Anion Dependent Particle Size Control of Platinum Nanoparticles Synthesized in Ethylene Glycol.

Johanna Schröder,Sebastian Kunz,Matthias Arenz,Sarah Neumann,Jonathan Quinson

doi:10.3390/nano11082092

Johanna Schröder, Sebastian Kunz + Show 3 more

Open Access

https://doi.org/10.3390/nano11082092

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Abstract

The polyol synthesis is a well-established method to form so-called “surfactant-free” nanoparticles (NPs). In the present study, the NP size resulting from the thermal reduction of the precursors H2PtCl6, H2Pt(OH)6, or Pt(acac)2 in presence of the bases NaOH or Na(acac) at different concentrations is studied. It is shown that the size control depends more strongly on the nature of the precursor (metal salt) than on the anion present in the base. The latter is surprising as the concentration of the base anion is often an important factor to achieve a size control. The reduction of H2PtCl6 or H2Pt(OH)6 in presence of NaOH and Na(acac) confirm the observation that the NP size is determined by the OH−/Pt molar ratio and expands it to the base anion/Pt molar ratio. In contrast, the reduction of Pt(acac)2 in presence of the bases NaOH (previous reports) or Na(acac) (shown in the present work) leads to larger NPs of ca. 3 nm, independent of the concentration of the base anions. Hence, the anion effect observed here seems to originate predominantly from the nature of the precursor (precursor anion dependence) and only for certain precursors as H2PtCl6 or H2Pt(OH)6 the size control depends on the base anion/Pt molar ratio.

Highlights

The polyol method performed in alkaline ethylene glycol (EG) is a versatile approach to synthesize “surfactant-free” Pt nanoparticle (NP) based tailored catalysts [1,2,3] for instance for CO oxidation [4,5] or fuel cell studies [6,7]
A comparable large particle size of ca. 3 nm is obtained here in the reduction of Pt(acac)2 in presence of Na(acac) or in the reduction of Pt(acac)2 in presence of NaOH as shown by Neumann et al [4]. This clearly shows the importance of the careful selection of the nature of the precursor compared to the nature of the base anion in order to achieve size control in ‘’surfactant-free”
H2 Pt(OH)6 was reduced in presence of NaOH to investigate if in a halide-free system the NP size is still controlled by a certain OH− /Pt ratio as reported before [7,13,15]

Summary

Introduction

The polyol method performed in alkaline ethylene glycol (EG) is a versatile approach to synthesize “surfactant-free” Pt nanoparticle (NP) based tailored catalysts [1,2,3] for instance for CO oxidation [4,5] or fuel cell studies [6,7]. Nanomaterials 2021, 11, 2092 observed that the presence of halides in the precursors H2 PtCl6 and H2 PtBr6 induces leaching leading to a size increase during the thermal reduction in presence of NaOH at 150 ◦ C during 17 h. 3 nm is obtained here in the reduction of Pt(acac) in presence of Na(acac) or in the reduction of Pt(acac) in presence of NaOH as shown by Neumann et al [4] This clearly shows the importance of the careful selection of the nature of the precursor (the precursor anion) compared to the nature of the base anion in order to achieve size control in ‘’surfactant-free”

NP Synthesis

Cleaning of “Surfactant-Free” NPs

Characterization of Nanoparticles

Results and Discussion

Conclusions