formation of gold nanorod-carbon dot nanocomposite with superior catalytic ability towards...

8/13/2019 Formation of gold nanorod-carbon dot nanocomposite with superior catalytic ability towards reduction of aromatic

1/19

Formation of gold nanorod-carbon dot nanocomposite withsuperior catalytic ability towards reduction of aromatic

nitrogroup in water

Journal: ChemComm

Manuscript ID: CC-COM-12-2013-049752

Article Type: Communication

Date Submitted by the Author: 24-Dec-2013

Complete List of Authors: Mandal, Pritiranjan; Ramakrishna Mission Vidyamandira, Department of

Applied Chemistry and Industrial ChemistryGhosal, Krishanu; Ramakrishna Mission Vidyamandira, Department ofApplied Chemistry and Industrial ChemistryBhattacharyya, Swarup; Ramakrishna Mission Vidyamandira, Departmentof Applied Chemistry and Industrial ChemistryGanguly, Debabrata; Ramakrishna Mission Vidyamandira, Department ofApplied Chemistry and Industrial ChemistryDas, Mithun; Ramakrishna Mission Vidyamandira, Department of AppliedChemistry and Industrial ChemistryBera, Abhijit; Ramakrishna Mission Vidyamandira, Department of AppliedChemistry and Industrial ChemistryGupta, R. K.; Pittsburg State University, Chemistry

Marti, Angel; Rice University, ChemistryGUPTA, BIPIN; National Physical Laboratory (CSIR) , Materials Physics andEngineering Division; Rice University, IUSSTF Fellow (Indo-US Science &Technology Forum) Department of Mechanical Engineering and Materials

Science, Rice University, MS-321Maiti, Subhabrata; Ramakrishna Mission Vidyamandira, Department ofIndustrial Chemistry and Applied Chemistry

ChemComm


2/19

Manuscript Title:Formation of gold nanorod-carbon dot nanocomposite with superior catalytic

ability towards reduction of aromatic nitrogroup in water

Authors:Pritiranjan Mondal,aKrishanu Ghosal,

aSwarup Krishna Bhattacharyya,

aDebabrata

Ganguly,a

Mithun Das,a

Abhijit Bera,a

R. K. Gupta,b

Angel A. Mart,cBipin Kumar Gupta*

d

and Subhabrata Maiti*

a

Justification for publication

Nanotechnology has found tremendous attention towards catalyzing chemical reactions including

their already established implication towards optics, electronics and so forth. The unique surface

properties of noble metallic nanoparticles like gold, silver are being exploited in catalyzingdiversified class of reactions ranging from carbon monoxide oxidation, C-C coupling to

hydrogenation. The advantages of using gold nanostructures in modulating catalysis lie to their

ease of synthesis in different forms, stability, surface functionalization etc. Typically, smallernanoparticles showed higher catalytic ability in various kinds of reactions. However, in case of

redox reactions, anisotropic nanostructures with high electron transporting ability like nanocageor nanobox have been observed to facilitate the catalytic rate. To this end, nanocomposite made

of carbon nanostructures and metallic nanomaterials are evolving as excellent materials fornanocatalysis, photovoltaics to nanoelectronics. Among all carbon nanostructures, carbon dots

(CD), the newest and exciting member of carbon family displays huge prospect towards sensing,

biomedical as well as photocatalytic application because of its intrinsic photoluminescentproperties. Surprisingly, exploitation of CDs in catalyzing redox type of reactions remains

unexplored. To this end, CDs can also exhibit high electron transporting ability as it has an

electron rich graphitic core. Therefore, a nanocomposite comprising CD and anisotropic goldnanorod (GNR) can emerge as a prospective material towards redox type of reactions.

We have chosen the catalytic reduction of aromatic nitro groups (p-nitrophenol, o-

nitrophenol, m-dinitrobenze) using NaBH4as the model reaction to check the catalytic ability ofthe designed GNR-CD nanocomposite. The presence of CD increased the rate of electrontransfer as well as firm localization of the reactant molecules within the catalyst and thus almost

a 2-fold enhanced catalytic activity in compared to only GNR was found almost in every cases.

