Creation of Controllable High-Density Defects in Silver Nanowires for

Subscriber access provided by United Arab Emirates University | Libraries Deanship

Communication

Creation of Controllable High-Density Defects in Silver Nanowires for Enhanced Catalytic Property Chaoqi Wang, Zhaorui Zhang, Guang Yang, Qiang Chen, Yadong Yin, and Mingshang Jin Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.6b02317 • Publication Date (Web): 17 Aug 2016 Downloaded from http://pubs.acs.org on August 18, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Nano Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Creation of Controllable High-Density Defects in Silver Nanowires for Enhanced Catalytic Property Chaoqi Wang,† Zhaorui Zhang, † Guang Yang,‡ Qiang Chen, †,* Yadong Yin,§ and Mingshang Jin†,*

†

Frontier Institute of Science and Technology and School of Chemical Engineering and

Technology, Center for Advancing Materials Performance from the Nanoscale (CAMP-Nano), State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China ‡

Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education &

International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China §

Department of Chemistry, University of California, Riverside, California 92521, USA

KEYWORDS. defects, silver, catalysis, nanowire, silane

ACS Paragon Plus Environment

1

Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 18

ABSTRACT. Structural defects have been proven to determine many of the materials’ properties. Here, we demonstrate a unique approach to the creation of Ag nanowires with high-density defects through controllable nanoparticles coalescence in one-dimensional pores of mesoporous silica. The density of defects can be easily adjusted by tuning the annealing temperature during synthetic process. The high-density defects promote the adsorption and activation of more reactants on the surface of Ag nanowires during catalytic reactions. As a result, the as-prepared Ag nanowires exhibit enhanced activities in catalyzing dehydrogenative coupling reaction of silane in terms of apparent activation energy and turnover frequency (TOF). We show further that the silane conversion rate can be enhanced by maximizing the defect density and thus the number of active sites on the Ag nanowires, reaching a remarkable TOF of 8288 h-1, which represents the highest TOF that has been achieved by far on Ag catalysts. This work not only proves the important role of structural defects in catalysis but also provides a new and general strategy for constructing high-density defects in metal catalysts.


2

Page 3 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

Structural defects (e.g., twins, dislocations, stacking faults, and grain boundaries) can lend nanomaterials with extraordinary properties thus are of great importance in many technological and fundamental challenges, including enhanced hardening of stainless steel, understanding plastic deformation mechanisms, and hydrogen embrittlement.1-3 For example, screw dislocations can act as fast hydrogen diffusion channel in palladium nanocrystals during the hydriding phase transformation and boundaries at the nanoscale can achieve strength increase by a factor of 7 to 10 in Cu grains.4-6 Especially in catalysis, structural defects can significantly enhance the catalytic activity of metal nanocrystals.7-13 Very recently, studies on Au/C catalysts indicate a linear correlation between the grain-boundary surface density and specific activity toward CO2 electro-reduction,8 while rhodium (Rh) nanowires (NWs) with variable structural defects can exhibit a defect-dependent catalytic activity in oxidation reaction of benzyl alcohol.10 These researches unambiguously demonstrate the important role of surface defects in catalytic applications of nanomaterials. Motivated by the opportunity for defect engineering, a number of researchers have focused on the development of new techniques and approaches capable of generating high-density defects on nanomaterials. By far, there have been three traditional approaches for the preparation of active defects:(i) liquid phase reduction,11,14-18 by which method Xia and co-workers prepared a large number of metal nanocrystals with twin defects (e.g., penta-twinned NWs, dodecahedrons, icosahedrons, and bipyramids) through manipulating the growth kinetics; (ii) thermal treatment,10 another effective way to achieve active defects on materials by heating particles at a high temperature to induce coalescence of particles, (iii) particle attachment,8,19 in which small nanoparticles (NPs) can go through an attachment process to generate defects. Till now, nearly all the above mentioned approaches can only generate structural defects at a relatively low


3

Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 18

density and are of poor tunability for defect densities. To this end, it is highly desired to develop an efficient approach for the construction of high-density structural defects on nanomaterials.

Figure 1. (a) Schematic illustrating a plausible mechanism for the formation of Ag NWs with highdensity defects through the coalescence of Ag NPs in 1D pore of SBA-15, and (b-e) the corresponding TEM images of the products at obtained at different steps: fresh SBA-15, NPs formed in 1D pores of SBA-15, Ag NWs in SBA-15, and Ag NWs after the removal of SBA-15. Scale bars are 50 nm.

