Surface properties of sol-gel synthesized δ-MnO2 as assessed by N2 sorptometry, electron microscopy, and X-ray photoelectron spectroscopy

Pure delta-MnO2 materials were prepared by calcination at 259-700 degrees C for 3 h of a parent gel obtained by (i) a sol-gel synthesis involving a mild reduction of KMnO4 solution; (ii) drying at room temperature (iii) calcination to 700 or 900 degrees C, and (iv) a subsequent acid treatment at room temperature. The bulk crystalline structure of the delta-MnO2 materials was evidenced by thermogravimetry, X-ray powder diffractometry (XRD) and high-resolution transmission electron microscopy (HRTEM). Then, surface properties were determined by X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy, and N-2 sorptometry. The results revealed that the bulk structure is morphologically organized in the form of needle-like nanofibers. Surfaces thereon exposed were found to assume high specific area (74 m(2) g(-1)) and heat of adsorption (BET-C = 130), as well as a mesoporous texture, when initially calcined to 700 degrees C. These surface properties were also found to withstand subsequent calcination at up to 350 degrees C for 3 h. (C) 2000 Elsevier Science B.V. All rights reserved.