11 journal of materials chemistry b

Journal ofMaterials Chemistry B

PAPER

Publ

ishe

d on

01

Sept

embe

r 20

14. D

ownl

oade

d by

Nat

iona

l Tai

pei U

nive

rsity

of

Tec

hnol

ogy

on 0

3/10

/201

4 06

:25:

51.

View Article OnlineView Journal

Controlled electr

Department of Chemical Engineering and Bio

Technology, Taipei 10608, Taiwan. E-mail:

Electronic supplementary informa10.1039/c4tb01325e

These authors contributed equally.

Cite this: DOI: 10.1039/c4tb01325e

Received 10th August 2014Accepted 1st September 2014

DOI: 10.1039/c4tb01325e

www.rsc.org/MaterialsB

This journal is The Royal Society of

ochemical synthesis of new rareearth metal lutetium hexacyanoferrate on reducedgraphene oxide and its application as a salicylic acidsensor

Balamurugan Devadas, Rajesh Madhu, Shen-Ming Chen* and Huai-Tse Yeh

The hexangular star building-like lutetium hexacyanoferrate (LuHCF) structure with an average size of ca.

8.0 0.5 mm was synthesized using a simple, one-step electrochemical method, and it was highlydispersed on to a reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) support for the

first time. The size and shape of the as-synthesized LuHCF micro stars were controlled by the deposition

time. The LuHCF/RGO samples were characterized by a variety of analytical and spectroscopy

techniques, viz. scanning electron microscopy (SEM), infra-red spectroscopy (IR), energy dispersive X-ray

spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In addition,

LuHCF/RGO/GCE was adopted for the novel electrochemical detection of salicylic acid (SA) using cyclic

voltammetry (CV) and amperometry methods. The charge transfer resistant value of LuHCF/RGO/GCE

was smaller than LuHCF and bare GCE, which exhibit a remarkable electrocatalytic performance towards

SA. Notably, the SA sensor was found to exhibit a lower detection limit and high sensitivity of ca. 0.49

mM and 77.2 mA mM1 cm2, respectively. The reported SA sensor possesses an excellent real time

application with commercially purchased aspirin tablets and salic ointment (which contains salicylic acid).

The excellent analytical parameters of the reported sensor, surpasses the previously reported modified

electrodes, rendering practical industrial applications.

1. Introduction

Salicylic acid (SA) is a type of phenolic acid, which is also knownas 2-hydroxybenzoic acid. SA has been found in plants, andplays a signicant role in the development of plant growth,photosynthesis, and transpiration. However, the treatment ofSA has grateful consideration toward the synthesis of patho-genesis-related proteins and alfalfa mosaic virus infectedplants.1 Owing to unique properties such as keratolytic, bacte-riostatic, fungicidal, and photo protective activity, SA is bene-cial for a wide range of applications, namely, topical use,dermatologic conditions, reducing the rate of keratinocyteproliferation.2 Moreover, SA is used to heal several skin prob-lems such as acne, hyperpigmentation, oily skin, large pores,and surface roughness.3 Therefore, SA has been widely used inthe preparation of cosmetics and ointment due its peeling andexible nature.4 Hence, the effective and sensitive

technology, National Taipei University of

[email protected]

tion (ESI) available. See DOI:

Chemistry 2014

determination of SA is very important in pharmaceuticals andother cosmetic industries.

Owing to the numerous activities of pharmaceutical analysis,it is highly signicant to develop sensitive and selective sensingsystems for the detection of SA. Previously, P. Trinder et al.,reported the determination of salicylate in biological uidsusing a ferric salt spectrophotometer.5 Nevertheless, there havebeen several reports on the detection of SA using differenttechniques including spectrophotometry,6 Raman spectros-copy,7 ultraviolet spectrometry,8 gas chromatography-massspectrometry (GC-MS),9 colorimetric techniques,10 liquid chro-matography-tandem mass spectrometry,11,12 and gasliquidchromatography.13 The aforementioned methods have disad-vantages such as high cost and the need of expensive instru-ments and technical operators. In contrast to these methods,electrochemical techniques are more convenient, cost effectiveand easy to operate. However, there are few reports on the use ofelectrochemical methods for SA detection.14,15 Interestingly, wehave developed a simple and convenient amperometric methodfor the electrochemical determination of SA.

