copper is also greatly limited due to its inherently unstable nature.
The most widely used technique to improve the stability of photocatalysts, as far as the inventors are aware, is ALD (atomic layer deposition), which is well known because it has rapidly evolved into an efficient method of synthesizing or modifying photocatalysts. However, the inventors have found that the application of ALD can be limited, since most catalysts or promoters are prepared in advance by other methods, and then ALD modification is performed to obtain excellent stability, which is very time consuming. Furthermore, since the active sites are covered, the enhanced catalytic activity may be affected and attenuated in the post-ALD deposition mode.
Disclosure of Invention
In order to solve the disadvantages of the prior art, the present invention is directed to an alternately deposited photocatalyst, a method for preparing the same, and an application thereof, which can simultaneously enhance stability and activity by ALD.
In order to achieve the purpose, the technical scheme of the invention is as follows:
on the one hand, the alternately deposited photocatalyst comprises a base material, wherein at least two mixed layers are sequentially attached to the surface of the base material from bottom to top, the base material is a titanium dioxide nanosheet material, and each mixed layer is formed by sequentially depositing copper and titanium dioxide through atomic layer deposition.
On the other hand, the preparation method of the alternately deposited photocatalyst takes titanium dioxide nanosheets as a base material, copper and titanium dioxide are alternately deposited on the surface of the base material through atomic layer deposition, the copper is deposited firstly and then the titanium dioxide is deposited in each alternate deposition, and the alternate deposition is carried out at least twice.
In order to solve the problem of reduced stability and activity caused by a post ALD deposition mode, the method adopts ALD to simultaneously deposit the promoter copper and the protective layer titanium dioxide, so that more active sites can be exposed, and the stability and the activity are simultaneously improved.
Experiments show that the super-cyclic ALD alternately deposits photocatalytic CO which shows enhancement under the condition of not sacrificing the performance of the super-cyclic ALD 2 Reduction stability, which is post-deposition of TiO 2 And deposition of Cu alone cannot be achieved. A series of characterizations indicate that more oxygen vacancies, partially capped copper species, and good charge separation capability retention may be responsible for improved activity and stability.
In a third aspect, use of an alternating deposited photocatalyst as described above for photocatalytic carbon dioxide reduction.
In a fourth aspect, a method for producing carbon monoxide and/or methane comprises dispersing the alternately deposited photocatalyst in water, introducing carbon dioxide, and performing a light reaction to obtain carbon monoxide and/or methane.
The invention has the beneficial effects that:
the supercycle ALD alternating deposited photocatalysts of the present invention exhibit enhanced photocatalytic CO without sacrificing performance 2 Activity, which is not achievable with post-deposition photocatalysts. Compared with a sample for depositing Cu only, the photocatalyst deposited by ALD (atomic layer deposition) alternately shows more excellent performance stabilityAnd (4) sex. Specifically, the average rate of the alternately deposited photocatalyst for photocatalytic carbon dioxide reduction to CO can reach 62 mu mol/g/h. A series of characterizations indicate that more oxygen vacancies, partially capped copper species, and good charge separation capability retention may be responsible for improved activity and stability.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are included to illustrate an exemplary embodiment of the invention and not to limit the invention.
FIG. 1 is a preparation of nanoplatelets and TiO according to an example 2 @(2Cu+2TiO 2 )×25、TiO 2 @50Cu and TiO 2 @50Cu+50TiO 2 A flow chart of (a);
FIG. 2 shows TiO prepared in example 2 @(2Cu+2TiO 2 )×25、TiO 2 @50Cu and TiO 2 @50Cu+50TiO 2 An XRD pattern of (a);
FIG. 3 shows TiO prepared in example 2 @(2Cu+2TiO 2 )×25(a)、TiO 2 @50Cu (b) and TiO 2 @50Cu+50TiO 2 (c) SEM image of (a);
FIG. 4 shows TiO prepared in example 2 Nanosheet (a) and TiO 2 @(2Cu+2TiO 2 )×25(b)、TiO 2 @50Cu (c) and TiO 2 @50Cu+50TiO 2 (d) A TEM image of (a);
FIG. 5 shows TiO prepared in example 2 @(2Cu+2TiO 2 )×25、TiO 2 @50Cu and TiO 2 @50Cu+50TiO 2 EDS spectrum of (a);
FIG. 6 shows TiO prepared in example 2 Nanosheet and TiO 2 @(2Cu+2TiO 2 )×25、TiO 2 @50Cu and TiO 2 @50Cu+50TiO 2 The a and b are reduction performance curves, the c is a stability histogram, and the d is a reduction performance histogram of different photocatalysts;
FIG. 7 shows TiO prepared in example 1 2 @(2Cu+2TiO 2 )×25、TiO 2 @50Cu and TiO 2 @50Cu+50TiO 2 Photocurrent ofAnd (6) responding.
