Plasma Processing Approach to Molecular Surface Tailoring of Nanoparticles:  Improved Photocatalytic Activity of TiO2

Plasma enhanced chemical vapor deposition (PECVD) was employed to modify surfaces of TiO2 nanoparticles. To help overcome nanoparticle aggregation, a 360° rotating reactor was employed to provide continuous agitation and mixing of the particles during the plasma induced film deposition process. The nanoparticles were coated with thin films produced from the plasma polymerization of tetramethyltin (TMT) monomer. Subsequently, the coated particles were heated in air to remove the carbonaceous material while, simultaneously, oxidizing the tin atoms to tin oxide. The photocatalytic activity of the tin oxide coated TiO2 was then measured and contrasted with that of untreated TiO2 particles. A significantly enhanced increase in the oxidation rate of acid orange (AO7) dye was observed with the modified particles. Additional experiments employing a mixture of TMT and perfluoropropylene oxide monomers were used to achieve surfaces possessing partially fluorinated tin oxide. The fluorine doped tin oxide coatings exhibited even higher catalytic activity than that obtained from TMT only experiments. Some experiments involving characterization of the films before and after the annealing process, specifically those involving X-ray diffraction and atomic force microscopy measurements, were carried our using flat glass or polished silicon substrates. Overall, this study demonstrates the general utility of PECVD technology to provide effective coating of ultrafine nanoscale particles.