On the other hand, progress on new materials using elec-trochemical technique is still a challenging task for manyresearchers. In spite of the overwhelming activity on metalhexacyanoferrate, rare earth metalHCFs have also been widely

J. Mater. Chem. B
http://crossmark.crossref.org/dialog/?doi=10.1039/c4tb01325e&domain=pdf&date_stamp=2014-10-01http://dx.doi.org/10.1039/c4tb01325ehttp://pubs.rsc.org/en/journals/journal/TB

Journal of Materials Chemistry B Paper

Publ

ishe

d on

01

Sept

embe

r 20

14. D

ownl

oade

d by

Nat

iona

l Tai

pei U

nive

rsity

of

Tec

hnol

ogy

on 0

3/10

/201

4 06

:25:

51.

View Article Online

used in electrochemical sensor applications.1620 To date,several rare earth metalHCFs such as dysprosium,21,22

samarium,23,24 and lanthanum HCF,25 respectively, have beenreported for preparation and characterization. Nonetheless,rare earth metalHCFs have fascinating morphologies such asower and christmas tree-like CeHCF,26 diamond-like NdHCF,27

LaHCF,28 and parabola-like HoHCF.29 Moreover, we havedemonstrated microstar-like DyHCF and ower-like YHCF forsensor applications in our previous reports.30,31 Among them, inthe order of rare earth metal, lutetium is one of the signicantmaterials for electrochemical sensor applications.32 In recentdecades, electrochemical properties and the applications oflutetium phthalocyanines have been investigated.3336 More-over, reduced graphene oxide (RGO) is an inspiring materialdue to its unique electrical, thermal and mechanical properties,which can be used as an efficient substrate material. Hence,RGO modied electrodes have been widely used for biofuelcells, energy storage devices and biosensor applications.3741

Moreover, RGO is more favorable to prevent the uncontrollablegrowth of the MHCF, hence, favorable for catalytic reactions.42,43

In contrast to earlier reports on electrochemical methods byJiang et al., and M. A. Raj et al., the reported electrochemicalreduction of GO was performed with a 0.1 M solution of KClcontaining the metal and ferricyanide. Moreover, only 10consecutive CV cycles were scanned for the electrochemicalreduction.44,45 Interestingly, RGO can retain the electrochemicalbehaviour of the hexacyanoferrate (HCF) lm and enhances theelectron transfer ability between the HCF and GCE. Hencecomposites of graphene with HCF have prevalent considerationfor different applications.46,47Owing to the distinctive propertiesof RGO-HCF it has received a lot of attention for applications inelectrocatalysis in recent years.31,48,49 To the best of our knowl-edge using an extensive literature survey, there is no report forthe LuHCF/RGO hybrid material. Hence, the electrochemical,structural and morphological characterisation, and wideapplications of LuHCF are still intriguing. Therefore, in thiswork, we have developed an amperometric method for theelectrochemical preparation of LuHCF for the rst time.

Herein, we demonstrate a novel electrochemical route for thepreparation of the LuHCF/RGO composite material for appli-cation as a SA sensor. The LuHCF micro star particle structurewas achieved by controlling the deposition time. The as-syn-thesised LuHCF/RGO composite material was characterizedusing a range of analytical and spectroscopic techniques. Thedetermination of SA was carried out using a amperometricmethod, and the real time application of the reported SA sensorwas performed with aspirin tablets and salic ointment samples.

2. Experimental section2.1 Materials and methods

Lutetium(III) chloride hexahydrate was obtained from SigmaAldrich. K3Fe(CN)6 and KCl were purchased from Wako purechemical industries, Ltd. Salicylic acid was purchased fromYakuri Chemicals. Co. Ltd. Sodium hydroxide was purchasedfrom Sigma Aldrich. All other chemicals were of analytical gradeand used as received. The supporting electrolyte 0.1 M KCl and

J. Mater. Chem. B

all reagents were prepared using doubly deionized distilledwater. Prior to electrochemical experiments, pure nitrogen gaswas purged through the experimental solution.

The entire electrochemical measurements were carried outusing a CHI 1205A work station using a three electrode systemconsisting of a glassy carbon electrode as the working electrode,Ag/AgCl as the reference electrode and Pt wire as the counterelectrode in the electrochemical cell. Amperometric studieswere carried out using a rotating ring disk electrode (RRDE-3A),BAS instrument made in Japan. The morphological studies werecarried out using a Hitachi S-3000H scanning electron micro-scope (SEM). Energy dispersive X-ray (EDX) spectra was recor-ded with a HORIBA EMAX X-ACT.