Detailed Description
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
In view of the problems of poor stability and activity of the photocatalyst prepared by the existing method, the invention provides an alternately deposited photocatalyst, and a preparation method and application thereof.
The invention provides an alternative deposited photocatalyst, which comprises a substrate, wherein at least two mixed layers are sequentially attached to the surface of the substrate from bottom to top, the substrate is a titanium dioxide nanosheet material, and each mixed layer is formed by sequentially depositing copper and titanium dioxide by adopting atomic layer deposition.
In some examples of this embodiment, the mixed layer comprises 20 to 30 layers.
In some examples of this embodiment, the atomic percent of copper is 0.90 to 1.10%.
In some embodiments of the present disclosure, each mixed layer is deposited by atomic layer deposition, wherein the deposition of copper is performed for 2-5 cycles, and the deposition of titanium dioxide is performed for 2-5 cycles.
In another embodiment of the invention, a preparation method of an alternately deposited photocatalyst is provided, wherein titanium dioxide nanosheets are used as a substrate, copper and titanium dioxide are alternately deposited on the surface of the substrate through atomic layer deposition, the copper is deposited firstly and then the titanium dioxide is deposited in each alternate deposition, and the number of alternate depositions is at least two.
According to the invention, ALD is adopted to simultaneously deposit the cocatalyst copper and the protective layer titanium dioxide, so that more active sites can be exposed, and the stability and the activity are simultaneously improved.
The alternate deposition is the cyclic deposition of copper and titanium dioxide, and the process of depositing copper first and then depositing titanium dioxide is one-time alternate deposition.
In some examples of this embodiment, the copper is deposited for 2-5 cycles first, followed by 2-5 cycles of titanium dioxide deposition. The deposition mode can not only reduce the interval between copper and titanium dioxide, but also realize high dispersibility of copper particles, and simultaneously avoid the copper particles from being covered by a titanium dioxide layer.
In some examples of this embodiment, the number of alternating depositions is 20 to 30.
One cycle of deposition by atomic layer deposition is carried out by alternately pulsing two reactants, each reactant being purged with an inert gas after the pulse. In the process of preparing the deposited copper, the reducing agent is required to reduce copper ions, however, researches show that hydrogen can be used as the reducing agent, and CuO and Cu can be obtained under the condition of only introducing He gas or water vapor 2 An O or Cu film may also be formed, and water vapor is selected as a reactant in the present invention for more convenient atomic layer deposition.
In some examples of this embodiment, the ratio of the pulse time of the copper source to the pulse time of the water vapor in one cycle of Atomic Layer Deposition (ALD) deposition of Cu is 200: 1-2.
In some embodiments of this embodiment, the ratio of the pulse time of the copper source to each inert gas purge time in one cycle of Atomic Layer Deposition (ALD) deposition of Cu is 1:19 to 21.
More specifically, in one cycle of depositing Cu by Atomic Layer Deposition (ALD), a copper source is pulsed for 1.9-2.1 s, then argon purging is performed for 38-42 s, then water vapor purging is performed for 0.014-0.016 s, and finally argon purging is performed for 38-42 s.
In some examples of this embodiment, Atomic Layer Deposition (ALD) deposits TiO 2 In the course of one cycle of (a) of (b),the ratio of the pulse time of the titanium source to the pulse time of the water vapor is 19-21: 1.
In some examples of this embodiment, Atomic Layer Deposition (ALD) deposits TiO 2 In one cycle of the titanium source, the ratio of the pulse time of the titanium source to the inert gas purging time is 1: 340-360.
More specifically, Atomic Layer Deposition (ALD) deposits TiO 2 In one cycle of the method, the titanium source is pulsed for 0.19-0.21 s, then argon purging is carried out for 68-72 s, then water vapor purging is carried out for 0.009-0.011 s, and finally argon purging is carried out for 68-72 s.
In some examples of this embodiment, the ratio of the pulse time per copper source to the pulse time per titanium source is 9 to 11: 1.
