Mechanism of Pt loading on multi-walled carbon nanotubes.

Microwave treatment of multi-walled carbon nanotubes (MWCNTs) with nitric acid (HNO3) and 0.2 M sodium chlorate (NaClO3) can generate and enhance defects on the surfaces of MWCNTs. These defects are the important sites to load Pt nanoparticles (NPs). We investigated the defect induced Raman spectra and observed a decrease in the R-values (D-band/G-band peak ratio) and a slight up-shift of the both peaks as the amount of loaded Pt NPs increased. Using the Brunauer-Emmett-Teller (BET) method, we observed that the pore size distribution and the pore volume changed according to the amount of Pt NPs loaded. Fewer micropores and mesopores were observed on MWCNTs loaded with Pt NPs. Based on the pore size distribution calculated from the BET results, Pt NPs loaded mainly on pores/defects with a size of 2-8 nm. Transmission electron microscopy and Raman spectroscopy results confirmed that most well-crystallized Pt NPs loaded on the surface defect sites and pores spontaneously through the exchange of electrons between Pt and C atoms.