The developed catalyst is stable in water as well as it has high recyclable efficiency towardscatalysis. Most interestingly, the catalysis can also be efficiently performed with water-insoluble

compound, like m-dinitrobenzene. Importantly, for the first time catalytic property of carbon dot

in conjugation with GNR is utilized in reduction of nitroarenes and thus endorsing itseffectiveness in designing various industrially important catalysts.

The present investigation unveiling the effectiveness of carbon dot in conjugation with

GNR towards catalysis of nitroarenes will find significant interest in the development of novel

materials for nanocatalysis as well as its application in interdisciplinary branches of sciences willfind significant interest in the development of novel materials and techniques for nanotechnology

and thus it would find interest among the interdisciplinary readers of Chemical

Communications.

ge 1 of 18 ChemComm


3/19

Journal Name

Cite this: DOI: 10.1039/c0xx00000x

www.rsc.org/xxxxxx

Dynamic Article Links

ARTICLE TYPARTICLE TYPEARTICLE TYPARTICLE TYPE

This journal is The Royal Society of Chemistry [year] [journal], [year], [vol], 0000 | 1

Formation of gold nanorod-carbon dot nanocomposite with superior catalytic

ability towards reduction of aromatic nitrogroup in water

Pritiranjan Mondal,aKrishanu Ghosal,


aDebabrata Ganguly,

aMithun Das,

a

Abhijit Bera,aR. K. Gupta,bAngel A. Mart,cBipin Kumar Gupta*dand Subhabrata Maiti*a

5

Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX

DOI: 10.1039/b000000x

We report the synthesis of gold nanorod-carbon dot

nanocomposite and its utility as a recyclable catalyst for

reduction of aromatic nitrogroup. Presence of carbon dot on10

gold nanorod surface enhanced the reduction rate by two-

fold.

Nanotechnology has found tremendous attention towards

catalyzing chemical reactions since the pioneering work of

Haruta.1 The unique surface properties of noble metallic15

nanoparticles such as gold and silver are being exploited in

catalyzing a variety of reactions ranging from carbon monoxide

oxidation and carbon-carbon coupling to hydrogenation.1-3 The

catalytic ability of metallic nanostructures is due to their size,

shape and nature (e.g. hollowness and porosity).3-4 The20

advantages of using gold nanostructures in modulating catalysis

lie in their straighforward synthesis in different forms, stability,

and surface functionalization, among others.4-5Typically, smaller

nanoparticles showed higher catalytic ability in various kinds of

reactions.5

However, in the case of redox reactions, anisotropic25

nanostructures with high electron transporting ability such as

nanocages or nanoboxes have been observed toenhance the

catalytic rate.4

Nanocomposites made of carbon nanostructures and metallic

nanomaterials are emerging as excellent materials for30

nanocatalysis, photovoltaics to nanoelectronics.6-7Among carbon

nanostructures, carbon dots (CDs), the newest and exciting

member of carbon family, are interesting prospects for sensing,

biomedical and photocatalytic applications due to their intrinsic

phophophysical properties.835

aDepartment of Applied Chemistry and Industrial Chemistry,

Ramakrishna Mission Vidyamandira, Belurmath, Howrah 711 202,India, E-mail: [email protected] of Chemistry, Pittsburg State University40

Pittsburg, KS 66762, USAcDept. of Chemistry and Bioengineering, Rice University

Houston, TX 77005dNational Physical Laboratory (CSIR) Dr K S Krishnan Road, New Delhi

110012, India ; E-mail:[email protected]

