Synthesis and microstructure of porous Mn-oxides Svetozar Music ´ a, * , Mira Ristic ´ a , Stanko Popovic ´ b a Division of Materials Chemistry, Ruder Boškovic ´ Institute, P.O. Box 180, HR-10002 Zagreb, Croatia b Department of Physics, Faculty of Science, University of Zagreb, P.O. Box 331, HR-10002 Zagreb, Croatia article info Article history: Received 13 August 2008 Accepted 6 October 2008 Available online 12 October 2008 Keywords: a-Mn 2 O 3 Mn 3 O 4 Porous oxides Urea processing abstract Porous Mn-oxide particles were synthesized by urea processing in combination with the thermal treat- ment of the precursor precipitated. The samples were characterized by XRD, FT-IR, DTA, FE-SEM and EDS. Upon heating of the precursor at 600 °C, a-Mn 2 O 3 particles containing nanopores (cheese-like) were obtained. Most nanopores varied from 20 to 60 nm, and some were close to 100 nm in size. The a- Mn 2 O 3 particles showed a strong twinning effect. At 1100 °C, Mn 3 O 4 particles, obtained as a single crystal phase, formed a microporous 3D structure. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Porous metal oxides find various applications in catalysis, chro- matography, separations, environmental sensing, etc. The investi- gation of porous metal oxides is also important from the academic standpoint and for that reason the relationships between the synthesis route and porosity of metal oxides were investigated. Different synthesis routes were used in the preparation of porous metal oxides, e.g., sol–gel processing, sonochemistry, water-in-oil microemulsion processing, etc. Influences of various templates on the formation of porous metal oxides were also investigated. Gen- erally, the control of the porous microstructure of metal oxides is not an easy task, because this property strongly depends on the conditions of the chemical synthesis. Small variations in the syn- thesis conditions may change the porosity, as well as the size and morphology of the particles. In the present work we are reporting new results in the synthe- sis of porous a-Mn 2 O 3 and Mn 3 O 4 particles. The synthesis route is based on the thermal treatment of the precursor produced by urea processing in an aqueous medium. Generally, porous Mn-oxides are important materials for possible applications as catalysts, sor- bents or electrode materials. 2. Experimental 2.1. Preparation of samples All chemicals were of analytical purity. Twice-distilled water was used. The precursor of porous Mn-oxides was prepared using the fol- lowing procedure. An aqueous solution containing 0.2 M Mn(NO 3 ) 2 and 2.0 M urea was heated under reflux in an oil-bath at 95 °C. The reaction was stopped when pH 7.54 (measured at RT) was reached. The isolated precipitate was subsequently washed with twice-dis- tilled water, then dried. After drying the precipitate was thermally treated at different temperatures. 2.2. Instrumentation pH measurement was carried out with a pH meter (model pHM- 26) manufactured by Radiometer. A combined glass electrode with an operating range of up to pH  14, also Radiometer make, was used. X-ray powder diffraction patterns were taken at RT using an automatic Philips diffractometer MPD 1880 (Cu Ka radiation; graphite monochromator; proportional counter). Fourier transform infrared spectra were recorded at RT using a Perkin–Elmer spectrometer (model 2000). The FT-IR spectrometer was connected to a personal computer. The spectra were processed using the IRDM (IR Data Manager) program. The specimens were pressed into KBr discs. DTA analysis was performed using a Netzsch instrument. The temperature was controlled by a Pt–Pt/Rh (10%) thermocouple, and the heating rate was 10 °C min 1 . A thermal field emission scanning electron microscope (JSM- 7000F), manufactured by Jeol Ltd., was used to inspect the size and morphology of the prepared particles. In the present case the particles inspected by FE-SEM were not coated with a con- ductive layer. FE-SEM was coupled with EDS/INCA 350 (energy dispersive X-ray analyzer) manufactured by Oxford Instruments Ltd. 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.10.005 * Corresponding author. Tel.: +385 1 4561 094. E-mail address: music@irb.hr (S. Music ´). Journal of Molecular Structure 924–926 (2009) 243–247 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc