Synergistic catalysis of monometallic (Ag, Au, Pd) and bimetallic (Agsingle bondAu, Ausingle bondPd) versus trimetallic (Ag-Au-Pd) nanostructures effloresced via analogical techniques

https://doi.org/10.1016/j.molliq.2019.110975Get rights and content

Highlights

  • Fabrication of monometallic, bimetallic, and trimetallic nanostructures by using dextran was presented.

  • AgNPs, Ag-AuNPs and Ag-Au-PdNPs were produced with 8.7, 15.7, and 3.8 nm, respectively.

  • Dextran alcoholic groups reduced metal ions to metallic nanostructures.

  • Trimetallic nanostructure as a catalyst accelerated the reduction of p-nitroaniline by 151 times.

  • The half time of reduction reaction was diminished from 3.93 min. for PdNPs to 0.90 min. for Ag-Au-PdNPs.

Abstract

Monometallic (Ag, Au, Pd), bimetallic (Agsingle bondAu, Ausingle bondPd) and trimetallic (Ag-Au-Pd) nanostructures, were generated using dextran as a natural polymer. The simultaneous co-reduction of multiple metal precursors with dextran gave a fine control to produce spherical shape Ag-Au-Pd trimetallic nanostructures. Small-sized Ag monometallic nanostructures of 8.7 nm were enlarged to 15.7 nm for Agsingle bondAu bimetallic nanostructures. While, trimetallic nanostructures from Ag-Au-Pd was produced with much smaller size of 3.8 nm and quite narrower size distribution of 2–7 nm. The spectral analysis confirmed that the alcoholic groups of dextran were responsible for the reduction of metal ions to produce nanostructures and consequently oxidized to aldehydic/ketonic groups. The catalytic performance of the synthesized nanostructures was evaluated for the reduction of p-nitroaniline and the results demonstrated that there was a strong correlation between catalytic activity and composition of nanostructures. Half time of the reduction was diminished from 3.93 to 0.90 min. for Pd monometallic and Ag-Au-Pd trimetallic nanostructures, respectively. Using of the trimetallic nanostructure as a catalyst results in acceleration the reduction reaction 151 times. The results showed a promising approach to boost catalytic activities of the trimetallic nanostructures which were prepared via quite simple green method at ambient conditions.

Introduction

Manufacturing of various metal nanostructures was extensively considered due to their fascinating properties to be applicable in different purposes, such as plasmonics [[1], [2], [3]], chemical sensing [4,5], surface-enhanced Raman scattering (SERS) [[6], [7], [8]], drug delivery [9,10], and catalysis [11]. Multi-metallic alloyed nanostructures were considerably interested because of their wide ranged structural tunability and functional diversity, which made these structures applicable in various applications including nano-devices and technologies [[12], [13], [14], [15]]. Additionally, some of the interesting properties for multi-metallic alloyed nanostructures could be achieved while could not be realized with monometallic particles (NPs), such as the electronic heterogeneity, site-specific response, and combinational effect of constituent metals. Also, the alloyed nanostructures can be flexibly applicable by tuning their optical [15,16], catalytic [[17], [18], [19]], electronic, and magnetic [[20], [21], [22]] properties via controlling particle shape, size, and density [23] as well as the elemental constitution.

According to the literature [17,[20], [21], [22],[24], [25], [26]], preparation of nano-alloyed structures based on Pd resulted in significant improvement in the durability of nano-catalytic activity by the incorporation of Pd in AuNPs [24,25]. In recent years, monometallic Au, Ag, and PdNPs have been successfully applicable in many fields due to their promising plasmonic and catalytic activities. Therefore, fabrication of Ag-Au-Pd alloyed nanostructures can offer novel application as well as enhance the performance of the as-existing applications [[26], [27], [28]]. The systematic fabrication of ternary Ag-Au-Pd alloyed nanostructures with tunable surface morphology and elemental composition was insignificantly reported in the literature.

