Experiment Section
In this work, the detailed information regarding all of the reagents,
the preparation process for ZnO and HSNs and characterization methods
can be found in the Supporting Information.
Results and Discussion
As a template, the prepared ZnO nanoparticles have a spheroid morphology
(Fig. 1a) with a narrow size distribution, and the average diameter of
nanoparticles is about 9 nm (Fig. 1b), which can be monodispersed in
water to form nanodispersion with high transparency (lower left of Fig.
S1, Supporting Information). Clear and continuous lattice fringes of ZnO
nanoparticles with 0.28 nm lattice spacing in the high resolution
transmission electron microscopy image (the lower right inset in Fig.
1a) correspond to the (100) crystal plane of ZnO, which indicates the
ZnO nanocrystals are well
crystallized.18X-ray diffraction (XRD) patterns of ZnO nanoparticles (Fig. 1c) present
all the peaks of unmodified and modified samples expectedly
corresponding to hexagonal wurtzite crystal form (JCPDS
No.361451).18, 19 All peaks of the modified sample are
slightly broadened and weakened than unmodified one, because organic
modifier molecules coated on the nanoparticles surface weaken the
detection of ZnO crystal components.18 The FTIR
spectrum of ZnO nanoparticles (Fig. 1d) shows that KH550 has been
successfully grafted onto the surface of nanoparticles because its
characteristic absorption peaks appear in the curve of modified ZnO such
as -CH- (~2947 cm-1), -CH2 (~1220
cm-1) and -NH2 (~1587
cm-1).20 Without doubt,
KH550-modified ZnO nanoparticles can be well dispersed in the aqueous
phase, as shown in Fig. 1a. In addition, the absorption peaks at ~3428
cm−1 corresponds to the characteristic peaks of -OH
stretching vibration. Thermo- gravimetric analysis (TGA) results
furtherly confirm that ZnO nanoparticles were wrapped by the KH550 and
the loading is 18.6% (Fig. S1, Supporting Information). It is noted
that surface amination treatment makes ZnO nanoparticles positively
charged up to 34.2 mv, which facilitates coating process of
SiO2 with negative charge.21
HSNs were prepared by the reverse microemulsion method. As shown in Fig.
2a, the microemulsion is composed of water as the disperse phase and
cyclohexane as the continuous oil phase, Igepal CO-630 as the
emulsifier
contributing to the formation of a stable water-in-oil emulsions. ZnO
nanoparticles are monodispersed in water nuclear and methyl
orthosilicate (TMOS) precursor is dissolved in cyclohexane. Moreover,
NH3·H2O
is selected as hydrolysis catalyst, and meanwhile as the etchant for
template agent. TMOS in oil phase hydrolyzes at the oil-water interface
under the catalytic effect of NH3·H2O in
water and the hydrolysis products enter into water nuclear for
heterogeneous nucleation on the surface of ZnO
nanoparticles.22, 23 The amount of water in
microemulsion is small, resulting in the achievement of the uniform
coating of SiO2 on ZnO by controlling the hydrolysis
reaction rate of TMOS. At the same time, ZnO nanoparticles are corroded
slowly and gradually by NH3·H2O in
water. After 2 h reaction, modifier such as polyethylene pyrro-