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 °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 °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 °C–1.6 mol% after calcination at 800 °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 °C. The specific surface varied between 0.5 m2/g and 45 m2/g.

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► Carbon can be doped automatically into the titania lattice during biotemplating.
► Band edge shift into VIS range by carbon auto-doping into the titania lattice.
► Carbon auto-doping increases the photocatalytic activity of titania.
► 800 °C is the optimum temperature for the preparation of biotemplated photocatalysts.