2.2 Synthesis of graphene oxide

Graphene oxide (GO) has synthesized by Hummers method.Briey, graphite oxide was synthesized by treating raw graphitewith sodium nitrate and potassium permanganate in an icebath. Then, aer the addition of 3% hydrogen peroxide toreduce the permanganate and manganese dioxide. Theobtained brownish graphite oxide was washed with warm waterand the graphite oxide collected by centrifugation. Further,graphite oxide was dispersed in water in the ratio of 1 mg mL1

using sonication to obtain a GO solution.

2.3 Fabrication of modied electrode

Prior to the fabrication of the electrode, the GCE was well pol-ished with alumina powder, ethanol and DD water and dried inan air atmosphere and 5 mL of the as-synthesized GO solutionwas drop-casted onto the GCE surface and dried. The GOmodied GCE was placed in a supporting electrolyte KCl solu-tion containing equal amounts of LuCl3$6H2O and K3Fe(CN)6.Then 10 consecutive CV scans were performed at the GO/GCE,and amperometric deposition performed on the same solutionwith a constant applied potential of 0.2 V for 500 s.

3. Result and discussion3.1 Amperometric deposition of LuHCF on RGO/GCE

Fig. 1 depicts the 10 consecutive CV cycles of the electro-chemical reduction of GO. As shown in Fig. 1, in the rst cycle alarge cathodic peak appears at 1.0 V, which was attributed tothe reduction of oxygen functionalities in GO. Meanwhile, theGO lm was stabilized with the ferricyanide solution, and RGO/GCE was turned back to the amperometric deposition ofLuHCF. At a constant potential of 0.2 V, the amperometricscan was performed for 500 s. The positively charged Lu3+ ionsare consequently adsorbed on to the negatively charged hex-aycanoferrate (HCF) particles, which formed the LuHCF parti-cles. Here GO has acted as a substrate material for the efficientdeposition of LuHCF. Based on a previously reported mecha-nism, the formation of LuHCF particles can be expressed usingeqn (1).

Fe(CN)64 + Lu3+ + K+ + H2O / KLu[Fe(CN)6]$H2O (1)

This journal is The Royal Society of Chemistry 2014
http://dx.doi.org/10.1039/c4tb01325e

Fig. 1 CVs of the electrochemical reduction of graphene oxide (GO) ina 0.1 M solution of KCl containing 5 mM of K3Fe(CN)6 and LuCl3$6H2Oat a scan rate of 50 mV s1.

Paper Journal of Materials Chemistry B

Publ

ishe

d on

01

Sept

embe

r 20

14. D

ownl

oade

d by

Nat

iona

l Tai

pei U

nive

rsity

of

Tec

hnol

ogy

on 0

3/10

/201

4 06

:25:

51.

View Article Online

Scheme 1 represents the mechanism of nucleation andgrowth of the LuHCF on RGO at different deposition times. Toprovide a clear insight into the mechanism of formation of theLuHCF particles, we monitored the nucleation and growth ofthe particles formed at different deposition times throughamperometry. As shown in Scheme 1, distorted spherical sha-ped particles with sizes (1.5 0.5 mm) were formed on thesurface of RGO at 100 s. The growth of petals occurred from theadjacent facets of the particles. At 300 s, increased nucleation ofthe particles from the side facets occurred on the surface of theRGO, leading to the formation of gooseberry shaped particleswith sizes two times that of the star shaped petals. When thedeposition time increased to 500 s, the nucleation of theparticles at the adjacent star shaped petals increased greatly,

Scheme 1 Electrochemical growth and nucleation mechanism ofLuHCF on RGO.


resulting in the formation of well-dened petals that are sepa-rated through dened edges. The as-formed particles resembledthat of hexangular star-fruit shaped particles. It has to be notedthat the deposition time played a key role in controlling thenucleation of the particles, the shape of the petals and themorphology of the particles.50

3.2 Characterization of RGO

The FT-IR spectra of GO and RGO is shown in Fig. 2A. Oxygenfunctional groups such as OH, epoxy, C]O and CO can beseen in the spectrum of GO. The high intensity peak at 3400cm1 conrms the presence of the stretching vibration of they(OH) group present in GO. The sharp peak at 1720 cm1 wasattributed to y(C]O) and 1619 cm1 corresponding toy(C]C) groups were present in GO. The peak at 1068 cm1

indicated the y(CO) groups of GO. All these peak intensitieswere ascribed to the stretching vibrations of the oxygen func-tionalities in GO. Whereas, signicant peaks were decreased,indicating reduction of oxygen functionalities in GO. BesidesUV-Vis spectroscopy of the as-synthesized GO and RGO weredemonstrated in Fig. 2B. As shown in the UV-Vis spectrum, abroad absorption peak at 230 nm corresponding to the pp*

Fig. 2 (A) FT-IR and (B) UV-Vis spectra of GO and RGO.

