Topochemical Oxidation Preparation of Regular Hexagonal

Sep 22, 2014 - ABSTRACT: The birnessite-type layered manganese oxide nanoplates with good dispersity and regular hexagonal morphology were obtained by...
7 downloads 6 Views 10MB Size
Download PDF
Article pubs.acs.org/crystal

Topochemical Oxidation Preparation of Regular Hexagonal Manganese Oxide Nanoplates with Birnessite-Type Layered Structure Jianfang Wang,†,‡ Gaini Zhang,† Lijun Ren,† Liping Kang,† Zhengping Hao,† Zhibin Lei,† and Zong-Huai Liu*,† †

Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, and School of Materials Science and Engineering, Shaanxi Normal University, Xi’an, 710062, P. R. China ‡ College of Chemical Engineering and Modern Materials, Shangluo University, Shangluo, 726000, P. R. China S Supporting Information *

ABSTRACT: The birnessite-type layered manganese oxide nanoplates with good dispersity and regular hexagonal morphology were obtained by topochemical oxidizing precursor Mn(OH)2 in NaClO solution for 24 h at room temperature, and its formation process was systematically investigated on the basis of the XRD pattern, FESEM and TEM images, XPS, Raman spectra, and TG-DTA analysis. The research results showed that the obtained birnessite-type layered manganese oxide nanoplates inherited the layered structure and regular hexagonal morphology from their Mn(OH)2 precursor. The regular hexagonal nanoplates were about 150 nm in each lateral edge with a thickness of 120 nm, which were selfassembled from MnO2 particles. The dispersity and regular morphology of the obtained materials were affected by the precursor Mn(OH)2 and the oxidation reaction times. This intermediate-mediated topochemical oxidation method could contribute to the design of new kinds of metal oxide materials with novel morphology and potential application.

1. INTRODUCTION The inorganic layered nanomaterials, including carbon group elements, transition metal chalcogenides, oxides, hydroxides, silicates, and nitrides, and so forth, due to their dimensiondependent properties, have attracted considerable attention because of their wide applications as electronic, photonic, magnetic, and mechanical materials.1−5 The novel layered structure gives these inorganic layered nanomaterials many excellent properties such as nanometer-scale thickness, high surface-to-volume ratio, ion-exchange property, and good mechanical durability.6,7 Because there are electrostatic attraction or van der Waals forces existing between the interlayers, the inorganic layered materials can be delaminated into unilamellar nanosheet units with the thickness on the order of around 1 nm and the lateral size ranging from submicrometer to several tens of micrometers,8−11 which allows them to serve as basic building blocks for reassembly into hybrid nanomaterials to fulfill technological desires for various new applications.12−14 Among the layered transition metal oxides, the birnessite-type manganese oxides with layered structure have been researched widely because of their special physical and chemical properties and potential applications in catalysis, ion exchange, molecular adsorption, and energy storage in lithium ion secondary batteries and supercapacitors.15−23 © 2014 American Chemical Society

Research results show that the morphology, dispersity, particle regularity, and specific surface area of the inorganic layered nanocomposites have a great effect on their properties.24−26 Therefore, it is important to controllably prepare the birnessite-type manganese oxides with layered structure possessing good dispersity and regular morphology from the viewpoint of the foundational research and technological application. Up to now, many efforts have been made to prepare the birnessite-type layered manganese oxides with different morphologies. One-dimensional (1D) birnessite nanowires and nanobelts are fabricated through a redox reaction between KMnO4 and MnCl2 in NaOH solution,27 or treating Mn2O3/K-birnessite in the KOH/NaOH solution by hydrothermal treatment.28,29 The two-dimensional (2D) birnessite-type manganese oxide with plate-like morphology is prepared by hydrothermally treating Mn(NO3)2 in a mixture solution composed of H2O2 and NaOH,30,31 and 2D birnessite nanowalls have been also fabricated on Si (111) substrate via a solution method and exhibit prominent magnetic anisotropy.32 The three-dimensional (3D) birnessite-type manganese oxides with honeycomb and hollow nanosphere morphology can be Received: June 24, 2014 Revised: August 31, 2014 Published: September 22, 2014 5626

