Table of Contents Author Guidelines Submit a Manuscript
Journal of Nanomaterials
Volume 2009 (2009), Article ID 940462, 8 pages
http://dx.doi.org/10.1155/2009/940462
Research Article

Synthesis and Characterization of Birnessite and Cryptomelane Nanostructures in Presence of Hoffmeister Anions

1Department of Natural Sciences, University of Maryland Eastern Shore, Princess Anne, MD 21853, USA
2Department of Chemistry, Rocky Mountain College, 1511 Poly Drive, Billings, MT 59102, USA
3Department of Aerospace Engineering Sciences, University of Colorado at Boulder, 429 UCB, Boulder, CO 80309, USA
4Department of Chemistry, University of Nevada Las Vegas, 4505 Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA
5Department of Aerospace Engineering, Old Dominion University, ECSB 1309, Elkhorn Ave, Norfolk, VA 23529-0247, USA

Received 19 November 2008; Accepted 16 March 2009

Academic Editor: Sherine Obare

Copyright © 2009 Marcos A. Cheney et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The effect of Hoffmeister anions C l , S O 4 2 , and C l O 4 on the structure and morphology of birnessite and cryptomelane-type manganese dioxide nanostructures, produced by the reduction reaction of K M n O 4 and M n S O 4 in aqueous acidic media, was studied. The syntheses were based on the decomposition of aqueous K M n O 4 in presence of HCl for birnessite-type and acidified M n S O 4 for cryptomelane-type manganese dioxide under soft hydrothermal conditions. They were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) techniques. XRD patterns show the formation of birnessite for the first synthesis and a mixture of cryptomelane and birnessite-types M n O 2 for the second synthesis. XRD data revealed that the Hoffmeister anions have a significant effect on the nanostructures of birnessite. The sulphate ion-treated birnessite has the smallest crystals, whereas the chloride ion-treated birnessite has the largest crystals. Their TEM and HRTEM studies revealed a transformation from nanoplatelet morphology for chloride-treated samples to nanofibrous morphology for sulphate-treated birnessite. For the cryptomelane nanostructures, Hoffmeister anions also show a profound effect on their crystalline structures as determined by XRD analyses revealing a transformation of the cryptomelane phase to birnessite phase of M n O 2 . This transformation is also supported by TEM and HRTEM studies.