J. Mater. Chem. B


Publ

ishe

d on

01

Sept

embe

r 20

14. D

ownl

oade

d by

Nat

iona

l Tai

pei U

nive

rsity

of

Tec

hnol

ogy

on 0

3/10

/201

4 06

:25:

51.

View Article Online

transition and shoulder peak at 295 nm for the n p* transitionwas observed for GO (black colour). The spectrum of RGO wasshown in red colour. The pp* transition peak was red shiedto 265 nm indicating the reduction of the oxygen functionalitiesin GO and rearrangement of the electron conjugationstructure.51

3.3 Structural and morphological studies of LuHCF

The morphological studies of rare earth LuHCF particle are veryinteresting to discern the size and shape of the particles con-cerned. Fig. 3 elucidates the different morphologies of LuHCFparticles. The deposition of LuHCF microparticles has beenmonitored at different interval time of the amperometricdeposition. As shown in Fig. 3A, the star fruit-like structureformed at 100 s with each particle having an equal size of 1.5 0.5 mm. Further, the particles became gooseberry-like structuresand the size of micro stars were increased two times at 300 s, asshown in Fig. 3B. Upon increasing the deposition time to 500 s,we obtained the closely packed star-like structure of LuHCF(Fig. 3C). Every star-like particle has a diameter of 8.0 0.5 mmand was deposited on the electrode surface uniformly as shownin Fig. 2D. Fig. 3E and F shows the LuHCF deposited on the GCEand RGO surface. It can be seen that LuHCF was highlydistributed on RGO in a manner similar to GCE.

3.4 Elemental analysis and FT-IR spectroscopy of LuHCF

Fig. 4A shows the EDX spectra of the as-deposited LuHCF. Asshown in the EDX graph, the elements carbon, lutetium, iron,

Fig. 3 SEM of LuHCF at different deposition times (A) 100 s (B) 300 s(C) 500 s. (D) Single particle image of LuHCF. (E) LuHCF on GCE and (F)LuHCF on the RGO surface.

Fig. 4 (A) EDX analysis and (B) FT-IR spectrum of LuHCF.

J. Mater. Chem. B

nitrogen and potassium were present in the deposited LuHCF,and revealed that the LuHCF possessed a signicant weight% ofthese elements. The EDX prole of a single LuHCF particlereveals the presence of 27 wt% carbon, 28 wt% lutetium, 15 wt%potassium, 20 wt% ferrous ion and 10 wt% nitrogen ion.Accordingly, the EDX result conrms the LuHCF complex wasformed efficiently. The FT-IR spectrum of the as-synthesizedLuHCF is displayed in Fig. 4B. According to prussian blue (PB)and its analogues the corresponding peaks of LuHCF arelocated in Fig. 3B. A very sharp peak with high intensity wasobserved at 2080.9 cm1, which validates the stretching vibra-tion of ferricyanide (y(CN)) present in LuHCF. The broad peak at1597.93 cm1 corresponded to the HOH bending mode of theLuHCF complex. Moreover, the two broad peaks at 2876 and2973 cm1 were assigned to the stretching vibration of the twokinds of water molecule present.

3.5 XRD and XPS analysis of LuHCF

Fig. 5A displays the XRD pattern of the as-deposited LuHCFmicro star particles. As shown in the XRD pattern, the highestpeak intensity of the LuHCF was described and mentioned forthe corresponding hkl value. Moreover, there is no literatureavailable for the KLu[Fe(CN)6] complex and its characteriza-tion. Nevertheless, the properties and high intensity XRD


Fig. 5 (A) XRD pattern and (B) XPS survey spectra of LuHCF.

Fig. 6 (A) CV of different modified films (a) LuHCF/RGO/GCE (b) RGO/GCE (c) LuHCF and (d) bare GCE in a 0.3 M solution of NaOH con-taining 1 mM of SA at a scan rate of 50 mV s1. (B) CV of LuHCF/RGO/GCE in a 0.3 M solution of NaOH containing different concentrationsof SA at a scan rate of 50 mV s1.


