Um

SYa

b

a

ARRAA

KACRDI

1

utmdaAdbs[npppr

ttde

0d

Journal of Hazardous Materials 190 (2011) 1030–1036

Contents lists available at ScienceDirect

Journal of Hazardous Materials

journa l homepage: www.e lsev ier .com/ locate / jhazmat

ltra-fast catalytic reduction of dyes by ionic liquid recoverable and reusableefenamic acid derived gold nanoparticles

yeda Sara Hassana, Sirajuddina,∗, Amber Rehana Solangia, Mohammad Hassan Agheemb,asmeen Junejoa, Nazar Hussain Kalwara, Zulfiqar Ali Tagara

National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, PakistanCenter for Pure and Applied Geology, University of Sindh, Jamshoro 76080, Pakistan

r t i c l e i n f o

rticle history:eceived 19 January 2011eceived in revised form 8 April 2011ccepted 12 April 2011vailable online 17 April 2011

a b s t r a c t

We synthesized mefenamic acid (MA) derived gold nanoparticles (MA-AuNps) in aqueous solution (MA-Au sol). Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) of the sol at 1,5, 15 and 60 min showed changes in size and shape of formed AuNps. Fourier Transform Infrared (FTIR)Spectroscopy revealed the interaction between AuNps and MA. Each Au sol exhibited exceptional catalyticactivity for the reduction of Methylene Blue (MB), Rose Bengal (RB) and Eosin B (EB) dye individually as

eywords:u nanoparticlesatalysteduction

well as collectively. However, complete reduction of dye(s) was accomplished by Au sol of 5 min in just15 s. The catalytic performance of Ma-Au sol was far superior to that adsorbed on glass. AuNps wererecovered with the help of water insoluble room temperature ionic liquid and reused with enhancedcatalytic potential. This finding is a novel, rapid and highly economical alternative for environmental

y dye

yesonic liquid

safety against pollution b

. Introduction

Gold nanoparticles (AuNps) possess unique catalytic behaviornder mild conditions and are considered catalysts of choice dueo higher stability and negligible poisoning [1] as compared to other

etal nanoparticles. Interest in gold based catalysts is increasingue to their fascinating properties, green nature and ability to cat-lyze selective reactions at low temperatures [2,3]. Application ofuNps as catalysts reveals that their catalytic potential is highlyependant upon variation in size [4–7]. Despite size, one of theig secrets for best catalytic results lies in strategic control of thehape of Nps in order to increase their unsaturated free surface sites8–10]. The application of Nps as heterogeneous [2,4] or homoge-eous [2,11] catalysts is generally needed in various studies andreferred by merit. The active sites in heterogeneous catalyst arerotected from full reactivity due to strong interaction with cap-ing agent or surface while homogenous catalyst shows maximumeactivity due to better access of sites [12–14].

Despite their application for various tasks, AuNps possessremendous potential as catalyst in various types of pollution con-

rol studies especially aquatic pollution. Among water pollutions,yeing methods in textile, paper, plastics, leather, food, cosmetics,tc. are the major source of producing toxic species in the form

∗ Corresponding author. Tel.: +92 9213429; fax: +92 9213431.E-mail address: drsiraj03@yahoo.com ( Sirajuddin).

304-3894/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.jhazmat.2011.04.047

s and extendable for control of other reducible contaminants as well.© 2011 Elsevier B.V. All rights reserved.

of coloured wastewaters that greatly interrupt the photosyntheticprocess in aquatic plants due to poor light penetration [11,15]. De-colorization/detoxification of dyes contaminated water is achievedby methods like adsorption [16], degradation [17–19], oxidation[20,21], and catalytic reduction [22–25]. Utilization of AuNps ofvarious sizes as catalysts has been reported for the reduction ofdye (eosin) [24]. The kinetic study showed that the increase in cat-alytic reduction rate was not dependant on the decrease in the sizeof AuNps over the whole range. In another report [25], AuNps weresynthesized in polymer with high internal phase emulsion (poly-HIPE) support to give rise to a hybrid material, Au@polyHIPE thatwas used as heterogeneous catalyst for the active reduction of eosinY. Kinetics study related to porosity, shape, gold concentration andtemperature verified that first order reaction was obeyed.