dx.doi.org/10.1021/cg500921u | Cryst. Growth Des. 2014, 14, 5626−5633

Crystal Growth & Design

Article

appropriate modification.42 In a typical experiment, 0.3160 g of KMnO4 was dissolved in 40 mL deionized water, and then 5 mL of hydrazine hydrate (N2H4, 50%) was added into the KMnO4 solution slowly and stirred for 10 min. The obtained suspension was then transferred into a 60 mL Teflon-lined stainless steel autoclave, sealed, and maintained at 180 °C for 12 h and then air-cooled to room temperature. The white product was filtered and thoroughly washed with water, and then dried under vacuum at 60 °C for 10 min. The obtained product was ready for further processing and characterization. Preparation of Regular Hexagonal Manganese Oxide Nanoplates with Birnessite-Type Layered Structure (HMON). A typical synthesis procedure for HMON was as follows: 0.l7 g of the asprepared Mn(OH)2 nanoplate precursor with hexagonal morphology was first added to the NaClO solution (120 mL, 0.28 M), and the mixed suspension was treated using an ultrasonic bath for 5 min. After the suspension was stirred for 24 h at room temperature, the obtained product was filtered, washed with distilled water, and dried under vacuum at 60 °C for 2 h, and then the final product, HMON, was prepared. 2.3. Characterization. The X-ray diffraction patterns were measured on a Rigaku MiniFlex600 diffractometer with Cu Kα (λ = 1.5406 Å), using an operation voltage and current of 40 kV and 15 mA, respectively. The FESEM images were taken using Quanta 600F field emission scanning electron microscopy. TEM images and SAED patterns were taken with a JEM-200c transmission electron microscope operated at 200 kV. Thermal analysis was determined on TGDTA analysis (Q1000DSC + LNCS + FACS Q600SDT) at a heating rate of 10 °C/min from 25 to 1000 °C under nitrogen atmosphere. The X-ray photoelectron spectra (XPS) were recorded with the Axis Ultra spectrometer from Kratos Analytical Ltd. The binding energy reference was taken at 284.6 eV for the C 1s peak arising from surface hydrocarbons. The Raman spectra were measured using an Invia Raman microscope (wavelength = 532 nm, light power = 20 mW) between 200 and 1200 cm−1 at room temperature.

obtained through the reaction between KMnO4 and oleic acid at low temperatures, which show high catalytic activity for oxidative decomposition of formaldehyde.33 Moreover, birnessite-type layered manganese oxide single crystal with hexagonal prism morphology has been prepared by heating the mixture of γ-MnOOH and KNO3 at 700 °C.34 Recently, the birnessitetype layered manganese oxide nanoplates have been prepared via a biomimetic route, but the morphology of nanoplates is irregular.35 Although great effort has been made to prepare birnessite-type layered manganese oxides with different morphologies, it is still a challenge to prepare birnessite-type layered manganese oxides with good dispersity and regular morphology. The topochemical preparation technique plays an important role in the synthesis of the layered-structure materials with good dispersity and regular morphology. Up to now, many layered-structure materials with good dispersity and regular morphology such as layered doubled hydroxides (LDH),36−38 BaTiO3,39 and Nb2O5,40 and so forth, have been obtained by this technique. Mn(OH)2 with good dispersity and regular morphology has been prepared by many methods,41,42 and possesses a brucite-like phase and has a close structural similarity to the birnessite-like manganese oxide. In Mn(OH)2 with brucite-like phase, Mn2+ cations occupy octahedral sites generated by hydroxyl groups and the octahedral host layers are held together by van der Waals force.41 If Mn2+ cations are completely oxidized into Mn (IV), the birnessite-like manganese oxide nanoplate should be obtained. However, because Mn2+ cations occupying octahedral sites generated by hydroxyl groups are partly oxidized into Mn (III), alkali metal or alkaline earth metal cations and water molecules are incorporated into the interlayer space to balance the extra negative charge carried by oxygen atoms, forming a birnessitelike manganese oxide nanoplate stabilized by electrostatic interaction between the host layers and the cations as well as by hydrogen bonds existing among host layers, cations, and interlayer water molecules.43 Therefore, with the idea of topochemical reaction, would the birnessite-type layered manganese oxides with good dispersity and regular morphology be prepared from layered Mn(OH)2 with good dispersity and regular morphology? In the present work, Mn(OH)2 with good dispersity and hexagonal morphology was first prepared by a modified hydrothermal treatment method. Then, the birnessite-type layered manganese oxide with good dispersity and hexagonal morphology was obtained by topochemical oxidizing precursor Mn(OH)2 in NaClO solution for 24 h at room temperature, of which the formation process was also researched. The effect of the topochemical oxidation time on the morphology and structure of the obtained materials was systematically investigated. This intermediate-mediated topochemical oxidation method could contribute to the design of new kinds of metal oxide materials with the novel morphology and potential application.

3. RESULTS AND DISCUSSION 3.1. Structure and Morphology of Both Mn(OH)2 and HMON. The XRD patterns of the as-prepared Mn(OH)2 precursor and HMON are shown in Figure 1. It can be seen that all the diffraction peaks are well-indexed to the hexagonal phase Mn(OH)2 for the precursor (JCPDS, No. 73−1604, a = b = 3.322 Å, c = 4.734 Å) (Figure 1a),42 suggesting that the Mn(OH)2 precursor with hexagonal phase is obtained. After the precursor Mn(OH)2 is dispersed in NaClO solution and

2. EXPERIMENTAL SECTION 2.1. Materials. All chemicals were of analytical grade without further purification. KMnO4 (99.5%), hydrazine hydrate (50%), and sodium hypochlorite solution (NaClO, 10%) were all purchased from Sinopharm Group Co. Ltd. 2.2. Sample Preparation. Preparation of Mn(OH)2 nanoplate precursor with hexagonal morphology: the precursor, Mn(OH)2 hexagonal nanoplates were prepared by the reported method with

