Qipeng Liu

From Nonluminescent Cs4PbX6 (X = Cl, Br, I) Nanocrystals to Highly Luminescent CsPbX3 Nanocrystals: Water-Triggered Transformation through a CsX-Stripping Mechanism

We report a novel CsX-stripping mechanism that enables the efficient chemical transformation of nonluminescent Cs4PbX6 (X = Cl, Br, I) nanocrystals (NCs) to highly luminescent CsPbX3 NCs. During the transformation, Cs4PbX6 NCs dispersed in a nonpolar solvent are converted into CsPbX3 NCs by stripping CsX through an interfacial reaction with water in a different phase. This process takes advantage of the high solubility of CsX in water as well as the ionic nature and high ion diffusion property of Cs4PbX6 NCs, and produces monodisperse and air-stable CsPbX3 NCs with controllable halide composition, tunable emission wavelength covering the full visible range, narrow emission width, and high photoluminescent quantum yield (up to 75%). An additional advantage is that this is a clean synthesis as Cs4PbX6 NCs are converted into CsPbX3 NCs in the nonpolar phase while the byproduct of CsX is formed in water that could be easily separated from the organic phase. The as-prepared CsPbX3 NCs show enhanced stability against moisture because of the passivated surface. Our finding not only provides a new pathway for the preparation of highly luminescent CsPbX3 NCs but also adds insights into the chemical transformation behavior and stabilization mechanism of these emerging perovskite nanocrystals.

The Synergy between Metal Facet and Oxide Support Facet for Enhanced Catalytic Performance: The Case of Pd-TiO2.

The demand for catalyst with higher activity and higher selectivity is still a central issue in current material science community. On the basis of first-principles calculations, we demonstrate that the catalytic performance of the Pd-TiO2 hybrid nanostructures can be selectively promoted or depressed by choosing the suitable shaped Pd and TiO2 nanocrystals. To be more specific, the catalytic activities of Pd nanoparticles enclosed by (100) or (111) facets can be promoted more significantly when dosed on the TiO2(001) than on TiO2(101) under irradiation. Such theoretical prediction has then been further verified by the experimental observations in which the Pd(100)-TiO2(001) composites exhibit the highest catalytic performance toward the activation of oxygen among all the other shaped hybrid nanostructures. As a result, the selection of facets of support materials can provide an extra tuning parameter to control the catalytic activities of metal nanoparticles. This research opened up a new direction for designing and preparing catalysts with enhanced catalytic performance.

Halide-free synthesis of Au nanoplates and monitoring the shape evolution process through a marker experiment

We demonstrate that uniform Au nanoplates capped with a nontoxic ligand have been prepared through a seeded growth method using Au/Ag nanorings as the template. A mechanistic study reveals that the growth process experienced both “back-filling” and “out-extending” processes. This research sheds some light on both the synthesis and the potential applications of gold nanoplates.

High-yield colloidal synthesis of monometallic Au nanorod–Au nanoparticle dimers and their application in SERS

Dimeric nanostructures have attracted much attention owing to their unique structure and excellent physiochemical properties. However, it has been very difficult to make monometallic nanodimers. In this work, we report a simple colloidal approach to synthesize high-yield monometallic Au nanorod–Au nanoparticle dimers by using a negatively charged polyelectrolyte, poly(sodium-p-styrenesulfonate) (PSS), to modify the positively charged Au nanorods. The growth process is studied by systematically tuning the reaction parameters. The as-obtained dimers can serve as a great SERS substrate for the detection of organic molecules because of the existence of “hot-spots”. The analytical enhancement factor (AEF) of the as-prepared dimers is up to 106, which is two magnitudes higher than that of Au nanorods.

Colloidal Synthesis of Au@Pd Core–Shell Nanorods with Tunable Dimensions and Enhanced Electrocatalytic Activities

Pd-based bimetallic nanoparticles have attracted much attention due to their promising applications in diverse fields. For example, in electro-oxidation of alcohol, the synergistic effects between different metals can significantly improve the resistance of Pd to sintering, coke deposition and CO poisoning. Although great progress has been achieved in the synthesis of Pd-based nanostructures, it is still lacking a robust protocol to synthesize Pd bimetallic nanostructures with desired shapes and dimensions. In this work, Au@Pd core–shell nanorods with tunable size of both core and shell were synthesized using a one-pot method. Both the dimensions of Pd shell and Au core can be tuned separately by altering reaction conditions. Compared with Pd cube and octahedron, Au@Pd core–shell nanorods exhibit superior activity in the electrochemical oxidation of ethanol due to the synergistic effects between Au core and Pd shell. This work not only develops a facile one-pot protocol for synthesizing Au@Pd core–shell nanostructures, but also sheds some light on the design and preparation of catalysts with enhanced electrocatalytic performance.

Dispersing hydrophilic nanoparticles in nonaqueous solvents with superior long-term stability

We report a general and robust polymerization–dissolution strategy for phase transfer of hydrophilic nanoparticles into nonaqueous solvents with a 100% transfer efficiency. This process involves the coating of hydrophilic nanoparticles with a layer of linear-chained polystyrene through seeded emulsion polymerization and a subsequent dissolution of polystyrene layer by toluene. Since one end of the linear polystyrene chain is covalently bonded to the particle surface which provides strong steric stabilization, the transferred nanoparticles exhibit superior dispersity and long-term colloidal stability in many nonpolar and polar aprotic solvents. Moreover, the present approach allows for the storage of transferred nanoparticles in a powder form which can be completely re-dispersed in solvents before the usage. Based on this strategy, we demonstrate the phase transfer of Au nanorods and nanospheres, silica, titania and resorcinol-formaldehyde spheres, which just represents a few examples of transferrable hydrophilic nanoparticles with different morphologies, sizes, compositions, functions and surface properties. This general and robust phase transfer protocol will greatly facilitate the applications of hydrophilic nanoparticle in organic catalysis, optoelectronics, energy storage and conversion, and organic light emitting diodes.