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CATTOD-9877; No. of Pages8
ARTICLE IN PRESS
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K. Yao et al. / Catalysis Today xxx (2015) xxx–xxx
region of the spectrum and can be more efficient photocata-
lysts than pure TiO2 toward degradation of a variety of organic
compounds [7,21–26]. The higher catalytic efficiency results from
tion of the electron–hole pairs. Particularly, under visible light,
electron–hole pairs only generate in Fe2O3 but not in TiO2. Thus
electrons could be transferred from to conduction band of Fe2O3
to TiO2, while the holes remain in the valence band of Fe2O3
process and overall catalytic efficiency. Recently, it was reported
that the enhanced photocatalysis of Fe2O3–TiO2 nanocomposites
catalytic processes, including the surface area, nanoparticle’s size
and shape, crystallinity, electron–hole recombination rate, het-
erojunction and synergistic effects between materials, as well as
adsorbent–adsorbate interaction [22,24,26–28].
microbalance (QCM), was achieved. Based on the nanorod sepa-
the vapor incident angle for the TiO2 shell deposition was deter-
mined to be ꢀ = 6.1◦. Further details describing this calculation
and the GLAD core–shell deposition method can be found in
Ref. [13]. Using the same substrate azimuthal rotation rate of
0.5 rev/s, the TiO2 shell was deposited to a nominal thickness of
50 nm. The as-deposited Fe2O3–TiO2 nanorod samples were then
annealed in a quartz tube furnace (Lindberg/Blue M Company) in
open air for 3 h, at different preset temperatures from 350 ◦C to
750 ◦C.
2.2. Characterization
The morphologies of the samples were examined by a field-
emission scanning electron microscope (SEM, FEI Inspect F)
equipped with an energy dispersive X-ray spectrometer (EDX).
The structural properties of the samples were characterized by a
PANalytical X’Pert PRO MRD X-ray diffractometer (XRD) with fixed
incidence angle of 1.5◦. The XRD patterns were recorded with Cu K␣
Therefore, it is interesting to explore new architectures and
fabrication techniques in order to further study and optimize the
TiO2–Fe2O3 system for highly efficient photocatalysts.
◦
radiation (ꢁ = 1.5405980 A) in the 2ꢀ range from 20 to 80◦ at step
size of 0.014◦. The optical properties of the samples were measured
by a double beam UV–visible light (UV–vis) spectrophotometer
(JASCO V-570) over a wavelength range from 300 to 800 nm. The
photocatalytic activities of the samples were evaluated by the pho-
tocatalytic degradation of a 10 ppm (∼31 M) methylene blue (MB)
aqueous solution (of pH value ∼6.2) under visible light irradiation.
The TiO2, Fe2O3, or Fe2O3–TiO2 samples on glass substrates were
placed into a 10 mm × 10 mm × 45 mm clear methacrylate cuvette
filled with 4.0 ml of MB solution. The cuvettes were illuminated
for a total time of 4 h by a 250 W quartz halogen lamp (UtiliTech)
covering wavelength range from 400 to 800 nm. The incident light
intensity on sample was kept constant at 65 mW/cm2, as measured
by an optical power meter (Thorlabs PM100D/S310C). A rectangu-
lar mask (2.4 cm2) was placed in front of the all samples to keep
the light power the same for all photodegradation experiments.
A water filter was placed in front of the cuvette to absorb the
IR light. The photodegradation the MB solution were measured
by examining the in-situ UV–vis transmission spectra of the MB
solution using an Ocean Optics spectrophotometer (USB 2000).
The absorbance peak at ꢁ = 664 nm was monitored at regular time
increments of 20 min and were used to evaluate the photodegrada-
tion rate of MB. For the CO2 photoconversion study, a syringe-type
chamber (volume of 20 ml) was designed as solar-gas convertor
reactor with gas inlets/outlets, optical window and sample stage
holder. It was loaded with three 1 × 1 cm2 Fe2O3–TiO2 core–shell
nanorod array samples (or control samples of TiO2 nanorod arrays)
in CO2 and H2O gas mixture in ambient light and atmospheric
conditions. The evolving gas in this system was probed by micro
gas-chromatograph (GC) instrumentation equipped with OV1 and
pora-plot columns.
˚
a substrate at large incident angles with respect to substrate sur-
face normal (>70◦), while the substrate is rotated azimuthally
at a constant speed, resulting in self-organized vertically align
nanorod arrays [13,29–31]. Our previous work has proven that
this is a versatile method in fabricating TiO2-WO3 core–shell struc-
tured photocatalysts [13,32]. Additionally, the dynamic shadowing
growth (DSG) technique has several advantages for metal oxide
nanostructure fabrication: simplicity, flexibility, and compatibility
with other microfabrication techniques.
In this work, we design and fabricate Fe2O3–TiO2 core–shell
nanorod arrays using the GLAD technique. The core–shell architec-
ture is chosen to maximize the interfacial contact between Fe2O3
and TiO2 and is expected to increase charge separation and catalytic
efficiency. A post-deposition annealing treatment is developed in
order to obtain a structure with twofold active crystalline phases,
␣-Fe2O3 and anatase TiO2. In addition to their morphological,
structural, and optical properties, the visible light photocatalytic
activities of the Fe2O3–TiO2 core–shell samples for methylene blue
destruction and CO2 conversion are investigated. It is found that the
␣-Fe2O3–TiO2 core–shell nanorods arrays are more efficient photo-
catalysts for both of these processes under visible light illumination
than either of the pure material photocatalysts, TiO2 and Fe2O3.
2. Materials and methods
The source materials used in this study, Fe2O3 (99.85+%, metal
base), and TiO2 (99.9%) were purchased from Alfa Aesar (Ward Hill,
MA) and Kurt J. Lesker (Clairton, PA), respectively and were used as
received. Cleaned glass microscope slides (Gold Seal® Catalog No.
3010) and Si (1 0 0) wafers (Montco Silicon Technologies Inc.) were
used as substrates for material deposition. High purity methylene
blue (MB, C16H18ClN3S; CAS No. 122965-43-9) was obtained from
Alfa-Aesar (Ward Hill, MA).
3. Results and discussion
The Fe2O3 nanorod samples, which serve as the “core” template
microscopy (SEM). As shown in Fig. 1a, the arrays consist of well
morphologies of the individual nanorods is consistent with a fiber
texture resulting from a preferred growth direction, where the
exposed facets are the low energy crystalline planes, most likely
[34,35]. Quantitative measurements of the SEM images reveal that
the average height of the Fe2O3 nanorods is h = 1220 30 nm, and
2.1. Fe2O3–TiO2 core–shell nanorod arrays preparation
The nanorod arrays were fabricated in a custom designed
electron-beam deposition system (Torr International, Inc.) [13,33].
Fe2O3 nanorods was first deposited onto Si and/or glass sub-
strates with the incident angle ꢀ = 86◦, with the substrate rotating
azimuthally at 0.5 rev/s. The deposition proceeded until a nom-
inal thickness of 3 m, as determined by
a quartz crystal
Please cite this article in press as: K. Yao, et al., Fe2O3–TiO2 core–shell nanorod arrays for visible light photocatalytic applications, Catal.