In this work, we propose an effective tactic to achieve high-density defects on nanomaterials by combining the template-assisted synthesis and NP coalescence. Using silver (Ag) as a proof of concept, we show that the reduction of Ag(I) ions in one dimensional (1D) pores of SBA-15, followed by the subsequent annealing process, can hopefully induce coalescence of Ag NPs in 1D pores to construct Ag NWs with high-density defects (Figure 1a). A fine control in the temperature of the annealing process should be able to adjust the defect densities of the NWs. Here, SBA-15 was chosen as 1D pore template due to its advantages of ordered 8-nm pore channels, rough inner surfaces, and easy preparation and removal. Although there have been a number of works for the preparation of metal NWs in SBA-15 templates, NWs


4

Page 5 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

with high-density defects have never been observed and reported by far.20-28 In a standard synthesis, a mixture of 34 mg AgNO3 (the metal precursor), 0.375 mL ethylene glycol (EG, the reducing agent), 0.25 mL deionized water (the solvent), and 200 mg SBA-15 (the template, Figure 1b) was heated at 180 °C in the tube furnace under nitrogen protection. During the reaction, Ag(I) ions could be firstly reduced by EG, thus forming small NPs in the pores of SBA15 (Figure 1c). Then, these Ag NPs can further attach to each other to form well-aligned Ag NWs with defects during thermal treatment at a relatively high temperature (Figures 1d and S1).29 Finally, SBA-15 can be removed via the etching by sodium hydrate aqueous solution (Figure 1e) to generate free standing Ag NWs. Additional large-area transmission electron microscope (TEM) image of free standing Ag NWs can be found in Figure S2. Clearly, the obtained Ag NWs are of high-quality and high-yield.


5

Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 18

Figure 2. TEM and HRTEM images of the obtained Ag NWs. (a) bright field TEM image, (b) dark field image, (c, e) HRTEM images, and (d, f) the corresponding enlarged HRTEM images of the regions marked by the white boxes in (c, e). The white dashed lines represent planar defects, where the white solid lines represent high-index facets (stepped surfaces) exposed on Ag NWs. The white line circle highlights a five-fold twinned like icosahedron along the three-fold symmetry axis orientation within a NW.

Figures 2a and 2b show bright field (BF) and dark field (DF) TEM images of the obtained Ag NWs. As can be seen, the diameter of the Ag NWs is about 8 nm, which is consistent with the pore size of SBA-15. Interestingly, alternating bright and dark lines can be observed in both of the BF and DF TEM images. This is mainly due to the existence of the planar defects, such as


6

Page 7 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

twins, which usually express stronger diffraction contrasts.30 The existence of planar defects can also be supported by spherical aberration correction TEM characterizations. As shown in Figures 2c and 2d, a set of parallel structural defects can be observed all over the whole NW. Most of the parallel defects can be indexed as {200} twin facets (marked by white dashed lines in Figure 2d). The distance between two adjacent defects is only 3 - 6 atomic layers. Meanwhile, a large number of steps (marked by white solid lines in Figure 2d) can be found on the surface of Ag NWs. The formation of the steps should be ascribed to the template effect of the rough innersurface of SBA-15. Besides the parallel defects, some multiple twined defects can also be surprisingly observed within the NWs (Figures 2e and 2f). Considering the formation process of Ag NWs, the existence of penta-twinned structure indicates that all of Ag NPs would suffer from the attachment process in 1D pores of SBA-15 under the reaction condition, regardless of their shapes and crystallinity. Additional HRTEM images of Ag NWs can be found in supporting information (Figure S3). In tradition approaches for the preparation of metal NPs, the concentration of metal precursor usually plays an important role in determining the shape and size. In our experiment, however, the concentration of AgNO3 won’t affect the shape of the final products, as the growth of Ag nanomaterials is strongly restricted in 1D pores of SBA-15. Figure S4 shows the TEM images of Ag NWs generated at different concentrations of AgNO3. In comparison, preparation temperature was found to play important role during the formation of Ag NWs. As shown in Figure S5, the lowest temperature for the formation of the Ag NWs is 120 °C. When the reaction temperature decreased to 80 °C or 100 °C, small Ag nanoparticles were obtained instead of nanowires. In our proposed synthetic protocol, the annealing temperature is another important reaction parameter. By controlling the annealing temperature, the density of defects in Ag NWs


