Photocatalytic degradation of organic pollutants
by shape selective synthesis of b-Ga
2
O
3
microspheres constituted by nanospheres for
environmental remediation
K. Girija,
*
ac
S. Thirumalairajan,
b
Valmor R. Mastelaro
b
and D. Mangalaraj
a
A potential single crystalline photocatalyst b-Ga
2
O
3
with unique spherical morphology has been
synthesized using a surfactant assisted hydrothermal process. Organic additive triblock co-polymer
pluronic F127 was used as a soft template. The morphology of the material was investigated using
scanning electron microscopy and it was confirmed that the nanospheres self-assembled to form
microspheres with diameters in the range 1–3 mm. The crystal phase and chemical composition of the
b-Ga
2
O
3
microspheres were revealed by X-ray diffraction and X-ray photoelectron spectroscopy.
Structural characterization exhibits the monoclinic phase of the microspheres with preferential growth
along the [111] direction. A plausible mechanism has been proposed to understand the formation of
microspheres. The optical absorbance spectrum showed an intense absorption feature in the UV spectral
region with a bandgap energy of 4.6 eV. The Brunauer–Emmett–Teller specific surface area was found
to be 82 m
2
g
1
. The photocatalytic activity of the material has been investigated for the degradation of
model organic pollutants Rhodamine B and methylene blue under ultraviolet light irradiation. The
photocatalytic mechanism towards the degradation of organic dyes has also been proposed.
1 Introduction
Earlier research activities emphasized mainly the control of the
stoichiometry of products, however with the development of
nanotechnology considerable effort has been put forth to
control the morphology and size.
1
Nanostructures as functional
building blocks are ideal candidates for the investigation of the
dependence of structural, morphological and optical properties
on the quantum connement effect, which paves way for novel
nanotechnological applications.
2,3
Both the physical and
chemical properties of nanostructures are associated with their
size, shape and dimensionality; therefore morphology-
controlled synthesis of functional nanostructures gains impor-
tance from a scientic and technological perspective.
4
The
precise control of the growth of nanomaterials allows a higher
level of selectivity, control over dimensionality and morphology,
and the possibility of incorporating these nanostructures into
nanotechnological devices. There is an increasing interest in
pursuing effective synthesis strategies for the fabrication of
advanced materials with complex shapes and hierarchical
organization. Synthesis of inorganic semiconducting b-Ga
2
O
3
nanostructures have gained interest in materials science due to
their potential applications in optoelectronics, such as wave-
guides and optical emitters for UV radiation, solar cells, gas
sensing and, recently, as photocatalysts.
5,6
In order to grow b-
Ga
2
O
3
nanostructures, wet chemical approaches such as the
reux condensation method, sol–gel, hydrothermal processes
and precipitation techniques have been employed.
7–11
Different
nanostructures can be synthesized via hydrothermal process
due to their obvious advantages such as being economically
cheap, efficient and environment friendly for the production of
the desired phase in a very short time using simple equipment.
However, to control the morphology, structure and properties,
the surfactant-assisted hydrothermal method has elicited great
interest, due to its signicant advantages such as controlled
size, low temperature growth, tunable shape and less-compli-
cated processes . The properties of the b-Ga
2
O
3
nanostructures
depend on the preparation method, which in turn plays an
important role in their potential application.
Semiconductor-mediated photocatalysts can degrade a wide
range of organic contaminants like Rhodamine B, methylene
blue, Congo red, etc.,
12
for photocatalysis applications; it has
been reported that b-Ga
2
O
3
exhibits high and stable photo-
catalytic activity over commercial TiO
2
due to the strong redox
ability of photogenerated electron–hole pairs.
13–15
Meanwhile,
a
Department of Nanoscience and Technology, Bharathiar University, Coimbatore-641
046, India. E-mail: kgirija.bu@gmail.com; Fax: +91 422 2369106; Tel: +91 422
2369130
b
Instituto de F´ ısica de S˜ ao Carlos (IFSC), University de S˜ ao Paulo, CP 369, 13560-970
S˜ ao Carlos, SP, Brazil
c
Department of Science and Humanities, Dr N.G.P. Institute of Technology,
Coimbatore-641 048, India
Cite this: DOI: 10.1039/c4ta05295a
Received 5th October 2014
Accepted 7th December 2014
DOI: 10.1039/c4ta05295a
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