Here we report the synthesis of unprotected and unsupportedMA derived AuNps in aqueous solution with their excellent cat-alytic behavior for the reduction of dyes, MB, EB and RB alone as wellas their solution mixture. These AuNps were recovered by meansof water insoluble room temperature ionic liquid (RTIL) and reusedeffectively. The big advantage of IL recovered AuNps was the theirreuse with efficient catalytic potential due to increased exposureof active sites for dye reduction as compared to those adsorbed atglass surface.

2. Materials and methods

All chemicals and reagent used in this work were of AR gradehave more than 99% purity and used as received.

rdous Materials 190 (2011) 1030–1036 1031

2

5vstaEas

2E

AscEwwfCfiu

2

ppaaaaT

2

wto9i1sp

2

1wooddtm

110010009008007006005004000.0

0.2

0.4

0.6

0.8

1.0

A

nm

D

C

B

A

Fig. 1. Visible spectra showing the synthesis of MA assisted Au sol at, (A) 1, (B) 5,

S.S. Hassan et al. / Journal of Haza

.1. Synthesis of MA-AuNps in aqueous solution

The aqueous AuNps solution was prepared by taking 0.1 ml from000 ppm of Au (III) ions containing gold chloride (HAuCl4) in a 5 mlolumetric flask. To this was added 0.01 ml of 0.5% mefenamic acidolution followed by 0.01 ml of 0.1 M NaOH solution and dilutedo the mark with de-ionized (DI) water. The resulting solution wasnalyzed by UV-Visible spectrometer model Lambda 2 of Perkinlmer in the range of 400–1100 nm at different times of 1, 5, 15nd 60 min in order to observe the resulting AuNps with differentizes and shapes.

.2. Scanning Electron Microscopy (SEM) and Transmissionlectron Microscopy (TEM)

SEM study was performed by model, JSM 6380A of Jeol Japan.ccording to procedure, 10 �l portion of MA-AuNps solution eachynthesized at 1, 5, 15 and 60 min was put on separate cleaned glassover slip in each case and dried on hot plate already set at 100 ◦C.ach cover slip was then cooled and mounted on aluminum stubith the help of double sided adhesive carbon tape. All samplesere gold coated for 15 min in Argon environment and processed

or SEM imaging. TEM images were recorded with the help of modelM20 of Philips equipped with Gatan 689/6900 Camera. The sample

or TEM was prepared by dip coating of carbon coated copper gridn the sample followed by drying first with filter paper and thennder N2.

.3. Sample preparation for Infra-red (IR) Spectroscopy

Big volume of MA-AuNps solution of 5 min was prepared,oured in big petri dish and dried on hot plate at 100 ◦C. The driedroduct was washed 4 times with methanol in order to removeny unused reagent and dried. The content in the petri dish wasgain thoroughly washed with de-ionized water, dried at 100 ◦Cnd cooled in a desiccator. The contents were scratched, collectednd processed in KBr pellet for FTIR studies by Nicolet 5700 ofhermo.

.4. Catalytic reduction of dye(s)

According to procedure, 0.35 ml of 100 �M aqueous dye solutionas diluted with sufficient de-ionized water in a 1 cm quartz cell. To

his was added 0.35 ml of 0.1 M NaBH4 solution followed by 0.05, 0.1r 0.2 ml of MA-AuNps solution so that a final volume of 3.5 ml (pH,.6 ± 0.1) was obtained at the end. Similar procedure was repeated

n case of mixture of dyes. UV–visible spectra were recorded in5 s times just after addition of last solution against a blank. Fastercan rate of 1920 nm min−1 was used to monitor the study at smallossible intervals.

