J. Li et al. / Inorganica Chimica Acta 442 (2016) 111–118
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120 °C under N2 protection for 8 h. Crude product was collected
and purified in ethanol/toluene to give CDO-NH2 as brown powder.
1H NMR (CDCl3): d 8.75 (s, 1H), 8.63 (s, 1H), 8.25 (s, 1H), 7.32 (s,
2H), 7.00–6.95 (m, 3H), 6.81–6.77 (m, 2H), 5.05 (s, 2H). 13C NMR
(CDCl3), d (ppm): 113.46, 118.29, 122.38, 124.56, 133.39, 134.72,
141.61, 147.83, 160.22. MS m/z: [m]+ Calc. for C17H12N4, 272.1;
found, 272.3.
was used to find the completeness of this reaction. During
this time, emission of this mixture was gradually increased
(kex = 365 nm). Maximum emission was observed after 8 h.
Another 2 h were allowed to guarantee a complete reaction. The
resulting solid product was collected and washed with ethanol:
acetone (1:1, V:V) to give Ru-Composite.
3. Results and discussion
2.3. Ru(DPPhen)2Cl2
3.1. Morphology analysis of Ru-Composite
Ru(DPPhen)2Cl2 was prepared following a literature procedure
[11,12]. The mixture of RuCl3ꢁ3H2O (1 mmol), DPPhen (2 mmol)
and DMF (30 mL) was heated to 120 °C and kept for 24 h under
N2 protection. Then solvent was vaporized under reduced pressure.
Cold acetone (50 mL, 0 °C) was added and held still overnight at
0 °C. The resulting solid sample was dissolved in mixed solvent
of ethanol and water (250 mL, V:V = 1:1). This mixture was heated
to 80 °C and kept for 1 h. Then anhydrous LiCl (20 g) was added
and stirred. Solvent ethanol was removed by thermal evaporation.
The resulting aqueous solution was held still at 0 °C overnight to
give solid product. Crude product was purified in mixed solvent
of ethanol and water (V:V = 1:1) and dried in vacuum at 110 °C.
MS m/z: [m]+ Calc. for C48H32N4RuCl2, 836.1; found, 836.4.
Our composite sample is firstly characterized by its scanning
electron microscope (SEM) and transmission electron microscope
(TEM) images shown in Fig. 1. SEM images of Fe3O4 core, silica
coated core, MCM-41 planted core and GPTS modified host are
shown for comparison. Rough surface with multiple protuberances
is observed for our as-synthesized Fe3O4 core. Mean diameter of
these particles is as wide as 370 nm which is slightly smaller than
literature values, owing to their decreased crystal growth time
[17,18]. Magnetic aggregation between these particles is obvious,
showing
a poor dispersal. Particle diameter is increased to
390 nm after silica coating procedure. Surface of these silica coated
particles is greatly smoothed, with magnetic aggregation weak-
ened. MCM-41 construction further increases diameter of MCM-
41 planted core to 510 nm with monodispersal, which means that
magnetic aggregation between Fe3O4 core has been successfully
blocked. From diameter comparison, MCM-41 thickness is deter-
mined as 60 nm which is slightly shorter than literature values
[17,18]. To covalently graft sensing probe, MCM-41 tunnels are
modified with GPTS. Diameter of GPTS modified host is still
510 nm, indicating that this silane coupling reagent is embedded
into MCM-41 tunnels, not on their surface. After loading CDO-NH2
ligand and Ru(II) complex, the final Ru-Composite exhibits
monodispersal and smooth surface with diameter of 510 nm. This
core–shell structure is further confirmed by TEM of Ru-Composite.
This core–shell structure is anticipated to hold and maintain fea-
tures of each component, where Fe3O4 core serves for magnetic
guiding, MCM-41 guarantees smooth O2 transportation and Ru(II)
complex offers sensing signals, respectively.