Figure 1. XRD patterns of Mn(OH)2 precursor (a) and the obtained HMON nanoplates (b). 5627

dx.doi.org/10.1021/cg500921u | Cryst. Growth Des. 2014, 14, 5626−5633

Crystal Growth & Design

Article

its precursor Mn(OH)2, despite the fact that the thickness of individual nanoplate increases from 50 to 120 nm (Figure 2a, right). These results indicate that the transformation process from Mn(OH)2 precursor to HMON is a topotactic reaction and regular hexagonal manganese oxide nanoplates with birnessite-type layered structure can be prepared by a topochemical oxidation technique. The oxidizing reagents have an obvious influence on the morphology of the obtained layered manganese oxides. Under the same experimental conditions, the layered manganese oxides with irregular hexagonal nanoplates are obtained by using KMnO4 as oxidizing reagent, while the layered manganese oxides with network structure are formed in H2O2 solution (Supporting Information Figure S2). Moreover, the manganese oxide nanoplates with regular hexagonal morphology are composed of the individual HMON nanoplate, suggesting that the manganese oxide nanoplates are self-assembled from HMON particles. Also, the topochemical reaction can be confirmed by TEM characterization. It can be observed that both the precursor Mn(OH)2 and HMON show quite similar hexagonal nanoplate morphology, only the thickness of the hexagonal nanoplate particles increases to 120 nm (Figure 2b). The transforming information on the crystal structure from precursor Mn(OH)2 to HMON is further analyzed by HRTEM and SAED. From HRTEM image of the precursor Mn(OH)2, the lattice fringe with an interplanar distance of 0.47 nm is consistent with the {001} facets of hexagonal phase Mn(OH)2,45 suggesting that the preferential growth direction of the hexagonal nanoplate is along the vertical [001] crystal axis (Figure 2c, left). On the other hand, the interplanar distance increases to 0.71 nm after the precursor Mn(OH)2 is oxidized into HMON, corresponding to the interplane distances of {001} facets in the birnessite-type layered manganese oxides (Figure 2c, right).29,34 The lattice fringes of the obtained Mn(OH)2 and HMON are only observed in some certain region instead of the whole area, suggesting that the hexagonal nanoplates of Mn(OH)2 and HMON are composed of many nanoparticles rather than whole hexagonal nanosheets. Moreover, the corresponding SAED patterns of both the precursor Mn(OH)2 and HMON show a singlecrystalline nature (inset of Figure 2c). These results indicate that the HMON inherits the morphology and layered structure of the precursor Mn(OH)2 crystals and the crystallinity of the brucite-like precursor nanoplates is perfectly maintained. The surface morphology of HMON hexagonal nanoplates is further characterized by FESEM and TEM images with high resolution. It can be seen that the surface of the uniform hexagonal nanoplates is very rough and accidented (Figure 3a). Further observed from TEM image, the rough and accidented surface is composed of many nanoparticles (Figure 3b,c). It is wellknown that the specific capacitance of manganese oxides is influenced by many factors, including porosity, morphology, defect chemistry, crystal structure, and residual water content,46 HMON hexagonal nanoplates assembled with MnO2 nanoparticles may be beneficial for the transport of electrolyte ions and electrons and can be used as a candidate of electrode material for supercapacitor. TG and DTA curves of the precursor Mn(OH)2 and HMON are shown in Figure 4. For the precursor Mn(OH)2, the weight loss of about 14.7% is associated with a sharp endothermic peak around 184 °C, which is nearly equal to the decomposition temperature of Mn(OH)2 (Figure 4a).47 In comparison with that of the precursor Mn(OH)2, the TG and DTA curves of

stirred for 24 h, the color of the suspension gradually changes from white to black−brown with the increase of the reaction time (Supporting Information Figure S1). The two obvious diffraction peaks in the XRD pattern of the black−brown product can be perfectly indexed to the monoclinic layered birnessite with lattice constants a = 5.175 Å, b = 2.849 Å, and c = 7.338 Å, which correspond with the (001) and (002) facets of birnessite (JCPDS, No. 73−1604) [space group: C2/m (12)] (Figure 1b).44 The d001 value of 0.71 nm is related to the interlayer spacing, with crystal water and exchangeable Na+ ions in the interlayer space,30 which is further confirmed by HRTEM characterization in the following section. The diffraction peaks are sharp and symmetric, indicating that the obtained HMON has good crystallinity. No peaks from other phases are observed, suggesting that the obtained HMON has high purity. These results suggest that Mn(OH)2 with divalent manganese can be transformed into HMON with a mixed valence of Mn(III) and Mn(IV), and HMON with high crystallinity can be controllably prepared when the precursor Mn(OH)2 is treated in NaClO solution at room temperature. The crystal structure and morphology transformation between Mn(OH)2 precursor and HMON are further characterized by FESEM, TEM, and HRTEM analysis, and the corresponding images are shown in Figure 2. FESEM

Figure 2. FESEM (a), TEM (b), and HRTEM images with the corresponding SAED patterns (inset) (c) of Mn(OH)2 precursor (left) and the obtained HMON nanoplates (right).

images show that the precursor Mn(OH)2 displays uniform nanoplate with hexagonal morphology, and the size of the hexagonal nanoplate particles is about 150 nm in each lateral edge with a thickness of 50 nm (Figure 2a, left). On the other hand, it can be seen that the obtained HMON almost maintains the morphology of uniform hexagonal nanoplate inherited from 5628

dx.doi.org/10.1021/cg500921u | Cryst. Growth Des. 2014, 14, 5626−5633

Crystal Growth & Design

Article

Figure 3. FESEM (a) and TEM images (b, c) with high resolution of the obtained HMON nanoplates.

