This work presents results demonstrating control over heterogenite (beta-CoOOH) nanoparticle properties through modifications to the synthetic preparation method. The particles are prepared by first precipitating cobalt (II) hydroxide, followed by oxidation to form heterogenite. The temperature during the synthesis yields control over the size and phase of the precursor cobalt (II) hydroxide particles generated, and the choice of oxidizing agent (H(2)O(2) or NaOCl) yields the greatest degree of control over the transformation from precursor to product. Oxidization by H(2)O(2) results in heterogenite crystallites that are substantially smaller than the precursor Co(OH)(2) particles, preserving very little of the Co(OH)(2) morphology and structure. Oxidization by NaOCl, in contrast, leaves intact features such as the shape and size of the Co(OH)(2) particles as well as preserves the intercalation of anions such as chloride. (C) 2011 Elsevier Ltd. All rights reserved.