A series of unique flake-tube structured p-n heterojunctions of BiOI/TiO2 nanotube arrays (TNTAs) were successfully prepared by loading large amounts of BiOI nanoflakes onto both the outer and inner walls of well-separated TiO2 nanotubes using anodization followed by the sequential chemical bath deposition (S-CBD) method. The as-prepared BiOI/TNTAs samples were characterized by X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy and nitrogen sorption. The photoelectrocatalytic (PEC) activity and stability of the BiOI/TNTAs samples toward degradation of methyl orange (MO) solutions under visible-light irradiation (λ > 420 nm) were evaluated. The visible-light PEC performance of BiOI/TNTAs samples was further confirmed by the transient photocurrent response test. The results from the current study revealed that the 5-BiOI/TNTAs sample exhibited the best PEC activity, favourable stability, and the highest photocurrent density among all the BiOI/TNTAs heterostructured samples. The combined effects of several factors may contribute to the remarkable visible-light PEC performance for the 5-BiOI/TNTAs sample including a 3D connected intertube spacing system and an open tube-mouth structure, strong visible-light absorption by BiOI, the formation of a p-n junction, larger specific surface area, and the impact of the applied external electrostatic field.
The effect of silicon content (0.54 and 1.55 wt.% Si) on carbide precipitation and low temperature toughness of Cr-Mo alloyed pressure vessel steels was investigated in this work. Microstructural examinations showed that both steels consisted of bainite and ferrite, after normalizing at 1000 ºC for 30 mins followed by tempering at 650 and 700 ºC for 180 mins. The average room temperature toughness decreased from 158 to 83 J and average size of carbides increased from 20∼30 nm to 40∼60 nm as the silicon content increased from 0.54 to 1.55 wt.%. Fine M6C and M23C6 carbides were found in the 0.54 % Si steel, whereas coarser M7C3 and M23C6 carbides were observed in the 1.55 % Si steel. The results of this work suggested that cementite was precipitated in the early stage of tempering in the low silicon steel. Then, fine dispersed Cr-Mo carbides were nucleated on the preformed cementite precipitates. These fine alloy carbides were accounted for the improved lowtemperature impact toughness of the low silicon steel.
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