Size and shape controlled synthesis of rhodium nanoparticles

Abstract

Controlling of the size and/or shape of noble metal nanoparticles (NMNPs) is crucial to make use of their unique properties and to optimize their performance for a given application. Within the past decades, the development of wet-chemistry methods enables fine tailoring of the size and morphology of NMNPs. We herein devote this review to introduce the wet-chemistry-based methods for the size and shape-controlled synthesis of rhodium (Rh) NPs. We start with a summarization of the wet-chemistry-based approaches developed for producing Rh NPs and then focus on recent fascinating advances in their size- and shape-control in the aspects of kinetic and thermodynamic regimes depending on the synthetic conditions. Then, we use several typical examples to showcase the applications of Rh NPs with tunable sizes and shapes. Finally, we make some perspectives for the further research trends and development of Rh NPs. We hope through this reviewing effort, one can easily understand the technical bases for effectively designing and producing Rh NPs with desired properties.

Keywords: Materials chemistry; Nanotechnology; Physical chemistry.

Fig. 1

TEM images showing the effects of temperature and the concentration of the precursor on the formation of branched Rh NPs: (a) 25 mM Na₃RhCl₆ at 110 °C, (b) 25 mM Na₃RhCl₆ at 180 °C, (c) 5 mM Na₃RhCl₆ at 140 °C, (d) 50 mM Na₃RhCl₆ at 140 °C (Adapted with permission from . Copyright 2006, Wiley-VCH).

Fig. 2

TEM images showing aliquots taken during the heat-up synthesis of Rh cubes from RhBr₃ in DEG (a–d), icosahedra from Rh₂(COOCF₃)₄ in EG (e–h), and triangular plates from RhCl₃ in TREG (i–l). Aliquots were collected at (a, e, i) the temperature corresponding to the visible onset of particle nucleation, (b, f, j) after 15 min maintaining that temperature, (c, g, k) upon increasing the temperature 30–40 °C, and (d, h, l) after 75 min of focusing at that temperature (Adapted with permission from . Copyright 2015, American Chemical Society).

Fig. 3

Rh NPs prepared by addition of RhCl₃ to Rh-PVP seeds in 1,2-propanediol at (a) 10 mg h⁻¹, (b) 40 mg h⁻¹, (c) 160 mg h⁻¹, (d) jigsaw piece-shaped particles obtained for all monomer addition rates in 1,2-butanediol (Adapted with permission from . Copyright 2007, American Chemical Society).

Fig. 4

Three different organometallic derivatives (compounds 1–3) used in the reaction for the synthesis of Rh NPs with different morphologies (Adapted with permission from . Copyright 2007, Wiley-VCH).

Fig. 5

Selected HRTEM images (a–c) of the particles in (d), (d) TEM image of the mixture of tetrahedral and spherical Rh NPs formed at 190 °C from precursor 1, (e) TEM image of the mixture of tetrahedral and spherical Rh NPs formed at 190 °C from precursor 2, (f) TEM image of rectangular rhodium nanoparticles formed at 220 °C by injection of precursor 3 into the hot solution (Adapted with permission from . Copyright 2007, Wiley-VCH).

Fig. 6

TEM images of monodispersed Rh NPs in ethanol from slow-injection methods, with corresponding average edge lengths of 15 nm (a), 21 (b), 27 nm (c), 39 nm (d), 47 nm (e), and 59 nm (f), respectively (Adapted with permission from . Copyright 2016, Royal Society of Chemistry).

Fig. 7

TEM images with insets of particle size distribution histograms of 100 particles for (a) 2 nm, (b) 2.5 nm, (c) 3.5 nm, (d) 7 nm, and (e) 11 nm Rh NPs, (f) Rh 3d XPS spectra of these Rh NPs (Adapted with permission from . Copyright 2008, Wiley-VCH).

Fig. 8

TEM images and size distribution histograms for different Rh nanoparticles (Adapted with permission from . Copyright 2009, Wiley-VCH).

Fig. 9

TEM micrographs of spherical Rh nanoparticle aggregates synthesized using 920 mg of PVP (MW = 40 000) are shown in (a) and (b). Panel (c) shows a hexagonal superlattice, and panel (d) shows a superlattice formed after drying a suspension that was size-focused by centrifugation at 1 000 rpm. The arrows in (d) point to small spheres that sit in interstitial sites formed by larger spheres. A submonolayer of spherical aggregates deposited on a TEM grid and heated to 100 °C is shown in (e) and (f) (Adapted with permission from . Copyright 2005, American Chemical Society).

