The formation of vanadyl hydrogen phosphate hemihydrate (VOHPO(4)(.)0.5H(2)O) by progressive attachment of phosphorous to a vanadium oxide lamellar phase in the presence of cetyltrimethylammonium bromide (CTAB) is described. Evidence from nuclear magnetic resonance (NMR), XPS, X-ray diffraction (XRD) and scanning electron microscopy (SEM) is presented for the initial formation of a vanadium oxide lamellar structure with no long-range order to which phosphate is then progressively attached. Phosphate attachment leads to lamellar collapse with the resultant formation of the hemihydrate phase, VOHPO(4)(.)0.5H(2)O. (C) 2003 Elsevier B.V. All rights reserved.