.5. Separation and re-use of AuNps

100 �l of water insoluble room temperature ionic liquid (IL),-butyl-3-methylimidazolium hexafluorophosphate, [bmim] [PF6]as added to the solution of MA-AuNps treated MB solution or

ther dye(s) and shaken well. The AuNps in solution were collectedn the surface of IL that appeared as a blackish spot and separated by

ecanting the supernatant. The AuNps loaded IL was washed withe-ionized water 3 times and used again and again by replacinghe MA-AuNps in the above experiment for catalytic reduction of

ixture of dyes.

(C) 15 and (D) 60 min after addition of all reagents.

3. Results and discussion

Strategically, we used mild reducing agent MA for the formationof Au sol by deliberately ignoring the addition of strong cappingagent and let the particles grow with time. Small volume of NaOHsolution accelerated the synthesis of AuNps [26]. Visible spec-troscopy provided qualitative informations about the size of formedAuNps [25]. The concentration of various reagents was optimizedfor getting smallest Nps as recognized by blue shifted signal around500 nm. The researchers use the strategy of keeping ratio of reduc-ing or protecting agent to Au always greater than unity in orderto get smaller particles [27]. We used the ratio of MA to Au as∼1:12 (the reverse of mentioned strategy) in order to synthesizemaximum particles unprotected so that some AuNps (formed byreduction) are protected (however not strongly) by oxidized MAand the rest (formed by seeding growth approach) [28] remainunprotected at the end. The percent concentration of unprotectedAuNps is however time dependant.

3.1. Time effect

The changes in absorbance and maximum wavelength (�max)with time are given in Fig. 1.

Fresh solution analyzed after 1 min of mixing of all reagentsshows the initial stages of formation of AuNps where most of theAu ions are still present as proved by visible spectrum with no sig-nal around 500 nm. The first signal is seen at 514 nm representingparticles of smallest diameter in case of Au sol of 5 min. However,the spectrum is not clear which means that the formation of AuNpsis still underway. A clear signal is observed in case of Au sol after15 min by the red shift in this case indicating the formation of big-ger particles. A further red shift in case of 60 min Au sol tells that thegrowth in the size of AuNps is still continued. Continuous changein absorbance and red shift in �max with time (Fig. 1) describes theformation and increase in size of AuNps according to Mie Theory[29].

3.2. SEM imaging of AuNps in Au sol

SEM images of the MA-Au sol formed at various times after mix-ing of all solutions (Fig. 2) show that AuNps are getting bigger insize with time. These results are in good agreement with the corre-

sponding visible spectra (Fig. 1). In case of one min MA-Au sol, fewclusters and extended network of MA protected with some unpro-tected AuNps are observed (Fig. 2a). Reportedly AuCl4− is reducedrapidly at initial stage and then the clusters are formed with chains

1032 S.S. Hassan et al. / Journal of Hazardous Materials 190 (2011) 1030–1036

) 1, (B

aTosgswcbAT

aAttmaac

3

atrsr

cspsg

Fig. 2. SEM images of MA-Au sol at various times, (A

nd networks of crystals interconnected by amorphous Au [30].he transparent nature of Au sol at 1 min confirms the presencef most of Au (I) ions along with few Au (0) as seen in Fig. 2A. Alightly reddish color was observed in Au sol in 4–10 min that wasetting intensified with time. Fig. 2B represents the image of welleparated smallest AuNps formed at 5 min in the range of 5–50 nmith average diameter of 23 nm (considering only spherical parti-

les). Fig. 2C shows well separated smaller AuNps along with a fewigger ones for Au sol at 15 min. The average diameter for smalleruNps was 16.5 nm while that for bigger particles it was 325 nm.he overall average diameter of AuNps was 42 nm.

However, nearly all smaller AuNps are porous that make themttractive candidates in catalysis [31]. Fig. 2D is the SEM image ofuNps formed at 60 min representing the fourth ascending spec-

rum in Fig. 1. An overall average size of 184 nm was estimated inhis case. Images of AuNps formed at 15 min and 60 min with low

agnifications (not shown here) tell that both size and shape of Npsre changed with time [32,33] showing a mix up of bigger sphericalnd cubic AuNps in former while mostly cubic AuNps in the laterase.