Publ

ishe

d on

01

Sept

embe

r 20

14. D

ownl

oade

d by

Nat

iona

l Tai

pei U

nive

rsity

of

Tec

hnol

ogy

on 0

3/10

/201

4 06

:25:

51.

View Article Online

peaks of LuHCF were similar to rare earth metal hex-acyanoferrate. The high intensity peaks at 15.5, 19.2 and24.5 were common for all lanthanide metals based on thosein previously reported literature (black colour).52 The broaddiffraction peak of RGO appeared at 28 indicating LuHCFmicros stars were distributed throughout the RGO sheets (redcolor). All the peaks were referred according to JCPDS cards.The referred JCPDS card numbers were JCPDS # 01-072-4771,JCPDS # 00-047-1329, JCPDS # 00-046-1089 and JCPDS # 01-071-8282. The presence of all peak intensities according to theJCPDS cards suggest a orthorhombic (Cmcm space group)structure model for the LuHCF complex. When compared tothe other rare earth metal hexacyanoferrate complexes, thestructure model was similar to the orthorhombic structure ofLuHCF.19,30,31,53 Furthermore, X-ray photoelectron spectros-copy (XPS) is known to analyze the chemical composition andbinding energy. Fig. 5B shows the XPS survey spectra ofLuHCF, which exhibits the corresponding peaks appearing forFeS3(CN)3, Fe 3s, Cl 2p, K 2p3/2 (chloride) and O 1s, which isconsistent with the EDS results.5456


3.6 Cyclic voltammetric determination of SA

To evaluate the electrocatalytic activity of the various electrodes,cyclic voltammograms (CVs) were recorded for: (a) LuHCF/RGO/GCE (b) RGO/GCE (c) LuHCF and (d) bare GCE in a 0.3M solutionof NaOH containing 1 mM of SA at a scan rate of 50 mV s1. Asshown in Fig. 6A, the well-dened SA oxidation initiation peakwas observed on (a) LuHCF/RGO/GCE at 0.45 V. Besides, othermodied electrodes (b) RGO/GCE (c) LuHCF/GCE and (d) bareGCE show a very poor SA oxidation initiation peak at 0.55 V, 0.6 Vand 0.65, respectively. It is noteworthy that the oxidation peakpotential of the LuHCF/RGO/GCE-modied electrode was 150and 230 mV less positive than the LuHCF modied and bareGCE. Moreover, the oxidation peak current of SA at LuHCF/RGO/GCE was several times higher than that of other modied GCEs.

To assess the analytical performances of the proposed SAsensor, the LuHCF/RGO/GCE-modied GCE was performed

J. Mater. Chem. B

Scheme 2 The electro-oxidation process of Salicylic acid.


Publ

ishe

d on

01

Sept

embe

r 20

14. D

ownl

oade

d by

Nat

iona

l Tai

pei U

nive

rsity

of

Tec

hnol

ogy

on 0

3/10

/201

4 06

:25:

51.

View Article Online

using CV measurements. The cyclic voltammetric electro-chemical determination of SA is shown in Fig. 6B. It can be seenthat the SA oxidation peak current at 0.5 V increased linearlywith increasing concentrations of SA, meanwhile no reductionpeak was observed, which was attributed to a fast irreversibleelectrochemical reaction. In the rst step, SA was adsorbed onthe LuHCF, causing the formation of a phenoxy radical andfurther oxidized into a phenoxy cation. Finally, the carboxylhydroquinone was obtained as the product of this electro-chemical reaction. Here the supporting electrolyte NaOH hasbeen used for the efficient oxidation of SA. The SA oxidationmechanism can be expressed as shown in Scheme 2.

Fig. 7 (A) EIS of the different modified GCE bare, LuHCF and RGO/LuHCF (B) CV of RGO/LuHCFmodifiedGCE in a 0.3 M solution of NaOHcontaining 100 mM of SA at different scan rates (100 to 1000 mV s1).

