Materials Letters 63 (2009) 2218–2220
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Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Synthesis and characterization of nanocrystalline manganese pyrophosphate Mn2P2O7 Banjong Boonchom a,b,⁎, Rattanai Baitahe b a b
Chumporn campus, King Mongkul's Institute of Technology Ladkrabang, 17/1M. 6 Patiuw Distict, Chumphon 86160, Thailand Department of Chemistry, Faculty of Science, King Mongkut's Institute of Technology Ladkrabang, Ladkrabang, Bangkok, 10520, Thailand
a r t i c l e
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Article history: Received 10 June 2009 Accepted 17 July 2009 Available online 23 July 2009 Keywords: Manganese pyrophosphate Mn2P2O7 Nanoparticles Synthesis FTIR and FT-Raman
a b s t r a c t Mn2P2O7 polyhedral particles were synthesized by simple and cost-effective method using manganese nitrate hydrate and phosphoric acid in the presence of nitric acid with further calcinations at the temperature of 800 °C. The crystallite size obtained from X-ray line broadening is 31 ± 13 nm for the Mn2P2O7. The X-ray diffraction and SEM results indicated that the synthesized nanoparticles have only the structure without the presence of any other phase impurities. The FT-IR and FT-Raman spectra show characteristic bands of the 2+ ion. P2O4− 7 anion. The UV–Vis–NIR spectrum confirms the octahedral coordination of Mn © 2009 Elsevier B.V. All rights reserved.
1. Introduction Manganese pyrophosphate Mn2P2O7 has been found to have a wide range of applications and can be used as catalysts, reactants in ionic conditions, intercalation reactions, laser host, ceramic dye pigments, ion exchangers, ionic conductors, and as superphosphate fertilizers [1–3]. This compound has synthesized either by hydrothermal or by high-temperature methods and characterized by single crystal structure determination [4]. Recently, the transition metal pyrophosphates are also currently of interest in the field of lithium ion batteries cathode materials [5–7] such as mixed orthophosphates LiM2P2O7 (M = Fe, Co, Cu, Ni, Mn) which give good electrochemical performances. In addition, manganese is environmental friendly and cheap. Herein we report for the first time the synthesis of nanocrystalline Mn2P2O7 with a crystallize size of ∼30–500 nm by a simple method using manganese nitrate hydrate and phosphoric acid in the presence of nitric acid. The synthesized nanocrystalline Mn2P2O7 sample was characterized by X-ray powder diffraction(XRD), Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Fourier transform Raman (FT-Raman), and UV–Vis–NIR techniques.
AR) was added. The resulting solution was stirred in hot plate at 40 °C until NO2 (g) ceased to evolve and finally the gray-green precursor precipitates. The gray-green powders were filtered by suction pump and washed with deionized water. In order to gain the decomposition and crystallization of nanoparticles, the prepared sample was calcined in a furnace at 800 K for 3 h in air. The final product was characterized for crystal phase identification by X-ray powder diffraction using a D8 Advanced powder diffractometer (Bruker AXS, Karlsruhe, Germany) with Cu Kα radiation (λ = 0.1546 Å). The morphology was examined with Scanning Electron Microscopy (SEM) using LEO SEM VP1450 after gold coating. The room temperature FTIR and FT-Raman spectra were recorded on a Perkin-Elmer Spectrum GX FT-IR/FT-Raman spectrometer with the resolution of 4 cm− 1. The FTIR spectrum was recorded using KBr pellets (KBr, Jasco, spectroscopy grade) in the range of 4000–370 cm− 1 with 8 scans. The FT-Raman spectrum was recorded with spectrum 2000R NIR FT-Raman system in a PerkinElmer Spectrum GX model equipped with a HeNe laser (1064 nm). The laser power about 500 mW was used for excitation in the range between 4000 and 100 cm− 1 with 32 scans. The diffuse reflectance spectrum (solid state UV–Vis–near IR) was obtained by a Shimadzu UV-3100 spectrophotometer using an integrating sphere and BaSO4 as the reference blank.
2. Experimental Following procedure, 5 mL of 86.4% H3PO4 (Fluka, AR) was added to 5 g of Mn(NO3)2·4H2O (Merck, AR) and then 3 mL of HNO3 (Merck, ⁎ Corresponding author. Chumporn campus, King Mongkul's Institute of Technology Ladkrabang, 17/1M. 6 Patiuw Distict, Chumphon 8610, Thailand. Tel.: +66 7750 6422x4565; fax: +66 7750 6410. E-mail address:
[email protected] (B. Boonchom). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.07.028
3. Results and discussion XRD pattern of the prepared sample in Fig. 1(a) shows same peak patterns, which can be indexed as manganese pyrophosphate (Mn2P2O7) structure in the standard data (PDF#771243). The result indicated that Mn2P2O7 crystal structure is monoclinic system with space group C2/m (Z= 2). Cell parameters were obtained from a least square
B. Boonchom, R. Baitahe / Materials Letters 63 (2009) 2218–2220
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Fig. 1. XRD pattern (a) and SEM micrograph (b) of Mn2P2O7.