.3. TEM characterization

Fig. 3 reveals the TEM images of AuNps formed in similar solss true in case of Fig. 2. The average size for AuNps formed inhis case was 95 nm, 21.5 nm, 40.5 nm and 180.5 nm for Fig. 3A–Despectively. The corresponding standard deviation (SD) of averageize for these particles was 74 nm, 16.5 nm, 34.5 nm and 54.5 nmespectively.

It is clear that TEM characterization provided better results withlear images as compared to SEM images (Fig. 2). The closeness of

izes between SEM and TEM images confirm the repeatability of therocedure however the difference in shapes is due to difference inupporting surface (glass in case of SEM and carbon coated copperrid in case of TEM).

) 5, (C) 15 and (D) 60 min after mixing all reagents.

3.4. FTIR study

Fig. 4 shows comparison of FTIR spectra between MA protectedAuNps of 5 min with pure MA compound.

The results show that the band at 3310 cm−1 in pure MAmolecule is assigned to combined effect of –NH and carboxylic –OHgroup while that at 3410 cm−1 in case of MA-AuNps is attributed to–OH stretching of carboxylic acid [34]. Absence of sharp signal atformer wavelength and appearance of broader signal at later provethe interaction of Au to C–N– of MA in the form of C–N-Au. Thesignals between 2900 cm−1 and 1600 cm−1 are almost common inboth MA and MA-AuNps. However, slight shift in wavelength andlittle intensity in later case confirm Au interaction and small quan-tity of MA-AuNps. The band at 1515 cm−1 [35] (1510 cm−1 in ourcase) in MA attributed to –NH, disappears in MA-AuNps that furtherconfirms the formation of –N-Au.

3.5. Application of AuNps as catalysts for reduction of dye(s)

Each experiment in application study was analyzed in triplicateand the mean value plotted accordingly.

Fig. 5a describes the reduction of MB after addition of 0.1 mlof MA-Au sol formed at different times with the catalytic trend of5 ≥ 15 > 1 > 60 min in the presence of 10 mM NaBH4. This changein MB reduction is attributed to size variation of AuNps from5–60 min. Reduction of MB by Au sol of 1 min however shows anintermediate catalytic response due to agglomeration effect at ini-tial stage [36] (Fig. 2A). Still the activity is remarkable which maybe due to the presence of oxidized Au (I) and Au (0) [34] and porousnature of particles [3,31]. The possibility of blockage of active sitesof AuNps by capped MA may be another factor of comparatively

reduced activity [10] of 1 min Au sol because most of MA pro-tected particles can form initially. However, its greater potentialthan 60 min Au sol is due to the difference in size despite higherpercentage of unprotected particles in later case.

S.S. Hassan et al. / Journal of Hazardous Materials 190 (2011) 1030–1036 1033

Fig. 3. TEM images of MA-Au sol at, (A) 1, (B) 5, (C)

50010001500200025003000350040000.0

0.3

0.6

0.9

1.2

1.5

b

A

Cm-1

a

obe

4tt

report, the rate of reduction was increased after 15 nm size. How-

Fig. 4. FTIR spectra of (a) pure mefenamic acid, (b) MA-AuNps.

Fig. 5b shows the reduction of MB after adding various volumesf Au sol formed at 5 min. It is seen that total reduction of MB occursy 0.2 ml of Au sol added to mixture in just 15 s. This represents thexample of an ultra-fast homogeneous catalysis.

The efficiency of NaBH4 for reduction of MB (without Au sol) was

.2%. The addition of 0.2 ml of MA-Au sol brings the reduction of MBo 100% as evident from Fig. 2B. MB reduction of 90.5% and 92.5% isrue for 0.05 and 0.1 ml MA-Au sol respectively in the presence of

15 and (D) 60 min after mixing all reagents.

NaBH4. Catalytic reduction of MB and other dyes has been reportedby other workers [22] using Pd nanoparticles.

