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Procedía Engineering 148 (2016) 1396 - 1401
Procedía Engineering
www.elsevier.com/locate/procedia
4th International Conference on Process Engineering and Advanced Materials
Parametric Study on Gold Nanoparticle Synthesis Using Aqueous Elaise Guineensis (Oil palm) Leaf Extract: Effect of Precursor Concentration
Tausif Ahmada, Muhammad Irfana, Sekhar Bhattacharjeea*
aUniversiti Teknologi PETRONAS, Chemical Engineering Department Bandar Seri Iskandar, 32610, Perak, Malaysia
Abstract
In this study, gold nanoparticles (AuNPs) were synthesized by using aqueous extract of Elaise guineensis (oil palm) leaves without addition of any external stabilizing agent. Effects of precursor concentrations (0.51 mM- 4.055 mM) on SPR absorbance and AuNP particle size distribution were investigated. The synthesis reaction was monitored by measuring time-variant SPR spectrum of the reaction medium with a UV-vis spectrophotometer. Biosynthesized AuNPs were characterized using TEM, DLS, UV-vis and FTIR spectroscopy. TEM image analysis showed formation of predominantly spherical gold nanoparticles with mean particle diameter of 27.89±14.59 nm were formed using 1.53 mM gold concentration. DLS data showed that AuNPs with hydrodynamic diameter 55.22 ± 42.86 nm were formed, indicating formation of multilayer coatings of biomolecules present in the leaf extract on nanoparticles. Spherical, triangular, pentagonal and hexagonal gold nanoparticles with mean particle diameter 22.88 ±8.21nm were formed when higher gold (III) precursor concentrations (4.055 mM) were used. FTIR analysis revealed that carboxylic and phenolic compounds present in leaf extract played dual roles as reducing and stabilizing agents during synthesis of AuNPs.
© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).
Peer-review underresponsibility of the organizing committee of ICPEAM 2016
Keywords: Elaise guineensis; gold nanoparticles; green synthesis
1. Introduction
Synthesis of gold nanoparticles (AuNPs) has received intense research interests due to their widespread applications in diverse fields such as electronics, biotechnology and medicine [1]. Their large surface area and small size make them suitable for various medical applications [2]. Gold nanoparticles (AuNPs) are usually synthesized through various physical and chemical methods, which are expensive and use hazardous chemicals that make them unsuitable for medical applications [3]. Gold nanoparticles are also synthesized by using different microorganisms and plant extracts [4]. Different plants extracts such as Aloe vera, Alfalfa, Neem, Mangifera indica leaf have been successfully utilized as reducing and stabilizing agents in synthesis of gold nanoparticles [5-8]. Plant extracts are preferred for synthesis of gold nanoparticles due to their excellent biocompatibility [9]. Plant extracts contain several phytochemicals, which simultaneously act as reducing and stabilizing agents during synthesis of AuNPs. These bio compounds form multilayer coating on the surface of AuNPs and thus increase their long-term stability. The biomolecules also enhance utilization potential of AuNPs for medical applications by imparting their inherent medicinal properties [10].
Oil palm plants are cultivated in different tropical areas such as Malaysia, Thailand, Africa and South Africa. Oil palm leaves are abundantly released as waste products from oil palm industries. Aqueous and alcoholic extracts of oil palm leaves are rich sources of polyphenols, antioxidants, flavonoids and catechins [11]. A study on effect of gold percurser concentrations on size and
* Corresponding author. Tel.: +605-368 7640; +fax: 605-368 6176. E-mail address: sekhar.bhatta@petronas.com.my
1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of ICPEAM 2016
doi:10.1016/j.proeng.2016.06.558
shape of AuNPs synthesized using (Elaise guineensis) oil palm leaves extract has not been reported in literature to the best of auther's knowledge. Objective of this study is to report experimental data on the effects of varying precursor concentrations on particle size distribution and morphology of AuNPs synthesized by using aqueous oil palm leaf extract. Identification of biofunctional groups present in oil palm leaf extract which are accountable for reduction, and stabilization of AuNPs are also reported in this article.
Nomenclature
AuNPs Gold Nanoparticles
TEM Transmission Electron Microscope FTIR Fourier Transform Infrared Spectroscopy
DLS Dynamic Light Scattering
SPR Surface Plasmon Resonance
2. Experimental
2.1 Materials and methods
Gold (III) chloride trihydrate (HAuCl4. 3H2O), 99.99 % purity was purchased from Sigma-Aldrich, Malaysia. Stock solution of choloroauric acid (12.69 mM) was prepared by dissolving 500 mg of gold (III) chloride trihydrate in 100 ml deionized water. This stock solution was further diluted with deionized water to prepare gold solutions of required concentrations. Oil palm leaves were brought from a local oil palm mill, Felcra Berhad Nasaruddin Oil Palm Mill in Perak, Malaysia.
