Preparation And Visible-light-induced Photocatalytic Property Of LaCoO₃ Epitaxial Films

LaCoO₃ is an important perovskite structure cobalt oxide with good photocatalytic activity.In particular,it can effectively utilize visible light with a high proportion in the solar spectrum to achieve photolysis of water,purification of air,photocatalytic degradation of organics,etc.,and it has broad application prospects.In this paper,based on the technique of polymer assisted deposition for preparing LaCoO₃epitaxial thin films,the film forming mechanism of polymer assisted deposition was analyzed and he influence of PEI molecular weight,heat treatment conditions and spin coating speed on the epitaxial quality of the films were examined.Furthermore,the structural characteristics of La CoO₃ under different orientations and stress states were studied,and the influence mechanism of crystal orientation and structure regulation on the visible light catalytic properties of LaCoO₃ was revealed.The results show that the core of PAD epitaxial technology lies in the chelation of PEI,and-NH groups play a key role in the chelation of cations by PEI.There are more-NH groups in PEI with higher molecular weight,which is beneficial to improve the crystallinity and epitaxial quality of the films.The increase of heat treatment temperature can improve the epitaxial quality of the films.Simultaneously,the thickness of the film can be easily adjusted by changing the spin coating speed.With the induced and restricted effects of single crystal substrate on the growth of the films,the regulation of crystal surface growth and the structural distortion of the LCO epitaxial films can be achieved.The increase of the bond length of Co-O bond length can reduce the field splitting energy of CoO₆ and the binding energy between Co³⁺and O^2-,further decreases the band gap of LCO and enhances its photocatalytic ability.As a result,the order of photocatalytic activity of LCO epitaxial films with different crystal orientations is:LCO/（100）LAO>LCO/（111）LAO>LCO/（110）LAO.In addition,the induction of single crystal substrates with different lattice constants can also lead to the difference in the degree of tetragonal distortion and the crystal field splitting energy of CoO₆ octahedron.The increase of the tetragonal distortion of CoO₆ octahedron can reduce the band gap of e_g-t_2gg and enhance the degree of Co^3d-O^2phybridization,which helps to improve the surface light absorption and photocatalytic activity of LCO epitaxial films.As a result,the order of photocatalytic activity of different structurally distorted LCO epitaxial films is:LCO/（100）SLAO>LCO/（100）LAO>LCO/（100）STO>LCO/（100）LSAT.