Electronic Supplementary Information (ESI) available: Details of

synthesis of GNPs and CDs, other experimental details, TEM images,

UV-vis spectra, kinetics graph, see DOI: 10.1039/b000000x/

Surprisingly, exploitation of CDs in catalyzing redox reactions50

remains unexplored. For example, CDs is expected to exhibit

high electron transporting ability due to its electron rich graphitic

core. Therefore, we envision that a nanocomposite that

synergitically combine CD and anisotropic gold nanorods (GNR)

could have important applications in redox reactions. GNR55

stabilized with cationic cetyltrimethylammonium bromide

(CTAB) can be conjugated with carbon dot having carboxylate

functional groups. Notably, the designed composite might also

offer several advantages: i) presence of anisotropic GNR which is

already known for its high catalytic efficiency due to presence of60

different facets;9ii) The availability of the graphitic core of CDs,

which can expedite the transfer rate of electrons; and most

importantly, iii) the hydrophobic domain between GNR and CD

can help trapping hydrophobic molecules which would allow

aqueous catalytic reactions of water-insoluble compounds. Thus,65

GNR-CD nanocomposite is an interesting approach for the

development of superior nanocatalyst.

Fig. 1 a) UV-vis spectra, b-c) TEM images of synthesized GNR-CD

nanocomposite ([Au] = 100 M, [CD] = 100 g mL-1) d) schematic

representation of the formation of the GNR-CD nanocomposite.70

Page 2ChemComm


4/19

2 | Journal Name, [year], [vol], 0000 This journal is The Royal Society of Chemistry [year]

Initially, we have synthesized GNR with a transverse surface

plasmon peak (trans, SPR) at 520 nm and longitudinal peak (long)

at 695 nm using standard protocols (Fig. 1a).10 Details of the

synthetic procedure can be found in the electronic supplementary

information (ESI). Transmission electron microscope (TEM)5

images revealed that the width of the GNR is 10 2 nm, having

aspect ratio of 2.8 0.3 (Fig. 1b-c and S1a, ESI). The synthesized

GNRs are highly stable as these are stabilized by the quaternary

ammonium group of cetltrimethylammonium bromide (CTAB).

10

In order to produce the GNR-CD nanocomposite, we have10

designed carbon dot functionalized with long chain anionic

carboxylate (Fig. 1d). CDs were synthesized by thermal coupling

between sodium-salt of 11-aminoundecanoic acid and citric acid

as discussed elsewhere (Fig. 1d).11 Here citric acid acts as the

carbon source and 11-amino undecanoic acid covalently linked15

with the carbon nanoparticle via amide bond. The size of the CDs

are of 3 1 nm as found from TEM images (Fig. S1b, ESI). Also

a negative zeta potential () value of -23.8 2 mV confirms the

presence of carboxylate moiety on the surface of the CD.

The synthesized GNR solution was centrifuged at 14,000 rpm20

for 90 min to remove excess CTAB and the residual material was

redispersed in aqueous phosphate buffer (pH 7.0, 25 mM). This

buffered GNR solution was then used to make the conjugate with

CD functionalized with carboxylate moiety. The nanoconjugate

was prepared by mixing GNR and CD solutions in phosphate25

buffer at different ratio. The formation of the GNR-CD

Fig. 2Fluorescence spectra of CD in absence and presence of GNR of

varying concentration (Inset: Visual fluorescent image of CD).

nanoconjugates was confirmed both by spectroscopic and

microscopic method. The strong photoluminescence properties of30

the CD (emission and excitation wavelength maxima = 420 and

340 nm) was quenched in presence of GNR as gold nanomaterialsare known for quenching the emission of fluorophores in close

proximity (Fig. 2).5The blue-shift in emission maxima (almost

by 20 nm, from 420 nm to 400 nm) in presence of GNR is likely35

due to the interaction between GNR and CD. In addition, the

TEM images (Fig. 1b-c) show the occurrence of CDs over the

GNR surface, which is consistent with the formation of the GNR-

CD composite. We propose that the electrostatic attractive force

between cationic GNR and anionic CDs as well as the40

hydrophobic attraction of the long carbon chain plays a crucial

role in nanocomposite formation (Fig. 1d).

