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Chemical state and coordination structure of La cations doped in KTaO3 photocatalysts


Hanggara Sudrajat, Indika Thusharic, Sandhya Babel

Source title: 
Journal of Physics and Chemistry of Solids, 127: 94-100, 2019 (ISI)
Academic year of acceptance: 

We here dope KTaO3 with La through a solid-state route, resulting in enhanced photocatalytic activity for the mineralization of p-nitrophenol under UV light. We suggest simultaneous substitution of K and Ta by La, leading to lattice expansion and surface nanosteps. With increasing the La concentration, the conduction band edge is raised, while the valence band remains unchanged. As a result, the band gap increases. The raised conduction band edge is proposed to be the key behind the enhanced photocatalytic activity since it results in an increased reduction power of photoproduced electrons. The raised conduction band edge is also an indication of the substitution of Ta, which mainly makes up the conduction band, by La. Furthermore, X-ray photoelectron spectroscopy and X-ray absorption near edge structure confirm the oxidation state of La residing on the surface and in the bulk to be +3, as anticipated. Extended X-ray absorption fine structure then confirms that increasing the La concentration slightly increases the length and the coordination number of La-O bond in the here prepared La-doped KTaO3. The increased bond length is due to the expanded lattice, while the increased coordination number is due to the increased numbers, and hence the contributions, of La-O pairs.