piquin ag nanostructures

8102019 Piquin Ag Nanostructures

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Synthesis of metallic silver nanoparticles and silver organometallic nanodisks mediated by extracts of

Capsicum annuum var aviculare (piquin) fruits

Raquel Mendoza-Resendeza Nuria O Nu~nezb Enrique Dıaz Barriga-Castroc

and Carlos Lunac

Silver-based nanostructures were prepared through reductionoxidation reactions of aqueous silver nitrate

solutions mediated by extracts of red fruits of the piquin pepper (Capsicum annuum var aviculare) at room

temperature Detailed morphological and microstructural studies using X-ray diffraction conventional and

high-resolution transmission electron microscopy and selected area electron diffraction revealed that the

product was constituted by three kinds of nanoparticles One of them was composed of twinned

metallic silver nanoparticles with a size of few nanometers Other kind of particles was ultra 1047297ne disk-like

single crystals of silver 440-dimethyldiazoaminobenzene being in our best knowledge the 1047297rst time that

this compound is reported in the form of nanoparticles Both kinds of nanoparticles experienced

processes of self-assembly and subsequent grain growth to form the third kind of nanoparticles Such

resulting nanostructures are monocrystalline and 1047298attened metallic silver nanoparticles that have

diameters around tens of nanometers the [112] direction perpendicular to the particle plane and are

coated by a surface organometallic layer and residues of biomolecules The ultraviolet-visible spectrum

of the biosynthesized product showed a surface plasmon resonance (SPR) extinction band with an

absorbance maximum at around 400 nm thereby con1047297rming the presence of 1047297ne Ag particles Studies

carried out by Fourier transform infrared spectroscopy indicated that the principal active compounds

responsible of the reduction of the Ag ions are proteins and capsaicin (through the amino groups) and

phenolic compounds (through hydroxyl groups)

Introduction

During the last decade new facile syntheses of nanostructures

(mainly of metal noble nanoparticles) mediated by extracts of

diff erent parts of plants such as seeds1 leaves23 barks4

owers56 gums78 and fruits9 have been presented as sustain-

able and economically competitive routes to obtain functional

nanomaterials In these preparation methods usually so-called

biosynthesis2 the extracts of the natural products provide

proteins phenols polysaccharides and vitamins among other

organic substances which play the roles of reducing and

stabilizing agents1011 These bio-components are biodegradable

and in contrast to the chemicals that are commonly used in the

conventional chemical methods dont pose dangers to both

human health and the environment On the other hand the

biosynthetic methods also off er new approaches and opportu-

nities to attach biomolecules to the nanoparticle surface

providing them enhanced biological activities exploitable in

diverse biomedical applications12 However compared to

conventional chemical methods these greener syntheses

generally have a poorer control over the size and morphology of

the resulting nanostructures probably due to these methods

are far to be optimized In fact the involved particle formation

mechanisms and the synthetic parameters that govern them

remain rather poorly studied

Recently the results of several works have shown that

extracts of the chili peppers (genus Capsicum) present proper-ties very suitable for its use in green synthesis of several kinds of

nanostructures due to their powerful reducing activity1314 In

particular Li et al11 have demonstrated that aqueous extracts of

Capsicum annuum L can mediate the synthesis of silver nano-

particles with controlled sizes in the range from 10 up to 40 nm

Also the same extract was used to prepare amorphous selenium

(a-Se) nanoparticles15

In the present contribution silver nanoparticles and silver

440-dimethyldiazoaminobenzene nanodisks have been

prepared using alcoholic extracts of ripe fruits of Capsicum

annuum var aviculare (piquin pepper) being the rst time in

a Facultad de Ingenier ıa Mecanica y El ectrica Universidad Aut onoma de Nuevo Leon

San Nicol as de los Garza 66450 Nuevo Leon Mexico E-mail raquelmendozars

uanledumxb Instituto de Ciencia de Materiales de Sevilla CSIC-US Avda AmericoVespucio no 49

Isla de la Cartuja 41092 Sevilla Spain

cCentro de Investigaci on en Ciencias F ısico MatematicasFacultad de Ciencias F ısico

Matematicas Universidad Aut onoma de Nuevo Leon San Nicol as de los Garza

66450 Nuevo Leon Mexico E-mail carloslunacduanledumx

Cite this RSC Adv 2013 3 20765

Received 10th July 2013

Accepted 2nd September 2013

DOI 101039c3ra43524e

wwwrscorgadvances

This journal is ordf The Royal Society of Chemistry 2013 RSC Adv 2013 3 20765ndash20771 | 20765

