Fusiform gold nanoparticles by pulsed plasma in liquid method
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We have synthesized fusiform gold nanoparticles by recovering gold from a solution of gold nanoparticles obtained by dispersing of gold electrodes in hexane by pulsed plasm in liquid method. Formation of fusiform gold nanoparticles with length from 50 to 150 nm, and diameter of 5–15 nm was achieved by pulsed plasma in liquid method. Fusiform gold nanoparticles obtained by our method are different from the spindle-shaped gold nanoparticles which were synthesized from the growth solution, due to their loose structure, while spindle-shaped gold nanoparticles are dense and much larger in size (length 300–400 nm, diameter ~ 100–150 nm). In addition to this work, dumbbell-shaped magnetite/gold (Fe3O4/Au) nanoparticles were synthesized by using magnetite nanoparticles obtained in a cetylpyridinium bromide (CpyBr) solution with concentration of 0.1% and a gold nanosolution, where 0.1% sodium citrate solution was applied as a reducing agent. Our proposed method is characterized by the forming of discharge localization during the electrodes erosion process, simpler and does not require use of nuclei in the form of spherical gold nanoparticles and presence of growth solution. Fusiform gold nanoparticles were formed by simple reduction with sodium citrate from gold nano-solution.
KeywordsFusiform Gold nanoparticles Magnetite Synthesis Pulsed plasma Nano-solution
Gold nanoparticles have been attracting big attention due to their extensive application in many fields such as chemistry, physics, material science, electronics, catalysis and bionanotechnology . Medical applications of gold nanoparticles have been tested in biomedicine  and surgery , in vitro biosensing, in vivo imaging, drug delivery, and tissue engineering [1, 24], therapy and imaging . Other applications of gold nanoparticles are including sensing  and antibacterial  were also reported recently.
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Gold nanoparticles (AuNPs) were synthesized at room temperature by a simple, rapid, and green route using fresh squeezed apple juice as a reducing reagent, where morphology of obtained AuNPs was based on the particle color, stability, and color change suitable for colorimetric detection of cysteine (Cys), are synthesized using 5 mL of 10% apple juice, 1 mL of 10 mM gold precursor solution, and 1 mL of 0.1 M NaOH .
In this article we are reporting the synthesis of fusiform gold nanoparticles by using the impulse plasma in a liquid method, used for the synthesis of metal oxide, carbon and carbon coated metal nanoparticles [5, 37, 38]. Pulsed plasma in a liquid method is based on a dispersion phenomenon of interfacing metal electrodes under vibration. Characteristic of this discharge form is the localization of the erosion process. A single pulse has an extremely short duration (10−3–10−5 s), a high current density (106–108 A/cm2) in the impact zone, and very high temperature in the discharge channel (104–105 K) and a pressure of 3−10 kbar. Drawback of this method is sometimes appearing in separation of synthesized nanoparticles, due to various phases and morphology of nanoparticles.
2 Experimental method
Pulsed plasma processes in the presence of organic liquids such as hexane may cause the introduction of reactive species (e.g., OH– and H– radicals) into organic compounds through spatial and temporal control of the plasma discharge . Recently, in-liquid plasma methods can be broadly classified into four categories, depending on the electrode configurations and energy sources, such as: (1) Plasma A: direct discharge between two electrodes using an AC (plus) power supply; (2) Plasma B: contact discharge between an electrode and the surface of the surrounding electrolyte using a DC power supply; (3) Plasma C: plasma generated with either radio frequency (RF) or microwave (MW) irradiation; (4) Plasma D: plasma generated using the laser ablation technique .
In our case, a single impulse discharge was generated between two gold electrodes immersed in a liquid medium (hexane). Pulsed plasma in dielectric liquid resulted from the breakdown of the inter-electrode space with a high potential difference between the electrodes and a relatively small source power, which is insufficient to initiate an arc discharge.
The energy of a single pulse (0.05 J) was regulated by changing the power of capacitors C in an electrical circuit. The energy value was selected as a result of numerous experiments conducted by the authors of this work in collaboration with colleagues for many years. Selected energy of a single pulse is sufficient to disperse any even the most refractory conductive material with the formation of nanostructures . During synthesis of fusiform gold nanoparticles electrodes of pure gold (99.99%) were adjusted inside hexane solution and pulsed discharge was applied. Obtained gold nanoparticles were placed in a conical flask and exposed to aqua regia for 20 min. As a result, a 1% gold–yellow–orange solution was obtained. After that, 1 ml of 1% sodium citrate solution was added to 1 ml of the resulting solution. Discoloration of the initial solution was observed. Precipitate was centrifuged at 2000 rpm for 30 min, and then separated from the medium by decantation and filtration. Dried powders were subjected to physicochemical analyses.
2.1 Reagents and materials
Gold metal rod electrodes with purity of 99.99%, diameter of 2 mm and length of 10–15 mm were used. Hydrochloric acid (HCl) with purity of 99.9% and nitric acid (HNO3) with concentration of 58.9%, hexane solution with concengtration of 97%, sodium citrate in water solution of 5.5% were used for experiments.
2.2 Characterization of gold NPs
X-ray diffraction (XRD) measurement was performed on a Rigaku RINT-2500HV diffractometer with Cu-Kα radiation wavelength of 0.15406 nm. Tube voltage was applied as 40 kV, and the current was 200 mA. XRD patterns were taken in the range of (2θ) 20°–80°. Transmission electron microscopy (TEM) images of as synthesized fusiform gold nanoparticles were taken using a JEOL 1400 microscope with Specification of maximum accelerating voltage 120 kV, maximum resolution of 0.2 nm installed in the Nanobiomedcenter of the Adam Mickiewicz University, Poznań, Poland.
3 Results and discussions
3.1 Transmission electron microscopy analyses
3.2 X-ray diffraction analysis
According to these calculations the interplanar d spacings for fusiform gold nanoparticles were as 2.36182 for (111), 2.04570 for (200), 1.44497 for (220) and 1.23268 for (311), respectively.
Fusiform gold nanoparticles were successfully synthesized by using the pulsed plasm in a liquid method. Pulsed plasma in dielectric liquid resulted from the breakdown of the inter-electrode space with a high potential difference between the electrodes and a relatively small source power, which is insufficient to initiate an arc discharge. A single pulse has an extremely short duration (10−3–10−5 s), a high current density (106–108 A/cm2), a very high temperature in the discharge channel (104–105 K), and a pressure of 3−10 kbar and spreads in the amount of 10−3–10−4 cm3, i.e. characterized by strong localization effects on the solid. TEM observations of as-synthesized sample clearly showed formation of fusiform gold nanoparticles with a length of 50 to 150 nm and diameter of 5 to 15 nm. As properties, morphology and synthesis of fusiform gold nanoparticles were not researched well enough, our work is original and valuable contribution to the synthesis of fusiform gold nanoparticles.
Authors are thankful to the Adam Mickiewicz University for TEM analyses of fusiform gold nanoparticles. This research was supported by funding from TOSCA II Post-doc Scholarships, from 19/09/2013 to 31/06/2014, Nanobiomedcenter of the Adam Mickiewicz University, Poznań, Poland.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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