Zhou Guanghong

High Visible-light Photocatalytic Activity of γ-Fe2O3/TiO2 Nanotube Heterojunction Arrays

Abstract This study presents the preparation and the application of γ -Fe 2 O 3 /TiO 2 nanotube magnetic heterojunction photocatalysts (MHPs) for photodegradation of methylene blue under visible light irradiation. The morphology, the microstructure, the magnetic properties and the photocatalytic activity of γ -Fe 2 O 3 /TiO 2 (NT) MHPs were studied. Results show that the MHPs are provided with highly ordered TiO 2 (titania) nanotube arrays (55 nm in diameter and 10 nm in wall thickness) and nano γ -Fe 2 O 3 (maghemite) particle (approximately 15 nm) co-deposition. The MHPs exhibit a superparamagnetic behavior of γ -Fe 2 O 3 /TiO 2 (NT) MHPs resulting from the small size of γ -Fe 2 O 3 particles. The photocatalytic activity of γ -Fe 2 O 3 /TiO 2 (NT) MHPs is greater than that of Fe 3 O 4 /TiO 2 (NT) MHPs or pure TiO 2 (NT) under visible light irradiation. The interaction between γ -Fe 2 O 3 and TiO 2 improves charge separation and extends TiO 2 response into the visible region. Moreover, the formed heterojunction between γ -Fe 2 O 3 and TiO 2 can further prevent the recombination between photoelectrons and holes.

Thermal Decay and Reversal of Exchange Bias Field of CoFe/PtMn Bilayer after Ga+ Irradiation

An applied field is used to perform Ga+ ion irradiation on a CoFe/PtMn bilayer. Effects of the applied field and energy transfer between Ga+ ions and antiferromagnetic (AFM) atoms on the exchange bias field Hex are investigated. A partially reversed Hex is found in CoFe/PtMn specimens irradiated at a dose of 1 × 1014 ions/cm2 with an applied field anti-parallel to the original exchange bias direction. We believe that the rapid energy transfer and local temperature increase originating from the interaction between Ga+ ions and AFM atoms result in spin reversal and the formation of reversed AFM domains when specimens are irradiated with anti-parallel fields. The decrease in Hex when annealing the film in a negative saturation field indicates a thermal decay process. The AFM moments are reversed by thermal activation over an energy barrier distribution, which may change in some way as the temperature increases.