To test the catalytic ability of the synthesized nanocomposite,

we have chosen the reduction of p-nitrophenol as the model

reaction.12 The conversion of p-aminophenol from its nitro45

analogue is a reaction of versatile applications that includes

antipyretic or analgesic drug development, dye industry, and

corrosion removal.13,14 Moreover, the reaction does not proceed

in absence of any catalyst. The progress of the reaction can be

easily monitored by observing the rate at which the characteristic50400 nm peak of p-nitrophenol decreases as it converts to p-

aminophenol, with a generation of a new peak at 300 nm (Fig. S2

and S3a, ESI). The reaction followed pseudo first order kinetics

as the concentration of NaBH4 is in excess (almost 1000 times

higher) than that ofp-nitrophenol.55

Initially, we have monitored the apparent rate constant (kapp)

of the reaction in presence of varying concentration of GNR

([Au] = 10-100 M). We have observed an increase in kapp(from

0.05 to 0.072 s-1) with increasing Au concentration up to 50 M

and then remain almost constant (Table S1, ESI). At this point,60

the GNR-CD composite was fabricated by varying CD

concentration from 12.5 to 100 g mL-1while concentration of

GNR was kept constant (50 M). Increasing GNR concentration

resulted in colloidal instability of the composite. Interestingly, an

increase in the CD concentration in the GNR-CD composite (up65

to 50 g mL-1) led to a 2-fold increase in the kapp from 0.072 to

0.143 s-1,while further increase in the CD concentration (100 g

mL-1) caused almost no effect in the kappat 0.135 s-1 (Fig. 3 and

S3, ESI). However, presence of only CD led to an almost

negligible effect towards catalyzing the reaction (Fig. S3, ESI).70

Fig. 3Variation in kappof p-nitrophenol reduction by NaBH4in presence

of GNR-CD nanocomposite in aqueous phosphate buffer (pH 7, 25 mM)

at 25 C ([Au] = 50 M in all GNR-CD composite).

Furthermore, we have also monitored the recyclability of the

GNR-CD nanocomposite in catalyzing the reduction. Our75

experiments showed that the catalytic ability remained about 80%

even after completing the fourth reduction cycle (Fig. 4). In fact,

the TEM image of the GNR-CD nanocomposite revealed the

encirclement of the CD on the GNR surface even after the fourth

cycle (Fig. S4, ESI). However, the gradual loss in the catalytic80

ability might be due to detachment of parts of CD from the GNR

ge 3 of 18 ChemComm


5/19

This journal is The Royal Society of Chemistry [year] Journal Name, [year], [vol], 0000 | 3

surface as the number of cycle is increased. This cyclic stability

and retainment of the catalytic activity of this nanocomposite is

of high significance in terms of its use as a potential catalyst.

It is obvious that the presence of CD resulted a 2-fold increase

in the catalytic rate of the reduction of p-nitrophenol when5

combined with GNR, which itself is known as a good catalyst for

this reaction.9 This might be due to the acceleration of the

electron transport through the graphitic carbonaceous core of the

CD. In addition, p-nitrophenol is firmly placed within closeproximity of the gold surface aided by the hydrophobic carbon10

chain of the nanocomposite. In fact, the presence ofp-nitrophenol

Fig. 4Recyclability of the GNR-CD nanocomposite as catalyst for the

reduction ofp-nitrophenol.

in the hydrophobic domain was is consistent with a slight blue-

shift in UV spectra of the compound in presence of GNR-CD15

composite in the aqueous buffer (Fig. S5, ESI). Thus, it is likely

that an enhanced capacity for transfering electron lead to an

increase in catalytic rate of the reduction. However, beyond acertain concentration of the CD in the GNR-CD nanocomposite,

the rate of catalysis remained same probably due to the lack of20

penetration space by the reactant molecules to get close to the

GNR surface.

To this end, we have also observed the ability of this GNR-CD

nanocomposite to catalyze reduction of o-nitrophenol to o-

aminophenol. The concentration of Au and CD in the25

nanocomposite were maintained at 50 M and 50 g mL-1. In this

case, progress of this pseudo first order reaction was monitored

spectrophotometrically by observing the rate of decrease in the

absorbance at 420 nm (characteristic UV peak of o-nitrophenol)

(Fig. S6, ESI). Here also, the rate of the reduction was increased30

by 1.6 fold in presence of CD. The observed kappwas 0.064 s-1in

only GNR solution, which increased to 0.104 s-1in the GNR-CD

nanocomposite in aqueous buffer (Fig. S6, ESI). However, in

absence of the catalyst almost no reduction occurred.