2.4. GPTS modified host
Our GPTS modified host was prepared following a four-step
procedure. Its first step was to grow Fe3O4 core following a
literature procedure [17,18]. The following chemicals were mixed
together and stirred to get a transparent solution, including
FeCl3ꢁ6H2O (2.7 g), SDS (1.0 g), NaAc (7.2 g) and glycol (100 mL).
This solution was aged for 30 min, then transferred into a Teflon
flask and heated to 200 °C for 8 h. Solid sample was collected and
washed with deionized water.
The second step was to coat Fe3O4 core with amorphous silica
by below procedure. The above obtained Fe3O4 (0.1 g) was dis-
persed in ethanol (20 mL) and treated with ultrasonic bath for
15 min. Then TEOS (0.15 g), deionized water (15 mL), concentrated
ammonia (1 mL) and ethanol (30 mL) were added into Fe3O4 turbid
liquid and stirred for 5 h. Solid product was collected and washed
with deionized water.
3.2. Magnetic feature of Ru-Composite
The third step was to grew MCM-41 onto silica coated Fe3O4
core following a literature procedure [11,12]. Silica coated Fe3O4
core (0.2 g), CTAB (0.2 g), concentrated ammonia (1 mL), deionized
water (40 mL) and ethanol (30 mL) were mixed together and
exposed to ultrasonic bath for 20 min. During this time, TEOS
(0.5 g) was dropwise added. The resulting mixture was allowed
to react at room temperature for 6 h. Solid product was collected
and stirred in mixed solvent of ethanol/concentrated HCl
(200 mL:10 mL) for 48 h to remove template reagent CTAB.
The fourth step was to modify MCM-41 planted core with a
silane coupling regent GPTS. The above obtained MCM-41 planted
core (0.1 g), GPTS (0.1 g, excess) and toluene (25 mL) were mixed
together and heated to reflux under N2 atmosphere for 6 h. Solid
product was collected and obtained as GPTS modified host.
Since Fe3O4 core is the basis of site-specific guiding, its magnetic
feature, along with that of Ru-Composite, is shown in Fig. 2. As for
our as-synthesized Fe3O4 core, a saturate magnetization value of
70.9 emu gꢀ1 is observed which is slightly lower than literature val-
ues owing to its smaller size [17,18]. Superamagnetic behavior is
observed for our as-synthesized Fe3O4 core without hysteresis.
According to Zhang’s statement, Fe3O4 dots whose diameter is wider
than 30 nm should be magnetic ones, showing obvious hysteresis
[19]. In this work, however, superamagnetic behavior is observed
even though corresponding diameter is as large as 370 nm. Bearing
the multiple protuberances on Fe3O4 core surface, it is assumed that
each Fe3O4 particle is constructed by lots of sub-particles whose
diameter is smaller than 30 nm, resulting in its superamagnetic
behavior. After silica/MCM-41 coating and probe loading proce-
dures, saturate magnetization of Ru-Composite is decreased to
31.5 emu gꢀ1. This fact can be explained by the decreased Fe3O4
weight ratio in Ru-Composite. Its superamagnetic character is pre-
served well, which satisfies site-specific requirement.
2.5. Ru-Composite
The final site-specific oxygen sensing composite (denoted as
Ru-Composite) was constructed following a two-step procedure.
The first step was to graft CDO-NH2 onto GPTS modified host.
CDO-NH2 (0.05 g), GPTS modified host (0.2 g) and toluene were
mixed together and heated to reflux under N2 atmosphere for
8 h. Solid product was collected and mixed with Ru(DPPhen)2Cl2
(0.1 g, excess) and ethanol (50 mL). This mixture was heated to
reflux under N2 atmosphere for 10 h. Fluorescence monitoring
3.3. WAXRD and SAXRD of Ru-Composite
To confirm the successful synthesis of our Fe3O4 core, wide
angle XRD (WAXRD) patterns of as-synthesized Fe3O4 core and