Hierarchical Î±-Ni(OH)2 Composed of Ultrathin Nanosheets with

Subscriber access provided by HKU Libraries

Article

Hierarchical #-Ni(OH)2 composed of ultrathin nanosheets with controlled interlayer distances and their enhanced catalytic performance Dandan Jia, Hongyi Gao, Wenjun Dong, Shuang Fan, Rui Dang, and Ge Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 03 May 2017 Downloaded from http://pubs.acs.org on May 4, 2017

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.

ACS Applied Materials & Interfaces 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 35

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

ACS Applied Materials & Interfaces

Hierarchical α-Ni(OH)2 composed of ultrathin nanosheets with controlled interlayer distances and their enhanced catalytic performance Dandan Jia, Hongyi Gao,* Wenjun Dong, Shuang Fan, Rui Dang, and Ge Wang*

Beijing Key Laboratory of Function Materials for Molecule & Structure Construction, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, PR China.

*Corresponding Author: Hongyi Gao and Ge Wang

E-mail: [email protected]

ACS Paragon Plus Environment

1


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 35

ABSTRACT: Hierarchical α-Ni(OH)2 assembled of ultrathin nanosheets with the intercalation of diatomic alcohol molecules were synthesized via a facile one-step solvothermal process. The assembly structure avoided the agglomeration of ultrathin nanosheets while retaining their atomic-scale thickness and high surface area. The intercalation of the diatomic alcohol molecules into the transition-metal layers provided larger interlayer spacing and more exposed active sites, which guaranteed the high activity of the α-Ni(OH)2. The as-obtained hierarchical α-Ni(OH)2 exhibited excellent catalytic performance in the reduction of p-nitrophenol, with a maximum reaction rate constant (k) of 6.23 × 10-3 s-1 and a super high activity factor K (K = k/m ) of 216.69 s-1 g-1. The layer spacing played the most important role in the reaction, the catalytic efficiency increased greatly with the increase of the layer spacing of the α-Ni(OH)2. This design concept and synthetic method can also be extended to the production of a wide variety of hierarchical catalysts for other reactions.

KEYWORDS: Hierarchical α-Ni(OH)2, Diatomic alcohol molecules, Specific surface area, Interlayer spacing, Catalytic reduction of p-nitrophenol

1. INTRODUCTION Over the past two decades, great efforts have been made to improve catalytic activity by designing hierarchical catalysts with controlled morphologies and structures to obtain more exposed active sites.1-2 Among various constructed hierarchical catalysts, two dimensional nanomaterials such as graphene, metal oxides/hydroxides, transition-metal chalcogenides and phosphate have received extensive attention due to their atomic-scale thickness and infinite plane dimension,3-10 which provide them with great advantages in catalysis such as high surface area,


2

Page 3 of 35

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


more exposed surface active sites and excellent electron transfer ability. Xie et al. synthesized ZrS3 ultrathin nanosheets, which showed good catalytic performance for the oxidation of water.11 Chhowalla et al. reported that WS2 ultrathin nanosheet was an ideal catalyst for hydrogen evolution.12 Nanosheets of transition metal oxides and hydroxides have been widely applied in catalysis fields as promising noble metal-free catalysts owing to their abundant resources, low cost, good activity and versatile structure.13-15 Wang et al. fabricated atomic thick nanosheets of TiO2 with high photocatalytic efficiency.16 Richards et al. provided the synthetic approach of MgO nanosheets, which showed excellent catalytic performance in the base-catalyzed Claisen-Schmidt condensation reaction.17 Nevertheless, the agglomeration of ultrathin nanosheets is difficult to avoid owing to their high surface energy and van der Waals attractions,18 which reduces the specific surface area, the active sites and further limits their practical applications.19 Recently, scientists designed and successfully fabricated a well-defined hierarchical architecture assembled from ultrathin nanosheets, which solved the agglomeration problem and improved the stability, as well as keeping the atomic-scale thickness and high surface area of the ultrathin nanosheets. Jiang et al. synthesized three-dimensional hierarchical Prussian blue assembled by ultrathin nanosheets, which exhibited remarkable catalysis performance for the degradation of methyl blue and excellent adsorption properties of Cs+.18 Yan et al. reported αFe2O3 hierarchical hollow spheres composed of ultrathin nanosheets, which showed attractive catalytic properties on visible-light photocatalytic water oxidation.20 In this paper, more surface active sites were provided, which was not only arose from the outstanding surface advantage of the assembled ultrathin nanosheets, but also due to the more exposed internal space and active sites in the adjustment of layer spacings. We employed a


3


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 35

solvent-induced intercalation strategy to fabricate hierarchical α-Ni(OH)2 composed of ultrathin nanosheets via a facile one-step process. During the synthesis procedure, the solvent (ethylene glycol, EG; propylene glycol, PG; Butyl glycol, BG) not only played the role of the structuredirecting agent in promoting the formation of the hierarchical structure, but also was used as an intercalating agent to control the interlayer spacing of the ultrathin nanosheets. The assembled hierarchical structure avoided the agglomeration of the ultrathin nanosheets while retaining their atomic-scale thickness and high surface area. The intercalation of the diatomic alcohol molecules provided larger interlayer spacing and further exposed more internal active sites, which guaranteed the high activity of the catalysts. The as-obtained hierarchical α-Ni(OH)2 exhibited excellent catalytic behavior in the reduction of p-nitrophenol, with a maximum reaction rate constant (k) of 6.23 × 10-3 s-1 and a super high activity factor K (K = k/m ) of 216.69 s-1 g-1, which is larger than most reported noble catalysts and supported catalysts.21-23 In addition, the molar mass of the catalysts is 6.2 % of the substrate p-nitrophenol, which is unlike most of other experiments in which the catalysts amount is much more than 6.2 %.24,25

