Development of new nanomaterials syntheses for mesostructured TiO2 and SiO2
Doctoral thesis, 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
Author
Erik Nilsson
Chalmers, Chemical and Biological Engineering, Applied Surface Chemistry
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.
Subject Categories
Inorganic Chemistry
Manufacturing, Surface and Joining Technology
Other Materials Engineering
Driving Forces
Sustainable development
Areas of Advance
Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)
Materials Science
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