High-quality spinel LiCoTiO4 single crystals with co-exposed {111} and {110} facets: flux growth, formation mechanism, magnetic behavior and their application in photocatalysis

Novel spinel LiCoTiO4 single crystals with co-exposed {111} and {110} facets were grown for the first time using a facile LiCl flux method. The obtained cubic-phase LiCoTiO4 crystals exhibit high crystallinity and regular octahedron-like geometric morphology. In this method, LiCl was used not only as an effective lithium source without any additives but also as the optimum molten medium compared with LiCl–NaCl and LiCl–KCl eutectic mixtures. The formation mechanism responsible for the flux-grown spinel LiCoTiO4 crystals with co-exposed {111} and {110} facets was also proposed. Moreover, the spinel LiCoTiO4 crystals showed a weak ferrimagnetic behavior with some antiferromagnetic effects. Photocatalytic tests revealed that the pure LiCoTiO4 sample had a relatively low photocatalytic activity although it had a relatively narrow band-gap energy (1.58 eV) corresponding well to the broad visible spectrum. However, the spinel LiCoTiO4 crystal could serve as an efficient visible-light sensitizer, and when coupled with graphitic carbon nitride (g-C3N4) nanosheets, the novel LiCoTiO4/g-C3N4 composites exhibited higher activity than pure g-C3N4 for the photocatalytic degradation of organic pollutants under simulated sunlight. A possible mechanism for the improved photocatalytic performance was also proposed. Overall, our present work opens a new approach to fabricating other lithiated transition-metal oxide spinel crystals for broad industrial applications.