Catalytic photooxidation of pentachlorophenol using semiconductor nanoclusters

Pentachlorophenol (PCP) is a toxic chlorinated aromatic molecule widely used as a fungicide, a bactericide, and a wood preservation, and thus is ubiquitous in the environment. We report photooxidation of PCP using a variety of nanosize semiconductor metal oxides and sulfides in both aqueous and polar organic solvents and compare the photooxidation kinetics of these nanoclusters to widely studied bulk powders such as Degussa P25 TiO2 and CdS. We study both the light- intensity dependence of PCP photooxidation for nanosize SnO2 and the size dependence of PCP photooxidation for both nanosize SnO2 and MoS2. We find an extremely strong size dependence for the latter which we attribute to its size-dependent band gap and the associated change in redox potentials due to quantum confinement of the hole-electron pair. We show that nanosize MoS2 with a diameter of d = 3.0 nm and an absorbance edge of similar to 450 nm is a very effective photooxidation catalyst for complete PCP mineralization, even when using only visible-light irradiation.