Ordering of TiO2 nanoparticles to mesoporous structures

Mesoporous titania is a cheap, non-toxic photocatalyst that can play an important role in for example hydrogen generation from water splitting, -air and water purification. Furthermore, porous titania is already used as a catalyst in different industrial processes, such as the recovery of elemental sulfur from waste gases. A generally applied synthesis strategy for this kind of materials is the soft-templating approach in which hydrolysis and condensation reactions around micelles of the template result in the formation of an amorphous network of titanium dioxide[1]. This is followed by a thermal treatment to remove the template and crystallize the TiO2. The disadvantage of this procedure is the use of high thermal treatment temperatures, necessary to create the photocatalytically active anatase crystal phase, which causes the collapse of the porous structure due to thermal instability of the organic soft template. A recently developed strategy to synthesize crystalline mesoporous TiO2 structures consists of first synthesizing TiO2 nanocrystals and their subsequent ordering by addition of a micelle forming surfactant that contains a functional chemical group that can chemically anchor to the nanoparticles[2]. This approach was used for the research depicted in this presentation. Two different surfactants were investigated, the self-synthetized PDMA-b-PS and PDEA-b-PS block copolymers. The acrylamide block copolymers differ only in the substituents on the amide functionality; two methyl-groups in the case of PDMA and two ethyl-groups for the PDEA block copolymer. These substituents influence the global thermal degradation temperature but also the polarity of the polar, nanocrystal-interacting polymersegment. By self-synthesizing the polymers the pore-diameter of the mesoporeus titataniaU+2019s could be controlled by changing the global length of the polymer, without changing the ratio of the polar/apolar segments. The obtained mesoporeus powders with the self-synthesized block copolymers were compared with a commercially available surfactant, pluronic P123, for specific surface area and crystallinity . We were able to obtain crystalline anatase TiO2 exhibiting a surface of 230 m²/g and a high degree of crystallinity. These powders were also investigated for their photocatalytic activity by following the degradation of methylene blue under UV-light. References [1] V. Meynen, P. Cool and E. F. Vansant, Microporous and Mesoporous Materials 2009, 125, 170-223. [2] R. Buonsanti, T. E. Pick, N. Krins, T. J. Richardson, B. A. Helms and D. J. Milliron, Nano Letters 2012, 12, 3872-3877.