The effect of Fe segregation on the photocatalytic growth of Ag nanoparticles on rutile TiO2(001)

The photocatalytic growth of silver nanoparticles (AgNPs) on rutile TiO2(001) and Fe-modified rutile TiO2(001) monocrystals was investigated. Various amount of Fe was segregated in a controlled way from the doped TiO2 substrates in ultra-high vacuum conditions resulting in low- medium- and high- content of Fe on TiO2 substrates. AgNPs were grown on pristine TiO2 and substrates containing Fe by photoreduction of Ag+ ions under UV illumination. It was found that the size of AgNPs was larger on Fe/TiO2 than on TiO2 while the surface density exhibited the opposite behavior - a large number of AgNPs were present on the TiO2 surface but only a few AgNPs were visible on the Fe/TiO2 substrates. The reason for the differences in size and number of AgNPs on TiO2 and Fe/TiO2 is the limited access of Ag+ to the TiO2 surface caused by the large number of Fe grains segregated onto the TiO2 surface. Another possible reason for the various AgNPs morphologies is alteration in the mechanism of Ag+ photoreduction caused by iron present as Fe3+ ions and by newly formed AgNPs playing the role of electron traps. The surface elemental analysis of the investigated materials was performed with the use of X-ray photoelectron spectroscopy (XPS) and confirmed the composition of AgNPs/Fe/TiO2 systems. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed sizes, morphology and distribution of the nanostructures.