We have also used one water-insoluble substrate (m-35

dinitrobenzene) to check the efficacy of our designed GNR-CD

nanocomposite towards its reduction. The m-dinitrobenzene

reduced to m-phenylenediamine in presence of NaBH4 and our

nanocomposite in aqueous phosphate buffer.14The corresponding

change in UV-vis spectra also delineated this fact (Fig. S7, ESI).40

In addition, the gradual blue shift in UV-vis spectral maxima of

m-dinitrobenzene (244 to 241 nm) in GNR and GNR-CD

composite validates the presence of the compound in the

hydrophobic domain of the nanocomposite (Fig. S8, ESI). In this

case also, the pseudo first order rate constant of the reaction was45

found to be increased by 2 fold in presence of CD (from 0.14 s -1

to 0.28 s-1) (Fig. S9, ESI).

In conclusion, we have developed a new class of GNR-CD

nanocomposite which shows high efficiency in catalyzing

reduction of different aromatic nitrogroups. We believe the50presence of CD increased the rate of electron transfer as well as

secures the localization of the reactant molecules within the

catalyst, and thus a 2-fold enhancement in catalytic activity in

comparison to only GNR was found almost in every case. This

novel catalyst is stable in water and has shown good recyclable55

efficiency towards catalysis. Most interestingly, the catalysis can

also be efficiently performed in water-insoluble compound, like

m-dinitrobenzene. Importantly, to the best of our knowledge, this

is the first report of the catalytic properties of carbon dot in

conjugation with GNR, for the reduction of nitroarenes and thus60

present potential applications in the design of various industrially

important catalysts.

Notes and references

1. M. Haruta, Catal. Today, 1997, 36, 153.65

2. G. A. Somorjai, A. M. Contreras, M. Montano and R. M. Rioux,

Proc. Natl. Acad. Sci. USA, 2006, 103, 10577; X. Yuan, G. Sun, H.

Asakura, T. Tanaka, X. Chen, Y. Yuan, G. Laurenczy, Y. Kou, P. J.

Dyson, N. Yan, Chem. Eur. J., 2013, 19, 1227.

3. M. Boronat and A. Corma,Langmuir, 2010, 26, 16607; A. Jakhmola,70

R. Bhandari, D. Pacardo and M. R. Knecht, J. Mater. Chem.2010,

20, 1522; C. Ornelas, J. Ruiz, L. Salmon and D. Astruc, Adv. Synth.

Catal., 2008, 350, 837; R. Bhandari and M. R. Knecht, ACS Catal.

2011, 1, 89; V. Polshettiwar, J.-M. Basset, and D. Astruc.

ChemSusChem, 2012, 5, 6.75

4. J. Zeng,Q. Zhang,J. Chenand Y. Xia, Nano Lett., 2010, 10, 30; J.

Lee, J. C. Park, J. U Bang and H. Song, Chem. Mater., 2008, 20,

5839.

5. J. Zhang, G. Chen, M. Chaker, F. Rosei and D. Ma,Appl. Catal. B:

Environmental, 2013, 107, 132; S. Maiti, M. Ghosh and P. K. Das,80

Chem Commun., 2011, 47, 9864.

6. Z. Liu, K. Yang, Y. Liu and S. -T. Lee,J. Mater. Chem., 2012, 22,

24230; J. C. G. E. da Silva and H. M. R. Goncalves, Trends Anal.

Chem.2011, 30, 1327; S. S. Chou, M. De, J. Luo, V. M. Rotello, J.

Huang and V. P. Dravid,J. Am. Chem. Soc., 2012, 134, 16725.85

7. K. Das, S. Maiti, M. Ghosh, D. Mandal and P. K. Das, J. Colloid

Interface Sci., 2013, 395, 111.