2. EXPERIMENTAL SECTION 2.1 Synthesis of α-Ni(OH)2 composed of ultrathin nanosheets In a typical synthesis, 3.746 mM urea and 0.935 mM Nickel nitrate hexahydrateare were mixed and added into 15 ml solution of EG under vigorous magnetic stirring for 60 min. The resulting solution was then transferred into a Teflon-lined autoclave (25 mL in volume). The Teflon-lined autoclave was sealed and heated at 120 ℃ for 4 h. Then the autoclave was naturally cooled down to room temperature and the obtained products were collected by centrifugation and washed with water and ethanol three times, respectively. The as-prepared products were dried at 50 ℃


4

Page 5 of 35

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


overnight. The EG was replaced by the PG or BG for preparing the other two products while keeping the rest of the experiment parameters the same. Three products were obtained and defined as follows: Ni(OH)2-EG (EG is the solvent), Ni(OH)2-PG (PG is the solvent), Ni(OH)2BG (BG is the solvent).

2.2 Characterizations The morphology and dimension of the as-synthesized samples were investigated using scanning electron microscopy (SEM, ZEISS SUPRA55) and transmission electron microscopy (TEM, JEM 1200EX). The phase structural characteristics were examined by X-ray diffraction (XRD, M21X, Cu Kα radiation: λ = 0.154 nm). The Fourier transform infrared spectroscopy (FT-IR) was recorded by a Nicolet 6700 using the potassium bromide (KBr) pellet technique in the range of 4000-400 cm-1. The N2 adsorption-desorption isotherms of all the samples were measured using ASAP 2460 and the specific surface areas were evaluated from the Brunauer-EmmettTeller (BET) plot of the nitrogen adsorption isotherm. Ultraviolet-visible (UV-vis) absorption spectra was carried out on a UV-2550 spectrometer.

2.3 Catalytic activity measurements The catalytic properties of the products were examined for the reduction of p-nitrophenol using NaBH4 as the reducing agent in an aqueous medium at 20 ℃. In a typical catalytic test, 115 uL of 2.696 mM aqueous solution of the obtained nickel hydroxide was added to 1 mL of 5 mM pnitrophenol aqueous solution (the molar mass of the catalyst is 6.2 % of the substrate pnitrophenol, the relative molecular weight of nickel hydroxide was counted as 92.714 the without water molecule). Then a 3.5 mL NaBH4 aqueous solution (226.578 mM) was added to begin the


5


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 35

reaction. UV-vis spectroscopy was used to monitor the reaction solution every 2 min.

3. RESULTS AND DISCUSSION 3.1 Characterization of structure and morphology

Figure 1. (a, c, e) SEM and (b, d, f) TEM images of the α-Ni(OH)2 prepared with different solvents: (a, b) Ni(OH)2-EG; (c, d) Ni(OH)2-PG; (e, f) Ni(OH)2-BG.

The morphologies and structures of products prepared with different solvents were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), as shown in Figure 1. When EG was used as the solvent (Ni(OH)2-EG), the products were homogeneous nanoparticles with the uniform diameter of ~220 nm assembled from many tiny nanosheets


6

Page 7 of 35

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


(Figure 1(a, b)). When the solvent was changed to PG, the morphologies of the products transformed into larger irregular spheres (Figure 1c). Nevertheless, these irregular spheres were still made up of more tightly connected nanosheets (Figure 1d). The more compact assembly between the pieces made them look like solid spheres. When the solvent was change to BG, uniform nanoflowers appeared. The nanoflowers were assembled from large and loosely connected nanosheets (Figure 1(e, f)). During the preparation of the products, diatomic alcohol played the role of the structuredirecting agent to chelate with metal ions and further control the nucleation, growth rate and assembly procedure of the nanocrystal, which ultimately governed the final composition and structure of the products. It should be noted that, all the samples prepared with different diatomic alcohols showed the assembled nanosheets morphologies, indicating the characteristics of a layered structure.

Figure 2. XRD patterns of Ni(OH)2: (a) Ni(OH)2-EG; (b) Ni(OH)2-PG; (c) Ni(OH)2-BG.

The crystal texture and chemical composition of the synthesized α-Ni(OH)2 were determined using the X-ray diffraction (XRD) characterization. Figure 2 illustrates the XRD patterns of the products prepared with different diatomic alcohols. All of the reflection peaks can