Fig. 6 describes the effect of 0.1 ml of supported MA-Au sol(adsorbed on glass surface) on the reduction of MB solution. Inother words it is a comparison between heterogeneous (Fig. 6)and homogeneous catalysts (Fig. 5a). In the former case the rate ofreduction of MB as well as the trend is changed as compared to latercase. Here the catalytic trend follows the order, 5 > 60 > 15 > 1 minrepresenting total reduction efficiency of 32.4%, 11.5%, 10.7% and8.4% respectively in the presence of NaBH4. Dramatically decreasedcatalytic response by supported AuNps (Fig. 6) in comparison toMA-Au sol (Fig. 5a) confirms the blockage of maximum active sitesof AuNps after adsorption at glass surface. Comparative change intrend is due to difference in interaction of AuNps with glass andchange in shape and hence in selectivity [10]. This study provesthat due to access of catalytic sites [12], homogeneous catalystsare better from activity, selectivity, high atom efficiency and cat-alytic properties like regio, chemo-, and stereo-selectivity are easilytuned due to well-defined nature of sites [14]. The role of supporthas been reported by other workers in catalysis [37].

The reduction of dye by unsupported AuNps in the range of10–46 nm has been reported however, TX-100 was used as stabiliz-ing agent [23] in that particular case. According to the mentioned

ever the catalysis was not faster than observed in our case.Similar trend was observed in case of reduction of EB and RB

dyes as observed in case of MB dye. Plots addressing the efficiency

1034 S.S. Hassan et al. / Journal of Hazardous Materials 190 (2011) 1030–1036

60 min15 min5 min1 min0

20

40

60

80

100

Red

ucti

on

eff

icie

ncy (

%)

MA-Au sol at different times

a

0.200.150.100.050

20

40

60

80

100

Red

ucti

on

eff

icie

ncy (

%)

MA-Au sol added (ml)

b

Fig. 5. Plots showing mean % reduction efficiency of MA-Au sol for 10 �M MB solution in the presence of 0.01 M NaBH4 solution (a) Au sol (0.1 ml) of, 1, 5, 15 and 60 minwith RSD of 0.8%, 0.4%, 0.5% and 0.6% respectively (b) Reduction efficiency of Au sol formed at 5 min after addition of 0.05 ml, 0.1 ml and 0.2 ml Au sol with RSD of 0.7%, 0.6%and 0.4% respectively; each spectrum recorded in 15 s after addition of respective Au sol. Scan rate, 1920 nm/min, final volume in quartz cell, 3.5 ml in each case.

1 min 5 min 15 min 60 min0

5

10

15

20

25

30

35

Red

ucti

on

Efi

icie

ncy (

%)

MA-AuNps of various times

on glass support

Fig. 6. Plot showing % efficiency of 0.1 ml of dried adsorbed Au sol of 1, 5, 15 and60 min on cover slip, for MB reduction with similar solutions of MB and NaBH4 ast

or

Rbthw

0.200.150.100.05

0

20

40

60

80

100

Red

ucti

on

eff

icie

ncy (

%)

MA-Au sol added (ml)

Fig. 8. Efficiency of 0.05 ml, 0.1 ml and 0.2 ml MA-Au sol of 5 min for reduction of

Frt

rue in case of Fig. 5a with RSD of 1.1%, 0.6%, 0.5% and 0.8% respectively.

f 0.05, 0.1 and 0.2 ml of MA-Au sol for reduction of EB and RB areecorded in Fig. 7a and b respectively.

Fig. 7 describes the same phenomenon for reduction of EB andB as observed in case of MB reduction (Fig. 5b). Similar studies cane seen in other report [22] but the time for reduction is longer in

hat case. Reduction of eosin by AuNps of various sizes in sol formas been described previously [24] however the rate of reductionas much slower as compared to our data.

0.200.150.100.050

20

40

60

80

100

Red

ucti

on

eff

icie

ncy (

%)

MA-Au sol of 5 minutes (ml)

a

ig. 7. Histograms describing % efficiency of similar volumes of Au sols of 5 min as givenespectively and (b) 10 �M RB solution in the presence of 0.01 M NaBH4 with RSD of 1.0aken at 15 s.

mixture of MB, EB and RB each 10 �M in the presence of 0.01MNaBH4 in 15 s showingRSD of 0.8%, 0.3% and 0.4% respectively.

