Controlled synthesis of graphene-Gd(OH)3 nanocomposites and their application for detection of ascorbic acid

Article abstract of DOI:10.1039/c5ra00064e

In this report, graphene-gadolinium hydroxide (GR-Gd(OH)₃) nanocomposites have been prepared using the hydrothermal process. The crystalline structures of GR-Gd(OH)₃ have been determined by X-ray diffraction (XRD) measurements and their morphologies have been revealed by field-emission scanning electron microscopy (FE-SEM) observations. The optical properties of GR-Gd(OH)₃ have been examined by UV-vis and Fourier transform infrared (FTIR) measurements which revealed mutual interactions between GR and Gd(OH)₃. GR-Gd(OH)₃ was used to modify the glassy carbon electrode (GCE) which was subsequently utilized for electro-oxidation of ascorbic acid (AA) by cyclic voltammetry method. It was found that the electro-catalytic behavior of GCE modified by GR-Gd(OH)₃ (GCE/GR-Gd(OH)₃) was superior to that of the bare GCE. The catalytic oxidation peak current showed a linear dependence on the AA concentration and a linear calibration curve was obtained in the concentration range of 0.1-2.5 mM of AA with the lowest limit of detection (LOD) of 0.06 mM. Simultaneously, the oxidation peaks of AA over GCE/GR-Gd(OH)₃ shifted to lower over potential compared to that of GCE modified by Gd(OH)₃ (GCE/Gd(OH)₃). The results indicate that GR-Gd(OH)₃ can be used as a promising electrode modifier, which offers a new promising platform for application of the rare earth compound in electrochemistry and bioelectronics. Synchronously, the controlled synthesis of GR-Gd(OH)₃ opens an efficient and facile strategy to design other GR-based, rare earth-containing nanocomposites.

Full text of DOI:10.1039/c5ra00064e

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Controlled synthesis of graphene–Gd(OH)3
nanocomposites and their application for detection
Cite this: RSC Adv., 2015, 5, 21242
of ascorbic acid†
*
Hong Ruan, Baoyong Liu and Hongguang Li
In this report, graphene–gadolinium hydroxide (GR–Gd(OH)3) nanocomposites have been prepared using
the hydrothermal process. The crystalline structures of GR–Gd(OH)3 have been determined by X-ray
diffraction (XRD) measurements and their morphologies have been revealed by field-emission scanning
electron microscopy (FE-SEM) observations. The optical properties of GR–Gd(OH)3 have been examined
by UV-vis and Fourier transform infrared (FTIR) measurements which revealed mutual interactions
between GR and Gd(OH)3. GR–Gd(OH)3 was used to modify the glassy carbon electrode (GCE) which
was subsequently utilized for electro-oxidation of ascorbic acid (AA) by cyclic voltammetry method. It
was found that the electro-catalytic behavior of GCE modified by GR–Gd(OH)3 (GCE/GR–Gd(OH)3) was
superior to that of the bare GCE. The catalytic oxidation peak current showed a linear dependence on
the AA concentration and a linear calibration curve was obtained in the concentration range of 0.1–
2.5 mM of AA with the lowest limit of detection (LOD) of 0.06 mM. Simultaneously, the oxidation peaks
of AA over GCE/GR–Gd(OH)3 shifted to lower over potential compared to that of GCE modified by
Gd(OH)3 (GCE/Gd(OH)3). The results indicate that GR–Gd(OH)3 can be used as a promising electrode
modifier, which offers a new promising platform for application of the rare earth compound in
electrochemistry and bioelectronics. Synchronously, the controlled synthesis of GR–Gd(OH)3 opens an
efficient and facile strategy to design other GR-based, rare earth-containing nanocomposites.
Received 3rd January 2015
Accepted 16th February 2015
DOI: 10.1039/c5ra00064e
www.rsc.org/advances
such as polymers5 and nanoparticles.6 The formed hybrid
materials usually show additional and/or superior properties
1. Introduction
compared to the individual components.
