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Materials Chemistry and Physics 110 (2008) 176–179
Template synthesized nano-crystalline natrotantite: Preparation
and photocatalytic activity for water decomposition
A. Ratnamala, G. Suresh, V. Durga Kumari, M. Subrahmanyam
∗
Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500007, India
Received 7 September 2007; received in revised form 15 January 2008; accepted 21 January 2008
Abstract
A new method for preparation of natrotantite (Na
2
Ta
4
O
11
) by hydrothermal method using cetyl trimethyl ammonium bromide (CTAB) template
is reported. The nano, mesoporous and crystalline natrotantite resulted during different methods adopted for surfactant removal. Nano-crystalline
natrotantite was observed during template removal using ethanol. The meso and crystalline samples resulted during the high temperature calcination
at 773 and 1373K, respectively. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), UV–vis
diffraction reflected spectra (DRS), N
2
-adsorption isotherm and surface area measurements. Nano, mesoporosity of the sample was confirmed
by TEM, N
2
-adsorption isotherm studies. The band gaps of the nano, mesoporous and crystalline natrotantite were estimated to be 4.1, 4.3 and
3.9 eV with surface areas of 42.4, 133.6 and 6.21 m
2
g
-1
, respectively. Furthermore, nano-crystalline Na
2
Ta
4
O
11
is found to be highly efficient
photocatalyst for water decomposition.
© 2008 Elsevier B.V. All rights reserved.
Keywords: Natrotantite; Semiconductors; Nano-crystalline materials; Water decomposition
1. Introduction
Preparation of nanomaterials with wide range of applications
has been of great importance because of their potential appli-
cations in the area of catalysis, chromatography, biomaterials,
microelectronics and photonic materials [1–3]. The properties
of nanomaterials are quite different from those of the bulk mate-
rials of the same composition. Template-directed methods have
been largely adapted to fabricate nanomaterials for industri-
ally important reactions and a precise control over final size
and structure are required from the steps adopted in prepa-
ration to get the fine tuned material. In the present study we
prepared the nano-crystalline natrotantite (Na
2
Ta
4
O
11
) with the
assistance of template. Natrotantite was first found in granitic
pigments in association with other tantalum minerals [4]. Ercit et
al. [5] reported crystalline powder of Na
2
Ta
4
O
11
by solid-state
reaction method. Single crystals of Na
2
Ta
4
O
11
were grown in
NaTaO
3
–WO
3
from MoO
3
and from Na
2
Mo
2
O
7
flux [6,7].
Hydrogen energy is gaining significance from the viewpoint
of both solar energy utilization and environment especially
∗
Corresponding author. Tel.: +91 40 27193165; fax: +91 40 27160921.
E-mail address: subrahmanyam@iict.res.in (M. Subrahmanyam).
with the depletion of fossil fuels. Its production by industrial
steam reforming process consumes fossil fuels and emits CO
2
.
An alternative solution for this issue is photocatalytic splitting
of water for hydrogen production. Therefore, development of
active catalyst is highly desirable. Semiconductor oxides like
TiO
2
and Ta, Nb-based oxides have been investigated exten-
sively [8]. Several tantalum-based oxides are reported by Kato
and Kudo and especially sodium tantalate (NaTaO
3
) was stud-
ied extensively and reported to have higher activity for water
decomposition [9]. The metal tantalite compounds such as
ATaO
3
, ATaO
4
, ATa
2
O
6
and ATa
2
O
9
are reported as repre-
sentative photocatalysts (A = alkali metal, alkaline earth metal,
rare earth metal or couple of them). They are normally synthe-
sized by solid-state reaction at relatively high temperature. In
this investigation, we are disclosing nano-crystalline natrotantite
(Na
2
Ta
4
O
11
) preparation by surfactant-assisted sol–gel method
under hydrothermal conditions. However, to the best of our
knowledge no Na
2
Ta
4
O
11
system synthesis is reported directly
to date.
2. Experimental
The XRD patterns of the Na Ta O samples are obtained by using Siemens
d 5000 X-ray diffractometer using Ni filtered Cu K radiation (λ = 1.5406)
0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.matchemphys.2008.01.039