7

Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 18

can be easily tuned. Here, defect surface density and average defect length have been used to describe the defect density of the Ag NWs. Figures S6 and S7 show the TEM images of the Ag NWs (including Ag NWs-180, Ag NWs-300, and Ag NWs-500) prepared at different annealing temperatures (180 °C, 300 °C, and 500 °C, respectively) for 2 hours. After annealing, the shape of Ag NWs is well maintained due to the protection of SBA-15 templates. The defect density and length derived from HRTEM images by counting ca. 300-nm lengths of Ag NWs are listed in Table S1. The calculation of defect density and defect length was based on the method proposed recently by Kanan and co-workers.10 The average defect density and defect length were calculated by dividing the sum of all the defects by the sum of the lengths of nanowires. Obviously, the defect densities of the Ag NWs decrease dramatically when the annealing temperature increase. When the annealing temperature is 180 °C, the defect density is about 6 per 10-nm length, indicating that there are 6 planar defect planes within 10-nm length of Ag NWs (Figures 2 and S5a). Further increasing the annealing temperature to 300 °C and 500 °C, the density will decrease to 4.39 and 1.51 per 10-nm length, respectively. It is worth pointing out that the decrease of the defect density is accompanied by an increase of the length of planar defects. As can be seen in Table S1 and Figure S7, the defect length increases from 8.48 to 9.89 and 10.19 nm when the annealing temperature increases from 180 °C to 300 °C and 500 °C, respectively. This phenomenon is probably due to the merge of the planar defects at high temperatures. Similar phenomenon has also been observed in previous studies.31 Alkoxysilanes and silanols play important roles both in synthesis of organic-inorganic composite materials and materials surface modification.32-34 Numerous reports have accounted the preparation

of alkoxyilanes

through

different

catalytic reactions,35-42

especially

dehydrogenative coupling reaction of silanes with alcohols or water.35-41 This reaction is


8

Page 9 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

typically catalyzed by gold (Au) catalysts.36-39 Considering the high cost and rare resource, efforts have been paid to the rational design and preparation of Ag nanocatalysts with high catalytic activities as an potential alternative to Au nanocatalysts.35,41 Theoretically, Ag catalysts serve as alternatives should exhibit a comparable catalytic activity to gold catalysts. By far, nanoporous Ag nanocatalysts, which have been reported to exhibit the highest activity among Ag nanomaterials, can only achieve a TOF of 576 h-1,41 ten times less active than any reported gold catalysts.

Figure 3. Correlations between the structure of Ag catalysts and their catalytic activities for dehydrogenative coupling reaction. (a) The rate of dehydrogenative coupling reaction of dimethylphenylsilane and n-propanol as a function of reaction time for model catalysts based on the Ag NWs with different densities of defects and Ag NPs without defects (reaction temperature T = 25 °C). (b) Arrhenius plots and the activation energies (Ea) for Ag NWs with different densities of defects and Ag NPs without defects.

In this work, we have prepared a set of Ag NWs with different defect densities. These NWs with similar wire structures, except different densities of defects, are model system to uncover the correlation between the defect and the catalytic performance. The obtained Ag NWs were then evaluated as the catalysts for the dehydrogenative coupling reaction, benchmarked against