7


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 35

be indexed to a pure phase of α-Ni(OH)2, corresponding to the SEM results. The synthesized Ni(OH)2-EG, Ni(OH)2-PG, and Ni(OH)2-BG have lamellar structures with 00l diffraction peaks located between 5° and 15° in Figure 2. The d values are calculated according to the characteristic peak (001) for the products in this experiment.26 The basal spacing of Ni(OH)2-EG is 8.87 Å, which is lower than that of Ni(OH)2-PG 9.15 Å, but higher than that of Ni(OH)2-BG 8.36 Å. Taking into account the layer thickness (4.8 Å) of α-Ni(OH)2,27 the interlayer spacing of Ni(OH)2-EG, Ni(OH)2-PG and Ni(OH)2-BG are 4.07 Å, 4.35 Å, and 3.56 Å, respectively. The interlayer spacing of Ni(OH)2-EG (4.07 Å) is close to the nominal diameter of EG (4.2 Å). This also confirmed the state of a nearly vertical insertion for EG molecules into the interlayer due to the formation of hydrogen bonds.28 The intercalation structure of Ni(OH)2-EG has been simulated by Materials Studio ( Figure S1). The interlayer spacing of Ni(OH)2-PG is larger than that of Ni(OH)2-EG which is probably due to the chain length of the PG molecule being longer than that of the EG molecule. The interlayer spacing of Ni(OH)2-BG (3.56 Å) is the shortest, although the corresponding chain is the longest. The interlayer spacing doesn’t keep increasing with the increasing chain length of diatomic alcohol molecules, which may be caused by the chain folding of the PG and BG molecules between the interlayers.

Figure 3. FTIR spectra of Ni(OH)2: (a) Ni(OH)2-EG; (b) EG; (c) Ni(OH)2-PG; (d) PG; (e) Ni(OH)2-BG; (f) BG.


8

Page 9 of 35

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


To obtain more information about the chemical composition, the products prepared with different diatomic alcohols were characterized by FTIR. As shown in Figure 3, for all the products (Figure 3(a, c, e)), the broad bands around 3353 cm-1 and the weak bands at 1630 cm-1 correspond to the O-H vibration of hydrogen-bonded hydroxyl groups and intercalated water molecules located in the interlamellar space of α -Ni(OH)2.29-31 For the diatomic alcohol (EG, PG, BG) in Figure 3(b, d, f), the characteristic peaks around 2944 cm-1 and 2875 cm-1 can be assigned to C-H vibration,29 and the C-O vibration characteristic peaks locate about 1052 cm-1. Simultaneously, the C-H vibration and C-O vibration characteristic peaks of diatomic alcohol can be found in all of the as-synthesised products in Figure 3(a, c, e), which proves the successful intercalation of diatomic alcohol molecules combined with the XRD result. For all the products: the strong absorption bands at 2181 cm-1 are the typical vibration of C≡N triple bonds in the OCN- anions, the byproducts of urea hydrolysis;32 the narrow bands at 1384 cm-1 are ascribed to the stretching vibration modes of NO3-, which is due to the hydrolysis of the nickel source; the two bands around 609-669 cm-1 and 470 cm-1 are ascribed to the δOH and νNi-OH vibrations, respectively.30 Therefore, there are charge compensating anions of OCN-, NO3- and neutralized molecules (EG/PG/BG and H2O) between the gallery of the α-Ni(OH)2. Based on the combination of XRD and FTIR analysis, it can be concluded that the solvent diatomic alcohol also plays the role of an intercalating agent during the synthesis procedure, which efficiently controls the interlayer spacing of the ultrathin nanosheets. Figure 4 displays the nitrogen adsorption/desorption isotherms of the α-Ni(OH)2. The isotherms of α-Ni(OH)2-EG, -PG, -BG, can be identified as type IV associated with the IUPC classification, which is an important trait of mesoporous materials. Evident hysteresis loops can be observed for all of the products in the range of 0.4-0.9 relative pressure. The Ni(OH)2-EG has


9


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 35

the highest BET surface area of 442.63 m²/g. The BET surface area for Ni(OH)2-PG and Ni(OH)2-BG are 178.86 and 96.67 m²/g, respectively. The adsorption capacity increased slowly in the low pressure section and increased sharply when relative pressure reached 0.9 which proves that capillary coagulation occurred.

Figure 4. Nitrogen adsorption-desorption isotherms

3.2 Influential factor affecting the morphology and structure of α-Ni(OH)2 It is apparent that the solvent is a very important factor influencing the morphologies and structures of the products in the experiment. Four additional products were obtained by adjusting the volume proportion of water and EG in Table S1, and the products are defined as follows: Ni(OH)2-1 (water is only solvent), Ni(OH)2-2 (the proportion is 1/1), Ni(OH)2-3 (the proportion is 1/7), Ni(OH)2-4 (the proportion is 1/13), respectively. The synthetic method is exactly the same as the above, but the solvent is replaced by the mixture of water and EG.


10

Page 11 of 35

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


Figure 5. (a, c, e, g) SEM and (b, d, f, h) TEM images of the α-Ni(OH)2 prepared with different volume ratio of water and EG: (a, b) Ni(OH)2-1; (c, d) Ni(OH)2-2; (e, f) Ni(OH)2-3; (g, h) Ni(OH)2-4.

