Structural and photocatalytic properties of Pd-deposited semiconductors with different morphology

Abstract

In this work, we studied the effect of Pd deposition (0.3 wt%) on the structural and photocatalytic properties of TiO₂ anatase with different morphologies (nanoparticles, nanotubes and nanofibers). The Pd-deposited semiconductor samples were synthesized by a simple deposition–precipitation method and used as catalysts for photocatalytic degradation of p-nitrophenol under visible light illumination. Pd-deposited TiO₂ nanofibers showed higher photocatalytic activity than Pd-deposited TiO₂ nanoparticles or nanotubes. Pd-deposited (0.3 wt%) CeO₂ and WO₃ nanofibers were also synthesized to investigate whether the advantages of nanofiber morphology extend to other semiconductors, with lower and higher band gap energies. The performance of Pd-deposited CeO₂ nanofibers was superior to that of all other Pd-deposited samples. The samples were characterized by elemental analysis, XRD, SEM, TEM, DR UV-vis, N₂ physisorption and XPS to investigate the role of structural properties on photocatalytic performance. The XRD data indicated that the crystal structures of TiO₂, WO₃ and CeO₂ were not modified after Pd deposition and TEM indicated that the Pd was well dispersed on the semiconductor surfaces, with particle sizes <20 nm. Pd deposition changed the morphology of the CeO₂ nanofibers to a unique ‘mat-like’ structure, with small (4 nm) Pd nanoparticles. This latter sample had the highest photocatalytic activity, which was attributed largely to high photocurrent density. Conditions for photocatalysis were investigated and Pd-deposited CeO₂ nanofibres were shown to be reusable for at least five cycles, without significant loss of photocatalytic activity. Our study suggests that Pd-deposited CeO₂ nanofibres could be used industrially to degrade p-nitrophenol.