Effect of titanium dioxide crystalline structure on the photocatalytic production of hydrogen

Abstract

PapersPerformance of the photo-Fenton process in the degradation of a model azo dye mixture J. Macías-Sánchez et al., Photochem. Photobiol. Sci., 2011, 10 The effect of the crystalline phase of TiO 2 (anatase, rutile and brookite) on its photocatalytic activity in hydrogen production from methanol-water vapours has been investigated by testing a series of both home-made and commercial TiO 2 photocatalysts, either bare or surface-modified by deposition of a fixed amount, i.e. 1 wt%, of platinum as co-catalyst. For all of the TiO 2 samples the rate of hydrogen production increased by one order of magnitude upon Pt deposition, because of the ability of Pt to enhance the separation of photoproduced electron-hole pairs. Under irradiation in the 350-450 nm wavelength range, brookite and anatase showed similar photoactivities, both superior to that of rutile. By contrast, rutile, possessing a narrower band gap, was active also under visible light (l > 400 nm), whereas no hydrogen evolution was observed with anatase and brookite under such conditions. Surface area proved to be a key parameter, strongly influencing photoactivity. However, as the particle size became ultra-small, the semiconductor absorption edge was blue-shifted because of size quantisation effects, with a consequent decrease in hydrogen production rate due to the smaller portion of incident photons absorbed by the photocatalyst.

Brookite, the Least Known TiO2 Photocatalyst

“…The phase composition was tuned by varying the water-isopropanol ratio. The samples were active for the degradation of methyl orange under UV irradiation and a following treatment with N-methylpyrrolidone enhanced the photocatalytic activity under visible light [123,[175][176][177].…”

“…A brookite sample with improved crystallinity and sufficient surface area obtained by calcination at 873 K exhibited the hydrogen evolution rate almost equal to that of P25 [118,119]. Chiarello et al [123] proved that Pt-deposited brookite is a very good photocatalyst for obtaining hydrogen from methanol steam reforming under UV-vis irradiation, also in consideration of its high selectivity to CO 2 formation and low CO production. Kandiel et al [23] reported that the photocatalytic hydrogen evolution of anatase/brookite mixtures and pure brookite was higher than that of pure anatase.…”

Understanding the Reaction Mechanism of Photocatalytic Reduction of CO2 with H2O on TiO2-Based Photocatalysts: A Review

“…Besides anatase/rutile mixtures, TiO 2 anatase/brookite mixtures have been applied for the photodegradation of organic compounds (e.g., methyl orange, rhodamine B) (Chiarello et al, 2011;Boppella et al, 2012;Gai et al, 2012;Jiao et al, 2012b;Zhao et al, 2012a), which exhibited higher activity than P25 and pure-phase anatase. Recently, bicrystalline TiO 2 with controllable anatase/brookite phase content has been used as a photocatalyst for CO 2 photoreduction with H 2 O (Zhao et al, 2013).…”

Engineering titania nanostructure to tune and improve its photocatalytic activity

“…Anatase and rutile TiO 2 polymorphs have been thoroughly investigated because they are thermodynamically favored in the nanoscale form and in the bulk, respectively (14). Brookite, in contrast, has rarely been studied, despite theoretical and experimental data supporting its higher activity in some photocatalyzed transformations (15)(16)(17)(18)(19)(20). Previously, structural modifications (21), doping (22), or the formation of heterojunctions with plasmonic building blocks (23) have shown promise in promoting its photocatalytic activity.…”