As shown in Figure 5, it is worth noting that all the samples prepared with different water/EG volume ratios are assembled by nanosheets. When water was used as the only solvent, the diameter of the products with spherical structures approximately ranged from 150 nm to 3 µm, demonstrating their dimensional inhomogeneity. The microspheres and nanospheres are assembled from closely packed tiny nanosheets, but the assembled structures are not very stable


11


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 35

as evinced by the surrounding broken pieces (Figure 5b). As the water/EG ratio decreases (Ni(OH)2-2), the microstructure of the product becomes nanoflowers assembled from loosely packed nanosheets with the diameter of about 1 µm. Due to the irregular and loose assembly of the nanosheets, the spherical structure can’t be retained. When the ratio decreases to 1/7 (Ni(OH)2-3), the morphology of the product totally transforms into crosslinked ultrathin nanosheets. As the proportion of EG in the mixed solvent continues to increase, the nanosheets become smaller and combine more closely to form a spherical structure (Figure 5 g-h). So with the increase in the volume fraction of EG, the morphology of the product transforms from irregular nanospheres to nanosheets, and then finally to uniform nanoparticles (Ni(OH)2-EG). In addition, it’s difficult to observe the lattice fringes for the products (Figure S2), which is perhaps due to the poor crystallization. Figure 6 (a) illustrates the X-ray diffraction (XRD) pattern and FT-IR spectra of the products as prepared with various volume ratios of water and EG. Interestingly, both the XRD patterns and FTIR spectra of the products show two group results. All of the reflection peaks can be indexed to a pure phase of α-Ni(OH)2. Compared to products Ni(OH)2-1 and Ni(OH)2-2, the reflections of products Ni(OH)2-3 and Ni(OH)2-4 are fewer in number and some peaks shift to lower angles and become broader. This phenomenon is related to the hydrotalcite-like structure of the α-Ni(OH)2. As a hydrotalcite-like structure, the diffraction angle increases gradually and the corresponding basal spacing decreases gradually compared with basal plane (00l) reflections, theoretically.33 As for α-Ni(OH)2, it has an inclination to lose its original crystal lamellar structure and become a turbostratic-disordered structure in which layers upon layers are stacked on to each other and random orientation appears along the c axis.34 For Ni(OH)2-3 and Ni(OH)24, only part of the peaks show the characteristics of the layered structure. The disappearance and


12

Page 13 of 35

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


expansion of some peaks are due to the intercalation of the EG molecules, water molecules and charge-compensating anions. The intercalation causes the interlamellar spacing expansion and the low crystallinity. The obtained basal spacing for Ni(OH)2-1, Ni(OH)2-2, Ni(OH)2-3, and Ni(OH)2-4 are 7.06 Å (12.52°), 7.11 Å (12.44°), 7.91 Å (11.18°), 8.26 Å (10.70°), respectively. For the Ni(OH)2-2 which has the strongest diffraction peak, the first (001) reflection appears at 7.11 Å (12.44°), followed by the second peak (002) at about 3.57 Å (24.92°). Similarly, for sample Ni(OH)2-1, a low-angle reflection appears at 7.06 Å (12.52°), followed by another reflection at about half of this spacing, 3.55 Å (25.04°). This relationship between the two peaks is attributed to the characteristics of the hydrotalcite-like structure.33 Previous research shows that the intercalation of EG is more superior to H2O molecules,35 and with the decrease of the volume ratio water/EG in the solution, more EG molecules intercalate into the interlayers of the α-Ni(OH)2, resulting in the increased interlayer spacing. The interlayer spacing of Ni(OH)2-1, Ni(OH)2-2, Ni(OH)2-3 and Ni(OH)2-4 are 2.26 Å, 2.31 Å, 3.11 Å, 3.46 Å, respectively. As shown in Figure 6 (b), there are also two sets of results. For Ni(OH)2-3 and Ni(OH)2-4, the broad bands around 3419 cm-1 and the weak bands at 1630 cm-1 correspond to the O-H vibration of hydrogen-bonded hydroxyl groups and intercalated water molecules located in the interlamellar space of α-Ni(OH)2.29-31 Ni(OH)2-1 and Ni(OH)2-2 have weaker peaks here than that of the rest products, which shows their interlayer water molecules are less than that of the others to a certain extent. For Ni(OH)2-3 and Ni(OH)2-4, the bands around 2853 cm-1 and 1083 cm-1 can be assigned to the C-H and C-O vibration of EG in the interlayer space of α-Ni(OH)2, respectively. There are very weak peak of C-H and C-O vibration observed for Ni(OH)2-2, which prove that few EG molecules existed in the Ni(OH)2-2. However, no peak of C-H and C-O is found for Ni(OH)2-1 as the solvent is pure water. (Figure S3).


13


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 35

Figure 6. (a) XRD pattern and (b) FTIR spectra of α-Ni(OH)2: (A) Ni(OH)2-1, (B) Ni(OH)2-2, (C) Ni(OH)2-3, (D) Ni(OH)2-4.

3.3 Catalytic properties of the hierarchical α-Ni(OH)2 nanostructure P-aminophenol is an important chemical and pharmaceutical intermediates that can be used in the synthesis of antipyretic analgesics, rubber additives, petroleum additives, photographic development, and so on.36 The reduction of p-nitrophenol to p-aminophenol over nanocatalysts using sodium borohydride as a reducing agent has attracted great interest in the efficient production of p-aminophenol.25 Generally, noble metal supported catalysts and composite metalcatalysts are favored to catalyze the reaction owing to the excellent properties of noble metals


14

Page 15 of 35

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


and the synergistic effect of composite metals. But their high cost and complex synthesis process limits application in industry for noble metals and composite metals, respectively. In this paper, we synthesized hierarchical α-Ni(OH)2 via a facile one-step and cost-effective process. To evaluate the catalytic activity of the α-Ni(OH)2, the reduction of p-nitrophenol to p-aminophenol by NaBH4 has been used as a benchmark system.