The discovery of graphene (GR) has instigated intense interest
in two-dimensional nanomaterials. Owing to its large specic
surface area, extraordinary electronic properties and excellent
thermal conductivity, GR has been used as a promising material
for application in electrochemical devices such as chemical
sensors, biosensors, supercapacitors and batteries.1,2 In the case
of electrochemical sensing, densities of attached analytic
molecules were increased due to the high surface area of GR,
which in turn can facilitate high sensitivity and device minia-
turization.3 In addition, the function of GR can be further
amplied by decoration with guest molecules and/or materials4
Rare earth compounds have been used in high performance
luminescent devices, optical transmission, lighting displays
and biochemical probes due to their outstanding optical, elec-
tronic and magnetic properties.7–9 One of the most attractive
members in rare earth materials is Gd(OH)3 which has been
used as catalyst, sorbent and precursor for the preparation of
Gd2O3 by thermal dehydration.10–12 It is generally accepted that
the size, morphology and crystallinity of a given rare earth
material have a key effect on its property.13,14 Hence consider-
able attention has been paid to the synthesis of Gd(OH)3
nanomaterials with well-controlled morphologies such as rods,
bundles and sheets.11,15–18 However, to the best of our knowl-
edge, reports on GR–Gd(OH)3 nanocomposites with well-
controlled shapes are yet to come. In addition, though the
preparation of Gd(OH)3 nanomaterials have already been well-
documented, little work has been carried out to investigate
their electro-catalytic behavior.
Laboratory of Clean Energy Chemistry and Materials, Lanzhou Institute of Chemical
Physics, Chinese Academy of Sciences, Lanzhou 730000, China. E-mail: hgli@licp.
cas.cn
† Electronic supplementary information (ESI) available: UV-vis spectra of GO,
GR–Gd(OH)3-1
and
GR–Gd(OH)3-2,
EIS
of
GR,
GCE/Gd(OH)3,
GCE/GR–Gd(OH)3-1, GCE/GR–Gd(OH)3-2 and bare GCE in 0.1 M PBS-0.5 mM AA
aqueous solution, CV of GCE/GR–Gd(OH)3-2 in 0.1 M PBS (pH ¼ 7) at varying
concentration of AA, CV of GCE/GR–Gd(OH)3-1 and GCE/GR–Gd(OH)3-2 in 0.1
M PBS with 0.5 mM AA at 100 mV sꢀ1, CV of GCE/GR–Gd(OH)3-2 in 2.5 mM AA
In this work, we aim to prepare GR–Gd(OH)3 nano-
composites with well-dened morphologies by a facile hydro-
thermal method and to systematically investigate their electro-
catalytic properties. For the latter purpose, oxidation of ascor-
bic acid (AA) was selected as a model reaction. It is known that
aqueous solution at varying scan rate (15–100 mV sꢀ1). BET surface area (SBET
)
and total pore volume of Gd(OH)3, GR–Gd(OH)3-1 and GR–Gd(OH)3-2. See DOI:
10.1039/c5ra00064e
21242 | RSC Adv., 2015, 5, 21242–21248
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
AA is difficult to be directly oxidized at a conventional electrode separated by centrifugation and washed with water. A series of
due to its high over potential, low selectivity, poor sensitivity GR–Gd(OH)3 nanocomposites were obtained upon drying.
and poor reproducibility.19 To solve this problem, numerous When NaOH was used as a precipitator, the obtained nano-
attempts have been made by modifying the electrode surface composites were labeled as GR–Gd(OH)3-1. If the precipitator is
with various nanostructured materials.20–24 However, little work NH3$H2O, the nanocomposites were named as GR–Gd(OH)3-2.
has been focused on lowering the over potential of AA oxidation. The content of GR in two kinds of GR–Gd(OH)3 nanocomposites
Here, by modifying the GCE with GR–Gd(OH)3 nanocomposites, is calculated to be 7 wt%. For comparison, pure Gd(OH)3 was
we have succeeded in improving the sensitivity and simulta- also synthesized at the absence of GO via the same procedure
neously lowering the over potential of AA oxidation, which using NaOH as a precipitator.
offers a new promising platform for application of the rare earth
compound in electrochemistry and bioelectronics.