Figure 5. XRD patterns of the obtained materials by oxidizing Mn(OH)2 precursor in NaClO solution at different reaction times: (a) 0 h, (b) 30 min, (c) 1.5 h, (d) 3 h, (e) 24 h, and (f) 48 h, respectively. Figure 4. TG-DTA curves of the Mn(OH)2 precursor (a) and the obtained HMON nanoplates (b).

reaction times. When the precursor Mn(OH)2 is oxidized in NaClO solution for 30 min, the obtained material almost maintains the typical structure of the precursor Mn(OH)2 except for the decrease in the peak intensity (Figure 5b). By prolonging the reaction time to 1.5 h, two new peaks appear at 12.3° and 24.9°, which correspond to the (001) and (002) facets of birnessite-type layered manganese oxides (Figure 5c).27,34 The typical peaks of Mn(OH)2 crystal are still observed, suggesting that the precursor Mn(OH)2 is incompletely oxidized to HMON. A new crystal corresponding to birnessite-type layered manganese oxides is completely obtained after the precursor Mn(OH)2 is oxidized in NaClO solution for 3 h (Figure 5d). By further prolonging the reaction time from 24 to 48 h, respectively, only the crystallinity of the obtained materials becomes weaker, while their crystal structure does not change (Figure 5e,f). These results indicate that the optimized topochemical oxidation time is 24 h for the transformation from Mn(OH)2 to HMON. TEM images suggest that the nanoplate with hexagonal morphology is almost maintained during the topochemical transformation from Mn(OH)2 to HMON at different reaction times (Figure 6). When the precursor Mn(OH)2 is stirred in NaClO solution for 30 min, the morphology of the obtained material is nearly similar to that of the precursor and no obvious change is observed (Figure 6a,b). By prolonging the reaction time into the range 1.5−3 h, the uniform hexagonal nanoplates are mainly observed and only a few nanoparticles are absorbed on

HMON are consisted of four steps (Figure 4b): (i) the weight loss of about 9.6 wt % is due to the physisorbed water on the surface of HMON from room temperature to 250 °C, (ii) the weight loss of 5.8 wt % is ascribed to the desorption of the crystal water existing in the interlayers of HMON in the temperature range of 250−350 °C, (iii) the significant weight loss between 400 and 600 °C is ascribed to the reduction of manganese from tetravalent to trivalent form accompanied by the evolution of oxygen, resulting in the phase transformation from MnO2 to Mn2O3, and (iv) the weight loss from 700 to 1000 °C is mainly attributed to the transformation from Mn2O3 to Mn3O4 accompanied by oxygen release.48,49 These results are very similar to those reported by refs 48−50 which also supports the transformation process from the precursor Mn(OH)2 to HMON. 3.2. Effect of the Topochemical Oxidation Time on the Morphology and Structure of the Obtained Materials. In order to investigate the topochemical oxidation process from Mn(OH)2 to HMON, the systematic timedependent experiments are carried out and the obtained materials are characterized by XRD and TEM techniques. The XRD patterns of the obtained materials at different reaction times are shown in Figure 5. It can be concluded that the crystal structure of the obtained materials are connected with the 5629

dx.doi.org/10.1021/cg500921u | Cryst. Growth Des. 2014, 14, 5626−5633

Crystal Growth & Design

Article

Figure 7. Mn 2p core level spectra (left) and Mn 3s core level spectra (right) of the obtained materials by oxidizing Mn(OH)2 nanoplate precursor in NaClO solution at different reaction times.

prepared MnO2,52 suggesting that a large number of Mn (IV) exists in HMON with layered structure. However, it is insufficient to determine the exact manganese oxidation state only from the Mn 2p spectrum because of the broadening or tailing of peaks at lower binding energy;53 therefore, more important information may be further obtained from Mn 3s core level spectrum. The Mn 3s core level spectra of the obtained materials at different oxidation times are shown in Figure 7, right. A peak splitting and a doublet can be observed due to a parallel spin coupling between the 3s electron and the 3d electron during the process of photoelectron ejection. In general, the splitting energy of Mn 3s can be used to determine the manganese valence, which is about 6.5 eV for Mn (II), 5.5 eV for Mn (III), and 4.5 eV for Mn (IV), respectively.54,55 The energy separation data (ΔE) between the two peaks for Mn 3s core level spectra is 5.95, 5.55, 5.45, 4.90, and 4.80 eV, respectively, for the obtained materials at 0 h, 30 min, and 1.5, 3, and 24 h, suggesting that the Mn valence of the obtained materials gradually rises with the increase of the oxidation reaction time. On the basis of an approximately linear relationship between the ΔE and the Mn oxidation state reported by Toupin group,56 the average oxidation state of Mn is estimated to be 3.8 for the obtained HMON, suggesting that the Mn (III) and Mn (IV) octahedra coexist and arrange orderly in the birnessite structure.57 The Raman bands of manganese oxides can be used to investigate the [MnO6] octahedral environment and identify the structure of the different crystalline phases. The Raman spectra of the obtained materials at different reaction times are shown in Figure 8. Because the precursor Mn(OH)2 is very susceptible in the air atmosphere, care must be taken when measuring its Raman spectrum. Through quick Raman measurement, the sharp Raman band of the precursor Mn(OH)2 is at 477 cm−1, similar to the value reported by ref 58. With the increase of the oxidation reaction times, the Raman band of about 477 cm−1 gradually disappears while a new Raman band around 640 cm−1 appears, suggesting that the [MnO6] octahedral environment changes with the increase of the oxidation reaction time. In addition, the Raman band in the