Figure 7. Catalytic reduction of p-nitrophenol with different products: Ni(OH)2-EG, Ni(OH)2-PG, Ni(OH)2-BG; and ln(Ct/C0) versus reaction time for the reaction.

Figure 7 shows the time-dependent UV-vis spectra changed in the catalytic reduction of pnitrophenol by the prepared α-Ni(OH)2. The p-nitrophenol aqueous solution with a strong absorption peak at 317 nm shifts to 400 nm immediately after adding NaBH4 in Figure S4, which means the formation of the p-nitrophenol ion.37 The reduction of p-nitrophenol can be regarded as a pseudo-first-order reaction due to the addition of excess amounts of NaBH4. The characteristic peak at 400 nm of p-nitrophenol is gradually reduced with a rising peak of paminophenol at 298 nm during the catalytic reaction. There are no by-products according to the


15


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 35

existence of the two isosbestic points. Only a little bit of reaction can occur without the catalysts in Figure S5. The reaction rate constant k for Ni(OH)2-EG, Ni(OH)2-PG, and Ni(OH)2-BG are 0.342·min-1, 0.374·min-1, 0.321·min-1, respectively. Ni(OH)2-PG with the maximum interlayer spacing has the best catalytic performance. In addition, commercial Ni(OH)2 has poor catalytic performance as shown in Figure S6.

Figure 8. The structural representation of the layered α-Ni(OH)2 and the two catalytic reaction routes.

There are mainly two important factors influencing the catalytic performance of the obtained α-Ni(OH)2; one is the specific surface area, the other is the layer spacing. Larger surface area can provide more active sites to enhance the catalytic efficiency on the surface of the catalysts, as shown in Route 1 (Figure 8). Larger layer spacing can offer more inner space for reactants between the layers. The electron transfers from BH4- to p-nitrophenol through the adsorption of reactants on the surfaces of the catalyst originally.38 The nitro-group of pnitrophenol can be adsorbed on the catalyst surface readily and it can pull electrons more strongly than the other, leading to the formation of the amine products.39 So the reactant pnitrophenol must be tilted between the layers when the nitro-group of p-nitrophenol is in contact with nickel ions on the laminates, taking into account the measurement of p-nitrophenol (Figure S7) and the interlayer spacing of the catalysts (The maximum value is 4.35 Å). In this case, of course, the greater the layer spacing, the more contact between p-nitrophenol and catalysts, the


16

Page 17 of 35

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


more the exposed active sites, ultimately resulting in better catalytic efficiency, as shown in Route 2 ( Figure 8). As the catalytic results show, Ni(OH)2-PG has the maximum reaction rate constant. This outcome owes to the maximum layer spacing (0.374·min-1) of Ni(OH)2-PG as shown in XRD. However, Ni(OH)2-EG with smaller layer spacing (8.87 Å) and maximum specific surface area (442.63 m²/g) has lower reaction rate constants. The catalytic effect of the Ni(OH)2-BG is the worst owing to its minimum specific surface area (96.67 m²/g) and layer spacing (8.36 Å). It reveals that the layer spacing is the more critical influence factor for the catalytic reaction than the specific surface area. As shown in Figure 9 and Figure S8, the reaction rate constant k for Ni(OH)2-1, Ni(OH)2-2, Ni(OH)2-3 and Ni(OH)2-4 are 0.093·min-1, 0.032·min-1, 0.212·min-1 and 0.220·min-1, respectively. Based on the catalytic result, we can conclude that the performance of the products Ni(OH)2-3 and Ni(OH)2-4 (the second group) is higher than that of the products Ni(OH)2-1 and Ni(OH)2-2 (the first group). This is caused by the larger layer spacing of Ni(OH)2-3 and Ni(OH)2-4, as shown in Figure 6 (a). Ni(OH)2-4 exhibits the best catalytic efficiency which is attributed to its larger specific surface area of 203.49 m²/g (Figure S9) and maximum layer spacing of 3.46 Å. The reaction rate constant of the Ni(OH)2-1 is lower than that of Ni(OH)2-3 which has the lower specific surface area (107.12 m²/g) but larger layer spacing. In addition, all of the four products have worse catalytic performance compared to Ni(OH)2-EG owing to the smaller layer spacing and specific surface area. These are proof of the above conclusion that the layer spacing is the more critical influence factor in the catalytic reaction than the specific surface area.


17


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 35

Figure 9. Ln(Ct/C0) versus reaction time for the reduction of p- nitrophenol.

4. CONCLUSIONS α-Ni(OH)2 composed of ultrathin nanosheets with excellent catalytic performance were successfully synthesized via a facile one-step process by solvent-induced intercalation strategy. The interlayer spacing could be easily controlled by adjusting the solvents. The as-obtained hierarchical α-Ni(OH)2 intercalated with diatomic alcohol exhibited extremely excellent catalytic behavior in the reduction of p-nitrophenol. The layer spacing plays the more important role in influencing the reaction than the specific surface area, and the catalytic efficiency increases greatly with the increase of the layer spacing of the nanosheets. This design concept and synthetic method can also be extended to the production of a wide variety of hierarchical catalysts for other reactions.


18

Page 19 of 35

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


ASSOCIATED CONTENT

Supporting Information

Catalytic reduction curves of p-nitrophenol, Nitrogen adsorption-desorption isotherms, Molecular structure and size of p-nitrophenol and other additional supporting data. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-10-62333765; Fax: +86-10-62327878;

*E-mail: [email protected]

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENT We thank National Key Research and Development Program of China (No. 2016 YFB0701100) for financial support.


