Photoelectrochemical and Photocatalytic Behaviors of Hematite-Decorated Titania Nanotube Arrays: Energy Level Mismatch versus Surface Specific Reactivity

Abstract

Nanocrystalline hematite particles (α-Fe2O3) were electrodeposited on the TiO2 nanotube (TiNT) arrays that were fabricated via anodization of Ti foils. The short precontact time (1 h) of aqueous ferric ions (Fe3+) on TiNT resulted in formation of hematite particles selectively on the mouth surface of TiNT (hematite@1 h/TiNT), whereas the long precontact time (24 h) resulted in complete filling of the TiNT inside and an even full-covering of the TiNT top surface with the hematite particles (hematite@24 h/TiNT). For comparison, hematite particles were also electrodeposited on TiO2-nanoparticulate films obtained via oxidative annealing of Ti foil resulting in hematite fully covered TiO2 nanoparticles (hematite/TiNP). Photoelectrochemical (PEC) study with AM 1.5 light (UV + Vis) indicated that the PEC activity of TiNT decreased by ca. 40% and almost completely vanished when hematite covered the full surface of TiNT (hematite@ 24 h/TiNT) and loaded on the mouth surface of TiNT (hematite@1 h/TiNT), respectively...