Microwave acid purification with H2SO4 was performed on multi-walled carbon nanotubes (MWNTs) synthesised by fluidised-bed chemical vapour deposition (CVD) to remove Fe catalysts and Al2O3 substrates. The surface of these purified MWNTs was then modified with HNO3 under the influence of an ultrasonic field followed by functionalised with Pt nanoparticles in methanol expanded with supercritical CO2. The weight loss profile of the purified sample treated at 200 degrees C under microwave irradiation shows the MWNT purity to be 96.5 wt%. TEM images of Pt functionalised MWNTs show that Pt nanoparticles of approximately 4nm were deposited on the outer tube walls. SEM/EDX results confirm that the Pt nanoparticles were mono-sized and evenly distributed. Raman spectroscopy suggested that supercritical processing conditions can repair wall defects in MWNTs. XRD analysis confirmed the presence of crystalline Pt particles. (C) 2010 Elsevier B.V. All rights reserved.