Titania nano-network film templated from microphase-separated block copolymer and its photocatalysis in fractured form
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Yih Hsing Lo Department of Polymerization Catalysis and Engineering, Union Chemical Laboratories, ITRI, Hsin-Chu, Taiwan 300, Republic of China (Received 26 January 2005; accepted 15 March 2005)
A thin-frame nano-network film of titania with backbone diameter of 20–30 nm was obtained from precursor templating of nano-porous polymer with nano-channels 50 nm in width. The nano-porous polymer templates were prepared by selective removal of the polyisoprene (PI) domain with ozone from the bicontinuous structure formed through blending a symmetric polystyrene-block-polyisoprene (PS-b-PI) copolymer with a PS homopolymer (h-PS). The titania network possessed the preferred anatase crystallinity for photocatalytic applications and a specific surface area of 53 m2/g, comparable to that of Degussa P25, a widely used commercial photocatalyst. Photocatalytic performance of the fractured titania network film was also comparable to that of Degussa P25 in both gas-phase NO oxidation and liquid phase methylene blue degradation. The much larger overall structure size of the fractured titania network film, however, offers advantages over the nano-particulate form of P25, namely, easy handling and rapid recycling from treated streams.
I. INTRODUCTION
Titania is probably the most important and widely studied photocatalyst, applied particularly in the area of environmental pollution control, due to its strong redox ability, chemical stability, nontoxic nature, and low cost. When applied as a photocatalyst, titania is commonly produced in particulate form tens of nanometers in size, since the relevant manufacturing processes have been well developed for mass production. There are, however, some drawbacks for such practices. It is well known that nano-sized particles are difficult to process because they tend to aggregate into large particle-clusters due to the high particle surface energy, thus losing much of their readily accessible surface area for catalytic function. Even when they are well dispersed in solvent, the nanoscale size of the catalyst particles presents much difficulty for catalyst separation from the treated stream and recycling back into the photoreactor because of the dominant random Brownian motion for nano-sized particles.1 One way to circumvent these disadvantages is to make larger porous titania structures, in the submicron or even a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0190 J. Mater. Res., Vol. 20, No. 6, Jun 2005
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micrometer ranges, with continuous large pores framed with thin backbones. Here, the large structure size, for which deterministic gravitational, centrifugal, or shear force is dominant over the random Brownian force, enables easier processing and handling. In addition, continuous large pores provide low intra-structure mass transfer resistance, and thin backbones offer reasonably large specific surface areas for catalytic function. To create larger size porous titania structures, template
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