2.2 Preparation of oil palm leaf extract
Oil palm leaves were washed three times with deionized water and dried under sunlight for one week. The dried leaves were washed again with deionized water to remove dust particles from the surface of oil palm leaves. These leaves were then dried in oven for 8 hr at 700 C. The dried leaves were grinded in an IKA grinder to fine powder (0.25 mm) and subsequently packed in an airtight box for further use.
Aqueous leaf extract was prepared by heating 1.0 g leaf powder in 20 ml of distilled water at 700 C for 10 min. The resulting slurry was filtered with a Whatman 40 filter paper. The filtrate was stored at 40 C for further use in experiments.
2.3 Synthesis of gold nanoparticles
Gold nanoparticles were synthesized by adding 2 ml of aqueous extract to 7 ml of 1.53 mM aqueous gold (III) solution under ambient conditions. The reaction medium was stirred at 300 C and 500 rpm for 60 min. Formation of AuNPs was visually identified by observing color change of the reaction medium from light yellow to light red. The synthesis reaction was also monitored by UV-vis spectrophotometric (400 nm-700 nm) scanning of aliquot samples collected from the reaction medium.
2.4 Characterization
Absorption spectra and SPR wavelength for AuNPs were recorded by using Perkin Elmer UV-vis spectrophotometer in 400 nm to 700 nm range. Particle size distribution, mean particle diameter and morphology were studied with DLS (Malvern Zetasizer Nano ZSP) and TEM (LIBRA 200FE). Identification of functional groups present in leaf extract and reaction medium was performed with an FTIR Perkin Elma Spectrum (450 cm-1 to 4500 cm-1) spectrophotometer.
2.5 Effect of gold (III) concentration on synthesis of gold nanoparticles
Effect of gold (III) precursor concentration (0.51mM to 4.055mM) on size and shape of gold nanoparticles was evaluated by carrying out AuNPs synthesis experiments at 300 C for 60 min. Absorption spectra were recorded after 60 min of reaction.
2.6Effect of volume of gold solution on synthesis of gold nanoparticles
Effect of volume of gold solution added to a fixed volume of aqueous leaf extract on synthesis of gold nanoparticles was studied by changing volume of 1.53 mM gold (III) solution from 1ml to 5 ml. Volume of aqueous extract was kept constant at 2 ml in this
2.6 Results and Discussions
The reaction medium changed its color from light yellow to light red after 8 min of stirring. Change in color of reaction medium indicated formation of gold nanoparticles due to surface plasmon resonance (SPR) phenomenon [12]. The redox reaction involves reduction of gold (III) ions to gold atoms primarily by the polyphenols and amides present in leaf extract, which in turn are oxidized into a complex mixture of intermediates and byproducts [13]. The UV-vis spectra for AuNPs obtained with different gold (III) concentrations are shown in Fig 1.
-0.51 mM
-0.76 mM
-1.27 mM
-1.53 mM
=—2.28 mM —■£T<j mM — 3.16 mM =3.3mM =—3.69 mM
400 450 500 550 600 550 700 ^=4.055 mM Wavelength (nm)
Fig 1. UV-vis spectra for gold nanoparticles for different Au(III) concentrations
No visible color change of the reaction medium or SPR peak was observed in 530 nm to 560 nm range when 0.51 mM- 1.27 mM of Au (III) concentrations were used for synthesis of AuNPs, possibly due to an extremely low rate of reaction. The reaction medium changed its color from light yellow to light red only when Au (III) concentrations equal to or higher than 1.53 mM were used. Repeated experiments revealed that 1.53 mM was the least gold (III) concentration required to synthesize AuNPs by using aqueous oil palm leaf extract.
A broad SPR peak at 538 nm was observed with 1.53 mM gold concentration (Fig 2). Intensity of SPR peak increased with an increase in gold precursor concentration. Increase in SPR peak intensity at higher precursor concentrationsis attributed to an increase in formation of more gold nanoparticles [14]. Sharpness of SPR peak was also found to increase with an increase in Au(III) concentration. Minor blue shift in SPR wavelength, from 538 nm to 536 nm was observed when precursor concentration was increased from 1.53 mM to 4.055 mM indicating a reduction of mean particle diameter of the synthesized AuNPs [15].Size reduction of AuNPs at higher precursor concentrations was confirmed with TEM image analysis as shown in Fig 5.
