Carbon-regulated titania crystallization to construct a comprehensive palette of anatase/rutile mixed phases for advanced photocatalysis

Abstract

In this work, a series of carbon-doped, amorphous titania was constructed by the calcination of titania xerogel in argon for carbonization and subsequent calcination in air at 300 °C to deliberately adjust carbon doping concentration and then subjected to calcination in argon. This method enabled us to quantitatively study the impact of carbon doping on anatase growth and anatase-to-rutile transition (ART), and the impact was studied through X-ray diffraction with the aid of Rietveld refinement, Raman spectroscopy, X-ray photoelectron spectroscopy, and thermal analysis coupled with mass spectroscopy. Regardless of the concentration, on the one hand, carbon doping demonstrated a conspicuous promotive impact on ART and can substantially reduce the ART temperature to as low as 525 °C. On the other hand, carbon doping demonstrated an unmistakable inhibitory impact on anatase growth, which became more pronounced with its concentration increasing. Capitalized on the concentration-regulated balance between the promotive and inhibitory effects of carbon doping on titania crystallization, we unveiled two structural criteria of the anatase phase – crystal size of about 14 nm and crystallinity of about 30% – for ART but also devised 125 titania samples of defined but varied anatase/rutile mixed (ARM) – phases. Using such a large collection of titania samples, we managed to independently interrogate the photocatalytic performance dependent on ARM-phase titania based on their anatase sizes and rutile fractions. Our findings revealed that the optimal anatase size was about 25 nm, and the rutile fraction was about 16% for the degradation of gaseous acetaldehyde under UV light.