Figure 6. TEM images of the obtained materials by oxidizing Mn(OH)2 nanoplate precursor in NaClO solution at different reaction times: (a) 0 h, (b) 30 min, (c) 1.5 h, (d) 3 h, (e) 24 h, and (f) 48 h, respectively.

the hexagonal nanoplates (Figure 6c,d). After the topochemical oxidation time is prolonged to 24 h, it can be seen that the few nanoparticles disappear completely and uniform hexagonal nanoplates form at the same time (Figure 6e). By further extending the reaction times to 48 h, the hexagonal nanoplates are almost maintained, except some edges of nanoplates are destroyed (Figure 6f). TEM images also indicate that the optimized topochemical oxidation time is 24 h to prepare HMON with layered structure. Because the obtained birnessitetype layered manganese oxide nanoplates inherit the layered structure and morphology of the precursor Mn(OH)2, the size of the as-prepared materials is much the same even in the different oxidizing reaction times. X-ray photoelectron spectroscopy (XPS) is also applied to track the topochemical oxidation process from Mn(OH)2 to HMON. The XPS spectra of Mn 2p and Mn 3s of the obtained materials at different reaction times are analyzed and the results are shown in Figure 7. From the Mn 2p and Mn 3s core level spectra, it can be seen that their corresponding binding energy shift to the higher energy with the increase of the topochemical oxidation time, suggesting that the Mn valences of the obtained materials change gradually. For the precursor Mn(OH)2, two peaks at 648.5 and 636.5 eV are observed, which correspond to the binding energy of Mn 2p1/2 and Mn 2p3/2 (Figure 7, left). The binding energy values agree well with those of the prepared Mn(OH)2,51 suggesting that Mn (II) exists in the precursor Mn(OH)2. On the other hand, the two binding energy peaks gradually increase to higher energy when the topochemical oxidation time is prolonged. For HMON material, two peaks at 654 and 642.4 eV are observed, which correspond to the binding energy of Mn 2p1/2 and Mn 2p3/2. The binding energy values are consistent with those of the 5630

dx.doi.org/10.1021/cg500921u | Cryst. Growth Des. 2014, 14, 5626−5633

Crystal Growth & Design

Article

nanoplates.61−63 In the present work, the Mn(OH)2 hexagonal nanoplates with good dispersity possesses a brucite crystal and layered structure, each nanolayer of which comprises an edgesharing MnO6 octahedron and neighboring nanolayers bonded together by weak van der Waals forces along the c axis. Therefore, the brucite crystal could easily form two-dimensional nanocrystals, resulting in the general formation of nanoplate morphology because of the inherent crystal tendency.41,42 The oxidation state of manganese in Mn(OH)2 precursor is +2 and the average Mn (II)−O bond length is 2.2 Å, with the interplanar distance of 0.47 nm between Mn(OH)2 nanosheets. When the NaClO solution is added, the obtained crystal structures are dependent on the oxidation reaction times. A new phase indexed to birnessite-type layered manganese oxide with high crystalline is completely obtained after the precursor Mn(OH)2 is oxidized in NaClO solution for 24 h. With the oxidation reaction progressing, the original brucite structure is deformed due to the shrinkage of Mn−O bonds, and the arrangement of MnO6 octahedra changes from hexagonal crystal phase to the monoclinic one; meanwhile, the manganese oxide nanolayers become negatively charged due to the existence of Mn (III). Then, the hydrated foreign cations such as Na+ ions are inserted into the layers to compensate the negative charge, resulting in interlayer spacing of 0.71 nm, and the layered manganese oxide nanoplates with good dispersity and hexagonal morphology are obtained. XPS analysis results show that the average state of Mn is estimated to be about 3.8, indicating that a large number of Mn (II) atoms are oxidized to Mn (IV) with a small number of Mn (III) atoms. Because of the negatively charged manganese oxide nanosheets, the binding force between the layers changes from van der Waals force of Mn(OH)2 to electrostatic attraction of HMON. The transformation from Mn(OH)2 to HMON is carried out by a topochemical reaction process, and the obtained HMON nanoplates inherit the layered structure and hexagonal morphology from their brucite-like Mn(OH)2 precursor due to the topotactic nature of the transformation. Moreover, the crystal structures of Mn(OH)2 and HMON are simulated by the Diamond software and the corresponding results are shown in Supporting Information Figure S3. The atom distances of Mn−Mn between neighboring MnO6 octahedra are shortened from 3.32 Å of Mn(OH)2 to 3.17 or 2.86 Å of HMON, suggesting that the MnO6 octahedra in the HMON nanoplates are more compact than those in the Mn(OH)2 crystals. It is worth noting that two different changes of Mn−O bond distance is observed: one is shortened from

