Rational design of protocols for the shape-controlled synthesis of palladium anocrystals

Abstract

A number of strategies for controlling the size and shape of noble-metal nanocrystals are introduced, with a particular interest in scaling-up approaches for the future commercial viability of nanomaterials. First, a simple and reliable method for the scalable production of Pd nanoplates is developed by using hydroxylamine as a reductant. The robustness of the method is validated through different experimental conditions such as acidity, temperature, and chemical environment and demonstrated that Pd nanoplates could be obtained as the final products in all scenarios. Second, a dual-reductant approach for the shape-controlled synthesis of Pd nanocrystals is presented. By the simultaneous addition of strong and weak reductants into the reaction solution, the reduction kinetics profile is programed to regulate the nucleation and growth processes and obtain Pd octahedra. Further, a new perspective on increasing the volume of production during a synthesis of colloidal nanocrystals via seed-mediated growth is introduced and validated. Geometric and stoichiometric analyses are applied to calculate the minimum amounts of reagents needed for the complete evolution of Pd cubic seeds into Pd octahedra, and subsequently for the formation of Pd@Pt3-4L core-shell octahedra through conformal Pt coating. Finally, a facile synthesis of Ir nanocrystals with well-controlled facets is reported. The essence of the approach is to coat an ultrathin, conformal shell of Ir on a Pd seed with a well-defined shape. The broader applications and future direction of these studies is discussed.