Abstract
It is a subject of exploration whether the phase pure anatase or rutile TiO2 or the band alignment due to the heterojunctions in the two polymorphs of TiO2 plays the determining role in efficacy of a photocatalytic reaction. In this work, the phase pure anatase and rutile TiO2 have been explored for photocatalytic nitroarenes reduction to understand the role of surface structures and band alignment towards the reduction mechanism. The conduction band of synthesized anatase TiO2 has been found to be more populated with electrons of higher energy than that of synthesized rutile. This has given the anatase an edge towards photocatalytic reduction of nitroarenes over rutile TiO2. The other factors like adsorption of the reactants and the proton generation did not play any decisive role in catalytic efficacy.
Highlights
It is a subject of exploration whether the phase pure anatase or rutile TiO2 or the band alignment due to the heterojunctions in the two polymorphs of TiO2 plays the determining role in efficacy of a photocatalytic reaction
X-ray diffraction (XRD) patterns in Fig. 1a and b represents the formation of phase pure tetragonal anatase (JCPDS: 89-4921; SG: I41/amd) and rutile TiO2 (JCPDS: 89–6975; SG:P42/mnm) synthesized by the solution combustion and polymerizable sol-gel approaches, respectively
The rutile TiO2 exhibited characteristic stretching peaks at 140, 430, and 590 cm−1 that correspond to the symmetries of B1g, exposed surfaces11–15. The bandgap (Eg), and A1g, respectively[55]
Summary
It is a subject of exploration whether the phase pure anatase or rutile TiO2 or the band alignment due to the heterojunctions in the two polymorphs of TiO2 plays the determining role in efficacy of a photocatalytic reaction. The general consensus over the conduction band position of the two polymorphs are arguable as the electrochemical impedance analyses established the conduction band of anatase lies 0.2 eV above that of rutile[18,19,20,21] while, the photoemission measurements have reported the reverse trend[22,23,24] This band alignment, would play a significant role on transferring the photogenerated electrons from anatase and rutile to the reactants. Phase pure anatase was synthesized by solution combustion method, whereas, rutile was synthesized by polymerizable sol-gel route Both the catalysts were structurally, morphologically and electronically characterized before studying their photocatalytic performances of nitroarenes reduction. The catalytic mechanism was understood from the surface structure and the electronic band structure
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