Enhanced photocatalytic performance: a β-Bi2O3 thin film by nanoporous surface

Beta-Bi2O3 film photoanodes with different surface structures were prepared by oxidizing bismuth films. The physical properties were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible absorbance spectra and atomic force microscopy (AFM). XRD shows that all films are beta phase crystal structure except the thinnest 12 nm film. SEM and AFM characterizations indicate that a nanoporous surface structure is generated on the surface after the film is annealed for 3 h, while the films annealed for 1 h show a dense surface. The direct band gaps vary from 2.63 to 2.88 eV, with the film thickness decreasing from 500 to 12 nm. The nanoporous surface structure film exhibits better light harvesting ability and incident photon-to-electron conversion efficiency (IPCE) than the dense surface films. The IPCE (61% at 350 nm and 43% at 400 nm, 0.197 VNHE) is the highest ever reported. The photocurrent density reaches 0.45 mA cm-2 when illuminated with a bias of 1.23 VNHE in 0.5M Na2SO3.