3.7 Electrochemical impedance spectroscopy

EIS has been employed to distinguish the electron transferbehavior of the fabricated electrode. Fig. 7A shows the Nyquistplot of the real component (Zre) and imaginary component(Zim). The inset gure represents the Randles circuit parameters(inset gure) corresponding to the charge transfer resistance(Rct), solution resistance (Rs) and double layer capacity (Cdl) ofthe lms. It can be seen that in Fig. 7A, bare GCE has the lowercharge transfer resistance than LuHCF/GCE, RGO/GCE andLuHCF/RGO/GCE. Though the LuHCF and RGO modied GCEhas a lower semicircle value than bare GCE, and a comparativelyhigher charge electron transfer resistance than the fabricatedLuHCF/RGO/GCE. Therefore, the modied GCE reported has anexcellent electron transfer capacity when compared to LuHCF,RGO modied and bare GCE.

3.8 Different scan rate

The CVs of RGO/LuHCF modied GCE in the presence of 100mM of SA in a 0.1 M solution of NaOH at different scan rates (10to 100 mV s1) are shown in Fig. 7B. The linear increase in bothredox peaks at 0.2 V corresponding to the LuHCF and SAoxidation peaks around 0.4 V were observed when increasingthe scan rates from 10 to 100 mV s1. The inset of Fig. 6Bdisplays the calibration plot of log scan rate (log y) vs. logcurrent (log Ipa). The linear regression equation of the calibra-tion plot can be expressed as Ipa (mA) 0.489 log y (mV s1) 1.053, R2 0.9901. As shown in the regression equation, thevalue of scan rate was observed at 0.489 log y, which is very nearto the theoretical value of 0.500, which reveals that the elec-trochemical reaction occurred on the electrode surface and wasa diffusion controlled process. Moreover, the redox peak of

J. Mater. Chem. B

LuHCF at 0.2 V increased linearly with scan rate indicating asurface conned process.

3.9 Amperometric determination of SA

To further assess the analytical performance of the proposed SAsensor, electrocatalytic activities of the LuHCF/RGO-modiedrotating ring disk electrode (RRDE) were evaluated using theamperometry method at an applied potential (Eapp) of +0.55 V,as shown in Fig. 8A. At constant regular intervals (50 s) 50 mm ofSA was injected while the RRDE (1500 rpm) rotates continuouslyinto the solution of NaOH. The excellent and sharp SA amper-ometric responses were observed within a 5 s. of every addition.The inset to Fig. 8A shows the calibration plot of SA concen-tration vs. current. It can be seen that the SA oxidation currentswere linearly increased with increasing concentrations of SA.The linear regression equation can be expressed as, I 0.0605C(mM) + 0.1802, R2 0.9863. The low limit of detection for thereported lm modied GCE for the SA sensor has been


Fig. 8 (A) Amperometric response of LuHCF/RGO/GCE for thesequential addition of SA at an applied potential (Eapp) of +0.55 V. (Inseta) Calibration plot of concentration vs. current (b) amperometricresponse of the interference compound. (B) CV of LuHCF/RGO/GCEin salic ointment (500 mg/10 mL).

Table 1 A comparison of analytical parameters for the detection of SA o

Modied electrodesa Detection limit (mM)

Well-aligned MWCNTs 0.8BDD in a sodium sulphate medium 1DNA/PPy nanober modied electrode 0.8BDD 2HPLC with uorescence detection 0.02, 0.2 (mg kg1)Ni/GCE 0.5PNP/Pt disk electrode 6.4Co/Al hydrotalcite coated-Pt 6LuHCF/RGO/GCE 0.49

a MWCNTs multi-walled carbon nanotube; BDD boron-doped diamondmodied GCE; Co/Al cobalt hydrotalcite-like.



Publ

ishe

d on

01

Sept

embe

r 20

14. D

ownl

oade

d by

Nat

iona

l Tai

pei U

nive

rsity

of

Tec

hnol

ogy

on 0

3/10

/201

4 06

:25:

51.

View Article Online

calculated using the formula of LOD 3s/S, where s is thestandard deviation of the three blank and S is the sensitivity.The calculated LOD and sensitivity of the SA sensor were 0.491mM and 77.2 mA mM1 cm2, respectively. The obtainedanalytical parameters are more feasible when compared tovarious modied electrodes available in the literature (Table 1).

3.9.1 Selectivity. The selectivity of the reported sensor isextremely important for practical applications. So we haveperformed the selectivity of SA sensor in the presence of somecommon co-existing interference compounds such as ascorbicacid (AA), dopamine (DA), uric acid (UA), glucose and para-cetamol (PA) using the amperometric technique. The rightbottom inset of Fig. 8A shows the selectivity of the SA sensor atthe RGO/LuHCFmodied GCE. As shown in the inset of Fig. 8A,the well-dened amperogram responses were observed at each100 mM addition of SA (a). But no remarkable response wasobserved for each addition of 100 mM of (b) glucose, (c) AA, (d)DA, (e) UA and (f) PA. However, a signicant response wasobserved by subsequent addition of SA, validating the selectivityof the reported sensor. Thus, SA could be determined selectivelyat the RGO/LuHCF modied GCE without interference from co-existing species.

