Abstract
LaCoO3 epitaxial films were grown on (100), (110) and (111) oriented LaAlO3 substrates by the polymer-assisted deposition method. Crystal structure measurement and cross-section observation indicate that all the LaCoO3 films are epitaxially grown in accordance with the orientation of LaAlO3 substrates, with biaxial compressive strain in the ab plane. Owing to the different strain directions of CoO6 octahedron, the mean Co–O bond length increases by different amounts in (100), (110) and (111) oriented films compared with that of bulk LaCoO3, and the (100) oriented LaCoO3 has the largest increase. Photocatalytic degradation of methyl orange indicates that the order of photocatalytic activity of the three oriented films is (100) > (111) > (110). Combined with analysis of electronic nature and band structure for LaCoO3 films, it is found that the change of the photocatalytic activity is closely related to the crystal field splitting energy of Co3+ and Co–O binding energy. The increase in the mean Co–O bond length will decrease the crystal field splitting energy of Co3+ and Co–O binding energy and further reduce the value of band gap energy, thus improving the photocatalytic activity. This may also provide a clue for expanding the visible-light-induced photocatalytic application of LaCoO3.
Highlights
In recent years, with the increasingly prominent problem of environmental pollution, photocatalytic materials based on2018 The Authors
The atomic force microscopy (AFM) images of (100), (110) and (111) oriented LCO films are shown in figure 2a–c
The asymmetric in-plane φ-scans of films and substrates indicate that the in-plane symmetry of each film is consistent with that of the corresponding substrate. These results demonstrate that each LCO film shows epitaxial growth in accordance with the orientation of the LAO substrate
Summary
With the increasingly prominent problem of environmental pollution, photocatalytic materials based on. The octahedral crystal field of CoO6 octahedron always splits the fivefold 3d orbital of Co3+ into higher doublet eg orbital and lower triplet t2 g orbital when disrupted by different effects such as doping and chemical or external pressure, making electrons transfer from the t2 g level to the eg level which is conducive to the generation of electron–hole pairs and the improvement of photocatalytic activity [10]. Based on this feature, LCO is considered as a promising photocatalytic material. The results will provide a striking proof to reveal the interrelationship between orientation-dependent structural and photocatalytic properties of the LCO nano-thin epitaxial films
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