Figure 8. Raman spectra of the obtained materials by oxidizing Mn(OH)2 nanoplate precursor in NaClO solution at different reaction times: (a) 0 h, (b) 30 min, (c) 1.5 h, (d) 3 h, and (e) 24 h, respectively.

range of 200−500 cm−1 is ascribed to the Mn−O−Mn bending vibrations in the MnO2 octahedral lattice, while the Raman band in the range 500−700 cm−1 is assigned to the Mn−O stretching of [MnO6] octahedra.59 Yang’s group found that the Raman frequency increases as the nanocrystal size enlarges in both narrow and wide bandgap semiconductors.60 In the present work, it is worth noting that the Raman band at around 635 cm−1 gradually increases to 641 cm−1, resulting in a blueshift when the reaction time is prolonged from 1.5 to 24 h, suggesting that the particle size of HMON increases step by step. The experimental phenomenon is in accordance with the observation of FESEM and TEM images, which shows the thickness of the hexagonal nanoplates gradually increases from 50 to 120 nm, indicating that the particles are self-assembled to uniform hexagonal nanoplates. 3.3. Formation Process of HMON with Layered Structure. On the basis of the XRD patterns, FESEM and TEM images, XPS, Raman spectra, and TG-DTA curves, the formation process of HMON with layered structure is presented in Figure 9. In general, the brucite crystals (M(OH)2, M = Mg, Mn, Ni, etc.) have always been found in the form of

Figure 9. Formation process of HMON hexagonal nanoplates. 5631

dx.doi.org/10.1021/cg500921u | Cryst. Growth Des. 2014, 14, 5626−5633

Crystal Growth & Design

Article

(2) Novoselov, K. S.; Jiang, D.; Schedin, F.; Booth, T. J.; Khotkevich, V. V.; Morozov, S. V.; Geim, A. K. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 10451−10453. (3) Dhas, N. A.; Suslick, K. S. J. Am. Chem. Soc. 2005, 127, 2368− 2369. (4) Zhang, Y.; Tan, Y.-W.; Stormer, H. L.; Kim, P. Nature 2005, 438, 201−204. (5) Wang, Q.; O’Hare, D. Chem. Rev. 2012, 112, 4124−4155. (6) Coleman, J. N.; Lotya, M.; O’ Neill, A. Science 2011, 331, 586− 571. (7) Kumar, B.; Lee, D.-H.; Kim, S.-H.; Yang, B.; Maeng, S.; Kim, S.W. J. Phys. Chem. C 2010, 114, 11050−11055. (8) Liu, Z.-H.; Ooi, K.; Kanoh, H.; Tang, W.-P.; Tomida, T. Langmuir 2000, 16, 4154−4164. (9) Ma, R.; Sasaki, T. Adv. Mater. 2010, 22, 5082−5104. (10) Osada, M.; Sasaki, T. Adv. Mater. 2012, 24, 210−228. (11) Geim, A. K.; Novoselov, K. S. Nat. Mater. 2007, 6, 183−191. (12) Chen, C.-H.; Crisostomo, V. M. B.; Li, W.-N.; Xu, L. P.; Suib, S. L. J. Am. Chem. Soc. 2008, 130, 14390−14391. (13) Liu, Z.-H.; Yang, X. J.; Makita, Y.; Ooi, K. Chem. Mater. 2002, 14, 4800−4806. (14) Zhang, J. T.; Jiang, J. W.; Zhao, X. S. J. Phys. Chem. C 2011, 115, 6448−6454. (15) Prieto, O.; Arco, M. D.; Rives, V. J. Mater. Sci. 2003, 38, 2815− 2824. (16) Bach, S.; Pereira-Ramos, J. P.; Baffier, N. J. Solid State Chem. 1995, 120, 70−73. (17) Bach, S.; Pereira-Ramos, J. P.; Baffier, N.; Messina, R. Electrochim. Acta 1991, 36, 1595−1603. (18) Yagi, H.; Ichikawa, T.; Hirano, A.; Imanishi, N.; Ogawa, S.; Takeda, Y. Solid State Ionics 2002, 154, 273−278. (19) Bach, S.; Pereira-Ramos, J. P.; Baffier, N. Electrochim. Acta 1993, 38, 1695−1698. (20) Thackeray, M. M. Prog. Solid State Chem. 1997, 25, 1−71. (21) Subramanian, V.; Zhu, H.; Vajtai, R.; Ajayan, P. M.; Wei, B. J. Phys. Chem. B 2005, 109, 20207−20214. (22) Cheng, F. Y.; Zhao, J. Z.; Song, W.; Li, C. S.; Ma, H.; Chen, J.; Shen, P. W. Inorg. Chem. 2006, 45, 2038−2044. (23) Cheng, F. Y.; Yi, S.; Jing, L.; Tao, Z. L.; Chen, J. Chem. Mater. 2010, 22, 898−905. (24) Koivula, R.; Pakarinen, J.; Sivenius, M.; Sirola, K.; Harjula, R.; Paatero, E. Sep. Purif. Technol. 2009, 70, 53−57. (25) Zhai, Y.; Zhai, J.; Zhou, M.; Dong, S. J. Mater. Chem. 2009, 19, 7030−7035. (26) Zhao, J.; Tao, Z.; Liang, J.; Chen. J. Cryst. Growth Des. 2008, 8, 2799−2805. (27) Zhang, H. T.; Chen, X. H.; Zhang, J. H.; Wang, G. Y.; Zhang, S. Y.; Long, Y. Z.; Chen, Z. J.; Wang, N. L. J. Cryst. Growth 2005, 280, 292−299. (28) Liu, Z. P.; Ma, R. Z.; Ebina, Y.; Takada, K.; Sasaki, T. Chem. Mater. 2007, 19, 6504−6512. (29) Tang, X. H.; Li, H. J.; Liu, Z.-H.; Yang, Z. P.; Wang, Z. L. J. Power Sources 2011, 196, 855−859. (30) Feng, Q.; Sun, E.-H.; Yanagisawa, K.; Yamasaki, N. J. Ceram. Soc. Jpn. 1997, 105, 564−568. (31) Ching, S.; Neupane, R. P.; Gray, T. P. J. Chem. Educ. 2006, 83, 1674−1676. (32) Zhu, H. T.; Luo, J.; Yang, H. X.; Liang, J. K.; Rao, G. H.; Li, J. B.; Du, Z. M. J. Phys. Chem. C 2008, 112, 17089−17094. (33) Chen, H.; He, J.; Zhang, C.; He, H. J. Phys. Chem. C 2007, 111, 18033−18038. (34) Yang, X. J.; Tang, W. P.; Feng, Q.; Ooi, K. Cryst. Growth Des. 2003, 3, 409−415. (35) Oba, M.; Oaki, Y.; Imai, H. Adv. Funct. Mater. 2010, 20, 4279− 4286. (36) Ma, R. Z.; Takada, K.; Fukuda, K.; Iyi, N.; Bando, Y.; Sasaki, T. Angew. Chem., Int. Ed. 2008, 47, 86−89. (37) Ma, R. Z.; Liu, Z. P.; Takada, K.; Iyi, N.; Bando, Y.; Sasaki, T. J. Am. Chem. Soc. 2007, 129, 5257−5263.