9

Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 18

single-crystalline Ag NPs with similar sizes (Figure S8). As aforementioned, defect density of Ag NWs can be adjusted by tuning the annealing temperature, while higher annealing temperature would result in the formation of Ag NWs with lower defect densities. Therefore, it is also an ideal model system for investigating the relationship between structural defects and the catalytic property. Figure 3a shows the time profile for the conversion of dimethylphenylsilane during dehydrogenative coupling reaction at room temperature (25°C). Notably, Ag NWs with active defects can exhibit much higher catalytic activity than Ag NPs. As can be seen, the conversion of dimethylphenylsilane over Ag NWs-180 is 100% in 60 min, while that over Ag NPs can only reach 10% in the same reaction time. More interestingly, we have observed strong influence of the defect densities of Ag NWs on the catalytic performance. The silane conversion rates turn out to decrease in the order of Ag NWs-180 > Ag NWs-300 > Ag NWs-500 at all reaction temperatures. This finding illustrates that increase the density of structural defects can efficiently promote the catalytic dehydrogenative coupling reaction, confirming the important role of structural defects in determining the number of active sites in catalytic reactions. In order to better describe the catalytic property of Ag catalysts, Arrhenius plots were further fitted by carrying out reaction at three different temperatures (25 °C, 45 °C, and 65 °C, Figures 3a and S9). Based on the Arrhenius plots, we can acquire their apparent activation energies Ea, as shown in Figure 3b. The data used to plot the Arrhenius plots are of conversions within 10 minutes and the surface reaction kinetic-controlled region. Ag NPs exhibits apparent activation energy of about 72 kJ/mol. In stark contrast, all the three Ag NWs samples with different densities of defects show much lower apparent activation energies (42.5 to 56.4 kJ/mol), demonstrating the role of surface defects in improving catalytic activities. Note that Ag NPs show the extremely low catalytic activity in this reaction, the activation sites should not be the


10

Page 11 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

single-crystalline sites of Ag. The apparent activation energy of a catalytic reaction is a constant whose physical meaning depends on the detailed reaction mechanism, but it can serve as a useful parameter to distinguish active sites of different catalysts. In particular, the activity trends among our catalysts are the same with silane conversions that we have measured. These results clearly indicate that the structural defects of Ag NWs are responsible for the lower apparent activation energies for catalyzing dehydrogenative coupling reaction. To further confirm its high catalytic activity, TOF of Ag NWs-180 was calculated based on dehydrogenative coupling reaction of dimethylphenylsilane and H2O (Table S2). Surprisingly, Ag NWs-180 can reach a remarkable TOF of 8288 h-1. This is the highest TOF that has been achieved by far on Ag nanocatalysts, about fourteen times higher than that of the reported most active Ag catalysts (TOF = 576 h-1), just slightly inferior to few noble Au-based catalysts.35-37,41

Figure 4. (a) Schematic illustration of the selective adsorption of dimethylphenylsilane on the active sites of structural defects, and the corresponding (b) FT-IR spectra. Lines are (1) pure dimethylphenylsilane, (2,3) Ag NWs-180 with and without dimethylphenylsilane adsorption, and (4) Ag NPs with dimethylphenylsilane adsorption. Green and pink rectangle highlights the regions of the chemical vibrations of Si-H and C-H of dimethylphenylsilane, respectively.


11

Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 18

The information gleaned above has identified the importance of structural defects to the dehydrogenative coupling reaction. Now we are in position to elucidate the underlying mechanism. Previous studies suggest that the structural defects are one of the major factors determining the activity and selectivity of heterogeneous catalysts.43-49 High energy of surface atoms at defects and enhanced adsorption of reactant due to the existence of structural defects have been recognized as two possible mechanisms for the enhanced catalytic activities. Here, the main defects are twins, which could not significantly increase the energy of the atoms at these sites. The enhancement of the catalytic activity could be thus ascribed to the improved adsorption/dissociation of reactants. To confirm this issue, FT-IR characterization was employed to examine the materials, as illustrated in Figures 4 and S10. Pure dimethylphenylsilane could exhibit a rather intense characteristic band at 2150 cm-1, which could be assigned to the stretching vibration of the Si-H moiety.50 This stretching vibration disappeared after adsorbed onto the surface of Ag NWs-180, which indicates that Si-H bond cleaved on the surface of Ag NWs-180 after adsorption. The peaks ranging from 2809 to 3300 cm-1 are mainly due to the C-H stretching of the aromatic ring or the methyl group for both the samples. Interestingly, red-shifts of the vibrations of dimethylphenylsilane on Ag NWs-180 can be observed. These shifts revealed the strong adsorption of dimethylphenylsilane onto the surface of Ag NWs-180. In comparison, adsorption of dimethylphenylsilane onto the Ag NPs did not give rise to any corresponding peaks, suggesting less reactants has adsorbed on their surfaces (beyond the detection limit of the instrument).