19


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 20 of 35

REFERENCES (1) Castillejos-López, E.; Agostini, G.; Di Michel, M.; Iglesias-Juez, A.; Bachiller-Baeza, B. Synergy of Contact between ZnO Surface Planes and PdZn Nanostructures: Morphology and Chemical Property Effects in the Intermetallic Sites for Selective 1,3-Butadiene Hydrogenation. ACS Catal. 2017, 7, 796-811. (2) Pi, W. B.; Mei, T.; Zhang, Z. X.; Li, X.; Wang, J. Y.; Li, J. H.; Wang, X. B. Synthesis of Disk-Like LiNi1/3Co1/3Mn1/3O2 Nanoplates with Exposed (001) Planes and their Enhanced Rate Performance in a Lithium Ion Battery. CrystEngComm 2017, 19, 442-446. (3) Zhu, J. B.; Bai, L. F.; Sun, Y. F.; Zhang, X. D.; Li, Q. Y.; Cao, B. X.; Yan, W. S.; Xie, Y. Topochemical Transformation Route to Atomically Thick Co3O4 Nanosheets Realizing Enhanced Lithium Storage Performance. Nanoscale 2013, 5, 5241-5246. (4) Feng, J.; Peng, L. L.; Wu, C. Z.; Sun, X.; Hu, S. L.; Lin, C. W.; Dai, J.; Yang, J. L.; Xie, Y. Giant Moisture Responsiveness of VS2 Ultrathin Nanosheets for Novel Touchless Positioning Interface. Adv. Mater. 2012, 24, 1969-1974. (5) Cheng, W. R.; He, J. F.; Yao, T.; Sun, Z. H.; Jiang, Y.; Liu, Q. H.; Jiang, S.; Hu, F. C.; Xie, Z.; He, B.; Yan, W. S.; Wei, S. Q. Half-Unit-Cell α-Fe2O3 Semiconductor Nanosheets with Intrinsic and Robust Ferromagnetism. J. Am. Chem. Soc. 2014, 136, 10393-10398. (6) Zhao, G. X.; Jiang, L.; He, Y. D.; Li, J. X.; Dong, H. L.; Wang, X. K.; Hu, W. P. Sulfonated Graphene for Persistent Aromatic Pollutant Management. Adv. Mater. 2011, 23, 3959-3963.


20

Page 21 of 35

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


(7) Rui, X. H.; Lu, Z. Y.; Yu, H.; Yang, D.; Hng, H. H.; Lim, T. M.; Yan, Q. Y. Ultrathin V2O5 Nanosheet Cathodes: Realizing Ultrafast Reversible Lithium Storage. Nanoscale 2013, 5, 556-560. (8) Zhuang, L. Z.; Ge, L.; Yang, Y. S.; Li, M. R.; Jia, Y.; Yao, X. D.; Zhu, Z. H. Ultrathin Iron-Cobalt Oxide Nanosheets with Abundant Oxygen Vacancies for the Oxygen Evolution Reaction. Adv. Mater. 2017, DOI: 10.1002/adma.201606793. (9) Xiao, X. F; He, C. T.; Zhao, S. L.; Li, J.; Lin, W. S.; Yuan, Z. K.; Zhang, Q.; Wang, S. Y.; Dai, L. M.; Yu, D. S. A General Approach to Cobalt-Based Homobimetallic Phosphide Ultrathin Nanosheets for Highly Efficient Oxygen Evolution in Alkaline Media. Energy Environ. Sci. 2017, DOI: 10.1039/c6ee03145e. (10) Li, B.; Gu, P.; Feng, Y. C.; Zhang, G. X.; Huang, K. S.; Xue, H. G.; Pang, H. Ultrathin Nickel-Cobalt Phosphate 2D Nanosheets for Electrochemical Energy Storage under

Aqueous/Solid-State

Electrolyte.

2017,

Adv.

Funct.

Mater.

DOI:

10.1002/adfm.201605784. (11) Xie, J. F.; Wang, R. X.; Bao, J.; Zhang, X. D.; Zhang, H.; Li, S.; Xie, Y. Zirconium Trisulfide Ultrathin Nanosheets as Efficient Catalysts for Water Oxidation in Both Alkaline and Neutral Solutions. Inorg. Chem. Front. 2014, 1, 751-756. (12) Voiry, D.; Yamaguchi, H.; Li, J. W.; Silva, R.; Alves, D. C. B.; Fujita, T.; Chen, M. W.; Asefa, T.; Shenoy, V. B.; Eda, G.; Chhowalla, M. Enhanced Catalytic Activity in Strained Chemically Exfoliated WS2 Nanosheets for Hydrogen Evolution. Nature Materials 2013, 12, 850-885.