RSC Advances

PAPER View Article OnlineView Journal | View Issue



which the mentioned organometallic phase is reported in form

of nanoparticles Piquin pepper is a variety of the Capsicum

annuum species whose fruits are hot (40 000ndash60 000 units in the

Scoville Heat Units Scale) due to their high content of cap-

saicinoids (mainly capsaicin and dihydrocapsaicin) that

provide the spicy character to peppers1617 In recent works it

has been shown that the antioxidant capacity of the extracts of

the Capsicum pepper fruits which is directly associated to the

content of phenolic compounds (including avonoids andcapsaicinoids) increases when these fruits have reached

maturity18ndash22 In addition piquin pepper is rich in proteins and

vitamins1723 which can also play the role of reducing agent in

green syntheses2425 Herein the piquin pepper extract was

prepared by boiling and stirring puried and nely chopped red

fruits in a 1 1 mixture of double distilled water and absolute

ethanol in order to successfully extract compounds such as

capsaicinoids carotenoids avonoids among others172627 A

concise investigation of the microstructural properties of the

obtained silver-based low dimensional systems is presented

leading us to propose a mechanism of particle growth

Experimental techniques

Chemicals

Red fruits of Capsicum annuum var aviculare (piquin pepper)

were purchased from a local supermarket in northeastern

Mexico Absolute ethanol and silver nitrate (AgNO3 99+) were

purchased from Sigma-Aldrich and were used as received The

water added in all experiments was doubly distilled

Preparation of the Capsicum annuum var aviculare extract

Red piquin pepper fruits were washed with double distilled water

two times 20 g of these puri

ed fruits were

nely chopped andmixed with 100 ml of a 1 1 mixture of double distilled water and

absolute ethanol under vigorous stirring A erwards the

mixtures were boiled for 30 minutes with continuous stirring

Subsequently the heating source was removed and the mixture

was allowed to cool to room temperature naturally Then the

mixture was kept overnight at room temperature in a capped

bottle A erwards the solid residues were removed by ltration

and the resulting extract named piquin pepper extract was

directly used in the synthesis of silver-based nanostructures

Synthesis of nanoparticles

In a typical experiment 30 ml of piquin pepper extract wasadded to 30 ml of 05 M AgNO3 solution under vigorous

magnetic stirring A erwards the reactions were allowed to

proceed during 6 hours at room temperature under continuous

stirring During this process the color of the reaction solution

changed from yellowish translucent to a turbid orange color

indicating the occurrence of the reduction of the Ag + ions The

resulting product named silver-based sample was washed

several times with 1 1 mixtures of distilled water and absolute

ethanol and centrifugation Finally a portion of the puried

powder was redispersed with distilled water for its further

characterization by transmission electron microscopy and

ultraviolet-visible spectroscopy The remaining sample was

dried at 50 C for 4 hours and characterized by X-ray diff raction

and Fourier transform infrared spectroscopy

Characterization techniques

The X-ray diff raction (XRD) pattern of the puried and dried

product of the bioreduction was recorded using a Xpert Pro X-

ray diff ractometer (PANalytical) with Cu Ka

radiation The mean

coherence lengths (MCL) perpendicular to some crystallo-

graphic planes of the silver-based sample were calculated from

the full width at half maximum (FWHM) of the corresponding

reection using the Scherrer equation28

Dhkl frac1409l

bcosq (1)

where l is the X-ray wavelength b is the broadening of the

diff raction peak and q is the diff raction angle Transmission

Electron Microscopy (TEM) studies were carried out with a FEI-

TITAN 80ndash300 kV microscope operating at an accelerating

voltage of 300 kV For the TEM characterizations a drop of the

sample in form of colloidal suspension was deposited onto alacey-carbon copper grid Selected area electron diff raction

(SAED) and high resolution transmission electron microscopy

(HRTEM) were used to gain more information about the

microstructure of the particles HRTEM images were analyzed

by fast Fourier transform (FFT) The elements present in the

samples were determined by chemical analyses through energy

dispersive spectrometry analyzer (EDS) integrated in the trans-

mission electron microscope The infrared spectra of the piquin

pepper extract and the silver-based sample diluted in KBr

pellets were recorded in a Nicolet 510 Fourier transform

infrared (FTIR) spectrometer Ultraviolet-visible spectra were

recorded using a Thermo Nicolet 60S

Results and discussion

TEM micrographs (Fig 1a) revealed that the silver-based sample

is constituted by ne particles with diameters in the range of

2ndash35 nm Fig 1b shows the particle diameter distribution of the

sample that can be described with a log-normal distribution

with a central value m frac14 72(03) nm and a standard deviation

s frac14 061(007) The elemental composition analysis of the

specimen performed by EDS (Fig 1e) indicates that the primary

component of the sample is Ag Moreover traces of C and O are

also detected Although the C peak could mostly come from the

lacey-carbon

lm of the TEM grid partially could come from thesample On the other hand the presence of lightest elements