8. S. N. Baker and G. A. Baker,Angew. Chem. Int. Ed 2010, 49, 6726;

J. C. G. E. da Silva and H. M. R. Goncalves, TrAC, Trends Anal.

Chem., 2011, 30, 1327.90

9. X. Guo, Q. Zhang, Y. Sun, Q. Zhao and J. Yang,ACS Nano, 2012, 6,

1165.

10. N. R. Jana, Small, 2005, 1, 875.

11. A. B. Bourlinos, A. Stassinopoulos, D. Anglos, R. Zboril, V.

Georgakilas and E. P. Giannelis, Chem. Mater., 2008, 20, 4539.95

12. P. Herves, M. Perez-Lorenzo, L. M. Liz-Marzan, J. Dzubiella, Y. Lub

and M. Ballauff, Chem. Soc. Rev., 2012, 41, 5569.

13. R. Jin, Y. Xing, X. Yu, S. Sun, D. Yu, F. Wang, W. Wu and S. Song,

Chem. Asian J., 2012, 7, 2955; S. Rana and K. M. Parida, Catal. Sci.

Technol., 2012, 2, 979.100

14. A. A. Vernekar, S. Patil, C. Bhat and S. G. Tilve,RSC Adv., 2013, 3,

13243.

Page 4ChemComm


6/19

Graphical abstract

Gold nanorod-carbon dot nanocomposite was developed which is highly efficient in catalyzing

reduction of nitroarenes. Presence of carbon dot on GNR surface enhanced the catalytic rate by

two fold.

ge 5 of 18 ChemComm


7/19

221x203mm (96 x 96 DPI)

Page 6ChemComm


8/19


9/19

224x188mm (150 x 150 DPI)

Page 8ChemComm


10/19

219x177mm (150 x 150 DPI)

ge 9 of 18 ChemComm


11/19

S1

Formation of gold nanorod-carbon dot nanocomposite with

superior catalytic ability towards reduction of aromatic nitrogroup

in water

Pritiranjan Mondal,aKrishanu Ghosal,


aDebabrata

Ganguly,

a

Mithun Das,

a

Abhijit Bera,

a

R. K. Gupta,

b

Angel A. Mart,

c

Bipin KumarGupta*d

and Subhabrata Maiti*a

aDepartment of Applied Chemistry and Industrial Chemistry, Ramakrishna Mission

Vidyamandira, Belurmath, Howrah 711 202, India, E-mail: [email protected].

bDepartment of Chemistry, Pittsburg State University, Pittsburg, KS 66762, USA

cDept. of Chemistry and Bioengineering, Rice University, Houston, TX 77005

dNational Physical Laboratory (CSIR) Dr K S Krishnan Road, New Delhi 110012, India ;

E-mail:[email protected]

Electronic Supplementary Information

Materials and instruments:

HAuCl4 (30 wt. %) solution, 11-aminoundecanoic acid were purchased from Sigma, USA.

Silver nitrate, citric acid, sodium borohydride, p-nitrophenol, o-nitrophenol, m-

dinitrobenzene, cetyltrimehylammonium bromide and other reagents were purchased from

Merck (India) and were of highest analytical grade. The UV-visible absorption spectra were

recorded on a Perkin-Elmer Lambda 25 spectrophotometer. Fluorescence spectra were

measured inVarian Cary Eclipse luminescence spectrometer. Zeta potential was recorded in

zetasizer Nano-ZS of Malvern instrument limited.

Synthesis of gold nanorod:

Gold nanorod was formed by following the protocol described elsewhere (reference 10 in the

main manuscript). Briefly, 5 mL of aqueous solution of cetyltrimethylammonium bromide

(CTAB) was mixed with solution of HAuCl4. The final concentrations of CTAB and HAuCl4

Page 10ChemComm


12/19

S2

were maintained at 0.1 M and 1 mM, respectively. Then, ascorbic acid and AgNO3 were

added in this solution so that the concentration of ascorbic acid and AgNO3 was 2 mM and

0.10 mM. Finally, 50 L of 1mM freshly prepared aqueous NaBH4solution was added. The

colorless solution (yellow to colorless transition occurred upon addition of ascorbic acid)

started to appear pink-violet within few min indicating the formation of gold nanorods.

