Versatile functional groups were covalently attached to the surface of multiwalled carbon nanotubes (MWNTs) by one-step free radical addition of water-soluble azo initiators. The coverage density of functional groups is rationally controlled either by adjusting the feed ratio of azo initiators to MWNTs or by utilizing the starting chemicals of multifunctional groups. TEM observations in conjunction with solubility data imply that the functionalized- MWNTs have much better dispersibility and stability than pristine MWNTs in polar solvents. The attached carboxylic groups were then used as scaffolds to chelate Ag+ ions affording Ag/MWNTs nanohybrids in the presence of NaBH4 reductant. This shows that the reactive groups anchored on MWNTs can be further chemically functionalized. The proposed method might open many new opportunities for the development of high-performance nanomaterials containing CNTs. (C) 2009 Elsevier B. V. All rights reserved.