Development of new nanomaterials syntheses for mesostructured TiO2 and SiO2
Doktorsavhandling, 2011

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.

X-ray diffraction

microemulsion synthesis

silica

high-resolution electron microscopy

gelation

nonionic amphiphiles

EISA

titania

mesostructured

waterglass

KC-salen, Kemigården, Chalmers
Opponent: Prof. Mika Lindén, Ulm University, Ulm, Germany

Författare

Erik Nilsson

Chalmers, Kemi- och bioteknik, Teknisk ytkemi

Mesoporösa material har en definierad porstorlek mellan 2-50 nm. I början på 1990-talet kom man på ett sätt att organisera porerna så att de hade en enhetlig storlek och var arrangerade i ett regelbundet mönster. Tänkbara användningsområden för mesoordnade material är, separationsteknik, katalysatorer, adsorbenter av föroreningar och kontrollerad frisättning av till exempel läkemedel. Den här avhandlingen behandlar nya metoder att framställa mesoordnad kiseldioxid och titandioxid. Dessa metoder bygger på användandet av vätskekristaller. Vattenglas är en basisk vattenlösning av kiseldioxid som används i många olika sammanhang för storskalig produktion av kiseldioxidbaserade produkter. Vattenglas som källa för mesoordnad kiseldioxid är intressant eftersom det möjliggör en direkt och billigare metod än de som typiskt används idag. Förutom att vattenglaset i sig är en billig kiselkälla så kan det också användas direkt som vattenfas i vätskekristallen vilket förenklar metoden eftersom antalet ingående komponenter i syntesen minskar. Mesoordnad titandioxid är intressant eftersom det potentiellt främjar de fotoaktiva egenskaperna på grund av sin större reaktiv yta, ökade kontakt mellan titandioxidpartiklarna samt en mer definierad porstorlek och porstruktur. I avhandlingen presenteras en metod att bilda kristallin titandioxid vid låga temperaturer och hur kristallstrukturen kan kontrolleras samt hur man sedan kan inkorporera dessa kristallina nanopartiklar i en mesoordnad form.

Mesoporous materials are defined as materials with pore size between 2-50 nm. In the early 1990s, a way to organize the pores so they had a uniform size and were arranged in a regular pattern, was invented. Potential uses for mesoordered materials are, separation technolgy, catalysts, adsorbents of pollutants and controlled release of such drugs. This thesis deals with new methods to produce mesoordered silica and titania. These methods are based on the use of liquid crystals. Waterglass is an alkaline aqueous solution of silica used in a wide variety of large-scale production of silicabased products. Waterglass as a source for mesoordered silica is interesting because it allows for more direct and less expensive methods than those typically used today. In addition the waterglass can also be used directly as the aqueous phase in liquid crystal, which simplifies the method because the number of components used in the synthesis is reduced. Mesoordered titanium dioxide is interesting because it potentially enhances the photo-active properties due to their greater reactive surface area, increased contact between the titanium dioxide particles and a more defined pore size and pore structure. The thesis presents a method to form crystalline titanium dioxide at low temperatures, how the crystal structure can be controlled and how these crystalline nano-particles can be incorporated in a mesoordered form.

Ämneskategorier

Oorganisk kemi

Bearbetnings-, yt- och fogningsteknik

Annan materialteknik

Drivkrafter

Hållbar utveckling

Styrkeområden

Nanovetenskap och nanoteknik

Materialvetenskap

ISBN

978-91-7385-553-2

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3234

KC-salen, Kemigården, Chalmers

Opponent: Prof. Mika Lindén, Ulm University, Ulm, Germany