Synthesis of carboxylate functionalized carbon dot (CD):

CD was synthesized by following the reported protocol (Reference 11 in the main

manuscript). For the synthesis of CD, initially 2 g H2N(CH2)10COOH were added in 25 mL

H2O and neutralized by 0.45 g NaOH. The solution was added to 25 mL of an aqueous

solution containing 2 g citric acid. The addition of citric acid resulted a thick precipitate after

stirring and the precipitate was collected by filtration. It was partially dried overnight at room

temperature. This gummy paste was further dried at 85 C for 2 h. The solid was crashed into

a fine powder and directly oxidized in air at 300 C for 2 h in a muffle oven. The crude

product was extracted with 25 mL of hot water using sonication. The mixture was then

centrifuged to remove any insoluble particles and the supernatant aqueous layer was

collected. The deep brown supernatant solution was precipitated by centrifuging at 14000

rpm for 1 h after addition of acetone at 1:10 volume ratio. The supernatant was removed and

the precipitated brownish black mass was further dried in hot oven at 80 C until it became

powder in nature.

Catalytic study. In a typical experiment, 2 L of p-nitrophenol/ o-nitrophenol/ m-

dinitrobenzene stock solution was added into 2.0 mL aqueous buffer of GNR-CD

nanoconjugate (of different composition, mentioned in the main manuscript), so that final

concentration of the reactant was 0.1 mM. Stock solution of o-nitrophenol, m-dinitrobenzene

was made in ethanol. To the mixed solution of catalyst and reactant, 0.1 mL of NaBH4was

added with stirring to start the reaction (final concentration of NaBH4=0.1 M). The progress

ge 11 of 18 ChemComm


13/19

S3

of the reaction was carried out by UV-vis study at ambient temperature (27 C). After the

completion of the reaction, the total solution was centrifuged for 60 second to separate the

catalyst. It was washed with MilliQ water and then, air dried for further using as catalyst.

Calculation of the rate constant. The pseudo-first-order kinetics with respect to the

reactants could be applied to our experimental system. The approximately linear shape of the

plot of -ln At/A0(A0represents the initial and Atthe absorbance after time t at corresponding

wavelength) versus time, as shown in Figure S3. As absorbance is proportional to

concentration it corresponds to the concentration of the reactants. From, the slop of the linear

equation the apparent rate constant (kapp) is calculated.

TEM study:For TEM, a drop of the GNR, CD and GNR-CD nanocomposite solution was

cast on 300-mesh Cu-coated TEM grid separately and dried under vacuum for 4 h before

taking the image. TEM images were taken on a JEOL JEM 2010 microscope.

Page 12ChemComm


14/19

S4

Fig. S1 TEM images of a) synthesized GNR, b)anionic carbon dot.

Fig. S2 Time-dependent UV-vis spectra of p-nitrophenol reduction in presence of GNR-CD

nanocomposite in aqueous phosphate buffer (pH 7.0, 25 mM) at 25 C.



15/19


16/19

S6

Fig. S5 UV-vis spectra ofp-nitrophenol in absence and presence of GNR-CD nanocomposite

in aqueous phosphate buffer.



17/19

S7

Fig. S6 a) The change in absorbance of o-nitrophenol in presence of the GNR-CD catalyst

and b)plot of lnAt/A0against time to find the rate constant for o-nitrophenol reduction.

Page 16ChemComm


18/19

S8

Fig. S7 Time-dependent UV-vis spectra of m-dinitrobenzene reduction in presence of GNR-

CD nanocomposite in aqueous phosphate buffer (pH 7.0, 25 mM) at 25 C.

Fig. S8 UV-vis spectra of m-dinitrobenzene in absence and presence of catalyst in aqueous

phosphate buffer.



19/19

S9

Fig. S9 Plot of ln At/A0 against time to find the rate constant for m-dinitrobenzene

reduction.

Page 18ChemComm

formation of gold nanorod-carbon dot nanocomposite with superior catalytic ability towards...

Documents