One-step Polyol Synthesis and Langmuir−Blodgett Monolayer Formation of Size-tunable Monodisperse Rhodium Nanocrystals with Catalytically Active (111) Surface Structures

Abstract

Size-tunable monodisperse Rh nanocrystals can offer unique properties for many heterogeneous catalytic reactions (such as hydrogenation, hydroformylation, and hydrocarbonylation) of both scientific and technological interest. In this article, we report the synthesis of monodisperse, well-shaped Rh nanocrystals in a range of 5-15 nm by a one-step polyol reduction at temperatures of 170-230 °C under Ar, using rhodium(III) acetylacetonate [Rh(acac) 3 ] as the source of metal ions, 1,4-butanediol as the reducing solvent, and poly-(vinylpyrrolidone) as the capping agent. Two-dimensional projects of the nanocrystals are polygons, dominated by hexagons, pentagons, and triangles with catalytically active (111) surfaces (>65% yield). Over 45% of the polygons are multiple (111) twinned particles (hexagons and pentagons), favored by thermodynamics. To achieve size uniformity, adjustment of the reduction kinetics of Rh(acac) 3 in the nucleation and crystal growth stages has been shown to depend upon several synthetic parameters including an Ar or air atmosphere, reaction temperature and time, and Rh(acac) 3 concentration. Due to the present well-controlled polyol reduction kinetics, the size of the Rh nanocrystals can be tuned by changing the Rh(acac) 3 concentration in a proper range. Monolayer films of the Rh polygons have been formed on silicon wafers by the Langmuir-Blodgett method and have been used as model heterogeneous catalysts for the study of ethylene hydrogenation.

Molecular surface chemistry by metal single crystals and nanoparticles from vacuum to high pressure

“…Pt-Rh bimetallic nanoparticles with variable composition and constant size (9 ± 1 nm) were synthesized by a one-pot polyol synthetic method 48 . The activity of CO oxidation on these bimetallic nanoparticles was studied 49 .…”

Rhodium Nanoparticle Shape Dependence in the Reduction of NO by CO

“…Rh NPs of (111)-oriented nanopolyhedra [29] and (100)-oriented nanocubes [30] were synthesized using two similar techniques, both of which have been published previously. In brief, to make the nanopolyhedra, 0.00625 mmol [Rh(Ac) 2 ] 2 and 0.25 mmol poly(vinylpyrrolidone) (Mw = 55,000, in terms of the repeating unit) were added to 20 ml ethylene glycol in a 50 mL threenecked flask at room temperature.…”

“…The flask was then heated to 185°C at 10°C min -1 , and maintained at this temperature for 2 h under Ar. When the reaction was complete, an excess of acetone was added at room temperature and the resulting Rh nanopolyhedra were separated by centrifugation and washed twice by precipitation/ dispersion [29].…”

Alcohol Oxidation at Platinum–Gas and Platinum–Liquid Interfaces: The Effect of Platinum Nanoparticle Size, Water Coadsorption, and Alcohol Concentration

“…The samples for 2-propanol oxidation were prepared by depositing Langmuir-Blodgett films 17,18 of silica embedded 4 nm Pt nanoparticles on sapphire prisms followed by calcination in air at 550 °C for 3h. To prepare 4 nm Pt nanoparticles embedded in silica, Pt nanoparticle ethanol suspension and tetraethyl orthosilicate were mixed with ethanol, to which ammonium hydroxide was added drop-wise within 5 min under stirring.…”