21


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 22 of 35

(13) Hu, C.; Zhang, X.; Li, W. T.; Yan, Y.; Xi, G. C.; Yang, H. F.; Li, J. F.; Bai, H. Large-scale, Ultrathin and (001) Facet Exposed TiO2Nanosheet Superstructures and their Applications in Photocatalysis. J. Mater. Chem. A 2014, 2, 2040-2043. (14) Takagaki, A.; Tagusagawa, C.; Domen, K. Glucose Production from Saccharides using Layered Transition Metal Oxide and Exfoliated Nanosheets as a Water-Tolerant Solid Acid Catalyst. Chem. Commun. 2008, 5363-5365. (15) Liang, H. F.; Meng, F.; Acevedo, M. C.; Li, L. S.; Forticaux, A.; Xiu, L. C.; Wang, Z. C.; Jin, S. Hydrothermal Continuous Flow Synthesis and Exfoliation of NiCo Layered Double Hydroxide Nanosheets for Enhanced Oxygen Evolution Catalysis. Nano Lett. 2015, 15, 1421-1427. (16) Xiang, G. L.; Li, T. Y.; Zhuang, J.; Wang, X. Large-Scale Synthesis of Metastable TiO2(B) Nanosheets with Atomic Thickness and their Photocatalytic Properties. Chem. Commun. 2010, 46, 6801-6803. (17) Zhu, K. K.; Hu, J. C.; Kübel, C.; Richards, R. Efficient Preparation and Catalytic Activity of MgO (111) Nanosheets. Angew. Chem. 2006, 118, 7435-7439. (18) Bu, F. X.; Hu, M.; Zhang, W.; Meng, Q.; Xu, L.; Jiang, D. M.; Jiang, J. S. ThreeDimensional Hierarchical Prussian Blue Composed of Ultrathin Nanosheets: Enhanced Hetero-Catalytic and Adsorption Properties. Chem. Commun.2015, 51, 17568-17571. (19) Jin, C. Y.; Hu, M.; Cheng, X. L.; Bu, F. X.; Xu, L.; Zhang, Q. H.; Jiang, J. S. ThreeDimensionalization of Ultrathin Nanosheets in a Two-Dimensional Nano-Reactor: Macroporous CuO Microstructures with Enhanced Cycling Performance. Chem. Commun. 2015, 51, 206-209.


22

Page 23 of 35

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


(20) Zhu, J. X.; Yin, Z. Y.; Yang, D.; Sun, T.; Yu, H.; Hoster, H. E.; Hng, H. H.; Zhang, H.; Yan, Q. Y. Hierarchical Hollow Spheres Composed of Ultrathin Fe2O3 Nanosheets for Lithium Storage and Photocatalytic Water Oxidation. Energy Environ. Sci. 2013, 6, 987993. (21) Haldar, K. K.; Kundu, S.; Patra, A. Core-Size-Dependent Catalytic Properties of Bimetallic Au/Ag Core-Shell Nanoparticles. ACS Appl. Mater. Interfaces 2014, 6, 2194621953. (22) Dong, W. J.; Zhang, L. F.; Li, B. Z.; Wang, L. N.; Wang, G.; Li, X. Y.; Chen, B. Y.; C. Li, R. Preparation of Hollow Multiple-Ag-Nanoclustes-C-Shell Nanostructures and their Catalytic Properties. Appl. Catal. B: Environ. 2016, 180, 13-19. (23) Yang, Y.; Ren, Y.; Sun, C. J.; Hao, S. J. Facile Route Fabrication of Nickel Based Mesoporous Carbons with High Catalytic Performance towards 4-Nitrophenol Reduction. Green Chem. 2014, 16, 2273-2280. (24) Li, Y. Z.; Cao, Y. L.; Jia, D. Z. A General Strategy for Synthesis of Metal Nanoparticles by a Solid-State Redox Route under Ambient Conditions. J. Mater. Chem. A 2014, 2, 3761-3765. (25) Li, J.; Liu, C. Y.; Liu, Y. Au/Graphene Hydrogel: Synthesis, Characterization and its Use for Catalytic Reduction of 4-Nitrophenol. J. Mater. Chem. 2012, 22, 8426-8430. (26) Schneiderova, B.; Demel, J.; PleŠtil, J.; Janda, P.; Bohuslav, J.; Ihiawakrim, D.; Ersen, O.; Rogez, G.; Lang, K. Nickel Hydroxide Ultrathin Nanosheets as Building Blocks for Electrochemically Active Layers. J. Mater. Chem. A 2013, 1, 11429-11437. (27) Shi, H. M.; Yu, C. G.; He, J. Constraining Titanium Tartrate in the Interlayer Space of Layered Double Hydroxides Induces Enantioselectivity. J. Catal. 2010, 271, 79-87.


