Multiple-structured nanocrystals towards bifunctional photoluminescent- superhydrophobic surfaces

Article abstract of DOI:10.1039/b926761a

We report a simple and efficient strategy for the preparation of diverse hierarchical structures of dithiocarbamate-functionalized CdS nanocrystals (NCs) exhibiting both photoluminescent and hydrophobic properties via a facile interfacial self-assembly te

Full text of DOI:10.1039/b926761a

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Volume 20 | Number 19 | 21 May 2010 | Pages 3777–3996
Title: Multiple-structured nanocrystals towards bifunctional
photoluminescent-superhydrophobic surfaces
The fabrication of bifunctional photoluminescent-
superhydrophobic surfaces can be induced by facile interfacial self-
assembly of nanocrystals and dithiocarbamates, generating new
strategies for diverse hierarchical structures of nanocrystals, e.g.,
wire-like, belt-like, and sheet-like microstructures. This approach
serves as a new and efficient procedure for designing more
practical photoluminescent-superhydrophobic films.
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Multiple-structured nanocrystals towards bifunctional
photoluminescent-superhydrophobic surfaces†
*
Linrui Hou, Caifeng Wang, Li Chen and Su Chen
Received 21st December 2009, Accepted 16th February 2010
First published as an Advance Article on the web 15th March 2010
DOI: 10.1039/b926761a
We report a simple and efficient strategy for the preparation of diverse hierarchical structures of
dithiocarbamate-functionalized CdS nanocrystals (NCs) exhibiting both photoluminescent and
hydrophobic properties via a facile interfacial self-assembly technique. The ligand exchange reaction of
thioglycolic acid (TGA) with dithiocarbamates at the biphase interface endowed CdS with diversiform
morphologies. Simultaneously, the resulting dithiocarbamate-functionalized NCs after interfacial
self-assembly exhibit good photochemical stability and enhanced photoluminescence (PL) in
comparison with the parent NCs. Moreover, the introduction of dithiocarbamate ligands with long
alkyl chains can significantly enhance the hydrophobic properties of NCs in this case. By simply varying
the directing ligands with different intrinsic hydrophobic natures, superhydrophobic surfaces
constructed from the fluorescent NCs can be fabricated.
can easily be made into devices, along with being reusable.11
Introduction
However, the commonly used organic materials have short life-
times which require the films to be changed frequently. Films
made of inorganic fluorescent materials will have a longer
stability period, but they unfortunately are still sparsely reported
for this purpose. Therefore, the fabrication of fluorescent and
self-cleaning superhydrophobic films will be of great promise for
smart materials with optical properties. Specifically, hierarchical
structures constructed on the micro/nanoscale give an efficient
approach to achieve superhydrophobic surfaces, which are
defined as those with a water contact angle (CA) larger than
150 ꢀC.12–14 Char and co-workers have prepared smart super-
hydrophobic films exhibiting responsive optical properties,
where hydrophobic fluorophores were incorporated into the
hydrophobic polystyrene (PS) cores of charged block copolymer
micelles by self-diffusion.15 Although a little progress has been
achieved,15,16 there are limited reports on the fabrication of
bifunctional photoluminescent-superhydrophobic films.
Self-assembly architectures of nanocrystals (NCs) have attracted
great attention because of their extensive scientific and industrial
interest in areas such as light-emitting devices (LEDs),1 nonlinear
optical devices,2 and nanosensors.3 To gain the desirable prop-
erties of NCs, tremendous efforts have been devoted to the
development of photostability and compatibility of NCs.4
Among them, the surface chemical processing and organization
of NCs are of major importance,5 because functional organic
surface ligands can serve to heal NC surface defects, and allow
NCs to organize into ordered hierarchical structures for the
coupling of their size- and shape-dependent properties.6,7 Also,
these organic surface ligands provide inorganic NCs with
compatibility, stability and processability in a range of organic
materials through favorable interactions. Recently, the water/oil
interface has been widely used as an ideal platform for manip-
ulating the self-assembly of NCs into hierarchical structures.8–10
Such an interface can favor prolonging the assembly time of
NCs, thus healing defects and diversifying the structural
complexity of NCs. Although great efforts on the interfacial
assembly technique have been made for this purpose, the
construction of versatile multiscale structures of NCs with
desired properties still remains a challenge.