3. Characterization techniques
Powder X-ray diffraction (XRD) was carried out on a Bruker D8
Advance X-ray diffractometer at 40 kV and 40 mA with a Ni-
ltered Cu Ka radiation. The Brunauer–Emmett–Teller (BET)
2. Experimental
2.1. Materials
surface areas and nitrogen adsorption–desorption isotherms
were measured at 77 K on a Quantachrome. The absorption
spectra of the nanocomposites dispersed in water were obtained
by a UV-vis spectrophotometer (PE Lambda 35). Field-emission
scanning electron microscopy (FE-SEM) images were obtained
on a JSM-6701F spectrophotometer. Electrochemical measure-
ments were performed on an electrochemical system (CHI-660D,
China) in PBS. Bare or modied GCE of 3 mm in diameter was
used as the working electrode. Ag/AgCl and Pt wire served as the
reference and counter electrode, respectively. GCE were polished
with alumina slurry (0.05 and 0.3 mm) on a microcloth and were
subsequently rinsed with water and ethanol. Then, the elec-
trodes were further cleaned in ethanol and water with sonication
for 5 min to remove any bound particles and nally rinsed with
water. The clean electrodes were dried under a gentle nitrogen
stream. To prepare the working electrodes, 1 mg of each nano-
composite was dispersed in 1 mL H2O under ultrasonication.
Then 10 mL of each suspension was dropped onto the surface of
the cleaned GCE and dried at room temperature.
Graphite akes (325 mesh), and all the other chemicals
including KMnO4, H2SO4 (98 wt%), concentrated HNO3 and
HCl, NaNO3, H2O2 (30 wt%), Gd(NO3)3, NaOH, Na2HPO4,
KH2PO4, ascorbic acid (AA) and ethanol were obtained from
Shanghai Chemical Company. AA solutions were prepared
freshly prior to use. Phosphate buffered saline (PBS) of
pH 7.0 were prepared using Na2HPO4 (0.1 mol Lꢀ1) and KH2PO4
(0.1 mol Lꢀ1). Deionized water was used throughout the
experiments.