The copper source in the present invention is preferably copper hexafluoroacetylacetonate (Cu (hfac) 2 ). The titanium source of the present invention is preferably titanium isopropoxide.
In some examples of this embodiment, the deposition temperature for atomic layer deposition is 260-300 ℃.
In some examples of this embodiment, the temperature of the copper source is 140 to 160 ℃.
In some examples of this embodiment, the temperature of the titanium source is 80 to 100 ℃.
In some embodiments of this embodiment, the process for preparing the titanium dioxide nanoplates is: adding hydrofluoric acid into tetrabutyl titanate, and carrying out hydrothermal reaction to obtain the product.
In some embodiments, the temperature of the hydrothermal reaction is 190-210 ℃. The time of the hydrothermal reaction is 22-26 h.
In some embodiments, the volume ratio of hydrofluoric acid to tetrabutyl titanate is 1:4.5 to 5.5. The hydrofluoric acid is common commercially available hydrofluoric acid, and the mass fraction of the hydrofluoric acid is 38-42%.
The purification process of the titanium dioxide nanosheet obtained after the hydrothermal reaction comprises washing and drying. The washing process is carried out for a plurality of times by adopting water and ethanol. The drying process is vacuum drying at 55-65 ℃ for 22-26 h.
In a third embodiment of the present invention, there is provided a use of the above-described alternately deposited photocatalyst in photocatalytic carbon dioxide reduction.
In a fourth embodiment of the present invention, there is provided a method for producing carbon monoxide and/or methane, comprising dispersing the alternately deposited photocatalyst in water, introducing carbon dioxide, and performing a light reaction to obtain carbon monoxide and/or methane.
In order to make the technical solutions of the present invention more clearly understood by those skilled in the art, the technical solutions of the present invention will be described in detail below with reference to specific embodiments.
The test materials used in the following examples are all conventional in the art and are commercially available.
Example 1
Catalyst TiO alternately deposited by utilizing atomic layer deposition technology 2 @(2Cu+2TiO 2 ) The preparation method and application of the X25 comprise the following steps:
(1) hydrothermal synthesis of TiO 2 Nanosheet:
3ml of HF solution (40% by mass) were initially introduced into 15ml of tetrabutyltitanate and stirred for 30 minutes, after which the mixture was transferred into a 50ml autoclave lined with polytetrafluoroethylene and held at 200 ℃ for 24 hours. After natural cooling, collecting blue-white precipitate, and washing with absolute ethyl alcohol and deionized water. Finally drying for 24h at 60 ℃ to obtain white powder, namely TiO 2 Nanosheets.
(2) ALD alternating Cu and TiO deposition 2 The sample preparation step of (2):
TiO obtained in the step (1) 2 The nano sheet is used as a base material, and the specific process is as follows: the powder is uniformly dispersed in a stainless steel powder cavity and is placed in a deposition cavity, and the upper layer of the powder cavity is formed by a stainless steel fine net, so that on one hand, the precursor is guaranteed to be capable of achieving effective powder wrapping, and on the other hand, the powder is prevented from being blown away due to vacuum.
The deposition process of Cu is as follows: mixing Cu (hfac) 2 And steam into the chamber alternately, each reactant pulse followed by a 40 second argon purge to remove excess reactants and ensure self-limiting reaction, cu (hfac) 2 The pulse time of (a) is 2 seconds,the pulse time of the water vapor was 0.015 s.
TiO 2 The deposition process comprises the following steps: each reactant pulse was followed by a 70 second Ar purge by alternating pulses of titanium tetraisopropoxide and water vapor for 0.2 seconds and 0.01 seconds, respectively.
Cu and TiO 2 With 2 cycles of Cu deposition and 2 cycles of TiO deposition 2 And (4) depositing. Alternate deposition was performed using 25 super cycles. The sample obtained in the super-cyclic deposition mode is denoted as TiO 2 @(2Cu+2TiO 2 )×25。
TiO 2 And the deposition temperature of Cu was maintained at 280 c, and the source temperatures of Cu and Ti were set to 150 c and 90 c, respectively. The preparation process is shown in figure 1.
Example 2
This example preparation of separately deposited Cu or TiO 2 And post-deposition of TiO 2 The catalyst of (1). Is expressed as TiO 2 The sample of @50Cu was 50Cu deposited alone and the sample obtained was denoted TiO 2 @10TiO 2 、TiO 2 @50Cu+10TiO 2 And TiO 2 @50Cu+50TiO 2 Respectively being a nanosheet and the aforementioned TiO 2 Continuously depositing 10 turns or 50 turns of TiO on the basis of @50Cu 2 . Other reaction conditions and alternate deposition parameters were kept consistent.