Wavelength (nm)
Fig 2. SPR spectra with different volume of Au(III) solution (1.53 mM)
Effect of volume of precursor (1.53 mM) added to the reaction medium containing a fixed volume of leaf extract was investigated. SPR peak intensity increased when volume of precursor added was increased from 1ml to 3 ml. However, at precursor volume higher than 3 ml, the SPR intensity decreased (Fig 3) possibly due to unavailability of sufficient amount of reducing biomolecules in the leaf extract.
0 -I-1-1-1-1-1-1
0 1 2 3 4 5 6
Volume of gold solution (ml)
Fig.3 Change in maximum absorbance with volume of gold solution
An increase in wavelength from 533 nm to 546 nm was observed when precursor volume was increased from 2 ml to 5 ml as shown in Fig 4. The red shift was due to size enlargement with an increase in yield of gold nanoparticles [16].
Fig 4. Change in maximum wavelength with volume of gold solution
TEM images showed predominantly spherical and sparsely triangular shaped gold nanoparticle with average particles diameter 27.89±14.59 nm were formed with 1.53 mM gold solution as shown in Fig 5. Spherical, cylindrical, triangular, pentagonal and hexagonal shaped gold nanoparticles were formed with average particle diameter 22.88±8.21 nm when 4.055 mM gold (III) solution was used for synthesis as shown in Fig 5. The gold nanoparticles were well dispersed in the reaction medium without any visible agglomeration. Our TEM results are in agreement with UV-vis SPR analysis. A minor blue shift observed in SPR (from 538 nm to 536 nm) was attributed to particle size reduction when higher precursor concentration (1.53 mM to 4.055 mM) was used for AuNPs synthesis . TEM results also showed AuNPs size reduction from mean particle diameter 27.89 ±14.59 nm to 22.88 ±8.21 nm when precursor concentration was increased from 1.53 mM to 4.055 mM, as shown below in Fig 5.
Fig 5. TEM images with (a) 1.53 mM (b) 4.055 mM Au (III) concentration
Dynamic light scattering (DLS) measurements indicated that the hydrodynamic diameter for AuNPs synthesized with 1.53 mM gold solution was 55.22 ± 42.86 nm, as shown in Fig 6. The difference in particle diameter with TEM and DLS measurement endorsed the fact that DLS measurements include thickness of biocompounds present on the surface of synthesized gold nanoparticles.
Hydrodynamic diameter (nm)
Fig. 6 particles size distribution from DLS with 1.53 mM gold solution
FTIR analysis of the gold sol obtained after 60 min of reaction was performed to detect involvement of different functional groups present in leaf extract. A broader peak observed at 3392 cm-1 is attributed the O-H bonds indicating presence of aromatic alcoholic and phenolic compounds. Two more peaks were found at 1634 cm-1 and 1642 cm-1 corresponding to the presence of amide groups. Smaller peaks observed at 1071 cm-1 ,1552 cm-1 and 1412 cm-1, 1370 cm-1, 1300 cm-1 confirmed the existence of aromatic C-O bonds, N-H bonds and C-H stretching as shown in Fig 7 [17]. A major difference was witnessed for two peaks at 3392 cm-1 and 1634 cm-1 indicating contributory roles of O-H and C=O bonds in reduction of gold (III) ions to gold atoms. Hence, phenolic, alcoholic and carboxylic compounds were considered to be accountable for reduction and stabilization of AuNPs [18].
-Oil palm leaves extract -Reaction solution
¿- 20 1 ¡5 \ nr \ f
i u V
5 1634cm'- 3392 on"'
450 1450 2450 3450 Wavenumb« (cm'1) 4450
Fig. 7 FTIR spectra for oil palm leaves extract and reaction solution
3. Conclusion
Gold nanoparticles were successfully synthesized by using aqueous oil palm leaves extract without addition of any reducing and stabilizing agent. Effect of gold salt concentrations (0.51 mM - 4.055 mM) on size and morphology of gold nanoparticles was investigated. A slight reduction in size of gold nanoparticles (27.89 ±14.59 nm to 22.88 ±8.21 nm) was observed with use of 1.53 mM and 4.055 mM gold concentrations respectively. Red shifting of SPR wavelength and AuNP size enlargement were detected when larger volume of gold precursor solution was used for synthesis of gold nanoparticles. Phenolic, alcoholic and carboxylic compounds present in leaf extract were responsible for reduction and stabilization of the synthesized gold nanoparticles.
Acknowledgements
This study was financially sponsored through FRGS (0153AB-I96) by Ministry of Higher Education Malaysia. The financial support through STIRF (0153AA-C77) is also acknowledged. The Author Tausif Ahmad acknowledges the opportunity provided by Universiti Teknologi PETRONAS Malaysia to pursue his PhD in Chemical Engineering.
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