So far, thiols are the most common motifs which present the
strongest affinity for NCs but they suffer from a major draw-
back, instability toward photooxidation, thus limiting the prac-
tical applications of these NCs.17–19 To improve the resistance of
NCs against photooxidation, introduction of dithiocarbamate
moieties for fabrication of NCs may be an efficient method due
to their strong chelating capability to metal atoms.20–23 In this
work, we report a simple and efficient strategy for the prepara-
tion of diverse hierarchical structures of dithiocarbamate-func-
tionalized CdS NCs exhibiting both photoluminescent and
hydrophobic properties in a facile interfacial self-assembly
process. The ligand exchange reaction of thioglycolic acid (TGA)
with dithiocarbamates at the biphase interface afforded hierar-
chical structures with diversiform morphologies. The resulting
dithiocarbamate-functionalized NCs offer advantages: good
stability toward photooxidation, enhanced PL, and controlled
hierarchical structure. Moreover, this procedure opens a way to
fabricate superhydrophobic surfaces of NCs by simply varying
Recently, one of the important applications of these NCs is
their use as fluorescent films. A fluorescent film possesses more
favorable properties than a molecular fluorescent solution and it
State Key Laboratory of Material-Oriented Chemical Engineering, College
of Chemistry and Chemical Engineering, Nanjing University of
Technology, Nanjing, 210009 Xin Mofan Rd. 5#, P. R. of China.
E-mail: chensu@njut.edu.cn; Fax: +86-25-83587194; Tel: +86-25-
83587194
† Electronic supplementary information (ESI) available: Summaries of
the various characterization studies, including the phase transfer
experiment and the results of X-ray diffraction (XRD), FT-IR, 1H
NMR, and contact angle (CA) measurements. See DOI:
10.1039/b926761a
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the directing ligands with different intrinsic hydrophobic nature.
Also, it represents the first example of hierarchical surfaces
created by small organic ligand functionalized NCs exhibiting
simultaneous luminescence and superhydrophobicity.
Synthesis of dithiocarbamate-functionalized CdS NCs
The dithiocarbamate-functionalized CdS NCs were prepared
as depicted in Fig. 1 (step II). The aqueous solution of TGA-
stabilized CdS NCs was layered carefully on top of the CHCl3
solution containing dithiocarbamate ligand in a vessel, which
was sealed and maintained at room temperature for several days,
and the NCs were slowly transferred from the water into the oil
phase via an interfacial diffusion process (ESI,† Fig. S1). Finally,
the chloroform phase containing dithiocarbamate-functionalized
CdS NCs was collected, precipitated by addition of ethanol, and
then isolated by centrifugation.
Experimental
Materials
Cadmium chloride (CdCl2$2.5H2O), thioglycolic acid (TGA),
sodium sulfide (Na2S$9H2O), sodium hydroxide (NaOH), pro-
pylamine (PAm), octylamine (OAm), dodecylamine (DDAm),
cyclohexylamine (CHAm), aniline (An), propylene acrylamide
(PAAm), carbon disulfide (CS2) and chloroform (CHCl3) were of
analytical grade and used as received.
Preparation of bifunctional photoluminescent-hydrophobic films
The glass slide was rinsed with water prior to use. The NC
solution was directly spin-coated onto the glass until a film was
formed, and the thickness was calculated to be ca. 0.3 mm. The
applied coatings were kept at room temperature for a week to
remove residual solvent.
Synthesis of water-soluble CdS NCs
The TGA-stabilized CdS NCs were synthesized according to
a modified literature method.19 Typically, TGA (0.46 g, 5 mmol)
dissolved in deionized water (10 mL) was added to a solution of
CdCl2$2.5H2O (0.571 g, 2.5 mmol) in deionized water (20 mL)
under vigorous stirring, followed by adjusting the pH value to
7 by dropwise addition of NaOH solution (5 M). Na2S$9H2O
(0.36 g, 1.5 mmol) dissolved in deionized water (20 mL) was then
added dropwise into the above mixed solution under stirring.
The reaction was carried out for an additional 3 h at room
temperature.