2.196 to 1.916 Å and the other is lengthened from 2.196 to 2.397 Å in the structure of MnO6 octahedra. Brousse et al. have reported that the tunnel size significantly affects the capacitance of manganese-based pseudocapacitors, and the layeredstructure electrodes are favorable to the cation storage and exhibit higher capacitance, whereas tunnel-structure electrodes are unsuitable for cation storage.64 In the present work, the Mn−O bond distance is 2.397 Å in the structure of HMON, which is longer than the average bond distance of the bond Mn−O (1.899 Å).65 Therefore, the obtained HMON birnessite-type layered structure may show good properties such as capacitance and catalytic activity in comparison with the other types of manganese oxides such as α-MnO2, β-MnO2 and ε-MnO266−68 because the Mn−O bond is easily broken in certain chemical environments.

4. CONCLUSION By means of a topochemical oxidation reaction, the transformation process from the precursor Mn(OH)2 with brucitelike structure into manganese oxide nanoplates with birnessitetype layered structure is carried out in NaClO solution for 24 h at room temperature, and the birnessite-type layered manganese oxide nanoplates with good dispersity and regular hexagonal morphology are obtained. The regular hexagonal manganese oxide nanoplates have a size of 150 nm in each lateral edge with a thickness of 120 nm, and they are selfassembled from MnO2 particles. This topochemical oxidation preparation method can be applied to prepare other transition metal oxides with layered structure and a variety of oxidation states.

■

ASSOCIATED CONTENT

S Supporting Information *

Digital photographs to track the experimental period and crystal structures of the obtained precursor Mn(OH)2 and final product HMON. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*Tel: ++86-29-81530706. Fax: ++86-29-81530702. E-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS

■

REFERENCES

This work was supported by the National Natural Science Foundation of China (51172137), the Program for Key Science Technology Innovation Team of Shaanxi Province (2012KCT21), the 111 Project, and the Fundamental Research Funds for the Central Universities (GK201101003 and GK201301002).