3.9.2 Real sample applications. To investigate the versatileapplication of the SA sensor for practical analysis of realsamples, the fabricated GCE was tested with commerciallyavailable tablets (aspirin) and ointment (salic ointment con-taining salicylic acid). The results are shown in Table 2 andFig. 8B, respectively. The 3 aspirin tablets were weighed on ananalytical balance and crushed using a cleaned mortar, andprepared for the required concentration. The CV technique wasemployed for the tablet sample analysis. Three differentconcentration of samples were analysed using the LuHCF/RGO

ver various modified electrodes

Concentrationrange (mM)

Sensitivity(mA mM1 cm2) Reference

23000 59.25 1410100 24.17 570.12 582.5105 58.66 59 602550 63.78 6120500 0.219 6210500 6351000 77.2 This work

electrode; PPy polypyrrole; PNR platinum nanoparticles; Ni nickel

Table 2 Performance of LuHCF/RGO/GCE for the determination ofsalicylic acid (SA) in real samples

S. no. Tablet sample Added (mM) Found (mM) Recovery %

1 Sample 1 200 199.45 99.72 Sample 2 400 377.26 94.33 Sample 3 700 692.72 98.96

J. Mater. Chem. B


Publ

ishe

d on

01

Sept

embe

r 20

14. D

ownl

oade

d by

Nat

iona

l Tai

pei U

nive

rsity

of

Tec

hnol

ogy

on 0

3/10

/201

4 06

:25:

51.

View Article Online

modied GCE under the same conditions. From the amount ofadded and found SA in the tablet samples, the calculatedrecoveries are summarized in Table 2. It is found that a satis-factory recovery rate exceeding ca. 99.7% for the 3 samples maybe inferred for these real samples, indicating the promisingperspective application of the proposed SA sensor for theanalysis of real samples.

Further, to widen the applications of the reported SA sensor,the CV technique was employed for the determination of SA inSalic ointment. The 1 g sample of Salic ointment containsstandard salicylic acid of 25 mg. We squeezed out all of the Salicointment into an empty bottle. Then 500 mg of ointment wasweighed and dissolved in a solution of NaOH with stirring andultrasonication. The 500 mg/10 mL solution of ointment wasplaced in an electrochemical cell and the CV recorded at theLuHCF/RGO/GCE. As shown in Fig. 8B, the SA oxidation peakwas observed at 0.55 V at a scan rate of 50 mV s1. It is notingthat the reported modied GCE would be worthy to reach up theprototype level sensor for the determination of SA.

3.9.3 Repeatability, reproducibility and stability. Therepeatability of the fabricated GCE for the SA sensor reportedwas performed by additional CV measurements using the sameelectrolyte conditions. The electrochemical sensor reportedshows good repeatability with a


Publ

ishe

d on

01

Sept

embe

r 20

14. D

ownl

oade

d by

Nat

iona

l Tai

pei U

nive

rsity

of

Tec

hnol

ogy

on 0

3/10

/201

4 06

:25:

51.

View Article Online

30 M. Rajkumar, B. Devadas and S. M. Chen, Electrochim. Acta,2013, 105, 439446.

31 B. Devadas, H. T. Yeh and S. M. Chen, Electroanalysis, 2014,26, 110.

32 M. G. Martn, M. L. R. Mendez and J. A. d. Saja, Langmuir,2010, 26, 1921719224.

33 T. V. Magdesieva, K. P. Butin, T. Yamamoto, D. A. Tryk andA. Fujishima, J. Electrochem. Soc., 2003, 150, E608E612.

34 I. Yilmaza, T. Nakanishi, A. Gurek and K. M. Kadish, J.Porphyrins Phthalocyanines, 2003, 7, 227238.

35 S. Karadag, C. Bozoglu, M. K. Sener and A. Koca, Dyes Pigm.,2014, 100, 168176.

36 C. Bozoglu, M. Arc, A. L. Ugur, A. Erdogmus and A. Koca,Synth. Met., 2014, 190, 5665.

37 F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake,M. I. Katsnelson and K. S. Novoselov, Nat. Mater., 2007, 6,652655.

