Showing papers by "Yijin Kang published in 2010"
TL;DR: A one-pot chemical approach for the synthesis of highly monodisperse colloidal nanophosphors displaying bright upconversion luminescence under 980 nm excitation and an interfacial assembly strategy to organize these nanocrystals into superlattices over multiple length scales facilitating the NC characterization and enabling systematic studies of shape-directed assembly are reported.
Abstract: We report a one-pot chemical approach for the synthesis of highly monodisperse colloidal nanophosphors displaying bright upconversion luminescence under 980 nm excitation. This general method optimizes the synthesis with initial heating rates up to 100 °C/minute generating a rich family of nanoscale building blocks with distinct morphologies (spheres, rods, hexagonal prisms, and plates) and upconversion emission tunable through the choice of rare earth dopants. Furthermore, we employ an interfacial assembly strategy to organize these nanocrystals (NCs) into superlattices over multiple length scales facilitating the NC characterization and enabling systematic studies of shape-directed assembly. The global and local ordering of these superstructures is programmed by the precise engineering of individual NC’s size and shape. This dramatically improved nanophosphor synthesis together with insights from shape-directed assembly will advance the investigation of an array of emerging biological and energy-related nanophosphor applications.
408 citations
TL;DR: The Mn-Pt nanocubes, which are enclosed by (100) surfaces, showed better activities than their spherical counterparts and are promising new candidates as cathode and anode catalysts in fuel cells.
Abstract: Mn-Pt nanocubes were synthesized from platinum acetylacetonate and manganese carbonyl in the presence of oleic acid and oleylamine. The Mn-Pt nanocubes were converted into an ordered MnPt(3) intermetallic phase upon annealing. The electrocatalytic properties of the Mn-Pt nanocubes and spheres (including oxygen reduction, formic acid oxidation, and methanol oxidation) were tested and found to be shape-dependent. The Mn-Pt nanocubes, which are enclosed by (100) surfaces, showed better activities than their spherical counterparts. These materials are promising new candidates as cathode and anode catalysts in fuel cells.
322 citations
TL;DR: The size- and shape-selective formation of metal nanostructures including Pt nanocubes, Pd spherical NCs, and Au nanowires (NWs) using carbon monoxide (CO, generated at point-of-use) as a reducing agent is reported.
Abstract: ties unobtainable simply by tuning the size of the spheres. The synthesis of metal NCs typically employs the reduction or decomposition of metal precursors in the presence of ligands, which prevent aggregation and improve the colloidal stability of the NCs. Among the wide spectrum of reducing agents that have been used, gases such as hydrogen under pressure have proven effective in delicately manipulating the growth kinetics and thus tailoring the size and morphology of the metal NCs. [15, 16] Despite these efforts, a one-pot synthesis of highly monodisperse metal NCs at ambient pressure using gaseous reducing agents generated at point-of-use is still an important advance. Herein we report the size- and shape-selective formation of metal nanostructures including Pt nanocubes, Pd spherical NCs, and Au nanowires (NWs) using carbon monoxide (CO, generated at point-of-use) as a reducing agent. We also discuss the implications of our observation on several recent reports of the preparation of Pt NCs utilizing metal carbonyls. In catalysis, it is well-known that particle shape (the facets exposed) can be as important as the particle surface area in activity and selectivity. For example, Pt(100) exhibits higher electrocatalytic activity than Pt(111) for the oxygen reduction reaction in H2SO4 electrolyte. [17, 18] Pt(100) also shows different selectivity from Pt(111) towards hydrogenation reactions. [19] Thus Pt nanocubes with well-defined {100} facets provide a model system for understanding microscopic surface phenomena in many catalytic processes. We report the synthesis of Pt nanocubes employing CO (generated by dehydration of formic acid; Supporting Information, Fig
188 citations
TL;DR: The growth and magnetic characterization of large-area BNSL membranes self-assembled from distinct magnetic NCs at the liquid-air interface are reported, which exhibit a single-phase-like magnetization alignment process, which is not observed in the phase-separated NC mixtures having the same stoichiometry.
Abstract: Co-assembly of two types of nanocrystals (NCs) into binary NC superlattices (BNSLs) provides a solution-based, inexpensive way to create novel metamaterials with rationally designed properties. The fundamental challenge is to probe and understand the nature and extent of complex interparticle interactions present in BNSLs, which can lead to collective properties that differ from their dispersed constituents or phase-separated counterparts. Here, we report the growth and magnetic characterization of large-area (∼1 cm2) BNSL membranes self-assembled from distinct magnetic NCs at the liquid−air interface. The resulting BNSL membranes exhibit a single-phase-like magnetization alignment process, which is not observed in the phase-separated NC mixtures having the same stoichiometry. This single-phase-like magnetic behavior is attributed to the collective interparticle dipolar interactions between two NC components in BNSLs, corroborated by calculation of the random dipolar fields as well as Monte Carlo simulati...
142 citations