(1) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Katsnelson, M. I.; Grigorieva, I. V.; Dubonos, S. V.; Firsov, A. A. Nature 2005, 438, 197−200. 5632

dx.doi.org/10.1021/cg500921u | Cryst. Growth Des. 2014, 14, 5626−5633

Crystal Growth & Design

Article

(38) Liang, J. B.; Ma, R. Z.; Iyi, N.; Ebina, Y.; Takada, K.; Sasaki, T. Chem. Mater. 2010, 22, 371−378. (39) Buscaglia, M. T.; Harnagea, C.; Dapiaggi, M.; Buscaglia, V.; Pignolet, A.; Nanni, P. Chem. Mater. 2009, 21, 5058−5065. (40) Li, L. H.; Deng, J. X.; Yu, R. B.; Chen, J.; Wang, X. W.; Xing, X. R. Inorg. Chem. 2010, 49, 1397−1403. (41) Zhang, X.; Qian, Y. T.; Zhu, Y. C.; Tang, K. B. Nanoscale 2014, 6, 1725−1731. (42) Zhang, X.; Xing, Z.; Wang, L. L.; Zhu, Y. C.; Li, Q. W.; Liang, J. W.; Yu, Y.; Huang, T.; Tang, K. B.; Qian, Y. T.; Shen, X. Y. J. Mater. Chem. 2012, 22, 17864−17869. (43) Gaillot, A.-C.; Lanson, B.; Drits, V. A. Chem. Mater. 2005, 17, 2959−2975. (44) Zhou, J. L.; Yu, L.; Sun, M.; Yang, S. Y.; Ye, F.; He, J.; Hao, Z. F. Ind. Eng. Chem. Res. 2013, 52, 9586−9593. (45) Li, Y. G.; Wu, Y. Y. Nano Res. 2009, 2, 54−60. (46) Wang, X. L.; Yuan, A. B.; Wang, Y. Q. J. Power Sources 2007, 172, 1007−1011. (47) Ohtsuka, K.; Suda, M.; Tsunoda, M.; Ono, M. Chem. Mater. 1990, 2, 511−517. (48) Schurz, F.; Bauchert, J. M.; Merker, T.; Schleid, T.; Hasse, H.; Gläer, R. Appl. Catal. A: Gen. 2009, 355, 42−49. (49) Ding, Y.; Shen, X.; Sithambaram, S.; Gomez, S.; Kumar, R.; Crisostomo, V. M.; Suib, S. L.; Aindow, M. Chem. Mater. 2005, 17, 5382−5389. (50) Athouel, L.; Moser, F.; Dugas, R.; Crosnier, O.; Be’langer, D.; Brousse, T. J. Phys. Chem. C 2008, 112, 7270−7277. (51) Anandan, S.; Raj, B. G. S.; Lee, G.-J.; Wu, J. J. Mater. Res. Bull. 2013, 48, 3357−3361. (52) Dubal, D. P.; Dhawale, D. S.; Salunkhe, R. R.; Lokhande, C. D. J. Electroanal. Chem. 2010, 647, 60−65. (53) Pinaud, B. A.; Chen, Z. B.; Abram, D. N.; Jaramillo, T. F. J. Phys. Chem. C 2011, 115, 11830−11838. (54) Brabers, V. A. M.; Vansetten, F. M.; Knapen, P. S. A. J. Solid State Chem. 1983, 49, 93−98. (55) Toupin, M.; Brouss, T.; Bélanger, D. Chem. Mater. 2002, 14, 3946−3952. (56) Toupin, M.; Brouss, T.; Bélanger, D. Chem. Mater. 2004, 16, 3184−3190. (57) Ressler, T.; Brock, S. L.; Wong, J.; Suib, S. L. J. Phys. Chem. B 1999, 103, 6407−6420. (58) Gosztola, D.; Weaver, M. J. J. Electroanal. Chem. 1989, 271, 141−154. (59) Julien, C.; Massot, M. Phys. Chem. Chem. Phys. 2002, 4, 4226− 4235. (60) Yang, C. C.; Li, S. J. Phys. Chem. B 2008, 112, 14193−14197. (61) Yu, J. C.; Xu, A. W.; Zhang, L. Z.; Song, R. Q.; Wu, L. J. Phys. Chem. B 2004, 108, 64−70. (62) Liu, Z. P.; Ma, R. Z.; Osada, M.; Takada, K.; Sasaki, T. J. Am. Chem. Soc. 2005, 127, 13869−13874. (63) Li, Y. G.; Tan, B.; Wu, Y. Y. Chem. Mater. 2008, 20, 567−576. (64) Brousse, T.; Toupin, M.; Dugas, R.; Athouel, L.; Crosnier, O.; Belanger, D. J. Electrochem. Soc. 2006, 153, A2171−A2180. (65) Palenik, J. G. Inorg. Chem. 1997, 36, 4888−4890. (66) Tang, N. A.; Tian, X. K.; Yang, C.; Pi, Z. B. Mater. Res. Bull. 2009, 44, 2062−2067. (67) Xu, M.; Kong, L.; Zhou, W.; Li, H. J. Phys. Chem. C 2007, 111, 19141−19147. (68) Yu, P.; Zhang, X.; Chen, Y.; Ma, Y. W.; Qi, Z. P. Mater. Chem. Phys. 2009, 118, 303−307.

5633

dx.doi.org/10.1021/cg500921u | Cryst. Growth Des. 2014, 14, 5626−5633