We report a large reduction in the work function of acid oxidised multi-wall carbon nanotubes upon exchange of protons associated with acidic surface groups with the alkali metal cations Li+, Na+ and K+ measured using ultra-violet photoelectron spectroscopy. X-ray photoelectron spectroscopy provides compelling evidence for the preferential uptake of Na+, over Li+ and K+ and yields an estimate of the density of surface bound carboxylic acid moieties onto which functional organic molecules can be chemically attached. (c) 2006 Elsevier B.V. All rights reserved.