Characterization
Ultraviolet–visible (UV-vis) spectra were recorded on a Perkin-
Elmer Lambda 900 UV-vis spectrometer. The X-ray diffraction
(XRD) patterns were conducted on
a
Bruker-AXS
D8 ADVANCE X-ray diffractometer with Cu-Ka radiation
(l ¼ 0.1542 nm) at a scanning speed of 60 rpm over 2q range of
10–80ꢀ. Fluorescence spectra were recorded on a Varian Cary
Eclipse spectrofluorometer with a 360 nm laser beam as a light
source, and the quantum yield (QY) was calculated by
comparing with 9,10-DPA with quantum yield at 95%. 1H
Nuclear Magnetic Resonance (NMR) spectra were obtained on
a Bruker ADVANCE DPX 400 spectrometer and chemical shifts
are given in ppm relative to CHCl3 (7.26 ppm). Transmission
electron microscope (TEM) images were collected on a JEOL
JEM-2100 electron microscope. High-resolution transmission
electron microscopic (HRTEM) observation and electron
diffraction patterns were performed with a JEOL JEM-2010
transmission electron microscope. The microstructures of the
dithiocarbamate-functionalized NCs were observed by scanning
electron microscopy (SEM) with a QUANTA 200 (Philips-FEI,
Holland) instrument at 30.0 kV. Fourier transform infrared
(FT-IR) spectra were recorded on a Nicolet 6700 FT-IR spec-
trometer: the samples were ground with KBr crystals, and the
mixture was pressed into a pellet for IR measurement with
32 scans from 4000 to 500 cmꢁ1 at a resolution of 4 cmꢁ1. Contact
angles (CAs) of a 5 mL water droplet on the surface were
Synthesis of dithiocarbamate ligands
A series of dithiocarbamate ligands were prepared as depicted in
Fig. 1 (step I). A certain amount (5 mmol) of PAm, OAm,
DDAm, CHAm, An or PAAm was added into a vessel con-
taining CHCl3 (45 mL). Then CS2 (5 mmol) dissolved in CHCl3
(5 mL) was added dropwise. The resulting solutions were stirred
for 3 h at room temperature and stored for use in the next step.
€
€
measured with a KRUSS DSA100 (KRUSS, Germany) contact
angle system at ambient temperature. The mean value was
calculated from at least five individual measurements.
Results and discussion
TGA-stabilized CdS NCs were synthesized by the reaction of
cadmium chloride and sulfur ions in the presence of TGA as the
organic ligand. The overall procedure for the self-assembly of
NCs is illustrated in Fig. 1. Firstly, a series of dithiocarbamate
ligands (D-PAm, D-OAm, D-DDAm, D-CHAm, D-An and
D-PAAm) are prepared with the reaction of CS2 and the
Fig. 1 Illustration of the route for the synthesis of the dithiocarbamate-
functionalized CdS NCs.
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corresponding amines in CHCl3 (Fig. 1, step I). Subsequently,
the resulting hydrophobic dithiocarbamates are used as exchange
ligands to replace the original hydrophilic ligand TGA via the
H2O–CHCl3 interface, where water-soluble TGA-stabilized CdS
NCs are finally converted to oil-soluble dithiocarbamate-func-
tionalized CdS NCs and a slow phase transfer of NCs from the
aqueous phase into the chloroform phase occurs (Fig. 1, Step II).
The digital pictures of the interfacial reactions as a function of
reaction time further visually confirm that the CdS NCs are
actually transferred slowly from the aqueous to the chloroform
phase with the reaction time (ESI,† Fig. S1). These changes in
NCs (ESI,† Fig. S4b–g) are almost the same as that of the parent
TGA-stabilized CdS NCs, which means that the surface ligand
exchange reaction of dithiocarbamate with TGA does not
change their parent crystal structure.
We explored the interfacial self-assembly behavior of TGA-
stabilized NCs with dithiocarbamates bearing different alkyl side
chains. The capping layer of CdS NCs was exchanged for
dithiocarbamates with alkyl chains varying in length between
3 and 12 carbon atoms (C3 for D-PAm, C8 for D-OAm and C12
for D-DDAm, Fig. 1), and different self-assembly structures of
NCs were obtained (Fig. 3a–c). D-PAm-functionalized CdS NCs
(CdS-D-PAm) exhibit the structure of uniform braid-like
microfringes consisting of nanowires with diameter of about
50 nm (inset in Fig. 3a). D-OAm-functionalized CdS NCs
(CdS-D-OAm) show belt-like morphology with about 0.6 mm
width, 80 nm thickness, and microscale length (inset in Fig. 3b).
CdS-D-DDAm demonstrates a leaf-like microstructure with
average length of 20 mm and width of 1 mm (Fig. 3c). The results
indicate the length of the alkyl chain in the dithiocarbamate can
serve to affect the morphologies of the end NC products during
the interfacial self-assembly process.
1
FT-IR and H NMR spectra before and after ligand exchange
are indications of displacement of the original hydrophilic ligand
TGA with the hydrophobic dithiocarbamate ligand (ESI,†
Fig. S2–3).