Fig. 8 shows the efficiency of various volumes of 5 min MA-Ausol per 3.5 ml for reduction of mixture of each 10 �M of MB, EB andRB.

It is evident that the 0.2 ml of 5 min Au sol is used for completereduction of all three dyes in the same way as true in case of each

individual dye in only 15 s. Reduction of mixed dyes is reportedelsewhere using PdNps as catalytic agents [22] but the longer timeand expensive material clearly distinguish their results from ours.

0.200.150.100.050

20

40

60

80

100

Red

ucti

on

eff

icie

ncy (

%)

MA-Au sol of 5 minutes (ml)

b

in Fig. 5b for reduction of (a) 10 �M EB solution with RSD of 0.8%, 0.5% and 0.4%, 0.4 and 0.4% respectively. Scan rate, 1920 nm/min, each spectrum of Au sol was

S.S. Hassan et al. / Journal of Hazardous Materials 190 (2011) 1030–1036 1035

(CH3)2 N+N (CH3)2 (CH3)2 N

+N (CH3)2 H

Only NaBH4 (Very slow)

+ AuNps ( Very fast )S

N

S

NH

)decuder( BM)dezidixo( BM

R T I L

R T I L-AuNps (Washed)

Re-used

Scheme 1. Catalytic and recovery

Cycle 5Cycle 4Cycle 3Cycle 2Cycle 1

0

20

40

60

80

100

Red

ucti

on

eff

icie

ncy (

%)

No

94%98%100%

89%82%

Fig. 9. Percent reduction efficiency of IL recovered and re-used AuNps for 5 suc-crm

ft

rtsfedes

S

d

4

Mtacooas

[

[

[

[

[

[

[

[

[

essive cycles for mixture of dyes with RSD of 0.4%, 0.7%, 0.4%, 0.4% and 0.6%espectively; IL recovered AuNps washed 3 times with DI water before each treat-ent (cycle).

Fig. 9 shows the stepwise reduction efficiency of re-used AuNpsor dyes mixture collected at the surface of RTIL for 5 cycles withhe same concentration of dyes and NaBH4 as true in case of Fig. 4.

The efficiency of reused IL loaded AuNps resulted in efficienteduction of dyes mixture for cycles 1–5. The first cycle indicateshat the IL recovery of AuNps results in complete exposure of activeites of AuNps for catalytic reduction of dyes because AuNps canreely move at the surface of IL. The stepwise decrease in catalyticfficiency is, however, due to continuous agglomeration (and henceecrease in number of active sites) of AuNps at RTIL surface afterach cycle. This work promises a sound environmental safety foreveral water based systems against dye pollution.

The catalytic and recovery mechanism of AuNps is presented incheme 1.

The Scheme 1 for MB is equally true for EB, RB or mixture ofyes.

. Conclusions

In conclusion, the combination of unprotected and unsupportedA-AuNps with smallest size formed after 5 min proved as excep-

ionally efficient catalyst for the reduction of MB, EB and RB dyelone or in the form of mixture. The work provides an economi-al solution to aquatic environment in terms of time saving, use

f small volume of catalytic sol and is equally useful for reductionf several other dyes. The recovery of AuNps by water insoluble ILnd their recycling economize the process to a greater extent. Thistudy could be extended for catalytic reduction of other hazardous

[

[

mechanisms of MA-AuNps.

materials such as phenols, CO2, SO2, as well as for the synthesis ofuseful compounds.

Acknowledgment

Facilities provided by National Center of Excellence in Analyti-cal Chemistry, University of Sindh, Jamshoro and Higher EducationCommission of Pakistan are highly acknowledged.

References

[1] D.T. Thomson, Using gold nanoparticles for catalysis, Nanotoday 2 (2007)40–43.

[2] S. Panigrahi, S. Basu, S. Praharaj, S. Pande, S. Jana, A. Pal, S.K. Ghosh, T. Pal,Synthesis, Size-selective catalysis by supported gold nanoparticles: study onheterogeneous and homogeneous catalytic process, J. Phys. Chem. C 111 (2007)4596–4605.

