In this work the hydrogen storage behaviors of chemically treated multi-walled carbon nanotubes (MWNTs) were investigated The surface properties of the functionalized MWNTs were confirmed by Fourier transfer infrared spectroscopy X-ray diffraction the Boehm titration method and zeta-potential measurements The hydrogen storage capacity of the MWNTs was evaluated at 298 K and 100 bar In the experimental results it was found that the chemical treatments introduced functional groups onto the MWNT surfaces The amount of hydrogen storage was enhanced by acidic surface treatment to 042 wt % in the acidic-treated MWNTs compared with 026 wt % in the as-received MWNTs Meanwhile the basic surface treatment actually reduced the hydrogen storage capacity to 0 24 wt % in the basic-treated MWNTs sample Consequently it could be concluded that hydrogen storage is greatly influenced by the acidic characteristics of MWNT surfaces resulting in enhanced electron acceptor-donor interaction at interfaces (c) 2010 Elsevier B V All rights reserved