The strategy involves the selection of suitable experimental
conditions. Fig. 2a shows the PL spectra of D-DDAm-func-
tionalized CdS NCs (CdS-D-DDAm) in chloroform phase after
phase transfer under different molar ratios of CS2 to amine (s).
The PL intensity of CdS-D-DDAm increases gradually with the
increase of s value and reaches a maximum at s ¼ 1/1, while
further increase of s results in the decrease of the PL intensity.
This behavior indicates that the formation of enough dithiocar-
bamates (i.e. stoichiometric ratio of CS2 to amine) can guarantee
the achievement of phase transfer and PL enhancement, whereas
redundant CS2 adsorbed on the surface of NCs can act as new
trap centers to induce the decrease or even extinction of PL
intensity. Fig. 2b presents the temporal evolution of PL spectra
for CdS-D-DDAm during the phase transfer process. As the
reaction time increases, the PL intensity of CdS-D-DDAm
increases and reaches a maximum at 25 d, which can be attrib-
uted to the better surface passivation of NCs.24 However, further
prolongation of the reaction time results in the decrease of PL
intensity due to the emerging of new surface traps in the end
products.24,25 Based on the optimal experimental procedure with
s ¼ 1/1 and reaction time of 25 d, the interfacial assemblies of
CdS NCs with various dithiocarbamates were carried out. The
XRD pattern for the parent CdS NCs (ESI,† Fig. S4a) shows the
face-centered cubic CdS phase and matches well with JCPDS
card No. 21-0829, indicated by the blue vertical lines in ESI,†
Fig. S4. The broadening of peaks originates from the small size of
CdS NCs. By using the Debye–Scherrer equation,26 the average
crystallite size of CdS NCs is estimated to be 4.0 nm. In addition,
the XRD patterns for these dithiocarbamate-functionalized CdS
For the different self-assembly morphologies of NCs, we
tentatively investigated the effects of the length of the alkyl chain
in the dithiocarbamate, and we attributed this structural varia-
tion to the combination of an oriented attachment mechanism
(dipolar-dipolar interaction) and a diffusion mechanism.27–29 As
shown in Fig. 4, dithiocarbamate ligand with strong chelation in
the chloroform phase drags TGA-stabilized NCs from the
aqueous phase to the biphase interface where the ligand exchange
reaction happens. When the short alkyl chain dithiocarbamate
D-PAm is used as the exchange ligand, the NCs driven under
dipolar-dipolar interaction rearrange orderly to obtain a wire-
like structure. However, a longer alkyl chain results in a slower
reaction rate and a longer assembly time due to the smaller
diffusion coefficient.29 Then, the misorientation of the con-
structing units occurs with the increase of length of the alkyl
chain, thus leading to the gradual increasing of the dimension of
the wire. Therefore, the self-assembly shapes of NCs vary from
Fig. 2 (a) PL spectra of CdS-D-DDAm with different s values (s ¼ 1/2,
2/3, 1/1, 2/1, and 10/1, reaction time: 25 d, lex ¼ 360 nm). (b) Temporal
evolution of PL spectra for CdS-D-DDAm during the phase transfer
process (s ¼ 1/1, lex ¼ 360 nm).
Fig. 3 SEM images of (a) CdS-D-PAm, (b) CdS-D-OAm, and (c)
CdS-D-DDAm (s ¼ 1/1, reaction time: 25 d).
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Fig. 4 Schematic representation of the interfacial assembly behaviors of
TGA-stabilized NCs ( ) with dithiocarbamates.
wire-like, belt-like, to flake-like structures with the increase of the
alkyl chain length of the dithiocarbamates.
Fig.
6
TEM (a) and HRTEM (b, c) of CdS-D-PAm. Inset:
corresponding SAED pattern.
