Single wall carbon nanotubes (SWNTs) with diameters below 1 nm prepared by chemical vapor deposition (CVD), and with diameters of 1.3 nm and higher prepared by laser ablation and carbon-arc techniques, were electrochemically functionalized with hydrogen and nitro groups, and chemically derivatized with 4-nitroaniline. Hydrogen adsorption on SWNTs was carried out in the presence or absence of electrodeposited catalytic nanoparticles of magnesium. SWNTs deposited on Teflon-coated membranes by vacuum filtration and lifted off as free-standing nanopaper, were used as the electrodes for electrochemical functionalization reactions. Hydrogen uptake on the nanotubes was characterized by micro-Raman spectroscopy, thermogravimetry and thermopower measurements. Electrochemically-induced functionalization with −NO2 groups on metallic, laser-synthesized SWNTs was clearly detected by Raman spectroscopy. Chemical functionalization was achieved on CVD-produced SWNTs by acidification to form −COOH groups followed by reaction with thionyl chloride and then with 4-nitroaniline. Photoacoustic effects that are likely to be precursors of photo-induced initiation of energetic reactions, were observed to occur at varying laser intensities for these materials in experiments using a pulsed Nd-YAG laser emitting at 532 nm.