23


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 24 of 35

(28) Inoue, M.; Kominami, H.; Kondo, Y.; Inui, T. Organic Derivatives of Layered Inorganics Having the Second Stage Structure. Chem. Mater. 1997, 9, 1614-1619. (29) Lee, J. W.; Ahn, T.; Soundararajan, D.; Ko, J. M.; Kim, J. D. Non-Aqueous Approach to the Preparation of Reduced Graphene Oxide/α-Ni(OH)2 Hybrid Composites and their High Capacitance Behavior. Chem. Commun. 2011, 47, 6305-6307. (30) Yan, J.; Fan, Z. J.; Sun, W.; Ning, G. Q.; Wei, T.; Zhang, Q.; Zhang, R. F.; Zhi, L. J.; Wei, F. Advanced Asymmetric Supercapacitors Based on Ni(OH)2/Graphene and Porous Graphene Electrodes with High Energy Density. Adv. Funct. Mater. 2012, 22, 2632-2641. (31) Gao, H. Y.; Wang, G.; Luan, Y.; Chaikittikul, K.; Zhang, X. W.; Yang, M.; Dong, W. J.; Shi, Z. A Fast Synthesis of Hierarchical Yolk-Shell Copper Hydroxysulfates at Room Temperature with Adjustable Sizes. CrystEngComm 2014, 16, 2520-2526. (32) Xu, L. P.; Ding, Y. S.; Chen, C. H.; Zhao, L. L.; Rimkus, C.; Joesten, R.; Suib, S. L. 3D Flowerlike α-Nickel Hydroxide with Enhanced Electrochemical Activity Synthesized by Microwave-Assisted Hydrothermal Method. Chem. Mater. 2008, 20, 308-316. (33) Luo, Y. Y.; Li, G. H.; Duan, G. T.; Zhang, L. One-Step Synthesis of Spherical αNi(OH)2 Nanoarchitectures. Nanotechnology 2006, 17, 4278-4283. (34) Wang, Q.; O’Hare, D. Recent Advances in the Synthesis and Application of Layered Double Hydroxide (LDH) Nanosheets. Chem. Rev. 2012, 112, 4124-4155. (35) Wang, C. H.; Zhang, X.; Xu, Z. T.; Sun, X. Z.; Ma, Y. W. Ethylene Glycol Intercalated Cobalt/Nickel Layered Double Hydroxide Nanosheet Assemblies with Ultrahigh Specific Capacitance: Structural Design and Green Synthesis for Advanced Electrochemical Storage. ACS Appl. Mater. Interfaces 2015, 7, 19601-19610.


24

Page 25 of 35

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


(36) Feng, J.; Su, L.; Ma, Y. H.; Ren, C. L.; Guo, Q.; Chen, X. G. CuFe2O4 Magnetic Nanoparticles: A Simple and Efficient Catalyst for the Reduction of Nitrophenol. Chem. Eng. J. 2013, 221, 16-24. (37) Gangula, A.; Podila, R.; M, R.; Karanam, L.; Janardhana, C.; Rao, A. M. Catalytic Reduction of 4-Nitrophenol using Biogenic Gold and Silver Nanoparticles Derived from Breyniarhamnoides. Langmuir 2011, 27, 15268-15274. (38) Veerakumar, P.; Madhu, R.; Chen, S. M.; Veeramani, V.; Hung, C. T.; Tang, P. H.; Wang, C. B.; Liu, S. B. Highly Stable and Active Palladium Nanoparticles Supported on Porous Carbon for Practical Catalytic Applications. J. Mater. Chem. A 2014, 2, 1601516022. (39) Farhadi, S.; Kazem, M.; Siadatnasab, F. NiO Nanoparticles Prepared via Thermal Decomposition of the Bis(Dimethylglyoximato) Nickel(II) Complex: A Novel Reusable Heterogeneous Catalyst for Fast and Efficient Microwave-Assisted Reduction of Nitroarenes with Ethanol. Polyhedron 2011, 30, 606-613.


25


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 26 of 35

Table of Contents Graphic


26

Page 27 of 35

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


Figure 1. (a, c, e) SEM and (b, d, f) TEM images of the α-Ni(OH)2 prepared with different solvents: (a, b) Ni(OH)2-EG; (c, d) Ni(OH)2-PG; (e, f) Ni(OH)2-BG. 99x124mm (300 x 300 DPI)



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

Figure 2. XRD patterns of Ni(OH)2: (a) Ni(OH)2-EG; (b) Ni(OH)2-PG; (c) Ni(OH)2-BG. 55x38mm (300 x 300 DPI)


Page 28 of 35

Page 29 of 35

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


Figure 3. FTIR spectra of Ni(OH)2: (a) Ni(OH)2-EG; (b) EG; (c) Ni(OH)2-PG; (d) PG; (e) Ni(OH)2-BG; (f) BG. 55x38mm (300 x 300 DPI)



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

Figure 4. Nitrogen adsorption-desorption isotherms 55x38mm (300 x 300 DPI)


Page 30 of 35

Page 31 of 35

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


Figure 5. (a, c, e, g) SEM and ( b, d, f, h) TEM images of the α-Ni(OH)2 prepared with different volume ratio of water and EG: (a, b) Ni(OH)2-1; (c, d) Ni(OH)2-2; (e, f) Ni(OH)2-3; (g, h) Ni(OH)2-4. 129x208mm (300 x 300 DPI)



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

Figure 6. (a) XRD pattern and (b) FTIR spectra of α-Ni(OH)2: (A) Ni(OH)2-1, (B) Ni(OH)2-2, (C) Ni(OH)2-3, (D) Ni(OH)2-4. 108x145mm (300 x 300 DPI)


Page 32 of 35

Page 33 of 35

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


Figure 7. Catalytic reduction of p-nitrophenol with different products: Ni(OH)2-EG, Ni(OH)2-PG, Ni(OH)2BG; and ln(Ct/C0) versus reaction time for the reaction. 86x62mm (300 x 300 DPI)



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

Figure 8. The structural representation of the layered α-Ni(OH)2 and the two catalytic reaction routes. 44x16mm (300 x 300 DPI)


Page 34 of 35

Page 35 of 35

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


Figure 9. Ln(Ct/C0) versus reaction time for the reduction of p- nitrophenol. 55x38mm (300 x 300 DPI)


Hierarchical Î±-Ni(OH)2 Composed of Ultrathin Nanosheets with

Recommend Documents