such as H which are not detected by the EDS technique should

not be discarded

Fig 1c shows a representative SAED pattern of nanoparticles

synthesized from piquin pepper extract In this pattern well-

dened spotty rings ascribed to the 111 200 220 311 and

331 planes of face-centered cubic (fcc) metallic silver (JCPDSle

no 87-0720) are clearly observed However additional spots were

found with associated d -spacing of around 321 278 and 196 ˚ A

indicating the presence of another crystalline phase in concrete

silver 440-dimethyldiazoaminobenzene (JCPDS le no 35-1540)

20766 | RSC Adv 2013 3 20765ndash20771 This journal is ordf The Royal Society of Chemistry 2013

RSC Advances Paper

View Article Online





contrast structures with diameters between 4 and 10 nm

(Fig 4andashd) Due to the fraction of the incident electrons which

are transmitted across the sample is inversely proportional to

the specimen thickness the low contrast of these structures

suggests that they are very thin therefore they are nanodisks

The lattice fringes observed in the HRTEM images of such

nanostructures have d -spacing of around 278 and 196 ˚ A that

correspond to the silver 440-dimethyldiazoaminobenzene

phase detected by SAED and XRD measurements These resultssuggest that the formation of these organometallic nanodisks

occurs by bidimensional agglomeration of Ag atoms that

combine with amino groups and residues of aromatic biomol-

ecules of the piquin pepper extract

The third particle family is constituted by particles with

diameters of 10ndash35 nm (Fig 4a d and 5a) Fig 5a and d give

typical HRTEM micrographs of these particles The lattice

fringes in these images match with the structure of metallic

silver In fact the corresponding FFT images (Fig 5b and the

inset images of Fig 5d) display spots consistent with the [112]

zone axis of the fcc silver single-crystal Additionally spots

corresponding to the 12(

31

1) and 12(

13

1) forbiddenreections are also observed These features were repeatedly

observed in the vast majority of these particles It suggests that

they tend to fall onto the TEM grid with the same orientation

because they are rather at being the [112] direction

perpendicular to the nanoparticle plane On the other hand the

observation of forbidden reections is very frequent in metallic

fcc nanostructures with attened morphologies35ndash37 which have

been associated by several authors to the presence of (111)

stacking faults and that could have an important role in the

formation of disk-like nanoparticles35 In agreement with this

hypothesis stacking faults were found in a small fraction of theparticles of the third family that probably lied onto the TEM grid

in a tilted position An illustrative example is found in Fig 4a

Two particles of diameters around 10 nm sharing the same

orientations are observed Both particles are viewed along the

[110] direction (see the FFT image of the inset of Fig 4a) and

both exhibit (111) stacking faults (Fig 4a and e)

Another interesting observation with respect to the nano-

structures of the third particle family is that very frequently

small metallic silver nanoparticles and silver organometallic

nanodisks appear attached to them In Fig 5a it can be

observed several nanodisks attached to a bigger particle One of

these nanodisks (highlighted by the above square) display lattice fringes corresponding to a metallic silver single-crystal

sharing exactly the same orientation that the biggest particle

(compare the FFT images of the inset of Fig 5a and b) In

addition another nanodisk attached to this particle present

lattice fringes with d -spacing of 321 ˚ A (see Fig 5c) corre-

sponding to the silver 440-dimethyldiazoaminobenzene These

observations suggest that the particles of the third family are

formed by the oriented attachment and coalescence of particles

of the rst and second families The crystallization of single-

crystal particles through the aggregation of twinned nano-

particles and subsequent grain growth is very common in the

Fig 4 (a) HRTEM micrograph of several nanoparticles of the silver-based

sample The inset is the FFT image of the region highlighted with a white square

where stacking faults are not observed (b) FFT image of the zone of panel (a)

highlighted by the continuous square where an organometallic nanodisk is

observed (c) Image of a silver 440-dimethyldiazoaminobenzene nanodisk 1047297ltered