Perhaps more interestingly, the exchange of the surface
capping ligand doesn’t change the particle size of NCs, but
significantly improves their luminescence. From the UV-vis
absorption spectra (Fig. 5a), it can be found that the positions of
the maximum absorption peaks of CdS-D-PAm, CdS-D-OAm
and CdS-D-DDAm are almost unchanged in comparison with
that of the parent TGA-CdS NCs, indicating the unchanged size
of NCs during the interfacial assembly process. Fig. 5b shows the
corresponding PL spectra and luminescent photographs of CdS
NCs before and after ligand exchange reaction. The PL emission
of TGA-stabilized CdS NCs is dominated by broad trap emission
and yellow luminescence, while almost all dithiocarbamate-
functionalized CdS NCs show narrow blue-shift exciton emission
and improved PL intensity (except CdS-D-PAm). The difference
in PL properties may be attributed to surface structural recon-
struction of NCs via ligand exchange.30 As documented in some
reports, the ligand exchange on the surface of NCs led to the
decrease or even quenching of luminescence,31,32 which also
happened in the ligand exchange reaction of TOPO-stabilized
CdSe NCs with dithiocarbamate carried out in a homogeneous
system.22 However, in our work, the two-phase interfacial
synthesis method may provide prolonged assembly (surface
reconstruction) time and offer better passivation on NCs to heal
surface defects, thus resulting in improved PL. The QYs of
as-prepared NCs after the interfacial assembly are improved
from 6.8% (TGA-CdS NCs) to 11.2% (CdS-D-PAm), 17.9%
(CdS-D-OAm) and 21.3% (CdS-D-DDAm). Another advantage
of the as-prepared NCs herein is excellent photochemical
stability: the quenching of luminescence of dithiocarbamate-
functionalized NCs does not occur even after more than
6 months, while TGA-CdS NCs present a decreased PL after
6 months (ESI,† Fig. S5), which could be attributed to the strong
chelation effects of dithiocarbamates to the metal atoms.20–22
This good PL stability makes the as-prepared self-assembled
micro/nanostructure of NCs able to produce fluorescent films
with high performance.
Evidence for the shape formation arising from the self-
assembly of NCs can be directly confirmed from the HRTEM
measurement. CdS-D-PAm was adopted as a model to investi-
gate the interfacial self-assembly behavior of NCs. Fig. 6a–c
show the self-assembly structures of CdS-D-PAm. As evident
from Fig. 6a, the product is aggregated nanowires with diameters
of about 50 nm. In the nanowires, the non-fused NCs retained
the final CdS structure, demonstrating an excellent dispersion
without obvious aggregation (Fig. 6b). The HRTEM image
shown in Fig. 6c depicts the assembly of NCs with differently
oriented lattice planes within the nanowire, and the clear lattice
image indicates the certain crystallinity of NCs. The detectable
rings in the selected area electron diffraction (SAED) pattern
further indicate the small grain polycrystalline structure of NCs
(inset in Fig. 6c).
The self-assembly architectures of NCs and their optical
properties are affected not only by the length of the alkyl chain in
dithiocarbamate as described above, but also by the use of other
dithiocarbamates with pendant ring or amide groups. Typical
SEM images of dithiocarbamate-functionalized CdS NCs of
CdS-D-CHAm, CdS-D-An and CdS-D-PAAm are shown in
Fig. 7a–c. CdS-D-CHAm is well-defined microsheets with
unequal six sides having thickness of about 40 nm (Fig. 7a). CdS-
D-An shows hackle-like nanobelt structure with width of about
200 nm, thickness of about 25 nm and microscale length
(Fig. 7b). Additionally, CdS-D-PAAm has regular nanobelt
structure with width of about 200 nm, thickness of about 60 nm
and microscale length (Fig. 7c). The UV-vis measurements
(Fig. 8a) show that the size of NCs almost remains unchanged
during the interfacial assembly process. Simultaneously, the
Fig. 5 UV-vis absorption (a) and PL (b) spectra of TGA-stabilized CdS
NCs, CdS-D-PAm, CdS-D-OAm and CdS-D-DDAm (lex ¼ 360 nm).
The insets of (b) are photographs of CHCl3 solutions of (1) CdS-D-
DDAm, (2) TGA-stabilized CdS NCs and (3) CdS-D-PAm taken under
irradiation with a 302 nm UV light.
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Fig. 9 Contact angles of the films of dithiocarbamate-functionalized
CdS NCs.
PL enhancement when surface ligands with acceptor groups are
substituted by those with donor groups.