[3] A. Wittstock, V. Zielasek, J. Biener, C.M. Friend, M. Bäumer, Nanoporous goldcatalysts for selective gas-phase oxidative coupling of methanol at low tem-perature, Science 327 (2010) 319–322.

[4] C.H. Tsenga, T.C.K. Yang, H.E. Wu, H.C. Chiang, Catalysis of oxidation of car-bon monoxide on supported gold nanoparticles, J. Hazard. Mater. 166 (2009)686–694.

[5] G.C. Bond, D.T. Thompson, Gold-catalysed oxidation of carbon monoxide, GoldBull. 33 (2000) 41–51.

[6] X.Y. Liu, F. Cheng, Y. Liu, H.J. Liu, Y. Chen, Preparation and characterizationof novel thermo responsive gold nanoparticles and their responsive catalysisproperties, J. Mater. Chem. 20 (2010) 360–368.

[7] A. Grirrane, A. Corma, H. García, Gold-catalyzed synthesis of aromatic azo com-pounds from anilines and nitro aromatics, Science 322 (2008) 1661–1664.

[8] D.L. Feldheim, The new face of catalysis, Science 316 (2007) 699–700.[9] T.K. Sau, A.L. Rogach, F. Jackel, T.A. Klar, J. Feldmann, Properties and applica-

tions of colloidal nonspherical noble metal nanoparticles, Adv. Mater. 21 (2009)1–21.

10] K.M. Bratlie, H. Lee, K. Komvopoulos, P. Yang, G.A. Somorjai, Platinum nanopar-ticle shape effects on benzene hydrogenation selectivity, Nano Letters 7 (2007)3097–3101.

11] N. Pradhan, A. Pal, T. Pal, Catalytic reduction of aromatic nitro compounds bycoinage metal nanoparticles, Langmuir 17 (2001) 1800–1802.

12] C. Burda, X. Chen, R. Narayanan, M.A. El-Sayed, Chemistry and properties ofnanocrystals of different shapes, Chem. Rev. 105 (2005) 1025–1102.

13] A. Siani, K.R. Wigel, O.S. Alexeev, M.D. Amiridis, Synthesis and characterizationof Pt clusters in aqueous solutions, J. Catal. 257 (2008) 5–15.

14] G.P.M. v-Klink, H.P. Dijkstra, G. v-Koten, Recyclable nanosize homogeneouscatalysts, C. R. Chim. 6 (2003) 1079–1085.

15] M.B. Cortie, E. van der Lingen, Catalytic gold nano-particles, Mater. Forum. 26(2002) 1–14.

16] I. Safarik, L. Ptackova, M. Safarikova, Adsorption of dyes on magnetically labeledbaker’s yeast cells, Eur. Cell Mater. 3 (2002) 52–55.

17] J. Lin, R. Zong, M. Zhou, Y. Zhu, Photoelectric catalytic degradation of methyleneblue by C60-modified TiO2 nanotube array, Appl. Catal. B: Environ. 89 (2009)425–431.

18] A.O. Ibhadon, G.M. Greenway, Y. Yue, Photocatalytic activity of surface modi-fied TiO2/RuO2/SiO2 nanoparticles for azo-dye degradation, Catal. Commun. 9(2008) 153–157.

19] H. Lachheb, E. Puzenat, A. Houas, M. Ksibi, E. Elaloui, C. Guillard, J.M. Herrmann,Appl. Catal. B: Environ. 39 (2002) 75–90.

20] V.S. Ferreira-Leitão, J.G. da Silva, E.P.S. Bon, Methylene blue and azure B oxida-tion by horseradish peroxidase: a comparative evaluation of class II and classIII peroxidases, Appl. Catal. B: Environ. 42 (2003) 213–221.

1 rdous

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

036 S.S. Hassan et al. / Journal of Haza

21] N. Daneshvar, A. Aleboyeh, A.R. Khataee, The evaluation of electrical energyper order (EEo) for photooxidative decolorization of four textile dye solutionsby the kinetic model, Chemosphere 59 (2005) 761–767.