For

Ag

NWs

annealed

at

different

temperatures,

FT-IR

signals

of

dimethylphenylsilane on Ag NWs-300 can still be detected. However, no signal has been observed on Ag NWs-500.These experimental results demonstrated that defect-rich nanostructure can adsorb and activate more reactant molecules, thus improving catalytic activity


12

Page 13 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

of Ag catalysts. This enhancement is believed to be effective for dehydrogenation reaction of various silanes with different oxidants. As indicated in Table S3, dehydrogenative coupling reaction can also take place with different oxidants (e.g., methanol, ethanol, nBuOH, and H2O, entries 1 - 4) to produce the corresponding products quantitatively under mild reaction condition. Other silanes, such as triphenylsilane and triethylsilane, can also be catalyzed to the desired silanol at a yield of 100% without the formation of disiloxane. Ag NWs with high density of defects can exhibit an extraordinary durability. As shown in Figure S11a, the catalytic activity could be well maintained even after six cycles. TEM image of the catalyst after six cycles indicates that there is no obvious change compared with fresh catalyst (Figure S11b). Meanwhile, FT-IR spectrum (Figure S11c) was further used to examine the stability of the defect sites during catalysis, which shows that the strong signals of dimethylphenylsilane could still be detected after six cycles’ catalytic reactions. This result suggests that the high-density defects of Ag NWs could be well maintained during catalysis. Combined with XRD characterization (Figure S11d), these results clearly indicate that Ag NWs exhibit excellent stabilities during catalysis. To further clarify whether the coupling reaction was truly catalyzed by the solid state of Ag NWs-180, a leaching experiment was carried out, and the result is shown in Scheme S1. After the reaction proceeded to 30 min, half of reaction mixture was filtered from the catalytic system; with a yield of 74%. Further stirring of the filtrate under the same reaction condition did not give any additional product. In contrast, the residue containing Ag NWs-180 catalyst has been totally transformed to the desired product at a yield of 100%. In addition, ICP-MS analysis indicates that there was no any silver drain during the reactions (Table S4). These results clearly demonstrate that the present reaction takes place exclusively on the defect sites of Ag NWs.


13

Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 18

In summary, we have reported an effective synthetic route toward the creation of highdensity defects in metal nanomaterials by combining NP coalescence and templating method. Ag NWs with defects of controllable density were thus synthesized in high-quality and high-yield. Thanks to the thermal stability of the template, the density of structural defects can be further manipulated by adjusting the temperature for thermal treatment. The presence of high-density defects allows significantly enhanced adsorption of reactants and their activation on the surface of Ag NWs. As a result, the as-prepared Ag NWs exhibit enhanced intrinsic activities in catalyzing dehydrogenative coupling reaction of silane in terms of apparent activation energy and TOF, as compared with Ag NPs without defects. Moreover, the silane conversion rate appears to be strongly defect-dependent, implying that the catalytic activity of Ag NWs can be significantly enhanced by maximizing the defect density and thus the number of active sites. Ag NWs-180 can reach a remarkable TOF of 8288 h-1, which is the highest TOF that has been achieved by far on Ag nanocatalysts, about fourteen times higher than that of the reported most active Ag catalysts. This work proves the important role of surface defects in catalysis and provides a new strategy for constructing structural defects in metal nanocatalysts. This method can be easily extended to the creation of high-density defects in other metal and bimetallic nanocatalysts, thus represents a general strategy for enhancing the performance of many other heterogeneous catalysts.

ASSOCIATED CONTENT Supporting Information. Experimental details, TEM, HRTEM, catalytic performance, ICP-MS analysis. This material is available free of charge via the Internet at http://pubs.acs.org.


14

Page 15 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

AUTHOR INFORMATION Corresponding Author To whom correspondence should be addressed: Mingshang Jin ([email protected]), Qiang Chen ([email protected]) Author Contributions C. W. and Z. Z. performed the catalyst preparation, catalytic testing, characterization, and wrote part of the paper. G. Y. conducted TEM and HRTEM analysis. Q. C. designed the catalytic reaction, M. J. and Y. Y. designed the experiments and wrote the paper. All authors discussed the results and commented on the manuscript. Funding Sources National Natural Science Foundation of China (NSFC), no. 21403160 and 21471123. China Postdoctoral Science Foundation (CPSF), no. 2015M582634. U. S. National Science Foundation (NSF-US), no.CHE-1308587 ACKNOWLEDGMENT M. J. thanks the National Natural Science Foundation of China (NSFC, no. 21403160 and 21471123) and the "start-up fund" provided by Xi'an Jiaotong University. Q. C. is grateful for the support of the China Postdoctoral Science Foundation (2015M582634) and the "start-up fund", "the Fundamental Research Funds for the Central Universities" provided by Xi'an Jiaotong University. Y. Y. Thanks the financial support from the U. S. National Science Foundation (CHE-1308587). REFERENCES (1) Zhang, X.; Misra, A.; Wang, H.; Shen, T.; Nastasi, M.; Mitchell, T. E.; Hirth, J. P.; Hoagland, R. G.; Embury, J. D. Acta Mater. 2004, 52, 995-1002. (2) Li, N.; Wang, J.; Misra, A.; Zhang, X.; Huang, J.; Hirth, J. P. Acta Mater. 2011, 59, 5989-5996. (3) Seita, M.; Hanson, J. P.; Gradečak, S.; Demkowicz, M. J. Nat.Commun. 2015, 6, 6164.