refinement of the XRD data with the aid of a computer program. The least squares refinement of the indexed pattern gave a cell with dimensions: a = 6.64(0), b = 8.57(0), c = 4.51(0) Å and β = 102.86(0) °. The cell parameters of Mn2P2O7 are close to those of the standard data PDF#771243 (a = 6.63(4), b = 8.58(4), c = 4.64(7) Å and β = 102.67 (0) °). The average crystallite size of Mn2P2O7 was calculated from X-ray line broadening of the reflections of (111), (−201), (220), (221) and (400), using Scherrer equation (i.e. D = 0.89λ/βcosθ, where λ is the wavelength of X-ray radiation, D is a constant taken as 0.89, θ is the diffraction angle and β is the full width at half maximum (FWHM)) and was obtained to be 31 ±13 nm. The average crystallite size of Mn2P2O7 from this work is smallest than that reported in our previous work [2,8]. The SEM micrograph of Mn2P2O7 is shown in Fig. 1(b). The Mn2P2O7 shows polyhedral grains and agglomeration, which consists nanoparticles having a distribution of small particles (100–200 nm) and large particles (N200–500 nm). The morphology of the studied compound is different from that reported in our previous work that exhibited a porous structure and agglomeration, which consist of small particles of 30–50 nm [2]. The formation of nanocrystalline Mn2P2O7 sample is further supported by FTIR and FT-Raman spectra (Fig. 2a and b). The FTIR and FT-Raman spectra of Mn2P2O7 samples from both prepared methods are quite similar but some band positions are little different. The FTIR spectra closely resemble those of M2P2O7 (M= Cu, Cd, Fe, Mn, Ni) [8,9]. The FTIR and FT-Raman bands are identified in terms of the fundamental vibrating 4+ units namely P2O4− 7 anion. The P–O stretching modes of the [P2O7] anion are known to appear in the 1250–950 cm− 1 region. The symmetric PO2 stretching vibrations (νsym PO2) are observed at 1127 and 1040 cm− 1, while the asymmetric stretching vibration (νasym PO2) is located at 1090 cm− 1. The asymmetric (νasym POP) and symmetric stretch (νsym POP) bridge vibrations for this salt are observed at 736 cm− 1. In addition, the PO3 deformation and rocking modes, the POP deformations, and the torsional and external modes are found in the 430–180 cm− 1 region [9]. The comparison of the vibrational bands from corresponding FTIR and FT-Raman shows exclusion principle, which can be interpreted to a centrosymmetric structure and the space group is C62h (C2/m). The XRD data along with FTIR and FT-Raman observations confirm that the studied sample is manganese pyrophosphate (Mn2P2O7). The excitation spectrum (Fig. 3) is constituted of different groups of absorption bands. The band located around 280 nm is associated with the charge transfer state of Mn2+–O2−. Those ranging from 300 to 780 nm correspond to the forbidden 3d→3d transitions of manganese. This broad band between 300 and 780 nm is associated with components of the 4T2(4G) and 4T1(4G) levels. On the other hand,
Fig. 2. FTIR spectra (a) and FT-Raman (b) spectra of Mn2P2O7.
the diffuse reflectance spectrum in the near IR region shows two sets of bands : (i) a very wide band (900–1480 nm) due to the overtones and combinations of the different OH stretching (ν(PO–H), ν(O–H), ν(MnO–H)) and (ii) two partially overlapping band centered at 1751 nm, which corresponds to the ν(PO–H) + δ(H3O+) and ν(PO– H) + δ(OHO) combination vibrations, respectively [10,11].
4. Conclusion Manganese pyrophosphate Mn2P2O7 was successfully synthesized by precipitation from manganese nitrate hydrate and phosphoric acid in the presence of nitric acid. The Mn2P2O7 product is polycrystalline, having the crystallite size of 30–100 nm, determined by XRD. Its morphology appears to be polyhedral grains and agglomeration, as revealed by SEM. The comparison of the vibrational bands from observed FTIR and FT-Raman confirmed to a centrosymmetric structure
Fig. 3. Diffuse reflectance spectrum of Mn2P2O7.
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and the space group is C62h (C2/m), which according to XRD data. Optical measurement using UV–Visible spectrometer showed the evidence for the Mn2+ ion the skeletal structure. This material may be useful for possible potentially as catalysts, reactants in ionic conditions, intercalation reactions and laser host applications. Acknowledgements This work is financially supported by the Thailand Research Fund (TRF) and the Commission on Higher Education (CHE): Research Grant for New Scholar, Ministry of Science and Technology and Ministry of Education, Thailand.
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