Carbon auto-doping improves photocatalytic properties of biotemplated ceramics

Biotemplated porous ceramics based on titania are promising candidates for the photo induced degradation of organic compounds in polluted streaming media, such as water or gas vapors. Reactors in various shapes can easily be produced by stringing a natural tissue template. Porous biotemplated ceramics were processed by vacuum infiltration of a titanium(IV)-isopropoxide-based sol into freeze dried stems of soft rush (Juncus effuses) and subsequent calcination between 400 and 800 degrees C. The solution of carbon in titania during calcination drastically improved the surface dependent photocatalytic activity, which was evaluated in comparison to commercially available titania powders. The biotemplated ceramics calcined below 600 degrees C showed the anatase phase, whereas calcination at higher temperatures leads to a mixture of anatase and rutile. The carbon content as measured by energy dispersive X-ray spectroscopy was reduced from 31.0 mol% after calcination at 400 degrees C-1.6 mol% after calcination at 800 degrees C. The auto-formation of Ti-OC/Ti-OCO bonds due to the temperature induced substitution of oxygen atoms by carbon atoms from the biotemplate and the formation of interstitial carbon was verified by X-ray Photoelectron Spectroscopy measurements. The lowest band edge energy, calculated from UV/vis-spectrometry measurements was found at 419 nm (2.96 eV) for the biotemplated samples calcined at 800 degrees C. The specific surface varied between 0.5 m(2)/g and 45 m(2)/g. (C) 2011 Elsevier B.V. All rights reserved.