2.2. Preparation of graphene oxide (GO)
GO was synthesized by a modied Hummers' method.25 In
brief, graphite akes were gradually added into a mixture of
20 mL of concentrated H2SO4 : HNO3 (with a volume ratio of
3 : 1). The solution was heated to 80 ꢁC followed by stirring for
8 h. The mixture was cooled to room temperature and poured
into 50 mL cold (0 ꢁC) water. Aer 12 h, the sample was
centrifuged and washed with water. A black sample labeled as
pre-oxidized graphite was obtained. To the mixed powder of 1 g
pre-oxidized graphite and 1.03 g NaNO3, 62 g concentrated
H2SO4 was slowly dropped, followed by the slow addition of 4.5
g KMnO4 under violent stirring. The temperature was kept
below 20 ꢁC during the whole process and the reaction was
allowed to continue for two days before it is ended by 140 mL
water. Then, 30 wt% H2O2 was added slowly until the solution
turned bright yellow, which was centrifuged and washed rst
with 1 M HCl aqueous solution and then with water for several
times until the pH of the mixture was neutral. Finally, the GO
slurry was puried by dialysis for a week and dried in vacuum at
4. Results and discussion
4.1. Structure and morphology
The crystalline properties of Gd(OH)3, GR–Gd(OH)3-1 and
GR–Gd(OH)3-2 were examined by XRD as shown in Fig. 1. It is
obvious that XRD patterns of all the samples are similar with
that of Gd(OH)3, which is known to be a hexagonal phase. This
means that the introduction of GR does not change the phase of
Gd(OH)3. Instead, it only provides an ideal platform for the
formation of Gd(OH)3. It should be noted that the typical peak
for the GR is not detected in both GR–Gd(OH)3-1 and
GR–Gd(OH)3-2, presumably due to the low content and rela-
tively low diffraction intensity of GR. Similar phenomenon has
ꢁ
60 C for further use.
2.3. Preparation of GR–Gd(OH)3 nanocomposites
3 mg GO was dispersed in 3 mL water and then ultrasonicated also been observed in an earlier report.26
for 1 h. Subsequently, 0.19 mmol Gd(NO3)3 in 5 mL water was
The existence of GR in the nanocomposites can be demon-
dropped slowly. The mixture was stirred for 30 min and 1 M strated by FTIR spectra (Fig. 2). The characteristic peaks at 1730,
NaOH or concentrated NH3$H2O solution was slowly added 1630, 1380 and 1250 cmꢀ1 are attributed to the C]O stretching
until the pH of the solution was 9. Finally 7 mL water was added vibrations of the –COOH group, the C]C stretching mode, the
and the mixture was stirred for 30 min before transferred to O–H deformation of the C–OH groups and the C–OH stretching
20 mL Teon-lined stainless steel autoclave. The hydrothermal peak, respectively.27 Compared to the spectra of GO, the peaks at
treatment was conducted at 120 ꢁC for 12 h followed by cooling 1730 cmꢀ1 could not be detected in both GR–Gd(OH)3-1 and
to ambient temperature naturally. The black precipitate was GR–Gd(OH)3-2, indicating the successful reduction of GO in the
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 21242–21248 | 21243

View Article Online
RSC Advances
Paper
which suggests that the introduction of GR has no inuence on
the morphology of Gd(OH)3 nanoparticles. In other words, GR
acts as an ideal platform for the formation and growth of
Gd(OH)3, with which Gd(OH)3 nanorods interact to hinder
the aggregation. Additionally, strong dependences of the
morphology of GR–Gd(OH)3 nanocomposites on the precipi-
tator have been found as seen from Fig. 3B and C. When NaOH
is used as a precipitator, Gd(OH)3 nanorods with big aspect
ratios are dispersed on GR. While with NH3$H2O as a
Fig.
1 XRD analysis of Gd(OH)3 (A), GR–Gd(OH)3-1 (B) and
GR–Gd(OH)3-2 (C).
Fig. 2 FT-IR spectra of GO (A), GR–Gd(OH)3-1 (B) and GR–Gd(OH)3-2 (C).
nanocomposites. On the other hand, the peaks from C]C
group shied from 1630 cmꢀ1 to 1520 cmꢀ1, which is believed
to be induced by the mutual interaction between Gd(OH)3 and
GR.28–30 That is, Gd(OH)3 nanoparticles are well bounded with
GR to form the nanocomposite. The inuence of the mutual
interaction between Gd(OH)3 and GR on the spectroscopic
properties of the nanocomposites can be also detected by UV-vis
measurements (Fig. S1†). The spectroscopy of GO in water
shows two peaks at about 226 and 300 nm. The former
absorption peak can be assigned to p–p* transition of aromatic
sp2 domains,31 while the later may be attributed to n–p* tran-
sition of the C]O band.32 For GR–Gd(OH)3-1 and GR–Gd(OH)3-
2, the peaks from p–p* transition have an obvious blue shi to
206 and 209 nm, respectively.
SEM images were taken not only to directly analyze the
morphologies of the samples, but also to specically investigate
the inuences of the precipitators. Typical images are shown in
Fig. 3. It can be observed that both bare Gd(OH)3 (Fig. 3A) and
GR–Gd(OH)3-1 (Fig. 3B) are nanorods with big aspect ratios,
Fig.
3 SEM images of Gd(OH)3 (A), GR–Gd(OH)3-1 (B) and
GR–Gd(OH)3-2 (C).
21244 | RSC Adv., 2015, 5, 21242–21248
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
precipitator, the aspect ratios of Gd(OH)3 nanorods decrease morphology and special surface of GR–Gd(OH)3-2, where short
and short nanorods formed. The differences between NaOH Gd(OH)3 nanorods induce a higher special surface area and
and NH3$H2O is partially due to the lower hydrolysis rate of improve the electro-catalytic activities. Besides, it is also found
NH3$H2O than that of NaOH, which provides basic media for that, the oxidation peaks in cases of GR–Gd(OH)3-1 and GR–
precipitation and is disadvantageous for the formation of Gd(OH)3-2 obviously shied to lower potentials compared to
Gd(OH)3 nanorods. Another possibility is that NH3$H2O can that of Gd(OH)3. This could be ascribed to the morphological
coordinate with Gd3+ ions to form Gd(NH3)x3+ complexes, which changes of the nanocomposites induced by the introduction of
prevents the reaction between Gd3+ and OHꢀ and lowers the GR. On the other hand, the intermolecular forces between the
growth rate of Gd(OH)3 nanorods. The strong dependence of the nanocomposite and AA molecules may also play a role.35
nanoparticle morphology on the precipitator has also been Therefore, it is quite predictable and reasonable that oxidation
observed previously during the preparation of ScOOH/Sc(OH)3 peaks of AA shi when different modied electrodes are used.