including the spots marked with circles in panel (b) (d) HRTEM of a silver 440-

dimethyldiazoaminobenzene nanodisk and Ag nanoparticles (e) HRTEM micro-

graph of a metallic Ag nanoparticle where stacking faults are clearly observed

The inset is the corresponding FFT image

Fig 5 (a) HRTEM micrograph of a silver particle of the third particle family The

inset is the FFT image of the region highlighted by the above continuous square(b) FFT image obtained from the region highlighted by the discontinuous square

of panel (a) (c) Magni1047297cation of the region highlighted by the continuous below

square of panel (a) (d) HRTEM micrograph of a silver particle of the third particle

familythat exhibits stripes with different contrast Thecorresponding FFT image is

showed in the inset


RSC Advances Paper

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formation of gold and silver nanoparticles and it has been

studied in detail in recent works1138 Assuming this crystal

growth mechanism the occurrence of the (111) stacking faults

could be a consequence of an imperfect arrangement of the self-

assembled nano-components and limitations in the atomic

diff usion during the coalescence of these disks Interestingly

several biggest particles observed along the [112] direction

appear in the TEM images showing particle regions or stripes

with diff erent contrast (Fig 5d) This fact suggests a multilayerstructure that it is in concordance with the proposed growth

mechanism

Fig 6 shows the UV-vis spectra of the piquin pepper extract

and silver-based sample In the last case an extinction band is

observed with an absorbance maximum at around 400 nm that

can be attributed to the plasmon absorption of very small silver

particles The large broadness of this band is due to the broad

Ag particle size distribution and the attened shape of the

bigger particles3940

Fig 7 depicts the FTIR spectra of the piquin pepper extract

and silver-based sample As it is expected the extract spectrum

displays bands of functional groups that are in agreement withthe presence of proteins polyphenols capsaicinoids and cap-

sinoids41 among other organic molecules

In this way the broad peak observed in the wavenumber

range of 4000ndash2000 cm1 and centered around 3315 cm1 is

associated to contributions of the OndashH and NndashH stretching

vibrations The shoulder near 1650 cm1 the shoulder at

around 1520 cm1 and the weak peak at around 1240 cm1

could correspond to the C]O stretching vibration of peptide

bond (amide I band) the NndashH bending vibration (amide II

band) and the CndashN stretching vibration (amide III band) from

proteins and capsaicinoids The band at 1406 cm1 could

correspond to the bending vibration of CndashOH groups mainly

associated to polyphenols and ethanol The strong peaks at 2928 and 2855 cm1 correspond to the CndashH asymmetric and

symmetric stretching bands of diff erent types of hydrocarbons

present in the extract and OndashCH3 vibrations of capsaicinoids

The peak at 1744 cm1 could be associated to the C]O

stretching mode of carboxylic acid groups The pronounced and

sharp peak observed at 1602 cm1 can be mainly associated to

the C]C aromatic ring stretching and the shoulder at 1460

cm1 arise from the methylene CndashH bend andor d (C]C) The

weak peak at 1262 cm1 could correspond to a CndashO stretching

band The intense shoulders at 1143 and 1101 cm

1

and theintense peak at 1073 cm1 could be associated to ndashOH aromatic

CndashOndashH and CndashO (of alcohols) vibrations respectively The peak

at 918 cm1 could be assigned to aromatic CndashH in plane and the

bands at around 836 820 780 cm1 can be associated to

aromatic CndashH out of plane bend The weak peaks at 704 665

and 635 could be assigned to OndashH out of plane vibrations4243

In the FTIR spectrum of silver-based sample the wave-

number of the NndashH bending vibration at 3314 cm1 appears

broadened and less intense with two very weak maximums at

3365 and 3264 cm1 which could be associated to ndashNndashN and Cndash

H bending vibrations respectively Also the shoulder at 1520

cm1 associated to the amide II band disappeared The peak of

the C]O stretching mode of carboxylic acid groups appearsshi ed at 1741 cm1 and the amide I and III bands appears

weakened The appearance of these bands and the inhibition of

the bands associated to the NndashH vibrations suggest that Ag

nanoparticles are capped by piquin biomolecules through the

nitrogen atom of amino groups The formation of such organic

capping layers could be a consequence of the initial bio-

reduction of the Ag ions through their interactions with the

amine groups of piquin extract On the other hand the wave-

number (1406 cm1) associated to the bending vibration of Cndash

OH groups in the piquin extract spectrum appears shi ed to a

lower frequency (1391 cm1) in the nanoparticle sample case

with an enhanced intensity In such change could be contrib-uting the appearance of the N]N stretching vibration44 arising

