Disposal of used optical disks utilizing thermally-excited holes in titanium dioxide at high temperatures: A complete decomposition of polycarbonate

Disposal of used optical disks is an urgent requirement for electronic industries. We propose a decomposition system of polycarbonates (PC) (used as substrate materials for optical disks) that utilizes thermally-excited holes at high temperatures. The present system is based on an oxide semiconductor (TiO2) heated at about 500°C in combination with a molten state of PC. Molten PC chains are first adsorbed on the surface of TiO2 due to electrostatic interactions between positively charged oxygen vacancies in TiO2 and the polar carbonyl group of PC: ∣O∣..⋯Oδ−Cδ+. Adsorbed PC is then oxidized by thermally-excited holes in TiO2 and decomposed into small fragments, followed by their combustion in the presence of oxygen to give solely H2O and CO2. The decomposition mechanism has been discussed on the basis of nonstoichiometric properties of TiO2 at high temperatures together with adsorption behavior of PC on the surface of TiO2.