and La(OH)3 nanocrystals.33,34
In order to further understand the electro-catalytic behavior of
electrodes with different modications, electrochemical imped-
ance spectroscopy has been carried out (Fig. S2†). The semicircle
portion of the Nyquist plot at high frequencies corresponds to
the charge transfer process. The diameter is equal to the charge
transfer resistance (Rct), which controls the electron transfer
kinetics of the redox probe at the electrode interface. GCE/GR
shows the lowest Rct among all the electrodes, which can be
ascribed to the high density of edge-plane sites and defects of GR.
This feature of GR also leads to a lower Rct of GCE/GR–Gd(OH)3-1
and GCE/GR–Gd(OH)3-2 compared to that of GCE/Gd(OH)3 and
bare GCE. It is also noted that Rct of GCE/GR–Gd(OH)3-2 is lower
than that of GCE/GR–Gd(OH)3-1, which can be explained by the
unique morphology of the GR–Gd(OH)3-2 where Gd(OH)3 nano-
rods have smaller aspect ratios than those in GR–Gd(OH)3-1. This
leads to a higher special surface area of GR–Gd(OH)3-2 which
accelerates charge transfer between AA and GCE/GR–Gd(OH)3-2
and lowers the Rct. The result is also consistent with the highest
activities of GCE/GR–Gd(OH)3-2 observed from Fig. 4.
4.2. Electro-catalytic properties
Cyclic voltammetry (CV) was used to investigate the application
of GR-based nanocomposites in electrochemical sensors for AA.
Fig. 4 shows CV curves for bare and modied GCE at a scan rate
of 100 mV sꢀ1 in 0.1 M phosphate buffered saline (PBS, pH ¼ 7.0)
at the presence of 0.5 mM AA. It is found that the oxidation
currents (ipa) of GCE modied by Gd(OH)3 (GCE/Gd(OH)3),
GR–Gd(OH)3-1 (GCE/GR–Gd(OH)3-1) and GR–Gd(OH)3-2 (GCE/
GR–Gd(OH)3-2, Fig. 4B–D) are all higher than that of bare GCE
(Fig. 4E). However, it is not the case for GCE modied by GR
(GCE/GR, Fig. 4A). The low performance of GCE/GR could be
ascribed to the poor dispersibility of GR in aqueous solution
due to its hydrophobicity. From Fig. 4, it can be also seen that
ipa of GCE/GR-Gd(OH)3-1 is higher than that of GCE/Gd(OH)3.
This may arise from the following two factors: (i) in
GR–Gd(OH)3-1, GR provides a pathway for rapid electron
transport due to its high conductivity; (ii) GR–Gd(OH)3-1
possesses a larger surface area than Gd(OH)3 due to the pres-
ence of GR. The synergistic effect of the above-mentioned two
factors promotes electrochemical reactions and induces an
enhancement of ipa. It should also be noticed that compared to
GCE/GR–Gd(OH)3-1, the performance of GCE/GR–Gd(OH)3-2 is
even better. This suggests GR–Gd(OH)3-2 has the highest
electro-catalytic properties. This can be explained by the unique
Additionally, the effect of AA concentration (cAA) on the CV
response of GCE/GR–Gd(OH)3-1 has been investigated under a
xed scan rate of 100 mV sꢀ1. Fig. 5A shows the change of ipa
when cAA was increased. A linear relationship between ipa and
cAA was found within the concentration range of 0.1–2.5 mM, as
shown in Fig. 5B. The resulting calibration plot is a straight line,
with a coefficient of 0.998, given by the equation:
ipa (mA) ¼ 7.34cAA (mM) + 4.61
(1)
The lowest limit of detection (LOD) (based on S/N ¼ 3) was
found to be 0.06 mM, the detailed calculation can be seen in the
ESI.† The sensitivity of the electrode is 103.8 mA mMꢀ1 cmꢀ2
.