22] N.R. Jana, Z.L. Wang, T. Pal, Redox catalytic properties of palladium nanopar-ticles: surfactant and electron donor–acceptor effects, Langmuir 16 (2000)2457–2463.

23] J. Fan, Y. Guo, J. Wang, M. Fan, Rapid decolorization of azo dye methyl orange inaqueous solution by nanoscale zerovalent iron particles, J. Hazard. Mater. 166(2009) 904–910.

24] T.K. Sau, A. Pal, T. Pal, Size regime dependent catalysis by gold nanoparticlesfor the reduction of eosin, J. Phys. Chem. B 105 (2001) 9266–9272.

25] C. Feral-Martin, M. Birot, H. Deleuze, A. Desforges, R. Backov, Inte-grative chemistry toward the first spontaneous generation of goldnanoparticles within macrocellular polyHIPE supports (Au@polyHIPE)and their application to eosin reduction, React. Funct. Polym. 67 (2007)1072–1082.

26] L.-J. Chen, C.-C. Wan, Y.-Y. Wang, Chemical preparation of Pd nanoparticlesin room temperature ethylene glycol system and its application to electrolesscopper deposition, J. Colloid Interface Sci. 297 (2006) 143–150.

27] G. Frens, Ctrolled nucleation for the regulation of particle size in monodisperse

gold suspensions, Nat. Phys. Sci. 241 (1973) 20–22.

28] N.R. Jana, L. Gearheart, C.J. Murphy, Seeding growth for size control of 5–40 nmdiameter gold nanoparticles, Langmuir 17 (2001) 6782–6786.

29] G.L. Hornyak, C.J. Patrissi, C.R. Martin, J.-C. Valmalette, J. Dutta, H. Hofmann,Dynamical maxwell-garnett optical modeling of nanogold-porous alumina

[

Materials 190 (2011) 1030–1036

composites: mie and kappa influence on absorption maxima, Nanostruct.Mater. 9 (1997) 575–578.

30] B.K. Pong, H.I. Elim, J.X. Chong, W. Ji, B.L. Trout, J.Y. Lee, New insights on thenanoparticle growth mechanism in the citrate reduction of gold(III) salt: for-mation of the au nanowire intermediate and its nonlinear optical properties, J.Phys. Chem. C 111 (2007) 6281–6287.

31] D.R. Rolison, Catalytic nanoarchitectures – the importance of nothing and theunimportance of periodicity, Science 299 (2003) 1698–1701.

32] J. Watt, S. Cheong, M.F. Toney, B. Ingham, J. Cookson, P.T. Bishop, R.D. Tilley,Ultrafast growth of highly branched palladium nanostructures for catalysis,ACS Nano 4 (2010) 396–402.

33] J.H. Fendler, Nanoparticles and Nanostructured Films, WILEY-VCH VerlagGmbH, D-69469 Weinheim, 1998, pp. 157–158.

34] R.T. Tom, V. Suryanarayanan, P.G. Reddy, S. Baskaran, T. Pradeep, Ciprofloxacin-protected gold nanoparticles, Langmuir 20 (2004) 1909–1914.

35] Z. Bouhsain, S. Garrigues, M. de la Guardia, Flow injection – Fourier trans-form infrared spectrometric determination of paracetamol in pharmaceuticals,Analyst 121 (1996) 635–639.

36] S. Kundu, M. Mandal, S.K. Ghosh, T. Pal, Photochemical deposition of SERSactive silver nanoparticles on silica gel and their application as catalysts for

the reduction of aromatic nitro compounds, J. Colloid Interface Sci. 272 (2004)134–144.

37] D. Matthey, J.G. Wang, S. Wendt, J. Matthiesen, R. Schaub, E. Laegsgaard, B.Hammer, F. Besenbacher, Enhanced bonding of gold nanoparticles on oxidizedTiO2(1 1 0), Science 315 (2007) 1692–1696.