COMMUNICATION
Organic–inorganic hybrid nanomaterial as a new fluorescent
chemosensor and adsorbent for copper ion{
Soo Jin Lee,a Shim Sung Lee,a Myoung Soo Lah,b Jae-Min Hongc and Jong Hwa Jung*a
Received (in Cambridge, UK) 1st August 2006, Accepted 30th August 2006
First published as an Advance Article on the web 18th September 2006
DOI: 10.1039/b611089d
the phenanthroline moiety would act as the binding site for specific
Functionalized silica nanotube (FSNT) possessing the phenan-
throline moiety as a fluorescent receptor was fabricated by sol–
gel reaction, and the binding ability of FSNT with metal ions
was evaluated by fluorophotometry.
metal ions. Also, the triethoxylsilyl group of 1 was introduced to
facilitate covalent attachment of the receptor onto the surface of
the silica nanotube (SNT) by sol–gel reaction.
The synthesis of nanotubes has greatly expanded the possibilities
for the design of open pore structures. Because of their large
surface area and their well-defined pore size and pore shape, these
materials have great potential in environmental and industrial
processes.1–4 However, many applications including adsorption,
ion exchange, catalysis and sensor require materials possessing
specific attributes such as binding sites, stereochemical configura-
tion, charge density and acidity.5,6
Based on our new concept of developing a selective fluorescent
chemosensor and adsorbent for Cu2+
In general, the development of most chemosensors is based on
molecular-level host–guest concept in solution.7–10 On the other
hand, it is clear that receptor-immobilized nanotubes have some
important advantages as solid chemosensors in heterogeneous
solid–liquid phases. First, such nanotubes as chemosensors can be
repeatedly utilized with suitable treatment. Second, nanotubes
would be useful as selective and efficient adsorbents for specific
guest molecules in environmental pollutants due to their larger
surface and well-defined pores in comparison to spherically
structured nanomaterials. Third, nanotubes can be easily isolated
from pollutants by simple filtration. Fourth, the single nanotube is
advantageously applicable as sensing material for the development
of nano-scaled devices. Fifth, if receptors can be immobilized onto
the inner-wall of silica nanotubes, such well-ordered silica
nanotubes could be expected to act as nanofilters to separate
specific guest molecules from a mixture by size inclusion. This fact
has attracted our attention in connection with the creation of new
hybrid species based on the fusion of specific receptors and
inorganic nanomaterials such as SiO2, Al2O3 or TiO2 as solid
supporting media. Here we report the immobilization of a
fluorescent receptor onto the surface of silica nanotubes and
examine its specific adsorption behavior for Cu2+.
, the phenanthroline
derivative 1 was covalently attached onto the SNT by sol–gel
reaction. The details of the preparative procedure are depicted in
Scheme S2. The high yield of SNT (.97%) was obtained by sol–
gel reaction of tetraethyl orthosilane (TEOS) using organogel 2 as
a template by a previously reported method.11 The unreacted
TEOS and the organogel template were completely removed by
calcination followed by washing with THF, and a white solid was
obtained. Immobilization of the fluorescent receptor 1 into the
SNT was conducted under reflux for 24 h in toluene. In this
process, the triethoxylsilyl group of 1 undergoes hydrolysis and
attaches covalently to the surface of SNT. After cooling to room
temperature, the slightly yellow solid product was filtered, washed
with THF, and then dried. Also, we used the commercial silica-gel
as a supporting material for receptor 1. These products were
characterized by scanning electron microscopy (SEM), transmis-
sion electron microscopy (TEM), fluorophotometry and thermo-
gravimetric analysis (TGA).
The silica product showed a well defined nanotube possessing a
diameter of ca. 260 nm and several micrometers in length (Fig. 1a).
The TEM image of the fluorescent silica displayed a hollow
structure with uniform size dimensions, i.e., inner diameter of ca.
210 nm and wall thickness of 25 nm (Fig. 1b), indicating that the
fluorescent receptor 1 was covalently attached onto the surface of
SNT by post sol–gel reaction. This material, called functionalized
silica nanotube (FSNT), was evaluated for its ability to detect and
separate specific metal ions from aqueous and organic solutions.
To confirm that the fluorescent receptor 1 was immobilized
onto the surface of SNT, we performed elemental mapping of
silicon (Si), carbon (C), nitrogen (N) and oxygen (O) by energy
dispersive X-ray spectroscopy (EDX) technique coupled with
TEM measurements.12 After complete removal of template with
THF, the material (Fig. S1a) contained silicon (Fig. S1b), oxygen
(Fig. S1c), nitrogen (Fig. S1d) and carbon (Fig. S1e) components.{
Compound 1 as a fluorescent receptor was synthesized by the
synthetic route depicted in Scheme S1 (hereafter S denotes:
Electronic Supplementary Information{). The nitrogen atoms in
aDepartment of Chemistry and Research Institute of Natural Sciences,
Gyeongsang National University, Chinju 660-701, Korea.
E-mail: jonghwa@gnu.ac.kr
bDepartment of Chemistry and Applied Chemistry, College of Science
and Technology, Hanyang University, Ansan, Kyunggi-Do 426-791,
Korea
cKorea Institute of Science and Technology, P.O Box 131, Cheongryang,
Seoul 130-650, Korea
{ Electronic supplementary information (ESI) available: Experimental
details. See DOI: 10.1039/b611089d
This journal is ß The Royal Society of Chemistry 2006
Chem. Commun., 2006, 4539–4541 | 4539