The effect of cAA on the CV response of GCE/GR–Gd(OH)3-2 is
shown in Fig. S3,† from which a linear relationship between ipa
and cAA can be found within the concentration range of 0.3–2.5
mM. The LOD and the sensitivity of GCE/GR–Gd(OH)3-2 can be
calculated to be 0.05 mM and 116.4 mA mMꢀ1 cmꢀ2, respec-
tively. Thus GCE/GR–Gd(OH)3-2 exhibits a lower LOD and a
higher sensitivity compared to GCE/GR–Gd(OH)3-1. Further-
more, in order to estimate the reproducibility of the results,
three series of experiments were carried out (Fig. S4†) and
the relative standard deviation of the current responses of
GCE/GR–Gd(OH)3-1 and GCE/GR–Gd(OH)3-2 are 5.7% and
5.1%, respectively, indicating a reproducible fabrication of the
GCE/GR–Gd(OH)3-1 and GCE/GR–Gd(OH)3-2 biosensors.
Fig. 4 CV of GCE/GR (A), GCE/Gd(OH)3 (B), GCE/GR–Gd(OH)3-1 (C),
GCE/GR–Gd(OH)3-2 (D) respectively. For comparison, the result of the
bare GCE in 0.5 mM AA is also shown (E). The scan rate is 100 mV sꢀ1
.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 21242–21248 | 21245

View Article Online
RSC Advances
Paper
Fig. 6 (A) CV of GCE/GR–Gd(OH)3-1 in 2.5 mM AA aqueous solution
at varying scan rate (15–100 mV sꢀ1) and (B) the relationship between
Fig. 5 (A) CV of GCE/GR–Gd(OH)3-1 in 0.1 M PBS (pH ¼ 7.0) at varying
concentration of AA (0.1–2.5 mM) and (B) relationship between ipa (mA)
and cAA (mM).
ipa and V1/2
.
C6H8O6(ascorbic acid) ꢀ 2eꢀ
/
C6H6O6(dehydroascorbic acid) + 2H+
Fig. 6 shows the effect of the scan rates on the electro-
catalytic properties of GCE/GR–Gd(OH)3-1 towards AA oxida-
tion. An increase in the scan rate not only leads to a corre-
sponding increase in ipa, but also results in a shi of the anodic
peak to more positive potentials (Fig. 6A). In addition, it can be
seen that ipa is proportional to the square root of the sweep rate
(V1/2) within the investigated range (15–100 mV sꢀ1) (with linear
regression coefficient of 0.996) (Fig. 6B), suggesting that the
oxidation reaction of AA molecules on GCE/GR–Gd(OH)3-1 is
primarily diffusion-controlled. The effect of the scan rate on the
electro-catalytic properties of GCE/GR–Gd(OH)3-2 follows
similar rules as those observed for GCE/GR–Gd(OH)3-1
(Fig. S5†). Similar results of AA oxidation by an Au/TiO2/Ti
electrode have also been reported by Hosseini et al.36 Therefore,
it highlights that the structure of GR skeleton provides an ideal
morphology for anchoring bioactive molecules, which gives rise
to a pathway for rapid mass transfer. Based on all the above
results, a proposed oxidation process of AA can be described in
Fig. 7. First, AA molecules in solution diffuse to the nearest
active sites on GR and are absorbed onto Gd(OH)3 nanorods.
Then AA molecules absorbed on the surface of the electrode are
oxidized to dehydroascorbic acid:
In order to study the inuence of GR on the surface area and
porosity of the nanocomposites, the Brunauer–Emmett–Teller
(BET) gas adsorption method was performed. BET specic
Fig. 7 Proposed mechanism for electro-catalytic oxidation of AA on
GCE which was pre-modified by GR–Gd(OH)3 hybrid materials.