Example 3
For transient photocurrent experiments, 5mg of the prepared sample was first dispersed in a solution containing 0.5ml ethanol and 25 μ Lnafion, and after 30 minutes of sonication, 50 μ L of the mixture was uniformly dispersed on 1X 2cm2 FTO glass by drop coating. Photocurrent response was measured by immersing half of the FTO (1cm2) in 0.5M NaSO4 solution, applying a 0.4V vs Ag/AgCl electrode, and then measuring photocurrent response by alternately blocking light at full light.
TiO prepared by example 2 @(2Cu+2TiO 2 )×25,TiO 2 @50Cu and TiO 2 @50Cu+50TiO 2 The XRD and SEM are shown in FIGS. 2-3, and TiO modified by ALD 2 The morphology of the nanoplatelets did not change significantly, all samples maintained a platelet morphology with an average width of about 10 nm. The top and side surfaces of the nanosheets are respectively classified as anatase TiO 2 The (001) and (101) planes of (1). Due to the small loading, little Cu is found on the nanosheet surface.
TiO prepared by example 2 @(2Cu+2TiO 2 )×25,TiO 2 @50Cu and TiO 2 @50Cu+50TiO 2 TEM as in FIG. 4 all samples retained the nanosheet structure, TiO 2 @(2Cu+2TiO 2 )×25、TiO 2 @50Cu and TiO 2 @50Cu+50TiO 2 There is no obvious difference between them.
TiO prepared by example 2 @(2Cu+2TiO 2 )×25,TiO 2 @50Cu and TiO 2 @50Cu+50TiO 2 The atomic percentages of Cu elements of the three samples are all around 0.95%, as shown in fig. 5, indicating that the three different modes of ALD process deposit substantially the same amount of Cu and the same growth rate of Cu.
Testing the photocatalytic carbon dioxide reduction activity:
1. the test method comprises the following steps:
photocatalytic CO 2 The reduction was carried out in a 45ml self-made reactor. First, 10mg of the sample was dispersed in a cap, 1ml of deionized water was injected therearound, the entire reactor was completely sealed and high purity CO was injected at a flow rate of 15ml min-1 2 For 30 minutes. A300W xenon lamp was placed 10 cm above the reactor as a light source. The whole system is kept at 20 ℃ by adopting a water cooling system. 0.2ml of gas was withdrawn every 1 hour and analyzed by GC-7920 gas chromatograph equipped with FID detector (TDX-01 column). To confirm that the product is from CO 2 Reduced, rather than originating from extraneous carbon contamination or the catalyst itself, the use of Ar instead of CO has been carried out 2 Control experiment of (1). Experiments without light or catalyst were also performed to demonstrate that they are photocatalytic CO 2 Is indispensable for the reduction reaction. In both cases no product was detected.
2. And (3) test results:
TiO in example 1 and example 2 2 The CO yield of the nanoplates was about 20. mu. mol/g/h, as shown in FIG. 6(a), while TiO for the alternate deposition sample 2 @(2Cu+2TiO 2 ) X 25, the average rate of CO production over three hours can be as high as 62. mu. mol/g/h. However, for the rearDeposit sample TiO 2 @50Cu+50TiO 2 CO production Rate with virgin TiO 2 The nanoplates were almost identical, indicating alternately deposited TiO 2 @(2Cu+2TiO 2 ) X 25 showed superiority over pure nanoplate and post ALD deposition. As shown in FIG. 6(b), TiO 2 The CO yield of @50Cu dropped dramatically after the first hour. However, with TiO 2 @50Cu comparison, TiO 2 @(2Cu+2TiO 2 ) CO production by 25 is relatively linear, although the initial yield is lower than TiO 2 @50Cu，TiO 2 @(2Cu+2TiO 2 ) X 25 gradually surpassed its competitors due to a linear increase, indicating ALD-prepared, alternately-deposited TiO 2 @(2Cu+2TiO 2 ) X 25 in photocatalytic CO 2 Also, excellent stability of CO formation during the reduction reaction was exhibited. Alternately deposited TiO 2 @(2Cu+2TiO 2 ) The cycle stability of x 25 is shown in fig. 6(c), and it still maintains excellent activity after three cycles of photocatalytic reaction.