Fig. 10

Spherical Rh nanoparticles with average sizes of 4.8 ± 0.4 nm (a) and 7.1 ± 0.7 nm (b) prepared with the precursor concentration of 0.12 mmol and 0.24 mmol, respectively (Adapted with permission from . Copyright 2007, Wiley-VCH).

Fig. 11

(a) Schematic illustration showing the seedless polyol synthesis of Rh nanocubes, (b) TEM and HRTEM (inset) images of as-obtained Rh nanocubes (Adapted with permission from . Copyright 2008, American Chemical Society).

Fig. 12

Summary of the four-stage formation process of Rh NCs from RhCl₃: the Rh species shown in the five boxes represent the predominant but not the exclusive Rh species present, and the chemical transformations illustrated under each arrow represent the major characteristic, but not necessarily the only process involved during each stage (Adapted with permission from . Copyright 2012, American Chemical Society).

Fig. 13

Representative TEM images of Rh nanoparticles synthesized using ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol solvents with the reagents (a–d) Rh₂(TFA)₄, (e–h) RhBr₃, and (i–l) RhCl₃ (TFA = trifluoroacetate). Outlined images indicate the set of reaction conditions which results in the most monodisperse yield of Rh icosahedra (red), cubes (green), and triangular plates (blue). Scale bars are 20 nm (Adapted with permission from . Copyright 2011, American Chemical Society).

Fig. 14

(a–c) Rh NPs of various sizes and shapes, including cubic, octahedral, and porous Rh NPs (with the addition of 0.002 M AgNO₃ synthesized by a polyol method in EG at 160 °C, the reduction time for RhCl₃ of ∼20 min), (d–f) individual particles with different morphologies, (g, h) models of multiply twinned icosahedron and decahedron (Adapted with permission from . Copyright 2011, Elsevier B. V.).

Fig. 15

(a) Low-magnification TEM and HRTEM images (insets) of 4.9 ± 0.4 nm tetrahedral, (b) TEM images of the mixture of tetrahedral and spherical Rh nanoparticles (Adapted with permission from . Copyright 2007, Wiley-VCH).

Fig. 16

Low-magnification TEM images of as-obtained Rh NPs synthesized in 20 mL of ethylene glycol under an Ar atmosphere (2.5 mM [Rh(Ac)₂]₂, 100 mM PVP, 185 °C, 2 h, 9.8 ± 1.6 nm) (Adapted with permission from . Copyright 2010, American Chemical Society).

Fig. 17

(a) TEM image of Rh decahedra prepared using the standard procedure, (b) TEM images and schematic models of a decahedron in two different orientations (axial and side view), (c) HAADF-STEM image of the Rh decahedra, (d) High-resolution TEM image taken from an individual particle in sample (a) where the twin defects are marked with orange lines (Adapted with permission from . Copyright 2018, Wiley-VCH).

Fig. 18

(a,b) TEM images of Rh icosahedra with an average diameter of 12.0 ± 0.8 nm, which were synthesized by reducing Rh(acac)₃ in benzyl alcohol containing PVP as a stabilizer and a reducing agent (In a, Rh plates and octahedra are indicated by P and O, respectively), (c) HRTEM images of an individual icosahedron, (d) atomic resolution TEM image taken from the edge marked by a box in c, revealing the twin boundary on the icosahedron (Adapted with permission from . Copyright 2016, Wiley-VCH).

Fig. 19

(a) Low- and (b) high-magnification SEM images of THH Rh NPs obtained at E_U of 0.70 V and E_L of −0.07 V, (c) TEM image and (d) SAED pattern of a THH Rh nanoparticle along the [001] direction, (e) atomic arranged model of {830} plane (Adapted with permission from . Copyright 2014, Wiley-VCH).

Fig. 20

(a) TEM image and shape distribution diagram by investigating 750 plates, (b) TEM and HRTEM images of the cross-sectional view and their thickness distribution diagram of the obtained rhodium nanoplates, (c) suggested growth mechanism of Rh nanoplates (Adapted with permission from . Copyright 2010, American Chemical Society).