from the silver organometallic nanodisks detected by HRTEM

SAED and XRD On the other hand the CndashH band at 2928 cm1

is strongly weakened and the peak at 2855 cm1 disappeared

Also the C]C bandat 1602cm1 is shi edto 1590cm1 and its

intensity is enhanced The pronounced peak observed at

1011 cm1 and the shoulder measured at 985 and 956 cm1 are

associated to aromatic CndashH in plane bend Also the bands of

the piquin pepper extract spectrum observed at 1143 and

1101 cm1 appears signicantly diminished in the silver-based

sample spectrum and notoriously the intense band at Fig 6 UV-visible spectra of the Capsicum annuum var aviculare extract and the

silver based sample

Fig 7 FTIR spectra of the piquin pepper extract and the silver based sample


Paper RSC Advances

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1073 cm1 associated to CndashO stretches of alcohols disappeared

in the silver-based sample The observation of some bands that

could be associated to polyphenols in the FTIR spectrum of the

Ag-based sample with an inhibition of the bands associated to

the hydroxyl groups suggests that phenolic compounds also

participate in the Ag ion reduction through the hydroxyl groups

These observations are in agreement with other works where

the interaction between silver surfaces and amino andor ndashOH

groups is well-established254546

From these results we can conclude that the main active

components of the biological reaction medium participant in

the interaction with Ag ions are the amino groups of proteins

and capsaicin and hydroxyl groups of phenolic compounds As

a consequence of these interactions the crystallization of very

thin silver 440-dimethyldiazoaminobenzene nanodisks and the

formation of Ag nanoparticles capped by biomolecules (mainly

residues of proteins and polyphenols) are simultaneously

produced This formation of nanostructures probably occurred

by recognitionndashreductionndashlimited nucleation and growth

processes15

Based on the experimental observations we propose thefollowing mechanism Firstly reductionoxidation reactions are

produced through the interactions between Ag + ions and resi-

dues of the piquin biomolecules These reactions simulta-

neously yield to the crystallization of organometallic nanodisks

and Ag nanoparticles coated by surface organic layer The

stabilizing action of this organic capping is not enough to

completely prevent the growth of the nest Ag nanoparticles

and they and the organometallic nanodisks tend to growth by

self-aggregation coalescence and grain growth processes as it

is schematically represented in Fig 8 The resulting particles are

attened Ag particles with (111) stacking faults and capped by

organometallic surface layers and residues of biomolecules

Conclusions

A low-cost and sustainable synthesis of silver nanostructuresmediated by extracts of ripe piquin pepper (Capsicum annuum

var aviculare) fruits has been presented The variety of active

biomolecules existing in such reaction medium gives rises that

several reactions take place at the same time producing simul-

taneously metallic silver nanoparticles and for rst time silver

triazene nanodisks The crystallization of these nanostructures

is mainly produced by the interaction of the Ag ions and the

amino nitrogen atom of the protein peptides and capsaicin and

the oxygen atom of the hydroxyl group of phenolic compounds

As a consequence of the instability of these ne particles due to

its high surfacevolume ratio both kinds of nanoparticles tend

to self-assemble and coalesce to form monocrystalline andattened metallic silver nanoparticles with diameters around

tens of nanometers coated by an organometallic surface layer

and residues of biomolecules

Therefore in the present contribution it has been demon-

strated that the use of extracts of plants (like the extract of

piquin pepper fruits) as reaction media in the synthesis of

nanostructures not only provide new sustainable facile and

low-cost routes to prepare functional nanomaterials but it also

represents new interesting experimental models for the inves-

tigation of novel crystallization phenomena where complex

crystal growth mechanisms can be studied and the formation of

new organometallic crystalline phases can take place

Acknowledgements

Financial support from the Mexican Secretariat of Public

Education (SEP-PROMEP) the Mexican Council of Science and

Technology (CONACYT) and Universidad Aut onoma de Nuevo

Leon under research projects CB-179486 Fortalecimiento de

Cuerpos Academicos UANL-CA-305 and PAICYT-CE793-11

respectively is acknowledged

References

1 U B Jagtap and V A Bapat Ind Crops Prod 2013 46 1322 J Huang Q Li D Sun Y Lu Y Su X Yang H Wang

Y Wang W Shao N He J Hong and C Chen

Nanotechnology 2007 18 105104

3 H X Wang N He and Y P Wang Chem Eng J 2010 162

852

4 M Sathishkumar K Sneha S W Won C-W Cho S Kim

and Y-S Yun Colloids Surf B 2009 73 332

5 R K Das N Gogoi and U Bora Bioprocess Biosyst Eng

2011 34(5) 615

6 M Noruzi D Zare K Khoshnevisan and D Davoodi

Spectrochim Acta Part A 2011 79(5) 1461Fig 8 Schematic representation of the proposed particle growth mechanism