15

Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 18

(4) Lu, L.; Shen, Y.; Chen, X.; Qian, L.; Lu, K. Science 2004, 304, 422-426. (5) Walker, A. M.; Slater, B.; Gale, J. D.; Wright, K. Nat. Mater. 2004, 3, 715-720. (6) Lu, L.; Chen, X.; Huang, X.; Lu, K. Science 2009, 323, 607-610. (7) Kasatkin, I.; Kurr, P.; Kniep, B.; Trunschke, A.; Schlögl, R. Angew. Chem. Int. Ed. 2007, 46, 73247327. (8) Huang, X.; Zhao, Z.; Chen, Y.; Chiu, C.; Ruan, L.; Liu, Y.; Li, M.; Duan, X.; Huang, Y. Nano lett. 2014, 14, 3887-3894. (9) Li, C. W.; Ciston, J.; Kanan, M. W. Nature 2014, 508, 504-507. (10) Feng, X.; Jiang, K.; Fan, S.; Kanan, M. W. J. Am. Chem. Soc. 2015, 137, 4606-4609. (11) Wang, X.; Figueroa-Cosme, L.; Yang, X.; Luo, M.; Liu, J.; Xie, Z.; Xia, Y. Nano lett. 2016, 16, 1467-1471. (12) Xie, S.; Xu, Q.; Huang, X. ChemCatChem 2016, 8, 480-485. (13) Ruan, L.; Zhu, E.; Chen, Y.; Lin, Z.; Huang, X.; Duan, X.; Huang, Y. Angew. Chem. Int. Ed. 2013, 52, 12577-12581. (14) Sun, Y.; Mayers, B.; Herricks, T.; Xia, Y. Nano lett. 2003, 3, 955-960. (15) Lim, B.; Xiong, Y.; Xia, Y. Angew. Chem. Int. Ed. 2007, 46, 9279-9282. (16) Xiong, Y.; Xia, Y. Adv. Mater. 2007, 19, 3385-3391. (17) Wang, Z.; Chen, Z.; Zhang, H.; Zhang, Z.; Wu, H.; Jin, M.; Wu, C.; Yang, D.; Yin, Y. ACS Nano 2015, 9, 3307-3313. (18) Wang, Y.; Peng, H.; Liu, J.; Huang, C.; Xia, Y. Nano lett. 2015, 15, 1445-1450. (19)Halder, A.; Ravishankar, N. Adv. Mater. 2007, 19, 1854-1858. (20) Zhao, D. Science 1998, 279, 548-552. (21) Han, Y.; Kim, J. M.; Stucky, G. D. Chem. Mater. 2000, 12, 2068-2069. (22) Huang, M. H.; Choudrey, A.; Yang, P. Chem. Commun. 2000,12, 1063-1064. (23) Zhang, Y.; Lam, F. L.; Hu, X.; Yan, Z.; Sheng, P. J. Phys. Chem. C 2007, 111, 12536-12541. (24) Wang, Z.; Xie, Y.; Liu, C. J. Phys. Chem. C 2008, 112, 19818-19824. (25) Takai, A.; Doi, Y.; Yamauchi, Y.; Kuroda, K. J. Phys. Chem. C 2010, 114, 7856-7593. (26) Kim, K.; Lee, E.; Kwon, Y. J. Nanopart. Res. 2012, 14, 1-7. (27) Yang, L.; Song, X.; Qi, M.; Xia, L.; Jin, M. J. Mater. Chem. A 2013, 1, 7316. (28) Yang, L.; Qi, M.; Jin, M. CrystEngComm 2013, 15, 2804-2808. (29) Liu, Z.; Che, R.; Elzatahry, A. A.; Zhao, D. ACS Nano 2014, 8, 10455-10460. (30) Williams, D. B.; Carter C. B. Transmission Electron Microscopy, Springer US: New York, 1996, Vol. 3, pp.381-385. (31) Paul, H.; Driver, J. H.; Maurice, C.; Piątkowski, A. Acta Mater. 2007, 55, 833-847.


