Development of new nanomaterials syntheses for mesostructured TiO2 and SiO2

Abstract: Mesostructured materials is a class of materials within the concept nanomaterials and characterized by structural features on the length scale 2-50 nm. This group of materials is interesting for several applications such as, membrane and separation technology, heterogeneous catalysis, controlled release, adsorption of pollutants, solar energy conversion, electrode materials etc. These materials can be prepared with a wide range of chemical compositions. The thesis focuses on syntheses of mesostructured silica and titania. The interests for mesostructured materials is growing and the need for low cost large scale production methods is becoming interestingly important. An alkaline silicate solution, also called waterglass, is a cheap silica source that has been studied for this purpose. Mesostructured materials are formed using a structure directing supramolecular assembly as template. These are either based on surfactants or block-copolymers and for a large scale application, nonionic amphiphiles are desired. Synthesis methods for mesostructured silica require tuning the conditions for inducing the gelation of the silica monomers within the amphiphilic liquid crystal template. The gelation behavior of water glass has therefore been studied by adjusting pH or solvent evaporation and found to be fundamentally different for this. Following this a study of the liquid crystal formation of waterglass and nonionic surfactant mixtures has been examined and the first direct synthesis of mesostructured silica from alkaline water glass and non-ionic block-copolymers developed. Titanium dioxide is a photoactive semiconductor in its crystalline state. Mesoordered crystalline titania is desired in photovoltaic and photocatalytic applications. However, titania normally crystalises through solid state reactions at several hundred degrees centigrade, whereas liquid crystals that are used for templating mesoorder exist at much lower temperatures as aqueous mixtures. A low temperature microemulsion synthesis of nanoparticulate crystalline titania was developed and further modified into a new direct synthesis methodology for the preparation of mesoporous titania with hexagonal mesostructure and with walls of tunable crystallinity and crystallite size.