To examine ALD deposited TiO 2 For TiO 2 2 Nanosheet photocatalytic CO 2 Influence of reducing Properties on TiO 2 Nanosheets (i.e., TiO) 2 @10TiO 2 ) On which a few layers of TiO are deposited 2 . As shown in FIG. 6(d), the CO yield decreased significantly, indicating ALD deposited amorphous TiO 2 Possibly coated with TiO 2 The high energy surface of the nanoplatelets and resulting in poor activity.
Example 3 experimental results TiO is compared to other ALD prepared samples as shown in figure 7 2 The photocurrent response of the nanoplatelets is the weakest. TiO 2 2 The nanoplates show significant enhancement after Cu loading, while TiO for post deposition samples 2 @50Cu+50TiO 2 The photocurrent response was significantly impaired, indicating post-incorporation of ALD-TiO 2 The promotion caused by copper deposition is significantly reduced. TiO 2 2 The post-deposition may cover a large part of the CO responsible for the photocatalysis 2 The active site of the reduction reaction also results in poor charge separation. Notably, TiO, although compared to copper alone, does 2 @(2Cu+2TiO 2 ) X 25 photocurrent response was weak, but its charge separation ability was higher than that of the post-deposited TiO 2 @50Cu+50TiO 2 Or better, indicating that this is in contrast to depositing TiO after ALD 2 The alternate ALD deposition mode is more favorable to maintain the enhanced charge separation capability caused by Cu, compared to the alternate ALD deposition mode. The photocurrent response of these samples was also consistent with the photocatalytic performance.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The alternately deposited photocatalyst is characterized by comprising a substrate, wherein at least two mixed layers are sequentially attached to the surface of the substrate from bottom to top, the substrate is a titanium dioxide nanosheet material, and each mixed layer is formed by sequentially depositing copper and titanium dioxide by adopting atomic layer deposition;
the mixed layer is 20-30 layers;
the atomic percentage of the copper element is 0.90-1.10%;
and (3) depositing each mixed layer by adopting atomic layer deposition, depositing copper for 2-5 cycles, and depositing titanium dioxide for 2-5 cycles.
2. The method for preparing the alternately deposited photocatalyst as claimed in claim 1, wherein the titanium dioxide nanosheet is used as a substrate, copper and titanium dioxide are alternately deposited on the surface of the substrate by atomic layer deposition, and the copper is deposited and then the titanium dioxide is deposited in each alternate deposition.
3. The method of claim 2, wherein the copper is deposited for 2-5 cycles and the titanium dioxide is deposited for 2-5 cycles;
The number of the alternate deposition times is 20-30.
4. The method according to claim 2, wherein in one cycle of the atomic layer deposition of Cu, the ratio of the pulse time of the copper source to the pulse time of the water vapor is 200: 1-2;
or in one cycle of atomic layer deposition of Cu, the ratio of the pulse time of the copper source to the inert gas purging time of each time is 1: 19-21;
or, atomic layer deposition of TiO 2 In one cycle of (2), the ratio of the pulse time of the titanium source to the pulse time of the water vapor is 19-21: 1;
or, atomic layer deposition of TiO 2 In one cycle of the method, the ratio of the pulse time of the titanium source to the inert gas purging time is 1: 340-360;
or the ratio of the pulse time of the copper source to the pulse time of the titanium source is 9-11: 1.
5. The method of claim 2, wherein the deposition temperature of the atomic layer deposition is 260-300 ℃;
or the temperature of the copper source is 140-160 ℃;
or the temperature of the titanium source is 80-100 ℃.
6. The method of claim 2, wherein the titanium dioxide nanosheets are prepared by: adding hydrofluoric acid into tetrabutyl titanate, and carrying out hydrothermal reaction to obtain the product.
7. The method of claim 6, wherein the hydrothermal reaction is carried out at a temperature of 190-210 ℃.
8. The method of claim 6, wherein the volume ratio of hydrofluoric acid to tetrabutyl titanate is 1: 4.5-5.5.
9. Use of the alternately deposited photocatalyst of claim 1 in photocatalytic carbon dioxide reduction.
10. A process for producing carbon monoxide and/or methane, which comprises dispersing the photocatalyst of claim 1 in water, introducing carbon dioxide, and carrying out a light reaction to obtain carbon monoxide and/or methane.
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