Given that the self-assembled micro/nanostructure of NCs are
constructed with the use of dithiocarbamates with hydrophobic
nature and low surface energy, multifunctional films with tunable
hydrophobicity and photoluminescence may be available. The
solution of as-synthesized fluorescent dithiocarbamate-func-
tionalized NCs was directly spin-coated onto glass to fabricate
uniform NC films. The wettability of the films was evaluated by
water CA measurements to be in the range 104–154ꢀ (Fig. 9),
displaying their obvious hydrophobic properties in contrast with
the film of TGA-stabilized CdS NCs (ESI,† Fig. S6). For the
films governed by the chain dithiocarbamate-functionalized CdS
NCs, the CA increases as the length of the alkyl side chains
increases: the CA for the film treated with CdS-D-PAm (C3) is
108ꢀ, while the film created by CdS-D-DDAm (C12) shows
improved superhydrophobic properties with a CA up to 154ꢀ;
this is due to dithiocarbamate with longer alkyl chain which has
lower surface free energy. The results suggest that the structural
variation of dithiocarbamates may provide an approach to
control the wettability of NC surfaces and superhydrophobic
films can be created from the hierarchical structures of NCs
functionalized by dithiocarbamates with long alkyl chains. The
films exhibiting tunable hydrophobic functionality also display
interesting optical properties. Fig. 10 (a, b) and (c, d) show the
photographs of a water drop placed on the surfaces created by
CdS-D-DDAm and CdS-D-PAm, respectively. These films both
display yellow-green color under daylight. Under UV light, the
film of CdS-D-DDAm shows blue emission while that of
CdS-D-PAm NCs shows light pink emission, which is consistent
Fig. 7 SEM images of (a) CdS-D-CHAm, (b) CdS-D-An and (c) CdS-
D-PAAm (s ¼ 1/1, reaction time: 25 d).
Fig. 8 UV-vis absorption (a) and PL (b) spectra of TGA-stabilized CdS
NCs, CdS-D-CHAm, CdS-D-An and CdS-D-PAAm (lex ¼ 360 nm).
spectroscopic studies indicate that all three as-prepared NCs also
show narrow blue-shift exciton emission with PL enhancement in
comparison with that of the parent NCs after ligand exchange
reaction (Fig. 8b), and the QYs of CdS-D-CHAm, CdS-D-An
and CdS-D-PAAm are 15.8%, 10.8% and 8.7%, respectively.
Moreover, the PL quantum yields of CdS-D-PAm,
CdS-D-OAm, CdS-D-DDAm and CdS-D-CHAm are higher
than those of CdS-D-An and CdS-D-PAAm (Table 1), which are
ascribed to their different transfer of electrons. Alkyl group
acting as a donor for the nitrogen atom contributes to the
stability of dithiocarbamate,33–35 while both phenyl and acyl
groups acting as an acceptor induce the delocalization of elec-
tronic pairs of the nitrogen atom.33 Therefore, the stabilization of
dithiocarbamate-functionalized CdS NCs is increased to result in
Table 1 The QYs of the TGA-stabilized CdS NCs and a series of
dithiocarbamate-functionalized CdS NCs (s ¼ 1/1, reaction time: 25 d,
lex ¼ 360 nm)
Materials
QY (%)
TGA-CdS NCs
CdS-D-PAm
CdS-D-OAm
CdS-D-DDAm
CdS-D-CHAm
CdS-D-An
6.8
11.2
17.9
21.3
15.8
10.8
8.7
Fig. 10 Digital photographs of a water drop on the surface of (a, b)
CdS-D-DDAm and (c, d) CdS-D-PAm: (a, c) under daylight, (b, d) under
irradiation with a 302 nm UV light. (e) The corresponding PL spectra of
the NCs (lex ¼ 360 nm).
CdS-D-PAAm
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with the corresponding PL spectra (Fig. 10e). These luminescent
photographs visually demonstrate the bifunctional photo-
luminescent-hydrophobic properties of the synthesized NCs.
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technologies requiring both optical imaging and self-cleaning
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Conclusions
This work has demonstrated a simple and facile strategy for
fabricating bifunctional photoluminescent-superhydrophobic
CdS NCs with controlled diverse hierarchical structures via
a novel interfacial self-assembly procedure. Wire-like, belt-like,
and even sheet-like microstructures can be obtained through
simply varying the structures of the directing molecules. The
dithiocarbamate-functionalized CdS NCs after interfacial
assembly present high performance of photoluminescence
compared with those of the parent CdS NCs, especially in high
quantum yields. Simultaneously, the introduction of dithiocar-
bamate ligands derived from the reactions of carbon disulfide
and amine-containing ligand with long alkyl chain can signifi-
cantly enhance the hydrophobic properties of NCs in this case,
which will contribute a promising way to fabricate bifunctional
photoluminescent-superhydrophobic films. More broadly prac-
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Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (Grants 20606016, 10676013
NASA, 10976012 NASA), ‘‘863’’ Important National Science &
Technology Specific Project (Grant 2007AA06A402), the
Natural Science Foundation for Jiangsu Higher Education
Institutions of China (Grant 07KJA53009), National Key
Technology R&D Program in the 11th Five Year Plan of China
(2006BAE03B02-1) and doctoral thesis innovation of NJUT
(Grant No. BSCX200708).
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