It was reported that controlling of particle size for trimetallic nanostructures was not relatively easy compared to bimetallic NPs. There are few pieces of research on the preparation of trimetallic nano-alloyed structures with well-defined morphologies, although trimetallic nanostructures were approved to exhibit new insights into the structure-composition-property relationships with the as-incorporated noble metal nanoparticles. For example, González et al., studied the synthesis of Pd-Au-Ag nano-boxes from Ag nano-cubes via sequential or simultaneous galvanic exchange [29]. Yamauchi and co-workers designed a methodology for the synthesis of spherical Au@Pd@Pt triple-layered core-shell nanostructures which had better catalytic activity than bimetallic core-shell nanostructures [30,31]. Recently, Choi et al., succeeded in manufacturing of Pt-Pd-Ag ternary alloyed nano-tubes with the nano-porous framework using ZnO nano-wires as sacrificial templates [32]. Nevertheless, it is still a highly interesting target to prepare multi-metallic nanostructures with well-defined morphologies due to the formidable difficulties in adjusting the nucleation/growth kinetics of multi-metallic nano-objects in the presence of different metal salts with different reduction potentials in the same reactor medium. As such, performed NP seeds or structure-directing templates have been commonly employed to generate nanostructures with multiple metallic constituents. Therefore, the manufacturing of an efficient and straightforward methodology for the preparation of multi-metallic nanostructures with desirable particle size and morphology is quietly requested to determine their properties and investigate their valuable applications.

Based on numerous approaches [[33], [34], [35], [36], [37], [38], [39], [40]], it was found that synthesis of nanoparticles could be successively carried out using different polymers, where, the polymer played an important role in controlling the particle size and morphological structure especially in bimetallic systems and the shape and crystal facet in catalytic ones [41,42]. The metal nanoparticles prepared from polymer-metal ion complexes were enough stable to work as an active catalyst for the organic reaction like hydrogenation of olefin in solution [43].

Therefore, the current study aims to study the catalytic performance of monometallic (AgNPs, AuNPs, PdNPs), bimetallic (Agsingle bondAu, Ausingle bondPd), and Ag-Au-Pd trimetallic nanostructures which were prepared by a sole design as quite simple, energy saving, and cost-effective method. The fabrication was depending on the employment of dextran as one type of the biological polymers, in generation, stabilization and in improving the long-term stability of the so-synthesized nanostructures. The successive preparation of the nanostructures was confirmed through various instrumental analyses like UV–Visible spectrophotometer, transmission electron microscope (TEM), Zetasizer and X-ray diffraction (XRD). Spectral data of infrared (FTIR) and 13C NMR were represented for approving the redox reaction between dextran macromolecules and metals precursors in addition to elucidating the reaction mechanism for the production of the nanostructures. Probing of the catalytic reactivity for the synthesized monometallic, bimetallic and trimetallic nanostructures in the reduction of para-nitroaniline was widely studied.

Section snippets

Materials and chemicals

Silver nitrate (AgNO3, 99.5%, from Panreac, Barcelona – Spain), Gold chloride (AuCl3, 99%, from Sigma-Aldrich – USA), Palladium chloride (PdCl2, 99%, from Sigma-Aldrich – USA), Sodium hydroxide (99%, from Merck, Darmstadt–Germany), Dextran ((C6H10O5)n, El-Nasser Company for Pharmaceuticals and Chemicals, Egypt), para-nitroaniline (O2NC6H4NH2, >99%, from Sigma-Aldrich – USA) and Sodium borohydride (NaBH4, ≥96%, from Sigma-Aldrich – USA), were all used without any further purification.

Nanostructures preparation procedure

The

Results and discussion

In general, multi- metallic nano-colloids can be basically synthesized in two processes; i) simultaneous co-reduction of metal salts in the presence of the certain protecting agent, which is often a polymer or surfactant; or ii) successive reduction of one metal over the nuclei of another one. The former reduction method mainly resulted in the generation of alloyed nanostructures while the latter produces core-shell nano-objects. Successive reduction, which is also described as the

Conclusion

The current approach represents one pot, efficient, green technique for manufacturing of monometallic (Ag, Au, Pd), bimetallic (Agsingle bondAu, Ausingle bondPd) and trimetallic (Ag-Au-Pd) nanostructures at ambient conditions by employing of dextran as nano-generator and capping agent, via simultaneous co-reduction method. Nanostructures of monometallic Ag, bimetallic Agsingle bondAu and trimetallic Ag-Au-Pd were produced with quite small size of 8.7, 15.7 and 3.8 nm. The spectral data approved that, the nanostructures formed

Compliance with ethical standards

The authors declare that they have no conflict of interest.

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