38 M. D. Stoller, S. Park, Y. Zhu, J. An and R. S. Ruof, Graphene-Based Ultracapacitors, Nano Lett., 2008, 8, 10.

39 B. Devadas, V. Mani and S. M. Chen, Int. J. Electrochem. Sci.,2012, 7, 80648075.

40 V. Mani, B. Devadas and S. M. Chen, Biosens. Bioelectron.,2013, 41, 309315.

41 Y. Shao, J. Wang, H. Wu, J. Liu, I. A. Aksay and Y. Lin,Electroanalysis, 2010, 22, 10271036.

42 K. Nakamoto, Infrared and Raman Spectroscopy of Inorganicand Coordination Compounds, John Wiley & Sons, Inc., NewYork, 1986.

43 G. Zhao, J. J. Feng, Q. L. Zhang, S. P. Li and H. Y. Chen, Chem.Mater., 2005, 17, 31543159.

44 J. Yang, J. R. Stricklerb and S. Gunasekaran, Nanoscale, 2012,4, 45944602.

45 M. A. Raj and S. A. John, J. Phys. Chem. C, 2013, 117, 432635.46 P. Lu, S. Liu, G. Dai, Y. Lei and Y. Liang, Aust. J. Chem., 2013,

66, 983988.


47 K. Subramani, D. Jeyakumar and M. Sathish, Phys. Chem.Chem. Phys., 2014, 16, 49524961.

48 M. B. Gholivand, M. Khodadadian and M. Omidi,Mater. Sci.Eng., C, 2013, 33, 774781.

49 B. Devadas, M. Rajkumar, S. M. Chen and R. Saraswathi, Int.J. Electrochem. Sci., 2012, 7, 33393349.

50 L. P. Bicelli, B. Bozzini, C. Mele and L. DUrzo, Int. J.Electrochem. Sci., 2008, 3, 356408.

51 C. Z. Zhu, S. J. Guo, Y. X. Fang and S. J. Dong, ACS Nano,2010, 4, 24292437.

52 D. M. Gil, M. C. Navarro, M. C. Lagarrigue, J. Guimpel,R. E. Carbonioc and M. I. Gomez, J. Mol. Struct., 2011,1003, 129133.

53 M. Broschoa, M. Mihalik, V. Kavecansky, M. Seberini andW. Suski, Czech J. Phys., 2002, 52, 325.

54 A. L. Oleksiak, A. P. Nowak, M. Wilamowska, M. Sikora,W. Szczerba and C. z. Kapusta, Synth. Met., 2010, 160,12341240.

55 T. R. I. Cataldi, G. E. D. Benedetto and A. Bianchini, J.Electroanal. Chem., 1998, 448, 111117.

56 A. P. Grosvenor, B. A. Kobe, M. C. Biesinger andN. S. McIntyre, Surf. Interface Anal., 2004, 36, 15641574.

57 C. Cofan and C. Radovan, Int. J. Electrochem., 2011, 2011,451830.

58 M. Yousef Elahi, S. Z. Bathaie, S. H. Kazemi andM. F. Mousavi, Anal. Biochem., 2011, 411, 176184.

59 E. R. Sartori, R. A. Medeiros, R. C. R. Filho and O. F. Filho, J.Braz. Chem. Soc., 2009, 20, 360366.

60 D. P. Venema, P. C. H. Hollman, K. P. L. T. M. Janssen andM. B. Katan, J. Agric. Food Chem., 1996, 44, 17621767.

61 M. Doulache, A. Benchettara and M. Trari, J. Anal. Chem.,2014, 69, 5156.

62 Z. Wang, F. Ai, Q. Xu, Q. Yang, J. H. Yub, W. H. Huang andY.-D. Zhao, Colloids Surf., B, 2010, 76, 370374.

63 I. Gualandi, E. Scavetta, S. Zappoli and D. Tonelli, Biosens.Bioelectron., 2011, 26, 32003206.

J. Mater. Chem. B
http://dx.doi.org/10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new rare earth metal lutetium hexacyanoferrate on reduced graphene oxide and its application as a salicylic acid sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c4tb01325e

11 journal of materials chemistry b

Documents

reported sa sensor

introductionsalicylic

determination of sa

reported sensor

hydroxybenzoic acid

type of phenolic acid

reported modifiedelectrodes

synthesized luhcf micro