Synthesis of AuPd alloyed nanoparticles via room-temperature electron reduction with argon glow discharge as electron source
© Yang et al.; licensee Springer. 2014
Received: 12 June 2014
Accepted: 13 August 2014
Published: 20 August 2014
Argon glow discharge has been employed as a cheap, environmentally friendly, and convenient electron source for simultaneous reduction of HAuCl4 and PdCl2 on the anodic aluminum oxide (AAO) substrate. The thermal imaging confirms that the synthesis is operated at room temperature. The reduction is conducted with a short time (30 min) under the pressure of approximately 100 Pa. This room-temperature electron reduction operates in a dry way and requires neither hydrogen nor extra heating nor chemical reducing agent. The analyses using X-ray photoelectron spectroscopy (XPS) confirm all the metallic ions have been reduced. The characterization with X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) shows that AuPd alloyed nanoparticles are formed. There also exist some highly dispersed Au and Pd monometallic particles that cannot be detected by XRD and transmission electron microscopy (TEM) because of their small particle sizes. The observed AuPd alloyed nanoparticles are spherical with an average size of 14 nm. No core-shell structure can be observed. The room-temperature electron reduction can be operated in a larger scale. It is an easy way for the synthesis of AuPd alloyed nanoparticles.
KeywordsNanoparticles Metals and alloys Au Pd Electron reduction
Alloyed AuPd bimetallic nanoparticles have drawn great attention because of their unique properties for optical, electronic, magnetic, and catalytic applications [1–3]. Especially, AuPd alloyed nanoparticles have been widely investigated as catalysts for benzyl oxidation, direct synthesis of hydrogen peroxide from H2 and O2, and CO oxidation [1, 3]. Currently, a variety of approaches have been reported on the preparation of alloyed AuPd nanoparticles, including chemical reduction [3–5], electrochemical reduction [1, 6], thermolysis of double metallic salts , and sonochemical reduction . Among all these methods, the chemical reduction is mostly applied. It is normally performed using a reducing agent, like NaBH4 or H2, in the presence of stabilizer or protective molecule for the size and structure control. With the development of green chemistry, the reduction with less chemicals and lower energy consumption has attracted more and more attentions. In this regard, low-temperature bioreduction has been developed [8–11]. For example, Li and his coworkers  reported a green synthesis of Ag-Pd alloyed nanoparticles using the aqueous extract of the Cacumen platycladi leaves as reducing agent and stabilizing agent . They found that the biomolecules like saccharides, polyphenols, or carbonyl compounds perform as the reducing agent and (NH)C = O groups are responsible for the stabilization of the AgPd alloyed nanoparticles. Recently, reduction using electron beam has been exploited . The reduction by electron beam can be directly performed with electricity only. No chemicals are needed except the precursors of metal ions. It is a green reduction for only reduction process itself is considered. The disadvantage of the electron beam reduction is that the specific equipment and high vacuum operation are required. On the other hand, some cold plasmas like glow discharge, radio frequency (RF) discharge, and microplasma contain a large amount of electrons. These energetic electrons can be employed as the reducing agent. Mougenot et al. reported a formation of surface PdAu alloyed nanoparticles on carbon using argon RF plasma reduction. Mariotti and Sankaran  and Yan et al. reported a microplasma reduction for synthesis of alloyed nanoparticles at atmospheric pressure. These represented a remarkable progress in the green and energy-efficient synthesis of alloyed nanoparticles.
Herein, we report a simple and facile method for the preparation of AuPd alloyed nanoparticles on the anodic aluminum oxide (AAO) surface using room-temperature electron reduction with argon glow discharge as electron source. This reduction operates in a dry way. It requires neither chemical reducing agent nor capping agent. The influence of chemicals on the formed nanoparticles can be eliminated. Glow discharge is well known as a conventional cold plasma phenomenon with energetic electrons. It has been extensively applied for light devices like neon lights and fluorescent lamps. It has also been employed for the preparation of nanoparticles and catalysts [16–20].
Synthesis of AuPd alloyed nanoparticles
The XRD patterns of samples were recorded on a Rigaku D/Max-2500 diffractometer (Rigaku, Shibuya-ku, Japan) (Cu-Kα radiation, λ = 0.154056 nm). Diffraction data were collected from 10° to 80° (2θ) at a scanning speed of 6°/min. The phase identification was made by comparison with the Joint Committee on Powder Diffraction Standards (JCPDSs). UV–Vis absorption spectra of samples were recorded on a Beckman DU-8B UV–Vis spectrophotometer (Beckman Coulter, Inc., Fullerton, CA, USA). TEM measurements were carried out with a Philips Tecnai G2 F20 system (Philips, Amsterdam, the Netherlands) operated at 200 kV.
Results and discussion
In summary, we have successfully prepared AuPd alloyed nanoparticles on the surface of AAO in a dry way directly via room-temperature electron reduction using argon glow discharge as the electron source. The XRD and TEM analyses confirm a formation of AuPd alloyed nanoparticles. The reduction is conducted with a short time (30 min) under the pressure of approximately 100 Pa. The room-temperature electron reduction provides us an easy, direct, green, and cheap way to fabricate AuPd alloyed nanoparticles. This study is leading to further fundamental study of formation of AuPd alloyed nanoparticle.
transmission electron microscopy
high-resolution transmission electron microscopy.
This work was supported by the National Natural Science Foundation of China (#91334206).
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