21246 | RSC Adv., 2015, 5, 21242–21248
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
surface area (SBET) and total volume of pores of the samples are has dramatically increased compared to that of Gd(OH)3. In
listed in Fig. 8 and Table S1.† The nitrogen adsorption– addition, compared with GR–Gd(OH)3-1, SBET and total volume
desorption isotherm of Gd(OH)3, GR–Gd(OH)3-1 and of pores of GR–Gd(OH)3-2 gradually increase from 18.02 m2 gꢀ1
GR–Gd(OH)3-2 all exhibits type II, which indicates the presence to 32.38 m2 gꢀ1 and from 0.36 cm3 gꢀ1 to 0.41 cm3 gꢀ1
,
of mesoporous materials according to the IUPAC classica- respectively. Here, we speculate that the enhancement in SBET
tion.37 A narrow pore size distribution with an averaged pore and total volume of pores induced by the introduction of GR is
diameter of 30 nm was recorded, as displayed in the inset of the most important reason that GR–Gd(OH)3-2 possesses the
Fig. 8A–C. The results suggest the addition of GR did not change highest electron-catalytic activity among all samples.
the nitrogen adsorption–desorption isotherm. However, SBET
and total volume of pores of GR–Gd(OH)3-1 and GR–Gd(OH)3-2
5. Conclusions
In summary, by selecting different precipitators, GR–Gd(OH)3
nanocomposites with different morphologies have been
successfully prepared by a facile hydrothermal method. When
NaOH is used as a precipitator, Gd(OH)3 nanorods with big
aspect ratios are dispersed on GR (GR–Gd(OH)3-1). When
NH3$H2O is selected, however, short Gd(OH)3 nanorods with
decreased aspect ratios formed (GR–Gd(OH)3-2). GR–Gd(OH)3-2
shows superior electrical chemical properties to Gd(OH)3
and GR–Gd(OH)3-1 due to its high surface area. The oxidation
current of AA on GCE/GR–Gd(OH)3-1 has a linear relationship
with cAA in the range of 0.1–2.5 mM and the oxidation reaction
of AA molecules on GCE/GR–Gd(OH)3-1 is a primary diffusion-
controlled process. It is expected that our work can convey a
new promising platform for the application of GR-based rare
earth hybrid materials in biosensing. Furthermore, the facile
methods could also be extended to other GR-based, rare earth-
containing nanocomposites with different morphologies.
Acknowledgements
This work was nancially supported by the Hundred Talents
Program of Chinese Academy of Sciences (Y20245YBR1) and
National Natural Science Foundation of China (no. 21402215).
References
1 Y. Shao, J. Wang, H. Wu, J. Liu, I. A. Aksay and Y. Lin,
Electroanalysis, 2010, 22, 1027–1036.
2 X. Huang, Z. Zeng, Z. Fan, J. Liu and H. Zhang, Adv. Mater.,
2012, 24, 5979–6004.
3 F. Zhang, J. Tang, Z. Wang and L. Qin, Chem. Phys. Lett.,
2013, 590, 121–125.
4 X. Huang, X. Qi, F. Boey and H. Zhang, Chem. Soc. Rev., 2012,
41, 666–686.
5 P. Manivel, M. Dhakshnamoorthy, A. Balamurugan,
N. Ponpandian, D. Mangalaraj and C. Viswanathan, RSC
Adv., 2013, 3, 14428–14437.
6 X. Pan, Y. Zhao, S. Liu, C. L. Korzeniewski, S. Wang and
Z. Fan, ACS Appl. Mater. Interfaces, 2012, 4, 3944–3950.
7 S. V. Dliseeva and J.-C. G. Buenzli, Chem. Soc. Rev., 2010, 39,
189–227.
8 Y. Liu, D. Tu, H. Zhu and X. Chen, Chem. Soc. Rev., 2013, 42,
6924–6958.
9 M. C. Heffern, L. M. Matosziuk and T. J. Meade, Chem. Rev.,
2014, 114, 4496–4539.
Fig. 8 Brunauer–Emmett–Teller specific surface area of Gd(OH)3 (A),
GR–Gd(OH)3-1 (B) and GR–Gd(OH)3-2 (C).
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 21242–21248 | 21247

View Article Online
RSC Advances
Paper
10 V. Parashar and A. C. Pandey, Anal. Methods, 2010, 2, 1227– 26 H. Zhang, X. Lv, Y. Li, Y. Wang and J. Li, ACS Nano, 2009, 4,
1229. 380–386.