RSC Advances Paper

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7 A J Koraa R B Sashidharb and J Arunachalama Process

Biochem 2012 47 1516

8 V T P Vinod P Saravanan B Sreedhar D K Devi and

R B Sashidhar Colloids Surf B 2011 83 291

9 T J I Edison and M G Sethuraman Process Biochem 2012

47 1351

10 D S Shenya J Mathewa and D Philip Spectrochim Acta

Part A 2011 79 254

11 S Li Y Shen A Xie X Yu L Qiu L Zhang and Q ZhangGreen Chem 2007 9 852

12 S Eckhardt P S Brunetto J Gagnon M Priebe B Giese

and K M Fromm Chem Rev 2013 113 4708

13 G Oboh J Batista and T Rocha Eur Food Res Technol

2007 225 239

14 G Oboh R L Puntel and J B T Rocha Food Chem 2007

102 178

15 S Li Y Shen A Xie X Yu X Zhang L Yang and C Li


16 R Arora N S Gill G Chauhan and A C Rana Int J Pharm

Sci Drug Res 2011 3(4) 280

17 M Contreras-Padilla and E M Yahia J Agric Food Chem1998 46 2075

18 M Materska and I Perucka J Agric Food Chem 2005 53

1750

19 R Tundis F Menichini M Bonesi F Conforti G Statti

F Menichini and M R Loizzo LWT ndash Food Sci Technol

2013 53 370

20 Y Wahyuni A-R Ballester E Sudarmonowati R J Bino

and A G Bovy Phytochemistry 2011 72 1358

21 E Alvarez-Parrilla L A de la Rosa R Amarowicz and

F Shahidi J Agric Food Chem 2011 59 163

22 L R Howard S T Talcott C H Brenes and B Villalon J

Agric Food Chem 2000 48 1713

23 O Cisneros-Pineda L W Torres-Tapia L C Gutierrez-Pacheco F Contreras-Mart ın T Gonzalez-Estrada and

S R Peraza-Sanchez Food Chem 2007 104 1755

24 M N Nadagouda and R S Varma Green Chem 2006 8 516

25 R Sanghi and P Verma Bioresour Technol 2009 100 501

26 R I Santamarıa M D Reyes-Duarte E Barzana

D Fernando F M Gama M Mota and A Lopez-Munguıa

J Agric Food Chem 2000 48 3063

27 G F Barbero A Liazid M Palma and C G Barroso Talanta

2008 75 1332

28 B D Cullity and S R Stock Elements of X-ray Di ff raction

Prentice-Hall Englewood Cliff s NJ 2001

29 A-R Ballester E Sudarmonowati R J Bino and A G Bovy

J Nat Prod 2013 76 783

30 P Mukherjee M Roy B P Mandal G K Dey

P K Mukherjee J Ghatak A K Tyagi and S P Kale


31 T C Prathna N Chandrasekaran A M Raichur and

A Mukherjee Colloids Surf B 2011 82 15232 D Philip C Unni S A Aromal V K Vidhu and M Koenigii

Spectrochim Acta Part A 2011 78 899

33 B Zaitsev V Zaitseva A Molodkin and E Lisitsina Russ J

Inorg Chem 1977 22 504

34 C G Hartinger and P J Dyson Chem Soc Rev 2009 38

391

35 J Li D Ingert Z L Wang and M P Pileni J Phys Chem B

2003 107(34) 8717

36 L Lu A Kobayashi Y Kikkawa K Tawa and Y Ozaki J

Phys Chem B 2006 110 23234

37 J Reyes-Gasga A Gomez-Rodrıguez X Gao and M Jose-

Yacamacutean Ultramicroscopy 2008 108 92938 B Ingham T H Lim C J Dotzler A Henning M F Toney

and R D Tilley Chem Mater 2011 23 3312

39 I Pastoriza-Santos and L M Liz-Marzan Nano Lett 2002 2

903

40 J Zhang X Li X Sun and Y Li J Phys Chem B 2005 109

12544

41 J Dıaz F Pomar A Bernal and F Merino Phytochem Rev

2004 3 141

42 D W Mayo F A Miller and R W Hannah Course Notes on

the Interpretation of Infrared and Raman Spectra John Wiley amp

Sons Inc Hoboken New Jersey 2003

43 J Coates Interpretation of Infrared Spectra A Practical

Approach in Encyclopedia of Analytical Chemistry ed R AMeyers John Wiley amp Sons Ltd Chichester 2000

