Effect of formaldehyde on the photochromic properties of ordered molybdenum oxide thin films produced by hydrothermal process

Molybdenum oxide thin films are prepared with different volume ratios of formaldehyde solution and sodium molybdate solution ranging from 0 to 0.5:10 via hydrothermal method. The results characterized from XRD and TEM demonstrate that all of the as-prepared films are MoO3 hexagonal structures. The SEM images reveal that the surface of the film formed without formaldehyde consists of hexagonal prisms, and the surface morphology of the film to be composed of fibration structures when the volume ratio of formaldehyde solution and sodium molybdate solution is 0.1:10. When increasing the volume ratio of formaldehyde solution and sodium molybdate solution, the surface morphologies of the film transformation to flower-like structures are observed. It is found that the higher the content of formaldehyde, the more complete the flower-like structures. The most ordered flower-like molybdenum oxide film which has the best photochromic performance exhibits a maximum color difference value of 8.921 when the volume ratio of formaldehyde solution and sodium molybdate solution is 0.3:10.