11 G. J. Xing, Q. Y. Guo, Q. J. Liu, Y. L. Li, Y. Wang, Z. L. Wu and 27 X. D. Wang, N. L. Zhou, J. Yuan, W. Y. Wang, Y. D. Tang,
G. M. Wu, Ceram. Int., 2014, 40, 6569–6577.
12 S. Liu, Y. Cai, X. Cai, H. Li, F. Zhang, Q. Mu, Y. Liu and
Y. Wang, Appl. Catal., A, 2013, 453, 45–53.
C. Y. Lu, J. Zhang and J. Shen, J. Mater. Chem., 2012, 22,
1673–1678.
28 J. Guo, S. Zhu, Z. Chen, Y. Li, Z. Yu, Q. Liu, J. Li, C. Feng and
D. Zhang, Ultrason. Sonochem., 2011, 18, 1082–1090.
13 Z. Yan and C. Yan, J. Mater. Chem., 2008, 18, 5046–5059.
14 R. Si, Y. Zhang, H. Zhou, L. Sun and C. Yan, Chem. Mater., 29 W. Wei, T. C. He, X. Teng, S. X. Wu, L. Ma, H. Zhang, J. Ma,
2006, 19, 18–27.
Y. H. Yang, H. Y. Chen, Y. Han, H. D. Sun and L. Huang,
Small, 2012, 8, 2271–2276.
30 X. Zhang, X. Yang, Y. Ma, Y. Huang and Y. Chen, J. Nanosci.
Nanotechnol., 2010, 10, 2984–2987.
31 D. Y. Pan, J. C. Zhang, Z. Li and M. H. Wu, Adv. Mater., 2010,
22, 734–738.
32 J. Peng, W. Gao, B. K. Gupta, Z. Liu, R. Romero-Aburto, L. Ge,
L. Song, L. B. Alemany, X. Zhan, G. Gao, S. A. Vithayathil,
B. A. Kaipparettu, A. A. Marti, T. Hayashi, J. J. Zhu and
P. M. Ajayan, Nano Lett., 2012, 12, 844–849.
33 Y. Zhang, J. Liu, R. Si, Z. Yan and C. Yan, J. Phys. Chem. B,
2005, 109, 18324–18331.
34 G. Li, C. Li, Z. Xu, Z. Cheng and J. Lin, CrystEngComm, 2010,
12, 4208–4216.
35 J. Xie, Q. Wu, D. Zhang and Y. Ding, Cryst. Growth Des., 2009,
9, 3889–3897.
15 Y. Yoon, B. Lee, K. S. Lee, G. H. Im, S. Byeon, J. H. Lee and
I. S. Lee, Adv. Funct. Mater., 2009, 19, 3375–3380.
16 X. Wang and Y. Li, Angew. Chem., Int. Ed., 2002, 41, 4790–
4793.
17 G. Jia, K. Liu, Y. Zheng, Y. Song, M. Yang and H. You, J. Phys.
Chem. C, 2009, 113, 6050–6055.
18 X. Wang and Y. Li, Chem.–Eur. J., 2003, 9, 5627–5635.
19 S. B. Khoo and F. Chen, Anal. Chem., 2002, 74, 5734–5741.
20 K. Deng, J. Zhou and X. Li, Electrochim. Acta, 2013, 114, 341–
346.
21 C. Zhou, S. Li, W. Zhu, H. Pang and H. Ma, Electrochim. Acta,
2013, 113, 454–463.
22 Y. Ma, M. Zhao, B. Cai, W. Wang, Z. Ye and J. Huang, Biosens.
Bioelectron., 2014, 59, 384–388.
23 G. Hu, Y. Guo, Q. Xue and S. Shao, Electrochim. Acta, 2010,
55, 2799–2804.
24 H. Li, Y. Wang, D. Ye, J. Luo, B. Su, S. Zhang and J. Kong,
Talanta, 2014, 127, 255–261.
36 M. G. Hosseini, M. Faraji and M. M. Momeni, Thin Solid
Films, 2011, 519, 3457–3461.
37 K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou,
´
25 H. Tetsuka, R. Asahi, A. Nagoya, K. Okamoto, I. Tajima,
R. Ohta and A. Okamoto, Adv. Mater., 2012, 24, 5333–5338.
R. A. Pierotti, J. Rouquerol and T. Siemieniewska, Pure
Appl. Chem., 1985, 57, 603–619.
21248 | RSC Adv., 2015, 5, 21242–21248
This journal is © The Royal Society of Chemistry 2015