Dependence of photocatalytic activity on aspect ratio of a brookite TiO2 nanorod and drastic improvement in visible light responsibility of a brookite TiO2 nanorod by site-selective modification of Fe3+ on exposed faces

• Pure brookite TiO2 was synthesized by a hydrothermal method.
• Reaction sites on brookite TiO2 nanorods were separated by controlling of its morphology.
• Brookite TiO2 nanorods loaded with Fe3+ ions showed visible light activity.

Exposed crystal face-controlled brookite titanium(IV) oxide (TiO2) nanorods with various aspect ratios were prepared by a hydrothermal process with or without PVA or PVP as an aspect reagent. The nanorod-shaped brookite TiO2 had larger {2 1 0} and smaller {2 1 2} exposed crystal faces, which were assigned by TEM with the SAED technique. Their aspect ratios were greatly influenced by the addition of PVA or PVP as an aspect ratio control reagent to the reaction solution used in the hydrothermal treatment. The photocatalytic activity for decomposition of acetaldehyde increased with increase in the aspect ratio because the surface area ratio of {2 1 0} to {2 1 2} exposed crystal faces, which are attributed to reduction and oxidation sites, respectively, became more optimal.The {2 1 2} exposed crystal faces of surface-controlled brookite TiO2 were site-selectively modified with trivalent iron(III) (Fe3+) ions by utilizing the adsorption property of iron(III)/iron(II) (Fe3+/Fe2+) ions. The brookite TiO2 nanorod with site-selective modification of Fe3+ ions showed much higher photocatalytic activity than that of commercial brookite TiO2 loaded with Fe ions under visible-light irradiation because of the separation of redox sites. In other words, oxidation and reduction proceed over Fe3+ ion-modified {2 1 2} faces of the TiO2 surface and on {2 1 0} faces of the TiO2 surface without modification of Fe3+, respectively.

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