44 F Zimmermann T H Lippert C H Beyer J Stebani

O Nuyken and A Wokaun Appl Spectrosc 1993 47 986

45 J Huang G Zhan B Zheng D Sun F Lu Y Lin H Chen

Z Zheng Y Zheng and Q Li Ind Eng Chem Res 2011 50

9095

46 M C Moulton L K Braydich-Stolle M N Nadagouda

S Kunzelman S M Hussain and R S Varma Nanoscale

2010 2 763


Paper RSC Advances

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which the mentioned organometallic phase is reported in form

of nanoparticles Piquin pepper is a variety of the Capsicum

annuum species whose fruits are hot (40 000ndash60 000 units in the

Scoville Heat Units Scale) due to their high content of cap-

saicinoids (mainly capsaicin and dihydrocapsaicin) that

provide the spicy character to peppers1617 In recent works it

has been shown that the antioxidant capacity of the extracts of

the Capsicum pepper fruits which is directly associated to the

content of phenolic compounds (including avonoids andcapsaicinoids) increases when these fruits have reached

maturity18ndash22 In addition piquin pepper is rich in proteins and

vitamins1723 which can also play the role of reducing agent in

green syntheses2425 Herein the piquin pepper extract was

prepared by boiling and stirring puried and nely chopped red

fruits in a 1 1 mixture of double distilled water and absolute

ethanol in order to successfully extract compounds such as

capsaicinoids carotenoids avonoids among others172627 A

concise investigation of the microstructural properties of the

obtained silver-based low dimensional systems is presented

leading us to propose a mechanism of particle growth

Experimental techniques

Chemicals

Red fruits of Capsicum annuum var aviculare (piquin pepper)

were purchased from a local supermarket in northeastern

Mexico Absolute ethanol and silver nitrate (AgNO3 99+) were

purchased from Sigma-Aldrich and were used as received The

water added in all experiments was doubly distilled

Preparation of the Capsicum annuum var aviculare extract

Red piquin pepper fruits were washed with double distilled water

two times 20 g of these puri

ed fruits were

nely chopped andmixed with 100 ml of a 1 1 mixture of double distilled water and

absolute ethanol under vigorous stirring A erwards the

mixtures were boiled for 30 minutes with continuous stirring

Subsequently the heating source was removed and the mixture

was allowed to cool to room temperature naturally Then the

mixture was kept overnight at room temperature in a capped

bottle A erwards the solid residues were removed by ltration

and the resulting extract named piquin pepper extract was

directly used in the synthesis of silver-based nanostructures

Synthesis of nanoparticles

In a typical experiment 30 ml of piquin pepper extract wasadded to 30 ml of 05 M AgNO3 solution under vigorous

magnetic stirring A erwards the reactions were allowed to

proceed during 6 hours at room temperature under continuous

stirring During this process the color of the reaction solution

changed from yellowish translucent to a turbid orange color

indicating the occurrence of the reduction of the Ag + ions The

resulting product named silver-based sample was washed

several times with 1 1 mixtures of distilled water and absolute

ethanol and centrifugation Finally a portion of the puried

powder was redispersed with distilled water for its further

characterization by transmission electron microscopy and

ultraviolet-visible spectroscopy The remaining sample was

dried at 50 C for 4 hours and characterized by X-ray diff raction

and Fourier transform infrared spectroscopy

Characterization techniques

The X-ray diff raction (XRD) pattern of the puried and dried

product of the bioreduction was recorded using a Xpert Pro X-

ray diff ractometer (PANalytical) with Cu Ka

radiation The mean

coherence lengths (MCL) perpendicular to some crystallo-

graphic planes of the silver-based sample were calculated from

the full width at half maximum (FWHM) of the corresponding

reection using the Scherrer equation28

Dhkl frac1409l

bcosq (1)

where l is the X-ray wavelength b is the broadening of the

diff raction peak and q is the diff raction angle Transmission

Electron Microscopy (TEM) studies were carried out with a FEI-

TITAN 80ndash300 kV microscope operating at an accelerating

voltage of 300 kV For the TEM characterizations a drop of the

sample in form of colloidal suspension was deposited onto alacey-carbon copper grid Selected area electron diff raction