16

Page 17 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano Letters

(32)Belelli, P. G.; Ferreira, M. L.; Damiani, D. E. J. Mol. Catal. A: Chem. 2000, 159, 315-325. (33)Díaz, I.; Pérez-Pariente, J. Chem. Mater. 2002, 14, 4641-4646. (34)Negrete-Herrera, N.; Letoffe, J.-M.;Putaux, J.-L.; David, L.; Bourgeat-Lami, E. Langmuir 2004, 20, 1564-1571. (35)Mitsudome, T.; Arita, S.; Mori, H.; Mizugaki, T.; Jitsukawa, K.; Kaneda, K. Angew. Chem. Int. Ed. 2008, 47, 7938-7940. (36) Asao, N.; Ishikawa, Y.; Hatakeyama, N.; Menggenbateer; Yamamoto, Y.; Chen, M.; Zhang, W.; Inoue, A. Angew. Chem. Int. Ed. 2010, 49, 10093-10095. (37) John, J.; Gravel, E.; Hagege, A.; Li, H.; Gacoin, T.; Doris, E. Angew.Chem.Int. Ed. 2011, 50, 75337536. (38) Taguchi, T.; Isozaki, K.; Miki, K. Adv. Mater. 2012, 24, 6462-6467. (39) Mitschang, F.; Schmalz, H.; Agarwal, S.; Greiner, A. Angew. Chem. Int. Ed. 2014, 53, 4972-4975. (40) Blandez, J. F.; Primo, A.; Asiri, A. M.; Alvaro, M.; Garcia, H. Angew. Chem. Int. Ed. 2014, 53, 12581-12586. (41) Li, Z.; Zhang, C.; Tian, J.; Zhang, Z.; Zhang, X.; Ding, Y.Catal.Commun. 2014, 53, 53-56. (42) Stratakis, M.; Garcia, H. Chem.Rev. 2012, 112, 4469-4506. (43) Wang, L.; Zhao, S.; Liu, C.; Li, C.; Li, X.; Li, H.; Wang, Y.; Ma, C.; Li, Z.; Zeng, J. Nano Lett. 2015, 15, 2875-2880. (44) Behrens, M.; Studt, F.; Kasatkin, I.; Kühl, S.; Hävecker, M.; Abild-Pedersen, F.; Zander, S.; Girgsdies, F.; Kurr, P.; Kniep, B.-L.; Tovar, M.; Fischer, R. W.; Nørskov, J. K.; Schlögl, R. Science 2012, 336, 893-897. (45) Bian, T.; Zhang, H.; Jiang, Y. Y.; Jin, C. H.; Wu, J. B.; Yang, H.; Yang, D. R. Nano Lett. 2015, 15, 7808-7815. (46) Zhou, W.; Wu, J. B.; Yang, H. Nano Lett. 2013, 13, 2870–2874. (47) Jia, W.; Wu, Y.; Chen, Y.; He, D.; Li, J.; Wang, Y.; Wang, Z.; Zhu, W.; Chen, C.; Peng, Q.; Wang, D.; Li Y. Nano Res. 2016, 9, 584-592. (48) Wang, X.; Choi, S.; Roling, L. T.; Luo, M.; Ma, C.; Zhang, L.; Chi, M.; Liu, J.; Xie, Z.; Herron, J. A.; Mavrikakis, M.; Xia Y. Nat. Commun. 2015, 6, 7594. (49) Lv, T.; Wang, Y.; Choi, S.; Chi, M.; J.; Tao, Pan, L.; Huang, C.; Zhu, Y.; Xia Y. ChemSusChem 2013, 6, 1923-1930. (50) Data were obtained from the National Institute of Advanced Industrial Science and Technology (Japan).


17

Nano Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 18

Table of Contents


18

Creation of Controllable High-Density Defects in Silver Nanowires for

Recommend Documents