High-Yield Synthesis of 1D Rh Nanostructures from Surfactant Mediated Reductive Pathway and their Shape Transformation

Abstract

Precise control over the size and shape of nanoparticles from solution-phase synthetic approach is currently a major objective in nanoscience. Metal nanorods and nanowires have attracted much attention because of their outstanding catalytic, magnetic, optical, and electrical properties. We have reported here the microwave (MW) assisted gram quantity synthesis of 1D nanostructures composed of Rh(0) and Rh(I). Thus, the rod-like assembly evolves through Rh(I)−Rh(I) interaction as the building blocker for the 1D nanostructure by using cetyltrimethylammonium bromide (CTAB) as a reducing agent as well as soft template. Reduction of Rh(III) to Rh(0)/Rh(I) occurred on the glass surface as a result of decomposition of CTAB upon MW heating without any other reducing agent. Uniform heating and the presence of CTAB, a face selective adsorption additive, helped the formation of 1D Rh nanostructures. Here, CTAB upon decomposition produced ammonia which in turn acted as a reducing agent ((a) Bal, R.; Tada, M.; Iwasawa, Y. Chem. Commun.2005, 3433. (b) Huang, Y.; Wang, W.; Liang, H.; Xu, H. Cryst. Growth Des.2009, 9, 858), and the undecomposed CTAB stabilized the nanostructure moiety. Hydrothermal condition produced only spherical Rh(0) nanoparticles, and boiling condition prompted anisotropic growth of the Rh(0)/Rh(I) nanoparticles with ill-defined morphology. The presence of impurity such as NH4Cl or CsCl produced distinct 1D nanorods or nanowires in microwave heating condition. Interestingly, the syntheses of different morphology of Rh nanomaterials have been obtained by keeping the Rh(III) ion precursor to CTAB molar ratio unaltered. It has been observed that the pH has a remarkable influence on the alteration of aspect ratio and sharpening of the edges of Rh nanorods. The evolved nanostructures in different stages were characterized ex situ by different physical methods. How and why thermodynamically rather unstable Rh nanorods and nanowires changed their shapes in a chosen redox environment is reported. Interesting shape transformation has also been shown in a selective redox environment for nanorods and nanowires to octahedral and spherical particles, respectively. Isolated intermediates, identified by FESEM and TEM measurements, supported and guarantee the rod-to-octahedral shape transformation. Cyclic voltammetric measurement shows that as-prepared nanorods can be used as a potential candidate for oxygen evolution.