(SAED) and high resolution transmission electron microscopy

(HRTEM) were used to gain more information about the

microstructure of the particles HRTEM images were analyzed

by fast Fourier transform (FFT) The elements present in the

samples were determined by chemical analyses through energy

dispersive spectrometry analyzer (EDS) integrated in the trans-

mission electron microscope The infrared spectra of the piquin

pepper extract and the silver-based sample diluted in KBr

pellets were recorded in a Nicolet 510 Fourier transform

infrared (FTIR) spectrometer Ultraviolet-visible spectra were

recorded using a Thermo Nicolet 60S

Results and discussion

TEM micrographs (Fig 1a) revealed that the silver-based sample

is constituted by ne particles with diameters in the range of

2ndash35 nm Fig 1b shows the particle diameter distribution of the

sample that can be described with a log-normal distribution

with a central value m frac14 72(03) nm and a standard deviation

s frac14 061(007) The elemental composition analysis of the

specimen performed by EDS (Fig 1e) indicates that the primary

component of the sample is Ag Moreover traces of C and O are

also detected Although the C peak could mostly come from the

lacey-carbon

lm of the TEM grid partially could come from thesample On the other hand the presence of lightest elements

such as H which are not detected by the EDS technique should

not be discarded

Fig 1c shows a representative SAED pattern of nanoparticles

synthesized from piquin pepper extract In this pattern well-

dened spotty rings ascribed to the 111 200 220 311 and

331 planes of face-centered cubic (fcc) metallic silver (JCPDSle

no 87-0720) are clearly observed However additional spots were

found with associated d -spacing of around 321 278 and 196 ˚ A

indicating the presence of another crystalline phase in concrete

silver 440-dimethyldiazoaminobenzene (JCPDS le no 35-1540)


RSC Advances Paper

View Article Online

























31

1) and 12(

13















































showed in the inset


RSC Advances Paper

View Article Online












mechanism
































1



































silver based sample



Paper RSC Advances

View Article Online






















processes15













Conclusions
























Acknowledgements







References





852




2011 34(5) 615




RSC Advances Paper

View Article Online




Biochem 2012 47 1516




47 1351


Part A 2011 79 254





2007 225 239


102 178




Sci Drug Res 2011 3(4) 280



1750



2013 53 370















2008 75 1332




J Nat Prod 2013 76 783










391


2003 107(34) 8717


Phys Chem B 2006 110 23234





903


12544


2004 3 141










9095



2010 2 763


Paper RSC Advances

View Article Online

























31

1) and 12(

13















































showed in the inset


RSC Advances Paper

View Article Online












mechanism
































1



































silver based sample



Paper RSC Advances

View Article Online






















processes15













Conclusions
























Acknowledgements







References





852




2011 34(5) 615




RSC Advances Paper

View Article Online




Biochem 2012 47 1516




47 1351


Part A 2011 79 254





2007 225 239


102 178




Sci Drug Res 2011 3(4) 280



1750



2013 53 370















2008 75 1332




J Nat Prod 2013 76 783










391


2003 107(34) 8717


Phys Chem B 2006 110 23234





903


12544


2004 3 141










9095



2010 2 763


Paper RSC Advances

View Article Online












mechanism
































1



































silver based sample



Paper RSC Advances

View Article Online






















processes15













Conclusions
























Acknowledgements







References





852




2011 34(5) 615




RSC Advances Paper

View Article Online




Biochem 2012 47 1516




47 1351


Part A 2011 79 254





2007 225 239


102 178




Sci Drug Res 2011 3(4) 280



1750



2013 53 370















2008 75 1332




J Nat Prod 2013 76 783










391


2003 107(34) 8717


Phys Chem B 2006 110 23234





903


12544


2004 3 141










9095



2010 2 763


Paper RSC Advances

View Article Online






















processes15













Conclusions
























Acknowledgements







References





852




2011 34(5) 615




RSC Advances Paper

View Article Online




Biochem 2012 47 1516




47 1351


Part A 2011 79 254





2007 225 239


102 178




Sci Drug Res 2011 3(4) 280



1750



2013 53 370















2008 75 1332




J Nat Prod 2013 76 783










391


2003 107(34) 8717


Phys Chem B 2006 110 23234





903


12544


2004 3 141










9095



2010 2 763


Paper RSC Advances

View Article Online




Biochem 2012 47 1516




47 1351


Part A 2011 79 254





2007 225 239


102 178




Sci Drug Res 2011 3(4) 280



1750



2013 53 370















2008 75 1332




J Nat Prod 2013 76 783










391


2003 107(34) 8717


Phys Chem B 2006 110 23234





903


12544


2004 3 141










9095



2010 2 763


Paper RSC Advances

View Article Online

piquin ag nanostructures

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