Fig. 21

(a) Low-magnification TEM image of the PVP-capped Rh nanosheets, (b) High-magnification TEM image of the PVP-capped Rh nanosheet, (c) Aberration-corrected microscopy image of a PVP-capped Rh nanosheet (inset, the corresponding filtered image using the crystallographic average method to improve signal-to-noise ratio), (d) AFM image and the corresponding height profiles of a bare Rh nanosheet (Adapted with permission from . Copyright 2014, Nature Publishing Group).

Fig. 22

Representative TEM and HRTEM (a, b, d) images of Rh nanodendrites synthesized at 220 °C for 6 h, the high-angle annular dark field (HAADF)-STEM image (c), and XRD profile of as-synthesized products (a, inset) (Adapted with permission from . Copyright 2010, American Chemical Society).

Fig. 23

(a, b) TEM images, (c) HRTEM image, and (d) XRD pattern of a typical sample of starfish-like Rh NPs prepared using polyol reduction at 180 °C for 6 h (Adapted with permission from . Copyright 2010, Wiley-VCH).

Fig. 24

(a) TEM image and (b) HRTEM image of the dendritic Rh NPs synthesized in oleylamine at temperature of 160 °C; (c) Schematic illustration showing the mechanism for forming dendritic Rh NPs via the reduction of Rh(acac)₃ in oleylamine at elevated temperature: (i) competition between particle aggregation and oleylamide passivation results in the formation of particle aggregates; (ii, iii) particle aggregates grow into nanodendrites via a ripening process (Adapted with permission from . Copyright 2014, Royal Society of Chemistry).

Fig. 25

Morphological and structural characterizations of a typical sample of Rh concave nanocubes prepared at 140 °C with an injection rate of 4 mL h⁻¹, (a, b) TEM images of the as-prepared sample, (c–e) HRTEM images of individual concave nanocubes recorded along the [100, 110,111] zone axes; the insets in a and b show a typical SEM image of the concave nanocubes and the 3D model, respectively (Adapted with permission from . Copyright 2011, American Chemical Society).

Fig. 26

(a) TEM images of Rh cubic nanoframes obtained by selectively etching away the Pd cores from the Pd-Rh core–frame nanocubes; (b, c) TEM images of Rh cubic nanoframes projected along <100> and <110> zone axes, respectively; (d) drawings that present a 3D model of the Rh cubic nanoframe and its projections along <100>, <110>, and <111> zone axes, (e) the three major steps involved in the synthesis of Pd-Rh core–frame nanocubes with concave faces and Rh cubic nanoframes (Adapted with permission from . Copyright 2012, Wiley-VCH).

Fig. 27

(a) Large-area STEM image of Rh concave nanocubes. (b, f, j) SAED patterns, (c, g, k) STEM images, (d, h, l) TEM images and (e, i, m) schematic geometric models of individual concave nanocubes oriented along the (b–e), (f–i), and (j–m) zone axes (Adapted with permission from . Copyright 2014, Royal Society of Chemistry).

Fig. 28

TEM images of WT phage coated with Rh nanoparticles using RhCl₃ as the metal salt reagent and SAED pattern confirming the presence of fcc Rh (Adapted with permission from . Copyright 2009, American Chemical Society).

Fig. 29

Propionaldehyde TOF vs. average Rh particle size (nm). Reaction conditions: 50 Torr CO: 50 Torr C₂H₄: 400 Torr H₂ at T = 500 K for 1 h. ±σ_y error bars represent error of repeated reactivity measurements, ±σ_x error bars represent the sigma of the Rh particle size distribution as determined from STM measurements (Adapted with permission from . Copyright 2011, the National Academy of Sciences of the United States of America).

Fig. 30

Electrochemical characterization of as-synthesized Rh NPs, irregular nanoparticles and commercial Rh black catalyst: (a) cyclic voltammograms (CVs) in 0.1 M H₂SO₄ solution, (b) linear sweep voltammograms (LSV) of CO oxidation in 0.1 M H₂SO₄ solution, (c) LSVs of ethanol oxidation in 1.0 M ethanol + 1.0 M NaOH solution (scan rate: 50 mV s⁻¹), (d) current–time curves for ethanol oxidation at −0.45 V (Adapted with permission from . Copyright 2014, Wiley-VCH).