This special issue contains selected peer-reviewed papers which were presented at the Third International Conference on Diffusion in Solids and Liquids (DSL-2007), held at the Hotel Pestana Alvor Praia, Algarve, Portugal during the 4th-6th July, 2007.

Current water-treatment technologies require considerable energy consumption. Thus, closely linked to the problem of water shortage is the impending energy crisis. Therefore, intensive research is being aimed at developing water purification processes that are based upon using renewable energy, such as solar energy, rather than energy generated using fossil fuels. There has been an accumulation of reports on the development of photocatalysts, which enable water purification using solar energy as the only driving force. Such photocatalysts, based upon oxide semiconductors, permit the conversion of solar energy into the chemical energy that is required for the oxidation of toxic organic compounds in water. The most promising photocatalyst is titanium dioxide, TiO2, and its solid solutions. The research on TiO2 photocatalysis is multidisciplinary, and progress in this area requires the application of concepts of catalysis and photocatalysis as well as concepts of solid-state chemistry.

Volume is indexed by Thomson Reuters CPCI-S (WoS). The goal of this special collection was to provide a unique opportunity to gather together the latest results as well as to review the current issues most relevant to diffusion research.

This special issue of Defect and Diffusion Forum contains selected refereed papers which were presented at the 7th International Conference on Diffusion in Solids and Liquids (DSL-2011) held on the 26 to 30th June 2011 at the Hilton Vilamoura, Algarve, Portugal. The goal of the conference was to provide a unique opportunity to exchange information, to present the latest results and review burning issues in contemporary diffusion research. Young scientists were especially encouraged to attend the conference and to establish international links with established scientists. Volume is indexed by Thomson Reuters CPCI-S (WoS)